Effect of Temperature Reversion on Hot Ductility and Flow Stress-Strain Curves of C-Mn Continuously Cast Steels

NASA Astrophysics Data System (ADS)

Dong, Zhihua; Li, Wei; Long, Mujun; Gui, Lintao; Chen, Dengfu; Huang, Yunwei; Vitos, Levente

2015-08-01

The influence of temperature reversion in secondary cooling and its reversion rate on hot ductility and flow stress-strain curve of C-Mn steel has been investigated. Tensile specimens were cooled at various regimes. One cooling regime involved cooling at a constant rate of 100 °C min-1 to the test temperature, while the others involved temperature reversion processes at three different reversion rates before deformation. After hot tensile test, the evolution of mechanical properties of steel was analyzed at various scales by means of microstructure observation, ab initio prediction, and thermodynamic calculation. Results indicated that the temperature reversion in secondary cooling led to hot ductility trough occurring at higher temperature with greater depth. With increasing temperature reversion rate, the low temperature end of ductility trough extended toward lower temperature, leading to wider hot ductility trough with slightly reducing depth. Microstructure examinations indicated that the intergranular fracture related to the thin film-like ferrite and (Fe,Mn)S particles did not changed with varying cooling regimes; however, the Widmanstatten ferrite surrounding austenite grains resulted from the temperature reversion process seriously deteriorated the ductility. In addition, after the temperature reversion in secondary cooling, the peak stress on the flow curve slightly declined and the peak of strain to peak stress occurred at higher temperature. With increasing temperature reversion rate, the strain to peak stress slightly increased, while the peak stress showed little variation. The evolution of plastic modulus and strain to peak stress of austenite with varying temperature was in line with the theoretical prediction on Fe.

Symmetry Relations in Chemical Kinetics Arising from Microscopic Reversibility

NASA Astrophysics Data System (ADS)

Adib, Artur B.

2006-01-01

It is shown that the kinetics of time-reversible chemical reactions having the same equilibrium constant but different initial conditions are closely related to one another by a directly measurable symmetry relation analogous to chemical detailed balance. In contrast to detailed balance, however, this relation does not require knowledge of the elementary steps that underlie the reaction, and remains valid in regimes where the concept of rate constants is ill defined, such as at very short times and in the presence of low activation barriers. Numerical simulations of a model of isomerization in solution are provided to illustrate the symmetry under such conditions, and potential applications in protein folding or unfolding are pointed out.

TR-ESR Investigation on Reaction of Vitamin C with Excited Triplet of 9,10-phenanthrenequinone in Reversed Micelle Solutions

NASA Astrophysics Data System (ADS)

Xu, Xin-sheng; Shi, Lei; Liu, Yi; Ji, Xue-han; Cui, Zhi-feng

2011-04-01

Time-resolved electron spin resonance has been used to study quenching reactions between the antioxidant Vitamin C (VC) and the triplet excited states of 9,10-phenanthrenequinone (PAQ) in ethylene glycol-water (EG-H2O) homogeneous and inhomogeneous reversed micelle solutions. Reversed micelle solutions were used to be the models of physiological environment of biological cell and tissue. In PAQ/EG-H2O homogeneous solution, the excited triplet of PAQ (3PAQ*) abstracts hydrogen atom from solvent EG. In PAQ/VC/EG-H2O solution, 3PAQ* abstracts hydrogen atom not only from solvent EG but also from VC. The quenching rate constant of 3PAQ* by VC is close to the diffusion-controlled value of 1.41 × 108 L/(mol ·s). In hexadecyltrimethylammonium bromide (CTAB)/EG-H2O and aerosol OT (AOT)/EG-H2O reversed micelle solutions, 3PAQ* and VC react around the water-oil interface of the reversed micelle. Exit of 3PAQ* from the lipid phase slows down the quenching reaction. For Triton X-100 (TX-100)/EG-H2O reversed micelle solution, PAQ and VC coexist inside the hydrophilic polyethylene glycol core, and the quenching rate constant of 3PAQ* by VC is larger than those in AOT/EG-H2O and CTAB/EG-H2O reversed micelle solutions, even a little larger than that in EG-H2O homogeneous solution. The strong emissive chemically induced dynamic electron polarization of As.- resulted from the effective TM spin polarization transfer in hydrogen abstraction of 3PAQ* from VC.

Is reverse total shoulder arthroplasty a feasible treatment option for failed shoulder arthroplasty? A retrospective study of 44 cases with special regards to stemless and stemmed primary implants.

PubMed

Holschen, M; Franetzki, B; Witt, K-A; Liem, D; Steinbeck, J

2017-08-01

Is reverse total shoulder arthroplasty a feasible treatment option for failed shoulder arthroplasty? A retrospective study of 44 cases with special regards to stemless and stemmed primary implants. Due to humeral or glenoid bone-loss and rotator cuff insufficiency reverse total shoulder arthroplasty often means the only remaining treatment option in revision shoulder arthroplasty. This study investigates the clinical outcome of patients treated with a reverse total shoulder in revision cases with special regard to stemless and stemmed primary implants. From 2010 to 2012 60 failed shoulder arthroplasties were converted to reverse total shoulder arthroplasty. Forty-four patients were available for follow-up after a mean of 24 months. Patients were assessed with X-rays, Constant- and ASES Score and a questionnaire about their subjective satisfaction. The total number of observed complications was seven (16%). Ninety-eight percent of the patients were satisfied with their clinical result. Patients achieved a mean normalized constant score of 70.2% and a mean ASES Score of 65.3. Patients with stemless primary implants achieved a higher normalized constant score than patients with stemmed primary implants (82 vs. 61.8%; p = 0009). Reverse total shoulder arthroplasty provides satisfactory clinical results and a high patient satisfaction in revision shoulder arthroplasty. The complication rate needs to be considered and discussed with the patient prior to surgery. Presence or absence of a stem of revised shoulder arthroplasties interferes with the outcome. LEVEL OF EVIDENCE IV: (Retrospective study).

Mechanistic information from the first volume profile analysis for a reversible intermolecular electron-transfer reaction involving pentaammine(isonicotinamide)ruthenium and cytochrome c

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

Baensch, B.; Meier, M.; Martinez, P.

1994-10-12

The reversible intermolecular electron-transfer reaction between pentaammine(isonicotinamide)ruthenium(II/III) and horse-heart cytochrome c iron(III/II) was subjected to a detailed kinetic and thermodynamic study as a function of temperature and pressure. Theoretical calculations based on the Marcus-Hush theory were employed to predict all rate and equilibrium constants as well as activation parameters. There is an excellent agreement between the kinetically and thermodynamically determined equilibrium constants and associated pressure parameters. These data are used to construct a volume profile for the overall process, from which it follows that the transition state lies halfway between the reactant and product states on a volume basis. Themore » reorganization in the transition state has reached a similar degree in both directions of the electron-transfer process and corresponds to a {lambda}{sup {double_dagger}} value of 0.44 for this reversible reaction. This is the first complete volume profile analysis for a reversible intermolecular electron-transfer reaction.« less

Numerical investigation on the effects of acceleration reversal times in Rayleigh-Taylor Instability with multiple reversals

NASA Astrophysics Data System (ADS)

Farley, Zachary; Aslangil, Denis; Banerjee, Arindam; Lawrie, Andrew G. W.

2017-11-01

An implicit large eddy simulation (ILES) code, MOBILE, is used to explore the growth rate of the mixing layer width of the acceleration-driven Rayleigh-Taylor instability (RTI) under variable acceleration histories. The sets of computations performed consist of a series of accel-decel-accel (ADA) cases in addition to baseline constant acceleration and accel-decel (AD) cases. The ADA cases are a series of varied times for the second acceleration reversal (t2) and show drastic differences in the growth rates. Upon the deceleration phase, the kinetic energy of the flow is shifted into internal wavelike patterns. These waves are evidenced by the examined differences in growth rate in the second acceleration phase for the set of ADA cases. Here, we investigate global parameters that include mixing width, growth rates and the anisotropy tensor for the kinetic energy to better understand the behavior of the growth during the re-acceleration period. Authors acknowledge financial support from DOE-SSAA (DE-NA0003195) and NSF CAREER (#1453056) awards.

Constant amplitude and post-overload fatigue crack growth behavior in PM aluminum alloy AA 8009

NASA Technical Reports Server (NTRS)

Reynolds, A. P.

1992-01-01

A recently developed, rapidly solidified, powder metallurgy, dispersion strengthened aluminum alloy, AA 8009, was fatigue tested at room temperature in lab air. Constant amplitude/constant delta kappa and single spike overload conditions were examined. High fatigue crack growth rates and low crack closure levels compared to typical ingot metallurgy aluminum alloys were observed. It was proposed that minimal crack roughness, crack path delection, and limited slip reversibility, resulting from ultra-fine microstructure, were responsible for the relatively poor da/dN-delta kappa performance of AA 8009 as compared to that of typical IM aluminum alloys.

Constant amplitude and post-overload fatigue crack growth behavior in PM aluminum alloy AA 8009

NASA Technical Reports Server (NTRS)

Reynolds, A. P.

1991-01-01

A recently developed, rapidly solidified, powder metallurgy, dispersion strengthened aluminum alloy, AA 8009, was fatigue tested at room temperature in lab air. Constant amplitude/constant delta kappa and single spike overload conditions were examined. High fatigue crack growth rates and low crack closure levels compared to typical ingot metallurgy aluminum alloys were observed. It was proposed that minimal crack roughness, crack path deflection, and limited slip reversibility, resulting from ultra-fine microstructure, were responsible for the relatively poor da/dN-delta kappa performance of AA 8009 as compared to that of typical IM aluminum alloys.

INFLUENCE OF ORGANIC COSOLVENTS ON THE SORPTION KINETICS OF HYDROPHOBIC ORGANIC CHEMICALS

EPA Science Inventory

A quantitative examination of the kinetics of sorption of hydrophobic organic chemicals by soils from mixed solvents reveals that the reverse sorption rate constant (k2) increases log-linearly with increasing volume fraction of organic cosolvent (fc). This relationship was expec...

Slowly switching between environments facilitates reverse evolution in small populations.

PubMed

Tan, Longzhi; Gore, Jeff

2012-10-01

Natural populations must constantly adapt to ever-changing environmental conditions. A particularly interesting question is whether such adaptations can be reversed by returning the population to an ancestral environment. Such evolutionary reversals have been observed in both natural and laboratory populations. However, the factors that determine the reversibility of evolution are still under debate. The time scales of environmental change vary over a wide range, but little is known about how the rate of environmental change influences the reversibility of evolution. Here, we demonstrate computationally that slowly switching between environments increases the reversibility of evolution for small populations that are subject to only modest clonal interference. For small populations, slow switching reduces the mean number of mutations acquired in a new environment and also increases the probability of reverse evolution at each of these "genetic distances." As the population size increases, slow switching no longer reduces the genetic distance, thus decreasing the evolutionary reversibility. We confirm this effect using both a phenomenological model of clonal interference and also a Wright-Fisher stochastic simulation that incorporates genetic diversity. Our results suggest that the rate of environmental change is a key determinant of the reversibility of evolution, and provides testable hypotheses for experimental evolution. © 2012 The Author(s). Evolution© 2012 The Society for the Study of Evolution.

Theory for rates, equilibrium constants, and Brønsted slopes in F1-ATPase single molecule imaging experiments

PubMed Central

Volkán-Kacsó, Sándor; Marcus, Rudolph A.

2015-01-01

A theoretical model of elastically coupled reactions is proposed for single molecule imaging and rotor manipulation experiments on F1-ATPase. Stalling experiments are considered in which rates of individual ligand binding, ligand release, and chemical reaction steps have an exponential dependence on rotor angle. These data are treated in terms of the effect of thermodynamic driving forces on reaction rates, and lead to equations relating rate constants and free energies to the stalling angle. These relations, in turn, are modeled using a formalism originally developed to treat electron and other transfer reactions. During stalling the free energy profile of the enzymatic steps is altered by a work term due to elastic structural twisting. Using biochemical and single molecule data, the dependence of the rate constant and equilibrium constant on the stall angle, as well as the Børnsted slope are predicted and compared with experiment. Reasonable agreement is found with stalling experiments for ATP and GTP binding. The model can be applied to other torque-generating steps of reversible ligand binding, such as ADP and Pi release, when sufficient data become available. PMID:26483483

Substituent Effects on Thermal Decolorization Rates of Bisbenzospiropyrans

PubMed Central

Lu, Nina T.; Nguyen, Vi N.; Kumar, Satish; McCurdy, Alison

2009-01-01

A novel application of photochromic molecules is to mimic physiological oscillatory calcium signals by reversibly binding and releasing calcium ions in response to light. Substituent changes on the largely unexplored photochromic bisbenzospiropyran scaffold led to significant changes in thermal fading rates in several organic solvents. Excellent correlations have been found between fading rates and empirical Hammett constants as well as calculated ground-state energies. These correlations can be used to improve scaffold design. PMID:16238356

Enhanced bimolecular exchange reaction through programmed coordination of a five-coordinate oxovanadium complex for efficient redox mediation in dye-sensitized solar cells.

PubMed

Oyaizu, Kenichi; Hayo, Noriko; Sasada, Yoshito; Kato, Fumiaki; Nishide, Hiroyuki

2013-12-07

Electrochemical reversibility and fast bimolecular exchange reaction found for VO(salen) gave rise to a highly efficient redox mediation to enhance the photocurrent of a dye-sensitized solar cell, leading to an excellent photovoltaic performance with a conversion efficiency of 5.4%. A heterogeneous electron-transfer rate constant at an electrode (k0) and a second-order rate constant for an electron self-exchange reaction (k(ex)) were proposed as key parameters that dominate the charge transport property, which afforded a novel design concept for the mediators based on their kinetic aspects.

Analysis of spontaneous oscillations for a three-state power-stroke model.

PubMed

Washio, Takumi; Hisada, Toshiaki; Shintani, Seine A; Higuchi, Hideo

2017-02-01

Our study considers the mechanism of the spontaneous oscillations of molecular motors that are driven by the power stroke principle by applying linear stability analysis around the stationary solution. By representing the coupling equation of microscopic molecular motor dynamics and mesoscopic sarcomeric dynamics by a rank-1 updated matrix system, we derived the analytical representations of the eigenmodes of the Jacobian matrix that cause the oscillation. Based on these analytical representations, we successfully derived the essential conditions for the oscillation in terms of the rate constants of the power stroke and the reversal stroke transitions of the molecular motor. Unlike the two-state model, in which the dependence of the detachment rates on the motor coordinates or the applied forces on the motors plays a key role for the oscillation, our three-state power stroke model demonstrates that the dependence of the rate constants of the power and reversal strokes on the strains in the elastic elements in the motor molecules plays a key role, where these rate constants are rationally determined from the free energy available for the power stroke, the stiffness of the elastic element in the molecular motor, and the working stroke size. By applying the experimentally confirmed values to the free energy, the stiffness, and the working stroke size, our numerical model reproduces well the experimentally observed oscillatory behavior. Furthermore, our analysis shows that two eigenmodes with real positive eigenvalues characterize the oscillatory behavior, where the eigenmode with the larger eigenvalue indicates the transient of the system of the quick sarcomeric lengthening induced by the collective reversal strokes, and the smaller eigenvalue correlates with the speed of sarcomeric shortening, which is much slower than lengthening. Applying the perturbation analyses with primal physical parameters, we find that these two real eigenvalues occur on two branches derived from a merge point of a pair of complex-conjugate eigenvalues generated by Hopf bifurcation.

Dynamic modeling of reversible methanolysis of Jatropha curcas oil to biodiesel.

PubMed

Syam, Azhari M; Hamid, Hamidah A; Yunus, Robiah; Rashid, Umer

2013-01-01

Many kinetics studies on methanolysis assumed the reactions to be irreversible. The aim of the present work was to study the dynamic modeling of reversible methanolysis of Jatropha curcas oil (JCO) to biodiesel. The experimental data were collected under the optimal reaction conditions: molar ratio of methanol to JCO at 6 : 1, reaction temperature of 60°C, 60 min of reaction time, and 1% w/w of catalyst concentration. The dynamic modeling involved the derivation of differential equations for rates of three stepwise reactions. The simulation study was then performed on the resulting equations using MATLAB. The newly developed reversible models were fitted with various rate constants and compared with the experimental data for fitting purposes. In addition, analysis of variance was done statistically to evaluate the adequacy and quality of model parameters. The kinetics study revealed that the reverse reactions were significantly slower than forward reactions. The activation energies ranged from 6.5 to 44.4 KJ mol⁻¹.

Dynamic Modeling of Reversible Methanolysis of Jatropha curcas Oil to Biodiesel

PubMed Central

Syam, Azhari M.; Hamid, Hamidah A.; Yunus, Robiah; Rashid, Umer

2013-01-01

Many kinetics studies on methanolysis assumed the reactions to be irreversible. The aim of the present work was to study the dynamic modeling of reversible methanolysis of Jatropha curcas oil (JCO) to biodiesel. The experimental data were collected under the optimal reaction conditions: molar ratio of methanol to JCO at 6 : 1, reaction temperature of 60°C, 60 min of reaction time, and 1% w/w of catalyst concentration. The dynamic modeling involved the derivation of differential equations for rates of three stepwise reactions. The simulation study was then performed on the resulting equations using MATLAB. The newly developed reversible models were fitted with various rate constants and compared with the experimental data for fitting purposes. In addition, analysis of variance was done statistically to evaluate the adequacy and quality of model parameters. The kinetics study revealed that the reverse reactions were significantly slower than forward reactions. The activation energies ranged from 6.5 to 44.4 KJ mol−1. PMID:24363616

Reactive transport of uranium in fractured crystalline rock: Upscaling in time and distance

DOE PAGES

Dittrich, Timothy M.; Reimus, Paul W.

2015-09-29

In this study, batch adsorption and breakthrough column experiments were conducted to evaluate uranium transport through altered material that fills fractures in a granite rock system at the Grimsel Test Site in Switzerland at pH 6.9 and 7.9. The role of adsorption and desorption kinetics was evaluated with reactive transport modeling by comparing one-, two-, and three-site models. Emphasis was placed on describing long desorption tails that are important for upscaling in time and distance. The effect of increasing pH in injection solutions was also evaluated. For pH 6.9, a three-site model with forward rate constants between 0.07 and 0.8more » ml g –1 h –1, reverse rate constants between 0.001 and 0.06 h –1, and site densities of 1.3, 0.104, and 0.026 μmol g –1 for ‘weak/fast’, ‘strong/slow’, and ‘very strong/very slow’ sites provided the best fits. For pH 7.9, a three-site model with forward rate constants between 0.05 and 0.8 mL g –1 h –1, reverse rate constants between 0.001 and 0.6 h –1, and site densities of 1.3, 0.039, and 0.013 μmol g –1 for a ‘weak/fast’, ‘strong/slow’, and ‘very strong/very slow’ sites provided the best fits. Column retardation coefficients (R d) were 80 for pH 6.9 and 10.3 for pH 7.9. Model parameters determined from the batch and column experiments were used in 50 year large-scale simulations for continuous and pulse injections and indicated that a three-site model is necessary at pH 6.9, although a K d-type equilibrium partition model with one-site was adequate for large scale predictions at pH 7.9. Batch experiments were useful for predicting early breakthrough times in the columns while column experiments helped differentiate the relative importance of sorption sites and desorption rate constants on transport.« less

Bromamine Decomposition Revisited: A Holistic Approach for Analyzing Acid and Base Catalysis Kinetics.

PubMed

Wahman, David G; Speitel, Gerald E; Katz, Lynn E

2017-11-21

Chloramine chemistry is complex, with a variety of reactions occurring in series and parallel and many that are acid or base catalyzed, resulting in numerous rate constants. Bromide presence increases system complexity even further with possible bromamine and bromochloramine formation. Therefore, techniques for parameter estimation must address this complexity through thoughtful experimental design and robust data analysis approaches. The current research outlines a rational basis for constrained data fitting using Brønsted theory, application of the microscopic reversibility principle to reversible acid or base catalyzed reactions, and characterization of the relative significance of parallel reactions using fictive product tracking. This holistic approach was used on a comprehensive and well-documented data set for bromamine decomposition, allowing new interpretations of existing data by revealing that a previously published reaction scheme was not robust; it was not able to describe monobromamine or dibromamine decay outside of the conditions for which it was calibrated. The current research's simplified model (3 reactions, 17 constants) represented the experimental data better than the previously published model (4 reactions, 28 constants). A final model evaluation was conducted based on representative drinking water conditions to determine a minimal model (3 reactions, 8 constants) applicable for drinking water conditions.

Statistical effects related to low numbers of reacting molecules analyzed for a reversible association reaction A + B = C in ideally dispersed systems: An apparent violation of the law of mass action

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

Szymanski, R., E-mail: rszymans@cbmm.lodz.pl; Sosnowski, S.; Maślanka, Ł.

2016-03-28

Theoretical analysis and computer simulations (Monte Carlo and numerical integration of differential equations) show that the statistical effect of a small number of reacting molecules depends on a way the molecules are distributed among the small volume nano-reactors (droplets in this study). A simple reversible association A + B = C was chosen as a model reaction, enabling to observe both thermodynamic (apparent equilibrium constant) and kinetic effects of a small number of reactant molecules. When substrates are distributed uniformly among droplets, all containing the same equal number of substrate molecules, the apparent equilibrium constant of the association is highermore » than the chemical one (observed in a macroscopic—large volume system). The average rate of the association, being initially independent of the numbers of molecules, becomes (at higher conversions) higher than that in a macroscopic system: the lower the number of substrate molecules in a droplet, the higher is the rate. This results in the correspondingly higher apparent equilibrium constant. A quite opposite behavior is observed when reactant molecules are distributed randomly among droplets: the apparent association rate and equilibrium constants are lower than those observed in large volume systems, being the lower, the lower is the average number of reacting molecules in a droplet. The random distribution of reactant molecules corresponds to ideal (equal sizes of droplets) dispersing of a reaction mixture. Our simulations have shown that when the equilibrated large volume system is dispersed, the resulting droplet system is already at equilibrium and no changes of proportions of droplets differing in reactant compositions can be observed upon prolongation of the reaction time.« less

Clinical and radiological outcomes after reverse shoulder arthroplasty in patients with failed deltoid or latissimus dorsi transfers. A review of ten cases.

PubMed

Valenti, Philippe; Maqdes, Ali; Werthel, Jean-David

2017-10-01

The purpose of this study was to report clinical and radiological results of reverse shoulder arthroplasty (RSA) after failure of either a deltoid and/or a latissimus dorsi transfer. Between 2001 and 2011, ten patients (average age, 61 years) underwent primary RSA after a failed tendon transfer for irreparable postero-superior rotator cuff tear (five deltoid muscle transfers, four latissimus dorsi transfers and one both). Average follow-up was 48 months. Outcome measures included pain, range of motion and postoperative Constant-Murley score. Pain score improved significantly from a mean 8.3 to a mean 0.3. Mean shoulder elevation improved from 66 to 134°, and absolute Constant-Murley scores increased from 25.8 to 62.8 The mean improvement in external rotation was limited to 7.5°. Subjectively, six patients rated the result as much better and three rated it as better than before surgery. Failure of the tendon transfer with deterioration of the functional outcomes can be salvaged with a RSA with no impact on the expected outcome.

Phosphoric acid as an electrolyte additive for lead/acid batteries in electric-vehicle applications

NASA Astrophysics Data System (ADS)

Meissner, E.

The influence of the addition of phosphoric acid to the electrolyte on the performance of gelled lead/acid electric-vehiicle batteries is investigated. This additive reduces the reversible capacity decay of the positive electrode significantly which is observed upon extended cycling when recharge of the battery is performed at low initial rate. This is important when low-rate on-board chargers are used. Pulsed discharge, typical for electric-vehicle application, induces reversible capacity decay more than constant-current discharge at a same depth-of-discharge, as well with as without the addition of phosphoric acid. By contrast, hindrance in presence of H 3PO 4 for both the recharge and the discharge reaction helps to homogenize the state of many individual cells during cycling in long battery strings. Reversible capacity loss, which occurs after extended cycling and when pulsed discharge is applied, can be recovered by a single discharge at very low rate with batteries with and without the addition of phosphoric acid. The discharge-rate dependency of the capacity is significantly reduced when phosphoric acid is added. The pulse discharge behaviour may be better, even if the nominal capacity is reduced. The experimental findings of the influence of phosphoric acid addition is discussed in terms of the aggregate-of-spheres model of reversible capacity decay.

Neutral Red and Ferroin as Reversible and Rapid Redox Materials for Redox Flow Batteries.

PubMed

Hong, Jeehoon; Kim, Ketack

2018-06-11

Neutral red and ferroin are used as redox indicators (RINs) in potentiometric titrations. The rapid response and reversibility that are prerequisites for RINs are also desirable properties for the active materials in redox flow batteries (RFBs). This study describes the electrochemical properties of ferroin and neutral red as a redox pair. The rapid reaction rates of the RINs allow a cell to run at a rate of 4 C with 89 % capacity retention after the 100 th  cycle. The diffusion coefficients, electrode reaction rates, and solubilities of the RINs were determined. The electron-transfer rate constants of ferroin and neutral red are 0.11 and 0.027 cm s -1 , respectively, which are greater than those of the components of all-vanadium and Zn/Br 2 cells. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Heating rates in furnace atomic absorption using the L'vov platform

USGS Publications Warehouse

Koirtyohann, S.R.; Giddings, R.C.; Taylor, Howard E.

1984-01-01

Heating rate profiles for the furnace tube wall, the furnace atmosphere, and a L'vov platform were established for a range of conditions in a cyclically heated graphite atomizer. The tube wall profile was made by direct observation with a recording optical pyrometer. The sodium line reversal method was used to establish the heating rate of the furnace atmosphere, and appearance temperatures for a series metals of differing volatility was used to establish platform profiles. The tube wall heating rate was nearly linear at 2240??C s- until the desired temperature was reached after which the temperature remained constant. The furnace atmosphere reached a given temperature 0.2-0.4 s later than the tube wall through most of the atomize cycle. The platform lagged the tube wall 0.5-0.8 s. Under typical operating conditions the furnace atmosphere was 100-200??C cooler than the tube wall and at nearly constant temperature when the analyte vaporized from the platform. The L'vov platform causes the cyclically heated commercial furnace to approximate the behavior of a constant temperature furnace during atomization. ?? 1984.

Ab initio chemical kinetic study on Cl + ClO and related reverse processes.

PubMed

Xu, Z F; Lin, M C

2010-11-04

The reaction of ClO with Cl and its related reverse processes have been studied theoretically by ab initio quantum chemical and statistical mechanical calculations. The geometric parameters of the reactants, products, and transition states are optimized by both UMPW1PW91 and unrestricted coupled-cluster single and double excitation (UCCSD) methods with the 6-311+G(3df) basis set. The potential energy surface has been further refined (with triple excitations, T) at the UCCSD(T)/6-311+G(3df) level of theory. The results show that Cl(2) and O ((3)P) can be produced by chlorine atom abstraction via a tight transition state, while ClOCl ((1)A(1)) and ClClO ((1)A') can be formed by barrierless association processes with exothermicities of 31.8 and 16.0 kcal/mol, respectively. In principle the O ((1)D) atom can be generated with a large endothermicity of 56.9 kcal/mol; on the other hand, its barrierless reaction with Cl(2) can readily form ClClO ((1)A'), which fragments rapidly to give ClO + Cl. The rate constants of both forward and reverse processes have been predicted at 150-2000 K by the microcanonical variational transition state theory (VTST)/Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The predicted rate constants are in good agreement with available experimental data within reported errors.

System analysis of the dynamic response of the coronary circulation to a sudden change in heart rate.

PubMed

Dankelman, J; Stassen, H G; Spaan, J A

1990-03-01

In this study the response of driving pressure/flow ration on an abrupt change in heart rate was analysed. The difference between the response obtained with constant pressure and constant flow perfusion was also studied. The responses show a fast initial reversed phase followed by a slow phase caused by regulation. To test whether the initial phase could be the result of mechanical changes in the coronary circulation, a model for regulation was extended by the addition of four different mechanical models originating from the literature. These extended models were able to explain the fast initial phase. However, the mechanical model consisting of an intramyocardial compliance (C = 0.08 ml mm Hg-1 100 g-1) with a variable venous resistance, and the model consisting of a waterfall and a small compliance (C = 0.007 ml mm Hg-1 100g-1) both explained these responses best. The analysis showed that there is no direct relationship between rate of change of vascular tone and rate of change of pressure/flow ratio. However, on the basis of the two extended models, it can be predicted that the half-time for the response of regulation to be complete is about 9s with constant pressure perfusion and 15 s with constant flow perfusion.

The action of the bacterial toxin microcin B17. Insight into the cleavage-religation reaction of DNA gyrase.

PubMed

Pierrat, Olivier A; Maxwell, Anthony

2003-09-12

We have examined the effects of the bacterial toxin microcin B17 (MccB17) on the reactions of Escherichia coli DNA gyrase. MccB17 slows down but does not completely inhibit the DNA supercoiling and relaxation reactions of gyrase. A kinetic analysis of the cleavage-religation equilibrium of gyrase was performed to determine the effect of the toxin on the forward (cleavage) and reverse (religation) reactions. A simple mechanism of two consecutive reversible reactions with a nicked DNA intermediate was used to simulate the kinetics of cleavage and religation. The action of MccB17 on the kinetics of cleavage and religation was compared with that of the quinolones ciprofloxacin and oxolinic acid. With relaxed DNA as substrate, only a small amount of gyrase cleavage complex is observed with MccB17 in the absence of ATP, whereas the presence of the nucleotide significantly enhances the effect of the toxin on both the cleavage and religation reactions. In contrast, ciprofloxacin, oxolinic acid, and Ca2+ show lesser dependence on ATP to stabilize the cleavage complex. MccB17 enhances the overall rate of DNA cleavage by increasing the forward rate constant (k2) of the second equilibrium. In contrast, ciprofloxacin increases the amount of cleaved DNA by a combined effect on the forward and reverse rate constants of both equilibria. Based on these results and on the observations that MccB17 only slowly inhibits the supercoiling and relaxation reactions, we suggest a model of the interaction of MccB17 with gyrase.

[Results from the German shoulder- and elbow arthroplasty register (SEPR) : Anatomic or reverse shoulder arthroplasty in B2-glenoids?

PubMed

Magosch, P; Habermeyer, P; Lichtenberg, S; Tauber, M; Gohlke, F; Mauch, F; Boehm, D; Loew, M; Zeifang, F; Pötzl, W

2017-12-01

Anatomic shoulder arthroplasty in osteoarthritis with biconcave glenoid wear results in decreased functional results and a higher rate of early glenoid loosening. The aim of the data analysis of the German shoulder arthroplasty register was to clarify whether reverse shoulder arthroplasty can provide better functional results and a lower complication rate than anatomic arthroplasty in osteoarthritis with biconcave glenoid wear. The analysis included 1052 completely documented primary implanted arthroplasties with a minimum follow-up of 2 years. In 119 cases, a B2-type glenoid was present. Out of these cases, 86 were treated with an anatomic shoulder arthroplasty, and in 33 cases a reverse shoulder arthroplasty was implanted. The mean follow-up was 47.6 months. The Constant score with its subcategories, as well as the active range of movement improved significantly after anatomic and after reverse shoulder arthroplasty. We observed no difference in functional results between both types of arthroplasty; however, reverse arthroplasty showed a significant higher revision rate (21.2%) (3% glenoid loosening, 6% prosthetic instability) than anatomic shoulder arthroplasty (12.8%) (11.6% glenoid loosening, 1.2% prosthetic instability), whereas anatomic shoulder arthroplasty showed a higher rate of glenoid loosening. Functional and radiographic results of both types of arthroplasty are comparable with the results reported in the literature, although our analysis represents results from an implant registry (data pertaining to medical care quality).

Slow equilibration of reversed-phase columns for the separation of ionized solutes.

PubMed

Marchand, D H; Williams, L A; Dolan, J W; Snyder, L R

2003-10-10

Reversed-phase columns that have been stored in buffer-free solvents can exhibit pronounced retention-time drift when buffered, low-pH mobile phases are used with ionized solutes. Whereas non-ionized compounds exhibit constant retention times within 20 min of the beginning of mobile phase flow, the retention of ionized compounds can continue to change (by 20% or more) for several hours. If mobile phase pH is changed from low to high and back again, an even longer time may be required before the column reaches equilibration at low pH. The speed of column equilibration for ionized solutes can vary significantly among different reversed-phase columns and is not affected by flow rate.

Reversion phenomena of Cu-Cr alloys

NASA Technical Reports Server (NTRS)

Nishikawa, S.; Nagata, K.; Kobayashi, S.

1985-01-01

Cu-Cr alloys which were given various aging and reversion treatments were investigated in terms of electrical resistivity and hardness. Transmission electron microscopy was one technique employed. Some results obtained are as follows: the increment of electrical resistivity after the reversion at a constant temperature decreases as the aging temperature rises. In a constant aging condition, the increment of electrical resistivity after the reversion increases, and the time required for a maximum reversion becomes shorter as the reversion temperature rises. The reversion phenomena can be repeated, but its amount decreases rapidly by repetition. At first, the amount of reversion increases with aging time and reaches its maximum, and then tends to decrease again. Hardness changes by the reversion are very small, but the hardness tends to soften slightly. Any changes in transmission electron micrographs by the reversion treatment cannot be detected.

Characteristics of Viscoelastic Crustal Deformation Following a Megathrust Earthquake: Discrepancy Between the Apparent and Intrinsic Relaxation Time Constants

NASA Astrophysics Data System (ADS)

Fukahata, Yukitoshi; Matsu'ura, Mitsuhiro

2018-02-01

The viscoelastic deformation of an elastic-viscoelastic composite system is significantly different from that of a simple viscoelastic medium. Here, we show that complicated transient deformation due to viscoelastic stress relaxation after a megathrust earthquake can occur even in a very simple situation, in which an elastic surface layer (lithosphere) is underlain by a viscoelastic substratum (asthenosphere) under gravity. Although the overall decay rate of the system is controlled by the intrinsic relaxation time constant of the asthenosphere, the apparent decay time constant at each observation point is significantly different from place to place and generally much longer than the intrinsic relaxation time constant of the asthenosphere. It is also not rare that the sense of displacement rate is reversed during the viscoelastic relaxation. If we do not bear these points in mind, we may draw false conclusions from observed deformation data. Such complicated transient behavior can be explained mathematically from the characteristics of viscoelastic solution: for an elastic-viscoelastic layered half-space, the viscoelastic solution is expressed as superposition of three decaying components with different relaxation time constants that depend on wavelength.

Theory of bi-molecular association dynamics in 2D for accurate model and experimental parameterization of binding rates

PubMed Central

Yogurtcu, Osman N.; Johnson, Margaret E.

2015-01-01

The dynamics of association between diffusing and reacting molecular species are routinely quantified using simple rate-equation kinetics that assume both well-mixed concentrations of species and a single rate constant for parameterizing the binding rate. In two-dimensions (2D), however, even when systems are well-mixed, the assumption of a single characteristic rate constant for describing association is not generally accurate, due to the properties of diffusional searching in dimensions d ≤ 2. Establishing rigorous bounds for discriminating between 2D reactive systems that will be accurately described by rate equations with a single rate constant, and those that will not, is critical for both modeling and experimentally parameterizing binding reactions restricted to surfaces such as cellular membranes. We show here that in regimes of intrinsic reaction rate (ka) and diffusion (D) parameters ka/D > 0.05, a single rate constant cannot be fit to the dynamics of concentrations of associating species independently of the initial conditions. Instead, a more sophisticated multi-parametric description than rate-equations is necessary to robustly characterize bimolecular reactions from experiment. Our quantitative bounds derive from our new analysis of 2D rate-behavior predicted from Smoluchowski theory. Using a recently developed single particle reaction-diffusion algorithm we extend here to 2D, we are able to test and validate the predictions of Smoluchowski theory and several other theories of reversible reaction dynamics in 2D for the first time. Finally, our results also mean that simulations of reactive systems in 2D using rate equations must be undertaken with caution when reactions have ka/D > 0.05, regardless of the simulation volume. We introduce here a simple formula for an adaptive concentration dependent rate constant for these chemical kinetics simulations which improves on existing formulas to better capture non-equilibrium reaction dynamics from dilute to dense systems. PMID:26328828

Quantitative aspects of 1-norepinephrine induced pathologic changes: a study in normal dogs

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

Szakacs, J.E.; Mehlman, B.

1959-08-01

The effects of constant rate intravenous infusions of norepinephrine were studied in 28 normal dogs, sedated with morphine. The range of dose rates in this experiment was from 0.5 to 15 mcg/min/kg. Blood levels of epinephrine and norepinephrine were determined in 12 animals up to 10 hours during constant rate infusions. The heart rate and blood pressure were recorded in frequent intervals. The reflex bradycardia was reversed in the animals by prolonged infusions of one or more mcg/min/kg of norepinephrine. Tachycardia and arrhythmia were regularly present in the animals that developed myocardial lesions. Death occurred due to cardiac arrest, massivemore » cerebral hemorrhage or pulmonary edema in the animals infused with 10 mcg/min/kg for 1/2 to 3 hours, or 5 mcg/min/kg for 6 hours. Post mortem examination was performed on all animals. The tissue changes were described and correlated with dosage rate and blood catecholamine levels. 17 references, 8 figures.« less

Rare behavior of growth processes via umbrella sampling of trajectories

NASA Astrophysics Data System (ADS)

Klymko, Katherine; Geissler, Phillip L.; Garrahan, Juan P.; Whitelam, Stephen

2018-03-01

We compute probability distributions of trajectory observables for reversible and irreversible growth processes. These results reveal a correspondence between reversible and irreversible processes, at particular points in parameter space, in terms of their typical and atypical trajectories. Thus key features of growth processes can be insensitive to the precise form of the rate constants used to generate them, recalling the insensitivity to microscopic details of certain equilibrium behavior. We obtained these results using a sampling method, inspired by the "s -ensemble" large-deviation formalism, that amounts to umbrella sampling in trajectory space. The method is a simple variant of existing approaches, and applies to ensembles of trajectories controlled by the total number of events. It can be used to determine large-deviation rate functions for trajectory observables in or out of equilibrium.

Electrochemistry and the mechanisms of nucleation and growth of neodymium during electroreduction from LiCl-KCl eutectic salts on Mo substrate

NASA Astrophysics Data System (ADS)

Tang, Hao; Pesic, Batric

2015-03-01

The electrochemical behavior of NdCl3 was studied on a Mo electrode in molten LiCl-KCl eutectic salts. The electroreduction of Nd(III)/Nd(0) involved two reaction steps, as confirmed by three different electrochemical techniques. In the first reaction step, Nd(III) is converted into soluble Nd(II), which undergoes further reduction into metallic Nd(0) in the second reaction step. The standard reaction rate constants for each reaction step were determined by Nicholson method. The rate constant values were used in Matsuda-Ayabe's criteria for testing the electrochemical reversibility. Accordingly, both reaction steps were quasi-reversible redox reactions. The nucleation mechanisms of neodymium metal deposited on a Mo substrate were predicted by using Scharifker-Hill model, and tested for the first time by scanning electron microscopy (SEM) studies of the electrode surface. The SEM studies confirmed that for the low initial concentration of NdCl3, neodymium nucleates and grows progressively, while for higher NdCl3 concentrations, the related mechanism is instantaneous. Both are governed by the aggregative growth mechanisms based on surface mobility of formed nanoclusters.

Atomic-scale reversibility in sheared glasses

NASA Astrophysics Data System (ADS)

Fan, Meng; Wang, Minglei; Liu, Yanhui; Schroers, Jan; Shattuck, Mark; O'Hern, Corey

Systems become irreversible on a macroscopic scale when they are sheared beyond the yield strain and begin flowing. Using computer simulations of oscillatory shear, we investigate atomic scale reversibility. We employ molecular dynamics simulations to cool binary Lennard-Jones liquids to zero temperature over a wide range of cooling rates. We then apply oscillatory quasistatic shear at constant pressure to the zero-temperature glasses and identify neighbor-switching atomic rearrangement events. We determine the critical strain γ*, beyond which atoms in the system do not return to their original positions upon reversing the strain. We show that for more slowly cooled glasses, the average potential energy is lower and the typical size of atomic rearrangements is smaller, which correlates with larger γ*. Finally, we connect atomic- and macro-scale reversibility by determining the number of and correlations between the atomic rearrangements that occur as the system reaches the yield strain.

Spin-oscillator model for the unzipping of biomolecules by mechanical force.

PubMed

Prados, A; Carpio, A; Bonilla, L L

2012-08-01

A spin-oscillator system models unzipping of biomolecules (such as DNA, RNA, or proteins) subject to an external force. The system comprises a macroscopic degree of freedom, represented by a one-dimensional oscillator, and internal degrees of freedom, represented by Glauber spins with nearest-neighbor interaction and a coupling constant proportional to the oscillator position. At a critical value F(c) of an applied external force F, the oscillator rest position (order parameter) changes abruptly and the system undergoes a first-order phase transition. When the external force is cycled at different rates, the extension given by the oscillator position exhibits a hysteresis cycle at high loading rates, whereas it moves reversibly over the equilibrium force-extension curve at very low loading rates. Under constant force, the logarithm of the residence time at the stable and metastable oscillator rest position is proportional to F-F(c) as in an Arrhenius law.

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

Bockris, J.O.; Devanathan, M.A.V.

The galvanostatic double charging method was applied to determine the coverage of Ni cathodes with adsorbed atomic H in 2 N NaOH solutions. Anodic current densities were varied from 0.05 to 1.8 amp/sq cm. The plateau indicating absence of readsorption was between 0.6 and 1.8 amp/sq cm, for a constant cathodic c.d. of 1/10,000 amp/sq cm. The variation of the adsorbed H over cathodic c.d.'s ranging from 10 to the -6th power to 1/10 at a constant anodic c.d. of 1 amp/sq cm were calculated and the coverage calculated. The mechanism of the H evolution reaction was elucidated. The ratemore » determining step is discharge from a water molecules followed by rapid Tafel recombination. The rate constants for these processes and the rate constant for the ionisation, calculated with the extrapolated value of coverage for the reversible H electrode, were determined. A modification of the Tafel equation which takes into account both coverage and ionisation is in harmony with the results. A new method for the determination of coverage suitable for corrodible metals is described which involves the measurement of the rate of permeation of H by electrochemical techniques which enhances the sensitivity of the method. (Author)« less

Theoretical study of the kinetics of chlorine atom abstraction from chloromethanes by atomic chlorine.

PubMed

Brudnik, Katarzyna; Twarda, Maria; Sarzyński, Dariusz; Jodkowski, Jerzy T

2013-10-01

Ab initio calculations at the G3 level were used in a theoretical description of the kinetics and mechanism of the chlorine abstraction reactions from mono-, di-, tri- and tetra-chloromethane by chlorine atoms. The calculated profiles of the potential energy surface of the reaction systems show that the mechanism of the studied reactions is complex and the Cl-abstraction proceeds via the formation of intermediate complexes. The multi-step reaction mechanism consists of two elementary steps in the case of CCl4 + Cl, and three for the other reactions. Rate constants were calculated using the theoretical method based on the RRKM theory and the simplified version of the statistical adiabatic channel model. The temperature dependencies of the calculated rate constants can be expressed, in temperature range of 200-3,000 K as [Formula: see text]. The rate constants for the reverse reactions CH3/CH2Cl/CHCl2/CCl3 + Cl2 were calculated via the equilibrium constants derived theoretically. The kinetic equations [Formula: see text] allow a very good description of the reaction kinetics. The derived expressions are a substantial supplement to the kinetic data necessary to describe and model the complex gas-phase reactions of importance in combustion and atmospheric chemistry.

Unsteady penetration of a target by a liquid jet

PubMed Central

Uth, Tobias; Deshpande, Vikram S.

2013-01-01

It is widely acknowledged that ceramic armor experiences an unsteady penetration response: an impacting projectile may erode on the surface of a ceramic target without substantial penetration for a significant amount of time and then suddenly start to penetrate the target. Although known for more than four decades, this phenomenon, commonly referred to as dwell, remains largely unexplained. Here, we use scaled analog experiments with a low-speed water jet and a soft, translucent target material to investigate dwell. The transient target response, in terms of depth of penetration and impact force, is captured using a high-speed camera in combination with a piezoelectric force sensor. We observe the phenomenon of dwell using a soft (noncracking) target material. The results show that the penetration rate increases when the flow of the impacting water jet is reversed due to the deformation of the jet–target interface––this reversal is also associated with an increase in the force exerted by the jet on the target. Creep penetration experiments with a constant indentation force did not show an increase in the penetration rate, confirming that flow reversal is the cause of the unsteady penetration rate. Our results suggest that dwell can occur in a ductile noncracking target due to flow reversal. This phenomenon of flow reversal is rather widespread and present in a wide range of impact situations, including water-jet cutting, needleless injection, and deposit removal via a fluid jet. PMID:24277818

Stability of sugar solutions: a novel study of the epimerization kinetics of lactose in water.

PubMed

Jawad, Rim; Drake, Alex F; Elleman, Carole; Martin, Gary P; Warren, Frederick J; Perston, Benjamin B; Ellis, Peter R; Hassoun, Mireille A; Royall, Paul G

2014-07-07

This article reports on the stereochemical aspects of the chemical stability of lactose solutions stored between 25 and 60 °C. The lactose used for the preparation of the aqueous solutions was α-lactose monohydrate with an anomer purity of 96% α and 4% β based on the supplied certificate of analysis (using a GC analytical protocol), which was further confirmed here by nuclear magnetic resonance (NMR) analysis. Aliquots of lactose solutions were collected at different time points after the solutions were prepared and freeze-dried to remove water and halt epimerization for subsequent analysis by NMR. Epimerization was also monitored by polarimetry and infrared spectroscopy using a specially adapted Fourier transform infrared attenuated total reflectance (FTIR-ATR) method. Hydrolysis was analyzed by ion chromatography. The three different analytical approaches unambiguously showed that the epimerization of lactose in aqueous solution follows first order reversible kinetics between 25 to 60 °C. The overall rate constant was 4.4 × 10(-4) s(-1) ± 0.9 (± standard deviation (SD)) at 25 °C. The forward rate constant was 1.6 times greater than the reverse rate constant, leading to an equilibrium constant of 1.6 ± 0.1 (±SD) at 25 °C. The rate of epimerization for lactose increased with temperature and an Arrhenius plot yielded an activation energy of +52.3 kJ/mol supporting the hypothesis that the mechanism of lactose epimerization involves the formation of extremely short-lived intermediate structures. The main mechanism affecting lactose stability is epimerization, as no permanent hydrolysis or chemical degradation was observed. When preparing aqueous solutions of lactose, immediate storage in an ice bath at 0 °C will allow approximately 3 min (180 s) of analysis time before the anomeric ratio alters significantly (greater than 1%) from the solid state composition of the starting material. In contrast a controlled anomeric composition (~38% α and ~62% β) will be achieved if an aqueous solution is left to equilibrate for over 4 h at 25 °C, while increasing the temperature up to 60 °C rapidly reduces the required equilibration time.

Ascorbyl radical disproportionation in reverse micellar systems

NASA Astrophysics Data System (ADS)

Gębicki, J. L.; Szymańska-Owczarek, M.; Pacholczyk-Sienicka, B.; Jankowski, S.

2018-04-01

Ascorbyl radical was generated by the pulse radiolysis method and observed with the fast kinetic spectrophotometry within reverse micelles stabilized by AOT in n-heptane or by Igepal CO-520 in cyclohexane at different water to surfactant molar ratio, w0. Rate constants for the disproportionation of the ascorbyl radicals were smaller than those for intermicellar exchange for both type of reverse micelles and slower than those in homogeneous aqueous solutions. However, they increased with increasing w0 for AOT/n-heptane system, while they decreased for Igepal CO-520 system. The absorption spectra of ascorbic acid AOT/n-heptane reverse micellar system showed that the "pH" sensed by this molecule is lower than that in respective homogeneous aqueous solutions. The obtained results were rationalized taking into account three main factors (i) preferential location of ascorbic acid molecules in the interfacial region of the both types of reverse micelles; (ii) postulate that the pH of the interface is lower than that of the water pool of reverse micelles and (iii) different structure of the interface of the reverse micelles made by AOT in n-heptane and those formed by Igepal CO-520 I cyclohexane. Some possible consequences of these findings are discussed.

A case of the tail wagging the dog? Reverse weathering and Earth's CO2 thermostat.

NASA Astrophysics Data System (ADS)

Higgins, J. A.

2017-12-01

Feedbacks between climate, the global carbon cycle, and the chemistry of seawater stabilize Earth's surface temperature on geologic timescales and are likely responsible for its habitability over billions of years of Earth history. The most important component of the geologic carbon cycle is the precipitation and burial of carbonate sediments. The amount of carbonate sediment produced depends, in turn, on the alkalinity generated during silicate weathering less the amount consumed during the formation of secondary clay minerals both on the continents and in the ocean. In marine enviroments this process, often referred to as reverse weathering, consumes seawater alkalinity (and cations) via reaction with degraded Al-silicate minerals. Because these reactions constitute a sink of seawater alkalinity, changes in the amount of reverse weathering will lead to imbalances between alkalinity sources and sinks. The net effect is that on timescales greater than the timescale of carbonate compensation (< 10 kyr), changes in reverse weathering will lead to changes in the rate of continental silicate weathering through the dependence of continental silicate weathering on atmospheric CO2 and climate. This mechanism is capable of changing rates of continental silicate weathering without changing either the rate of volcanic outgassing or the rate constant for continental silicate weathering (i.e. through mountain-building or the exposure of different rock types) and as a result represents a unique way of modulating the global carbon cycle and Earth's climate on geologic timescales.

System for improving measurement accuracy of transducer by measuring transducer temperature and resistance change using thermoelectric voltages

NASA Technical Reports Server (NTRS)

Anderson, Karl F. (Inventor); Parker, Allen R., Jr. (Inventor)

1993-01-01

A constant current loop measuring system measures a property including the temperature of a sensor responsive to an external condition being measured. The measuring system includes thermocouple conductors connected to the sensor, sensing first and second induced voltages responsive to the external condition. In addition, the measuring system includes a current generator and reverser generating a constant current, and supplying the constant current to the thermocouple conductors in forward and reverse directions generating first and second measured voltages, and a determining unit receiving the first and second measured voltages from the current generator and reverser, and determining the temperature of the sensor responsive to the first and second measured voltages.

Single Turnover Kinetics of Tryptophan Hydroxylase: Evidence for a New Intermediate in the Reaction of the Aromatic Amino Acid Hydroxylases

PubMed Central

Pavon, Jorge Alex; Eser, Bekir; Huynh, Michaela T.; Fitzpatrick, Paul F.

2010-01-01

Tryptophan hydroxylase (TrpH) uses a non-heme mononuclear iron center to catalyze the tetrahydropterin-dependent hydroxylation of tryptophan to 5-hydroxytryptophan. The reactions of the TrpH·Fe(II), TrpH·Fe(II)·tryptophan, TrpH·Fe(II)·6MePH4·tryptophan, and TrpH·Fe(II)·6MePH4·phenylalanine complexes with O2 were monitored by stopped-flow absorbance spectroscopy and rapid quench methods. The second-order rate constant for the oxidation of TrpH·Fe(II) has a value of 104 M−1s−1 irrespective of the presence of tryptophan. Stopped-flow absorbance analyses of the reaction of the TrpH·Fe(II)·6MePH4·tryptophan complex with oxygen are consistent with the initial step being reversible binding of oxygen, followed by the formation with a rate constant of 65 s−1 of an intermediate I that has maximal absorbance at 420 nm. The rate constant for decay of I, 4.4 s−1, matches that for formation of the 4a-hydroxypterin product monitored at 248 nm. Chemical-quench analyses show that 5-hydroxytryptophan forms with a rate constant of 1.3 s−1, and that overall turnover is limited by a subsequent slow step, presumably product release, with a rate constant of 0.2 s−1. All of the data with tryptophan as substrate can be described by a five-step mechanism. In contrast, with phenylalanine as substrate, the reaction can be described by three steps: a second-order reaction with oxygen to form I, decay of I as tyrosine forms, and slow product release. PMID:20687613

Gibbs Free Energy of Hydrolytic Water Molecule in Acyl-Enzyme Intermediates of a Serine Protease: A Potential Application for Computer-Aided Discovery of Mechanism-Based Reversible Covalent Inhibitors.

PubMed

Masuda, Yosuke; Yamaotsu, Noriyuki; Hirono, Shuichi

2017-01-01

In order to predict the potencies of mechanism-based reversible covalent inhibitors, the relationships between calculated Gibbs free energy of hydrolytic water molecule in acyl-trypsin intermediates and experimentally measured catalytic rate constants (k cat ) were investigated. After obtaining representative solution structures by molecular dynamics (MD) simulations, hydration thermodynamics analyses using WaterMap™ were conducted. Consequently, we found for the first time that when Gibbs free energy of the hydrolytic water molecule was lower, logarithms of k cat were also lower. The hydrolytic water molecule with favorable Gibbs free energy may hydrolyze acylated serine slowly. Gibbs free energy of hydrolytic water molecule might be a useful descriptor for computer-aided discovery of mechanism-based reversible covalent inhibitors of hydrolytic enzymes.

Iminoboronate Formation Leads to Fast and Reversible Conjugation Chemistry of α-Nucleophiles at Neutral pH

PubMed Central

Bandyopadhyay, Anupam

2015-01-01

Bioorthogonal reactions that are fast and reversible under physiologic conditions are in high demand for biological applications. Herein, we show that an ortho boronic acid substituent makes aryl ketones to rapidly conjugate with α-nucleophiles at neutral pH. Specifically, 2-acetylphenylboronic acid and derivatives were found to conjugate with phenylhydrazine with rate constants of 102 to 103 M−1 s−1, comparable to the fastest bioorthogonal conjugations known to date. 11B-NMR analysis reveals varied extent of iminoboronate formation of the conjugates, in which the imine nitrogen forms a dative bond with boron. The iminoboronate formation activates the imines for hydrolysis and exchange, rendering these oxime/hydrazone conjugations reversible and dynamic under physiologic conditions. The fast and dynamic nature of the iminoboronate chemistry should find wide applications in biology. PMID:26311464

Observing the Heterogeneous Electro-redox of Individual Single-Layer Graphene Sheets.

PubMed

Chen, Tao; Zhang, Yuwei; Xu, Weilin

2016-09-27

Electro-redox-induced heterogeneous fluorescence of an individual single-layer graphene sheet was observed in real time by a total internal reflection fluorescence microscope. It was found that the fluorescence intensity of an individual sheet can be tuned reversibly by applying periodic voltages to control the redox degree of graphene sheets. Accordingly, the oxidation and reduction kinetics of an individual single-layer graphene sheet was studied at different voltages. The electro-redox-induced reversible variation of fluorescence intensity of individual sheets indicates a reversible band gap tuning strategy. Furthermore, correlation analysis of redox rate constants on individual graphene sheets revealed a redox-induced spatiotemporal heterogeneity or dynamics of graphene sheets. The observed controllable redox kinetics can rationally guide the precise band gap tuning of individual graphene sheets and then help their extensive applications in optoelectronics and devices for renewable energy.

Reversible intermolecular energy transfer between saturated amines and benzene in non-polar solution

NASA Astrophysics Data System (ADS)

Halpern, Arthur M.; Wryzykowska, Krystyna

1981-01-01

Excitation of a mixture of dimethylethylamine (DEMA) and benzene in n-hexane at 222 nm primarily produces excited amine, while at 261 nm excited benzene predominantly results. The fluorescence spectra appreciably overlap. With 222 nm excitation, DEMA fluorescence is quenched by benzene at the diffusion-controlled rate; this quenching results with nearly unit efficiency in sensitized benzene fluorescence. With 261 nm excitation, some sensitized DEMA fluorescence is observed: the rate constant for tins process is ≈ 2.6 × 10 9 M -1 s -1.

Bioavailability of Oral Pyridostigmine and Inhibition of Red Blood Cell Acetylcholinesterase by Oral and Intravenous Pyridostigmine

DTIC Science & Technology

1989-03-22

Case Report Forms 134 1. INTRODUCTION Studies in animals have indicated that carbamate acetyl- cholinesterase inhibitors have protective effects...effect compartment with a rate constant KE0. Furthermore, it was assumed that pyridostigmine behaves as a standard competitive inhibitor of the...really reversible, at least in the classical sense of almost instantaneous association and dissociation of eruzyme with inhibitor . After carbamylation

Polyurethane intravaginal ring for controlled delivery of dapivirine, a nonnucleoside reverse transcriptase inhibitor of HIV-1.

PubMed

Gupta, Kavita M; Pearce, Serena M; Poursaid, Azadeh E; Aliyar, Hyder A; Tresco, Patrick A; Mitchnik, Mark A; Kiser, Patrick F

2008-10-01

Women-controlled methods for prevention of male-to-female sexual transmission of HIV-1 are urgently needed. Providing inhibitory concentrations of HIV-1 reverse transcriptase inhibitors to impede the replication of the virus in the female genital tissue offers a mechanism for prophylaxis of HIV-1. To this end, an intravaginal ring device that can provide long duration delivery of dapivirine, a nonnucleoside reverse transcriptase inhibitor of HIV-1, was developed utilizing a medical-grade polyether urethane. Monolithic intravaginal rings were fabricated and sustained release with cumulative flux linear with time was demonstrated under sink conditions for a period of 30 days. The release rate was directly proportional to the amount of drug loaded. Another release study conducted for a week utilizing liposome dispersions as sink conditions, to mimic the partitioning of dapivirine into vaginal tissue, also demonstrated release rates constant with time. These results qualify polyether urethanes for development of intravaginal rings for sustained delivery of microbicidal agents. (c) 2008 Wiley-Liss, Inc. and the American Pharmacists Association

Cryogenic liquid resettlement activated by impulsive thrust in space-based propulsion system

NASA Technical Reports Server (NTRS)

Hung, R. J.; Shyu, K. L.

1991-01-01

The purpose of present study is to investigate most efficient technique for propellant resettling through the minimization of propellant usage and weight penalties. Comparison between the constant reverse gravity acceleration and impulsive reverse gravity acceleration to be used for the activation of propellant resettlement, it shows that impulsive reverse gravity thrust is superior to constant reverse gravity thrust for liquid reorientation in a reduced gravity environment. Comparison among impulsive reverse gravity thrust with 0.1, 1.0 and 10 Hz frequencies for liquid filled level in the range between 30 to 80 percent, it shows that the selection of 1.0 Hz frequency impulsive thrust over the other frequency ranges of impulsive thrust is most proper based on the present study.

Cryogenic liquid resettlement activated by impulsive thrust in space-based propulsion system

NASA Technical Reports Server (NTRS)

Hung, R. J.; Shyu, K. L.

1991-01-01

The purpose of present study is to investigate the most efficient technique for propellant resettling through the minimization of propellant usage and weight penalties. Comparison between the constant reverse gravity acceleration and impulsive reverse gravity acceleration to be used for the activation of propellant resettlement shows that impulsive reverse gravity thrust is superior to constant reverse gravity thrust for liquid reorientation in a reduced gravity environment. Comparison among impulsive reverse gravity thrust with 0.1, 1.0, and 10 Hz frequencies for liquid-filled level in the range between 30 to 80 percent shows that the selection of a medium frequency of 1.0 Hz impulsive thrust over the other frequency ranges of impulsive thrust is the most proper.

Multiscale Model of Swarming Bacteria

NASA Astrophysics Data System (ADS)

Alber, Mark

2011-03-01

Many bacteria can rapidly traverse surfaces from which they are extracting nutrient for growth. They generate flat, spreading colonies, called swarms because they resemble swarms of insects. In the beginning of the talk, swarms of the M. xanthus will be described in detail. Individual M. xanthus cells are elongated; they always move in the direction of their long axis; and they are in constant motion, repeatedly touching each other. As a cell glides, the slime capsule of a cell interacts with the bare agar surface, non-oriented slime which arises from the surface contact with the slime capsule, or oriented slime trails. Remarkably, cells regularly reverse their gliding directions. In this talk a detailed cell- and behavior-based computational model of M. xanthus swarming will be used to demonstrate that reversals of gliding direction and cell bending are essential for swarming and that specific reversal frequencies result in optimal swarming rate of the whole population. This suggests that the circuit regulating reversals evolved to its current sensitivity under selection for growth achieved by swarming.

A model describing the effect of sex-reversed YY fish in an established wild population: The use of a Trojan Y chromosome to cause extinction of an introduced exotic species.

PubMed

Gutierrez, Juan B; Teem, John L

2006-07-21

A novel means of inducing extinction of an exotic fish population is proposed using a genetic approach to shift the ratio of male to females within a population. In the proposed strategy, sex-reversed fish containing two Y chromosomes are introduced into a normal fish population. These YY fish result in the production of a disproportionate number of male fish in subsequent generations. Mathematical modeling of the system following introduction of YY fish at a constant rate reveals that female fish decline in numbers over time, leading to eventual extinction of the population.

A Stopped-Flow Kinetics Experiment for Advanced Undergraduate Laboratories: Formation of Iron(III) Thiocyannate

NASA Astrophysics Data System (ADS)

Clark, Charles R.

1997-10-01

A series of 15 stopped-flow kinetic experiments relating to the formation of iron(III)- thiocyanate at 25.0 °C and I = 1.0 M (NaClO4) is described. A methodology is given whereby solution preparation and data collection are able to be carried out within the time scale of a single laboratory period (3-4 h). Kinetic data are obtained using constant [SCN-], and at three H+ concentrations (0.10, 0.20, 0.30 M) for varying concentrations of Fe3+ (ca. 0.0025 - 0.020 M). Rate data (450 nm) are consistent with rate laws for the forward and reverse reactions: kf = (k1 + k2Ka1/[H+])[Fe3+] and kr = k-1 + k-2Ka2/[H+] respectively, with k1,k-1 corresponding to the rate constants for formation and decay of FeSCN2+, k2, k-2 to the rate constants for formation and decay of the FeSCN(OH)+ ion and Ka1,Ka2 to the acid dissociation constants (coordinated OH2 ionization) of Fe3+ and FeSCN2+. Using literature values for the latter two quantities ( Ka1 = 2.04 x 10-3 M, Ka2 = 6.5 x 10-5 M) allows values for the four rate constants to be obtained. A typical data set is analyzed to give k1 = 109(10) M-1s-1, k-1 = 0.79(0.10) s-1, k2= 8020(800) M-1s-1, k-2 = 2630(230) s-1. Absorbance change data for reaction (DeltaA) follow the expression: DeltaA = Alim.Kf.[Fe3+]/(1 + Kf.[Fe3+]), with Alim corresponding to the absorbance of fully formed FeSCN2+ (i.e. free SCN- absent) and Kf to the formation constant of this complex (value in the example 112(5) M-1, c.f. 138(29) M-1 from the kinetic data).

Thermochemistry is not a lower bound to the activation energy of endothermic reactions: a kinetic study of the gas-phase reaction of atomic chlorine with ammonia.

PubMed

Gao, Yide; Alecu, I M; Hsieh, P-C; Morgan, Brad P; Marshall, Paul; Krasnoperov, Lev N

2006-06-01

The rate constant for Cl + NH3 --> HCl + NH2 has been measured over 290-570 K by the time-resolved resonance fluorescence technique. Ground-state Cl atoms were generated by 193 nm excimer laser photolysis of CCl4 and reacted under pseudo-first-order conditions with excess NH3. The forward rate constant was fit by the expression k1 = (1.08 +/- 0.05) x 10(-11) exp(-11.47 +/- 0.16 kJ mol(-1)/RT) cm3 molecule(-1) s(-1), where the uncertainties in the Arrhenius parameters are +/-1 sigma and the 95% confidence limits for k1 are +/-11%. To rationalize the activation energy, which is 7.4 kJ mol(-1) below the endothermicity in the middle of the 1/T range, the potential energy surface was characterized with MPWB1K/6-31++G(2df,2p) theory. The products NH2 + HCl form a hydrogen-bonded adduct, separated from Cl + NH3 by a transition state lower in energy than the products. The rate constant for the reverse process k(-1) was derived via modified transition state theory, and the computed k(-1) exhibits a negative activation energy, which in combination with the experimental equilibrium constant yields k1 in fair accord with experiment.

Modular rate laws for enzymatic reactions: thermodynamics, elasticities and implementation.

PubMed

Liebermeister, Wolfram; Uhlendorf, Jannis; Klipp, Edda

2010-06-15

Standard rate laws are a key requisite for systematically turning metabolic networks into kinetic models. They should provide simple, general and biochemically plausible formulae for reaction velocities and reaction elasticities. At the same time, they need to respect thermodynamic relations between the kinetic constants and the metabolic fluxes and concentrations. We present a family of reversible rate laws for reactions with arbitrary stoichiometries and various types of regulation, including mass-action, Michaelis-Menten and uni-uni reversible Hill kinetics as special cases. With a thermodynamically safe parameterization of these rate laws, parameter sets obtained by model fitting, sampling or optimization are guaranteed to lead to consistent chemical equilibrium states. A reformulation using saturation values yields simple formulae for rates and elasticities, which can be easily adjusted to the given stationary flux distributions. Furthermore, this formulation highlights the role of chemical potential differences as thermodynamic driving forces. We compare the modular rate laws to the thermodynamic-kinetic modelling formalism and discuss a simplified rate law in which the reaction rate directly depends on the reaction affinity. For automatic handling of modular rate laws, we propose a standard syntax and semantic annotations for the Systems Biology Markup Language. An online tool for inserting the rate laws into SBML models is freely available at www.semanticsbml.org. Supplementary data are available at Bioinformatics online.

On the Malthusian theory of long swings.

PubMed

Waterman, A M

1987-05-01

"In the Essay on Population economic growth consists of alternating surges of population (during which real wages fall and the rate of profit rises) and capital (during which the reverse occurs). A series of temporary equilibria exists at which wages are maximal, the rate of profit minimal, and fully employed work-force in technically determined relation to fixed capital stock. Between these equilibria occur episodes of excess labour, below-maximum wages, above minimum profit-rate and capital accumulation. Malthus's 'ratios' presuppose a logarithmic production function that implies first, that the full-employment real wage will fall to subsistence; secondly, that the full-employment 'wages fund' is constant." (SUMMARY IN FRE) excerpt

A LATENT PERIOD IN THE ACTION OF COPPER ON RESPIRATION

PubMed Central

Cook, S. F.

1926-01-01

1. When copper chloride is allowed to act on Aspergillus niger there is at first a period during which there is no change in the rate of the production of carbon dioxide, following which the rate of respiration falls. The interval of no change is called the latent period. 2. When the copper is removed from the external solution before the end of the latent period this interval is prolonged. The rate of respiration then falls to a new level below the normal level. 3. Experiments on Nitella and on Valonia indicate that the copper penetrates the cell almost immediately. 4. The length of the latent period varies inversely as a constant power of the concentration of the copper. 5. These results are explained by assuming that the copper is made active in the respiration system by means of a reversible reaction. By using appropriate velocity constants the experimental curves can be duplicated by calculated curves. PMID:19872281

Reverse total shoulder arthroplasty. Survivorship analysis of eighty replacements followed for five to ten years.

PubMed

Guery, Jacques; Favard, Luc; Sirveaux, François; Oudet, Didier; Mole, Daniel; Walch, Gilles

2006-08-01

Reverse total shoulder arthroplasty is currently being used to treat selected patients with disabling shoulder arthropathy. The purposes of this study were to investigate the medium-term results of reverse total shoulder arthroplasty and to analyze the influence of etiology on the result. We carried out a multicenter study with a minimum follow-up of five years and determined the survival rate of the prosthesis according to the initial etiology of the shoulder arthropathy. Eighty prostheses were implanted in seventy-seven patients between 1992 and 1998. Sixty-six shoulders had an arthropathy with a massive rotator cuff tear, and fourteen shoulders had a disorder with another etiology (rheumatoid arthritis, trauma, or revision arthropathy). At the time of review, eighteen patients had died and two were lost to follow-up. The remaining fifty-seven patients (sixty shoulders) were examined or interviewed by telephone at a mean follow-up of 69.6 months. Cumulative survival curves were generated with replacement of the prosthesis, glenoid loosening, and a functional Constant score of <30 as the end points. The survival rate with replacement of the prosthesis and glenoid loosening as the end points were 91% and 84%, respectively, at 120 months, with shoulders that had arthropathy with a massive rotator cuff tear demonstrating a significantly better result than those that had a disorder with another etiology (p < 0.05). On the other hand, the survival rate with an absolute Constant score of <30 as an end point was 58% at 120 months, with no significant difference with respect to etiology. Two breaks were observed in the survival curves. The first concerned survival until replacement of the prosthesis and occurred at around three years, reflecting early loosening of the prosthesis. The curve then became stable. A second break started at around six years and reflected progressive deterioration of the functional result. Our findings indicate that the reverse total prosthesis should be reserved for the treatment of very disabling shoulder arthropathy with a massive rotator cuff rupture, and it should be used exclusively in patients over seventy years old with low functional demands.

Iminoboronate Formation Leads to Fast and Reversible Conjugation Chemistry of α-Nucleophiles at Neutral pH.

PubMed

Bandyopadhyay, Anupam; Gao, Jianmin

2015-10-12

Bioorthogonal reactions that are fast and reversible under physiological conditions are in high demand for biological applications. Herein, it is shown that an ortho boronic acid substituent makes aryl ketones rapidly conjugate with α-nucleophiles at neutral pH. Specifically, 2-acetylphenylboronic acid and derivatives were found to conjugate with phenylhydrazine with rate constants of 10(2) to 10(3) M(-1) s(-1) , comparable to the fastest bioorthogonal conjugations known to date. (11) B NMR analysis revealed the varied extent of iminoboronate formation of the conjugates, in which the imine nitrogen forms a dative bond with boron. The iminoboronate formation activates the imines for hydrolysis and exchange, rendering these oxime/hydrazone conjugations reversible and dynamic under physiological conditions. The fast and dynamic nature of the iminoboronate chemistry should find wide applications in biology. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effect of varying internal geometry on the static performance of rectangular thrust-reverser ports

NASA Technical Reports Server (NTRS)

Re, Richard J.; Mason, Mary L.

1987-01-01

An investigation has been conducted to evaluate the effects of several geometric parameters on the internal performance of rectangular thrust-reverser ports for nonaxisymmetric nozzles. Internal geometry was varied with a test apparatus which simulated a forward-flight nozzle with a single, fully deployed reverser port. The test apparatus was designed to simulate thrust reversal (conceptually) either in the convergent section of the nozzle or in the constant-area duct just upstream of the nozzle. The main geometric parameters investigated were port angle, port corner radius, port location, and internal flow blocker angle. For all reverser port geometries, the port opening had an aspect ratio (throat width to throat height) of 6.1 and had a constant passage area from the geometric port throat to the exit. Reverser-port internal performance and thrust-vector angles computed from force-balance measurements are presented.

MULTIPLE DIFFERENTIAL ROTARY MECHANICAL DRIVE

DOEpatents

Smits, R.G.

1964-01-28

This patent relates to a mechanism suitable for such applications as driving two spaced-apart spools which carry a roll film strip under conditions where the film movement must be rapidly started, stopped, and reversed while maintaining a constant tension on the film. The basic drive is provided by a variable speed, reversible rnotor coupled to both spools through a first differential mechanism and driving both spools in the same direction. A second motor, providing a constant torque, is connected to the two spools through a second differential mechanism and is coupled to impart torque to one spool in a first direction anid to the other spool in the reverse direction thus applying a constant tension to the film passing over the two spools irrespective of the speed or direction of rotation thereof. (AEC)

Determination of thermodynamics and kinetics of RNA reactions by force

PubMed Central

Tinoco, Ignacio; Li, Pan T. X.; Bustamante, Carlos

2008-01-01

Single-molecule methods have made it possible to apply force to an individual RNA molecule. Two beads are attached to the RNA; one is on a micropipette, the other is in a laser trap. The force on the RNA and the distance between the beads are measured. Force can change the equilibrium and the rate of any reaction in which the product has a different extension from the reactant. This review describes use of laser tweezers to measure thermodynamics and kinetics of unfolding/refolding RNA. For a reversible reaction the work directly provides the free energy; for irreversible reactions the free energy is obtained from the distribution of work values. The rate constants for the folding and unfolding reactions can be measured by several methods. The effect of pulling rate on the distribution of force-unfolding values leads to rate constants for unfolding. Hopping of the RNA between folded and unfolded states at constant force provides both unfolding and folding rates. Force-jumps and force-drops, similar to the temperature jump method, provide direct measurement of reaction rates over a wide range of forces. The advantages of applying force and using single-molecule methods are discussed. These methods, for example, allow reactions to be studied in non-denaturing solvents at physiological temperatures; they also simplify analysis of kinetic mechanisms because only one intermediate at a time is present. Unfolding of RNA in biological cells by helicases, or ribosomes, has similarities to unfolding by force. PMID:17040613

Microgravity liquid propellant management

NASA Technical Reports Server (NTRS)

Hung, R. J.

1990-01-01

The requirement to settle or to position liquid fluid over the outlet end of a spacecraft propellant tank prior to main engine restart, poses a microgravity fluid behavior problem. Resettlement or reorientation of liquid propellant can be accomplished by providing optimal acceleration to the spacecraft such that the propellant is reoriented over the tank outlet without any vapor entrainment, any excessive geysering, or any other undersirable fluid motion for the space fluid management under microgravity environment. The most efficient technique is studied for propellant resettling through the minimization of propellant usage and weight penalties. Both full scale and subscale liquid propellant tank of Space Transfer Vehicle were used to simulate flow profiles for liquid hydrogen reorientation over the tank outlet. In subscale simulation, both constant and impulsive resettling acceleration were used to simulate the liquid flow reorientation. Comparisons between the constant reverse gravity acceleration and impulsive reverse gravity acceleration to be used for activation of propellant resettlement shows that impulsive reverse gravity thrust is superior to constant reverse gravity thrust.

Reverse shoulder arthroplasty for the treatment of acute complex proximal humeral fractures: Influence of greater tuberosity healing on the functional outcomes.

PubMed

Torrens, Carlos; Alentorn-Geli, Eduard; Mingo, Felipe; Gamba, Carlo; Santana, Fernando

2018-01-01

To investigate the influence of greater tuberosity healing on the functional outcomes of reverse shoulder arthroplasty (RSA) for the treatment of acute complex proximal humeral fractures (PHFs), and to investigate the influence of patient- and surgery-related factors in the healing of the greater tuberosity. Retrospective study including 41 consecutive PHFs treated using RSA with minimum 2-year follow-up. In all the cases, tuberosities were reattached with a standardized technique. All the patients were assessed at the last follow-up with constant score. Body mass index, surgery delay, comorbidities, polyethylene size, glenosphere size, overhanging of glenosphere, and scapular notch were recorded, and their influence in final constant score and in greater tuberosity healing was analyzed. Mean final constant score was of 60.7 points (standard deviation (SD) = 9.9). Greater tuberosity healed in proper position in 68% of the cases. There were no significant differences in constant score between patients with (mean = 61; SD = 9.5) and without (mean = 61; SD = 11.3) the healing of greater tuberosity. All patients scored above 90° in forward elevation. Scapular notch was reported in 14.6% of the cases. Age significantly affected the constant score ( p = 0.008). Comorbidities significantly interfered with greater tuberosity healing ( p = 0.03). There was one reoperation after dislocation. In spite of expecting good functional outcome with low complication rate after RSA for acute PHFs, the influence of greater tuberosity healing on shoulder function could not be demonstrated. The presence of comorbidities, but not age or gender, negatively influenced the healing of the greater tuberosity.

Rate dependency of delayed rectifier currents during the guinea-pig ventricular action potential

PubMed Central

Rocchetti, Marcella; Besana, Alessandra; Gurrola, Georgina B; Possani, Lourival D; Zaza, Antonio

2001-01-01

The action potential clamp technique was exploited to evaluate the rate dependency of delayed rectifier currents (IKr and IKs) during physiological electrical activity. IKr and IKs were measured in guinea-pig ventricular myocytes at pacing cycle lengths (CL) of 1000 and 250 ms.A shorter CL, with the attendant changes in action potential shape, was associated with earlier activation and increased magnitude of both IKr and IKs. Nonetheless, the relative contributions of IKr and IKs to total transmembrane current were independent of CL.Shortening of diastolic interval only (constant action potential shape) enhanced IKs, but not IKr.IKr was increased by a change in the action potential shape only (constant diastolic interval).In ramp clamp experiments, IKr amplitude was directly proportional to repolarization rate at values within the low physiological range (< 1.0 V s−1); at higher repolarization rates proportionality became shallower and finally reversed.When action potential duration (APD) was modulated by constant current injection (I-clamp), repolarization rates > 1.0 V s−1 were associated with a reduced effect of IKr block on APD. The effect of changes in repolarization rate was independent of CL and occurred in the presence of IKs blockade.In spite of its complexity, the behaviour of IKr was accurately predicted by a numerical model based entirely on known kinetic properties of the current.Both IKr and IKs may be increased at fast heart rates, but this may occur through completely different mechanisms. The mechanisms identified are such as to contribute to abnormal rate dependency of repolarization in prolonged repolarization syndromes. PMID:11483703

Polycomb group protein complexes exchange rapidly in living Drosophila.

PubMed

Ficz, Gabriella; Heintzmann, Rainer; Arndt-Jovin, Donna J

2005-09-01

Fluorescence recovery after photobleaching (FRAP) microscopy was used to determine the kinetic properties of Polycomb group (PcG) proteins in whole living Drosophila organisms (embryos) and tissues (wing imaginal discs and salivary glands). PcG genes are essential genes in higher eukaryotes responsible for the maintenance of the spatially distinct repression of developmentally important regulators such as the homeotic genes. Their absence, as well as overexpression, causes transformations in the axial organization of the body. Although protein complexes have been isolated in vitro, little is known about their stability or exact mechanism of repression in vivo. We determined the translational diffusion constants of PcG proteins, dissociation constants and residence times for complexes in vivo at different developmental stages. In polytene nuclei, the rate constants suggest heterogeneity of the complexes. Computer simulations with new models for spatially distributed protein complexes were performed in systems showing both diffusion and binding equilibria, and the results compared with our experimental data. We were able to determine forward and reverse rate constants for complex formation. Complexes exchanged within a period of 1-10 minutes, more than an order of magnitude faster than the cell cycle time, ruling out models of repression in which access of transcription activators to the chromatin is limited and demonstrating that long-term repression primarily reflects mass-action chemical equilibria.

Nucleocapsid Protein Annealing of a Primer-Template Enhances (+)-Strand DNA Synthesis and Fidelity by HIV-1 Reverse Transcriptase†

PubMed Central

Kim, Jiae; Roberts, Anne; Yuan, Hua; Xiong, Yong; Anderson, Karen S.

