Rate constant for the reaction of atomic chlorine with methane

NASA Technical Reports Server (NTRS)

Lin, C. L.; Leu, M. T.; Demore, W. B.

1978-01-01

The rate constant and temperature dependence of the Cl + CH4 reaction have been investigated by the techniques of competitive chlorination of CH4/C2H6 mixtures and by discharge-flow/mass spectroscopy. The objectives were to determine an accurate value for the rate constant for use in stratospheric modeling, and to clarify discrepancies in results previously obtained by different techniques. The results deduced from the competitive chlorination study are in good agreement with the absolute values measured by the mass spectrometric method, and at temperatures above 300 K are in good agreement with measurements by other techniques based on resonance fluorescence detection of atomic chlorine. However, in the 220-300 K region, the competitive experiments indicate lower rate constants than those obtained by resonance fluorescence methods, and do not reproduce the curved Arrhenius plots seen in some of those studies.

Linear free energy relationships between aqueous phase hydroxyl radical reaction rate constants and free energy of activation.

PubMed

Minakata, Daisuke; Crittenden, John

2011-04-15

The hydroxyl radical (HO(•)) is a strong oxidant that reacts with electron-rich sites on organic compounds and initiates complex radical chain reactions in aqueous phase advanced oxidation processes (AOPs). Computer based kinetic modeling requires a reaction pathway generator and predictions of associated reaction rate constants. Previously, we reported a reaction pathway generator that can enumerate the most important elementary reactions for aliphatic compounds. For the reaction rate constant predictor, we develop linear free energy relationships (LFERs) between aqueous phase literature-reported HO(•) reaction rate constants and theoretically calculated free energies of activation for H-atom abstraction from a C-H bond and HO(•) addition to alkenes. The theoretical method uses ab initio quantum mechanical calculations, Gaussian 1-3, for gas phase reactions and a solvation method, COSMO-RS theory, to estimate the impact of water. Theoretically calculated free energies of activation are found to be within approximately ±3 kcal/mol of experimental values. Considering errors that arise from quantum mechanical calculations and experiments, this should be within the acceptable errors. The established LFERs are used to predict the HO(•) reaction rate constants within a factor of 5 from the experimental values. This approach may be applied to other reaction mechanisms to establish a library of rate constant predictions for kinetic modeling of AOPs.

Constant-load versus heart rate-targeted exercise - Responses of systolic intervals

NASA Technical Reports Server (NTRS)

Lance, V. Q.; Spodick, D. H.

1975-01-01

Various systolic intervals were measured prior to and during heart rate-targeted bicycle ergometer exercise. There were striking similarities within each matched exercise set for Q-Im, isovolumetric contraction time, preejection period (PEP), and PEP/left ventricular ejection time (LVET). LVET was significantly shorter for rate-targeted exercise. It is concluded that either constant-load or rate-targeted bicycle ergometry may be used with the choice of method determined by the purpose of the protocol, and that systolic intervals (except LVET) should not be much altered owing to the method chosen.

KABAM Version 1.0 User's Guide and Technical Documentation - Appendix H - Methods for Estimating Metabolism Rate Constant

EPA Pesticide Factsheets

Appendix H of KABAM Version 1.0 documentation related to estimating the metabolism rate constant. KABAM is a simulation model used to predict pesticide concentrations in aquatic regions for use in exposure assessments.

Fast gradient separation by very high pressure liquid chromatography: reproducibility of analytical data and influence of delay between successive runs.

PubMed

Stankovicha, Joseph J; Gritti, Fabrice; Beaver, Lois Ann; Stevensona, Paul G; Guiochon, Georges

2013-11-29

Five methods were used to implement fast gradient separations: constant flow rate, constant column-wall temperature, constant inlet pressure at moderate and high pressures (controlled by a pressure controller),and programmed flow constant pressure. For programmed flow constant pressure, the flow rates and gradient compositions are controlled using input into the method instead of the pressure controller. Minor fluctuations in the inlet pressure do not affect the mobile phase flow rate in programmed flow. There producibilities of the retention times, the response factors, and the eluted band width of six successive separations of the same sample (9 components) were measured with different equilibration times between 0 and 15 min. The influence of the length of the equilibration time on these reproducibilities is discussed. The results show that the average column temperature may increase from one separation to the next and that this contributes to fluctuation of the results.

Leak Rate Quantification Method for Gas Pressure Seals with Controlled Pressure Differential

NASA Technical Reports Server (NTRS)

Daniels, Christopher C.; Braun, Minel J.; Oravec, Heather A.; Mather, Janice L.; Taylor, Shawn C.

2015-01-01

An enhancement to the pressure decay leak rate method with mass point analysis solved deficiencies in the standard method. By adding a control system, a constant gas pressure differential across the test article was maintained. As a result, the desired pressure condition was met at the onset of the test, and the mass leak rate and measurement uncertainty were computed in real-time. The data acquisition and control system were programmed to automatically stop when specified criteria were met. Typically, the test was stopped when a specified level of measurement uncertainty was attained. Using silicone O-ring test articles, the new method was compared with the standard method that permitted the downstream pressure to be non-constant atmospheric pressure. The two methods recorded comparable leak rates, but the new method recorded leak rates with significantly lower measurement uncertainty, statistical variance, and test duration. Utilizing this new method in leak rate quantification, projects will reduce cost and schedule, improve test results, and ease interpretation between data sets.

A simple method relating specific rate constants k(E,J) and Thermally averaged rate constants k(infinity)(T) of unimolecular bond fission and the reverse barrierless association reactions.

PubMed

Troe, J; Ushakov, V G

2006-06-01

This work describes a simple method linking specific rate constants k(E,J) of bond fission reactions AB --> A + B with thermally averaged capture rate constants k(cap)(T) of the reverse barrierless combination reactions A + B --> AB (or the corresponding high-pressure dissociation or recombination rate constants k(infinity)(T)). Practical applications are given for ionic and neutral reaction systems. The method, in the first stage, requires a phase-space theoretical treatment with the most realistic minimum energy path potential available, either from reduced dimensionality ab initio or from model calculations of the potential, providing the centrifugal barriers E(0)(J). The effects of the anisotropy of the potential afterward are expressed in terms of specific and thermal rigidity factors f(rigid)(E,J) and f(rigid)(T), respectively. Simple relationships provide a link between f(rigid)(E,J) and f(rigid)(T) where J is an average value of J related to J(max)(E), i.e., the maximum J value compatible with E > or = E0(J), and f(rigid)(E,J) applies to the transitional modes. Methods for constructing f(rigid)(E,J) from f(rigid)(E,J) are also described. The derived relationships are adaptable and can be used on that level of information which is available either from more detailed theoretical calculations or from limited experimental information on specific or thermally averaged rate constants. The examples used for illustration are the systems C6H6+ <==> C6H5+ + H, C8H10+ --> C7H7+ + CH3, n-C9H12+ <==> C7H7+ + C2H5, n-C10H14+ <==> C7H7+ + C3H7, HO2 <==> H + O2, HO2 <==> HO + O, and H2O2 <==> 2HO.

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.

Rate constant for the reaction SO + BrO yields SO2 + Br

NASA Technical Reports Server (NTRS)

Brunning, J.; Stief, L.

1986-01-01

The rate of the radical-radical reaction SO + BrO yields SO2 + Br has been determined at 298 K in a discharge flow system near 1 torr pressure with detection of SO and BrO via collision-free sampling mass spectrometry. The rate constant was determined using two different methods: measuring the decay of SO radicals in the presence of an excess of BrO and measuring the decay of BrO radicals in excess SO. The results from the two methods are in reasonable agreement and the simple mean of the two values gives the recommended rate constant at 298 K, k = (5.7 + or - 2.0) x 10 to the -11th cu cm/s. This represents the first determination of this rate constant and it is consistent with a previously derived lower limit based on SO2 formation. Comparison is made with other radical-radical reactions involving SO or BrO. The reaction SO + BrO yields SO2 + Br is of interest for models of the upper atmosphere of the earth and provides a potential coupling between atmospheric sulfur and bromine chemistry.

Precisely and Accurately Inferring Single-Molecule Rate Constants

PubMed Central

Kinz-Thompson, Colin D.; Bailey, Nevette A.; Gonzalez, Ruben L.

2017-01-01

The kinetics of biomolecular systems can be quantified by calculating the stochastic rate constants that govern the biomolecular state versus time trajectories (i.e., state trajectories) of individual biomolecules. To do so, the experimental signal versus time trajectories (i.e., signal trajectories) obtained from observing individual biomolecules are often idealized to generate state trajectories by methods such as thresholding or hidden Markov modeling. Here, we discuss approaches for idealizing signal trajectories and calculating stochastic rate constants from the resulting state trajectories. Importantly, we provide an analysis of how the finite length of signal trajectories restrict the precision of these approaches, and demonstrate how Bayesian inference-based versions of these approaches allow rigorous determination of this precision. Similarly, we provide an analysis of how the finite lengths and limited time resolutions of signal trajectories restrict the accuracy of these approaches, and describe methods that, by accounting for the effects of the finite length and limited time resolution of signal trajectories, substantially improve this accuracy. Collectively, therefore, the methods we consider here enable a rigorous assessment of the precision, and a significant enhancement of the accuracy, with which stochastic rate constants can be calculated from single-molecule signal trajectories. PMID:27793280

Determination of acidity and nucleophilicity in thiols by reaction with monobromobimane and fluorescence detection.

PubMed

Sardi, Florencia; Manta, Bruno; Portillo-Ledesma, Stephanie; Knoops, Bernard; Comini, Marcelo A; Ferrer-Sueta, Gerardo

2013-04-01

A method based on the differential reactivity of thiol and thiolate with monobromobimane (mBBr) has been developed to measure nucleophilicity and acidity of protein and low-molecular-weight thiols. Nucleophilicity of the thiolate is measured as the pH-independent second-order rate constant of its reaction with mBBr. The ionization constants of the thiols are obtained through the pH dependence of either second-order rate constant or initial rate of reaction. For readily available thiols, the apparent second-order rate constant is measured at different pHs and then plotted and fitted to an appropriate pH function describing the observed number of ionization equilibria. For less available thiols, such as protein thiols, the initial rate of reaction is determined in a wide range of pHs and fitted to the appropriate pH function. The method presented here shows excellent sensitivity, allowing the use of nanomolar concentrations of reagents. The method is suitable for scaling and high-throughput screening. Example determinations of nucleophilicity and pK(a) are presented for captopril and cysteine as low-molecular-weight thiols and for human peroxiredoxin 5 and Trypanosoma brucei monothiol glutaredoxin 1 as protein thiols. Copyright © 2013 Elsevier Inc. All rights reserved.

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.

A novel frame-level constant-distortion bit allocation for smooth H.264/AVC video quality

NASA Astrophysics Data System (ADS)

Liu, Li; Zhuang, Xinhua

2009-01-01

It is known that quality fluctuation has a major negative effect on visual perception. In previous work, we introduced a constant-distortion bit allocation method [1] for H.263+ encoder. However, the method in [1] can not be adapted to the newest H.264/AVC encoder directly as the well-known chicken-egg dilemma resulted from the rate-distortion optimization (RDO) decision process. To solve this problem, we propose a new two stage constant-distortion bit allocation (CDBA) algorithm with enhanced rate control for H.264/AVC encoder. In stage-1, the algorithm performs RD optimization process with a constant quantization QP. Based on prediction residual signals from stage-1 and target distortion for smooth video quality purpose, the frame-level bit target is allocated by using a close-form approximations of ratedistortion relationship similar to [1], and a fast stage-2 encoding process is performed with enhanced basic unit rate control. Experimental results show that, compared with original rate control algorithm provided by H.264/AVC reference software JM12.1, the proposed constant-distortion frame-level bit allocation scheme reduces quality fluctuation and delivers much smoother PSNR on all testing sequences.

Accurate acceleration of kinetic Monte Carlo simulations through the modification of rate constants.

PubMed

Chatterjee, Abhijit; Voter, Arthur F

2010-05-21

We present a novel computational algorithm called the accelerated superbasin kinetic Monte Carlo (AS-KMC) method that enables a more efficient study of rare-event dynamics than the standard KMC method while maintaining control over the error. In AS-KMC, the rate constants for processes that are observed many times are lowered during the course of a simulation. As a result, rare processes are observed more frequently than in KMC and the time progresses faster. We first derive error estimates for AS-KMC when the rate constants are modified. These error estimates are next employed to develop a procedure for lowering process rates with control over the maximum error. Finally, numerical calculations are performed to demonstrate that the AS-KMC method captures the correct dynamics, while providing significant CPU savings over KMC in most cases. We show that the AS-KMC method can be employed with any KMC model, even when no time scale separation is present (although in such cases no computational speed-up is observed), without requiring the knowledge of various time scales present in the system.

Reduced-Dimensionality Semiclassical Transition State Theory: Application to Hydrogen Atom Abstraction and Exchange Reactions of Hydrocarbons.

PubMed

Greene, Samuel M; Shan, Xiao; Clary, David C

2015-12-17

Quantum mechanical methods for calculating rate constants are often intractable for reactions involving many atoms. Semiclassical transition state theory (SCTST) offers computational advantages over these methods but nonetheless scales exponentially with the number of degrees of freedom (DOFs) of the system. Here we present a method with more favorable scaling, reduced-dimensionality SCTST (RD SCTST), that treats only a subset of DOFs of the system explicitly. We apply it to three H abstraction and exchange reactions for which two-dimensional potential energy surfaces (PESs) have previously been constructed and evaluated using RD quantum scattering calculations. We differentiated these PESs to calculate harmonic frequencies and anharmonic constants, which were then used to calculate cumulative reaction probabilities and rate constants by RD SCTST. This method yielded rate constants in good agreement with quantum scattering results. Notably, it performed well for a heavy-light-heavy reaction, even though it does not explicitly account for corner-cutting effects. Recent extensions to SCTST that improve its treatment of deep tunneling were also evaluated within the reduced-dimensionality framework. The success of RD SCTST in this study suggests its potential applicability to larger systems.

Accuracy of the energy-corrected sudden (ECS) scaling procedure for rotational excitation of CO by collisions with Ar

NASA Technical Reports Server (NTRS)

Green, S.; Cochrane, D. L.; Truhlar, D. G.

1986-01-01

The utility of the energy-corrected sudden (ECS) scaling method is evaluated on the basis of how accurately it predicts the entire matrix of state-to-state rate constants, when the fundamental rate constants are independently known. It is shown for the case of Ar-CO collisions at 500 K that when a critical impact parameter is about 1.75-2.0 A, the ECS method yields excellent excited state rates on the average and has an rms error of less than 20 percent.

Using Maximum Likelihood Statistical Methods and Pigment Flux Data to Constrain Particle Exchange and Organic Matter Remineralization Rate Constants in the Mediterranean Sea

NASA Astrophysics Data System (ADS)

Wang, W.; Lee, C.; Cochran, K. K.; Armstrong, R. A.

2016-02-01

Sinking particles play a pivotal role transferring material from the surface to the deeper ocean via the "biological pump". To quantify the extent to which these particles aggregate and disaggregate, and thus affect particle settling velocity, we constructed a box model to describe organic matter cycling. The box model was fit to chloropigment data sampled in the 2005 MedFlux project using Indented Rotating Sphere sediment traps operating in Settling Velocity (SV) mode. Because of the very different pigment compositions of phytoplankton and fecal pellets, chloropigments are useful as proxies to record particle exchange. The maximum likelihood statistical method was used to estimate particle aggregation, disaggregation, and organic matter remineralization rate constants. Eleven settling velocity categories collected by SV sediment traps were grouped into two sinking velocity classes (fast- and slow-sinking) to decrease the number of parameters that needed to be estimated. Organic matter degradation rate constants were estimated to be 1.2, 1.6, and 1.1 y^-1, which are equivalent to degradation half-lives of 0.60, 0.45, and 0.62 y^-1, at 313, 524, and 1918 m, respectively. Rate constants of chlorophyll a degradation to pheopigments (pheophorbide, pheophytin, and pyropheophorbide) were estimated to be 0.88, 0.93, and 1.2 y^-1, at 313, 524, and 1918 m, respectively. Aggregation rate constants varied little with depth, with the highest value being 0.07 y^-1 at 524 m. Disaggregation rate constants were highest at 524 m (14 y^-1) and lowest at 1918 m (9.6 y^-1)

Efficient quantum-classical method for computing thermal rate constant of recombination: application to ozone formation.

PubMed

Ivanov, Mikhail V; Babikov, Dmitri

2012-05-14

Efficient method is proposed for computing thermal rate constant of recombination reaction that proceeds according to the energy transfer mechanism, when an energized molecule is formed from reactants first, and is stabilized later by collision with quencher. The mixed quantum-classical theory for the collisional energy transfer and the ro-vibrational energy flow [M. Ivanov and D. Babikov, J. Chem. Phys. 134, 144107 (2011)] is employed to treat the dynamics of molecule + quencher collision. Efficiency is achieved by sampling simultaneously (i) the thermal collision energy, (ii) the impact parameter, and (iii) the incident direction of quencher, as well as (iv) the rotational state of energized molecule. This approach is applied to calculate third-order rate constant of the recombination reaction that forms the (16)O(18)O(16)O isotopomer of ozone. Comparison of the predicted rate vs. experimental result is presented.

Effects of tunnelling and asymmetry for system-bath models of electron transfer

NASA Astrophysics Data System (ADS)

Mattiat, Johann; Richardson, Jeremy O.

2018-03-01

We apply the newly derived nonadiabatic golden-rule instanton theory to asymmetric models describing electron-transfer in solution. The models go beyond the usual spin-boson description and have anharmonic free-energy surfaces with different values for the reactant and product reorganization energies. The instanton method gives an excellent description of the behaviour of the rate constant with respect to asymmetry for the whole range studied. We derive a general formula for an asymmetric version of the Marcus theory based on the classical limit of the instanton and find that this gives significant corrections to the standard Marcus theory. A scheme is given to compute this rate based only on equilibrium simulations. We also compare the rate constants obtained by the instanton method with its classical limit to study the effect of tunnelling and other quantum nuclear effects. These quantum effects can increase the rate constant by orders of magnitude.

Studies of ARO-Relevant Fuels using Shock Tube/Laser Absorption Methods

DTIC Science & Technology

2017-08-19

elementary reaction rate constants. These experimental methods are the mainstay of this ARO research program at Stanford. The primary scientific... methods and able to pursue careers as leaders in science and engineering in the United States. Results Dissemination: Descriptions of the research have...constants. These experimental methods are the mainstay of this ARO research program at Stanford. The primary scientific problem that this research

Evaluation and comparison of diffusion MR methods for measuring apparent transcytolemmal water exchange rate constant

NASA Astrophysics Data System (ADS)

Tian, Xin; Li, Hua; Jiang, Xiaoyu; Xie, Jingping; Gore, John C.; Xu, Junzhong

2017-02-01

Two diffusion-based approaches, CG (constant gradient) and FEXI (filtered exchange imaging) methods, have been previously proposed for measuring transcytolemmal water exchange rate constant kin, but their accuracy and feasibility have not been comprehensively evaluated and compared. In this work, both computer simulations and cell experiments in vitro were performed to evaluate these two methods. Simulations were done with different cell diameters (5, 10, 20 μm), a broad range of kin values (0.02-30 s-1) and different SNR's, and simulated kin's were directly compared with the ground truth values. Human leukemia K562 cells were cultured and treated with saponin to selectively change cell transmembrane permeability. The agreement between measured kin's of both methods was also evaluated. The results suggest that, without noise, the CG method provides reasonably accurate estimation of kin especially when it is smaller than 10 s-1, which is in the typical physiological range of many biological tissues. However, although the FEXI method overestimates kin even with corrections for the effects of extracellular water fraction, it provides reasonable estimates with practical SNR's and more importantly, the fitted apparent exchange rate AXR showed approximately linear dependence on the ground truth kin. In conclusion, either CG or FEXI method provides a sensitive means to characterize the variations in transcytolemmal water exchange rate constant kin, although the accuracy and specificity is usually compromised. The non-imaging CG method provides more accurate estimation of kin, but limited to large volume-of-interest. Although the accuracy of FEXI is compromised with extracellular volume fraction, it is capable of spatially mapping kin in practice.

High-level theoretical study of the reaction between hydroxyl and ammonia: Accurate rate constants from 200 to 2500 K

NASA Astrophysics Data System (ADS)

Nguyen, Thanh Lam; Stanton, John F.

2017-10-01

Hydrogen abstraction from NH3 by OH to produce H2O and NH2—an important reaction in combustion of NH3 fuel—was studied with a theoretical approach that combines high level quantum chemistry and advanced chemical kinetics methods. Thermal rate constants calculated from first principles agree well (within 5%-20%) with available experimental data over a temperature range that extends from 200 to 2500 K. Quantum mechanical tunneling effects were found to be important; they lead to a decided curvature and non-Arrhenius behavior for the rate constant.

High-level theoretical study of the reaction between hydroxyl and ammonia: Accurate rate constants from 200 to 2500 K.

PubMed

Nguyen, Thanh Lam; Stanton, John F

2017-10-21

Hydrogen abstraction from NH 3 by OH to produce H 2 O and NH 2 -an important reaction in combustion of NH 3 fuel-was studied with a theoretical approach that combines high level quantum chemistry and advanced chemical kinetics methods. Thermal rate constants calculated from first principles agree well (within 5%-20%) with available experimental data over a temperature range that extends from 200 to 2500 K. Quantum mechanical tunneling effects were found to be important; they lead to a decided curvature and non-Arrhenius behavior for the rate constant.

Room-temperature and temperature-dependent QSRR modelling for predicting the nitrate radical reaction rate constants of organic chemicals using ensemble learning methods.

PubMed

Gupta, S; Basant, N; Mohan, D; Singh, K P

2016-07-01

Experimental determinations of the rate constants of the reaction of NO3 with a large number of organic chemicals are tedious, and time and resource intensive; and the development of computational methods has widely been advocated. In this study, we have developed room-temperature (298 K) and temperature-dependent quantitative structure-reactivity relationship (QSRR) models based on the ensemble learning approaches (decision tree forest (DTF) and decision treeboost (DTB)) for predicting the rate constant of the reaction of NO3 radicals with diverse organic chemicals, under OECD guidelines. Predictive powers of the developed models were established in terms of statistical coefficients. In the test phase, the QSRR models yielded a correlation (r(2)) of >0.94 between experimental and predicted rate constants. The applicability domains of the constructed models were determined. An attempt has been made to provide the mechanistic interpretation of the selected features for QSRR development. The proposed QSRR models outperformed the previous reports, and the temperature-dependent models offered a much wider applicability domain. This is the first report presenting a temperature-dependent QSRR model for predicting the nitrate radical reaction rate constant at different temperatures. The proposed models can be useful tools in predicting the reactivities of chemicals towards NO3 radicals in the atmosphere, hence, their persistence and exposure risk assessment.

Simple, reliable, and nondestructive method for the measurement of vacuum pressure without specialized equipment.

PubMed

Yuan, Jin-Peng; Ji, Zhong-Hua; Zhao, Yan-Ting; Chang, Xue-Fang; Xiao, Lian-Tuan; Jia, Suo-Tang

2013-09-01

We present a simple, reliable, and nondestructive method for the measurement of vacuum pressure in a magneto-optical trap. The vacuum pressure is verified to be proportional to the collision rate constant between cold atoms and the background gas with a coefficient k, which can be calculated by means of the simple ideal gas law. The rate constant for loss due to collisions with all background gases can be derived from the total collision loss rate by a series of loading curves of cold atoms under different trapping laser intensities. The presented method is also applicable for other cold atomic systems and meets the miniaturization requirement of commercial applications.

[Effects of different drying methods on processing performance and quality in bulbus of Tulipa edulis].

PubMed

Yang, Xiao-hua; Guo, Qiao-sheng; Zhu, Zai-biao; Chen, Jun; Miao, Yuan-yuan; Yang, Ying; Sun, Yuan

2015-10-01

Effects of different drying methods including sun drying, steamed, boiled, constant temperature drying (at 40, 50, 60 °C) on appearance, hardness, rehydration ratio, dry rate, moisture, total ash, extractive and polysaccharides contents were studied to provide the basis of standard processing method for Tulipa edulis bulbus. The results showed that the treatments of sun drying and 40 °C drying showed higher rehydration ratios, but lower dry rate, higher hardness, worse color, longer time and obvious distortion and shrinkage in comparison with other drying methods. The treatments of 60 °C constant temperature drying resulted in shorter drying time, lower water and higher polysaccharides content. Drying time is shorter and appearance quality is better in the treatment of steaming and boiling compared with other treatments, but the content of extractive and polysaccharides decreased significantly. The treatments of 50 °C constant temperature drying led to similar appearance quality of bulb to commercial bulb, and it resulted in lowest hardness and highest dry rate as well as higher rehydration ratio, extractive and polysaccharides content, moderate moisture and total ash contents among these treatments. Based on the results obtained, 50 °C constant temperature drying is the better way for the processing of T. edulis bulbus.

Determining the folding and unfolding rate constants of nucleic acids by biosensor. Application to telomere G-quadruplex.

PubMed

Zhao, Yong; Kan, Zhong-yuan; Zeng, Zhi-xiong; Hao, Yu-hua; Chen, Hua; Tan, Zheng

2004-10-20

Nucleic acid molecules may fold into secondary structures, and the formation of such structures is involved in many biological processes and technical applications. The folding and unfolding rate constants define the kinetics of conformation interconversion and the stability of these structures and is important in realizing their functions. We developed a method to determine these kinetic parameters using an optical biosensor based on surface plasmon resonance. The folding and unfolding of a nucleic acid is coupled with a hybridization reaction by immobilization of the target nucleic acid on a sensor chip surface and injection of a complementary probe nucleic acid over the sensor chip surface. By monitoring the time course of duplex formation, both the folding and unfolding rate constants for the target nucleic acid and the association and dissociation rate constants for the target-probe duplex can all be derived from the same measurement. We applied this method to determine the folding and unfolding rate constants of the G-quadruplex of human telomere sequence (TTAGGG)(4) and its association and dissociation rate constants with the complementary strand (CCCTAA)(4). The results show that both the folding and unfolding occur on the time scale of minutes at physiological concentration of K(+). We speculate that this property might be important for telomere elongation. A complete set of the kinetic parameters for both of the structures allows us to study the competition between the formation of the quadruplex and the duplex. Calculations indicate that the formation of both the quadruplex and the duplex is strand concentration-dependent, and the quadruplex can be efficiently formed at low strand concentration. This property may provide the basis for the formation of the quadruplex in vivo in the presence of a complementary strand.

Triacylglycerol secretion in rats: validation of a tracer method employing radioactive glycerol

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

Bird, M.; Williams, M.A.; Baker, N.

1984-10-01

A two-compartment model was developed to analyze the temporal changes in plasma triacylglycerol (TG)-specific radioactivity after injection of (2-/sup 3/H)glycerol into rats. The analysis, which yielded fractional rate constants of TG secretion, was tested in rats fed diets either adequate or deficient in essential fatty acids (EFA) and containing either glucose, fructose or sucrose as the dietary carbohydrate. The method of analysis appeared valid, first, because of a close agreement between experimental and computer-fitted TG-specific radioactivity curves, and second, because the fractional rate constants obtained were quite similar to fractional rate constants determined previously by the Triton WR-1339 technique inmore » rats maintained on identical diets. The results show that EFA deficiency increased the fractional rate constant of TG secretion 1.7-, 1.8- and 3.3-fold and the rate of TG secretion 1.8-, 1.6- and 1.4-fold when the dietary carbohydrate was glucose, sucrose and fructose, respectively, in comparison with control rats fed diets supplying these same carbohydrates but adequate in EFA. In the latter groups, the rates of plasma TG secretion were in the range of 0.14-0.17 mg/min per 100 g body weight, and the rate of secretion in the fructose-fed rats was only 20% higher than in the glucose-fed rats.« less

Hammett analyses of halocarbene-halocarbanion equilibria.

PubMed

Wang, Lei; Moss, Robert A; Krogh-Jespersen, Karsten

2013-04-19

Substituted arylchlorocarbenes (X = H, p-Cl, p-CF3, p-F, m-Cl) reacted reversibly with Cl(-) in dichloroethane to form the corresponding aryldichloromethide carbanions. Equilibrium constants and rate constants for the forward and reverse reactions were correlated by the Hammett equation. DFT methods were used to compute equilibrium constants and electronic absorption spectra.

Absolute rate of the reaction of Cl(p-2) with molecular hydrogen from 200 - 500 K

NASA Technical Reports Server (NTRS)

Whytock, D. A.; Lee, J. H.; Michael, J. V.; Payne, W. A.; Stief, L. J.

1976-01-01

Rate constants for the reaction of atomic chlorine with hydrogen are measured from 200 - 500 K using the flash photolysis-resonance fluorescence technique. The results are compared with previous work and are discussed with particular reference to the equilibrium constant for the reaction and to relative rate data for chlorine atom reactions. Theoretical calculations, using the BEBO method with tunneling, give excellent agreement with experiment.

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

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.

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

Potential Energy Surface for Large Barrierless Reaction Systems: Application to the Kinetic Calculations of the Dissociation of Alkanes and the Reverse Recombination Reactions.

PubMed

Yao, Qian; Cao, Xiao-Mei; Zong, Wen-Gang; Sun, Xiao-Hui; Li, Ze-Rong; Li, Xiang-Yuan

2018-05-31

The isodesmic reaction method is applied to calculate the potential energy surface (PES) along the reaction coordinates and the rate constants of the barrierless reactions for unimolecular dissociation reactions of alkanes to form two alkyl radicals and their reverse recombination reactions. The reaction class is divided into 10 subclasses depending upon the type of carbon atoms in the reaction centers. A correction scheme based on isodesmic reaction theory is proposed to correct the PESs at UB3LYP/6-31+G(d,p) level. To validate the accuracy of this scheme, a comparison of the PESs at B3LYP level and the corrected PESs with the PESs at CASPT2/aug-cc-pVTZ level is performed for 13 representative reactions, and it is found that the deviations of the PESs at B3LYP level are up to 35.18 kcal/mol and are reduced to within 2 kcal/mol after correction, indicating that the PESs for barrierless reactions in a subclass can be calculated meaningfully accurately at a low level of ab initio method using our correction scheme. High-pressure limit rate constants and pressure dependent rate constants of these reactions are calculated based on their corrected PESs and the results show the pressure dependence of the rate constants cannot be ignored, especially at high temperatures. Furthermore, the impact of molecular size on the pressure-dependent rate constants of decomposition reactions of alkanes and their reverse reactions has been studied. The present work provides an effective method to generate meaningfully accurate PESs for large molecular system.

Thermodynamic Analysis of Chemically Reacting Mixtures-Comparison of First and Second Order Models.

PubMed

Pekař, Miloslav

2018-01-01

Recently, a method based on non-equilibrium continuum thermodynamics which derives thermodynamically consistent reaction rate models together with thermodynamic constraints on their parameters was analyzed using a triangular reaction scheme. The scheme was kinetically of the first order. Here, the analysis is further developed for several first and second order schemes to gain a deeper insight into the thermodynamic consistency of rate equations and relationships between chemical thermodynamic and kinetics. It is shown that the thermodynamic constraints on the so-called proper rate coefficient are usually simple sign restrictions consistent with the supposed reaction directions. Constraints on the so-called coupling rate coefficients are more complex and weaker. This means more freedom in kinetic coupling between reaction steps in a scheme, i.e., in the kinetic effects of other reactions on the rate of some reaction in a reacting system. When compared with traditional mass-action rate equations, the method allows a reduction in the number of traditional rate constants to be evaluated from data, i.e., a reduction in the dimensionality of the parameter estimation problem. This is due to identifying relationships between mass-action rate constants (relationships which also include thermodynamic equilibrium constants) which have so far been unknown.

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.

High-level theoretical study of the reaction between hydroxyl and ammonia: Accurate rate constants from 200 to 2500 K

DOE PAGES

Nguyen, Thanh Lam; Stanton, John F.

2017-06-02

Hydrogen abstraction from NH 3 by OH to produce H 2O and NH 2 — an important reaction in combustion of NH 3 fuel — was studied with a theoretical approach that combines high level quantum chemistry and advanced chemical kinetics methods. Thermal rate constants calculated from first principles agree well (within 5 to 20%) with available experimental data over a temperature range that extends from 200 to 2500 K. Here, quantum mechanical tunneling effects were found to be important; they lead to a decided curvature and non-Arrhenius behavior for the rate constant.

Short-term standard litter decomposition across three different ecosystems in middle taiga zone of West Siberia

NASA Astrophysics Data System (ADS)

Filippova, Nina V.; Glagolev, Mikhail V.

2018-03-01

The method of standard litter (tea) decomposition was implemented to compare decomposition rate constants (k) between different peatland ecosystems and coniferous forests in the middle taiga zone of West Siberia (near Khanty-Mansiysk). The standard protocol of TeaComposition initiative was used to make the data usable for comparisons among different sites and zonobiomes worldwide. This article sums up the results of short-term decomposition (3 months) on the local scale. The values of decomposition rate constants differed significantly between three ecosystem types: it was higher in forest compared to bogs, and treed bogs had lower decomposition constant compared to Sphagnum lawns. In general, the decomposition rate constants were close to ones reported earlier for similar climatic conditions and habitats.

An experimental comparison of several current viscoplastic constitutive models at elevated temperature

NASA Technical Reports Server (NTRS)

James, G. H.; Imbrie, P. K.; Hill, P. S.; Allen, D. H.; Haisler, W. E.

1988-01-01

Four current viscoplastic models are compared experimentally for Inconel 718 at 593 C. This material system responds with apparent negative strain rate sensitivity, undergoes cyclic work softening, and is susceptible to low cycle fatigue. A series of tests were performed to create a data base from which to evaluate material constants. A method to evaluate the constants is developed which draws on common assumptions for this type of material, recent advances by other researchers, and iterative techniques. A complex history test, not used in calculating the constants, is then used to compare the predictive capabilities of the models. The combination of exponentially based inelastic strain rate equations and dynamic recovery is shown to model this material system with the greatest success. The method of constant calculation developed was successfully applied to the complex material response encountered. Backstress measuring tests were found to be invaluable and to warrant further development.

Constitutive Model Constants for Al7075-T651 and Al7075-T6

NASA Astrophysics Data System (ADS)

Brar, N. S.; Joshi, V. S.; Harris, B. W.

2009-12-01

Aluminum 7075-T651 and 7075-T6 are characterized at quasi-static and high strain rates to determine Johnson-Cook (J-C) strength and fracture model constants. Constitutive model constants are required as input to computer codes to simulate projectile (fragment) impact or similar impact events on structural components made of these materials. Although the two tempers show similar elongation at breakage, the ultimate tensile strength of T651 temper is generally lower than the T6 temper. Johnson-Cook strength model constants (A, B, n, C, and m) for the two alloys are determined from high strain rate tension stress-strain data at room and high temperature to 250°C. The Johnson-Cook fracture model constants are determined from quasi-static and medium strain rate as well as high temperature tests on notched and smooth tension specimens. Although the J-C strength model constants are similar, the fracture model constants show wide variations. Details of the experimental method used and the results for the two alloys are presented.

Influencing factors and kinetic studies of imidacloprid degradation by ozonation.

PubMed

Chen, Shi; Deng, Jing; Deng, Yang; Gao, Naiyun

2018-03-02

Batch kinetic tests in ozonation of imidacloprid from water were performed in this study. The pseudo-first-order rate constant of imidacloprid degradation was increased from 0.079 to 0.326 min -1 with the increasing pH from 6.02 to 8.64 at an average ozone dose of 1.149 mg L -1 . When the alkalinity was increased from 0 to 250 mg L -1 NaHCO 3 , the pseudo-first-order rate constants decreased from 0.121 to 0.034 min -1 . These results suggested that the predominant oxidant gradually switched from ozone to hydroxyl radicals ([Formula: see text]) with the increase in solution pH. The secondary rate constant [Formula: see text] (10.92 ± 0.12 M -1 s -1 ) for the reaction of imidacloprid and molecular ozone was determined at pH 2.0 and in the presence of 50 mM ter-butyl alcohol (p-chlorobenzoic acid, pCBA), respectively. An indirect competition method was used to determine the secondary rate constant for [Formula: see text] oxidation of imidacloprid in the presence of pCBA as the reference compound. The rate constants [Formula: see text] were estimated to range 2.65-3.79 M -1 s -1 at pH 6.02-8.64. Results obtained from this study demonstrate that ozonation appears to be an effective method to remove imidacloprid from water.

Theoretical chemical kinetic study of the H-atom abstraction reactions from aldehydes and acids by Ḣ atoms and ȮH, HȮ2, and ĊH3 radicals.

PubMed

Mendes, Jorge; Zhou, Chong-Wen; Curran, Henry J

2014-12-26

We have performed a systematic, theoretical chemical kinetic investigation of H atom abstraction by Ḣ atoms and ȮH, HȮ2, and ĊH3 radicals from aldehydes (methanal, ethanal, propanal, and isobutanal) and acids (methanoic acid, ethanoic acid, propanoic acid, and isobutanoic acid). The geometry optimizations and frequencies of all of the species in the reaction mechanisms of the title reactions were calculated using the MP2 method and the 6-311G(d,p) basis set. The one-dimensional hindered rotor treatment for reactants and transition states and the intrinsic reaction coordinate calculations were also determined at the MP2/6-311G(d,p) level of theory. For the reactions of methanal and methanoic acid with Ḣ atoms and ȮH, HȮ2, and ĊH3 radicals, the calculated relative electronic energies were obtained with the CCSD(T)/cc-pVXZ (where X = D, T, and Q) method and were extrapolated to the complete basis set limit. The electronic energies obtained with the CCSD(T)/cc-pVTZ method were benchmarked against the CCSD(T)/CBS energies and were found to be within 1 kcal mol(-1) of one another. Thus, the energies calculated using the less expensive CCSD(T)/cc-pVTZ method were used in all of the reaction mechanisms and in calculating our high-pressure limit rate constants for the title reactions. Rate constants were calculated using conventional transition state theory with an asymmetric Eckart tunneling correction, as implemented in Variflex. Herein, we report the individual and average rate constants, on a per H atom basis, and total rate constants in the temperature range 500-2000 K. We have compared some of our rate constant results to available experimental and theoretical data, and our results are generally in good agreement.

Semiclassical Calculation of Reaction Rate Constants for Homolytical Dissociations

NASA Technical Reports Server (NTRS)

Cardelino, Beatriz H.

2002-01-01

There is growing interest in extending organometallic chemical vapor deposition (OMCVD) to III-V materials that exhibit large thermal decomposition at their optimum growth temperature, such as indium nitride. The group III nitrides are candidate materials for light-emitting diodes and semiconductor lasers operating into the blue and ultraviolet regions. To overcome decomposition of the deposited compound, the reaction must be conducted at high pressures, which causes problems of uniformity. Microgravity may provide the venue for maintaining conditions of laminar flow under high pressure. Since the selection of optimized parameters becomes crucial when performing experiments in microgravity, efforts are presently geared to the development of computational OMCVD models that will couple the reactor fluid dynamics with its chemical kinetics. In the present study, we developed a method to calculate reaction rate constants for the homolytic dissociation of III-V compounds for modeling OMCVD. The method is validated by comparing calculations with experimental reaction rate constants.

RATE CONSTANTS FOR THE REACTIONS OF OH RADICALS AND CL ATOMS WITH DI-N-PROPYL ETHER AND DI-N-BUTYL ETHER AND THEIR DEUTERATED ANALOGS. (R825252)

EPA Science Inventory

Using relative rate methods, rate constants for the gas-phase reactions of OH radicals and Cl atoms with di-n-propyl ether, di-n-propyl ether-d₁₄, di-n-butyl ether and di-n-butyl ether-d₁₈ have been measured at 296 ? 2 K and atmos...

Method for measuring and controlling beam current in ion beam processing

DOEpatents

Kearney, Patrick A.; Burkhart, Scott C.

2003-04-29

A method for producing film thickness control of ion beam sputter deposition films. Great improvements in film thickness control is accomplished by keeping the total current supplied to both the beam and suppressor grids of a radio frequency (RF) in beam source constant, rather than just the current supplied to the beam grid. By controlling both currents, using this method, deposition rates are more stable, and this allows the deposition of layers with extremely well controlled thicknesses to about 0.1%. The method is carried out by calculating deposition rates based on the total of the suppressor and beam currents and maintaining the total current constant by adjusting RF power which gives more consistent values.

The Gaseous Explosive Reaction : The Effect of Inert Gases

NASA Technical Reports Server (NTRS)

Stevens, F W

1928-01-01

Attention is called in this report to previous investigations of gaseous explosive reactions carried out under constant volume conditions, where the effect of inert gases on the thermodynamic equilibrium was determined. The advantage of constant pressure methods over those of constant volume as applied to studies of the gaseous explosive reaction is pointed out and the possibility of realizing for this purpose a constant pressure bomb mentioned. The application of constant pressure methods to the study of gaseous explosive reactions, made possible by the use of a constant pressure bomb, led to the discovery of an important kinetic relation connecting the rate of propagation of the zone of explosive reaction within the active gases, with the initial concentrations of those gases: s = K(sub 1)(A)(sup n1)(B)(sup n2)(C)(sup n3)------. By a method analogous to that followed in determining the effect of inert gases on the equilibrium constant K, the present paper records an attempt to determine their kinetic effect upon the expression given above.

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].

Detection limit for rate fluctuations in inhomogeneous Poisson processes

NASA Astrophysics Data System (ADS)

Shintani, Toshiaki; Shinomoto, Shigeru

2012-04-01

Estimations of an underlying rate from data points are inevitably disturbed by the irregular occurrence of events. Proper estimation methods are designed to avoid overfitting by discounting the irregular occurrence of data, and to determine a constant rate from irregular data derived from a constant probability distribution. However, it can occur that rapid or small fluctuations in the underlying density are undetectable when the data are sparse. For an estimation method, the maximum degree of undetectable rate fluctuations is uniquely determined as a phase transition, when considering an infinitely long series of events drawn from a fluctuating density. In this study, we analytically examine an optimized histogram and a Bayesian rate estimator with respect to their detectability of rate fluctuation, and determine whether their detectable-undetectable phase transition points are given by an identical formula defining a degree of fluctuation in an underlying rate. In addition, we numerically examine the variational Bayes hidden Markov model in its detectability of rate fluctuation, and determine whether the numerically obtained transition point is comparable to those of the other two methods. Such consistency among these three principled methods suggests the presence of a theoretical limit for detecting rate fluctuations.

Detection limit for rate fluctuations in inhomogeneous Poisson processes.

PubMed

Shintani, Toshiaki; Shinomoto, Shigeru

2012-04-01

Estimations of an underlying rate from data points are inevitably disturbed by the irregular occurrence of events. Proper estimation methods are designed to avoid overfitting by discounting the irregular occurrence of data, and to determine a constant rate from irregular data derived from a constant probability distribution. However, it can occur that rapid or small fluctuations in the underlying density are undetectable when the data are sparse. For an estimation method, the maximum degree of undetectable rate fluctuations is uniquely determined as a phase transition, when considering an infinitely long series of events drawn from a fluctuating density. In this study, we analytically examine an optimized histogram and a Bayesian rate estimator with respect to their detectability of rate fluctuation, and determine whether their detectable-undetectable phase transition points are given by an identical formula defining a degree of fluctuation in an underlying rate. In addition, we numerically examine the variational Bayes hidden Markov model in its detectability of rate fluctuation, and determine whether the numerically obtained transition point is comparable to those of the other two methods. Such consistency among these three principled methods suggests the presence of a theoretical limit for detecting rate fluctuations.

Regional Myocardial Blood Flow*

PubMed Central

Sullivan, Jay M.; Taylor, Warren J.; Elliott, William C.; Gorlin, Richard

1967-01-01

A method is described which measures the local effectiveness of the myocardial circulation, expressed as a clearance constant. Uniform clearance constants have been demonstrated in the normal canine and human myocardium. A distinct difference in clearance constants has been demonstrated between the normal canine myocardium and areas of naturally occurring disease. Heterogeneous clearance constants have been found in a majority of human subjects with coronary artery disease—the lowest rates being noted in areas of fibrous aneurysm. PMID:6036537

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

OH{sup +} in astrophysical media: state-to-state formation rates, Einstein coefficients and inelastic collision rates with He

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

Gómez-Carrasco, Susana; Godard, Benjamin; Lique, François

The rate constants required to model the OH{sup +} observations in different regions of the interstellar medium have been determined using state of the art quantum methods. First, state-to-state rate constants for the H{sub 2}(v = 0, J = 0, 1) + O{sup +}({sup 4} S) → H + OH{sup +}(X {sup 3}Σ{sup –}, v', N) reaction have been obtained using a quantum wave packet method. The calculations have been compared with time-independent results to assess the accuracy of reaction probabilities at collision energies of about 1 meV. The good agreement between the simulations and the existing experimental cross sectionsmore » in the 0.01-1 eV energy range shows the quality of the results. The calculated state-to-state rate constants have been fitted to an analytical form. Second, the Einstein coefficients of OH{sup +} have been obtained for all astronomically significant rovibrational bands involving the X {sup 3}Σ{sup –} and/or A {sup 3}Π electronic states. For this purpose, the potential energy curves and electric dipole transition moments for seven electronic states of OH{sup +} are calculated with ab initio methods at the highest level, including spin-orbit terms, and the rovibrational levels have been calculated including the empirical spin-rotation and spin-spin terms. Third, the state-to-state rate constants for inelastic collisions between He and OH{sup +}(X {sup 3}Σ{sup –}) have been calculated using a time-independent close coupling method on a new potential energy surface. All these rates have been implemented in detailed chemical and radiative transfer models. Applications of these models to various astronomical sources show that inelastic collisions dominate the excitation of the rotational levels of OH{sup +}. In the models considered, the excitation resulting from the chemical formation of OH{sup +} increases the line fluxes by about 10% or less depending on the density of the gas.« less

A theoretical and shock tube kinetic study on hydrogen abstraction from phenyl formate.

PubMed

Ning, Hongbo; Liu, Dapeng; Wu, Junjun; Ma, Liuhao; Ren, Wei; Farooq, Aamir

2018-06-12

The hydrogen abstraction reactions of phenyl formate (PF) by different radicals (H/O(3P)/OH/HO2) were theoretically investigated. We calculated the reaction energetics for PF + H/O/OH using the composite method ROCBS-QB3//M06-2X/cc-pVTZ and that for PF + HO2 at the M06-2X/cc-pVTZ level of theory. The high-pressure limit rate constants were calculated using the transition state theory in conjunction with the 1-D hindered rotor approximation and tunneling correction. Three-parameter Arrhenius expressions of rate constants were provided over the temperature range of 500-2000 K. To validate the theoretical calculations, the overall rate constants of PF + OH → Products were measured in shock tube experiments at 968-1128 K and 1.16-1.25 atm using OH laser absorption. The predicted overall rate constants agree well with the shock tube data (within 15%) over the entire experimental conditions. Rate constant analysis indicates that the H-abstraction at the formic acid site dominates the PF consumption, whereas the contribution of H-abstractions at the aromatic ring increases with temperature. Additionally, comparisons of site-specific H-abstractions from PF with methyl formate, ethyl formate, benzene, and toluene were performed to understand the effects of the aromatic ring and side-chain substituent on H-abstraction rate constants.

Direct measurement of electron transfer distance decay constants of single redox proteins by electrochemical tunneling spectroscopy.

PubMed

Artés, Juan M; Díez-Pérez, Ismael; Sanz, Fausto; Gorostiza, Pau

2011-03-22

We present a method to measure directly and at the single-molecule level the distance decay constant that characterizes the rate of electron transfer (ET) in redox proteins. Using an electrochemical tunneling microscope under bipotentiostatic control, we obtained current−distance spectroscopic recordings of individual redox proteins confined within a nanometric tunneling gap at a well-defined molecular orientation. The tunneling current decays exponentially, and the corresponding decay constant (β) strongly supports a two-step tunneling ET mechanism. Statistical analysis of decay constant measurements reveals differences between the reduced and oxidized states that may be relevant to the control of ET rates in enzymes and biological electron transport chains.

Single-Specimen Technique to Establish the J-Resistance of Linear Viscoelastic Solids with Constant Poisson's Ratio

NASA Technical Reports Server (NTRS)

Gutierrez-Lemini, Danton; McCool, Alex (Technical Monitor)

2001-01-01

A method is developed to establish the J-resistance function for an isotropic linear viscoelastic solid of constant Poisson's ratio using the single-specimen technique with constant-rate test data. The method is based on the fact that, for a test specimen of fixed crack size under constant rate, the initiation J-integral may be established from the crack size itself, the actual external load and load-point displacement at growth initiation, and the relaxation modulus of the viscoelastic solid, without knowledge of the complete test record. Since crack size alone, of the required data, would be unknown at each point of the load-vs-load-point displacement curve of a single-specimen test, an expression is derived to estimate it. With it, the physical J-integral at each point of the test record may be established. Because of its basis on single-specimen testing, not only does the method not require the use of multiple specimens with differing initial crack sizes, but avoids the need for tracking crack growth as well.

Dynamics of Perceived Exertion in Constant-Power Cycling: Time- and Workload-Dependent Thresholds

ERIC Educational Resources Information Center

Balagué, Natàlia; Hristovski, Robert; García, Sergi; Aguirre, Cecilia; Vázquez, Pablo; Razon, Selen; Tenenbaum, Gershon

2015-01-01

Purpose: The purpose of this study was to test the dynamics of perceived exertion shifts (PES) as a function of time and workload during constant-power cycling. Method: Fifty-two participants assigned to 4 groups performed a cycling task at 4 different constant workloads corresponding to their individual rates of perceived exertion (RPEs = 13, 15,…

Effect of surface curvature on diffusion-limited reactions on a curved surface

NASA Astrophysics Data System (ADS)

Eun, Changsun

2017-11-01

To investigate how the curvature of a reactive surface can affect reaction kinetics, we use a simple model in which a diffusion-limited bimolecular reaction occurs on a curved surface that is hollowed inward, flat, or extended outward while keeping the reactive area on the surface constant. By numerically solving the diffusion equation for this model using the finite element method, we find that the rate constant is a non-linear function of the surface curvature and that there is an optimal curvature providing the maximum value of the rate constant, which indicates that a spherical reactant whose entire surface is reactive (a uniformly reactive sphere) is not the most reactive species for a given reactive surface area. We discuss how this result arises from the interplay between two opposing effects: the exposedness of the reactive area to its partner reactants, which causes the rate constant to increase as the curvature increases, and the competition occurring on the reactive surface, which decreases the rate constant. This study helps us to understand the role of curvature in surface reactions and allows us to rationally design reactants that provide a high reaction rate.

Assessing infrared intensity using the evaporation rate of liquid hydrogen inside a cryogenic integrating sphere for laser fusion targets

NASA Astrophysics Data System (ADS)

Iwano, K.; Iwamoto, A.; Asahina, T.; Yamanoi, K.; Arikawa, Y.; Nagatomo, H.; Nakai, M.; Norimatsu, T.; Azechi, H.

2017-07-01

Infrared (IR) heating processes have been studied to form a deuterium layer in an inertial confinement fusion target. To understand the relationship between the IR intensity and the fuel layering time constant, we have developed a new method to assess the IR intensity during irradiation. In our method, a glass flask acting as a dummy target is filled with liquid hydrogen (LH2) and is then irradiated with 2-μm light. The IR intensity is subsequently calculated from the time constant of the LH2 evaporation rate. Although LH2 evaporation is also caused by the heat inflow from the surroundings and by the background heat, the evaporation rate due to IR heating can be accurately determined by acquiring the time constant with and without irradiation. The experimentally measured IR intensity is 0.66 mW/cm2, which agrees well with a value estimated by considering the IR photon energy balance. Our results suggest that the present method can be used to measure the IR intensity inside a cryogenic system during IR irradiation of laser fusion targets.

Assessing infrared intensity using the evaporation rate of liquid hydrogen inside a cryogenic integrating sphere for laser fusion targets.

PubMed

Iwano, K; Iwamoto, A; Asahina, T; Yamanoi, K; Arikawa, Y; Nagatomo, H; Nakai, M; Norimatsu, T; Azechi, H

2017-07-01

Infrared (IR) heating processes have been studied to form a deuterium layer in an inertial confinement fusion target. To understand the relationship between the IR intensity and the fuel layering time constant, we have developed a new method to assess the IR intensity during irradiation. In our method, a glass flask acting as a dummy target is filled with liquid hydrogen (LH 2 ) and is then irradiated with 2-μm light. The IR intensity is subsequently calculated from the time constant of the LH 2 evaporation rate. Although LH 2 evaporation is also caused by the heat inflow from the surroundings and by the background heat, the evaporation rate due to IR heating can be accurately determined by acquiring the time constant with and without irradiation. The experimentally measured IR intensity is 0.66 mW/cm 2 , which agrees well with a value estimated by considering the IR photon energy balance. Our results suggest that the present method can be used to measure the IR intensity inside a cryogenic system during IR irradiation of laser fusion targets.