2012-01-01

Human immunodeficiency virus type-1 (HIV-1) requires reverse transcriptase (RT) and HIV-1 nucleocapsid protein (NCp7) for proper viral replication. HIV-1 NCp7 has been shown to enhance various steps in reverse transcription including tRNA initiation and strand transfer which may be mediated through interactions with RT as well as RNA and DNA oligonucleotides. With the use of DNA oligonucleotides, we have examined the interaction of NCp7 with RT and the kinetics of reverse transcription during (+)-strand synthesis with an NCp7-facilitated annealed primer-template. Using a pre-steady state kinetics approach, the NCp7-annealed primer-template has a substantial increase (3-7 fold) in the rate of incorporation (kpol) by RT as compared to heat annealed primer-template with single nucleotide incorporation. There was also a 2-fold increase in the binding affinity constant (Kd) of the nucleotide. These differences in kpol and Kd were not through direct interactions between HIV-1 RT and NCp7. When examining extension by RT, the data suggests that the NCp7-annealed primer-template facilitates the formation of a longer product more quickly compared to the heat annealed primer-template. This enhancement in rate is mediated through interactions with NCp7’s zinc fingers and N-terminal domain and nucleic acids. The NCp7-annealed primer-template also enhances the fidelity of RT (3-fold) by slowing the rate of incorporation of an incorrect nucleotide. Taken together, this study elucidates a new role of NCp7 by facilitating DNA-directed DNA synthesis during reverse transcription by HIV-1 RT that may translate into enhanced viral fitness and offers an avenue to exploit for targeted therapeutic intervention against HIV. PMID:22210155

Role of Reversible Histidine Coordination in Hydroxylamine Reduction by Plant Hemoglobins (Phytoglobins).

PubMed

Athwal, Navjot Singh; Alagurajan, Jagannathan; Andreotti, Amy H; Hargrove, Mark S

2016-10-18

Reduction of hydroxylamine to ammonium by phytoglobin, a plant hexacoordinate hemoglobin, is much faster than that of other hexacoordinate hemoglobins or pentacoordinate hemoglobins such as myoglobin, leghemoglobin, and red blood cell hemoglobin. The reason for differences in reactivity is not known but could be intermolecular electron transfer between protein molecules in support of the required two-electron reduction, hydroxylamine binding, or active site architecture favoring the reaction. Experiments were conducted with phytoglobins from rice, tomato, and soybean along with human neuroglobin and soybean leghemoglobin that reveal hydroxylamine binding as the rate-limiting step. For hexacoordinate hemoglobins, binding is limited by the dissociation rate constant for the distal histidine, while leghemoglobin is limited by an intrinsically low affinity for hydroxylamine. When the distal histidine is removed from rice phytoglobin, a hydroxylamine-bound intermediate is formed and the reaction rate is diminished, indicating that the distal histidine imidazole side chain is critical for the reaction, albeit not for electron transfer but rather for direct interaction with the substrate. Together, these results demonstrate that phytoglobins are superior at hydroxylamine reduction because they have distal histidine coordination affinity constants near 1, and facile rate constants for binding and dissociation of the histidine side chain. Hexacoordinate hemoglobins such as neuroglobin are limited by tighter histidine coordination that blocks hydroxylamine binding, and pentacoordinate hemoglobins have intrinsically lower hydroxylamine affinities.

Reversible conformational transition gives rise to 'zig-zag' temperature dependence of the rate constant of irreversible thermoinactivation of enzymes.

PubMed

Levitsky VYu; Melik-Nubarov, N S; Siksnis, V A; Grinberg VYa; Burova, T V; Levashov, A V; Mozhaev, V V

1994-01-15

We have obtained unusual 'zig-zag' temperature dependencies of the rate constant of irreversible thermoinactivation (k(in)) of enzymes (alpha-chymotrypsin, covalently modified alpha-chymotrypsin, and ribonuclease) in a plot of log k(in) versus reciprocal temperature (Arrhenius plot). These dependencies are characterized by the presence of both ascending and descending linear portions which have positive and negative values of the effective activation energy (Ea), respectively. A kinetic scheme has been suggested that fits best for a description of these zig-zag dependencies. A key element of this scheme is the temperature-dependent reversible conformational transition of enzyme from the 'low-temperature' native state to a 'high-temperature' denatured form; the latter form is significantly more stable against irreversible thermoinactivation than the native enzyme. A possible explanation for a difference in thermal stabilities is that low-temperature and high-temperature forms are inactivated according to different mechanisms. Existence of the suggested conformational transition was proved by the methods of fluorescence spectroscopy and differential scanning calorimetry. The values of delta H and delta S for this transition, determined from calorimetric experiments, are highly positive; this fact underlies a conclusion that this heat-induced transition is caused by an unfolding of the protein molecule. Surprisingly, in the unfolded high-temperature conformation, alpha-chymotrypsin has a pronounced proteolytic activity, although this activity is much smaller than that of the native enzyme.

Fiber Optic Immunochemical Sensors For Continuous Monitoring Of Hapten Concentrations

NASA Astrophysics Data System (ADS)

Miller, W. Greg; Anderson, F. Philip

1989-06-01

We describe a fiber optic sensor based on a homogeneous fluorescence energy transfer immunoassay which operates in a continuous, reversible manner to quantitate the anticonvulsant drug phenytoin. B-phycoerythrin-phenytoin and Texas Red labeled anti-phenytoin antibody were sealed inside a short length of cellulose dialysis tubing which was cemented to the distal end of an optical fiber. When the sensor was placed into a solution of phenytoin, the drug crossed the dialysis membrane, displaced a fraction of the B-phycoerythrin-phenytoin from the antibody, and produced a change in fluorescence signal which was measured with a fiber optic fluorometer. The sensor had a concentration response of 5 to 500μmo1/L phenytoin with a response time of 5 to 15 min and precision of <2.5% CV. The chemical kinetics of the antibody-hapten indicator reaction were modeled mathematically and simulation showed that response time in the minutes range can be achieved when the dissociation rate constant is greater than approximately 10-3 sec-1. The dissociation rate constant influences the time to reach equilibrium and the unbound P* concentration range available for instrumental measurement. The ratio of the labeled and unlabeled hapten dissociation rate constants influences the analyte concentration range to which the sensor will respond.

Theory of single-molecule controlled rotation experiments, predictions, tests, and comparison with stalling experiments in F1-ATPase.

PubMed

Volkán-Kacsó, Sándor; Marcus, Rudolph A

2016-10-25

A recently proposed chemomechanical group transfer theory of rotary biomolecular motors is applied to treat single-molecule controlled rotation experiments. In these experiments, single-molecule fluorescence is used to measure the binding and release rate constants of nucleotides by monitoring the occupancy of binding sites. It is shown how missed events of nucleotide binding and release in these experiments can be corrected using theory, with F 1 -ATP synthase as an example. The missed events are significant when the reverse rate is very fast. Using the theory the actual rate constants in the controlled rotation experiments and the corrections are predicted from independent data, including other single-molecule rotation and ensemble biochemical experiments. The effective torsional elastic constant is found to depend on the binding/releasing nucleotide, and it is smaller for ADP than for ATP. There is a good agreement, with no adjustable parameters, between the theoretical and experimental results of controlled rotation experiments and stalling experiments, for the range of angles where the data overlap. This agreement is perhaps all the more surprising because it occurs even though the binding and release of fluorescent nucleotides is monitored at single-site occupancy concentrations, whereas the stalling and free rotation experiments have multiple-site occupancy.

Comparison of rate constants for (PO3-) transfer by the Mg(II), Cd(II), and Li(I) forms of phosphoglucomutase.

PubMed

Ray, W J; Post, C B; Puvathingal, J M

1989-01-24

Net rate constants that define the steady-state rate through a sequence of steps and the corresponding effective energy barriers for two (PO3-)-transfer steps in the phosphoglucomutase reaction were compared as a function of metal ion, M, where M = Mg2+ and Cd2+. These steps involve the reaction of either the 1-phosphate or the 6-phosphate of glucose 1,6-bisphosphate (Glc-P2) bound to the dephosphoenzyme (ED) to produce the phosphoenzyme (EP) and the free monophosphates, glucose 1-phosphate (Glc-1-P) or glucose 6-phosphate (Glc-6-P): EP.M + Glc-1-P----ED.M.Glc-P2----EP.M.Glc-6-P6. Before this comparison was made, net rate constants for the Cd2+ enzyme, obtained at high enzyme concentration via 31P NMR saturation-transfer studies [Post, C. B., Ray, W. J., Jr., & Gorenstein, D. G. (1989) Biochemistry (preceding paper in this issue)], were appropriately scaled by using the observed constants to calculate both the expected isotope-transfer rate at equilibrium and the steady-state rate under initial velocity conditions and comparing the calculated values with those measured in dilute solution. For the Mg2+ enzyme, narrow limits on possible values of the corresponding net rate constants were imposed on the basis of initial velocity rate constants for the forward and reverse directions plus values for the equilibrium distribution of central complexes, since direct measurement is not feasible. The effective energy barriers for both the Mg2+ and Cd2+ enzymes, calculated from the respective net rate constants, together with previously values for the equilibrium distribution of complexes in both enzymic systems [Ray, W. J., Jr., & Long, J. W. (1976) Biochemistry 15, 4018-4025], show that the 100-fold decrease in the kappa cat for the Cd2+ relative to the Mg2+ enzyme is caused by two factors: the increased stability of the intermediate bisphosphate complex and the decreased ability to cope with the phosphate ester involving the 1-hydroxyl group of the glucose ring. In fact, it is unlikely that the efficiency of (PO3-) transfer to the 6-hydroxyl group of bound Glc-1-P (thermodynamically favorable direction) is reduced by more than an order of magnitude in the Cd2+ enzyme. By contrast, the efficiency of the Li+ enzyme in the same (PO3-)-transfer step is less than 4 x 10(-8) that of the Mg2+ enzyme.(ABSTRACT TRUNCATED AT 400 WORDS)

Reversible Reduction of Nitroxides to Hydroxylamines: the Roles for Ascorbate and Glutathione

PubMed Central

Bobko, Andrey A.; Kirilyuk, Igor A.; Grigor'ev, Igor A.; Zweier, Jay L.; Khramtsov, Valery V.

2007-01-01

Biological applications of stable nitroxyl radicals, NR, include their use as contrast agents for magnetic resonance imaging, spin labels, superoxide dismutase mimics, and antioxidants. The rapid reduction of NR in biological samples into hydroxylamines, HA, significantly limits their application. In its turn, reoxidation of HA back to the NR has been used for detection of reactive oxygen species, ROS. In this work comparative studies of the reduction of pyrrolidine, imidazoline and imidazolidine NR by ascorbate were performed taking advantage of recently synthesized tetraethyl substituted NR with much higher stability towards reduction both in vitro and in vivo. Surprisingly, these NR kept 10-50% of initial intensity of electron paramagnetic resonance signal for about 1 h in the presence of hundred fold excess of ascorbate. To explain this data, reoxidation of the corresponding HA by ascorbate radical and dehydroascorbic acid back to the NR was proposed. This hypothesis was supported by direct measurement of the NR appearance from the HA upon ascorbate radical generation by ascorbate oxidase, or in the presence of the dehydroascorbic acid. The reversible reaction between NR and ascorbate was observed for the various types of the NR, and the rate constants for direct and reverse reactions were determined. The equilibrium constants for one-electron reduction of the tetraethyl substituted NR by ascorbate were found to be in the range from 2.65×10−6 to 10−5 which is significantly lower than corresponding values for the tetramethyl substituted NR (less or about 10−4). This explains an establishment of EPR-detectable quasi-equilibrium level of tetraethyl substituted NR in the presence of excess of ascorbate. The redox reactions of the NR-HA couple in ascorbate containing medium was found to be significantly affected by glutathione, GSH. This effect was attributed to the reduction of ascorbate radical by GSH, and the rate constant of this reaction was found to be equal to 10 M−1s−1. In summary, the data provide new insight into the redox chemistry of NR and HA, and significantly affect interpretation and strategy of their use as redox- and ROS-sensitive probes, or as antioxidants. PMID:17210453

The mechanism and thermodynamics of transesterification of acetate-ester enolates in the gas phase

NASA Astrophysics Data System (ADS)

Haas, George W.; Giblin, Daryl E.; Gross, Michael L.

1998-01-01

In solution, base-catalyzed hydrolysis and transesterification of esters are initiated by hydroxide- or alkoxide-ion attack at the carbonyl carbon. At low pressures in the gas phase, however, transesterification proceeds by an attack of the enolate anion of an acetate ester on an alcohol. Fourier transform mass spectrometry (FTMS) indicates that the reaction is the second-order process: -CH2-CO2-R + R'-OH --> - CH2-CO2-R' + R-OH and there is little to no detectable production of either alkoxide anion. Labeling studies show that the product and reactant enolate anion esters undergo exchange of hydrogens located [alpha] to the carbonyl carbon with the deuterium of R'-OD. The extent of the H/D exchange increases with reaction time, pointing to a short-lived intermediate. The alcoholysis reaction rate constants increase with increasing acidity of the primary, straight-chained alkyl alcohols, whereas steric effects associated with branched alcohols cause the rate constants to decrease. Equilibrium constants, which were determined directly from measurements at equilibrium and which were calculated from the forward and reverse rate constants, are near unity and show internal consistency. In the absence of steric effects, the larger enolate is always the favored product at equilibrium. The intermediate for the transesterification reaction, which can be generated at a few tenths of a torr in a tandem mass spectrometer, is tetrahedral, but other adducts that are collisionally stabilized under these conditions are principally loosely bound complexes.

Novel bio-electro-Fenton technology for azo dye wastewater treatment using microbial reverse-electrodialysis electrolysis cell.

PubMed

Li, Xiaohu; Jin, Xiangdan; Zhao, Nannan; Angelidaki, Irini; Zhang, Yifeng

2017-03-01

Development of sustainable technologies for treatment of azo dyes containing wastewaters has long been of great interest. In this study, we proposed an innovative concept of using microbial reverse-electrodialysis electrolysis cell (MREC) based Fenton process to treat azo dye wastewater. In such MREC-Fenton integrated process, the production of H 2 O 2 which is the key reactant of fenton-reaction was driven by the electrons harvested from the exoelectrogens and salinity-gradient between sea water and fresh water in MREC. Complete decolorization and mineralization of 400mgL -1 Orange G was achieved with apparent first order rate constants of 1.15±0.06 and 0.26±0.03h -1 , respectively. Furthermore, the initial concentration of orange G, initial solution pH, catholyte concentration, high and low concentration salt water flow rate and air flow rate were all found to significantly affect the dye degradation. This study provides an efficient and cost-effective system for the degradation of non-biodegradable pollutants. Copyright © 2017 Elsevier Ltd. All rights reserved.

Initiation of geyser during the resettlement of cryogenic liquid under impulsive reverse gravity acceleration in microgravity environment

NASA Technical Reports Server (NTRS)

Hung, R. J.; Shyu, K. L.

1991-01-01

The requirement to settle or to position liquid fluid over the outlet end of spacecraft propellant tank prior to main engine restart poses a microgravity fluid behavior problem. Resettlement or reorientation of liquid propellant can be accomplished by providing optimal acceleration to the spacecraft such that the propellant is reoriented over the tank outlet without any vapor entrainment, any excessive geysering, or any other undesirable fluid motion for the space fluid management under microgravity environment. The purpose of present study is to investigate most efficient technique for propellant resettling through the minimization of propellant usage and weight penalties. Comparison between the constant reverse gravity acceleration and impulsive reverse gravity acceleration to be used for the activation of propellant resettlement, it shows that impulsive reverse gravity thrust is superior to constant reverse gravity thrust for liquid reorientation in a reduced gravity environment.

Esterification of palm fatty acid distillate with epychlorohydrin using cation exchange resin catalyst

NASA Astrophysics Data System (ADS)

Budhijanto, Budhijanto; Subagyo, Albertus F. P. H.

2017-05-01

Palm Fatty Acid Distillate (PFAD) is one of the wastes from the conversion of crude palm oil (CPO) into cooking oil. The PFAD is currently only utilized as the raw material for low grade soap and biofuel. To improve the economic value of PFAD, it was converted into monoglyceride by esterification process. Furthermore, the monoglyceride could be polymerized to form alkyd resin, which is a commodity of increasing importance. This study aimed to propose a kinetics model for esterification of PFAD with epichlorohydrin using cation exchange resin catalyst. The reaction was the first step from a series of reactions to produce the monoglyceride. In this study, the reaction between PFAD and epichlorohydirne was run in a stirred batch reactor. The stirrer was operated at a constant speed of 400 RPM. The reaction was carried out for 180 minutes on varied temperatures of 60°C, 70°C, 80°C, dan 90°C. Cation exchange resin was applied as solid catalysts. Analysis was conducted periodically by measuring the acid number of the samples, which was further used to calculate PFAD conversion. The data were used to determine the rate constants and the equilibrium constants of the kinetics model. The kinetics constants implied that the reaction was reversible and controlled by the intrinsic surface reaction. Despite the complication of the heterogeneous nature of the reaction, the kinetics data well fitted the elementary rate law. The effect of temperature on the equilibrium constants indicated that the reaction is exothermic.

Acetylcholine-induced current in perfused rat myoballs

PubMed Central

1980-01-01

Spherical "myoballs" were grown under tissue culture conditions from striated muscle of neonatal rat thighs. The myoballs were examined electrophysiologically with a suction pipette which was used to pass current and perfuse internally. A microelectrode was used to record membrane potential. Experiments were performed with approximately symmetrical (intracellular and extracellular) sodium aspartate solutions. The resting potential, acetylcholine (ACh) reversal potential, and sodium channel reversal potential were all approximately 0 mV. ACh-induced currents were examined by use of both voltage jumps and voltage ramps in the presence of iontophoretically applied agonist. The voltage-jump relaxations had a single exponential time-course. The time constant, tau, was exponentially related to membrane potential, increasing e-fold for 81 mV hyperpolarization. The equilibrium current- voltage relationship was also approximately exponential, from -120 to +81 mV, increasing e-fold for 104 mV hyperpolarization. The data are consistent with a first-order gating process in which the channel opening rate constant is slightly voltage dependent. The instantaneous current-voltage relationship was sublinear in the hyperpolarizing direction. Several models are discussed which can account for the nonlinearity. Evidence is presented that the "selectivity filter" for the ACh channel is located near the intracellular membrane surface. PMID:7381423

The Investigation of Electrochemistry Behaviors of Tyrosinase Based on Directly-Electrodeposited Grapheneon Choline-Gold Nanoparticles.

PubMed

He, Yaping; Yang, Xiaohui; Han, Quan; Zheng, Jianbin

2017-06-23

A novel catechol (CA) biosensor was developed by embedding tyrosinase (Tyr) onto in situ electrochemical reduction graphene (EGR) on choline-functionalized gold nanoparticle (AuNPs-Ch) film. The results of UV-Vis spectra indicated that Tyr retained its original structure in the film, and an electrochemical investigation of the biosensor showed a pair of well-defined, quasi-reversible redox peaks with E pa = -0.0744 V and E pc = -0.114 V (vs. SCE) in 0.1 M, pH 7.0 sodium phosphate-buffered saline at a scan rate of 100 mV/s. The transfer rate constant k s is 0.66 s -1 . The Tyr-EGR/AuNPs-Ch showed a good electrochemical catalytic response for the reduction of CA, with the linear range from 0.2 to 270 μM and a detection limit of 0.1 μM (S/N = 3). The apparent Michaelis-Menten constant was estimated to be 109 μM.

Reverse arthroplasty for osteoarthritis and rotator cuff deficiency after previous surgery for recurrent anterior shoulder instability.

PubMed

Raiss, Patric; Zeifang, Felix; Pons-Villanueva, Juan; Smithers, Christopher J; Loew, Markus; Walch, Gilles

2014-07-01

Osteoarthritis in combination with rotator cuff deficiency following previous shoulder stabilisation surgery and after failed surgical treatment for chronic anterior shoulder dislocation is a challenging condition. The aim of this study was to analyse the results of reverse shoulder arthroplasty in such patients. Thirteen patients with a median follow-up of 3.5 (range two to eight) years and a median age of 70 (range 48-82) years were included. In all shoulders a tear of at least one rotator cuff tendon in combination with osteoarthritis was present at the time of arthroplasty. The Constant score, shoulder flexion and external and internal rotation with the elbow at the side were documented pre-operatively and at the final follow-up. Pre-operative, immediate post-operative and final follow-up radiographs were analysed. All complications and revisions were documented. Twelve patients were either satisfied or very satisfied with the procedure. The median Constant score increased from 26 points pre-operatively to 67 points at the final follow-up (p = 0.001). The median shoulder flexion increased significantly from 70° to 130° and internal rotation from two to four points (p = 0.002). External rotation did not change significantly (p = 0.55). Glenoid notching was present in five cases and was graded as mild in three cases and moderate in two. One complication occurred leading to revision surgery. Reverse arthroplasty leads to high satisfaction rates for patients with osteoarthritis and rotator cuff deficiency who had undergone previous shoulder stabilisation procedures. The improvements in clinical outcome as well as the radiographic results seem to be comparable with those of other studies reporting on the outcome of reverse shoulder arthroplasty for other conditions.

The Influence of Sulfur on Dephosphorization Kinetics Between Bloated Metal Droplets and Slag Containing FeO

NASA Astrophysics Data System (ADS)

Gu, Kezhuan; Dogan, Neslihan; Coley, Kenneth S.

2017-10-01

The bloating behavior of metal droplets and the dephosphorization behavior of bloated droplets at 1853 K (1580 °C) were investigated using X-ray fluoroscopy coupled with constant volume pressure change measurements and chemical analysis of quenched samples. The effect of sulfur content on dephosphorization kinetics was studied during the decarburization period. The slag foamed during the reaction forming a foamy layer over a dense layer. After a short incubation period, the droplets became bloated due to internal decarburization. The bloated droplets floated from the dense slag into the foamy slag. The behavioral changes are directly related to the effect of sulfur on the incubation time for swelling. The dephosphorization reaction was very fast; droplets with low sulfur contents experienced phosphorus reversion shortly after entering the foamy slag, while those with higher sulfur content took a longer time to swell and went through reversion before they entered the foam. The dephosphorization rate and maximum phosphorus partition were higher at lower CO evolution rates because the dynamic interfacial oxygen potential increased with the decreasing oxygen consumption rate. The rate controlling step for dephosphorization was initially a combination of mass transport in both the metal and the slag. As the iron oxide in the slag was depleted, the rate control shifted to mass transport in slag.

Falloff curve and specific rate constants for the reaction NO/sub 2/ + NO/sub 2/ /r reversible/ N/sub 2/O/sub 4/

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

Borrell, P.; Cobos, C.J.; Luther, K.

1988-07-28

The rate of association of NO/sub 2/ to N/sub 2/O/sub 4/ was measured in N/sub 2/ at pressures from 1 to 207 bar. This way the reaction was observed in a large section of its falloff range. The relaxation of NO/sub 2//N/sub 2/O/sub 4/ mixtures was followed after laser flash photolysis of N/sub 2/O/sub 4/ at 248 nm. From the results the falloff curve was constructed, which gives the high- and low-pressure rate constants at 298 K (in cm/sup 3/ molecule/sup /minus/1/ s/sup /minus/1/): k/sub ass//sup infinity/ = (8.3 /plus minus/ 1.0) /times/ 10/sup /minus/13/ and k/sub ass//sup 0/ =more » (1.4 /plus minus/ 0.2) /times/ 10/sup /minus/33/(N/sub 2/). Earlier measurements believed to be in the low-pressure regime, have not been free from falloff effects. The low value of k/sup infinity/ was analyzed with the statistic adiabatic channel model, and specific rate constants, k(E,J), were calculated. They increase very steeply with energy just above the reaction threshold and go through maxima at low excess energies. These unusual effects are analyzed theoretically and the strong contributions are pointed out of the low-frequency vibrations which disappear during the dissociation of N/sub 2/O/sub 4/.« less

Amino acid residues in Anabaena ferredoxin crucial to interaction with ferredoxin-NADP+ reductase: site-directed mutagenesis and laser flash photolysis.

PubMed

Hurley, J K; Salamon, Z; Meyer, T E; Fitch, J C; Cusanovich, M A; Markley, J L; Cheng, H; Xia, B; Chae, Y K; Medina, M

1993-09-14

Ferredoxin (Fd) functions in photosynthesis to transfer electrons from photosystem I to ferredoxin-NADP+ reductase (FNR). We have made several site-directed mutants of Anabaena 7120 Fd and have used laser flash photolysis to investigate the effects of these mutations on the kinetics of reduction of oxidized Fd by deazariboflavin semiquinone (dRfH.) and the reduction of oxidized Anabaena FNR by reduced Fd. None of the mutations influenced the second-order rate constant for dRfH. reduction by more than a factor of 2, suggesting that the ability of the [2Fe-2S] cluster to participate in electron transfer was not seriously affected. In contrast, a surface charge reversal mutation, E94K, resulted in a 20,000-fold decrease in the second-order rate constant for electron transfer from Fd to FNR, whereas a similar mutation at an adjacent site, E95K, produced little or no change in reaction rate constant compared to wild-type Fd. Such a dramatic difference between contiguous surface mutations suggests a very precise surface complementarity at the protein-protein interface. Mutations introduced at F65 (F65I and F65A) also decreased the rate constant for the Fd/FNR electron transfer reaction by more than 3 orders of magnitude. Spectroscopic and thermodynamic measurements with both the E94 and F65 mutants indicated that the kinetic differences cannot be ascribed to changes in gross conformation, redox potential, or FNR binding constant but rather reflect the protein-protein interactions that control electron transfer. Several mutations at other sites in the vicinity of E94 and F65 (R42, T48, D68, and D69) resulted in little or no perturbation of the Fd/FNR interaction.(ABSTRACT TRUNCATED AT 250 WORDS)

ATMOSPHERIC CHEMISTRY FOR ASTROPHYSICISTS: A SELF-CONSISTENT FORMALISM AND ANALYTICAL SOLUTIONS FOR ARBITRARY C/O

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

Heng, Kevin; Tsai, Shang-Min; Lyons, James R., E-mail: kevin.heng@csh.unibe.ch

2016-01-10

We present a self-consistent formalism for computing and understanding the atmospheric chemistry of exoplanets from the viewpoint of an astrophysicist. Starting from the first law of thermodynamics, we demonstrate that the van’t Hoff equation (which describes the equilibrium constant), Arrhenius equation (which describes the rate coefficients), and procedures associated with the Gibbs free energy (minimization, rescaling) have a common physical and mathematical origin. We address an ambiguity associated with the equilibrium constant, which is used to relate the forward and reverse rate coefficients, and restate its two definitions. By necessity, one of the equilibrium constants must be dimensionless and equatemore » to an exponential function involving the Gibbs free energy, while the other is a ratio of rate coefficients and must therefore possess physical units. We demonstrate that the Arrhenius equation takes on a functional form that is more general than previously stated without recourse to tagging on ad hoc functional forms. Finally, we derive analytical models of chemical systems, in equilibrium, with carbon, hydrogen, and oxygen. We include acetylene and are able to reproduce several key trends, versus temperature and carbon-to-oxygen ratio, published in the literature. The rich variety of behavior that mixing ratios exhibit as a function of the carbon-to-oxygen ratio is merely the outcome of stoichiometric book-keeping and not the direct consequence of temperature or pressure variations.« less

Atmospheric Chemistry for Astrophysicists: A Self-consistent Formalism and Analytical Solutions for Arbitrary C/O

NASA Astrophysics Data System (ADS)

Heng, Kevin; Lyons, James R.; Tsai, Shang-Min

2016-01-01

We present a self-consistent formalism for computing and understanding the atmospheric chemistry of exoplanets from the viewpoint of an astrophysicist. Starting from the first law of thermodynamics, we demonstrate that the van’t Hoff equation (which describes the equilibrium constant), Arrhenius equation (which describes the rate coefficients), and procedures associated with the Gibbs free energy (minimization, rescaling) have a common physical and mathematical origin. We address an ambiguity associated with the equilibrium constant, which is used to relate the forward and reverse rate coefficients, and restate its two definitions. By necessity, one of the equilibrium constants must be dimensionless and equate to an exponential function involving the Gibbs free energy, while the other is a ratio of rate coefficients and must therefore possess physical units. We demonstrate that the Arrhenius equation takes on a functional form that is more general than previously stated without recourse to tagging on ad hoc functional forms. Finally, we derive analytical models of chemical systems, in equilibrium, with carbon, hydrogen, and oxygen. We include acetylene and are able to reproduce several key trends, versus temperature and carbon-to-oxygen ratio, published in the literature. The rich variety of behavior that mixing ratios exhibit as a function of the carbon-to-oxygen ratio is merely the outcome of stoichiometric book-keeping and not the direct consequence of temperature or pressure variations.

Erratum to "The mechanism and thermodynamics of transesterification of acetate-ester enolates in the gas phase" : [Int. J. Mass Spectrom. Ion Process. 172 (1998) 25

NASA Astrophysics Data System (ADS)

Haas, George W.; Giblin, Daryl E.; Gross, Michael L.

1998-02-01

In solution, base-catalyzed hydrolysis and transesterification of esters are initiated by hydroxide- or alkoxide-ion attack at the carbonyl carbon. At low pressures in the gas phase, however, transesterification proceeds by an attack of the enolate anion of an acetate ester on an alcohol. Fourier transform mass spectrometry (FTMS) indicates that the reaction is the second-order process: -CH2-CO2-R+R'-OH-->-CH2-CO2-R'+R-OH and there is little to no detectable production of either alkoxide anion. Labeling studies show that the product and reactant enolate anion esters undergo exchange of hydrogens located [alpha] to the carbonyl carbon with the deuterium of R'--OD. The extent of the H/D exchange increases with reaction time, pointing to a short-lived intermediate. The alcoholysis reaction rate constants increase with increasing acidity of the primary, straight-chained alkyl alcohols, whereas steric effects associated with branched alcohols cause the rate constants to decrease. Equilibrium constants, which were determined directly from measurements at equilibrium and which were calculated from the forward and reverse rate constants, are near unity and show internal consistency. In the absence of steric effects, the larger enolate is always the favored product at equilibrium. The intermediate for the transesterification reaction, which can be generated at a few tenths of a torr in a tandem mass spectrometer, is tetrahedral, but other adducts that are collisionally stabilized under these conditions are principally loosely bound complexes.

Application of one-dimensional semiclassical transition state theory to the CH3OH + H ⇌ CH2OH/CH3O + H2 reactions.

PubMed

Shan, Xiao; Clary, David C

2018-03-13

The rate constants of the two branches of H-abstractions from CH 3 OH by the H-atom and the corresponding reactions in the reverse direction are calculated using the one-dimensional semiclassical transition state theory (1D SCTST). In this method, only the reaction mode vibration of the transition state (TS) is treated anharmonically, while the remaining internal degrees of freedom are treated as they would have been in a standard TS theory calculation. A total of eight ab initio single-point energy calculations are performed in addition to the computational cost of a standard TS theory calculation. This allows a second-order Richardson extrapolation method to be employed to improve the numerical estimation of the third- and fourth-order derivatives, which in turn are used in the calculation of the anharmonic constant. Hindered-rotor (HR) vibrations are identified in the equilibrium states of CH 3 OH and CH 2 OH, and the TSs of the reactions. The partition function of the HRs are calculated using both a simple harmonic oscillator model and a more sophisticated one-dimensional torsional eigenvalue summation (1D TES) method. The 1D TES method can be easily adapted in 1D SCTST computation. The resulting 1D SCTST with 1D TES rate constants show good agreement to previous theoretical and experimental works. The effects of the HR on rate constants for different reactions are also investigated.This article is part of the theme issue 'Modern theoretical chemistry'. © 2018 The Author(s).

[Total reverse shoulder replacement. Evaluation of the clinical results and complications in a series of 52 cases].

PubMed

Cáceres-Sánchez, L; Mesa-Mateo, A; Barrionuevo-Sánchez, F J; García-Benítez, B; Expósito-Triano, S

2015-01-01

To evaluate the clinical results and analyse the complications of total reverse shoulder replacement performed in our centre over an 8 year period. A retrospective study was conducted on 50 patients (52 shoulders), with a mean age of 70.15 years (range 51 to 84 years) between December 2004 and December 2012, who received a total reverse shoulder replacement, all performed by the same surgeon. The results have been evaluated according to clinical data, radiography study, a satisfaction scale, and the Constant scale, with a minimum follow-up of 16 months. Five of the cases (9.62%) had been intervened due to fractures of the proximal end of the humerus, 6 cases (11.53%) as surgical consequence of a prosthesis revision, 10 cases (19.23%) due to fracture sequelae, and 30 cases (59.62%) were patients with arthropathy due to a massive fracture of the rotator cuff. After a mean follow up of 35.78 months (range, 16-82), satisfactory clinical results were obtained in 80% of cases, with a mean preoperative Constant of 27.7 points, and reaching 67.1 points 12 months after the operation. On the visual analogue scale, 8.25 points were obtained before the surgery, which decreased to 2.25 points 12 months later. The complications rate was 15.38%, which were due to an intra-operative fracture (1.92%), deep infection (3.84%), instability (3.84%), and early mechanical loosening (3.84%). Scapular notching was observed in the radiographic study in 9 (17.3%) cases. After the results obtained, it could be said that total reverse shoulder replacement achieved encouraging results in the short term for the treatment of glenohumeral arthrosis and massive tears of the rotary cuff. On analysing our series, it can be seen that the complications rate is much higher when it is used to treat fracture sequelae in which there is a loss of proximal humerus bone stock. Copyright © 2014 SECOT. Published by Elsevier Espana. All rights reserved.

Gallium uptake by transferrin and interaction with receptor 1.

PubMed

Chikh, Zohra; Ha-Duong, Nguyêt-Thanh; Miquel, Geneviève; El Hage Chahine, Jean-Michel

2007-01-01

The kinetics and thermodynamics of Ga(III) exchange between gallium mononitrilotriacetate and human serum transferrin as well as those of the interaction between gallium-loaded transferrin and the transferrin receptor 1 were investigated in neutral media. Gallium is exchanged between the chelate and the C-site of human serum apotransferrin in interaction with bicarbonate in about 50 s to yield an intermediate complex with an equilibrium constant K (1) = (3.9 +/- 1.2) x 10(-2), a direct second-order rate constant k (1) = 425 +/- 50 M(-1) s(-1) and a reverse second-order rate constant k (-1) = (1.1 +/- 3) x 10(4) M(-1) s(-1). The intermediate complex loses a single proton with proton dissociation constant K (1a) = 80 +/- 40 nM to yield a first kinetic product. This product then undergoes a modification in its conformation which lasts about 500 s to produce a second kinetic intermediate, which in turn undergoes a final extremely slow (several hours) modification in its conformation to yield the gallium-saturated transferrin in its final state. The mechanism of gallium uptake differs from that of iron and does not involve the same transitions in conformation reported during iron uptake. The interaction of gallium-loaded transferrin with the transferrin receptor occurs in a single very fast kinetic step with a dissociation constant K (d) = 1.10 +/- 0.12 microM and a second-order rate constant k (d) = (1.15 +/- 0.3) x 10(10) M(-1) s(-1). This mechanism is different from that observed with the ferric holotransferrin and suggests that the interaction between the receptor and gallium-loaded transferrin probably takes place on the helical domain of the receptor which is specific for the C-site of transferrin and HFE. The relevance of gallium incorporation by the transferrin receptor-mediated iron-acquisition pathway is discussed.

Myxococcus xanthus Swarms Are Driven by Growth and Regulated by a Pacemaker ▿

PubMed Central

Kaiser, Dale; Warrick, Hans

2011-01-01

The principal social activity of Myxococcus xanthus is to organize a dynamic multicellular structure, known as a swarm. Although its cell density is high, the swarm can grow and expand rapidly. Within the swarm, the individual rod-shaped cells are constantly moving, transiently interacting with one another, and independently reversing their gliding direction. Periodic reversal is, in fact, essential for creating a swarm, and the reversal frequency controls the rate of swarm expansion. Chemotaxis toward nutrient has been thought to drive swarming, but here the nature of swarm growth and the impact of genetic deletions of members of the Frz family of proteins suggest otherwise. We find that three cytoplasmic Frz proteins, FrzCD, FrzF, and FrzE, constitute a cyclic pathway that sets the reversal frequency. Within each cell these three proteins appear to be connected in a negative-feedback loop that produces oscillations whose frequencies are finely tuned by methylation and by phosphorylation. This oscillator, in turn, drives MglAB, a small G-protein switch, to oscillate between its GTP- and GDP-bound states that ultimately determine when the cell moves forward or backward. The periodic reversal of interacting rod-shaped cells promotes their alignment. Swarm organization ensures that each cell can move without blocking the movement of others. PMID:21856842

High-rate operant behavior in two mouse strains: a response-bout analysis.

PubMed

Johnson, Joshua E; Pesek, Erin F; Newland, M Christopher

2009-06-01

Operant behavior sometimes occurs in bouts characterized by an initiation rate, within-bout response rate, and bout length. The generality of this structure was tested using high-rate nose-poking in mice. Reinforcement of short interresponse times produced high response rates while a random-interval schedule held reinforcement rates constant. BALB/c mice produced bouts that were more frequent, longer, and contained a higher within-bout rate of responding (nine nose-pokes/s) than did the C57BL/6 mice (five nose-pokes/s). Adding a running wheel decreased total nose-pokes and bout length, and increased bout-initiation rate. Free-feeding reduced nose-poking by decreasing bout-initiation rate. Photoperiod reversal decreased bout-initiation rate but not total nose-poke rate. Despite strain differences in bout structure, both strains responded similarly to the interventions. The three bout measures were correlated with overall rate but not with each other. Log-survival analyses provided independent descriptors of the structure of high-rate responding in these two strains.

Changes in the Levels of Abscisic Acid and Its Metabolites in Excised Leaf Blades of Xanthium strumarium during and after Water Stress 1

PubMed Central

Zeevaart, Jan A. D.

1980-01-01

The time course of abscisic acid (ABA) accumulation during water stress and of degradation following rehydration was investigated by analyzing the levels of ABA and its metabolites phaseic acid (PA) and alkalihydrolyzable conjugated ABA in excised leaf blades of Xanthium strumarium. Initial purification was by reverse-phase, preparative, high performance liquid chromatography (HPLC) which did not require prior partitioning. ABA and PA were purified further by analytical HPLC with a μBondapak-NH2 column, and quantified by GLC with an electron capture detector. The ABA content of stressed leaves increased for 4 to 5 hours and then leveled off due to a balance between synthesis and degradation. Since PA accumulated at a constant rate throughout the wilting period, it was concluded that the rate of ABA synthesis decreased after the first 4 to 5 hours stress. Conjugated ABA increased at a low rate during stress. This is interpreted to indicate that free ABA was converted to the conjugated form, rather than the reverse. Following rehydration of wilted leaves, the ABA level immediately ceased increasing; it remained constant for 1 hour and then declined rapidly to the prestress level over a 2- to 3-hour period with a concomitant rise in the PA level. In contrast to the rapid disappearance of ABA after relief of stress, the high PA content of rehydrated leaves declined only slowly. The level of conjugated ABA did not change following rehydration, indicating that conjugation of ABA was irreversible. Detached Xanthium leaves that were subjected to a wilting-recovery-rewilting cycle in darkness, responded to the second wilting period by formation of the same amount of ABA as accumulated after the first stress period. PMID:16661500

Changes in the Levels of Abscisic Acid and Its Metabolites in Excised Leaf Blades of Xanthium strumarium during and after Water Stress.

PubMed

Zeevaart, J A

1980-10-01

The time course of abscisic acid (ABA) accumulation during water stress and of degradation following rehydration was investigated by analyzing the levels of ABA and its metabolites phaseic acid (PA) and alkalihydrolyzable conjugated ABA in excised leaf blades of Xanthium strumarium. Initial purification was by reverse-phase, preparative, high performance liquid chromatography (HPLC) which did not require prior partitioning. ABA and PA were purified further by analytical HPLC with a muBondapak-NH(2) column, and quantified by GLC with an electron capture detector.The ABA content of stressed leaves increased for 4 to 5 hours and then leveled off due to a balance between synthesis and degradation. Since PA accumulated at a constant rate throughout the wilting period, it was concluded that the rate of ABA synthesis decreased after the first 4 to 5 hours stress. Conjugated ABA increased at a low rate during stress. This is interpreted to indicate that free ABA was converted to the conjugated form, rather than the reverse.Following rehydration of wilted leaves, the ABA level immediately ceased increasing; it remained constant for 1 hour and then declined rapidly to the prestress level over a 2- to 3-hour period with a concomitant rise in the PA level. In contrast to the rapid disappearance of ABA after relief of stress, the high PA content of rehydrated leaves declined only slowly. The level of conjugated ABA did not change following rehydration, indicating that conjugation of ABA was irreversible.Detached Xanthium leaves that were subjected to a wilting-recovery-rewilting cycle in darkness, responded to the second wilting period by formation of the same amount of ABA as accumulated after the first stress period.

Mechanism of product inhibition for cellobiohydrolase Cel7A during hydrolysis of insoluble cellulose.

PubMed

Olsen, Johan P; Alasepp, Kadri; Kari, Jeppe; Cruys-Bagger, Nicolaj; Borch, Kim; Westh, Peter

2016-06-01

The cellobiohydrolase cellulase Cel7A is extensively utilized in industrial treatment of lignocellulosic biomass under conditions of high product concentrations, and better understanding of inhibition mechanisms appears central in attempts to improve the efficiency of this process. We have implemented an electrochemical biosensor assay for product inhibition studies of cellulases acting on their natural substrate, cellulose. Using this method we measured the hydrolytic rate of Cel7A as a function of both product (inhibitor) concentration and substrate load. This data enabled analyses along the lines of conventional enzyme kinetic theory. We found that the product cellobiose lowered the maximal rate without affecting the Michaelis constant, and this kinetic pattern could be rationalized by two fundamentally distinct molecular mechanisms. One was simple reversibility, that is, an increasing rate of the reverse reaction, lowering the net hydrolytic velocity as product concentrations increase. Strictly this is not a case of inhibition, as no catalytically inactive is formed. The other mechanism that matched the kinetic data was noncompetitive inhibition with an inhibition constant of 490 ± 40 μM. Noncompetitive inhibition implies that the inhibitor binds with comparable strength to either free enzyme or an enzymesubstrate complex, that is, that association between enzyme and substrate has no effect on the binding of the inhibitor. This mechanism is rarely observed, but we argue, that the special architecture of Cel7A with numerous subsites for binding of both substrate and product could give rise to a true noncompetitive inhibition mechanism. Biotechnol. Bioeng. 2016;113: 1178-1186. © 2015 Wiley Periodicals, Inc. © 2015 Wiley Periodicals, Inc.

Flow convergence caused by a salinity minimum in a tidal channel

USGS Publications Warehouse

Warner, John C.; Schoellhamer, David H.; Burau, Jon R.; Schladow, S. Geoffrey

2006-01-01

Residence times of dissolved substances and sedimentation rates in tidal channels are affected by residual (tidally averaged) circulation patterns. One influence on these circulation patterns is the longitudinal density gradient. In most estuaries the longitudinal density gradient typically maintains a constant direction. However, a junction of tidal channels can create a local reversal (change in sign) of the density gradient. This can occur due to a difference in the phase of tidal currents in each channel. In San Francisco Bay, the phasing of the currents at the junction of Mare Island Strait and Carquinez Strait produces a local salinity minimum in Mare Island Strait. At the location of a local salinity minimum the longitudinal density gradient reverses direction. This paper presents four numerical models that were used to investigate the circulation caused by the salinity minimum: (1) A simple one-dimensional (1D) finite difference model demonstrates that a local salinity minimum is advected into Mare Island Strait from the junction with Carquinez Strait during flood tide. (2) A three-dimensional (3D) hydrodynamic finite element model is used to compute the tidally averaged circulation in a channel that contains a salinity minimum (a change in the sign of the longitudinal density gradient) and compares that to a channel that contains a longitudinal density gradient in a constant direction. The tidally averaged circulation produced by the salinity minimum is characterized by converging flow at the bed and diverging flow at the surface, whereas the circulation produced by the constant direction gradient is characterized by converging flow at the bed and downstream surface currents. These velocity fields are used to drive both a particle tracking and a sediment transport model. (3) A particle tracking model demonstrates a 30 percent increase in the residence time of neutrally buoyant particles transported through the salinity minimum, as compared to transport through a constant direction density gradient. (4) A sediment transport model demonstrates increased deposition at the near-bed null point of the salinity minimum, as compared to the constant direction gradient null point. These results are corroborated by historically noted large sedimentation rates and a local maximum of selenium accumulation in clams at the null point in Mare Island Strait.

Device for adapting continuously variable transmissions to infinitely variable transmissions with forward-neutral-reverse capabilities

DOEpatents

Wilkes, Donald F.; Purvis, James W.; Miller, A. Keith

1997-01-01

An infinitely variable transmission is capable of operating between a maximum speed in one direction and a minimum speed in an opposite direction, including a zero output angular velocity, while being supplied with energy at a constant angular velocity. Input energy is divided between a first power path carrying an orbital set of elements and a second path that includes a variable speed adjustment mechanism. The second power path also connects with the orbital set of elements in such a way as to vary the rate of angular rotation thereof. The combined effects of power from the first and second power paths are combined and delivered to an output element by the orbital element set. The transmission can be designed to operate over a preselected ratio of forward to reverse output speeds.

Kinetics of cyclopentene isomerization at 1200 K

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

Lewis, D.K.; Baldwin, J.E.; Cianciosi, S.J.

1990-09-20

This study was conducted to determine the rate of intramolecular degenerate rearrangement of cyclopentene (CP), presumably via reversible conversion to vinylcyclopropane (VCP). Cyclopentene-3-{sup 13}C was synthesized and heated to 1,200 K in a single-pulse shock tube and then analyzed by {sup 13}C NMR to ascertain the extent of migration of the {sup 13}C label to the 4-position. The very small amounts of migration observed were consistent with log k(CP {yields} VCP) = 15.7 {minus} (16,000/T). This rate constant for CP {yields} VCP is too small to account for the previously reported evidence of multiple channels for H{sub 2} elimination frommore » CP.« less

Quantitative analysis of PMR-15 polyimide resin by HPLC

NASA Technical Reports Server (NTRS)

Roberts, Gary D.; Lauver, Richard W.

1987-01-01

The concentration of individual components and of total solids of 50 wt pct PMR-15 resin solutions was determined using reverse-phase HPLC to within + or - 8 percent accuracy. Acid impurities, the major source of impurities in 3,3', 4,4'-benzophenonetetracarboxylic acid (BTDE), were eliminated by recrystallizing the BTDE prior to esterification. Triester formation was not a problem because of the high rate of esterification of the anhydride relative to that of the carboxylic acid. Aging of PMR-15 resin solutions resulted in gradual formation of the mononadimide and bisnadimide of 4,4'-methylenedianiline, with the BTDE concentration remaining constant. Similar chemical reactions occurred at a reduced rate in dried films of PMR-15 resin.

Ab initio thermal rate calculations of HO + HO = O(3P) + H2O reaction and isotopologues.

PubMed

Nguyen, Thanh Lam; Stanton, John F

2013-04-04

The forward and reverse reactions, HO + HO ⇌ O((3)P) + H2O, which play roles in both combustion and laboratory studies, were theoretically characterized with a master equation approach to compute thermal reaction rate constants at both the low and high pressure limits. Our ab initio k(T) results for the title reaction and two isotopic variants agree very well with experiments (within 15%) over a wide temperature range. The calculated reaction rate shows a distinctly non-Arrhenius behavior and a strong curvature consistent with the experiment. This characteristic behavior is due to effects of positive barrier height and quantum mechanical tunneling. Tunneling is very important and contributes more than 70% of total reaction rate at room temperature. A prereactive complex is also important in the overall reaction scheme.

[Does time spent traveling to regional hub cities to receive healthcare influence mortality in small towns in Rio Grande do Sul State, Brazil?

PubMed

Zuanazzi, Pedro Tonon; Cabral, Pedro Henrique Vargas; Stella, Milton André; Moraes, Gustavo Inácio de

2017-12-18

The current study aims to determine whether the time spent travelling to regional hub cities to receive healthcare affects mortality from avoidable causes and the standardized crude mortality rate in towns with up to 5,000 inhabitants in Rio Grande do Sul State, Brazil. Without adjusting for control variables, the longest time spent to reach cities with 100,000 inhabitants or more was associated with an increase in both rates. However, while the pattern in the avoidable mortality rate was similar after including controls, the standardized crude mortality rate reversed its signal. This suggests that if other socioeconomic and healthcare characteristics are kept constant, the distance to reference cities is associated with both a reduction in deaths from avoidable causes and an increase in other causes of death.

Magnetic properties of electrical iron sheet under controlled magnetization

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

Takada, Shunji; Sasaki, Tadashi

1993-11-01

Power losses of electrical iron sheet were measured under the controlled magnetizing condition in which magnetic induction changes at a constant time rate for a fixed time and pauses at a certain induction for a varied time in every half magnetizing cycle. Considerable increase of losses per magnetizing cycle with a pause time has been found only in the case of magnetization pause at the maximum induction. The increase of losses is considered from magnetostriction measurements to be caused by internal magnetization rearrangement accompanied with flux reversal after the pause period.

Growth rate of a penny-shaped crack in hydraulic fracturing of rocks

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

Abe, H.; Keer, L.M.; Mura, T.

1976-01-01

The deformation and growth of a crack, fractured hydraulically, is investigated when fluid is injected from an inlet into the crack at a constant flow rate. The total flow rate at the inlet is divided as follows: flow rate extracted from an outlet hole; fluid loss rate from the crack surface; and total fluid mass change in the crack. Two cases are considered: (1) inlet flow rate is initially greater than the sum of the outlet flow and fluid loss rates; and (2) the reverse holds true. Ranges are shown for which the crack attains stationary states for given inletmore » flow rate and outlet pressure. For these two cases reasonable outlet flow rates are obtained when the outlet pressure is less than or equal to the difference between the tectonic stress and the fluid head at the inlet. Results are expected to be of use in considerations of heat extraction from hot, dry rock.« less

Inappropriate use of the quasi-reversible electrode kinetic model in simulation-experiment comparisons of voltammetric processes that approach the reversible limit.

PubMed

Simonov, Alexandr N; Morris, Graham P; Mashkina, Elena A; Bethwaite, Blair; Gillow, Kathryn; Baker, Ruth E; Gavaghan, David J; Bond, Alan M

2014-08-19

Many electrode processes that approach the "reversible" (infinitely fast) limit under voltammetric conditions have been inappropriately analyzed by comparison of experimental data and theory derived from the "quasi-reversible" model. Simulations based on "reversible" and "quasi-reversible" models have been fitted to an extensive series of a.c. voltammetric experiments undertaken at macrodisk glassy carbon (GC) electrodes for oxidation of ferrocene (Fc(0/+)) in CH3CN (0.10 M (n-Bu)4NPF6) and reduction of [Ru(NH3)6](3+) and [Fe(CN)6](3-) in 1 M KCl aqueous electrolyte. The confidence with which parameters such as standard formal potential (E(0)), heterogeneous electron transfer rate constant at E(0) (k(0)), charge transfer coefficient (α), uncompensated resistance (Ru), and double layer capacitance (CDL) can be reported using the "quasi-reversible" model has been assessed using bootstrapping and parameter sweep (contour plot) techniques. Underparameterization, such as that which occurs when modeling CDL with a potential independent value, results in a less than optimal level of experiment-theory agreement. Overparameterization may improve the agreement but easily results in generation of physically meaningful but incorrect values of the recovered parameters, as is the case with the very fast Fc(0/+) and [Ru(NH3)6](3+/2+) processes. In summary, for fast electrode kinetics approaching the "reversible" limit, it is recommended that the "reversible" model be used for theory-experiment comparisons with only E(0), Ru, and CDL being quantified and a lower limit of k(0) being reported; e.g., k(0) ≥ 9 cm s(-1) for the Fc(0/+) process.

Femtosecond Heterodyne Transient Grating Detection of Conformational Dynamics in the S0 (11Ag-) State of Carotenoids After Nonradiative Decay of the S2 (11Bu+) State

NASA Astrophysics Data System (ADS)

Roscioli, Jerome D.; Ghosh, Soumen; Bishop, Michael M.; Lafountain, Amy M.; Frank, Harry A.; Beck, Warren F.

Transient grating spectroscopy was used to study the dynamics of nonradiative decay of the S1 (21Ag-) state in ß-carotene and peridinin after optical preparation of the S2) state. The kinetics of the recovery of the absorption and dispersion components of the third-order signal exhibit significantly different time constants. For β-carotene in benzonitrile, the absorption and dispersion recovery time constants are 11.6 and 10.2 ps. For peridinin in methanol, the time constants are 9.9 and 7.4 ps. These results indicate that the initial product of the decay of the S1 state is a conformationally displaced structure. The decay rate for the S1 state and the conformational relaxation rate are both slowed in peridinin as the polarity of the solvent decreases; in ethyl acetate, the conformational relaxation time constant is 45 ps, which rules out a dominant contribution from vibrational cooling. These results indicate that the S1 state develops intramolecular charge transfer character owing to distortions along torsional and out-of-plane coordinates, with a pyramidal structure favored as the most stable conformation. Recovery of the photoselected ground state conformation involves a reverse charge-transfer event followed by relaxation to a planar structure. Work supported by Photosynthetic Systems Program of the U.S. Department of Energy under Grant DE-SC0010847.

Understanding temperature and magnetic-field actuated magnetization polarity reversal in the Prussian blue analogue Cu 0.73 Mn 0.77 [Fe(CN) 6 ]. z H 2 O, using XMCD

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

Lahiri, Debdutta; Choi, Yongseong; Yusuf, S. M.

2016-02-23

We have investigated the microscopic origin of temperature and magnetic-field actuated magnetization reversal in Cu0.73Mn0.77[Fe(CN)(6)]center dot zH(2)O, using XMCD. Our results show a fair deviation from the mean-field-theory in the form of different ordering temperatures of Fe and Mn sublattices. A preferential sign reversal of Mn spin under magnetic field and different spin cant angles for the two sublattices have also been observed. An antiferromagnetic coupling between the Fe and Mn sublattices along with different ordering temperatures (sublattice decoupling) for these sublattices explain the temperature-dependent magnetization reversal. Whereas, Mn spin reversal alone (under external magnetic field) is responsible for themore » observed field-dependent magnetization reversal. The dissimilar magnetic behavior of Fe and Mn sublattices in this cubic 3d-orbital system has been understood by invoking disparity and competition among inter-sublattice magnetic control parameters, viz. magnetic Zeeman energy, exchange coupling constant and magnetic anisotropy constant. Our results have significant design implications for future magnetic switches, by optimizing the competition among these magnetic control parameters.« less

Estimation of apparent rate coefficients for radionuclides interacting with marine sediments from Novaya Zemlya.

PubMed

Børretzen, P; Salbu, B

2000-10-30

To assess the impact of radionuclides entering the marine environment from dumped nuclear waste, information on the physico-chemical forms of radionuclides and their mobility in seawater-sediment systems is essential. Due to interactions with sediment components, sediments may act as a sink, reducing the mobility of radionuclides in seawater. Due to remobilisation, however, contaminated sediments may also act as a potential source of radionuclides to the water phase. In the present work, time-dependent interactions of low molecular mass (LMM, i.e. species < 10 kDa) radionuclides with sediments from the Stepovogo Fjord, Novaya Zemlya and their influence on the distribution coefficients (Kd values) have been studied in tracer experiments using 109Cd2+ and 60Co2+ as gamma tracers. Sorption of the LMM tracers occurred rapidly and the estimated equilibrium Kd(eq)-values for 109Cd and 60Co were 500 and 20000 ml/g, respectively. Remobilisation of 109Cd and 60Co from contaminated sediment fractions as a function of contact time was studied using sequential extraction procedures. Due to redistribution, the reversibly bound fraction of the gamma tracers decreased with time, while the irreversibly (or slowly reversibly) associated fraction of the gamma tracers increased. Two different three-compartment models, one consecutive and one parallel, were applied to describe the time-dependent interaction of the LMM tracers with operationally defined reversible and irreversible (or slowly reversible) sediment fractions. The interactions between these fractions were described using first order differential equations. By fitting the models to the experimental data, apparent rate constants were obtained using numerical optimisation software. The model optimisations showed that the interactions of LMM 60Co were well described by the consecutive model, while the parallel model was more suitable to describe the interactions of LMM 109Cd with the sediments, when the squared sum of residuals were compared. The rate of sorption of the irreversibly (or slowly reversibly) associated fraction was greater than the rate of desorption of the reversibly bound fractions (i.e. k3 > k2) for both radionuclides. Thus, the Novaya Zemlya sediment are supposed to act as a sink for the radionuclides under oxic conditions, and transport to the water phase should mainly be attributed to resuspended particles.

Transient state kinetics of transcription elongation by T7 RNA polymerase.

PubMed

Anand, Vasanti Subramanian; Patel, Smita S

2006-11-24

The single subunit DNA-dependent RNA polymerase (RNAP) from bacteriophage T7 catalyzes both promoter-dependent transcription initiation and promoter-independent elongation. Using a promoter-free substrate, we have dissected the kinetic pathway of single nucleotide incorporation during elongation. We show that T7 RNAP undergoes a slow conformational change (0.01-0.03 s(-1)) to form an elongation competent complex with the promoter-free substrate (dissociation constant (Kd) of 96 nM). The complex binds to a correct NTP (Kd of 80 microM) and incorporates the nucleoside monophosphate (NMP) into RNA primer very efficiently (220 s(-1) at 25 degrees C). An overall free energy change (-5.5 kcal/mol) and internal free energy change (-3.7 kcal/mol) of single NMP incorporation was calculated from the measured equilibrium constants. In the presence of inorganic pyrophosphate (PPi), the elongation complex catalyzes the reverse pyrophosphorolysis reaction at a maximum rate of 0.8 s(-1) with PPi Kd of 1.2 mM. Several experiments were designed to investigate the rate-limiting step in the pathway of single nucleotide addition. Acid-quench and pulse-chase kinetics indicated that an isomerization step before chemistry is rate-limiting. The very similar rate constants of sequential incorporation of two nucleotides indicated that the steps after chemistry are fast. Based on available data, we propose that the preinsertion to insertion isomerization of NTP observed in the crystallographic studies of T7 RNAP is a likely candidate for the rate-limiting step. The studies here provide a kinetic framework to investigate structure-function and fidelity of RNA synthesis and to further explore the role of the conformational change in nucleotide selection during RNA synthesis.

Phenotype of hepatocyte spheroids in Arg-GLY-Asp (RGD) containing a thermo-reversible extracellular matrix.

PubMed

Park, Keun-Hong; Bae, You Han

2002-07-01

The spheroid of specific cells is often regarded as the better form in artificial organs and mammalian cell bioreactors for improved cell-specific functions. In this study, freshly harvested primary rat hepatocytes, which had been cultivated as spheroids and entrapped in a synthetic thermo-reversible extracellular matrix, were examined for differentiated morphology and enhanced liver-specific functions as compared to a control set (hepatocytes in single-cell form). A copolymer of N-isopropylacrylamide (98 mole % in the feed) and acrylic acid (poly(NiPAAm-co-AAc)), and the adhesion molecule, an Arg-Gly-Asp (RGD)-incorporated thermo-reversible matrix, were used to entrap hepatocytes in the form of either spheroids or single cells. In a 28-day culture period, the spheroids in the RGD-incorporated gel maintained higher viability and produced albumin and urea at constant rates, while there was lower cell viability and less albumin secretion by the spheroids in p(NiPAAm-co-AAc). Hepatocytes cultured as spheroids in the RGD-incorporated gel would constitute a potentially useful three-dimensional cell system for application in a bio-artificial liver device.

Method for controlling a motor vehicle powertrain

DOEpatents

Burba, Joseph C.; Landman, Ronald G.; Patil, Prabhakar B.; Reitz, Graydon A.

1990-01-01

A multiple forward speed automatic transmission produces its lowest forward speed ratio when a hydraulic clutch and hydraulic brake are disengaged and a one-way clutch connects a ring gear to the transmission casing. Second forward speed ratio results when the hydraulic clutch is engaged to connect the ring gear to the planetary carrier of a second gear set. Reverse drive and regenerative operation result when an hydraulic brake fixes the planetary and the direction of power flow is reversed. Various sensors produce signals representing the position of the gear selector lever operated manually by the vehicle operator, the speed of the power source, the state of the ignition key, and the rate of release of an accelerator pedal. A control algorithm produces input data representing a commanded upshift, a commanded downshift and a torque command and various constant torque signals. A microprocessor processes the input and produces a response to them in accordance with the execution of a control algorithm. Output or response signals cause selective engagement and disengagement of the clutch and brake to produce the forward drive, reverse and regenerative operation of the transmission.

Method for controlling a motor vehicle powertrain

DOEpatents

Burba, J.C.; Landman, R.G.; Patil, P.B.; Reitz, G.A.

1990-05-22

A multiple forward speed automatic transmission produces its lowest forward speed ratio when a hydraulic clutch and hydraulic brake are disengaged and a one-way clutch connects a ring gear to the transmission casing. Second forward speed ratio results when the hydraulic clutch is engaged to connect the ring gear to the planetary carrier of a second gear set. Reverse drive and regenerative operation result when an hydraulic brake fixes the planetary and the direction of power flow is reversed. Various sensors produce signals representing the position of the gear selector lever operated manually by the vehicle operator, the speed of the power source, the state of the ignition key, and the rate of release of an accelerator pedal. A control algorithm produces input data representing a commanded upshift, a commanded downshift and a torque command and various constant torque signals. A microprocessor processes the input and produces a response to them in accordance with the execution of a control algorithm. Output or response signals cause selective engagement and disengagement of the clutch and brake to produce the forward drive, reverse and regenerative operation of the transmission. 7 figs.

Irrelevance of the Power Stroke for the Directionality, Stopping Force, and Optimal Efficiency of Chemically Driven Molecular Machines

PubMed Central

Astumian, R. Dean

2015-01-01

A simple model for a chemically driven molecular walker shows that the elastic energy stored by the molecule and released during the conformational change known as the power-stroke (i.e., the free-energy difference between the pre- and post-power-stroke states) is irrelevant for determining the directionality, stopping force, and efficiency of the motor. Further, the apportionment of the dependence on the externally applied force between the forward and reverse rate constants of the power-stroke (or indeed among all rate constants) is irrelevant for determining the directionality, stopping force, and efficiency of the motor. Arguments based on the principle of microscopic reversibility demonstrate that this result is general for all chemically driven molecular machines, and even more broadly that the relative energies of the states of the motor have no role in determining the directionality, stopping force, or optimal efficiency of the machine. Instead, the directionality, stopping force, and optimal efficiency are determined solely by the relative heights of the energy barriers between the states. Molecular recognition—the ability of a molecular machine to discriminate between substrate and product depending on the state of the machine—is far more important for determining the intrinsic directionality and thermodynamics of chemo-mechanical coupling than are the details of the internal mechanical conformational motions of the machine. In contrast to the conclusions for chemical driving, a power-stroke is very important for the directionality and efficiency of light-driven molecular machines and for molecular machines driven by external modulation of thermodynamic parameters. PMID:25606678

Combination of human acetylcholinesterase and serum albumin sensing surfaces as highly informative analytical tool for inhibitor screening.

PubMed

Fabini, Edoardo; Tramarin, Anna; Bartolini, Manuela

2018-06-05

In the continuous research for potential drug lead candidates, the availability of highly informative screening methodologies may constitute a decisive element in the selection of best-in-class compounds. In the present study, a surface plasmon resonance (SPR)-based assay was developed and employed to investigate interactions between human recombinant AChE (hAChE) and four known ligands: galantamine, tacrine, donepezil and edrophonium. To this aim, a sensor chip was functionalized with hAChE using mild immobilization conditions to best preserve enzyme integrity. Binding affinities and, for the first time, kinetic rate constants for all drug-hAChE complexes formation/disruption were determined. Inhibitors were classified in two groups: slow-reversible and fast-reversible binders according to respective target residence time. Combining data obtained on drug-target residence time with data obtained on serum albumin binding levels, a good correlation with potency, plasma protein binding in vivo, and administration regimen was found. The outcomes of this work demonstrated that the developed SPR-based assay is suitable for the screening, the binding affinity ranking and the kinetic evaluation of hAChE inhibitors. The method proposed ensures a simpler and cost-effective assay to quantify kinetic rate constants for inhibitor-hAChE interaction as compared with other proposed and published methods. Eventually, the determination of residence time in combination with preliminary ADME studies might constitute a better tool to predict in vivo behaviour, a key information for the research of new potential drug candidates. Copyright © 2018 Elsevier B.V. All rights reserved.

Toward the Development of a Fundamentally Based Chemical Model for Cyclopentanone: High-Pressure-Limit Rate Constants for H Atom Abstraction and Fuel Radical Decomposition

DOE PAGES

Zhou, Chong-Wen; Simmie, John M.; Pitz, William J.; ...

2016-08-25

Theoretical aspects of the development of a chemical kinetic model for the pyrolysis and combustion of a cyclic ketone, cyclopentanone, are considered. We present calculated thermodynamic and kinetic data for the first time for the principal species including 2- and 3-oxo-cyclopentyl radicals, which are in reasonable agreement with the literature. Furthermore, these radicals can be formed via H atom abstraction reactions by H and Ö atoms and OH, HO 2, and CH 3 radicals, the rate constants of which have been calculated. Abstraction from the β-hydrogen atom is the dominant process when OH is involved, but the reverse holds truemore » for HO 2 radicals. We also determined the subsequent β-scission of the radicals formed, and it is shown that recent tunable VUV photoionization mass spectrometry experiments can be interpreted in this light. The bulk of the calculations used the composite model chemistry G4, which was benchmarked in the simplest case with a coupled cluster treatment, CCSD(T), in the complete basis set limit.« less

Suitable combination of promoter and micellar catalyst for kilo fold rate acceleration on benzaldehyde to benzoic acid conversion in aqueous media at room temperature: a kinetic approach.

PubMed

Ghosh, Aniruddha; Saha, Rumpa; Ghosh, Sumanta K; Mukherjee, Kakali; Saha, Bidyut

2013-05-15

The kinetics of oxidation of benzaldehyde by chromic acid in aqueous and aqueous surfactant (sodium dodecyl sulfate, SDS, alkyl phenyl polyethylene glycol, Triton X-100 and N-cetylpyridinium chloride, CPC) media have been investigated in the presence of promoter at 303 K. The pseudo-first-order rate constants (kobs) were determined from a logarithmic plot of absorbance as a function time. The rate constants were found to increase with introduction of heteroaromatic nitrogen base promoters such as Picolinic acid (PA), 2,2'-bipyridine (bipy) and 1,10-phenanthroline (phen). The product benzoic acid has been characterized by conventional melting point experiment, NMR, HRMS and FTIR spectral analysis. The mechanism of both unpromoted and promoted reaction path has been proposed for the reaction. In presence of the anionic surfactant SDS, cationic surfactant CPC and neutral surfactant TX-100 the reaction can undergo simultaneously in both aqueous and micellar phase with an enhanced rate of oxidation in the micellar phase. Both SDS and TX-100 produce normal micellar effect whereas CPC produce reverse micellar effect in the presence of benzaldehyde. The observed net enhancement of rate effects has been explained by considering the hydrophobic and electrostatic interaction between the surfactants and reactants. SDS and bipy combination is the suitable one for benzaldehyde oxidation. Copyright © 2013 Elsevier B.V. All rights reserved.

Reversible exciplex formation followed charge separation.

PubMed

Petrova, M V; Burshtein, A I

2008-12-25

The reversible exciplex formation followed by its decomposition into an ion pair is considered, taking into account the subsequent geminate and bulk ion recombination to the triplet and singlet products (in excited and ground states). The integral kinetic equations are derived for all state populations, assuming that the spin conversion is performed by the simplest incoherent (rate) mechanism. When the forward and backward electron transfer is in contact as well as all dissociation/association reactions of heavy particles, the kernels of integral equations are specified and expressed through numerous reaction constants and characteristics of encounter diffusion. The solutions of these equations are used to specify the quantum yields of the excited state and exciplex fluorescence induced by pulse or stationary pumping. In the former case, the yields of the free ions and triplet products are also found, while in the latter case their stationary concentrations are obtained.

Strain doping: Reversible single-axis control of a complex oxide lattice via helium implantation

DOE PAGES

Guo, Hangwen; Dong, Shuai; Rack, Philip D.; ...

2015-06-25

We report on the use of helium ion implantation to independently control the out-of-plane lattice constant in epitaxial La 0.7Sr 0.3MnO 3 thin films without changing the in-plane lattice constants. The process is reversible by a vacuum anneal. Resistance and magnetization measurements show that even a small increase in the out-of-plane lattice constant of less than 1% can shift the metal-insulator transition and Curie temperatures by more than 100 °C. Unlike conventional epitaxy-based strain tuning methods which are constrained not only by the Poisson effect but by the limited set of available substrates, the present study shows that strain canmore » be independently and continuously controlled along a single axis. This permits novel control over orbital populations through Jahn-Teller effects, as shown by Monte Carlo simulations on a double-exchange model. As a result, the ability to reversibly control a single lattice parameter substantially broadens the phase space for experimental exploration of predictive models and leads to new possibilities for control over materials’ functional properties.« less

Migration-driven aggregation behaviors in job markets with direct foreign immigration

NASA Astrophysics Data System (ADS)

Sun, Ruoyan

2014-09-01

This Letter introduces a new set of rate equations describing migration-driven aggregation behaviors in job markets with direct foreign immigration. We divide the job market into two groups: native and immigrant. A reversible migration of jobs exists in both groups. The interaction between two groups creates a birth and death rate for the native job market. We find out that regardless of initial conditions or the rates, the total number of cities with either job markets decreases. This indicates a more concentrated job markets for both groups in the future. On the other hand, jobs available for immigrants increase over time but the ones for natives are uncertain. The native job markets can either expand or shrink or remain constant due to combined effects of birth and death rates. Finally, we test our analytical results with the population data of all counties in the US from 2000 to 2011.

One- and two-dimensional chemical exchange nuclear magnetic resonance studies of the creatine kinase catalyzed reaction

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

Gober, J.R.

1988-01-01

The equilibrium chemical exchange dynamics of the creatine kinase enzyme system were studied by one- and two-dimensional {sup 31}P NMR techniques. Pseudo-first-order reaction rate constants were measured by the saturation transfer method under an array of experimental conditions of pH and temperature. Quantitative one-dimensional spectra were collected under the same conditions in order to calculate the forward and reverse reaction rates, the K{sub eq}, the hydrogen ion stoichiometry, and the standard thermodynamic functions. The pure absorption mode in four quadrant two-dimensional chemical exchange experiment was employed so that the complete kinetic matrix showing all of the chemical exchange process couldmore » be realized.« less

Pitfalls of inferring annual mortality from inspection of published survival curves.

PubMed

Singer, R B

1994-01-01

In many FU articles currently published, results are given primarily in the form of graphs of survival curves, rather than in the form of life table data. Sometimes the authors may comment on the slope of the survival curve as though it were equal to the annual mortality rate (after reversal of the minus sign to a plus sign). Even if no comment of this sort is made, medical directors and underwriters may be tempted to think along similar lines in trying to interpret the significance of the survival curve in terms of mortality. However it is a very serious error of life table methodology to conceive of mortality rate as equal to the negative slope of the survival curve. The nature of the error is demonstrated in this article. An annual mortality rate derived from the survival curve actually depends on two variables: a quotient with the negative slope (sign reversed), delta P/ delta as the numerator, and the survival rate, P, itself as the denominator. The implications of this relationship are discussed. If there are two "parallel" survival curves with the same slope at a given time duration, the lower curve will have a higher mortality rate than the upper curve. A constant slope with increasing duration means that the annual mortality rate also increases with duration. Some characteristics of high initial mortality are also discussed and their relation to different units of FU time.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of pressure in reversed-phase liquid chromatography to study protein conformational changes by differential deuterium exchange.

PubMed

Makarov, Alexey A; Schafer, Wes A; Helmy, Roy

2015-02-17

The market of protein therapeutics is exploding, and characterization methods for proteins are being further developed to understand and explore conformational structures with regards to function and activity. There are several spectroscopic techniques that allow for analyzing protein secondary structure in solution. However, a majority of these techniques need to use purified protein, concentrated enough in the solution to produce a relevant spectrum. In this study, we describe a novel approach which uses ultrahigh pressure liquid chromatography (UHPLC) coupled with mass-spectrometry (MS) to explore compressibility of the secondary structure of proteins under increasing pressure detected by hydrogen-deuterium exchange (HDX). Several model proteins were used for these studies. The studies were conducted with UHPLC in isocratic mode at constant flow rate and temperature. The pressure was modified by a backpressure regulator up to about 1200 bar. It was found that the increase of retention factors upon pressure increase, at constant flow rate and temperature, was based on reduction of the proteins' molecular molar volume. The change in the proteins' molecular molar volume was caused by changes in protein folding, as was revealed by differential deuterium exchange. The degree of protein folding under certain UHPLC conditions can be controlled by pressure, at constant temperature and flow rate. By modifying pressure during UHPLC separation, it was possible to achieve changes in protein folding, which were manifested as changes in the number of labile protons exchanged to deuterons, or vice versa. Moreover, it was demonstrated with bovine insulin that a small difference in the number of protons exchanged to deuterons (based on protein folding under pressure) could be observed between batches obtained from different sources. The use of HDX during UHPLC separation allowed one to examine protein folding by pressure at constant flow rate and temperature in a mixture of sample solution with minimal amounts of sample used for analysis.

Reverse total shoulder replacement for nonunion of a fracture of the proximal humerus.

PubMed

Zafra, M; Uceda, P; Flores, M; Carpintero, P

2014-09-01

Patients with pain and loss of shoulder function due to nonunion of a fracture of the proximal third of the humerus may benefit from reverse total shoulder replacement. This paper reports a prospective, multicentre study, involving three hospitals and three surgeons, of 35 patients (28 women, seven men) with a mean age of 69 years (46 to 83) who underwent a reverse total shoulder replacement for the treatment of nonunion of a fracture of the proximal humerus. Using Checchia's classification, nine nonunions were type I, eight as type II, 12 as type III and six as type IV. The mean follow-up was 51 months (24 to 99). Post-operatively, the patients had a significant decrease in pain (p < 0.001), and a significant improvement in flexion, abduction, external rotation and Constant score (p < 0.001), but not in internal rotation. A total of nine complications were recorded in seven patients: six dislocations, one glenoid loosening in a patient who had previously suffered dislocation, one transitory paresis of the axillary nerve and one infection. Reverse total shoulder replacement may lead to a significant reduction in pain, improvement in function and a high degree of satisfaction. However, the rate of complications, particularly dislocation, was high. ©2014 The British Editorial Society of Bone & Joint Surgery.

Evidence of preorganization in quinonoid intermediate formation from L-Trp in H463F mutant Escherichia coli tryptophan indole-lyase from effects of pressure and pH.

PubMed

Phillips, Robert S; Kalu, Ukoha; Hay, Sam

2012-08-21

The effects of pH and hydrostatic pressure on the reaction of H463F tryptophan indole-lyase (TIL) have been evaluated. The mutant TIL shows very low activity for elimination of indole but is still competent to form a quinonoid intermediate from l-tryptophan [Phillips, R. S., Johnson, N., and Kamath, A. V. (2002) Biochemistry 41, 4012-4019]. Stopped-flow measurements show that the formation of the quinonoid intermediate at 505 nm is affected by pH, with a bell-shaped dependence for the forward rate constant, k(f), and dependence on a single basic group for the reverse rate constant, k(r), with the following values: pK(a1) = 8.14 ± 0.15, pK(a2) = 7.54 ± 0.15, k(f,min) = 18.1 ± 1.3 s(-1), k(f,max) = 179 ± 46.3 s(-1), k(r,min) = 11.4 ± 1.2 s(-1), and k(r,max) = 33 ± 1.6 s(-1). The pH effects may be due to ionization of Tyr74 as the base and Cys298 as the acid influencing the rate constant for deprotonation. High-pressure stopped-flow measurements were performed at pH 8, which is the optimum for the forward reaction. The rate constants show an increase with pressure up to 100 MPa and a subsequent decrease above 100 MPa. Fitting the pressure data gives the following values: k(f,0) = 15.4 ± 0.8 s(-1), ΔV(‡) = -29.4 ± 2.9 cm(3) mol(-1), and Δβ(‡) = -0.23 ± 0.03 cm(3) mol(-1) MPa(-1) for the forward reaction, and k(r,0) = 20.7 ± 0.8 s(-1), ΔV(‡) = -9.6 ± 2.3 cm(3) mol(-1), and Δβ(‡) = -0.05 ± 0.02 cm(3) mol(-1) MPa(-1) for the reverse reaction. The primary kinetic isotope effect on quinonoid intermediate formation at pH 8 is small (~2) and is not significantly pressure-dependent, suggesting that the effect of pressure on k(f) may be due to perturbation of an active site preorganization step. The negative activation volume is also consistent with preorganization of the ES complex prior to quinonoid intermediate formation, and the negative compressibility may be due to the effect of pressure on the enzyme conformation. These results support the conclusion that the preorganization of the H463F TIL Trp complex, which is probably dominated by motion of the l-Trp indole moiety of the aldimine complex, contributes to quinonoid intermediate formation.

Creep of Ni(3)Al in the temperature regime of anomalous flow behavior

NASA Astrophysics Data System (ADS)

Uchic, Michael David

Much attention has been paid to understanding the dynamics of dislocation motion and substructure formation in Ni3Al in the anomalous flow regime. However, most of the experimental work that has been performed in the lowest temperatures of the anomalous flow regime has been under constant-strain-rate conditions. An alternative and perhaps more fundamental way to probe the plastic behavior of materials is a monotonic creep test, in which the stress and temperature are held constant while the time-dependent strain is measured. The aim of this study is to use constant-stress experiments to further explore the plastic flow anomaly in L12 alloys at low temperatures. Tension creep experiments have been carried out on <123> oriented single crystals of Ni75Al24Ta1 at temperatures between 293 and 473 K. We have observed primary creep leading to exhaustion at all temperatures and stresses, with creep rates declining faster than predicted by the logarithmic creep law. The total strain and creep strain have an anomalous dependence on temperature, which is consistent with the flow stress anomaly. We have also observed other unusual behavior in our creep experiments; for example, the reinitiation of plastic flow at low temperatures after a modest increment in applied stress shows a sigmoidal response, i.e., there is a significant time delay before the plastic strain rate accelerates to a maximum value. We also examined the ability to reinitiate plastic flow in samples that have been crept to exhaustion by simply lowering the test temperature. In addition, we have also performed conventional constant-displacement-rate experiments in the same temperature range. From these experiments, we have discovered that unlike most metals, Ni3Al displays a negative dependence of the work hardening rate (WHR) with increasing strain rate. For tests at intermediate temperatures (373 and 423 K), the WHRs of crystals tested at moderately high strain rates (10-2 s-1) are half the WHRs of crystals tested at conventional strain rates (10 -5 s-1), and this anomalous dependence has also been shown to be reversible with changes in strain rate. The implications of all results are discussed in light of our efforts to model plastic deformation in these alloys.