Accelerated Testing Methodology for the Determination of Slow Crack Growth of Advanced Ceramics

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Salem, Jonathan A.; Gyekenyesi, John P.

1997-01-01

Constant stress-rate (dynamic fatigue) testing has been used for several decades to characterize slow crack growth behavior of glass and ceramics at both ambient and elevated temperatures. The advantage of constant stress-rate testing over other methods lies in its simplicity: Strengths are measured in a routine manner at four or more stress rates by applying a constant crosshead speed or constant loading rate. The slow crack growth parameters (n and A) required for design can be estimated from a relationship between strength and stress rate. With the proper use of preloading in constant stress-rate testing, an appreciable saving of test time can be achieved. If a preload corresponding to 50 % of the strength is applied to the specimen prior to testing, 50 % of the test time can be saved as long as the strength remains unchanged regardless of the applied preload. In fact, it has been a common, empirical practice in strength testing of ceramics or optical fibers to apply some preloading (less then 40%). The purpose of this work is to study the effect of preloading on the strength to lay a theoretical foundation on such an empirical practice. For this purpose, analytical and numerical solutions of strength as a function of preloading were developed. To verify the solution, constant stress-rate testing using glass and alumina at room temperature and alumina silicon nitride, and silicon carbide at elevated temperatures was conducted in a range of preloadings from O to 90 %.

Radiometric Dating in Geology.

ERIC Educational Resources Information Center

Pankhurst, R. J.

1980-01-01

Described are several aspects and methods of quantitatively measuring geologic time using a constant-rate natural process of radioactive decay. Topics include half lives and decay constants, radiogenic growth, potassium-argon dating, rubidium-strontium dating, and the role of geochronology in support of geological exploration. (DS)

Study of rare encounters in a membrane using quenching of cascade reaction between triplet and photochrome probes with nitroxide radicals.

PubMed

Medvedeva, Nataly; Papper, Vladislav; Likhtenshtein, Gertz I

2005-09-21

Measurements of active encounters between molecules in native membranes containing ingredients, including proteins, are of prime importance. To estimate rare encounters in a high range of rate constants (rate coefficients) and distances between interacting molecules in membranes, a cascade of photochemical reactions for molecules diffusing in multilamellar liposomes was investigated. The sensitised cascade triplet cis-trans photoisomerisation of the excited stilbene involves the use of a triplet sensitiser (Erythrosin B), a photochrome stilbene-derivative probe (4-dimethylamino-4'-aminostilbene) exhibiting the phenomenon of trans-cis photoisomerisation, and nitroxide radicals (5-doxyl stearic acid) to quench the excited triplet state of the sensitiser. Measurement of the phosphorescence lifetime of Erythrosin B and the fluorescence enhancement of the stilbene-derivative photochrome probe, at various concentrations of the nitroxide probe, made it possible to calculate the quenching rate constant k(q)= 1.1 x 10(15) cm2 M(-1) s(-1) and the rate constant of the triplet-triplet energy transfer between the sensitiser and stilbene probe k(T)= 1.0 x 10(12) cm2 M(-1) s(-1). These values, together with the data on diffusion rate constant, obtained by methods utilising various theoretical characteristic times of about seven orders of magnitude and the experimental rate constants of about five orders of magnitude, were found to be in good agreement with the advanced theory of diffusion-controlled reactions in two dimensions. Because the characteristic time of the proposed cascade method is relatively large (0.1 s), it is possible to follow rare collisions between molecules and free radicals in model and biological membranes with a very sensitive fluorescence spectroscopy technique, using a relatively low concentration of probes.

Sinterable Ceramic Powders from Laser Heated Gas Phase Reactions and Rapidly Solidified Ceramic Materials.

DTIC Science & Technology

1984-07-01

Growth Rate and Calculated Growth Rate (Transport Limited). 68 V.I. Hamaker Constants 8) V.2. A Comparison of Two Methods of Agglomerate Size...particles of the same material is given by: A ix A 12 x2+ 2x where x is A/2a and A is the Hamaker constant. Because the denominator goes to zero as A goes...20-H20 4.4* J. Visser, "On Hamaker Constants", Adv. Coll. Inter. Sci., 3,331-63, 1972. + B. Vincent, "The van der Waals Attraction Between Colloidal

Concentration dependence of biotransformation in fish liver S9: Optimizing substrate concentrations to estimate hepatic clearance for bioaccumulation assessment.

PubMed

Lo, Justin C; Allard, Gayatri N; Otton, S Victoria; Campbell, David A; Gobas, Frank A P C

2015-12-01

In vitro bioassays to estimate biotransformation rate constants of contaminants in fish are currently being investigated to improve bioaccumulation assessments of hydrophobic contaminants. The present study investigates the relationship between chemical substrate concentration and in vitro biotransformation rate of 4 environmental contaminants (9-methylanthracene, pyrene, chrysene, and benzo[a]pyrene) in rainbow trout (Oncorhynchus mykiss) liver S9 fractions and methods to determine maximum first-order biotransformation rate constants. Substrate depletion experiments using a series of initial substrate concentrations showed that in vitro biotransformation rates exhibit strong concentration dependence, consistent with a Michaelis-Menten kinetic model. The results indicate that depletion rate constants measured at initial substrate concentrations of 1 μM (a current convention) could underestimate the in vitro biotransformation potential and may cause bioconcentration factors to be overestimated if in vitro biotransformation rates are used to assess bioconcentration factors in fish. Depletion rate constants measured using thin-film sorbent dosing experiments were not statistically different from the maximum depletion rate constants derived using a series of solvent delivery-based depletion experiments for 3 of the 4 test chemicals. Multiple solvent delivery-based depletion experiments at a range of initial concentrations are recommended for determining the concentration dependence of in vitro biotransformation rates in fish liver fractions, whereas a single sorbent phase dosing experiment may be able to provide reasonable approximations of maximum depletion rates of very hydrophobic substances. © 2015 SETAC.

Determination of Peukert's Constant Using Impedance Spectroscopy: Application to Supercapacitors.

PubMed

Mills, Edmund Martin; Kim, Sangtae

2016-12-15

Peukert's equation is widely used to model the rate dependence of battery capacity, and has recently attracted attention for application to supercapacitors. Here we present a newly developed method to readily determine Peukert's constant using impedance spectroscopy. Impedance spectroscopy is ideal for this purpose as it has the capability of probing electrical performance of a device over a wide range of time-scales within a single measurement. We demonstrate that the new method yields consistent results with conventional galvanostatic measurements through applying it to commercially available supercapacitors. Additionally, the novel method is much simpler and more precise, making it an attractive alternative for the determination of Peukert's constant.

Optical factors determined by the T-matrix method in turbidity measurement of absolute coagulation rate constants.

PubMed

Xu, Shenghua; Liu, Jie; Sun, Zhiwei

2006-12-01

Turbidity measurement for the absolute coagulation rate constants of suspensions has been extensively adopted because of its simplicity and easy implementation. A key factor in deriving the rate constant from experimental data is how to theoretically evaluate the so-called optical factor involved in calculating the extinction cross section of doublets formed during aggregation. In a previous paper, we have shown that compared with other theoretical approaches, the T-matrix method provides a robust solution to this problem and is effective in extending the applicability range of the turbidity methodology, as well as increasing measurement accuracy. This paper will provide a more comprehensive discussion of the physical insight for using the T-matrix method in turbidity measurement and associated technical details. In particular, the importance of ensuring the correct value for the refractive indices for colloidal particles and the surrounding medium used in the calculation is addressed, because the indices generally vary with the wavelength of the incident light. The comparison of calculated results with experiments shows that the T-matrix method can correctly calculate optical factors even for large particles, whereas other existing theories cannot. In addition, the data of the optical factor calculated by the T-matrix method for a range of particle radii and incident light wavelengths are listed.

The Kinetic Rate Law for Autocatalytic Reactions.

ERIC Educational Resources Information Center

Mata-Perez, Fernando; Perez-Benito, Joaquin F.

1987-01-01

Presented is a method of obtaining accurate rate constants for autocatalytic reactions. The autocatalytic oxidation of dimethylamine by permanganate ion in aqueous solution is used as an example. (RH)

Study on improving the turbidity measurement of the absolute coagulation rate constant.

PubMed

Sun, Zhiwei; Liu, Jie; Xu, Shenghua

2006-05-23

The existing theories dealing with the evaluation of the absolute coagulation rate constant by turbidity measurement were experimentally tested for different particle-sized (radius = a) suspensions at incident wavelengths (lambda) ranging from near-infrared to ultraviolet light. When the size parameter alpha = 2pi a/lambda > 3, the rate constant data from previous theories for fixed-sized particles show significant inconsistencies at different light wavelengths. We attribute this problem to the imperfection of these theories in describing the light scattering from doublets through their evaluation of the extinction cross section. The evaluations of the rate constants by all previous theories become untenable as the size parameter increases and therefore hampers the applicable range of the turbidity measurement. By using the T-matrix method, we present a robust solution for evaluating the extinction cross section of doublets formed in the aggregation. Our experiments show that this new approach is effective in extending the applicability range of the turbidity methodology and increasing measurement accuracy.

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.

Variation of strain rate sensitivity index of a superplastic aluminum alloy in different testing methods

NASA Astrophysics Data System (ADS)

Majidi, Omid; Jahazi, Mohammad; Bombardier, Nicolas; Samuel, Ehab

2017-10-01

The strain rate sensitivity index, m-value, is being applied as a common tool to evaluate the impact of the strain rate on the viscoplastic behaviour of materials. The m-value, as a constant number, has been frequently taken into consideration for modeling material behaviour in the numerical simulation of superplastic forming processes. However, the impact of the testing variables on the measured m-values has not been investigated comprehensively. In this study, the m-value for a superplastic grade of an aluminum alloy (i.e., AA5083) has been investigated. The conditions and the parameters that influence the strain rate sensitivity for the material are compared with three different testing methods, i.e., monotonic uniaxial tension test, strain rate jump test and stress relaxation test. All tests were conducted at elevated temperature (470°C) and at strain rates up to 0.1 s-1. The results show that the m-value is not constant and is highly dependent on the applied strain rate, strain level and testing method.

On determining dose rate constants spectroscopically.

PubMed

Rodriguez, M; Rogers, D W O

2013-01-01

To investigate several aspects of the Chen and Nath spectroscopic method of determining the dose rate constants of (125)I and (103)Pd seeds [Z. Chen and R. Nath, Phys. Med. Biol. 55, 6089-6104 (2010)] including the accuracy of using a line or dual-point source approximation as done in their method, and the accuracy of ignoring the effects of the scattered photons in the spectra. Additionally, the authors investigate the accuracy of the literature's many different spectra for bare, i.e., unencapsulated (125)I and (103)Pd sources. Spectra generated by 14 (125)I and 6 (103)Pd seeds were calculated in vacuo at 10 cm from the source in a 2.7 × 2.7 × 0.05 cm(3) voxel using the EGSnrc BrachyDose Monte Carlo code. Calculated spectra used the initial photon spectra recommended by AAPM's TG-43U1 and NCRP (National Council of Radiation Protection and Measurements) Report 58 for the (125)I seeds, or TG-43U1 and NNDC(2000) (National Nuclear Data Center, 2000) for (103)Pd seeds. The emitted spectra were treated as coming from a line or dual-point source in a Monte Carlo simulation to calculate the dose rate constant. The TG-43U1 definition of the dose rate constant was used. These calculations were performed using the full spectrum including scattered photons or using only the main peaks in the spectrum as done experimentally. Statistical uncertainties on the air kerma/history and the dose rate/history were ≤0.2%. The dose rate constants were also calculated using Monte Carlo simulations of the full seed model. The ratio of the intensity of the 31 keV line relative to that of the main peak in (125)I spectra is, on average, 6.8% higher when calculated with the NCRP Report 58 initial spectrum vs that calculated with TG-43U1 initial spectrum. The (103)Pd spectra exhibit an average 6.2% decrease in the 22.9 keV line relative to the main peak when calculated with the TG-43U1 rather than the NNDC(2000) initial spectrum. The measured values from three different investigations are in much better agreement with the calculations using the NCRP Report 58 and NNDC(2000) initial spectra with average discrepancies of 0.9% and 1.7% for the (125)I and (103)Pd seeds, respectively. However, there are no differences in the calculated TG-43U1 brachytherapy parameters using either initial spectrum in both cases. Similarly, there were no differences outside the statistical uncertainties of 0.1% or 0.2%, in the average energy, air kerma/history, dose rate/history, and dose rate constant when calculated using either the full photon spectrum or the main-peaks-only spectrum. Our calculated dose rate constants based on using the calculated on-axis spectrum and a line or dual-point source model are in excellent agreement (0.5% on average) with the values of Chen and Nath, verifying the accuracy of their more approximate method of going from the spectrum to the dose rate constant. However, the dose rate constants based on full seed models differ by between +4.6% and -1.5% from those based on the line or dual-point source approximations. These results suggest that the main value of spectroscopic measurements is to verify full Monte Carlo models of the seeds by comparison to the calculated spectra.

Evaluation of kinetic constants of biomolecular interaction on optical surface plasmon resonance sensor with Newton Iteration Method

NASA Astrophysics Data System (ADS)

Zhao, Yuanyuan; Jiang, Guoliang; Hu, Jiandong; Hu, Fengjiang; Wei, Jianguang; Shi, Liang

2010-10-01

In the immunology, there are two important types of biomolecular interaction: antigens-antibodies and receptors-ligands. Monitoring the response rate and affinity of biomolecular interaction can help analyze the protein function, drug discover, genomics and proteomics research. Moreover the association rate constant and dissociation rate constant of receptors-ligands are the important parameters for the study of signal transmission between cells. Recent advances in bioanalyzer instruments have greatly simplified the measurement of the kinetics of molecular interactions. Non-destructive and real-time monitoring the response to evaluate the parameters between antigens and antibodies can be performed by using optical surface plasmon resonance (SPR) biosensor technology. This technology provides a quantitative analysis that is carried out rapidly with label-free high-throughput detection using the binding curves of antigens-antibodies. Consequently, the kinetic parameters of interaction between antigens and antibodies can be obtained. This article presents a low cost integrated SPR-based bioanalyzer (HPSPR-6000) designed by ourselves. This bioanalyzer is mainly composed of a biosensor TSPR1K23, a touch-screen monitor, a microprocessor PIC24F128, a microflow cell with three channels, a clamp and a photoelectric conversion device. To obtain the kinetic parameters, sensorgrams may be modeled using one of several binding models provided with BIAevaluation software 3.0, SensiQ or Autolab. This allows calculation of the association rate constant (ka) and the dissociation rate constant (kd). The ratio of ka to kd can be used to estimate the equilibrium constant. Another kind is the analysis software OriginPro, which can process the obtained data by nonlinear fitting and then get some correlative parameters, but it can't be embedded into the bioanalyzer, so the bioanalyzer don't support the use of OriginPro. This paper proposes a novel method to evaluate the kinetic parameters of biomolecular interaction by using Newton Iteration Method and Least Squares Method. First, the pseudo first order kinetic model of biomolecular interaction was established. Then the data of molecular interaction of HBsAg and HBsAb was obtained by bioanalyzer. Finally, we used the optical SPR bioanalyzer software which was written by ourselves to make nonlinear fit about the association and dissociation curves. The correlation coefficient R-squared is 0.99229 and 0.99593, respectively. Furthermore, the kinetic parameters and affinity constants were evaluated using the obtained data from the fitting results.

Mechanism of Kinetically Controlled Capillary Condensation in Nanopores: A Combined Experimental and Monte Carlo Approach.

PubMed

Hiratsuka, Tatsumasa; Tanaka, Hideki; Miyahara, Minoru T

2017-01-24

We find the rule of capillary condensation from the metastable state in nanoscale pores based on the transition state theory. The conventional thermodynamic theories cannot achieve it because the metastable capillary condensation inherently includes an activated process. We thus compute argon adsorption isotherms on cylindrical pore models and atomistic silica pore models mimicking the MCM-41 materials by the grand canonical Monte Carlo and the gauge cell Monte Carlo methods and evaluate the rate constant for the capillary condensation by the transition state theory. The results reveal that the rate drastically increases with a small increase in the chemical potential of the system, and the metastable capillary condensation occurs for any mesopores when the rate constant reaches a universal critical value. Furthermore, a careful comparison between experimental adsorption isotherms and the simulated ones on the atomistic silica pore models reveals that the rate constant of the real system also has a universal value. With this finding, we can successfully estimate the experimental capillary condensation pressure over a wide range of temperatures and pore sizes by simply applying the critical rate constant.

Linear and non-linear regression analysis for the sorption kinetics of methylene blue onto activated carbon.

PubMed

Kumar, K Vasanth

2006-10-11

Batch kinetic experiments were carried out for the sorption of methylene blue onto activated carbon. The experimental kinetics were fitted to the pseudo first-order and pseudo second-order kinetics by linear and a non-linear method. The five different types of Ho pseudo second-order expression have been discussed. A comparison of linear least-squares method and a trial and error non-linear method of estimating the pseudo second-order rate kinetic parameters were examined. The sorption process was found to follow a both pseudo first-order kinetic and pseudo second-order kinetic model. Present investigation showed that it is inappropriate to use a type 1 and type pseudo second-order expressions as proposed by Ho and Blanachard et al. respectively for predicting the kinetic rate constants and the initial sorption rate for the studied system. Three correct possible alternate linear expressions (type 2 to type 4) to better predict the initial sorption rate and kinetic rate constants for the studied system (methylene blue/activated carbon) was proposed. Linear method was found to check only the hypothesis instead of verifying the kinetic model. Non-linear regression method was found to be the more appropriate method to determine the rate kinetic parameters.

Nonparametric change point estimation for survival distributions with a partially constant hazard rate.

PubMed

Brazzale, Alessandra R; Küchenhoff, Helmut; Krügel, Stefanie; Schiergens, Tobias S; Trentzsch, Heiko; Hartl, Wolfgang

2018-04-05

We present a new method for estimating a change point in the hazard function of a survival distribution assuming a constant hazard rate after the change point and a decreasing hazard rate before the change point. Our method is based on fitting a stump regression to p values for testing hazard rates in small time intervals. We present three real data examples describing survival patterns of severely ill patients, whose excess mortality rates are known to persist far beyond hospital discharge. For designing survival studies in these patients and for the definition of hospital performance metrics (e.g. mortality), it is essential to define adequate and objective end points. The reliable estimation of a change point will help researchers to identify such end points. By precisely knowing this change point, clinicians can distinguish between the acute phase with high hazard (time elapsed after admission and before the change point was reached), and the chronic phase (time elapsed after the change point) in which hazard is fairly constant. We show in an extensive simulation study that maximum likelihood estimation is not robust in this setting, and we evaluate our new estimation strategy including bootstrap confidence intervals and finite sample bias correction.

On determining dose rate constants spectroscopically

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

Rodriguez, M.; Rogers, D. W. O.

2013-01-15

Purpose: To investigate several aspects of the Chen and Nath spectroscopic method of determining the dose rate constants of {sup 125}I and {sup 103}Pd seeds [Z. Chen and R. Nath, Phys. Med. Biol. 55, 6089-6104 (2010)] including the accuracy of using a line or dual-point source approximation as done in their method, and the accuracy of ignoring the effects of the scattered photons in the spectra. Additionally, the authors investigate the accuracy of the literature's many different spectra for bare, i.e., unencapsulated {sup 125}I and {sup 103}Pd sources. Methods: Spectra generated by 14 {sup 125}I and 6 {sup 103}Pd seedsmore » were calculated in vacuo at 10 cm from the source in a 2.7 Multiplication-Sign 2.7 Multiplication-Sign 0.05 cm{sup 3} voxel using the EGSnrc BrachyDose Monte Carlo code. Calculated spectra used the initial photon spectra recommended by AAPM's TG-43U1 and NCRP (National Council of Radiation Protection and Measurements) Report 58 for the {sup 125}I seeds, or TG-43U1 and NNDC(2000) (National Nuclear Data Center, 2000) for {sup 103}Pd seeds. The emitted spectra were treated as coming from a line or dual-point source in a Monte Carlo simulation to calculate the dose rate constant. The TG-43U1 definition of the dose rate constant was used. These calculations were performed using the full spectrum including scattered photons or using only the main peaks in the spectrum as done experimentally. Statistical uncertainties on the air kerma/history and the dose rate/history were Less-Than-Or-Slanted-Equal-To 0.2%. The dose rate constants were also calculated using Monte Carlo simulations of the full seed model. Results: The ratio of the intensity of the 31 keV line relative to that of the main peak in {sup 125}I spectra is, on average, 6.8% higher when calculated with the NCRP Report 58 initial spectrum vs that calculated with TG-43U1 initial spectrum. The {sup 103}Pd spectra exhibit an average 6.2% decrease in the 22.9 keV line relative to the main peak when calculated with the TG-43U1 rather than the NNDC(2000) initial spectrum. The measured values from three different investigations are in much better agreement with the calculations using the NCRP Report 58 and NNDC(2000) initial spectra with average discrepancies of 0.9% and 1.7% for the {sup 125}I and {sup 103}Pd seeds, respectively. However, there are no differences in the calculated TG-43U1 brachytherapy parameters using either initial spectrum in both cases. Similarly, there were no differences outside the statistical uncertainties of 0.1% or 0.2%, in the average energy, air kerma/history, dose rate/history, and dose rate constant when calculated using either the full photon spectrum or the main-peaks-only spectrum. Conclusions: Our calculated dose rate constants based on using the calculated on-axis spectrum and a line or dual-point source model are in excellent agreement (0.5% on average) with the values of Chen and Nath, verifying the accuracy of their more approximate method of going from the spectrum to the dose rate constant. However, the dose rate constants based on full seed models differ by between +4.6% and -1.5% from those based on the line or dual-point source approximations. These results suggest that the main value of spectroscopic measurements is to verify full Monte Carlo models of the seeds by comparison to the calculated spectra.« less

Estimation of Slow Crack Growth Parameters for Constant Stress-Rate Test Data of Advanced Ceramics and Glass by the Individual Data and Arithmetic Mean Methods

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Salem, Jonathan A.; Holland, Frederic A.

1997-01-01

The two estimation methods, individual data and arithmetic mean methods, were used to determine the slow crack growth (SCG) parameters (n and D) of advanced ceramics and glass from a large number of room- and elevated-temperature constant stress-rate ('dynamic fatigue') test data. For ceramic materials with Weibull modulus greater than 10, the difference in the SCG parameters between the two estimation methods was negligible; whereas, for glass specimens exhibiting Weibull modulus of about 3, the difference was amplified, resulting in a maximum difference of 16 and 13 %, respectively, in n and D. Of the two SCG parameters, the parameter n was more sensitive to the estimation method than the other. The coefficient of variation in n was found to be somewhat greater in the individual data method than in the arithmetic mean method.

Screening of a dust particle charge in a humid air plasma created by an electron beam

NASA Astrophysics Data System (ADS)

Filippov, A. V.; Derbenev, I. N.; Kurkin, S. A.

2018-01-01

A kinetic model has been developed for charged particle reactions in a humid air plasma produced by a fast electron beam. The model includes over 550 reactions with electrons, 33 positive ion species and 14 negative ion species. The model has been tested by solving 48 non-steady state equations for number densities of charged particles in humid air electron beam plasma, and by comparing with the available experimental data. The system of 48 steady state equations has been solved by iterative method in order to define the main ion species of the humid air plasma. A reduced kinetic model has been developed to describe the processes with the main ions and electrons. Screening constants have been calculated on the basis of the reduced system by means of Leverrier-Fadeev method. The dependencies of screening constants on gas ionization rates have been found for the rates from 10 to 1018 cm-3s-1 and the fraction of water molecules from 0 to 2%. The analysis of the constants has revealed that one of them is close to the inverse Debye length, and the other constants are defined by the inverse diffusion lengths passed by ions in the characteristic times of the attachment, recombination, and ion conversion. Pure imaginary screening constants appear at low rates of gas ionization.

Propagation rate constants for the peroxidation of sterols on the biosynthetic pathway to cholesterol.

PubMed

Lamberson, Connor R; Muchalski, Hubert; McDuffee, Kari B; Tallman, Keri A; Xu, Libin; Porter, Ned A

2017-10-01

The free radical chain autoxidation of cholesterol and the oxidation products formed, i.e. oxysterols, have been the focus of intensive study for decades. The peroxidation of sterol precursors to cholesterol such as 7-dehydrocholesterol (7-DHC) and desmosterol as well as their oxysterols has received less attention. The peroxidation of these sterol precursors can become important under circumstances in which genetic conditions or exposures to small molecules leads to an increase of these biosynthetic intermediates in tissues and fluids. 7-DHC, for example, has a propagation rate constant for peroxidation some 200 times that of cholesterol and this sterol is found at elevated levels in a devastating human genetic condition, Smith-Lemli-Opitz syndrome (SLOS). The propagation rate constants for peroxidation of sterol intermediates on the biosynthetic pathway to cholesterol were determined by a competition kinetic method, i.e. a peroxyl radical clock. In this work, propagation rate constants for lathosterol, zymostenol, desmosterol, 7-dehydrodesmosterol and other sterols in the Bloch and Kandutsch-Russell pathways are assigned and these rate constants are related to sterol structural features. Furthermore, potential oxysterols products are proposed for sterols whose oxysterol products have not been determined. Copyright © 2017 Elsevier B.V. All rights reserved.

Variability in nest survival rates and implications to nesting studies

USGS Publications Warehouse

Klett, A.T.; Johnson, D.H.

1982-01-01

We used four reasonably large samples (83-213) of Mallard (Anas platyrhynchos) and Blue-winged Teal (A. discors) nests on an interstate highway right-of-way in southcentral North Dakota to evaluate potential biases in hatch-rate estimates. Twelve consecutive, weekly searches for nests were conducted with a cable-chain drag in 1976 and 1977. Nests were revisited at weekly intervals. Four methods were used to estimate hatch rates for the four data sets: the Traditional Method, the Mayfield Method, and two modifications of the Mayfield Method that are sometimes appropriate when daily mortality rates of nests are not constant. Hatch rates and the average age of nests at discovery declined as the interval between searches decreased, suggesting that mortality rates were not constant in our samples. An analysis of variance indicated that daily mortality rates varied with the age of nests in all four samples. Mortality was generally highest during the early laying period, moderately high during the late laying period, and lowest during incubation. We speculate that this relationship of mortality to nest age might be due to the presence of hens at nests or to differences in the vulnerability of nest sites to predation. A modification of the Mayfield Method that accounts for age-related variation in nest mortality was most appropriate for our samples. We suggest methods for conducting nesting studies and estimating nest success for species possessing similar nesting habits.

The nano-epsilon dot method for strain rate viscoelastic characterisation of soft biomaterials by spherical nano-indentation.

PubMed

Mattei, G; Gruca, G; Rijnveld, N; Ahluwalia, A

2015-10-01

Nano-indentation is widely used for probing the micromechanical properties of materials. Based on the indentation of surfaces using probes with a well-defined geometry, the elastic and viscoelastic constants of materials can be determined by relating indenter geometry and measured load and displacement to parameters which represent stress and deformation. Here we describe a method to derive the viscoelastic properties of soft hydrated materials at the micro-scale using constant strain rates and stress-free initial conditions. Using a new self-consistent definition of indentation stress and strain and corresponding unique depth-independent expression for indentation strain rate, the epsilon dot method, which is suitable for bulk compression testing, is transformed to nano-indentation. We demonstrate how two materials can be tested with a displacement controlled commercial nano-indentor using the nano-espilon dot method (nano-ε̇M) to give values of instantaneous and equilibrium elastic moduli and time constants with high precision. As samples are tested in stress-free initial conditions, the nano-ε̇M could be useful for characterising the micro-mechanical behaviour of soft materials such as hydrogels and biological tissues at cell length scales. Copyright © 2015 Elsevier Ltd. All rights reserved.

Impact of transverse and longitudinal dispersion on first-order degradation rate constant estimation

NASA Astrophysics Data System (ADS)

Stenback, Greg A.; Ong, Say Kee; Rogers, Shane W.; Kjartanson, Bruce H.

2004-09-01

A two-dimensional analytical model is employed for estimating the first-order degradation rate constant of hydrophobic organic compounds (HOCs) in contaminated groundwater under steady-state conditions. The model may utilize all aqueous concentration data collected downgradient of a source area, but does not require that any data be collected along the plume centerline. Using a least squares fit of the model to aqueous concentrations measured in monitoring wells, degradation rate constants were estimated at a former manufactured gas plant (FMGP) site in the Midwest U.S. The estimated degradation rate constants are 0.0014, 0.0034, 0.0031, 0.0019, and 0.0053 day -1 for acenaphthene, naphthalene, benzene, ethylbenzene, and toluene, respectively. These estimated rate constants were as low as one-half those estimated with the one-dimensional (centerline) approach of Buscheck and Alcantar [Buscheck, T.E., Alcantar, C.M., 1995. Regression techniques and analytical solutions to demonstrate intrinsic bioremediation. In: Hinchee, R.E., Wilson, J.T., Downey, D.C. (Eds.), Intrinsic Bioremediation, Battelle Press, Columbus, OH, pp. 109-116] which does not account for transverse dispersivity. Varying the transverse and longitudinal dispersivity values over one order of magnitude for toluene data obtained from the FMGP site resulted in nearly a threefold variation in the estimated degradation rate constant—highlighting the importance of reliable estimates of the dispersion coefficients for obtaining reasonable estimates of the degradation rate constants. These results have significant implications for decision making and site management where overestimation of a degradation rate may result in remediation times and bioconversion factors that exceed expectations. For a complex source area or non-steady-state plume, a superposition of analytical models that incorporate longitudinal and transverse dispersion and time may be used at sites where the centerline method would not be applicable.

Measurements of HO2 chemical kinetics with a new detection method

NASA Technical Reports Server (NTRS)

Lee, L. C.; Manzanares, E. R.

1985-01-01

In this research program, HO2 was detected by the OH(A-X) photofragment from dissociative excitation of HO2 at 147 nm. This detection method was applied to measure the reaction rate constant of HO2 + O3. This reaction rate constant is needed for the understanding of stratospheric chemistry. Since C12 was used in the flow system, photoexcitation of C12 may produce fluorescence to interfere with the measurements. Thus, the photoexcitation process of C12 in the vacuum ultraviolet region was also examined in this research period using synchrotron radiation as a light source. The research results are summarized.

Rate constants for reactions of ClO/x/ of atmospheric interest

NASA Technical Reports Server (NTRS)

Watson, R. T.

1977-01-01

Chemical kinetics measurements on 82 gas phase reactions of chlorine containing species are reviewed. Recommended rate constants are given. The principal species of interest are Cl, Cl2, ClO, Cl2O, ClOO, OClO, CINO, HCl and halo derivatives of methane and ethane. Absorption spectra are given for 21 species. In addition the chemical kinetics methods used to obtain these data are discussed with regard to their applicability and reliability.

Doppler-resolved kinetics of saturation recovery

DOE PAGES

Forthomme, Damien; Hause, Michael L.; Yu, Hua -Gen; ...

2015-04-08

Frequency modulated laser transient absorption has been used to monitor the ground state rotational energy transfer rates of CN radicals in a double-resonance, depletion recovery experiment. When a pulsed laser is used to burn a hole in the equilibrium ground state population of one rotational state without velocity selection, the population recovery rate is found to depend strongly on the Doppler detuning of a narrow-band probe laser. Similar effects should be apparent for any relaxation rate process that competes effectively with velocity randomization. Alternative methods of extracting thermal rate constants in the presence of these non-thermal conditions are evaluated. Totalmore » recovery rate constants, analogous to total removal rate constants in an experiment preparing a single initial rotational level, are in good agreement with quantum scattering calculations, but are slower than previously reported experiments and show qualitatively different rotational state dependence between Ar and He collision partners. As a result, quasi-classical trajectory studies confirm that the differing rotational state dependence is primarily a kinematic effect.« less

Use of photovoltaic detector for photocatalytic activity estimation

NASA Astrophysics Data System (ADS)

Das, Susanta Kumar; Satapathy, Pravakar; Rao, P. Sai Shruti; Sabar, Bilu; Panda, Rudrashish; Khatua, Lizina

2018-05-01

Photocatalysis is a very important process and have numerous applications. Generally, to estimate the photocatalytic activity of newly grown material, its reaction rate constant w.r.t to some standard commercial TiO2 nanoparticles like Degussa P25 is evaluated. Here a photovoltaic detector in conjunction with laser is used to determine this rate constant. This method is tested using Zinc Orthotitanate (Zn2TiO4) nanoparticles prepared by solid state reaction and it is found that its reaction rate constant is six times higher than that of P25. The value is found to be close to the value found by a conventional system. Our proposed system is much more cost-effective than the conventional one and has the potential to do real time monitoring of the photocatalytic activity.

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).

Kinetics and Thermodynamics of the Reaction between the (•)OH Radical and Adenine: A Theoretical Investigation.

PubMed

Milhøj, Birgitte O; Sauer, Stephan P A

2015-06-18

The accessibility of all possible reaction paths for the reaction between the nucleobase adenine and the (•)OH radical is investigated through quantum chemical calculations of barrier heights and rate constants at the ωB97X-D/6-311++G(2df,2pd) level with Eckart tunneling corrections. First the computational method is validated by considering the hydrogen abstraction from the heterocyclic N9 nitrogen in adenine as a test system. Geometries for all molecules in the reaction are optimized with four different DFT exchange-correlation functionals (B3LYP, BHandHLYP, M06-2X, and ωB97X-D), in combination with Pople and Dunning basis sets, all of which have been employed in similar investigations in the literature. Improved energies are obtained through single point calculations with CCSD(T) and the same basis sets, and reaction rate constants are calculated for all methods both without tunneling corrections and with the Wigner, Bell, and Eckart corrections. In comparison to CCSD(T)//BHandHLYP/aug-cc-pVTZ reference results, the ωB97X-D/6-311++G(2df,2pd) method combined with Eckart tunneling corrections provides a sensible compromise between accuracy and time. Using this method, all subreactions of the reaction between adenine and the (•)OH radical are investigated. The total rate constants for hydrogen abstraction and addition for adenine are predicted with this method to be 1.06 × 10(-12) and 1.10 × 10(-12) cm(3) molecules(-1) s(-1), respectively. Abstractions of H61 and H62 contribute the most, while only addition to the C8 carbon is found to be of any significance, in contrast to previous claims that addition is the dominant reaction pathway. The overall rate constant for the complete reaction is found to be 2.17 × 10(-12) cm(3) molecules(-1) s(-1), which agrees exceptionally well with experimental results.

Direct Measurement of Equilibrium Constants for High-Affinity Hemoglobins

PubMed Central

Kundu, Suman; Premer, Scott A.; Hoy, Julie A.; Trent, James T.; Hargrove, Mark S.

2003-01-01

The biological functions of heme proteins are linked to their rate and affinity constants for ligand binding. Kinetic experiments are commonly used to measure equilibrium constants for traditional hemoglobins comprised of pentacoordinate ligand binding sites and simple bimolecular reaction schemes. However, kinetic methods do not always yield reliable equilibrium constants with more complex hemoglobins for which reaction mechanisms are not clearly understood. Furthermore, even where reaction mechanisms are clearly understood, it is very difficult to directly measure equilibrium constants for oxygen and carbon monoxide binding to high-affinity (KD ≪ 1 μM) hemoglobins. This work presents a method for direct measurement of equilibrium constants for high-affinity hemoglobins that utilizes a competition for ligands between the "target" protein and an array of "scavenger" hemoglobins with known affinities. This method is described for oxygen and carbon monoxide binding to two hexacoordinate hemoglobins: rice nonsymbiotic hemoglobin and Synechocystis hemoglobin. Our results demonstrate that although these proteins have different mechanisms for ligand binding, their affinities for oxygen and carbon monoxide are similar. Their large affinity constants for oxygen, 285 and ∼100 μM−1 respectively, indicate that they are not capable of facilitating oxygen transport. PMID:12770899

Pulsed EPR measurements on reaction rate constants for addition of photo-generated radicals to double bonds of diethyl fumarate and diethyl maleate

NASA Astrophysics Data System (ADS)

Takahashi, Hirona; Hagiwara, Kenta; Kawai, Akio

2016-11-01

Addition reaction of photo-generated radicals to double bonds of diethyl fumarate (deF) and diethyl maleate (deM), which are geometrical isomers, was studied by means of time-resolved- (TR-) and pulsed-electron paramagnetic resonance (EPR). Analysis of TR-EPR spectra indicates that adduct radicals from deF and deM should have the same structure. The double bonds of these monomers are converted to single ones by addition reaction, which allows hindered internal rotation to give the same structure of adduct radical. The rate constants for addition reaction of photo-generated radicals were determined by Stern-Volmer analysis of the decay time of electron spin-echo intensity of these radicals measured by the pulsed EPR method. Rate constants for deF were found to be larger than those for deM. This relation is in good consistent with efficiency of polymerisation of deF and deM. Experimentally determined rate constants were evaluated by introducing the addition reaction model on the basis of two important factors enthalpy and polar effects.

A method to quantify at late imaging a release rate of 18F-FDG in tissues.

PubMed

Laffon, Eric; Allard, Michèle; Marthan, Roger; Ducassou, Dominique

2005-08-01

This theoretical work shows that the rate constant for the (18)F-FDG release in tissues can be assessed without needing any arterial blood sampling. The method requires that the clearance of (18)F-FDG from plasma has occurred, whereas (18)F-FDG is still present in the tissue. This condition can be met dating from 3 h after (18)F-FDG injection, when hydration and/or phlorizin injection are applied after the routine static acquisition. The release rate constant can be obtained from a graphical analysis performed at the later decreasing phase of the tissue tracer activity. A two-compartment and a three-compartment model are developed, both in accordance with one another. To cite this article: E. Laffon et al., C. R. Biologies 328 (2005).

METHOD AND APPARATUS FOR DETERMINING AMALGAM DECOMPOSITION RATE

DOEpatents

Johnson, R.W.; Wright, C.C.

1962-04-24

A method and apparatus for measuring the rate at which an amalgam decomposes in contact with aqueous solutions are described. The amalgam and an aqueous hydroxide solution are disposed in an electrolytic cell. The amalgam is used as the cathode of the cell, and an electrode and anode are disposed in the aqueous solution. A variable source of plating potential is connected across the cell. The difference in voltage between the amalgam cathode and a calibrated source of reference potential is used to control the variable source to null the difference in voltage and at the same time to maintain the concentration of the amalgam at some predetermined constant value. The value of the current required to maintain this concentration constant is indicative of the decomposition rate of the amalgam. (AEC)

[Evaluation of the influence of humidity and temperature on the drug stability by initial average rate experiment].

PubMed

He, Ning; Sun, Hechun; Dai, Miaomiao

2014-05-01

To evaluate the influence of temperature and humidity on the drug stability by initial average rate experiment, and to obtained the kinetic parameters. The effect of concentration error, drug degradation extent, humidity and temperature numbers, humidity and temperature range, and average humidity and temperature on the accuracy and precision of kinetic parameters in the initial average rate experiment was explored. The stability of vitamin C, as a solid state model, was investigated by an initial average rate experiment. Under the same experimental conditions, the kinetic parameters obtained from this proposed method were comparable to those from classical isothermal experiment at constant humidity. The estimates were more accurate and precise by controlling the extent of drug degradation, changing humidity and temperature range, or by setting the average temperature closer to room temperature. Compared with isothermal experiments at constant humidity, our proposed method saves time, labor, and materials.

Effect of solvent on crystallization behavior of xylitol

NASA Astrophysics Data System (ADS)

Hao, Hongxun; Hou, Baohong; Wang, Jing-Kang; Lin, Guangyu

2006-04-01

Effect of organic solvents content on crystallization behavior of xylitol was studied. Solubility and crystallization kinetics of xylitol in methanol-water system were experimentally determined. It was found that the solubility of xylitol at various methanol content all increases with increase of temperature. But it decreases when increasing methanol content at constant temperature. Based on the theory of population balance, the nucleation and growth rates of xylitol in methanol-water mixed solvents were calculated by moments method. From a series of experimental population density data of xylitol gotten from a batch-operated crystallizer, parameters of crystal nucleation and growth rate equations at different methanol content were got by the method of nonlinear least-squares. By analyzing, it was found that the content of methanol had an apparent effect on nucleation and growth rate of xylitol. At constant temperature, the nucleation and growth rate of xylitol all decrease with increase of methanol content.

Measurement of Rate Constants for Homodimer Subunit Exchange Using Double Electron-Electron Resonance and Paramagnetic Relaxation Enhancements

PubMed Central

Yang, Yunhuang; Ramelot, Theresa A.; Ni, Shuisong; McCarrick, Robert M.; Kennedy, Michael A.

2013-01-01

Here, we report novel methods to measure rate constants for homodimer subunit exchange using double electron-electron resonance (DEER) electron paramagnetic resonance spectroscopy measurements and nuclear magnetic resonance spectroscopy based paramagnetic relaxation enhancement (PRE) measurements. The techniques were demonstrated using the homodimeric protein Dsy0195 from the strictly anaerobic bacterium Desulfitobacterium hafniense Y51. At specific times following mixing site-specific MTSL-labeled Dsy0195 with uniformly 15N-labeled Dsy0195, the extent of exchange was determined either by monitoring the decrease of MTSL-labeled homodimer from the decay of the DEER modulation depth or by quantifying the increase of MTSL-labeled/15N-labeled heterodimer using PREs. Repeated measurements at several time points following mixing enabled determination of the homodimer subunit dissociation rate constant, k−1;, which was 0.037 ± 0.005 min−1 derived from DEER experiments with a corresponding half-life time of 18.7 minutes. These numbers agreed with independent measurements obtained from PRE experiments. These methods can be broadly applied to protein-protein and protein-DNA complex studies. PMID:23180051

CN radical reactions with hydrogen cyanide and cyanogen - Comparison of theory and experiment

NASA Technical Reports Server (NTRS)

Yang, D. L.; Yu, T.; Lin, M. C.; Melius, C. F.

1992-01-01

The method of laser photolysis/laser-induced fluorescence is used to obtain absolute rate constants for CN radical reactions with HCN and C2N2. The rate constants were found to be temperature-dependent in the range 300-740 K and pressure independent in the range 100-600 Torr. Rice-Remsperger-Kassel-Marcus theory for both reactions employing the transition state parameters obtained by the BAC-MP4 method are made. These calculations yielded reasonable results for the CN + HCN reaction, predicting both the temperature dependence and pressure independence. No pressure effect was observed in the pressure range 100-1000 Torr at temperatures below 900 K, confirming the experimental results.

Separation of Gadolinium (Gd) using Synergic Solvent Mixed Topo-D2EHPA with Extraction Method.

NASA Astrophysics Data System (ADS)

Effendy, N.; Basuki, K. T.; Biyantoro, D.; Perwira, N. K.

2018-04-01

The main problem to obtain Gd with high purity is the similarity of chemical properties and physical properties with the other rare earth elements (REE) such as Y and Dy, it is necessary to do separation by the extraction process. The purpose of this research to determine the best solvent type, amount of solvent, feed and solvent ratio in the Gd extraction process, to determine the rate order and the value of the rate constant of Gd concentration based on experimental data of aqueous phase concentration as a function of time and to know the effect of temperature on the reaction speed constant. This research was conducted on variation of solvent, amount of solvent, feed and solvent ratio in the extraction process of Gd separation, extraction time to determine the order value and the rate constant of Gd concentration in extraction process based on the aqueous phase concentration data as a function of time, to the rate constant of decreasing concentration of Gd. Based on the calculation results, the solvent composition was obtained with the best feed to separate the rare earth elements Gd in the extraction process is 1 : 4 with 15% concentration of TOPO and 10% concentration of D2EHPA. The separation process of Gd using extraction method by solvent TOPO-D2EHPA 2 : 1 comparison is better than single solvent D2EHPA / TOPO because of the synergistic effect. The rate order of separation process of Gd follows order 1. The Arrhenius Gd equation becomes k = 1.46 x 10-7 exp (-6.96 kcal / mol / RT).

Characterization of solution-phase drug-protein interactions by ultrafast affinity extraction.

PubMed

Beeram, Sandya R; Zheng, Xiwei; Suh, Kyungah; Hage, David S

2018-03-03

A number of tools based on high-performance affinity separations have been developed for studying drug-protein interactions. An example of one recent approach is ultrafast affinity extraction. This method has been employed to examine the free (or non-bound) fractions of drugs and other solutes in simple or complex samples that contain soluble binding agents. These free fractions have also been used to determine the binding constants and rate constants for the interactions of drugs with these soluble agents. This report describes the general principles of ultrafast affinity extraction and the experimental conditions under which it can be used to characterize such interactions. This method will be illustrated by utilizing data that have been obtained when using this approach to measure the binding and dissociation of various drugs with the serum transport proteins human serum albumin and alpha 1 -acid glycoprotein. A number of practical factors will be discussed that should be considered in the design and optimization of this approach for use with single-column or multi-column systems. Techniques will also be described for analyzing the resulting data for the determination of free fractions, rate constants and binding constants. In addition, the extension of this method to complex samples, such as clinical specimens, will be considered. Copyright © 2018 Elsevier Inc. All rights reserved.

Estimating rock and slag wool fiber dissolution rate from composition.

PubMed

Eastes, W; Potter, R M; Hadley, J G

2000-12-01

A method was tested for calculating the dissolution rate constant in the lung for a wide variety of synthetic vitreous silicate fibers from the oxide composition in weight percent. It is based upon expressing the logarithm of the dissolution rate as a linear function of the composition and using a different set of coefficients for different types of fibers. The method was applied to 29 fiber compositions including rock and slag fibers as well as refractory ceramic and special-purpose, thin E-glass fibers and borosilicate glass fibers for which in vivo measurements have been carried out. These fibers had dissolution rates that ranged over a factor of about 400, and the calculated dissolution rates agreed with the in vivo values typically within a factor of 4. The method presented here is similar to one developed previously for borosilicate glass fibers that was accurate to a factor of 1.25. The present coefficients work over a much broader range of composition than the borosilicate ones but with less accuracy. The dissolution rate constant of a fiber may be used to estimate whether disease would occur in animal inhalation or intraperitoneal injection studies of that fiber.

Numerical determination of Paris law constants for carbon steel using a two-scale model

NASA Astrophysics Data System (ADS)

Mlikota, M.; Staib, S.; Schmauder, S.; Božić, Ž.

2017-05-01

For most engineering alloys, the long fatigue crack growth under a certain stress level can be described by the Paris law. The law provides a correlation between the fatigue crack growth rate (FCGR or da/dN), the range of stress intensity factor (ΔK), and the material constants C and m. A well-established test procedure is typically used to determine the Paris law constants C and m, considering standard specimens, notched and pre-cracked. Definition of all the details necessary to obtain feasible and comparable Paris law constants are covered by standards. However, these cost-expensive tests can be replaced by appropriate numerical calculations. In this respect, this paper deals with the numerical determination of Paris law constants for carbon steel using a two-scale model. A micro-model containing the microstructure of a material is generated using the Finite Element Method (FEM) to calculate the fatigue crack growth rate at a crack tip. The model is based on the Tanaka-Mura equation. On the other side, a macro-model serves for the calculation of the stress intensity factor. The analysis yields a relationship between the crack growth rates and the stress intensity factors for defined crack lengths which is then used to determine the Paris law constants.

Uncertainty quantification of reaction mechanisms accounting for correlations introduced by rate rules and fitted Arrhenius parameters

DOE PAGES

Prager, Jens; Najm, Habib N.; Sargsyan, Khachik; ...

2013-02-23

We study correlations among uncertain Arrhenius rate parameters in a chemical model for hydrocarbon fuel-air combustion. We consider correlations induced by the use of rate rules for modeling reaction rate constants, as well as those resulting from fitting rate expressions to empirical measurements arriving at a joint probability density for all Arrhenius parameters. We focus on homogeneous ignition in a fuel-air mixture at constant-pressure. We also outline a general methodology for this analysis using polynomial chaos and Bayesian inference methods. Finally, we examine the uncertainties in both the Arrhenius parameters and in predicted ignition time, outlining the role of correlations,more » and considering both accuracy and computational efficiency.« less

Quantitative Assessment of Heterogeneity in Tumor Metabolism Using FDG-PET

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

Vriens, Dennis, E-mail: d.vriens@nucmed.umcn.nl; Disselhorst, Jonathan A.; Oyen, Wim J.G.

2012-04-01

Purpose: [{sup 18}F]-fluorodeoxyglucose-positron emission tomography (FDG-PET) images are usually quantitatively analyzed in 'whole-tumor' volumes of interest. Also parameters determined with dynamic PET acquisitions, such as the Patlak glucose metabolic rate (MR{sub glc}) and pharmacokinetic rate constants of two-tissue compartment modeling, are most often derived per lesion. We propose segmentation of tumors to determine tumor heterogeneity, potentially useful for dose-painting in radiotherapy and elucidating mechanisms of FDG uptake. Methods and Materials: In 41 patients with 104 lesions, dynamic FDG-PET was performed. On MR{sub glc} images, tumors were segmented in quartiles of background subtracted maximum MR{sub glc} (0%-25%, 25%-50%, 50%-75%, and 75%-100%).more » Pharmacokinetic analysis was performed using an irreversible two-tissue compartment model in the three segments with highest MR{sub glc} to determine the rate constants of FDG metabolism. Results: From the highest to the lowest quartile, significant decreases of uptake (K{sub 1}), washout (k{sub 2}), and phosphorylation (k{sub 3}) rate constants were seen with significant increases in tissue blood volume fraction (V{sub b}). Conclusions: Tumor regions with highest MR{sub glc} are characterized by high cellular uptake and phosphorylation rate constants with relatively low blood volume fractions. In regions with less metabolic activity, the blood volume fraction increases and cellular uptake, washout, and phosphorylation rate constants decrease. These results support the hypothesis that regional tumor glucose phosphorylation rate is not dependent on the transport of nutrients (i.e., FDG) to the tumor.« less

Tunneling in hydrogen-transfer isomerization of n-alkyl radicals.

PubMed

Sirjean, Baptiste; Dames, Enoch; Wang, Hai; Tsang, Wing

2012-01-12

The role of quantum tunneling in hydrogen shift in linear heptyl radicals is explored using multidimensional, small-curvature tunneling method for the transmission coefficients and a potential energy surface computed at the CBS-QB3 level of theory. Several one-dimensional approximations (Wigner, Skodje and Truhlar, and Eckart methods) were compared to the multidimensional results. The Eckart method was found to be sufficiently accurate in comparison to the small-curvature tunneling results for a wide range of temperature, but this agreement is in fact fortuitous and caused by error cancellations. High-pressure limit rate constants were calculated using the transition state theory with treatment of hindered rotations and Eckart transmission coefficients for all hydrogen-transfer isomerizations in n-pentyl to n-octyl radicals. Rate constants are found in good agreement with experimental kinetic data available for n-pentyl and n-hexyl radicals. In the case of n-heptyl and n-octyl, our calculated rates agree well with limited experimentally derived data. Several conclusions made in the experimental studies of Tsang et al. (Tsang, W.; McGivern, W. S.; Manion, J. A. Proc. Combust. Inst. 2009, 32, 131-138) are confirmed theoretically: older low-temperature experimental data, characterized by small pre-exponential factors and activation energies, can be reconciled with high-temperature data by taking into account tunneling; at low temperatures, transmission coefficients are substantially larger for H-atom transfers through a five-membered ring transition state than those with six-membered rings; channels with transition ring structures involving greater than 8 atoms can be neglected because of entropic effects that inhibit such transitions. The set of computational kinetic rates were used to derive a general rate rule that explicitly accounts for tunneling. The rate rule is shown to reproduce closely the theoretical rate constants.

Determination of the slow crack growth susceptibility coefficient of dental ceramics using different methods.