Extracellular Zinc Ion Inhibits ClC-0 Chloride Channels by Facilitating Slow Gating

PubMed Central

Chen, Tsung-Yu

1998-01-01

Extracellular Zn2+ was found to reversibly inhibit the ClC-0 Cl− channel. The apparent on and off rates of the inhibition were highly temperature sensitive, suggesting an effect of Zn2+ on the slow gating (or inactivation) of ClC-0. In the absence of Zn2+, the rate of the slow-gating relaxation increased with temperature, with a Q10 of ∼37. Extracellular Zn2+ facilitated the slow-gating process at all temperatures, but the Q10 did not change. Further analysis of the rate constants of the slow-gating process indicates that the effect of Zn2+ is mostly on the forward rate (the rate of inactivation) rather than the backward rate (the rate of recovery from inactivation) of the slow gating. When ClC-0 is bound with Zn2+, the equilibrium constant of the slow-gating process is increased by ∼30-fold, reflecting a 30-fold higher Zn2+ affinity in the inactivated channel than in the open-state channel. As examined through a wide range of membrane potentials, Zn2+ inhibits the opening of the slow gate with equal potency at all voltages, suggesting that a two-state model is inadequate to describe the slow-gating transition. Following a model originally proposed by Pusch and co-workers (Pusch, M., U. Ludewig, and T.J. Jentsch. 1997. J. Gen. Physiol. 109:105–116), the effect of Zn2+ on the activation curve of the slow gate can be well described by adding two constraints: (a) the dissociation constant for Zn2+ binding to the open channel is 30 μM, and (b) the difference in entropy between the open state and the transition state of the slow-gating process is increased by 27 J/ mol/°K for the Zn2+-bound channel. These results together indicate that extracellular Zn2+ inhibits ClC-0 by facilitating the slow-gating process. PMID:9834141

PRECISION INTEGRATOR FOR MINUTE ELECTRIC CURRENTS

DOEpatents

Hemmendinger, A.; Helmer, R.J.

1961-10-24

An integrator is described for measuring the value of integrated minute electrical currents. The device consists of a source capacitor connected in series with the source of such electrical currents, a second capacitor of accurately known capacitance and a source of accurately known and constant potential, means responsive to the potentials developed across the source capacitor for reversibly connecting the second capacitor in series with the source of known potential and with the source capacitor and at a rate proportional to the potential across the source capacitor to maintain the magnitude of the potential across the source capacitor at approximately zero. (AEC)

Cyclic strain rate effects in fatigued face-centred and body-centred cubic metals

NASA Astrophysics Data System (ADS)

Mughrabi, Haël

2013-09-01

The present work deals mainly with the effect and the use of strain rate and temperature changes during cyclic deformation as a means to obtain valuable information on the thermally activated dislocation glide processes, based on the assessment of reversible changes of the thermal effective stress and of transient changes of the athermal stress. The importance of closed-loop testing in true plastic strain control with constant cyclic plastic strain rate throughout the cycle is explained and emphasized, especially with respect to the case of strain rate sensitive materials. Stress responses of face-centred cubic and body-centred cubic (bcc) metals to cyclic strain rate changes are presented to illustrate that the deformation modes of these two classes of materials differ characteristically at temperatures below that the so-called knee temperature of bcc metals. When such tests are performed in cyclic saturation, the temperature and strain rate dependence of bcc metals can be measured very accurately on one and the same specimen, permitting a thorough analysis of thermal activation.

The role of thin, mechanical discontinuities on the propagation of reverse faults: insights from analogue models

NASA Astrophysics Data System (ADS)

Bonanno, Emanuele; Bonini, Lorenzo; Basili, Roberto; Toscani, Giovanni; Seno, Silvio

2016-04-01

Fault-related folding kinematic models are widely used to explain accommodation of crustal shortening. These models, however, include simplifications, such as the assumption of constant growth rate of faults. This value sometimes is not constant in isotropic materials, and even more variable if one considers naturally anisotropic geological systems. , This means that these simplifications could lead to incorrect interpretations of the reality. In this study, we use analogue models to evaluate how thin, mechanical discontinuities, such as beddings or thin weak layers, influence the propagation of reverse faults and related folds. The experiments are performed with two different settings to simulate initially-blind master faults dipping at 30° and 45°. The 30° dip represents one of the Andersonian conjugate fault, and 45° dip is very frequent in positive reactivation of normal faults. The experimental apparatus consists of a clay layer placed above two plates: one plate, the footwall, is fixed; the other one, the hanging wall, is mobile. Motor-controlled sliding of the hanging wall plate along an inclined plane reproduces the reverse fault movement. We run thirty-six experiments: eighteen with dip of 30° and eighteen with dip of 45°. For each dip-angle setting, we initially run isotropic experiments that serve as a reference. Then, we run the other experiments with one or two discontinuities (horizontal precuts performed into the clay layer). We monitored the experiments collecting side photographs every 1.0 mm of displacement of the master fault. These images have been analyzed through PIVlab software, a tool based on the Digital Image Correlation method. With the "displacement field analysis" (one of the PIVlab tools) we evaluated, the variation of the trishear zone shape and how the master-fault tip and newly-formed faults propagate into the clay medium. With the "strain distribution analysis", we observed the amount of the on-fault and off-fault deformation with respect to the faulting pattern and evolution. Secondly, using MOVE software, we extracted the positions of fault tips and folds every 5 mm of displacement on the master fault. Analyzing these positions in all of the experiments, we found that the growth rate of the faults and the related fold shape vary depending on the number of discontinuities in the clay medium. Other results can be summarized as follows: 1) the fault growth rate is not constant, but varies especially while the new faults interacts with precuts; 2) the new faults tend to crosscut the discontinuities when the angle between them is approximately 90°; 3) the trishear zone change its shape during the experiments especially when the main fault interacts with the discontinuities.

Chemical Principles Revisited: Chemical Equilibrium.

ERIC Educational Resources Information Center

Mickey, Charles D.

1980-01-01

Describes: (1) Law of Mass Action; (2) equilibrium constant and ideal behavior; (3) general form of the equilibrium constant; (4) forward and reverse reactions; (5) factors influencing equilibrium; (6) Le Chatelier's principle; (7) effects of temperature, changing concentration, and pressure on equilibrium; and (8) catalysts and equilibrium. (JN)

Evidence for the absence of cerebral glucose-6-phosphatase activity in glycogen storage disease type I (Von Gierke's disease)

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

Phelps, M.E.; Mazziotta, J.C.; Hawkins, R.A.

1981-01-01

Glycogen storage disease type I (GSD-I) is characterized by a functional deficit in glucose-6-phosphatase that normally hydrolyzes glucose-6-PO/sub 4/ to glucose. This enzyme is primarily found in liver, kidney, and muscle but it is also present in brain, where it appears to participate in the regulation of cerebral tissue glucose. Since most neurological symptoms in GSD-I patients involve systemic hypoglycemia, previous reports have not examined possible deficiencies in phosphatase activity in the brain. Positron computed tomography, F-18-labeled 2-fluorodeoxyglucose (FDG) and a tracer kinetic model for FDG were used to measure the cortical plasma/tissue forward and reverse transport, phosphorylation and dephosphorylationmore » rate constants, tissue/plasma concentration gradient, tissue concentration turnover rate for this competitive analog of glucose, and the cortical metabolic rates for glucose. Studies were carried out in age-matched normals (N = 13) and a single GSD-I patient. The dephosphorylation rate constant in the GSD-I patient was about one tenth the normal value indicating a low level of cerebral phosphatase activity. The other measured parameters were within normal limits except for the rate of glucose phosphorylation which reflected a cortical glucose metabolic rate one half the normal value. Since glucose transport and tissue glucose concentration was normal, the reduced cortical glucose metabolism probably results from the use of alternative substrates (..beta..-hydroxybutyrate and acetoacetate) which are consistently elevated in the plasma of GSD-I patients.« less

Salting Constants of Small Organic Molecules in Aerosol-Relevant Salts and Application to Aerosol Formation in the Southeastern United States

NASA Astrophysics Data System (ADS)

Waxman, E.; Carlton, A. M. G.; Ziemann, P. J.; Volkamer, R. M.

2014-12-01

Secondary organic aerosol (SOA) formation from small water-soluble molecules such as glyoxal and methyl glyoxal is a topic of emerging interest. Results from recent field campaigns, e.g. Waxman et al. (2013, GRL) and Knote et al. (2014, ACP), show that these molecules can form significant SOA mass as a result of 'salting-in'. Salting-in happens when a molecule's solubility increases with salt concentration and salting-out is the reverse. Salting effects modify the solubility exponentially with increasing salt concentration, and thus the effective Henry's law constant can strongly modify partitioning, and multiphase chemical reaction rates in aerosol water. Moreover, the solubility in aerosol water cannot easily inferred based on the solubility in cloud water, as the salting effects could change the solubility by a factor of 104 or more. In this work, we have devised and applied a novel experimental setup to measure salting constants using an ion trap mass spectrometer. We focus on small, water soluble molecules like methyl glyoxal and similar compounds and measure salting constants for aerosol-relevant salts including ammonium sulfate, ammonium nitrate, and sodium chloride. The Setschenow salting-constant values are then used to parameterize the effects of salting in CMAQ. We present a series of sensitivity studies of the effects that inorganic aerosols have on the SOA formation from small soluble molecules in the southeastern United States.

The Development of Ambiguous Figure Perception

ERIC Educational Resources Information Center

Wimmer, Marina C.; Doherty, Martin J.

2011-01-01

Ambiguous figures have fascinated researchers for almost 200 years. The physical properties of these figures remain constant, yet two distinct interpretations are possible; these reverse (switch) from one percept to the other. The consensus is that reversal requires complex interaction of perceptual bottom-up and cognitive top-down elements. The…

Response of the human vestibulo-ocular reflex system to constant angular acceleration. I. Theoretical study.

PubMed

Boumans, L J; Rodenburg, M; Maas, A J

1983-01-01

The response of the human vestibulo-ocular reflex system to a constant angular acceleration is calculated using a second order model with an adaptation term. After first reaching a maximum the peracceleratory response declines. When the stimulus duration is long the decay is mainly governed by the adaptation time constant Ta, which enables to reliably estimate this time constant. In the postacceleratory period of constant velocity there is a reversal in response. The magnitude and the time course of the per- and postacceleratory response are calculated for various values of the cupular time constant T1, the adaptation time constant Ta, and the stimulus duration, thus enabling their influence to be assessed.

Production and Isolation of Amphibactin siderophores in Iron-stressed cultures of the marine bacteria Vibrio spp.

NASA Astrophysics Data System (ADS)

McLean, C.; Boiteau, R.; Bundy, R.; Gauglitz, J.; Repeta, D.

2016-02-01

Iron is an important micronutrient for marine microbes. Low concentrations of dissolved iron limit production in much of the ocean, putting pressure on microbial communities to develop efficient iron acquisition strategies. One such strategy is the production of siderophores, high affinity iron binding ligands, to facilitate iron uptake to meet their physiological iron quota. Recently, our lab has shown that amphibactins, siderophores with lipid side chains, are present in iron-deficient regions of the ocean. However, little is known about which organisms can utilize amphibactin bound iron. Here we describe a method to isolate amphibactins from laboratory cultures in order to identify the conditional stability constants and uptake rates of purified amphibactin compounds. We searched the National Center for Biotechnology Information database to identify microbial genomes containing homologous to the known amphibactin biosynthesis genes. Several of these strains were screened with high performance reverse-phase liquid chromatography electrospray ionization mass spectrometry (HPLC-ESIMS) to confirm amphibactin production. We then optimized amphibactin production for the strain Vibrio cyclitrophicus 1F53 under different shaking speeds and iron concentrations, using a chrome azurol S (CAS) assay to screen for siderophore abundance. Maximum production was found after 38 hours of shaking at 150-rpm, and with the addition of 10nM of desferrioxamine B to induce iron limitation. Amphibactins were extracted from the media by solid phase extraction and purified by reverse phase HPLC. The conditional stability constants for several amphibactins were then measured in seawater using competitive ligand exchange absorptive cathodic stripping voltammetry with salicylaldoxime as the added ligand. Future work will determine the uptake rates of these compounds by natural communities of marine bacteria, and give insight on the bioavailability of amphibactins in the marine environment.

Kinetics of surface processes for Mo(CO){sub 6} on partially dehydroxylated alumina and hydroxylated alumina. Observation of Mo(CO){sub 5}(ads)

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

Reddy, K.P.; Brown, T.L.

1995-03-15

The adsorption of Mo(CO){sub 6} on partially dehydroxylated alumina (PDA) and hydroxylated alumina (HA) has been studied using IR and UV-vis spectroscopy. The results from these experiments suggest that the initially physisorbed Mo(CO){sub 6} coordinates to two distinct Lewis acid sites on the surface of PDA, one much more abundant than the other, with an apparent single rate constant 2.3 x 10{sup {minus}3} s{sup {minus}1} at 298 K. The Mo(CO){sub 6}(ads) in turn loses CO reversibly, with an apparent single rate constant 1.8 x 10{sup {minus}4} s{sup {minus}1} at 298 K to form Mo(CO){sub 5}(ads). Upon removal of gas phasemore » CO released in the first step, Mo(CO){sub 5}(ads) loses two additional COs to form Mo(CO){sub 3}(ads). Alternatively, on HA physisorbed Mo(CO){sub 6} undergoes nucleophilic attack by hydroxyl groups, which results in cis-labilization of a carbonyl group, leading in turn to the formation of Mo(CO){sub 5}(L), where L is a surface hydroxyl. The Mo(CO){sub 5}(L) so formed loses additional carbonyls to form a lower subcarbonyl. The decarbonylation process appears to be faster than on PDA. The experimental data indicate that there are no Al{sup 31} exposed on HA. All the observed decarbonylation processes are reversible under CO at room temperature on both HA and PDA. The addition of CO{sub 2} to the subcarbonyl on HA results in the formation of a bicarbonate, with displacement of the subcarbonyls. 24 refs., 11 figs., 1 tab.« less

Kinetics of force recovery following length changes in active skinned single fibres from rabbit psoas muscle

PubMed Central

Burton, Kevin; Simmons, Robert M; Sleep, John; Smith, David A

2006-01-01

Redevelopment of isometric force following shortening of skeletal muscle is thought to result from a redistribution of cross-bridge states. We varied the initial force and cross-bridge distribution by applying various length-change protocols to active skinned single fibres from rabbit psoas muscle, and observed the effect on the slowest phase of recovery (‘late recovery’) that follows transient changes. In response to step releases that reduced force to near zero (∼8 nm (half sarcomere)−1) or prolonged shortening at high velocity, late recovery was well described by two exponentials of approximately equal amplitude and rate constants of ∼2 s−1 and ∼9 s−1 at 5°C. When a large restretch was applied at the end of rapid shortening, recovery was accelerated by (1) the introduction of a slow falling component that truncated the rise in force, and (2) a relative increase in the contribution of the fast exponential component. The rate of the slow fall was similar to that observed after a small isometric step stretch, with a rate of 0.4–0.8 s−1, and its effects could be reversed by reducing force to near zero immediately after the stretch. Force at the start of late recovery was varied in a series of shortening steps or ramps in order to probe the effect of cross-bridge strain on force redevelopment. The rate constants of the two components fell by 40–50% as initial force was raised to 75–80% of steady isometric force. As initial force increased, the relative contribution of the fast component decreased, and this was associated with a length constant of about 2 nm. The results are consistent with a two-state strain-dependent cross-bridge model. In the model there is a continuous distribution of recovery rate constants, but two-exponential fits show that the fast component results from cross-bridges initially at moderate positive strain and the slow component from cross-bridges at high positive strain. PMID:16497718

The Neural Circuit Mechanisms Underlying the Retinal Response to Motion Reversal

PubMed Central

Chen, Eric Y.; Chou, Janice; Park, Jeongsook; Schwartz, Greg

2014-01-01

To make up for delays in visual processing, retinal circuitry effectively predicts that a moving object will continue moving in a straight line, allowing retinal ganglion cells to anticipate the object's position. However, a sudden reversal of motion triggers a synchronous burst of firing from a large group of ganglion cells, possibly signaling a violation of the retina's motion prediction. To investigate the neural circuitry underlying this response, we used a combination of multielectrode array and whole-cell patch recordings to measure the responses of individual retinal ganglion cells in the tiger salamander to reversing stimuli. We found that different populations of ganglion cells were responsible for responding to the reversal of different kinds of objects, such as bright versus dark objects. Using pharmacology and designed stimuli, we concluded that ON and OFF bipolar cells both contributed to the reversal response, but that amacrine cells had, at best, a minor role. This allowed us to formulate an adaptive cascade model (ACM), similar to the one previously used to describe ganglion cell responses to motion onset. By incorporating the ON pathway into the ACM, we were able to reproduce the time-varying firing rate of fast OFF ganglion cells for all experimentally tested stimuli. Analysis of the ACM demonstrates that bipolar cell gain control is primarily responsible for generating the synchronized retinal response, as individual bipolar cells require a constant time delay before recovering from gain control. PMID:25411485

The Chemical Basis of Thiol Addition to Nitro-conjugated Linoleic Acid, a Protective Cell-signaling Lipid*♦

PubMed Central

Turell, Lucía; Vitturi, Darío A.; Coitiño, E. Laura; Lebrato, Lourdes; Möller, Matías N.; Sagasti, Camila; Salvatore, Sonia R.; Woodcock, Steven R.; Alvarez, Beatriz; Schopfer, Francisco J.

2017-01-01

Nitroalkene fatty acids are formed in vivo and exert protective and anti-inflammatory effects via reversible Michael addition to thiol-containing proteins in key signaling pathways. Nitro-conjugated linoleic acid (NO2-CLA) is preferentially formed, constitutes the most abundant nitrated fatty acid in humans, and contains two carbons that could potentially react with thiols, modulating signaling actions and levels. In this work, we examined the reactions of NO2-CLA with low molecular weight thiols (glutathione, cysteine, homocysteine, cysteinylglycine, and β-mercaptoethanol) and human serum albumin. Reactions followed reversible biphasic kinetics, consistent with the presence of two electrophilic centers in NO2-CLA located on the β- and δ-carbons with respect to the nitro group. The differential reactivity was confirmed by computational modeling of the electronic structure. The rates (kon and koff) and equilibrium constants for both reactions were determined for different thiols. LC-UV-Visible and LC-MS analyses showed that the fast reaction corresponds to β-adduct formation (the kinetic product), while the slow reaction corresponds to the formation of the δ-adduct (the thermodynamic product). The pH dependence of the rate constants, the correlation between intrinsic reactivity and thiol pKa, and the absence of deuterium solvent kinetic isotope effects suggested stepwise mechanisms with thiolate attack on NO2-CLA as rate-controlling step. Computational modeling supported the mechanism and revealed additional features of the transition states, anionic intermediates, and final neutral products. Importantly, the detection of cysteine-δ-adducts in human urine provided evidence for the biological relevance of this reaction. Finally, human serum albumin was found to bind NO2-CLA both non-covalently and to form covalent adducts at Cys-34, suggesting potential modes for systemic distribution. These results provide new insights into the chemical basis of NO2-CLA signaling actions. PMID:27923813

Effects of the rate of formant-frequency variation on the grouping of formants in speech perception.

PubMed

Summers, Robert J; Bailey, Peter J; Roberts, Brian

2012-04-01

How speech is separated perceptually from other speech remains poorly understood. Recent research suggests that the ability of an extraneous formant to impair intelligibility depends on the modulation of its frequency, but not its amplitude, contour. This study further examined the effect of formant-frequency variation on intelligibility by manipulating the rate of formant-frequency change. Target sentences were synthetic three-formant (F1 + F2 + F3) analogues of natural utterances. Perceptual organization was probed by presenting stimuli dichotically (F1 + F2C + F3C; F2 + F3), where F2C + F3C constitute a competitor for F2 and F3 that listeners must reject to optimize recognition. Competitors were derived using formant-frequency contours extracted from extended passages spoken by the same talker and processed to alter the rate of formant-frequency variation, such that rate scale factors relative to the target sentences were 0, 0.25, 0.5, 1, 2, and 4 (0 = constant frequencies). Competitor amplitude contours were either constant, or time-reversed and rate-adjusted in parallel with the frequency contour. Adding a competitor typically reduced intelligibility; this reduction increased with competitor rate until the rate was at least twice that of the target sentences. Similarity in the results for the two amplitude conditions confirmed that formant amplitude contours do not influence across-formant grouping. The findings indicate that competitor efficacy is not tuned to the rate of the target sentences; most probably, it depends primarily on the overall rate of frequency variation in the competitor formants. This suggests that, when segregating the speech of concurrent talkers, differences in speech rate may not be a significant cue for across-frequency grouping of formants.

The ancestral selection graph under strong directional selection.

PubMed

Pokalyuk, Cornelia; Pfaffelhuber, Peter

2013-08-01

The ancestral selection graph (ASG) was introduced by  Neuhauser and Krone (1997) in order to study populations of constant size which evolve under selection. Coalescence events, which occur at rate 1 for every pair of lines, lead to joint ancestry. In addition, splitting events in the ASG at rate α, the scaled selection coefficient, produce possible ancestors, such that the real ancestor depends on the ancestral alleles. Here, we use the ASG in the case without mutation in order to study fixation of a beneficial mutant. Using our main tool, a reversibility property of the ASG, we provide a new proof of the fact that a beneficial allele fixes roughly in time (2logα)/α if α is large. Copyright © 2012 Elsevier Inc. All rights reserved.

Integrating biofiltration with SVE: A case study

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

Lesley, M.P.; Rangan, C.R.

1996-12-01

A prototype integrated soil vacuum extraction/biofiltration system has been designed and installed at a gasoline contaminated LUST site in southern Delaware. The prototype system remediates contaminated moisture entrained in the air stream, employs automatic water level controls in the filters, and achieves maximum vapor extraction and VOC destruction efficiency with an optimum power input. In addition, the valving and piping layout allows the direction of air flow through the filters to be reversed at a given time interval, which minimizes biofouling, thereby increasing efficiency by minimizing the need for frequent cleaning. This integrated system achieves constant VOC destruction rates ofmore » 40 to 70% while maintaining optimal VOC removal rates from the subsurface. The modular design allows for easy mobilization, setup and demobilization at state-lead LUST sites throughout Delaware.« less

GLT-1 Transport Stoichiometry Is Constant at Low and High Glutamate Concentrations when Chloride Is Substituted by Gluconate

PubMed Central

Kabakov, Anatoli Y.; Rosenberg, Paul A.

2015-01-01

Glutamate is the major excitatory neurotransmitter, but prolonged exposure even at micromolar concentrations causes neuronal death. Extracellular glutamate is maintained at nanomolar level by glutamate transporters, which, however, may reverse transport and release glutamate. If and when the reverse occurs depends on glutamate transport stoichiometry (GTS). Previously we found that in the presence of chloride, the coupled GLT-1 glutamate transporter current and its relationship to radiolabeled glutamate flux significantly decreased when extracellular glutamate concentration increased above 0.2 mM, which implies a change in GTS. Such high concentrations are feasible near GLT-1 expressed close to synaptic release site during excitatory neurotransmission. The aim of this study was to determine GLT-1 GTS at both low (19–75 μM) and high (300–1200 μM) glutamate concentration ranges. GTS experiments were conducted in the absence of chloride to avoid contributions by the GLT-1 uncoupled chloride conductance. Mathematical analysis of the transporter thermodynamic equilibrium allowed us to derive equations revealing the number of a particular type of ion transported per elementary charge based on the measurements of the transporter reversal potential. We found that GLT-1a expressed in COS-7 cells co-transports 1.5 Na+, 0.5 Glu-, 0.5 H+ and counter-transports 0.6 K+ per elementary charge in both glutamate concentration ranges, and at both 37°C and 26°C temperatures. The thermodynamic parameter Q 10 = 2.4 for GLT-1 turnover rate of 19 s-1 (37°C, -50 mV) remained constant in the 10 μM–10 mM glutamate concentration range. Importantly, the previously reported decrease in the current/flux ratio at high glutamate concentration was not seen in the absence of chloride in both COS-7 cells and cultured rat neurons. Therefore, only in the absence of chloride, GLT-1 GTS remains constant at all glutamate concentrations. Possible explanations for why apparent GTS might vary in the presence of chloride are discussed. PMID:26301411

Communication: Equilibrium rate coefficients from atomistic simulations: The O((3)P) + NO((2)Π) → O2(X(3)Σg(-)) + N((4)S) reaction at temperatures relevant to the hypersonic flight regime.

PubMed

Castro-Palacio, Juan Carlos; Bemish, Raymond J; Meuwly, Markus

2015-03-07

The O((3)P) + NO((2)Π) → O2(X(3)Σg(-)) + N((4)S) reaction is among the N- and O- involving reactions that dominate the energetics of the reactive air flow around spacecraft during hypersonic atmospheric re-entry. In this regime, the temperature in the bow shock typically ranges from 1000 to 20,000 K. The forward and reverse rate coefficients for this reaction derived directly from trajectory calculations over this range of temperature are reported in this letter. Results compare well with the established equilibrium constants for the same reaction from thermodynamic quantities derived from spectroscopy in the gas phase which paves the way for large-scale in silico investigations of equilibrium rates under extreme conditions.

Changing incidence of psychotic disorders among the young in Zurich.

PubMed

Ajdacic-Gross, Vladeta; Lauber, Christoph; Warnke, Inge; Haker, Helene; Murray, Robin M; Rössler, Wulf

2007-09-01

There is controversy over whether the incidence rates of schizophrenia and psychotic disorders have changed in recent decades. To detect deviations from trends in incidence, we analysed admission data of patients with an ICD-8/9/10 diagnosis of psychotic disorders in the Canton Zurich / Switzerland, for the period 1977-2005. The data was derived from the central psychiatric register of the Canton Zurich. Ex-post forecasting with ARIMA (Autoregressive Integrated Moving Average) models was used to assess departures from existing trends. In addition, age-period-cohort analysis was applied to determine hidden birth cohort effects. First admission rates of patients with psychotic disorders were constant in men and showed a downward trend in women. However, the rates in the youngest age groups showed a strong increase in the second half of the 1990's. The trend reversal among the youngest age groups coincides with the increased use of cannabis among young Swiss in the 1990's.

On the Nonsmooth, Nonconstant Velocity of Braille Reading and Reversals

ERIC Educational Resources Information Center

Hughes, Barry; McClelland, Amber; Henare, Dion

2014-01-01

Relative to print reading, braille-reading finger movements are held to be of more constant speed, with continuous and exhaustive contact with all words. However, the continuity of movements is intermittent in two distinct ways: (a) readers reverse direction and reread material already encountered and (b) the continual fluctuations of velocity…

Sensitivity of geomagnetic reversal rate on core evolution from numerical dynamos

NASA Astrophysics Data System (ADS)

Driscoll, P. E.; Davies, C. J.

2017-12-01

The paleomagnetic record indicates the geodynamo has evolved from frequently reversing to non-reversing (superchron) magnetic states several times over the Phanerozoic. Previous theoretical studies demonstrated a positive correlation between magnetic reversal rate and core-mantle boundary heat flux. However, attempts to identify such a correlation between reversal rates and proxies for internal cooling rate, such as plume events, superchron cycles, and subduction rates, have been inconclusive. Here we revisit the magnetic reversal occurrence rate in numerical dynamos at low Ekman numbers (faster rotation) and high magnetic Prandtl numbers (ratio of viscous and magnetic diffusivities). We focus on how the correlation between reversal rate and convective power depends on the core evolution rate and on other factors, such as Ek, Pm, and thermal boundary conditions. We apply our results to the seafloor reversal record in an attempt to infer the energetic evolution of the lower mantle and core over that period.

Development of quantitative radioactive methodologies on paper to determine important lateral-flow immunoassay parameters.

PubMed

Mosley, Garrett L; Nguyen, Phuong; Wu, Benjamin M; Kamei, Daniel T

2016-08-07

The lateral-flow immunoassay (LFA) is a well-established diagnostic technology that has recently seen significant advancements due in part to the rapidly expanding fields of paper diagnostics and paper-fluidics. As LFA-based diagnostics become more complex, it becomes increasingly important to quantitatively determine important parameters during the design and evaluation process. However, current experimental methods for determining these parameters have certain limitations when applied to LFA systems. In this work, we describe our novel methods of combining paper and radioactive measurements to determine nanoprobe molarity, the number of antibodies per nanoprobe, and the forward and reverse rate constants for nanoprobe binding to immobilized target on the LFA test line. Using a model LFA system that detects for the presence of the protein transferrin (Tf), we demonstrate the application of our methods, which involve quantitative experimentation and mathematical modeling. We also compare the results of our rate constant experiments with traditional experiments to demonstrate how our methods more appropriately capture the influence of the LFA environment on the binding interaction. Our novel experimental approaches can therefore more efficiently guide the research process for LFA design, leading to more rapid advancement of the field of paper-based diagnostics.

A novel nitrite biosensor based on gold dendrites with egg white as template.

PubMed

He, Yaping; Zhang, Dawei; Dong, Sheying; Zheng, Jianbin

2012-01-01

Gold dendrites (AuD) were synthesized with egg white as the soft template and a novel nitrite (NO(2)(-)) biosensor was fabricated by assembly of a myoglobin (Mb)-L-cysteamine (Cys)-AuD biological hybrid. The results of Fourier transform infrared spectra and UV-visible spectra indicated that Mb retained its original structure in the resulting Mb-Cys-AuD. Electrochemical investigation of the biosensor showed a pair of well-defined, quasi-reversible redox peaks with E(pa) = -0.314 V and E(pc) = -0.344 V (vs. SCE) in 0.1 M, pH 7.0 sodium phosphate buffered saline at the scan rate of 200 mV/s. The transfer rate constant (k(s)) was 1.49 s(-1). The Mb-Cys-AuD showed a good electrochemical catalytic response for the reduction of NO(2)(-), with the linear range from 0.5 to 400 µM and the detection limit of 0.3 µM (S/N = 3). The apparent Michaelis-Menten constant (K(M)(app)) was estimated to be 0.2 mM. Therefore, the assembled bio-hybrid as a novel matrix opened up a further possibility for study on the design of enzymatic biosensors with potential applications.

Lost in Loess: Paleomagnetic investigation into loess and tephra deposits in interior Alaska

NASA Astrophysics Data System (ADS)

Semler, L.; Arnold, K. E.; Williams, D.; Morton, J.; Layer, P. W.; Stone, D. B.; Beget, J.; Schaefer, J.

2003-12-01

As a part of a NSF-funded Research Experience for Undergraduates (REU) program at the University of Alaska Fairbanks, loess and tephra samples were collected at a road cut near Tok, Alaska, to determine if the site was suitable for paleoclimate reconstruction of the Pleistocene. Oriented cubes and cores were obtained from a section of loess just below the Sheep Creek tephra dated at 190 +/- 20 ka, through the Tetlin tephra (1.2 meters below the Sheep Creek tephra) dated at 630 +/- 50 ka to two meters below the Tetlin tephra. The accumulated amount of loess between dated tephra layers suggests a span of more than one million years for the whole section assuming a constant sedimentation rate for the loess. The samples were measured for natural remanent magnetization (NRM) and magnetic susceptibility before magnetic cleaning techniques (Alternating Field Demagnetization and Thermal Demagnetization) were employed. Samples were analyzed using a cryogenic magnetometer. The demagnetizations show stable magnetic vectors and demonstrate that loess is a reliable paleomagnetic recorder. At Tok, we found that the entire section is of normal polarity and shows no sign of the 780 ka Brunhes-Matuyama polarity reversal, which was expected to be 42 cm below the Tetlin tephra. Absence of the reversal may be due to discontinuities or other changes in the sedimentation rate in the loess, a problem with the sampling methods, or incorrect ages of the tephras. Based on our studies, we feel that changing rates of loess deposition or other unseen discontinuities are the reason the reversal was not found. Because of the uncertainty of the depositional history of the Tok loess, this section is not useful for obtaining a continuous record of ancient climate.

Reactivity of fluoroalkanes in reactions of coordinated molecular decomposition

NASA Astrophysics Data System (ADS)

Pokidova, T. S.; Denisov, E. T.

2017-08-01

Experimental results on the coordinated molecular decomposition of RF fluoroalkanes to olefin and HF are analyzed using the model of intersecting parabolas (IPM). The kinetic parameters are calculated to allow estimates of the activation energy ( E) and rate constant ( k) of these reactions, based on enthalpy and IPM algorithms. Parameters E and k are found for the first time for eight RF decomposition reactions. The factors that affect activation energy E of RF decomposition (the enthalpy of the reaction, the electronegativity of the atoms of reaction centers, and the dipole-dipole interaction of polar groups) are determined. The values of E and k for reverse reactions of addition are estimated.

The unusual electrochemical characteristics of a novel three-dimensional ordered bicontinuous mesoporous carbon

NASA Astrophysics Data System (ADS)

Wang, Tao; Liu, Xiaoying; Zhao, Dongyuan; Jiang, Zhiyu

2004-05-01

The electrochemical properties of the ordered three-dimensional (3D) mesoporous carbon, synthesized by using mesoporous silica (FDU-5) as a hard template from an impregnation procedure, has been firstly explored as an anode material for lithium-ion batteries. The material presents uniform pore size of 7.4 nm, BET surface area of 750 m 2/g. As a novel nano-material C-FDU-5 shows almost constant resistance and Li + diffusion coefficient when the potential is lower than the critical potential. The material also presents a reversible capacity higher than that of carbon nanotubes, and can be charge/discharged at the large current rate.

Electrochemical behavior of monolayer and bilayer graphene.

PubMed

Valota, Anna T; Kinloch, Ian A; Novoselov, Kostya S; Casiraghi, Cinzia; Eckmann, Axel; Hill, Ernie W; Dryfe, Robert A W

2011-11-22

Results of a study on the electrochemical properties of exfoliated single and multilayer graphene flakes are presented. Graphene flakes were deposited on silicon/silicon oxide wafers to enable fast and accurate characterization by optical microscopy and Raman spectroscopy. Conductive silver paint and silver wires were used to fabricate contacts; epoxy resin was employed as a masking coating in order to expose a stable, well-defined area of graphene. Both multilayer and monolayer graphene microelectrodes showed quasi-reversible behavior during voltammetric measurements in potassium ferricyanide. However, the standard heterogeneous charge transfer rate constant, k°, was estimated to be higher for monolayer graphene flakes. © 2011 American Chemical Society

Gas Exchange of Algae

PubMed Central

Ammann, Elizabeth C. B.; Lynch, Victoria H.

1966-01-01

Changes in the oxygen partial pressure of air over the range of 8 to 258 mm of Hg did not adversely affect the photosynthetic capacity of Chlorella pyrenoidosa. Gas exchange and growth measurements remained constant for 3-week periods and were similar to air controls (oxygen pressure of 160 mm of Hg). Oxygen partial pressures of 532 and 745 mm of Hg had an adverse effect on algal metabolism. Carbon dioxide consumption was 24% lower in the gas mixture containing oxygen at a pressure 532 mm of Hg than in the air control, and the growth rate was slightly reduced. Oxygen at a partial pressure of 745 mm of Hg decreased the photosynthetic rate 39% and the growth rate 37% over the corresponding rates in air. The lowered metabolic rates remained constant during 14 days of measurements, and the effect was reversible after this time. Substitution of helium or argon for the nitrogen in air had no effect on oxygen production, carbon dioxide consumption, or growth rate for 3-week periods. All measurements were made at a total pressure of 760 mm of Hg, and all gas mixtures were enriched with 2% carbon dioxide. Thus, the physiological functioning and reliability of a photosynthetic gas exchanger should not be adversely affected by: (i) oxygen partial pressures ranging from 8 to 258 mm of Hg; (ii) the use of pure oxygen at reduced total pressure (155 to 258 mm of Hg) unless pressure per se affects photosynthesis, or (iii) the inclusion of helium or argon in the gas environment (up to a partial pressure of 595 mm of Hg). PMID:5927028

Kinetic Analysis of Competitive Electrocatalytic Pathways: New Insights into Hydrogen Production with Nickel Electrocatalysts

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

Wiedner, Eric S.; Brown, Houston J.; Helm, Monte L.

2016-01-20

The hydrogen production electrocatalyst Ni(PPh2NPh2)22+ (1) is capable of traversing multiple electrocatalytic pathways. When using dimethylformamidium, DMF(H)+, the mechanism of formation of H2 catalyzed by 1 changes from an ECEC to an EECC mechanism as the potential approaches the Ni(I/0) couple. Two recent electrochemical methods, current-potential analysis and foot-of-the-wave analysis (FOWA), were performed on 1 to measure the detailed chemical kinetics of the competing ECEC and EECC pathways. A sensitivity analysis was performed on the electrochemical methods using digital simulations to gain a better understanding of their strengths and limitations. Notably, chemical rate constants were significantly underestimated when not accountingmore » for electron transfer kinetics, even when electron transfer was fast enough to afford a reversible non-catalytic wave. The EECC pathway of 1 was found to be faster than the ECEC pathway under all conditions studied. Using buffered DMF: DMF(H)+ mixtures led to an increase in the catalytic rate constant (kobs) of the EECC pathway, but kobs for the ECEC pathway did not change when using buffered acid. Further kinetic analysis of the ECEC path revealed that added base increases the rate of isomerization of the exo-protonated Ni(0) isomers to the catalytically active endo-isomers, but decreases the net rate of protonation of Ni(I). FOWA on 1 did not provide accurate rate constants due to incomplete reduction of the exo-protonated Ni(I) intermediate at the foot of the wave, but FOWA could be used to estimate the reduction potential of this previously undetected intermediate. This research was supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.« less

Stabilities and partitioning of arenonium ions in aqueous media.

PubMed

Lawlor, D A; More O'Ferrall, R A; Rao, S N

2008-12-31

The phenathrenonium ion is formed as a reactive intermediate in the solvolysis of 9-dichloroacetoxy-9,10-dihydrophenanthrene in aqueous acetonitrile and undergoes competing reactions with water acting as a base and nucleophile. Measurements of product ratios in the presence of azide ion as a trap and 'clock' yield rate constants kp = 3.7 x 10(10) and kH2O = 1.5 x 10(8) s(-1), respectively. Combining these with rate constants for the reverse reactions (protonation of phenanthrene and acid-catalyzed aromatization of its water adduct) gives equilibrium constants pKa = -20.9 and pK(R) = -11.6. For a series of arenonium and benzylic cations, correlation of log kp with pKa, taking account of the limit to kp set by the relaxation of water (10(11) s(-1)), leads to extrapolation of kp = 9.0 x 10(10) s(-1) and pKa = -24.5 for the benzenonium ion and kp = 6.5 x 10(10) s(-1) and pKa = -22.5 for the 1-naphthalenonium ion. Combining these pKa's with estimates of equilibrium constants pKH2O for the hydration of benzene and naphthalene, and the relationship pKR = pKa + pKH2O based on Hess's law, gives pKR = -2.3 and -8.0 respectively, and highlights the inherent stability of the benzenonium ion. A correlation exists between the partitioning ratio, kp/kH2O, for carbocations reacting in water and KH2O the equilibrium constant between the respective reaction products, i.e., log(kp/kH2O) = 0.46pKH2O - 3.7. It implies that kp exceeds kH2O only when KH2O > 10(8). This is consistent with the proton transfer (a) possessing a lower intrinsic reactivity than reaction of the carbocation with water as a nucleophile and (b) being rate-determining in the hydration of alkenes (and dehydration of alcohols) except when the double bond of the alkene is unusually stabilized, as in the case of aromatic molecules.

Probing Reversible Chemistry in Coenzyme B12-Dependent Ethanolamine Ammonia Lyase with Kinetic Isotope Effects

PubMed Central

Jones, Alex R; Rentergent, Julius; Scrutton, Nigel S; Hay, Sam

2015-01-01

Coenzyme B12-dependent enzymes such as ethanolamine ammonia lyase have remarkable catalytic power and some unique properties that enable detailed analysis of the reaction chemistry and associated dynamics. By selectively deuterating the substrate (ethanolamine) and/or the β-carbon of the 5′-deoxyadenosyl moiety of the intrinsic coenzyme B12, it was possible to experimentally probe both the forward and reverse hydrogen atom transfers between the 5′-deoxyadenosyl radical and substrate during single-turnover stopped-flow measurements. These data are interpreted within the context of a kinetic model where the 5′-deoxyadenosyl radical intermediate may be quasi-stable and rearrangement of the substrate radical is essentially irreversible. Global fitting of these data allows estimation of the intrinsic rate constants associated with CoC homolysis and initial H-abstraction steps. In contrast to previous stopped-flow studies, the apparent kinetic isotope effects are found to be relatively small. PMID:25950663

Magnetization Switching of a Co /Pt Multilayered Perpendicular Nanomagnet Assisted by a Microwave Field with Time-Varying Frequency

NASA Astrophysics Data System (ADS)

Suto, Hirofumi; Kanao, Taro; Nagasawa, Tazumi; Mizushima, Koichi; Sato, Rie

2018-05-01

Microwave-assisted magnetization switching (MAS) is attracting attention as a method for reversing nanomagnets with a high magnetic anisotropy by using a small-amplitude magnetic field. We experimentally study MAS of a perpendicularly magnetized nanomagnet by applying a microwave magnetic field with a time-varying frequency. Because the microwave field frequency can follow the nonlinear decrease of the resonance frequency, larger magnetization excitation than that in a constant-frequency microwave field is induced, which enhances the MAS effect. The switching field decreases almost linearly as the start value of the time-varying microwave field frequency increases, and it becomes smaller than the minimum switching field in a constant-frequency microwave field. To obtain this enhancement of the MAS effect, the end value of the time-varying microwave field frequency needs to be almost the same as or lower than the critical frequency for MAS in a constant-frequency microwave field. In addition, the frequency change typically needs to take 1 ns or longer to make the rate of change slow enough for the magnetization to follow the frequency change. This switching behavior is qualitatively explained by the theory based on the macrospin model.

Development of a rapid diagnostic assay for the detection of tomato chlorotic dwarf viroid based on isothermal reverse-transcription-recombinase polymerase amplification

USDA-ARS?s Scientific Manuscript database

A molecular diagnostic assay utilizing reverse transcription-recombinase polymerase amplification (RT-RPA) at an isothermal constant temperature of 39 °C and target-specific primers and probe were developed for the rapid, sensitive, and specific detection of tomato chlorotic dwarf viroid (TCDVd) in ...

Reversible geminate recombination of hydrogen-bonded water molecule pair

NASA Astrophysics Data System (ADS)

Markovitch, Omer; Agmon, Noam

2008-08-01

The (history independent) autocorrelation function for a hydrogen-bonded water molecule pair, calculated from classical molecular dynamics trajectories of liquid water, exhibits a t-3/2 asymptotic tail. Its whole time dependence agrees quantitatively with the solution for reversible diffusion-influenced geminate recombination derived by Agmon and Weiss [J. Chem. Phys. 91, 6937 (1989)]. Agreement with diffusion theory is independent of the precise definition of the bound state. Given the water self-diffusion constant, this theory enables us to determine the dissociation and bimolecular recombination rate parameters for a water dimer. (The theory is indispensable for obtaining the bimolecular rate coefficient.) Interestingly, the activation energies obtained from the temperature dependence of these rate coefficients are similar, rather than differing by the hydrogen-bond (HB) strength. This suggests that recombination requires displacing another water molecule, which meanwhile occupied the binding site. Because these activation energies are about twice the HB strength, cleavage of two HBs may be required to allow pair separation. The autocorrelation function without the HB angular restriction yields a recombination rate coefficient that is larger than that for rebinding to all four tetrahedral water sites (with angular restrictions), suggesting the additional participation of interstitial sites. Following dissociation, the probability of the pair to be unbound but within the reaction sphere rises more slowly than expected, possibly because binding to the interstitial sites delays pair separation. An extended diffusion model, which includes an additional binding site, can account for this behavior.

pH-Dependence of Binding Constants and Desorption Rates of Phosphonate- and Hydroxamate-Anchored [Ru(bpy)3]2+ on TiO2 and WO3.

PubMed

Esarey, Samuel L; Bartlett, Bart M

2018-04-17

The binding constants and rate constants for desorption of the modified molecular dye [Ru(bpy) 3 ] 2+ anchored by either phosphonate or hydroxamate on the bipyridine ligand to anatase TiO 2 and WO 3 have been measured. In aqueous media at pH 1-10, repulsive electrostatic interactions between the negatively charged anchor and the negatively charged surface govern phosphonate desorption under neutral and basic conditions for TiO 2 anatase due to the high acidity of phosphonic acid (p K a,4 = 5.1). In contrast, the lower acidity of hydroxamate (p K a,1 = 6.5, p K a,2 = 9.1) leads to little change in adsorption/desorption properties as a function of pH from 1 to 7. The binding constant for hydroxamate is 10 3 in water, independent of pH in this range. These results are true for WO 3 as well, but are not reported at pH > 4 due to its Arrhenius acidity. Kinetics for desorption as a function of pH are reported, with a proposed mechanism for phosphonate desorption at high pH being the electrostatic repulsion of negative charges between the surface and the anionic anchor. Further, the hydroxamic acid anchor itself is likely the site of quasi-reversible redox activity in [Ru(bpy) 2 (2,2'-bpy-4,4'-(C(O)N(OH)) 2 )] 2+ , which does not lead to any measurable deterioration of the complex within 2 h of dark cyclic voltammogram scans in aqueous media. These results posit phosphonate as the preferred anchoring group under acidic conditions and hydroxamate for neutral/basic conditions.

Using a visual discrimination model for the detection of compression artifacts in virtual pathology images.

PubMed

Johnson, Jeffrey P; Krupinski, Elizabeth A; Yan, Michelle; Roehrig, Hans; Graham, Anna R; Weinstein, Ronald S

2011-02-01

A major issue in telepathology is the extremely large and growing size of digitized "virtual" slides, which can require several gigabytes of storage and cause significant delays in data transmission for remote image interpretation and interactive visualization by pathologists. Compression can reduce this massive amount of virtual slide data, but reversible (lossless) methods limit data reduction to less than 50%, while lossy compression can degrade image quality and diagnostic accuracy. "Visually lossless" compression offers the potential for using higher compression levels without noticeable artifacts, but requires a rate-control strategy that adapts to image content and loss visibility. We investigated the utility of a visual discrimination model (VDM) and other distortion metrics for predicting JPEG 2000 bit rates corresponding to visually lossless compression of virtual slides for breast biopsy specimens. Threshold bit rates were determined experimentally with human observers for a variety of tissue regions cropped from virtual slides. For test images compressed to their visually lossless thresholds, just-noticeable difference (JND) metrics computed by the VDM were nearly constant at the 95th percentile level or higher, and were significantly less variable than peak signal-to-noise ratio (PSNR) and structural similarity (SSIM) metrics. Our results suggest that VDM metrics could be used to guide the compression of virtual slides to achieve visually lossless compression while providing 5-12 times the data reduction of reversible methods.

Bony increased-offset reversed shoulder arthroplasty: minimizing scapular impingement while maximizing glenoid fixation.

PubMed

Boileau, Pascal; Moineau, Grégory; Roussanne, Yannick; O'Shea, Kieran

2011-09-01

Scapular notching, prosthetic instability, limited shoulder rotation and loss of shoulder contour are associated with conventional medialized design reverse shoulder arthroplasty. Prosthetic (ie, metallic) lateralization increases torque at the baseplate-glenoid interface potentially leading to failure. We asked whether bony lateralization of reverse shoulder arthroplasty would avoid the problems caused by humeral medialization without increasing torque or shear force applied to the glenoid component. We prospectively followed 42 patients with rotator cuff deficiency treated with bony increased-offset reverse shoulder arthroplasty. A cylinder of autologous cancellous bone graft, harvested from the humeral head, was placed between the reamed glenoid surface and baseplate. Graft and baseplate fixation was achieved using a lengthened central peg (25 mm) and four screws. Patients underwent clinical, radiographic, and CT assessment at a minimum of 2 years after surgery. The humeral graft incorporated completely in 98% of cases (41 of 42) and partially in one. At a mean of 28 months postoperatively, no graft resorption, glenoid loosening, or postoperative instability was observed. Inferior scapular notching occurred in 19% (eight of 42). The absolute Constant-Murley score improved from 31 to 67. Thirty-six patients (86%) were able to internally rotate sufficiently to reach their back over the sacrum. Grafting of the glenoid surface during reverse shoulder arthroplasty effectively creates a long-necked scapula, providing the benefits of lateralization. Bony increased-offset reverse shoulder arthroplasty is associated with low rates of inferior scapular notching, improved shoulder rotation, no prosthetic instability and improved shoulder contour. In contrast to metallic lateralization, bony lateralization has the advantage of maintaining the prosthetic center of rotation at the prosthesis-bone interface, thus minimizing torque on the glenoid component. Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

A new rate law describing microbial respiration.

PubMed

Jin, Qusheng; Bethke, Craig M

2003-04-01

The rate of microbial respiration can be described by a rate law that gives the respiration rate as the product of a rate constant, biomass concentration, and three terms: one describing the kinetics of the electron-donating reaction, one for the kinetics of the electron-accepting reaction, and a thermodynamic term accounting for the energy available in the microbe's environment. The rate law, derived on the basis of chemiosmotic theory and nonlinear thermodynamics, is unique in that it accounts for both forward and reverse fluxes through the electron transport chain. Our analysis demonstrates how a microbe's respiration rate depends on the thermodynamic driving force, i.e., the net difference between the energy available from the environment and energy conserved as ATP. The rate laws commonly applied in microbiology, such as the Monod equation, are specific simplifications of the general law presented. The new rate law is significant because it affords the possibility of extrapolating in a rigorous manner from laboratory experiment to a broad range of natural conditions, including microbial growth where only limited energy is available. The rate law also provides a new explanation of threshold phenomena, which may reflect a thermodynamic equilibrium where the energy released by electron transfer balances that conserved by ADP phosphorylation.

Thermodynamics and kinetics of cyanidin 3-glucoside and caffeine copigments.

PubMed

Limón, Piedad M; Gavara, Raquel; Pina, Fernando

2013-06-05

The multiequilibrium system of reactions of cyanidin 3-glucoside at acidic and mildly acidic pH values was studied in the presence of caffeine as a copigment. The thermodynamic and kinetic constants were determined using the so-called direct and reverse pH jump experiments that were followed by conventional UV-vis spectroscopy or stopped flow coupled to a UV-vis detector, depending on the rate of the monitored process. Compared with that of free anthocyanin, the copigmentation with caffeine extends the domain of the flavylium cation up to less acidic pH values, while in a moderately acidic medium, the quinoidal base becomes more stabilized. As a consequence, the hydration to give the colorless hemiketal is difficult over the entire range of pH values. At pH 1, two adducts were found for the flavylium cation-caffeine interaction, with stoichiometries of 1:1 and 1:2 and association constants of 161 M⁻¹ (K₁) and 21 M⁻¹ (K₂), respectively.

Synthesis and improved photochromic properties of pyrazolones in the solid state by incorporation of halogen

NASA Astrophysics Data System (ADS)

Guo, Jixi; Yuan, Hui; Jia, Dianzeng; Guo, Mingxi; Li, Yinhua

2017-01-01

Four novel photochromic pyrazolones have been prepared by introducing halogen atoms as substituents on the benzene ring. All as-synthesized compounds exhibited excellent reversible photochromic performances in the solid state. Upon UV light irradiation, the as-synthesized compounds can change their structures from E-form to K-form with yellow coloration. Further processed by heating, they rapidly reverted to their initial states at 120 °С. Their photo-response and thermal bleaching kinetics were detailed investigated by UV absorption spectra. The results showed that the time constants were higher than that of our previously reported compounds at least one order of magnitude and the rate constants of the as-synthesized compounds were significantly influenced by the size and electronegativity of different halogen atoms. The fluorescence emission were modulated in a high degree via photoisomerization of pyrazolones, which might be due to the efficient energy transfer from E-form to K-form isomers for their partly overlaps between their E-form absorption spectra and K-form fluorescence spectra.

A specific transition state for S-peptide combining with folded S-protein and then refolding

PubMed Central

Goldberg, Jonathan M.; Baldwin, Robert L.

1999-01-01

We measured the folding and unfolding kinetics of mutants for a simple protein folding reaction to characterize the structure of the transition state. Fluorescently labeled S-peptide analogues combine with S-protein to form ribonuclease S analogues: initially, S-peptide is disordered whereas S-protein is folded. The fluorescent probe provides a convenient spectroscopic probe for the reaction. The association rate constant, kon, and the dissociation rate constant, koff, were both determined for two sets of mutants. The dissociation rate constant is measured by adding an excess of unlabeled S-peptide analogue to a labeled complex (RNaseS*). This strategy allows kon and koff to be measured under identical conditions so that microscopic reversibility applies and the transition state is the same for unfolding and refolding. The first set of mutants tests the role of the α-helix in the transition state. Solvent-exposed residues Ala-6 and Gln-11 in the α-helix of native RNaseS were replaced by the helix destabilizing residues glycine or proline. A plot of log kon vs. log Kd for this series of mutants is linear over a very wide range, with a slope of −0.3, indicating that almost all of the molecules fold via a transition state involving the helix. A second set of mutants tests the role of side chains in the transition state. Three side chains were investigated: Phe-8, His-12, and Met-13, which are known to be important for binding S-peptide to S-protein and which also contribute strongly to the stability of RNaseS*. Only the side chain of Phe-8 contributes significantly, however, to the stability of the transition state. The results provide a remarkably clear description of a folding transition state. PMID:10051587

Reaction wheel low-speed compensation using a dither signal

NASA Astrophysics Data System (ADS)

Stetson, John B., Jr.

1993-08-01

A method for improving low-speed reaction wheel performance on a three-axis controlled spacecraft is presented. The method combines a constant amplitude offset with an unbiased, oscillating dither to harmonically linearize rolling solid friction dynamics. The complete, nonlinear rolling solid friction dynamics using an analytic modification to the experimentally verified Dahl solid friction model were analyzed using the dual-input describing function method to assess the benefits of dither compensation. The modified analytic solid friction model was experimentally verified with a small dc servomotor actuated reaction wheel assembly. Using dither compensation abrupt static friction disturbances are eliminated and near linear behavior through zero rate can be achieved. Simulated vehicle response to a wheel rate reversal shows that when the dither and offset compensation is used, elastic modes are not significantly excited, and the uncompensated attitude error reduces by 34:1.

Programming temporal shapeshifting

NASA Astrophysics Data System (ADS)

Hu, Xiaobo; Zhou, Jing; Vatankhah-Varnosfaderani, Mohammad; Daniel, William F. M.; Li, Qiaoxi; Zhushma, Aleksandr P.; Dobrynin, Andrey V.; Sheiko, Sergei S.

2016-09-01

Shapeshifting enables a wide range of engineering and biomedical applications, but until now transformations have required external triggers. This prerequisite limits viability in closed or inert systems and puts forward the challenge of developing materials with intrinsically encoded shape evolution. Herein we demonstrate programmable shape-memory materials that perform a sequence of encoded actuations under constant environment conditions without using an external trigger. We employ dual network hydrogels: in the first network, covalent crosslinks are introduced for elastic energy storage, and in the second one, temporary hydrogen-bonds regulate the energy release rate. Through strain-induced and time-dependent reorganization of the reversible hydrogen-bonds, this dual network allows for encoding both the rate and pathway of shape transformations on timescales from seconds to hours. This generic mechanism for programming trigger-free shapeshifting opens new ways to design autonomous actuators, drug-release systems and active implants.

Synthesis of nanostructured materials by using metal-cyanide coordination polymers and their lithium storage properties

NASA Astrophysics Data System (ADS)

Nie, Ping; Shen, Laifa; Luo, Haifeng; Li, Hongsen; Xu, Guiyin; Zhang, Xiaogang

2013-10-01

Herein, we demonstrate a novel and simple two-step process for preparing LiCoO2 nanocrystals by using a Prussian blue analogue Co3[Co(CN)6]2 as a precursor. The resultant LiCoO2 nanoparticles possess single crystalline nature and good uniformity with an average size of ca. 360 nm. The unique nanostructure of LiCoO2 provides relatively shorter Li+ diffusion pathways, thus facilitating the fast kinetics of electrochemical reactions. As a consequence, high reversible capacity, excellent cycling stability and rate capability are achieved with these nanocrystals as cathodes for lithium storage. The LiCoO2 nanocrystals deliver specific capacities of 154.5, 135.8, 119, and 100.3 mA h g-1 at 0.2, 0.4, 1, and 2 C rates, respectively. Even at a high current density of 4 C, a reversible capacity of 87 mA h g-1 could be maintained. Importantly, a capacity retention of 83.4% after 100 cycles is achieved at a constant discharge rate of 1 C. Furthermore, owing to facile control of the morphology and size of Prussian blue analogues by varying process parameters, as well as the tailored design of multi-component metal-cyanide hybrid coordination polymers, with which we have successfully prepared porous Fe2O3@NixCo3-xO4 nanocubes, one of the potential anode materials for lithium-ion batteries, such a simple and scalable approach could also be applied to the synthesis of other nanomaterials for energy storage devices.Herein, we demonstrate a novel and simple two-step process for preparing LiCoO2 nanocrystals by using a Prussian blue analogue Co3[Co(CN)6]2 as a precursor. The resultant LiCoO2 nanoparticles possess single crystalline nature and good uniformity with an average size of ca. 360 nm. The unique nanostructure of LiCoO2 provides relatively shorter Li+ diffusion pathways, thus facilitating the fast kinetics of electrochemical reactions. As a consequence, high reversible capacity, excellent cycling stability and rate capability are achieved with these nanocrystals as cathodes for lithium storage. The LiCoO2 nanocrystals deliver specific capacities of 154.5, 135.8, 119, and 100.3 mA h g-1 at 0.2, 0.4, 1, and 2 C rates, respectively. Even at a high current density of 4 C, a reversible capacity of 87 mA h g-1 could be maintained. Importantly, a capacity retention of 83.4% after 100 cycles is achieved at a constant discharge rate of 1 C. Furthermore, owing to facile control of the morphology and size of Prussian blue analogues by varying process parameters, as well as the tailored design of multi-component metal-cyanide hybrid coordination polymers, with which we have successfully prepared porous Fe2O3@NixCo3-xO4 nanocubes, one of the potential anode materials for lithium-ion batteries, such a simple and scalable approach could also be applied to the synthesis of other nanomaterials for energy storage devices. Electronic supplementary information (ESI) available: Detailed experimental procedures and supplementary figures. See DOI: 10.1039/c3nr03289b

Measurements of VOC adsorption/desorption characteristics of typical interior building materials

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

An, Y.; Zhang, J.S.; Shaw, C.Y.

2000-07-01

The adsorption/desorption of volatile organic compounds (VOCs) on interior building material surfaces (i.e., the sink effect) can affect the VOC concentrations in a building, and thus need to be accounted for an indoor air quality (IAQ) prediction model. In this study, the VOC adsorption/desorption characteristics (sink effect) were measured for four typical interior building materials including carpet, vinyl floor tile, painted drywall, and ceiling tile. The VOCs tested were ethylbenzene, cyclohexanone, 1,4-dichlorobenzene, benzaldehyde, and dodecane. These five VOCs were selected because they are representative of hydrocarbons, aromatics, ketones, aldehydes, and chlorine substituted compounds. The first order reversible adsorption/desorption model wasmore » based on the Langmuir isotherm was used to analyze the data and to determine the equilibrium constant of each VOC-material combination. It was found that the adsorption/desorption equilibrium constant, which is a measure of the sink capacity, increased linearly with the inverse of the VOC vapor pressure. For each compound, the adsorption/desorption equilibrium constant, and the adsorption rate constant differed significantly among the four materials tested. A detailed characterization of the material structure in the micro-scale would improve the understanding and modeling of the sink effect in the future. The results of this study can be used to estimate the impact of sink effect on the VOC concentrations in buildings.« less

Aqueous extraction kinetics of soluble solids, phenolics and flavonoids from sage (Salvia fruticosa Miller) leaves.

PubMed

Torun, Mehmet; Dincer, Cuneyt; Topuz, Ayhan; Sahin-Nadeem, Hilal; Ozdemir, Feramuz

2015-05-01

In the present study, aqueous extraction kinetics of total soluble solids (TSS), total phenolic content (TPC) and total flavonoid content (TFC) from Salvia fruticosa leaves were investigated throughout 150 min. of extraction period against temperature (60-80 °C), particle size (2-8 mm) and loading percentage (1-4 %). The extract yielded 25 g/100 g TSS which contained 30 g/100 g TPC and 25 g/100 g TFC. The extraction data in time course fit with reversible first order kinetic model. All tested variables showed significant effect on the estimated kinetic parameters except equilibrium concentration. Increasing the extraction temperature resulted high extraction rate constants and equilibrium concentrations of the tested variables notably above 70 °C. By using the Arrhenius relationship, activation energy of the TSS, TPC and TFC were determined as 46.11 ± 5.61, 36.80 ± 3.12 and 33.52 ± 2.23 kj/mol, respectively. By decreasing the particle size, the extraction rate constants and diffusion coefficients exponentially increased whereas equilibrium concentrations did not change significantly. The equilibrium concentrations of the tested parameters showed linear behavior with increasing the loading percentage of the sage, however; the change in extraction rates did not show linear behavior due to submerging effect of 4 % loading.

Continuous delivery of ropinirole reverses motor deficits without dyskinesia induction in MPTP-treated common marmosets.

PubMed

Stockwell, K A; Virley, D J; Perren, M; Iravani, M M; Jackson, M J; Rose, S; Jenner, P

2008-05-01

L-DOPA treatment of Parkinson's disease induces a high incidence of motor complications, notably dyskinesia. Longer acting dopamine agonists, e.g. ropinirole, are thought to produce more continuous dopaminergic stimulation and less severe dyskinesia. However, standard oral administration of dopamine agonists does not result in constant plasma drug levels, therefore, more continuous drug delivery may result in both prolonged reversal of motor deficits and reduced levels of dyskinesia. Therefore, we compared the effects of repeated oral administration of ropinirole to constant subcutaneous infusion in MPTP-treated common marmosets. Animals received oral administration (0.4 mg/kg, BID) or continuous infusion of ropinirole (0.8 mg/kg/day) via osmotic minipumps for 14 days (Phase I). The treatments were then switched and continued for a further 14 days (Phase II). In Phase I, locomotor activity was similar between treatment groups but reversal of motor disability was more pronounced in animals receiving continuous infusion. Dyskinesia intensity was low in both groups however there was a trend suggestive of less marked dyskinesia in those animals receiving continuous infusion. In Phase II, increased locomotor activity was maintained but animals switched from oral to continuous treatment showing an initial period of enhanced locomotor activity. The reversal of motor disability was maintained in both groups, however, motor disability tended towards greater improvement following continuous infusion. Importantly, dyskinesia remained low in both groups suggesting that constant delivery of ropinirole neither leads to priming nor expression of dyskinesia. These results suggest that a once-daily controlled-release formulation may provide improvements over existing benefits with standard oral ropinirole in Parkinson's disease patients.

Two-way shape memory behavior of semi-crystalline elastomer under stress-free condition

NASA Astrophysics Data System (ADS)

Qian, Chen; Dong, Yubing; Zhu, Yaofeng; Fu, Yaqin

2016-08-01

Semi-crystalline shape memory polymers exhibit two-way shape memory effect (2W-SME) under constant stresses through crystallization-induced elongation upon cooling and melting-induced constriction upon heating. The applied constant stress influenced the prediction and usability of 2W-SME in practical applications without any external force. Here the reversible shape transition in EVA-shaped memory polymer was quantitative analyzed under a suitable temperature range and external stress-free condition. The fraction of reversible strain increased with increasing upper temperature (T high) within the temperature range and reached the maximum value of 13.62% at 70 °C. However, reversible strain transition was almost lost when T high exceeded 80 °C because of complete melting of crystalline scaffold, known as the latent recrystallization template. The non-isothermal annealing of EVA 2W-SMP under changing circulating temperatures was confirmed. Moreover, the orientation of crystallization was retained at high temperatures. These findings may contribute to design an appropriate shape memory protocol based on application-specific requirements.

Real space mapping of oxygen vacancy diffusion and electrochemical transformations by hysteretic current reversal curve measurements

DOEpatents

Kalinin, Sergei V.; Balke, Nina; Borisevich, Albina Y.; Jesse, Stephen; Maksymovych, Petro; Kim, Yunseok; Strelcov, Evgheni

2014-06-10

An excitation voltage biases an ionic conducting material sample over a nanoscale grid. The bias sweeps a modulated voltage with increasing maximal amplitudes. A current response is measured at grid locations. Current response reversal curves are mapped over maximal amplitudes of the bias cycles. Reversal curves are averaged over the grid for each bias cycle and mapped over maximal bias amplitudes for each bias cycle. Average reversal curve areas are mapped over maximal amplitudes of the bias cycles. Thresholds are determined for onset and ending of electrochemical activity. A predetermined number of bias sweeps may vary in frequency where each sweep has a constant number of cycles and reversal response curves may indicate ionic diffusion kinetics.

How important is thermodynamics for identifying elementary flux modes?

PubMed Central

Peres, Sabine; Jolicœur, Mario; Moulin, Cécile

2017-01-01

We present a method for computing thermodynamically feasible elementary flux modes (tEFMs) using equilibrium constants without need of internal metabolite concentrations. The method is compared with the method based on a binary distinction between reversible and irreversible reactions. When all reactions are reversible, adding the constraints based on equilibrium constants reduces the number of elementary flux modes (EFMs) by a factor of two. Declaring in advance some reactions as irreversible, based on reliable biochemical expertise, can in general reduce the number of EFMs by a greater factor. But, even in this case, computing tEFMs can rule out some EFMs which are biochemically irrelevant. We applied our method to two published models described with binary distinction: the monosaccharide metabolism and the central carbon metabolism of Chinese hamster ovary cells. The results show that the binary distinction is in good agreement with biochemical observations. Moreover, the suppression of the EFMs that are not consistent with the equilibrium constants appears to be biologically relevant. PMID:28222104

Reverse total shoulder arthroplasty for acute head-splitting, 3- and 4-part fractures of the proximal humerus in the elderly.

PubMed

Grubhofer, Florian; Wieser, Karl; Meyer, Dominik C; Catanzaro, Sabrina; Beeler, Silvan; Riede, Ulf; Gerber, Christian

2016-10-01

Anatomic reduction and stable internal fixation of complex proximal humeral fractures in the elderly is challenging. Secondary displacement, screw perforation, and humeral head necrosis are common complications. The outcome of hemiarthroplasty is unpredictable and strongly dependent on the uncertain healing of the greater tuberosity. This multicenter study retrospectively analyzes the midterm results of primary reverse total shoulder arthroplasty for the treatment of acute, complex fractures of the humerus in an elderly population. Fifty-two shoulders in 51 patients with a mean age of 77 years treated with reverse total shoulder arthroplasty for an acute, complex fracture of the proximal humerus were clinically and radiographically analyzed after a mean follow-up period of 35 months (range, 12-90 months). There were no intraoperative complications. Revision surgery was performed in 4 shoulders. At final follow-up, the absolute and relative Constant scores averaged 62 points (range, 21-83 points) and 86% (range, 30%-100%), respectively, with a mean Subjective Shoulder Value of 83% (range, 30%-100%). Of the patients, 92% rated the treatment outcome as excellent or good. Patients with a resected or secondarily displaced greater tuberosity had an inferior clinical outcome to those with a healed greater tuberosity. The midterm clinical results are predictably good, with low complication rates and a rapid postoperative recovery of painfree everyday function. If secondary displacement of the greater tuberosity occurs, revision surgery may warrant consideration in view of potential improvement of ultimate outcome. Copyright © 2016 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Elsevier Inc. All rights reserved.

Geomagnetic fluctuations during a polarity transition

NASA Astrophysics Data System (ADS)

Audunsson, Haraldur; Levi, Shaul

1997-01-01

The extensive Roza Member of the Columbia River Basalt Group (Washington State) has intermediate paleomagnetic directions, bracketed by underlying normal and overlying reverse polarity flows. A consistent paleomagnetic direction was measured at 11 widely distributed outcrops; the average direction has a declination of 189° and an inclination of -5°, with greater variation in the inclination [Rietman, 1966]. In this study the Roza Member was sampled in two Pasco Basin drillcores, where it is a single cooling unit and its thickness exceeds 50 m. Excellent core recovery allowed uniform and dense sampling of the drillcores. During its protracted cooling, the Roza flow in the drillcores recorded part of a 15.5 Ma geomagnetic polarity transition. The inclination has symmetric, quasicyclic intraflow variation, while the declination is nearly constant, consistent with the results from the outcrops. Thermal models of the cooling flow provide the timing for remanence acquisition. The inclination is inferred to have progressed from 0° to -15° and back to -3°over a period of 15 to 60 years, at rates of 1.6° to 0.5°/yr. Because the geomagnetic intensity was probably weak during the transition, these apparently high rates of change are not significantly different from present-day secular variation. These results agree with the hypothesis that normal secular variation persists through geomagnetic transitions. The Iow-amplitude quasicyclical fluctuations of the field over tens of years, recorded by Roza, suggest that the geomagnetic field reverses in discrete steps, and that more than 15-60 years were required to complete this reversal.

Pituitary Adenylate Cyclase-Activating Polypeptide Reverses Ammonium Metavanadate-Induced Airway Hyperresponsiveness in Rats

PubMed Central

Tlili, Mounira; Sriha, Badreddine; Ben Rhouma, Khémais; Sakly, Mohsen; Wurtz, Olivier

2015-01-01

The rate of atmospheric vanadium is constantly increasing due to fossil fuel combustion. This environmental pollution favours vanadium exposure in particular to its vanadate form, causing occupational bronchial asthma and bronchitis. Based on the well admitted bronchodilator properties of the pituitary adenylate cyclase-activating polypeptide (PACAP), we investigated the ability of this neuropeptide to reverse the vanadate-induced airway hyperresponsiveness in rats. Exposure to ammonium metavanadate aerosols (5 mg/m3/h) for 15 minutes induced 4 hours later an array of pathophysiological events, including increase of bronchial resistance and histological alterations, activation of proinflammatory alveolar macrophages, and increased oxidative stress status. Powerfully, PACAP inhalation (0.1 mM) for 10 minutes alleviated many of these deleterious effects as demonstrated by a decrease of bronchial resistance and histological restoration. PACAP reduced the level of expression of mRNA encoding inflammatory chemokines (MIP-1α, MIP-2, and KC) and cytokines (IL-1α and TNF-α) in alveolar macrophages and improved the antioxidant status. PACAP reverses the vanadate-induced airway hyperresponsiveness not only through its bronchodilator activity but also by counteracting the proinflammatory and prooxidative effects of the metal. Then, the development of stable analogs of PACAP could represent a promising therapeutic alternative for the treatment of inflammatory respiratory disorders. PMID:26199679

Dynamics and kinetics of reversible homo-molecular dimerization of polycyclic aromatic hydrocarbons

NASA Astrophysics Data System (ADS)

Mao, Qian; Ren, Yihua; Luo, K. H.; van Duin, Adri C. T.

2017-12-01

Physical dimerization of polycyclic aromatic hydrocarbons (PAHs) has been investigated via molecular dynamics (MD) simulation with the ReaxFF reactive force field that is developed to bridge the gap between the quantum mechanism and classical MD. Dynamics and kinetics of homo-molecular PAH collision under different temperatures, impact parameters, and orientations are studied at an atomic level, which is of great value to understand and model the PAH dimerization. In the collision process, the enhancement factors of homo-molecular dimerizations are quantified and found to be larger at lower temperatures or with smaller PAH instead of size independent. Within the capture radius, the lifetime of the formed PAH dimer decreases as the impact parameter increases. Temperature and PAH characteristic dependent forward and reverse rate constants of homo-molecular PAH dimerization are derived from MD simulations, on the basis of which a reversible model is developed. This model can predict the tendency of PAH dimerization as validated by pyrene dimerization experiments [H. Sabbah et al., J. Phys. Chem. Lett. 1(19), 2962 (2010)]. Results from this study indicate that the physical dimerization cannot be an important source under the typical flame temperatures and PAH concentrations, which implies a more significant role played by the chemical route.

Slowly switching between environments facilitates reverse evolution in small populations

NASA Astrophysics Data System (ADS)

Tan, Longzhi; Gore, Jeff

2011-03-01

The rate at which a physical process occurs usually changes the behavior of a system. In thermodynamics, the reversibility of a process generally increases when it occurs at an infinitely slow rate. In biological evolution, adaptations to a new environment may be reversed by evolution in the ancestral environment. Such fluctuating environments are ubiquitous in nature, although how the rate of switching affects reverse evolution is unknown. Here we use a computational approach to quantify evolutionary reversibility as a function of the rate of switching between two environments. For small population sizes, which travel on landscapes as random walkers, we find that both genotypic and phenotypic reverse evolution increase at slow switching rates. However, slow switching of environments decreases evolutionary reversibility for a greedy walker, corresponding to large populations (extensive clonal interference). We conclude that the impact of the switching rate for biological evolution is more complicated than other common physical processes, and that a quantitative approach may yield significant insight into reverse evolution.

External Validity of Contingent Valuation: Comparing Hypothetical and Actual Payments.

PubMed

Ryan, Mandy; Mentzakis, Emmanouil; Jareinpituk, Suthi; Cairns, John

2017-11-01

Whilst contingent valuation is increasingly used in economics to value benefits, questions remain concerning its external validity that is do hypothetical responses match actual responses? We present results from the first within sample field test. Whilst Hypothetical No is always an Actual No, Hypothetical Yes exceed Actual Yes responses. A constant rate of response reversals across bids/prices could suggest theoretically consistent option value responses. Certainty calibrations (verbal and numerical response scales) minimise hypothetical-actual discrepancies offering a useful solution. Helping respondents resolve uncertainty may reduce the discrepancy between hypothetical and actual payments and thus lead to more accurate policy recommendations. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

Utilization of membranes for H2O recycle system

NASA Technical Reports Server (NTRS)

Ohya, H.; Oguchi, M.

1986-01-01

Conceptual studies of closed ecological life support systems (CELSS) carried out at NAL in Japan for a water recycle system using membranes are reviewed. The system will treat water from shower room, urine, impure condensation from gas recycle system, and so on. The H2O recycle system is composed of prefilter, ultrafiltration membrane, reverse osmosis membrane, and distillator. Some results are shown for a bullet train of toilet-flushing water recycle equipment with an ultraviltration membrane module. The constant value of the permeation rate with a 4.7 square meters of module is about 70 1/h after 500th of operation. Thermovaporization with porous polytetrafluorocarbon membrane is also proposed to replce the distillator.

Single-Molecule Kinetics Reveal Cation-Promoted DNA Duplex Formation Through Ordering of Single-Stranded Helices

PubMed Central

Dupuis, Nicholas F.; Holmstrom, Erik D.; Nesbitt, David J.

2013-01-01

In this work, the kinetics of short, fully complementary oligonucleotides are investigated at the single-molecule level. Constructs 6–9 bp in length exhibit single exponential kinetics over 2 orders of magnitude time for both forward (kon, association) and reverse (koff, dissociation) processes. Bimolecular rate constants for association are weakly sensitive to the number of basepairs in the duplex, with a 2.5-fold increase between 9 bp (k′on = 2.1(1) × 106 M−1 s−1) and 6 bp (k′on = 5.0(1) × 106 M−1 s−1) sequences. In sharp contrast, however, dissociation rate constants prove to be exponentially sensitive to sequence length, varying by nearly 600-fold over the same 9 bp (koff = 0.024 s−1) to 6 bp (koff = 14 s−1) range. The 8 bp sequence is explored in more detail, and the NaCl dependence of kon and koff is measured. Interestingly, konincreases by >40-fold (kon = 0.10(1) s−1 to 4.0(4) s−1 between [NaCl] = 25 mM and 1 M), whereas in contrast, koffdecreases by fourfold (0.72(3) s−1 to 0.17(7) s−1) over the same range of conditions. Thus, the equilibrium constant (Keq) increases by ≈160, largely due to changes in the association rate, kon. Finally, temperature-dependent measurements reveal that increased [NaCl] reduces the overall exothermicity (ΔΔH° > 0) of duplex formation, albeit by an amount smaller than the reduction in entropic penalty (−TΔΔS° < 0). This reduced entropic cost is attributed to a cation-facilitated preordering of the two single-stranded species, which lowers the association free-energy barrier and in turn accelerates the rate of duplex formation. PMID:23931323

Photocatalytic events of CdSe quantum dots in confined media. Electrodic behavior of coupled platinum nanoparticles.

PubMed

Harris, Clifton; Kamat, Prashant V

2010-12-28

The electrodic behavior of platinum nanoparticles (2.8 nm diameter) and their role in influencing the photocatalytic behavior of CdSe quantum dots (3.4 nm diameter) has been evaluated by confining both nanoparticles together in heptane/dioctyl sulphosuccinate/water reverse micelles. The particles spontaneously couple together within the micelles via micellar exchange processes and thus facilitate experimental observation of electron transfer reactions inside the water pools. Electron transfer from CdSe to Pt is found to occur with a rate constant of 1.22 × 10(9) s(-1). With the use of methyl viologen (MV(2+)) as a probe molecule, the role of Pt in the photocatalytic process is established. Ultrafast oxidation of the photogenerated MV(+•) radicals indicates that Pt acts as an electron sink, scavenging electrons from MV(+•) with a rate constant of 3.1 × 10(9) s(-1). The electron transfer between MV(+•) and Pt, and a drastically lower yield of MV(+•) under steady state irradiation, confirms the ability of Pt nanoparticles to discharge electrons quickly. The kinetic details of photoinduced processes in CdSe-Pt assemblies and the electrodic behavior of Pt nanoparticles provide important information for the development of light energy conversion devices.

Suicide inactivation of catechol 2,3-dioxygenase from Pseudomonas putida mt-2 by 3-halocatechols

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

Bartels, I.; Knackmuss, H.J.; Reineke, W.