PubMed

Gonzaga, Carla Castiglia; Cesar, Paulo Francisco; Miranda, Walter Gomes; Yoshimura, Humberto Naoyuki

2011-11-01

This study compared three methods for the determination of the slow crack growth susceptibility coefficient (n) of two veneering ceramics (VM7 and d.Sign), two glass-ceramics (Empress and Empress 2) and a glass-infiltrated alumina composite (In-Ceram Alumina). Discs (n = 10) were prepared according to manufacturers' recommendations and polished. The constant stress-rate test was performed at five constant stress rates to calculate n(d) . For the indentation fracture test to determine n(IF) , Vickers indentations were performed and the crack lengths were measured under an optical microscope. For the constant stress test (performed only for d.Sign for the determination of n(s) ) four constant stresses were applied and held constant until the specimens' fracture and the time to failure was recorded. All tests were performed in artificial saliva at 37°C. The n(d) values were 17.2 for Empress 2, followed by d.Sign (20.5), VM7 (26.5), Empress (30.2), and In-Ceram Alumina (31.1). In-Ceram Alumina and Empress 2 showed the highest n(IF) values, 66.0 and 40.2, respectively. The n(IF) values determined for Empress (25.2), d.Sign (25.6), and VM7 (20.1) were similar. The n(s) value determined for d.Sign was 31.4. It can be concluded that the n values determined for the dental ceramics evaluated were significantly influenced by the test method used. 2011 Wiley Periodicals, Inc.

Simplified half-life methods for the analysis of kinetic data

NASA Technical Reports Server (NTRS)

Eberhart, J. G.; Levin, E.

1988-01-01

The analysis of reaction rate data has as its goal the determination of the order rate constant which characterize the data. Chemical reactions with one reactant and present simplified methods for accomplishing this goal are considered. The approaches presented involve the use of half lives or other fractional lives. These methods are particularly useful for the more elementary discussions of kinetics found in general and physical chemistry courses.

Influence of Geometry on the Drug Release Profiles of Stereolithographic (SLA) 3D-Printed Tablets.

PubMed

Martinez, Pamela Robles; Goyanes, Alvaro; Basit, Abdul W; Gaisford, Simon

2018-06-08

Additive manufacturing (3D printing) permits the fabrication of tablets in shapes unattainable by powder compaction, and so the effects of geometry on drug release behavior is easily assessed. Here, tablets (printlets) comprising of paracetamol dispersed in polyethylene glycol were printed using stereolithographic 3D printing. A number of geometric shapes were produced (cube, disc, pyramid, sphere and torus) with either constant surface area (SA) or constant surface area/volume ratio (SA/V). Dissolution testing showed that printlets with constant SA/V ratio released drug at the same rate, while those with constant SA released drug at different rates. A series of tori with increasing SA/V ratio (from 0.5 to 2.4) were printed, and it was found that dissolution rate increased as the SA/V ratio increased. The data show that printlets can be fabricated in multiple shapes and that dissolution performance can be maintained if the SA/V ratio is constant or that dissolution performance of printlets can be fine-tuned by varying SA/V ratio. The results suggest that 3D printing is therefore a suitable manufacturing method for personalized dosage forms.

Segregation control in vertical Bridgman crystal growth

NASA Astrophysics Data System (ADS)

Tao, Y.; Kou, S.

1996-11-01

To help the crystal grow at a constant dopant concentration in vertical Bridgman crystal growth, the dopant concentration of the growth melt, i.e. the melt from which the crystal grows, was kept constant. To achieve this, three different methods were used to replenish the growth melt at a controlled rate and suppress dopant diffusion between the growth melt and the replenishing melt. In method one, a replenishing crucible having a long melt passageway was immersed in the growth melt. In method two, a replenishing crucible having an independent feed-rate control mechanism was held above the growth melt. In method three, a submerged diffusion baffle was used to form a long melt passageway between the growth melt and the replenishing melt. NaNO 3 was used as a model material for crystal growth. Single crystals were grown by these three methods with effective segregation control. Method two was applied to InSb and single crystals were also grown with effective segregation control.

Pseudo-extravasation rate constant of dynamic susceptibility contrast-MRI determined from pharmacokinetic first principles.

PubMed

Li, Xin; Varallyay, Csanad G; Gahramanov, Seymur; Fu, Rongwei; Rooney, William D; Neuwelt, Edward A

2017-11-01

Dynamic susceptibility contrast-magnetic resonance imaging (DSC-MRI) is widely used to obtain informative perfusion imaging biomarkers, such as the relative cerebral blood volume (rCBV). The related post-processing software packages for DSC-MRI are available from major MRI instrument manufacturers and third-party vendors. One unique aspect of DSC-MRI with low-molecular-weight gadolinium (Gd)-based contrast reagent (CR) is that CR molecules leak into the interstitium space and therefore confound the DSC signal detected. Several approaches to correct this leakage effect have been proposed throughout the years. Amongst the most popular is the Boxerman-Schmainda-Weisskoff (BSW) K 2 leakage correction approach, in which the K 2 pseudo-first-order rate constant quantifies the leakage. In this work, we propose a new method for the BSW leakage correction approach. Based on the pharmacokinetic interpretation of the data, the commonly adopted R 2 * expression accounting for contributions from both intravascular and extravasating CR components is transformed using a method mathematically similar to Gjedde-Patlak linearization. Then, the leakage rate constant (K L ) can be determined as the slope of the linear portion of a plot of the transformed data. Using the DSC data of high-molecular-weight (~750 kDa), iron-based, intravascular Ferumoxytol (FeO), the pharmacokinetic interpretation of the new paradigm is empirically validated. The primary objective of this work is to empirically demonstrate that a linear portion often exists in the graph of the transformed data. This linear portion provides a clear definition of the Gd CR pseudo-leakage rate constant, which equals the slope derived from the linear segment. A secondary objective is to demonstrate that transformed points from the initial transient period during the CR wash-in often deviate from the linear trend of the linearized graph. The inclusion of these points will have a negative impact on the accuracy of the leakage rate constant, and even make it time dependent. Copyright © 2017 John Wiley & Sons, Ltd.

Vibrational energy transfer in OH X 2Pi(i), v = 2 and 1

NASA Technical Reports Server (NTRS)

Raiche, George A.; Jeffries, Jay B.; Rensberger, Karen J.; Crosley, David R.

1990-01-01

Using an IR-pump/UV-probe method in a flow discharge cell, vibrational energy transfer in OH X 2Pi(i) has been studied. OH is prepared in v = 2 by overtone excitation, and the time evolution of population in v = 2 and 1 monitored by laser-induced fluorescence. Rate constants for vibrational relaxation by the colliders H2O, NH3, CO2, and CH4 were measured. Ratios of rate constants for removal from the two states, k2/k1, range from two to five.

SU-G-201-06: Directional Low-Dose Rate Brachytherapy: Determination of the TG-43 Dose-Rate Constant Analog for a New Pd-103 Source

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

Aima, M; Culberson, W; Hammer, C

Purpose: The aim of this work is to determine the TG-43 dose-rate constant analog for a new directional low-dose rate brachytherapy source based on experimental methods and comparison to Monte Carlo simulations. The CivaSheet™ is a new commercially available planar source array comprised of a variable number of discrete directional source elements called “CivaDots”. Given the directional nature and non-conventional design of the source, modifications to the AAPM TG-43 protocol for dosimetry are required. As a result, various parameters of the TG-43 dosimetric formalism have to be adapted to accommodate this source. This work focuses on the dose-rate constant analogmore » determination for a CivaDot. Methods: Dose to water measurements of the CivaDot were performed in a polymethyl methacrylate phantom (20×20×12 cm{sup 3}) using thermoluminescent dosimeters (TLDs) and Gafchromic EBT3 film. The source was placed in the center of the phantom, and nine TLD micro-cubes were irradiated along its central axis at a distance of 1 cm. For the film measurements, the TLDs were substituted by a (3×3) cm{sup 2} EBT3 film. Primary air-kerma strength measurements of the source were performed using a variable-aperture free-air chamber. Finally, the source was modeled using the Monte Carlo N-Particle Transport Code 6. Results: Dose-rate constant analog observed for a total of eight CivaDots using TLDs and five CivaDots using EBT3 film was within ±7.0% and ±2.9% of the Monte Carlo predicted value respectively. The average difference observed was −4.8% and −0.1% with a standard deviation of 1.7% and 2.1% for the TLD and the film measurements respectively, which are both within the comparison uncertainty. Conclusion: A preliminary investigation to determine the doserate constant analog for a CivaDot was conducted successfully with good agreement between experimental and Monte Carlo based methods. This work will aid in the eventual realization of a clinically-viable dosimetric framework for the CivaSheet. This work was partially supported by NCI contract (HHSN261201200052C) through CivaTech Oncology Inc.« less

Kinetics and Quantitative Structure—Activity Relationship Study on the Degradation Reaction from Perfluorooctanoic Acid to Trifluoroacetic Acid

PubMed Central

Gong, Chen; Sun, Xiaomin; Zhang, Chenxi; Zhang, Xue; Niu, Junfeng

2014-01-01

Investigation of the degradation kinetics of perfluorooctanoic acid (PFOA) has been carried out to calculate rate constants of the main elementary reactions using the multichannel Rice-Ramsperger-Kassel-Marcus theory and canonical variational transition state theory with small-curvature tunneling correction over a temperature range of 200~500 K. The Arrhenius equations of rate constants of elementary reactions are fitted. The decarboxylation is role step in the degradation mechanism of PFOA. For the perfluorinated carboxylic acids from perfluorooctanoic acid to trifluoroacetic acid, the quantitative structure–activity relationship of the decarboxylation was analyzed with the genetic function approximation method and the structure–activity model was constructed. The main parameters governing rate constants of the decarboxylation reaction from the eight-carbon chain to the two-carbon chain were obtained. As the structure–activity model shows, the bond length and energy of C1–C2 (RC1–C2 and EC1–C2) are positively correlated to rate constants, while the volume (V), the energy difference between EHOMO and ELUMO (ΔE), and the net atomic charges on atom C2 (QC2) are negatively correlated. PMID:25196516

Applying constraints on model-based methods: Estimation of rate constants in a second order consecutive reaction

NASA Astrophysics Data System (ADS)

Kompany-Zareh, Mohsen; Khoshkam, Maryam

2013-02-01

This paper describes estimation of reaction rate constants and pure ultraviolet/visible (UV-vis) spectra of the component involved in a second order consecutive reaction between Ortho-Amino benzoeic acid (o-ABA) and Diazoniom ions (DIAZO), with one intermediate. In the described system, o-ABA was not absorbing in the visible region of interest and thus, closure rank deficiency problem did not exist. Concentration profiles were determined by solving differential equations of the corresponding kinetic model. In that sense, three types of model-based procedures were applied to estimate the rate constants of the kinetic system, according to Levenberg/Marquardt (NGL/M) algorithm. Original data-based, Score-based and concentration-based objective functions were included in these nonlinear fitting procedures. Results showed that when there is error in initial concentrations, accuracy of estimated rate constants strongly depends on the type of applied objective function in fitting procedure. Moreover, flexibility in application of different constraints and optimization of the initial concentrations estimation during the fitting procedure were investigated. Results showed a considerable decrease in ambiguity of obtained parameters by applying appropriate constraints and adjustable initial concentrations of reagents.

QSPR prediction of the hydroxyl radical rate constant of water contaminants.

PubMed

Borhani, Tohid Nejad Ghaffar; Saniedanesh, Mohammadhossein; Bagheri, Mehdi; Lim, Jeng Shiun

2016-07-01

In advanced oxidation processes (AOPs), the aqueous hydroxyl radical (HO) acts as a strong oxidant to react with organic contaminants. The hydroxyl radical rate constant (kHO) is important for evaluating and modelling of the AOPs. In this study, quantitative structure-property relationship (QSPR) method is applied to model the hydroxyl radical rate constant for a diverse dataset of 457 water contaminants from 27 various chemical classes. The constricted binary particle swarm optimization and multiple-linear regression (BPSO-MLR) are used to obtain the best model with eight theoretical descriptors. An optimized feed forward neural network (FFNN) is developed to investigate the complex performance of the selected molecular parameters with kHO. Although the FFNN prediction results are more accurate than those obtained using BPSO-MLR, the application of the latter is much more convenient. Various internal and external validation techniques indicate that the obtained models could predict the logarithmic hydroxyl radical rate constants of a large number of water contaminants with less than 4% absolute relative error. Finally, the above-mentioned proposed models are compared to those reported earlier and the structural factors contributing to the AOP degradation efficiency are discussed. Copyright © 2016 Elsevier Ltd. All rights reserved.

DQM: Decentralized Quadratically Approximated Alternating Direction Method of Multipliers

NASA Astrophysics Data System (ADS)

Mokhtari, Aryan; Shi, Wei; Ling, Qing; Ribeiro, Alejandro

2016-10-01

This paper considers decentralized consensus optimization problems where nodes of a network have access to different summands of a global objective function. Nodes cooperate to minimize the global objective by exchanging information with neighbors only. A decentralized version of the alternating directions method of multipliers (DADMM) is a common method for solving this category of problems. DADMM exhibits linear convergence rate to the optimal objective but its implementation requires solving a convex optimization problem at each iteration. This can be computationally costly and may result in large overall convergence times. The decentralized quadratically approximated ADMM algorithm (DQM), which minimizes a quadratic approximation of the objective function that DADMM minimizes at each iteration, is proposed here. The consequent reduction in computational time is shown to have minimal effect on convergence properties. Convergence still proceeds at a linear rate with a guaranteed constant that is asymptotically equivalent to the DADMM linear convergence rate constant. Numerical results demonstrate advantages of DQM relative to DADMM and other alternatives in a logistic regression problem.

A new method to characterize the kinetics of cholinesterases inhibited by carbamates.

PubMed

Xiao, Qiaoling; Zhou, Huimin; Wei, Hong; Du, Huaqiao; Tan, Wen; Zhan, Yiyi; Pistolozzi, Marco

2017-09-10

The inhibition of cholinesterases (ChEs) by carbamates includes a carbamylation (inhibition) step, in which the drug transfers its carbamate moiety to the active site of the enzyme and a decarbamylation (activity recovery) step, in which the carbamyl group is hydrolyzed from the enzyme. The carbamylation and decarbamylation kinetics decide the extent and the duration of the inhibition, thus the full characterization of candidate carbamate inhibitors requires the measurement of the kinetic constants describing both steps. Carbamylation and decarbamylation rate constants are traditionally measured by two separate set of experiments, thus making the full characterization of candidate inhibitors time-consuming. In this communication we show that by the analysis of the area under the inhibition-time curve of cholinesterases inhibited by carbamates it is possible to calculate the decarbamylation rate constant from the same data traditionally used to characterize only the carbamylation kinetics, therefore it is possible to obtain a full characterization of the inhibition with a single set of experiments. The characterization of the inhibition kinetics of human and dog plasma butyrylcholinesterase and of human acetylcholinesterase by bambuterol and bambuterol monocarbamate enantiomers was used to demonstrate the validity of the approach. The results showed that the proposed method provides reliable estimations of carbamylation and decarbamylation rate constants thus representing a simple and useful approach to reduce the time required for the characterization of carbamate inhibitors. Copyright © 2017 Elsevier B.V. All rights reserved.

Pulse radiolysis studies of the reactions of bromine atoms and dimethyl sulfoxide bromine atom complexes with alcohols

NASA Astrophysics Data System (ADS)

Sumiyoshi, Takashi; Fujiyoshi, Ryoko; Katagiri, Miho; Sawamura, Sadashi

2007-05-01

Dimethylsulfoxide (DMSO)-Br complexes were generated by pulse radiolysis of DMSO/bromomethane mixtures and the formation mechanism and spectral characteristics of the formed complexes were investigated in detail. The rate constant for the reaction of bromine atoms with DMSO and the extinction coefficient of the complex were obtained to be 4.6×10 9 M -1 s -1 and 6300 M -1 cm -1 at the absorption maximum of 430 nm. Rate constants for the reaction of bromine atoms with a series of alcohols were determined in CBrCl 3 solutions applying a competitive kinetic method using the DMSO-Br complex as the reference system. The obtained rate constants were ˜10 8 M -1 s -1, one or two orders larger than those reported for highly polar solvents. Rate constants of DMSO-Br complexes with alcohols were determined to be ˜ 10 7 M -1 s -1. A comparison of the reactivities of Br atoms and DMSO-Br complexes with those of chlorine atoms and chlorine atom complexes which are ascribed to hydrogen abstracting reactants strongly indicates that hydrogen abstraction from alcohols is not the rate determining step in the case of Br atoms and DMSO-Br complexes.

Rate Constant and Reaction Coordinate of Trp-Cage Folding in Explicit Water

PubMed Central

Juraszek, Jarek; Bolhuis, Peter G.

2008-01-01

We report rate constant calculations and a reaction coordinate analysis of the rate-limiting folding and unfolding process of the Trp-cage mini-protein in explicit solvent using transition interface sampling. Previous transition path sampling simulations revealed that in this (un)folding process the protein maintains its compact configuration, while a (de)increase of secondary structure is observed. The calculated folding rate agrees reasonably with experiment, while the unfolding rate is 10 times higher. We discuss possible origins for this mismatch. We recomputed the rates with the forward flux sampling method, and found a discrepancy of four orders of magnitude, probably caused by the method's higher sensitivity to the choice of order parameter with respect to transition interface sampling. Finally, we used the previously computed transition path-sampling ensemble to screen combinations of many order parameters for the best model of the reaction coordinate by employing likelihood maximization. We found that a combination of the root mean-square deviation of the helix and of the entire protein was, of the set of tried order parameters, the one that best describes the reaction coordination. PMID:18676648

Concepts, challenges, and successes in modeling thermodynamics of metabolism.

PubMed

Cannon, William R

2014-01-01

The modeling of the chemical reactions involved in metabolism is a daunting task. Ideally, the modeling of metabolism would use kinetic simulations, but these simulations require knowledge of the thousands of rate constants involved in the reactions. The measurement of rate constants is very labor intensive, and hence rate constants for most enzymatic reactions are not available. Consequently, constraint-based flux modeling has been the method of choice because it does not require the use of the rate constants of the law of mass action. However, this convenience also limits the predictive power of constraint-based approaches in that the law of mass action is used only as a constraint, making it difficult to predict metabolite levels or energy requirements of pathways. An alternative to both of these approaches is to model metabolism using simulations of states rather than simulations of reactions, in which the state is defined as the set of all metabolite counts or concentrations. While kinetic simulations model reactions based on the likelihood of the reaction derived from the law of mass action, states are modeled based on likelihood ratios of mass action. Both approaches provide information on the energy requirements of metabolic reactions and pathways. However, modeling states rather than reactions has the advantage that the parameters needed to model states (chemical potentials) are much easier to determine than the parameters needed to model reactions (rate constants). Herein, we discuss recent results, assumptions, and issues in using simulations of state to model metabolism.

Phase-Division-Based Dynamic Optimization of Linkages for Drawing Servo Presses

NASA Astrophysics Data System (ADS)

Zhang, Zhi-Gang; Wang, Li-Ping; Cao, Yan-Ke

2017-11-01

Existing linkage-optimization methods are designed for mechanical presses; few can be directly used for servo presses, so development of the servo press is limited. Based on the complementarity of linkage optimization and motion planning, a phase-division-based linkage-optimization model for a drawing servo press is established. Considering the motion-planning principles of a drawing servo press, and taking account of work rating and efficiency, the constraints of the optimization model are constructed. Linkage is optimized in two modes: use of either constant eccentric speed or constant slide speed in the work segments. The performances of optimized linkages are compared with those of a mature linkage SL4-2000A, which is optimized by a traditional method. The results show that the work rating of a drawing servo press equipped with linkages optimized by this new method improved and the root-mean-square torque of the servo motors is reduced by more than 10%. This research provides a promising method for designing energy-saving drawing servo presses with high work ratings.

Determination of association constants at moderately fast chemical exchange: complexation of camphor enantiomers by alpha-cyclodextrin.

PubMed

Bernatowicz, Piotr; Nowakowski, Michał; Dodziuk, Helena; Ejchart, Andrzej

2006-08-01

Association constants in weak molecular complexes can be determined by analysis of chemical shifts variations resulting from changes of guest to host concentration ratio. In the regime of very fast exchange, i.e., when exchange rate is several orders of magnitude larger than the Larmor angular frequency difference of the observed resonance in free and complexed molecule, the apparent position of averaged resonance is a population-weighted mean of resonances of particular forms involved in the equilibrium. The assumption of very fast exchange is often, however, tacitly admitted in literature even in cases where the process of interest is much slower than required. We show that such an unjustified simplification may, under certain circumstances, lead to significant underestimation of association constant and, in consequence, to non-negligible errors in Gibbs free energy under determination. We present a general method, based on iterative numerical NMR line shape analysis, which allows one for the compensation of chemical exchange effects, and delivers both the correct association constants and the exchange rates. The latter are not delivered by the other mentioned method. Practical application of our algorithm is illustrated by the case of camphor-alpha-cyclodextrin complexes.

Competition kinetics using the UV/H2O2 process: a structure reactivity correlation for the rate constants of hydroxyl radicals toward nitroaromatic compounds.

PubMed

García Einschlag, Fernando S; Carlos, Luciano; Capparelli, Alberto L

2003-10-01

The rate constants for hydroxyl radical reaction toward a set of nitroaromatic substrates kS, have been measured at 25 degrees C using competition experiments in the UV/H2O2 process. For a given pair of substrates S1 and S2, the relative reactivity beta (defined as kS1/kS2) was calculated from the slope of the corresponding double logarithmic plot, i.e., of ln[S1] vs. ln[S2]. This method is more accurate and remained linear for larger conversions in comparison with the plots of ln[S1] and ln[S2] against time. The rate constants measured ranged from 0.33 to 8.6 x 10(9) M(-1)s(-1). A quantitative structure-reactivity relationship was found using the Hammett equation. Assuming sigma values to be additive, a value of -0.60 was obtained for the reaction constant rho. This value agrees with the high reactivity and the electrophilic nature of HO* radical.

Limitations of the Conventional Phase Advance Method for Constant Power Operation of the Brushless DC Motor

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

Lawler, J.S.

2001-10-29

The brushless dc motor (BDCM) has high-power density and efficiency relative to other motor types. These properties make the BDCM well suited for applications in electric vehicles provided a method can be developed for driving the motor over the 4 to 6:1 constant power speed range (CPSR) required by such applications. The present state of the art for constant power operation of the BDCM is conventional phase advance (CPA) [1]. In this paper, we identify key limitations of CPA. It is shown that the CPA has effective control over the developed power but that the current magnitude is relatively insensitivemore » to power output and is inversely proportional to motor inductance. If the motor inductance is low, then the rms current at rated power and high speed may be several times larger than the current rating. The inductance required to maintain rms current within rating is derived analytically and is found to be large relative to that of BDCM designs using high-strength rare earth magnets. Th us, the CPA requires a BDCM with a large equivalent inductance.« less

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.

Estimation of Free Radical Ionization Energies by the Kinetic Method and the Relationship between the Kinetic Method and the Hammett Equation.

PubMed

Chen, G; Wong, P; Cooks, R G

1997-09-01

Substituted 1,2-diphenylethanes undergo competitive dissociations upon electron ionization (EI) to generate substituted benzyl cation and benzyl radical pairs. Application of the kinetic method to the previous reported EI mass spectra of these covalently bound precursor ions (data are taken from McLafferty et al. J. Am. Chem. Soc. 1970, 92, 6867)) is used to estimate the ionization energies of substituted benzyl free radicals. A correlation is observed between the Hammett σ constant of the substituents and the kinetic method parameter, ln(k(x)/k(H)), where k(x) is the rate of fragmentation to give the substituted product ion and k(H) is the rate to give the benzyl ion itself. Systems involving weakly bound cluster ions, including proton-bound dimers of meta- and para-substituted pyridines and meta- and para-substituted anilines, and electron-bound dimers of meta- and para-substituted nitrobenzenes, also show good correlations between the kinetic method parameter and the Hammett σ constant.

APPROXIMATION OF BIODEGRADATION RATE CONSTANTS FOR MONOAROMATIC HYDROCARBONS (BTEX) IN GROUND WATER

EPA Science Inventory

Two methods were used to approximate site-specific biodegradation rates of monoaromatic hydrocarbons (benzene, toluene, ethylbenzene, and xylenes [BTEX]) dissolved in ground water. Both use data from monitoring wells and the hydrologic properties of the quifer to estimate a biode...

Subcutaneous blood flow in psoriasis

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

Klemp, P.

1985-03-01

The simultaneously recorded disappearance rates of /sup 133/xe from subcutaneous adipose tissue in the crus were studied in 10 patients with psoriasis vulgaris using atraumatic labeling of the tissue in lesional skin (LS) areas and symmetrical, nonlesional skin (NLS) areas. Control experiments were performed bilaterally in 10 younger, healthy subjects. The subcutaneous washout rate constant was significantly higher in LS, 0.79 +/- 0.05 min-1 x 10(2) compared to the washout rate constant of NLS, 0.56 +/- 0.07 min-1. 10(2), or the washout rate constant in the normal subjects, 0.46 +/- 0.17 min-1 x 10(2). The mean washout rate constant inmore » NLS was 25% higher than the mean washout rate constant in the normal subjects. The difference was, however, not statistically significant. Differences in the washout rate constants might be due to abnormal subcutaneous tissue-to-blood partition (lambda) in the LS--and therefore not reflecting the real differences in the subcutaneous blood flow (SBF). The lambda for /sup 133/Xe was therefore measured--using a double isotope washout method (/sup 133/Xe and (/sup 131/I)antipyrine)--in symmetrical sites of the lateral crus in LS and NLS of 10 patients with psoriasis vulgaris and in 10 legs of normal subjects. In LS the lambda was 4.52 +/- 1.67 ml/g, which was not statistically different from that of NLS, 5.25 +/- 2.19 ml/g, nor from that of normal subcutaneous tissue, 4.98 +/- 1.04 ml/g. Calculations of the SBF using the obtained lambda values gave a significantly higher SBF in LS, 3.57 +/- 0.23 ml/100 g/min, compared to SBF in the NLS, 2.94 +/- 0.37 ml/100 g/min. There was no statistically significant difference between SBF in NLS and SBF in the normal subjects. The increased SBF in LS of psoriatics might be a secondary phenomenon to an increased heat loss in the lesional skin.« less

Phototransformation Rate Constants of PAHs Associated with Soot Particles

PubMed Central

Kim, Daekyun; Young, Thomas M.; Anastasio, Cort

2013-01-01

Photodegradation is a key process governing the residence time and fate of polycyclic aromatic hydrocarbons (PAHs) in particles, both in the atmosphere and after deposition. We have measured photodegradation rate constants of PAHs in bulk deposits of soot particles illuminated with simulated sunlight. The photodegradation rate constants at the surface (k0p), the effective diffusion coefficients (Deff), and the light penetration depths (z0.5) for PAHs on soot layers of variable thickness were determined by fitting experimental data with a model of coupled photolysis and diffusion. The overall disappearance rates of irradiated low molecular weight PAHs (with 2-3 rings) on soot particles were influenced by fast photodegradation and fast diffusion kinetics, while those of high molecular weight PAHs (with 4 or more rings) were apparently controlled by either the combination of slow photodegradation and slow diffusion kinetics or by very slow diffusion kinetics alone. The value of z0.5 is more sensitive to the soot layer thickness than the k0p value. As the thickness of the soot layer increases, the z0.5 values increase, but the k0p values are almost constant. The effective diffusion coefficients calculated from dark experiments are generally higher than those from the model fitting method for illumination experiments. Due to the correlation between k0p and z0.5 in thinner layers, Deff should be estimated by an independent method for better accuracy. Despite some limitations of the model used in this study, the fitted parameters were useful for describing empirical results of photodegradation of soot-associated PAHs. PMID:23247292

Ab initio and kinetic study of the reaction of ketones with OH for T = 500-2000 K. Part I: hydrogen-abstraction from H3CC(O)CH(3-x)(CH3)x, x = 0 ↦ 2.

PubMed

Zhou, Chong-Wen; Simmie, John M; Curran, Henry J

2011-06-21

A theoretical study is presented of the mechanism and kinetics of the reactions of the hydroxyl radical with three ketones: dimethyl (DMK), ethylmethyl (EMK) and iso-propylmethyl (iPMK) ketones. CCSD(T) values extrapolated to the basis set limit are used to benchmark the computationally less expensive methods G3 and G3MP2BH&H, for the DMK + OH reaction system. These latter methods are then used in computations involving the reactions of the larger ketones. All possible abstraction channels have been modeled. A stepwise mechanism involving the formation of a reactant complex in the entrance channel and a product complex in the exit channel has been recognized in part of the abstracting processes. High-pressure limit rate constants of the title reactions have been calculated in the temperature range of 500-2000 K using the Variflex code including Eckart tunneling corrections. Variable reaction coordinate transition state theory (VRC-TST) has been used for the rate constants of the barrier-less entrance channel. Calculated total rate constants (cm(3) mol(-1) s(-1)) are reported as follows: k(DMK) = 1.32 × 10(2)×T(3.30)exp(503/T), k(EMK) = 3.84 × 10(1)×T(3.51)exp(1515/T), k(iPMK) = 2.08 × 10(1)×T(3.58)exp(2161/T). Group rate constants (on a per H atom basis) for different carbon sites in title reactions have also been provided.

Rate constants of chemical reactions from semiclassical transition state theory in full and one dimension.

PubMed

Greene, Samuel M; Shan, Xiao; Clary, David C

2016-06-28

Semiclassical Transition State Theory (SCTST), a method for calculating rate constants of chemical reactions, offers gains in computational efficiency relative to more accurate quantum scattering methods. In full-dimensional (FD) SCTST, reaction probabilities are calculated from third and fourth potential derivatives along all vibrational degrees of freedom. However, the computational cost of FD SCTST scales unfavorably with system size, which prohibits its application to larger systems. In this study, the accuracy and efficiency of 1-D SCTST, in which only third and fourth derivatives along the reaction mode are used, are investigated in comparison to those of FD SCTST. Potential derivatives are obtained from numerical ab initio Hessian matrix calculations at the MP2/cc-pVTZ level of theory, and Richardson extrapolation is applied to improve the accuracy of these derivatives. Reaction barriers are calculated at the CCSD(T)/cc-pVTZ level. Results from FD SCTST agree with results from previous theoretical and experimental studies when Richardson extrapolation is applied. Results from our implementation of 1-D SCTST, which uses only 4 single-point MP2/cc-pVTZ energy calculations in addition to those for conventional TST, agree with FD results to within a factor of 5 at 250 K. This degree of agreement and the efficiency of the 1-D method suggest its potential as a means of approximating rate constants for systems too large for existing quantum scattering methods.

Single genome retrieval of context-dependent variability in mutation rates for human germline.

PubMed

Sahakyan, Aleksandr B; Balasubramanian, Shankar

2017-01-13

Accurate knowledge of the core components of substitution rates is of vital importance to understand genome evolution and dynamics. By performing a single-genome and direct analysis of 39,894 retrotransposon remnants, we reveal sequence context-dependent germline nucleotide substitution rates for the human genome. The rates are characterised through rate constants in a time-domain, and are made available through a dedicated program (Trek) and a stand-alone database. Due to the nature of the method design and the imposed stringency criteria, we expect our rate constants to be good estimates for the rates of spontaneous mutations. Benefiting from such data, we study the short-range nucleotide (up to 7-mer) organisation and the germline basal substitution propensity (BSP) profile of the human genome; characterise novel, CpG-independent, substitution prone and resistant motifs; confirm a decreased tendency of moieties with low BSP to undergo somatic mutations in a number of cancer types; and, produce a Trek-based estimate of the overall mutation rate in human. The extended set of rate constants we report may enrich our resources and help advance our understanding of genome dynamics and evolution, with possible implications for the role of spontaneous mutations in the emergence of pathological genotypes and neutral evolution of proteomes.

A Green's function method for simulation of time-dependent solute transport and reaction in realistic microvascular geometries

PubMed Central

Secomb, Timothy W.

2016-01-01

A novel theoretical method is presented for simulating the spatially resolved convective and diffusive transport of reacting solutes between microvascular networks and the surrounding tissues. The method allows for efficient computational solution of problems involving convection and non-linear binding of solutes in blood flowing through microvascular networks with realistic 3D geometries, coupled with transvascular exchange and diffusion and reaction in the surrounding tissue space. The method is based on a Green's function approach, in which the solute concentration distribution in the tissue is expressed as a sum of fields generated by time-varying distributions of discrete sources and sinks. As an example of the application of the method, the washout of an inert diffusible tracer substance from a tissue region perfused by a network of microvessels is simulated, showing its dependence on the solute's transvascular permeability and tissue diffusivity. Exponential decay of the washout concentration is predicted, with rate constants that are about 10–30% lower than the rate constants for a tissue cylinder model with the same vessel length, vessel surface area and blood flow rate per tissue volume. PMID:26443811

Terminal base pairs of oligodeoxynucleotides: imino proton exchange and fraying.

PubMed

Nonin, S; Leroy, J L; Guéron, M

1995-08-22

We have estimated the dissociation constant of the terminal base pairs of the B-DNA duplexes formed by 5'-d(CGCGATCGCG) and 5'-d(TAGCGCTA) by two methods, one based on the change in imino proton chemical shift with temperature and the other on the apparent pK shift of the imino proton, as monitored by the change in chemical shift of aromatic protons. These methods do not rely on imino proton exchange, whose rate was also measured. (1) The effect of ammonia on the imino proton exchange rate of the terminal pair of the 5'-d(CGCGATCGCG) duplex is 67 times less than on the isolated nucleoside. This provides an upper limit on the exchange rate from the closed pair. In fact, the effect is just as predicted from the dissociation constant, assuming that there is no exchange at all from the closed pair and that, as has been argued previously, external catalysts act on the open state as they do on the isolated nucleoside. The inhibition of catalyzed proton exchange in the closed pair, despite exposure of one face of the pair to solvent, is a new feature of the exchange process. It will allow determination of the dissociation constant of terminal pairs from the exchange rate. (2) Intrinsic catalysis of proton exchange is less efficient for the terminal pair than for an internal one. A possible explanation is that proton transfer across the water bridge responsible for intrinsic catalysis is slower, as expected if the open-state separation of the bases is larger in a terminal pair. This observation may lead to a direct method for the study of fraying. (3) At 0 degrees C, the dissociation constant of the second pair of the 5'-d(CGCGATCGCG) duplex is close to the square of the constant for the terminal pair, as predicted from a simple model of fraying. The enthalpy and entropy of opening of the terminal pairs may be compared with those of nearest neighbor interactions derived from calorimetry [Breslauer, K. J., et al. (1986) Proc. Natl. Acad. Sci. U.S.A. 83, 3746-3750].

Effect of water vapor on fatigue crack growth in 7475-T651 aluminum alloy plate. [for aerospace applications

NASA Technical Reports Server (NTRS)

Dicus, D. L.

1984-01-01

The effects of water vapor on fatigue crack growth in 7475-T651 aluminum alloy plate at frequencies of 1 Hz and 10 Hz were investigated. Twenty-five mm thick compact specimens were subjected to constant amplitude fatigue testing at a load ratio of 0.2. Fatigue crack growth rates were calculated from effective crack lengths determined using a compliance method. Tests were conducted in hard vacuum and at water vapor partial pressures ranging from 94 Pa to 3.8 kPa. Fatigue crack growth rates were frequency insensitive under all environment conditions tested. For constant stress intensity factor ranges crack growth rate transitions occurred at low and high water vapor pressures. Crack growth rates at intermediate pressures were relatively constant and showed reasonable agreement with published data for two Al-Cu-Mg alloys. The existence of two crack growth rate transitions suggests either a change in rate controlling kinetics or a change in corrosion fatigue mechanism as a function of water vapor pressure. Reduced residual deformation and transverse cracking specimens tested in water vapor versus vacuum may be evidence of embrittlement within the plastic zone due to environmental interaction.

The effect of water vapor on fatigue crack Growth in 7475-t651 aluminum alloy plate. [for aerospace applications

NASA Technical Reports Server (NTRS)

Dicus, D. L.

1982-01-01

The effects of water vapor on fatigue crack growth in 7475-T651 aluminum alloy plate at frequencies of 1 Hz and 10 Hz were investigated. Twenty-five mm thick compact specimens were subjected to constant amplitude fatigue testing at a load ratio of 0.2. Fatigue crack growth rates were calculated from effective crack lengths determined using a compliance method. Tests were conducted in hard vacuum and at water vapor partial pressures ranging from 94 Pa to 3.8 kPa. Fatigue crack growth rates were frequency insensitive under all environment conditions tested. For constant stress intensity factor ranges crack growth rate transitions occurred at low and high water vapor pressures. Crack growth rates at intermediate pressures were relatively constant and showed reasonable agreement with published data for two Al-Cu-Mg alloys. The existence of two crack growth rate transitions suggests either a change in rate controlling kinetics or a change in corrosion fatigue mechanism as a function of water vapor pressure. Reduced residual deformation and transverse cracking specimens tested in water vapor versus vacuum may be evidence of embrittlement within the plastic zone due to environmental interaction.

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

Decarboxylation Study of Acidic Cannabinoids: A Novel Approach Using Ultra-High-Performance Supercritical Fluid Chromatography/Photodiode Array-Mass Spectrometry

PubMed Central

Wang, Mei; Wang, Yan-Hong; Avula, Bharathi; Radwan, Mohamed M.; Wanas, Amira S.; van Antwerp, John; Parcher, Jon F.; ElSohly, Mahmoud A.; Khan, Ikhlas A.

2016-01-01

Abstract Introduction: Decarboxylation is an important step for efficient production of the major active components in cannabis, for example, Δ9-tetrahydrocannabinol (Δ9-THC), cannabidiol (CBD), and cannabigerol (CBG). These cannabinoids do not occur in significant concentrations in cannabis but can be formed by decarboxylation of their corresponding acids, the predominant cannabinoids in the plant. Study of the kinetics of decarboxylation is of importance for phytocannabinoid isolation and dosage formulation for medical use. Efficient analytical methods are essential for simultaneous detection of both neutral and acidic cannabinoids. Methods: C. sativa extracts were used for the studies. Decarboxylation conditions were examined at 80°C, 95°C, 110°C, 130°C, and 145°C for different times up to 60 min in a vacuum oven. An ultra-high performance supercritical fluid chromatography/photodiode array-mass spectrometry (UHPSFC/PDA-MS) method was used for the analysis of acidic and neutral cannabinoids before and after decarboxylation. Results: Decarboxylation at different temperatures displayed an exponential relationship between concentration and time indicating a first-order or pseudo-first-order reaction. The rate constants for Δ9-tetrahydrocannabinolic acid-A (THCA-A) were twice those of the cannabidiolic acid (CBDA) and cannabigerolic acid (CBGA). Decarboxylation of THCA-A was forthright with no side reactions or by-products. Decarboxylation of CBDA and CBGA was not as straightforward due to the unexplained loss of reactants or products. Conclusion: The reported UHPSFC/PDA-MS method provided consistent and sensitive analysis of phytocannabinoids and their decarboxylation products and degradants. The rate of change of acidic cannabinoid concentrations over time allowed for determination of rate constants. Variations of rate constants with temperature yielded values for reaction energy. PMID:28861498

Mechanism of Na+ binding to thrombin resolved by ultra-rapid kinetics

PubMed Central

Gianni, Stefano; Ivarsson, Ylva; Bah, Alaji; Bush-Pelc, Leslie A.; Di Cera, Enrico

2007-01-01

The interaction of Na+ and K+ with proteins is at the basis of numerous processes of biological importance. However, measurement of the kinetic components of the interaction has eluded experimentalists for decades because the rate constants are too fast to resolve with conventional stopped-flow methods. Using a continuous-flow apparatus with a dead time of 50 μs we have been able to resolve the kinetic rate constants and entire mechanism of Na+ binding to thrombin, an interaction that is at the basis of the procoagulant and prothrombotic roles of the enzyme in the blood. PMID:17935858

Somatic and gastrointestinal in vivo biotransformation rates of hydrophobic chemicals in fish.

PubMed

Lo, Justin C; Campbell, David A; Kennedy, Christopher J; Gobas, Frank A P C

2015-10-01

To improve current bioaccumulation assessment methods, a methodology is developed, applied, and investigated for measuring in vivo biotransformation rates of hydrophobic organic substances in the body (soma) and gastrointestinal tract of the fish. The method resembles the Organisation for Economic Co-operation and Development (OECD) 305 dietary bioaccumulation test but includes reference chemicals to determine both somatic and gastrointestinal biotransformation rates of test chemicals. Somatic biotransformation rate constants for the test chemicals ranged between 0 d(-1) and 0.38 (standard error [SE] 0.03)/d(-1) . Gastrointestinal biotransformation rate constants varied from 0 d(-1) to 46 (SE 7) d(-1) . Gastrointestinal biotransformation contributed more to the overall biotransformation in fish than somatic biotransformation for all test substances but 1. Results suggest that biomagnification tests can reveal the full extent of biotransformation in fish. The common presumption that the liver is the main site of biotransformation may not apply to many substances exposed through the diet. The results suggest that the application of quantitative structure-activity relationships (QSARs) for somatic biotransformation rates and hepatic in vitro models to assess the effect of biotransformation on bioaccumulation can underestimate biotransformation rates and overestimate the biomagnification potential of chemicals that are biotransformed in the gastrointestinal tract. With some modifications, the OECD 305 test can generate somatic and gastrointestinal biotransformation data to develop biotransformation QSARs and test in vitro-in vivo biotransformation extrapolation methods. © 2015 SETAC.

Steady-State Computation of Constant Rotational Rate Dynamic Stability Derivatives

NASA Technical Reports Server (NTRS)

Park, Michael A.; Green, Lawrence L.

2000-01-01

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

Processes and kinetics of Cd2+ sorption by a calcareous aquifer sand

USGS Publications Warehouse

Fuller, C.C.; Davis, J.A.

1987-01-01

The rate of Cd2+ sorption by a calcareous aquifer sand was characterized by two reaction steps, with the first step reaching completion in 24 hours. The second step proceeded at a slow and nearly constant rate for at least seven days. The first step includes a fast adsorption reaction which is followed by diffusive transport into either a disordered surface film of hydrated calcium carbonate or into pore spaces. After 24 hours the rate of Cd2+ sorption was constant and controlled by the rate of surface coprecipitation, as a solid solution of CdCO3 in CaCO3 formed in recrystallizing material. Desorption of Cd2+ from the sand was slow. Clean grains of primary minerals, e.g. quartz and aluminosilicates. sorbed much less Cd2+ than grains which had surface patches of secondary minerals, e.g. carbonates, iron and manganese oxides. Calcite grains sorbed the greatest amount of Cd2+ on a weight-normalized basis despite the greater abundance of quartz. A method is illustrated for determining empirical binding constants for trace metals at in situ pH values without introducing the experimental problem of supersaturation. The binding constants are useful for solute transport models which include a computation of aqueous speciation. ?? 1987.

Dose equivalent rate constants and barrier transmission data for nuclear medicine facility dose calculations and shielding design.

PubMed

Kusano, Maggie; Caldwell, Curtis B

2014-07-01

A primary goal of nuclear medicine facility design is to keep public and worker radiation doses As Low As Reasonably Achievable (ALARA). To estimate dose and shielding requirements, one needs to know both the dose equivalent rate constants for soft tissue and barrier transmission factors (TFs) for all radionuclides of interest. Dose equivalent rate constants are most commonly calculated using published air kerma or exposure rate constants, while transmission factors are most commonly calculated using published tenth-value layers (TVLs). Values can be calculated more accurately using the radionuclide's photon emission spectrum and the physical properties of lead, concrete, and/or tissue at these energies. These calculations may be non-trivial due to the polyenergetic nature of the radionuclides used in nuclear medicine. In this paper, the effects of dose equivalent rate constant and transmission factor on nuclear medicine dose and shielding calculations are investigated, and new values based on up-to-date nuclear data and thresholds specific to nuclear medicine are proposed. To facilitate practical use, transmission curves were fitted to the three-parameter Archer equation. Finally, the results of this work were applied to the design of a sample nuclear medicine facility and compared to doses calculated using common methods to investigate the effects of these values on dose estimates and shielding decisions. Dose equivalent rate constants generally agreed well with those derived from the literature with the exception of those from NCRP 124. Depending on the situation, Archer fit TFs could be significantly more accurate than TVL-based TFs. These results were reflected in the sample shielding problem, with unshielded dose estimates agreeing well, with the exception of those based on NCRP 124, and Archer fit TFs providing a more accurate alternative to TVL TFs and a simpler alternative to full spectral-based calculations. The data provided by this paper should assist in improving the accuracy and tractability of dose and shielding calculations for nuclear medicine facility design.

Fitting the Elementary Rate Constants of the P-gp Transporter Network in the hMDR1-MDCK Confluent Cell Monolayer Using a Particle Swarm Algorithm

PubMed Central

Agnani, Deep; Acharya, Poulomi; Martinez, Esteban; Tran, Thuy Thanh; Abraham, Feby; Tobin, Frank; Ellens, Harma; Bentz, Joe

2011-01-01

P-glycoprotein, a human multidrug resistance transporter, has been extensively studied due to its importance to human health and disease. In order to understand transport kinetics via P-gp, confluent cell monolayers overexpressing P-gp are widely used. The purpose of this study is to obtain the mass action elementary rate constants for P-gp's transport and to functionally characterize members of P-gp's network, i.e., other transporters that transport P-gp substrates in hMDR1-MDCKII confluent cell monolayers and are essential to the net substrate flux. Transport of a range of concentrations of amprenavir, loperamide, quinidine and digoxin across the confluent monolayer of cells was measured in both directions, apical to basolateral and basolateral to apical. We developed a global optimization algorithm using the Particle Swarm method that can simultaneously fit all datasets to yield accurate and exhaustive fits of these elementary rate constants. The statistical sensitivity of the fitted values was determined by using 24 identical replicate fits, yielding simple averages and standard deviations for all of the kinetic parameters, including the efflux active P-gp surface density. Digoxin required additional basolateral and apical transporters, while loperamide required just a basolateral tranporter. The data were better fit by assuming bidirectional transporters, rather than active importers, suggesting that they are not MRP or active OATP transporters. The P-gp efflux rate constants for quinidine and digoxin were about 3-fold smaller than reported ATP hydrolysis rate constants from P-gp proteoliposomes. This suggests a roughly 3∶1 stoichiometry between ATP hydrolysis and P-gp transport for these two drugs. The fitted values of the elementary rate constants for these P-gp substrates support the hypotheses that the selective pressures on P-gp are to maintain a broad substrate range and to keep xenobiotics out of the cytosol, but not out of the apical membrane. PMID:22028772

Creatine kinase rate constant in the human heart measured with 3D‐localization at 7 tesla

PubMed Central

Robson, Matthew D.; Neubauer, Stefan; Rodgers, Christopher T.

2016-01-01

Purpose We present a new Bloch‐Siegert four Angle Saturation Transfer (BOAST) method for measuring the creatine kinase (CK) first‐order effective rate constant kf in human myocardium at 7 tesla (T). BOAST combines a variant of the four‐angle saturation transfer (FAST) method using amplitude‐modulated radiofrequency pulses, phosphorus Bloch‐Siegert B1+‐mapping to determine the per‐voxel flip angles, and nonlinear fitting to Bloch simulations for postprocessing. Methods Optimal flip angles and repetition time parameters were determined from Monte Carlo simulations. BOAST was validated in the calf muscle of two volunteers at 3T and 7T. The myocardial CK forward rate constant was then measured in 10 volunteers at 7T in 82 min (after 1H localization). Results BOAST kfCK values were 0.281 ± 0.002 s−1 in the calf and 0.35 ± 0.05 s−1 in myocardium. These are consistent with literature values from lower fields. Using a literature values for adenosine triphosphate concentration, we computed CK flux values of 4.55 ± 1.52 mmol kg−1 s−1. The sensitive volume for BOAST depends on the B1 inhomogeneity of the transmit coil. Conclusion BOAST enables measurement of the CK rate constant in the human heart at 7T, with spatial localization in three dimensions to 5.6 mL voxels, using a 10‐cm loop coil. Magn Reson Med 78:20–32, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. PMID:27579566

The Hydroxyl Radical Reaction Rate Constant and Products of Dimethyl Succinate

DTIC Science & Technology

2008-03-01

phase reaction of OH + DMS, 10 liters of chamber content were flowed over 2,4- dinitrophenylhydrazine (DNPH) impregnated cartridges. Hydrazones formed... dinitrophenylhydrazine (DNPH) derivatization (method described in experimental methods), and GC/MS/MS (where samples were directly introduced into the mass

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

Prediction of Metabolite Concentrations, Rate Constants and Post-Translational Regulation Using Maximum Entropy-Based Simulations with Application to Central Metabolism of Neurospora crassa

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

Cannon, William; Zucker, Jeremy; Baxter, Douglas

We report the application of a recently proposed approach for modeling biological systems using a maximum entropy production rate principle in lieu of having in vivo rate constants. The method is applied in four steps: (1) a new ODE-based optimization approach based on Marcelin’s 1910 mass action equation is used to obtain the maximum entropy distribution, (2) the predicted metabolite concentrations are compared to those generally expected from experiment using a loss function from which post-translational regulation of enzymes is inferred, (3) the system is re-optimized with the inferred regulation from which rate constants are determined from the metabolite concentrationsmore » and reaction fluxes, and finally (4) a full ODE-based, mass action simulation with rate parameters and allosteric regulation is obtained. From the last step, the power characteristics and resistance of each reaction can be determined. The method is applied to the central metabolism of Neurospora crassa and the flow of material through the three competing pathways of upper glycolysis, the non-oxidative pentose phosphate pathway, and the oxidative pentose phosphate pathway are evaluated as a function of the NADP/NADPH ratio. It is predicted that regulation of phosphofructokinase (PFK) and flow through the pentose phosphate pathway are essential for preventing an extreme level of fructose 1, 6-bisphophate accumulation. Such an extreme level of fructose 1,6-bisphophate would otherwise result in a glassy cytoplasm with limited diffusion, dramatically decreasing the entropy and energy production rate and, consequently, biological competitiveness.« less

Reaction rate constants and mean population percentage for nitrifiers in an alternating oxidation ditch system.

PubMed

Mantziaras, I D; Katsiri, A

2011-01-01

This paper presents a methodology for the determination of reaction rate constants for nitrifying bacteria and their mean population percentage in biomass in an alternating oxidation ditch system. The method used is based on the growth rate equations of the ASM1 model (IWA) (Henze et al. in Activated sludge models ASM1, ASM2, ASM2d, and ASM3. IWA Scientific and Technical Report no. 9, IWA Publishing, London, UK, 2000) and the application of mass balance equations for nitrifiers and ammonium nitrogen in an operational cycle of the ditch system. The system consists of two ditches operating in four phases. Data from a large-scale oxidation ditch pilot plant with a total volume of 120 m(3) within an experimental period of 8 months was used. Maximum specific growth rate for autotrophs (μ(A)) and the half-saturation constant for ammonium nitrogen (K(NH)) were found to be 0.36 day(-1) and 0.65 mgNH(4)-N/l, respectively. Additionally, the average population percentage of the nitrifiers in the biomass was estimated to be around 3%.

Hierarchical coarse-graining model for photosystem II including electron and excitation-energy transfer processes.

PubMed

Matsuoka, Takeshi; Tanaka, Shigenori; Ebina, Kuniyoshi

2014-03-01

We propose a hierarchical reduction scheme to cope with coupled rate equations that describe the dynamics of multi-time-scale photosynthetic reactions. To numerically solve nonlinear dynamical equations containing a wide temporal range of rate constants, we first study a prototypical three-variable model. Using a separation of the time scale of rate constants combined with identified slow variables as (quasi-)conserved quantities in the fast process, we achieve a coarse-graining of the dynamical equations reduced to those at a slower time scale. By iteratively employing this reduction method, the coarse-graining of broadly multi-scale dynamical equations can be performed in a hierarchical manner. We then apply this scheme to the reaction dynamics analysis of a simplified model for an illuminated photosystem II, which involves many processes of electron and excitation-energy transfers with a wide range of rate constants. We thus confirm a good agreement between the coarse-grained and fully (finely) integrated results for the population dynamics. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

Non-steady state mass action dynamics without rate constants: dynamics of coupled reactions using chemical potentials

NASA Astrophysics Data System (ADS)

Cannon, William R.; Baker, Scott E.

2017-10-01

Comprehensive and predictive simulation of coupled reaction networks has long been a goal of biology and other fields. Currently, metabolic network models that utilize enzyme mass action kinetics have predictive power but are limited in scope and application by the fact that the determination of enzyme rate constants is laborious and low throughput. We present a statistical thermodynamic formulation of the law of mass action for coupled reactions at both steady states and non-stationary states. The formulation uses chemical potentials instead of rate constants. When used to model deterministic systems, the method corresponds to a rescaling of the time dependent reactions in such a way that steady states can be reached on the same time scale but with significantly fewer computational steps. The relationships between reaction affinities, free energy changes and generalized detailed balance are central to the discussion. The significance for applications in systems biology are discussed as is the concept and assumption of maximum entropy production rate as a biological principle that links thermodynamics to natural selection.

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.

Sources of variation in oxygen consumption of aquatic animals demonstrated by simulated constant oxygen consumption and respirometers of different sizes.