The inactivation of catechol 2,3-dioxygenase from Pseudomonas putida mt-2 by 3-chloro- and 3-fluorocatechol and the iron-chelating agent Tiron (catechol-3,5-disulfonate) was studied. Whereas inactivation by Tiron is an oxygen-independent and mostly reversible process, inactivation by the 3-halocatechols was only observed in the presence of oxygen and was largely irreversible. The rate constants for inactivation (K/sub 2/) were 1.62 x 10/sup -3/ sec/sup -1/ for 3-chlorocatechol and 2.38 x 10/sup -3/ sec/sup -1/ for 3-fluorocatechol. The inhibitor constants (K/sub i/) were 23 ..mu..M for 3-chlorocatechol and 17 ..mu..M for 3-fluorocatechol. The kinetic data for 3-fluorocatechol could only be obtained in the presencemore » of 2-mercaptoethanol. Besides inactivated enzyme, some 2-hydroxyhexa-2,4-dienoic acid as the actual suicide product of meta-cleavage. A side product of 3-fluorocatechol cleavage is a yellow compound with the spectral characteristics of a 2-hydroxy-6-oxohexa-2,4-dienoci acid indicating 1,6-cleavage. Rates of inactivation by 3-fluorocatechol were reduced in the presence of superoxide dismutase, catalase, formate, and mannitol, which implies that superoxide anion, hydrogen peroxide, and hydroxyl radical exhibit additional inactivation. 64 references.« less

A Semi-Empirical Two Step Carbon Corrosion Reaction Model in PEM Fuel Cells

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

Young, Alan; Colbow, Vesna; Harvey, David

2013-01-01

The cathode CL of a polymer electrolyte membrane fuel cell (PEMFC) was exposed to high potentials, 1.0 to 1.4 V versus a reversible hydrogen electrode (RHE), that are typically encountered during start up/shut down operation. While both platinum dissolution and carbon corrosion occurred, the carbon corrosion effects were isolated and modeled. The presented model separates the carbon corrosion process into two reaction steps; (1) oxidation of the carbon surface to carbon-oxygen groups, and (2) further corrosion of the oxidized surface to carbon dioxide/monoxide. To oxidize and corrode the cathode catalyst carbon support, the CL was subjected to an accelerated stressmore » test cycled the potential from 0.6 VRHE to an upper potential limit (UPL) ranging from 0.9 to 1.4 VRHE at varying dwell times. The reaction rate constants and specific capacitances of carbon and platinum were fitted by evaluating the double layer capacitance (Cdl) trends. Carbon surface oxidation increased the Cdl due to increased specific capacitance for carbon surfaces with carbon-oxygen groups, while the second corrosion reaction decreased the Cdl due to loss of the overall carbon surface area. The first oxidation step differed between carbon types, while both reaction rate constants were found to have a dependency on UPL, temperature, and gas relative humidity.« less

Investigation of the dynamic stereochemistry of dimesityl-2,4,6-trimethoxyphenylmethane by complete lineshape analysis and 2D EXSY NMR spectroscopy.

PubMed

Denkova, Pavletta; Vassilev, Nikolay; Van Lokeren, Luk; Willem, Rudolph

2008-04-01

The static and dynamic stereochemistry of dimesityl-2,4,6-trimethoxyphenylmethane in solution was investigated by lineshape analysis of 1D NMR spectra and cross-peak amplitude processing in 2D EXSY spectra, recorded at variable temperatures. Previous studies on this propeller-shaped chiral compound show that the stereomer threshold interconversion is associated with helicity reversal and occurs through [1,2]- and [1,3]-two ring flips of one mesityl and the 2,4,6-trimethoxyphenyl rings. In the present study, the experimental rate constants of the [1,2]- and [1,3]-two ring flips, which are identical, were determined at various temperatures by combining quantitative 2D EXSY spectra processing and complete lineshape analysis (CLSA) of 1D NMR spectra. The latter were subjected to reference deconvolution and linear prediction in order to eliminate the lineshape distortions due to magnetic field inhomogeneity. The activation parameters of these ring flips were determined by an Eyring equation analysis of the temperature dependence of the rate constant. The experimentally determined activation enthalpy and entropy for the two-ring flips, and those obtained from theoretical ab initio calculations at different levels of theory and basis sets, were found to be in good agreement. Copyright (c) 2008 John Wiley & Sons, Ltd.

[Effects of ranitidine on pharmacokinetics of rhein from Dachengqi Decoction in rats after oral administration].

PubMed

Ren, Yan-yi; Gong, Han-lin; Tang, Wen-fu; Wan, Mei-fua; Huang, Xi

2009-09-01

To explore the effects of ranitidine on pharmacokinetics of rhein in rats after oral administration of Dachengqi Decoction (DCQD), a compound traditional Chinese herbal medicine. Twelve male Sprague-Dawley rats were divided into DCQD group and DCQD plus ranitidine group, and were orally administered with DCQD at a dose of 10 g/kg or DCQD (10 g/kg) combined with ranitidine (150 mg/kg), respectively. Blood samples were gathered after a series of time intervals. Metabolism of rhein was determined with a reversed-phase high-performance liquid chromatography with internal standard of 1, 8-dihydroxyanthraquinone and the data were analyzed with DAS 2.1 program. The pharmacokinetic parameters were compared between the two groups. The pharmacokinetic parameters of rhein in the DCQD group, including peak concentration (C(max)), area under the plasma concentration-time curve (AUC), distribution phase half-life (t(1/2alpha)), elimination rate constant (K(10)) and central to peripheral transfer rate constant (K(12)), were significantly different to those in the DCQD plus ranitidine group (P<0.05, P<0.01). There were no significant differences in the other parameters between the two groups. Ranitidine can influence the pharmacokinetics of rhein in rats after oral administration of DCQD.

Chickadees discriminate contingency reversals presented consistently, but not frequently.

PubMed

McMillan, Neil; Hahn, Allison H; Congdon, Jenna V; Campbell, Kimberley A; Hoang, John; Scully, Erin N; Spetch, Marcia L; Sturdy, Christopher B

2017-07-01

Chickadees are high-metabolism, non-migratory birds, and thus an especially interesting model for studying how animals follow patterns of food availability over time. Here, we studied whether black-capped chickadees (Poecile atricapillus) could learn to reverse their behavior and/or to anticipate changes in reinforcement when the reinforcer contingencies for each stimulus were not stably fixed in time. In Experiment 1, we examined the responses of chickadees on an auditory go/no-go task, with constant reversals in reinforcement contingencies every 120 trials across daily testing intervals. Chickadees did not produce above-chance discrimination; however, when trained with a procedure that only reversed after successful discrimination, chickadees were able to discriminate and reverse their behavior successfully. In Experiment 2, we examined the responses of chickadees when reversals were structured to occur at the same time once per day, and chickadees were again able to discriminate and reverse their behavior over time, though they showed no reliable evidence of reversal anticipation. The frequency of reversals throughout the day thus appears to be an important determinant for these animals' performance in reversal procedures.

Communication: Equilibrium rate coefficients from atomistic simulations: The O({sup 3}P) + NO({sup 2}Π) → O{sub 2}(X{sup 3}Σ{sub g}{sup −}) + N({sup 4}S) reaction at temperatures relevant to the hypersonic flight regime

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

Castro-Palacio, Juan Carlos; Bemish, Raymond J.; Meuwly, Markus, E-mail: m.meuwly@unibas.ch

2015-03-07

The O({sup 3}P) + NO({sup 2}Π) → O{sub 2}(X{sup 3}Σ{sub g}{sup −}) + N({sup 4}S) reaction is among the N- and O- involving reactions that dominate the energetics of the reactive air flow around spacecraft during hypersonic atmospheric re-entry. In this regime, the temperature in the bow shock typically ranges from 1000 to 20 000 K. The forward and reverse rate coefficients for this reaction derived directly from trajectory calculations over this range of temperature are reported in this letter. Results compare well with the established equilibrium constants for the same reaction from thermodynamic quantities derived from spectroscopy in the gasmore » phase which paves the way for large-scale in silico investigations of equilibrium rates under extreme conditions.« less

Shear Resistance Variations in Experimentally Sheared Mudstone Granules: A Possible Shear-Thinning and Thixotropic Mechanism

NASA Astrophysics Data System (ADS)

Hu, Wei; Xu, Qiang; Wang, Gonghui; Scaringi, Gianvito; Mcsaveney, Mauri; Hicher, Pierre-Yves

2017-11-01

We present results of ring shear frictional resistance for mudstone granules of different size obtained from a landslide shear zone. Little rate dependency of shear resistance was observed in sand-sized granules in any wet or dry test, while saturated gravel-sized granules exhibited significant and abrupt reversible rate-weakening (from μ = 0.6 to 0.05) at about 2 mm/s. Repeating resistance variations occurred also under constant shear displacement rate. Mudstone granules generate mud as they are crushed and softened. Shear-thinning and thixotropic behavior of the mud can explain the observed behavior: with the viscosity decreasing, the mud can flow through the coarser soil pores and migrate out from the shear zone. This brings new granules into contact which produces new mud. Thus, the process can start over. Similarities between experimental shear zones and those of some landslides in mudstone suggest that the observed behavior may play a role in some landslide kinematics.

Kinetics of a Migration-Driven Aggregation-Fragmentation Process

NASA Astrophysics Data System (ADS)

Zhuang, You-Yi; Lin, Zhen-Quan; Ke, Jian-Hong

2003-08-01

We propose a reversible model of the migration-driven aggregation-fragmentation process with the symmetric migration rate kernels K(k;j)=K^'(k;j)=λ kj^v and the constant aggregation rates I1, I2 and fragmentation rates J1, J2. Based on the mean-field theory, we investigate the evolution behavior of the aggregate size distributions in several cases with different values of index υ. We find that the fragmentation reaction plays a more important role in the kinetic behaviors of the system than the aggregation and migration. When J1=0 and J2 =0, the aggregate size distributions ak(t) and bk(t) obey the conventional scaling law, while when J1>0 and J2>0, they obey the modified scaling law with an exponential scaling function. The total mass of either species remains conserved. The project supported by National Natural Science Foundation of China under Grant Nos. 10275048 and 10175008, and Natural Science Foundation of Zhejiang Province of China under Grant No. 102067

Human heart rate variability relation is unchanged during motion sickness

NASA Technical Reports Server (NTRS)

Mullen, T. J.; Berger, R. D.; Oman, C. M.; Cohen, R. J.

1998-01-01

In a study of 18 human subjects, we applied a new technique, estimation of the transfer function between instantaneous lung volume (ILV) and instantaneous heart rate (HR), to assess autonomic activity during motion sickness. Two control recordings of ILV and electrocardiogram (ECG) were made prior to the development of motion sickness. During the first, subjects were seated motionless, and during the second they were seated rotating sinusoidally about an earth vertical axis. Subjects then wore prism goggles that reverse the left-right visual field and performed manual tasks until they developed moderate motion sickness. Finally, ILV and ECG were recorded while subjects maintained a relatively constant level of sickness by intermittent eye closure during rotation with the goggles. Based on analyses of ILV to HR transfer functions from the three conditions, we were unable to demonstrate a change in autonomic control of heart rate due to rotation alone or due to motion sickness. These findings do not support the notion that moderate motion sickness is manifested as a generalized autonomic response.

Repeated action of a constant magnetic field on the blood coagulation system in artificially produced anemia

NASA Technical Reports Server (NTRS)

Zabrodina, L. V.

1974-01-01

Changes are discussed in the coagulatory system of the blood in rabbits under the influence of a constant magnetic field of an intensity of 2500 oersteds against the background of artificially induced anemia. Reversibility of the changes produced and the presence of the adaptational effect are noted. Taking all this into consideration, the changes involving the coagulatory system of the blood which arise under the influence of a constant magnetic field may be considered to have a nerve-reflex nature.

Rate constants for the reactions of OH with CH3Cl, CH2Cl2, CHCl3, and CH3Br

NASA Technical Reports Server (NTRS)

Hsu, K.-J.; Demore, W. B.

1994-01-01

Rate constants for the reactions of OH with CH3Cl, CH2Cl2, CHCl3, and CH3Br have been measured by a relative rate technique in which the reaction rate of each compound was compared to that of HFC-152a (CH3CHF2) and (for CH2Cl2) HFC-161 (CH3CH2F). Using absolute rate constants for HFC-152a and HFC-161, which we have determined relative to those for CH4, CH3CCl3, and C2H6, temperature dependent rate constants of both compounds were derived. The derived rate constant for CH3Br is in good agreement with recent absolute measurements. However, for the chloromethanes all the rate constants are lower at atmospheric temperatures than previously reported, especially for CH2Cl2 where the present rate constant is about a factor of 1.6 below the JPL 92-20 value. The new rate constant appears to resolve a discrepancy between the observed atmospheric concentrations and those calculated from the previous rate constant and estimated release rates.

Controlled drug release by polymer dissolution. II: Enzyme-mediated delivery device.

PubMed

Heller, J; Trescony, P V

1979-07-01

A novel, closed-loop drug delivery system was developed where the presence or absence of an external compound controls drug delivery from a bioerodible polymer. In the described delivery system, hydrocortisone was incorporated into a n-hexyl half-ester of a methyl vinyl ehter-maleic anhydride copolymer, and the polymer-drug mixture was fabricated into disks. These disks were then coated with a hydrogel containing immobilized urease. In a medium of constant pH and in the absence of external urea, the hydrocortisone release was that normally expected for that polymer at the given pH. With external urea, ammonium bicarbonate and ammonium hydroxide were generated within the hydrogel, which accelerated polymer erosion and drug release. The drug delivery rate increase was proportional to the amount of external urea and was reversible; that is, when external urea was removed, the drug release rate gradually returned to its original value.

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

Hu, Xiaobo; Zhou, Jing; Vatankhah-Varnosfaderani, Mohammad

Shapeshifting enables a wide range of engineering and biomedical applications, but until now transformations have required external triggers. This prerequisite limits viability in closed or inert systems and puts forward the challenge of developing materials with intrinsically encoded shape evolution. Herein we demonstrate programmable shape-memory materials that perform a sequence of encoded actuations under constant environment conditions without using an external trigger. We employ dual network hydrogels: in the first network, covalent crosslinks are introduced for elastic energy storage, and in the second one, temporary hydrogen-bonds regulate the energy release rate. Through strain-induced and time-dependent reorganization of the reversible hydrogen-bonds,more » this dual network allows for encoding both the rate and pathway of shape transformations on timescales from seconds to hours. In conclusion, this generic mechanism for programming trigger-free shapeshifting opens new ways to design autonomous actuators, drug-release systems and active implants.« less

Programming temporal shapeshifting

DOE PAGES

Hu, Xiaobo; Zhou, Jing; Vatankhah-Varnosfaderani, Mohammad; ...

2016-09-27

Shapeshifting enables a wide range of engineering and biomedical applications, but until now transformations have required external triggers. This prerequisite limits viability in closed or inert systems and puts forward the challenge of developing materials with intrinsically encoded shape evolution. Herein we demonstrate programmable shape-memory materials that perform a sequence of encoded actuations under constant environment conditions without using an external trigger. We employ dual network hydrogels: in the first network, covalent crosslinks are introduced for elastic energy storage, and in the second one, temporary hydrogen-bonds regulate the energy release rate. Through strain-induced and time-dependent reorganization of the reversible hydrogen-bonds,more » this dual network allows for encoding both the rate and pathway of shape transformations on timescales from seconds to hours. In conclusion, this generic mechanism for programming trigger-free shapeshifting opens new ways to design autonomous actuators, drug-release systems and active implants.« less

Coordinated DNA dynamics during the human telomerase catalytic cycle

NASA Astrophysics Data System (ADS)

Parks, Joseph W.; Stone, Michael D.

2014-06-01

The human telomerase reverse transcriptase (hTERT) utilizes a template within the integral RNA subunit (hTR) to direct extension of telomeres. Telomerase exhibits repeat addition processivity (RAP) and must therefore translocate the nascent DNA product into a new RNA:DNA hybrid register to prime each round of telomere repeat synthesis. Here, we use single-molecule FRET and nuclease protection assays to monitor telomere DNA structure and dynamics during the telomerase catalytic cycle. DNA translocation during RAP proceeds through a previously uncharacterized kinetic substep during which the 3‧-end of the DNA substrate base pairs downstream within the hTR template. The rate constant for DNA primer realignment reveals this step is not rate limiting for RAP, suggesting a second slow conformational change repositions the RNA:DNA hybrid into the telomerase active site and drives the extrusion of the 5‧-end of the DNA primer out of the enzyme complex.

The repetitive portion of the Xenopus IgH Mu switch region mediates orientation-dependent class switch recombination.

PubMed

Zhang, Zheng Z; Pannunzio, Nicholas R; Lu, Zhengfei; Hsu, Ellen; Yu, Kefei; Lieber, Michael R

2015-10-01

Vertebrates developed immunoglobulin heavy chain (IgH) class switch recombination (CSR) to express different IgH constant regions. Most double-strand breaks for Ig CSR occur within the repetitive portion of the switch regions located upstream of each set of constant domain exons for the Igγ, Igα or Igϵ heavy chain. Unlike mammalian switch regions, Xenopus switch regions do not have a high G-density on the non-template DNA strand. In previous studies, when Xenopus Sμ DNA was moved to the genome of mice, it is able to support substantial CSR when it is used to replace the murine Sγ1 region. Here, we tested both the 2kb repetitive portion and the 4.6 kb full-length portions of the Xenopus Sμ in both their natural (forward) orientation relative to the constant domain exons, as well as the opposite (reverse) orientation. Consistent with previous work, we find that the 4.6 kb full-length Sμ mediates similar levels of CSR in both the forward and reverse orientations. Whereas, the forward orientation of the 2kb portion can restore the majority of the CSR level of the 4.6 kb full-length Sμ, the reverse orientation poorly supports R-looping and no CSR. The forward orientation of the 2kb repetitive portion has more GG dinucleotides on the non-template strand than the reverse orientation. The correlation of R-loop formation with CSR efficiency, as demonstrated in the 2kb repetitive fragment of the Xenopus switch region, confirms a role played by R-looping in CSR that appears to be conserved through evolution. Copyright © 2015 Elsevier Ltd. All rights reserved.

Force probe simulations of a reversibly rebinding system: Impact of pulling device stiffness

NASA Astrophysics Data System (ADS)

Jaschonek, Stefan; Diezemann, Gregor

2017-03-01

We present a detailed study of the parameter dependence of force probe molecular dynamics (FPMD) simulations. Using a well studied calix[4]arene catenane dimer as a model system, we systematically vary the pulling velocity and the stiffness of the applied external potential. This allows us to investigate how the results of pulling simulations operating in the constant velocity mode (force-ramp mode) depend on the details of the simulation setup. The system studied has the further advantage of showing reversible rebinding meaning that we can monitor the opening and the rebinding transition. Many models designed to extract kinetic information from rupture force distributions work in the limit of soft springs and all quantities are found to depend solely on the so-called loading rate, the product of spring stiffness and pulling velocity. This approximation is known to break down when stiff springs are used, a situation often encountered in molecular simulations. We find that while some quantities only depend on the loading rate, others show an explicit dependence on the spring constant used in the FPMD simulation. In particular, the force versus extension curves show an almost stiffness independent rupture force but the force jump after the rupture transition does depend roughly linearly on the value of the stiffness. The kinetic rates determined from the rupture force distributions show a dependence on the stiffness that can be understood in terms of the corresponding dependence of the characteristic forces alone. These dependencies can be understood qualitatively in terms of a harmonic model for the molecular free energy landscape. It appears that the pulling velocities employed are so large that the crossover from activated dynamics to diffusive dynamics takes place on the time scale of our simulations. We determine the effective distance of the free energy minima of the closed and the open configurations of the system from the barrier via an analysis of the hydrogen-bond network with results in accord with earlier simulations. We find that the system is quite brittle in the force regime monitored in the sense that the barrier is located near to the closed state.

Molecular Mechanisms of Increased Heart Rate in Shenxianshengmai-treated Bradycardia Rabbits.

PubMed

Liu, Zhou-Ying; Huang, Jian; Liu, Na-Na; Zheng, Min; Zhao, Tao; Zhao, Bu-Chang; Wang, Yi-Min; Pu, Jie-Lin

2017-01-20

The molecular mechanisms of Shenxianshengmai (SXSM), a traditional Chinese medicine, on bradycardia have been incompletely understood. The study tried to investigate the gene expression profile and proteomics of bradycardia rabbits' hearts after SXSM treatment. Twenty-four adult rabbits were randomly assigned in four groups: sham, model, model plus SXSM treatment, and sham plus SXSM treatment groups. Heart rate was recorded in all rabbits. Then, total RNA of atria and proteins of ventricle were isolated and quantified, respectively. Gene expression profiling was conducted by gene expression chip, and quantitative real-time reverse transcription-polymerase chain reaction (RT-PCR) was performed to confirm the results of gene expression chip. We used isobaric tags for elative and absolute quantitation and Western blotting to identify altered proteins after SXSM treatment. There was a constant decrease in the mean heart rate (32%, from 238 ± 6 beats/min to 149 ± 12 beats/min) after six weeks in model compared with that in sham group. This effect was partially reversed by 4-week SXSM treatment. Complementary DNA microarray demonstrated that the increased acetylcholinesterase and reduced nicotinic receptor were take responsibility for the increased heart rate. In addition, proteins involved in calcium handling and signaling were affected by SXSM treatment. Real-time RT-PCR verified the results from gene chip. Results from proteomics demonstrated that SXSM enhanced oxidative phosphorylation and tricarboxylic acid (TCA) cycle in ventricular myocardium to improve ATP generation. Long-term SXSM stimulates sympathetic transmission by increasing the expression of acetylcholinesterase and reduces the expression of nicotinic receptor to increase heart rate. SXSM also restored the calcium handling genes and altered genes involved in signaling. In addition, SXSM improves the ATP supply of ventricular myocardium by increasing proteins involved in TCA cycle and oxidation-respiratory chain.

Molecular Mechanisms of Increased Heart Rate in Shenxianshengmai-treated Bradycardia Rabbits

PubMed Central

Liu, Zhou-Ying; Huang, Jian; Liu, Na-Na; Zheng, Min; Zhao, Tao; Zhao, Bu-Chang; Wang, Yi-Min; Pu, Jie-Lin

2017-01-01

Background: The molecular mechanisms of Shenxianshengmai (SXSM), a traditional Chinese medicine, on bradycardia have been incompletely understood. The study tried to investigate the gene expression profile and proteomics of bradycardia rabbits’ hearts after SXSM treatment. Methods: Twenty-four adult rabbits were randomly assigned in four groups: sham, model, model plus SXSM treatment, and sham plus SXSM treatment groups. Heart rate was recorded in all rabbits. Then, total RNA of atria and proteins of ventricle were isolated and quantified, respectively. Gene expression profiling was conducted by gene expression chip, and quantitative real-time reverse transcription-polymerase chain reaction (RT-PCR) was performed to confirm the results of gene expression chip. We used isobaric tags for elative and absolute quantitation and Western blotting to identify altered proteins after SXSM treatment. Results: There was a constant decrease in the mean heart rate (32%, from 238 ± 6 beats/min to 149 ± 12 beats/min) after six weeks in model compared with that in sham group. This effect was partially reversed by 4-week SXSM treatment. Complementary DNA microarray demonstrated that the increased acetylcholinesterase and reduced nicotinic receptor were take responsibility for the increased heart rate. In addition, proteins involved in calcium handling and signaling were affected by SXSM treatment. Real-time RT-PCR verified the results from gene chip. Results from proteomics demonstrated that SXSM enhanced oxidative phosphorylation and tricarboxylic acid (TCA) cycle in ventricular myocardium to improve ATP generation. Conclusions: Long-term SXSM stimulates sympathetic transmission by increasing the expression of acetylcholinesterase and reduces the expression of nicotinic receptor to increase heart rate. SXSM also restored the calcium handling genes and altered genes involved in signaling. In addition, SXSM improves the ATP supply of ventricular myocardium by increasing proteins involved in TCA cycle and oxidation-respiratory chain. PMID:28091410

Polymer electrolyte membrane water electrolysis: Restraining degradation in the presence of fluctuating power

NASA Astrophysics Data System (ADS)

Rakousky, Christoph; Reimer, Uwe; Wippermann, Klaus; Kuhri, Susanne; Carmo, Marcelo; Lueke, Wiebke; Stolten, Detlef

2017-02-01

Polymer electrolyte membrane (PEM) water electrolysis generates 'green' hydrogen when conducted with electricity from renewable - but fluctuating - sources like wind or solar photovoltaic. Unfortunately, the long-term stability of the electrolyzer performance is still not fully understood under these input power profiles. In this study, we contrast the degradation behavior of our PEM water electrolysis single cells that occurs under operation with constant and intermittent power and derive preferable operating states. For this purpose, five different current density profiles are used, of which two were constant and three dynamic. Cells operated at 1 A cm-2 show no degradation. However, degradation was observed for the remaining four profiles, all of which underwent periods of high current density (2 A cm-2). Hereby, constant operation at 2 A cm-2 led to the highest degradation rate (194 μV h-1). Degradation can be greatly reduced when the cells are operated with an intermittent profile. Current density switching has a positive effect on durability, as it causes reversible parts of degradation to recover and results in a substantially reduced degradation per mole of hydrogen produced. Two general degradation phenomena were identified, a decreased anode exchange current density and an increased contact resistance at the titanium porous transport layer (Ti-PTL).

Control of the Protein Turnover Rates in Lemna minor

PubMed Central

Trewavas, A.

1972-01-01

The control of protein turnover in Lemna minor has been examined using a method described in the previous paper for determining the rate constants of synthesis and degradation of protein. If Lemna is placed on water, there is a reduction in the rate constants of synthesis of protein and an increase (3- to 6-fold) in the rate constant of degradation. The net effect is a loss of protein from the tissue. Omission of nitrate, phosphate, sulfate, magnesium, or calcium results in increases in the rate constant of degradation of protein. An unusual dual effect of benzyladenine on the turnover constants has been observed. Treatment of Lemna grown on sucrose-mineral salts with benzyladenine results in alterations only in the rate constant of synthesis. Treatment of Lemna grown on water with benzyladenine alters only the rate constant of degradation. Abscisic acid on the other hand alters both rate constants of synthesis and degradation of protein together. Inclusion of growth-inhibiting amino acids in the medium results in a reduction in the rate constants of synthesis and increases in the rate constant of degradation of protein. It is concluded that the rate of turnover of protein in Lemna is very dependent on the composition of the growth medium. Conditions which reduce growth rates also reduce the rates of synthesis of protein and increase those of degradation. PMID:16657895

Design of a pulsed-mode fluidic pump using a venturi-like reverse flow diverter. [With no packing glands, mechanical seals or moving parts

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

Smith, G.V.; Lewis, B.E.

1987-02-01

This report presents a design procedure for pulsed-mode, venturi-like reverse flow diverter (RFD) pumping systems. Design techniques are presented for systems in which the output line area is allowed to vary proportionally with the throat area of the RFD as well as situations in which the output line area is held constant. The results show that for cases in which the output line area is allowed to vary, an optimum RFD throat area exists for a given input pressure. For situations in which the output line area is held constant, the average output flow decreases in almost a linear fashionmore » with increasing RFD throat area. 6 refs., 8 figs.« less

Development of anion-exchange/reversed-phase high performance liquid chromatography-inductively coupled plasma-mass spectrometry methods for the speciation of bio-available iodine and bromine from edible seaweed.

PubMed

Romarís-Hortas, Vanessa; Bermejo-Barrera, Pilar; Moreda-Piñeiro, Antonio

2012-05-04

Anion exchange high performance liquid chromatography hyphenated with inductively coupled plasma-mass spectrometry has been novelly applied to assess inorganic (iodide and iodate) and organic (3-iodotyrosine - MIT, and 3,5-diiodotyrosine - DIT) iodine species in a single chromatographic run. The optimized operating conditions (Dionex IonPac AS7, gradient elution with 175 mM ammonium nitrate plus 15% (v/v) methanol, pH 3.8, as a mobile phase and flow rates within the 0.5-1.5 mL min(-1) range) have also been used to perform inorganic bromine speciation analysis (bromide and bromate). The developed method has been applied for determining the bio-available contents of iodine and bromine species in dialyzates from edible seaweed. Reverse phase high performance liquid chromatography (Zorbax Eclipse XDB-C8, gradient elution with 0.2% (m/m) acetic acid, and 0.2% (m/m) acetic acid in methanol, as mobile phases, and a constant flow rate of 0.75 mL min(-1)) also hyphenated with inductively coupled plasma-mass spectrometry was used to confirm the presence of organic iodine species (MIT and DIT) in the dialyzates. The verification of the presence of iodinated amino acids (MIT and DIT) in the extracts was also performed by reverse phase high performance liquid chromatography-electrospray ionization-mass spectrometry (LTQ Orbitrap). The developed methods have provided good repeatability (RSD values lower than 10% for both anion exchange and reverse phase separations) and analytical recoveries within the 90-105% range for all cases. The in vitro bio-availability method consisted of a simulated gastric and an intestinal digestion/dialysis (10 kDa molecular weight cut-off - MWCO) two-stage procedure. Iodide and MIT were the main bio-available species quantified, whereas bromide was the major bromine species found in the extracts. Copyright © 2012 Elsevier B.V. All rights reserved.

Designing Novel Quaternary Quantum Reversible Subtractor Circuits

NASA Astrophysics Data System (ADS)

Haghparast, Majid; Monfared, Asma Taheri

2018-01-01

Reversible logic synthesis is an important area of current research because of its ability to reduce energy dissipation. In recent years, multiple valued logic has received great attention due to its ability to reduce the width of the reversible circuit which is a main requirement in quantum technology. Subtractor circuits are between major components used in quantum computers. In this paper, we will discuss the design of a quaternary quantum reversible half subtractor circuit using quaternary 1-qudit, 2-qudit Muthukrishnan-Stroud and 3-qudit controlled gates and a 2-qudit Generalized quaternary gate. Then a design of a quaternary quantum reversible full subtractor circuit based on the quaternary half subtractor will be presenting. The designs shall then be evaluated in terms of quantum cost, constant input, garbage output, and hardware complexity. The proposed quaternary quantum reversible circuits are the first attempt in the designing of the aforementioned subtractor.

The Lévy noise-induced current reversal phenomenon for self-propelled particles in a two-dimensional potential

NASA Astrophysics Data System (ADS)

Wang, Bing; Qu, Zhongwei; Li, Xuechao; Ma, Jianli

2017-08-01

Effects of Lévy noise on self-propelled particles in a two-dimensional potential is investigated. The current reversal phenomenon appears in the system. V (x-direction average velocity) changes from negative to positive with increasing asymmetry parameter β, and changes from positive to negative with increasing self-propelled velocity v0. V has a maximum with increasing modulation constant λ.

A New Rate Law Describing Microbial Respiration

PubMed Central

Jin, Qusheng; Bethke, Craig M.

2003-01-01

The rate of microbial respiration can be described by a rate law that gives the respiration rate as the product of a rate constant, biomass concentration, and three terms: one describing the kinetics of the electron-donating reaction, one for the kinetics of the electron-accepting reaction, and a thermodynamic term accounting for the energy available in the microbe's environment. The rate law, derived on the basis of chemiosmotic theory and nonlinear thermodynamics, is unique in that it accounts for both forward and reverse fluxes through the electron transport chain. Our analysis demonstrates how a microbe's respiration rate depends on the thermodynamic driving force, i.e., the net difference between the energy available from the environment and energy conserved as ATP. The rate laws commonly applied in microbiology, such as the Monod equation, are specific simplifications of the general law presented. The new rate law is significant because it affords the possibility of extrapolating in a rigorous manner from laboratory experiment to a broad range of natural conditions, including microbial growth where only limited energy is available. The rate law also provides a new explanation of threshold phenomena, which may reflect a thermodynamic equilibrium where the energy released by electron transfer balances that conserved by ADP phosphorylation. PMID:12676718

Target-directed catalytic metallodrugs

PubMed Central

Joyner, J.C.; Cowan, J.A.

2013-01-01

Most drugs function by binding reversibly to specific biological targets, and therapeutic effects generally require saturation of these targets. One means of decreasing required drug concentrations is incorporation of reactive metal centers that elicit irreversible modification of targets. A common approach has been the design of artificial proteases/nucleases containing metal centers capable of hydrolyzing targeted proteins or nucleic acids. However, these hydrolytic catalysts typically provide relatively low rate constants for target inactivation. Recently, various catalysts were synthesized that use oxidative mechanisms to selectively cleave/inactivate therapeutic targets, including HIV RRE RNA or angiotensin converting enzyme (ACE). These oxidative mechanisms, which typically involve reactive oxygen species (ROS), provide access to comparatively high rate constants for target inactivation. Target-binding affinity, co-reactant selectivity, reduction potential, coordination unsaturation, ROS products (metal-associated vs metal-dissociated; hydroxyl vs superoxide), and multiple-turnover redox chemistry were studied for each catalyst, and these parameters were related to the efficiency, selectivity, and mechanism(s) of inactivation/cleavage of the corresponding target for each catalyst. Important factors for future oxidative catalyst development are 1) positioning of catalyst reduction potential and redox reactivity to match the physiological environment of use, 2) maintenance of catalyst stability by use of chelates with either high denticity or other means of stabilization, such as the square planar geometric stabilization of Ni- and Cu-ATCUN complexes, 3) optimal rate of inactivation of targets relative to the rate of generation of diffusible ROS, 4) targeting and linker domains that afford better control of catalyst orientation, and 5) general bio-availability and drug delivery requirements. PMID:23828584

Voltage gating by molecular subunits of Na+ and K+ ion channels: higher-dimensional cubic kinetics, rate constants, and temperature

PubMed Central

2015-01-01

The structural similarity between the primary molecules of voltage-gated Na and K channels (alpha subunits) and activation gating in the Hodgkin-Huxley model is brought into full agreement by increasing the model's sodium kinetics to fourth order (m3 → m4). Both structures then virtually imply activation gating by four independent subprocesses acting in parallel. The kinetics coalesce in four-dimensional (4D) cubic diagrams (16 states, 32 reversible transitions) that show the structure to be highly failure resistant against significant partial loss of gating function. Rate constants, as fitted in phase plot data of retinal ganglion cell excitation, reflect the molecular nature of the gating transitions. Additional dimensions (6D cubic diagrams) accommodate kinetically coupled sodium inactivation and gating processes associated with beta subunits. The gating transitions of coupled sodium inactivation appear to be thermodynamically irreversible; response to dielectric surface charges (capacitive displacement) provides a potential energy source for those transitions and yields highly energy-efficient excitation. A comparison of temperature responses of the squid giant axon (apparently Arrhenius) and mammalian channel gating yields kinetic Q10 = 2.2 for alpha unit gating, whose transitions are rate-limiting at mammalian temperatures; beta unit kinetic Q10 = 14 reproduces the observed non-Arrhenius deviation of mammalian gating at low temperatures; the Q10 of sodium inactivation gating matches the rate-limiting component of activation gating at all temperatures. The model kinetics reproduce the physiologically large frequency range for repetitive firing in ganglion cells and the physiologically observed strong temperature dependence of recovery from inactivation. PMID:25867741

Contribution of a submerged membrane bioreactor in the treatment of synthetic effluent contaminated by Bisphenol-A: mechanism of BPA removal and membrane fouling.

PubMed

Seyhi, Brahima; Drogui, Patrick; Buelna, Gerardo; Azaïs, Antonin; Heran, Marc

2013-09-01

A submerged membrane bioreactor has been operated at the laboratory scale for the treatment of a synthetic effluent containing Bisphenol-A (BPA). COD, NH4-N, PO4-P and BPA were eliminated respectively, at 99%, 99%, 61% and 99%. The increase of volumetric loading rate from 0 to 21.6 g/m(3)/d did not affect the performance of the MBR system. However, the removal rate decreased rapidly when the BPA loading rate increased above 21.6 g/m(3)/d. The adsorption process of BPA on the biomass was very well described by Freundlich and Langmuir isotherms. Subsequently, biodegradation of BPA occurred and followed the first order kinetic reaction, with a constant rate of 1.13 ± 0.22 h(-1). During treatment, membrane fouling was reversible in the first 84 h of filtration, and then became irreversible. The membrane fouling was mainly due to the accumulation of suspended solid and development of biofilm on the membrane surface. Copyright © 2013 Elsevier Ltd. All rights reserved.

Thermally activated switching at long time scales in exchange-coupled magnetic grains

NASA Astrophysics Data System (ADS)

Almudallal, Ahmad M.; Mercer, J. I.; Whitehead, J. P.; Plumer, M. L.; van Ek, J.; Fal, T. J.

2015-10-01

Rate coefficients of the Arrhenius-Néel form are calculated for thermally activated magnetic moment reversal for dual layer exchange-coupled composite (ECC) media based on the Langer formalism and are applied to study the sweep rate dependence of M H hysteresis loops as a function of the exchange coupling I between the layers. The individual grains are modeled as two exchange-coupled Stoner-Wohlfarth particles from which the minimum energy paths connecting the minimum energy states are calculated using a variant of the string method and the energy barriers and attempt frequencies calculated as a function of the applied field. The resultant rate equations describing the evolution of an ensemble of noninteracting ECC grains are then integrated numerically in an applied field with constant sweep rate R =-d H /d t and the magnetization calculated as a function of the applied field H . M H hysteresis loops are presented for a range of values I for sweep rates 105Oe /s ≤R ≤1010Oe /s and a figure of merit that quantifies the advantages of ECC media is proposed. M H hysteresis loops are also calculated based on the stochastic Landau-Lifshitz-Gilbert equations for 108Oe /s ≤R ≤1010Oe /s and are shown to be in good agreement with those obtained from the direct integration of rate equations. The results are also used to examine the accuracy of certain approximate models that reduce the complexity associated with the Langer-based formalism and which provide some useful insight into the reversal process and its dependence on the coupling strength and sweep rate. Of particular interest is the clustering of minimum energy states that are separated by relatively low-energy barriers into "metastates." It is shown that while approximating the reversal process in terms of "metastates" results in little loss of accuracy, it can reduce the run time of a kinetic Monte Carlo (KMC) simulation of the magnetic decay of an ensemble of dual layer ECC media by 2 -3 orders of magnitude. The essentially exact results presented in this work for two coupled grains are analogous to the Stoner-Wohlfarth model of a single grain and serve as an important precursor to KMC-based simulation studies on systems of interacting dual layer ECC media.

Nonlinear coupled equations for electrochemical cells as developed by the general equation for nonequilibrium reversible-irreversible coupling.

PubMed

Bedeaux, Dick; Kjelstrup, Signe; Öttinger, Hans Christian

2014-09-28

We show how the Butler-Volmer and Nernst equations, as well as Peltier effects, are contained in the general equation for nonequilibrium reversible and irreversible coupling, GENERIC, with a unique definition of the overpotential. Linear flux-force relations are used to describe the transport in the homogeneous parts of the electrochemical system. For the electrode interface, we choose nonlinear flux-force relationships. We give the general thermodynamic basis for an example cell with oxygen electrodes and electrolyte from the solid oxide fuel cell. In the example cell, there are two activated chemical steps coupled also to thermal driving forces at the surface. The equilibrium exchange current density obtains contributions from both rate-limiting steps. The measured overpotential is identified at constant temperature and stationary states, in terms of the difference in electrochemical potential of products and reactants. Away from these conditions, new terms appear. The accompanying energy flux out of the surface, as well as the heat generation at the surface are formulated, adding to the general thermodynamic basis.

Nonlinear coupled equations for electrochemical cells as developed by the general equation for nonequilibrium reversible-irreversible coupling

NASA Astrophysics Data System (ADS)

Bedeaux, Dick; Kjelstrup, Signe; Öttinger, Hans Christian

2014-09-01

We show how the Butler-Volmer and Nernst equations, as well as Peltier effects, are contained in the general equation for nonequilibrium reversible and irreversible coupling, GENERIC, with a unique definition of the overpotential. Linear flux-force relations are used to describe the transport in the homogeneous parts of the electrochemical system. For the electrode interface, we choose nonlinear flux-force relationships. We give the general thermodynamic basis for an example cell with oxygen electrodes and electrolyte from the solid oxide fuel cell. In the example cell, there are two activated chemical steps coupled also to thermal driving forces at the surface. The equilibrium exchange current density obtains contributions from both rate-limiting steps. The measured overpotential is identified at constant temperature and stationary states, in terms of the difference in electrochemical potential of products and reactants. Away from these conditions, new terms appear. The accompanying energy flux out of the surface, as well as the heat generation at the surface are formulated, adding to the general thermodynamic basis.

Selective attention to visual compound stimuli in squirrel monkeys (Saimiri sciureus).

PubMed

Ploog, Bertram O

2011-05-01

Five squirrel monkeys served under a simultaneous discrimination paradigm with visual compound stimuli that allowed measurement of excitatory and inhibitory control exerted by individual stimulus components (form and luminance/"color"), which could not be presented in isolation (i.e., form could not be presented without color). After performance exceeded a criterion of 75% correct during training, unreinforced test trials with stimuli comprising recombined training stimulus components were interspersed while the overall reinforcement rate remained constant for training and testing. The training-testing series was then repeated with reversed reinforcement contingencies. The findings were that color acquired greater excitatory control than form under the original condition, that no such difference was found for the reversal condition or for inhibitory control under either condition, and that overall inhibitory control was less pronounced than excitatory control. The remarkably accurate performance throughout suggested that a forced 4-s delay between the stimulus presentation and the opportunity to respond was effective in reducing "impulsive" responding, which has implications for suppressing impulsive responding in children with autism and with attention deficit disorder. Copyright © 2011 Elsevier B.V. All rights reserved.

The vibrational dependence of dissociative recombination: Rate constants for N{sub 2}{sup +}

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

Guberman, Steven L., E-mail: slg@sci.org

Dissociative recombination rate constants are reported with electron temperature dependent uncertainties for the lowest 5 vibrational levels of the N{sub 2}{sup +} ground state. The rate constants are determined from ab initio calculations of potential curves, electronic widths, quantum defects, and cross sections. At 100 K electron temperature, the rate constants overlap with the exception of the third vibrational level. At and above 300 K, the rate constants for excited vibrational levels are significantly smaller than that for the ground level. It is shown that any experimentally determined total rate constant at 300 K electron temperature that is smaller thanmore » 2.0 × 10{sup −7} cm{sup 3}/s is likely to be for ions that have a substantially excited vibrational population. Using the vibrational level specific rate constants, the total rate constant is in very good agreement with that for an excited vibrational distribution found in a storage ring experiment. It is also shown that a prior analysis of a laser induced fluorescence experiment is quantitatively flawed due to the need to account for reactions with unknown rate constants. Two prior calculations of the dissociative recombination rate constant are shown to be inconsistent with the cross sections upon which they are based. The rate constants calculated here contribute to the resolution of a 30 year old disagreement between modeled and observed N{sub 2}{sup +} ionospheric densities.« less

The Arrow of Time In a Universe with a Positive Cosmological Constant Λ

NASA Astrophysics Data System (ADS)

Mersini-Houghton, Laura

There is a mounting evidence that our universe is propelled into an accelerated expansion driven by Dark Energy. The simplest form of Dark Energy is a cosmological constant Λ, which is woven into the fabric of spacetime. For this reason it is often referred to as vacuum energy. It has the "strange" property of maintaining a constant energy density despite the expanding volume of the universe. Universes whose energy ismade of Λ posses an event horizon with and eternally finite constant temperature and entropy, and are known as DeSitter geometries. Since the entropy of DeSitter spaces remains a finite constant, then the meaning of a thermodynamic arrow of time becomes unclear. Here we explore the consequences of a fundamental cosmological constant Λ for our universe. We show that when the gravitational entropy of a pure DeSitter state ultimately dominates over the matter entropy, then the thermodynamic arrow of time in our universe may reverse in scales of order a Hubble time. We find that due to the dynamics of gravity and entanglement with other domain, a finite size system such as a DeSitter patch with horizon size H 0 -1 has a finite lifetime ∆t. This phenomenon arises from the dynamic gravitational instabilities that develop during a DeSitter epoch and turn catastrophic. A reversed arrow of time is in disagreementwith observations. Thus we explore the possibilities that: Nature may not favor a fundamental Λ, or else general relativity may be modified in the infrared regime when Λ dominates the expansion of the Universe.

Chromatographic determination of itopride hydrochloride in the presence of its degradation products.

PubMed

Kaul, Neeraj; Agrawal, Himani; Maske, Pravin; Rao, Janhavi Ramchandra; Mahadik, Kakasaheb Ramoo; Kadam, Shivajirao S

2005-08-01

Two sensitive and reproducible methods are described for the quantitative determination of itopride hydrochloride (IH) in the presence of its degradation products. The first method is based on HPLC separation on a reversed phase Kromasil column [C18 (5-microm, 25 cm x 4.6 mm, ID)] at ambient temperature using a mobile phase consisting of methanol and water (70:30, v/v) adjusted to pH 4.0 with orthophosphoric acid with UV detection at 258 nm. The flow rate was 1.0 mL per min with an average operating pressure of 180 kg/cm2. The second method is based on HPTLC separation on silica gel 60 F254 using toluene:methanol:chloroform:10% ammonia (5.0:3.0:6.0:0.1, v/v/v/v) as mobile phase at 270 nm. The analysis of variance (ANOVA) and Student's t-test were applied to correlate the results of IH determination in dosage form by means of HPLC and HPTLC methods. The drug was subjected to acid and alkali hydrolysis, oxidation, dry heat, wet heat treatment, UV, and photodegradation. The proposed HPLC method was utilized to investigate the kinetics of the acidic, alkaline, and oxidative degradation processes at different temperatures and the apparent pseudo-first-order rate constant, half-life, and activation energy were calculated. In addition the pH-rate profile of degradation of IH in constant ionic strength buffer solutions in the pH range 2-11 was studied.

Enhancement of exchange bias in ferromagnetic/antiferromagnetic core-shell nanoparticles through ferromagnetic domain wall formation

NASA Astrophysics Data System (ADS)

Wu, Rui; Ding, Shilei; Lai, Youfang; Tian, Guang; Yang, Jinbo

2018-01-01

The spin configuration in the ferromagnetic part during the magnetization reversal plays a crucial role in the exchange bias effect. Through Monte Carlo simulation, the exchange bias effect in ferromagnetic-antiferromagnetic core-shell nanoparticles is investigated. Magnetization reversals in the ferromagnetic core were controlled between the coherent rotation and the domain wall motion by modulating the ferromagnetic domain wall width with parameters of uniaxial anisotropy constant and exchange coupling strength. An anomalous monotonic dependence of exchange bias on the uniaxial anisotropy constant is found in systems with small exchange coupling, showing an obvious violation of classic Meiklejohn-Bean model, while domain walls are found to form close to the interface and propagate in the ferromagnetic core with larger uniaxial anisotropy in both branches of the hysteresis. The asymmetric magnetization reversal with the formation of a spherical domain wall dramatically reduces the coercive field in the ascending branch, leading to the enhancement of the exchange bias. The results provide another degree of freedom to optimize the magnetic properties of magnetic nanoparticles for applications.

Reverse process of usual optical analysis of boson-exchange superconductors: impurity effects on s- and d-wave superconductors.

PubMed

Hwang, Jungseek

2015-03-04

We performed a reverse process of the usual optical data analysis of boson-exchange superconductors. We calculated the optical self-energy from two (MMP and MMP+peak) input model electron-boson spectral density functions using Allen's formula for one normal and two (s- and d-wave) superconducting cases. We obtained the optical constants including the optical conductivity and the dynamic dielectric function from the optical self-energy using an extended Drude model, and finally calculated the reflectance spectrum. Furthermore, to investigate impurity effects on optical quantities we added various levels of impurities (from the clean to the dirty limit) in the optical self-energy and performed the same reverse process to obtain the optical conductivity, the dielectric function, and reflectance. From these optical constants obtained from the reverse process we extracted the impurity-dependent superfluid densities for two superconducting cases using two independent methods (the Ferrel-Glover-Tinkham sum rule and the extrapolation to zero frequency of -ϵ1(ω)ω(2)); we found that a certain level of impurities is necessary to get a good agreement on results obtained by the two methods. We observed that impurities give similar effects on various optical constants of s- and d-wave superconductors; the greater the impurities the more distinct the gap feature and the lower the superfluid density. However, the s-wave superconductor gives the superconducting gap feature more clearly than the d-wave superconductor because in the d-wave superconductors the optical quantities are averaged over the anisotropic Fermi surface. Our results supply helpful information to see how characteristic features of the electron-boson spectral function and the s- and d-wave superconducting gaps appear in various optical constants including raw reflectance spectrum. Our study may help with a thorough understanding of the usual optical analysis process. Further systematic study of experimental data collected at various conditions using the optical analysis process will help to reveal the origin of the mediated boson in the boson-exchange superconductors.

On the development and benchmarking of an approach to model gas transport in fractured media with immobile water storage

NASA Astrophysics Data System (ADS)

Harp, D. R.; Ortiz, J. P.; Pandey, S.; Karra, S.; Viswanathan, H. S.; Stauffer, P. H.; Anderson, D. N.; Bradley, C. R.

2017-12-01

In unsaturated fractured media, the rate of gas transport is much greater than liquid transport in many applications (e.g., soil vapor extraction operations, methane leaks from hydraulic fracking, shallow CO2 transport from geologic sequestration operations, and later-time radionuclide gas transport from underground nuclear explosions). However, the relatively immobile pore water can inhibit or promote gas transport for soluble constituents by providing storage. In scenarios with constant pressure gradients, the gas transport will be retarded. In scenarios with reversing pressure gradients (i.e. barometric pressure variations) pore water storage can enhance gas transport by providing a ratcheting mechanism. Recognizing the computational efficiency that can be gained using a single-phase model and the necessity of considering pore water storage, we develop a Richard's solution approach that includes kinetic dissolution/volatilization of constituents. Henry's Law governs the equilibrium gaseous/aqueous phase partitioning in the approach. The approach is implemented in a development branch of the PFLOTRAN simulator. We verify the approach with analytical solutions of: (1) 1D gas diffusion, (2) 1D gas advection, (3) sinusoidal barometric pumping of a fracture, and (4) gas transport along a fracture with uniform flow and diffusive walls. We demonstrate the retardation of gas transport in cases with constant pressure gradients and the enhancement of gas transport with reversing pressure gradients. The figure presents the verification of our approach to the analytical solution of barometric pumping of a fracture from Nilson et al (1991) where the x-axis "Horizontal axis" is the distance into the matrix block from the fracture.

On the development and benchmarking of an approach to model gas transport in fractured media with immobile water storage

NASA Astrophysics Data System (ADS)

Harp, D. R.; Ortiz, J. P.; Pandey, S.; Karra, S.; Viswanathan, H. S.; Stauffer, P. H.; Anderson, D. N.; Bradley, C. R.

2016-12-01

In unsaturated fractured media, the rate of gas transport is much greater than liquid transport in many applications (e.g., soil vapor extraction operations, methane leaks from hydraulic fracking, shallow CO2 transport from geologic sequestration operations, and later-time radionuclide gas transport from underground nuclear explosions). However, the relatively immobile pore water can inhibit or promote gas transport for soluble constituents by providing storage. In scenarios with constant pressure gradients, the gas transport will be retarded. In scenarios with reversing pressure gradients (i.e. barometric pressure variations) pore water storage can enhance gas transport by providing a ratcheting mechanism. Recognizing the computational efficiency that can be gained using a single-phase model and the necessity of considering pore water storage, we develop a Richard's solution approach that includes kinetic dissolution/volatilization of constituents. Henry's Law governs the equilibrium gaseous/aqueous phase partitioning in the approach. The approach is implemented in a development branch of the PFLOTRAN simulator. We verify the approach with analytical solutions of: (1) 1D gas diffusion, (2) 1D gas advection, (3) sinusoidal barometric pumping of a fracture, and (4) gas transport along a fracture with uniform flow and diffusive walls. We demonstrate the retardation of gas transport in cases with constant pressure gradients and the enhancement of gas transport with reversing pressure gradients. The figure presents the verification of our approach to the analytical solution of barometric pumping of a fracture from Nilson et al (1991) where the x-axis "Horizontal axis" is the distance into the matrix block from the fracture.

Kinetics and Thermochemistry of Reversible Adduct Formation in the Reaction of Cl((sup 2)P(sub J)) with CS2

NASA Technical Reports Server (NTRS)

Nicovich, J. M.; Shackelford, C. J.; Wine, P. H.

1997-01-01

Reversible adduct formation in the reaction of Cl((sup 2)P(sub J)) with CS2 has been observed over the temperature range 193-258 K by use of time-resolved resonance fluorescence spectroscopy to follow the decay of pulsed-laser-generated Cl((sup 2)P(sub J)) into equilbrium with CS2Cl. Rate coefficients for CS2Cl formation and decomposition have been determined as a function of temperature and pressure; hence, the equilbrium constant has been determined as a function of temperature. A second-law analysis of the temperature dependence of Kp and heat capacity corrections calculated with use of an assumed CS2Cl structure yields the following thermodynamic parameters for the association reaction: Delta-H(sub 298) = -10.5 +/- 0.5 kcal/mol, Delta-H(sub 0) = -9.5 +/- 0.7 kcal/mol, Delta-S(sub 298) = -26.8 +/- 2.4 cal/mol.deg., and Delta-H(sub f,298)(CS2Cl) = 46.4 +/- 0.6 kcal/mol. The resonance fluorescence detection scheme has been adapted to allow detection of Cl((sup 2)P(sub J)) in the presence of large concentrations of O2, thus allowing the CS2Cl + Cl + O2 reaction to be investigated. We find that the rate coefficient for CS2Cl + O2 reaction via all channels that do not generate Cl((sup 2)P(sub J)) is less than 2.5 x 10(exp-16) cu cm/(molecule.s) at 293 K and 300-Torr total pressure and that the total rate coefficient is less than 2 x 10 (exp -15) cu cm/(molecule.s) at 230 K and 30-Torr total pressure. Evidence for reversible adduct formation in the reaction of Cl((sup 2)P(sub J)) with COS was sought but not observed, even at temperatures as low as 194 K.

The impact of pH on side reactions for aqueous redox flow batteries based on nitroxyl radical compounds

NASA Astrophysics Data System (ADS)

Orita, A.; Verde, M. G.; Sakai, M.; Meng, Y. S.

2016-07-01

Electrochemical and UV-VIS measurements demonstrate that the pH value of a 4-hydroxy-2,2,6,6-tetramethyl-1-pipperidinyloxyl (TEMPOL) electrolyte significantly impacts its redox reversibility. The diffusion coefficient and kinetic rate constant of TEMPOL in neutral aqueous solution are determined and shown to be comparable to those of vanadium ions used for industrially utilized redox flow batteries (RFBs). RFBs that incorporate a TEMPOL catholyte and Zn-based anolyte have an average voltage of 1.46 V and an energy efficiency of 80.4% during the initial cycle, when subject to a constant current of 10 mA cm-2. We demonstrate several factors that significantly influence the concentration and capacity retention of TEMPOL upon cycling; namely, pH and atmospheric gases dissolved in electrolyte. We expand upon the known reactions of TEMPOL in aqueous electrolyte and propose several concepts to improve its electrochemical performance in a RFB. Controlling these factors will be the key to enable the successful implementation of this relatively inexpensive and environmentally friendly battery.

The interaction of trimethylamine dehydrogenase and electron-transferring flavoprotein.

PubMed

Shi, Weiwei; Mersfelder, John; Hille, Russ

2005-05-27

The interaction between the physiological electron transfer partners trimethylamine dehydrogenase (TMADH) and electron-transferring flavoprotein (ETF) from Methylophilus methylotrophus has been examined with particular regard to the proposal that the former protein "imprints" a conformational change on the latter. The results indicate that the absorbance change previously attributed to changes in the environment of the FAD of ETF upon binding to TMADH is instead caused by electron transfer from partially reduced, as-isolated TMADH to ETF. Prior treatment of the as-isolated enzyme with the oxidant ferricenium essentially abolishes the observed spectral change. Further, when the semiquinone form of ETF is used instead of the oxidized form, the mirror image of the spectral change seen with as-isolated TMADH and oxidized ETF is observed. This is attributable to a small amount of electron transfer in the reverse of the physiological direction. Kinetic determination of the dissociation constant and limiting rate constant for electron transfer within the complex of (reduced) TMADH with (oxidized) ETF is reconfirmed and discussed in the context of a recently proposed model for the interaction between the two proteins that involves "structural imprinting" of ETF.

The influence of the "cage effect" on the mechanism of reversible bimolecular multistage chemical reactions in solutions.

PubMed

Doktorov, Alexander B

2015-08-21

Manifestations of the "cage effect" at the encounters of reactants are theoretically treated by the example of multistage reactions in liquid solutions including bimolecular exchange reactions as elementary stages. It is shown that consistent consideration of quasi-stationary kinetics of multistage reactions (possible only in the framework of the encounter theory) for reactions proceeding near reactants contact can be made on the basis of the concepts of a "cage complex." Though mathematically such a consideration is more complicated, it is more clear from the standpoint of chemical notions. It is established that the presence of the "cage effect" leads to some important effects not inherent in reactions in gases or those in solutions proceeding in the kinetic regime, such as the appearance of new transition channels of reactant transformation that cannot be caused by elementary event of chemical conversion for the given mechanism of reaction. This results in that, for example, rate constant values of multistage reaction defined by standard kinetic equations of formal chemical kinetics from experimentally measured kinetics can differ essentially from real values of these constants.

Ab Initio Chemical Kinetics for the CH3 + O((3)P) Reaction and Related Isomerization-Decomposition of CH3O and CH2OH Radicals.

PubMed

Xu, Z F; Raghunath, P; Lin, M C

2015-07-16

The kinetics and mechanism of the CH3 + O reaction and related isomerization-decomposition of CH3O and CH2OH radicals have been studied by ab initio molecular orbital theory based on the CCSD(T)/aug-cc-pVTZ//CCSD/aug-cc-pVTZ, CCSD/aug-cc-pVDZ, and G2M//B3LYP/6-311+G(3df,2p) levels of theory. The predicted potential energy surface of the CH3 + O reaction shows that the CHO + H2 products can be directly generated from CH3O by the TS3 → LM1 → TS7 → LM2 → TS4 path, in which both LM1 and LM2 are very loose and TS7 is roaming-like. The result for the CH2O + H reaction shows that there are three low-energy barrier processes including CH2O + H → CHO + H2 via H-abstraction and CH2O + H → CH2OH and CH2O + H → CH3O by addition reactions. The predicted enthalpies of formation of the CH2OH and CH3O radicals at 0 K are in good agreement with available experimental data. Furthermore, the rate constants for the forward and some key reverse reactions have been predicted at 200-3000 K under various pressures. Based on the new reaction pathway for CH3 + O, the rate constants for the CH2O + H and CHO + H2 reactions were predicted with the microcanonical variational transition-state/Rice-Ramsperger-Kassel-Marcus (VTST/RRKM) theory. The predicted total and individual product branching ratios (i.e., CO versus CH2O) are in good agreement with experimental data. The rate constant for the hydrogen abstraction reaction of CH2O + H has been calculated by the canonical variational transition-state theory with quantum tunneling and small-curvature corrections to be k(CH2O + H → CHO + H2) = 2.28 × 10(-19) T(2.65) exp(-766.5/T) cm(3) molecule(-1) s(-1) for the 200-3000 K temperature range. The rate constants for the addition giving CH3O and CH2OH and the decomposition of the two radicals have been calculated by the microcanonical RRKM theory with the time-dependent master equation solution of the multiple quantum well system in the 200-3000 K temperature range at 1 Torr to 100 atm. The predicted rate constants are in good agreement with most of the available data.

Chaotic and stable perturbed maps: 2-cycles and spatial models

NASA Astrophysics Data System (ADS)

Braverman, E.; Haroutunian, J.

2010-06-01

As the growth rate parameter increases in the Ricker, logistic and some other maps, the models exhibit an irreversible period doubling route to chaos. If a constant positive perturbation is introduced, then the Ricker model (but not the classical logistic map) experiences period doubling reversals; the break of chaos finally gives birth to a stable two-cycle. We outline the maps which demonstrate a similar behavior and also study relevant discrete spatial models where the value in each cell at the next step is defined only by the values at the cell and its nearest neighbors. The stable 2-cycle in a scalar map does not necessarily imply 2-cyclic-type behavior in each cell for the spatial generalization of the map.

The stability properties of cylindrical force-free fields - Effect of an external potential field

NASA Technical Reports Server (NTRS)

Chiuderi, C.; Einaudi, G.; Ma, S. S.; Van Hoven, G.

1980-01-01

A large-scale potential field with an embedded smaller-scale force-free structure gradient x B equals alpha B is studied in cylindrical geometry. Cases in which alpha goes continuously from a constant value alpha 0 on the axis to zero at large r are considered. Such a choice of alpha (r) produces fields which are realistic (few field reversals) but not completely stable. The MHD-unstable wavenumber regime is found. Since the considered equilibrium field exhibits a certain amount of magnetic shear, resistive instabilities can arise. The growth rates of the tearing mode in the limited MHD-stable region of k space are calculated, showing time-scales much shorter than the resistive decay time.

Improved resolution of single channel dwell times reveals mechanisms of binding, priming, and gating in muscle AChR

PubMed Central

Mukhtasimova, Nuriya; daCosta, Corrie J.B.

2016-01-01

The acetylcholine receptor (AChR) from vertebrate skeletal muscle initiates voluntary movement, and its kinetics of activation are crucial for maintaining the safety margin for neuromuscular transmission. Furthermore, the kinetic mechanism of the muscle AChR serves as an archetype for understanding activation mechanisms of related receptors from the Cys-loop superfamily. Here we record currents through single muscle AChR channels with improved temporal resolution approaching half an order of magnitude over our previous best. A range of concentrations of full and partial agonists are used to elicit currents from human wild-type and gain-of-function mutant AChRs. For each agonist–receptor combination, rate constants are estimated from maximum likelihood analysis using a kinetic scheme comprised of agonist binding, priming, and channel gating steps. The kinetic scheme and rate constants are tested by stochastic simulation, followed by incorporation of the experimental step response, sampling rate, background noise, and filter bandwidth. Analyses of the simulated data confirm all rate constants except those for channel gating, which are overestimated because of the established effect of noise on the briefest dwell times. Estimates of the gating rate constants were obtained through iterative simulation followed by kinetic fitting. The results reveal that the agonist association rate constants are independent of agonist occupancy but depend on receptor state, whereas those for agonist dissociation depend on occupancy but not on state. The priming rate and equilibrium constants increase with successive agonist occupancy, and for a full agonist, the forward rate constant increases more than the equilibrium constant; for a partial agonist, the forward rate and equilibrium constants increase equally. The gating rate and equilibrium constants also increase with successive agonist occupancy, but unlike priming, the equilibrium constants increase more than the forward rate constants. As observed for a full and a partial agonist, the gain-of-function mutation affects the relationship between rate and equilibrium constants for priming but not for channel gating. Thus, resolving brief single channel currents distinguishes priming from gating steps and reveals how the corresponding rate and equilibrium constants depend on agonist occupancy. PMID:27353445

Topological quantization in units of the fine structure constant.

PubMed

Maciejko, Joseph; Qi, Xiao-Liang; Drew, H Dennis; Zhang, Shou-Cheng

2010-10-15

Fundamental topological phenomena in condensed matter physics are associated with a quantized electromagnetic response in units of fundamental constants. Recently, it has been predicted theoretically that the time-reversal invariant topological insulator in three dimensions exhibits a topological magnetoelectric effect quantized in units of the fine structure constant α=e²/ℏc. In this Letter, we propose an optical experiment to directly measure this topological quantization phenomenon, independent of material details. Our proposal also provides a way to measure the half-quantized Hall conductances on the two surfaces of the topological insulator independently of each other.

Regional evaluation of hydrologic factors and effects of pumping, St Peter-Jordan aquifer, Iowa

USGS Publications Warehouse

Burkart, M.R.; Buchmiller, Robert

1990-01-01

Pumping has caused changes in the flow system that include regional declines in the potentiometric surface of the aquifer. Simulation indicates that pumping through 1980 increased net vertical leakage into the aquifer to about double the predevelopment rate. Discharge across lateral boundaries has been substantially reduced or reversed by pumping. Aquifer storage provided about one-third of the water required to supply pumping in the 1970's. Simulation of future conditions, assuming no increase in pumping rates, indicates that the rate of decline in water levels will decrease by the year 2020. As equilibrium with pumping is approached in 2020, 75 percent of the pumpage will be balanced by vertical leakage, eight percent by water released from aquifer storage, and 17 percent by increases in boundary recharge or decreases in boundary discharge. Future pumping at an increasing rate of about 10 percent per decade of the average pumping rate in 1975 will require about one and one-half times the vertical leakage of the 1971-1980 period and about fivetimes the net inflow from lateral boundaries; however, the rate of water released from aquifer storage will be about half the 1970's rate. Under these conditions, the head in the aquifer will continue to decline at an almost constant rate until 2020.

Relationship of compressive stress-strain response of engineering materials obtained at constant engineering and true strain rates

DOE PAGES

Song, Bo; Sanborn, Brett

2018-05-07

In this paper, a Johnson–Cook model was used as an example to analyze the relationship of compressive stress-strain response of engineering materials experimentally obtained at constant engineering and true strain rates. There was a minimal deviation between the stress-strain curves obtained at the same constant engineering and true strain rates. The stress-strain curves obtained at either constant engineering or true strain rates could be converted from one to the other, which both represented the intrinsic material response. There is no need to specify the testing requirement of constant engineering or true strain rates for material property characterization, provided that eithermore » constant engineering or constant true strain rate is attained during the experiment.« less

Relationship of compressive stress-strain response of engineering materials obtained at constant engineering and true strain rates

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

Song, Bo; Sanborn, Brett

In this paper, a Johnson–Cook model was used as an example to analyze the relationship of compressive stress-strain response of engineering materials experimentally obtained at constant engineering and true strain rates. There was a minimal deviation between the stress-strain curves obtained at the same constant engineering and true strain rates. The stress-strain curves obtained at either constant engineering or true strain rates could be converted from one to the other, which both represented the intrinsic material response. There is no need to specify the testing requirement of constant engineering or true strain rates for material property characterization, provided that eithermore » constant engineering or constant true strain rate is attained during the experiment.« less

On the meaning of the diffusion layer thickness for slow electrode reactions.

PubMed

Molina, A; González, J; Laborda, E; Compton, R G

2013-02-21

A key concept underpinning electrochemical science is that of the diffusion layer - the zone of depletion around an electrode accompanying electrolysis. The size of this zone can be found either from the simulated or measured concentration profiles (yielding the 'true' diffusion layer thickness) or, in the case of the Nernst ('linear') diffusion layer by extrapolating the concentration gradient at the electrode surface to the distance at which the concentration takes its bulk value. The latter concept is very well developed in the case of fast (so-called reversible) electrode processes, however the study of the linear diffusion layer has received scant attention in the case of slow charge transfer processes, despite its study being of great interest in the analysis of the influence of different experimental variables which determine the electrochemical response. Analytical explicit solutions for the concentration profiles, surface concentrations and real and linear diffusion layers corresponding to the application of a potential step to a slow charge transfer process are presented. From these expressions the dependence of the diffusion layer thickness on the potential, pulse time, heterogeneous rate constant and ratio of bulk concentrations of electroactive species and of diffusion coefficients is quantified. A profound influence of the reversibility degree of the charge transfer on the diffusion layer thickness is clear, showing that for non-reversible processes the real and linear diffusion layers reveal a minimum thickness which coincides with the equilibrium potential of the redox couple in the former case and with the reversible half-wave potential in the latter one.

Comparison of TID Effects in Space-Like Variable Dose Rates and Constant Dose Rates

NASA Technical Reports Server (NTRS)

Harris, Richard D.; McClure, Steven S.; Rax, Bernard G.; Evans, Robin W.; Jun, Insoo

2008-01-01

The degradation of the LM193 dual voltage comparator has been studied at different TID dose rate profiles, including several different constant dose rates and a variable dose rate that simulates the behavior of a solar flare. A comparison of results following constant dose rate vs. variable dose rates is made to explore how well the constant dose rates used for typical part testing predict the performance during a simulated space-like mission. Testing at a constant dose rate equal to the lowest dose rate seen during the simulated flare provides an extremely conservative estimate of the overall amount of degradation. A constant dose rate equal to the average dose rate is also more conservative than the variable rate. It appears that, for this part, weighting the dose rates by the amount of total dose received at each rate (rather than the amount of time at each dose rate) results in an average rate that produces an amount of degradation that is a reasonable approximation to that received by the variable rate.

Application of the compensated Arrhenius formalism to explain the dielectric constant dependence of rates for Menschutkin reactions.

PubMed

Petrowsky, Matt; Glatzhofer, Daniel T; Frech, Roger

2013-11-21

The dependence of the reaction rate on solvent dielectric constant is examined for the reaction of trihexylamine with 1-bromohexane in a series of 2-ketones over the temperature range 25-80 °C. The rate constant data are analyzed using the compensated Arrhenius formalism (CAF), where the rate constant assumes an Arrhenius-like equation that also contains a dielectric constant dependence in the exponential prefactor. The CAF activation energies are substantially higher than those obtained using the simple Arrhenius equation. A master curve of the data is observed by plotting the prefactors against the solvent dielectric constant. The master curve shows that the reaction rate has a weak dependence on dielectric constant for values approximately less than 10 and increases more rapidly for dielectric constant values greater than 10.

A simple statistical model for geomagnetic reversals

NASA Technical Reports Server (NTRS)

Constable, Catherine

1990-01-01

The diversity of paleomagnetic records of geomagnetic reversals now available indicate that the field configuration during transitions cannot be adequately described by simple zonal or standing field models. A new model described here is based on statistical properties inferred from the present field and is capable of simulating field transitions like those observed. Some insight is obtained into what one can hope to learn from paleomagnetic records. In particular, it is crucial that the effects of smoothing in the remanence acquisition process be separated from true geomagnetic field behavior. This might enable us to determine the time constants associated with the dominant field configuration during a reversal.

Clinical and Radiographic Mid-Term Outcomes After Total Shoulder Replacement: A Retrospective Study Protocol Including 400 Anatomical and Reverse Prosthetic Implants

PubMed Central

Merolla, Giovanni; Tartarone, Antonio; Porcellini, Giuseppe

2016-01-01

Objectives: To obtain outcomes data on anatomical and reverse total shoulder arthroplasty by analysis of clinical scores and standard radiographs. Subject selection and enrollment: 400 consecutive series of patients replaced with anatomical and reverse total shoulder arthroplasty (minimum 3 years follow-up). Study Design: retrospective monocenter. Preoperative assessment: Demographics, clinical scores (Constant-Murley) as available, shoulder X-ray (AP, outlet and axillary views) . Last follow-up: Postoperative radiographhs and clinical scores. Adverse events and complications to be reported as occurred since implantation. Statistical analysis: Data collected will be summarized and analyzed for statistical significance. PMID:27326389

Reactivity of Biliatresone, a Natural Biliary Toxin, with Glutathione, Histamine, and Amino Acids

PubMed Central

Koo, Kyung A.; Waisbourd-Zinman, Orith; Wells, Rebecca G.; Pack, Michael; Porter, John R.

2016-01-01

In our previous work, we identified a natural toxin, biliatresone, from Dysphania glomulifera and D. littoralis, endemic plants associated with outbreaks of biliary atresia in Australian neonatal livestock. Biliatresone is a very rare isoflavonoid with an α-methylene ketone between two phenyls, 1,2-diaryl-2-propenone, along with methylenedioxy, dimethoxyl, and hydroxyl functional groups, that causes extrahepatic biliary toxicity in zebrafish. The toxic core of biliatresone is a methylene in the α-position relative to the ketone of 1,2-diaryl-2-propenone that serves as an electrophilic Michael acceptor. The α-methylene of biliatresone spontaneously conjugated with water and methanol (MeOH), respectively, via Michael addition in a reverse phase high-performance liquid chromatography (RP-HPLC) analysis. We here report the reactivity of biliatresone toward glutathione (GSH), several amino acids, and other thiol- or imidazole-containing biomolecules. LC-MS and HPLC analysis of the conjugation reaction showed the reactivity of biliatresone to be in the order histidine > N-acetyl-d-cysteine (D-NAC) = N-acetyl-l-cysteine (L-NAC) > histamine > glutathione ≥ cysteine ≫ glycine > glutamate > phenylalanine, while serine and adenine had no reactivity due to intramolecular hydrogen bonding in the protic solvents. The reactivity of ethyl vinyl ketone (EVK, 1-penten-3-one), an example of a highly reactive α,ß-unsaturated ketone, toward GSH gave a 6.7-fold lower reaction rate constant than that of biliatresone. The reaction rate constant of synthetic 1,2-diaryl-2-propen-1-one (DP), a core structure of the toxic molecule, was 10-fold and 1.5-fold weaker in potency compared to the reaction rate constants of biliatresone and EVK, respectively. These results demostrated that the methylenedioxy, dimethoxyl, and hydroxyl functional groups of biliatresone contribute to the stronger reactivity of the Michael acceptor α-methylene ketone toward nucleophiles compared to that of DP and EVK. PMID:26713899

Reactivity of Biliatresone, a Natural Biliary Toxin, with Glutathione, Histamine, and Amino Acids.

PubMed

Koo, Kyung A; Waisbourd-Zinman, Orith; Wells, Rebecca G; Pack, Michael; Porter, John R

2016-02-15

In our previous work, we identified a natural toxin, biliatresone, from Dysphania glomulifera and D. littoralis, endemic plants associated with outbreaks of biliary atresia in Australian neonatal livestock. Biliatresone is a very rare isoflavonoid with an α-methylene ketone between two phenyls, 1,2-diaryl-2-propenone, along with methylenedioxy, dimethoxyl, and hydroxyl functional groups, that causes extrahepatic biliary toxicity in zebrafish. The toxic core of biliatresone is a methylene in the α-position relative to the ketone of 1,2-diaryl-2-propenone that serves as an electrophilic Michael acceptor. The α-methylene of biliatresone spontaneously conjugated with water and methanol (MeOH), respectively, via Michael addition in a reverse phase high-performance liquid chromatography (RP-HPLC) analysis. We here report the reactivity of biliatresone toward glutathione (GSH), several amino acids, and other thiol- or imidazole-containing biomolecules. LC-MS and HPLC analysis of the conjugation reaction showed the reactivity of biliatresone to be in the order histidine > N-acetyl-d-cysteine (D-NAC) = N-acetyl-l-cysteine (L-NAC) > histamine > glutathione ≥ cysteine ≫ glycine > glutamate > phenylalanine, while serine and adenine had no reactivity due to intramolecular hydrogen bonding in the protic solvents. The reactivity of ethyl vinyl ketone (EVK, 1-penten-3-one), an example of a highly reactive α,ß-unsaturated ketone, toward GSH gave a 6.7-fold lower reaction rate constant than that of biliatresone. The reaction rate constant of synthetic 1,2-diaryl-2-propen-1-one (DP), a core structure of the toxic molecule, was 10-fold and 1.5-fold weaker in potency compared to the reaction rate constants of biliatresone and EVK, respectively. These results demostrated that the methylenedioxy, dimethoxyl, and hydroxyl functional groups of biliatresone contribute to the stronger reactivity of the Michael acceptor α-methylene ketone toward nucleophiles compared to that of DP and EVK.

Race and socioeconomic disparities in national stoma reversal rates.

PubMed

Zafar, Syed Nabeel; Changoor, Navin R; Williams, Kibileri; Acosta, Rafael D; Greene, Wendy R; Fullum, Terrence M; Haider, Adil H; Cornwell, Edward E; Tran, Daniel D

2016-04-01

Many temporary stomas are never reversed leading to significantly worse quality of life. Recent evidence suggests a lower rate of reversal among minority patients. Our study aimed to elucidate disparities in national stoma closure rates by race, medical insurance status, and household income. Five years of data from the Nationwide Inpatient Sample (2008 to 2012) was used to identify the annual rates of stoma formation and annual rates of stoma closure. Stomas labeled as "permanent" or those created secondary to colorectal cancers were excluded. Temporary stoma closure rates were calculated, and differences were tested with the chi-square test. Separate analyses were performed by race/ethnicity, insurance status, and household income. Nationally representative estimates were calculated using discharge-level weights. The 5-year average annual rate of temporary stoma creation was 76,551 per year (46% colostomies and 54% ileostomies). The annual rate of stoma reversal was 50,155 per year that equated to an annual reversal rate of 65.5%. Reversal rates were higher among white patients compared with black patients (67% vs 56%, P < .001) and among privately insured patients compared with uninsured patients (88% vs 63%, P < .001). Reversal rates increased as the household income increased from 61% in the lowest income quartile to 72% in the highest quartile (P < .001). Stark disparities exist in national rates of stoma closure. Stoma closure is associated with race, insurance, and income status. This study highlights the lack of access to surgical health care among patients of minority race and low-income status. Copyright © 2016 Elsevier Inc. All rights reserved.

Effect of salicylate on outer hair cell plasma membrane viscoelasticity: studies using optical tweezers

NASA Astrophysics Data System (ADS)

Ermilov, Sergey A.; Brownell, William E.; Anvari, Bahman

2004-06-01

The plasma membrane (PM) of mammalian outer hair cells (OHCs) generates mechanical forces in response to changes in the transmembrane electrical potential. The resulting change in the cell length is known as electromotility. Salicylate (Sal), the anionic, amphipathic derivative of aspirin induces reversible hearing loss and decreases electromotile response of the OHCs. Sal may change the local curvature and mechanical properties of the PM, eventually resulting in reduced electromotility or it may compete with intracellular monovalent anions, particularly Cl-, which are essential for electromotility. In this work we have used optical tweezers to study the effects of Sal on viscoelastic properties of the OHC PM when separated from the underlying composite structures of the cell wall. In this procedure, an optically trapped microsphere is brought in contact with PM and subsequently pulled away to form a tether. We measured the force exerted on the tether as a function of time during the process of tether growth at different pulling rates. Effective tether viscosity, steady-state tethering force extrapolated to zero pulling rate, and the time constant for tether growth were estimated from the measurements of the instantaneous tethering force. The time constant for the tether growth measured for the OHC basal end decreased 1.65 times after addition of 10 mM Sal, which may result from an interaction between Sal and cholesterol, which is more prevalent in the PM of OHC basal end. The time constants for the tether growth calculated for the OHC lateral wall and control human embryonic kidney cells as well as the other calculated viscoelastic parameters remained the same after Sal perfusion, favoring the hypothesis of competitive inhibition of electromotility by salicylate.

Rate constants measured for hydrated electron reactions with peptides and proteins

NASA Technical Reports Server (NTRS)

Braams, R.

1968-01-01

Effects of ionizing radiation on the amino acids of proteins and the reactivity of the protonated amino group depends upon the pK subscript a of the group. Estimates of the rate constants for reactions involving the amino acid side chains are presented. These rate constants gave an approximate rate constant for three different protein molecules.

A polishing hybrid AER/UF membrane process for the treatment of a high DOC content surface water.