PubMed

Svendsen, M B S; Bushnell, P G; Christensen, E A F; Steffensen, J F

2016-01-01

As intermittent-flow respirometry has become a common method for the determination of resting metabolism or standard metabolic rate (SMR), this study investigated how much of the variability seen in the experiments was due to measurement error. Experiments simulated different constant oxygen consumption rates (M˙O2 ) of a fish, by continuously injecting anoxic water into a respirometer, altering the injection rate to correct for the washout error. The effect of respirometer-to-fish volume ratio (RFR) on SMR measurement and variability was also investigated, using the simulated constant M˙O2 and the M˙O2 of seven roach Rutilus rutilus in respirometers of two different sizes. The results show that higher RFR increases measurement variability but does not change the mean SMR established using a double Gaussian fit. Further, the study demonstrates that the variation observed when determining oxygen consumption rates of fishes in systems with reasonable RFRs mainly comes from the animal, not from the measuring equipment. © 2016 The Fisheries Society of the British Isles.

Application of the Initial Rate Method in Anaerobic Digestion of Kitchen Waste

PubMed Central

Lang, Xianming; Liu, Yiwei; Li, Rundong; Yu, Meiling; Shao, Lijie; Wang, Xiaoming

2017-01-01

This article proposes a methane production approach through sequenced anaerobic digestion of kitchen waste, determines the hydrolysis constants and reaction orders at both low total solid (TS) concentrations and high TS concentrations using the initial rate method, and examines the population growth model and first-order hydrolysis model. The findings indicate that the first-order hydrolysis model better reflects the kinetic process of gas production. During the experiment, all the influential factors of anaerobic fermentation retained their optimal values. The hydrolysis constants and reaction orders at low TS concentrations are then employed to demonstrate that the first-order gas production model can describe the kinetics of the gas production process. At low TS concentrations, the hydrolysis constants and reaction orders demonstrated opposite trends, with both stabilizing after 24 days at 0.99 and 1.1252, respectively. At high TS concentrations, the hydrolysis constants and the reaction orders stabilized at 0.98 (after 18 days) and 0.3507 (after 14 days), respectively. Given sufficient reaction time, the hydrolysis involved in anaerobic fermentation of kitchen waste can be regarded as a first-order reaction in terms of reaction kinetics. This study serves as a good reference for future studies regarding the kinetics of anaerobic digestion of kitchen waste. PMID:28546964

Application of the Initial Rate Method in Anaerobic Digestion of Kitchen Waste.

PubMed

Feng, Lei; Gao, Yuan; Kou, Wei; Lang, Xianming; Liu, Yiwei; Li, Rundong; Yu, Meiling; Shao, Lijie; Wang, Xiaoming

2017-01-01

This article proposes a methane production approach through sequenced anaerobic digestion of kitchen waste, determines the hydrolysis constants and reaction orders at both low total solid (TS) concentrations and high TS concentrations using the initial rate method, and examines the population growth model and first-order hydrolysis model. The findings indicate that the first-order hydrolysis model better reflects the kinetic process of gas production. During the experiment, all the influential factors of anaerobic fermentation retained their optimal values. The hydrolysis constants and reaction orders at low TS concentrations are then employed to demonstrate that the first-order gas production model can describe the kinetics of the gas production process. At low TS concentrations, the hydrolysis constants and reaction orders demonstrated opposite trends, with both stabilizing after 24 days at 0.99 and 1.1252, respectively. At high TS concentrations, the hydrolysis constants and the reaction orders stabilized at 0.98 (after 18 days) and 0.3507 (after 14 days), respectively. Given sufficient reaction time, the hydrolysis involved in anaerobic fermentation of kitchen waste can be regarded as a first-order reaction in terms of reaction kinetics. This study serves as a good reference for future studies regarding the kinetics of anaerobic digestion of kitchen waste.

Effect of positive pulse charge waveforms on the energy efficiency of lead-acid traction cells

NASA Technical Reports Server (NTRS)

Smithrick, J. J.

1981-01-01

The effects of four different charge methods on the energy conversion efficiency of 300 ampere hour lead acid traction cells were investigated. Three of the methods were positive pulse charge waveforms; the fourth, a constant current method, was used as a baseline of comparison. The positive pulse charge waveforms were: 120 Hz full wave rectified sinusoidal; 120 Hz silicon controlled rectified; and 1 kHz square wave. The constant current charger was set at the time average pulse current of each pulse waveform, which was 150 amps. The energy efficiency does not include charger losses. The lead acid traction cells were charged to 70 percent of rated ampere hour capacity in each case. The results of charging the cells using the three different pulse charge waveforms indicate there was no significant difference in energy conversion efficiency when compared to constant current charging at the time average pulse current value.

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

Phototransformation rate constants of PAHs associated with soot particles.

PubMed

Kim, Daekyun; Young, Thomas M; Anastasio, Cort

2013-01-15

Photodegradation is a key process governing the residence time and fate of polycyclic aromatic hydrocarbons (PAHs) in particles, both in the atmosphere and after deposition. We have measured photodegradation rate constants of PAHs in bulk deposits of soot particles illuminated with simulated sunlight. The photodegradation rate constants at the surface (k(p)(0)), the effective diffusion coefficients (D(eff)), and the light penetration depths (z(0.5)) for PAHs on soot layers of variable thickness were determined by fitting experimental data with a model of coupled photolysis and diffusion. The overall disappearance rates of irradiated low molecular weight PAHs (with 2-3 rings) on soot particles were influenced by fast photodegradation and fast diffusion kinetics, while those of high molecular weight PAHs (with 4 or more rings) were apparently controlled by either the combination of slow photodegradation and slow diffusion kinetics or by very slow diffusion kinetics alone. The value of z(0.5) is more sensitive to the soot layer thickness than the k(p)(0) value. As the thickness of the soot layer increases, the z(0.5) values increase, but the k(p)(0) values are almost constant. The effective diffusion coefficients calculated from dark experiments are generally higher than those from the model fitting method for illumination experiments. Due to the correlation between k(p)(0) and z(0.5) in thinner layers, D(eff) should be estimated by an independent method for better accuracy. Despite some limitations of the model used in this study, the fitted parameters were useful for describing empirical results of photodegradation of soot-associated PAHs. Copyright © 2012 Elsevier B.V. All rights reserved.

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.

Absolute rate constants for O + NO + M /= He, Ne, Ar, Kr/ yields NO2 + M from 217-500 K

NASA Technical Reports Server (NTRS)

Michael, J. V.; Payne, W. A.; Whytock, D. A.

1976-01-01

Rate constants for the reaction O + NO + M yields NO2 + M have been obtained at temperatures from 217-500 K in four different rare gases by a method combining flash photolysis with time resolved detection of O(3-P) by resonance fluorescence. The measured rate constants in Arrhenius form are (10.8 plus or minus 1.2) x 10 to the -33rd exp(1040 plus or minus 60/1.987 T) for helium; (9.01 plus or minus 1.16) x 10 to the -33rd exp(1180 plus or minus 70/1.987 T) for argon; (9.33 plus or minus 1.10) x 10 to the -33rd exp(1030 plus or minus 60/1.987 T) for neon; and (9.52 plus or minus 1.10) x 10 to the -33rd exp(1140 plus or minus 70/1.987 T) for krypton in units of cm to the 6th/sq molecule/s.

Barrierless association of CF2 and dissociation of C2F4 by variational transition-state theory and system-specific quantum Rice–Ramsperger–Kassel theory

PubMed Central

Bao, Junwei Lucas; Zhang, Xin

2016-01-01

Bond dissociation is a fundamental chemical reaction, and the first principles modeling of the kinetics of dissociation reactions with a monotonically increasing potential energy along the dissociation coordinate presents a challenge not only for modern electronic structure methods but also for kinetics theory. In this work, we use multifaceted variable-reaction-coordinate variational transition-state theory (VRC-VTST) to compute the high-pressure limit dissociation rate constant of tetrafluoroethylene (C2F4), in which the potential energies are computed by direct dynamics with the M08-HX exchange correlation functional. To treat the pressure dependence of the unimolecular rate constants, we use the recently developed system-specific quantum Rice–Ramsperger–Kassel theory. The calculations are carried out by direct dynamics using an exchange correlation functional validated against calculations that go beyond coupled-cluster theory with single, double, and triple excitations. Our computed dissociation rate constants agree well with the recent experimental measurements. PMID:27834727

Barrierless association of CF2 and dissociation of C2F4 by variational transition-state theory and system-specific quantum Rice-Ramsperger-Kassel theory.

PubMed

Bao, Junwei Lucas; Zhang, Xin; Truhlar, Donald G

2016-11-29

Bond dissociation is a fundamental chemical reaction, and the first principles modeling of the kinetics of dissociation reactions with a monotonically increasing potential energy along the dissociation coordinate presents a challenge not only for modern electronic structure methods but also for kinetics theory. In this work, we use multifaceted variable-reaction-coordinate variational transition-state theory (VRC-VTST) to compute the high-pressure limit dissociation rate constant of tetrafluoroethylene (C 2 F 4 ), in which the potential energies are computed by direct dynamics with the M08-HX exchange correlation functional. To treat the pressure dependence of the unimolecular rate constants, we use the recently developed system-specific quantum Rice-Ramsperger-Kassel theory. The calculations are carried out by direct dynamics using an exchange correlation functional validated against calculations that go beyond coupled-cluster theory with single, double, and triple excitations. Our computed dissociation rate constants agree well with the recent experimental measurements.

Rate constants of agonist binding to muscarinic receptors in rat brain medulla. Evaluation by competition kinetics

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

Schreiber, G.; Henis, Y.I.; Sokolovsky, M.

The method of competition kinetics, which measures the binding kinetics of an unlabeled ligand through its effect on the binding kinetics of a labeled ligand, was employed to investigate the kinetics of muscarinic agonist binding to rat brain medulla pons homogenates. The agonists studied were acetylcholine, carbamylcholine, and oxotremorine, with N-methyl-4-(TH)piperidyl benzilate employed as the radiolabeled ligand. Our results suggested that the binding of muscarinic agonists to the high affinity sites is characterized by dissociation rate constants higher by 2 orders of magnitude than those of antagonists, with rather similar association rate constants. Our findings also suggest that isomerization ofmore » the muscarinic receptors following ligand binding is significant in the case of antagonists, but not of agonists. Moreover, it is demonstrated that in the medulla pons preparation, agonist-induced interconversion between high and low affinity bindings sites does not occur to an appreciable extent.« less

Dosimetric characterizations of GZP6 60Co high dose rate brachytherapy sources: application of superimposition method

PubMed Central

Bahreyni Toossi, Mohammad Taghi; Ghorbani, Mahdi; Mowlavi, Ali Asghar; Meigooni, Ali Soleimani

2012-01-01

Background Dosimetric characteristics of a high dose rate (HDR) GZP6 Co-60 brachytherapy source have been evaluated following American Association of Physicists in MedicineTask Group 43U1 (AAPM TG-43U1) recommendations for their clinical applications. Materials and methods MCNP-4C and MCNPX Monte Carlo codes were utilized to calculate dose rate constant, two dimensional (2D) dose distribution, radial dose function and 2D anisotropy function of the source. These parameters of this source are compared with the available data for Ralstron 60Co and microSelectron192Ir sources. Besides, a superimposition method was developed to extend the obtained results for the GZP6 source No. 3 to other GZP6 sources. Results The simulated value for dose rate constant for GZP6 source was 1.104±0.03 cGyh-1U-1. The graphical and tabulated radial dose function and 2D anisotropy function of this source are presented here. The results of these investigations show that the dosimetric parameters of GZP6 source are comparable to those for the Ralstron source. While dose rate constant for the two 60Co sources are similar to that for the microSelectron192Ir source, there are differences between radial dose function and anisotropy functions. Radial dose function of the 192Ir source is less steep than both 60Co source models. In addition, the 60Co sources are showing more isotropic dose distribution than the 192Ir source. Conclusions The superimposition method is applicable to produce dose distributions for other source arrangements from the dose distribution of a single source. The calculated dosimetric quantities of this new source can be introduced as input data to the GZP6 treatment planning system (TPS) and to validate the performance of the TPS. PMID:23077455

A comparison between computer-controlled and set work rate exercise based on target heart rate

NASA Technical Reports Server (NTRS)

Pratt, Wanda M.; Siconolfi, Steven F.; Webster, Laurie; Hayes, Judith C.; Mazzocca, Augustus D.; Harris, Bernard A., Jr.

1991-01-01

Two methods are compared for observing the heart rate (HR), metabolic equivalents, and time in target HR zone (defined as the target HR + or - 5 bpm) during 20 min of exercise at a prescribed intensity of the maximum working capacity. In one method, called set-work rate exercise, the information from a graded exercise test is used to select a target HR and to calculate a corresponding constant work rate that should induce the desired HR. In the other method, the work rate is controlled by a computer algorithm to achieve and maintain a prescribed target HR. It is shown that computer-controlled exercise is an effective alternative to the traditional set work rate exercise, particularly when tight control of cardiovascular responses is necessary.

Accelerated Testing Methodology Developed for Determining the Slow Crack Growth of Advanced Ceramics

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Gyekenyesi, John P.

1998-01-01

Constant stress-rate ("dynamic fatigue") testing has been used for several decades to characterize the slow crack growth behavior of glass and structural ceramics at both ambient and elevated temperatures. The advantage of such testing over other methods lies in its simplicity: strengths are measured in a routine manner at four or more stress rates by applying a constant displacement or loading rate. The slow crack growth parameters required for component design can be estimated from a relationship between strength and stress rate. With the proper use of preloading in constant stress-rate testing, test time can be reduced appreciably. If a preload corresponding to 50 percent of the strength is applied to the specimen prior to testing, 50 percent of the test time can be saved as long as the applied preload does not change the strength. In fact, it has been a common, empirical practice in the strength testing of ceramics or optical fibers to apply some preloading (<40 percent). The purpose of this work at the NASA Lewis Research Center is to study the effect of preloading on measured strength in order to add a theoretical foundation to the empirical practice.

Determination of 1-octanol-air partition coefficient using gaseous diffusion in the air boundary layer.

PubMed

Ha, Yeonjeong; Kwon, Jung-Hwan

2010-04-15

Exact determination of the partition coefficient between 1-octanol and air (K(OA)) is very important because it is a key descriptor for describing the thermodynamic partitioning between the air and organic phases. In spite of its importance, the number and quality of experimental K(OA) values for hydrophobic organic chemicals are limited because of experimental difficulties. Thus, to measure K(OA) values, a high-throughput method was developed that used liquid-phase extraction with 1-octanol drop at the tip of a microsyringe needle. The concentration in the headspace surrounding the 1 muL octanol drop was equilibrated with liquid octanol containing polycyclic aromatic hydrocarbons (PAHs). The change in concentrations of PAHs in the octanol drop was measured to obtain mass transfer rate constants, and these rate constants were then converted into K(OA) values using a film diffusion model. Thirteen polycyclic aromatic hydrocarbons with log K(OA) between 5 and 12 were chosen for the proof of the principle. Experimental determination of log K(OA) was accomplished in 30 h for PAHs with their log K(OA) less than 11. The measured log K(OA) values were very close to those obtained by various experimental and estimation methods in the literature, suggesting that this new method can provide a fast and easy determination of log K(OA) values for many chemicals of environmental interests. In addition, the applicability of the method can be extended to determine Henry's law constant for compounds with low vapor pressure and to estimate gaseous transfer rate of semivolatile compounds for environmental fate modeling.

An approximate analytical solution for describing surface runoff and sediment transport over hillslope

NASA Astrophysics Data System (ADS)

Tao, Wanghai; Wang, Quanjiu; Lin, Henry

2018-03-01

Soil and water loss from farmland causes land degradation and water pollution, thus continued efforts are needed to establish mathematical model for quantitative analysis of relevant processes and mechanisms. In this study, an approximate analytical solution has been developed for overland flow model and sediment transport model, offering a simple and effective means to predict overland flow and erosion under natural rainfall conditions. In the overland flow model, the flow regime was considered to be transitional with the value of parameter β (in the kinematic wave model) approximately two. The change rate of unit discharge with distance was assumed to be constant and equal to the runoff rate at the outlet of the plane. The excess rainfall was considered to be constant under uniform rainfall conditions. The overland flow model developed can be further applied to natural rainfall conditions by treating excess rainfall intensity as constant over a small time interval. For the sediment model, the recommended values of the runoff erosion calibration constant (cr) and the splash erosion calibration constant (cf) have been given in this study so that it is easier to use the model. These recommended values are 0.15 and 0.12, respectively. Comparisons with observed results were carried out to validate the proposed analytical solution. The results showed that the approximate analytical solution developed in this paper closely matches the observed data, thus providing an alternative method of predicting runoff generation and sediment yield, and offering a more convenient method of analyzing the quantitative relationships between variables. Furthermore, the model developed in this study can be used as a theoretical basis for developing runoff and erosion control methods.

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.

Rate constants for proteins binding to substrates with multiple binding sites using a generalized forward flux sampling expression

NASA Astrophysics Data System (ADS)

Vijaykumar, Adithya; ten Wolde, Pieter Rein; Bolhuis, Peter G.

2018-03-01

To predict the response of a biochemical system, knowledge of the intrinsic and effective rate constants of proteins is crucial. The experimentally accessible effective rate constant for association can be decomposed in a diffusion-limited rate at which proteins come into contact and an intrinsic association rate at which the proteins in contact truly bind. Reversely, when dissociating, bound proteins first separate into a contact pair with an intrinsic dissociation rate, before moving away by diffusion. While microscopic expressions exist that enable the calculation of the intrinsic and effective rate constants by conducting a single rare event simulation of the protein dissociation reaction, these expressions are only valid when the substrate has just one binding site. If the substrate has multiple binding sites, a bound enzyme can, besides dissociating into the bulk, also hop to another binding site. Calculating transition rate constants between multiple states with forward flux sampling requires a generalized rate expression. We present this expression here and use it to derive explicit expressions for all intrinsic and effective rate constants involving binding to multiple states, including rebinding. We illustrate our approach by computing the intrinsic and effective association, dissociation, and hopping rate constants for a system in which a patchy particle model enzyme binds to a substrate with two binding sites. We find that these rate constants increase as a function of the rotational diffusion constant of the particles. The hopping rate constant decreases as a function of the distance between the binding sites. Finally, we find that blocking one of the binding sites enhances both association and dissociation rate constants. Our approach and results are important for understanding and modeling association reactions in enzyme-substrate systems and other patchy particle systems and open the way for large multiscale simulations of such systems.

Derivative spectrophotometry for the determination of faropenem in the presence of degradation products: an application for kinetic studies.

PubMed

Cielecka-Piontek, Judyta

2013-07-01

A simple and selective derivative spectrophotometric method was developed for the quantitative determination of faropenem in pure form and in pharmaceutical dosage. The method is based on the zero-crossing effect of first-derivative spectrophotometry (λ = 324 nm), which eliminates the overlapping effect caused by the excipients present in the pharmaceutical preparation, as well as degradation products, formed during hydrolysis, oxidation, photolysis, and thermolysis. The method was linear in the concentration range 2.5-300 μg/mL (r = 0.9989) at λ = 341 nm; the limits of detection and quantitation were 0.16 and 0.46 μg/mL, respectively. The method had good precision (relative standard deviation from 0.68 to 2.13%). Recovery of faropenem ranged from 97.9 to 101.3%. The first-order rate constants of the degradation of faropenem in pure form and in pharmaceutical dosage were determined by using first-derivative spectrophotometry. A statistical comparison of the validation results and the observed rate constants for faropenem degradation with these obtained with the high-performance liquid chromatography method demonstrated that both were compatible.

Quantal Study of the Exchange Reaction for N + N2 using an ab initio Potential Energy Surface

NASA Technical Reports Server (NTRS)

Wang, Dunyou; Stallcop, James R.; Huo, Winifred M.; Dateo, Christopher E.; Schwenke, David W.; Partridge, Harry; Kwak, Dochan (Technical Monitor)

2002-01-01

The N + N2 exchange rate is calculated using a time-dependent quantum dynamics method on a newly determined ab initio potential energy surface (PES) for the ground A" state. This ab initio PES shows a double barrier feature in the interaction region with the barrier height at 47.2 kcal/mol, and a shallow well between these two barriers, with the minimum at 43.7 kcal/mol. A quantum dynamics wave packet calculation has been carried out using the fitted PES to compute the cumulative reaction probability for the exchange reaction of N + N2(J=O). The J - K shift method is then employed to obtain the rate constant for this reaction. The calculated rate constant is compared with experimental data and a recent quasi-classical calculation using a LEPS PES. Significant differences are found between the present and quasiclassical results. The present rate calculation is the first accurate 3D quantal dynamics study for N + N2 reaction system and the ab initio PES reported here is the first such surface for N3.

Theory of long binding events in single-molecule–controlled rotation experiments on F1-ATPase

PubMed Central

Volkán-Kacsó, Sándor; Marcus, Rudolph A.

2017-01-01

The theory of elastic group transfer for the binding and release rate constants for nucleotides in F1-ATPase as a function of the rotor angle is further extended in several respects. (i) A method is described for predicting the experimentally observed lifetime distribution of long binding events in the controlled rotation experiments by taking into account the hydrolysis and synthesis reactions occurring during these events. (ii) A method is also given for treating the long binding events in the experiments and obtaining the rate constants for the hydrolysis and synthesis reactions occurring during these events. (iii) The theory in the previous paper is given in a symmetric form, an extension that simplifies the application of the theory to experiments. It also includes a theory-based correction of the reported “on” and “off” rates by calculating the missed events. A near symmetry of the data about the angle of −40° and a “turnover” in the binding rate data vs. rotor angle for angles greater than ∼40° is also discussed. PMID:28652332

A Green's function method for simulation of time-dependent solute transport and reaction in realistic microvascular geometries.

PubMed

Secomb, Timothy W

2016-12-01

A novel theoretical method is presented for simulating the spatially resolved convective and diffusive transport of reacting solutes between microvascular networks and the surrounding tissues. The method allows for efficient computational solution of problems involving convection and non-linear binding of solutes in blood flowing through microvascular networks with realistic 3D geometries, coupled with transvascular exchange and diffusion and reaction in the surrounding tissue space. The method is based on a Green's function approach, in which the solute concentration distribution in the tissue is expressed as a sum of fields generated by time-varying distributions of discrete sources and sinks. As an example of the application of the method, the washout of an inert diffusible tracer substance from a tissue region perfused by a network of microvessels is simulated, showing its dependence on the solute's transvascular permeability and tissue diffusivity. Exponential decay of the washout concentration is predicted, with rate constants that are about 10-30% lower than the rate constants for a tissue cylinder model with the same vessel length, vessel surface area and blood flow rate per tissue volume. © The authors 2015. Published by Oxford University Press on behalf of the Institute of Mathematics and its Applications. All rights reserved.

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.

Kinetic study and mechanism of Niclosamide degradation.

PubMed

Zaazaa, Hala E; Abdelrahman, Maha M; Ali, Nouruddin W; Magdy, Maimana A; Abdelkawy, M

2014-11-11

A spectrophotometric kinetic study of Niclosamide alkaline degradation as a function of drug concentration, alkaline concentration and temperature has been established utilizing double divisor-ratio spectra spectrophotometric method. The developed method allowed determination of Niclosamide in presence of its alkaline degradation products; namely; 2-chloro-4-nitro aniline (DEG I) and 5-chloro salicylic acid (DEG II) with characterization of its degradation mechanism. It was found that degradation kinetic of Niclosamide followed pseudo-first order under the established experimental conditions with a degradation rate constant (k) of 0.0829 mol/h and half life (t1/2) of 8.35 h. The overall degradation rate constant as a function of the temperature under the given conditions obeyed Arrhenius equation where the activation energy was calculated to be 3.41 kcal/mol. Copyright © 2014 Elsevier B.V. All rights reserved.

Annealed importance sampling with constant cooling rate

NASA Astrophysics Data System (ADS)

Giovannelli, Edoardo; Cardini, Gianni; Gellini, Cristina; Pietraperzia, Giangaetano; Chelli, Riccardo

2015-02-01

Annealed importance sampling is a simulation method devised by Neal [Stat. Comput. 11, 125 (2001)] to assign weights to configurations generated by simulated annealing trajectories. In particular, the equilibrium average of a generic physical quantity can be computed by a weighted average exploiting weights and estimates of this quantity associated to the final configurations of the annealed trajectories. Here, we review annealed importance sampling from the perspective of nonequilibrium path-ensemble averages [G. E. Crooks, Phys. Rev. E 61, 2361 (2000)]. The equivalence of Neal's and Crooks' treatments highlights the generality of the method, which goes beyond the mere thermal-based protocols. Furthermore, we show that a temperature schedule based on a constant cooling rate outperforms stepwise cooling schedules and that, for a given elapsed computer time, performances of annealed importance sampling are, in general, improved by increasing the number of intermediate temperatures.

Rapid computation of directional wellbore drawdown in a confined aquifer via Poisson resummation

NASA Astrophysics Data System (ADS)

Blumenthal, Benjamin J.; Zhan, Hongbin

2016-08-01

We have derived a rapidly computed analytical solution for drawdown caused by a partially or fully penetrating directional wellbore (vertical, horizontal, or slant) via Green's function method. The mathematical model assumes an anisotropic, homogeneous, confined, box-shaped aquifer. Any dimension of the box can have one of six possible boundary conditions: 1) both sides no-flux; 2) one side no-flux - one side constant-head; 3) both sides constant-head; 4) one side no-flux; 5) one side constant-head; 6) free boundary conditions. The solution has been optimized for rapid computation via Poisson Resummation, derivation of convergence rates, and numerical optimization of integration techniques. Upon application of the Poisson Resummation method, we were able to derive two sets of solutions with inverse convergence rates, namely an early-time rapidly convergent series (solution-A) and a late-time rapidly convergent series (solution-B). From this work we were able to link Green's function method (solution-B) back to image well theory (solution-A). We then derived an equation defining when the convergence rate between solution-A and solution-B is the same, which we termed the switch time. Utilizing the more rapidly convergent solution at the appropriate time, we obtained rapid convergence at all times. We have also shown that one may simplify each of the three infinite series for the three-dimensional solution to 11 terms and still maintain a maximum relative error of less than 10-14.

Study of kinetic desorption rate constant in fish muscle and agarose gel model using solid phase microextraction coupled with liquid chromatography with tandem mass spectrometry.

PubMed

Togunde, Oluranti Paul; Oakes, Ken; Servos, Mark; Pawliszyn, Janusz

2012-09-12

This study aims to use solid phase microextraction (SPME), a simple tool to investigate diffusion rate (time) constant of selected pharmaceuticals in gel and fish muscle by comparing desorption rate of diffusion of the drugs in both agarose gel prepared with phosphate-buffered saline (PBS; pH 7.4) and fish muscle. The gel concentration (agarose gel model) that could be used to simulate tissue matrix (fish muscle) for free diffusion of drugs under in vitro and in vivo conditions was determined to model mass transfer phenomena between fibre polymer coating and environmental matrix such that partition coefficients and desorption time constant (diffusion coefficient) can be determined. SPME procedure involves preloading the extraction phase (fibre) with the standards from spiked PBS for 1h via direct extraction. Subsequently, the preloaded fibre is introduced to the sample such fish or agarose gel for specified time ranging from 0.5 to 60 h. Then, fibre is removed at specified time and desorbed in 100 μL of desorption solution (acetonitrile: water 1:1) for 90 min under agitation speed of 1000 rpm. The samples extract were immediately injected to the instrument and analysed using liquid chromatography coupled with tandem mass spectrometry (LC/MS/MS). The limit of detection of the method in gel and fish muscle was 0.01-0.07 ng mL(-1) and 0.07-0.34 ng g(-1), respectively, while the limit quantification was 0.10-0.20 ng mL(-1) in gel samples and 0.40-0.97 ng g(-1) in fish sample. The reproducibility of the method was good (5-15% RSD). The results suggest that kinetics of desorption of the compounds in fish tissue and different viscosity of gel can be determined using desorption time constant. In this study, desorption time constant which is directly related to desorption rate (diffusion kinetics) of selected drugs from the fibre to the gel matrix is faster as the viscosity of the gel matrix reduces from 2% (w/v) to 0.8% (w/v). As the concentration of gel reduces, viscosity of the gel will be reduced therefore allowing faster diffusion which invariably affect desorption time constant. Also, desorption time constant of model drugs in the fish muscle and 0.8-0.9% (w/v) gel model are similar based on free diffusion of studied compounds. In addition, in vitro and in vivo desorption time constant comparison shows that desorption time constant in an in vivo system (live fish muscle) is generally higher than an in vitro system (dead fish muscle) except for sertraline and nordiazepam. This study demonstrates SPME as a simple investigative tool to understand kinetics of desorption in an in vivo system with a goal to measure desorption rate of pharmaceuticals in fish. Copyright © 2011 Elsevier B.V. All rights reserved.

Tensile Properties of 17-7 PH and 12 MoV Stainless-Steel Sheet under Rapid-Heating and Constant-Temperature Conditions

NASA Technical Reports Server (NTRS)

Manning, Charles R., Jr.; Price, Howard L.

1961-01-01

Results are presented of rapid-heating tests of 17-7 PH and 12 MoV stainless-steel sheet heated to failure at temperature rates from about 1 F to 170 F per second under constant-load conditions. Yield and rupture strengths obtained from rapid-heating tests are compared with yield and tensile strengths obtained from short-time elevated-temperature tensile tests (30-minute exposure). A rate-temperature parameter was used to construct master curves from which yield and rupture stresses or temperatures can be predicted. A method for measuring strain by optical means is described.

Virtual Instrument for Determining Rate Constant of Second-Order Reaction by pX Based on LabVIEW 8.0.

PubMed

Meng, Hu; Li, Jiang-Yuan; Tang, Yong-Huai

2009-01-01

The virtual instrument system based on LabVIEW 8.0 for ion analyzer which can measure and analyze ion concentrations in solution is developed and comprises homemade conditioning circuit, data acquiring board, and computer. It can calibrate slope, temperature, and positioning automatically. When applied to determine the reaction rate constant by pX, it achieved live acquiring, real-time displaying, automatical processing of testing data, generating the report of results; and other functions. This method simplifies the experimental operation greatly, avoids complicated procedures of manual processing data and personal error, and improves veracity and repeatability of the experiment results.

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

Bioconcentration of sediment-associated fluoranthene by the filter-feeding bivalve mollusk, Crassostrea virginica

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

Siewicki, T.C.; Chandler, G.T.

1995-12-31

Eastern oysters (Crassostrea virginica) were continuously exposed to suspended {sup 14}C-fluoranthene spiked-sediment for either: (1) five days followed by 24 days deputation, or (2) 28 days exposure. Sediment less than 63 um contained fluoranthene concentrations one or ten times that measured at suburbanized sites in southeastern estuaries (133 or 1,300 ng/g). The data were evaluated both raw and normalized for tissue lipid and sediment organic carbon concentrations. Uptake rate constants were estimated using non-linear regression methods. Depuration rate constants were estimated by linear regression of the deputation phase following five-days exposure and as the second partial derivative of the non-linearmore » regression for the 28-day exposures. Uptake and deputation rate constants, bioconcentration factors and half-lives were similar regardless of exposure time, sediment fluoranthene concentration or use of data normalization. Uptake and deputation rate constants, bioconcentration factors and half-lives (days) were similar and low for all experiments, ranging from 0.02 to 0.10, 0.14 to 0.30, 0.09 to 0.46, and 2.4 to 5.0, respectively. Degradation by the mixed function oxidase system is not expected in oysters allowing the use of radiotracers for measuring very low concentrations of fluoranthene. The results suggest that short-term exposures followed by deputation are effective for estimating kinetic rate constants and that normalization provides little benefit in these controlled studies. The results further show that bioconcentration of sediment-associated fluoranthene, and possibly other polycyclic aromatic hydrocarbons, is very low compared to either dissolved forms or levels commonly used in regulatory actions.« less

SU-F-T-344: Commissioning Constant Dose Rate VMAT in the Raystation Treatment Planning System for a Varian Clinac IX

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

Pursley, J; Gueorguiev, G; Prichard, H

Purpose: To demonstrate the commissioning of constant dose rate volumetric modulated arc therapy (VMAT) in the Raystation treatment planning system for a Varian Clinac iX with Exact couch. Methods: Constant dose rate (CDR) VMAT is an option in the Raystation treatment planning system, enabling VMAT delivery on Varian linacs without a RapidArc upgrade. Raystation 4.7 was used to commission CDR-VMAT for a Varian Clinac iX. Raystation arc model parameters were selected to match machine deliverability characteristics. A Varian Exact couch model was added to Raystation 4.7 and commissioned for use in VMAT optimization. CDR-VMAT commissioning checks were performed on themore » linac, including patient-specific QA measurements for 10 test patients using both the ArcCHECK from Sun Nuclear Corporation and COMPASS from IBA Dosimetry. Multi-criteria optimization (MCO) in Raystation was used for CDR-VMAT planning. Results: Raystation 4.7 generated clinically acceptable and deliverable CDR-VMAT plans for the Varian Clinac. VMAT plans were optimized including a model of the Exact couch with both rails in the out positions. CDR-VMAT plans generated with MCO in Raystation were dosimetrically comparable to Raystation MCO-generated IMRT plans. Patient-specific QA measurements with the ArcCHECK on the couch showed good agreement with the treatment planning system prediction. Patient-specific, structure-specific, multi-statistical parameter 3D QA measurements with gantry-mounted COMPASS also showed good agreement. Conclusion: Constant dose rate VMAT was successfully modeled in Raystation 4.7 for a Varian Clinac iX, and Raystation’s multicriteria optimization generated constant dose rate VMAT plans which were deliverable and dosimetrically comparable to IMRT plans.« less

Effect of positive pulse charge waveforms on cycle life of nickel-zinc cells

NASA Technical Reports Server (NTRS)

Smithrick, J. J.

1979-01-01

Five amp-hour nickel-zinc cells were life cycled to evaluate four different charge methods. Three of the four waveforms investigated were 120 Hz full wave rectified sinusoidal (FWRS), 120 Hz silicon controlled rectified (SCR), and 1 kHz square wave (SW). The fourth, a constant current method, was used as a baseline of comparison. Three sealed Ni-Zn cells connected in series were cycled. Each series string was charged at an average c/20 rate, and discharged at a c/2.5 rate to a 75% rated depth.

Estimation of dissolution rate from in vivo studies of synthetic vitreous fibers.

PubMed

Eastes, W; Potter, R M; Hadley, J G

2000-11-01

Although the dissolution rate of a fiber was originally defined by a measurement of dissolution in simulated lung fluid in vitro, it is feasible to determine it from animal studies as well. The dissolution rate constant for a fiber may be extracted from the decrease in long fiber diameter observed in certain intratracheal instillation experiments or from the observed long fiber retention in short-term biopersistence studies. These in vivo dissolution rates agree well with those measured in vitro for the same fibers. For those special types of fibers, the high-alumina rock wool fibers that could not be measured in vitro, the method provides a way of obtaining a chemical dissolution rate constant from an animal study. The inverse of the in vivo dissolution rate, the fiber dissolution time, correlates well with the weighted half life of long fibers in a biopersistence study, and the in vivo dissolution rate may be estimated accurately from this weighted half-life.

Diffusional falsification of kinetic constants on Lineweaver-Burk plots.

PubMed

Ghim, Y S; Chang, H N

1983-11-07

The effect of mass transfer resistances on the Lineweaver-Burk plots in immobilized enzyme systems has been investigated numerically and with analytical approximate solutions. While Hamilton, Gardner & Colton (1974) studied the effect of internal diffusion resistances in planar geometry, our study was extended to the combined effect of internal and external diffusion in cylindrical and spherical geometries as well. The variation of Lineweaver-Burk plots with respect to the geometries was minimized by modifying the Thiele modulus and the Biot number with the shape factor. Especially for a small Biot number all the three Lineweaver-Burk plots fell on a single line. As was discussed by Hamilton et al. (1974), the curvature of the line for large external diffusion resistances was small enough to be assumed linear, which was confirmed from the two approximate solutions for large and small substrate concentrations. Two methods for obtaining intrinsic kinetic constants were proposed: First, we obtained both maximum reaction rate and Michaelis constant by fitting experimental data to a straight line where external diffusion resistance was relatively large, and second, we obtained Michaelis constant from apparent Michaelis constant from the figure in case we knew maximum reaction rate a priori.

Incorporating the gas analyzer response time in gas exchange computations.

PubMed

Mitchell, R R

1979-11-01

A simple method for including the gas analyzer response time in the breath-by-breath computation of gas exchange rates is described. The method uses a difference equation form of a model for the gas analyzer in the computation of oxygen uptake and carbon dioxide production and avoids a numerical differentiation required to correct the gas fraction wave forms. The effect of not accounting for analyzer response time is shown to be a 20% underestimation in gas exchange rate. The present method accurately measures gas exchange rate, is relatively insensitive to measurement errors in the analyzer time constant, and does not significantly increase the computation time.

A simplified method for determining reactive rate parameters for reaction ignition and growth in explosives

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

Miller, P.J.

1996-07-01

A simplified method for determining the reactive rate parameters for the ignition and growth model is presented. This simplified ignition and growth (SIG) method consists of only two adjustable parameters, the ignition (I) and growth (G) rate constants. The parameters are determined by iterating these variables in DYNA2D hydrocode simulations of the failure diameter and the gap test sensitivity until the experimental values are reproduced. Examples of four widely different explosives were evaluated using the SIG model. The observed embedded gauge stress-time profiles for these explosives are compared to those calculated by the SIG equation and the results are described.

Numerical simulation of transport processes in injection mold-filling during production of a cylindrical object under isothermal and non-isothermal conditions

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

Kumar, A.; Ghoshdastidar, P.S.

1999-07-01

In this paper, numerical simulation of injection mold-filling during the production of a cylindrical object under isothermal and non-isothermal conditions is presented. The material of the object is low density polyethylene (LDPE) following power-law viscosity model for non-zero shear rate zone. However, where shear rate becomes zero, zero-shear viscosity value has been used. Three cases have been considered, namely (1) Isothermal filling at constant injection pressure, (2) Isothermal filling at constant flow rate, and (3) Non-isothermal filling at constant flow rate. For the case-(3), the viscosity of LDPE is also a function of temperature. The material of the mold ismore » steel. For the non-isothermal filling, the concept of melt-mold thermal contact resistance coefficient has been incorporated in the model. The length and diameter of the body in all three cases have been taken as 0.254 m and 0.00508 m respectively. The finite-difference method has been used to solve the governing differential equations for the processes. The results show excellent agreement with the corresponding equations for the processes. The results show excellent agreement with the corresponding analytical solutions for the first two cases showing the correctness of the numerical method. The simulation results for non-isothermal filling show physically realistic trends and lend insight into various important aspects of mold-filling including frozen skin layer.« less

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.

Oxygen transfer rate estimation in oxidation ditches from clean water measurements.

PubMed

Abusam, A; Keesman, K J; Meinema, K; Van Straten, G

2001-06-01

Standard methods for the determination of oxygen transfer rate are based on assumptions that are not valid for oxidation ditches. This paper presents a realistic and simple new method to be used in the estimation of oxygen transfer rate in oxidation ditches from clean water measurements. The new method uses a loop-of-CSTRs model, which can be easily incorporated within control algorithms, for modelling oxidation ditches. Further, this method assumes zero oxygen transfer rates (KLa) in the unaerated CSTRs. Application of a formal estimation procedure to real data revealed that the aeration constant (k = KLaVA, where VA is the volume of the aerated CSTR) can be determined significantly more accurately than KLa and VA. Therefore, the new method estimates k instead of KLa. From application to real data, this method proved to be more accurate than the commonly used Dutch standard method (STORA, 1980).

Investigation of Charge Transfer Kinetics at Carbon/Hydroquinone Interfaces for Redox-Active-Electrolyte Supercapacitors.

PubMed

Park, Jinwoo; Kumar, Vipin; Wang, Xu; Lee, Pooi See; Kim, Woong

2017-10-04

The redox-active electrolyte supercapacitor (RAES) is a relatively new type of energy storage device. Simple addition of selected redox species in the electrolyte can greatly enhance the energy density of supercapacitors relative to traditional electric double layer capacitors (EDLCs) owing to redox reactions. Studies on the kinetics at the interface of the electrode and redox mediator are important when developing RAESs. In this work, we employ highly accurate scanning electrochemical microscopy (SECM) to extract the kinetic constants at carbon/hydroquinone interfaces. The charge transfer rate constants are 1.2 × 10 -2 and 1.3 × 10 -2 cm s -1 for the carbon nanotube/hydroquinone and reduced graphene oxide/hydroquinone interfaces, respectively. These values are higher than those obtained by the conventional cyclic voltammetry method, approximately by an order of magnitude. The evaluation of heterogeneous rate constants with SECM would be the cornerstone for understanding and developing high performance RAESs.

Rate Constants and Activation Energies for Gas‐Phase Reactions of Three Cyclic Volatile Methyl Siloxanes with the Hydroxyl Radical

PubMed Central

Safron, Andreas; Strandell, Michael; Kierkegaard, Amelie

2015-01-01

ABSTRACT Reaction with hydroxyl radicals (OH) is the major pathway for removal of cyclic volatile methyl siloxanes (cVMS) from air. We present new measurements of second‐order rate constants for reactions of the cVMS octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6) with OH determined at temperatures between 313 and 353 K. Our measurements were made using the method of relative rates with cyclohexane as a reference substance and were conducted in a 140‐mL gas‐phase reaction chamber with online mass spectrometry analysis. When extrapolated to 298 K, our measured reaction rate constants of D4 and D5 with the OH radical are 1.9 × 10−12 (95% confidence interval (CI): (1.7–2.2) × 10−12) and 2.6 × 10−12 (CI: (2.3–2.9) × 10−12) cm3 molecule−1 s−1, respectively, which are 1.9× and 1.7× faster than previous measurements. Our measured rate constant for D6 is 2.8 × 10−12 (CI: (2.5–3.2) × 10−12) cm3 molecule−1 s−1 and to our knowledge there are no comparable laboratory measurements in the literature. Reaction rates for D5 were 33% higher than for D4 (CI: 30–37%), whereas the rates for D6 were only 8% higher than for D5 (CI: 5–10%). The activation energies of the reactions of D4, D5, and D6 with OH were not statistically different and had a value of 4300 ± 2800 J/mol. PMID:27708500

Rate Constants and Activation Energies for Gas-Phase Reactions of Three Cyclic Volatile Methyl Siloxanes with the Hydroxyl Radical.

PubMed

Safron, Andreas; Strandell, Michael; Kierkegaard, Amelie; Macleod, Matthew

2015-07-01

Reaction with hydroxyl radicals (OH) is the major pathway for removal of cyclic volatile methyl siloxanes (cVMS) from air. We present new measurements of second-order rate constants for reactions of the cVMS octamethylcyclotetrasiloxane (D 4 ), decamethylcyclopentasiloxane (D 5 ), and dodecamethylcyclohexasiloxane (D 6 ) with OH determined at temperatures between 313 and 353 K. Our measurements were made using the method of relative rates with cyclohexane as a reference substance and were conducted in a 140-mL gas-phase reaction chamber with online mass spectrometry analysis. When extrapolated to 298 K, our measured reaction rate constants of D 4 and D 5 with the OH radical are 1.9 × 10 -12 (95% confidence interval (CI): (1.7-2.2) × 10 -12 ) and 2.6 × 10 -12 (CI: (2.3-2.9) × 10 -12 ) cm 3 molecule -1 s -1 , respectively, which are 1.9× and 1.7× faster than previous measurements. Our measured rate constant for D 6 is 2.8 × 10 -12 (CI: (2.5-3.2) × 10 -12 ) cm 3 molecule -1 s -1 and to our knowledge there are no comparable laboratory measurements in the literature. Reaction rates for D 5 were 33% higher than for D 4 (CI: 30-37%), whereas the rates for D 6 were only 8% higher than for D 5 (CI: 5-10%). The activation energies of the reactions of D 4 , D 5 , and D 6 with OH were not statistically different and had a value of 4300 ± 2800 J/mol.

A method of monitoring contact (pointed) welding

NASA Astrophysics Data System (ADS)

Bessonov, V. B.; Staroverov, N. E.; Larionov, I. A.; Guk, K. K.; Obodovskiy, A. V.

2018-02-01

The technology of welding parts of different thicknesses from various materials is improved, which is why the range of applied types and methods of welding is constantly expanding. In this regard, the issue of monitoring welded joints is particularly acute. The goal was: to develop a method of non-destructive radiographic inspection of point welds with a high accuracy rating of its quality.

Investigating the Mechanism of Heteroaromatic Decarboxylation Using Solvent Kinetic Isotope Effects and Eyring Transition-State Theory

ERIC Educational Resources Information Center

Mundle, Scott O. C.; Opinska, Liliana Guevara; Kluger, Ronald; Dicks, Andrew P.

2011-01-01

An upper-level mechanistic organic experiment is outlined where undergraduates measure kinetic rate constants for decarboxylation of pyrrole-2-carboxylic acid by the initial-rates method. UV spectroscopy is used to monitor reactant disappearance in both hydrochloric acid and deuterium chloride at different temperatures. Individual data are pooled…

Determination of the reference air kerma rate for 192Ir brachytherapy sources and the related uncertainty.

PubMed

van Dijk, Eduard; Kolkman-Deurloo, Inger-Karine K; Damen, Patricia M G

2004-10-01

Different methods exist to determine the air kerma calibration factor of an ionization chamber for the spectrum of a 192Ir high-dose-rate (HDR) or pulsed-dose-rate (PDR) source. An analysis of two methods to obtain such a calibration factor was performed: (i) the method recommended by [Goetsch et al., Med. Phys. 18, 462-467 (1991)] and (ii) the method employed by the Dutch national standards institute NMi [Petersen et al., Report S-EI-94.01 (NMi, Delft, The Netherlands, 1994)]. This analysis showed a systematic difference on the order of 1% in the determination of the strength of 192Ir HDR and PDR sources depending on the method used for determining the air kerma calibration factor. The definitive significance of the difference between these methods can only be addressed after performing an accurate analysis of the associated uncertainties. For an NE 2561 (or equivalent) ionization chamber and an in-air jig, a typical uncertainty budget of 0.94% was found with the NMi method. The largest contribution in the type-B uncertainty is the uncertainty in the air kerma calibration factor for isotope i, N(i)k, as determined by the primary or secondary standards laboratories. This uncertainty is dominated by the uncertainties in the physical constants for the average mass-energy absorption coefficient ratio and the stopping power ratios. This means that it is not foreseeable that the standards laboratories can decrease the uncertainty in the air kerma calibration factors for ionization chambers in the short term. When the results of the determination of the 192Ir reference air kerma rates in, e.g., different institutes are compared, the uncertainties in the physical constants are the same. To compare the applied techniques, the ratio of the results can be judged by leaving out the uncertainties due to these physical constants. In that case an uncertainty budget of 0.40% (coverage factor=2) should be taken into account. Due to the differences in approach between the method used by NMi and the method recommended by Goetsch et al., an extra type-B uncertainty of 0.9% (k= 1) has to be taken into account when the method of Goetsch et al. is applied. Compared to the uncertainty of 1% (k= 2) found for the air calibration of 192Ir, the difference of 0.9% found is significant.

Measurement of Hubble constant: non-Gaussian errors in HST Key Project data

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

Singh, Meghendra; Gupta, Shashikant; Pandey, Ashwini

2016-08-01

Assuming the Central Limit Theorem, experimental uncertainties in any data set are expected to follow the Gaussian distribution with zero mean. We propose an elegant method based on Kolmogorov-Smirnov statistic to test the above; and apply it on the measurement of Hubble constant which determines the expansion rate of the Universe. The measurements were made using Hubble Space Telescope. Our analysis shows that the uncertainties in the above measurement are non-Gaussian.

Correcting reaction rates measured by saturation-transfer magnetic resonance spectroscopy

NASA Astrophysics Data System (ADS)

Gabr, Refaat E.; Weiss, Robert G.; Bottomley, Paul A.

2008-04-01

Off-resonance or spillover irradiation and incomplete saturation can introduce significant errors in the estimates of chemical rate constants measured by saturation-transfer magnetic resonance spectroscopy (MRS). Existing methods of correction are effective only over a limited parameter range. Here, a general approach of numerically solving the Bloch-McConnell equations to calculate exchange rates, relaxation times and concentrations for the saturation-transfer experiment is investigated, but found to require more measurements and higher signal-to-noise ratios than in vivo studies can practically afford. As an alternative, correction formulae for the reaction rate are provided which account for the expected parameter ranges and limited measurements available in vivo. The correction term is a quadratic function of experimental measurements. In computer simulations, the new formulae showed negligible bias and reduced the maximum error in the rate constants by about 3-fold compared to traditional formulae, and the error scatter by about 4-fold, over a wide range of parameters for conventional saturation transfer employing progressive saturation, and for the four-angle saturation-transfer method applied to the creatine kinase (CK) reaction in the human heart at 1.5 T. In normal in vivo spectra affected by spillover, the correction increases the mean calculated forward CK reaction rate by 6-16% over traditional and prior correction formulae.

40 CFR 63.365 - Test methods and procedures.

Code of Federal Regulations, 2012 CFR

2012-07-01

...)); the flowrate must be constant during time (t) t=time, min %EOV=volume fraction ethylene oxide SV... 40 Protection of Environment 10 2012-07-01 2012-07-01 false Test methods and procedures. 63.365... ethylene oxide charged, g (lb) Fv=volumetric flow rate, liters per minute (L/min) corrected to 20 °C and...

40 CFR 63.365 - Test methods and procedures.

Code of Federal Regulations, 2013 CFR

2013-07-01

...)); the flowrate must be constant during time (t) t=time, min %EOV=volume fraction ethylene oxide SV... 40 Protection of Environment 10 2013-07-01 2013-07-01 false Test methods and procedures. 63.365... ethylene oxide charged, g (lb) Fv=volumetric flow rate, liters per minute (L/min) corrected to 20 °C and...

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.

Direct measurements of rate coefficients for thermal decomposition of CF3I using shock—tube ARAS technique

NASA Astrophysics Data System (ADS)

Bystrov, N. S.; Emelianov, A. V.; Eremin, A. V.; Yatsenko, P. I.

2018-05-01

The kinetics of the dissociation of CF3I behind shock waves was experimentally investigated. The reaction CF3I  +  Ar  →  CF3  +  I  +  Ar was studied at temperatures between 900 and 1250 K and pressures of 2–3 bar. For this purpose, the time profiles of the concentration of atomic iodine were measured using a highly sensitive atomic resonance absorption spectroscopy method at a wavelength of 183.04 nm. From these data, the experimental value of the dissociation rate constant of CF3I was obtained: . We found that the investigated range of pressures and temperatures for the CF3I dissociation lies in the pressure transition region. Based on the Rice-Ramsperger–Kassel–Marcus theory, the threshold high and low-pressure rate constants ( and k 0) and falloff curves are calculated for the temperatures of 950–1200 K. As a result of this calculation, the threshold rate constants could be evaluated in the forms: and , and the center broadening factor, which takes into account the contribution of strong and weak collisions in the transition region, is .

Evaluation of selected strapdown inertial instruments and pulse torque loops, volume 1

NASA Technical Reports Server (NTRS)

Sinkiewicz, J. S.; Feldman, J.; Lory, C. B.

1974-01-01

Design, operational and performance variations between ternary, binary and forced-binary pulse torque loops are presented. A fill-in binary loop which combines the constant power advantage of binary with the low sampling error of ternary is also discussed. The effects of different output-axis supports on the performance of a single-degree-of-freedom, floated gyroscope under a strapdown environment are illustrated. Three types of output-axis supports are discussed: pivot-dithered jewel, ball bearing and electromagnetic. A test evaluation on a Kearfott 2544 single-degree-of-freedom, strapdown gyroscope operating with a pulse torque loop, under constant rates and angular oscillatory inputs is described and the results presented. Contributions of the gyroscope's torque generator and the torque-to-balance electronics on scale factor variation with rate are illustrated for a SDF 18 IRIG Mod-B strapdown gyroscope operating with various pulse rebalance loops. Also discussed are methods of reducing this scale factor variation with rate by adjusting the tuning network which shunts the torque coil. A simplified analysis illustrating the principles of operation of the Teledyne two-degree-of-freedom, elastically-supported, tuned gyroscope and the results of a static and constant rate test evaluation of that instrument are presented.

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.