PubMed

Humbert, H; Gallard, H; Croué, J-P

2012-03-15

The efficacy of a combined AER/UF (Anion Exchange Resin/Ultrafiltration) process for the polishing treatment of a high DOC (Dissolved Organic Carbon) content (>8 mgC/L) surface water was investigated at lab-scale using a strong base AER. Both resin dose and bead size had a significant impact on the kinetic removal of DOC for short contact times (i.e. <15 min). For resin doses higher than 700 mg/L and median bead sizes below 250 μm DOC removal remained constant after 30 min of contact time with very high removal rates (80%). Optimum AER treatment conditions were applied in combination with UF membrane filtration on water previously treated by coagulation-flocculation (i.e. 3 mgC/L). A more severe fouling was observed for each filtration run in the presence of AER. This fouling was shown to be mainly reversible and caused by the progressive attrition of the AER through the centrifugal pump leading to the production of resin particles below 50 μm in diameter. More important, the presence of AER significantly lowered the irreversible fouling (loss of permeability recorded after backwash) and reduced the DOC content of the clarified water to l.8 mgC/L (40% removal rate), concentration that remained almost constant throughout the experiment. Copyright © 2011 Elsevier Ltd. All rights reserved.

Measuring two-dimensional receptor-ligand binding kinetics by micropipette.

PubMed Central

Chesla, S E; Selvaraj, P; Zhu, C

1998-01-01

We report a novel method for measuring forward and reverse kinetic rate constants, kf0 and kr0, for the binding of individual receptors and ligands anchored to apposing surfaces in cell adhesion. Not only does the method examine adhesion between a single pair of cells; it also probes predominantly a single receptor-ligand bond. The idea is to quantify the dependence of adhesion probability on contact duration and densities of the receptors and ligands. The experiment was an extension of existing micropipette protocols. The analysis was based on analytical solutions to the probabilistic formulation of kinetics for small systems. This method was applied to examine the interaction between Fc gamma receptor IIIA (CD16A) expressed on Chinese hamster ovary cell transfectants and immunoglobulin G (IgG) of either human or rabbit origin coated on human erythrocytes, which were found to follow a monovalent biomolecular binding mechanism. The measured rate constants are Ackf0 = (2.6 +/- 0.32) x 10(-7) micron 4 s-1 and kr0 = (0.37 +/- 0.055) s-1 for the CD16A-hIgG interaction and Ackf0 = (5.7 +/- 0.31) X 10(-7) micron 4 s-1 and kr0 = (0.20 +/- 0.042) s-1 for the CD16A-rIgG interaction, respectively, where Ac is the contact area, estimated to be a few percent of 3 micron 2. PMID:9726957

Glutathione-complexed [2Fe-2S] clusters function in Fe-S cluster storage and trafficking.

PubMed

Fidai, Insiya; Wachnowsky, Christine; Cowan, J A

2016-10-01

Glutathione-coordinated [2Fe-2S] complex is a non-protein-bound [2Fe-2S] cluster that is capable of reconstituting the human iron-sulfur cluster scaffold protein IscU. This complex demonstrates physiologically relevant solution chemistry and is a viable substrate for iron-sulfur cluster transport by Atm1p exporter protein. Herein, we report on some of the possible functional and physiological roles for this novel [2Fe-2S](GS4) complex in iron-sulfur cluster biosynthesis and quantitatively characterize its role in the broader network of Fe-S cluster transfer reactions. UV-vis and circular dichroism spectroscopy have been used in kinetic studies to determine second-order rate constants for [2Fe-2S] cluster transfer from [2Fe-2S](GS4) complex to acceptor proteins, such as human IscU, Schizosaccharomyces pombe Isa1, human and yeast glutaredoxins (human Grx2 and Saccharomyces cerevisiae Grx3), and human ferredoxins. Second-order rate constants for cluster extraction from these holo proteins were also determined by varying the concentration of glutathione, and a likely common mechanism for cluster uptake was determined by kinetic analysis. The results indicate that the [2Fe-2S](GS4) complex is stable under physiological conditions, and demonstrates reversible cluster exchange with a wide range of Fe-S cluster proteins, thereby supporting a possible physiological role for such centers.

Voltage gating by molecular subunits of Na+ and K+ ion channels: higher-dimensional cubic kinetics, rate constants, and temperature.

PubMed

Fohlmeister, Jürgen F

2015-06-01

The structural similarity between the primary molecules of voltage-gated Na and K channels (alpha subunits) and activation gating in the Hodgkin-Huxley model is brought into full agreement by increasing the model's sodium kinetics to fourth order (m(3) → m(4)). Both structures then virtually imply activation gating by four independent subprocesses acting in parallel. The kinetics coalesce in four-dimensional (4D) cubic diagrams (16 states, 32 reversible transitions) that show the structure to be highly failure resistant against significant partial loss of gating function. Rate constants, as fitted in phase plot data of retinal ganglion cell excitation, reflect the molecular nature of the gating transitions. Additional dimensions (6D cubic diagrams) accommodate kinetically coupled sodium inactivation and gating processes associated with beta subunits. The gating transitions of coupled sodium inactivation appear to be thermodynamically irreversible; response to dielectric surface charges (capacitive displacement) provides a potential energy source for those transitions and yields highly energy-efficient excitation. A comparison of temperature responses of the squid giant axon (apparently Arrhenius) and mammalian channel gating yields kinetic Q10 = 2.2 for alpha unit gating, whose transitions are rate-limiting at mammalian temperatures; beta unit kinetic Q10 = 14 reproduces the observed non-Arrhenius deviation of mammalian gating at low temperatures; the Q10 of sodium inactivation gating matches the rate-limiting component of activation gating at all temperatures. The model kinetics reproduce the physiologically large frequency range for repetitive firing in ganglion cells and the physiologically observed strong temperature dependence of recovery from inactivation. Copyright © 2015 the American Physiological Society.

Reversible uptake of molecular oxygen by heteroligand Co(II)-L-α-amino acid-imidazole systems: equilibrium models at full mass balance.

PubMed

Pająk, Marek; Woźniczka, Magdalena; Vogt, Andrzej; Kufelnicki, Aleksander

2017-09-19

The paper examines Co(II)-amino acid-imidazole systems (where amino acid = L-α-amino acid: alanine, asparagine, histidine) which, when in aqueous solutions, activate and reversibly take up dioxygen, while maintaining the structural scheme of the heme group (imidazole as axial ligand and O 2 uptake at the sixth, trans position) thus imitating natural respiratory pigments such as myoglobin and hemoglobin. The oxygenated reaction shows higher reversibility than for Co(II)-amac systems with analogous amino acids without imidazole. Unlike previous investigations of the heteroligand Co(II)-amino acid-imidazole systems, the present study accurately calculates all equilibrium forms present in solution and determines the [Formula: see text]equilibrium constants without using any simplified approximations. The equilibrium concentrations of Co(II), amino acid, imidazole and the formed complex species were calculated using constant data obtained for analogous systems under oxygen-free conditions. Pehametric and volumetric (oxygenation) studies allowed the stoichiometry of O 2 uptake reaction and coordination mode of the central ion in the forming oxygen adduct to be determined. The values of dioxygen uptake equilibrium constants [Formula: see text] were evaluated by applying the full mass balance equations. Investigations of oxygenation of the Co(II)-amino acid-imidazole systems indicated that dioxygen uptake proceeds along with a rise in pH to 9-10. The percentage of reversibility noted after acidification of the solution to the initial pH ranged within ca 30-60% for alanine, 40-70% for asparagine and 50-90% for histidine, with a rising tendency along with the increasing share of amino acid in the Co(II): amino acid: imidazole ratio. Calculations of the share of the free Co(II) ion as well as of the particular complex species existing in solution beside the oxygen adduct (regarding dioxygen bound both reversibly and irreversibly) indicated quite significant values for the systems with alanine and asparagine-in those cases the of oxygenation reaction is right shifted to a relatively lower extent. The experimental results indicate that the "active" complex, able to take up dioxygen, is a heteroligand CoL 2 L'complex, where L = amac (an amino acid with a non-protonated amine group) while L' = Himid, with the N1 nitrogen protonated within the entire pH range under study. Moreover, the corresponding log  [Formula: see text] value at various initial total Co(II), amino acid and imidazole concentrations was found to be constant within the limits of error, which confirms those results. The highest log [Formula: see text] value, 14.9, occurs for the histidine system; in comparison, asparagine is 7.8 and alanine is 9.7. This high value is most likely due to the participation of the additional effective N3 donor of the imidazole side group of histidine. The Co(II)-amac-Himid systems formed by using a [Co(imid) 2 ] n polymer as starting material demonstrate that the reversible uptake of molecular oxygen occurs by forming dimeric μ-peroxy adducts. The essential impact on the electron structure of the dioxygen bridge, and therefore, on the reversibility of O 2 uptake, is due to the imidazole group at axial position (trans towards O 2 ). However, the results of reversibility measurements of O 2 uptake, unequivocally indicate a much higher effectiveness of dioxygenation than in systems in which the oxygen adducts are formed in equilibrium mixtures during titration of solutions containing Co(II) ions, the amino acid and imidazole, separately.

The dynamic of FUS-induced BBB Opening in Mouse Brain assessed by contrast enhanced MRI

NASA Astrophysics Data System (ADS)

Jenne, Jürgen W.; Krafft, Axel J.; Maier, Florian; Krause, Marie N.; Kleber, Susanne; Huber, Peter E.; Martin-Villalba, Ana; Bock, Michael

2010-03-01

Focused ultrasound (FUS) in combination with the administration of gas-filled microbubbles, can induce a localized and reversible opening of the blood brain barrier (BBB). Contrast enhanced magnetic resonance imaging (MRI) has been demonstrated as a precise tool to monitor such a local BBB disruption. However, the opening/closing mechanisms of the BBB with FUS are still largely unknown. In this ongoing project, we study the BBB opening dynamics in mouse brain comparing an interstitial and an intravascular MR contrast agent (CA). FUS in mouse brain was performed with an MRI compatible treatment setup (1.7 MHz fix-focus US transducer, f' = 68 mm, NA = 0.44; focus: 8.1 mm length; O/ = 1.1 mm) in a 1.5 T whole body MRI system. For BBB opening, forty 10 ms-long FUS-pulses were applied at a repetition rate of 1 Hz at 1 MPa. The i.v. administration of the micro bubbles (50 μl SonoVue®) was started simultaneously with FUS exposure. To analyze the BBB opening process, short-term and long-term MRI signal dynamics of the interstitial MR contrast agent Magnevist® and the intravascular CA Vasovist® (Bayer-Schering) were studied. To assess short-term signal dynamics, T1-weighted inversion recovery turbo FLASH images (1s) were repeatedly acquired. Repeated 3D FLASH acquisitions (90 s) were used to assess long-term MRI signal dynamics. The short-term MRI signal enhancements showed comparable time constants for both types of MR contrast agents: 1.1 s (interstitial) vs. 0.8 s (intravascular). This time constant may serve as a time constant of the BBB opening process with the given FUS exposure parameters. For the long-term signal dynamics the intravascular CA (62±10 min) showed a fife times greater time constant as the interstitial contrast agent (12±10 min). This might be explained by the high molecular weight (˜60 kDa) of the intravascular Vasovist due to its reversible binding to blood serum albumin resulting in a prolonged half-life in the blood stream compared to the interstitial CA. As the intravascular CA offers a much longer time window for therapy assessment, FUS-BBB therapy control with an intravascular CA might be favorable.

Prolonged Perceptual Learning of Positional Acuity in Adult Amblyopia

PubMed Central

Li, Roger W; Klein, Stanley A; Levi, Dennis M

2009-01-01

Amblyopia is a developmental abnormality that results in physiological alterations in the visual cortex and impairs form vision. It is often successfully treated by patching the sound eye in infants and young children, but is generally considered to be untreatable in adults. However, a number of recent studies suggest that repetitive practice of a visual task using the amblyopic eye results in improved performance in both children and adults with amblyopia. These perceptual learning studies have used relatively brief periods of practice; however, clinical studies have shown that the time-constant for successful patching is long. The time-constant for perceptual learning in amblyopia is still unknown. Here we show that the time-constant for perceptual learning depends on the degree of amblyopia. Severe amblyopia requires more than 50 hours (≈35,000 trials) to reach plateau, yielding as much as a five-fold improvement in performance at a rate of ≈1.5% per hour. There is significant transfer of learning from the amblyopic to the dominant eye, suggesting that the learning reflects alterations in higher decision stages of processing. Using a reverse correlation technique, we document, for the first time, a dynamic retuning of the amblyopic perceptual decision template and a substantial reduction in internal spatial distortion. These results show that the mature amblyopic brain is surprisingly malleable, and point to more intensive treatment methods for amblyopia. PMID:19109504

Estimation of vertical slip rate in an active fault-propagation fold from the analysis of a progressive unconformity at the NE segment of the Carrascoy Fault (SE Iberia)

NASA Astrophysics Data System (ADS)

Martin-Banda, Raquel; Insua-Arevalo, Juan Miguel; Garcia-Mayordomo, Julian

2017-04-01

Many studies have dealt with the calculation of fault-propagation fold growth rates considering a variety of kinematics models, from limb rotation to hinge migration models. In most cases, the different geometrical and numeric growth models are based on horizontal pre-growth strata architecture and a constant known slip rate. Here, we present the estimation of the vertical slip rate of the NE Segment of the Carrascoy Fault (SE Iberian Peninsula) from the geometrical modeling of a progressive unconformity developed on alluvial fan sediments with a high depositional slope. The NE Segment of the Carrascoy Fault is a left-lateral strike slip fault with reverse component belonging to the Eastern Betic Shear Zone, a major structure that accommodates most of the convergence between Iberian and Nubian tectonics plates in Southern Spain. The proximity of this major fault to the city of Murcia encourages the importance of carrying out paleosismological studies in order to determinate the Quaternary slip rate of the fault, a key geological parameter for seismic hazard calculations. This segment is formed by a narrow fault zone that articulates abruptly the northern edge of the Carrascoy Range with the Guadalentin Depression through high slope, short alluvial fans Upper-Middle Pleistocene in age. An outcrop in a quarry at the foot of this front reveals a progressive unconformity developed on these alluvial fan deposits, showing the important reverse component of the fault. The architecture of this unconformity is marked by well-developed calcretes on the top some of the alluvial deposits. We have determined the age of several of these calcretes by the Uranium-series disequilibrium dating method. The results obtained are consistent with recent published studies on the SW segment of the Carrascoy Fault that together with offset canals observed at a few locations suggest a net slip rate close to 1 m/ka.

Isokinetic strength differences between patients with primary reverse and total shoulder prostheses: muscle strength quantified with a dynamometer.

PubMed

Alta, Tjarco D W; Veeger, DirkJan H E J; de Toledo, Joelly M; Janssen, Thomas W J; Willems, W Jaap

2014-11-01

Range of motion after total shoulder arthroplasty is better than after reverse shoulder arthroplasty, however with similar clinical outcome. It is unclear if this difference can only be found in the different range of motion or also in the force generating capacity. (1) are isokinetically produced joint torques of reverse shoulder arthroplasty comparable to those of total shoulder arthroplasty? (2) Does this force-generating capacity correlate with functional outcome? Eighteen reverse shoulder arthroplasty patients (71years (SD 9years)) (21 shoulders, follow-up of 21months (SD 10months)) were recruited, 12 total shoulder arthroplasty patients (69years (SD 9years)) (14 shoulders, follow-up of 35months (SD 11months)). Pre- and post-operative Constant-Murley scores were obtained; two isokinetic protocols (ab-/adduction and ex-/internal rotations) at 60°/s were performed. Twelve of 18 reverse shoulder arthroplasty patients generated enough speed to perform the test (13 shoulders). Mean ab-/adduction torques are 16.3Nm (SD 5.6Nm) and 20.4Nm (SD 11.8Nm). All total shoulder arthroplasty patients generated enough speed (14 shoulders). Mean ab-/adduction torques are 32.1Nm (SD 13.3Nm) and 43.1Nm (SD 21.5Nm). Only 8 reverse shoulder arthroplasty patients (9 shoulders) could perform ex-/internal rotation tasks and all total shoulder arthroplasty patients. Mean ex-/internal rotation torques are 9.3Nm (SD 4.7Nm) and 9.2Nm (SD 2.1Nm) for reverse shoulder arthroplasty, and 17.9Nm (SD 7.7Nm) and 23.5Nm (SD 10.6Nm) for total shoulder arthroplasty. Significant correlations between sub-scores: activity, mobility and strength and external rotation torques for reverse shoulder arthroplasty. Moderate to strong correlation for sub-scores: strength in relation to abduction, adduction and internal rotation torques for total shoulder arthroplasty. Shoulders with a total shoulder arthroplasty are stronger. This can be explained by the absence of rotator cuff muscles and (probably) medialized center of rotation in reverse shoulder arthroplasty. The strong correlation between external rotation torques and post-operative Constant-Murley sub-scores demonstrates that external rotation is essential for good clinical functioning in reverse shoulder arthroplasty. Copyright © 2014 Elsevier Ltd. All rights reserved.

High-gradient compact linear accelerator

DOEpatents

Carder, B.M.

1998-05-26

A high-gradient linear accelerator comprises a solid-state stack in a vacuum of five sets of disc-shaped Blumlein modules each having a center hole through which particles are sequentially accelerated. Each Blumlein module is a sandwich of two outer conductive plates that bracket an inner conductive plate positioned between two dielectric plates with different thicknesses and dielectric constants. A third dielectric core in the shape of a hollow cylinder forms a casing down the series of center holes, and it has a dielectric constant different that the two dielectric plates that sandwich the inner conductive plate. In operation, all the inner conductive plates are charged to the same DC potential relative to the outer conductive plates. Next, all the inner conductive plates are simultaneously shorted to the outer conductive plates at the outer diameters. The signal short will propagate to the inner diameters at two different rates in each Blumlein module. A faster wave propagates quicker to the third dielectric core across the dielectric plates with the closer spacing and lower dielectric constant. When the faster wave reaches the inner extents of the outer and inner conductive plates, it reflects back outward and reverses the field in that segment of the dielectric core. All the field segments in the dielectric core are then in unipolar agreement until the slower wave finally propagates to the third dielectric core across the dielectric plates with the wider spacing and higher dielectric constant. During such unipolar agreement, particles in the core are accelerated with gradients that exceed twenty megavolts per meter. 10 figs.

High-gradient compact linear accelerator

DOEpatents

Carder, Bruce M.

1998-01-01

A high-gradient linear accelerator comprises a solid-state stack in a vacuum of five sets of disc-shaped Blumlein modules each having a center hole through which particles are sequentially accelerated. Each Blumlein module is a sandwich of two outer conductive plates that bracket an inner conductive plate positioned between two dielectric plates with different thicknesses and dielectric constants. A third dielectric core in the shape of a hollow cylinder forms a casing down the series of center holes, and it has a dielectric constant different that the two dielectric plates that sandwich the inner conductive plate. In operation, all the inner conductive plates are charged to the same DC potential relative to the outer conductive plates. Next, all the inner conductive plates are simultaneously shorted to the outer conductive plates at the outer diameters. The signal short will propagate to the inner diameters at two different rates in each Blumlein module. A faster wave propagates quicker to the third dielectric core across the dielectric plates with the closer spacing and lower dielectric constant. When the faster wave reaches the inner extents of the outer and inner conductive plates, it reflects back outward and reverses the field in that segment of the dielectric core. All the field segments in the dielectric core are then in unipolar agreement until the slower wave finally propagates to the third dielectric core across the dielectric plates with the wider spacing and higher dielectric constant. During such unipolar agreement, particles in the core are accelerated with gradients that exceed twenty megavolts per meter.

Electrochemical and theoretical analysis of the reactivity of shikonin derivatives: dissociative electron transfer in esterified compounds.

PubMed

Armendáriz-Vidales, Georgina; Frontana, Carlos

2014-09-07

An electrochemical and theoretical analysis of a series of shikonin derivatives in aprotic media is presented. Results showed that the first electrochemical reduction signal is a reversible monoelectronic transfer, generating a stable semiquinone intermediate; the corresponding E(I)⁰ values were correlated with calculated values of electroaccepting power (ω(+)) and adiabatic electron affinities (A(Ad)), obtained with BH and HLYP/6-311++G(2d,2p) and considering the solvent effect, revealing the influence of intramolecular hydrogen bonding and the substituting group at position C-2 in the experimental reduction potential. For the second reduction step, esterified compounds isobutyryl and isovalerylshikonin presented a coupled chemical reaction following dianion formation. Analysis of the variation of the dimensionless cathodic peak potential values (ξ(p)) as a function of the scan rate (v) functions and complementary experiments in benzonitrile suggested that this process follows a dissociative electron transfer, in which the rate of heterogeneous electron transfer is slow (~0.2 cm s(-1)), and the rate constant of the chemical process is at least 10(5) larger.

To be Stiff or to be Soft-the Dilemma of the Echinoid Tooth Ligament. II. Mechanical Properties.

PubMed

Birenheide, R; Tsuchi, A; Motokawa, T

1996-04-01

The teeth of sea urchins are connected to jaws by means of ligaments. Their sliding along the jaw during continuous growth requires a pliant ligament, whereas scraping on rocks for feeding requires a stiff ligament for firm support. We investigated the mechanical properties of the tooth ligament of Diadema setosum to clarify how sea urchins solve this dilemma. In creep tests a load of 30 g caused a shift of the tooth that continued until the tooth was pulled out of the jaw. The creep curve had three phases: an initial phase of high creep rate, a long phase of constant creep rate, and a final phase of accelerating creep rate. The ligaments had a shear viscosity of about 550 MPa {middot} s. Viscosity increased reversibly after stimulation with seawater containing a high concentration of potassium ions or acetylcholine. Frozen and rethawed ligaments did not show an increase of viscosity after stimulation. The data indicate that sea urchins can change the stiffness of their tooth ligaments through nervous control. We suggest that the tooth ligament is a catch connective tissue.

Thermal denaturation of β-glucosidase B from Paenibacillus polymyxa proceeds through a Lumry-Eyring mechanism.

PubMed

Camarillo-Cadena, Menandro; Garza-Ramos, Georgina; Peimbert, Mariana; Pérez-Hernández, Gerardo; Zubillaga, Rafael A

2011-06-01

β-glucosidase B (BglB), 1,4-β-D: -glucanohydrolase, is an enzyme with various technological applications for which some thermostable mutants have been obtained. Because BglB denatures irreversibly with heating, the stabilities of these mutants are assessed kinetically. It, therefore, becomes relevant to determine whether the measured rate constants reflect one or several elementary kinetic steps. We have analyzed the kinetics of heat denaturation of BglB from Paenibacillus polymyxa under various conditions by following the loss of secondary structure and enzymatic activity. The denaturation is accompanied by aggregation and an initial reversible step at low temperatures. At T ≥ T ( m ), the process follows a two-state irreversible mechanism for which the kinetics does not depend on the enzyme concentration. This behavior can be explained by a Lumry-Eyring model in which the difference between the rates of the irreversible and the renaturation steps increases with temperature. Accordingly, at high scan rates (≥1 °C min(-1)) or temperatures (T ≥ T ( m )), the measurable activation energy involves only the elementary step of denaturation.

A simple physical mechanism enables homeostasis in primitive cells

NASA Astrophysics Data System (ADS)

Engelhart, Aaron E.; Adamala, Katarzyna P.; Szostak, Jack W.

2016-05-01

The emergence of homeostatic mechanisms that enable maintenance of an intracellular steady state during growth was critical to the advent of cellular life. Here, we show that concentration-dependent reversible binding of short oligonucleotides, of both specific and random sequence, can modulate ribozyme activity. In both cases, catalysis is inhibited at high concentrations, and dilution activates the ribozyme via inhibitor dissociation, thus maintaining near-constant ribozyme specific activity throughout protocell growth. To mimic the result of RNA synthesis within non-growing protocells, we co-encapsulated high concentrations of ribozyme and oligonucleotides within fatty acid vesicles, and ribozyme activity was inhibited. Following vesicle growth, the resulting internal dilution produced ribozyme activation. This simple physical system enables a primitive homeostatic behaviour: the maintenance of constant ribozyme activity per unit volume during protocell volume changes. We suggest that such systems, wherein short oligonucleotides reversibly inhibit functional RNAs, could have preceded sophisticated modern RNA regulatory mechanisms, such as those involving miRNAs.

Estimation of dark and active dielectric constants in the sub-THz frequency domain of an optically tunable organic semiconductor blend of poly(3-hexylthiophene) and phenyl-C61-butyric acid methyl ester

NASA Astrophysics Data System (ADS)

Andy, Andre S.; Kneller, James W. E.; Sushko, Oleksandr; Dubrovka, Rostyslav; Parini, Clive; Scott, Ken; Kreouzis, Theo; Donnan, Robert S.

2018-06-01

The dielectric properties of a 95% poly(3-hexylthiophene):5% phenyl-C61-butyric acid methyl ester blend are measured in the dark and under white light illumination by quasi-optical transmissometry and terahertz time-domain spectroscopy. The real part of the dielectric constant varies monotonically between 2.75 and 3.50, in agreement with the literature, and displays a reversible photoinduced drop of 0.05–0.55 at sub-THz. The imaginary part fluctuates between 0.1 and 1.5 in the dark and displays a reversible increase upon illumination of 0.10–0.52 at sub-THz. The corresponding charge carrier concentration under illumination (using transient and steady-state photoconduction) is 1014 to 1015 cm‑3.

Higher outcomes of vasectomy reversal in men with the same female partner as before vasectomy.

PubMed

Ostrowski, Kevin A; Polackwich, A Scott; Kent, Joe; Conlin, Michael J; Hedges, Jason C; Fuchs, Eugene F

2015-01-01

We reviewed fertility outcomes of vasectomy reversal at a high surgical volume center in men with the same female partner as before vasectomy. We retrospectively studied a prospective database. All vasectomy reversals were performed by a single surgeon (EFF). Patients who underwent microsurgical vasectomy reversal and had the same female partner as before vasectomy were identified from 1978 to 2011. Pregnancy and live birth rates, procedure type (bilateral vasovasostomy, bilateral vasoepididymostomy, unilateral vasovasostomy or unilateral vasoepididymostomy), patency rate, time from reversal and spouse age were evaluated. We reviewed the records of 3,135 consecutive microsurgical vasectomy reversals. Of these patients 524 (17%) who underwent vasectomy reversal had the same female partner as before vasectomy. Complete information was available on 258 patients (49%), who had a 94% vas patency rate. The clinical pregnancy rate was 83% by natural means compared to 60% in our general vasectomy reversal population (p <0.0001). On logistic regression analysis controlling for female partner and patient ages, years from vasectomy and vasectomy reversal with the same female partner the OR was 2 (p <0.007). Average time from vasectomy was 5.7 years. Average patient and female partner age at reversal was 38.9 and 33.2 years, respectively. Outcomes of clinical pregnancy and live birth rates are higher in men who undergo microsurgical vasectomy reversal with the same female partner. These outcomes may be related to a shorter interval from vasectomy, previous fertility and couple motivation. Copyright © 2015 American Urological Association Education and Research, Inc. Published by Elsevier Inc. All rights reserved.

Estimation of thermodynamic acidity constants of some penicillinase-resistant penicillins.

PubMed

Demiralay, Ebru Çubuk; Üstün, Zehra; Daldal, Y Doğan

2014-03-01

In this work, thermodynamic acidity constants (pssKa) of methicillin, oxacillin, nafcillin, cloxacilin, dicloxacillin were determined with reverse phase liquid chromatographic method (RPLC) by taking into account the effect of the activity coefficients in hydro-organic water-acetonitrile binary mixtures. From these values, thermodynamic aqueous acidity constants of these drugs were calculated by different approaches. The linear relationships established between retention factors of the species and the polarity parameter of the mobile phase (ET(N)) was proved to predict accurately retention in LC as a function of the acetonitrile content (38%, 40% and 42%, v/v). Copyright © 2013 Elsevier B.V. All rights reserved.

Higher success rate with transcranial electrical stimulation of motor-evoked potentials using constant-voltage stimulation compared with constant-current stimulation in patients undergoing spinal surgery.

PubMed

Shigematsu, Hideki; Kawaguchi, Masahiko; Hayashi, Hironobu; Takatani, Tsunenori; Iwata, Eiichiro; Tanaka, Masato; Okuda, Akinori; Morimoto, Yasuhiko; Masuda, Keisuke; Tanaka, Yuu; Tanaka, Yasuhito

2017-10-01

During spine surgery, the spinal cord is electrophysiologically monitored via transcranial electrical stimulation of motor-evoked potentials (TES-MEPs) to prevent injury. Transcranial electrical stimulation of motor-evoked potential involves the use of either constant-current or constant-voltage stimulation; however, there are few comparative data available regarding their ability to adequately elicit compound motor action potentials. We hypothesized that the success rates of TES-MEP recordings would be similar between constant-current and constant-voltage stimulations in patients undergoing spine surgery. The objective of this study was to compare the success rates of TES-MEP recordings between constant-current and constant-voltage stimulation. This is a prospective, within-subject study. Data from 100 patients undergoing spinal surgery at the cervical, thoracic, or lumbar level were analyzed. The success rates of the TES-MEP recordings from each muscle were examined. Transcranial electrical stimulation with constant-current and constant-voltage stimulations at the C3 and C4 electrode positions (international "10-20" system) was applied to each patient. Compound muscle action potentials were bilaterally recorded from the abductor pollicis brevis (APB), deltoid (Del), abductor hallucis (AH), tibialis anterior (TA), gastrocnemius (GC), and quadriceps (Quad) muscles. The success rates of the TES-MEP recordings from the right Del, right APB, bilateral Quad, right TA, right GC, and bilateral AH muscles were significantly higher using constant-voltage stimulation than those using constant-current stimulation. The overall success rates with constant-voltage and constant-current stimulations were 86.3% and 68.8%, respectively (risk ratio 1.25 [95% confidence interval: 1.20-1.31]). The success rates of TES-MEP recordings were higher using constant-voltage stimulation compared with constant-current stimulation in patients undergoing spinal surgery. Copyright © 2017 Elsevier Inc. All rights reserved.

Elongational flow of polymer melts at constant strain rate, constant stress and constant force

NASA Astrophysics Data System (ADS)

Wagner, Manfred H.; Rolón-Garrido, Víctor H.

2013-04-01

Characterization of polymer melts in elongational flow is typically performed at constant elongational rate or rarely at constant tensile stress conditions. One of the disadvantages of these deformation modes is that they are hampered by the onset of "necking" instabilities according to the Considère criterion. Experiments at constant tensile force have been performed even more rarely, in spite of the fact that this deformation mode is free from necking instabilities and is of considerable industrial relevance as it is the correct analogue of steady fiber spinning. It is the objective of the present contribution to present for the first time a full experimental characterization of a long-chain branched polyethylene melt in elongational flow. Experiments were performed at constant elongation rate, constant tensile stress and constant tensile force by use of a Sentmanat Extensional Rheometer (SER) in combination with an Anton Paar MCR301 rotational rheometer. The accessible experimental window and experimental limitations are discussed. The experimental data are modelled by using the Wagner I model. Predictions of the steady-start elongational viscosity in constant strain rate and creep experiments are found to be identical, albeit only by extrapolation of the experimental data to Hencky strains of the order of 6. For constant stress experiments, a minimum in the strain rate and a corresponding maximum in the elongational viscosity is found at a Hencky strain of the order of 3, which, although larger than the steady-state value, follows roughly the general trend of the steady-state elongational viscosity. The constitutive analysis also reveals that constant tensile force experiments indicate a larger strain hardening potential than seen in constant elongation rate or constant tensile stress experiments. This may be indicative of the effect of necking under constant elongation rate or constant tensile stress conditions according to the Considère criterion.

Instanton rate constant calculations close to and above the crossover temperature.

PubMed

McConnell, Sean; Kästner, Johannes

2017-11-15

Canonical instanton theory is known to overestimate the rate constant close to a system-dependent crossover temperature and is inapplicable above that temperature. We compare the accuracy of the reaction rate constants calculated using recent semi-classical rate expressions to those from canonical instanton theory. We show that rate constants calculated purely from solving the stability matrix for the action in degrees of freedom orthogonal to the instanton path is not applicable at arbitrarily low temperatures and use two methods to overcome this. Furthermore, as a by-product of the developed methods, we derive a simple correction to canonical instanton theory that can alleviate this known overestimation of rate constants close to the crossover temperature. The combined methods accurately reproduce the rate constants of the canonical theory along the whole temperature range without the spurious overestimation near the crossover temperature. We calculate and compare rate constants on three different reactions: H in the Müller-Brown potential, methylhydroxycarbene → acetaldehyde and H 2  + OH → H + H 2 O. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Kinetics of the creatine kinase reaction in neonatal rabbit heart: An empirical analysis of the rate equation

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

McAuliffe, J.J.; Perry, S.B.; Brooks, E.E.

1991-03-12

Here the authors define the kinetics of the creatine kinase (CK) reaction in an intact mammalian heart containing the full rnage of CK isoenzymes. Previously derived kinetic constants were refit for the reaction occurring at 37C. Steady-state metabolite concentrations from {sup 31}P NMR and standard biochemical techniques were determined. {sup 31}P magnetization transfer data were obtained to determine unidirectional creatine kinase fluxes in hearts with differing total creatine contents and differing mitochondrial CK activities during KCl arrest and isovolumic work for both the forward reaction (MgATP synthesis) and reverse reaction (phosphocreatine synthesis). The NMR kinetic data and substrate concentrations datamore » were used in conjunction with a kinetic model based on MM-CK in solution to determine the applicability of the solution-based kinetic models to the CK kinetics of the intact heart. The results indicated that no single set of rate equation constants could describe both the KCl-arrested and working hearts. Analysis of the results indicated that the CK reaction is rate limited in the direction of ATP synthesis, the size of the guanidino substrate pool drives the measured CK flux in the intact heart, and during isovolumic work, the CK reaction operates under saturating conditions; that is, the substrate concentrations are at least 2-fold greater than the K{sub m} or K{sub im} for each substrate. However, during KCl arrest the reaction does not operate under saturating conditions and the CK reaction velocity is strongly influenced by the guanidino substrate pool size.« less

Upscaling of nanoparticle transport in porous media under unfavorable conditions: Pore scale to Darcy scale

NASA Astrophysics Data System (ADS)

Seetha, N.; Raoof, Amir; Mohan Kumar, M. S.; Majid Hassanizadeh, S.

2017-05-01

Transport and deposition of nanoparticles in porous media is a multi-scale problem governed by several pore-scale processes, and hence, it is critical to link the processes at pore scale to the Darcy-scale behavior. In this study, using pore network modeling, we develop correlation equations for deposition rate coefficients for nanoparticle transport under unfavorable conditions at the Darcy scale based on pore-scale mechanisms. The upscaling tool is a multi-directional pore-network model consisting of an interconnected network of pores with variable connectivities. Correlation equations describing the pore-averaged deposition rate coefficients under unfavorable conditions in a cylindrical pore, developed in our earlier studies, are employed for each pore element. Pore-network simulations are performed for a wide range of parameter values to obtain the breakthrough curves of nanoparticle concentration. The latter is fitted with macroscopic 1-D advection-dispersion equation with a two-site linear reversible deposition accounting for both equilibrium and kinetic sorption. This leads to the estimation of three Darcy-scale deposition coefficients: distribution coefficient, kinetic rate constant, and the fraction of equilibrium sites. The correlation equations for the Darcy-scale deposition coefficients, under unfavorable conditions, are provided as a function of measurable Darcy-scale parameters, including: porosity, mean pore throat radius, mean pore water velocity, nanoparticle radius, ionic strength, dielectric constant, viscosity, temperature, and surface potentials of the particle and grain surfaces. The correlation equations are found to be consistent with the available experimental results, and in qualitative agreement with Colloid Filtration Theory for all parameters, except for the mean pore water velocity and nanoparticle radius.

Numerical investigation for entropy generation in hydromagnetic flow of fluid with variable properties and slip

NASA Astrophysics Data System (ADS)

Khan, M. Ijaz; Hayat, Tasawar; Alsaedi, Ahmed

2018-02-01

This modeling and computations present the study of viscous fluid flow with variable properties by a rotating stretchable disk. Rotating flow is generated through nonlinear rotating stretching surface. Nonlinear thermal radiation and heat generation/absorption are studied. Flow is conducting for a constant applied magnetic field. No polarization is taken. Induced magnetic field is not taken into account. Attention is focused on the entropy generation rate and Bejan number. The entropy generation rate and Bejan number clearly depend on velocity and thermal fields. The von Kármán approach is utilized to convert the partial differential expressions into ordinary ones. These expressions are non-dimensionalized, and numerical results are obtained for flow variables. The effects of the magnetic parameter, Prandtl number, radiative parameter, heat generation/absorption parameter, and slip parameter on velocity and temperature fields as well as the entropy generation rate and Bejan number are discussed. Drag forces (radial and tangential) and heat transfer rates are calculated and discussed. Furthermore the entropy generation rate is a decreasing function of magnetic variable and Reynolds number. The Bejan number effect on the entropy generation rate is reverse to that of the magnetic variable. Also opposite behavior of heat transfers is observed for varying estimations of radiative and slip variables.

Spreading out of perturbations in reversible reaction networks

NASA Astrophysics Data System (ADS)

Maslov, Sergei; Sneppen, Kim; Ispolatov, I.

2007-08-01

Using an example of physical interactions between proteins, we study how a perturbation propagates in the equilibrium of a network of reversible reactions governed by the law of mass action. We introduce a matrix formalism to describe the linear response of all equilibrium concentrations to shifts in total abundances of individual reactants, and reveal its heuristic analogy to the flow of electric current in a network of resistors. Our main conclusion is that, on average, the induced changes in equilibrium concentrations decay exponentially as a function of network distance from the source of perturbation. We analyze how this decay is influenced by such factors as the topology of a network, binding strength, and correlations between concentrations of neighboring nodes. We find that the minimal branching of the network, small values of dissociation constants, and low equilibrium free (unbound) concentrations of reacting substances all decrease the decay constant and thus increase the range of propagation. Exact analytic expressions for the decay constant are obtained for the case of equally strong interactions and uniform as well as oscillating concentrations on the Bethe lattice. Our general findings are illustrated using a real network of protein-protein interactions in baker's yeast with experimentally determined protein concentrations.

Geomagnetic Reversals during the Phanerozoic.

PubMed

McElhinny, M W

1971-04-09

An antalysis of worldwide paleomagnetic measurements suggests a periodicity of 350 x 10(6) years in the polarity of the geomagnetic field. During the Mesozoic it is predominantly normal, whereas during the Upper Paleozoic it is predominantly reversed. Although geomagnetic reversals occur at different rates throughout the Phanerozoic, there appeaars to be no clear correlation between biological evolutionary rates and reversal frequency.

Kinetics Analysis of Synthesis Reaction of Struvite With Air-Flow Continous Vertical Reactors

NASA Astrophysics Data System (ADS)

Edahwati, L.; Sutiyono, S.; Muryanto, S.; Jamari, J.; Bayuseno, dan A. P.

2018-01-01

Kinetics reaction is a knowledge about a rate of chemical reaction. The differential of the reaction rate can be determined from the reactant material or the formed material. The reaction mechanism of a reactor may include a stage of reaction occurring sequentially during the process of converting the reactants into products. In the determination of reaction kinetics, the order of reaction and the rate constant reaction must be recognized. This study was carried out using air as a stirrer as a medium in the vertical reactor for crystallization of struvite. Stirring is one of the important aspects in struvite crystallization process. Struvite crystals or magnesium ammonium phosphate hexahydrates (MgNH4PO4·6H2O) is commonly formed in reversible reactions and can be generated as an orthorhombic crystal. Air is selected as a stirrer on the existing flow pattern in the reactor determining the reaction kinetics of the crystal from the solution. The experimental study was conducted by mixing an equimolar solution of 0.03 M NH4OH, MgCl2 and H3PO4 with a ratio of 1: 1: 1. The crystallization process of the mixed solution was observed in an inside reactor at the flow rate ranges of 16-38 ml/min and the temperature of 30°C was selected in the study. The air inlet rate was kept constant at 0.25 liters/min. The pH solution was adjusted to be 8, 9 and 10 by dropping wisely of 1 N KOH solution. The crystallization kinetics was examined until the steady state of the reaction was reached. The precipitates were filtered and dried at a temperature for subsequent material characterization, including Scanning Electron Microscope (SEM) and XRD (X-Ray diffraction) method. The results show that higher flow rate leads to less mass of struvite.

Specific Hardening Function Definition and Characterization of a Multimechanism Generalized Potential-based Viscoelastoplasticity Model

NASA Technical Reports Server (NTRS)

Arnold, S. M.; Saleeb, A. F.

2003-01-01

Given the previous complete-potential structure framework together with the notion of strain- and stress-partitioning in terms of separate contributions of several submechanisms (viscoelastic and viscoplastic) to the thermodynamic functions (stored energy and dissipation) a detailed viscoelastoplastic multimechanism characterization of a specific hardening functional form of the model is presented and discussed. TIMETAL 21S is the material of choice as a comprehensive test matrix, including creep, relaxation, constant strain-rate tension tests, etc. are available at various temperatures. Discussion of these correlations tests, together with comparisons to several other experimental results, are given to assess the performance and predictive capabilities of the present model particularly with regard to the notion of hardening saturation as well as the interaction of multiplicity of dissipative (reversible/irreversible) mechanisms.

Synthesis and characterization of lithium intercalation electrodes based on iron oxide thin films

NASA Astrophysics Data System (ADS)

Sarradin, J.; Guessous, A.; Ribes, M.

Sputter-deposited iron oxide thin films are investigated as a possible negative electrode for rocking-chair microbatteries. Experimental conditions related to the manufacturing of amorphous thin films suitable to a large number of available intercalation sites are described. Structural and physical properties of the thin layer films are presented. The conductivities of the amorphous thin films were found to be very high compared with those of the respective crystalline forms. Regarding the electrochemical behaviour, Fe 2O 3-based thin films electrodes are able to store and reversibly exchange lithium ions. At a C/2 charge/discharge rate with 100% depth-of-discharge (DOD), the specific capacity of these amorphous thin film electrodes remains almost constant and close to 330 Ah/kg after more than 120 charge/discharge cycles.

Mechanism of inhibition of cholinesterases by Huperzine A. (Reannouncement with new availability information)

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

Ashani, Y.; Peggins, J.O.; Doctor, B.P.

1992-04-30

Huperzine A, an alkaloid isolated from Huperzia serrata was found to reversibly inhibit acetylcholinesterases (EC 3.1.7) and (EC 3.1.1.8) with i 3.1 on- and off-rates that depend on both the type and the source of enzyme. Long incubation of high concentrations of purified (1-8 PM) with huperzine-A did not show any chemical modification of huperzine-A. A low dissociation constant K sub 1 was obtained for mammalian acetylcholinesterase-huperzine (20-40 nM) compared to mammalian butyrylcholinesterase-huperzine (20-40 microns.) This indicates that the thermodynamic stability of huperzine-cholinesterase complex may depend on the number and type of aromatic amino acid residues in the catalytic pocketmore » region of the cholinesterase molecule.« less

Mechanisms and Factors that Influence High Frequency Retroviral Recombination

PubMed Central

Delviks-Frankenberry, Krista; Galli, Andrea; Nikolaitchik, Olga; Mens, Helene; Pathak, Vinay K.; Hu, Wei-Shau

2011-01-01

With constantly changing environmental selection pressures, retroviruses rely upon recombination to reassort polymorphisms in their genomes and increase genetic diversity, which improves the chances for the survival of their population. Recombination occurs during DNA synthesis, whereby reverse transcriptase undergoes template switching events between the two copackaged RNAs, resulting in a viral recombinant with portions of the genetic information from each parental RNA. This review summarizes our current understanding of the factors and mechanisms influencing retroviral recombination, fidelity of the recombination process, and evaluates the subsequent viral diversity and fitness of the progeny recombinant. Specifically, the high mutation rates and high recombination frequencies of HIV-1 will be analyzed for their roles in influencing HIV-1 global diversity, as well as HIV-1 diagnosis, drug treatment, and vaccine development. PMID:21994801

The mechanism of Klebsiella pneumoniae nitrogenase action. Pre-steady-state kinetics of H2 formation.

PubMed Central

Lowe, D J; Thorneley, R N

1984-01-01

A comprehensive model for the mechanism of nitrogenase action is used to simulate pre-steady-state kinetic data for H2 evolution in the presence and in the absence of N2, obtained by using a rapid-quench technique with nitrogenase from Klebsiella pneumoniae. These simulations use independently determined rate constants that define the model in terms of the following partial reactions: component protein association and dissociation, electron transfer from Fe protein to MoFe protein coupled to the hydrolysis of MgATP, reduction of oxidized Fe protein by Na2S2O4, reversible N2 binding by H2 displacement and H2 evolution. Two rate-limiting dissociations of oxidized Fe protein from reduced MoFe protein precede H2 evolution, which occurs from the free MoFe protein. Thus Fe protein suppresses H2 evolution by binding to the MoFe protein. This is a necessary condition for efficient N2 binding to reduced MoFe protein. PMID:6395861

CO/sub 2/ absorption into aqueous MDEA and MDEA/MEA solutions

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

Critchfield, J.; Rochelle, G.T.

1987-01-01

The rate of absorption of CO/sub 2/ into 2 molal MDEA was measured by following solution composition in a stirred-cell batch reactor. The conditions investigated were 9.5 - 62/sup 0/C at a nominal CO/sub 2/ pressure of 1 atm. The data were modelled with a combined mass transfer and equilibrium model which treated the reaction of CO/sub 2/ with MDEA as second order and reversible, rather than pseudo-first order. The resulting activation energy was 13.7 kcal/gmol, and the rate constant at 30.5/sup 0/C was 4.0 (Ms)/sup -1/. The assumption of pseudo-first order conditions was found to reduce the apparent activationmore » energy to approximately 9 kcal/gmol. CO/sub 2/ absorption into 1.36 molal MDEA/0.61 molal MEA was studied at 31/sup 0/C. The experimental data were predicted better by a mass transfer model based on a shuttle mechanism than by one with two parallel reactions.« less

Coupling of kinesin ATP turnover to translocation and microtubule regulation: one engine, many machines.

PubMed

Friel, Claire T; Howard, Jonathon

2012-12-01

The cycle of ATP turnover is integral to the action of motor proteins. Here we discuss how variation in this cycle leads to variation of function observed amongst members of the kinesin superfamily of microtubule associated motor proteins. Variation in the ATP turnover cycle among superfamily members can tune the characteristic kinesin motor to one of the range of microtubule-based functions performed by kinesins. The speed at which ATP is hydrolysed affects the speed of translocation. The ratio of rate constants of ATP turnover in relation to association and dissociation from the microtubule influence the processivity of translocation. Variation in the rate-limiting step of the cycle can reverse the way in which the motor domain interacts with the microtubule producing non-motile kinesins. Because the ATP turnover cycle is not fully understood for the majority of kinesins, much work remains to show how the kinesin engine functions in such a wide variety of molecular machines.

Application of the principle of linked functions to ATP-driven ion pumps: kinetics of activation by ATP.

PubMed Central

Reynolds, J A; Johnson, E A; Tanford, C

1985-01-01

If a ligand binds with unequal affinity to two distinct states of a protein, then the equilibrium between the two states becomes a function of the concentration of the ligand. A necessary consequence is that the ligand must also affect the forward and/or reverse rate constants for transition between the two states. For an enzyme or transport protein with such a transition as a slow step in the catalytic cycle, the overall rate also becomes a function of ligand concentration. These conclusions are independent of whether or not the ligand is a direct participant in the reaction. If it is a direct participant, then the kinetic effect arising from the principle of linked functions is distinct from the direct catalytic effect. These principles suffice to account for the biphasic response of the hydrolytic activity of ATP-driven ion pumps to the concentration of ATP, without the need to invoke more than one ATP binding site per catalytic center. PMID:2987939

The temperature dependence of the rate constant for the reaction of hydroxyl radicals with nitric acid

NASA Technical Reports Server (NTRS)

Kurylo, M. J.; Cornett, K. D.; Murphy, J. L.

1982-01-01

The rate constant for the reaction of hydroxyl radicals with nitric acid in the 225-443 K temperature range has been measured by means of the flash photolysis resonance fluorescence technique. Above 300 K, the rate constant levels off in a way that can only be explained by the occurrence of two reaction channels, of which one, operative at low temperatures, proceeds through the formation of an adduct intermediate. The implications of these rate constant values for stratospheric reaction constants is discussed.

Very high pressure liquid chromatography using core-shell particles: quantitative analysis of fast gradient separations without post-run times.

PubMed

Stankovich, Joseph J; Gritti, Fabrice; Stevenson, Paul G; Beaver, Lois A; Guiochon, Georges

2014-01-17

Five methods for controlling the mobile phase flow rate for gradient elution analyses using very high pressure liquid chromatography (VHPLC) were tested to determine thermal stability of the column during rapid gradient separations. To obtain rapid separations, instruments are operated at high flow rates and high inlet pressure leading to uneven thermal effects across columns and additional time needed to restore thermal equilibrium between successive analyses. The purpose of this study is to investigate means to minimize thermal instability and obtain reliable results by measuring the reproducibility of the results of six replicate gradient separations of a nine component RPLC standard mixture under various experimental conditions with no post-run times. Gradient separations under different conditions were performed: constant flow rates, two sets of constant pressure operation, programmed flow constant pressure operation, and conditions which theoretically should yield a constant net heat loss at the column's wall. The results show that using constant flow rates, programmed flow constant pressures, and constant heat loss at the column's wall all provide reproducible separations. However, performing separations using a high constant pressure with programmed flow reduces the analysis time by 16% compared to constant flow rate methods. For the constant flow rate, programmed flow constant pressure, and constant wall heat experiments no equilibration time (post-run time) was required to obtain highly reproducible data. Copyright © 2013 Elsevier B.V. All rights reserved.

Sex Ratio and Sex Reversal in Two-year-old Class of Oyster, Crassostrea gigas (Bivalvia: Ostreidae)

PubMed Central

Park, Jung Jun; Kim, Hyejin; Kang, Seung Wan; An, Cheul Min; Lee, Sung-Ho; Gye, Myung Chan; Lee, Jung Sick

2012-01-01

The sex ratio (F:M) in the same population of oyster, Crassostrea gigas at the commencement of the study (2007) was 1:1.0, but changed to 1:2.8 by the end of the study (2008). The sex reversal rate in two-year-old oysters was 40.2%. Specifically, female to male sex reversal rate was 66.1%, which is higher than the male to female sex reversal rate of 21.1%. The sex reversal pattern of C. gigas appears to go from male⇒female⇒male, and as such is determined to be rhythmical hermaphroditism. PMID:25949114

Reversal of Fortune: Increased Star Formation Efficiencies in the Early Histories of Dwarf Galaxies?

NASA Astrophysics Data System (ADS)

Madau, Piero; Weisz, Daniel R.; Conroy, Charlie

2014-08-01

On dwarf galaxy scales, the different shapes of the galaxy stellar mass function and the dark halo mass function require a star-formation efficiency (SFE) in these systems that is currently more than 1 dex lower than that of Milky Way-size halos. Here, we argue that this trend may actually be reversed at high redshift. Specifically, by combining the resolved star-formation histories of nearby isolated dwarfs with the simulated mass-growth rates of dark matter halos, we show that the assembly of these systems occurs in two phases: (1) an early, fast halo accretion phase with a rapidly deepening potential well, characterized by a high SFE; and (2) a late, slow halo accretion phase where, perhaps as a consequence of reionization, the SFE is low. Nearby dwarfs have more old stars than predicted by assuming a constant or decreasing SFE with redshift, a behavior that appears to deviate qualitatively from the trends seen among more massive systems. Taken at face value, the data suggest that at sufficiently early epochs, dwarf galaxy halos above the atomic cooling mass limit can be among the most efficient sites of star formation in the universe.

The key nickel enzyme of methanogenesis catalyses the anaerobic oxidation of methane.

PubMed

Scheller, Silvan; Goenrich, Meike; Boecher, Reinhard; Thauer, Rudolf K; Jaun, Bernhard

2010-06-03

Large amounts (estimates range from 70 Tg per year to 300 Tg per year) of the potent greenhouse gas methane are oxidized to carbon dioxide in marine sediments by communities of methanotrophic archaea and sulphate-reducing bacteria, and thus are prevented from escaping into the atmosphere. Indirect evidence indicates that the anaerobic oxidation of methane might proceed as the reverse of archaeal methanogenesis from carbon dioxide with the nickel-containing methyl-coenzyme M reductase (MCR) as the methane-activating enzyme. However, experiments showing that MCR can catalyse the endergonic back reaction have been lacking. Here we report that purified MCR from Methanothermobacter marburgensis converts methane into methyl-coenzyme M under equilibrium conditions with apparent V(max) (maximum rate) and K(m) (Michaelis constant) values consistent with the observed in vivo kinetics of the anaerobic oxidation of methane with sulphate. This result supports the hypothesis of 'reverse methanogenesis' and is paramount to understanding the still-unknown mechanism of the last step of methanogenesis. The ability of MCR to cleave the particularly strong C-H bond of methane without the involvement of highly reactive oxygen-derived intermediates is directly relevant to catalytic C-H activation, currently an area of great interest in chemistry.

Turbulent Plane Wakes Subjected to Successive Strains

NASA Technical Reports Server (NTRS)

Rogers, Michael M.

2003-01-01

Six direct numerical simulations of turbulent time-evolving strained plane wakes have been examined to investigate the response of a wake to successive irrotational plane strains of opposite sign. The orientation of the applied strain field has been selected so that the flow is the time-developing analogue of a spatially developing wake evolving in the presence of either a favourable or an adverse streamwise pressure gradient. The magnitude of the applied strain rate a is constant in time t until the total strain e(sup at) reaches about four. At this point, a new simulation is begun with the sign of the applied strain being reversed (the original simulation is continued as well). When the total strain is reduced back to its original value of one, yet another simulation is begun with the sign of the strain being reversed again back to its original sign. This process is done for both initially "favourable" and initially "adverse" strains, providing simulations for each of these strain types from three different initial conditions. The evolution of the wake mean velocity deficit and width is found to be very similar for all the adversely strained cases, with both measures rapidly achieving exponential growth at the rate associated with the cross-stream expansive strain e(sup at). In the "favourably" strained cases, the wake widths approach a constant and the velocity deficits ultimately decay rapidly as e(sup -2at). Although all three of these cases do exhibit the same asymptotic exponential behaviour, the time required to achieve this is longer for the cases that have been previously adversely strained (by at approx. equals 1). These simulations confirm the generality of the conclusions drawn in Rogers (2002) regarding the response of plane wakes to strain. The evolution of strained wakes is not consistent with the predictions of classical self-similar analysis; a more general equilibrium similarity solution is required to describe the results. At least for the cases considered here, the wake Reynolds number and the ratio of the turbulent kinetic energy to the square of the wake mean velocity deficit are determined nearly entirely by the total strain. For these measures the order in which the strains are applied does not matter and the changes brought about by the strain are nearly reversible. The wake mean velocity deficit and width, on the other hand, differ by about a factor of three when the total strain returns to one, depending on whether the wake was first "favourably" or "adversely" strained. The strain history is important for predicting the evolution of these quantities.

Reverse shoulder arthroplasty in 3 and 4 part proximal humeral fractures in patients aged more than 65 years: Results and complications.

PubMed

Villodre-Jiménez, J; Estrems-Díaz, V; Diranzo-García, J; Bru-Pomer, A

The treatment of 3and 4 part proximal humeral fractures in elderly patients is still controversial. The frequent co-existence of poor quality bone and rotator cuff abnormalities in patients with multiple clinical conditions and with difficulties for physical rehabilitation leads to disappointing clinical results, even when the radiological images are acceptable. To evaluate the clinical, radiological, and functional results in patients over 65 years old with complex proximal humerus fractures treated with reverse shoulder arthroplasty. A prospective review was carried out on 30 patients (26 women and 4 men) with proximal humeral fractures treated with reverse shoulder arthroplasty in our department. The mean age was 74.9 years (SD=6.3), and the mean follow-up was 34.5 months (SD=19.3). Clinical and functional results were acceptable, with a mean forward flexion of 124° and a mean external rotation of 13°. The mean abbreviated Constant abbreviated score was 49.1 (SD=14.1), 27 (SD=6.3) in the UCLA scale, and 32.2 (SD=19.2) in the QuickDASH questionnaire. The large majority (80%) of the patients are pain free, and they do not need medication to do daily activities. The complication rate was 13.3%. We consider that reverse shoulder arthroplasty is a valid option to treat 3and 4 part proximal humeral fractures in elderly patients. The surgical goals should include the anatomical reconstruction of the tuberosities, avoiding enlargement of the operated arm greater than 2cm. Copyright © 2016 SECOT. Publicado por Elsevier España, S.L.U. All rights reserved.

Effect of irreversibility on the thermodynamic characterization of the thermal denaturation of Aspergillus saitoi acid proteinase.

PubMed Central

Tello-Solis, S R; Hernandez-Arana, A

1995-01-01

The thermal denaturation of the acid proteinase from Aspergillus saitoi was studied by CD and differential scanning calorimetry (DSC). This process seemed to be completely irreversible, as protein samples that were heated to temperatures at which the transition had been completed and then cooled at 25 degrees C did not show any reversal of the change in the CD signal. Similar results were obtained with DSC. Nevertheless, we were able to detect the presence of reversibly unfolded species in experiments in which the enzyme solution was heated to a temperature within the transition region, followed by rapid cooling at 25 degrees C. Accordingly, the denaturation of behaviour of the acid proteinase seems to be consistent with the existence of one (or more) reversible unfolding transition followed by an irreversible step. The van't Hoff enthalpy, delta HvH, which corresponds to the reversible transition was calculated from extrapolation to infinite heating rate as 310 kJ.mol-1. This parameter was also determined from direct estimation of the equilibrium constant at several temperatures (delta HvH = 176 kJ.mol-1). Comparison of the average delta HvH with the calorimetric enthalpy (delta Hcal. = 770 kJ.mol-1) gave a value of 3.2 for the delta Hcal./delta HvH ratio, indicating that the molecular structure of the enzyme is probably formed by three or four cooperative regions, a number similar to that of the acid proteinase, pepsin. It should be noted that a completely different conclusion would be obtained from a straightforward analysis of the calorimetric curves, disregarding the effect of irreversibility on the denaturation process. PMID:7487958

Reversible Tailoring of Mechanical Properties of Carbon Nanotube Forests by Immersing in Solvents

DTIC Science & Technology

2014-12-07

quantify the strength of vdW interactions between CNTs, Hamaker constant of CNTs in vacuum, Av ¼ V 12pD 2 G , was evaluated where ‘V’ is the vdW...effectively do not interact with each other. Therefore, we assumed curved surface–surface vdW interaction between two CNTs to evaluate the Hamaker ...of the vdW forces are directly proportional to Hamaker constant, which depends on the macroscopic properties of the interacting objects and the

THE NATURE AND CONTROL OF REACTIONS IN BIOLUMINESCENCE

PubMed Central

Johnson, F. H.; Eyring, H.; Steblay, R.; Chaplin, H.; Huber, C.; Gherardi, G.

1945-01-01

On the basis of available data with regard to the chemical and physical properties of the "substrate" luciferin (LH2) and enzyme, luciferase (A), and of kinetic data derived both from the reaction in extracts of Cypridina, and from the luminescence of intact bacteria, the fundamental reactions involved in the phenomenon of bioluminescence have been schematized. These reactions provide a satisfactory basis for interpreting the known characteristics of the system, as well as the theoretical chemistry with regard to the control of its over-all velocity in relation to various factors. These factors, here studied experimentally wholly with bacteria, Photobacterium phosphoreum in particular, include pH, temperature, pressure, and the drugs sulfanilamide, urethane, and alcohol, separately and in relation to each other. Under steady state conditions of bacterial luminescence, with excess of oxidizable substrate and with oxygen not limiting, the data indicate that the chief effects of these agents center around the pace setting reactions, which may be designated by the equation: A + LH2 → ALH2 following which light emission is assumed proportional to the amount of the excited molecule, AL*. The relation between pH and luminescence intensity varies with (a), the buffer mixture and concentration, (b), the temperature, and (c), the hydrostatic pressure. At an optimum temperature for luminescence of about 22° C. in P. phosphoreum, the effects of increasing or decreasing the hydrogen ion concentration are largely reversible over the range between pH 3.6 and pH 8.8. The relation between luminescence intensity and pH, under the experimental conditions employed, is given by the following equation, in which I 1 represents the maximum intensity, occurring about pH 6.5; I 2 the intensity at any other given pH; K 5 the equilibrium constant between hydrogen ions and the AL-; and K 6 the corresponding constant with respect to hydroxyl ions: See PDF for Equation The value of K 5, as indicated by the data, amounts to 4.84 x 104, while that of K 6 amounts to 4.8 x 105. Beyond the range between approximately pH 3.8 and 8.8, destructive effects of the hydrogen and hydroxyl ions, respectively, were increasingly apparent. By raising the temperature above the optimum, the destructive effects were apparent at all pH, and the intensity of the luminescence diminished logarithmically with time. With respect to pH, the rate of destruction of the light-emitting system at temperatures above the optimum was slowest between pH 6.5 and 7.0, and increased rapidly with more acid or more alkaline reactions of the medium. The reversible effects of slightly acid pH vary with the temperature in the manner of an inhibitor (Type I) that acts independently of the normal, reversible denaturation equilibrium (K 1) of the enzyme. The per cent inhibition caused by a given acid pH in relation to the luminescence intensity at optimum pH, is much greater at low temperatures, and decreases as the temperature is raised towards the optimum temperature. The observed maximum intensity of luminescence is thus shifted to slightly higher temperatures by increase in (H+). The apparent activation energy of luminescence is increased by a decrease in pH. The value of ΔH‡ at pH 5.05 was calculated to be 40,900 calories, in comparison with 20,700 at a pH of 6.92. The difference of 20,200 is taken to represent an estimate of the heat of ionization of ALH in the activation process, and compares roughtly with the 14,000 calories estimated for the same process, by analyzing the data from the point of view of hydrogen ions as an inhibitor. The decreasing temperature coefficient for luminescence in proceeding from low temperatures towards the optimum is accounted for in part by the greater degree of ionization of ALH. At the optimum temperature and acid reactions, pressures up to about 500 atmospheres retard the velocity of the luminescent oxidation. At the same temperature, with decrease in hydrogen ion concentration, the pressure effect is much less, indicating a considerable volume increase in the process of ionization and activation. In the extremely alkaline range, beyond pH 9, luminescence is greatly reduced, as compared with the intensity at neutrality, and under these conditions pressure causes a pronounced increase in intensity, presumably by acting upon the reversible denaturation equilibrium of the protein enzyme, A. Sulfanilamide, in neutral solutions, acts on luminescence in a manner very much resembling that of hydrogen ions at acidities between pH 4.0 and pH 6.5. Like the hydrogen ion equilibrium, the sulfanilamide equilibrium involves a ratio of approximately one inhibitor molecule to one enzyme molecule. The heat of reaction amounts to about 11,600 calories or more in a reversible combination that evidently evolves heat. Like the action of H ions, sulfanilamide causes a slight shifting of maximum luminescence intensity in the direction of higher temperatures, and an increase in the energy of activation. The effect of sulfanilamide on the growth of broth cultures of eight species of luminous bacteria indicates that there is no regular relationship among the different organisms between the concentration of the drug that prevents growth, and that which prevents luminescence in the cells which develop in the presence of sulfanilamide. p-Aminobenzoic acid (PAB) antagonizes the sulfanilamide inhibition of growth in luminous bacteria, and the cultures that develop are luminous. When (PAB) is added to cells from fully developed cultures, it has no effect on luminescence, or causes a slight inhibition, depending on the concentration. With luminescence partly inhibited by sulfanilamide, the addition of PAB has no effect, or has an inhibitory effect which adds to that caused by sulfanilamide. Two different, though possibly related, enzyme systems thus appear to limit growth and luminescence, respectively. The possible mechanism through which both the inhibitions and the antagonism take place is discussed. The irreversible destruction of the luminescent system at temperatures above that of the maximum luminescence, in a medium of favorable pH to which no inhibitors have been added, proceeds logarithmically with time at both normal and increased hydrostatic pressures. Pressure retards the rate of the destruction, and the analysis of the data indicates that a volume increase of roughly 71 cc. per gm. molecule at 32° C. takes place in going from the normal to the activated state in this reaction. At normal pressure, the rate of destruction has a temperature coefficient of approximately 90,000 calories, or about 20,000 calories more than the heat of reaction in the reversible denaturation equilibrium. The data indicate that the equilibrium and the rate process are two distinct reactions. The equation for luminescence intensity, taking into account both the reversible and irreversible phases of the reaction is given below. In the equation b is a proportionality constant; k' the rate constant of the luminescent reaction; A0 the total luciferase; A0i the total initial luciferase at time t equals 0; kn the rate constant for the destruction of the native, active form of the enzyme; kd the rate constant for the destruction of the reversibly denatured, inactive form; t the time; and the other symbols are as indicated above: See PDF for Equation For reasons cited in the text, kn evidently equals kd. Urethane and alcohol, respectively, act in a manner (Type II) that promotes the breaking of the type of bonds broken in both the reversible and irreversible reactions and so promotes the irreversible denaturation. This result is in contrast to the effects of sulfanilamide, which at appropriate concentrations may give rise to the same initial inhibition as that caused by urethane, but remains constant with time. The inhibition caused by urethane and alcohol, respectively, increases as the temperature is raised. As a result, the apparent optimum is shifted to lower temperatures, and the activation energy for the over-all process of luminescence diminishes. An analysis for the approximate heat of reaction in the equilibrium between these drugs and the enzyme, indicates 65,000 calories for urethane, and 37,000 for alcohol. A similar analysis with respect to the effect of hydroxyl ions as the inhibitor gives 60,300 calories. The effects of alcohol and urethane are sensitive to hydrostatic pressure. Moderate inhibitions at optimum temperature and pH, caused by relatively small concentrations of either drug, are completely abolished by pressures of 3,000 to 4,000 pounds per square inch. At optimum temperature and pH, increasing concentrations of alcohol caused the apparent optimum pressure for luminescence to shift markedly in the direction of higher pressures. Analysis of the data with respect to concentration of alcohol at different pressures indicated that the ratio of alcohol to enzyme molecules amounted to approximately 4, at 7,000 pounds, but only about 2.8 at normal pressures. This phenomenon was taken to indicate that more than one equilibrium is established between the alcohol and the protein. A similar interpretation was suggested in connection with the fact that analysis of the relation between concentration of urethane and amount of inhibition at different temperatures also indicated a ratio of urethane to enzyme molecules that increased with temperature in the equilibria involved. Analysis of the data with respect to pressure and the inhibition caused by a given concentration of alcohol at different temperatures indicated that the volume change involved in the combination of alcohol with the enzyme must be very small, while the actual effect of pressure is apparently mediated through the reversible denaturation of the protein enzyme, which is promoted by alcohol, urethane, and drugs of similar type. PMID:19873433

Switching catalysis from hydrolysis to perhydrolysis in P. fluorescens esterase

PubMed Central

Yin, De Lu (Tyler); Bernhardt, Peter; Morley, Krista L.; Jiang, Yun; Cheeseman, Jeremy D.; Purpero, Vincent; Schrag, Joseph D.; Kazlauskas, Romas J.

2010-01-01

Many serine hydrolases catalyze perhydrolysis – the reversible formation of per-acids from carboxylic acids and hydrogen peroxide. Recently we showed that a single amino acid substitution in the alcohol binding pocket - L29P - in Pseudomonas fluorescens (SIK WI) aryl esterase (PFE) increased the specificity constant of PFE for peracetic acid formation >100-fold [Bernhardt et al. Angew. Chem. Intl. Ed. 2005, 44, 2742]. In this paper, we extend this work to address the three following questions. First, what is the molecular basis of the increase in perhydrolysis activity? We previously proposed that the L29P substitution creates a hydrogen bond between the enzyme and hydrogen peroxide in the transition state. Here we report two x-ray structures of L29P PFE that support this proposal. Both structures show a main chain carbonyl oxygen closer to the active-site serine as expected. One structure further shows acetate in the active site in an orientation consistent with reaction by an acyl-enzyme mechanism. We also detected an acyl-enzyme intermediate in the hydrolysis of ε-caprolactone by mass spectrometry. Second, can we further increase perhydrolysis activity? We discovered that the reverse reaction – hydrolysis of peracetic acid to acetic acid and hydrogen peroxide – occurs at nearly the diffusion limited rate. Since the reverse reaction cannot increase further, neither can the forward reaction. Consistent with this prediction, two variants with additional amino acid substitutions showed two fold higher kcat, but Km also increased so the specificity constant, kcat/Km, remained similar. Third, how does the L29P substitution change the esterase activity? Ester hydrolysis decreased for most esters (75-fold for ethyl acetate), but not for methyl esters. In contrast, L29P PFE catalyzed hydrolysis of ε-caprolactone five times more efficiently than wild-type PFE. Molecular modeling suggests that moving the carbonyl group closer to the active site blocks access for larger alcohol moieties, but binds ε-caprolactone more tightly. These results are consistent with the natural function of perhydrolases being either hydrolysis of peroxycarboxylic acids or hydrolysis of lactones. PMID:20112920

Illusory motion reversal is caused by rivalry, not by perceptual snapshots of the visual field.

PubMed

Kline, Keith; Holcombe, Alex O; Eagleman, David M

2004-10-01

In stroboscopic conditions--such as motion pictures--rotating objects may appear to rotate in the reverse direction due to under-sampling (aliasing). A seemingly similar phenomenon occurs in constant sunlight, which has been taken as evidence that the visual system processes discrete "snapshots" of the outside world. But if snapshots are indeed taken of the visual field, then when a rotating drum appears to transiently reverse direction, its mirror image should always appeared to reverse direction simultaneously. Contrary to this hypothesis, we found that when observers watched a rotating drum and its mirror image, almost all illusory motion reversals occurred for only one image at a time. This result indicates that the motion reversal illusion cannot be explained by snapshots of the visual field. The same result is found when the two images are presented within one visual hemifield, further ruling out the possibility that discrete sampling of the visual field occurs separately in each hemisphere. The frequency distribution of illusory reversal durations approximates a gamma distribution, suggesting perceptual rivalry as a better explanation for illusory motion reversal. After adaptation of motion detectors coding for the correct direction, the activity of motion-sensitive neurons coding for motion in the reverse direction may intermittently become dominant and drive the perception of motion.

Rate Constants and Mechanisms of Protein–Ligand Binding

PubMed Central

Pang, Xiaodong; Zhou, Huan-Xiang

2017-01-01

Whereas protein–ligand binding affinities have long-established prominence, binding rate constants and binding mechanisms have gained increasing attention in recent years. Both new computational methods and new experimental techniques have been developed to characterize the latter properties. It is now realized that binding mechanisms, like binding rate constants, can and should be quantitatively determined. In this review, we summarize studies and synthesize ideas on several topics in the hope of providing a coherent picture of and physical insight into binding kinetics. The topics include microscopic formulation of the kinetic problem and its reduction to simple rate equations; computation of binding rate constants; quantitative determination of binding mechanisms; and elucidation of physical factors that control binding rate constants and mechanisms. PMID:28375732

12 CFR Appendix K to Part 226 - Total Annual Loan Cost Rate Computations for Reverse Mortgage Transactions

Code of Federal Regulations, 2014 CFR

2014-01-01

... 12 Banks and Banking 3 2014-01-01 2014-01-01 false Total Annual Loan Cost Rate Computations for Reverse Mortgage Transactions K Appendix K to Part 226 Banks and Banking FEDERAL RESERVE SYSTEM (CONTINUED..., App. K Appendix K to Part 226—Total Annual Loan Cost Rate Computations for Reverse Mortgage...

12 CFR Appendix K to Part 226 - Total Annual Loan Cost Rate Computations for Reverse Mortgage Transactions

Code of Federal Regulations, 2013 CFR

2013-01-01

... 12 Banks and Banking 3 2013-01-01 2013-01-01 false Total Annual Loan Cost Rate Computations for Reverse Mortgage Transactions K Appendix K to Part 226 Banks and Banking FEDERAL RESERVE SYSTEM (CONTINUED..., App. K Appendix K to Part 226—Total Annual Loan Cost Rate Computations for Reverse Mortgage...

Rate Constant and Temperature Dependence for the Reaction of Hydroxyl Radicals with 2-Flouropropane (FC-281ea) and Comparison with an Estimated Rate Constant

NASA Technical Reports Server (NTRS)

DeMore, W.; Wilson, E., Jr.

1998-01-01

Relative rate experiments were used to measure the rate constant and temperature dependence of the reaction of OH radicals with 2-fluoropropane (HFC-281ea), using ethane, propane, ethyl chloride as reference standards.

ParaCEST Agents Encapsulated in Reverse Nano-Assembled Capsules (RACs): How Slow Molecular Tumbling Can Quench CEST Contrast.

PubMed

Farashishiko, Annah; Slack, Jacqueline R; Botta, Mauro; Woods, Mark

2018-01-01

Although paraCEST is a method with immense scope for generating image contrast in MRI, it suffers from the serious drawback of high detection limits. For a typical discrete paraCEST agent the detection limit is roughly an order of magnitude higher than that of a clinically used relaxation agent. One solution to this problem may be the incorporation of a large payload of paraCEST agents into a single macromolecular agent. Here we report a new synthetic method for accomplishing this goal: incorporating a large payload of the paraCEST agent DyDOTAM 3+ into a Reverse Assembled nano-Capsule. An aggregate can be generated between this chelate and polyacrylic acid (PAA) after the addition of ethylene diamine. Subsequent addition of polyallylamine hydrochloride (PAH) followed by silica nanoparticles generated a robust encapsulating shell and afforded capsule with a mean hydrodynamic diameter of 650 ± 250 nm. Unfortunately this encapsulation did not have the effect of amplifying the CEST effect per agent, but quenched the CEST altogether. The quenching effect of encapsulation could be attributed to the effect of slowing molecular tumbling, which is inevitable when the chelate is incorporated into a nano-scale material. This increases the transverse relaxation rate of chelate protons and a theoretical examination using Solomon Bloembergen Morgan theory and the Bloch equations shows that the increase in the transverse relaxation rate constant for the amide protons, in even modestly sized nano-materials, is sufficient to significantly quench CEST.

ParaCEST Agents Encapsulated in Reverse Nano-Assembled Capsules (RACs): How Slow Molecular Tumbling Can Quench CEST Contrast

PubMed Central

Farashishiko, Annah; Slack, Jacqueline R.; Botta, Mauro; Woods, Mark

2018-01-01

Although paraCEST is a method with immense scope for generating image contrast in MRI, it suffers from the serious drawback of high detection limits. For a typical discrete paraCEST agent the detection limit is roughly an order of magnitude higher than that of a clinically used relaxation agent. One solution to this problem may be the incorporation of a large payload of paraCEST agents into a single macromolecular agent. Here we report a new synthetic method for accomplishing this goal: incorporating a large payload of the paraCEST agent DyDOTAM3+ into a Reverse Assembled nano-Capsule. An aggregate can be generated between this chelate and polyacrylic acid (PAA) after the addition of ethylene diamine. Subsequent addition of polyallylamine hydrochloride (PAH) followed by silica nanoparticles generated a robust encapsulating shell and afforded capsule with a mean hydrodynamic diameter of 650 ± 250 nm. Unfortunately this encapsulation did not have the effect of amplifying the CEST effect per agent, but quenched the CEST altogether. The quenching effect of encapsulation could be attributed to the effect of slowing molecular tumbling, which is inevitable when the chelate is incorporated into a nano-scale material. This increases the transverse relaxation rate of chelate protons and a theoretical examination using Solomon Bloembergen Morgan theory and the Bloch equations shows that the increase in the transverse relaxation rate constant for the amide protons, in even modestly sized nano-materials, is sufficient to significantly quench CEST. PMID:29682499

Modelling the diffusive transport and remobilisation of 137Cs in sediments: The effects of sorption kinetics and reversibility

NASA Astrophysics Data System (ADS)

Smith, J. T.; Comans, R. N. J.

1996-03-01

In determining the mobility of ions in sediments it is important to take account of the solid phase sorption and speciation. Measurements were made of activity depth profiles of 137Cs from fallout from Nuclear Weapons Testing and from the Chernobyl accident in two lake sediments. The fraction of 137Cs in the aqueous, exchangeably sorbed and "fixed" phases was determined at each depth interval. A model was developed to simulate the transport of 137Cs in these sediments, taking account of changes in sorption properties as the concentration of the competing ammonium ion changes with depth, as well as transfers of activity to less-exchangeable sites on the solids. The model simulations give reasonable agreement with experimental data, and the fitted rate constant for slow transfers to less-exchangeable sites ( T1/2 = 50-125 d) is in agreement with independent measurements. The modelling gave evidence for a reverse reaction from less-exchangeable to exchangeable sites with a half-life of order 10 y. Model results were compared with those generated by a physical mixing model and the standard molecular diffusion model assuming equilibrium sorption to the solid phase. Estimates were made of the remobilisation of Chernobyl 137Cs from these sediments to the water column: predicted rates vary from around 3% of the inventory per year 2 years after the fallout event to 0.04% per year 30 years after the fallout.

Rapid estimation of glucosinolate thermal degradation rate constants in leaves of Chinese kale and broccoli (Brassica oleracea) in two seasons.

PubMed

Hennig, Kristin; Verkerk, Ruud; Bonnema, Guusje; Dekker, Matthijs

2012-08-15

Kinetic modeling was used as a tool to quantitatively estimate glucosinolate thermal degradation rate constants. Literature shows that thermal degradation rates differ in different vegetables. Well-characterized plant material, leaves of broccoli and Chinese kale plants grown in two seasons, was used in the study. It was shown that a first-order reaction is appropriate to model glucosinolate degradation independent from the season. No difference in degradation rate constants of structurally identical glucosinolates was found between broccoli and Chinese kale leaves when grown in the same season. However, glucosinolate degradation rate constants were highly affected by the season (20-80% increase in spring compared to autumn). These results suggest that differences in glucosinolate degradation rate constants can be due to variation in environmental as well as genetic factors. Furthermore, a methodology to estimate rate constants rapidly is provided to enable the analysis of high sample numbers for future studies.

Methane steam reforming rates over Pt, Rh and Ni(111) accounting for H tunneling and for metal lattice vibrations

NASA Astrophysics Data System (ADS)

German, Ernst D.; Sheintuch, Moshe

2017-02-01

Microkinetic models of methane steam reforming (MSR) over bare platinum and rhodium (111) surfaces are analyzed in present work using calculated rate constants. The individual rate constants are classified into three different sets: (i) rate constants of adsorption and desorption steps of CH4, H2O, CO and of H2; (ii) rate constants of dissociation and formation of A-H bonds (A = C, O, and H), and (iii) rate constants of dissociation and formation of C-O bond. The rate constants of sets (i) and (iii) are calculated using transition state theory and published thermochemical data. The rate constants of H-dissociation reactions (set (ii)) are calculated in terms of a previously-developed approach that accounts for thermal metal lattice vibrations and for H tunneling through a potential barrier of height which depends on distance of AH from a surface. Pre-exponential factors of several group (ii) steps were calculated to be usually lower than the traditional kBT/h due to tunneling effect. Surface composition and overall MSR rates over platinum and rhodium surfaces are compared with those over nickel surface showing that operating conditions strongly affect on the activity order of the catalysts.

F-centers mechanism of long-term relaxation in lead zirconate-titanate based piezoelectric ceramics. 2. After-field relaxation

NASA Astrophysics Data System (ADS)

Ishchuk, V. M.; Kuzenko, D. V.

2016-08-01

The paper presents results of experimental study of the dielectric constant relaxation during aging process in Pb(Zr,Ti)O3 based solid solutions (PZT) after action of external DC electric field. The said process is a long-term one and is described by the logarithmic function of time. Reversible and nonreversible relaxation process takes place depending on the field intensity. The relaxation rate depends on the field strength also, and the said dependence has nonlinear and nonmonotonic form, if external field leads to domain disordering. The oxygen vacancies-based model for description of the long-term relaxation processes is suggested. The model takes into account the oxygen vacancies on the sample's surface ends, their conversion into F+- and F0-centers under external effects and subsequent relaxation of these centers into the simple oxygen vacancies after the action termination. F-centers formation leads to the violation of the original sample's electroneutrality, and generate intrinsic DC electric field into the sample. Relaxation of F-centers is accompanied by the reduction of the electric field, induced by them, and relaxation of the dielectric constant, as consequent effect.

1H nuclear magnetic resonance studies of sarcoplasmic oxygenation in the red cell-perfused rat heart.

PubMed

Jelicks, L A; Wittenberg, B A

1995-05-01

The proximal histidine N delta H proton of deoxymyoglobin experiences a large hyperfine shift resulting in its 1H nuclear magnetic resonance (NMR) signal appearing at approximately 76 ppm (at 35 degrees C), downfield of the diamagnetic spectral region. 1H NMR of this proton is used to monitor sarcoplasmic oxygen pressure in isolated perfused rat heart. This method monitors intracellular oxygenation in the whole heart and does not reflect oxygenation in a limited region. The deoxymyoglobin resonance intensity is reduced upon conversion of myoglobin to the ferric form by sodium nitrite. 1H resonances of the N delta H protons of the alpha and beta subunits of bovine deoxyhemoglobin do not interfere with the measurement of myoglobin deoxygenation in blood-perfused rat heart. We find that steady-state myoglobin deoxygenation is increased progressively (and reversibly) as oxygenation of the perfusing medium is decreased in both saline and red blood cell-perfused hearts at constant work output. An eightfold increase in the heart rate of the blood-perfused heart resulted in no change in the deoxymyoglobin signal intensity. Intracellular PO2 of myoglobin-containing cells is maintained remarkably constant in changing work states.

Creep rupture of fiber bundles: A molecular dynamics investigation

NASA Astrophysics Data System (ADS)

Linga, G.; Ballone, P.; Hansen, Alex

2015-08-01

The creep deformation and eventual breaking of polymeric samples under a constant tensile load F is investigated by molecular dynamics based on a particle representation of the fiber bundle model. The results of the virtual testing of fibrous samples consisting of 40 000 particles arranged on Nc=400 chains reproduce characteristic stages seen in the experimental investigations of creep in polymeric materials. A logarithmic plot of the bundle lifetime τ versus load F displays a marked curvature, ruling out a simple power-law dependence of τ on F . A power law τ ˜F-4 , however, is recovered at high load. We discuss the role of reversible bond breaking and formation on the eventual fate of the sample and simulate a different type of creep testing, imposing a constant stress rate on the sample up to its breaking point. Our simulations, relying on a coarse-grained representation of the polymer structure, introduce new features into the standard fiber bundle model, such as real-time dynamics, inertia, and entropy, and open the way to more detailed models, aiming at material science aspects of polymeric fibers, investigated within a sound statistical mechanics framework.

Reverse shoulder arthroplasty combined with latissimus dorsi transfer using the bone-chip technique.

PubMed

Ortmaier, Reinhold; Resch, Herbert; Hitzl, Wolfgang; Mayer, Michael; Blocher, Martina; Vasvary, Imre; Mattiassich, Georg; Stundner, Ottokar; Tauber, Mark

2014-03-01

Reverse shoulder arthroplasty (RSA) can restore active elevation in rotator-cuff-deficient shoulders. However, RSA cannot restore active external rotation. The combination of latissimus dorsi transfer with RSA has been reported to restore both active elevation and external rotation. We hypothesised that in the combined procedure, harvesting the latissimus dorsi with a small piece of bone, leads to good tendon integrity, low rupture rates and good clinical outcome. Between 2004 and 2010, 13 patients (13 shoulders) were treated with RSA in combination with latissimus dorsi transfer in a modified manner. The mean follow-up was 65.4 months, and the mean age at index surgery was 71.1 years. All patients had external rotation lag sign and positive hornblower's sign, as well as radiological signs of cuff-tear arthropathy (Hamada 3, 4 or 5) and fatty infiltration grade 3 according to Goutallier et al. on magnetic resonance imaging (MRI). The outcome measures included the Constant Murley Score, University of California-Los Angeles (UCLA) shoulder score, Simple Shoulder Test (SST), visual analogue scale (VAS) and the Activities of Daily Living Requiring External Rotation (ADLER) score. Tendon integrity was evaluated with dynamic ultrasound. All patients were asked at final follow-up to rate their satisfaction as excellent, good, satisfied or dissatisfied. The overall mean Constant-Murley Shoulder Outcome Score (CMS) improved from 20.4 to 64.3 points (p < 0.001). Mean VAS pain score decreased from 6.8 to 1.1 (p < 0.001)., mean UCLA score improved from 7.9 to 26.4 (p < 0.001), mean SST score improved from 2.3 to 7.9 (p < 0.001) and mean postoperative ADLER score was 26 points. The average degree of abduction improved from 45° to 129° (p < 0.001), the average degree of anterior flexion improved from 55° to 138° (p < 0.001) and the average degree of external rotation improved from -16° to 21° (p < 0.001). Eight patients rated their results as very satisfied, three as satisfied and two as dissatisfied. This modified technique, which avoids cutting the pectoralis major tendon and involves harvesting the tendon together with a small piece of bone, leads to good or even better functional results compared with the results reported in the literature, and also has high patient satisfaction and low failure rates.

Prediction of Chain Propagation Rate Constants of Polymerization Reactions in Aqueous NIPAM/BIS and VCL/BIS Systems.

PubMed

Kröger, Leif C; Kopp, Wassja A; Leonhard, Kai

2017-04-06

Microgels have a wide range of possible applications and are therefore studied with increasing interest. Nonetheless, the microgel synthesis process and some of the resulting properties of the microgels, such as the cross-linker distribution within the microgels, are not yet fully understood. An in-depth understanding of the synthesis process is crucial for designing tailored microgels with desired properties. In this work, rate constants and reaction enthalpies of chain propagation reactions in aqueous N-isopropylacrylamide/N,N'-methylenebisacrylamide and aqueous N-vinylcaprolactam/N,N'-methylenebisacrylamide systems are calculated to identify the possible sources of an inhomogeneous cross-linker distribution in the resulting microgels. Gas-phase reaction rate constants are calculated from B2PLYPD3/aug-cc-pVTZ energies and B3LYPD3/tzvp geometries and frequencies. Then, solvation effects based on COSMO-RS are incorporated into the rate constants to obtain the desired liquid-phase reaction rate constants. The rate constants agree with experiments within a factor of 2-10, and the reaction enthalpies deviate less than 5 kJ/mol. Further, the effect of rate constants on the microgel growth process is analyzed, and it is shown that differences in the magnitude of the reaction rate constants are a source of an inhomogeneous cross-linker distribution within the resulting microgel.

Projected ground-water development, ground-water levels, and stream-aquifer leakage in the South Fork Solomon River Valley between Webster Reservoir and Waconda Lake, north-central Kansas, 1979-2020

USGS Publications Warehouse

Kume, Jack; Lindgren, R.J.; Stullken, L.E.

1985-01-01

A two-dimensional finite difference computer model was used to project changes in the potentiometric surface, saturated thickness, and stream aquifer leakage in an alluvial aquifer resulting from four instances of projected groundwater development. The alluvial aquifer occurs in the South Fork Solomon River valley between Webster Reservoir and Waconda Lake in north-central Kansas. In the first two projections, pumpage for irrigation was held constant at 1978 rates throughout the projection period (1979-2020). In the second two projections, the 1978 pumpage was progressively increased each yr through 2020. In the second and fourth projections, surface water diversions in the Osborne Irrigation Canal were decreased by 50 %. For the third and fourth projections, each grid-block in the modeled area was classified initially as one of six types according to whether it represented irrigable or nonirrigable land, to its saturated thickness, to its location inside or outside the canal-river area, and to its pumping rate. The projected base-flow rates (leakage from the aquifer to the river) were lower during the irrigation season (June, July, and August) than during the other months of the yr because of the decline in hydraulic head produced by groundwater pumpage. Stream depletion, calculated as a decrease below the average (1970-78) estimated winter base-flow rate of 16.5 cu ft/sec, varied inversely with base flow. For the first two projections, a constant annual cycle of well pumpage and recharge was used throughout the projection period. Aquifer leakage to the river was nearly constant by the mid-to-late 1990's, implying that flow conditions had attained a stabilized annual cycle. The third and fourth projections never attained an annual stabilized cycle because the irrigation pumpage rate was increased each year. By the early 1980's, the hydraulic head had fallen below river stage, reversing the hydraulic gradient at the stream-aquifer interface and resulting in net leakage from the river to the aquifer during the summer months. By the early 1990 's, the projected potentiometric surface of the aquifer was lower than the river stage even during the winter and spring months. (Author 's abstract)

High temperature monotonic and cyclic deformation in a directionally solidified nickel-base superalloy

NASA Technical Reports Server (NTRS)

Huron, Eric S.

1986-01-01

Directionally solidified (DS) MAR-M246+Hf was tested in tension and fatigue, at temperatures from 20 C to 1093 C. Tests were performed on (001) oriented specimens at strain rates of 50 % and 0.5 % per minute. In tension, the yield strength was constant up to 704 C, above which the strength dropped off rapidly. A strong dependence of strength on strain rate was seen at the higher temperatures. The deformation mode was observed to change from heterogeneous to homogeneous with increasing temperature. Low Cycle Fatigue tests were done using a fully reversed waveform and total strain control. For a given plastic strain range, lives increased with increasing temperature. For a given temperature strain rate had a strong effect on life. At 704 C, decreasing strain rates decreased life, while at the higher temperatures, decreasing strain rates increased life, for a given plastic strain range. These results could be explained through considerations of the deformation modes and stress levels. At the higher temperatures, marked coarsening caused beneficial stress reductions, but oxidation limited the life. The longitudinal grain boundaries were found to influence slip behavior. The degree of secondary slip adjacent to the boundaries was found to be related to the degree of misorientation between the grains.

Multidimensional Cyclic Voltammetry Simulations of Pseudocapacitive Electrodes with a Conducting Nanorod Scaffold

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

Mei, Bing-Ang; Li, Bin; Lin, Jie

This paper aims to understand the effect of nanoarchitecture on the performance of pseudocapacitive electrodes consisting of conducting scaffold coated with pseudocapacitive material. To do so, two-dimensional numerical simulations of ordered conducting nanorods coated with a thin film of pseudocapacitive material were performed. The simulations reproduced three-electrode cyclic voltammetry measurements based on a continuum model derived from first principles. Two empirical approaches commonly used experimentally to characterize the contributions of surface-controlled and diffusion-controlled charge storage mechanisms to the total current density with respect to scan rate were theoretically validated for the first time. Moreover, the areal capacitive capacitance, attributed tomore » EDL formation, remained constant and independent of electrode dimensions, at low scan rates. However, at high scan rates, it decreased with decreasing conducting nanorod radius and increasing pseudocapacitive layer thickness due to resistive losses. By contrast, the gravimetric faradaic capacitance, due to reversible faradaic reactions, decreased continuously with increasing scan rate and pseudocapacitive layer thickness but was independent of conducting nanorod radius. Note that the total gravimetric capacitance predicted numerically featured values comparable to experimental measurements. Finally, an optimum pseudocapacitive layer thickness that maximizes total areal capacitance was identified as a function of scan rate and confirmed by scaling analysis.« less

Automatic detection of key innovations, rate shifts, and diversity-dependence on phylogenetic trees.

PubMed

Rabosky, Daniel L

2014-01-01

A number of methods have been developed to infer differential rates of species diversification through time and among clades using time-calibrated phylogenetic trees. However, we lack a general framework that can delineate and quantify heterogeneous mixtures of dynamic processes within single phylogenies. I developed a method that can identify arbitrary numbers of time-varying diversification processes on phylogenies without specifying their locations in advance. The method uses reversible-jump Markov Chain Monte Carlo to move between model subspaces that vary in the number of distinct diversification regimes. The model assumes that changes in evolutionary regimes occur across the branches of phylogenetic trees under a compound Poisson process and explicitly accounts for rate variation through time and among lineages. Using simulated datasets, I demonstrate that the method can be used to quantify complex mixtures of time-dependent, diversity-dependent, and constant-rate diversification processes. I compared the performance of the method to the MEDUSA model of rate variation among lineages. As an empirical example, I analyzed the history of speciation and extinction during the radiation of modern whales. The method described here will greatly facilitate the exploration of macroevolutionary dynamics across large phylogenetic trees, which may have been shaped by heterogeneous mixtures of distinct evolutionary processes.

Automatic Detection of Key Innovations, Rate Shifts, and Diversity-Dependence on Phylogenetic Trees

PubMed Central

Rabosky, Daniel L.

2014-01-01

A number of methods have been developed to infer differential rates of species diversification through time and among clades using time-calibrated phylogenetic trees. However, we lack a general framework that can delineate and quantify heterogeneous mixtures of dynamic processes within single phylogenies. I developed a method that can identify arbitrary numbers of time-varying diversification processes on phylogenies without specifying their locations in advance. The method uses reversible-jump Markov Chain Monte Carlo to move between model subspaces that vary in the number of distinct diversification regimes. The model assumes that changes in evolutionary regimes occur across the branches of phylogenetic trees under a compound Poisson process and explicitly accounts for rate variation through time and among lineages. Using simulated datasets, I demonstrate that the method can be used to quantify complex mixtures of time-dependent, diversity-dependent, and constant-rate diversification processes. I compared the performance of the method to the MEDUSA model of rate variation among lineages. As an empirical example, I analyzed the history of speciation and extinction during the radiation of modern whales. The method described here will greatly facilitate the exploration of macroevolutionary dynamics across large phylogenetic trees, which may have been shaped by heterogeneous mixtures of distinct evolutionary processes. PMID:24586858

Multidimensional Cyclic Voltammetry Simulations of Pseudocapacitive Electrodes with a Conducting Nanorod Scaffold

DOE PAGES

Mei, Bing-Ang; Li, Bin; Lin, Jie; ...

2017-10-27

This paper aims to understand the effect of nanoarchitecture on the performance of pseudocapacitive electrodes consisting of conducting scaffold coated with pseudocapacitive material. To do so, two-dimensional numerical simulations of ordered conducting nanorods coated with a thin film of pseudocapacitive material were performed. The simulations reproduced three-electrode cyclic voltammetry measurements based on a continuum model derived from first principles. Two empirical approaches commonly used experimentally to characterize the contributions of surface-controlled and diffusion-controlled charge storage mechanisms to the total current density with respect to scan rate were theoretically validated for the first time. Moreover, the areal capacitive capacitance, attributed tomore » EDL formation, remained constant and independent of electrode dimensions, at low scan rates. However, at high scan rates, it decreased with decreasing conducting nanorod radius and increasing pseudocapacitive layer thickness due to resistive losses. By contrast, the gravimetric faradaic capacitance, due to reversible faradaic reactions, decreased continuously with increasing scan rate and pseudocapacitive layer thickness but was independent of conducting nanorod radius. Note that the total gravimetric capacitance predicted numerically featured values comparable to experimental measurements. Finally, an optimum pseudocapacitive layer thickness that maximizes total areal capacitance was identified as a function of scan rate and confirmed by scaling analysis.« less

Microcomputer-Based Programs for Pharmacokinetic Simulations.

ERIC Educational Resources Information Center

Li, Ronald C.; And Others

1995-01-01

Microcomputer software that simulates drug-concentration time profiles based on user-assigned pharmacokinetic parameters such as central volume of distribution, elimination rate constant, absorption rate constant, dosing regimens, and compartmental transfer rate constants is described. The software is recommended for use in undergraduate…

Relating economic conditions to vasectomy and vasectomy reversal frequencies: a multi-institutional study.

PubMed

Sharma, Vidit; Zargaroff, Sherwin; Sheth, Kunj R; Le, Brian V; Dupree, James M; Sandlow, Jay I; Polackwich, A Scott; Hedges, Jason C; Fuchs, Eugene F; Goldstein, Marc; Brannigan, Robert E

2014-06-01

It was theorized that the use of permanent contraceptive methods may vary with economic conditions. We evaluated the relationship between vasectomy/vasectomy reversal frequencies at several large referral centers and national economic indicators during 2 recessions spanning 2001 to 2011. We performed an institutional review board approved, retrospective chart review to identify the number of vasectomies/vasectomy reversals per month at several large referral centers from January 2001 to July 2011. The rates of these procedures were pooled, correlated with national economic data and analyzed in a multivariate linear regression model. A total of 4,599 vasectomies and 1,549 vasectomy reversals were performed at our institutions during the study period. The number of vasectomies per month positively correlated with the unemployment rate (r=0.556, p<0.001) and personal income per capita (r=0.276, p=0.002). The number of reversals per month negatively correlated with the unemployment rate (r=-0.399, p<0.001) and personal income per capita (r=-0.305, p<0.001). Neither vasectomy nor vasectomy reversal frequency significantly correlated with the inflation rate or the S&P 500®. Regression models confirmed that the unemployment rate explained more of the variance in vasectomy/vasectomy reversal frequencies than other indicators. We noted a correlation between the number of vasectomies/vasectomy reversals performed at our institutions and national economic indicators. The strongest association was with the unemployment rate. This points to the importance of financial pressure on family planning decisions. Copyright © 2014 American Urological Association Education and Research, Inc. Published by Elsevier Inc. All rights reserved.

Grammont humeral design versus onlay curved-stem reverse shoulder arthroplasty: comparison of clinical and radiographic outcomes with minimum 2-year follow-up.

PubMed

Merolla, Giovanni; Walch, Gilles; Ascione, Francesco; Paladini, Paolo; Fabbri, Elisabetta; Padolino, Antonio; Porcellini, Giuseppe

2018-04-01

There are few investigations comparing lateralized and medialized reverse total shoulder arthroplasty (RTSA) in patients with cuff tear arthropathy. This study assessed the outcomes of 2 RTSA designs. Sixty-eight consecutive cuff tear arthropathy patients (74 shoulders) with a follow-up of at least 24 months received a Grammont or an onlay curved short-stem humeral component, with or without glenoid lateralization; a cementless humeral stem was implanted in >90%. Clinical outcome measures included active range of motion (anterior and lateral elevation, external and internal rotation), pain, and the Constant-Murley score. Radiologic outcomes included radiolucency, condensation lines, cortical thinning, spot weld, loosening and subsidence, and tuberosity resorption for the humeral component and radiolucency, scapular notching, formation of scapular bone spurs, ossifications, and loosening for the glenoid component. Both prostheses provided significant differences between preoperative and postoperative scores and showed a similar complication rate. Scapular fractures were found only in the patients who received the curved short-stem implant. Glenoid bone grafting did not significantly affect clinical scores. Both implants provided similar postoperative shoulder mobility, even though the lateralized curved stem was associated with higher delta scores for external rotation (P = .002) and lower rates of scapular notching (P = .0003), glenoid radiolucency (P = .016), and humeral bone remodeling (P = .004 and P = .030 for cortical thinning and spot weld, respectively). Medialized and short-stem lateralized RTSA implants provided similar midterm clinical outcomes and range of motion. The curved short stem was associated with higher delta scores for external rotation and a lower rate of radiographic risk factors. Copyright © 2017 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Elsevier Inc. All rights reserved.

Neogene contraction between the San Andreas fault and the Santa Clara Valley, San Francisco Bay region, California

USGS Publications Warehouse

McLaughlin, R.J.; Langenheim, V.E.; Schmidt, K.M.; Jachens, R.C.; Stanley, R.G.; Jayko, A.S.; McDougall, K.A.; Tinsley, J.C.; Valin, Z.C.

1999-01-01

In the southern San Francisco Bay region of California, oblique dextral reverse faults that verge northeastward from the San Andreas fault experienced triggered slip during the 1989 M7.1 Loma Prieta earthquake. The role of these range-front thrusts in the evolution of the San Andreas fault system and the future seismic hazard that they may pose to the urban Santa Clara Valley are poorly understood. Based on recent geologic mapping and geophysical investigations, we propose that the range-front thrust system evolved in conjunction with development of the San Andreas fault system. In the early Miocene, the region was dominated by a system of northwestwardly propagating, basin-bounding, transtensional faults. Beginning as early as middle Miocene time, however, the transtensional faulting was superseded by transpressional NE-stepping thrust and reverse faults of the range-front thrust system. Age constraints on the thrust faults indicate that the locus of contraction has focused on the Monte Vista, Shannon, and Berrocal faults since about 4.8 Ma. Fault slip and fold reconstructions suggest that crustal shortening between the San Andreas fault and the Santa Clara Valley within this time frame is ~21%, amounting to as much as 3.2 km at a rate of 0.6 mm/yr. Rates probably have not remained constant; average rates appear to have been much lower in the past few 100 ka. The distribution of coseismic surface contraction during the Loma Prieta earthquake, active seismicity, late Pleistocene to Holocene fluvial terrace warping, and geodetic data further suggest that the active range-front thrust system includes blind thrusts. Critical unresolved issues include information on the near-surface locations of buried thrusts, the timing of recent thrust earthquake events, and their recurrence in relation to earthquakes on the San Andreas fault.

Assessing Chemical Retention Process Controls in Ponds

NASA Astrophysics Data System (ADS)

Torgersen, T.; Branco, B.; John, B.

2002-05-01

Small ponds are a ubiquitous component of the landscape and have earned a reputation as effective chemical retention devices. The most common characterization of pond chemical retention is the retention coefficient, Ri= ([Ci]inflow-[Ci] outflow)/[Ci]inflow. However, this parameter varies widely in one pond with time and among ponds. We have re-evaluated literature reported (Borden et al., 1998) monthly average retention coefficients for two ponds in North Carolina. Employing a simple first order model that includes water residence time, the first order process responsible for species removal have been separated from the water residence time over which it acts. Assuming the rate constant for species removal is constant within the pond (arguable at least), the annual average rate constant for species removal is generated. Using the annual mean rate constant for species removal and monthly water residence times results in a significantly enhanced predictive capability for Davis Pond during most months of the year. Predictive ability remains poor in Davis Pond during winter/unstratified periods when internal loading of P and N results in low to negative chemical retention. Predictive ability for Piedmont Pond (which has numerous negative chemical retention periods) is improved but not to the same extent as Davis Pond. In Davis Pond, the rate constant for sediment removal (each month) is faster than the rate constant for water and explains the good predictability for sediment retention. However, the removal rate constant for P and N is slower than the removal rate constant for sediment (longer water column residence time for P,N than for sediment). Thus sedimentation is not an overall control on nutrient retention. Additionally, the removal rate constant for P is slower than for TOC (TOC is not the dominate removal process for P) and N is removed slower than P (different in pond controls). For Piedmont Pond, sediment removal rate constants are slower than the removal rate constant for water indicating significant sediment resuspension episodes. It appears that these sediment resuspension events are aperiodic and control the loading and the chemical retention capability of Piedmont Pond for N,P,TOC. These calculated rate constants reflect the differing internal loading processes for each component and suggest means and mechanisms for the use of ponds in water quality management.

Dynamic Characteristics of The DSI-Type Constant-Flow Valves

NASA Astrophysics Data System (ADS)

Kang, Yuan; Hu, Sheng-Yan; Chou, Hsien-Chin; Lee, Hsing-Han

Constant flow valves have been presented in industrial applications or academic studies, which compensate recess pressures of a hydrostatic bearing to resist load fluctuating. The flow rate of constant-flow valves can be constant in spite of the pressure changes in recesses, however the design parameters must be specified. This paper analyzes the dynamic responses of DSI-type constant-flow valves that is designed as double pistons on both ends of a spool with single feedback of working pressure and regulating restriction at inlet. In this study the static analysis presents the specific relationships among design parameters for constant flow rate and the dynamic analyses give the variations around the constant flow rate as the working pressure fluctuates.

Pre-steady-state kinetic studies of redox reactions catalysed by Bacillus subtilis ferredoxin-NADP(+) oxidoreductase with NADP(+)/NADPH and ferredoxin.

PubMed

Seo, Daisuke; Soeta, Takahiro; Sakurai, Hidehiro; Sétif, Pierre; Sakurai, Takeshi

2016-06-01

Ferredoxin-NADP(+) oxidoreductase ([EC1.18.1.2], FNR) from Bacillus subtilis (BsFNR) is a homodimeric flavoprotein sharing structural homology with bacterial NADPH-thioredoxin reductase. Pre-steady-state kinetics of the reactions of BsFNR with NADP(+), NADPH, NADPD (deuterated form) and B. subtilis ferredoxin (BsFd) using stopped-flow spectrophotometry were studied. Mixing BsFNR with NADP(+) and NADPH yielded two types of charge-transfer (CT) complexes, oxidized FNR (FNR(ox))-NADPH and reduced FNR (FNR(red))-NADP(+), both having CT absorption bands centered at approximately 600n m. After mixing BsFNR(ox) with about a 10-fold molar excess of NADPH (forward reaction), BsFNR was almost completely reduced at equilibrium. When BsFNR(red) was mixed with NADP(+), the amount of BsFNR(ox) increased with increasing NADP(+) concentration, but BsFNR(red) remained as the major species at equilibrium even with about 50-fold molar excess NADP(+). In both directions, the hydride-transfer was the rate-determining step, where the forward direction rate constant (~500 s(-1)) was much higher than the reverse one (<10 s(-1)). Mixing BsFd(red) with BsFNR(ox) induced rapid formation of a neutral semiquinone form. This process was almost completed within 1 ms. Subsequently the neutral semiquinone form was reduced to the hydroquinone form with an apparent rate constant of 50 to 70 s(-1) at 10°C, which increased as BsFd(red) increased from 40 to 120 μM. The reduction rate of BsFNR(ox) by BsFd(red) was markedly decreased by premixing BsFNR(ox) with BsFd(ox), indicating that the dissociation of BsFd(ox) from BsFNR(sq) is rate-limiting in the reaction. The characteristics of the BsFNR reactions with NADP(+)/NADPH were compared with those of other types of FNRs. Copyright © 2016 Elsevier B.V. All rights reserved.

Experimental and Estimated Rate Constants for the Reactions of Hydroxyl Radicals with Several Halocarbons

NASA Technical Reports Server (NTRS)

DeMore, W.B.

1996-01-01

Relative rate experiments are used to measure rate constants and temperature dependencies of the reactions of OH with CH3F (41), CH2FCl (31), CH2BrCl (30B1), CH2Br2 (3OB2), CHBr3 (2OB3), CF2BrCHFCl (123aBl(alpha)), and CF2ClCHCl2 (122). Rate constants for additional compounds of these types are estimated using an empirical rate constant estimation method which is based on measured rate constants for a wide range of halocarbons. The experimental data are combined with the estimated and previously reported rate constants to illustrate the effects of F, Cl, and Br substitution on OH rate constants for a series of 19 halomethanes and 25 haloethanes. Application of the estimation technique is further illustrated for some higher hydrofluorocarbons (HFCs), including CHF2CF2CF2CF2H (338pcc), CF3CHFCHFCF2CF3 (43-10mee), CF3CH2CH2CF3 (356ffa), CF3CH2CF2CH2CF3 (458mfcf), CF3CH2CHF2 (245fa), and CF3CH2CF2CH3 (365mfc). The predictions are compared with literature data for these compounds.

Alterations of red blood cell sodium transport during malarial infection

PubMed Central

Dunn, Michael J.

1969-01-01

Previous studies have suggested that malaria induces changes in erythrocytic membrane permeability and susceptibility to osmotic lysis. The present study investigated erythrocytic transport of sodium with cells from Rhesus monkeys infected with Plasmodium knowlesi. Red blood cell sodium concentration was significantly elevated in 37 parasitized animals (21.8±1.2 mM; mean ±SEM), as compared to 23 control animals (10.0±0.38 mM). The cellular sodium increased with the density of parasitemia and the cellular potassium decreased in proportion to the elevation of sodium. Nonparasitized as well as parasitized erythrocytes possessed this abnormality of cation metabolism. Effective chloroquine therapy reversed the changes over a period of 4 days. Active sodium outflux rate constants were depressed in animals with malaria (0.202±0.012), as compared to controls (0.325±0.027). Passive sodium influx rate constants were higher in infected monkeys (0.028±0.002) than in control animals (0.019±0.002). The cross incubation of malarial plasma with normal red blood cells induced a 22% diminution in active sodium outflux but no changes were observed in sodium influx. It is concluded that malaria alters erythrocytic sodium transport in all erythrocytes. The elevated intracellular sodium concentration is the net result of decreased sodium outflux and increased sodium influx. The plasmodium organism or the affected host may produce a circulating substance that is deleterious to erythrocytic membrane cation transport. PMID:4975361

Approximation methods of European option pricing in multiscale stochastic volatility model

NASA Astrophysics Data System (ADS)

Ni, Ying; Canhanga, Betuel; Malyarenko, Anatoliy; Silvestrov, Sergei

2017-01-01

In the classical Black-Scholes model for financial option pricing, the asset price follows a geometric Brownian motion with constant volatility. Empirical findings such as volatility smile/skew, fat-tailed asset return distributions have suggested that the constant volatility assumption might not be realistic. A general stochastic volatility model, e.g. Heston model, GARCH model and SABR volatility model, in which the variance/volatility itself follows typically a mean-reverting stochastic process, has shown to be superior in terms of capturing the empirical facts. However in order to capture more features of the volatility smile a two-factor, of double Heston type, stochastic volatility model is more useful as shown in Christoffersen, Heston and Jacobs [12]. We consider one modified form of such two-factor volatility models in which the volatility has multiscale mean-reversion rates. Our model contains two mean-reverting volatility processes with a fast and a slow reverting rate respectively. We consider the European option pricing problem under one type of the multiscale stochastic volatility model where the two volatility processes act as independent factors in the asset price process. The novelty in this paper is an approximating analytical solution using asymptotic expansion method which extends the authors earlier research in Canhanga et al. [5, 6]. In addition we propose a numerical approximating solution using Monte-Carlo simulation. For completeness and for comparison we also implement the semi-analytical solution by Chiarella and Ziveyi [11] using method of characteristics, Fourier and bivariate Laplace transforms.

Kinetics and Thermodynamics of Watson-Crick Base Pairing Driven DNA Origami Dimerization.

PubMed

Zenk, John; Tuntivate, Chanon; Schulman, Rebecca

2016-03-16

We investigate the kinetics and thermodynamics of DNA origami dimerization using flat rectangle origami components and different architectures of Watson-Crick complementary single-stranded DNA ("sticky end") linking strategies. We systematically vary the number of linkers, the length of the sticky ends on the linker, and linker architecture and measure the corresponding yields as well as forward and reverse reaction rate constants through fluorescence quenching assays. Yields were further verified using atomic force microscopy. We calculate values of H° and ΔS° for various interface designs and find nonlinear van't Hoff behavior, best described by two linear equations, suggesting distinct regimes of dimerization between those with and those without well-formed interfaces. We find that self-assembly reactions can be tuned by manipulating the interface architecture without suffering a loss in yield, even when yield is high, ∼75-80%. We show that the second-order forward reaction rate constant (k(on)) depends on both linker architecture and number of linkers used, with typical values on the order of 10(5)-10(6) (M·s)(-1), values that are similar to those of bimolecular association of small, complementary DNA strands. The k(on) values are generally non-Arrhenius, tending to increase with decreasing temperature. Finally, we use kinetic and thermodynamic information about the optimal linking architecture to extend the system to an infinite, two-component repeating lattice system and show that we can form micron-sized lattices, with well-formed structures up to 8 μm(2).

Kirkendall void formation in reverse step graded Si1-xGex/Ge/Si(001) virtual substrates

NASA Astrophysics Data System (ADS)

Sivadasan, Vineet; Rhead, Stephen; Leadley, David; Myronov, Maksym

2018-02-01

Formation of Kirkendall voids is demonstrated in the Ge underlayer of reverse step graded Si1-xGex/Ge buffer layers grown on Si(001) using reduced pressure chemical vapour deposition (RP-CVD). This phenomenon is seen when the constant composition Si1-xGex layer is grown at high temperatures and for x ≤ 0.7. The density and size of the spherical voids can be tuned by changing Ge content in the Si1-xGex and other growth parameters.

First interactions between hydrogen and stress-induced reverse transformation of Ni-Ti superelastic alloy

NASA Astrophysics Data System (ADS)

Yokoyama, Ken'ichi; Hashimoto, Tatsuki; Sakai, Jun'ichi

2017-11-01

The first dynamic interactions between hydrogen and the stress-induced reverse transformation have been investigated by performing an unloading test on a Ni-Ti superelastic alloy subjected to hydrogen charging under a constant applied strain in the elastic deformation region of the martensite phase. Upon unloading the specimen, charged with a small amount of hydrogen, no change in the behaviour of the stress-induced reverse transformation is observed in the stress-strain curve, although the behaviour of the stress-induced martensite transformation changes. With increasing amount of hydrogen charging, the critical stress for the reverse transformation markedly decreases. Eventually, for a larger amount of hydrogen charging, the reverse transformation does not occur, i.e. there is no recovery of the superelastic strain. The residual martensite phase on the side surface of the unloaded specimen is confirmed by X-ray diffraction. Upon training before the unloading test, the properties of the reverse transformation slightly recover after ageing in air at room temperature. The present study indicates that to change the behaviour of the reverse transformation a larger amount of hydrogen than that for the martensite transformation is necessary. In addition, it is likely that a substantial amount of hydrogen in solid solution more strongly suppresses the reverse transformation than hydrogen trapped at defects, thereby stabilising the martensite phase.

Structure of HIV-1 nonnucleoside reverse transcriptase inhibitors derivatives of N-benzyl-benzimidazole with different substituents in position 4

NASA Astrophysics Data System (ADS)

Ziółkowska, Natasza E.; Michejda, Christopher J.; Bujacz, Grzegorz D.

2010-01-01

The constant development of new drugs against HIV-1 is necessary due to global expansion of AIDS and HIV-1 drug resistance. Nonnucleoside reverse transcriptase inhibitors of HIV-1 (NNRTIs) are potentially effective and nontoxic drugs in AIDS therapy. The crystal structures of six nonnucleoside inhibitors of HIV-1 reverse transcriptase (RT) derivatives of N-benzyl-benzimidazole are reported here. The investigated compounds belong to the group of so called "butterfly like" inhibitors with characteristic two π-electron moieties with an angled orientation. The structural data show the influence of the substituents of the benzimidazole ring on the geometry of the molecule and correlation between the structure of the inhibitor and its biological activity.

How reverse shoulder arthroplasty works.

PubMed

Walker, Matthew; Brooks, Jordan; Willis, Matthew; Frankle, Mark

2011-09-01

The reverse total shoulder arthroplasty was introduced to treat the rotator cuff-deficient shoulder. Since its introduction, an improved understanding of the biomechanics of rotator cuff deficiency and reverse shoulder arthroplasty has facilitated the development of modern reverse arthroplasty designs. We review (1) the basic biomechanical challenges associated with the rotator cuff-deficient shoulder; (2) the biomechanical rationale for newer reverse shoulder arthroplasty designs; (3) the current scientific evidence related to the function and performance of reverse shoulder arthroplasty; and (4) specific technical aspects of reverse shoulder arthroplasty. A PubMed search of the English language literature was conducted using the key words reverse shoulder arthroplasty, rotator cuff arthropathy, and biomechanics of reverse shoulder arthroplasty. Articles were excluded if the content fell outside of the biomechanics of these topics, leaving the 66 articles included in this review. Various implant design factors as well as various surgical implantation techniques affect stability of reverse shoulder arthroplasty and patient function. To understand the implications of individual design factors, one must understand the function of the normal and the cuff-deficient shoulder and coalesce this understanding with the pathology presented by each patient to choose the proper surgical technique for reconstruction. Several basic science and clinical studies improve our understanding of various design factors in reverse shoulder arthroplasty. However, much work remains to further elucidate the performance of newer designs and to evaluate patient outcomes using validated instruments such as the American Society for Elbow Surgery, simple shoulder test, and the Constant-Murley scores.

Design of a reversible single precision floating point subtractor.

PubMed

Anantha Lakshmi, Av; Sudha, Gf

2014-01-04

In recent years, Reversible logic has emerged as a major area of research due to its ability to reduce the power dissipation which is the main requirement in the low power digital circuit design. It has wide applications like low power CMOS design, Nano-technology, Digital signal processing, Communication, DNA computing and Optical computing. Floating-point operations are needed very frequently in nearly all computing disciplines, and studies have shown floating-point addition/subtraction to be the most used floating-point operation. However, few designs exist on efficient reversible BCD subtractors but no work on reversible floating point subtractor. In this paper, it is proposed to present an efficient reversible single precision floating-point subtractor. The proposed design requires reversible designs of an 8-bit and a 24-bit comparator unit, an 8-bit and a 24-bit subtractor, and a normalization unit. For normalization, a 24-bit Reversible Leading Zero Detector and a 24-bit reversible shift register is implemented to shift the mantissas. To realize a reversible 1-bit comparator, in this paper, two new 3x3 reversible gates are proposed The proposed reversible 1-bit comparator is better and optimized in terms of the number of reversible gates used, the number of transistor count and the number of garbage outputs. The proposed work is analysed in terms of number of reversible gates, garbage outputs, constant inputs and quantum costs. Using these modules, an efficient design of a reversible single precision floating point subtractor is proposed. Proposed circuits have been simulated using Modelsim and synthesized using Xilinx Virtex5vlx30tff665-3. The total on-chip power consumed by the proposed 32-bit reversible floating point subtractor is 0.410 W.

Nonadiabatic rate constants for proton transfer and proton-coupled electron transfer reactions in solution: Effects of quadratic term in the vibronic coupling expansion

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

Soudackov, Alexander V.; Hammes-Schiffer, Sharon

2015-11-21

Rate constant expressions for vibronically nonadiabatic proton transfer and proton-coupled electron transfer reactions are presented and analyzed. The regimes covered include electronically adiabatic and nonadiabatic reactions, as well as high-frequency and low-frequency proton donor-acceptor vibrational modes. These rate constants differ from previous rate constants derived with the cumulant expansion approach in that the logarithmic expansion of the vibronic coupling in terms of the proton donor-acceptor distance includes a quadratic as well as a linear term. The analysis illustrates that inclusion of this quadratic term in the framework of the cumulant expansion framework may significantly impact the rate constants at highmore » temperatures for proton transfer interfaces with soft proton donor-acceptor modes that are associated with small force constants and weak hydrogen bonds. The effects of the quadratic term may also become significant in these regimes when using the vibronic coupling expansion in conjunction with a thermal averaging procedure for calculating the rate constant. In this case, however, the expansion of the coupling can be avoided entirely by calculating the couplings explicitly for the range of proton donor-acceptor distances sampled. The effects of the quadratic term for weak hydrogen-bonding systems are less significant for more physically realistic models that prevent the sampling of unphysical short proton donor-acceptor distances. Additionally, the rigorous relation between the cumulant expansion and thermal averaging approaches is clarified. In particular, the cumulant expansion rate constant includes effects from dynamical interference between the proton donor-acceptor and solvent motions and becomes equivalent to the thermally averaged rate constant when these dynamical effects are neglected. This analysis identifies the regimes in which each rate constant expression is valid and thus will be important for future applications to proton transfer and proton-coupled electron transfer in chemical and biological processes.« less

Correlation between cross-bridge kinetics obtained from Trp fluorescence of myofibril suspensions and mechanical studies of single muscle fibers in rabbit psoas.

PubMed

Candau, Robin; Kawai, Masataka

2011-12-01

Our goal is to correlate kinetic constants obtained from fluorescence studies of myofibril suspension with those from mechanical studies of skinned muscle fibers from rabbit psoas. In myofibril studies, the stopped-flow technique with tryptophan fluorescence was used; in muscle fiber studies, tension transients with small amplitude sinusoidal length perturbations were used. All experiments were performed using the equivalent solution conditions (200 mM ionic strength, pH 7.00) at 10°C. The concentration of MgATP was varied to characterize kinetic constants of the ATP binding step 1 (K (1): dissociation constant), the binding induced cross-bridge detachment step 2 (k (2), k (-2): rate constants), and the ATP cleavage step 3 (k (3), k (-3)). In myofibrils we found that K (1) = 0.52 ± 0.08 mM (±95% confidence limits), k (2) = 242 ± 24 s(-1), and k (-2) ≈ 0; in muscle fibers, K (1) = 0.46 ± 0.06 mM, k (2) = 286 ± 32 s(-1), and k (-2) = 57 ± 21 s(-1). From these results, we conclude that myofibrils and muscle fibers exhibit nearly equal ATP binding step, and nearly equal ATP binding induced cross-bridge detachment step. Consequently, there is a good correlation between process C (phase 2 of step analysis) and the cross-bridge detachment step. The reverse detachment step is finite in fibers, but almost absent in myofibrils. We further studied partially cross-linked myofibrils and found little change in steps 2 and 3, indicating that cross-linking does not affect these steps. However, we found that K (1) is 2.5× of native myofibrils, indicating that MgATP binding is weakened by the presence of the extra load. We further studied the phosphate (Pi) effect in myofibrils, and found that Pi is a competitive inhibitor of MgATP, with the inhibitory dissociation constant of ~9 mM. Similar results were also deduced from fiber studies. To characterize the ATP cleavage step in myofibrils, we measured the slow rate constant in fluorescence, and found that k (3) + k (-3) = 16 ± 1 s(-1).

Reversed headspace analysis for characterization, identification, and analysis of solid and liquid matrices: Part I.

PubMed

Markelov, M; Bershevits, O

2006-03-01

This paper offers a methodology of an experimentally simple reversed headspace (RHS) analysis for measuring of matrix effects and their use for identification and characterization of condensed matrices such as pharmaceuticals, polymers, chromatographic packing, etc. applicable for both quality control monitoring and research and development investigation. In RHS methods, the matrix is spiked and equilibrated with a mixture of volatile chemicals containing various functional groups (molecular sensor array or MSA mixture). Headspace chromatograms of the same spikes of a sample and an empty vial are compared. Examination of basic headspace theory shows that matrix specific constants (M), rather than partition coefficients (K), can be calculated from the headspace chromatograms and M=(K-1)xbeta, where beta is a degree of matrix volume change during equilibration. Matrix specific constants can be plotted against any property of chemicals (polarity, dielectric constant, solubility parameter, vapor pressure, etc.) or just against a set of consecutive numbers, each representing a chemical in MSA. This plot is, in a sense, a molecular affinity spectrum (MAS) specific for a given matrix at a given temperature and is independent of an instrument. Changes in MAS that correspond to chemicals with a particular functional group give an insight to the type of differences between matrices and may quantitatively define them.

Nonlinear dielectric effects in liquids: a guided tour

NASA Astrophysics Data System (ADS)

Richert, Ranko

2017-09-01

Dielectric relaxation measurements probe how the polarization of a material responds to the application of an external electric field, providing information on structure and dynamics of the sample. In the limit of small fields and thus linear response, such experiments reveal the properties of the material in the same thermodynamic state it would have in the absence of the external field. At sufficiently high fields, reversible changes in enthalpy and entropy of the system occur even at constant temperature, and these will in turn alter the polarization responses. The resulting nonlinear dielectric effects feature field induced suppressions (saturation) and enhancements (chemical effect) of the amplitudes, as well as time constant shifts towards faster (energy absorption) and slower (entropy reduction) dynamics. This review focuses on the effects of high electric fields that are reversible and observed at constant temperature for single component glass-forming liquids. The experimental challenges involved in nonlinear dielectric experiments, the approaches to separating and identifying the different sources of nonlinear behavior, and the current understanding of how high electric fields affect dielectric materials will be discussed. Covering studies from Debye’s initial approach to the present state-of-the-art, it will be emphasized what insight can be gained from the nonlinear responses that are not available from dielectric relaxation results obtained in the linear regime.

High Pressure Experimental Studies on CuO: Indication of Re-entrant Multiferroicity at Room Temperature

PubMed Central

Jana, Rajesh; Saha, Pinku; Pareek, Vivek; Basu, Abhisek; Kapri, Sutanu; Bhattacharyya, Sayan; Mukherjee, Goutam Dev

2016-01-01

We have carried out detailed experimental investigations on polycrystalline CuO using dielectric constant, dc resistance, Raman spectroscopy and X-ray diffraction measurements at high pressures. Observation of anomalous changes both in dielectric constant and dielectric loss in the pressure range 3.7–4.4 GPa and reversal of piezoelectric current with reversal of poling field direction indicate to a change in ferroelectric order in CuO at high pressures. A sudden jump in Raman integrated intensity of Ag mode at 3.4 GPa and observation of Curie-Weiss type behaviour in dielectric constant below 3.7 GPa lends credibility to above ferroelectric transition. A slope change in the linear behaviour of the Ag mode and a minimum in the FWHM of the same indicate indirectly to a change in magnetic ordering. Since all the previous studies show a strong spin-lattice interaction in CuO, observed change in ferroic behaviour at high pressures can be related to a reentrant multiferroic ordering in the range 3.4 to 4.4 GPa, much earlier than predicted by theoretical studies. We argue that enhancement of spin frustration due to anisotropic compression that leads to change in internal lattice strain brings the multiferroic ordering to room temperature at high pressures. PMID:27530329

Comparative analysis of the photocatalytic reduction of drinking water oxoanions using titanium dioxide.

PubMed

Marks, Randal; Yang, Ting; Westerhoff, Paul; Doudrick, Kyle

2016-11-01

Regulated oxidized pollutants in drinking water can have significant health effects, resulting in the need for ancillary treatment processes. Oxoanions (e.g., nitrate) are one important class of oxidized inorganic ions. Ion exchange and reverse osmosis are often used treatment processes for oxoanions, but these separation processes leave behind a concentrated waste product that still requires treatment or disposal. Photocatalysis has emerged as a sustainable treatment technology capable of catalytically reducing oxoanions directly to innocuous byproducts. Compared with the large volume of knowledge available for photocatalytic oxidation, very little knowledge exists regarding photocatalytic reduction of oxoanion pollutants. This study investigates the reduction of various oxoanions of concern in drinking water (nitrate, nitrite, bromate, perchlorate, chlorate, chlorite, chromate) using a commercial titanium dioxide photocatalyst and a polychromatic light source. Results showed that oxoanions were readily reduced under acidic conditions in the presence of formate, which served as a hole scavenger, with the first-order rate decreasing as follows: bromate > nitrite > chlorate > nitrate > dichromate > perchlorate, corresponding to rate constants of 0.33, 0.080, 0.052, 0.0074, 0.0041, and 0 cm 2 /photons × 10 18 , respectively. Only bromate and nitrite were reduced at neutral pH, with substantially lower rate constants of 0.034 and 0.0021 cm 2 /photons × 10 18 , respectively. No direct relationship between oxoanion physicochemical properties, including electronegativity of central atom, internal bond strength, and polarizability was discovered. However, observations presented herein suggest the presence of kinetic barriers unique to each oxoanion and provides a framework for investigating photocatalytic reduction mechanisms of oxoanions in order to design better photocatalysts and optimize treatment. Copyright © 2016 Elsevier Ltd. All rights reserved.

d-3-Hydroxybutyrate dehydrogenase from Rhodopseudomonas spheroides. Kinetic mechanism from steady-state kinetics of the reaction catalysed by the enzyme in solution and covalently attached to diethylaminoethylcellulose

PubMed Central

Preuveneers, M. J.; Peacock, D.; Crook, E. M.; Clark, J. B.; Brocklehurst, K.

1973-01-01

1. The reversible NAD+-linked oxidation of d-3-hydroxybutyrate to acetoacetate in 0.1m-sodium pyrophosphate buffer, pH8.5, at 25.0°C, catalysed by d-3-hydroxybutyrate dehydrogenase (d-3-hydroxybutyrate–NAD+ oxidoreductase, EC 1.1.1.30), was studied by initial-velocity, dead-end inhibition and product-inhibition analysis. 2. The reactions were carried out on (a) the soluble enzyme from Rhodopseudomonas spheroides and (b) an insoluble derivative of this enzyme prepared by its covalent attachment to DEAE-cellulose by using 2-amino-4,6-dichloro-s-triazine as coupling agent. 3. The insolubilized enzyme preparation contained 5mg of protein/g wet wt. of total material, and when freshly prepared its specific activity was 1.2μmol/min per mg of protein, which is 67% of that of the soluble dialysed enzyme. 4. The reactions catalysed by both the enzyme in solution and the insolubilized enzyme were shown to follow sequential pathways in which the nicotinamide nucleotides bind obligatorily first to the enzyme. Evidence is presented for kinetically significant ternary complexes and that the rate-limiting step(s) of both catalyses probably involves isomerization of the enzyme–nicotinamide nucleotide complexes and/or dissociation of the nicotinamide nucleotides from the enzyme. Both catalyses therefore are probably best described as ordered Bi Bi mechanisms, possibly with multiple enzyme–nicotinamide nucleotide complexes. 5. The kinetic parameters and the calculable rate constants for the catalysis by the soluble enzyme are similar to the corresponding parameters and rate constants for the catalysis by the insolubilized enzyme. PMID:4352835

Kinetic and thermodynamic framework for P4-P6 RNA reveals tertiary motif modularity and modulation of the folding preferred pathway

PubMed Central

Bisaria, Namita; Greenfeld, Max; Limouse, Charles; Pavlichin, Dmitri S.; Mabuchi, Hideo; Herschlag, Daniel

2016-01-01

The past decade has seen a wealth of 3D structural information about complex structured RNAs and identification of functional intermediates. Nevertheless, developing a complete and predictive understanding of the folding and function of these RNAs in biology will require connection of individual rate and equilibrium constants to structural changes that occur in individual folding steps and further relating these steps to the properties and behavior of isolated, simplified systems. To accomplish these goals we used the considerable structural knowledge of the folded, unfolded, and intermediate states of P4-P6 RNA. We enumerated structural states and possible folding transitions and determined rate and equilibrium constants for the transitions between these states using single-molecule FRET with a series of mutant P4-P6 variants. Comparisons with simplified constructs containing an isolated tertiary contact suggest that a given tertiary interaction has a stereotyped rate for breaking that may help identify structural transitions within complex RNAs and simplify the prediction of folding kinetics and thermodynamics for structured RNAs from their parts. The preferred folding pathway involves initial formation of the proximal tertiary contact. However, this preference was only ∼10 fold and could be reversed by a single point mutation, indicating that a model akin to a protein-folding contact order model will not suffice to describe RNA folding. Instead, our results suggest a strong analogy with a modified RNA diffusion-collision model in which tertiary elements within preformed secondary structures collide, with the success of these collisions dependent on whether the tertiary elements are in their rare binding-competent conformations. PMID:27493222

Outcomes of reverse shoulder arthroplasty using a mini 25-mm glenoid baseplate.

PubMed

Athwal, George S; Faber, Kenneth J

2016-01-01

As worldwide use of reverse shoulder arthroplasty (RSA) increases, a range of implant sizes may be required to match regional and ethnic variation in patients' height and bone size. The purpose of this study was to report the outcomes of RSA using a mini 25-mm-diameter glenoid baseplate in smaller patients with rotator cuff arthropathy. Between 2009 and 2012, 28 patients underwent RSA for cuff-tear arthropathy using a 25-mm circular glenoid baseplate (Aequlais Reversed, Tornier, Bloomington, MN, USA). Twenty-four patients were able to return for comprehensive follow-up. The mean height of the entire cohort was 158 ± 10 cm (5 ft. 2 in.). The indication to use a smaller baseplate was a combination of preoperative templating using computed tomography (CT) and intraoperative measurements of glenoid width. At a mean of 36 ± 8 months' follow-up, there were no revisions or glenoid-sided failures. The mean American Shoulder and Elbow Surgeons (ASES) score was 70 ± 10, the Simple Shoulder Test (SST) was 10 ± 2, the Constant was 60 ± 10 and the Disabilities of the Arm, Shoulder and Hand (DASH) was 18 ± 15. Mean active forward elevation was 140 ± 15°, active external rotation was 21 ± 15° and active internal rotation was to the sacroiliac joint. Mean shoulder strength in flexion was 5.2 ± 1.7 kg, in external rotation was 2.9 ± 1.4 kg and in internal rotation was 4.3 ± 1.2 kg. Radiographs demonstrated no evidence of glenoid loosening. There was, however, a 62 % rate of scapular notching. Short-term outcomes of mini 25-mm baseplate RSA in proportionally smaller patients are good and demonstrate implant safety and effectiveness. Scapular notching rates are worrisome, and additional follow-up is necessary to determine if notching is progressive and becomes symptomatic.

Protein-mediated antagonism between HIV reverse transcriptase ligands nevirapine and MgATP.

PubMed

Zheng, Xunhai; Mueller, Geoffrey A; DeRose, Eugene F; London, Robert E

2013-06-18

Nonnucleoside reverse transcriptase inhibitors (NNRTIs) play a central role in the treatment of AIDS, but their mechanisms of action are incompletely understood. The interaction of the NNRTI nevirapine (NVP) with HIV-1 reverse transcriptase (RT) is characterized by a preference for the open conformation of the fingers/thumb subdomains, and a reported variation of three orders of magnitude between the binding affinity of NVP for RT in the presence or absence of primer/template DNA. To investigate the relationship between conformation and ligand binding, we evaluated the use of methionine NMR probes positioned near the tip of the fingers or thumb subdomains. Such probes would be expected to be sensitive to changes in the local environment depending on the fractions of open and closed RT. Comparisons of the NMR spectra of three conservative mutations, I63M, L74M, and L289M, indicated that M63 showed the greatest shift sensitivity to the addition of NVP. The exchange kinetics of the M63 resonance are fast on the chemical shift timescale, but become slow in the presence of NVP due to the slow binding of RT with the inhibitor. The simplest model consistent with this behavior involves a rapid open/closed equilibrium coupled with a slow interaction of the inhibitor with the open conformation. Studies of RT in the presence of both NVP and MgATP indicate a strong negative cooperativity. Binding of MgATP reduces the fraction of RT bound to NVP, as indicated by the intensity of the NVP-perturbed M230 resonance, and enhances the dissociation rate constant of the NVP, resulting in an increase of the open/closed interconversion rate, so that the M63 resonance moves into the fast/intermediate-exchange regime. Protein-mediated interactions appear to explain most of the affinity variation of NVP for RT. Copyright © 2013 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Separation of aromatic carboxylic acids using quaternary ammonium salts on reversed-phase HPLC. 1. Separation behavior of aromatic carboxylic acids

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

Kawamura, K.; Okuwaki, A.; Verheyen, T.

In order to develop separation processes and analytical methods for aromatic carboxylic acids for the coal oxidation products, the separation behavior of aromatic carboxylic acids on a reversed-phase HPLC using eluent containing quaternary ammonium salt has been investigated. The retention mechanism of aromatic carboxylic acids was discussed on the basis of both ion-pair partition model and ion-exchange model. The retention behavior of aromatic carboxylic acids possessing one (or two) carboxylic acid group(s) followed the ion-pair partition model, where linear free energy relationship was observed between the capacity factor and the extraction equilibrium constants of benzoic acid and naphthalene carboxylic acid.more » Besides, the retention behavior followed ion-exchange model with increasing the number of carboxylic acids, where the capacity factor of benzene polycarboxylic acids is proportional to the association constants between aromatic acids and quaternary ammonium ions calculated on the basis of an electrostatic interaction model.« less

Diffusion in Deterministic Interacting Lattice Systems

NASA Astrophysics Data System (ADS)

Medenjak, Marko; Klobas, Katja; Prosen, Tomaž

2017-09-01

We study reversible deterministic dynamics of classical charged particles on a lattice with hard-core interaction. It is rigorously shown that the system exhibits three types of transport phenomena, ranging from ballistic, through diffusive to insulating. By obtaining an exact expressions for the current time-autocorrelation function we are able to calculate the linear response transport coefficients, such as the diffusion constant and the Drude weight. Additionally, we calculate the long-time charge profile after an inhomogeneous quench and obtain diffusive profilewith the Green-Kubo diffusion constant. Exact analytical results are corroborated by Monte Carlo simulations.

Research on the influencing factors of reverse logistics carbon footprint under sustainable development.

PubMed

Sun, Qiang

2017-10-01

With the concerns of ecological and circular economy along with sustainable development, reverse logistics has attracted the attention of enterprise. How to achieve sustainable development of reverse logistics has important practical significance of enhancing low carbon competitiveness. In this paper, the system boundary of reverse logistics carbon footprint is presented. Following the measurement of reverse logistics carbon footprint and reverse logistics carbon capacity is provided. The influencing factors of reverse logistics carbon footprint are classified into five parts such as intensity of reverse logistics, energy structure, energy efficiency, reverse logistics output, and product remanufacturing rate. The quantitative research methodology using ADF test, Johansen co-integration test, and impulse response is utilized to interpret the relationship between reverse logistics carbon footprint and the influencing factors more accurately. This research finds that energy efficiency, energy structure, and product remanufacturing rate are more capable of inhibiting reverse logistics carbon footprint. The statistical approaches will help practitioners in this field to structure their reverse logistics activities and also help academics in developing better decision models to reduce reverse logistics carbon footprint.

GROUND WATER ISSUE - CALCULATION AND USE OF FIRST-ORDER RATE CONSTANTS FOR MONITORED NATURAL ATTENUATION STUDIES

EPA Science Inventory

This issue paper explains when and how to apply first-order attenuation rate constant calculations in monitored natural attenuation (MNA) studies. First-order attenuation rate constant calculations can be an important tool for evaluating natural attenuation processes at ground-wa...

Trends in electron-ion dissociative recombination of benzene analogs with functional group substitutions: Negative Hammett σpara values

NASA Astrophysics Data System (ADS)

Osborne, David; Lawson, Patrick Andrew; Adams, Nigel; Dotan, Itzhak

2014-06-01

An in-depth study of the effects of functional group substitution on benzene's electron-ion dissociative recombination (e-IDR) rate constant has been conducted. The e-IDR rate constants for benzene, biphenyl, toluene, ethylbenzene, anisole, phenol, and aniline have been measured using a Flowing Afterglow equipped with an electrostatic Langmuir probe (FALP). These measurements have been made over a series of temperatures from 300 to 550 K. A relationship between the Hammett σpara values for each compound and rate constant has indicated a trend in the e-IDR rate constants and possibly in their temperature dependence data. The Hammett σpara value is a method to describe the effect a functional group substituted to a benzene ring has upon the reaction rate constant.

Equilibrium muscle cross-bridge behavior. Theoretical considerations.

PubMed Central

Schoenberg, M

1985-01-01

We have developed a model for the equilibrium attachment and detachment of myosin cross-bridges to actin that takes into account the possibility that a given cross-bridge can bind to one of a number of actin monomers, as seems likely, rather than to a site on only a single actin monomer, as is often assumed. The behavior of this multiple site model in response to constant velocity, as well as instantaneous stretches, was studied and the influence of system parameters on the force response explored. It was found that in the multiple site model the detachment rate constant has considerably greater influence on the mechanical response than the attachment rate constant. It is shown that one can obtain information about the detachment rate constants either by examining the relationship between the apparent stiffness and duration of stretch for constant velocity stretches or by examining the force-decay rate constants following an instantaneous stretch. The main effect of the attachment rate constant is to scale the mechanical response by influencing the number of attached cross-bridges. The significance of the modeling for the interpretation of experimental results is discussed. PMID:4041539

Electron-ion dissociative recombination rate constants relevant to the Titan atmosphere and the Interstellar Medium

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

Osborne, David; Lawson, Patrick; Adams, Nigel, E-mail: ngadams@uga.edu

Following the arrival of Cassini at Titan in 2004, the Titan atmosphere has been shown to contain large complex polycyclic-aromatic hydrocarbons. Since Cassini has provided a great deal of data, there exists a need for kinetic rate data to help with modeling this atmosphere. One type of kinetic data needed is electron-ion dissociative recombination (e-IDR) rate constants. These data are not readily available for larger compounds, such as naphthalene, or oxygen containing compounds, such as 1,4 dioxane or furan. Here, the rate constants for naphthalene, 1,4 dioxane, and furan have been measured and their temperature dependencies are determined when possible,more » using the University of Georgia's Variable Temperature Flowing Afterglow. The rate constants are compared with those previously published for other compounds; these show trends which illustrate the effects which multi-rings and oxygen heteroatoms substitutions have upon e-IDR rate constants.« less

Electron-ion dissociative recombination rate constants relevant to the Titan atmosphere and the Interstellar Medium

NASA Astrophysics Data System (ADS)

Osborne, David; Lawson, Patrick; Adams, Nigel

2014-01-01

Following the arrival of Cassini at Titan in 2004, the Titan atmosphere has been shown to contain large complex polycyclic-aromatic hydrocarbons. Since Cassini has provided a great deal of data, there exists a need for kinetic rate data to help with modeling this atmosphere. One type of kinetic data needed is electron-ion dissociative recombination (e-IDR) rate constants. These data are not readily available for larger compounds, such as naphthalene, or oxygen containing compounds, such as 1,4 dioxane or furan. Here, the rate constants for naphthalene, 1,4 dioxane, and furan have been measured and their temperature dependencies are determined when possible, using the University of Georgia's Variable Temperature Flowing Afterglow. The rate constants are compared with those previously published for other compounds; these show trends which illustrate the effects which multi-rings and oxygen heteroatoms substitutions have upon e-IDR rate constants.

Global and regional drivers of accelerating CO2 emissions

PubMed Central

Raupach, Michael R.; Marland, Gregg; Ciais, Philippe; Le Quéré, Corinne; Canadell, Josep G.; Klepper, Gernot; Field, Christopher B.

2007-01-01

CO2 emissions from fossil-fuel burning and industrial processes have been accelerating at a global scale, with their growth rate increasing from 1.1% y−1 for 1990–1999 to >3% y−1 for 2000–2004. The emissions growth rate since 2000 was greater than for the most fossil-fuel intensive of the Intergovernmental Panel on Climate Change emissions scenarios developed in the late 1990s. Global emissions growth since 2000 was driven by a cessation or reversal of earlier declining trends in the energy intensity of gross domestic product (GDP) (energy/GDP) and the carbon intensity of energy (emissions/energy), coupled with continuing increases in population and per-capita GDP. Nearly constant or slightly increasing trends in the carbon intensity of energy have been recently observed in both developed and developing regions. No region is decarbonizing its energy supply. The growth rate in emissions is strongest in rapidly developing economies, particularly China. Together, the developing and least-developed economies (forming 80% of the world's population) accounted for 73% of global emissions growth in 2004 but only 41% of global emissions and only 23% of global cumulative emissions since the mid-18th century. The results have implications for global equity. PMID:17519334

Well hydraulics in pumping tests with exponentially decayed rates of abstraction in confined aquifers

NASA Astrophysics Data System (ADS)

Wen, Zhang; Zhan, Hongbin; Wang, Quanrong; Liang, Xing; Ma, Teng; Chen, Chen

2017-05-01

Actual field pumping tests often involve variable pumping rates which cannot be handled by the classical constant-rate or constant-head test models, and often require a convolution process to interpret the test data. In this study, we proposed a semi-analytical model considering an exponentially decreasing pumping rate started at a certain (higher) rate and eventually stabilized at a certain (lower) rate for cases with or without wellbore storage. A striking new feature of the pumping test with an exponentially decayed rate is that the drawdowns will decrease over a certain period of time during intermediate pumping stage, which has never been seen before in constant-rate or constant-head pumping tests. It was found that the drawdown-time curve associated with an exponentially decayed pumping rate function was bounded by two asymptotic curves of the constant-rate tests with rates equaling to the starting and stabilizing rates, respectively. The wellbore storage must be considered for a pumping test without an observation well (single-well test). Based on such characteristics of the time-drawdown curve, we developed a new method to estimate the aquifer parameters by using the genetic algorithm.

Impact of uncertainties in inorganic chemical rate constants on tropospheric composition and ozone radiative forcing

NASA Astrophysics Data System (ADS)

Newsome, Ben; Evans, Mat

2017-12-01

Chemical rate constants determine the composition of the atmosphere and how this composition has changed over time. They are central to our understanding of climate change and air quality degradation. Atmospheric chemistry models, whether online or offline, box, regional or global, use these rate constants. Expert panels evaluate laboratory measurements, making recommendations for the rate constants that should be used. This results in very similar or identical rate constants being used by all models. The inherent uncertainties in these recommendations are, in general, therefore ignored. We explore the impact of these uncertainties on the composition of the troposphere using the GEOS-Chem chemistry transport model. Based on the Jet Propulsion Laboratory (JPL) and International Union of Pure and Applied Chemistry (IUPAC) evaluations we assess the influence of 50 mainly inorganic rate constants and 10 photolysis rates on tropospheric composition through the use of the GEOS-Chem chemistry transport model. We assess the impact on four standard metrics: annual mean tropospheric ozone burden, surface ozone and tropospheric OH concentrations, and tropospheric methane lifetime. Uncertainty in the rate constants for NO2 + OH →M HNO3 and O3 + NO → NO2 + O2 are the two largest sources of uncertainty in these metrics. The absolute magnitude of the change in the metrics is similar if rate constants are increased or decreased by their σ values. We investigate two methods of assessing these uncertainties, addition in quadrature and a Monte Carlo approach, and conclude they give similar outcomes. Combining the uncertainties across the 60 reactions gives overall uncertainties on the annual mean tropospheric ozone burden, surface ozone and tropospheric OH concentrations, and tropospheric methane lifetime of 10, 11, 16 and 16 %, respectively. These are larger than the spread between models in recent model intercomparisons. Remote regions such as the tropics, poles and upper troposphere are most uncertain. This chemical uncertainty is sufficiently large to suggest that rate constant uncertainty should be considered alongside other processes when model results disagree with measurement. Calculations for the pre-industrial simulation allow a tropospheric ozone radiative forcing to be calculated of 0.412 ± 0.062 W m-2. This uncertainty (13 %) is comparable to the inter-model spread in ozone radiative forcing found in previous model-model intercomparison studies where the rate constants used in the models are all identical or very similar. Thus, the uncertainty of tropospheric ozone radiative forcing should expanded to include this additional source of uncertainty. These rate constant uncertainties are significant and suggest that refinement of supposedly well-known chemical rate constants should be considered alongside other improvements to enhance our understanding of atmospheric processes.

Special feature of kinetics of ZcE isomerization of β-N-methylaminovinyl trifluoromethyl ketone in Ar matrix exposed to UV radiation and spontaneous E⇌Z isomerization of α-methyl-β-N-methylaminovinyl trifluoromethyl ketone.

PubMed

Vdovenko, Sergey I; Gerus, Igor I; Pagacz-Kostrzewa, Magdalena; Wierzejewska, Maria; Zhuk, Yuri I; Kukhar, Valery P

2018-06-15

Although it is well known that reactivity of α,β-unsaturated enaminoketones is closely associated with spatial and electronic structure but until now little attention was devoted to quantitative investigation of interconversion of different stereoisomeric forms of enaminoketones. In present work we studied peculiarities of kinetics of Z⇌E isomerization of enaminoketone 4-(N-methylamino)-1,1,1-trifluorobut-3-en-2-one F 3 C-COCHCHNH(CH 3 ) (1) in Ar-matrix exposed to UV-radiation (λ=340nm) with IR Fourier and 2D correlation spectroscopy and we found that Z-s-Z-s-trans isomer transforms primarily into two E-isomers, E-s-E-s-trans and E-s-Z-s-trans which further turn into the E-s-E-s-cis and E-s-Z-s-cis conformers all interconversion rate constants being comparable in magnitude. Along with this process long-term exposure to the UV-radiation results in proton transfer from nitrogen of methylamino group to carbonyl oxygen with simultaneous isomerization of 'cyclic' iminoenol form into 'linear'one. In solution of enaminoketone 4-(N-methylamino)-1,1,1-trifluoro-3-methylbut-3-en-2-one F 3 C-CO-C(CH 3 )CH-NH(CH 3 ) (2) we observed reversed process, namely, spontaneous interconversion of the E-s-E-s-trans and E-s-Z-s-trans conformers into the Z-s-Z-trans isomer. It was found that rate constants of the dimeric forms of the E-s-E-s-trans and E-s-Z-s-trans conformers are higher than those of the monomers and are independent on total enaminoketone concentration. Addition of highly polar HMPA promotes proton transfer from nitrogen to oxygen in the Z-s-Z-s-trans isomer of 2 with subsequent isomerization into the linear imino-enol product but the rate constant of this transformation is ten-fold smaller than that for 1 in the Ar matrix exposed to UV radiation. Copyright © 2018 Elsevier B.V. All rights reserved.

Modelling Pre-eruptive Progressive Damage in Basaltic Volcanoes: Consequences for the Pre-eruptive Process

NASA Astrophysics Data System (ADS)

Got, J. L.; Amitrano, D.; Carrier, A.; Marsan, D.; Jouanne, F.; Vogfjord, K. S.

2017-12-01

At Grimsvötn volcano, high-quality earthquake and continuous GPS data were recorded by the Icelandic Meteorological Office during its 2004-2011 inter-eruptive period and exhibited remarkable patterns : acceleration of the cumulated earthquake number, and a 2-year exponential decrease in displacement rate followed by a 4-year constant inflation rate. We proposed a model with one magma reservoir in a non-linear elastic damaging edifice, with incompressible magma and a constant pressure at the base of the magma conduit. We first modelled seismicity rate and damage as a function of time, and show that Kachanov's elastic brittle damage law may be used to express the decrease of the effective shear modulus with time. We then derived simple analytical expressions for the magma reservoir overpressure and the surface displacement as a function of time. We got a very good fit of the seismicity and surface displacement data by adjusting only three phenomenological parameters and computed magma reservoir overpressure, magma flow and strain power as a function of time. Overpressure decrease is controlled by damage and shear modulus decrease. Displacement increases, although overpressure is decreasing, because shear modulus decreases more than overpressure. Normalized strain power reaches a maximum 0.25 value. This maximum is a physical limit, after which the elasticity laws are no longer valid, earthquakes cluster, cumulative number of earthquakes departs from the model. State variable extrema provide four reference times that may be used to assess the mechanical state and dynamics of the volcanic edifice. We also performed the spatial modelling of the progressive damage and strain localization around a pressurized magma reservoir. We used Kachanov's damage law and finite element modelling of an initially elastic volcanic edifice pressurized by a spherical magma reservoir, with a constant pressure in the reservoir and various external boundary conditions. At each node of the model, Young's modulus is decreased if deviatoric stress locally reaches the Mohr-Coulomb plastic threshold. For a compressive horizontal stress, the result shows a complex strain localization pattern, showing reverse and normal faulting very similar to what is obtained from analog modelling and observed at volcanic resurgent domes.

Application of an Artificial Neural Network to the Prediction of OH Radical Reaction Rate Constants for Evaluating Global Warming Potential.

PubMed

Allison, Thomas C

2016-03-03

Rate constants for reactions of chemical compounds with hydroxyl radical are a key quantity used in evaluating the global warming potential of a substance. Experimental determination of these rate constants is essential, but it can also be difficult and time-consuming to produce. High-level quantum chemistry predictions of the rate constant can suffer from the same issues. Therefore, it is valuable to devise estimation schemes that can give reasonable results on a variety of chemical compounds. In this article, the construction and training of an artificial neural network (ANN) for the prediction of rate constants at 298 K for reactions of hydroxyl radical with a diverse set of molecules is described. Input to the ANN consists of counts of the chemical bonds and bends present in the target molecule. The ANN is trained using 792 (•)OH reaction rate constants taken from the NIST Chemical Kinetics Database. The mean unsigned percent error (MUPE) for the training set is 12%, and the MUPE of the testing set is 51%. It is shown that the present methodology yields rate constants of reasonable accuracy for a diverse set of inputs. The results are compared to high-quality literature values and to another estimation scheme. This ANN methodology is expected to be of use in a wide range of applications for which (•)OH reaction rate constants are required. The model uses only information that can be gathered from a 2D representation of the molecule, making the present approach particularly appealing, especially for screening applications.

Modern Chemical Technology, Volume 7.

ERIC Educational Resources Information Center

Pecsok, Robert L.; Chapman, Kenneth

This volume is one of the series for the Chemical Technician Curriculum Project (ChemTeC) of the American Chemical Society funded by the National Science Foundation. It consists of discussions, exercises, and experiments on the following topics: the nature of reversible processes, equilibrium constants, variable reaction tendencies, practical…

A Computational Framework for Analyzing Stochasticity in Gene Expression

PubMed Central

Sherman, Marc S.; Cohen, Barak A.

2014-01-01

Stochastic fluctuations in gene expression give rise to distributions of protein levels across cell populations. Despite a mounting number of theoretical models explaining stochasticity in protein expression, we lack a robust, efficient, assumption-free approach for inferring the molecular mechanisms that underlie the shape of protein distributions. Here we propose a method for inferring sets of biochemical rate constants that govern chromatin modification, transcription, translation, and RNA and protein degradation from stochasticity in protein expression. We asked whether the rates of these underlying processes can be estimated accurately from protein expression distributions, in the absence of any limiting assumptions. To do this, we (1) derived analytical solutions for the first four moments of the protein distribution, (2) found that these four moments completely capture the shape of protein distributions, and (3) developed an efficient algorithm for inferring gene expression rate constants from the moments of protein distributions. Using this algorithm we find that most protein distributions are consistent with a large number of different biochemical rate constant sets. Despite this degeneracy, the solution space of rate constants almost always informs on underlying mechanism. For example, we distinguish between regimes where transcriptional bursting occurs from regimes reflecting constitutive transcript production. Our method agrees with the current standard approach, and in the restrictive regime where the standard method operates, also identifies rate constants not previously obtainable. Even without making any assumptions we obtain estimates of individual biochemical rate constants, or meaningful ratios of rate constants, in 91% of tested cases. In some cases our method identified all of the underlying rate constants. The framework developed here will be a powerful tool for deducing the contributions of particular molecular mechanisms to specific patterns of gene expression. PMID:24811315

Class Projects in Physical Organic Chemistry: The Hydrolysis of Aspirin

ERIC Educational Resources Information Center

Marrs, Peter S.

2004-01-01

An exercise that provides a hands-on demonstration of the hydrolysis of aspirin is presented. The key to understanding the hydrolysis is recognizing that all six process may occur simultaneously and that the observed rate constant is the sum of the rate constants that one rate constant dominates the overall process.

Two-stage reimplantation for treating prosthetic shoulder infections.

PubMed

Sabesan, Vani J; Ho, Jason C; Kovacevic, David; Iannotti, Joseph P

2011-09-01

Two-stage reimplantation for prosthetic joint infection reportedly has the lowest risk for recurrent infection. Most studies to date have evaluated revision surgery for infection using an anatomic prosthetic. As compared with anatomic prostheses, reverse total shoulder arthroplasty is reported to have a higher rate of infection. We determined reinfection rates, functional improvement, types and rates of complications, and influence of rotator cuff tissue on function for two-stage reimplantation for prosthetic joint infection treated with reverse shoulder arthroplasty. We retrospectively reviewed 27 patients treated with a two-stage reimplantation for prosthetic shoulder infection using a uniform protocol for management of infection; of these, 17 had reverse shoulder arthroplasty at second-stage surgery. Types of organisms cultured, recurrence rates, complications, function, and radiographic followup were reviewed for all patients. One of the 17 patients had recurrence of infection. The mean (± SD) Penn shoulder scores for patients treated with reverse shoulder arthroplasty improved from 24.9 ± 22.3 to 66.4 ± 20.8. The average motion at last followup was 123° ± 33° of forward flexion and 26° ± 8° of external rotation in patients treated with a reverse shoulder arthroplasty. The major complication rate was 35% in reverse shoulder arthroplasty, with five dislocations and one reinfection. There was no difference in final Penn score between patients with and without external rotation weakness. Shoulder function and pain improved in patients treated with a second-stage reimplantation of a reverse prosthesis and the reinfection rate was low. Level IV, case series. See Guidelines for Authors for a complete description of levels of evidence.

Quantum calculations of the rate constant for the O(3P)+HCl reaction on new ab initio 3A″ and 3A' surfaces

NASA Astrophysics Data System (ADS)

Xie, Tiao; Bowman, Joel M.; Peterson, K. A.; Ramachandran, B.

2003-11-01

We report the thermal rate constant of the O(3P)+HCl→OH+Cl reaction calculated from 200 to 3200 K, using new fits to extensive ab initio calculations [B. Ramachandran and K. A. Peterson, J. Chem. Phys. 119, 9590 (2003), preceding paper]. The rate constants are obtained for both the 3A″ and 3A' surfaces using exact quantum reactive scattering calculations for selected values of the total angular momentum and the J-shifting approximation for both the 3A″ and 3A' surfaces. The results are compared with the ICVT/μOMT rate constants calculated by the POLYRATE program and all available experimental data. Other related high-energy reaction channels are also studied qualitatively for their contribution to the total thermal rate constant at high temperature.

Inflation with a constant rate of roll

NASA Astrophysics Data System (ADS)

Motohashi, Hayato; Starobinsky, Alexei A.; Yokoyama, Jun'ichi

2015-09-01

We consider an inflationary scenario where the rate of inflaton roll defined by ̈phi/H dot phi remains constant. The rate of roll is small for slow-roll inflation, while a generic rate of roll leads to the interesting case of 'constant-roll' inflation. We find a general exact solution for the inflaton potential required for such inflaton behaviour. In this model, due to non-slow evolution of background, the would-be decaying mode of linear scalar (curvature) perturbations may not be neglected. It can even grow for some values of the model parameter, while the other mode always remains constant. However, this always occurs for unstable solutions which are not attractors for the given potential. The most interesting particular cases of constant-roll inflation remaining viable with the most recent observational data are quadratic hilltop inflation (with cutoff) and natural inflation (with an additional negative cosmological constant). In these cases even-order slow-roll parameters approach non-negligible constants while the odd ones are asymptotically vanishing in the quasi-de Sitter regime.