Thermodynamic Modeling and Optimization of the Copper Flash Converting Process Using the Equilibrium Constant Method

NASA Astrophysics Data System (ADS)

Li, Ming-zhou; Zhou, Jie-min; Tong, Chang-ren; Zhang, Wen-hai; Chen, Zhuo; Wang, Jin-liang

2018-05-01

Based on the principle of multiphase equilibrium, a mathematical model of the copper flash converting process was established by the equilibrium constant method, and a computational system was developed with the use of MetCal software platform. The mathematical model was validated by comparing simulated outputs, industrial data, and published data. To obtain high-quality blister copper, a low copper content in slag, and increased impurity removal rate, the model was then applied to investigate the effects of the operational parameters [oxygen/feed ratio (R OF), flux rate (R F), and converting temperature (T)] on the product weights, compositions, and the distribution behaviors of impurity elements. The optimized results showed that R OF, R F, and T should be controlled at approximately 156 Nm3/t, within 3.0 pct, and at approximately 1523 K (1250 °C), respectively.

The effect of axial ligands on the quantum yield of singlet oxygen of new silicon phthalocyanine

NASA Astrophysics Data System (ADS)

Lv, Huafei; Zhang, Xuemei; Yu, Xinxin; Pan, Sujuan; Xie, Shusen; Yang, Hongqin; Peng, Yiru

2016-10-01

The singlet oxygen (1O2) production abilitity is an important factor to assess their potential as effective of photosensitizers. In this paper, the 1O2 production rate, production rate constant and quantum yield of silicon(IV) phthalocyanine axially bearing 1-3 generation dendritic substituents were evaluated by a high performance liquid chromatographic method. The results show that the 1O2 production rate and production rate constant of these compounds increase gradually with dendritic generations increase. And the 1O2 quantum yield of silicon(IV) phthalocyanine with first generation dendritic ligand was the highest. This may be due to the isolation effect of the dendritic ligands on the phthalocyanine core. The parameters of the observed 1O2 production properties will provide valuable data for these dendrimer phthalocyanines as promising photosensitizer in PDT application.

How Actuated Particles Effectively Capture Biomolecular Targets

PubMed Central

2017-01-01

Because of their high surface-to-volume ratio and adaptable surface functionalization, particles are widely used in bioanalytical methods to capture molecular targets. In this article, a comprehensive study is reported of the effectiveness of protein capture by actuated magnetic particles. Association rate constants are quantified in experiments as well as in Brownian dynamics simulations for different particle actuation configurations. The data reveal how the association rate depends on the particle velocity, particle density, and particle assembly characteristics. Interestingly, single particles appear to exhibit target depletion zones near their surface, caused by the high density of capture molecules. The depletion effects are even more limiting in cases with high particle densities. The depletion effects are overcome and protein capture rates are enhanced by applying dynamic particle actuation, resulting in an increase in the association rate constants by up to 2 orders of magnitude. PMID:28192952

Degradation of progestagens by oxidation with potassium permanganate in wastewater effluents.

PubMed

Fayad, Paul B; Zamyadi, Arash; Broseus, Romain; Prévost, Michèle; Sauvé, Sébastien

2013-01-01

This study investigated the oxidation of selected progestagenic steroid hormones by potassium permanganate at pH 6.0 and 8.0 in ultrapure water and wastewater effluents, using bench-scale assays. Second order rate constants for the reaction of potassium permanganate with progestagens (levonorgestrel, medroxyprogesterone, norethindrone and progesterone) was determined as a function of pH, presence of natural organic matter and temperature. This work also illustrates the advantages of using a novel analytical method, the laser diode thermal desorption (LDTD-APCI) interface coupled to tandem mass spectrometry apparatus, allowing for the quick determination of oxidation rate constants and increasing sample throughput. The second-order rate constants for progestagens with permanganate determined in bench-scale experiments ranged from 23 to 368 M(-1) sec(-1) in both wastewater and ultrapure waters with pH values of 6.0 and 8.0. Two pairs of progestagens exhibited similar reaction rate constants, i.e. progesterone and medroxyprogesterone (23 to 80 M(-1) sec(-1) in ultrapure water and 26 to 149 M(-1) sec(-1) in wastewaters, at pH 6.0 and 8.0) and levonorgestrel and norethindrone (179 to 224 M(-1) sec(-1) in ultrapure water and 180 to 368 M(-1) sec(-1) in wastewaters, at pH 6.0 and 8.0). The presence of dissolved natural organic matter and the pH conditions improved the oxidation rate constants for progestagens with potassium permanganate only at alkaline pH. Reaction rates measured in Milli-Q water could therefore be used to provide conservative estimates for the oxidation rates of the four selected progestagens in wastewaters when exposed to potassium permanganate. The progestagen removal efficiencies was lower for progesterone and medroxyprogesterone (48 to 87 %) than for levonorgestrel and norethindrone (78 to 97%) in Milli-Q and wastewaters at pH 6.0-8.2 using potassium permanganate dosages of 1 to 5 mg L(-1) after contact times of 10 to 60 min. This work presents the first results on the permanganate-promoted oxidation of progestagens, as a function of pH, temperature as well as NOM. Progestagen concentrations used to determine rate constants were analyzed using an ultrafast laser diode thermal desorption interface coupled to tandem mass spectrometry for the analysis of water sample for progestagens.

Imaging regional renal function parameters using radionuclide tracers

NASA Astrophysics Data System (ADS)

Qiao, Yi

A compartmental model is given for evaluating kidney function accurately and noninvasively. This model is cast into a parallel multi-compartment structure and each pixel region (picture element) of kidneys is considered as a single kidney compartment. The loss of radionuclide tracers from the blood to the kidney and from the kidney to the bladder are modelled in great detail. Both the uptake function and the excretion function of the kidneys can be evaluated pixel by pixel, and regional diagnostic information on renal function is obtained. Gamma Camera image data are required by this model and a screening test based renal function measurement is provided. The regional blood background is subtracted from the kidney region of interest (ROI) and the kidney regional rate constants are estimated analytically using the Kuhn-Pucker multiplier method in convex programming by considering the input/output behavior of the kidney compartments. The detailed physiological model of the peripheral compartments of the system, which is not available for most radionuclide tracers, is not required in the determination of the kidney regional rate constants and the regional blood background factors within the kidney ROI. Moreover, the statistical significance of measurements is considered to assure the improved statistical properties of the estimated kidney rate constants. The relations between various renal function parameters and the kidney rate constants are established. Multiple renal function measurements can be found from the renal compartmental model. The blood radioactivity curve and the regional (or total) radiorenogram determining the regional (or total) summed behavior of the kidneys are obtained analytically with the consideration of the statistical significance of measurements using convex programming methods for a single peripheral compartment system. In addition, a new technique for the determination of 'initial conditions' in both the blood compartment and the kidney compartment is presented. The blood curve and the radiorenogram are analyzed in great detail and a physiological analysis from the radiorenogram is given. Applications of Kuhn-Tucker multiplier methods are illustrated for the renal compartmental model in the field of nuclear medicine. Conventional kinetic data analysis methods, the maximum likehood method, and the weighted integration method are investigated and used for comparisons. Moreover, the effect of the blood background subtraction is shown by using the gamma camera images in man. Several functional images are calculated and the functional imaging technique is applied for evaluating renal function in man quantitatively and visually and compared with comments from a physician.

Computation of restoration of ligand response in the random kinetics of a prostate cancer cell signaling pathway.

PubMed

Dana, Saswati; Nakakuki, Takashi; Hatakeyama, Mariko; Kimura, Shuhei; Raha, Soumyendu

2011-01-01

Mutation and/or dysfunction of signaling proteins in the mitogen activated protein kinase (MAPK) signal transduction pathway are frequently observed in various kinds of human cancer. Consistent with this fact, in the present study, we experimentally observe that the epidermal growth factor (EGF) induced activation profile of MAP kinase signaling is not straightforward dose-dependent in the PC3 prostate cancer cells. To find out what parameters and reactions in the pathway are involved in this departure from the normal dose-dependency, a model-based pathway analysis is performed. The pathway is mathematically modeled with 28 rate equations yielding those many ordinary differential equations (ODE) with kinetic rate constants that have been reported to take random values in the existing literature. This has led to us treating the ODE model of the pathways kinetics as a random differential equations (RDE) system in which the parameters are random variables. We show that our RDE model captures the uncertainty in the kinetic rate constants as seen in the behavior of the experimental data and more importantly, upon simulation, exhibits the abnormal EGF dose-dependency of the activation profile of MAP kinase signaling in PC3 prostate cancer cells. The most likely set of values of the kinetic rate constants obtained from fitting the RDE model into the experimental data is then used in a direct transcription based dynamic optimization method for computing the changes needed in these kinetic rate constant values for the restoration of the normal EGF dose response. The last computation identifies the parameters, i.e., the kinetic rate constants in the RDE model, that are the most sensitive to the change in the EGF dose response behavior in the PC3 prostate cancer cells. The reactions in which these most sensitive parameters participate emerge as candidate drug targets on the signaling pathway. 2011 Elsevier Ireland Ltd. All rights reserved.

Single atom catalysts on amorphous supports: A quenched disorder perspective

NASA Astrophysics Data System (ADS)

Peters, Baron; Scott, Susannah L.

2015-03-01

Phenomenological models that invoke catalyst sites with different adsorption constants and rate constants are well-established, but computational and experimental methods are just beginning to provide atomically resolved details about amorphous surfaces and their active sites. This letter develops a statistical transformation from the quenched disorder distribution of site structures to the distribution of activation energies for sites on amorphous supports. We show that the overall kinetics are highly sensitive to the precise nature of the low energy tail in the activation energy distribution. Our analysis motivates further development of systematic methods to identify and understand the most reactive members of the active site distribution.

Effect of positive pulse charge waveforms on cycle life of nickel-zinc cells

NASA Technical Reports Server (NTRS)

Smithrick, J. J.

1980-01-01

Five amp-hour nickel-zinc cells were life cycled to evaluate four different charge methods. Three of the four waveforms investigated were 120 Hz full wave rectified sinusoidal (FWRS), 120 Hz silicon controlled rectified (SCR), and 1 kHz square wave (SW). The fourth, a constant current method, was used as a baseline of comparison. Three sealed Ni-Zn cells connected in series were cycled. Each series string was charged at an average c/20 rate, and discharged at a c/2.5 rate to a 75% rated depth. Results indicate that the relatively inexpensive 120 Hz FWRS charger appears feasible for charging 5 amp-hour nickel-zinc cells with no significant loss in average cycle life when compared to constant current charging. The 1-kHz SW charger could also be used with no significant loss in average cycle life, and suggests the possibility of utilizing the existing electric vehicle chopper controller circuitry for an on-board charger. There was an apparent difference using the 120 Hz SCR charger compared to the others, however, this difference could be due to an inadvertent severe overcharge, which occurred prior to cell failure. The remaining two positive pulse charging waveforms, FWRS and 1 kHz, did not improve the cycle life of 5 amp-hour nickel-zinc cells over that of constant current charging.

Approximate convective heating equations for hypersonic flows

NASA Technical Reports Server (NTRS)

Zoby, E. V.; Moss, J. N.; Sutton, K.

1979-01-01

Laminar and turbulent heating-rate equations appropriate for engineering predictions of the convective heating rates about blunt reentry spacecraft at hypersonic conditions are developed. The approximate methods are applicable to both nonreacting and reacting gas mixtures for either constant or variable-entropy edge conditions. A procedure which accounts for variable-entropy effects and is not based on mass balancing is presented. Results of the approximate heating methods are in good agreement with existing experimental results as well as boundary-layer and viscous-shock-layer solutions.

Calculated rate constants for the reaction ClO + O yields Cl + O2 between 220 and 1000 deg K. [molecular trajectories and stratospheric ozone

NASA Technical Reports Server (NTRS)

Jaffee, R. L.

1978-01-01

Classical trajectory calculations are presented for the reaction ClO + O yields Cl + O2, a reaction which is an important step in the chlorine-catalyzed destruction of ozone which is thought to occur in the 220 and 1000 K. The calculated rate constant is 4.36 x 10 to the minus 11th power exp (-191/T)cu cm molecule (-1)s(-1) and its value at 300 K is 2.3 plus or minus 10 to the 11th power cu cm molecule (-1)s(-1), about a factor of 2 lower than recent experimental data. The empirical potential energy surface used in the calculations was constructed to fit experimental data for ClO, O2 and ClOO molecules. Other important features of this potential surface, such as the barrier to reaction, were varied systematically and calculations were performed for a range of conditions to determine the best theoretical rate constants. Results demonstrate the utility of classical trajectory methods for determining activation energies and other kinetic data for important atmospheric reactions.

A Monte Carlo method for the simulation of coagulation and nucleation based on weighted particles and the concepts of stochastic resolution and merging

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

Kotalczyk, G., E-mail: Gregor.Kotalczyk@uni-due.de; Kruis, F.E.

Monte Carlo simulations based on weighted simulation particles can solve a variety of population balance problems and allow thus to formulate a solution-framework for many chemical engineering processes. This study presents a novel concept for the calculation of coagulation rates of weighted Monte Carlo particles by introducing a family of transformations to non-weighted Monte Carlo particles. The tuning of the accuracy (named ‘stochastic resolution’ in this paper) of those transformations allows the construction of a constant-number coagulation scheme. Furthermore, a parallel algorithm for the inclusion of newly formed Monte Carlo particles due to nucleation is presented in the scope ofmore » a constant-number scheme: the low-weight merging. This technique is found to create significantly less statistical simulation noise than the conventional technique (named ‘random removal’ in this paper). Both concepts are combined into a single GPU-based simulation method which is validated by comparison with the discrete-sectional simulation technique. Two test models describing a constant-rate nucleation coupled to a simultaneous coagulation in 1) the free-molecular regime or 2) the continuum regime are simulated for this purpose.« less

Anharmonic Effect in CH3CH2C(=O)OCH2CH3 Decomposition

NASA Astrophysics Data System (ADS)

Ding, Yang; Song, Liguo; Yao, Li; Xia, Wenwen

2017-12-01

In this paper, using the B3LYP functional and CCSD(T) method with 6-311++G** basis set, the harmonic and anharmonic rate constants in the unimolecular dissociation of ethyl propanoate have been calculated using Rice-Ramsperger-Kassel-Marcus theory. The anharmonic rate constants of the title reaction have also been examined, the comparison shows that, the anharmonic effect especially in the case of high total energies and temperature for channels 3 to 6 is significant, so that the anharmonic effect cannot be neglected for unimolecular dissociation reaction of CH3CH2C(=O)OCH2CH3 both in microcanonical and canonical systems.

Virtual Instrument for Determining Rate Constant of Second-Order Reaction by pX Based on LabVIEW 8.0

PubMed Central

Meng, Hu; Li, Jiang-Yuan; Tang, Yong-Huai

2009-01-01

The virtual instrument system based on LabVIEW 8.0 for ion analyzer which can measure and analyze ion concentrations in solution is developed and comprises homemade conditioning circuit, data acquiring board, and computer. It can calibrate slope, temperature, and positioning automatically. When applied to determine the reaction rate constant by pX, it achieved live acquiring, real-time displaying, automatical processing of testing data, generating the report of results; and other functions. This method simplifies the experimental operation greatly, avoids complicated procedures of manual processing data and personal error, and improves veracity and repeatability of the experiment results. PMID:19730752

Automated real time constant-specificity surveillance for disease outbreaks.

PubMed

Wieland, Shannon C; Brownstein, John S; Berger, Bonnie; Mandl, Kenneth D

2007-06-13

For real time surveillance, detection of abnormal disease patterns is based on a difference between patterns observed, and those predicted by models of historical data. The usefulness of outbreak detection strategies depends on their specificity; the false alarm rate affects the interpretation of alarms. We evaluate the specificity of five traditional models: autoregressive, Serfling, trimmed seasonal, wavelet-based, and generalized linear. We apply each to 12 years of emergency department visits for respiratory infection syndromes at a pediatric hospital, finding that the specificity of the five models was almost always a non-constant function of the day of the week, month, and year of the study (p < 0.05). We develop an outbreak detection method, called the expectation-variance model, based on generalized additive modeling to achieve a constant specificity by accounting for not only the expected number of visits, but also the variance of the number of visits. The expectation-variance model achieves constant specificity on all three time scales, as well as earlier detection and improved sensitivity compared to traditional methods in most circumstances. Modeling the variance of visit patterns enables real-time detection with known, constant specificity at all times. With constant specificity, public health practitioners can better interpret the alarms and better evaluate the cost-effectiveness of surveillance systems.

Molecular dynamics simulations of thermally activated edge dislocation unpinning from voids in α -Fe

NASA Astrophysics Data System (ADS)

Byggmästar, J.; Granberg, F.; Nordlund, K.

2017-10-01

In this study, thermal unpinning of edge dislocations from voids in α -Fe is investigated by means of molecular dynamics simulations. The activation energy as a function of shear stress and temperature is systematically determined. Simulations with a constant applied stress are compared with dynamic simulations with a constant strain rate. We found that a constant applied stress results in a temperature-dependent activation energy. The temperature dependence is attributed to the elastic softening of iron. If the stress is normalized with the softening of the specific shear modulus, the activation energy is shown to be temperature-independent. From the dynamic simulations, the activation energy as a function of critical shear stress was determined using previously developed methods. The results from the dynamic simulations are in good agreement with the constant stress simulations, after the normalization. This indicates that the computationally more efficient dynamic method can be used to obtain the activation energy as a function of stress and temperature. The obtained relation between stress, temperature, and activation energy can be used to introduce a stochastic unpinning event in larger-scale simulation methods, such as discrete dislocation dynamics.

Flow and volume dependence of rat airway resistance during constant flow inflation and deflation.

PubMed

Rubini, Alessandro; Carniel, Emanuele Luigi; Parmagnani, Andrea; Natali, Arturo Nicola

2011-12-01

The aim of this study was to measure the flow and volume dependence of both the ohmic and the viscoelastic pressure dissipations of the normal rat respiratory system separately during inflation and deflation. The study was conducted in the Respiratory Physiology Laboratory in our institution. Measurements were obtained for Seven albino Wistar rats of both sexes by using the flow interruption method during constant flow inflations and deflations. Measurements included anesthesia induction, tracheostomy and positioning of a tracheal cannula, positive pressure ventilation, constant flow respiratory system inflations and deflations at two different volumes and flows. The ohmic resistance exhibited volume and flow dependence, decreasing with lung volume and increasing with flow rate, during both inflation and deflation. The stress relaxation-related viscoelastic resistance also exhibited volume and flow dependence. It decreased with the flow rate at a constant lung volume during both inflation and deflation, but exhibited a different behavior with the lung volume at a constant flow rate (i.e., increased during inflations and decreased during deflations). Thus, stress relaxation in the rat lungs exhibited a hysteretic behavior. The observed flow and volume dependence of respiratory system resistance may be predicted by an equation derived from a model of the respiratory system that consists of two distinct compartments. The equation agrees well with the experimental data and indicates that the loading time is the critical parameter on which stress relaxation depends, during both lung inflation and deflation.

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.

Estimation of uptake rate constants for PCB congeners accumulated by semipermeable membrane devices and brown treat (Salmo trutta)

USGS Publications Warehouse

Meadows, J.C.; Echols, K.R.; Huckins, J.N.; Borsuk, F.A.; Carline, R.F.; Tillitt, D.E.

1998-01-01

The triolein-filled semipermeable membrane device (SPMD) is a simple and effective method of assessing the presence of waterborne hydrophobic chemicals. Uptake rate constants for individual chemicals are needed to accurately relate the amounts of chemicals accumulated by the SPMD to dissolved water concentrations. Brown trout and SPMDs were exposed to PCB- contaminated groundwater in a spring for 28 days to calculate and compare uptake rates of specific PCB congeners by the two matrixes. Total PCB congener concentrations in water samples from the spring were assessed and corrected for estimated total organic carbon (TOC) sorption to estimate total dissolved concentrations. Whole and dissolved concentrations averaged 4.9 and 3.7 ??g/L, respectively, during the exposure. Total concentrations of PCBs in fish rose from 0.06 to 118.3 ??g/g during the 28-day exposure, while concentrations in the SPMD rose from 0.03 to 203.4 ??g/ g. Uptake rate constants (k1) estimated for SPMDs and brown trout were very similar, with k1 values for SPMDs ranging from one to two times those of the fish. The pattern of congener uptake by the fish and SPMDs was also similar. The rates of uptake generally increased or decreased with increasing K(ow), depending on the assumption of presence or absence of TOC.The triolein-filled semipermeable membrane device (SPMD) is a simple and effective method of assessing the presence of waterborne hydrophobic chemicals. Uptake rate constants for individual chemicals are needed to accurately relate the amounts of chemicals accumulated by the SPMB to dissolved water concentrations. Brown trout and SPMDs were exposed to PCB-contaminated groundwater in a spring for 28 days to calculate and compare uptake rates of specific PCB congeners by the two matrixes. Total PCB congener concentrations in water samples from the spring were assessed and corrected for estimated total organic carbon (TOC) sorption to estimate total dissolved concentrations. Whole and dissolved concentrations averaged 4.9 and 3.7 ??g/L, respectively, during the exposure. Total concentrations of PCBs in fish rose from 0.06 to 118.3 ??g/g during the 28-day exposure, while concentrations in the SPMD rose from 0.03 to 203.4 ??g/g. Uptake rate constants (k1) estimated for SPMDs and brown trout were very similar, with k1 values for SPMDs ranging from one to two times those of the fish. The pattern of congener uptake by the fish and SPMBs was also similar. The rates of uptake generally increased or decreased with increasing KOW, depending on the assumption of presence or absence of TOC.

ESTER HYDROLYSIS RATE CONSTANT PREDICTION FROM INFRARED INTERFEROGRAMS

EPA Science Inventory

A method for predicting reactivity parameters of organic chemicals from spectroscopic data is being developed to assist in assessing the environmental fate of pollutants. he prototype system, which employs multiple linear regression analysis using selected points from the Fourier...

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.

Dissolution of quartz in aqueous basic solution, 106-236 C - Surface kinetics of 'perfect' crystallographic faces

NASA Technical Reports Server (NTRS)

Gratz, Andrew J.; Bird, Peter; Quiro, Glenn B.

1990-01-01

A highly accurate method, called the negative crystal method, for determining the rate of dissolution on specific crystallographic faces of crystals was developed, in which the dissolution rates of nominally perfect crystal faces are obtained by measuring the size of individual negative crystals during a sequence of dissolution steps. The method was applied to determine the apparent activation energy and rate constants for the dissolution of quartz in 0.01 M KOH solutions at temperatures from 106 to 236 C. Also investigated were the effects of hydroxyl activity and ionic strength. The apparent activation energies for the dissolution of the prism and of the rhomb were determined.

40 CFR 1065.650 - Emission calculations.

Code of Federal Regulations, 2010 CFR

2010-07-01

... from a changing flow rate or a constant flow rate (including discrete-mode steady-state testing), as...·hr e NOx = 64.975/25.783 e NOx = 2.520 g/(kW·hr) (2) For discrete-mode steady-state testing, you may... method not be used if there are any work flow paths described in § 1065.210 that cross the system...

Theoretical Kinetics Analysis for Ḣ Atom Addition to 1,3-Butadiene and Related Reactions on the Ċ4H7 Potential Energy Surface.

PubMed

Li, Yang; Klippenstein, Stephen J; Zhou, Chong-Wen; Curran, Henry J

2017-10-12

The oxidation chemistry of the simplest conjugated hydrocarbon, 1,3-butadiene, can provide a first step in understanding the role of polyunsaturated hydrocarbons in combustion and, in particular, an understanding of their contribution toward soot formation. On the basis of our previous work on propene and the butene isomers (1-, 2-, and isobutene), it was found that the reaction kinetics of Ḣ-atom addition to the C═C double bond plays a significant role in fuel consumption kinetics and influences the predictions of high-temperature ignition delay times, product species concentrations, and flame speed measurements. In this study, the rate constants and thermodynamic properties for Ḣ-atom addition to 1,3-butadiene and related reactions on the Ċ 4 H 7 potential energy surface have been calculated using two different series of quantum chemical methods and two different kinetic codes. Excellent agreement is obtained between the two different kinetics codes. The calculated results including zero-point energies, single-point energies, rate constants, barrier heights, and thermochemistry are systematically compared among the two quantum chemical methods. 1-Methylallyl (Ċ 4 H 7 1-3) and 3-buten-1-yl (Ċ 4 H 7 1-4) radicals and C 2 H 4 + Ċ 2 H 3 are found to be the most important channels and reactivity-promoting products, respectively. We calculated that terminal addition is dominant (>80%) compared to internal Ḣ-atom addition at all temperatures in the range 298-2000 K. However, this dominance decreases with increasing temperature. The calculated rate constants for the bimolecular reaction C 4 H 6 + Ḣ → products and C 2 H 4 + Ċ 2 H 3 → products are in excellent agreement with both experimental and theoretical results from the literature. For selected C 4 species, the calculated thermochemical values are also in good agreement with literature data. In addition, the rate constants for H atom abstraction by Ḣ atoms have also been calculated, and it is found that abstraction from the central carbon atoms is the dominant channel (>70%) at temperatures in the range of 298-2000 K. Finally, by incorporating our calculated rate constants for both Ḣ atom addition and abstraction into our recently developed 1,3-butadiene model, we show that laminar flame speed predictions are significantly improved, emphasizing the value of this study.

Estimating site occupancy rates for aquatic plants using spatial sub-sampling designs when detection probabilities are less than one

USGS Publications Warehouse

Nielson, Ryan M.; Gray, Brian R.; McDonald, Lyman L.; Heglund, Patricia J.

2011-01-01

Estimation of site occupancy rates when detection probabilities are <1 is well established in wildlife science. Data from multiple visits to a sample of sites are used to estimate detection probabilities and the proportion of sites occupied by focal species. In this article we describe how site occupancy methods can be applied to estimate occupancy rates of plants and other sessile organisms. We illustrate this approach and the pitfalls of ignoring incomplete detection using spatial data for 2 aquatic vascular plants collected under the Upper Mississippi River's Long Term Resource Monitoring Program (LTRMP). Site occupancy models considered include: a naïve model that ignores incomplete detection, a simple site occupancy model assuming a constant occupancy rate and a constant probability of detection across sites, several models that allow site occupancy rates and probabilities of detection to vary with habitat characteristics, and mixture models that allow for unexplained variation in detection probabilities. We used information theoretic methods to rank competing models and bootstrapping to evaluate the goodness-of-fit of the final models. Results of our analysis confirm that ignoring incomplete detection can result in biased estimates of occupancy rates. Estimates of site occupancy rates for 2 aquatic plant species were 19–36% higher compared to naive estimates that ignored probabilities of detection <1. Simulations indicate that final models have little bias when 50 or more sites are sampled, and little gains in precision could be expected for sample sizes >300. We recommend applying site occupancy methods for monitoring presence of aquatic species.

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.

A tale of two cores: Evaluation of 210Pb dating methods of salt marsh sediments for two cores collected 30 years apart

NASA Astrophysics Data System (ADS)

Fuller, C.; Drexler, J. Z.

2016-12-01

210Pb dating of wetland sediments is commonly used to constrain recent C accumulation rates and contaminant input histories. However, uncertainties in 210Pb-derived rates and validation of accumulation and accretion rates using an independent tracer are often not reported. We describe here 210Pb and 137Cs profiles in two cores from a salt marsh in south San Francisco Bay, California, collected in 1981 and 2011 within 5 m of each other, to compare and evaluate 210Pb dating methods. In the 1981 core, unsupported 210Pb (210PbXS) was detected to 12 cm and yielded mass accumulation rates (MAR) of 0.043 and 0.036 g/cm2/y using the Constant Flux-Constant Sedimentation method (CF:CS) and Constant Rate of Supply (CRS) methods, respectively. Accretion rates (S) of 0.17 (CF:CS) and 0.12 cm/y (CRS) were calculated from these MARs. The distinct 137Cs peak at 4-6 cm in the 1981 core is in good agreement with the210Pb-based 1963 depth (3.4 and 4 cm, CF:CS and CRS, respectively). 210PbXS was detectable to 18 cm in the 2011 core, and yielded a CF:CS MAR (0.077 g/cm2/y; S = 0.35 cm/y) that is about two times greater than the mass-weighted average CRS MAR (0.044 g/cm2/y; S = 0.16 cm/y). Broad subsurface maxima in 137Cs and 239Pu were observed between 16 and 24 cm in the 2011 core, which are 5 to 11 cm deeper than the 1963 depth calculated by the 2011 and 1981 210Pb-derived MARs. The apparent migration and broadening of bomb-fallout radionuclide peaks over 30 years negates their use in validating 210Pb dating. Because of low 210PbXS activities in both cores, the base of the 210PbXS profile and integrated activity used in CRS are underestimated, resulting in the lower CRS MARs that decrease with increasing depth. The range of MARs determined for two cores within 5 m but separated by 30 years will be used as an example to evaluate the uncertainties that need to be reported with C accumulation rates and contaminant histories derived from 210Pb dating of sediment archives.

[Does intraoperative nerve monitoring reduce the rate of recurrent nerve palsies during thyroid surgery?].

PubMed

Timmermann, W; Dralle, H; Hamelmann, W; Thomusch, O; Sekulla, C; Meyer, Th; Timm, S; Thiede, A

2002-05-01

Two different aspects of the influence of neuromonitoring on the possible reduction of post-operative recurrent laryngeal nerve palsies require critical examination: the nerve identification and the monitoring of it's functions. Due to the additional information from the EMG signals, neuromonitoring is the best method for identifying the nerves as compared to visual identification alone. There are still no randomized studies available that compare the visual and electrophysiological recurrent laryngeal nerve detection in thyroid operations with respect to the postoperative nerve palsies. Nevertheless, comparisons with historical collectives show that a constant low nerve-palsy-rate was achieved with electrophysiological detection in comparison to visual detection. The rate of nerve identification is normally very high and amounts to 99 % in our own patients. The data obtained during the "Quality assurance of benign and malignant Goiter" study show that in hemithyreoidectomy and subtotal resection, lower nerve-palsy-rates are achieved with neuromonitoring as compared to solely visual detection. Following subtotal resection, this discrepancy becomes even statistically significant. While monitoring the nerve functions with the presently used neuromonitoring technique, it is possible to observe the EMG-signal remaining constant or decreasing in volume. Assuming that a constant neuromonitoring signal represents a normal vocal cord, our evaluation shows that there is a small percentage of false negative and positive results. Looking at the permanent recurrent nerve palsy rates, this method has a specificity of 98 %, a sensitivity of 100 %, a positive prognostic value of 10 %, and a negative prognostic value of 100 %. Although an altered neuromonitoring signal can be taken as a clear indication of eventual nerve damage, an absolutely reliable statement about the postoperative vocal cord function is presently not possible with intraoperative neuromonitoring.

Simultaneous measurement of glucose blood–brain transport constants and metabolic rate in rat brain using in-vivo 1H MRS

PubMed Central

Du, Fei; Zhang, Yi; Zhu, Xiao-Hong; Chen, Wei

2012-01-01

Cerebral glucose consumption and glucose transport across the blood–brain barrier are crucial to brain function since glucose is the major energy fuel for supporting intense electrophysiological activity associated with neuronal firing and signaling. Therefore, the development of noninvasive methods to measure the cerebral metabolic rate of glucose (CMRglc) and glucose transport constants (KT: half-saturation constant; Tmax: maximum transport rate) are of importance for understanding glucose transport mechanism and neuroenergetics under various physiological and pathological conditions. In this study, a novel approach able to simultaneously measure CMRglc, KT, and Tmax via monitoring the dynamic glucose concentration changes in the brain tissue using in-vivo 1H magnetic resonance spectroscopy (MRS) and in plasma after a brief glucose infusion was proposed and tested using an animal model. The values of CMRglc, Tmax, and KT were determined to be 0.44±0.17 μmol/g per minute, 1.35±0.47 μmol/g per minute, and 13.4±6.8 mmol/L in the rat brain anesthetized with 2% isoflurane. The Monte-Carlo simulations suggest that the measurements of CMRglc and Tmax are more reliable than that of KT. The overall results indicate that the new approach is robust and reliable for in-vivo measurements of both brain glucose metabolic rate and transport constants, and has potential for human application. PMID:22714049

Simultaneous measurement of glucose blood-brain transport constants and metabolic rate in rat brain using in-vivo 1H MRS.

PubMed

Du, Fei; Zhang, Yi; Zhu, Xiao-Hong; Chen, Wei

2012-09-01

Cerebral glucose consumption and glucose transport across the blood-brain barrier are crucial to brain function since glucose is the major energy fuel for supporting intense electrophysiological activity associated with neuronal firing and signaling. Therefore, the development of noninvasive methods to measure the cerebral metabolic rate of glucose (CMR(glc)) and glucose transport constants (K(T): half-saturation constant; T(max): maximum transport rate) are of importance for understanding glucose transport mechanism and neuroenergetics under various physiological and pathological conditions. In this study, a novel approach able to simultaneously measure CMR(glc), K(T), and T(max) via monitoring the dynamic glucose concentration changes in the brain tissue using in-vivo (1)H magnetic resonance spectroscopy (MRS) and in plasma after a brief glucose infusion was proposed and tested using an animal model. The values of CMR(glc), T(max), and K(T) were determined to be 0.44 ± 0.17 μmol/g per minute, 1.35 ± 0.47 μmol/g per minute, and 13.4 ± 6.8 mmol/L in the rat brain anesthetized with 2% isoflurane. The Monte-Carlo simulations suggest that the measurements of CMR(glc) and T(max) are more reliable than that of K(T). The overall results indicate that the new approach is robust and reliable for in-vivo measurements of both brain glucose metabolic rate and transport constants, and has potential for human application.

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…

Optimization of magnetization transfer measurements: statistical analysis by stochastic simulation. Application to creatine kinase kinetics.

PubMed

Rydzy, M; Deslauriers, R; Smith, I C; Saunders, J K

1990-08-01

A systematic study was performed to optimize the accuracy of kinetic parameters derived from magnetization transfer measurements. Three techniques were investigated: time-dependent saturation transfer (TDST), saturation recovery (SRS), and inversion recovery (IRS). In the last two methods, one of the resonances undergoing exchange is saturated throughout the experiment. The three techniques were compared with respect to the accuracy of the kinetic parameters derived from experiments performed in a given, fixed, amount of time. Stochastic simulation of magnetization transfer experiments was performed to optimize experimental design. General formulas for the relative accuracies of the unidirectional rate constant (k) were derived for each of the three experimental methods. It was calculated that for k values between 0.1 and 1.0 s-1, T1 values between 1 and 10 s, and relaxation delays appropriate for the creatine kinase reaction, the SRS method yields more accurate values of k than does the IRS method. The TDST method is more accurate than the SRS method for reactions where T1 is long and k is large, within the range of k and T1 values examined. Experimental verification of the method was carried out on a solution in which the forward (PCr----ATP) rate constant (kf) of the creatine kinase reaction was measured.

Impact of actuarial assumptions on pension costs: A simulation analysis

NASA Astrophysics Data System (ADS)

Yusof, Shaira; Ibrahim, Rose Irnawaty

2013-04-01

This study investigates the sensitivity of pension costs to changes in the underlying assumptions of a hypothetical pension plan in order to gain a perspective on the relative importance of the various actuarial assumptions via a simulation analysis. Simulation analyses are used to examine the impact of actuarial assumptions on pension costs. There are two actuarial assumptions will be considered in this study which are mortality rates and interest rates. To calculate pension costs, Accrued Benefit Cost Method, constant amount (CA) modification, constant percentage of salary (CS) modification are used in the study. The mortality assumptions and the implied mortality experience of the plan can potentially have a significant impact on pension costs. While for interest rate assumptions, it is inversely related to the pension costs. Results of the study have important implications for analyst of pension costs.

Validated HPLC method for determination of sennosides A and B in senna tablets.

PubMed

Sun, Shao Wen; Su, Hsiu Ting

2002-07-31

This study developed an efficient and reliable ion-pair liquid chromatographic method for quantitation of sennosides A and B in commercial senna tablets. Separation was conducted on a Hypersil C 18 column (250 x 4.6 mm, 5 microm) at a temperature of 40 degrees C, using a mixture of 0.1 M acetate buffer (pH 6.0) and acetonitrile (70:30, v/v) containing 5 mM tetrahexylammonium bromide as mobile phase. Sennosides A and B were completely separated from other constituents within 14 min. The developed method was validated. Both run-to-run repeatability (n=10) and day-to-day reproducibility (n=3) of peak area were below 0.4% RSD. Linearity of peak area was tested in the range 30-70 microg/ml (r>0.9997). Accuracy was assessed with recovery and the recoveries for sennosides A and B were 101.73+/-1.30% and 101.81+/-2.18% (n=3 x 6), respectively. Robustness of the analytical method was tested using a three-leveled Plackett-Burman design in which 11 factors were assessed with 23 experiments. Eight factors (column, concentration of ion pair reagent, % of organic modifier (acetonitrile), buffer pH, column temperature, flow rate, time constant and detection wavelength) were investigated in a specified range above and below the nominal method conditions. It was found that: (1) column and % acetonitrile affected significantly resolution and retention time, (2) column, % acetonitrile, column temperature, flow rate and time constant affected significantly the plate number of sennoside A, and (3) column and time constant affected significantly the tailing factor.

Acceleration and sensitivity analysis of lattice kinetic Monte Carlo simulations using parallel processing and rate constant rescaling

NASA Astrophysics Data System (ADS)

Núñez, M.; Robie, T.; Vlachos, D. G.

2017-10-01

Kinetic Monte Carlo (KMC) simulation provides insights into catalytic reactions unobtainable with either experiments or mean-field microkinetic models. Sensitivity analysis of KMC models assesses the robustness of the predictions to parametric perturbations and identifies rate determining steps in a chemical reaction network. Stiffness in the chemical reaction network, a ubiquitous feature, demands lengthy run times for KMC models and renders efficient sensitivity analysis based on the likelihood ratio method unusable. We address the challenge of efficiently conducting KMC simulations and performing accurate sensitivity analysis in systems with unknown time scales by employing two acceleration techniques: rate constant rescaling and parallel processing. We develop statistical criteria that ensure sufficient sampling of non-equilibrium steady state conditions. Our approach provides the twofold benefit of accelerating the simulation itself and enabling likelihood ratio sensitivity analysis, which provides further speedup relative to finite difference sensitivity analysis. As a result, the likelihood ratio method can be applied to real chemistry. We apply our methodology to the water-gas shift reaction on Pt(111).

Comparison of nitric oxide-induced oxidation of recombinant oxyhemoglobin subunits using a competition experiment.

PubMed

Lin, Yen-Lin; Huang, Kuang-Tse

2009-08-01

A low reaction rate with nitric oxide (NO) is one of the important characteristics of hemoglobin (Hb)-based oxygen carriers. The reaction rate between oxyHb and NO is usually measured by stopped-flow spectrophotometry. However, the reported rates vary due to the difficulty of accurately determining the NO concentration and the limit of the instrument dead time. To circumvent these problems, we developed an experiment using oxymyoglobin (oxyMb) to compete with oxyHb for NO that is released from an NO donor. Determination of the rate constants in the competition experiment no longer depends on accurate measurement of time or NO concentration, since this approach instead measures the ratio of rate constants for the reaction of oxyHb and oxyMb with NO. For recombinant mutant Hb alpha(L29F)beta the rates for alpha(L29F) and beta are approximately 15- and 1.6-fold smaller than for wild-type Hb. In conclusion, the competition experiment provides an alternative method for determination of relative reaction rates of recombinant Hb subunits with NO.

Creatine kinase rate constant in the human heart measured with 3D-localization at 7 tesla.

PubMed

Clarke, William T; Robson, Matthew D; Neubauer, Stefan; Rodgers, Christopher T

2017-07-01

We present a new Bloch-Siegert four Angle Saturation Transfer (BOAST) method for measuring the creatine kinase (CK) first-order effective rate constant k f in human myocardium at 7 tesla (T). BOAST combines a variant of the four-angle saturation transfer (FAST) method using amplitude-modulated radiofrequency pulses, phosphorus Bloch-Siegert B1+-mapping to determine the per-voxel flip angles, and nonlinear fitting to Bloch simulations for postprocessing. Optimal flip angles and repetition time parameters were determined from Monte Carlo simulations. BOAST was validated in the calf muscle of two volunteers at 3T and 7T. The myocardial CK forward rate constant was then measured in 10 volunteers at 7T in 82 min (after 1 H localization). BOAST kfCK values were 0.281 ± 0.002 s -1 in the calf and 0.35 ± 0.05 s -1 in myocardium. These are consistent with literature values from lower fields. Using a literature values for adenosine triphosphate concentration, we computed CK flux values of 4.55 ± 1.52 mmol kg -1 s -1 . The sensitive volume for BOAST depends on the B 1 inhomogeneity of the transmit coil. BOAST enables measurement of the CK rate constant in the human heart at 7T, with spatial localization in three dimensions to 5.6 mL voxels, using a 10-cm loop coil. Magn Reson Med 78:20-32, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine.

A theoretical study of the H-abstraction reactions from HOI by moist air radiolytic products (H, OH, and O (3P)) and iodine atoms (2P(3/2)).

PubMed

Hammaecher, Catherine; Canneaux, Sébastien; Louis, Florent; Cantrel, Laurent

2011-06-23

The rate constants of the reactions of HOI molecules with H, OH, O ((3)P), and I ((2)P(3/2)) atoms have been estimated over the temperature range 300-2500 K using four different levels of theory. Geometry optimizations and vibrational frequency calculations are performed using MP2 methods combined with two basis sets (cc-pVTZ and 6-311G(d,p)). Single-point energy calculations are performed with the highly correlated ab initio coupled cluster method in the space of single, double, and triple (pertubatively) electron excitations CCSD(T) using the cc-pVTZ, cc-pVQZ, 6-311+G(3df,2p), and 6-311++G(3df,3pd) basis sets. Reaction enthalpies at 0 K were calculated at the CCSD(T)/cc-pVnZ//MP2/cc-pVTZ (n = T and Q), CCSD(T)/6-311+G(3df,2p)//MP2/6-311G(d,p), and CCSD(T)/6-311++G(3df,3pd)//MP2/6-311G(d,p) levels of theory and compared to the experimental values taken from the literature. Canonical transition-state theory with an Eckart tunneling correction is used to predict the rate constants as a function of temperature. The computational procedure has been used to predict rate constants for H-abstraction elementary reactions because there are actually no literature data to which the calculated rate constants can be directly compared. The final objective is to implement kinetics of gaseous reactions in the ASTEC (accident source term evaluation code) program to improve speciation of fission products, which can be transported along the reactor coolant system (RCS) of a pressurized water reactor (PWR) in the case of a severe accident.

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.

Validating Whole-Airway CFD Predictions of DPI Aerosol Deposition at Multiple Flow Rates

PubMed Central

Tian, Geng; Khajeh-Hosseini-Dalasm, Navvab; Hindle, Michael

2016-01-01

Abstract Background: The objective of this study was to compare aerosol deposition predictions of a new whole-airway CFD model with available in vivo data for a dry powder inhaler (DPI) considered across multiple inhalation waveforms, which affect both the particle size distribution (PSD) and particle deposition. Methods: The Novolizer DPI with a budesonide formulation was selected based on the availability of 2D gamma scintigraphy data in humans for three different well-defined inhalation waveforms. Initial in vitro cascade impaction experiments were conducted at multiple constant (square-wave) particle sizing flow rates to characterize PSDs. The whole-airway CFD modeling approach implemented the experimentally determined PSDs at the point of aerosol formation in the inhaler. Complete characteristic airway geometries for an adult were evaluated through the lobar bronchi, followed by stochastic individual pathway (SIP) approximations through the tracheobronchial region and new acinar moving wall models of the alveolar region. Results: It was determined that the PSD used for each inhalation waveform should be based on a constant particle sizing flow rate equal to the average of the inhalation waveform's peak inspiratory flow rate (PIFR) and mean flow rate [i.e., AVG(PIFR, Mean)]. Using this technique, agreement with the in vivo data was acceptable with <15% relative differences averaged across the three regions considered for all inhalation waveforms. Defining a peripheral to central deposition ratio (P/C) based on alveolar and tracheobronchial compartments, respectively, large flow-rate-dependent differences were observed, which were not evident in the original 2D in vivo data. Conclusions: The agreement between the CFD predictions and in vivo data was dependent on accurate initial estimates of the PSD, emphasizing the need for a combination in vitro–in silico approach. Furthermore, use of the AVG(PIFR, Mean) value was identified as a potentially useful method for characterizing a DPI aerosol at a constant flow rate. PMID:27082824

Some theoretical considerations of longitudinal stability in power-on flight with special reference to wind-tunnel testing, November 1942

NASA Technical Reports Server (NTRS)

Donlan, C. J.

1976-01-01

Some problems relating to longitudinal stability in power-on flight are considered. A derivation is included which shows that, under certain conditions, the rate of change of the pitching moment coefficient with lift coefficient as obtained in wind tunnel tests simulating constant power operation is directly proportional to one of the indices of stability commonly associated with flight analysis, (the slope of the curve relating the elevator angle for trim and lift coefficient). The necessity of analyzing power-on wind tunnel data for trim conditions is emphasized, and a method is provided for converting data obtained from constant thrust tests to simulated constant throttle flight conditions.

Quantitative rotating frame relaxometry methods in MRI.

PubMed

Gilani, Irtiza Ali; Sepponen, Raimo

2016-06-01

Macromolecular degeneration and biochemical changes in tissue can be quantified using rotating frame relaxometry in MRI. It has been shown in several studies that the rotating frame longitudinal relaxation rate constant (R1ρ ) and the rotating frame transverse relaxation rate constant (R2ρ ) are sensitive biomarkers of phenomena at the cellular level. In this comprehensive review, existing MRI methods for probing the biophysical mechanisms that affect the rotating frame relaxation rates of the tissue (i.e. R1ρ and R2ρ ) are presented. Long acquisition times and high radiofrequency (RF) energy deposition into tissue during the process of spin-locking in rotating frame relaxometry are the major barriers to the establishment of these relaxation contrasts at high magnetic fields. Therefore, clinical applications of R1ρ and R2ρ MRI using on- or off-resonance RF excitation methods remain challenging. Accordingly, this review describes the theoretical and experimental approaches to the design of hard RF pulse cluster- and adiabatic RF pulse-based excitation schemes for accurate and precise measurements of R1ρ and R2ρ . The merits and drawbacks of different MRI acquisition strategies for quantitative relaxation rate measurement in the rotating frame regime are reviewed. In addition, this review summarizes current clinical applications of rotating frame MRI sequences. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

Mass spectrometric screening of ligands with lower off-rate from a clicked-based pooled library.

PubMed

Arai, Satoshi; Hirosawa, Shota; Oguchi, Yusuke; Suzuki, Madoka; Murata, Atsushi; Ishiwata, Shin'ichi; Takeoka, Shinji

2012-08-13

This paper describes a convenient screening method using ion trap electrospray ionization mass spectrometry to classify ligands to a target molecule in terms of kinetic parameters. We demonstrate this method in the screening of ligands to a hexahistidine tag from a pooled library synthesized by click chemistry. The ion trap mass spectrometry analysis revealed that higher stabilities of ligand-target complexes in the gas phase were related to lower dissociation rate constants, i.e., off-rates in solution. Finally, we prepared a fluorescent probe utilizing the ligand with lowest off-rate and succeeded in performing single molecule observations of hexahistidine-tagged myosin V walking on actin filaments.

Inhibition of calcium carbonate crystal growth by organic additives using the constant composition method in conditions of recirculating cooling circuits

NASA Astrophysics Data System (ADS)

Chhim, Norinda; Kharbachi, Chams; Neveux, Thibaut; Bouteleux, Céline; Teychené, Sébastien; Biscans, Béatrice

2017-08-01

The cooling circuits used in power plants are subject to mineral crystallization which can cause scaling on the surfaces of equipment and construction materials reducing their heat exchange efficiency. Precipitated calcium carbonate is the predominant mineral scale commonly observed in cooling systems. Supersaturation is the key parameter controlling the nucleation and growth of calcite in these systems. The present work focuses on the precipitation of calcite using the constant composition method at constant supersaturation, through controlled addition of reactants to a semi-batch crystallizer, in order to maintain constant solution pH. The determination of the thermodynamic driving force (supersaturation) was based on the relevant chemical equilibria, total alkalinity and calculation of the activity coefficients. Calcite crystallization rates were derived from the experiments performed at supersaturation levels similar to those found in industrial station cooling circuits. Several types of seeds particles were added into the aqueous solution to mimic natural river water conditions in terms of suspended particulate matters content, typically: calcite, silica or illite particles. The effect of citric and copolycarboxylic additive inhibitors added to the aqueous solution was studied. The calcium carbonate growth rate was reduced by 38.6% in the presence of the citric additive and a reduction of 92.7% was observed when the copolycarboxylic additive was used under identical experimental conditions. These results are explained by the location of the adsorbed inhibitor at the crystal surface and by the degree of chemical bonding to the surface.

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

A moment-convergence method for stochastic analysis of biochemical reaction networks.

PubMed

Zhang, Jiajun; Nie, Qing; Zhou, Tianshou

2016-05-21

Traditional moment-closure methods need to assume that high-order cumulants of a probability distribution approximate to zero. However, this strong assumption is not satisfied for many biochemical reaction networks. Here, we introduce convergent moments (defined in mathematics as the coefficients in the Taylor expansion of the probability-generating function at some point) to overcome this drawback of the moment-closure methods. As such, we develop a new analysis method for stochastic chemical kinetics. This method provides an accurate approximation for the master probability equation (MPE). In particular, the connection between low-order convergent moments and rate constants can be more easily derived in terms of explicit and analytical forms, allowing insights that would be difficult to obtain through direct simulation or manipulation of the MPE. In addition, it provides an accurate and efficient way to compute steady-state or transient probability distribution, avoiding the algorithmic difficulty associated with stiffness of the MPE due to large differences in sizes of rate constants. Applications of the method to several systems reveal nontrivial stochastic mechanisms of gene expression dynamics, e.g., intrinsic fluctuations can induce transient bimodality and amplify transient signals, and slow switching between promoter states can increase fluctuations in spatially heterogeneous signals. The overall approach has broad applications in modeling, analysis, and computation of complex biochemical networks with intrinsic noise.

Equilibration kinetics in isolated and membrane-bound photosynthetic reaction centers upon illumination: a method to determine the photoexcitation rate.

PubMed

Manzo, Anthony J; Goushcha, Alexander O; Barabash, Yuri M; Kharkyanen, Valery N; Scott, Gary W

2009-07-01

Kinetics of electron transfer, following variation of actinic light intensity, for photosynthetic reaction centers (RCs) of purple bacteria (isolated and membrane-bound) were analyzed by measuring absorbance changes in the primary photoelectron donor absorption band at 865 nm. The bleaching of the primary photoelectron donor absorption band in RCs, following a sudden increase of illumination from the dark to an actinic light intensity of I(exp), obeys a simple exponential law with the rate constant alphaI(exp) + k(rec), in which alpha is a parameter relating the light intensity, measured in mW/cm(2), to a corresponding theoretical rate in units of reciprocal seconds, and k(rec) is the effective rate constant of the charge recombination in the photosynthetic RCs. In this work, a method for determining the alpha parameter value is developed and experimentally verified for isolated and membrane-bound RCs, allowing for rigorous modeling of RC macromolecule dynamics under varied photoexcitation conditions. Such modeling is necessary for RCs due to alterations of the forward photoexcitation rates and relaxation rates caused by illumination history and intramolecular structural dynamics effects. It is demonstrated that the classical Bouguer-Lambert-Beer formalism can be applied for the samples with relatively low scattering, which is not necessarily the case with strongly scattering media or high light intensity excitation.

Prediction of in situ root decomposition rates in an interspecific context from chemical and morphological traits

PubMed Central

Aulen, Maurice; Shipley, Bill; Bradley, Robert

2012-01-01

Background and Aims We quantitatively relate in situ root decomposition rates of a wide range of trees and herbs used in agroforestry to root chemical and morphological traits in order to better describe carbon fluxes from roots to the soil carbon pool across a diverse group of plant species. Methods In situ root decomposition rates were measured over an entire year by an intact core method on ten tree and seven herb species typical of agroforestry systems and were quantified using decay constants (k values) from Olson's single exponential model. Decay constants were related to root chemical (total carbon, nitrogen, soluble carbon, cellulose, hemicellulose, lignin) and morphological (specific root length, specific root length) traits. Traits were measured for both absorbing and non-absorbing roots. Key Results From 61 to 77 % of the variation in the different root traits and 63 % of that in root decomposition rates was interspecific. N was positively correlated, but total carbon and lignin were negatively correlated with k values. Initial root traits accounted for 75 % of the variation in interspecific decomposition rates using partial least squares regressions; partial slopes attributed to each trait were consistent with functional ecology expectations. Conclusions Easily measured initial root traits can be used to predict rates of root decomposition in soils in an interspecific context. PMID:22003237

Transport, biodegradation and isotopic fractionation of chlorinated ethenes: modeling and parameter estimation methods

NASA Astrophysics Data System (ADS)

Béranger, Sandra C.; Sleep, Brent E.; Lollar, Barbara Sherwood; Monteagudo, Fernando Perez

2005-01-01

An analytical, one-dimensional, multi-species, reactive transport model for simulating the concentrations and isotopic signatures of tetrachloroethylene (PCE) and its daughter products was developed. The simulation model was coupled to a genetic algorithm (GA) combined with a gradient-based (GB) method to estimate the first order decay coefficients and enrichment factors. In testing with synthetic data, the hybrid GA-GB method reduced the computational requirements for parameter estimation by a factor as great as 300. The isotopic signature profiles were observed to be more sensitive than the concentration profiles to estimates of both the first order decay constants and enrichment factors. Including isotopic data for parameter estimation significantly increased the GA convergence rate and slightly improved the accuracy of estimation of first order decay constants.