Temperature-Dependent Rate Constants and Substituent Effects for the Reactions of Hydroxyl Radicals With Three Partially Fluorinated Ethers

NASA Technical Reports Server (NTRS)

Hsu, K.-J.; DeMore, W. B.

1995-01-01

Rate constants and temperature dependencies for the reactions of OH with CF3OCH3 (HFOC-143a), CF2HOCF2H (HFOC-134), and CF3OCF2H (HFOC-125) were studied using a relative rate technique in the temperature range 298-393 K. The following absolute rate constants were derived: HFOC-143a, 1.9E-12 exp(-1555/T); HFOC-134, 1.9E-12 exp(-2006/T); HFOC-125, 4.7E-13 exp(-2095/T). Units are cm(exp 3)molecule(exp -1) s(exp -1). Substituent effects on OH abstraction rate constants are discussed, and it is shown that the CF3O group has an effect on the OH rate constants similar to that of a fluorine atom. The effects are related to changes in the C-H bond energies of the reactants (and thereby the activation energies) rather than changes in the preexponential factors. On the basis of a correlation of rate constants with bond energies, the respective D(C-H) bond strengths in the three ethers are found to be 102, 104, and 106 kcal/mol, with an uncertainty of about 1 kcal/mol.

12 CFR Appendix K to Part 226 - Total Annual Loan Cost Rate Computations for Reverse Mortgage Transactions

Code of Federal Regulations, 2011 CFR

2011-01-01

... Reverse Mortgage Transactions K Appendix K to Part 226 Banks and Banking FEDERAL RESERVE SYSTEM (CONTINUED) BOARD OF GOVERNORS OF THE FEDERAL RESERVE SYSTEM TRUTH IN LENDING (REGULATION Z) Pt. 226, App. K Appendix K to Part 226—Total Annual Loan Cost Rate Computations for Reverse Mortgage Transactions (a...

12 CFR Appendix K to Part 226 - Total Annual Loan Cost Rate Computations for Reverse Mortgage Transactions

Code of Federal Regulations, 2012 CFR

2012-01-01

... Reverse Mortgage Transactions K Appendix K to Part 226 Banks and Banking FEDERAL RESERVE SYSTEM (CONTINUED) BOARD OF GOVERNORS OF THE FEDERAL RESERVE SYSTEM TRUTH IN LENDING (REGULATION Z) Pt. 226, App. K Appendix K to Part 226—Total Annual Loan Cost Rate Computations for Reverse Mortgage Transactions (a...

12 CFR Appendix K to Part 226 - Total Annual Loan Cost Rate Computations for Reverse Mortgage Transactions

Code of Federal Regulations, 2010 CFR

2010-01-01

... Reverse Mortgage Transactions K Appendix K to Part 226 Banks and Banking FEDERAL RESERVE SYSTEM (CONTINUED) BOARD OF GOVERNORS OF THE FEDERAL RESERVE SYSTEM TRUTH IN LENDING (REGULATION Z) Pt. 226, App. K Appendix K to Part 226—Total Annual Loan Cost Rate Computations for Reverse Mortgage Transactions (a...

Optically reversible electrical soft-breakdown in wide-bandgap oxides—A factorial study

NASA Astrophysics Data System (ADS)

Zhou, Y.; Ang, D. S.; Kalaga, P. S.

2018-04-01

In an earlier work, we found that an electrical soft-breakdown region in wide-bandgap oxides, such as hafnium dioxide, silicon dioxide, etc., could be reversed when illuminated by white light. The effect is evidenced by a decrease in the breakdown leakage current, termed as a negative photoconductivity response. This finding raises the prospect for optical sensing applications based on these traditionally non-photo-responsive but ubiquitous oxide materials. In this study, we examine the statistical distribution for the rate of breakdown reversal as well as the influence of factors such as wavelength, light intensity, oxide stoichiometry (or oxygen content) and temperature on the reversal rate. The rate of breakdown reversal is shown to be best described by the lognormal distribution. Light in the range of ˜400-700 nm is found to have relatively little influence on the reversal rate. On the other hand, light intensity, oxygen content and temperature, each of them has a clear impact; a stronger light intensity, an oxide that is richer in oxygen content and a reduced temperature all speed up the reversal process substantially. These experimental results are consistent with the proposed phenomenological redox model involving photo-assisted recombination of the surrounding oxygen interstitials with vacancy defects in the breakdown path.

Reaction of SO2 with OH in the atmosphere.

PubMed

Long, Bo; Bao, Junwei Lucas; Truhlar, Donald G

2017-03-15

The OH + SO 2 reaction plays a critical role in understanding the oxidation of SO 2 in the atmosphere, and its rate constant is critical for clarifying the fate of SO 2 in the atmosphere. The rate constant of the OH + SO 2 reaction is calculated here by using beyond-CCSDT correlation energy calculations for a benchmark, validated density functional methods for direct dynamics, canonical variational transition state theory with anharmonicity and multidimensional tunneling for the high-pressure rate constant, and system-specific quantum RRK theory for pressure effects; the combination of these methods can compete in accuracy with experiments. There has been a long-term debate in the literature about whether the OH + SO 2 reaction is barrierless, but our calculations indicate a positive barrier with an transition structure that has an enthalpy of activation of 0.27 kcal mol -1 at 0 K. Our results show that the high-pressure limiting rate constant of the OH + SO 2 reaction has a positive temperature dependence, but the rate constant at low pressures has a negative temperature dependence. The computed high-pressure limiting rate constant at 298 K is 1.25 × 10 -12 cm 3 molecule -1 s -1 , which agrees excellently with the value (1.3 × 10 -12 cm 3 molecule -1 s -1 ) recommended in the most recent comprehensive evaluation for atmospheric chemistry. We show that the atmospheric lifetime of SO 2 with respect to oxidation by OH depends strongly on altitude (in the range 0-50 km) due to the falloff effect. We introduce a new interpolation procedure for fitting the combined temperature and pressure dependence of the rate constant, and it fits the calculated rate constants over the whole range with a mean unsigned error of only 7%. The present results provide reliable kinetics data for this specific reaction, and also they demonstrate convenient theoretical methods that can be reliable for predicting rate constants of other gas-phase reactions.

Chiral cavity ring down polarimetry: Chirality and magnetometry measurements using signal reversals.

PubMed

Bougas, Lykourgos; Sofikitis, Dimitris; Katsoprinakis, Georgios E; Spiliotis, Alexandros K; Tzallas, Paraskevas; Loppinet, Benoit; Rakitzis, T Peter

2015-09-14

We present the theory and experimental details for chiral-cavity-ring-down polarimetry and magnetometry, based on ring cavities supporting counterpropagating laser beams. The optical-rotation symmetry is broken by the presence of both chiral and Faraday birefringence, giving rise to signal reversals which allow rapid background subtractions. We present the measurement of the specific rotation at 800 nm of vapors of α-pinene, 2-butanol, and α-phellandrene, the measurement of optical rotation of sucrose solutions in a flow cell, the measurement of the Verdet constant of fused silica, and measurements and theoretical treatment of evanescent-wave optical rotation at a prism surface. Therefore, these signal-enhancing and signal-reversing methods open the way for ultrasensitive polarimetry measurements in gases, liquids and solids, and at surfaces.

An Additional Method for Analyzing the Reversible Inhibition of an 
Enzyme Using Acid Phosphatase as a Model.

PubMed

Baumhardt, Jordan M; Dorsey, Benjamin M; McLauchlan, Craig C; Jones, Marjorie A

2015-08-01

Using wheat germ acid phosphatase and sodium orthovanadate as a competitive inhibitor, a novel method for analyzing reversible inhibition was carried out. Our alternative approach involves plotting the initial velocity at which product is formed as a function of the ratio of substrate concentration to inhibitor concentration at a constant enzyme concentration and constant assay conditions. The concept of initial concentrations driving equilibrium leads to the chosen axes. Three apparent constants can be derived from this plot: K max , K min , and K inflect . K max and K min represent the substrate to inhibitor concentration ratio for complete inhibition and minimal inhibition, respectively. K inflect represents the substrate to inhibitor concentration ratio at which the enzyme-substrate complex is equal to the inhibitory complex. These constants can be interpolated from the graph or calculated using the first and second derivative of the plot. We conclude that a steeper slope and a shift of the line to the right (increased x-axis values) would indicate a better inhibitor. Since initial velocity is not a linear function of the substrate/inhibitor ratio, this means that inhibition changes more quickly with the change in the [S]/ [I] ratio. When preincubating the enzyme with substrate before the addition of inhibitor, preincubating the enzyme with inhibitor before the addition of substrate or with concurrent addition of both substrate and inhibitor, modest changes in the slopes and y-intercepts were obtained. This plot appears useful for known competitive and non-competitive inhibitors and may have general applicability.

Rate constant for the fraction of atomic chlorine with formaldehyde from 200 to 500K

NASA Technical Reports Server (NTRS)

Michael, J. V.; Nava, D. F.; Payne, W. A.; Stief, L. J.

1978-01-01

A flash photolysis - resonance fluorescence technique was used to measure rate constant. The results were independent of substantial variations in H2CO, total pressure (Ar), and flash intensity (i.e., initial Cl). The rate constant was shown to be invariant with temperature, the best representation for this temperature range being K = (7.48 + or - 0.50) x 10 to the minus 11 power cu cm molecule-1 s-1 where the error is one standard deviation. The rate constant is theoretically discussed and the potential importance of the reaction in stratospheric chemistry is considered.

Substrate specificity of sheep liver sorbitol dehydrogenase.

PubMed Central

Lindstad, R I; Köll, P; McKinley-McKee, J S

1998-01-01

The substrate specificity of sheep liver sorbitol dehydrogenase has been studied by steady-state kinetics over the range pH 7-10. Sorbitol dehydrogenase stereo-selectively catalyses the reversible NAD-linked oxidation of various polyols and other secondary alcohols into their corresponding ketones. The kinetic constants are given for various novel polyol substrates, including L-glucitol, L-mannitol, L-altritol, D-altritol, D-iditol and eight heptitols, as well as for many aliphatic and aromatic alcohols. The maximum velocities (kcat) and the substrate specificity-constants (kcat/Km) are positively correlated with increasing pH. The enzyme-catalysed reactions occur by a compulsory ordered kinetic mechanism with the coenzyme as the first, or leading, substrate. With many substrates, the rate-limiting step for the overall reaction is the enzyme-NADH product dissociation. However, with several substrates there is a transition to a mechanism with partial rate-limitation at the ternary complex level, especially at low pH. The kinetic data enable the elucidation of new empirical rules for the substrate specificity of sorbitol dehydrogenase. The specificity-constants for polyol oxidation vary as a function of substrate configuration with D-xylo> D-ribo > L-xylo > D-lyxo approximately L-arabino > D-arabino > L-lyxo. Catalytic activity with a polyol or an aromatic substrate and various 1-deoxy derivatives thereof varies with -CH2OH > -CH2NH2 > -CH2OCH3 approximately -CH3. The presence of a hydroxyl group at each of the remaining chiral centres of a polyol, apart from the reactive C2, is also nonessential for productive ternary complex formation and catalysis. A predominantly nonpolar enzymic epitope appears to constitute an important structural determinant for the substrate specificity of sorbitol dehydrogenase. The existence of two distinct substrate binding regions in the enzyme active site, along with that of the catalytic zinc, is suggested to account for the lack of stereospecificity at C2 in some polyols. PMID:9461546

Reverse shoulder arthroplasty due to glenoid bone defects.

PubMed

Díaz Miñarro, J C; Izquierdo Fernández, A; Muñoz Reyes, F; Carpintero Lluch, R; Uceda Carrascosa, P; Muñoz Luna, F; López Jordán, A; Carpintero Benítez, P

2016-01-01

Reverse shoulder arthroplasty is becoming a useful tool for many diseases of the shoulder. Any severe glenoid bone defect may affect the fixing of the glenoid component. The aim of this paper is to evaluate the medium-term outcomes of reverse shoulder arthroplasty associated with a glenoplasty. A retrospective study was conducted on 5 patients from our hospital, selected due to glenoid defects of different etiology. All of them where treated with reverse shoulder arthroplasty associated with glenoplasty with bone graft. The minimum follow-up was one year (mean 30.4 months). All grafts were radiologically integrated, with no signs of resorption or necrosis being observed. At 12 months, the Constant score was 66.75 and the mean EVA score was 1. Glenoplasty surgery is technically demanding for restoring original bone size in patients with glenoid structural defects, enabling a reverse shoulder arthroplasty to be implanted. Thus improving both the function and clinical outcomes in selected patients with glenohumeral pathology and providing them with a solution. Copyright © 2014 SECOT. Published by Elsevier Espana. All rights reserved.

Combined Thermochromic And Plasmonic: Optical Responses In Novel Nanocomposite Au-VO2 Films Prepared By RF Inverted Cylindrical Magnetron Sputtering

NASA Astrophysics Data System (ADS)

Kana, J. B. Kana; Ndjaka, J. M.; Manyala, N.; Nemraoui, O.; Beye, A. C.; Maaza, M.

2008-09-01

We prepared gold/Vanadium dioxide nanocomposites thin films by the rf reactive inverted cylindrical magnetron sputtering (ICMS) for the first time and report their enhanced surface plasmon resonance (SPR) tunable shift reversibility. ICMS has been attracting much attention for its ability for uniform coating of three-dimensional objects and high-rate deposition of dielectric materials. To investigate the optical properties of gold nanoparticles embedded in an active matrix (VO2) composite film was synthesized on corning glass substrates for several substrate temperatures ranging from 400 °C to 600 °C. The X-ray diffraction results demonstrated that the Au and VO2 were well crystallized. The optical transmission properties were measured from 300nm to 1100nm and the absorption peak due to the surface plasmon resonance (SPR) of Au nanoparticles were observed. Under external temperature stimuli, the tunable reversibility of the SPR shift was observed when the nanocomposites temperature varies from 20 °C to 100 °C. The enhancement of this shift of SPR was observed as the substrate temperature increases and it was found that the shift of SPR increased rapidly with increasing substrate temperature but then remained constant at ˜57 nm for substrate temperature higher than 500 °C.

Thermodynamic and kinetic characterization of polycyclic aromatic hydrocarbons in reversed-phase liquid chromatography.

PubMed

Howerton, Samuel B; McGuffin, Victoria L

2003-07-15

The retention of six polycyclic aromatic hydrocarbons (PAHs) was characterized by reversed-phase liquid chromatography. The PAHs were detected by laser-induced fluorescence at four points along an optically transparent capillary column. The profiles were characterized in space and time using an exponentially modified Gaussian equation. The resulting parameters were used to calculate the retention factors, as well as the concomitant changes in molar enthalpy and molar volume, for each PAH on monomeric (2.7 micromol/m2) and polymeric (5.4 micromol/m2) octadecylsilica. The changes in molar enthalpy become more exothermic as ring number increases and as annelation structure becomes less condensed. The changes in molar volume become more negative as ring number increases for the planar PAHs, but are positive for the nonplanar solutes. In addition, the rate constants, as well as the concomitant activation enthalpy and activation volume, are calculated for the first time. The kinetic data demonstrate that many of the PAHs exhibit very fast transitions between the mobile and stationary phases. The transition state is very high in energy, and the activation enthalpies and volumes become greater as ring number increases and as annelation structure becomes less condensed. The changes in thermodynamic and kinetic behavior are much more pronounced for the polymeric phase than for the monomeric phase.

Secondary Organic Aerosol Formation from Glyoxal: photochemical versus dark uptake and reversible versus irreversible SOA formation

NASA Astrophysics Data System (ADS)

Waxman, E.; Slowik, J. G.; Kampf, C. J.; Timkovsky, J.; Noziere, B.; Praplan, A. P.; Pfaffenberger, L.; Holzinger, R.; Hoffmann, T.; Dommen, J.; Prevot, A. S.; Baltensperger, U.; Volkamer, R.

2011-12-01

Glyoxal forms secondary organic aerosol (SOA) by partitioning to the aerosol aqueous phase according to Henry's law. The subsequent processing by heterogeneous and multiphase reactions shifts the partitioning towards aerosols. Currently it is not well understood whether these reactions result in reversible or irreversible SOA formation, and what parameters influence the rate limiting step of multiphase processing. We conducted a series of simulation chamber experiments at PSI in April and May 2011 to investigate processing under dark conditions, UV and/or visible light irradiated conditions, and in the presence and absence of OH radicals. Experiments used ammonium sulfate or ammonium sulfate/fulvic acid mixtures as seed aerosols, and were conducted between 50% and 85% relative humidity at approximately constant RH over the course of any given experiment. Glyoxal was produced photochemically from acetylene, using HONO photolysis as the OH radical source. Gas-phase glyoxal was measured by the CU LED-Cavity Enhanced-DOAS. The Thermal-Desorption Proton-Transfer-Reaction Mass Spectrometer (TD-PTR-MS) and Ion Chromatography Mass Spectrometer (IC-MS) monitored both gas and aerosol-phase organic reaction products. Particle composition was monitored by High-Resolution Time-of-Flight Aerosol Mass Spectrometry (HR-ToF-AMS), and HPLC-ESI MS/MS and LC-MS analysis of filter samples.

Secondary Organic Aerosol Formation from Glyoxal: photochemical versus dark uptake and reversible versus irreversible SOA formation

NASA Astrophysics Data System (ADS)

Waxman, E.; Slowik, J.; Kampf, C.; Timkovsky, J.; Noziere, B.; Praplan, A.; Pffafenberger, L.; Holzinger, R.; Hoffmann, T.; Dommen, J.; Prevot, A.; Baltensperger, U.; Volkamer, R.

2012-04-01

Glyoxal forms secondary organic aerosol (SOA) by partitioning to the aerosol aqueous phase according to Henry's law. The subsequent processing by heterogeneous and multiphase reactions shifts the partitioning towards aerosols. Currently it is not well understood whether these reactions result in reversible or irreversible SOA formation, and what parameters influence the rate limiting step of multiphase processing. We conducted a series of simulation chamber experiments at PSI in April and May 2011 to investigate processing under dark conditions, UV and/or visible light irradiated conditions, and in the presence and absence of OH radicals. Experiments used ammonium sulfate or ammonium sulfate/fulvic acid mixtures as seed aerosols, and were conducted between 50% and 85% relative humidity at approximately constant RH over the course of any given experiment. Glyoxal was produced photochemically from acetylene, using HONO photolysis as the OH radical source. Gas-phase glyoxal was measured by the CU LED-Cavity Enhanced-DOAS. The Thermal-Desorption Proton-Transfer-Reaction Mass Spectrometer (TD-PTR-MS) and Ion Chromatography Mass Spectrometer (IC-MS) monitored both gas and aerosol-phase organic reaction products. Particle composition was monitored by High-Resolution Time-of-Flight Aerosol Mass Spectrometry (HR-ToF-AMS), and HPLC-ESI MS/MS and LC-MS analysis of filter samples.

Reaction kinetics of resveratrol with tert-butoxyl radicals

NASA Astrophysics Data System (ADS)

Džeba, Iva; Pedzinski, Tomasz; Mihaljević, Branka

2012-09-01

The rate constant for the reaction of t-butoxyl radicals with resveratrol was studied under pseudo-first order conditions. The rate constant was determined by measuring the phenoxyl radical formation rate at 390 nm as function of resveratrol concentration in acetonitrile. The rate constant was determined to be 6.5×108 M-1s-1. This high value indicates the high reactivity consistent with the strong antioxidant activity of resveratrol.

Kinetic Analysis for the Multistep Profiles of Organic Reactions: Significance of the Conformational Entropy on the Rate Constants of the Claisen Rearrangement.

PubMed

Sumiya, Yosuke; Nagahata, Yutaka; Komatsuzaki, Tamiki; Taketsugu, Tetsuya; Maeda, Satoshi

2015-12-03

The significance of kinetic analysis as a tool for understanding the reactivity and selectivity of organic reactions has recently been recognized. However, conventional simulation approaches that solve rate equations numerically are not amenable to multistep reaction profiles consisting of fast and slow elementary steps. Herein, we present an efficient and robust approach for evaluating the overall rate constants of multistep reactions via the recursive contraction of the rate equations to give the overall rate constants for the products and byproducts. This new method was applied to the Claisen rearrangement of allyl vinyl ether, as well as a substituted allyl vinyl ether. Notably, the profiles of these reactions contained 23 and 84 local minima, and 66 and 278 transition states, respectively. The overall rate constant for the Claisen rearrangement of allyl vinyl ether was consistent with the experimental value. The selectivity of the Claisen rearrangement reaction has also been assessed using a substituted allyl vinyl ether. The results of this study showed that the conformational entropy in these flexible chain molecules had a substantial impact on the overall rate constants. This new method could therefore be used to estimate the overall rate constants of various other organic reactions involving flexible molecules.

Free energy gap laws for the pulse-induced and stationary fluorescence quenching by reversible charge transfer in polar solutions.

PubMed

Khokhlova, Svetlana S; Burshtein, Anatoly I

2011-01-21

The Stern-Volmer constants for either pulse-induced or stationary fluorescence being quenched by a contact charge transfer are calculated and their free energy dependencies (the free energy gap laws) are specified. The reversibility of charge transfer is taken into account as well as spin conversion in radical ion pairs, followed by their recombination in either singlet or triplet neutral products. The natural decay of triplets as well as their impurity quenching by ionization are accounted for when estimating the fluorescence quantum yield and its free energy dependence.

Sorption-desorption of rimsulfuron, nicosulfuron, and their metabolites in soils from Argentina and USA

USDA-ARS?s Scientific Manuscript database

For many pesticides, sorption coefficients increase with residence time in the soil, becoming constant after weeks of aging in the soil. Pesticide sorption is often slowly reversible with some fraction being recalcitrant to desorption. Dissipation in soil often follows a biphasic trend, in which the...

Kinetics of Molybdenum Adsorption and Desorption in Soils.

PubMed

Sun, Wenguang; Selim, H Magdi

2018-05-01

Much uncertainty exists in mechanisms and kinetics controlling the adsorption and desorption of molybdenum (Mo) in the soil environment. To investigate the characteristics of Mo adsorption and desorption and predict Mo behavior in the vadose zone, kinetic batch experiments were performed using three soils: Webster loam, Windsor sand and Mahan sand. Adsorption isotherms for Mo were strongly nonlinear for all three soils. Strong kinetic adsorption of Mo by all soils was also observed, where the rate of retention was rapid initially and was followed by slow retention behavior with time. The time-dependent Mo sorption rate was not influenced when constant pH was maintained. Desorption or release results indicated that there were significant fractions of Mo that appeared to be irreversible or slowly reversibly sorbed by Windsor and Mahan. X-ray absorption near edge structure (XANES) analysis for Windsor and Mahan soils indicated that most of Mo had been bound to kaolinite, whereas Webster had similar XANES features to those of Mo sorbed to montmorillonite. A sequential extraction procedure provided evidence that a significant amount of Mo was irreversibly sorbed. A multireaction model (MRM) with nonlinear equilibrium and kinetic sorption parameters was used to describe the adsorption-desorption kinetics of Mo on soils. Our results demonstrated that a formulation of MRM with two sorption sites (equilibrium and reversible) successfully described Mo adsorption-desorption data for Webster loam, and an additional irreversible reaction phase was recommended to describe Mo desorption or release with time for Windsor and Mahan soils. Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.

ParaCEST agents encapsulated in Reverse nano-Assembled Capsules (RACs): How slow molecular tumbling can quench CEST

NASA Astrophysics Data System (ADS)

Farashishiko, Annah; Slack, Jacqueline R.; Botta, Mauro; Woods, Mark

2018-04-01

Although paraCEST is a method with immense scope for generating image contrast in MRI, it suffers from the series the serious drawback of high detection limits. For a typical discrete paraCEST agent the detection limit is roughly an order of magnitude higher than that of a clinically used relaxation agent. One solution to this problem may be the incorporation of a large payload of paraCEST agents into a single macromolecular agent. Here we report a new synthetic method for accomplishing this goal: incorporating a large payload of the paraCEST agent DyDOTAM3+ into a Reverse Assembled nano-Capsule. An aggregate can be generated between this chelate and polyacrylic acid after the addition of ethylene diamine. Subsequent addition of polyallylamine hydrochloride followed by silica nanoparticles generated a robust encapsulating shell and afforded capsule with a mean hydrodynamic diameter of 650 ± 250 nm. Unfortunately this encapsulation did not have the effect of amplifying the CEST effect per agent, but quenched the CEST altogether. A significant proportion of the quenching effect of encapsulation could be attributed to the effect of slowing molecular tumbling, which is inevitable when the chelate is incorporated into a nano-scale material. This increases the transverse relaxation rate of chelate protons and a theoretical examination using Solomon Bloembergen Morgan theory and the Bloch equations shows that the increase in the transverse relaxation rate constant for the amide protons, in even modestly sized nano-materials, is sufficient to significantly quench CEST.

A constitutive rheological model for agglomerating blood derived from nonequilibrium thermodynamics

NASA Astrophysics Data System (ADS)

Tsimouri, Ioanna Ch.; Stephanou, Pavlos S.; Mavrantzas, Vlasis G.

2018-03-01

Red blood cells tend to aggregate in the presence of plasma proteins, forming structures known as rouleaux. Here, we derive a constitutive rheological model for human blood which accounts for the formation and dissociation of rouleaux using the generalized bracket formulation of nonequilibrium thermodynamics. Similar to the model derived by Owens and co-workers ["A non-homogeneous constitutive model for human blood. Part 1. Model derivation and steady flow," J. Fluid Mech. 617, 327-354 (2008)] through polymer network theory, each rouleau in our model is represented as a dumbbell; the corresponding structural variable is the conformation tensor of the dumbbell. The kinetics of rouleau formation and dissociation is treated as in the work of Germann et al. ["Nonequilibrium thermodynamic modeling of the structure and rheology of concentrated wormlike micellar solutions," J. Non-Newton. Fluid Mech. 196, 51-57 (2013)] by assuming a set of reversible reactions, each characterized by a forward and a reverse rate constant. The final set of evolution equations for the microstructure of each rouleau and the expression for the stress tensor turn out to be very similar to those of Owens and co-workers. However, by explicitly considering a mechanism for the formation and breakage of rouleaux, our model further provides expressions for the aggregation and disaggregation rates appearing in the final transport equations, which in the kinetic theory-based network model of Owens were absent and had to be specified separately. Despite this, the two models are found to provide similar descriptions of experimental data on the size distribution of rouleaux.

Survival and recovery rates of American woodcock banded in Michigan

USGS Publications Warehouse

Krementz, David G.; Hines, James E.; Luukkonen, David R.

2003-01-01

American woodcock (Scolopax minor) population indices have declined since U.S. Fish and Wildlife Service (USFWS) monitoring began in 1968. Management to stop and/or reverse this population trend has been hampered by the lack of recent information on woodcock population parameters. Without recent information on survival rate trends, managers have had to assume that the recent declines in recruitment indices are the only parameter driving woodcock declines. Using program MARK, we estimated annual survival and recovery rates of adult and juvenile American woodcock, and estimated summer survival of local (young incapable of sustained flight) woodcock banded in Michigan between 1978 and 1998. We constructed a set of candidate models from a global model with age (local, juvenile, adult) and time (year)-dependent survival and recovery rates to no age or time-dependent survival and recovery rates. Five models were supported by the data, with all models suggesting that survival rates differed among age classes, and 4 models had survival rates that were constant over time. The fifth model suggested that juvenile and adult survival rates were linear on a logit scale over time. Survival rates averaged over likelihood-weighted model results were 0.8784 +/- 0.1048 (SE) for locals, 0.2646 +/- 0.0423 (SE) for juveniles, and 0.4898 +/- 0.0329 (SE) for adults. Weighted average recovery rates were 0.0326 +/- 0.0053 (SE) for juveniles and 0.0313 +/- 0.0047 (SE) for adults. Estimated differences between our survival estimates and those from prior years were small, and our confidence around those differences was variable and uncertain. juvenile survival rates were low.

Integrated survey on toxic effects of lindane on neotropical fish: Corydoras paleatus and Jenynsia multidentata.

PubMed

Pesce, Silvia F; Cazenave, Jimena; Monferrán, Magdalena V; Frede, Silvia; Wunderlin, Daniel A

2008-12-01

We report the effect of lindane on fish experimentally exposed to lindane. Sublethal toxicity was assessed through (a) changes in histopathology; (b) the activity of GST in different organs; and (c) bioaccumulation in exposed fish. We present a survey on toxic effects of lindane at these three levels, proposing a sequence of dose-dependent effects. Physiological damage was reversible at lowest doses, but severe at the highest, including damage consistent with fibrosis in liver and karyolitic nucleus in brain of both studied species. Exposure of Jenynsia multidentata above 6 microg L(-1) caused activation a GST in liver and gills, followed by inhibition at 75 microg L(-1). Interestingly, the bioaccumulation rate was suddenly increased when GST was inhibited. Corydoras paleatus exposed to 6.0 microg L(-1) lindane did not present significant changes in GST activity; however, enzymatic inhibition was observed above 25 microg L(-1). The bioaccumulation rate in C. paleatus remained constant throughout the experiments. All in all, these results evidence that C. paleatus is more sensitive to lindane than J. multidentata.

Adsorption, desorption, and removal of polymeric nanomedicine on and from cellulose surfaces: effect of size.

PubMed

Zhang, Ming; Akbulut, Mustafa

2011-10-18

The increased production and commercial use of nanoparticulate drug delivery systems combined with a lack of regulation to govern their disposal may result in their introduction to soils and ultimately into groundwater systems. To better understand how such particles interact with environmentally significant interfaces, we study the adsorption, desorption, and removal behavior of poly(ethylene glycol)-based nanoparticulate drug delivery systems on and from cellulose, which is the most common organic compound on Earth. It is shown that such an adsorption process is only partially reversible, and most of the adsorbate particles do not desorb from the cellulose surface even upon rinsing with a large amount of water. The rate constant of adsorption decreases with increasing particle size. Furthermore, hydrodynamic forces acting parallel to the surfaces are found to be of great importance in the context of particle dynamics near the cellulose surface, and ultimately responsible for the removal of some fraction of particles via rolling or sliding. As the particle size increases, the removal rates of the particles increase for a given hydrodynamical condition. © 2011 American Chemical Society

Molecular model for the diffusion of associating telechelic polymer networks

NASA Astrophysics Data System (ADS)

Ramirez, Jorge; Dursch, Thomas; Olsen, Bradley

Understanding the mechanisms of motion and stress relaxation of associating polymers at the molecular level is critical for advanced technological applications such as enhanced oil-recovery, self-healing materials or drug delivery. In associating polymers, the strength and rates of association/dissociation of the reversible physical crosslinks govern the dynamics of the network and therefore all the macroscopic properties, like self-diffusion and rheology. Recently, by means of forced Rayleigh scattering experiments, we have proved that associating polymers of different architectures show super-diffusive behavior when the free motion of single molecular species is slowed down by association/dissociation kinetics. Here we discuss a new molecular picture for unentangled associating telechelic polymers that considers concentration, molecular weight, number of arms of the molecules and equilibrium and rate constants of association/dissociation. The model predicts super-diffusive behavior under the right combination of values of the parameters. We discuss some of the predictions of the model using scaling arguments, show detailed results from Brownian dynamics simulations of the FRS experiments, and attempt to compare the predictions of the model to experimental data.

Soft switching resonant converter with duty-cycle control in DC micro-grid system

NASA Astrophysics Data System (ADS)

Lin, Bor-Ren

2018-01-01

Resonant converter has been widely used for the benefits of low switching losses and high circuit efficiency. However, the wide frequency variation is the main drawback of resonant converter. This paper studies a new modular resonant converter with duty-cycle control to overcome this problem and realise the advantages of low switching losses, no reverse recovery current loss, balance input split voltages and constant frequency operation for medium voltage direct currentgrid or system network. Series full-bridge (FB) converters are used in the studied circuit in order to reduce the voltage stresses and power rating on power semiconductors. Flying capacitor is used between two FB converters to balance input split voltages. Two circuit modules are paralleled on the secondary side to lessen the current rating of rectifier diodes and the size of magnetic components. The resonant tank is operated at inductive load circuit to help power switches to be turned on at zero voltage with wide load range. The pulse-width modulation scheme is used to regulate output voltage. Experimental verifications are provided to show the performance of the proposed circuit.

Novel carbapenem derivative SF2103A: studies on the mode of beta-lactamase inactivation.

PubMed Central

Yamaguchi, A; Hirata, T; Sawai, T

1984-01-01

A novel carbapenem, SF2103A, is a strong inhibitor of various types of beta-lactamase. Equimolar concentrations of SF2103A completely inactivated the cephalosporinases of Proteus vulgaris and Citrobacter freundii and type Ib and type II penicillinases mediated by R plasmids in a progressive manner. The inactivation of the two penicillinases and P. vulgaris cephalosporinase was apparently irreversible; however, when the inactivated enzymes were separated from excess SF2103A by gel filtration, they showed very slow reactivation. The hydrolysis of SF2103A by these three beta-lactamases was below the limit of detection. It is concluded that SF2103A acts as a tight-binding competitive inhibitor for the penicillinases and P. vulgaris cephalosporinase. In contrast, the inactivation of C. freundii cephalosporinase by SF2103A was evidently reversible. The rate constant of reactivation of the enzyme was compatible with the turnover rate of the enzyme in the steady state of SF2103A hydrolysis. Thus, SF2103A simply acts as a poor substrate for C. freundii cephalosporinase. PMID:6372682

A first-passage scheme for determination of overall rate constants for non-diffusion-limited suspensions

NASA Astrophysics Data System (ADS)

Lu, Shih-Yuan; Yen, Yi-Ming

2002-02-01

A first-passage scheme is devised to determine the overall rate constant of suspensions under the non-diffusion-limited condition. The original first-passage scheme developed for diffusion-limited processes is modified to account for the finite incorporation rate at the inclusion surface by using a concept of the nonzero survival probability of the diffusing entity at entity-inclusion encounters. This nonzero survival probability is obtained from solving a relevant boundary value problem. The new first-passage scheme is validated by an excellent agreement between overall rate constant results from the present development and from an accurate boundary collocation calculation for the three common spherical arrays [J. Chem. Phys. 109, 4985 (1998)], namely simple cubic, body-centered cubic, and face-centered cubic arrays, for a wide range of P and f. Here, P is a dimensionless quantity characterizing the relative rate of diffusion versus surface incorporation, and f is the volume fraction of the inclusion. The scheme is further applied to random spherical suspensions and to investigate the effect of inclusion coagulation on overall rate constants. It is found that randomness in inclusion arrangement tends to lower the overall rate constant for f up to the near close-packing value of the regular arrays because of the inclusion screening effect. This screening effect turns stronger for regular arrays when f is near and above the close-packing value of the regular arrays, and consequently the overall rate constant of the random array exceeds that of the regular array. Inclusion coagulation too induces the inclusion screening effect, and leads to lower overall rate constants.

A new analytical method for estimating lumped parameter constants of linear viscoelastic models from strain rate tests

NASA Astrophysics Data System (ADS)

Mattei, G.; Ahluwalia, A.

2018-04-01

We introduce a new function, the apparent elastic modulus strain-rate spectrum, E_{app} ( \\dot{ɛ} ), for the derivation of lumped parameter constants for Generalized Maxwell (GM) linear viscoelastic models from stress-strain data obtained at various compressive strain rates ( \\dot{ɛ}). The E_{app} ( \\dot{ɛ} ) function was derived using the tangent modulus function obtained from the GM model stress-strain response to a constant \\dot{ɛ} input. Material viscoelastic parameters can be rapidly derived by fitting experimental E_{app} data obtained at different strain rates to the E_{app} ( \\dot{ɛ} ) function. This single-curve fitting returns similar viscoelastic constants as the original epsilon dot method based on a multi-curve global fitting procedure with shared parameters. Its low computational cost permits quick and robust identification of viscoelastic constants even when a large number of strain rates or replicates per strain rate are considered. This method is particularly suited for the analysis of bulk compression and nano-indentation data of soft (bio)materials.

Quantification aspects of constant pressure (ultra) high pressure liquid chromatography using mass-sensitive detectors with a nebulizing interface.

PubMed

Verstraeten, M; Broeckhoven, K; Lynen, F; Choikhet, K; Landt, K; Dittmann, M; Witt, K; Sandra, P; Desmet, G

2013-01-25

The present contribution investigates the quantitation aspects of mass-sensitive detectors with nebulizing interface (ESI-MSD, ELSD, CAD) in the constant pressure gradient elution mode. In this operation mode, the pressure is controlled and maintained at a set value and the liquid flow rate will vary according to the inverse mobile phase viscosity. As the pressure is continuously kept at the allowable maximum during the entire gradient run, the average liquid flow rate is higher compared to that in the conventional constant flow rate operation mode, thus shortening the analysis time. The following three mass-sensitive detectors were investigated: mass spectrometry detector (MS), evaporative light scattering detector (ELSD) and charged aerosol detector (CAD) and a wide variety of samples (phenones, polyaromatic hydrocarbons, wine, cocoa butter) has been considered. It was found that the nebulizing efficiency of the LC-interfaces of the three detectors under consideration changes with the increasing liquid flow rate. For the MS, the increasing flow rate leads to a lower peak area whereas for the ELSD the peak area increases compared to the constant flow rate mode. The peak area obtained with a CAD is rather insensitive to the liquid flow rate. The reproducibility of the peak area remains similar in both modes, although variation in system permeability compromises the 'long-term' reproducibility. This problem can however be overcome by running a flow rate program with an optimized flow rate and composition profile obtained from the constant pressure mode. In this case, the quantification remains reproducibile, despite any occuring variations of the system permeability. Furthermore, the same fragmentation pattern (MS) has been found in the constant pressure mode compared to the customary constant flow rate mode. Copyright © 2012 Elsevier B.V. All rights reserved.

Kinetics of phloretin binding to phosphatidylcholine vesicle membranes

PubMed Central

1980-01-01

The submillisecond kinetics for phloretin binding to unilamellar phosphatidylcholine (PC) vesicles was investigated using the temperature-jump technique. Spectrophotometric studies of the equilibrium binding performed at 328 nm demonstrated that phloretin binds to a single set of independent, equivalent sites on the vesicle with a dissociation constant of 8.0 microM and a lipid/site ratio of 4.0. The temperature of the phloretin-vesicle solution was jumped by 4 degrees C within 4 microseconds producing a monoexponential, concentration-dependent relaxation process with time constants in the 30--200-microseconds time range. An analysis of the concentration dependence of relaxation time constants at pH 7.30 and 24 degrees C yielded a binding rate constant of 2.7 X 10(8) M-1 s-1 and an unbinding constant of 2,900 s-1; approximately 66 percent of total binding sites are exposed at the outer vesicle surface. The value of the binding rate constant and three additional observations suggest that the binding kinetics are diffusion limited. The phloretin analogue, naringenin, which has a diffusion coefficient similar to phloretin yet a dissociation constant equal to 24 microM, bound to PC vesicle with the same rate constant as phloretin did. In addition, the phloretin-PC system was studied in buffers made one to six times more viscous than water by addition of sucrose or glycerol to the differ. The equilibrium affinity for phloretin binding to PC vesicles is independent of viscosity, yet the binding rate constant decreases with the expected dependence (kappa binding alpha 1/viscosity) for diffusion-limited processes. Thus, the binding rate constant is not altered by differences in binding affinity, yet depends upon the diffusion coefficient in buffer. Finally, studies of the pH dependence of the binding rate constant showed a dependence (kappa binding alpha [1 + 10pH-pK]) consistent with the diffusion-limited binding of a weak acid. PMID:7391812

Actinomycin D binding mode reveals the basis for its potent HIV-1 and cancer activity

NASA Astrophysics Data System (ADS)

Paramanathan, Thayaparan; Vladescu, Ioana D.; McCauley, Micah J.; Rouzina, Ioulia; Williams, Mark C.

2011-03-01

Actinomycin D (ActD) is one of the most studied antibiotics, which has been used as an anti-cancer agent and also shown to inhibit HIV reverse transcription. Initial studies with ActD established that it intercalates double stranded DNA (dsDNA). However, recent studies have shown that ActD binds with even higher affinity to single stranded DNA (ssDNA). In our studies we use optical tweezers to stretch and hold single dsDNA molecule at constant force in the presence of varying ActD concentrations until the binding reaches equilibrium. The change in dsDNA length upon ActD binding measured as a function of time yields the rate of binding in addition to the equilibrium lengthening of DNA. The results suggest extremely slow kinetics, on the order of several minutes and 0.52 +/- 0.06 μ M binding affinity. Holding DNA at constant force while stretching and relaxing suggests that ActD binds to two single strands that are close to each other rather than to pure dsDNA or ssDNA. This suggests that biological activity of ActD that contributes towards the inhibition of cellular replication is due to its ability to bind at DNA bubbles during RNA transcription, thereby stalling the transcription process.

Direct electrochemistry of glucose oxidase and glucose biosensing on a hydroxyl fullerenes modified glassy carbon electrode.

PubMed

Gao, Yun-Fei; Yang, Tian; Yang, Xiao-Lu; Zhang, Yu-Shuai; Xiao, Bao-Lin; Hong, Jun; Sheibani, Nader; Ghourchian, Hedayatollah; Hong, Tao; Moosavi-Movahedi, Ali Akbar

2014-10-15

Direct electrochemistry of glucose oxidase (GOD) was achieved when GOD-hydroxyl fullerenes (HFs) nano-complex was immobilized on a glassy carbon (GC) electrode and protected with a chitosan (Chit) membrane. The ultraviolet-visible absorption spectrometry (UV-vis), transmission electron microscopy (TEM), and circular dichroism spectropolarimeter (CD) methods were utilized for additional characterization of the GOD, GOD-HFs and Chit/GOD-HFs. Chit/HFs may preserve the secondary structure and catalytic properties of GOD. The cyclic voltammograms (CVs) of the modified GC electrode showed a pair of well-defined quasi-reversible redox peaks with the formal potential (E°') of 353 ± 2 mV versus Ag/AgCl at a scan rate of 0.05 V/s. The heterogeneous electron transfer constant (ks) was calculated to be 2.7 ± 0.2s(-1). The modified electrode response to glucose was linear in the concentrations ranging from 0.05 to 1.0mM, with a detection limit of 5 ± 1 μM. The apparent Michaelis-Menten constant (Km(app)) was 694 ± 8 μM. Thus, the modified electrode could be applied as a third generation biosensor for glucose with high sensitivity, selectivity and low detection limit. Copyright © 2014 Elsevier B.V. All rights reserved.

Creep fatigue life prediction for engine hot section materials (isotropic)

NASA Technical Reports Server (NTRS)

Moreno, Vito; Nissley, David; Lin, Li-Sen Jim

1985-01-01

The first two years of a two-phase program aimed at improving the high temperature crack initiation life prediction technology for gas turbine hot section components are discussed. In Phase 1 (baseline) effort, low cycle fatigue (LCF) models, using a data base generated for a cast nickel base gas turbine hot section alloy (B1900+Hf), were evaluated for their ability to predict the crack initiation life for relevant creep-fatigue loading conditions and to define data required for determination of model constants. The variables included strain range and rate, mean strain, strain hold times and temperature. None of the models predicted all of the life trends within reasonable data requirements. A Cycle Damage Accumulation (CDA) was therefore developed which follows an exhaustion of material ductility approach. Material ductility is estimated based on observed similarities of deformation structure between fatigue, tensile and creep tests. The cycle damage function is based on total strain range, maximum stress and stress amplitude and includes both time independent and time dependent components. The CDA model accurately predicts all of the trends in creep-fatigue life with loading conditions. In addition, all of the CDA model constants are determinable from rapid cycle, fully reversed fatigue tests and monotonic tensile and/or creep data.

Temperature and pressure dependence of the absolute rate constant for the reactions of NH2 radicals with acetylene and ethylene

NASA Technical Reports Server (NTRS)

Bosco, S. R.; Nava, D. F.; Brobst, W. D.; Stief, L. J.

1984-01-01

The absolute rate constants for the reaction between the NH2 free radical and acetylene and ethylene is measured experimentally using a flash photolysis technique. The constant is considered to be a function of temperature and pressure. At each temperature level of the experiment, the observed pseudo-first-order rate constants were assumed to be independent of flash intensity. The results of the experiment indicate that the bimolecular rate constant for the NH2 + C2H2 reaction increases with pressure at 373 K and 459 K but not at lower temperatures. Results near the pressure limit conform to an Arrhenius expression of 1.11 (+ or -) 0.36 x 10 to the -13th over the temperature range from 241 to 459 K. For the reaction NH2 + C2H4, a smaller rate of increase in the bimolecular rate constant was observed over the temperature range 250-465 K. The implications of these results for current theoretical models of NH2 + C2H2 (or H4) reactions in the atmospheres of Jupiter and Saturn are discussed.

Determination of Bimolecular Rate Constants for Reactions of Hydroxyl Radical with Pharmaceutical and Cosmetics Chemicals - Implications to the Fate in the Aquatic Environment

NASA Astrophysics Data System (ADS)

Nakajima, H.; Arakaki, T.; Anastasio, C.

2008-12-01

Large organic compounds such as hyaluronic acid and chondroitin sulfate are often used in pharmaceutical and cosmetics products, but their chemical degradation pathways are not well understood. To better elucidate their fate in the aquatic environment, we initiated a study to determine bimolecular rate constants between these organic compounds and hydroxyl radical (OH), which is a potent oxidant in the environment. The lifetimes of many organic compounds are determined by reactions with OH radicals, and the lifetime of OH is often controlled by reactions with organic compounds. To determine these bimolecular rate constants we used a competition kinetics technique with either hydrogen peroxide or nitrate as a source of OH and benzoate as the competing sink. Since the molecular weights of some of the large organic compounds we studied were not known, we used dissolved organic carbon (DOC) concentrations to determine mole-carbon based bimolecular rate constants, instead of the commonly used molar-based bimolecular rate constants. We will report the mole-carbon based bimolecular rate constants of OH, determined at room temperature, with hyaluronic acid, chondroitin sulfate and some other large organic compounds.

Coefficient of performance and its bounds with the figure of merit for a general refrigerator

NASA Astrophysics Data System (ADS)

Long, Rui; Liu, Wei

2015-02-01

A general refrigerator model with non-isothermal processes is studied. The coefficient of performance (COP) and its bounds at maximum χ figure of merit are obtained and analyzed. This model accounts for different heat capacities during the heat transfer processes. So, different kinds of refrigerator cycles can be considered. Under the constant heat capacity condition, the upper bound of the COP is the Curzon-Ahlborn (CA) coefficient of performance and is independent of the time durations of the heat exchanging processes. With the maximum χ criterion, in the refrigerator cycles, such as the reversed Brayton refrigerator cycle, the reversed Otto refrigerator cycle and the reversed Atkinson refrigerator cycle, where the heat capacity in the heat absorbing process is not less than that in the heat releasing process, their COPs are bounded by the CA coefficient of performance; otherwise, such as for the reversed Diesel refrigerator cycle, its COP can exceed the CA coefficient of performance. Furthermore, the general refined upper and lower bounds have been proposed.

Reversible Phase Transition with Ultralarge Dielectric Relaxation Behaviors in Succinimide Lithium(I) Hybrids.

PubMed

Tang, Yun-Zhi; Wang, Bin; Zhou, Hai-Tao; Chen, Shao-Peng; Tan, Yu-Hui; Wang, Chang-Feng; Yang, Chang-Shan; Wen, He-Rui

2018-02-05

Dielectric relaxations have widely applied on high permittivity capacitors, dielectric switches, ferroelectrics, pyroelectrics, and electrical insulating materials. However, few investigations of large dielectric relaxation behaviors on organic-inorganic hybrid materials have been documented before. Here we present a novel two-dimensional succinimide lithium(I) hybrid compound, [Li(PDD) 2 ClO 4 ] n , 1, (PDD = 2,5-pyrrolidinedione = succinimide) which shows reversible phase transition behavior in the vicinity of 228 K accompanied by an unusual symmetry breaking from I4 1 /amd to C2/c. X-ray single crystal diffractions analysis indicates the twist motion of pyrrolidine heterocycles, and order-disorder motion of ClO 4 - anions triggered the reversible phase transition. By means of an intuitive crystallographic model (rattling ion model), we further illustrated the mechanism of the interesting reversible phase transition. Particularly, 1 shows ultralarge dielectric relaxation behavior in the vicinity of the phase transition by its dielectric constant dependence on temperatures and frequencies as well as its Cole-Cole relation.

Myxobacteria, Polarity, and Multicellular Morphogenesis

PubMed Central

Kaiser, Dale; Robinson, Mark; Kroos, Lee

2010-01-01

Myxobacteria are renowned for the ability to sporulate within fruiting bodies whose shapes are species-specific. The capacity to build those multicellular structures arises from the ability of M. xanthus to organize high cell-density swarms, in which the cells tend to be aligned with each other while constantly in motion. The intrinsic polarity of rod-shaped cells lays the foundation, and each cell uses two polar engines for gliding on surfaces. It sprouts retractile type IV pili from the leading cell pole and secretes capsular polysaccharide through nozzles from the trailing pole. Regularly periodic reversal of the gliding direction was found to be required for swarming. Those reversals are generated by a G-protein switch which is driven by a sharply tuned oscillator. Starvation induces fruiting body development, and systematic reductions in the reversal frequency are necessary for the cells to aggregate rather than continue to swarm. Developmental gene expression is regulated by a network that is connected to the suppression of reversals. PMID:20610548

The energetic ion signature of an O-type neutral line in the geomagnetic tail

NASA Technical Reports Server (NTRS)

Martin, R. F., Jr.; Johnson, D. F.; Speiser, T. W.

1991-01-01

An energetic ion signature is presented which has the potential for remote sensing of an O-type neutral line embedded in a current sheet. A source plasma with a tailward flowing Kappa distribution yields a strongly non-Kappa distribution after interacting with the neutral line: sharp jumps, or ridges, occur in the velocity space distribution function f(nu-perpendicular, nu-parallel) associated with both increases and decreases in f. The jumps occur when orbits are reversed in the x-direction: a reversal causing initially earthward particles (low probability in the source distribution) to be observed results in a decrease in f, while a reversal causing initially tailward particles to be observed produces an increase in f. The reversals, and hence the jumps, occur at approximately constant values of perpendicular velocity in both the positive nu parallel and negative nu parallel half planes. The results were obtained using single particle simulations in a fixed magnetic field model.

An omnipotent Li-ion battery charger with multimode control and polarity reversible techniques

NASA Astrophysics Data System (ADS)

Chen, Jiann-Jong; Ku, Yi-Tsen; Yang, Hong-Yi; Hwang, Yuh-Shyan; Yu, Cheng-Chieh

2016-07-01

The omnipotent Li-ion battery charger with multimode control and polarity reversible techniques is presented in this article. The proposed chip is fabricated with TSMC 0.35μm 2P4M complementary metal-oxide- semiconductor processes, and the chip area including pads is 1.5 × 1.5 mm2. The structure of the omnipotent charger combines three charging modes and polarity reversible techniques, which adapt to any Li-ion batteries. The three reversible Li-ion battery charging modes, including trickle-current charging, large-current charging and constant-voltage charging, can charge in matching polarities or opposite polarities. The proposed circuit has a maximum charging current of 300 mA and the input voltage of the proposed circuit is set to 4.5 V. The maximum efficiency of the proposed charger is about 91% and its average efficiency is 74.8%. The omnipotent charger can precisely provide the charging current to the battery.

The uncertainty of biodegradation rate constants of emerging organic compounds in soil and groundwater - A compilation of literature values for 82 substances.

PubMed

Greskowiak, Janek; Hamann, Enrico; Burke, Victoria; Massmann, Gudrun

2017-12-01

The present study reports on biodegradation rate constants of emerging organic compounds (EOCs) in soil and groundwater available in the literature. The major aim of this compilation was to provide an assessment of the uncertainty of hydrological models with respect to the fate of EOCs. The literature search identified a total number of 82 EOCs for which 1st-order rate constants could be derived. It was found that for the majority of compounds degradation rate constants vary over more than three orders of magnitude. Correlation to factors that are well known to affect the degradation rate, such as temperature or redox condition was weak. No correlation at all was found with results from available quantitative structure-activity relationship models. This suggests that many unknown site specific or experimentally specific factors influence the degradation behavior of EOCs in the environment. Thus, local and catchment scale predictive models to estimate EOC concentration at receptors, e.g., receiving waters or drinking water wells, need to consider the large uncertainty in 1st-order rate constants. As a consequence, applying rate constants that were derived from one experiment or field site investigation to other experiments or field sites should be done with extreme caution. Copyright © 2017 Elsevier Ltd. All rights reserved.

Assessment of rate of drug release from oil vehicle using a rotating dialysis cell.

PubMed

Larsen, D H; Fredholt, K; Larsen, C

2000-09-01

The rate constants for transfer of model compounds (naproxen and lidocaine) from oily vehicle (Viscoleo) to aqueous buffer phases were determined by use of the rotating dialysis cell. Release studies were done for the partly ionized compounds at several pH values. A correlation between the overall first-order rate constant related to attainment of equilibrium, k(obs), and the pH-dependent distribution coefficient, D, determined between oil vehicle and aqueous buffer was established according to the equation: logk(obs)=-0.71 logD-0.22 (k(obs) in h(-1)). Based on this correlation it was suggested that the rate constant of a weak electrolyte at a specified D value could be considered equal to the k(obs) value for a non-electrolyte possessing a partition coefficient, P(app), the magnitude of which was equal to D. Specific rate constants k(ow) and k(wo) were calculated from the overall rate constant and the pH-dependent distribution coefficient. The rate constant representing the transport from oily vehicle to aqueous phase, k(ow), was found to be significantly influenced by the magnitude of the partition coefficient P(app) according to: logk(ow)=-0.71 logP(app)-log(P(app)+1)-0.22 (k(ow) in h(-1)).

One-step electrolytic preparation of Si-Fe alloys as anodes for lithium ion batteries

NASA Astrophysics Data System (ADS)

Wang, Hailong; Sun, Diankun; Song, Qiqi; Xie, Wenqi; Jiang, Xu; Zhang, Bo

2016-06-01

One-step electrolytic formation of uniform crystalline Si-Fe alloy particles was successfully demonstrated in direct electro-reduction of solid mixed oxides of SiO2 and Fe2O3 in molten CaCl2 at 900∘C. Upon constant voltage electrolysis of solid mixed oxides at 2.8V between solid oxide cathode and graphite anode for 5h, electrolytic Si-Fe with the same Si/Fe stoichimetry of the precursory oxides was generated. The firstly generated Fe could function as depolarizers to enhance reduction rate of SiO2, resulting in the enhanced reduction kinetics to the electrolysis of individual SiO2. When evaluated as anode for lithium ion batteries, the prepared SiFe electrode showed a reversible lithium storage capacity as high as 470mAh g-1 after 100 cycles at 200mA g-1, promising application in high-performance lithium ion batteries.

Probing the General Time Scale Question of Boronic Acid Binding with Sugars in Aqueous Solution at Physiological pH

PubMed Central

Ni, Nanting; Laughlin, Sarah; Wang, Yingji; Feng, You; Zheng, Yujun

2012-01-01

The boronic acid group is widely used in chemosensor design due to its ability to reversibly bind diol-containing compounds. The thermodynamic properties of the boronic acid-diol binding process have been investigated extensively. However, there are few studies of the kinetic properties of such binding processes. In this report, stopped-flow method was used for the first time to study the kinetic properties of the binding between three model arylboronic acids, 4-, 5-, and 8-isoquinolinylboronic acids, and various sugars. With all the boronic acid-diol pair sexamined, reactions were complete within seconds. The kon values with various sugars follow the order of D-fructose >D-tagatose>D-mannose >D-glucose. This trend tracks the thermodynamic binding affinities for these sugars and demonstrates that the “on” rate is the key factor determining the binding constant. PMID:22464680

Kinetic determinations of accurate relative oxidation potentials of amines with reactive radical cations.

PubMed

Gould, Ian R; Wosinska, Zofia M; Farid, Samir

2006-01-01

Accurate oxidation potentials for organic compounds are critical for the evaluation of thermodynamic and kinetic properties of their radical cations. Except when using a specialized apparatus, electrochemical oxidation of molecules with reactive radical cations is usually an irreversible process, providing peak potentials, E(p), rather than thermodynamically meaningful oxidation potentials, E(ox). In a previous study on amines with radical cations that underwent rapid decarboxylation, we estimated E(ox) by correcting the E(p) from cyclic voltammetry with rate constants for decarboxylation obtained using laser flash photolysis. Here we use redox equilibration experiments to determine accurate relative oxidation potentials for the same amines. We also describe an extension of these experiments to show how relative oxidation potentials can be obtained in the absence of equilibrium, from a complete kinetic analysis of the reversible redox kinetics. The results provide support for the previous cyclic voltammetry/laser flash photolysis method for determining oxidation potentials.

Well-Defined High Molecular Weight Polystyrene with High Rates and High Livingness Synthesized via Two-Stage RAFT Emulsion Polymerization.

PubMed

Yan, Kun; Gao, Xiang; Luo, Yingwu

2015-07-01

A highly living polymer with over 100 kg mol(-1) molecular weight is very difficult to achieve by controlled radical polymerization since the unavoidable side reactions of irreversible radical termination and radical chain transfer to monomer reaction become significant. It is reported that over 500 kg mol(-1) polystyrene with high livingness and low dispersity could be synthesized by a facile two-stage reversible addition-fragmentation transfer emulsion polymerization. The monomer conversion reaches 90% within 10 h. High livingness of the product is ascribed to the extremely low initiator concentration and the chain transfer constant for monomer unexpectedly much lower than the well-accepted values in the conventional radical polymerization. The two-stage monomer feeding policy much decreases the dispersity of the product. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Under pressure: evolutionary engineering of yeast strains for improved performance in fuels and chemicals production.

PubMed

Mans, Robert; Daran, Jean-Marc G; Pronk, Jack T

2018-04-01

Evolutionary engineering, which uses laboratory evolution to select for industrially relevant traits, is a popular strategy in the development of high-performing yeast strains for industrial production of fuels and chemicals. By integrating whole-genome sequencing, bioinformatics, classical genetics and genome-editing techniques, evolutionary engineering has also become a powerful approach for identification and reverse engineering of molecular mechanisms that underlie industrially relevant traits. New techniques enable acceleration of in vivo mutation rates, both across yeast genomes and at specific loci. Recent studies indicate that phenotypic trade-offs, which are often observed after evolution under constant conditions, can be mitigated by using dynamic cultivation regimes. Advances in research on synthetic regulatory circuits offer exciting possibilities to extend the applicability of evolutionary engineering to products of yeasts whose synthesis requires a net input of cellular energy. Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.

Mechanism of silver-mediated di-tert-butylsilylene transfer from a silacyclopropane to an alkene.

PubMed

Driver, Tom G; Woerpel, K A

2004-08-18

Kinetic studies of the reactions of cyclohexene silacyclopropane 1 and monosubstituted alkenes in the presence of 5 mol % of (Ph3P)2AgOTf suggested a possible mechanism for silver-mediated di-tert-butylsilylene transfer. The kinetic order in cyclohexene silacyclopropane 1 was determined to be one. Inverse kinetic saturation behavior (rate inhibition) was observed in monosubstituted alkene and cyclohexene concentrations. Saturation kinetic behavior in catalyst concentration was observed. A reactive intermediate, a silylsilver complex, was observed using low temperature 29Si NMR spectroscopy. Competition experiments between substituted styrenes and a deficient amount of 1 correlated well with the Hammett equation and provided a rho value of -0.62 +/- 0.02 using sigmap constants. These data support a mechanism involving reversible silver-promoted di-tert-butylsilylene extrusion from 1 followed by irreversible concerted electrophilic attack of the silylsilver intermediate on the alkene.

Pretransitional phenomena and pinning in liquid-crystalline blue phases

NASA Astrophysics Data System (ADS)

Demikhov, E.; Stegemeyer, H.; Tsukruk, V.

1992-10-01

Blue phases (BP's) in liquid-crystalline systems of high chirality exhibiting a short cholesteric temperature interval are investigated. In a BP I supercooled with respect to the cholesteric phase, the orientation of the cubic lattice with the (1,1,0) wave vector perpendicular to the substrate is spontaneously turned to a [200] orientation within small areas of several tenths of micrometers in diameter. A pinning of BP I lattice temperature waves is observed on the [200] orientational inhomogeneities. The pinning effect explains the observed saturation of the BP I lattice constant on decreasing temperature and its dependence on the cooling rate observed in supercooled region. A different type of cubic blue phase, BP S (``S'' represents supercooled), is observed transforming reversibly from the supercooled BP I but metastable with respect to the cholesteric phase. The BP S has two scales of order: a long-range orientational blue-phase-like order and a short-range positional smecticlike order.

Dark energy from the motions of neutrinos

NASA Astrophysics Data System (ADS)

Simpson, Fergus; Jimenez, Raul; Pena-Garay, Carlos; Verde, Licia

2018-06-01

Ordinarily, a scalar field may only play the role of dark energy if it possesses a potential that is either extraordinarily flat or extremely fine-tuned. Here we demonstrate that these restrictions are lifted when the scalar field undergoes persistent energy exchange with another fluid. In this scenario, the field is prevented from reversing its direction of motion, and instead may come to rest while displaced from the local minimum of its potential. Therefore almost any scalar potential is capable of initiating a prolonged phase of cosmic acceleration. If the rate of energy transfer is modulated via a derivative coupling, the field undergoes a rapid process of freezing, after which the field's equation of state mimicks that of a cosmological constant. We present a physically motivated realisation in the form of a neutrino-majoron coupling, which avoids the dynamical instabilities associated with mass-varying neutrino models. Finally we discuss possible means by which this model could be experimentally verified.

Elucidation of the Key Role of [Ru(bpy)3 ](2+) in Photocatalyzed RAFT Polymerization.

PubMed

Christmann, Julien; Ibrahim, Ahmad; Charlot, Vincent; Croutxé-Barghorn, Céline; Ley, Christian; Allonas, Xavier

2016-08-04

Photocatalysis reactions using [Ru(II) (bpy)3 ](2+) were studied on the example of visible-light-sensitized reversible addition-fragmentation chain transfer (RAFT) polymerization. Although both photoinduced electron- and energy-transfer mechanisms are able to describe this interaction, no definitive experimental proof has been presented so far. This paper investigates the actual mechanism governing this reaction. A set of RAFT agents was selected, their redox potentials measured by cyclic voltammetry, and relaxed triplet energies calculated by quantum mechanics. Gibbs free-energy values were calculated for both electron- and energy-transfer mechanisms. Quenching rate constants were determined by laser flash photolysis. The results undoubtedly evidence the involvement of a photoinduced energy-transfer reaction. Controlled photopolymerization experiments are discussed in the light of the primary photochemical process and photodissociation ability of RAFT agent triplet states. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Design of liposomal colloidal systems for ocular delivery of ciprofloxacin

PubMed Central

Taha, Ehab I.; El-Anazi, Magda H.; El-Bagory, Ibrahim M.; Bayomi, Mohsen A.

2013-01-01

Ophthalmic drug bioavailability is limited due to protective mechanisms of the eye which require the design of a system to enhance ocular delivery. In this study several liposomal formulations containing ciprofloxacin (CPX) have been formulated using reverse phase evaporation technique with final dispersion of pH 7.4. Different types of phospholipids including Phosphatidylcholine, Dipalmitoylphosphatidylcholine and Dimyristoyl-sn-glycero-3-phosphocholine were utilized. The effect of formulation factors such as type of phospholipid, cholesterol content, incorporation of positively charging inducing agents and ultrasonication on the properties of the liposomal vesicles was studied. Bioavailability of selected liposomal formulations in rabbit eye aqueous humor has been investigated and compared with that of commercially available CPX eye drops (Ciprocin®). Pharmacokinetic parameters including Cmax, Tmax, elimination rate constant, t1/2, MRT and AUC0–∞, were determined. The investigated formulations showed more than three folds of improvement in CPX ocular bioavailability compared with the commercial product. PMID:25061409

Study of CO 2 stability and electrochemical oxygen activation of mixed conductors with low thermal expansion coefficient based on the TbBaCo 3ZnO 7+ δ system

NASA Astrophysics Data System (ADS)

Vert, Vicente B.; Serra, José M.

The influence of different application-oriented factors on the electrochemical activity and stability of TbBaCo 3ZnO 7+ δ when used as a solid oxide fuel cell cathode has been studied. Calcination at temperatures above 900 °C (e.g. 1000 °C) leads to a significant increase in the electrode polarization resistance. The effect of the sintering temperature of the TbBaCo 3ZnO 7+ δ cathode seems to be more important than the effect produced by the Tb substitution as observed when compared with 900 °C-sintered YBaCo 3ZnO 7+ δ; and ErBaCo 3ZnO 7+ δ electrode performances. The presence of CO 2 in the air flow leads to an increase of roughly 10% in the polarization resistance for the whole studied temperature range (500-850 °C) while this effect is reversible. Analysis of the impedance spectroscopy measurements shows that the exchange rate constant (k G from Gerischer element) is significantly affected by CO 2 at temperatures below 700 °C, while the diffusion coefficient related parameter is slightly influenced at low temperatures. Electrode degrades with a low constant rate of 1 mΩ cm 2 h -1 after 60 h. This cathode material exhibits high CO 2 tolerance, as shown by temperature programmed treatment under a continuous gas flow of air with 5% CO 2, and a relatively low thermal expansion coefficient.

Reversion of QuantiFERON-TB Gold In-Tube test in individuals with and without prophylactic treatment for latent tuberculosis infection: a Systematic Review and Meta-Analysis.

PubMed

Zhang, Haoran; Xin, Henan; Li, Xiangwei; Li, Hengjing; Li, Mufei; Feng, Boxuan; Gao, Lei

2018-05-07

Reversion of tuberculosis (TB) infection testing has been suggested to be associated with prophylactic treatment efficacy. However, evidences based on randomized controlled study were sparse. Studies on serial QuantiFERON-TB Gold In-Tube (QFT) test, among individuals with and without prophylactic treatment were identified in the databases of PubMed, MEDLINE and EMBASE up to 28 February 2018. The reversion rates were quantitatively summarized by means of meta-analysis using the random-effect model. A total of 52 eligible studies were included in the meta-analysis on QFT test reversion rate among participants with (20 studies) and without (32 studies) prophylactic treatment. Summarized reversion rate was found to be 24.9% (95% confidence interval [CI]: 18.4%-32.9%) and 25.3% (95% CI: 19.6%-32.0%) for those completed or without treatment, respectively. When the analysis was restricted to the participants completed treatment, higher summarized rate of QFT reversion was found among those with longer course therapy (9INH vs. the other regimens), studies from Asia (vs. Europe and America), and individuals with immunosuppression disorders (vs. general populations). Our results suggested that QFT reversion was frequently observed regardless of with or without prophylactic treatment. Serial QFT testing might be inappropriate for evaluating preventive treatment efficacy. Copyright © 2018. Published by Elsevier Ltd.

Geomagnetic reversal rates following Palaeozoic superchrons have a fast restart mechanism.

PubMed

Hounslow, Mark W

2016-08-30

Long intervals of single geomagnetic polarity (superchrons) reflect geodynamo processes, driven by core-mantle boundary interactions; however, it is not clear what initiates the start and end of superchrons, other than superchrons probably reflect lower heat flow across the core-mantle boundary compared with adjacent intervals. Here geomagnetic polarity timescales, with confidence intervals, are constructed before and following the reverse polarity Kiaman (Carboniferous-Permian) and Moyero (Ordovician) superchrons, providing a window into the geodynamo processes. Similar to the Cretaceous, asymmetry in reversal rates is seen in the Palaeozoic superchrons, but the higher reversal rates imply higher heatflow thresholds for entering the superchron state. Similar to the Cretaceous superchron, unusually long-duration chrons characterize the ∼10 Myr interval adjacent to the superchrons, indicating a transitional reversing state to the superchrons. This may relate to a weak pattern in the clustering of chron durations superimposed on the dominant random arrangement of chron durations.

Geomagnetic reversal rates following Palaeozoic superchrons have a fast restart mechanism

PubMed Central

Hounslow, Mark W.

2016-01-01

Long intervals of single geomagnetic polarity (superchrons) reflect geodynamo processes, driven by core–mantle boundary interactions; however, it is not clear what initiates the start and end of superchrons, other than superchrons probably reflect lower heat flow across the core–mantle boundary compared with adjacent intervals. Here geomagnetic polarity timescales, with confidence intervals, are constructed before and following the reverse polarity Kiaman (Carboniferous–Permian) and Moyero (Ordovician) superchrons, providing a window into the geodynamo processes. Similar to the Cretaceous, asymmetry in reversal rates is seen in the Palaeozoic superchrons, but the higher reversal rates imply higher heatflow thresholds for entering the superchron state. Similar to the Cretaceous superchron, unusually long-duration chrons characterize the ∼10 Myr interval adjacent to the superchrons, indicating a transitional reversing state to the superchrons. This may relate to a weak pattern in the clustering of chron durations superimposed on the dominant random arrangement of chron durations. PMID:27572303

Application of the compensated arrhenius formalism to dielectric relaxation.

PubMed

Petrowsky, Matt; Frech, Roger

2009-12-17

The temperature dependence of the dielectric rate constant, defined as the reciprocal of the dielectric relaxation time, is examined for several groups of organic solvents. Early studies of linear alcohols using a simple Arrhenius equation found that the activation energy was dependent on the chain length of the alcohol. This paper re-examines the earlier data using a compensated Arrhenius formalism that assumes the presence of a temperature-dependent static dielectric constant in the exponential prefactor. Scaling temperature-dependent rate constants to isothermal rate constants so that the dielectric constant dependence is removed results in calculated energies of activation E(a) in which there is a small increase with chain length. These energies of activation are very similar to those calculated from ionic conductivity data using compensated Arrhenius formalism. This treatment is then extended to dielectic relaxation data for n-alkyl bromides, n-nitriles, and n-acetates. The exponential prefactor is determined by dividing the temperature-dependent rate constants by the Boltzmann term exp(-E(a)/RT). Plotting the prefactors versus the static dielectric constant places the data on a single master curve for each group of solvents.

Inflation with a constant rate of roll

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

Motohashi, Hayato; Starobinsky, Alexei A.; Yokoyama, Jun'ichi, E-mail: motohashi@kicp.uchicago.edu, E-mail: alstar@landau.ac.ru, E-mail: yokoyama@resceu.s.u-tokyo.ac.jp

2015-09-01

We consider an inflationary scenario where the rate of inflaton roll defined by {sup ··}φ/H φ-dot remains constant. The rate of roll is small for slow-roll inflation, while a generic rate of roll leads to the interesting case of 'constant-roll' inflation. We find a general exact solution for the inflaton potential required for such inflaton behaviour. In this model, due to non-slow evolution of background, the would-be decaying mode of linear scalar (curvature) perturbations may not be neglected. It can even grow for some values of the model parameter, while the other mode always remains constant. However, this always occurs formore » unstable solutions which are not attractors for the given potential. The most interesting particular cases of constant-roll inflation remaining viable with the most recent observational data are quadratic hilltop inflation (with cutoff) and natural inflation (with an additional negative cosmological constant). In these cases even-order slow-roll parameters approach non-negligible constants while the odd ones are asymptotically vanishing in the quasi-de Sitter regime.« less

Vasectomy as a reversible form of contraception for select patients.

PubMed

Samplaski, Mary K; Daniel, Ariande; Jarvi, Keith

2014-04-01

To provide an effective form of birth control, men may choose a reversible or permanent form of contraception. Vasectomy is presently offered as a permanent option for male contraception. We have had patients who were interested in vasectomy and reversal as a temporary birth control option. The purpose of this paper is to determine if vasectomy should be offered for selected couples as a temporary form of contraception and under which circumstances. A literature review was conducted to determine the available reversible contraceptive options, risks, failure rates and contraindications to each, and the risks and success rates of vasectomy and vasectomy reversal. Reversible contraceptives include hormonally based methods for women, non-hormonal anatomic barrier devices and spermatocidal agents. Hormone based therapies may be contraindicated in women with cardiovascular disease, hypertension, and some cancers. Non-hormonal contraceptives are generally less effective and may be unacceptable for some couples due to higher failure rates, difficulty of use and lack of acceptance. Both vasectomy and vasectomy reversal are low risk procedures. Reversal may be performed with a high degree of success, particularly with a short obstructive interval (97% patency if performed < 3 years following vasectomy). While vasectomy should be considered a permanent form of sterilization for most couples, there are select couples, unable or unwilling to use other forms of birth control, who would benefit from an informed discussion about using a vasectomy as a reversible form of contraception.

Multi-target QSPR modeling for simultaneous prediction of multiple gas-phase kinetic rate constants of diverse chemicals

NASA Astrophysics Data System (ADS)

Basant, Nikita; Gupta, Shikha

2018-03-01

The reactions of molecular ozone (O3), hydroxyl (•OH) and nitrate (NO3) radicals are among the major pathways of removal of volatile organic compounds (VOCs) in the atmospheric environment. The gas-phase kinetic rate constants (kO3, kOH, kNO3) are thus, important in assessing the ultimate fate and exposure risk of atmospheric VOCs. Experimental data for rate constants are not available for many emerging VOCs and the computational methods reported so far address a single target modeling only. In this study, we have developed a multi-target (mt) QSPR model for simultaneous prediction of multiple kinetic rate constants (kO3, kOH, kNO3) of diverse organic chemicals considering an experimental data set of VOCs for which values of all the three rate constants are available. The mt-QSPR model identified and used five descriptors related to the molecular size, degree of saturation and electron density in a molecule, which were mechanistically interpretable. These descriptors successfully predicted three rate constants simultaneously. The model yielded high correlations (R2 = 0.874-0.924) between the experimental and simultaneously predicted endpoint rate constant (kO3, kOH, kNO3) values in test arrays for all the three systems. The model also passed all the stringent statistical validation tests for external predictivity. The proposed multi-target QSPR model can be successfully used for predicting reactivity of new VOCs simultaneously for their exposure risk assessment.

Stoma reversal after surgery for complicated acute diverticulitis: A multicentre retrospective study.

PubMed

Roig, José Vicente; Salvador, Antonio; Frasson, Matteo; García-Mayor, Lucas; Espinosa, Javier; Roselló, Vicente; Hernandis, Juan; Ruiz-Carmona, María Dolores; Uribe, Natalia; García-Calvo, Rafael; Bernal, Juan Carlos; García-Armengol, Juan; García-Granero, Eduardo

2018-03-09

INTRODUCTION THE AIM: was to analyse the stoma reversal rate after surgery for complicated acute diverticulitis (CAD), and more specifically the end-stoma-reversal, as well as the delay, feasibility, complications and risk factors for stoma maintenance. A multicentre retrospective study of patients who had undergone urgent surgery for CAD with stoma formation in ten hospitals during a period of 6 years. The frequency of reversal over time and the factors affecting the decision for reversal were analysed. Out of 385 patients operated for CAD, 312 underwent stoma creation: 292 end colostomies and 20 diverting stomas. During follow-up, stoma reversal surgery was performed in 161 patients (51.6%) after a median of 9 months. The main causes for not performing stoma reversal were comorbidities and the death of the patient. Advanced age was an adverse factor in the multivariate analysis, and the actuarial rate of reversal was higher in men and in patients with no previous Hartmann's operation. Stoma reversal surgery was completed in all but one patient, and a loop ileostomy was associated in four. Morbidity and mortality rates were 35.7% and 1.9%, respectively. A total of 8.4% of patients underwent re-operation, and 6% experienced an anastomotic leak. Twelve patients remained with a stoma after the attempted reconstruction surgery. Surgery for CAD is frequently associated with an end stoma, which will ultimately not be reversed in almost 50% of patients. Moreover, reversal surgery is frequently delayed and is associated with significant morbidity and mortality. Copyright © 2018 AEC. Publicado por Elsevier España, S.L.U. All rights reserved.

Monte Carlo Study of Melting of a Model Bulk Ice.

NASA Astrophysics Data System (ADS)

Han, Kyu-Kwang

The methods of NVT (constant number, volume and temperature) and NPT (constant number, pressure and temperature) Monte Carlo computer simulations are used to examine the melting of a periodic hexagonal ice (ice Ih) sample with a unit cell of 192 (rigid) water molecules interacting via the revised central force potentials of Stillinger and Rahman (RSL2). In NVT Monte Carlo simulation of P-T plot for a constant density (0.904g/cm^3) is used to locate onset of the liquid-solid coexistence region (where the slope of the pressure changes sign) and estimate the (constant density) melting point. The slope reversal is a natural consequence of the constant density condition for substances which expand upon freezing and it is pointed out that this analysis is extremely useful for substances such as water. In this study, a sign reversal of the pressure slope is observed near 280 K, indicating that the RSL2 potentials reproduce the freezing expansion expected for water and support a bulk ice Ih system which melts <280 K. The internal energy, specific heat, and two dimensional structure factors for the constant density H_2O system are also examined at a range of temperatures between 100 and 370 K and support the P-T analysis for location of the melting point. This P-T analysis might likewise be useful for determining a (constant density) freezing point, or, with multiple simulations at appropriate densities, the triple point. For NPT Monte Carlo simulations preliminary results are presented. In this study the density, enthalpy, specific heat, and structure factor dependences on temperature are monitored during a sequential heating of the system from 100 to 370 K at a constant pressure (1 atm.). A jump in density upon melting is observed and indicates that the RSL2 potentials reproduce the melting contraction of ice. From the dependences of monitored physical properties on temperature an upper bound on the melting temperature is estimated. In this study we made the first analysis and calculation of the P-T curve for ice Ih melting at constant volume and the first NPT study of ice and of ice melting. In the NVT simulation we found for rho = 0.904g/cm^3 T_ {rm m} ~eq 280 K which is much closer to physical T_ {rm m} than any other published NVT simulation of ice. Finally it is shown that RSL2 potentials do a credible job of describing the thermodynamic properties of ice Ih near its melting point.