Efficient estimation of diffusion during dendritic solidification

NASA Technical Reports Server (NTRS)

Yeum, K. S.; Poirier, D. R.; Laxmanan, V.

1989-01-01

A very efficient finite difference method has been developed to estimate the solute redistribution during solidification with diffusion in the solid. This method is validated by comparing the computed results with the results of an analytical solution derived by Kobayashi (1988) for the assumptions of a constant diffusion coefficient, a constant equilibrium partition ratio, and a parabolic rate of the advancement of the solid/liquid interface. The flexibility of the method is demonstrated by applying it to the dendritic solidification of a Pb-15 wt pct Sn alloy, for which the equilibrium partition ratio and diffusion coefficient vary substantially during solidification. The fraction eutectic at the end of solidification is also obtained by estimating the fraction solid, in greater resolution, where the concentration of solute in the interdendritic liquid reaches the eutectic composition of the alloy.

Reaction diffusion in the nickel-chromium-aluminum and cobalt-chromium-aluminum systems

NASA Technical Reports Server (NTRS)

Levine, S. R.

1977-01-01

The effects of MCrAl coating-substrate interdiffusion on oxidation life and the general mutliphase, multicomponent diffusion problem were examined. Semi-infinite diffusion couples that had sources representing coatings and sinks representing gas turbine alloys were annealed at 1,000, 1,095, 1,150, or 1,205 C for as long as 500 hours. The source and sink aluminum and chromium contents and the base metal (cobalt or nickel) determined the parabolic diffusion rate constants of the couples and predicted finite coating lives. The beta source strength concept provided a method (1) for correlating beta recession rate constants with composition; (2) for determining reliable average total, diffusion, and constitutional activation energies; and (3) for calculating interdiffusion coefficients.

O+OH-->O(2)+H: A key reaction for interstellar chemistry. New theoretical results and comparison with experiment.

PubMed

Lique, F; Jorfi, M; Honvault, P; Halvick, P; Lin, S Y; Guo, H; Xie, D Q; Dagdigian, P J; Kłos, J; Alexander, M H

2009-12-14

We report extensive, fully quantum, time-independent (TID) calculations of cross sections at low collision energies and rate constants at low temperatures for the O+OH reaction, of key importance in the production of molecular oxygen in cold, dark, interstellar clouds and in the chemistry of the Earth's atmosphere. Our calculations are compared with TID calculations within the J-shifting approximation, with wave-packet calculations, and with quasiclassical trajectory calculations. The fully quantum TID calculations yield rate constants higher than those from the more approximate methods and are qualitatively consistent with a low-temperature extrapolation of earlier experimental values but not with the most recent experiments at the lowest temperatures.

The Br+HO 2 reaction revisited: Absolute determination of the rate constant at 298 K

NASA Astrophysics Data System (ADS)

Laverdet, G.; Le Bras, G.; Mellouki, A.; Poulet, G.

1990-09-01

The absolute determination of the rate constant for the reaction Br+HO 2→HBr+O 2 has been done at 298 K using the discharge-flor EPR method. The value k1 = (1.5±0.2) × 10 -12 cm 3 molecule -1 s -1 was obtained. Previous indirect measurements of k1 from a discharge-flow, LIF/mass spectrometric study of the Br/H 2CO/O 2 system have been reinterpreted, leading to values for k1 ranging from 1.0 × 10 -12 to 2.2 × 10 -12 cm 3 molecule -1 s -1 at 298 K. These results are discussed and compared with other literature values.

Semiclassical fermion pair creation in de Sitter spacetime

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

Stahl, Clément, E-mail: clement.stahl@icranet.org; Eckhard, Strobel, E-mail: eckhard.strobel@irap-phd.eu; Dipartimento di Fisica, Università di Roma “La Sapienza”, Piazzale Aldo Moro 5, 00185 Rome

2015-12-17

We present a method to semiclassically compute the pair creation rate of bosons and fermions in de Sitter spacetime. The results in the bosonic case agree with the ones in the literature. We find that for the constant electric field the fermionic and bosonic pair creation rate are the same. This analogy of bosons and fermions in the semiclassical limit is known from several flat spacetime examples.

Theoretical study of the gas-phase reactions of iodine atoms ((2)P(3/2)) with H(2), H(2)O, HI, and OH.

PubMed

Canneaux, Sébastien; Xerri, Bertrand; Louis, Florent; Cantrel, Laurent

2010-09-02

The rate constants of the reactions of iodine atoms with H(2), H(2)O, HI, and OH have been estimated using 39, 21, 13, and 39 different levels of theory, respectively, and have been compared to the available literature values over the temperature range of 250-2500 K. The aim of this methodological work is to demonstrate that standard theoretical methods are adequate to obtain quantitative rate constants for the reactions involving iodine-containing species. Geometry optimizations and vibrational frequency calculations are performed using three methods (MP2, MPW1K, and BHandHLYP) combined with three basis sets (cc-pVTZ, cc-pVQZ, and 6-311G(d,p)). Single-point energy calculations are performed with the highly correlated ab initio coupled cluster method in the space of single, double, and triple (pertubatively) electron excitations CCSD(T) using the cc-pVnZ (n = T, Q, and 5), aug-cc-pVnZ (n = T, Q, and 5), 6-311G(d,p), 6-311+G(3df,2p), and 6-311++G(3df,3pd) basis sets. Canonical transition state theory with a simple Wigner tunneling correction is used to predict the rate constants as a function of temperature. CCSD(T)/cc-pVnZ//MP2/cc-pVTZ (n = T and Q), CCSD(T)/6-311+G(3df,2p)//MP2/6-311G(d,p), and CCSD(T)/6-311++G(3df,3pd)//MP2/6-311G(d,p) levels of theory provide accurate kinetic rate constants when compared to available literature data. The use of the CCSD(T)/cc-pVQZ//MP2/cc-pVTZ and CCSD(T)/6-311++G(3df,3pd) levels of theory allows one to obtain a better agreement with the literature data for all reactions with the exception of the I + H(2) reaction R(1) . This computational procedure has been also used to predict rate constants for some reactions where no available experimental data exist. The use of quantum chemistry tools could be therefore extended to other elements and next applied to develop kinetic networks involving various fission products, steam, and hydrogen in the absence of literature data. The final objective is to implement the kinetics of gaseous reactions in the ASTEC (Accident Source Term Evaluation Code) code to improve speciation of fission transport, which can be transported along the Reactor Coolant System (RCS) of a Pressurized Water Reactor (PWR) in case of a severe accident.

Measurement of rheology of distiller's grain slurries using a helical impeller viscometer.

PubMed

Houchin, Tiffany L; Hanley, Thomas R

2004-01-01

Current research is focused on developing a process to convert the cellulose and hemicellulose in distiller's grains into fermentable sugars, increasing both ethanol yield and the amount of protein in the remaining solid product. The rheologic properties of distiller's grain slurries were determined for concentrations of 21, 23, and 25%. Distiller's grain slurries are non-Newtonian, heterogeneous fluids subject to particle settling. Traditional methods of viscosity measurement, such as cone-and-plate and concentric cylinder viscometers, are not adequate for these fluids. A helical impeller viscometer was employed to measure impeller torque over a range of rotational speeds. Newtonian and non-Newtonian calibration fluids were utilized to obtain constants that relate shear stresses and shear rates to the experimental data. The Newtonian impeller constant, c, was 151; the non-Newtonian shear rate constant, k, was 10.30. Regression analysis of experimental data was utilized for comparison to power law, Herschel-Bulkley, and Casson viscosity models with regression coefficients exceeding 0.99 in all cases.

Analysis of Hydrodynamics and Heat Transfer in a Thin Liquid Film Flowing over a Rotating Disk by Integral Method

NASA Technical Reports Server (NTRS)

Basu, S.; Cetegen, B. M.

2005-01-01

An integral analysis of hydrodynamics and heat transfer in a thin liquid film flowing over a rotating disk surface is presented for both constant temperature and constant heat flux boundary conditions. The model is found to capture the correct trends of the liquid film thickness variation over the disk surface and compare reasonably well with experimental results over the range of Reynolds and Rossby numbers covering both inertia and rotation dominated regimes. Nusselt number variation over the disk surface shows two types of behavior. At low rotation rates, the Nusselt number exhibits a radial decay with Nusselt number magnitudes increasing with higher inlet Reynolds number for both constant wall temperature and heat flux cases. At high rotation rates, the Nusselt number profiles exhibit a peak whose location advances radially outward with increasing film Reynolds number or inertia. The results also compare favorably with the full numerical simulation results from an earlier study as well as with the reported experimental results.

Heteronuclear Adiabatic Relaxation Dispersion (HARD) for quantitative analysis of conformational dynamics in proteins.

PubMed

Traaseth, Nathaniel J; Chao, Fa-An; Masterson, Larry R; Mangia, Silvia; Garwood, Michael; Michaeli, Shalom; Seelig, Burckhard; Veglia, Gianluigi

2012-06-01

NMR relaxation methods probe biomolecular motions over a wide range of timescales. In particular, the rotating frame spin-lock R(1ρ) and Carr-Purcell-Meiboom-Gill (CPMG) R(2) experiments are commonly used to characterize μs to ms dynamics, which play a critical role in enzyme folding and catalysis. In an effort to complement these approaches, we introduced the Heteronuclear Adiabatic Relaxation Dispersion (HARD) method, where dispersion in rotating frame relaxation rate constants (longitudinal R(1ρ) and transverse R(2ρ)) is created by modulating the shape and duration of adiabatic full passage (AFP) pulses. Previously, we showed the ability of the HARD method to detect chemical exchange dynamics in the fast exchange regime (k(ex)∼10(4)-10(5) s(-1)). In this article, we show the sensitivity of the HARD method to slower exchange processes by measuring R(1ρ) and R(2ρ) relaxation rates for two soluble proteins (ubiquitin and 10C RNA ligase). One advantage of the HARD method is its nominal dependence on the applied radio frequency field, which can be leveraged to modulate the dispersion in the relaxation rate constants. In addition, we also include product operator simulations to define the dynamic range of adiabatic R(1ρ) and R(2ρ) that is valid under all exchange regimes. We conclude from both experimental observations and simulations that this method is complementary to CPMG-based and rotating frame spin-lock R(1ρ) experiments to probe conformational exchange dynamics for biomolecules. Finally, this approach is germane to several NMR-active nuclei, where relaxation rates are frequency-offset independent. Copyright © 2012 Elsevier Inc. All rights reserved.

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

Dang, Liem X.; Vo, Quynh N.; Nilsson, Mikael

We report one of the first simulations using a classical rate theory approach to predict the mechanism of the exchange process between water and aqueous uranyl ions. Using our water and ion-water polarizable force fields and molecular dynamics techniques, we computed the potentials of mean force for the uranyl ion-water pair as the function of pressures at ambient temperature. Subsequently, these simulated potentials of mean force were used to calculate rate constants using the transition rate theory; the time dependent transmission coefficients were also examined using the reactive flux method and Grote-Hynes treatments of the dynamic response of the solvent.more » The computed activation volumes using transition rate theory and the corrected rate constants are positive, thus the mechanism of this particular water-exchange is a dissociative process. We discuss our rate theory results and compare them with previously studies in which non-polarizable force fields were used. This work was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences. The calculations were carried out using computer resources provided by the Office of Basic Energy Sciences.« less

Intracellular crowding effects on the self-association of the bacterial cell division protein FtsZ.

PubMed

Naddaf, Lamis; Sayyed-Ahmad, Abdallah

2014-12-15

The dimerization rate of the bacterial cell division protein FtsZ is strongly affected by the intracellular crowding. Yet the complexity of the intracellular environment makes it difficult to investigate via all-atom molecular dynamics or other detailed theoretical methods. We study the crowding effect on FtsZ dimerization which is the first step of an oligomerization process that results in more elaborate supramolecular structures. In particular, we consider the effect of intracellular crowding on the reaction rates, and their dependence on the different concentrations of crowding agents. We achieved this goal by using Brownian dynamics (BD) simulation techniques and a modified post-processing approach in which we decompose the rate constant in crowded media as a product of the rate constant in the dilute solution times a factor that incorporates the crowding effect. The latter factor accounts for the diffusion reduction and crowder induced energy. In addition we include the crowding effects on water viscosity in the BD simulations of crowded media. We finally show that biomolecular crowding has a considerable effect on the FtsZ dimerization by increasing the dimerization rate constant from 2.6×10(7)M(-1)s(-1) in the absence of crowders to 1.0×10(8)M(-1)s(-1) at crowding level of 0.30. Copyright © 2014 Elsevier Inc. All rights reserved.

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...

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 multi-center preclinical study of gadoxetate DCE-MRI in rats as a biomarker of drug induced inhibition of liver transporter function

PubMed Central

Lenhard, Stephen C.; Yerby, Brittany; Forsgren, Mikael F.; Liachenko, Serguei; Johansson, Edvin; Pilling, Mark A.; Peterson, Richard A.; Yang, Xi; Williams, Dominic P.; Ungersma, Sharon E.; Morgan, Ryan E.; Brouwer, Kim L. R.; Jucker, Beat M.; Hockings, Paul D.

2018-01-01

Drug-induced liver injury (DILI) is a leading cause of acute liver failure and transplantation. DILI can be the result of impaired hepatobiliary transporters, with altered bile formation, flow, and subsequent cholestasis. We used gadoxetate dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), combined with pharmacokinetic modelling, to measure hepatobiliary transporter function in vivo in rats. The sensitivity and robustness of the method was tested by evaluating the effect of a clinical dose of the antibiotic rifampicin in four different preclinical imaging centers. The mean gadoxetate uptake rate constant for the vehicle groups at all centers was 39.3 +/- 3.4 s-1 (n = 23) and 11.7 +/- 1.3 s-1 (n = 20) for the rifampicin groups. The mean gadoxetate efflux rate constant for the vehicle groups was 1.53 +/- 0.08 s-1 (n = 23) and for the rifampicin treated groups was 0.94 +/- 0.08 s-1 (n = 20). Both the uptake and excretion transporters of gadoxetate were statistically significantly inhibited by the clinical dose of rifampicin at all centers and the size of this treatment group effect was consistent across the centers. Gadoxetate is a clinically approved MRI contrast agent, so this method is readily transferable to the clinic. Conclusion: Rate constants of gadoxetate uptake and excretion are sensitive and robust biomarkers to detect early changes in hepatobiliary transporter function in vivo in rats prior to established biomarkers of liver toxicity. PMID:29771932

Degradation of progestagens by oxidation with potassium permanganate in wastewater effluents

PubMed Central

2013-01-01

Background This study investigated the oxidation of selected progestagenic steroid hormones by potassium permanganate at pH 6.0 and 8.0 in ultrapure water and wastewater effluents, using bench-scale assays. Second order rate constants for the reaction of potassium permanganate with progestagens (levonorgestrel, medroxyprogesterone, norethindrone and progesterone) was determined as a function of pH, presence of natural organic matter and temperature. This work also illustrates the advantages of using a novel analytical method, the laser diode thermal desorption (LDTD-APCI) interface coupled to tandem mass spectrometry apparatus, allowing for the quick determination of oxidation rate constants and increasing sample throughput. Results The second-order rate constants for progestagens with permanganate determined in bench-scale experiments ranged from 23 to 368 M-1 sec-1 in both wastewater and ultrapure waters with pH values of 6.0 and 8.0. Two pairs of progestagens exhibited similar reaction rate constants, i.e. progesterone and medroxyprogesterone (23 to 80 M-1 sec-1 in ultrapure water and 26 to 149 M-1 sec-1 in wastewaters, at pH 6.0 and 8.0) and levonorgestrel and norethindrone (179 to 224 M-1 sec-1 in ultrapure water and 180 to 368 M-1 sec-1 in wastewaters, at pH 6.0 and 8.0). The presence of dissolved natural organic matter and the pH conditions improved the oxidation rate constants for progestagens with potassium permanganate only at alkaline pH. Reaction rates measured in Milli-Q water could therefore be used to provide conservative estimates for the oxidation rates of the four selected progestagens in wastewaters when exposed to potassium permanganate. The progestagen removal efficiencies was lower for progesterone and medroxyprogesterone (48 to 87 %) than for levonorgestrel and norethindrone (78 to 97%) in Milli-Q and wastewaters at pH 6.0-8.2 using potassium permanganate dosages of 1 to 5 mg L-1 after contact times of 10 to 60 min. Conclusion This work presents the first results on the permanganate-promoted oxidation of progestagens, as a function of pH, temperature as well as NOM. Progestagen concentrations used to determine rate constants were analyzed using an ultrafast laser diode thermal desorption interface coupled to tandem mass spectrometry for the analysis of water sample for progestagens. PMID:23675917

Focused Flow During Infiltration Into Ethanol-Contaminated Unsaturated Porous Media

NASA Astrophysics Data System (ADS)

Jazwiec, A.; Smith, J. E.

2017-12-01

The increasing commercial and industrial use of ethanol, e.g. in biofuels, has generated increased incidents of vadose zone contamination by way of ethanol spills and releases. This has increased the interest in better understanding behaviors of ethanol in unsaturated porous media and it's multiphase interactions in the vadose zone. This study uses highly controlled laboratory experiments in a 2-D (0.6mx0.6mx0.01m) flow cell to investigate water infiltration behaviors into ethanol-contaminated porous media. Ethanol and water were applied by either constant head or constant flux methods onto the surface of sands homogenously packed into the flow cell. The constant flux experiments at both low and high application rates were conducted using a rainulator with a row of hypodermic needles connected to a peristaltic pump. The constant head experiments were conducted using an 8cm diameter tension disk infiltrometer set to both low and high tensions. The presence of ethanol contamination generated solute-dependent capillarity induced focused flow (SCIFF) of water infiltration, which was primarily due to decreases in interfacial tensions at the air-liquid interfaces in the unsaturated sands as a function of ethanol concentration. SCIFF was clearly expressed as an unsaturated water flow phenomenon comprised of narrowly focused vertical flow fingers of water within the initially ethanol contaminated porous media. Using analyses of photos and video, comparisons were made between constant flux and constant head application methods. Further comparisons were made between low and high infiltration rates and the two sand textures used. A high degree of sensitivity to minor heterogeneity in relatively homogeneous sands was also observed. The results of this research have implications for rainfall infiltration into ethanol contaminated vadose zones expressing SCIFF, including implications for associated mass fluxes and the nature of flushing of ethanol from the unsaturated zone to groundwaters.

Kinetics of GLUT4 Trafficking in Rat and Human Skeletal Muscle

PubMed Central

Karlsson, Håkan K.R.; Chibalin, Alexander V.; Koistinen, Heikki A.; Yang, Jing; Koumanov, Francoise; Wallberg-Henriksson, Harriet; Zierath, Juleen R.; Holman, Geoffrey D.

2009-01-01

OBJECTIVE In skeletal muscle, insulin stimulates glucose transport activity three- to fourfold, and a large part of this stimulation is associated with a net translocation of GLUT4 from an intracellular compartment to the cell surface. We examined the extent to which insulin or the AMP-activated protein kinase activator AICAR can lead to a stimulation of the exocytosis limb of the GLUT4 translocation pathway and thereby account for the net increase in glucose transport activity. RESEARCH DESIGN AND METHODS Using a biotinylated photoaffinity label, we tagged endogenous GLUT4 and studied the kinetics of exocytosis of the tagged protein in rat and human skeletal muscle in response to insulin or AICAR. Isolated epitrochlearis muscles were obtained from male Wistar rats. Vastus lateralis skeletal muscle strips were prepared from open muscle biopsies obtained from six healthy men (age 39 ± 11 years and BMI 25.8 ± 0.8 kg/m2). RESULTS In rat epitrochlearis muscle, insulin exposure leads to a sixfold stimulation of the GLUT4 exocytosis rate (with basal and insulin-stimulated rate constants of 0.010 and 0.067 min−1, respectively). In human vastus lateralis muscle, insulin stimulates GLUT4 translocation by a similar sixfold increase in the exocytosis rate constant (with basal and insulin-stimulated rate constants of 0.011 and 0.075 min−1, respectively). In contrast, AICAR treatment does not markedly increase exocytosis in either rat or human muscle. CONCLUSIONS Insulin stimulation of the GLUT4 exocytosis rate constant is sufficient to account for most of the observed increase in glucose transport activity in rat and human muscle. PMID:19188436

Kinetics of oxytocin and deaminooxytocin displacement from the OXTR-receptor compartment in rat uterus ex vivo.

PubMed

Pliska, Vladimir; Jutz, Guido

2018-02-01

The oil immersion method suggested earlier by Kalsner and Nickerson for analysing actions of sympathomimetic drugs upon smooth muscle tissues was applied to isometric preparations of rat myometrium stimulated by oxytocin and deaminooxytocin. An exchange of the aqueous medium by mineral oil allows monitoring the displacement of the peptides from their receptor compartment in absence of free diffusion transport between tissue and organ medium. Exponential analysis of the data from the uterotonic decay phase allows several inferences to be drawn: 1) Transport rate constants (roughly equal for the two peptides) are higher than rate constants of (irreversible) elimination from the receptor compartment. 2) The response decay rate in the oil immersion phase is proportional solely to the peptide elimination and thus offers estimates of elimination rate constants. 3) Peptide elimination kinetics in the receptor compartment is only insignificantly influenced by the kinetics of ligand-receptor binding. 4) As expected, the elimination rate constant of deaminooxytocin is considerably lower than for oxytocin. The apparent concentration of receptors in the paracellular space of the myometrium ("apparent", since receptor molecules are embedded in the cell membrane and hence not exposed to a diffusive flux), estimated from histometric parameters, appears rather high: 7 and 120 μM for high and low affinity receptors, respectively. Concentration-response curves for rat uterus stimulated by oxytocin or deaminooxytocin indicate that only about 0.25 to 5 per cent of the available receptors are involved in eliciting a maximal uterus contraction. The remnant receptor pool is likely to behave as a receptor reserve ("spare receptors"). Copyright © 2018 Elsevier Inc. All rights reserved.

Double proton transfer in the complex of acetic acid with methanol: Theory versus experiment

NASA Astrophysics Data System (ADS)

Fernández-Ramos, Antonio; Smedarchina, Zorka; Rodríguez-Otero, Jesús

2001-01-01

To test the approximate instanton approach to intermolecular proton-transfer dynamics, we report multidimensional ab initio bimolecular rate constants of HH, HD, and DD exchange in the complex of acetic acid with methanol in tetrahydrofuran-d8, and compare them with the NMR (nuclear magnetic resonance) experiments of Gerritzen and Limbach. The bimolecular rate constants are evaluated as products of the exchange rates and the equilibrium rate constants of complex formation in solution. The two molecules form hydrogen-bond bridges and the exchange occurs via concerted transfer of two protons. The dynamics of this transfer is evaluated in the complete space of 36 vibrational degrees of freedom. The geometries of the two isolated molecules, the complex, and the transition states corresponding to double proton transfer are fully optimized at QCISD (quadratic configuration interaction including single and double substitutions) level of theory, and the normal-mode frequencies are calculated at MP2 (Møller-Plesset perturbation theory of second order) level with the 6-31G (d,p) basis set. The presence of the solvent is taken into account via single-point calculations over the gas phase geometries with the PCM (polarized continuum model). The proton exchange rate constants, calculated with the instanton method, show the effect of the structure and strength of the hydrogen bonds, reflected in the coupling between the tunneling motion and the other vibrations of the complex. Comparison with experiment, which shows substantial kinetic isotopic effects (KIE), indicates that tunneling prevails over classic exchange for the whole temperature range of observation. The unusual behavior of the experimental KIE upon single and double deuterium substitution is well reproduced and is related to the synchronicity of two-atom tunneling.

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.

Conformation of methyl beta-lactoside bound to the ricin B-chain: Interpretation of transferred nuclear Overhauser effects facilitated by spin simulation and selective deuteration

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

Bevilacqua, V.L.; Thomson, D.S.; Prestegard, J.H.

1990-06-12

Spin simulation and selective deuteration have been used to aid in the interpretation of 1D transferred nuclear Overhauser effect (TRNOE) NMR experiments on ricin B-chain/ligand systems. Application of these methods has revealed a change in the conformation of deuterated methyl beta-lactoside upon binding to the ricin B-chain which results in a slight change in glycosidic torsional angels which appear to dominate in the solution conformation. The combination of simulation and experiment also shows an important sensitivity of TRNOE magnitudes to dissociation rate constants and available spin-diffusion pathways for the ricin B-chain/ligand systems under study. The sensitivity to dissociation rates allowsmore » determination of rate constants for methyl beta-lactoside and methyl beta-galactoside of 50 and 300 s-1, respectively.« less

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.

Theoretical studies on the unimolecular decomposition of ethylene glycol.

PubMed

Ye, Lili; Zhao, Long; Zhang, Lidong; Qi, Fei

2012-01-12

The unimolecular decomposition processes of ethylene glycol have been investigated with the QCISD(T) method with geometries optimized at the B3LYP/6-311++G(d,p) level. Among the decomposition channels identified, the H(2)O-elimination channels have the lowest barriers, and the C-C bond dissociation is the lowest-energy dissociation channel among the barrierless reactions (the direct bond cleavage reactions). The temperature and pressure dependent rate constant calculations show that the H(2)O-elimination reactions are predominant at low temperature, whereas at high temperature, the direct C-C bond dissociation reaction is dominant. At 1 atm, in the temperature range 500-2000 K, the calculated rate constant is expressed to be 7.63 × 10(47)T(-10.38) exp(-42262/T) for the channel CH(2)OHCH(2)OH → CH(2)CHOH + H(2)O, and 2.48 × 10(51)T(-11.58) exp(-43593/T) for the channel CH(2)OHCH(2)OH → CH(3)CHO + H(2)O, whereas for the direct bond dissociation reaction CH(2)OHCH(2)OH → CH(2)OH + CH(2)OH the rate constant expression is 1.04 × 10(71)T(-16.16) exp(-52414/T).

Assessment of chloroethene degradation rates based on ratios of daughter/parent compounds in groundwater plumes

NASA Astrophysics Data System (ADS)

Höhener, Patrick

2014-05-01

Chlorinated solvent spills at industrial and urban sites create groundwater plumes where tetrachloro- and trichloroethene may degrade to their daughter compounds, dichloroethenes, vinyl chloride and ethane. The assessment of degradation and natural attenuation at such sites may be based on the analysis and inverse modelling of concentration data, on the calculation of mass fluxes in transsects, and/or on the analysis of stable isotope ratios in the ethenes. Relatively few work has investigated the possibility of using ratio of concentrations for gaining information on degradation rates. The use of ratios bears the advantage that dilution of a single sample with contaminant-free water does not matter. It will be shown that molar ratios of daughter to parent compounds measured along a plume streamline are a rapid and robust mean of determining whether degradation rates increase or decrease along the degradation chain, and allow furthermore a quantitation of the relative magnitude of degradation rates compared to the rate of the parent compound. Furthermore, ratios of concentration will become constant in zones where degradation is absent, and this allows to sketching the extension of actively degrading zones. The assessment is possible for pure sources and also for mixed sources. A quantification method is proposed in order to estimate first-order degradation rates in zones of constant degradation activity. This quantification method includes corrections that are needed due to longitudinal and transversal dispersivity. The method was tested on a number of real field sites from literature. At the majority of these sites, the first-order degradation rates were decreasing along the degradation chain from tetrachloroethene to vinyl chloride, meaning that the latter was often reaching important concentrations. This is bad news for site owners due to the increased toxicity of vinyl chloride compared to its parent compounds.

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.

Aqueous Humor Dynamics of the Brown-Norway Rat

PubMed Central

Ficarrotta, Kayla R.; Bello, Simon A.; Mohamed, Youssef H.; Passaglia, Christopher L.

2018-01-01

Purpose The study aimed to provide a quantitative description of aqueous humor dynamics in healthy rat eyes. Methods One eye of 26 anesthetized adult Brown-Norway rats was cannulated with a needle connected to a perfusion pump and pressure transducer. Pressure-flow data were measured in live and dead eyes by varying pump rate (constant-flow technique) or by modulating pump duty cycle to hold intraocular pressure (IOP) at set levels (modified constant-pressure technique). Data were fit by the Goldmann equation to estimate conventional outflow facility (\\begin{document}\

Measurement of Passive Uptake Rates for Volatile Organic Compounds on Commercial Thermal Desorption Tubes and the Effect of Ozone on Sampling

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

Maddalena, Randy; Parra, Amanda; Russell, Marion

Diffusive or passive sampling methods using commercially filled axial-sampling thermal desorption tubes are widely used for measuring volatile organic compounds (VOCs) in air. The passive sampling method provides a robust, cost effective way to measure air quality with time-averaged concentrations spanning up to a week or more. Sampling rates for VOCs can be calculated using tube geometry and Fick’s Law for ideal diffusion behavior or measured experimentally. There is evidence that uptake rates deviate from ideal and may not be constant over time. Therefore, experimentally measured sampling rates are preferred. In this project, a calibration chamber with a continuous stirredmore » tank reactor design and constant VOC source was combined with active sampling to generate a controlled dynamic calibration environment for passive samplers. The chamber air was augmented with a continuous source of 45 VOCs ranging from pentane to diethyl phthalate representing a variety of chemical classes and physiochemical properties. Both passive and active samples were collected on commercially filled Tenax TA thermal desorption tubes over an 11-day period and used to calculate passive sampling rates. A second experiment was designed to determine the impact of ozone on passive sampling by using the calibration chamber to passively load five terpenes on a set of Tenax tubes and then exposing the tubes to different ozone environments with and without ozone scrubbers attached to the tube inlet. During the sampling rate experiment, the measured diffusive uptake was constant for up to seven days for most of the VOCs tested but deviated from linearity for some of the more volatile compounds between seven and eleven days. In the ozone experiment, both exposed and unexposed tubes showed a similar decline in terpene mass over time indicating back diffusion when uncapped tubes were transferred to a clean environment but there was no indication of significant loss by ozone reaction.« less

High modulation bandwidth of a light-emitting diode with surface plasmon coupling (Conference Presentation)

NASA Astrophysics Data System (ADS)

Lin, Chun-Han; Tu, Charng-Gan; Yao, Yu-Feng; Chen, Sheng-Hung; Su, Chia-Ying; Chen, Hao-Tsung; Kiang, Yean-Woei; Yang, Chih-Chung

2017-02-01

Besides lighting, LEDs can be used for indoor data transmission. Therefore, a large modulation bandwidth becomes an important target in the development of visible LED. In this regard, enhancing the radiative recombination rate of carriers in the quantum wells of an LED is a useful method since the modulation bandwidth of an LED is related to the carrier decay rate besides the device RC time constant To increase the carrier decay rate in an LED without sacrificing its output power, the technique of surface plasmon (SP) coupling in an LED is useful. In this paper, the increases of modulation bandwidth by reducing mesa size, decreasing active layer thickness, and inducing SP coupling in blue- and green-emitting LEDs are illustrated. The results are demonstrated by comparing three different LED surface structures, including bare p-type surface, GaZnO current spreading layer, and Ag nanoparticles (NPs) for inducing SP coupling. In a single-quantum-well, blue-emitting LED with a circular mesa of 10 microns in radius, SP coupling results in a modulation bandwidth of 528.8 MHz, which is believed to be the record-high level. A smaller RC time constant can lead to a higher modulation bandwidth. However, when the RC time constant is smaller than 0.2 ns, its effect on modulation bandwidth saturates. The dependencies of modulation bandwidth on injected current density and carrier decay time confirm that the modulation bandwidth is essentially inversely proportional to a time constant, which is inversely proportional to the square-root of carrier decay rate and injected current density.

Ab initio chemical kinetics for the ClOO + NO reaction: Effects of temperature and pressure on product branching formation

NASA Astrophysics Data System (ADS)

Raghunath, P.; Lin, M. C.

2012-07-01

The kinetics and mechanism for the reaction of ClOO with NO have been investigated by ab initio molecular orbital theory calculations based on the CCSD(T)/6-311+G(3df)//PW91PW91/6-311+G(3df) method, employed to evaluate the energetics for the construction of potential energy surfaces and prediction of reaction rate constants. The results show that the reaction can produce two key low energy products ClNO + 3O2 via the direct triplet abstraction path and ClO + NO2 via the association and decomposition mechanism through long-lived singlet pc-ClOONO and ClONO2 intermediates. The yield of ClNO + O2 (1△) from any of the singlet intermediates was found to be negligible because of their high barriers and tight transition states. As both key reactions initially occur barrierlessly, their rate constants were evaluated with a canonical variational approach in our transition state theory and Rice-Ramspergen-Kassel-Marcus/master equation calculations. The rate constants for ClNO + 3O2 and ClO + NO2 production from ClOO + NO can be given by 2.66 × 10-16 T1.91 exp(341/T) (200-700 K) and 1.48 × 10-24 T3.99 exp(1711/T) (200-600 K), respectively, independent of pressure below atmospheric pressure. The predicted total rate constant and the yields of ClNO and NO2 in the temperature range of 200-700 K at 10-760 Torr pressure are in close agreement with available experimental results.

Determination of the Effects of Medium Composition on the Monochloramine Disinfection Kinetics of Nitrosomonas europaea by the Propidium Monoazide Quantitative PCR and Live/Dead BacLight Methods ▿

PubMed Central

Wahman, David G.; Schrantz, Karen A.; Pressman, Jonathan G.

2010-01-01

Various medium compositions (phosphate, 1 to 50 mM; ionic strength, 2.8 to 150 meq/liter) significantly affected Nitrosomonas europaea monochloramine disinfection kinetics, as determined by the Live/Dead BacLight (LD) and propidium monoazide quantitative PCR (PMA-qPCR) methods (lag coefficient, 37 to 490 [LD] and 91 to 490 [PMA-qPCR] mg·min/liter; Chick-Watson rate constant, 4.0 × 10−3 to 9.3 × 10−3 [LD] and 1.6 × 10−3 to 9.6 × 10−3 [PMA-qPCR] liter/mg·min). Two competing effects may account for the variation in disinfection kinetic parameters: (i) increasing kinetics (disinfection rate constant [k] increased, lag coefficient [b] decreased) with increasing phosphate concentration and (ii) decreasing kinetics (k decreased, b increased) with increasing ionic strength. The results support development of a standard medium for evaluating disinfection kinetics in drinking water. PMID:20952645

Method and apparatus for combinatorial logic signal processor in a digitally based high speed x-ray spectrometer

DOEpatents

Warburton, William K.; Zhou, Zhiquing

1999-01-01

A high speed, digitally based, signal processing system which accepts a digitized input signal and detects the presence of step-like pulses in the this data stream, extracts filtered estimates of their amplitudes, inspects for pulse pileup, and records input pulse rates and system livetime. The system has two parallel processing channels: a slow channel, which filters the data stream with a long time constant trapezoidal filter for good energy resolution; and a fast channel which filters the data stream with a short time constant trapezoidal filter, detects pulses, inspects for pileups, and captures peak values from the slow channel for good events. The presence of a simple digital interface allows the system to be easily integrated with a digital processor to produce accurate spectra at high count rates and allow all spectrometer functions to be fully automated. Because the method is digitally based, it allows pulses to be binned based on time related values, as well as on their amplitudes, if desired.

Decomposition of persistent pharmaceuticals in wastewater by ionizing radiation

NASA Astrophysics Data System (ADS)

Kimura, Atsushi; Osawa, Misako; Taguchi, Mitsumasa

2012-09-01

Pharmaceuticals in wastewater were treated by the combined method of activated sludge and ionizing radiation in laboratory scale. Oseltamivir, aspirin, and ibuprofen at 5 μmol dm-3 in wastewater were decomposed by the activated sludge at reaction time for 4 h. Carbamazepine, ketoprofen, mefenamic acid, clofibric acid, and diclofenac were not biodegraded completely, but were eliminated by γ-ray irradiation at 2 kGy. The rate constants of the reactions of these pharmaceuticals with hydroxyl radicals were estimated by the competition reaction method to be 4.0-10×109 mol-1 dm3 s-1. Decompositions of the pharmaceuticals in wastewater by ionizing radiation were simulated by use of the rate constants and the amount of total organic carbon as parameters. Simulation curves of concentrations of these pharmaceuticals as a function of dose described the experimental data, and the required dose for the elimination of them in wastewater by ionizing radiation can be estimated by this simulation.

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.

Apparatus and method for determining solids circulation rate

DOEpatents

Ludlow, J Christopher [Morgantown, WV; Spenik, James L [Morgantown, WV

2012-02-14

The invention relates to a method of determining bed velocity and solids circulation rate in a standpipe experiencing a moving packed bed flow, such as the in the standpipe section of a circulating bed fluidized reactor The method utilizes in-situ measurement of differential pressure over known axial lengths of the standpipe in conjunction with in-situ gas velocity measurement for a novel application of Ergun equations allowing determination of standpipe void fraction and moving packed bed velocity. The method takes advantage of the moving packed bed property of constant void fraction in order to integrate measured parameters into simultaneous solution of Ergun-based equations and conservation of mass equations across multiple sections of the standpipe.

On the value of nonremovable reminders for behavior modification: an application to nail-biting (onychophagia).

PubMed

Koritzky, Gilly; Yechiam, Eldad

2011-11-01

The authors examined the effectiveness of a novel behavior modification method for dysfunctional and impulsive habits, based on nonremovable reminders (NrRs). NrRs were implemented by having participants wear nonremovable wristbands designated to constantly remind them of their resolution to quit the targeted habit (nail-biting). Participants were 80 nail-biters who resolved to quit. The NrR approach was contrasted with an aversion-based behavioral modification technique. Recovery was assessed after 3 and 6 weeks of treatment and in a 5-month follow-up. The NrR method was associated with lower drop-out rate and was as successful as the aversion-based method altogether. When considering only non-dropouts, the aversion-based method was more effective. This suggests that the use of constantly present reminders broadens the target population that can benefit from reminders in the course of behavior modification.

Mussel-inspired histidine-based transient network metal coordination hydrogels

PubMed Central

Fullenkamp, Dominic E.; He, Lihong; Barrett, Devin G.; Burghardt, Wesley R.; Messersmith, Phillip B.

2013-01-01

Transient network hydrogels cross-linked through histidine-divalent cation coordination bonds were studied by conventional rheologic methods using histidine-modified star poly(ethylene glycol) (PEG) polymers. These materials were inspired by the mussel, which is thought to use histidine-metal coordination bonds to impart self-healing properties in the mussel byssal thread. Hydrogel viscoelastic mechanical properties were studied as a function of metal, pH, concentration, and ionic strength. The equilibrium metal-binding constants were determined by dilute solution potentiometric titration of monofunctional histidine-modified methoxy-PEG and were found to be consistent with binding constants of small molecule analogs previously studied. pH-dependent speciation curves were then calculated using the equilibrium constants determined by potentiometric titration, providing insight into the pH dependence of histidine-metal ion coordination and guiding the design of metal coordination hydrogels. Gel relaxation dynamics were found to be uncorrelated with the equilibrium constants measured, but were correlated to the expected coordination bond dissociation rate constants. PMID:23441102

Anaerobic work calculated in cycling time trials of different length.

PubMed

Mulder, Roy C; Noordhof, Dionne A; Malterer, Katherine R; Foster, Carl; de Koning, Jos J

2015-03-01

Previous research showed that gross efficiency (GE) declines during exercise and therefore influences the expenditure of anaerobic and aerobic resources. To calculate the anaerobic work produced during cycling time trials of different length, with and without a GE correction. Anaerobic work was calculated in 18 trained competitive cyclists during 4 time trials (500, 1000, 2000, and 4000-m). Two additional time trials (1000 and 4000 m) that were stopped at 50% of the corresponding "full" time trial were performed to study the rate of the decline in GE. Correcting for a declining GE during time-trial exercise resulted in a significant (P<.001) increase in anaerobically attributable work of 30%, with a 95% confidence interval of [25%, 36%]. A significant interaction effect between calculation method (constant GE, declining GE) and distance (500, 1000, 2000, 4000 m) was found (P<.001). Further analysis revealed that the constant-GE calculation method was different from the declining method for all distances and that anaerobic work calculated assuming a constant GE did not result in equal values for anaerobic work calculated over different time-trial distances (P<.001). However, correcting for a declining GE resulted in a constant value for anaerobically attributable work (P=.18). Anaerobic work calculated during short time trials (<4000 m) with a correction for a declining GE is increased by 30% [25%, 36%] and may represent anaerobic energy contributions during high-intensity exercise better than calculating anaerobic work assuming a constant GE.

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.

METHOD FOR THE STUDY OF THE LIVER BLOOD FLOW USING GAMMA-EMITTING RADIONUCLIDES

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

Baptista, A.M.; Carvalho, J.S.

1959-10-31

A method is described for the evaluation of liver blood flow values by radioactivity measurements of gamma-emitting radionuclides, in colloid form, using a scintillation detector positioned over the liver region. It is shown that the disappearance rate constant of the nuclide from the blood can be calculated from the curves obtained. Advantages of the method, including the use of small amounts of radioactive materials, are discussed. (auth)

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.

Determination of human albumin in serum and urine samples by constant-energy synchronous fluorescence method.

PubMed

Madrakian, Tayyebeh; Bagheri, Habibollah; Afkhami, Abbas

2015-08-01

A sensitive spectrofluorimetric method using constant-energy synchronous fluorescence technique is proposed for the determination of human albumin without separation. In this method, no reagent was used for enhancement of the fluorescence signal of albumin in the solution. Effects of some parameters, such as energy difference between excitation and emission monochromators (ΔE), emission and excitation slit widths and scan rate of wavelength were studied and the optimum conditions were established. For this purpose factorial design and response surface method were employed for optimization of the effective parameters on the fluorescence signal. The results showed that the scan rate of the wavelength has no significant effect on the analytical signal. The calibration curve was linear in the range 0.1-220.0 µg mL(-1) of albumin with a detection limit of 7.0 × 10(-3)  µg mL(-1). The relative standard deviations (RSD) for six replicate measurements of albumin were calculated as 2.2%, 1.7% and 1.3% for 0.5, 10.0 and 100.0 µg mL(-1) albumin, respectively. Furthermore the proposed method has been employed for the determination of albumin in human serum and urine samples. Copyright © 2014 John Wiley & Sons, Ltd.

Selective Injection of Magnetization by Slow Chemical Exchange in NMR

NASA Astrophysics Data System (ADS)

Boulat, Benoit; Epstein, David M.; Rance, Mark

1999-06-01

In a system in slow dynamic equilibrium two NMR methods are shown to be suitable for injecting magnetization from one resonance to another by means of slow chemical exchange. The combined outputs of the methods may be employed to measure the value of the off-rate constant κoff in the complex. The methods are implemented experimentally using the complex of molecules composed of the enzyme Esherichia coli dihydrofolate reductase (DHFR) and the ligand folate. In an equilibrium solution with DHFR, folate is known to undergo chemical exchange between a free state and a bound state. The modified synchronous nutation method is applied to a spin of the folate molecule in the free and bound states; magnetization transfer occurs between the two sites due to the underlying exchange process. As a preliminary step for the application of the synchronous nutation method, a new one-dimensional 1H NMR technique is proposed which facilitates the assignment of the resonance of a spin in the bound state, provided the resonance of its exchange partner in the free state is known. This experiment is also used to obtain quantitative estimates of the transverse relaxation rate constant of the bound resonance. The numerical procedure necessary to analyze the experimental results of the synchronous nutation experiment is presented.

(210)Pb and compositional data of sediments from Rondonian lakes, Madeira River basin, Brazil.

PubMed

Bonotto, Daniel Marcos; Vergotti, Marcelo

2015-05-01

Gold exploration has been intensive in Brazilian Amazon over the last 40 years, where the use of mercury as an amalgam has caused abnormal Hg concentrations in water bodies. Special attention has been directed to Madeira River due to fact it is a major tributary of Amazon River and that since 1986, gold exploration has been officially permitted along a 350km sector of the river. The (21)(0)Pb method has been used to date sediments taken from nine lakes situated in Madeira River basin, Rondônia State, and to verify where anthropogenic Hg might exist due to gold exploitation in Madeira River. Activity profiles of excess (21)(0)Pb determined in the sediment cores provided a means to evaluate the sedimentation rates using a Constant Flux: Constant Sedimentation (CF:CS) and Constant Rate of Supply (CRS) of unsupported/excess (21)(0)Pb models. A significant relationship was found between the CF:CS sedimentation rates and the mean values of the CRS sedimentation rates (Pearson correlation coefficient r=0.59). Chemical data were also determined in the sediments for identifying possible relationships with Hg occurring in the area. Significant values were found in statistical correlation tests realized among the Hg, major oxides and Total Organic Carbon (TOC) content in the sediments. The TOC increased in the sediment cores accompanied by a loss on ignition (LOI) increment, whereas silica decreased following a specific surface area raising associated to the TOC increase. The CRS model always provided ages within the permitted range of the (21)(0)Pb-method in the studied lakes, whereas the CF:CS model predicted two values above 140 years. Copyright © 2015 Elsevier Ltd. All rights reserved.

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.

Protein A chromatography increases monoclonal antibody aggregation rate during subsequent low pH virus inactivation hold

PubMed Central

Mazzer, Alice R.; Perraud, Xavier; Halley, Jennifer; O’Hara, John; Bracewell, Daniel G.

2015-01-01

Protein A chromatography is a near-ubiquitous method of mAb capture in bioprocesses. The use of low pH buffer for elution from protein A is known to contribute to product aggregation. Yet, a more limited set of evidence suggests that low pH may not be the sole cause of aggregation in protein A chromatography, rather, other facets of the process may contribute significantly. This paper presents a well-defined method for investigating this problem. An IgG4 was incubated in elution buffer after protein A chromatography (typical of the viral inactivation hold) and the quantity of monomer in neutralised samples was determined by size exclusion chromatography; elution buffers of different pH values predetermined to induce aggregation of the IgG4 were used. Rate constants for monomer decay over time were determined by fitting exponential decay functions to the data. Similar experiments were implemented in the absence of a chromatography step, i.e. IgG4 aggregation at low pH. Rate constants for aggregation after protein A chromatography were considerably higher than those from low pH exposure alone; a distinct shift in aggregation rates was apparent across the pH range tested. PMID:26346187

Spectral separation of gaseous fluorocarbon mixtures and measurement of diffusion constants by 19F gas phase DOSY NMR.

PubMed

Marchione, Alexander A; McCord, Elizabeth F

2009-11-01

Diffusion-ordered (DOSY) NMR techniques have for the first time been applied to the spectral separation of mixtures of fluorinated gases by diffusion rates. A mixture of linear perfluoroalkanes from methane to hexane was readily separated at 25 degrees C in an ordinary experimental setup with standard DOSY pulse sequences. Partial separation of variously fluorinated ethanes was also achieved. The constants of self-diffusion of a set of pure perfluoroalkanes were obtained at pressures from 0.25 to 1.34 atm and temperatures from 20 to 122 degrees C. Under all conditions there was agreement within 20% of experimental self-diffusion constant D and values calculated by the semiempirical Fuller method.

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.

Chemical Action of Halogenated Agents in Fire Extinguishing

NASA Technical Reports Server (NTRS)

Belles, Frank E.

1955-01-01

The action of halogenated agents in preventing flame propagation in fuel-air mixtures in laboratory tests is discussed in terms of a possible chemical mechanism. The mechanism chosen is that of chain-breaking reactions between agent and active particles (hydrogen and oxygen atoms and hydroxyl radicsls). Data from the literature on the flammability peaks of n-heptane agent-air mixtures are treated. Ratings of agent effectiveness in terms of the fuel equivalent of the agent, based on both fuel and agent concentrations at the peak, are proposed as preferable to ratings in terms of agent concentration alone. These fuel-equivalent ratings are roughly correlated by reactivities assigned to halogen and hydrogen atoms in the agent molecules. It is concluded that the presence of hydrogen in agent need not reduce its fire-fighting ability, provided there is enough halogen to make the agent nonflammable. A method is presented for estimating from quenching-distance data a rate constant for the reaction of agent with active particles. A quantitative result is obtained for methyl bromide. This rate constant predicts the observed peak concentration of methyl bromide quite well. However, more data are needed to prove the validity of the method. The assumption that hal.ogenatedagents act mainly by chain-bresking reactions with active particles is consistent with the experimental facts and should help guide the selection of agents for further tests.

Comparison of in situ and in vitro techniques for measuring ruminal degradation of animal by-product proteins.

PubMed

England, M L; Broderick, G A; Shaver, R D; Combs, D K

1997-11-01

Ruminally undegraded protein (RUP) values of blood meal (n = 2), hydrolyzed feather meal (n = 2), fish meal (n = 2), meat and bone meal, and soybean meal were estimated using an in situ method, an inhibitor in vitro method, and an inhibitor in vitro technique applying Michaelis-Menten saturation kinetics. Degradation rates for in situ and inhibitor in vitro methods were calculated by regression of the natural log of the proportion of crude protein (CP) remaining undegraded versus time. Nonlinear regression analysis of the integrated Michaelis-Menten equation was used to determine maximum velocity, the Michaelis constant, and degradation rate (the ratio of maximum velocity to the Michaelis constant). A ruminal passage rate of 0.06/h was assumed in the calculation of RUP. The in situ and inhibitor in vitro techniques yielded similar estimates of ruminal degradation. Mean RUP estimated for soybean meal, blood meal, hydrolyzed feather meal, fish meal, and meat and bone meal were, respectively, 28.6, 86.0, 77.4, 52.9, and 52.6% of CP by the in situ method and 26.4, 86.1, 76.0, 59.6, and 49.5% of CP by the inhibitor in vitro technique. The Michaelis-Menten inhibitor in vitro technique yielded more rapid CP degradation rates and decreased estimates of RUP. The inhibitor in vitro method required less time and labor than did the other two techniques to estimate the RUP values of animal by-product proteins. Results from in vitro incubations with pepsin.HCl suggested that low postruminal digestibility of hydrolyzed feather meal may impair its value as a source of RUP.

Comparison of a discrete steepest ascent method with the continuous steepest ascent method for optimal programing

NASA Technical Reports Server (NTRS)

Childs, A. G.

1971-01-01

A discrete steepest ascent method which allows controls which are not piecewise constant (for example, it allows all continuous piecewise linear controls) was derived for the solution of optimal programming problems. This method is based on the continuous steepest ascent method of Bryson and Denham and new concepts introduced by Kelley and Denham in their development of compatible adjoints for taking into account the effects of numerical integration. The method is a generalization of the algorithm suggested by Canon, Cullum, and Polak with the details of the gradient computation given. The discrete method was compared with the continuous method for an aerodynamics problem for which an analytic solution is given by Pontryagin's maximum principle, and numerical results are presented. The discrete method converges more rapidly than the continuous method at first, but then for some undetermined reason, loses its exponential convergence rate. A comparsion was also made for the algorithm of Canon, Cullum, and Polak using piecewise constant controls. This algorithm is very competitive with the continuous algorithm.

40 CFR Appendix J to Part 50 - Reference Method for the Determination of Particulate Matter as PM10 in the Atmosphere

Code of Federal Regulations, 2010 CFR

2010-07-01

... of Particulate Matter as PM10 in the Atmosphere J Appendix J to Part 50 Protection of Environment... STANDARDS Pt. 50, App. J Appendix J to Part 50—Reference Method for the Determination of Particulate Matter... sampler draws ambient air at a constant flow rate into a specially shaped inlet where the suspended...

40 CFR Appendix J to Part 50 - Reference Method for the Determination of Particulate Matter as PM10 in the Atmosphere

Code of Federal Regulations, 2011 CFR

2011-07-01

... of Particulate Matter as PM10 in the Atmosphere J Appendix J to Part 50 Protection of Environment... STANDARDS Pt. 50, App. J Appendix J to Part 50—Reference Method for the Determination of Particulate Matter... sampler draws ambient air at a constant flow rate into a specially shaped inlet where the suspended...

Using Generic Data to Establish Dormancy Failure Rates

NASA Technical Reports Server (NTRS)

Reistle, Bruce

2014-01-01

Many hardware items are dormant prior to being operated. The dormant period might be especially long, for example during missions to the moon or Mars. In missions with long dormant periods the risk incurred during dormancy can exceed the active risk contribution. Probabilistic Risk Assessments (PRAs) need to account for the dormant risk contribution as well as the active contribution. A typical method for calculating a dormant failure rate is to multiply the active failure rate by a constant, the dormancy factor. For example, some practitioners use a heuristic and divide the active failure rate by 30 to obtain an estimate of the dormant failure rate. To obtain a more empirical estimate of the dormancy factor, this paper uses the recently updated database NPRD-2011 [1] to arrive at a set of distributions for the dormancy factor. The resulting dormancy factor distributions are significantly different depending on whether the item is electrical, mechanical, or electro-mechanical. Additionally, this paper will show that using a heuristic constant fails to capture the uncertainty of the possible dormancy factors.

KINETIC STUDY ON THE INHIBITION OF HEN BRAIN NEUROTOXIC ESTERASE BY MIPAFOX

EPA Science Inventory

A direct method of assaying neurotoxic esterase (NTE) activity, using 4-nitrophenyl valerate, has been described. The technique was used to determine the biomolecular rate (ki), phosphorylation (k2), and affinity (kd) constants for the reaction of hen brain microsomal NTE with mi...

Estimating evolutionary rates using time-structured data: a general comparison of phylogenetic methods.

PubMed

Duchêne, Sebastián; Geoghegan, Jemma L; Holmes, Edward C; Ho, Simon Y W

2016-11-15

In rapidly evolving pathogens, including viruses and some bacteria, genetic change can accumulate over short time-frames. Accordingly, their sampling times can be used to calibrate molecular clocks, allowing estimation of evolutionary rates. Methods for estimating rates from time-structured data vary in how they treat phylogenetic uncertainty and rate variation among lineages. We compiled 81 virus data sets and estimated nucleotide substitution rates using root-to-tip regression, least-squares dating and Bayesian inference. Although estimates from these three methods were often congruent, this largely relied on the choice of clock model. In particular, relaxed-clock models tended to produce higher rate estimates than methods that assume constant rates. Discrepancies in rate estimates were also associated with high among-lineage rate variation, and phylogenetic and temporal clustering. These results provide insights into the factors that affect the reliability of rate estimates from time-structured sequence data, emphasizing the importance of clock-model testing. sduchene@unimelb.edu.au or garzonsebastian@hotmail.comSupplementary information: Supplementary data are available at Bioinformatics online. © The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.

Theoretical Kinetics Analysis for $$\\dot{H}$$ Atom Addition to 1,3-Butadiene and Related Reactions on the $$\\dot{C}$$ 4H 7 Potential Energy Surface

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

Li, Yang; Klippenstein, Stephen J.; Zhou, Chong-Wen

The oxidation chemistry of the simplest conjugated hydrocarbon, 1,3-butadiene, can provide a first step in understanding the role of poly-unsaturated hydrocarbons in combustion and, in particular, an understanding of their contribution towards soot formation. Based on our previous work on propene and the butene isomers (1-, 2- and isobutene), it was found that the reaction kinetics of H-atom addition to the C=C double bond plays a significant role in fuel consumption kinetics and influences the predictions of high-temperature ignition delay times, product species concentrations and flame speed measurements. In this study, the rate constants and thermodynamic properties formore » $$\\dot{H}$$-atom addition to 1,3-butadiene and related reactions on the $$\\dot{C}$$ 4H 7 potential energy surface have been calculated using two different series of quantum chemical methods and two different kinetic codes. Excellent agreement is obtained between the two different kinetics codes. The calculated results including zero point energies, single point energies, rate constants, barrier heights and thermochemistry are systematically compared among the two quantum chemical methods. 1-methylallyl ($$\\dot{C}$$ 4H 71-3) and 3-buten-1- yl ($$\\dot{C}$$ 4H 71-4) radicals and C 2H 4 + $$\\dot{C}$$2H3 are found to be the most important channels and reactivity promoting products, respectively. We calculated that terminal addition is dominant (> 80%) compared to internal $$\\dot{H}$$-atom addition at all temperatures in the range 298 – 2000 K. However, this dominance decreases with increasing temperature. The calculated rate constants for the bimolecular reaction C 4H 6 + $$\\dot{H}$$ → products and C 2H 4 + $$\\dot{C}$$ 2H 3 → products are in excellent agreement with both experimental and theoretical results from the literature. For selected C 4 species the calculated thermochemical values are also in good agreement with literature data. In addition, the rate constants for H-atom abstraction by $$\\dot{H}$$ atoms have also been calculated, and it is found that abstraction from the central carbon atoms is the dominant channel (> 70%) at temperatures in the range 298 – 2000 K. Lastly, by incorporating our calculated rate constants for both H-atom addition and abstraction into our recently developed 1,3-butadiene model, we show that laminar flame speed predictions are significantly improved, emphasizing the value of this study.« less

Combined valence bond-molecular mechanics potential-energy surface and direct dynamics study of rate constants and kinetic isotope effects for the H + C2H6 reaction.

PubMed

Chakraborty, Arindam; Zhao, Yan; Lin, Hai; Truhlar, Donald G

2006-01-28

This article presents a multifaceted study of the reaction H+C(2)H(6)-->H(2)+C(2)H(5) and three of its deuterium-substituted isotopologs. First we present high-level electronic structure calculations by the W1, G3SX, MCG3-MPWB, CBS-APNO, and MC-QCISD/3 methods that lead to a best estimate of the barrier height of 11.8+/-0.5 kcal/mol. Then we obtain a specific reaction parameter for the MPW density functional in order that it reproduces the best estimate of the barrier height; this yields the MPW54 functional. The MPW54 functional, as well as the MPW60 functional that was previously parametrized for the H+CH(4) reaction, is used with canonical variational theory with small-curvature tunneling to calculate the rate constants for all four ethane reactions from 200 to 2000 K. The final MPW54 calculations are based on curvilinear-coordinate generalized-normal-mode analysis along the reaction path, and they include scaled frequencies and an anharmonic C-C bond torsion. They agree with experiment within 31% for 467-826 K except for a 38% deviation at 748 K; the results for the isotopologs are predictions since these rate constants have never been measured. The kinetic isotope effects (KIEs) are analyzed to reveal the contributions from subsets of vibrational partition functions and from tunneling, which conspire to yield a nonmonotonic temperature dependence for one of the KIEs. The stationary points and reaction-path potential of the MPW54 potential-energy surface are then used to parametrize a new kind of analytical potential-energy surface that combines a semiempirical valence bond formalism for the reactive part of the molecule with a standard molecular mechanics force field for the rest; this may be considered to be either an extension of molecular mechanics to treat a reactive potential-energy surface or a new kind of combined quantum-mechanical/molecular mechanical (QM/MM) method in which the QM part is semiempirical valence bond theory; that is, the new potential-energy surface is a combined valence bond molecular mechanics (CVBMM) surface. Rate constants calculated with the CVBMM surface agree with the MPW54 rate constants within 12% for 534-2000 K and within 23% for 200-491 K. The full CVBMM potential-energy surface is now available for use in variety of dynamics calculations, and it provides a prototype for developing CVBMM potential-energy surfaces for other reactions.

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.

Quantum yield and rate constant of the singlet 1Δ g oxygen luminescence in an aqueous medium in the presence of nanoscale inhomogeneities

NASA Astrophysics Data System (ADS)

Jarnikova, E. S.; Parkhats, M. V.; Stasheuski, A. S.; Lepeshkevich, S. V.; Dzhagarov, B. M.

2017-04-01

The quantum yields and lifetimes of photosensitized luminescence of the 1Δ g state of singlet oxygen in an aquatic media with a controlled concentration of dielectric anisotropy centers (polyethylene glycol) have been measured using the methods of laser fluorometry. It is established that the quantum yield and the rate constant ( k r ) of the a 1Δ g → X 3Σ g - luminescence of 1O2 increase as the polymer concentration increases. The effect is analyzed within a general approach involving a relationship between kr and dielectric properties of the medium and is explained by the increased density of photon states and the local field factor in the space around O2( a 1Δ g ).

Theoretical investigation on H abstraction reaction mechanisms and rate constants of sevoflurane with the OH radical

NASA Astrophysics Data System (ADS)

Ren, Hongjiang; Li, Xiaojun; Qu, Yingjuan; Li, Feng

2018-01-01

The H abstraction reaction mechanism for sevoflurane with an ·OH radical was investigated theoretically using dual levels B3LYP/6-311++G(d, p)//QCISD(T)/6-311G(d, p). Thermochemistry properties at 298.15-2000 K were analyzed with the standard statistical thermodynamics method. Three pathways P(1), P(2) and P(3) were found and corresponded to the H13, H14 and H15 abstractions reactions with the Gibbs free barriers of 54.86, 55.05 and 54.86 kJ mol-1, respectively. The corresponding rate constants for three pathways over a wide temperature range of 298.15-2000 K were calculated and the results are in good agreement with the experimental data.

Unusual solvent effects on the fluorescence quenching rate constants of a thioxanthone derivative by n-butylamine and isoprene

NASA Astrophysics Data System (ADS)

Burget, D.; Jacques, P.

1998-07-01

The fluorescence quenching rate constants of a thioxanthone derivative by two electron donors ( n-butylamine and isoprene) were studied in eighteen solvents of different polarity. Both the empirical polarity parameter ET(30) and the more elaborate solvatochromic comparative method (SCM) π*, α, β (used without any precautions) failed to explain the relevant data. However, when in the frame of the SCM the sequential procedure is applied, unexpected solvent effects were revealed for hydroxylic solvents. These effects can be well accounted for by introducing a parameter χ for the whole set of solvents studied, equal to one or zero, depending on whether OH groups are involved or not in the quenching mechanism. A clue to the introduction of the parameter χ is presented.

Kinetic modeling and fitting software for interconnected reaction schemes: VisKin.

PubMed

Zhang, Xuan; Andrews, Jared N; Pedersen, Steen E

2007-02-15

Reaction kinetics for complex, highly interconnected kinetic schemes are modeled using analytical solutions to a system of ordinary differential equations. The algorithm employs standard linear algebra methods that are implemented using MatLab functions in a Visual Basic interface. A graphical user interface for simple entry of reaction schemes facilitates comparison of a variety of reaction schemes. To ensure microscopic balance, graph theory algorithms are used to determine violations of thermodynamic cycle constraints. Analytical solutions based on linear differential equations result in fast comparisons of first order kinetic rates and amplitudes as a function of changing ligand concentrations. For analysis of higher order kinetics, we also implemented a solution using numerical integration. To determine rate constants from experimental data, fitting algorithms that adjust rate constants to fit the model to imported data were implemented using the Levenberg-Marquardt algorithm or using Broyden-Fletcher-Goldfarb-Shanno methods. We have included the ability to carry out global fitting of data sets obtained at varying ligand concentrations. These tools are combined in a single package, which we have dubbed VisKin, to guide and analyze kinetic experiments. The software is available online for use on PCs.

Artificial neural networks for processing fluorescence spectroscopy data in skin cancer diagnostics

NASA Astrophysics Data System (ADS)

Lenhardt, L.; Zeković, I.; Dramićanin, T.; Dramićanin, M. D.

2013-11-01

Over the years various optical spectroscopic techniques have been widely used as diagnostic tools in the discrimination of many types of malignant diseases. Recently, synchronous fluorescent spectroscopy (SFS) coupled with chemometrics has been applied in cancer diagnostics. The SFS method involves simultaneous scanning of both emission and excitation wavelengths while keeping the interval of wavelengths (constant-wavelength mode) or frequencies (constant-energy mode) between them constant. This method is fast, relatively inexpensive, sensitive and non-invasive. Total synchronous fluorescence spectra of normal skin, nevus and melanoma samples were used as input for training of artificial neural networks. Two different types of artificial neural networks were trained, the self-organizing map and the feed-forward neural network. Histopathology results of investigated skin samples were used as the gold standard for network output. Based on the obtained classification success rate of neural networks, we concluded that both networks provided high sensitivity with classification errors between 2 and 4%.

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.

[Positron emission tomographic evaluations on hemodynamics and glucose metabolism of brain tumors and perifocal edematous tissues].

PubMed

Mizukawa, N; Hino, A; Imahori, Y; Tenjin, H; Yano, I; Yoshino, E; Hirakawa, K; Yamashita, M; Oki, F; Nakahashi, H

1989-03-01

Blood flow and glucose metabolism of the tumors and perifocal edematous tissues were evaluated using positron emission tomography (PET). Thirty-one brain tumor cases were investigated 12 non glial tumors (9 meningiomas and 3 metastatic tumors) and 19 gliomas (these were classified in 5 astrocytomas, 7 anaplastic astrocytomas and 7 glioblastomas, according to the malignancy). The diagnosis were confirmed pathologically in 30 cases. Cerebral blood flow (CBF), cerebral metabolic rate for oxygen (CMRO2), oxygen extraction fraction (OEF) and cerebral blood volume (CBV) were measured by O-15 labeled gases inhalation methods. Cerebral metabolic rate for glucose (CMFglu) were measured by F-18 Deoxyglucose intravenous injection method and calculated by Hutchins's formula. The rate constant (ks) and lumped constant (LC) used in this study were the same as those published by Phelps et al. in 1979. The blood flow and glucose metabolic rates of tumors were measured by the same methods. The results were as follows: 1) Meningiomas showed very high blood flow and blood volume with a wide range. The OEF and metabolic rate for glucose (MRglu) values were very low. 2) Metastatic tumors showed the low values of blood flow, metabolic rate for oxygen (MRO2) and OEF. 3) The blood flow and MRglu values on gliomas were varied with no significant differences between the three subgroups. On the other hands, as the malignancy of the glioma increased, a statistically significant increase in blood volume and a decrease in OEF were noted. 4) The OEF values from the various types of tumors studied were significantly lower than those obtained from the normal tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

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

Comparison between the Prebolus T1 Measurement and the Fixed T1 Value in Dynamic Contrast-Enhanced MR Imaging for the Differentiation of True Progression from Pseudoprogression in Glioblastoma Treated with Concurrent Radiation Therapy and Temozolomide Chemotherapy.

PubMed

Nam, J G; Kang, K M; Choi, S H; Lim, W H; Yoo, R-E; Kim, J-H; Yun, T J; Sohn, C-H

2017-12-01

Glioblastoma is the most common primary brain malignancy and differentiation of true progression from pseudoprogression is clinically important. Our purpose was to compare the diagnostic performance of dynamic contrast-enhanced pharmacokinetic parameters using the fixed T1 and measured T1 on differentiating true from pseudoprogression of glioblastoma after chemoradiation with temozolomide. This retrospective study included 37 patients with histopathologically confirmed glioblastoma with new enhancing lesions after temozolomide chemoradiation defined as true progression ( n = 15) or pseudoprogression ( n = 22). Dynamic contrast-enhanced pharmacokinetic parameters, including the volume transfer constant, the rate transfer constant, the blood plasma volume per unit volume, and the extravascular extracellular space per unit volume, were calculated by using both the fixed T1 of 1000 ms and measured T1 by using the multiple flip-angle method. Intra- and interobserver reproducibility was assessed by using the intraclass correlation coefficient. Dynamic contrast-enhanced pharmacokinetic parameters were compared between the 2 groups by using univariate and multivariate analysis. The diagnostic performance was evaluated by receiver operating characteristic analysis and leave-one-out cross validation. The intraclass correlation coefficients of all the parameters from both T1 values were fair to excellent (0.689-0.999). The volume transfer constant and rate transfer constant from the fixed T1 were significantly higher in patients with true progression ( P = .048 and .010, respectively). Multivariate analysis revealed that the rate transfer constant from the fixed T1 was the only independent variable (OR, 1.77 × 10 5 ) and showed substantial diagnostic power on receiver operating characteristic analysis (area under the curve, 0.752; P = .002). The sensitivity and specificity on leave-one-out cross validation were 73.3% (11/15) and 59.1% (13/20), respectively. The dynamic contrast-enhanced parameter of rate transfer constant from the fixed T1 acted as a preferable marker to differentiate true progression from pseudoprogression. © 2017 by American Journal of Neuroradiology.

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.

Development of a new free radical absorption capacity assay method for antioxidants: aroxyl radical absorption capacity (ARAC).

PubMed

Nagaoka, Shin-ichi; Nagai, Kanae; Fujii, Yuko; Ouchi, Aya; Mukai, Kazuo

2013-10-23

A new free radical absorption capacity assay method is proposed with use of an aroxyl radical (2,6-di-tert-butyl-4-(4'-methoxyphenyl)phenoxyl radical) and stopped-flow spectroscopy and is named the aroxyl radical absorption capacity (ARAC) assay method. The free radical absorption capacity (ARAC value) of each tocopherol was determined through measurement of the radical-scavenging rate constant in ethanol. The ARAC value could also be evaluated through measurement of the half-life of the aroxyl radical during the scavenging reaction. For the estimation of the free radical absorption capacity, the aroxyl radical was more suitable than the DPPH radical, galvinoxyl, and p-nitrophenyl nitronyl nitroxide. The ARAC value in tocopherols showed the same tendency as the free radical absorption capacities reported previously, and the tendency was independent of an oxygen radical participating in the scavenging reaction and of a medium surrounding the tocopherol and oxygen radical. The ARAC value can be directly connected to the free radical-scavenging rate constant, and the ARAC method has the advantage of treating a stable and isolable radical (aroxyl radical) in a user-friendly organic solvent (ethanol). The ARAC method was also successfully applied to a palm oil extract. Accordingly, the ARAC method would be useful in free radical absorption capacity assay of antioxidative reagents and foods.

A moment-convergence method for stochastic analysis of biochemical reaction networks

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

Zhang, Jiajun; Nie, Qing; Zhou, Tianshou, E-mail: mcszhtsh@mail.sysu.edu.cn

Traditional moment-closure methods need to assume that high-order cumulants of a probability distribution approximate to zero. However, this strong assumption is not satisfied for many biochemical reaction networks. Here, we introduce convergent moments (defined in mathematics as the coefficients in the Taylor expansion of the probability-generating function at some point) to overcome this drawback of the moment-closure methods. As such, we develop a new analysis method for stochastic chemical kinetics. This method provides an accurate approximation for the master probability equation (MPE). In particular, the connection between low-order convergent moments and rate constants can be more easily derived in termsmore » of explicit and analytical forms, allowing insights that would be difficult to obtain through direct simulation or manipulation of the MPE. In addition, it provides an accurate and efficient way to compute steady-state or transient probability distribution, avoiding the algorithmic difficulty associated with stiffness of the MPE due to large differences in sizes of rate constants. Applications of the method to several systems reveal nontrivial stochastic mechanisms of gene expression dynamics, e.g., intrinsic fluctuations can induce transient bimodality and amplify transient signals, and slow switching between promoter states can increase fluctuations in spatially heterogeneous signals. The overall approach has broad applications in modeling, analysis, and computation of complex biochemical networks with intrinsic noise.« less

The kinetics of competitive antagonists on guinea-pig ileum.

PubMed Central

Roberts, F; Stephenson, R P

1976-01-01

1 The kinetics of action of some competitive muscarinic and histamine antagonists were examined on guinea-pig isolated ileum and their behaviour compared with the predictions of the interaction-limited model described by Paton (1961). 2 The kinetics of antagonism were not consistent with the predictions of this model: (1) The apparent dissociation rate constant calculated from the decrease in occupancy on washout was not independent of the concentration of antagonist. (2) The dissociation rate constant of a 'slow' antagonist calculated from the change in occupancy when a 'fast' antagonist was superimposed varied with the concentration of fast antagonist. (3) If the concentration of slow antagonist was increased when the fast antagonist was superimposed so that the equilibrium occupancy of the 'slow' was the same as before, a transitional phase was observed. 3 The kinetics of antagonism were observed in longitudinal muscle strips and intact pieces of ileum, bathed in Tyrode or Krebs solution, and with isometric and isotonic recording. No evidence was found that the discrepancies between the interaction-limited model and the observed kinetics could be accounted for by the experimental method used. 4 It is therefore concluded that either access is rate-limiting in these circumstances or, if interaction is rate-limiting, some alternative interaction-limited model is required to describe the kinetics of antagonism. In either case it would seem unwise at this time to calculate antagonist-receptor rate constants from the observed kinetics of antagonism. PMID:974378

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)).

Cold Incineration of Chlorophenols in Aqueous Solution by Advanced Electrochemical Process Electro-Fenton. Effect of Number and Position of Chlorine Atoms on the Degradation Kinetics

NASA Astrophysics Data System (ADS)

Oturan, Nihal; Panizza, Marco; Oturan, Mehmet A.

2009-09-01

This study reports the kinetics of the degradation of several chlorophenols (CPs), such as monochlorophenols (2-chlorophenol and 4-chlorophenol), dichlorophenols (2,4-dichlorophenol and 2,6- dichlorophenol), trichlorophenols (2,3,5- trichlorophenol and 2,4,5-trichlorophenol), 2,3,5,6-tetrachlorophenol, and pentachlorophenol, by the electro-Fenton process using a carbon felt cathode and a Pt anode. The effect of number and the position of the chlorine atoms in the aromatic ring on the oxidative degradation rate was evaluated and discussed. The oxidation reaction of all the CPs with hydroxyl radicals evidenced a pseudo-first-order kinetics and the rate constant decreased with increasing the number of chlorine atoms. The absolute rate constant of second-order reaction kinetics between CPs and •OH was determined by the competition kinetics method in the range of (3.56-7.75) × 109 M-1 s-1 and follows the same sequence of the apparent rate constants. The mineralization of several CPs and of a mixture of all CPs under study was monitored by the total organic carbon (TOC) removal and the chlorine release during mineralization was followed by ion chromatography. Our results demonstrated that more chlorinated phenols are more difficult to mineralize; however for all the tested CPs, almost quantitative release of chloride ions was obtained after 6 h of treatment.

Minimum reaction network necessary to describe Ar/CF4 plasma etch

NASA Astrophysics Data System (ADS)

Helpert, Sofia; Chopra, Meghali; Bonnecaze, Roger T.

2018-03-01

Predicting the etch and deposition profiles created using plasma processes is challenging due to the complexity of plasma discharges and plasma-surface interactions. Volume-averaged global models allow for efficient prediction of important processing parameters and provide a means to quickly determine the effect of a variety of process inputs on the plasma discharge. However, global models are limited based on simplifying assumptions to describe the chemical reaction network. Here a database of 128 reactions is compiled and their corresponding rate constants collected from 24 sources for an Ar/CF4 plasma using the platform RODEo (Recipe Optimization for Deposition and Etching). Six different reaction sets were tested which employed anywhere from 12 to all 128 reactions to evaluate the impact of the reaction database on particle species densities and electron temperature. Because many the reactions used in our database had conflicting rate constants as reported in literature, we also present a method to deal with those uncertainties when constructing the model which includes weighting each reaction rate and filtering outliers. By analyzing the link between a reaction's rate constant and its impact on the predicted plasma densities and electron temperatures, we determine the conditions at which a reaction is deemed necessary to the plasma model. The results of this study provide a foundation for determining which minimal set of reactions must be included in the reaction set of the plasma model.

Relationships Between Base-Catalyzed Hydrolysis Rates or Glutathione Reactivity for Acrylates and Methacrylates and Their NMR Spectra or Heat of Formation

PubMed Central

Fujisawa, Seiichiro; Kadoma, Yoshinori

2012-01-01

The NMR chemical shift, i.e., the π-electron density of the double bond, of acrylates and methacrylates is related to the reactivity of their monomers. We investigated quantitative structure-property relationships (QSPRs) between the base-catalyzed hydrolysis rate constants (k1) or the rate constant with glutathione (GSH) (log kGSH) for acrylates and methacrylates and the 13C NMR chemical shifts of their α,β-unsaturated carbonyl groups (δCα and δCβ) or heat of formation (Hf) calculated by the semi-empirical MO method. Reported data for the independent variables were employed. A significant linear relationship between k1 and δCβ, but not δCα, was obtained for methacrylates (r2 = 0.93), but not for acrylates. Also, a significant relationship between k1 and Hf was obtained for both acrylates and methacrylates (r2 = 0.89). By contrast, log kGSH for acrylates and methacrylates was linearly related to their δCβ (r2 = 0.99), but not to Hf. These findings indicate that the 13C NMR chemical shifts and calculated Hf values for acrylates and methacrylates could be valuable for estimating the hydrolysis rate constants and GSH reactivity of these compounds. Also, these data for monomers may be an important tool for examining mechanisms of reactivity. PMID:22754331

FAST TRACK COMMUNICATION: Open string pair creation from worldsheet instantons

NASA Astrophysics Data System (ADS)

Schubert, Christian; Torrielli, Alessandro

2010-10-01

Worldline instantons provide a particularly elegant way to derive Schwinger's well-known formula for the pair creation rate due to a constant electric field in quantum electrodynamics. In this communication, we show how to extend this method to the corresponding problem of open string pair creation.

Analytical Method of Approximating the Motion of a Spinning Vehicle with Variable Mass and Inertia Properties Acted Upon by Several Disturbing Parameters

NASA Technical Reports Server (NTRS)

Buglia, James J.; Young, George R.; Timmons, Jesse D.; Brinkworth, Helen S.

1961-01-01

An analytical method has been developed which approximates the dispersion of a spinning symmetrical body in a vacuum, with time-varying mass and inertia characteristics, under the action of several external disturbances-initial pitching rate, thrust misalignment, and dynamic unbalance. The ratio of the roll inertia to the pitch or yaw inertia is assumed constant. Spin was found to be very effective in reducing the dispersion due to an initial pitch rate or thrust misalignment, but was completely Ineffective in reducing the dispersion of a dynamically unbalanced body.

Mean field treatment of heterogeneous steady state kinetics

NASA Astrophysics Data System (ADS)

Geva, Nadav; Vaissier, Valerie; Shepherd, James; Van Voorhis, Troy

2017-10-01

We propose a method to quickly compute steady state populations of species undergoing a set of chemical reactions whose rate constants are heterogeneous. Using an average environment in place of an explicit nearest neighbor configuration, we obtain a set of equations describing a single fluctuating active site in the presence of an averaged bath. We apply this Mean Field Steady State (MFSS) method to a model of H2 production on a disordered surface for which the activation energy for the reaction varies from site to site. The MFSS populations quantitatively reproduce the KMC results across the range of rate parameters considered.

Likelihood inference of non-constant diversification rates with incomplete taxon sampling.

PubMed

Höhna, Sebastian

2014-01-01

Large-scale phylogenies provide a valuable source to study background diversification rates and investigate if the rates have changed over time. Unfortunately most large-scale, dated phylogenies are sparsely sampled (fewer than 5% of the described species) and taxon sampling is not uniform. Instead, taxa are frequently sampled to obtain at least one representative per subgroup (e.g. family) and thus to maximize diversity (diversified sampling). So far, such complications have been ignored, potentially biasing the conclusions that have been reached. In this study I derive the likelihood of a birth-death process with non-constant (time-dependent) diversification rates and diversified taxon sampling. Using simulations I test if the true parameters and the sampling method can be recovered when the trees are small or medium sized (fewer than 200 taxa). The results show that the diversification rates can be inferred and the estimates are unbiased for large trees but are biased for small trees (fewer than 50 taxa). Furthermore, model selection by means of Akaike's Information Criterion favors the true model if the true rates differ sufficiently from alternative models (e.g. the birth-death model is recovered if the extinction rate is large and compared to a pure-birth model). Finally, I applied six different diversification rate models--ranging from a constant-rate pure birth process to a decreasing speciation rate birth-death process but excluding any rate shift models--on three large-scale empirical phylogenies (ants, mammals and snakes with respectively 149, 164 and 41 sampled species). All three phylogenies were constructed by diversified taxon sampling, as stated by the authors. However only the snake phylogeny supported diversified taxon sampling. Moreover, a parametric bootstrap test revealed that none of the tested models provided a good fit to the observed data. The model assumptions, such as homogeneous rates across species or no rate shifts, appear to be violated.

Sensorless Sinusoidal Drives for Fan and Pump Motors by V/f Control

NASA Astrophysics Data System (ADS)

Kiuchi, Mitsuyuki; Ohnishi, Tokuo

This paper proposes sensorless sinusoidal driving methods of permanent magnet synchronous motors for fans and pumps by V/f control. The proposed methods are simple methods that control the motor peak current constant by voltage or frequency control, and are characterized by DC link current detection using a single shunt resistor at carrier wave signal bottom timing. As a result of the dumping factor from square torque load characteristics of fan and pump motors, it is possible to control stable starting and stable steady state by V/f control. In general, pressure losses as a result of the fluid pass of fan and pump systems are nearly constant; therefore, the flow rate and motor torque are determined by revolutions. Accordingly, high efficiency driving is possible by setting corresponding currents to q-axis currents (torque currents) at target revolutions. Because of the simple current detection and motor control methods, the proposed methods are optimum for fan and pump motor driving systems of home appliances.

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

Modeling the reactivities of hydroxyl radical and ozone towards atmospheric organic chemicals using quantitative structure-reactivity relationship approaches.

PubMed

Gupta, Shikha; Basant, Nikita; Mohan, Dinesh; Singh, Kunwar P

2016-07-01

The persistence and the removal of organic chemicals from the atmosphere are largely determined by their reactions with the OH radical and O3. Experimental determinations of the kinetic rate constants of OH and O3 with a large number of chemicals are tedious and resource intensive and development of computational approaches has widely been advocated. Recently, ensemble machine learning (EML) methods have emerged as unbiased tools to establish relationship between independent and dependent variables having a nonlinear dependence. In this study, EML-based, temperature-dependent quantitative structure-reactivity relationship (QSRR) models have been developed for predicting the kinetic rate constants for OH (kOH) and O3 (kO3) reactions with diverse chemicals. Structural diversity of chemicals was evaluated using a Tanimoto similarity index. The generalization and prediction abilities of the constructed models were established through rigorous internal and external validation performed employing statistical checks. In test data, the EML QSRR models yielded correlation (R (2)) of ≥0.91 between the measured and the predicted reactivities. The applicability domains of the constructed models were determined using methods based on descriptors range, Euclidean distance, leverage, and standardization approaches. The prediction accuracies for the higher reactivity compounds were relatively better than those of the low reactivity compounds. Proposed EML QSRR models performed well and outperformed the previous reports. The proposed QSRR models can make predictions of rate constants at different temperatures. The proposed models can be useful tools in predicting the reactivities of chemicals towards OH radical and O3 in the atmosphere.

Detection of the YORP effect in asteroid (1620) Geographos

NASA Astrophysics Data System (ADS)

Durech, J.; Vokrouhlický, D.; Kaasalainen, M.; Higgins, D.; Krugly, Yu. N.; Gaftonyuk, N. M.; Shevchenko, V. G.; Chiorny, V. G.; Hamanowa, H.; Hamanowa, H.; Reddy, V.; Dyvig, R. R.

2008-10-01

Aims: The rotation state of small asteroids is affected by the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) torque. The directly observable consequence of the YORP effect is the secular change of the asteroid's rotation period. We carried out new photometric observations of asteroid (1620) Geographos in 2008 to extend the time line that, if long enough, would enable us to see possible deviations from a constant period rotation. Methods: We used the lightcurve inversion method to model the shape and spin state of Geographos. We assumed that the rotation rate evolves in time as ω(t) = ω0 + \\upsilon t, where both the constant term of the rotation rate ω0 and the linear term \\upsilon are parameters to be optimized. In total, we used 94 lightcurves observed in 1969-2008. Results: We show that for \\upsilon = 0, a constant-period model, the whole dataset of lightcurves cannot be satisfactorily fitted. However, when relaxing \\upsilon in the optimization process we obtain an excellent agreement between the model and observations. The best-fit value \\upsilon = (1.15 ± 0.15) × 10-8 rad d-2 implies that Geographos' rotation rate accelerates by ≃2.7 ms yr-1. This is in agreement with the theoretically predicted value 1.4 × 10-8 rad d-2 obtained from numerical integration of YORP torques acting on our convex shape model. Geographos is only the third asteroid (after (1862) Apollo and (54509) YORP) for which the YORP effect has been detected. It is also the largest object for which effects of thermal torques were revealed.

A transport equation for the scalar dissipation in reacting flows with variable density: First results

NASA Technical Reports Server (NTRS)

Mantel, T.

1993-01-01

Although the different regimes of premixed combustion are not well defined, most of the recent developments in turbulent combustion modeling are led in the so-called flamelet regime. The goal of these models is to give a realistic expression to the mean reaction rate (w). Several methods can be used to estimate (w). Bray and coworkers (Libby & Bray 1980, Bray 1985, Bray & Libby 1986) express the instantaneous reaction rate by means of a flamelet library and a frequency which describes the local interaction between the laminar flamelets and the turbulent flowfield. In another way, the mean reaction rate can be directly connected to the flame surface density (Sigma). This quantity can be given by the transport equation of the coherent flame model initially proposed by Marble & Broadwell 1977 and developed elsewhere. The mean reaction rate, (w), can also be estimated thanks to the evolution of an arbitrary scalar field G(x, t) = G(sub O) which represents the flame sheet. G(x, t) is obtained from the G-equation proposed by Williams 1985, Kerstein et al. 1988 and Peters 1993. Another possibility proposed in a recent study by Mantel & Borghi 1991, where a transport equation for the mean dissipation rate (epsilon(sub c)) of the progress variable c is used to determine (w). In their model, Mantel & Borghi 1991 considered a medium with constant density and constant diffusivity in the determination of the transport equation for (epsilon(sub c)). A comparison of different flamelet models made by Duclos et al. 1993 shows the realistic behavior of this model even in the case of constant density. Our objective in this present report is to present preliminary results on the study of this equation in the case of variable density and variable diffusivity. Assumptions of constant pressure and a Lewis number equal to unity allow us to significantly simplify the equation. A systematic order of magnitude analysis based on adequate scale relations is performed on each term of the equation. As in the case of constant density and constant diffusivity, the effects of stretching of the scalar field by the turbulent strain field, of local curvature, and of chemical reactions are predominant. In this preliminary work, we suggest closure models for certain terms, which will be validated after comparisons with DNS data.

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

Fast transient currents in Na,K-ATPase induced by ATP concentration jumps from the P3-[1-(3',5'-dimethoxyphenyl)-2-phenyl-2-oxo]ethyl ester of ATP.

PubMed Central

Sokolov, V S; Apell, H J; Corrie, J E; Trentham, D R

1998-01-01

Electrogenic ion transport by Na,K-ATPase was investigated by analysis of transient currents in a model system of protein-containing membrane fragments adsorbed to planar lipid bilayers. Sodium transport was triggered by ATP concentration jumps in which ATP was released from an inactive precursor by an intense near-UV light flash. The method has been used previously with the P3-1-(2-nitrophenyl)ethyl ester of ATP (NPE-caged ATP), from which the relatively slow rate of ATP release limits analysis of processes in the pump mechanism controlled by rate constants greater than 100 s(-1) at physiological pH. Here Na,K-ATPase was reinvestigated using the P3-[1-(3,5-dimethoxyphenyl)-2-phenyl-2-oxo]ethyl ester of ATP (DMB-caged ATP), which has an ATP release rate of >10(5) s(-1). Under otherwise identical conditions, photorelease of ATP from DMB-caged ATP showed faster kinetics of the transient current compared to that from NPE-caged ATP. With DMB-caged ATP, transient currents had rate profiles that were relatively insensitive to pH and the concentration of caged compound. Rate constants of ATP binding and of the E1 to E2 conformational change were compatible with earlier studies. Rate constants of enzyme phosphorylation and ADP-dependent dephosphorylation were 600 s(-1) and 1.5 x 10(6) M(-1) s(-1), respectively, at pH 7.2 and 22 degrees C. PMID:9591656

A Simple Approach to Evaluate the Kinetic Rate Constant for ATP Synthesis in Resting Human Skeletal Muscle at 7 T

PubMed Central

Ren, Jimin; Sherry, A. Dean; Malloy, Craig R.

2015-01-01

Inversion transfer (IT) is a well-established technique with multiple attractive features for analysis of kinetics. However, its application in measurement of ATP synthesis rate in vivo has lagged behind the more common ST techniques. One well-recognized issue with IT is the complexity of data analysis in comparison to much simpler analysis by ST. This complexity arises, in part, because the γ-ATP spin is involved in multiple chemical reactions and magnetization exchanges, whereas Pi is involved in a single reaction, Pi → γ-ATP. By considering the reactions involving γ-ATP only as a lumped constant, the rate constant for the reaction of physiological interest, kPi→γATP, can be determined. Here, we present a new IT data analysis method to evaluate kPi→γATP using data collected from resting human skeletal muscle at 7T. The method is based on the basic Bloch-McConnell equation, which relates kPi→γATP with ṁPi, the rate of Pi magnetization change. The kPi→γATP value is accessed from ṁPi data by more familiar linear correlation approaches. For a group of human subjects (n = 15), the kPi→γATP value derived for resting calf muscle was 0.066 ± 0.017 s−1, in agreement with literature reported values. In this study we also explored possible time-saving strategies to speed up data acquisition for kPi→γATP evaluation using simulations. The analysis indicates that it is feasible to carry out a 31P inversion transfer experiment in ~10 minutes or shorter at 7T with reasonable outcome in kPi→γATP variance for measurement of ATP synthesis in resting human skeletal muscle. We believe that this new IT data analysis approach will facilitate the wide acceptance of IT to evaluate ATP synthesis rate in vivo. PMID:25943328

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

A fluorescence-based method for direct measurement of submicrosecond intramolecular contact formation in biopolymers: an exploratory study with polypeptides.

PubMed

Hudgins, Robert R; Huang, Fang; Gramlich, Gabriela; Nau, Werner M

2002-01-30

A fluorescent amino acid derivative (Fmoc-DBO) has been synthesized, which contains 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) as a small, hydrophilic fluorophore with an extremely long fluorescence lifetime (325 ns in H2O and 505 ns in D2O under air). Polypeptides containing both the DBO residue and an efficient fluorescence quencher allow the measurement of rate constants for intramolecular end-to-end contact formation. Bimolecular quenching experiments indicated that Trp, Cys, Met, and Tyr are efficient quenchers of DBO (k(q) = 20, 5.1, 4.5, and 3.6 x 10(8) M(-1) x s(-1) in D2O), while the other amino acids are inefficient. The quenching by Trp, which was selected as an intrinsic quencher, is presumed to involve exciplex-induced deactivation. Flexible, structureless polypeptides, Trp-(Gly-Ser)n-DBO-NH2, were prepared by standard solid-phase synthesis, and the rates of contact formation were measured through the intramolecular fluorescence quenching of DBO by Trp with time-correlated single-photon counting, laser flash photolysis, and steady-state fluorometry. Rate constants of 4.1, 6.8, 4.9, 3.1, 2.0, and 1.1 x 10(7) s(-1) for n = 0, 1, 2, 4, 6, and 10 were obtained. Noteworthy was the relatively slow quenching for the shortest peptide (n = 0). The kinetic data are in agreement with recent transient absorption studies of triplet probes for related peptides, but the rate constants are significantly larger. In contrast to the flexible structureless Gly-Ser polypeptides, the polyproline Trp-Pro4-DBO-NH2 showed insignificant fluorescence quenching, suggesting that a high polypeptide flexibility and the possibility of probe-quencher contact is essential to induce quenching. Advantages of the new fluorescence-based method for measuring contact formation rates in biopolymers include high accuracy, fast time range (100 ps-1 micros), and the possibility to perform measurements in water under air.

Evaluation of three statistical prediction models for forensic age prediction based on DNA methylation.

PubMed

Smeers, Inge; Decorte, Ronny; Van de Voorde, Wim; Bekaert, Bram

2018-05-01

DNA methylation is a promising biomarker for forensic age prediction. A challenge that has emerged in recent studies is the fact that prediction errors become larger with increasing age due to interindividual differences in epigenetic ageing rates. This phenomenon of non-constant variance or heteroscedasticity violates an assumption of the often used method of ordinary least squares (OLS) regression. The aim of this study was to evaluate alternative statistical methods that do take heteroscedasticity into account in order to provide more accurate, age-dependent prediction intervals. A weighted least squares (WLS) regression is proposed as well as a quantile regression model. Their performances were compared against an OLS regression model based on the same dataset. Both models provided age-dependent prediction intervals which account for the increasing variance with age, but WLS regression performed better in terms of success rate in the current dataset. However, quantile regression might be a preferred method when dealing with a variance that is not only non-constant, but also not normally distributed. Ultimately the choice of which model to use should depend on the observed characteristics of the data. Copyright © 2018 Elsevier B.V. All rights reserved.

Association rate constants for reactions between resonance-stabilized radicals: C 3H 3 + C 3H 3, C 3H 3 + C 3H 5, and C 3H 5 + C 3H 5

DOE PAGES

Georgievskii, Yuri; Miller, James A.; Klippenstein, Stephen J.

2007-05-18

Reactions between resonance-stabilized radicals play an important role in combustion chemistry. The theoretical prediction of rate coefficients and product distributions for such reactions is complicated by the fact that the initial complex-formation steps and some dissociation steps are barrierless. In this work, direct variable reaction coordinate transition state theory (VRC-TST) is used to predict accurately the association rate constants for the self and cross reactions of propargyl and allyl radicals. For each reaction, a set of multifaceted dividing surfaces is used to account for the multiple possible addition channels. Because of their resonant nature the geometric relaxation of the radicalsmore » is important. Here, the effect of this relaxation is explicitly calculated with the UB3LYP/cc-pvdz method for each mutual orientation encountered in the configurational integrals over the transition state dividing surfaces. The final energies are obtained from CASPT2/cc-pvdz calculations with all π-orbitals in the active space. Evaluations along the minimum energy path suggest that basis set corrections are negligible. The VRC-TST approach was also used to calculate the association rate constant and the corresponding number of states for the C 6H 5 + H → C 6H 6 exit channel of the C 3H 3 + C 3H 3 reaction, which is also barrierless. For this reaction, the interaction energies were evaluated with the CASPT2(2e,2o)/cc-pvdz method and a 1-D correction is included on the basis of CAS+1+2+QC/aug-cc-pvtz calculations for the CH 3 + H reference system. For the C 3H 3 + C 3H 3 reaction, the VRC-TST results for the energy and angular momentum resolved numbers of states in the entrance channels and in the C 6H 5 + H exit channel are incorporated in a master equation simulation to determine the temperature and pressure dependence of the phenomenological rate coefficients. The rate constants for the C 3H 3 + C 3H 3 and C 3H 5 + C 3H 5 self-reactions compare favorably with the available experimental data. Finally, to our knowledge there are no experimental rate data for the C 3H 3 + C 3H 5 reaction.« less

Reconstruction of input functions from a dynamic PET image with sequential administration of 15O2 and [Formula: see text] for noninvasive and ultra-rapid measurement of CBF, OEF, and CMRO2.

PubMed

Kudomi, Nobuyuki; Maeda, Yukito; Yamamoto, Hiroyuki; Yamamoto, Yuka; Hatakeyama, Tetsuhiro; Nishiyama, Yoshihiro

2018-05-01

CBF, OEF, and CMRO 2 images can be quantitatively assessed using PET. Their image calculation requires arterial input functions, which require invasive procedure. The aim of the present study was to develop a non-invasive approach with image-derived input functions (IDIFs) using an image from an ultra-rapid O 2 and C 15 O 2 protocol. Our technique consists of using a formula to express the input using tissue curve with rate constants. For multiple tissue curves, the rate constants were estimated so as to minimize the differences of the inputs using the multiple tissue curves. The estimated rates were used to express the inputs and the mean of the estimated inputs was used as an IDIF. The method was tested in human subjects ( n = 24). The estimated IDIFs were well-reproduced against the measured ones. The difference in the calculated CBF, OEF, and CMRO 2 values by the two methods was small (<10%) against the invasive method, and the values showed tight correlations ( r = 0.97). The simulation showed errors associated with the assumed parameters were less than ∼10%. Our results demonstrate that IDIFs can be reconstructed from tissue curves, suggesting the possibility of using a non-invasive technique to assess CBF, OEF, and CMRO 2 .

Pressure-dependent kinetics of initial reactions in iso-octane pyrolysis.

PubMed

Ning, HongBo; Gong, ChunMing; Li, ZeRong; Li, XiangYuan

2015-05-07

This study focuses on the studies of the main pressure-dependent reaction types of iso-octane (iso-C8H18) pyrolysis, including initial C-C bond fission of iso-octane, isomerization, and β-scission reactions of the alkyl radicals produced by the C-C bond fission of iso-octane. For the C-C bond fission of iso-octane, the minimum energy potentials are calculated at the CASPT2(2e,2o)/6-31+G(d,p)//CAS(2e,2o)/6-31+G(d,p) level of theory. For the isomerization and the β-scission reactions of the alkyl radicals, the optimization of the geometries and the vibrational frequencies of the reactants, transition states, and products are performed at the B3LYP/CBSB7 level, and their single point energies are calculated by using the composite CBS-QB3 method. Variable reaction coordinate transition state theory (VRC-TST) is used for the high-pressure limit rate constant calculation and Rice-Ramsperger-Kassel-Marcus/master equation (RRKM/ME) is used to calculate the pressure-dependent rate constants of these channels with pressure varying from 0.01-100 atm. The rate constants obtained in this work are in good agreement with those available from literatures. We have updated the rate constants and thermodynamic parameters for species involved in these reactions into a current chemical kinetic mechanism and also have improved the concentration profiles of main products such as C3H6 and C4H6 in the shock tube pyrolysis of iso-octane. The results of this study provide insight into the pyrolysis of iso-octane and will be helpful in the future development of branched paraffin kinetic mechanisms.

Quantum dynamics of the C(1D)+HD and C(1D)+n-D2 reactions on the ã 1A' and b 1A" surfaces.

PubMed

Defazio, Paolo; Gamallo, Pablo; González, Miguel; Akpinar, Sinan; Bussery-Honvault, Béatrice; Honvault, Pascal; Petrongolo, Carlo

2010-03-14

We present the Born-Oppenheimer, quantum dynamics of the reactions C((1)D)+HD and C((1)D)+n-D(2) on the uncoupled potential energy surfaces ã (1)A' and b (1)A", considering the Coriolis interactions and the nuclear-spin statistics. Using the real wavepacket method, we obtain initial-state-resolved probabilities, cross sections, isotopic branching ratios, and rate constants. Similarly to the C+n-H(2) reaction, the probabilities present many ã (1)A' or few b (1)A" sharp resonances, and the cross sections are very large at small collision energies and decrease at higher energies. At any initial condition, the C+HD reaction gives preferentially the CD+H products. Thermal cross sections, isotopic branching ratios, and rate constant k vary slightly with temperature and agree very well with the experimental values. At 300 K, we obtain for the various products k(CH+H)=(2.45+/-0.08) x 10(-10), k(CD+H)=(1.19+/-0.04) x 10(-10), k(CH+D)=(0.71+/-0.02) x 10(-10), k(CD+D)=(1.59+/-0.05) x 10(-10) cm(3) s(-1), and k(CD+H)/k(CH+D)=1.68+/-0.01. The b (1)A" contribution to cross sections and rate constants is always large, up to a maximum value of 62% for a rotationally resolved C+D(2) rate constant. The upper b (1)A" state is thus quite important in the C((1)D) collision with H(2) and its deuterated isotopes, as the agreement between theory and experiment shows.

Ab initio rate constants from hyperspherical quantum scattering: Application to H+C2H6 and H+CH3OH

NASA Astrophysics Data System (ADS)

Kerkeni, Boutheïna; Clary, David C.

2004-10-01

The dynamics and kinetics of the abstraction reactions of H atoms with ethane and methanol have been studied using a quantum mechanical procedure. Bonds being broken and formed are treated with explicit hyperspherical quantum dynamics. The ab initio potential energy surfaces for these reactions have been developed from a minimal number of grid points (average of 48 points) and are given by analytical functionals. All the degrees of freedom except the breaking and forming bonds are optimized using the second order perturbation theory method with a correlation consistent polarized valence triple zeta basis set. Single point energies are calculated on the optimized geometries with the coupled cluster theory and the same basis set. The reaction of H with C2H6 is endothermic by 1.5 kcal/mol and has a vibrationally adiabatic barrier of 12 kcal/mol. The reaction of H with CH3OH presents two reactive channels: the methoxy and the hydroxymethyl channels. The former is endothermic by 0.24 kcal/mol and has a vibrationally adiabatic barrier of 13.29 kcal/mol, the latter reaction is exothermic by 7.87 kcal/mol and has a vibrationally adiabatic barrier of 8.56 kcal/mol. We report state-to-state and state-selected cross sections together with state-to-state rate constants for the title reactions. Thermal rate constants for these reactions exhibit large quantum tunneling effects when compared to conventional transition state theory results. For H+CH3OH, it is found that the CH2OH product is the dominant channel, and that the CH3O channel contributes just 2% at 500 K. For both reactions, rate constants are in good agreement with some measurements.

A surprisingly complex aqueous chemistry of the simplest amino acid. A pulse radiolysis and theoretical study on H/D kinetic isotope effects in the reaction of glycine anions with hydroxyl radicals.

PubMed

Stefanić, I; Ljubić, I; Bonifacić, M; Sabljić, A; Asmus, K-D; Armstrong, D A

2009-04-07

A pulse radiolysis study was carried out of the reaction rate constants and kinetic isotope effects of hydroxyl-radical-induced H/D abstraction from the most-simple alpha-amino acid glycine in its anionic form in water. The rate constants and yields of three predominantly formed radical products, glycyl (NH2-*CH-CO2-), aminomethyl (NH2-*CH2), and aminyl (*NH-CH2-CO2-) radicals, as well as of their partially or fully deuterated analogs, were found to be of comparable magnitude. The primary, secondary, and primary/secondary H/D kinetic isotope effects on the rate constants were determined with respect to each of the three radicals. The unusual variety of products for such an elementary reaction between two small and simple species indicates a complex mechanism with several reactions taking place simultaneously. Thus, a theoretical modeling of the reaction mechanism and kinetics in the gas- and aqueous phase was performed by using the unrestricted density functional theory with the BB1K functional (employing the polarizable continuum model for the aqueous phase), unrestricted coupled cluster UCCSD(T) method, and improved canonical variational theory. Several hydrogen-bonded prereaction complexes and transition states were detected. In particular, the calculations pointed to a significant mechanistic role of the three-electron two-orbital (sigma/sigma* N therefore O) hemibonded prereaction complexes in the aqueous phase. A good agreement with the experimental rate constants and kinetic isotope effects was achieved by downshifting the calculated reaction barriers by 3 kcal mol(-1) and damping the NH(D) stretching frequency by a factor of 0.86.

Method of deposition by molecular beam epitaxy

DOEpatents

Chalmers, Scott A.; Killeen, Kevin P.; Lear, Kevin L.

1995-01-01

A method is described for reproducibly controlling layer thickness and varying layer composition in an MBE deposition process. In particular, the present invention includes epitaxially depositing a plurality of layers of material on a substrate with a plurality of growth cycles whereby the average of the instantaneous growth rates for each growth cycle and from one growth cycle to the next remains substantially constant as a function of time.

Method of deposition by molecular beam epitaxy

DOEpatents

Chalmers, S.A.; Killeen, K.P.; Lear, K.L.

1995-01-10

A method is described for reproducibly controlling layer thickness and varying layer composition in an MBE deposition process. In particular, the present invention includes epitaxially depositing a plurality of layers of material on a substrate with a plurality of growth cycles whereby the average of the instantaneous growth rates for each growth cycle and from one growth cycle to the next remains substantially constant as a function of time. 9 figures.

Multicomponent aerosol particle deposition in a realistic cast of the human upper respiratory tract.

PubMed

Nordlund, Markus; Belka, Miloslav; Kuczaj, Arkadiusz K; Lizal, Frantisek; Jedelsky, Jan; Elcner, Jakub; Jicha, Miroslav; Sauser, Youri; Le Bouhellec, Soazig; Cosandey, Stephane; Majeed, Shoaib; Vuillaume, Grégory; Peitsch, Manuel C; Hoeng, Julia

2017-02-01

Inhalation of aerosols generated by electronic cigarettes leads to deposition of multiple chemical compounds in the human airways. In this work, an experimental method to determine regional deposition of multicomponent aerosols in an in vitro segmented, realistic human lung geometry was developed and applied to two aerosols, i.e. a monodisperse glycerol aerosol and a multicomponent aerosol. The method comprised the following steps: (1) lung cast model preparation, (2) aerosol generation and exposure, (3) extraction of deposited mass, (4) chemical quantification and (5) data processing. The method showed good agreement with literature data for the deposition efficiency when using a monodisperse glycerol aerosol, with a mass median aerodynamic diameter (MMAD) of 2.3 μm and a constant flow rate of 15 L/min. The highest deposition surface density rate was observed in the bifurcation segments, indicating inertial impaction deposition. The experimental method was also applied to the deposition of a nebulized multicomponent aerosol with a MMAD of 0.50 μm and a constant flow rate of 15 L/min. The deposited amounts of glycerol, propylene glycol and nicotine were quantified. The three analyzed compounds showed similar deposition patterns and fractions as for the monodisperse glycerol aerosol, indicating that the compounds most likely deposited as parts of the same droplets. The developed method can be used to determine regional deposition for multicomponent aerosols, provided that the compounds are of low volatility. The generated data can be used to validate aerosol deposition simulations and to gain insight in deposition of electronic cigarette aerosols in human airways.