Rationalizing 5000-Fold Differences in Receptor-Binding Rate Constants of Four Cytokines

PubMed Central

Pang, Xiaodong; Qin, Sanbo; Zhou, Huan-Xiang

2011-01-01

The four cytokines erythropoietin (EPO), interleukin-4 (IL4), human growth hormone (hGH), and prolactin (PRL) all form four-helix bundles and bind to type I cytokine receptors. However, their receptor-binding rate constants span a 5000-fold range. Here, we quantitatively rationalize these vast differences in rate constants by our transient-complex theory for protein-protein association. In the transient complex, the two proteins have near-native separation and relative orientation, but have yet to form the short-range specific interactions of the native complex. The theory predicts the association rate constant as ka=ka0exp(−ΔGel∗/kBT) where ka0 is the basal rate constant for reaching the transient complex by random diffusion, and the Boltzmann factor captures the rate enhancement due to electrostatic attraction. We found that the vast differences in receptor-binding rate constants of the four cytokines arise mostly from the differences in charge complementarity among the four cytokine-receptor complexes. The basal rate constants (ka0) of EPO, IL4, hGH, and PRL were similar (5.2 × 105 M−1s−1, 2.4 × 105 M−1s−1, 1.7 × 105 M−1s−1, and 1.7 × 105 M−1s−1, respectively). However, the average electrostatic free energies (ΔGe1∗) were very different (−4.2 kcal/mol, −2.4 kcal/mol, −0.1 kcal/mol, and −0.5 kcal/mol, respectively, at ionic strength = 160 mM). The receptor-binding rate constants predicted without adjusting any parameters, 6.2 × 108 M−1s−1, 1.3 × 107 M−1s−1, 2.0 × 105 M−1s−1, and 7.6 × 104 M−1s−1, respectively, for EPO, IL4, hGH, and PRL agree well with experimental results. We uncover that these diverse rate constants are anticorrelated with the circulation concentrations of the cytokines, with the resulting cytokine-receptor binding rates very close to the limits set by the half-lives of the receptors, suggesting that these binding rates are functionally relevant and perhaps evolutionarily tuned. Our calculations also reproduced well-observed effects of mutations and ionic strength on the rate constants and produced a set of mutations on the complex of hGH with its receptor that putatively enhances the rate constant by nearly 100-fold through increasing charge complementarity. To quantify charge complementarity, we propose a simple index based on the charge distribution within the binding interface, which shows good correlation with ΔGe1∗. Together these results suggest that protein charges can be manipulated to tune ka and control biological function. PMID:21889455

Dissection of the mechanism of manganese porphyrin-catalyzed chlorine dioxide generation.

PubMed

Umile, Thomas P; Wang, Dong; Groves, John T

2011-10-17

Chlorine dioxide, an industrially important biocide and bleach, is produced rapidly and efficiently from chlorite ion in the presence of water-soluble, manganese porphyrins and porphyrazines at neutral pH under mild conditions. The electron-deficient manganese(III) tetra-(N,N-dimethyl)imidazolium porphyrin (MnTDMImP), tetra-(N,N-dimethyl)benzimidazolium (MnTDMBImP) porphyrin, and manganese(III) tetra-N-methyl-2,3-pyridinoporphyrazine (MnTM23PyPz) were found to be the most efficient catalysts for this process. The more typical manganese tetra-4-N-methylpyridiumporphyrin (Mn-4-TMPyP) was much less effective. Rates for the best catalysts were in the range of 0.24-32 TO/s with MnTM23PyPz being the fastest. The kinetics of reactions of the various ClO(x) species (e.g., chlorite ion, hypochlorous acid, and chlorine dioxide) with authentic oxomanganese(IV) and dioxomanganese(V)MnTDMImP intermediates were studied by stopped-flow spectroscopy. Rate-limiting oxidation of the manganese(III) catalyst by chlorite ion via oxygen atom transfer is proposed to afford a trans-dioxomanganese(V) intermediate. Both trans-dioxomanganese(V)TDMImP and oxoaqua-manganese(IV)TDMImP oxidize chlorite ion by 1-electron, generating the product chlorine dioxide with bimolecular rate constants of 6.30 × 10(3) M(-1) s(-1) and 3.13 × 10(3) M(-1) s(-1), respectively, at pH 6.8. Chlorine dioxide was able to oxidize manganese(III)TDMImP to oxomanganese(IV) at a similar rate, establishing a redox steady-state equilibrium under turnover conditions. Hypochlorous acid (HOCl) produced during turnover was found to rapidly and reversibly react with manganese(III)TDMImP to give dioxoMn(V)TDMImP and chloride ion. The measured equilibrium constant for this reaction (K(eq) = 2.2 at pH 5.1) afforded a value for the oxoMn(V)/Mn(III) redox couple under catalytic conditions (E' = 1.35 V vs NHE). In subsequent processes, chlorine dioxide reacts with both oxomanganese(V) and oxomanganese(IV)TDMImP to afford chlorate ion. Kinetic simulations of the proposed mechanism using experimentally measured rate constants were in agreement with observed chlorine dioxide growth and decay curves, measured chlorate yields, and the oxoMn(IV)/Mn(III) redox potential (1.03 V vs NHE). This acid-free catalysis could form the basis for a new process to make ClO(2).

Very high pressure liquid chromatography using fully porous particles: quantitative analysis of fast gradient separations without post-run times.

PubMed

Stankovich, Joseph J; Gritti, Fabrice; Stevenson, Paul G; Beaver, Lois Ann; Guiochon, Georges

2014-01-10

Using a column packed with fully porous particles, four methods for controlling the flow rates at which gradient elution runs are conducted in very high pressure liquid chromatography (VHPLC) were tested to determine whether reproducible thermal conditions could be achieved, such that subsequent analyses would proceed at nearly the same initial temperature. In VHPLC high flow rates are achieved, producing fast analyses but requiring high inlet pressures. The combination of high flow rates and high inlet pressures generates local heat, leading to temperature changes in the column. Usually in this case a post-run time is input into the analytical method to allow the return of the column temperature to its initial state. An alternative strategy involves operating the column without a post-run equilibration period and maintaining constant temperature variations for subsequent analysis after conducting one or a few separations to bring the column to a reproducible starting temperature. A liquid chromatography instrument equipped with a pressure controller was used to perform constant pressure and constant flow rate VHPLC separations. Six replicate gradient separations of a nine component mixture consisting of acetophenone, propiophenone, butyrophenone, valerophenone, hexanophenone, heptanophenone, octanophenone, benzophenone, and acetanilide dissolved in water/acetonitrile (65:35, v/v) were performed under various experimental conditions: constant flow rate, two sets of constant pressure, and constant pressure operation with a programmed flow rate. The relative standard deviations of the response factors for all the analytes are lower than 5% across the methods. Programming the flow rate to maintain a fairly constant pressure instead of using instrument controlled constant pressure improves the reproducibility of the retention times by a factor of 5, when plotting the chromatograms in time. Copyright © 2013 Elsevier B.V. All rights reserved.

Theoretical rate constants of super-exchange hole transfer and thermally induced hopping in DNA.

PubMed

Shimazaki, Tomomi; Asai, Yoshihiro; Yamashita, Koichi

2005-01-27

Recently, the electronic properties of DNA have been extensively studied, because its conductivity is important not only to the study of fundamental biological problems, but also in the development of molecular-sized electronics and biosensors. We have studied theoretically the reorganization energies, the activation energies, the electronic coupling matrix elements, and the rate constants of hole transfer in B-form double-helix DNA in water. To accommodate the effects of DNA nuclear motions, a subset of reaction coordinates for hole transfer was extracted from classical molecular dynamics (MD) trajectories of DNA in water and then used for ab initio quantum chemical calculations of electron coupling constants based on the generalized Mulliken-Hush model. A molecular mechanics (MM) method was used to determine the nuclear Franck-Condon factor. The rate constants for two types of mechanisms of hole transfer-the thermally induced hopping (TIH) and the super-exchange mechanisms-were determined based on Marcus theory. We found that the calculated matrix elements are strongly dependent on the conformations of the nucleobase pairs of hole-transferable DNA and extend over a wide range of values for the "rise" base-step parameter but cluster around a particular value for the "twist" parameter. The calculated activation energies are in good agreement with experimental results. Whereas the rate constant for the TIH mechanism is not dependent on the number of A-T nucleobase pairs that act as a bridge, the rate constant for the super-exchange process rapidly decreases when the length of the bridge increases. These characteristic trends in the calculated rate constants effectively reproduce those in the experimental data of Giese et al. [Nature 2001, 412, 318]. The calculated rate constants were also compared with the experimental results of Lewis et al. [Nature 2000, 406, 51].

Magnetisation reversal in anisotropy graded Co/Pd multilayers

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

Barton, C. W., E-mail: craig.barton-2@postgrad.manchester.ac.uk; Thomson, T.

2015-08-14

We demonstrate high precision controllability of the magnetization reversal nucleation process in [Co/Pd]{sub 8} multilayer films consisting of two sets of bilayers with high and low perpendicular anisotropy, respectively. The anisotropy of the entire film is set by the degree of Co/Pd interfacial mixing during deposition which provides fine control of the anisotropy of an individual bilayer in the multilayer stack. The relative number of each type of bilayer is used to select the magnetisation reversal behavior such that changing one bilayer changes the properties of the entire multilayer through anisotropy averaging. A simple extension to the sputtering protocol wouldmore » provide multilayer films with fully graded anisotropy, while maintaining a constant saturation magnetization opening new possibilities for the creation of highly engineered multilayer structures for spin torque devices and future magnetic recording media.« less

Uncertainty analysis of multi-rate kinetics of uranium desorption from sediments

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

Zhang, Xiaoying; Liu, Chongxuan; Hu, Bill X.

2014-01-01

A multi-rate expression for uranyl [U(VI)] surface complexation reactions has been proposed to describe diffusion-limited U(VI) sorption/desorption in heterogeneous subsurface sediments. An important assumption in the rate expression is that its rate constants follow a certain type probability distribution. In this paper, a Bayes-based, Differential Evolution Markov Chain method was used to assess the distribution assumption and to analyze parameter and model structure uncertainties. U(VI) desorption from a contaminated sediment at the US Hanford 300 Area, Washington was used as an example for detail analysis. The results indicated that: 1) the rate constants in the multi-rate expression contain uneven uncertaintiesmore » with slower rate constants having relative larger uncertainties; 2) the lognormal distribution is an effective assumption for the rate constants in the multi-rate model to simualte U(VI) desorption; 3) however, long-term prediction and its uncertainty may be significantly biased by the lognormal assumption for the smaller rate constants; and 4) both parameter and model structure uncertainties can affect the extrapolation of the multi-rate model with a larger uncertainty from the model structure. The results provide important insights into the factors contributing to the uncertainties of the multi-rate expression commonly used to describe the diffusion or mixing-limited sorption/desorption of both organic and inorganic contaminants in subsurface sediments.« less

[Key physical parameters of hawthorn leaf granules by stepwise regression analysis method].

PubMed

Jiang, Qie-Ying; Zeng, Rong-Gui; Li, Zhe; Luo, Juan; Zhao, Guo-Wei; Lv, Dan; Liao, Zheng-Gen

2017-05-01

The purpose of this study was to investigate the effect of key physical properties of hawthorn leaf granule on its dissolution behavior. Hawthorn leaves extract was utilized as a model drug. The extract was mixed with microcrystalline cellulose or starch with the same ratio by using different methods. Appropriate amount of lubricant and disintegrating agent was added into part of the mixed powder, and then the granules were prepared by using extrusion granulation and high shear granulation. The granules dissolution behavior was evaluated by using equilibrium dissolution quantity and dissolution rate constant of the hypericin as the indicators. Then the effect of physical properties on dissolution behavior was analyzed through the stepwise regression analysis method. The equilibrium dissolution quantity of hypericin and adsorption heat constant in hawthorn leaves were positively correlated with the monolayer adsorption capacity and negatively correlated with the moisture absorption rate constant. The dissolution rate constants were decreased with the increase of Hausner rate, monolayer adsorption capacity and adsorption heat constant, and were increased with the increase of Carr index and specific surface area. Adsorption heat constant, monolayer adsorption capacity, moisture absorption rate constant, Carr index and specific surface area were the key physical properties of hawthorn leaf granule to affect its dissolution behavior. Copyright© by the Chinese Pharmaceutical Association.

Constitutive Modelling of Resins in the Compliance Domain

NASA Astrophysics Data System (ADS)

Klasztorny, M.

2004-07-01

A rheological HWKK/H model for resins is developed taking into consideration the up-to-date analyses of experimental results. Constitutive compliance equations of linear are formulated for this model in the shear/bulk form, which describes, among other things, the first-rank reversible isothermal creep. The shear (distorsional) deformations are simulated with three independent stress history functions of fractional and normal exponential types. The volume deformations are simulated as perfectly elastic. The model is described by two elastic and six viscoelastic constants, namely three long-term creep coefficients and three retardation times. The constitutive compliance equations of viscoealsticity for resins are also formulated in the coupled form. Formulae for converting the constants of shear/bulk (uncoupled) viscoelasticity into the constants of coupled viscoelasticity are given too. An algorithm for identifying the material constants, based on the creep of uniaxially tensioned bar samples, is formulated in a way that gives unique results. The material constants are fiund for Epidian 53 epoxy and Polimal 109 polyester resins. The creep processes, simulated based on the experimental data, are presented graphically for both the resins examined.

Improved transistorized AC motor controller for battery powered urban electric passenger vehicles

NASA Technical Reports Server (NTRS)

Peak, S. C.

1982-01-01

An ac motor controller for an induction motor electric vehicle drive system was designed, fabricated, tested, evaluated, and cost analyzed. A vehicle performance analysis was done to establish the vehicle tractive effort-speed requirements. These requirements were then converted into a set of ac motor and ac controller requirements. The power inverter is a three-phase bridge using power Darlington transistors. The induction motor was optimized for use with an inverter power source. The drive system has a constant torque output to base motor speed and a constant horsepower output to maximum speed. A gear shifting transmission is not required. The ac controller was scaled from the base 20 hp (41 hp peak) at 108 volts dec to an expanded horsepower and battery voltage range. Motor reversal was accomplished by electronic reversal of the inverter phase sequence. The ac controller can also be used as a boost chopper battery charger. The drive system was tested on a dynamometer and results are presented. The current-controlled pulse width modulation control scheme yielded improved motor current waveforms. The ac controller favors a higher system voltage.

Determination of equilibrium and rate constants for complex formation by fluorescence correlation spectroscopy supplemented by dynamic light scattering and Taylor dispersion analysis.

PubMed

Zhang, Xuzhu; Poniewierski, Andrzej; Jelińska, Aldona; Zagożdżon, Anna; Wisniewska, Agnieszka; Hou, Sen; Hołyst, Robert

2016-10-04

The equilibrium and rate constants of molecular complex formation are of great interest both in the field of chemistry and biology. Here, we use fluorescence correlation spectroscopy (FCS), supplemented by dynamic light scattering (DLS) and Taylor dispersion analysis (TDA), to study the complex formation in model systems of dye-micelle interactions. In our case, dyes rhodamine 110 and ATTO-488 interact with three differently charged surfactant micelles: octaethylene glycol monododecyl ether C 12 E 8 (neutral), cetyltrimethylammonium chloride CTAC (positive) and sodium dodecyl sulfate SDS (negative). To determine the rate constants for the dye-micelle complex formation we fit the experimental data obtained by FCS with a new form of the autocorrelation function, derived in the accompanying paper. Our results show that the association rate constants for the model systems are roughly two orders of magnitude smaller than those in the case of the diffusion-controlled limit. Because the complex stability is determined by the dissociation rate constant, a two-step reaction mechanism, including the diffusion-controlled and reaction-controlled rates, is used to explain the dye-micelle interaction. In the limit of fast reaction, we apply FCS to determine the equilibrium constant from the effective diffusion coefficient of the fluorescent components. Depending on the value of the equilibrium constant, we distinguish three types of interaction in the studied systems: weak, intermediate and strong. The values of the equilibrium constant obtained from the FCS and TDA experiments are very close to each other, which supports the theoretical model used to interpret the FCS data.

Rate constant for reaction of atomic hydrogen with germane

NASA Technical Reports Server (NTRS)

Nava, David F.; Payne, Walter A.; Marston, George; Stief, Louis J.

1990-01-01

Due to the interest in the chemistry of germane in the atmospheres of Jupiter and Saturn, and because previously reported kinetic reaction rate studies at 298 K gave results differing by a factor of 200, laboratory measurements were performed to determine the reaction rate constant for H + GeH4. Results of the study at 298 K, obtained via the direct technique of flash photolysis-resonance fluorescence, yield the reaction rate constant, k = (4.08 + or - 0.22) x 10(exp -12) cu cm/s.

Efficiency of Adaptive Temperature-Based Replica Exchange for Sampling Large-Scale Protein Conformational Transitions.

PubMed

Zhang, Weihong; Chen, Jianhan

2013-06-11

Temperature-based replica exchange (RE) is now considered a principal technique for enhanced sampling of protein conformations. It is also recognized that existence of sharp cooperative transitions (such as protein folding/unfolding) can lead to temperature exchange bottlenecks and significantly reduce the sampling efficiency. Here, we revisit two adaptive temperature-based RE protocols, namely, exchange equalization (EE) and current maximization (CM), that were previously examined using atomistic simulations (Lee and Olson, J. Chem. Physics2011, 134, 24111). Both protocols aim to overcome exchange bottlenecks by adaptively adjusting the simulation temperatures, either to achieve uniform exchange rates (in EE) or to maximize temperature diffusion (CM). By designing a realistic yet computationally tractable coarse-grained protein model, one can sample many reversible folding/unfolding transitions using conventional constant temperature molecular dynamics (MD), standard REMD, EE-REMD, and CM-REMD. This allows rigorous evaluation of the sampling efficiency, by directly comparing the rates of folding/unfolding transitions and convergence of various thermodynamic properties of interest. The results demonstrate that both EE and CM can indeed enhance temperature diffusion compared to standard RE, by ∼3- and over 10-fold, respectively. Surprisingly, the rates of reversible folding/unfolding transitions are similar in all three RE protocols. The convergence rates of several key thermodynamic properties, including the folding stability and various 1D and 2D free energy surfaces, are also similar. Therefore, the efficiency of RE protocols does not appear to be limited by temperature diffusion, but by the inherent rates of spontaneous large-scale conformational rearrangements. This is particularly true considering that virtually all RE simulations of proteins in practice involve exchange attempt frequencies (∼ps(-1)) that are several orders of magnitude faster than the slowest protein motions (∼μs(-1)). Our results also suggest that the efficiency of RE will not likely be improved by other protocols that aim to accelerate exchange or temperature diffusion. Instead, protocols with some types of guided tempering will likely be necessary to drive faster large-scale conformational transitions.

Dynamic ground-effect measurements on the F-15 STOL and Maneuver Technology Demonstrator (S/MTD) configuration

NASA Technical Reports Server (NTRS)

Kemmerly, Guy T.

1990-01-01

A moving-model ground-effect testing method was used to study the influence of rate-of-descent on the aerodynamic characteristics for the F-15 STOL and Maneuver Technology Demonstrator (S/MTD) configuration for both the approach and roll-out phases of landing. The approach phase was modeled for three rates of descent, and the results were compared to the predictions from the F-15 S/MTD simulation data base (prediction based on data obtained in a wind tunnel with zero rate of descent). This comparison showed significant differences due both to the rate of descent in the moving-model test and to the presence of the ground boundary layer in the wind tunnel test. Relative to the simulation data base predictions, the moving-model test showed substantially less lift increase in ground effect, less nose-down pitching moment, and less increase in drag. These differences became more prominent at the larger thrust vector angles. Over the small range of rates of descent tested using the moving-model technique, the effect of rate of descent on longitudinal aerodynamics was relatively constant. The results of this investigation indicate no safety-of-flight problems with the lower jets vectored up to 80 deg on approach. The results also indicate that this configuration could employ a nozzle concept using lower reverser vector angles up to 110 deg on approach if a no-flare approach procedure were adopted and if inlet reingestion does not pose a problem.

Advancing reversible shape memory by tuning the polymer network architecture

DOE PAGES

Li, Qiaoxi; Zhou, Jing; Vatankhah-Varnoosfaderani, Mohammad; ...

2016-02-02

Because of counteraction of a chemical network and a crystalline scaffold, semicrystalline polymer networks exhibit a peculiar behavior—reversible shape memory (RSM), which occurs naturally without applying any external force and particular structural design. There are three RSM properties: (i) range of reversible strain, (ii) rate of strain recovery, and (iii) decay of reversibility with time, which can be improved by tuning the architecture of the polymer network. Different types of poly(octylene adipate) networks were synthesized, allowing for control of cross-link density and network topology, including randomly cross-linked network by free-radical polymerization, thiol–ene clicked network with enhanced mesh uniformity, and loosemore » network with deliberately incorporated dangling chains. It is shown that the RSM properties are controlled by average cross-link density and crystal size, whereas topology of a network greatly affects its extensibility. In conclusion, we have achieved 80% maximum reversible range, 15% minimal decrease in reversibility, and fast strain recovery rate up to 0.05 K –1, i.e., ca. 5% per 10 s at a cooling rate of 5 K/min.« less

Toward an understanding of the turbidity measurement of heterocoagulation rate constants of dispersions containing particles of different sizes.

PubMed

Liu, Jie; Xu, Shenghua; Sun, Zhiwei

2007-11-06

Our previous studies have shown that the determination of coagulation rate constants by turbidity measurement becomes impossible for a certain operating wavelength (that is, its blind point) because at this wavelength the change in the turbidity of a dispersion completely loses its response to the coagulation process. Therefore, performing the turbidity measurement in the wavelength range near the blind point should be avoided. In this article, we demonstrate that the turbidity measurement of the rate constant for coagulation of a binary dispersion containing particles of two different sizes (heterocoagulation) presents special difficulties because the blind point shifts with not only particle size but also with the component fraction. Some important aspects of the turbidity measurement for the heterocoagulation rate constant are discussed and experimentally tested. It is emphasized that the T-matrix method can be used to correctly evaluate extinction cross sections of doublets formed during the heterocoagulation process, which is the key data determining the rate constant from the turbidity measurement, and choosing the appropriate operating wavelength and component fraction are important to achieving a more accurate rate constant. Finally, a simple scheme in experimentally determining the sensitivity of the turbidity changes with coagulation over a wavelength range is proposed.

A reversible transition in liquid Bi under pressure.

PubMed

Emuna, M; Matityahu, S; Yahel, E; Makov, G; Greenberg, Y

2018-01-21

The electrical resistance of solid and liquid Bi has been measured at high pressures and temperatures using a novel experimental design for high sensitivity measurements utilizing a "Paris-Edinburgh" toroid large volume press. An anomalous sharp decrease in resistivity with increasing temperature at constant pressures was observed in the region beyond melting which implies a possible novel transition in the melt. The proposed transition was observed across a range of pressures both in heating and cooling cycles of the sample demonstrating its reversibility. From the measurements it was possible to determine a "phase-line" of this transition on the Bi pressure-temperature phase diagram terminating at the melting curve.

[Conservative treatment of idiopathic scoliosis with effective braces: early response to trunk asymmetry may avoid curvature progress].

PubMed

Matussek, J; Dingeldey, E; Wagner, F; Rezai, G; Nahr, K

2014-07-01

Vertical posture of the growing child requires minute central nervous control mechanisms in order to maintain symmetry of the torso in its various activities. Scoliosis describes a constant deviation in the frontal, transverse and sagittal planes from the dynamic symmetry of the trunk. Early intervention with effective bracing, physiotherapy and sports can reverse curve progression during growth spurts, once these are identified in screening. Modern braces have a derotating and reducing effect (mirror effect) on asymmetric body volumes, thus influencing the growing torso and restoring lasting symmetry. Recent data support the use of braces to reverse progressing scoliosis.

Calculation of the lateral control of swept and unswept flexible wings of arbitrary stiffness

NASA Technical Reports Server (NTRS)

Diederich, Franklin W

1951-01-01

A method similar to that of NACA rep. 1000 is presented for calculating the effectiveness and the reversal speed of lateral-control devices on swept and unswept wings of arbitrary stiffness. Provision is made for using either stiffness curves and root-rotation constants or structural influence coefficients in the analysis. Computing forms and an illustrative example are included to facilitate calculations by means of the method. The effectiveness of conventional aileron configurations and the margin against aileron reversal are shown to be relatively low for swept wings at all speeds and for all wing plan forms at supersonic speeds.

Altered sensory-motor control of the head as an etiological factor in space-motion sickness

NASA Technical Reports Server (NTRS)

Lackner, J. R.; DiZio, P.

1989-01-01

Mechanical unloading during head movements in weightlessness may be an etiological factor in space-motion sickness. We simulated altered head loading on Earth without affecting vestibular stimulation by having subjects wear a weighted helmet. Eight subjects were exposed to constant velocity rotation about a vertical axis with direction reversals every 60 sec. for eight reversals with the head loaded and eight with the head unloaded. The severity of motion sickness elicited was significantly higher when the head was loaded. This suggests that altered sensory-motor control of the head is also an etiological factor in space-motion sickness.

Longitudinal Evaluation of Myocardial Fatty Acid and Glucose Metabolism in Fasted and Nonfasted Spontaneously Hypertensive Rats Using MicroPET/CT

DOE PAGES

Huber, Jennifer S.; Hernandez, Andrew M.; Janabi, Mustafa; ...

2017-09-06

Using longitudinal micro positron emission tomography (microPET)/computed tomography (CT) studies, we quantified changes in myocardial metabolism and perfusion in spontaneously hypertensive rats (SHRs), a model of left ventricular hypertrophy (LVH). Fatty acid and glucose metabolism were quantified in the hearts of SHRs and Wistar-Kyoto (WKY) normotensive rats using long-chain fatty acid analog 18F-fluoro-6-thia heptadecanoic acid ( 18F-FTHA) and glucose analog 18F-fluorodeoxyglucose ( 18F-FDG) under normal or fasting conditions. We also used 18F-fluorodihydrorotenol ( 18F-FDHROL) to investigate perfusion in their hearts without fasting. Rats were imaged at 4 or 5 times over their life cycle. Compartment modeling was used to estimatemore » the rate constants for the radiotracers. Blood samples were obtained and analyzed for glucose and free fatty acid concentrations. SHRs demonstrated no significant difference in 18F-FDHROL wash-in rate constant (P = .1) and distribution volume (P = .1), significantly higher 18F-FDG myocardial influx rate constant (P = 4×10 –8), and significantly lower 18F-FTHA myocardial influx rate constant (P = .007) than WKYs during the 2009-2010 study without fasting. SHRs demonstrated a significantly higher 18F-FDHROL wash-in rate constant (P = 5×10 –6) and distribution volume (P = 3×10 –8), significantly higher 18F-FDG myocardial influx rate constant (P = 3×10 –8), and a higher trend of 18F-FTHA myocardial influx rate constant (not significant, P = .1) than WKYs during the 2011–2012 study with fasting. Changes in glucose plasma concentrations were generally negatively correlated with corresponding radiotracer influx rate constant changes. The study indicates a switch from preferred fatty acid metabolism to increased glucose metabolism with hypertrophy. Increased perfusion during the 2011-2012 study may be indicative of increased aerobic metabolism in the SHR model of LVH.« less

Longitudinal Evaluation of Myocardial Fatty Acid and Glucose Metabolism in Fasted and Nonfasted Spontaneously Hypertensive Rats Using MicroPET/CT

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

Huber, Jennifer S.; Hernandez, Andrew M.; Janabi, Mustafa

Using longitudinal micro positron emission tomography (microPET)/computed tomography (CT) studies, we quantified changes in myocardial metabolism and perfusion in spontaneously hypertensive rats (SHRs), a model of left ventricular hypertrophy (LVH). Fatty acid and glucose metabolism were quantified in the hearts of SHRs and Wistar-Kyoto (WKY) normotensive rats using long-chain fatty acid analog 18F-fluoro-6-thia heptadecanoic acid ( 18F-FTHA) and glucose analog 18F-fluorodeoxyglucose ( 18F-FDG) under normal or fasting conditions. We also used 18F-fluorodihydrorotenol ( 18F-FDHROL) to investigate perfusion in their hearts without fasting. Rats were imaged at 4 or 5 times over their life cycle. Compartment modeling was used to estimatemore » the rate constants for the radiotracers. Blood samples were obtained and analyzed for glucose and free fatty acid concentrations. SHRs demonstrated no significant difference in 18F-FDHROL wash-in rate constant (P = .1) and distribution volume (P = .1), significantly higher 18F-FDG myocardial influx rate constant (P = 4×10 –8), and significantly lower 18F-FTHA myocardial influx rate constant (P = .007) than WKYs during the 2009-2010 study without fasting. SHRs demonstrated a significantly higher 18F-FDHROL wash-in rate constant (P = 5×10 –6) and distribution volume (P = 3×10 –8), significantly higher 18F-FDG myocardial influx rate constant (P = 3×10 –8), and a higher trend of 18F-FTHA myocardial influx rate constant (not significant, P = .1) than WKYs during the 2011–2012 study with fasting. Changes in glucose plasma concentrations were generally negatively correlated with corresponding radiotracer influx rate constant changes. The study indicates a switch from preferred fatty acid metabolism to increased glucose metabolism with hypertrophy. Increased perfusion during the 2011-2012 study may be indicative of increased aerobic metabolism in the SHR model of LVH.« less

Addressing reverse osmosis fouling within water reclamation--a side-by-side comparison of low-pressure membrane pretreatments.

PubMed

Kent, Fraser C; Farahbakhsh, Khosrow

2011-06-01

A tertiary membrane filtration (TMF) pilot operating on secondary effluent and a membrane bioreactor (MBR) were setup in a side-by-side study as pretreatments for two identical reverse osmosis pilot systems. The water quality of the permeate from both low-pressure membrane pretreatment systems and the fouling rate of the reverse osmosis systems were compared to assess the capabilities of the two low-pressure membrane pretreatments to prevent organic fouling of the reverse osmosis systems. Both pretreatment pilots were setup using typical operating conditions (i.e., solids retention time and mixed-liquor suspended solids). A consistent difference in water quality and reverse osmosis performance was demonstrated during the 12-month study. The MBR permeate consistently had significantly lower total organic carbon (TOC) and chemical oxygen demand concentrations, but higher color and specific UV absorbance compared with the permeate from the TMF pretreatment. The pretreatment with the MBR gave an average reverse osmosis fouling rate over the entire study (0.27 Lmh/bar.month) that was less than half of the value found for the reverse osmosis with TMF pretreatment (0.60 Lmh/bar.month). A correlation of reverse osmosis feed TOC concentration with average reverse osmosis fouling rate also was established, independent of the pretreatment method used. Results from a cleaning analysis, energy dispersive spectroscopy, and fourier transformed infrared reflectometry confirmed that the foulants were primarily organic in nature. It is concluded that, for this type of application and setup, MBR systems present an advantage over tertiary membrane polishing of secondary effluent for reverse osmosis pretreatment.

(In)validity of the constant field and constant currents assumptions in theories of ion transport.

PubMed Central

Syganow, A; von Kitzing, E

1999-01-01

Constant electric fields and constant ion currents are often considered in theories of ion transport. Therefore, it is important to understand the validity of these helpful concepts. The constant field assumption requires that the charge density of permeant ions and flexible polar groups is virtually voltage independent. We present analytic relations that indicate the conditions under which the constant field approximation applies. Barrier models are frequently fitted to experimental current-voltage curves to describe ion transport. These models are based on three fundamental characteristics: a constant electric field, negligible concerted motions of ions inside the channel (an ion can enter only an empty site), and concentration-independent energy profiles. An analysis of those fundamental assumptions of barrier models shows that those approximations require large barriers because the electrostatic interaction is strong and has a long range. In the constant currents assumption, the current of each permeating ion species is considered to be constant throughout the channel; thus ion pairing is explicitly ignored. In inhomogeneous steady-state systems, the association rate constant determines the strength of ion pairing. Among permeable ions, however, the ion association rate constants are not small, according to modern diffusion-limited reaction rate theories. A mathematical formulation of a constant currents condition indicates that ion pairing very likely has an effect but does not dominate ion transport. PMID:9929480

Improved confinement region without large magnetohydrodynamic activity in TPE-RX reversed-field pinch plasma

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

Yambe, Kiyoyuki; Hirano, Yoichi; Sakakita, Hajime

2014-11-15

We found that spontaneous improved confinement was brought about depending on the operating region in the Toroidal Pinch Experiment-Reversed eXperiment (TPE-RX) reversed-field pinch plasma [Y. Yagi et al., Fusion Eng. Des. 45, 421 (1999)]. Gradual decay of the toroidal magnetic field at plasma surface B{sub tw} reversal makes it possible to realize a prolonged discharge, and the poloidal beta value and energy confinement time increase in the latter half of the discharge, where reversal and pinch parameters become shallow and low, respectively. In the latter half of the discharge, the plasma current and volume-averaged toroidal magnetic field 〈B{sub t}〉 increasemore » again, the electron density slowly decays, the electron temperature and soft X-ray radiation intensity increase, and the magnetic fluctuations are markedly reduced. In this period of improved confinement, the value of (〈B{sub t}〉-B{sub tw})/B{sub pw}, where B{sub pw} is the poloidal magnetic field at the plasma surface, stays almost constant, which indicates that the dynamo action occurs without large magnetohydrodynamic activities.« less

The response of dense dry granular material to the shear reversal

NASA Astrophysics Data System (ADS)

Zhang, Jie; Ren, Jie; Farhadi, Somayeh; Behringer, Robert

2008-11-01

We have performed two dimensional granular experiments under pure shear using bidisperse photo-elastic disks. Starting from a stress free state, a square box filled with granular particles is subject to shear. The forward shears involved various number of steps, leading to maximum strains between 0.1 and 0.3. The area is kept constant during the shear. The network of force chains gradually built up as the strain increased, leading to increased pressure and shear stress. Reverse shear was then applied to the system. Depending on the initial packing fraction and the strain at which the shear is reversed, the force chain network built prior to the shear reversal may be destroyed completely or partially destroyed. Following the force chain weakening, when the reserve shear is continuously applied to the system, there is a force chain strengthening. Following each change of the system, contact forces of individual disks were measured by applying an inverse algorithm. We also kept track of the displacement and angle of rotation of every particle from frame to frame. We present the results for the structure failure and reconstruction during shear reversals. We also present data for stresses, contact force distributions and other statistical measures.

MODIFIED REVERSE OSMOSIS SYSTEM FOR TREATMENT OF PRODUCED WATERS

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

T.M. Whitworth; Liangxiong Li

2002-09-15

This report describes work performed during the first year of the project ''Modified Reverse Osmosis System for Treatment of Produced Waters.'' This research project has two objectives. The first objective is to test the use of clay membranes in the treatment of produced waters by reverse osmosis. The second objective is to test the ability of a system patented by the New Mexico Tech Research Foundation to remove salts from reverse osmosis waste streams as a solid. We performed 12 experiments using clay membranes in cross-flow experimental cells. We found that, due to dispersion in the porous frit used adjacentmore » to the membrane, the concentration polarization layer seems to be completely (or nearly completely) destroyed at low flow rates. This observation suggests that clay membranes used with porous frit material many reach optimum rejection rates at lower pumping rates than required for use with synthetic membranes. The solute rejection efficiency decreases with increasing solution concentration. For the membranes and experiments reported here, the rejection efficiency ranged from 71% with 0.01 M NaCl solution down to 12% with 2.3 M NaCl solution. More compacted clay membranes will have higher rejection capabilities. The clay membranes used in our experiments were relatively thick (approximately 0.5 mm). The active layer of most synthetic membranes is only 0.04 {micro}m (0.00004 mm), approximately 1250 times thinner than the clay membranes used in these experiments. Yet clay membranes as thin as 12 {micro}m have been constructed (Fritz and Eady, 1985). Since Darcy's law states that the flow through a material of constant permeability is inversely proportional to it's the material's thickness, then, based on these experimental observations, a very thin clay membrane would be expected to have much higher flow rates than the ones used in these experiments. Future experiments will focus on testing very thin clay membranes. The membranes generally exhibited reasonable stable rejection rates over time for chloride for a range of concentrations between 0.01 and 2.5 M. One membrane ran in excess of three months with no apparent loss of usability. This suggests that clay membranes may have a long useable life. Twenty different hyperfiltration-induced solute precipitation experiments were either attempted or completed and are reported here. The results of these experiments suggest that hyperfiltration-induced solute precipitation is possible, even for very soluble substances such as NaCl. However, the precipitation rates obtained in the laboratory do not appear to be adequate for commercial application at this time. Future experiments will focus on making the clay membranes more compact and thinner in order to obtain higher flux rates. Two alternative methods of removing solutes from solution, for which the New Mexico Tech Research Foundation is preparing patent applications, are also being investigated. These methods will be described in the next annual report after the patent applications are filed. Technology transfer efforts included two meetings (one in Farmington NM, and one in Hobbs, NM) where the results of this research were presented to independent oil producers and other interested parties. In addition, members of the research team gave seven presentations concerning this research and because of this research project T. M. (Mike) Whitworth was asked to sit on the advisory board for development of a new water treatment facility for the City of El Paso, Texas. Several papers are in preparation for submission to peer-reviewed journals based on the data presented in this report.« less

Clay catalysis of oligonucleotide formation: kinetics of the reaction of the 5'-phosphorimidazolides of nucleotides with the non-basic heterocycles uracil and hypoxanthine

NASA Technical Reports Server (NTRS)

Kawamura, K.; Ferris, J. P.

1999-01-01

The montmorillonite clay catalyzed condensation of activated monocleotides to oligomers of RNA is a possible first step in the formation of the proposed RNA world. The rate constants for the condensation of the phosphorimidazolide of adenosine were measured previously and these studies have been extended to the phosphorimidazolides of inosine and uridine in the present work to determine of substitution of neutral heterocycles for the basic adenine ring changes the reaction rate or regioselectivity. The oligomerization reactions of the 5'-phosphoromidazolides of uridine (ImpU) and inosine (ImpI) on montmorillonite yield oligo(U)s and oligo(I)s as long as heptamers. The rate constants for oligonucleotide formation were determined by measuring the rates of formation of the oligomers by HPLC. Both the apparent rate constants in the reaction mixture and the rate constants on the clay surface were calculated using the partition coefficients of the oligomers between the aqueous and clay phases. The rate constants for trimer formation are much greater than those dimer synthesis but there was little difference in the rate constants for the formation of trimers and higher oligomers. The overall rates of oligomerization of the phosphorimidazolides of purine and pyrimidine nucleosides in the presence of montmorillonite clay are the same suggesting that RNA formed on the primitive Earth could have contained a variety of heterocyclic bases. The rate constants for oligomerization of pyrimidine nucleotides on the clay surface are significantly higher than those of purine nucleotides since the pyrimidine nucleotides bind less strongly to the clay than do the purine nucleotides. The differences in the binding is probably due to Van der Waals interactions between the purine bases and the clay surface. Differences in the basicity of the heterocyclic ring in the nucleotide have little effect on the oligomerization process.

Superior outcomes of microsurgical vasectomy reversal in men with the same female partners.

PubMed

Chan, Peter T K; Goldstein, Marc

2004-05-01

To evaluate the outcomes of vasectomy reversals in men with the same female partners. Retrospective analysis with comparison with a historical cohort. University hospital. Among 1,048 patients who underwent microsurgical vasectomy reversal from 1986 to 2002, 27 men (2.6%) were identified who had the same partners as before their vasectomy. Microsurgical vasovasostomy or vasoepididymostomy. Semen parameters, clinical pregnancy, and live birth rates. The mean age of the men was 38.5 years, and 37.2 years for their female partners. The reasons for vasectomy reversal were death of a child in 33% of cases and desire for more children in 66% of cases. The overall patency rate was 100% at 1 month postoperatively, with an average sperm concentration of 30 million/mL and 24% motility. Among patients with follow-up beyond 1 year, the natural pregnancy rate was 86%, which was achieved at 8.3 months postoperatively, with a live birth rate of 82%. The live birth rate in couples with the death of a child was 100%. The outcomes of vasectomy reversal in men with the same female partners are better than for men with new partners. Possible reasons for these superior results are previous proven fecundity as a couple, shorter time interval since vasectomy, and emotional dedication.

THE UPTAKE OF RADIOCOLLOIDS BY MACROPHAGES IN VITRO

PubMed Central

Gosselin, Robert E.

1956-01-01

Macrophages isolated from the rabbit peritoneal cavity extract radioactive colloidal gold from solutions in vitro. This reaction (ultraphagocytosis) involves two phases: the reversible adsorption of gold on the cell surface and the subsequent irreversible removal of surface-bound colloid into the cell. The latter process (called ingestion) appears to proceed at a rate which is proportional at any moment to the amount of gold attached to the cell surface; the latter in turn can be related to the concentration in extracellular fluid by a simple adsorption isotherm. In terms of rate, therefore, ingestion is related to the extracellular gold concentration in the same way that many enzyme reactions are related to the substrate concentration. Although enzyme kinetics are useful in describing rates of ultraphagocytosis, there is no evidence that enzymes participate in either adsorption or ingestion or that metabolic energy is required of the macrophage. Exudative leucocytes of the heterophilic series show little or no interaction with these finely dispersed gold sols (mean particle diameter 6 to 9 millimicrons). 37°C. three parameters are sufficient to characterize the reaction between gold and a suspension of macrophages, namely an affinity constant (1/Ks), an adsorption maximum (L), and a rate constant of ingestion (k 3). Although numerical values differed markedly among cells of different exudates, all three parameters were estimated in three instances. In these suspensions between 2 and 20 per cent of the surface-bound gold was ingested each minute (37°C., pH 7.4). Under conditions of surface saturation, it was estimated that tens of thousands of gold particles were attached to the surface of an average macrophage; this amount of colloid, however, occupied less than 1 per cent of the geometric area of the cell surface. Although surface saturation imposed an upper limit on the rate of ingestion, no practical limit was noted in the capacity of macrophages to continue the reaction. Optical measurements imply that within the cell agglutination of colloidal gold began promptly after its ingestion. These data are compared with published kinetic studies on the phagocytosis of microscopic particulates and on the parasitism of bacteria by virus. PMID:13319653

Novel kinetic model of the removal of divalent heavy metal ions from aqueous solutions by natural clinoptilolite.

PubMed

Jovanovic, Mina; Rajic, Nevenka; Obradovic, Bojana

2012-09-30

Removal of heavy metal ions from aqueous solutions using zeolites is widely described by pseudo-second order kinetics although this model may not be valid under all conditions. In this work, we have extended approaches used for derivation of this model in order to develop a novel kinetic model that is related to the ion exchange mechanism underlying sorption of metal ions in zeolites. The novel model assumed two reversible steps, i.e. release of sodium ions from the zeolite lattice followed by bonding of the metal ion. The model was applied to experimental results of Cu(II) sorption by natural clinoptilolite-rich zeolitic tuff at different initial concentrations and temperatures and then validated by predictions of ion exchange kinetics of other divalent heavy metal ions (i.e. Mn(II), Zn(II) and Pb(II)). Model predictions were in excellent agreements with experimental data for all investigated systems. In regard to the proposed mechanism, modeling results implied that the sodium ion release rate was constant for all investigated metals while the overall rate was mainly determined by the rate of heavy metal ion bonding to the lattice. In addition, prediction capabilities of the novel model were demonstrated requiring one experimentally determined parameter, only. Copyright © 2012 Elsevier B.V. All rights reserved.

Viscous propulsion in active transversely isotropic media

NASA Astrophysics Data System (ADS)

Cupples, Gemma; Dyson, Rosemary; Smith, David

2017-11-01

Taylor's swimming sheet is a classical model of microscale propulsion and pumping. Many biological fluids and substances are fibrous, having a preferred direction in their microstructure; for example cervical mucus. To understand how these effects modify viscous propulsion, we extend Taylor's classical model of small-amplitude viscous propulsion of a `swimming sheet' via the transversely-isotropic fluid model of Ericksen, which is linear in strain rate and possesses a distinguished direction. The energetic costs of swimming are significantly altered by all rheological parameters and the initial fibre angle. Propulsion in a passive transversely-isotropic fluid enhances mean rate of working, independent of the initial fibre orientation. In this regime the mean swimming velocity is unchanged from the Newtonian case. The effect of fibre tension, or alternatively a stresslet characterising an active fluid, is also considered. This stress introduces an angular dependence and dramatically changes the streamlines and flow field; fibres aligned with the swimming direction increase the energetic demands of the sheet. The constant fibre stress may result in a reversal of the mean swimming velocity and a negative mean rate of working if sufficiently large relative to the other parameters. Funding is provided by a Biotechnology and Biological Sciences Research Council (BBSRC) Industrial CASE Studentship (BB/L015587/1).

Kinetics of DNA Tile Dimerization

PubMed Central

2015-01-01

Investigating how individual molecular components interact with one another within DNA nanoarchitectures, both in terms of their spatial and temporal interactions, is fundamentally important for a better understanding of their physical behaviors. This will provide researchers with valuable insight for designing more complex higher-order structures that can be assembled more efficiently. In this report, we examined several spatial factors that affect the kinetics of bivalent, double-helical (DH) tile dimerization, including the orientation and number of sticky ends (SEs), the flexibility of the double helical domains, and the size of the tiles. The rate constants we obtained confirm our hypothesis that increased nucleation opportunities and well-aligned SEs accelerate tile–tile dimerization. Increased flexibility in the tiles causes slower dimerization rates, an effect that can be reversed by introducing restrictions to the tile flexibility. The higher dimerization rates of more rigid tiles results from the opposing effects of higher activation energies and higher pre-exponential factors from the Arrhenius equation, where the pre-exponential factor dominates. We believe that the results presented here will assist in improved implementation of DNA tile based algorithmic self-assembly, DNA based molecular robotics, and other specific nucleic acid systems, and will provide guidance to design and assembly processes to improve overall yield and efficiency. PMID:24794259

Kinetics of DNA tile dimerization.

PubMed

Jiang, Shuoxing; Yan, Hao; Liu, Yan

2014-06-24

Investigating how individual molecular components interact with one another within DNA nanoarchitectures, both in terms of their spatial and temporal interactions, is fundamentally important for a better understanding of their physical behaviors. This will provide researchers with valuable insight for designing more complex higher-order structures that can be assembled more efficiently. In this report, we examined several spatial factors that affect the kinetics of bivalent, double-helical (DH) tile dimerization, including the orientation and number of sticky ends (SEs), the flexibility of the double helical domains, and the size of the tiles. The rate constants we obtained confirm our hypothesis that increased nucleation opportunities and well-aligned SEs accelerate tile-tile dimerization. Increased flexibility in the tiles causes slower dimerization rates, an effect that can be reversed by introducing restrictions to the tile flexibility. The higher dimerization rates of more rigid tiles results from the opposing effects of higher activation energies and higher pre-exponential factors from the Arrhenius equation, where the pre-exponential factor dominates. We believe that the results presented here will assist in improved implementation of DNA tile based algorithmic self-assembly, DNA based molecular robotics, and other specific nucleic acid systems, and will provide guidance to design and assembly processes to improve overall yield and efficiency.

Rate Constants for the Reactions of Hydroxyl Radical with Several Alkanes, Cycloalkanes, and Dimethyl Ether

NASA Technical Reports Server (NTRS)

DeMore, W.; Bayes, K.

1998-01-01

Relative rate experiements were used to measure rate constants and temperature denpendencies of the reactions of OH with propane, n-butane, n-pentane, n-hexane, cyclopropane, cyclobutane, cyclopentane, and dimethyl ether.

Silicon Carbide Diodes Characterization at High Temperature and Comparison With Silicon Devices

NASA Technical Reports Server (NTRS)

Lebron-Velilla, Ramon C.; Schwarze, Gene E.; Gardner, Brent G.; Adams, Jerry D., Jr.

2004-01-01

Commercially available silicon carbide (SiC) Schottky diodes from different manufacturers rated at 200, 300, 600, and 1200 V, were electrically tested and characterized as a function of temperature up to 300 C. Electrical tests included both steady state and dynamic tests. Steady state tests produced forward and reverse I-V characteristic curves. Transient tests evaluated the switching performance of the diodes in either a hard-switched DC to DC buck converter or a half-bridge boost converter. For evaluation and comparison purposes, the same tests were performed with current state-of-the-art ultra fast silicon (Si) pn-junction diodes of similar ratings and also a Si Schottky diode. The comparisons made were forward voltage drop at rated current, reverse current at rated voltage, and turn-off peak reverse recovery current and reverse recovery time. In addition, efficiency measurements were taken for the buck DC to DC converter using both the SiC Schottky diodes and the Si pn-junction diodes at different temperatures and frequencies. The test results showed that at high temperature, the forward voltage drop for SiC Schottky diodes is higher than the forward drop of the ultra fast Si pn-junction diodes. As the temperature increased, the forward voltage drop of the SiC Schottky increased while for the ultra fast Si pn-junction diodes, the forward voltage drop decreased as temperature increased. For the elevated temperature steady state reverse voltage tests, the SiC Schottky diodes showed low leakage current at their rated voltage. Likewise, for the transient tests, the SiC Schottky diodes displayed low reverse recovery currents over the range of temperatures tested. Conversely, the Si pn-junction diodes showed increasing peak reverse current values and reverse recovery times with increasing temperature. Efficiency measurements in the DC to DC buck converter showed the advantage of the SiC Schottky diodes over the ultra fast Si pn-junction diodes, especially at the higher temperatures and higher frequencies.

Product development studies of amino acid conjugate of Aceclofenac.

PubMed

Singh, Ajay Pal; Ramadan, Wafa Mossa; Dahiya, Rajiv; Sarpal, A S; Pathak, Kamla

2009-04-01

The prodrugs designed by classical approach increase lipophilicity of the drug, which decreases the water solubility thus decreasing the concentration gradient, which controls drug absorption. To overcome the limitations of traditional prodrug approach, water soluble prodrugs can be designed by adding selected amino acid to the drug moiety that are the substrates for the enzyme located at the intestinal brush border thus overcoming pharmaceutical problem without compromising bioavailability. ACaa (Amino acid conjugate of Aceclofenac) was synthesized by conjugation with l-phenylalanine by conventional coupling method using N, N-dicyclohexylcarbodiimide and ACaa was characterized by melting point, TLC, photomicrograph, UV, FT-IR, FT-NMR, MS-FAB, XRD and DSC. As a part of product development study ACaa was subjected to studies like In-vivo in albino rats and in-vitro like ACaa reversion to AC (Aceclofenac) in aqueous buffers of pH 1.21, 2.38. 3.10, 6.22 and 7.41, at a constant concentration (0.05M), ionic strength (micro = 0.5) and at a temperature of 37 degrees C +/- 0.5 degrees C, ACaa showed negligible reversion (2.15 %) up to 24 hrs study at acidic pH thus suggesting stability in acidic environment of stomach, the rate of reversion increased as pH of medium increased. pH- partition profile, pH- solubility profile and micromeritic studies were also carried out in comparison to pure drug. The solubility and lipophilicity of ACaa exhibited higher values at all pH range when compared to AC. The micromeritic properties also evaluated in terms of particle shape and size, IQCS and kurtosis. Resulting IQCS value approached zero thus suggesting reducing in the degree of skewness.

Linear Discriminant Analysis for the in Silico Discovery of Mechanism-Based Reversible Covalent Inhibitors of a Serine Protease: Application of Hydration Thermodynamics Analysis and Semi-empirical Molecular Orbital Calculation.

PubMed

Masuda, Yosuke; Yoshida, Tomoki; Yamaotsu, Noriyuki; Hirono, Shuichi

2018-01-01

We recently reported that the Gibbs free energy of hydrolytic water molecules (ΔG wat ) in acyl-trypsin intermediates calculated by hydration thermodynamics analysis could be a useful metric for estimating the catalytic rate constants (k cat ) of mechanism-based reversible covalent inhibitors. For thorough evaluation, the proposed method was tested with an increased number of covalent ligands that have no corresponding crystal structures. After modeling acyl-trypsin intermediate structures using flexible molecular superposition, ΔG wat values were calculated according to the proposed method. The orbital energies of antibonding π* molecular orbitals (MOs) of carbonyl C=O in covalently modified catalytic serine (E orb ) were also calculated by semi-empirical MO calculations. Then, linear discriminant analysis (LDA) was performed to build a model that can discriminate covalent inhibitor candidates from substrate-like ligands using ΔG wat and E orb . The model was built using a training set (10 compounds) and then validated by a test set (4 compounds). As a result, the training set and test set ligands were perfectly discriminated by the model. Hydrolysis was slower when (1) the hydrolytic water molecule has lower ΔG wat ; (2) the covalent ligand presents higher E orb (higher reaction barrier). Results also showed that the entropic term of hydrolytic water molecule (-TΔS wat ) could be used for estimating k cat and for covalent inhibitor optimization; when the rotational freedom of the hydrolytic water molecule is limited, the chance for favorable interaction with the electrophilic acyl group would also be limited. The method proposed in this study would be useful for screening and optimizing the mechanism-based reversible covalent inhibitors.

High-Temperature Slow Crack Growth of Silicon Carbide Determined by Constant-Stress-Rate and Constant-Stress Testing

NASA Technical Reports Server (NTRS)

Choi, Sung H.; Salem, J. A.; Nemeth, N. N.

1998-01-01

High-temperature slow-crack-growth behaviour of hot-pressed silicon carbide was determined using both constant-stress-rate ("dynamic fatigue") and constant-stress ("static fatigue") testing in flexure at 1300 C in air. Slow crack growth was found to be a governing mechanism associated with failure of the material. Four estimation methods such as the individual data, the Weibull median, the arithmetic mean and the median deviation methods were used to determine the slow crack growth parameters. The four estimation methods were in good agreement for the constant-stress-rate testing with a small variation in the slow-crack-growth parameter, n, ranging from 28 to 36. By contrast, the variation in n between the four estimation methods was significant in the constant-stress testing with a somewhat wide range of n= 16 to 32.

Simple Model for Detonation Energy and Rate

NASA Astrophysics Data System (ADS)

Lauderbach, Lisa M.; Souers, P. Clark

2017-06-01

A simple model is used to derive the Eyring equation for the size effect and detonation rate, which depends on a constant energy density. The rate derived from detonation velocities is then converted into a rate constant to be used in a reactive flow model. The rate might be constant if the size effect curve is straight, but the rate constant will change with the radius of the sample and cannot be a constant. This is based on many careful cylinder tests have been run recently on LX-17 with inner copper diameters ranging from 12.7 to 101.6 mm. Copper wall velocities at scaled displacements of 6, 12.5 and 19 mm equate to values at relative volumes of 2.4, 4.4 and 7.0. At each point, the velocities from 25.4 to 101.6 mm are constant within error whereas the 12.7 mm velocities are lower. Using the updated Gurney model, the energy densities at the three larger sizes are also constant. Similar behavior has been seen in LX-14, LX-04, and an 83% RDX mix. A rough saturation has also been in old ANFO data for diameters of 101.6 mm and larger. Although the energy densities saturate, the detonation velocities continue to increase with size. These observations suggest that maximum energy density is a constant for a given explosive of a given density. The correlation of energy density with detonation velocity is not good because the latter depends on the total energy of the sample. This work performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Reverse Engineering of Oxygen Transport in the Lung: Adaptation to Changing Demands and Resources through Space-Filling Networks

PubMed Central

Hou, Chen; Gheorghiu, Stefan; Huxley, Virginia H.; Pfeifer, Peter

2010-01-01

The space-filling fractal network in the human lung creates a remarkable distribution system for gas exchange. Landmark studies have illuminated how the fractal network guarantees minimum energy dissipation, slows air down with minimum hardware, maximizes the gas- exchange surface area, and creates respiratory flexibility between rest and exercise. In this paper, we investigate how the fractal architecture affects oxygen transport and exchange under varying physiological conditions, with respect to performance metrics not previously studied. We present a renormalization treatment of the diffusion-reaction equation which describes how oxygen concentrations drop in the airways as oxygen crosses the alveolar membrane system. The treatment predicts oxygen currents across the lung at different levels of exercise which agree with measured values within a few percent. The results exhibit wide-ranging adaptation to changing process parameters, including maximum oxygen uptake rate at minimum alveolar membrane permeability, the ability to rapidly switch from a low oxygen uptake rate at rest to high rates at exercise, and the ability to maintain a constant oxygen uptake rate in the event of a change in permeability or surface area. We show that alternative, less than space-filling architectures perform sub-optimally and that optimal performance of the space-filling architecture results from a competition between underexploration and overexploration of the surface by oxygen molecules. PMID:20865052

The Influence of Uncompensated Solution Resistance on the Determination and Standard Electrochemical Rate Constants Using Cyclic Voltammetry, and Some Comparisons with AC Voltammetry.

DTIC Science & Technology

1987-09-25

rate constants, k2r using cyclic voltametry . The res tss are expressed in terms of systematic deviations oP sapparent measured" rate constants, k~b(app...concentration was taken to be lum unless otherwise noted. The voltammetric sweep rate was set at 20 V sŕ unless specified otherwise. The general procedure...peaks for the negative- and positive-going potential sweeps have opposite signs, the measured cathodic-anodic peak separation, AEp, will clearly be

Assessment of long-term donor-site morbidity after harvesting the latissimus dorsi flap for neonatal myelomeningocele repair.

PubMed

Osinga, R; Mazzone, L; Meuli, M; Meuli-Simmen, C; von Campe, A

2014-08-01

The latissimus dorsi flap (LDF) has been employed very successfully over decades to cover large soft-tissue defects. Its donor-site morbidity has been extensively investigated in adults - but not in children - and is considered to be nonrestrictive. The aim of this long-term study was to assess donor-site morbidity with the modified Constant score more than 8 years after coverage of large myelomeningocele (MMC) defects with a reverse latissimus dorsi flap. Within the first days after birth, the reverse latissimus dorsi muscle flap was used uni- or bilaterally in three neonates to cover a large MMC defect. Bilateral shoulder function was tested more than 8 years postoperatively according to the modified Constant score. The mean age at follow-up was 11.7 years. None of the patients experienced any pain or shoulder restrictions during normal daily activities. They all managed to position both of their arms comfortably above the head. Forward flexion was normal in all patients as was abduction and external rotation. Dorsal extension was minimally reduced on the operated side. Internal rotation was symmetric in all patients; the extent of active movement varied from excellent to poor. Our long-term data suggest that there is no specific and significant impairment of shoulder function after using the distally pedicled reverse LDF for neonatal MMC repair. Copyright © 2014 British Association of Plastic, Reconstructive and Aesthetic Surgeons. Published by Elsevier Ltd. All rights reserved.

Passive air sampling theory for semivolatile organic compounds.

PubMed

Bartkow, Michael E; Booij, Kees; Kennedy, Karen E; Müller, Jochen F; Hawker, Darryl W

2005-07-01

The mathematical modelling underlying passive air sampling theory can be based on mass transfer coefficients or rate constants. Generally, these models have not been inter-related. Starting with basic models, the exchange of chemicals between the gaseous phase and the sampler is developed using mass transfer coefficients and rate constants. Importantly, the inter-relationships between the approaches are demonstrated by relating uptake rate constants and loss rate constants to mass transfer coefficients when either sampler-side or air-side resistance is dominating chemical exchange. The influence of sampler area and sampler volume on chemical exchange is discussed in general terms and as they relate to frequently used parameters such as sampling rates and time to equilibrium. Where air-side or sampler-side resistance dominates, an increase in the surface area of the sampler will increase sampling rates. Sampling rates are not related to the sampler/air partition coefficient (K(SV)) when air-side resistance dominates and increase with K(SV) when sampler-side resistance dominates.

Electronic structure and exchange interactions in diluted semimagnetic semiconductors (Zn,Co)Se and (Zn,Mn)Se

NASA Astrophysics Data System (ADS)

Mašek, J.

1991-05-01

A comparative study of the electronic structure of (Zn,Co)Se and (Zn,Mn)Se is done by using a tight-binding version of the coherent potential approximation. The densities of states, relevant for a photoemission experiment, are calculated for a magnetically disordered phase. The exchange constant Jpd is obtained from the splitting of the valence band top in the ferromagnetic phase of the mixed crystal; Jdd is estimated from the energy of a spin reversal. We explain the large exchange constant in the Co-based systems as a result of efficient hybridization of the d-states with the valence band.

Reverse hybrid total hip arthroplasty.

PubMed

Wangen, Helge; Havelin, Leif I; Fenstad, Anne M; Hallan, Geir; Furnes, Ove; Pedersen, Alma B; Overgaard, Søren; Kärrholm, Johan; Garellick, Göran; Mäkelä, Keijo; Eskelinen, Antti; Nordsletten, Lars

2017-06-01

Background and purpose - The use of a cemented cup together with an uncemented stem in total hip arthroplasty (THA) has become popular in Norway and Sweden during the last decade. The results of this prosthetic concept, reverse hybrid THA, have been sparsely described. The Nordic Arthroplasty Register Association (NARA) has already published 2 papers describing results of reverse hybrid THAs in different age groups. Based on data collected over 2 additional years, we wanted to perform in depth analyses of not only the reverse hybrid concept but also of the different cup/stem combinations used. Patients and methods - From the NARA, we extracted data on reverse hybrid THAs from January 1, 2000 until December 31, 2013. 38,415 such hips were studied and compared with cemented THAs. The Kaplan-Meier method and Cox regression analyses were used to estimate the prosthesis survival and the relative risk of revision. The main endpoint was revision for any reason. We also performed specific analyses regarding the different reasons for revision and analyses regarding the cup/stem combinations used in more than 500 cases. Results - We found a higher rate of revision for reverse hybrids than for cemented THAs, with an adjusted relative risk of revision (RR) of 1.4 (95% CI: 1.3-1.5). At 10 years, the survival rate was 94% (CI: 94-95) for cemented THAs and 92% (95% CI: 92-93) for reverse hybrids. The results for the reverse hybrid THAs were inferior to those for cemented THAs in patients aged 55 years or more (RR =1.1, CI: 1.0-1.3; p < 0.05). We found a higher rate of early revision due to periprosthetic femoral fracture for reverse hybrids than for cemented THAs in patients aged 55 years or more (RR =3.1, CI: 2.2-4.5; p < 0.001). Interpretation - Reverse hybrid THAs had a slightly higher rate of revision than cemented THAs in patients aged 55 or more. The difference in survival was mainly caused by a higher incidence of early revision due to periprosthetic femoral fracture in the reversed hybrid THAs.

Assessing the effect of different treatments on decomposition rate of dairy manure.

PubMed

Khalil, Tariq M; Higgins, Stewart S; Ndegwa, Pius M; Frear, Craig S; Stöckle, Claudio O

2016-11-01

Confined animal feeding operations (CAFOs) contribute to greenhouse gas emission, but the magnitude of these emissions as a function of operation size, infrastructure, and manure management are difficult to assess. Modeling is a viable option to estimate gaseous emission and nutrient flows from CAFOs. These models use a decomposition rate constant for carbon mineralization. However, this constant is usually determined assuming a homogenous mix of manure, ignoring the effects of emerging manure treatments. The aim of this study was to measure and compare the decomposition rate constants of dairy manure in single and three-pool decomposition models, and to develop an empirical model based on chemical composition of manure for prediction of a decomposition rate constant. Decomposition rate constants of manure before and after an anaerobic digester (AD), following coarse fiber separation, and fine solids removal were determined under anaerobic conditions for single and three-pool decomposition models. The decomposition rates of treated manure effluents differed significantly from untreated manure for both single and three-pool decomposition models. In the single-pool decomposition model, AD effluent containing only suspended solids had a relatively high decomposition rate of 0.060 d(-1), while liquid with coarse fiber and fine solids removed had the lowest rate of 0.013 d(-1). In the three-pool decomposition model, fast and slow decomposition rate constants (0.25 d(-1) and 0.016 d(-1) respectively) of untreated AD influent were also significantly different from treated manure fractions. A regression model to predict the decomposition rate of treated dairy manure fitted well (R(2) = 0.83) to observed data. Copyright © 2016 Elsevier Ltd. All rights reserved.

Comparison of MFI-UF constant pressure, MFI-UF constant flux and Crossflow Sampler-Modified Fouling Index Ultrafiltration (CFS-MFI UF).

PubMed

Sim, Lee Nuang; Ye, Yun; Chen, Vicki; Fane, Anthony G

2011-02-01

Understanding the foulant deposition mechanism during crossflow filtration is critical in developing indices to predict fouling propensity of feed water for reverse osmosis (RO). Factors affecting the performance on different fouling indices such as MFI-UF constant pressure, MFI-UF constant flux and newly proposed fouling index, CFS-MFI(UF) were investigated. Crossflow Sampler-Modified Fouling Index Ultrafiltration (CFS-MFI(UF)) utilises a typical crossflow unit to simulate the hydrodynamic conditions in the actual RO units followed by a dead-end unit to measure the fouling propensity of foulants. CFS-MFI(UF) was found sensitive to crossflow velocity. The crossflow velocity in the crossflow sampler unit influences the particle concentration and the particle size distribution in its permeate. CFS-MFI(UF) was also found sensitive to the permeate flux of both CFS and the dead-end cell. To closely simulate the hydrodynamic conditions of a crossflow RO unit, the flux used for CFS-MFI(UF) measurement was critical. The best option is to operate both the CFS and dead-end permeate flux at flux which is normally operated at industry RO units (∼20 L/m(2)h), but this would prolong the test duration excessively. In this study, the dead-end flux was accelerated by reducing the dead-end membrane area while maintaining the CFS permeate flux at 20 L/m(2)h. By doing so, a flux correction factor was investigated and applied to correlate the CFS-MFI(UF) measured at dead-end flux of 120 L/m(2)h to CFS-MFI(UF) measured at dead-end flux of 20 L/m(2)h for RO fouling rate prediction. Using this flux correction factor, the test duration of CFS-MFI(UF) can be shortened from 15 h to 2h. © 2010 Elsevier Ltd. All rights reserved.

Using bromine gas to enhance mercury removal from flue gas of coal-fired power plants.

PubMed

Liu, Shou-Heng; Yan, Nai-Qiang; Liu, Zhao-Rong; Qu, Zan; Wang, H Paul; Chang, Shih-Ger; Miller, Charles

2007-02-15

Bromine gas was evaluated for converting elemental mercury (Hg0) to oxidized mercury, a form that can readily be captured by the existing air pollution control device. The gas-phase oxidation rates of Hg0 by Br2 decreased with increasing temperatures. SO2, CO, HCl, and H2O had insignificant effect, while NO exhibited a reverse course of effect on the Hg0 oxidation: promotion at low NO concentrations and inhibition at high NO concentrations. A reaction mechanism involving the formation of van der Waals clusters is proposed to accountfor NO's reverse effect. The apparent gas-phase oxidation rate constant, obtained under conditions simulating a flue gas without flyash, was 3.61 x 10(-17) cm3 x molecule(-1) x s(-1) at 410 K corresponding to a 50% Hg0 oxidation using 52 ppm Br2 in a reaction time of 15 s. Flyash in flue gas significantly promoted the oxidation of Hg0 by Br2, and the unburned carbon component played a major role in the promotion primarily through the rapid adsorption of Br2 which effectively removed Hg0 from the gas phase. At a typical flue gas temperature, SO2 slightly inhibited the flyash-induced Hg0 removal. Conversely, NO slightly promoted the flyash induced Hg0 removal by Br2. Norit Darco-Hg-LH and Darco-Hg powder activated carbons, which have been demonstrated in field tests, were inferred for estimating the flyash induced Hg0 oxidation by Br2. Approximately 60% of Hg0 is estimated to be oxidized with the addition of 0.4 ppm of gaseous Br2 into full scale power plant flue gas.

Isothermal Fatigue, Damage Accumulation, and Life Prediction of a Woven PMC

NASA Technical Reports Server (NTRS)

Gyekenyesi, Andrew L.

1998-01-01

This dissertation focuses on the characterization of the fully reversed fatigue behavior exhibited by a carbon fiber/polyimide resin, woven laminate at room and elevated temperatures. Nondestructive video edge view microscopy and destructive sectioning techniques were used to study the microscopic damage mechanisms that evolved. The residual elastic stiffness was monitored and recorded throughout the fatigue life of the coupon. In addition, residual compressive strength tests were conducted on fatigue coupons with various degrees of damage as quantified by stiffness reduction. Experimental results indicated that the monotonic tensile properties were only minimally influenced by temperature, while the monotonic compressive and fully reversed fatigue properties displayed noticeable reductions due to the elevated temperature. The stiffness degradation, as a function of cycles, consisted of three stages; a short-lived high degradation period, a constant degradation rate segment composing the majority of the life, and a final stage demonstrating an increasing rate of degradation up to failure. Concerning the residual compressive strength tests at room and elevated temperatures, the elevated temperature coupons appeared much more sensitive to damage. At elevated temperatures, coupons experienced a much larger loss in compressive strength when compared to room temperature coupons with equivalent damage. The fatigue damage accumulation law proposed for the model incorporates a scalar representation for damage, but admits a multiaxial, anisotropic evolutionary law. The model predicts the current damage (as quantified by residual stiffness) and remnant life of a composite that has undergone a known load at temperature. The damage/life model is dependent on the applied multiaxial stress state as well as temperature. Comparisons between the model and data showed good predictive capabilities concerning stiffness degradation and cycles to failure.

Using the reversible inhibition of gastric lipase by Orlistat for investigating simultaneously lipase adsorption and substrate hydrolysis at the lipid-water interface.

PubMed

Bénarouche, Anaïs; Point, Vanessa; Carrière, Frédéric; Cavalier, Jean-François

2014-06-01

The lipolysis reaction carried out by lipases at the water-lipid interface is a complex process including enzyme conformational changes, adsorption/desorption equilibrium and substrate hydrolysis. Mixed monomolecular films of the lipase inhibitor Orlistat and 1,2-dicaprin were used here to investigate the adsorption of dog gastric lipase (DGL) followed by the hydrolysis of 1,2-dicaprin. The combined study of these two essential catalysis steps was made possible thanks to the highest affinity of DGL for Orlistat than 1,2-dicaprin and the fact that the inhibition of DGL by Orlistat is reversible. Upon DGL binding to mixed 1,2-dicaprin/Orlistat monolayers, an increase in surface pressure reflecting lipase adsorption was first recorded. Limited amounts of Orlistat allowed to maintain DGL inactive on 1,2-dicaprin during a period of time that was sufficient to determine DGL adsorption and desorption rate constants. A decrease in surface pressure reflecting 1,2-dicaprin hydrolysis and product desorption was observed after the slow hydrolysis of the covalent DGL-Orlistat complex was complete. The rate of 1,2-dicaprin hydrolysis was recorded using the surface barostat technique. Based on a kinetic model describing the inhibition by Orlistat and the activity of DGL on a mixed 1,2-dicaprin/Orlistat monolayer spread at the air-water interface combined with surface pressure measurements, it was possible to monitor DGL adsorption at the lipid-water interface and substrate hydrolysis in the course of a single experiment. This allowed to assess the kcat/KM* ratio for DGL acting on 1,2-dicaprin monolayer, after showing that mixed monolayers containing a low fraction of Orlistat were similar to pure 1,2-dicaprin monolayers. Copyright © 2014 Elsevier Masson SAS. All rights reserved.

Reversing Period-Doubling Bifurcations in Models of Population Interactions Using Constant Stocking or Harvesting

Treesearch

James F. Selgrade; James H. Roberds

1998-01-01

This study considers a general class of two-dimensional, discrete population models where each per capita transition function (fitness) depends on a linear combination of the densities of the interacting populations. The fitness functions are either monotone decreasing functions (pioneer fitnesses) or one-humped functions (climax fitnesses). Conditions are derived...

Periprosthetic shoulder infection in the United States: incidence and economic burden.

PubMed

Padegimas, Eric M; Maltenfort, Mitchell; Ramsey, Matthew L; Williams, Gerald R; Parvizi, Javad; Namdari, Surena

2015-05-01

Periprosthetic joint infection (PJI) is a major cause of morbidity after shoulder arthroplasty. PJI epidemiology has not been well studied. We aimed to analyze the historical incidence, predisposing factors, and economic burden of PJI after shoulder arthroplasty in the United States. Primary shoulder arthroplasty patients were identified by the International Classification of Diseases, Ninth Revision, Clinical Modification codes 81.80 (total shoulder arthroplasty), 81.81 (hemiarthroplasty), and 81.88 (reverse arthroplasty) in the Nationwide Inpatient Sample from 2002 to 2011. PJI was identified by codes 80.01 (arthrotomy for device removal) and 996.66 (prosthetic infection). Multivariate logistic regression analysis was used to identify predisposing factors for PJI. PJI rate was 0.98% from 2002 to 2011 and did not vary significantly. Comorbidities associated with PJI were weight loss/nutritional deficiency (odds ratio [OR], 2.62; 95% confidence interval [CI], 1.53-4.51; P = .00047), drug abuse (OR, 2.38; 95% CI, 1.41-4.02; P = .0011), and anemia from blood loss (OR, 2.43; 95% CI, 1.50-3.93; P = .00031) or iron deficiency (OR, 2.05; 95% CI, 1.69-2.49; P < .0001). Demographic factors associated with PJI were younger age (OR, 1.020; 95% CI, 1.017-1.024; P < .0001) and male gender (OR, 1.961; 95% CI, 1.816-2.117; P < .0001). In 2011, median hospitalization costs for PJI were $17,163.57 compared with $16,132.68, $13,955.83, and $20,007.87 for total shoulder arthroplasty, hemiarthroplasty, and reverse arthroplasty, respectively. Increasing incidence of shoulder arthroplasty and a constant infection rate will result in greater overall PJI burden. Whereas hospitalization costs for PJI are comparable to those of primary arthroplasty, they are incurred after the original cost of shoulder arthroplasty. Certain identifiable patient variables correlate with higher PJI rates. Risk factor modification may decrease PJI incidence and help contain costs. Copyright © 2015 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Elsevier Inc. All rights reserved.

ESTIMATION OF PHOSPHATE ESTER HYDROLYSIS RATE CONSTANTS - ALKALINE HYDROLYSIS

EPA Science Inventory

SPARC (SPARC Performs Automated Reasoning in Chemistry) chemical reactivity models were extended to allow the calculation of alkaline hydrolysis rate constants of phosphate esters in water. The rate is calculated from the energy difference between the initial and transition state...

Proton-driven spin diffusion in rotating solids via reversible and irreversible quantum dynamics

PubMed Central

Veshtort, Mikhail; Griffin, Robert G.

2011-01-01

Proton-driven spin diffusion (PDSD) experiments in rotating solids have received a great deal of attention as a potential source of distance constraints in large biomolecules. However, the quantitative relationship between the molecular structure and observed spin diffusion has remained obscure due to the lack of an accurate theoretical description of the spin dynamics in these experiments. We start with presenting a detailed relaxation theory of PDSD in rotating solids that provides such a description. The theory applies to both conventional and radio-frequency-assisted PDSD experiments and extends to the non-Markovian regime to include such phenomena as rotational resonance (R2). The basic kinetic equation of the theory in the non-Markovian regime has the form of a memory function equation, with the role of the memory function played by the correlation function. The key assumption used in the derivation of this equation expresses the intuitive notion of the irreversible dissipation of coherences in macroscopic systems. Accurate expressions for the correlation functions and for the spin diffusion constants are given. The theory predicts that the spin diffusion constants governing the multi-site PDSD can be approximated by the constants observed in the two-site diffusion. Direct numerical simulations of PDSD dynamics via reversible Liouville-von Neumann equation are presented to support and compliment the theory. Remarkably, an exponential decay of the difference magnetization can be observed in such simulations in systems consisting of only 12 spins. This is a unique example of a real physical system whose typically macroscopic and apparently irreversible behavior can be traced via reversible microscopic dynamics. An accurate value for the spin diffusion constant can be usually obtained through direct simulations of PDSD in systems consisting of two 13C nuclei and about ten 1H nuclei from their nearest environment. Spin diffusion constants computed by this method are in excellent agreement with the spin diffusion constants obtained through equations given by the relaxation theory of PDSD. The constants resulting from these two approaches were also in excellent agreement with the results of 2D rotary resonance recoupling proton-driven spin diffusion (R3-PDSD) experiments performed in three model compounds, where magnetization exchange occurred over distances up to 4.9 Å. With the methodology presented, highly accurate internuclear distances can be extracted from such data. Relayed transfer of magnetization between distant nuclei appears to be the main (and apparently resolvable) source of uncertainty in such measurements. The non-Markovian kinetic equation was applied to the analysis of the R2 spin dynamics. The conventional semi-phenomenological treatment of relxation in R2 has been shown to be equivalent to the assumption of the Lorentzian spectral density function in the relaxatoin theory of PDSD. As this assumption is a poor approximation in real physical systems, the conventional R2 treatment is likely to carry a significant model error that has not been recognized previously. The relaxation theory of PDSD appears to provide an accurate, parameter-free alternative. Predictions of this theory agreed well with the full quantum mechanical simulations of the R2 dynamics in the few simple model systems we considered. PMID:21992326

Magnetic-time model at off-season germination

NASA Astrophysics Data System (ADS)

Mahajan, Tarlochan Singh; Pandey, Om Prakash

2014-03-01

Effect of static magnetic field on germination of mung beans is described. Seeds of mung beans, were exposed in batches to static magnetic fields of 87 to 226 mT intensity for 100 min. Magnetic time constant - 60.743 Th (Tesla hour) was determined experimentally. High value of magnetic time constant signifies lower effect of magnetic field on germination rate as this germination was carried out at off-season (13°C). Using decay function, germination magnetic constant was calculated. There was a linear increase in germination magnetic constant with increasing intensity of magnetic field. Calculated values of mean germination time, mean germination rate, germination rate coefficient, germination magnetic constant, transition time, water uptake, indicate that the impact of applied static magnetic field improves the germination of mung beans seeds even in off-season

Kinetic analysis of cooperative interactions induced by Mn2+ binding to the chloroplast H(+)-ATPase.

PubMed

Hiller, R; Carmeli, C

1990-07-03

The kinetics of Mn2+ binding to three cooperatively interacting sites in chloroplast H(+)-ATPase (CF1) were measured by EPR following rapid mixing of the enzyme with MnCl2 with a time resolution of 8 ms. Mixing of the enzyme-bound Mn2+ with MgCl2 gave a measure of the rate of exchange. The data could be best fitted to a kinetic model assuming three sequential, positively cooperative binding sites. (1) In the latent CF1, the binding to all three sites had a similar on-rate constants of (1.1 +/- 0.04) X 10(4) M-1s-1. (2) Site segregation was found in the release of ions with off-rate constants of 0.69 +/- 0.04 s-1 for the first two and 0.055 +/- 0.003 s-1 for the third. (3) Addition of one ADP per CF1 caused a decrease in the off-rate constants to 0.31 +/- 0.02 and 0.033 +/- 0.008 s-1 for the first two and the third sites, respectively. (4) Heat activation of CF1 increased the on-rate constant to (4.2 +/- 0.92) X 10(4) M-1s-1 and the off-rate constants of the first two and the third site to 1.34 +/- 0.08 and 0.16 +/- 0.07 s-1, respectively. (5) The calculated thermodynamic dissociation constants were similar to those previously obtained from equilibrium binding studies. These findings were correlated to the rate constants obtained from studies of the catalysis and regulation of the H(+)-ATPase. The data support the suggestion that regulation induces sequential progress of catalysis through the three active sites of the enzyme.