Improved Predictions of Drug-Drug Interactions Mediated by Time-Dependent Inhibition of CYP3A.

PubMed

Yadav, Jaydeep; Korzekwa, Ken; Nagar, Swati

2018-05-07

Time-dependent inactivation (TDI) of cytochrome P450s (CYPs) is a leading cause of clinical drug-drug interactions (DDIs). Current methods tend to overpredict DDIs. In this study, a numerical approach was used to model complex CYP3A TDI in human-liver microsomes. The inhibitors evaluated included troleandomycin (TAO), erythromycin (ERY), verapamil (VER), and diltiazem (DTZ) along with the primary metabolites N-demethyl erythromycin (NDE), norverapamil (NV), and N-desmethyl diltiazem (NDD). The complexities incorporated into the models included multiple-binding kinetics, quasi-irreversible inactivation, sequential metabolism, inhibitor depletion, and membrane partitioning. The resulting inactivation parameters were incorporated into static in vitro-in vivo correlation (IVIVC) models to predict clinical DDIs. For 77 clinically observed DDIs, with a hepatic-CYP3A-synthesis-rate constant of 0.000 146 min -1 , the average fold difference between the observed and predicted DDIs was 3.17 for the standard replot method and 1.45 for the numerical method. Similar results were obtained using a synthesis-rate constant of 0.000 32 min -1 . These results suggest that numerical methods can successfully model complex in vitro TDI kinetics and that the resulting DDI predictions are more accurate than those obtained with the standard replot approach.

A New TCP Congestion Control Supporting RTT-Fairness

NASA Astrophysics Data System (ADS)

Ogura, Kazumine; Nemoto, Yohei; Su, Zhou; Katto, Jiro

This paper focuses on RTT-fairness of multiple TCP flows over the Internet, and proposes a new TCP congestion control named “HRF (Hybrid RTT-Fair)-TCP”. Today, it is a serious problem that the flows having smaller RTT utilize more bandwidth than others when multiple flows having different RTT values compete in the same network. This means that a user with longer RTT may not be able to obtain sufficient bandwidth by the current methods. This RTT fairness issue has been discussed in many TCP papers. An example is CR (Constant Rate) algorithm, which achieves RTT-fairness by multiplying the square of RTT value in its window increment phase against TCP-Reno. However, the method halves its windows size same as TCP-Reno when a packet loss is detected. This makes worse its efficiency in certain network cases. On the other hand, recent proposed TCP versions essentially require throughput efficiency and TCP-friendliness with TCP-Reno. Therefore, we try to keep these advantages in our TCP design in addition to RTT-fairness. In this paper, we make intuitive analytical models in which we separate resource utilization processes into two cases: utilization of bottleneck link capacity and that of buffer space at the bottleneck link router. These models take into account three characteristic algorithms (Reno, Constant Rate, Constant Increase) in window increment phase where a sender receives an acknowledgement successfully. Their validity is proved by both simulations and implementations. From these analyses, we propose HRF-TCP which switches two modes according to observed RTT values and achieves RTT fairness. Experiments are carried out to validate the proposed method. Finally, HRF-TCP outperforms conventional methods in RTT-fairness, efficiency and friendliness with TCP-Reno.

A Method to Estimate the Masses of Asymptotic Giant Branch Variable Stars

NASA Astrophysics Data System (ADS)

Takeuti, Mine; Nakagawa, Akiharu; Kurayama, Tomoharu; Honma, Mareki

2013-06-01

AGB variable stars are at the transient phase between low and high mass-loss rates; estimating the masses of these stars is necessary to study the evolutionary processes and mass-loss processes during the AGB stage. We applied the pulsation constant theoretically derived by Xiong and Deng (2007 MNRAS, 378, 1270) to 15 galactic AGB stars in order to estimate their masses. We found that using the pulsation constant is effective to estimate the mass of a star pulsating with two different pulsation modes, such as S Crt and RX Boo, which provides mass estimates comparable to theoretical results of AGB star evolution. We also extended the use of the pulsation constant to single-mode variables, and analyzed the properties of AGB stars related to their masses.

Antarctic Firn Compaction Rates from Repeat-Track Airborne Radar Data: I. Methods

NASA Technical Reports Server (NTRS)

Medley, B.; Ligtenberg, S. R. M.; Joughin, I.; Van Den Broeke, M. R.; Gogineni, S.; Nowicki, S.

2015-01-01

While measurements of ice-sheet surface elevation change are increasingly used to assess mass change, the processes that control the elevation fluctuations not related to ice-flow dynamics (e.g. firn compaction and accumulation) remain difficult to measure. Here we use radar data from the Thwaites Glacier (West Antarctica) catchment to measure the rate of thickness change between horizons of constant age over different time intervals: 2009-10, 2010-11 and 2009-11. The average compaction rate to approximately 25m depth is 0.33ma(exp -1), with largest compaction rates near the surface. Our measurements indicate that the accumulation rate controls much of the spatio-temporal variations in the compaction rate while the role of temperature is unclear due to a lack of measurements. Based on a semi-empirical, steady-state densification model, we find that surveying older firn horizons minimizes the potential bias resulting from the variable depth of the constant age horizon. Our results suggest that the spatiotemporal variations in the firn compaction rate are an important consideration when converting surface elevation change to ice mass change. Compaction rates varied by up to 0.12ma(exp -1) over distances less than 6km and were on average greater than 20% larger during the 2010-11 interval than during 2009-10.

Molten salt synthesis of nanocrystalline phase of high dielectric constant material CaCu3Ti4O12.

PubMed

Prakash, B Shri; Varma, K B R

2008-11-01

Nanocrystalline powders of giant dielectric constant material, CaCu3Ti4O12 (CCTO), have been prepared successfully by the molten salt synthesis (MSS) using KCl at 750 degrees C/10 h, which is significantly lower than the calcination temperature (approximately 1000 degrees C) that is employed to obtain phase pure CCTO in the conventional solid-state reaction route. The water washed molten salt synthesized powder, characterized by X-ray powder diffraction (XRD), Scanning electron microscopy (SEM), and Transmission electron microscopy (TEM) confirmed to be a phase pure CCTO associated with approximately 150 nm sized crystallites of nearly spherical shape. The decrease in the formation temperature/duration of CCTO in MSS method was attributed to an increase in the diffusion rate or a decrease in the diffusion length of reacting ions in the molten salt medium. As a consequence of liquid phase sintering, pellets of as-synthesized KCl containing CCTO powder exhibited higher sinterability and grain size than that of KCl free CCTO samples prepared by both MSS method and conventional solid-state reaction route. The grain size and the dielectric constant of KCl containing CCTO ceramics increased with increasing sintering temperature (900 degrees C-1050 degrees C). Indeed the dielectric constants of these ceramics were higher than that of KCl free CCTO samples prepared by both MSS method and those obtained via the solid-state reaction route and sintered at the same temperature. Internal barrier layer capacitance (IBLC) model was invoked to correlate the observed dielectric constant with the grain size in these samples.

Mapping {sup 15}O Production Rate for Proton Therapy Verification

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

Grogg, Kira; Alpert, Nathaniel M.; Zhu, Xuping

Purpose: This work was a proof-of-principle study for the evaluation of oxygen-15 ({sup 15}O) production as an imaging target through the use of positron emission tomography (PET), to improve verification of proton treatment plans and to study the effects of perfusion. Methods and Materials: Dynamic PET measurements of irradiation-produced isotopes were made for a phantom and rabbit thigh muscles. The rabbit muscle was irradiated and imaged under both live and dead conditions. A differential equation was fitted to phantom and in vivo data, yielding estimates of {sup 15}O production and clearance rates, which were compared to live versus dead rates formore » the rabbit and to Monte Carlo predictions. Results: PET clearance rates agreed with decay constants of the dominant radionuclide species in 3 different phantom materials. In 2 oxygen-rich materials, the ratio of {sup 15}O production rates agreed with the expected ratio. In the dead rabbit thighs, the dynamic PET concentration histories were accurately described using {sup 15}O decay constant, whereas the live thigh activity decayed faster. Most importantly, the {sup 15}O production rates agreed within 2% (P>.5) between conditions. Conclusions: We developed a new method for quantitative measurement of {sup 15}O production and clearance rates in the period immediately following proton therapy. Measurements in the phantom and rabbits were well described in terms of {sup 15}O production and clearance rates, plus a correction for other isotopes. These proof-of-principle results support the feasibility of detailed verification of proton therapy treatment delivery. In addition, {sup 15}O clearance rates may be useful in monitoring permeability changes due to therapy.« less

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.

Use of an exchange method to estimate the association and dissociation rate constants of cadmium complexes formed with low-molecular-weight organic acids commonly exuded by plant roots.

PubMed

Schneider, André; Nguyen, Christophe

2011-01-01

Organic acids released from plant roots can form complexes with cadmium (Cd) in the soil solution and influence metal bioavailability not only due to the nature and concentration of the complexes but also due to their lability. The lability of a complex influences its ability to buffer changes in the concentration of free ions (Cd); it depends on the association (, m mol s) and dissociation (, s) rate constants. A resin exchange method was used to estimate and (m mol s), which is the conditional estimate of depending on the calcium (Ca) concentration in solution. The constants were estimated for oxalate, citrate, and malate, three low-molecular-weight organic acids commonly exuded by plant roots and expected to strongly influence Cd uptake by plants. For all three organic acids, the and estimates were around 2.5 10 m mol s and 1.3 × 10 s, respectively. Based on the literature, these values indicate that the Cd- low-molecular-weight organic acids complexes formed between Cd and low-molecular-weight organic acids may be less labile than complexes formed with soil soluble organic matter but more labile than those formed with aminopolycarboxylic chelates. Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.

Pulse Shaped 8-PSK Bandwidth Efficiency and Spectral Spike Elimination

NASA Technical Reports Server (NTRS)

Tao, Jian-Ping

1998-01-01

The most bandwidth-efficient communication methods are imperative to cope with the congested frequency bands. Pulse shaping methods have excellent effects on narrowing bandwidth and increasing band utilization. The position of the baseband filters for the pulse shaping is crucial. Post-modulation pulse shaping (a low pass filter is located after the modulator) can change signals from constant envelope to non-constant envelope, and non-constant envelope signals through non-linear device (a SSPA or TWT) can further spread the power spectra. Pre-modulation pulse shaping (a filter is located before the modulator) will have constant envelope. These two pulse shaping methods have different effects on narrowing the bandwidth and producing bit errors. This report studied the effect of various pre-modulation pulse shaping filters with respect to bandwidth, spectral spikes and bit error rate. A pre-modulation pulse shaped 8-ary Phase Shift Keying (8PSK) modulation was used throughout the simulations. In addition to traditional pulse shaping filters, such as Bessel, Butterworth and Square Root Raised Cosine (SRRC), other kinds of filters or pulse waveforms were also studied in the pre-modulation pulse shaping method. Simulations were conducted by using the Signal Processing Worksystem (SPW) software package on HP workstations which simulated the power spectral density of pulse shaped 8-PSK signals, end to end system performance and bit error rates (BERS) as a function of Eb/No using pulse shaping in an AWGN channel. These results are compared with the post-modulation pulse shaped 8-PSK results. The simulations indicate traditional pulse shaping filters used in pre-modulation pulse shaping may produce narrower bandwidth, but with worse BER than those in post-modulation pulse shaping. Theory and simulations show pre- modulation pulse shaping could also produce discrete line power spectra (spikes) at regular frequency intervals. These spikes may cause interference with adjacent channel and reduce power efficiency. Some particular pulses (filters), such as trapezoid and pulses with different transits (such as weighted raised cosine transit) were found to reduce bandwidth and not generate spectral spikes. Although a solid state power amplifier (SSPA) was simulated in the non-linear (saturation) region, output power spectra did not spread due to the constant envelope 8-PSK signals.

Maximum likelihood methods for investigating reporting rates of rings on hunter-shot birds

USGS Publications Warehouse

Conroy, M.J.; Morgan, B.J.T.; North, P.M.

1985-01-01

It is well known that hunters do not report 100% of the rings that they find on shot birds. Reward studies can be used to estimate what this reporting rate is, by comparison of recoveries of rings offering a monetary reward, to ordinary rings. A reward study of American Black Ducks (Anas rubripes) is used to illustrate the design, and to motivate the development of statistical models for estimation and for testing hypotheses of temporal and geographic variation in reporting rates. The method involves indexing the data (recoveries) and parameters (reporting, harvest, and solicitation rates) by geographic and temporal strata. Estimates are obtained under unconstrained (e.g., allowing temporal variability in reporting rates) and constrained (e.g., constant reporting rates) models, and hypotheses are tested by likelihood ratio. A FORTRAN program, available from the author, is used to perform the computations.

Directional solidification processing of alloys using an applied electric field

NASA Technical Reports Server (NTRS)

McKannan, Eugene C. (Inventor); Schmidt, Deborah D. (Inventor); Ahmed, Shaffiq (Inventor); Bond, Robert W. (Inventor)

1992-01-01

A method is provided for obtaining an alloy having an ordered microstructure which comprises the steps of heating the central portion of the alloy under uniform temperature so that it enters a liquid phase while the outer portions remain solid, applying a constant electric current through the alloy during the heating step, and solidifying the liquid central portion of the alloy by subjecting it to a temperature-gradient zone so that cooling occurs in a directional manner and at a given rate of speed while maintaining the application of the constant electric current through the alloy. The method is particularly suitable for use with nickel-based superalloys. The method of the present invention produces an alloy having superior characteristics such as reduced segregation. After subsequent precipitation by heat-treatment, the alloys produced by the present invention will have excellent strength and high-temperature resistance.

Singlet Oxygen Reactions with Flavonoids. A Theoretical – Experimental Study

PubMed Central

Morales, Javier; Günther, Germán; Zanocco, Antonio L.; Lemp, Else

2012-01-01

Detection of singlet oxygen emission, λmax = 1270 nm, following laser excitation and steady-state methods were employed to measure the total reaction rate constant, kT, and the reactive reaction rate constant, kr, for the reaction between singlet oxygen and several flavonoids. Values of kT determined in deuterated water, ranging from 2.4×107 M−1s−1 to 13.4×107 M−1s−1, for rutin and morin, respectively, and the values measured for kr, ranging from 2.8×105 M−1s−1 to 65.7×105 M−1s−1 for kaempferol and morin, respectively, being epicatechin and catechin chemically unreactive. These results indicate that all the studied flavonoids are good quenchers of singlet oxygen and could be valuable antioxidants in systems under oxidative stress, in particular if a flavonoid-rich diet was previously consumed. Analysis of the dependence of rate constant values with molecular structure in terms of global descriptors and condensed Fukui functions, resulting from electronic structure calculations, supports the formation of a charge transfer exciplex in all studied reactions. The fraction of exciplex giving reaction products evolves through a hydroperoxide and/or an endoperoxide intermediate produced by singlet oxygen attack on the double bond of the ring C of the flavonoid. PMID:22802966

Effects of Water Molecule on CO Oxidation by OH: Reaction Pathways, Kinetic Barriers, and Rate Constants.

PubMed

Zhang, Linyao; Yang, Li; Zhao, Yijun; Zhang, Jiaxu; Feng, Dongdong; Sun, Shaozeng

2017-07-06

The water dilute oxy-fuel combustion is a clean combustion technology for near-zero emission power; and the presence of water molecule could have both kinetic and dynamic effects on combustion reactions. The reaction OH + CO → CO 2 + H, one of the most important elementary reactions, has been investigated by extensive electronic structure calculations. And the effects of a single water molecule on CO oxidation have been studied by considering the preformed OH(H 2 O) complex reacts with CO. The results show little change in the reaction pathways, but the additional water molecule actually increases the vibrationally adiabatic energy barriers (V a G ). Further thermal rate constant calculations in the temperature range of 200 to 2000 K demonstrate that the total low-pressure limit rate constant for the water assisted OH(H 2 O) + CO → CO 2 + H 2 O + H reaction is 1-2 orders lower than that of the water unassisted one, which is consistent with the change of V a G . Therefore, the hydrated radical OH(H 2 O) would actually slow down the oxidation of CO. Meanwhile, comparisons show that the M06-2X/aug-cc-pVDZ method gives a much better estimation in energy and thus is recommended to be employed for direct dynamics simulations.

Singlet oxygen reactions with flavonoids. A theoretical-experimental study.

PubMed

Morales, Javier; Günther, Germán; Zanocco, Antonio L; Lemp, Else

2012-01-01

Detection of singlet oxygen emission, λ(max) = 1270 nm, following laser excitation and steady-state methods were employed to measure the total reaction rate constant, k(T), and the reactive reaction rate constant, k(r), for the reaction between singlet oxygen and several flavonoids. Values of k(T) determined in deuterated water, ranging from 2.4×10(7) M(-1) s(-1) to 13.4×10(7) M(-1) s(-1), for rutin and morin, respectively, and the values measured for k(r), ranging from 2.8×10(5) M(-1) s(-1) to 65.7×10(5) M(-1) s(-1) for kaempferol and morin, respectively, being epicatechin and catechin chemically unreactive. These results indicate that all the studied flavonoids are good quenchers of singlet oxygen and could be valuable antioxidants in systems under oxidative stress, in particular if a flavonoid-rich diet was previously consumed. Analysis of the dependence of rate constant values with molecular structure in terms of global descriptors and condensed Fukui functions, resulting from electronic structure calculations, supports the formation of a charge transfer exciplex in all studied reactions. The fraction of exciplex giving reaction products evolves through a hydroperoxide and/or an endoperoxide intermediate produced by singlet oxygen attack on the double bond of the ring C of the flavonoid.

Effects of packaging and heat transfer kinetics on drug-product stability during storage under uncontrolled temperature conditions.

PubMed

Nakamura, Toru; Yamaji, Takayuki; Takayama, Kozo

2013-05-01

To predict the stability of pharmaceutical preparations under uncontrolled temperature conditions accurately, a method to compute the average reaction rate constant taking into account the heat transfer from the atmosphere to the product was developed. The average reaction rate constants computed with taken into consideration heat transfer (κ(re) ) were then compared with those computed without taking heat transfer into consideration (κ(in) ). The apparent thermal diffusivity (κ(a) ) exerted some influence on the average reaction rate constant ratio (R, R = κ(re) /κ(in) ). In the regions where the κ(a) was large (above 1 h(-1) ) or very small, the value of R was close to 1. On the contrary, in the middle region (0.001-1 h(-1) ), the value of R was less than 1.The κ(a) of the central part of a large-size container and that of the central part of a paper case of 10 bottles of liquid medicine (100 mL) fell within this middle region. On the basis of the above-mentioned considerations, heat transfer may need to be taken into consideration to enable a more accurate prediction of the stability of actual pharmaceutical preparations under nonisothermal atmospheres. Copyright © 2013 Wiley Periodicals, Inc.

3-methylcyclohexanone thiosemicarbazone: determination of E/Z isomerization barrier by dynamic high-performance liquid chromatography, configuration assignment and theoretical study of the mechanisms involved by the spontaneous, acid and base catalyzed processes.

PubMed

Carradori, Simone; Cirilli, Roberto; Dei Cicchi, Simona; Ferretti, Rosella; Menta, Sergio; Pierini, Marco; Secci, Daniela

2012-12-21

Here, we report on the simultaneous direct HPLC diastereo- and enantioseparation of 3-methylcyclohexanone thiosemicarbazone (3-MCET) on a polysaccharide-based chiral stationary phase under normal-phase conditions. The optimized chromatographic system was employed in dynamic HPLC experiments (DHPLC), as well as detection technique in a batch wise approach to determine the rate constants and the corresponding free energy activation barriers of the spontaneous, base- and acid-promoted E/Z diastereomerization of 3-MCET. The stereochemical characterization of four stereoisomers of 3-MCET was fully accomplished by integrating the results obtained by chemical correlation method with those derived by theoretical calculations and experimental investigations of circular dichroism (CD). As a final goal, a deepened analysis of the perturbing effect exercised by the stationary phase on rate constant values measured through DHPLC determinations as a function of the chromatographic separation factor α of the interconverting species was successfully accomplished. This revealed quite small deviations from the equivalent kinetic values obtained by off-column batch wise procedure, and suggested a possible effective correction of rate constants measured by DHPLC approach. Copyright © 2012 Elsevier B.V. All rights reserved.

A mechanistic approach on the self-organization of the two-component thermoreversible hydrogel of riboflavin and melamine.

PubMed

Saha, Abhijit; Manna, Swarup; Nandi, Arun K

2007-12-18

The riboflavin (R) and melamine (M) supramolecular complex in the mole ratio of 3:1 (RM31) produces a thermoreversible gel in aqueous medium. The gelation mechanism has been elucidated from morphological investigations using optical, electron, and atomic force microscopy together with time-dependent circular dichroism (CD) and photoluminescence (PL) spectroscopy. Optical microscopy indicates spherulitic morphology at lower gelation temperature (

Test Standard Developed for Determining the Slow Crack Growth of Advanced Ceramics at Ambient Temperature

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Salem, Jonathan A.

1998-01-01

The service life of structural ceramic components is often limited by the process of slow crack growth. Therefore, it is important to develop an appropriate testing methodology for accurately determining the slow crack growth design parameters necessary for component life prediction. In addition, an appropriate test methodology can be used to determine the influences of component processing variables and composition on the slow crack growth and strength behavior of newly developed materials, thus allowing the component process to be tailored and optimized to specific needs. At the NASA Lewis Research Center, work to develop a standard test method to determine the slow crack growth parameters of advanced ceramics was initiated by the authors in early 1994 in the C 28 (Advanced Ceramics) committee of the American Society for Testing and Materials (ASTM). After about 2 years of required balloting, the draft written by the authors was approved and established as a new ASTM test standard: ASTM C 1368-97, Standard Test Method for Determination of Slow Crack Growth Parameters of Advanced Ceramics by Constant Stress-Rate Flexural Testing at Ambient Temperature. Briefly, the test method uses constant stress-rate testing to determine strengths as a function of stress rate at ambient temperature. Strengths are measured in a routine manner at four or more stress rates by applying constant displacement or loading rates. The slow crack growth parameters required for design are then estimated from a relationship between strength and stress rate. This new standard will be published in the Annual Book of ASTM Standards, Vol. 15.01, in 1998. Currently, a companion draft ASTM standard for determination of the slow crack growth parameters of advanced ceramics at elevated temperatures is being prepared by the authors and will be presented to the committee by the middle of 1998. Consequently, Lewis will maintain an active leadership role in advanced ceramics standardization within ASTM. In addition, the authors have been and are involved with several international standardization organizations including the Versailles Project on Advanced Materials and Standards (VAMAS), the International Energy Agency (IEA), and the International Organization for Standardization (ISO). The associated standardization activities involve fracture toughness, strength, elastic modulus, and the machining of advanced ceramics.

The Original Michaelis Constant: Translation of the 1913 Michaelis-Menten Paper

PubMed Central

Johnson, Kenneth A.; Goody, Roger S.

2011-01-01

Nearly 100 years ago Michaelis and Menten published their now classic paper (Michaelis, L., and Menten, M. L. (1913) Die Kinetik der Invertinwirkung, Biochemische Zeitschrift 49, 333–369), in which they show that the rate of an enzyme-catalyzed reaction is proportional to the concentration of enzyme-substrate complex predicted by the Michaelis-Menten equation. Because the original text was written in German, yet is often quoted by English speaking authors, we undertook a complete translation of the 1913 publication, which we provide as an online supplement (http://pubs.acs.org). Here we introduce the translation, describe the historical context of the work, and show a new analysis of the original data. In doing so, we uncovered several surprises that reveal an interesting glimpse into the early history of enzymology. In particular, our re-analysis of Michaelis and Menten’s data using modern computational methods revealed an unanticipated rigor and precision in the original publication and uncovered a sophisticated, comprehensive analysis that has been overlooked in the century since their work was published. Michaelis and Menten not only analyzed initial velocity measurements, but they also fit their full time course data to the integrated form of the rate equations, including product inhibition, and derived a single global constant to represent all of their data. That constant was not the Michaelis constant, but rather, Vmax/Km, the specificity constant times the enzyme concentration (kcat/Km*E0). PMID:21888353

METHOD OF MAKING DELTA ZIRCONIUM HYDRIDE MONOLITHIC MODERATOR PIECES

DOEpatents

Vetrano, J.B.

1962-01-23

A method is given for preparing large, sound bodies of delta zirconium hydride. The method includes the steps of heating a zirconium body to a temperature of not less than l000 deg C, providing a hydrogen atmosphere for the zirconium body at a pressure not greater than one atmosphere, reducing the temperature slowly to 800 deg C at such a rate that cracks do not form while maintaining the hydrogen pressure substantially constant, and cooling in an atmosphere of hydrogen. (AEC)

Apparatus and method for constant flow oxidizing of organic materials

DOEpatents

Surma, Jeffrey E.; Nelson, Norvell; Steward, G. Anthony; Bryan, Garry H.

1999-01-01

The invention is a method and apparatus using high cerium concentration in the anolyte of an electrochemical cell to oxidize organic materials. The method and apparatus further use an ultrasonic mixer to enhance the oxidation rate of the organic material in the electrochemical cell. A reaction vessel provides an advantage of independent reaction temperature control and electrochemical cell temperature control. A separate or independent reaction vessel may be used without an ultrasonic mixer to oxidize gaseous phase organic materials.

Probabilistic Determination of Green Infrastructure Pollutant Removal Rates from the International Stormwater BMP Database

NASA Astrophysics Data System (ADS)

Gilliom, R.; Hogue, T. S.; McCray, J. E.

2017-12-01

There is a need for improved parameterization of stormwater best management practices (BMP) performance estimates to improve modeling of urban hydrology, planning and design of green infrastructure projects, and water quality crediting for stormwater management. Percent removal is commonly used to estimate BMP pollutant removal efficiency, but there is general agreement that this approach has significant uncertainties and is easily affected by site-specific factors. Additionally, some fraction of monitored BMPs have negative percent removal, so it is important to understand the probability that a BMP will provide the desired water quality function versus exacerbating water quality problems. The widely used k-C* equation has shown to provide a more adaptable and accurate method to model BMP contaminant attenuation, and previous work has begun to evaluate the strengths and weaknesses of the k-C* method. However, no systematic method exists for obtaining first-order removal rate constants needed to use the k-C* equation for stormwater BMPs; thus there is minimal application of the method. The current research analyzes existing water quality data in the International Stormwater BMP Database to provide screening-level parameterization of the k-C* equation for selected BMP types and analysis of factors that skew the distribution of efficiency estimates from the database. Results illustrate that while certain BMPs are more likely to provide desired contaminant removal than others, site- and design-specific factors strongly influence performance. For example, bioretention systems show both the highest and lowest removal rates of dissolved copper, total phosphorous, and total nitrogen. Exploration and discussion of this and other findings will inform the application of the probabilistic pollutant removal rate constants. Though data limitations exist, this research will facilitate improved accuracy of BMP modeling and ultimately aid decision-making for stormwater quality management in urban systems.

Determination of the apparent transfer coefficient for CO oxidation on Pt(poly), Pt(111), Pt(665) and Pt(332) using a potential modulation technique.

PubMed

Wang, Han-Chun; Ernst, Siegfried; Baltruschat, Helmut

2010-03-07

The apparent transfer coefficient, which gives the magnitude of the potential dependence of the electrochemical reaction rates, is the key quantity for the elucidation of electrochemical reaction mechanisms. We introduce the application of an ac method to determine the apparent transfer coefficient alpha' for the oxidation of pre-adsorbed CO at polycrystalline and single-crystalline Pt electrodes in sulfuric acid. The method allows to record alpha' quasi continuously as a function of potential (and time) in cyclic voltammetry or at a fixed potential, with the reaction rate varying with time. At all surfaces (Pt(poly), Pt(111), Pt(665), and Pt(332)) we clearly observed a transition of the apparent transfer coefficient from values around 1.5 at low potentials to values around 0.5 at higher potentials. Changes of the apparent transfer coefficients for the CO oxidation with potential were observed previously, but only from around 0.7 to values as low as 0.2. In contrast, our experimental findings completely agree with the simulation by Koper et al., J. Chem. Phys., 1998, 109, 6051-6062. They can be understood in the framework of a Langmuir-Hinshelwood mechanism. The transition occurs when the sum of the rate constants for the forward reaction (first step: potential dependent OH adsorption, second step: potential dependent oxidation of CO(ad) with OH(ad)) exceeds the rate constant for the back-reaction of the first step. We expect that the ac method for the determination of the apparent transfer coefficient, which we used here, will be of great help also in many other cases, especially under steady conditions, where the major limitations of the method are avoided.

Novel operation and control of an electric vehicle aluminum/air battery system

NASA Astrophysics Data System (ADS)

Zhang, Xin; Yang, Shao Hua; Knickle, Harold

The objective of this paper is to create a method to size battery subsystems for an electric vehicle to optimize battery performance. Optimization of performance includes minimizing corrosion by operating at a constant current density. These subsystems will allow for easy mechanical recharging. A proper choice of battery subsystem will allow for longer battery life, greater range and performance. For longer life, the current density and reaction rate should be nearly constant. The control method requires control of power by controlling electrolyte flow in battery sub modules. As power is increased more sub modules come on line and more electrolyte is needed. Solenoid valves open in a sequence to provide the required power. Corrosion is limited because there is no electrolyte in the modules not being used.

Gene delivery by microfluidic flow-through electroporation based on constant DC and AC field.

PubMed

Geng, Tao; Zhan, Yihong; Lu, Chang

2012-01-01

Electroporation is one of the most widely used physical methods to deliver exogenous nucleic acids into cells with high efficiency and low toxicity. Conventional electroporation systems typically require expensive pulse generators to provide short electrical pulses at high voltage. In this work, we demonstrate a flow-through electroporation method for continuous transfection of cells based on disposable chips, a syringe pump, and a low-cost power supply that provides a constant voltage. We successfully transfect cells using either DC or AC voltage with high flow rates (ranging from 40 µl/min to 20 ml/min) and high efficiency (up to 75%). We also enable the entire cell membrane to be uniformly permeabilized and dramatically improve gene delivery by inducing complex migrations of cells during the flow.

Solidification processing of alloys using an applied electric field

NASA Technical Reports Server (NTRS)

Mckannan, Eugene C. (Inventor); Schmidt, Deborah D. (Inventor); Ahmed, Shaffiq (Inventor); Bond, Robert W. (Inventor)

1990-01-01

A method is provided for obtaining an alloy having an ordered microstructure which comprises the steps of heating the central portion of the alloy under uniform temperature so that it enters a liquid phase while the outer portions remain solid, applying a constant electric current through the alloy during the heating step, and solidifying the liquid central portion of the alloy by subjecting it to a temperature-gradient zone so that cooling occurs in a directional manner and at a given rate of speed while maintaining the application of the constant electric current through the alloy. The method of the present invention produces an alloy having superior characteristics such as reduced segregation. After subsequent precipitation by heat-treatment, the alloys produced by the present invention will have excellent strength and high-temperature resistance.

Material characterization of structural adhesives in the lap shear mode

NASA Technical Reports Server (NTRS)

Sancaktar, E.; Schenck, S. C.

1983-01-01

A general method for characterizing structual adhesives in the bonded lap shear mode is proposed. Two approaches in the form of semiempirical and theoretical approaches are used. The semiempirical approach includes Ludwik's and Zhurkov's equations to describe respectively, the failure stresses in the constant strain rate and constant stress loading modes with the inclusion of the temperature effects. The theoretical approach is used to describe adhesive shear stress-strain behavior with the use of viscoelastic or nonlinear elastic constitutive equations. Two different model adhesives are used in the single lap shear mode with titanium adherends. These adhesives (one of which was developed at NASA Langley Research Center) are currently considered by NASA for possible aerospace applications. Use of different model adhesives helps in assessment of the generality of the method.

High-current-density electrodeposition using pulsed and constant currents to produce thick CoPt magnetic films on silicon substrates

NASA Astrophysics Data System (ADS)

Ewing, Jacob; Wang, Yuzheng; Arnold, David P.

2018-05-01

This paper investigates methods for electroplating thick (>20 μm), high-coercivity CoPt films using high current densities (up to 1 A/cm2) and elevated bath temperatures (70 °C). Correlations are made tying current-density and temperature process parameters with plating rate, elemental ratio and magnetic properties of the deposited CoPt films. It also investigates how pulsed currents can increase the plating rate and film to substrate adhesion. Using 500 mA/cm2 and constant current, high-quality, dense CoPt films were successfully electroplated up to 20 μm thick in 1 hr on silicon substrates (0.35 μm/min plating rate). After standard thermal treatment (675°C, 30 min) to achieve the ordered L10 crystalline phase, strong magnetic properties were measured: coercivities up 850 kA/m, remanences >0.5 T, and maximum energy products up to 46 kJ/m3.

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

Solvent Assisted Delamination Crack Growth Behavior of Amorphous Thermoplastic Materials

DTIC Science & Technology

1989-02-01

72CRD285. October 1972. 4. Standard Method of Test for Plane- Strain Fracture Toughness of Metallic Materials. 1988 Annual Book of ASTM Standards, Technical...intensity factor K I or the associated strain energy release rate, G I . ASTM compact tension test yields stress intensity factor, KI, via Equation 1...are such that a constant deadweight load results in increasing strain energy release rate with increasing crack length. Figure 3 shows the neat resin

Electromagnetic Metrics of Mental Workload.

DTIC Science & Technology

1987-09-01

anxiety ). A decrease in performance accuracy has been used in the context of over- load, however it has also been associated with a "high workload". 1.2...heart rate variability ( HRV ) to refer to any varia- tion from a constant heart rate. The term HRV shall not refer to any specific method of numerically...in using HRV as a measure of mental load arose after Kalsbeek & Ettema (1963) reported that HRV was "gradu- ally suppressed when increasing the

Kinetics and mechanism of hydroxyapatite crystal dissolution in weak acid buffers using the rotating disk method.

PubMed

Wu, M S; Higuchi, W I; Fox, J L; Friedman, M

1976-01-01

The model given in this report and the rotating disk method provide a useful combination in the study of dental enamel and hydroxyapatite dissolution kinetics. The present approach is a significant improvement over earlier studies, and both the ionic activity product that governs the dissolution reaction and the apparent surface dissolution reaction rate constant may be simultaneously obtained. Thus, these investigations have established the baseline for the dissolution rate studies under sink conditions. Concurrent studies, under conditions where the acidic buffer mediums are partially saturated with respect to hydroxyapatite have shown another dissolution site for hydroxyapatite that operates at a higher ionic activity product but has a much smaller apparent surface reaction rate constant. This has raised the question of whether the presence of this second site may interfere with the proper theoretical analysis of the experimental results obtained under sink conditions. A preliminary analysis of the two-site model has shown that the dissolution kinetics of hydroxyapatite under sink conditions is almost completely governed by the sink condition site (KHAP = 10(-124.5), k' = 174) established in this report. The difference between the predicted dissolution rate for the one-site model and the two-site model are generally of the order of 4 to 5% where the experiments are conducted under sink conditions and over the range of variables covered in the present study.

(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

Scalable video transmission over Rayleigh fading channels using LDPC codes

NASA Astrophysics Data System (ADS)

Bansal, Manu; Kondi, Lisimachos P.

2005-03-01

In this paper, we investigate an important problem of efficiently utilizing the available resources for video transmission over wireless channels while maintaining a good decoded video quality and resilience to channel impairments. Our system consists of the video codec based on 3-D set partitioning in hierarchical trees (3-D SPIHT) algorithm and employs two different schemes using low-density parity check (LDPC) codes for channel error protection. The first method uses the serial concatenation of the constant-rate LDPC code and rate-compatible punctured convolutional (RCPC) codes. Cyclic redundancy check (CRC) is used to detect transmission errors. In the other scheme, we use the product code structure consisting of a constant rate LDPC/CRC code across the rows of the `blocks' of source data and an erasure-correction systematic Reed-Solomon (RS) code as the column code. In both the schemes introduced here, we use fixed-length source packets protected with unequal forward error correction coding ensuring a strictly decreasing protection across the bitstream. A Rayleigh flat-fading channel with additive white Gaussian noise (AWGN) is modeled for the transmission. The rate-distortion optimization algorithm is developed and carried out for the selection of source coding and channel coding rates using Lagrangian optimization. The experimental results demonstrate the effectiveness of this system under different wireless channel conditions and both the proposed methods (LDPC+RCPC/CRC and RS+LDPC/CRC) outperform the more conventional schemes such as those employing RCPC/CRC.

Four-dimensional dose distributions of step-and-shoot IMRT delivered with real-time tumor tracking for patients with irregular breathing: Constant dose rate vs dose rate regulation

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

Yang Xiaocheng; Han-Oh, Sarah; Gui Minzhi

2012-09-15

Purpose: Dose-rate-regulated tracking (DRRT) is a tumor tracking strategy that programs the MLC to track the tumor under regular breathing and adapts to breathing irregularities during delivery using dose rate regulation. Constant-dose-rate tracking (CDRT) is a strategy that dynamically repositions the beam to account for intrafractional 3D target motion according to real-time information of target location obtained from an independent position monitoring system. The purpose of this study is to illustrate the differences in the effectiveness and delivery accuracy between these two tracking methods in the presence of breathing irregularities. Methods: Step-and-shoot IMRT plans optimized at a reference phase weremore » extended to remaining phases to generate 10-phased 4D-IMRT plans using segment aperture morphing (SAM) algorithm, where both tumor displacement and deformation were considered. A SAM-based 4D plan has been demonstrated to provide better plan quality than plans not considering target deformation. However, delivering such a plan requires preprogramming of the MLC aperture sequence. Deliveries of the 4D plans using DRRT and CDRT tracking approaches were simulated assuming the breathing period is either shorter or longer than the planning day, for 4 IMRT cases: two lung and two pancreatic cases with maximum GTV centroid motion greater than 1 cm were selected. In DRRT, dose rate was regulated to speed up or slow down delivery as needed such that each planned segment is delivered at the planned breathing phase. In CDRT, MLC is separately controlled to follow the tumor motion, but dose rate was kept constant. In addition to breathing period change, effect of breathing amplitude variation on target and critical tissue dose distribution is also evaluated. Results: Delivery of preprogrammed 4D plans by the CDRT method resulted in an average of 5% increase in target dose and noticeable increase in organs at risk (OAR) dose when patient breathing is either 10% faster or slower than the planning day. In contrast, DRRT method showed less than 1% reduction in target dose and no noticeable change in OAR dose under the same breathing period irregularities. When {+-}20% variation of target motion amplitude was present as breathing irregularity, the two delivery methods show compatible plan quality if the dose distribution of CDRT delivery is renormalized. Conclusions: Delivery of 4D-IMRT treatment plans, stemmed from 3D step-and-shoot IMRT and preprogrammed using SAM algorithm, is simulated for two dynamic MLC-based real-time tumor tracking strategies: with and without dose-rate regulation. Comparison of cumulative dose distribution indicates that the preprogrammed 4D plan is more accurately and efficiently conformed using the DRRT strategy, as it compensates the interplay between patient breathing irregularity and tracking delivery without compromising the segment-weight modulation.« less

Calcification responses to diurnal variation in seawater carbonate chemistry by the coral Acropora formosa

NASA Astrophysics Data System (ADS)

Chan, W. Y.; Eggins, S. M.

2017-09-01

Significant diurnal variation in seawater carbonate chemistry occurs naturally in many coral reef environments, yet little is known of its effect on coral calcification. Laboratory studies on the response of corals to ocean acidification have manipulated the carbonate chemistry of experimental seawater to compare calcification rate changes under present-day and predicted future mean pH/Ωarag conditions. These experiments, however, have focused exclusively on differences in mean chemistry and have not considered diurnal variation. The aim of this study was to compare calcification responses of branching coral Acropora formosa under conditions with and without diurnal variation in seawater carbonate chemistry. To achieve this aim, we explored (1) a method to recreate natural diurnal variation in a laboratory experiment using the biological activities of a coral-reef mesocosm, and (2) a multi-laser 3D scanning method to accurately measure coral surface areas, essential to normalize their calcification rates. We present a cost- and time-efficient method of coral surface area estimation that is reproducible within 2% of the mean of triplicate measurements. Calcification rates were compared among corals subjected to a diurnal range in pH (total scale) from 7.8 to 8.2, relative to those at constant pH values of 7.8, 8.0 or 8.2. Mean calcification rates of the corals at the pH 7.8-8.2 (diurnal variation) treatment were not statistically different from the pH 8.2 treatment and were 34% higher than the pH 8.0 treatment despite similar mean seawater pH and Ωarag. Our results suggest that calcification of adult coral colonies may benefit from diurnal variation in seawater carbonate chemistry. Experiments that compare calcification rates at different constant pH without considering diurnal variation may have limitations.

THE UNIQUE VALUE OF BREATH BIOMARKERS FOR ESTIMATING PHAMACOKINETIC RATE CONSTANTS AND BODY BURDEN FROM RANDOM/INTERMITTENT DOSE

EPA Science Inventory

Biomarker measurements are used in three ways: 1) evaluating the time course and distribution of a chemical in the body, 2) estimating previous exposure or dose, and 3) assessing disease state. Blood and urine measurements are the primary methods employed. Of late, it has been ...

Treatment of Electronic Energy Level Transition and Ionization Following the Particle-Based Chemistry Model

NASA Technical Reports Server (NTRS)

Liechty, Derek S.; Lewis, Mark

2010-01-01

A new method of treating electronic energy level transitions as well as linking ionization to electronic energy levels is proposed following the particle-based chemistry model of Bird. Although the use of electronic energy levels and ionization reactions in DSMC are not new ideas, the current method of selecting what level to transition to, how to reproduce transition rates, and the linking of the electronic energy levels to ionization are, to the author s knowledge, novel concepts. The resulting equilibrium temperatures are shown to remain constant, and the electronic energy level distributions are shown to reproduce the Boltzmann distribution. The electronic energy level transition rates and ionization rates due to electron impacts are shown to reproduce theoretical and measured rates. The rates due to heavy particle impacts, while not as favorable as the electron impact rates, compare favorably to values from the literature. Thus, these new extensions to the particle-based chemistry model of Bird provide an accurate method for predicting electronic energy level transition and ionization rates in gases.

EVALUATION OF FREEZE DRIED ALOE VERA AND NOPAL CACTUS FOR POSSIBLE HEALTH TREATMENTS BY COMPARISON OF ANTIOXIDANT PROPERTIES AND FREE RADICAL INHIBITION.

PubMed

Rodriguez, Kenneth R; Jones, Anthony E; Belmont, Barbara

2014-01-01

The goal of this project was to characterize the antioxidant powers of lyophilized Aloe Vera ( Aloe barbadensis ) and Nopal Cactus (Opuntia ficus-indica) by quantifying the phenolics content and radical scavenging abilities of preparations derived from these plants. Extracts of these lyophylized succulents were assayed for phenolic compounds by the Folin Ciocalteau method and compared for free radical scavenging capability by the DPPH method. We found that even though the Aloe lyophilizate extract contained more phenolic content, the Nopal lyophilizate exhibited better free radical scavenging ability. Aloe Vera extract contained 0.278 g/L of phenolic content and exhibited 11.1% free radical inhibition, with a free radical scavenging rate constant of 0.177±0.015 min -1 . Nopal Cactus extract contained 0.174 g/L of phenolic content and exhibited 13.2% free radical inhibition, with a free radical scavenging rate constant of 0.155±0.009 min -1 . These results showed Nopal to have greater antioxidant potency than Aloe.

Automated Method for Estimating Nutation Time Constant Model Parameters for Spacecraft Spinning on Axis

NASA Technical Reports Server (NTRS)

2008-01-01

Calculating an accurate nutation time constant (NTC), or nutation rate of growth, for a spinning upper stage is important for ensuring mission success. Spacecraft nutation, or wobble, is caused by energy dissipation anywhere in the system. Propellant slosh in the spacecraft fuel tanks is the primary source for this dissipation and, if it is in a state of resonance, the NTC can become short enough to violate mission constraints. The Spinning Slosh Test Rig (SSTR) is a forced-motion spin table where fluid dynamic effects in full-scale fuel tanks can be tested in order to obtain key parameters used to calculate the NTC. We accomplish this by independently varying nutation frequency versus the spin rate and measuring force and torque responses on the tank. This method was used to predict parameters for the Genesis, Contour, and Stereo missions, whose tanks were mounted outboard from the spin axis. These parameters are incorporated into a mathematical model that uses mechanical analogs, such as pendulums and rotors, to simulate the force and torque resonances associated with fluid slosh.

EVALUATION OF FREEZE DRIED ALOE VERA AND NOPAL CACTUS FOR POSSIBLE HEALTH TREATMENTS BY COMPARISON OF ANTIOXIDANT PROPERTIES AND FREE RADICAL INHIBITION

PubMed Central

Jones, Anthony E.; Belmont, Barbara

2016-01-01

The goal of this project was to characterize the antioxidant powers of lyophilized Aloe Vera (Aloe barbadensis) and Nopal Cactus (Opuntia ficus-indica) by quantifying the phenolics content and radical scavenging abilities of preparations derived from these plants. Extracts of these lyophylized succulents were assayed for phenolic compounds by the Folin Ciocalteau method and compared for free radical scavenging capability by the DPPH method. We found that even though the Aloe lyophilizate extract contained more phenolic content, the Nopal lyophilizate exhibited better free radical scavenging ability. Aloe Vera extract contained 0.278 g/L of phenolic content and exhibited 11.1% free radical inhibition, with a free radical scavenging rate constant of 0.177±0.015 min−1. Nopal Cactus extract contained 0.174 g/L of phenolic content and exhibited 13.2% free radical inhibition, with a free radical scavenging rate constant of 0.155±0.009 min−1. These results showed Nopal to have greater antioxidant potency than Aloe. PMID:27284273

Method and apparatus for combinatorial logic signal processor in a digitally based high speed x-ray spectrometer

DOEpatents

Warburton, W.K.

1999-02-16

A high speed, digitally based, signal processing system is disclosed which accepts a digitized input signal and detects the presence of step-like pulses in the this data stream, extracts filtered estimates of their amplitudes, inspects for pulse pileup, and records input pulse rates and system lifetime. The system has two parallel processing channels: a slow channel, which filters the data stream with a long time constant trapezoidal filter for good energy resolution; and a fast channel which filters the data stream with a short time constant trapezoidal filter, detects pulses, inspects for pileups, and captures peak values from the slow channel for good events. The presence of a simple digital interface allows the system to be easily integrated with a digital processor to produce accurate spectra at high count rates and allow all spectrometer functions to be fully automated. Because the method is digitally based, it allows pulses to be binned based on time related values, as well as on their amplitudes, if desired. 31 figs.

Method for determining thermal conductivity and thermal capacity per unit volume of earth in situ

DOEpatents

Poppendiek, Heinz F.

1982-01-01

A method for determining the thermal conductivity of the earth in situ is based upon a cylindrical probe (10) having a thermopile (16) for measuring the temperature gradient between sets of thermocouple junctions (18 and 20) of the probe after it has been positioned in a borehole and has reached thermal equilibrium with its surroundings, and having means (14) for heating one set of thermocouple junctions (20) of the probe at a constant rate while the temperature gradient of the probe is recorded as a rise in temperature over several hours (more than about 3 hours). A fluid annulus thermally couples the probe to the surrounding earth. The recorded temperature curves are related to the earth's thermal conductivity, k.sub..infin., and to the thermal capacity per unit volume, (.gamma.c.sub.p).sub..infin., by comparison with calculated curves using estimates of k.sub..infin. and (.gamma.c.sub.p).sub..infin. in an equation which relates these parameters to a rise in the earth's temperature for a known and constant heating rate.

TB3 - Measurement of vibrational-vibrational exchange of highly excited states of diatomic molecules where the collisional probability is approaching unity

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

Nachshon, Y.; Coleman, P.

1975-08-01

An experimental method, employing a fast population perturbation technique, is described to measure the vibrational-vibrational (VV) collisional probability P/sub r,r-1/sup/v,v+1/ of a diatomic molecule for large vibrational quantum numbers r and v. The relaxation of the perturbed gain of a pair of vibrational levels is a function of the vibrational populations and VV rate constants k/sub r,r-1/sup v,v+1/. The numerical inversion of the VV master rate equations determining this relaxation does not give unique value for k/sub r,r-1/ sup v,v+1/ (or P/sub r,r-1/sup v,v+1), but lower bounds can be evaluated and with empirical formulas, having several adjustable constants, it canmore » be shown that probabilities of the order of unity are required to satisfy the experimental data. The method has been specifically applied to the CO molecule, but other molecules such as HX(X = F, Cl, Br), NO, etc., could also be measured.« less

Regularized learning of linear ordered-statistic constant false alarm rate filters (Conference Presentation)

NASA Astrophysics Data System (ADS)

Havens, Timothy C.; Cummings, Ian; Botts, Jonathan; Summers, Jason E.

2017-05-01

The linear ordered statistic (LOS) is a parameterized ordered statistic (OS) that is a weighted average of a rank-ordered sample. LOS operators are useful generalizations of aggregation as they can represent any linear aggregation, from minimum to maximum, including conventional aggregations, such as mean and median. In the fuzzy logic field, these aggregations are called ordered weighted averages (OWAs). Here, we present a method for learning LOS operators from training data, viz., data for which you know the output of the desired LOS. We then extend the learning process with regularization, such that a lower complexity or sparse LOS can be learned. Hence, we discuss what 'lower complexity' means in this context and how to represent that in the optimization procedure. Finally, we apply our learning methods to the well-known constant-false-alarm-rate (CFAR) detection problem, specifically for the case of background levels modeled by long-tailed distributions, such as the K-distribution. These backgrounds arise in several pertinent imaging problems, including the modeling of clutter in synthetic aperture radar and sonar (SAR and SAS) and in wireless communications.

Photocatalytic degradation of an azo textile dye (C.I. Reactive Red 195 (3BF)) in aqueous solution over copper cobaltite nanocomposite coated on glass by Doctor Blade method

NASA Astrophysics Data System (ADS)

Habibi, Mohammad Hossein; Rezvani, Zoya

2015-08-01

The degradation of C.I. Reactive Red 195 (3BF) in aqueous solution using copper cobaltite nanocomposite coated on glass by Doctor Blade method was studied. Structural, optical and morphological properties of nanocomposite coatings were characterized by X-ray powder diffractometry (XRD), diffuse reflectance spectroscopy (DRS) and field emission scanning electron microscopy (FESEM). The nanoparticles exhibit a particle size of 31 nm, showing a good nanoscale crystalline morphology. The photocatalytic activity of copper cobaltite nanocomposite coated on glass was studied by performing the photocatalytic degradation of 3BF at different irradiation time. The effect of irradiation time on the degradation of 3BF was studied and the results showed that more than 85% of the 3BF was degraded in 45 min of irradiation. The pseudo-first-order kinetic models were used and the rate constants were evaluated with pseudo first order rate constants of 4.10 × 10-2 min-1. The main advantage of the photocatalyst coated on glass overcomes the difficulties in separation and recycle of photocatalyst suspensions.

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.

Synthesis, characterization and sonocatalytic applications of nano-structured carbon based TiO2 catalysts.

PubMed

Choi, Jongbok; Cui, Mingcan; Lee, Yonghyeon; Kim, Jeonggwan; Yoon, Yeomin; Jang, Min; Khim, Jeehyeong

2018-05-01

In order to enhance sonocatalytic oxidation of a recalcitrant organic pollutant, rhodamine B (RhB), it is necessary to study the fundamental aspects of sonocatalysis. In this study, TiO 2 -incorporated nano-structured carbon (i.e., carbon nanotubes (CNTs) or graphene (GR)) composites were synthesized by coating TiO 2 on CNTs or GR of different mass percentages (0.5, 1, 5, and 10 wt%) by a facile hydrothermal method. The sonocatalytic degradation rates of RhB were examined for the effect of ultrasound (US) frequency and calcination temperature by using the prepared TiO 2 -NSC composites. Since US frequency affected the sonoluminescence (SL) intensities, it was proposed that there exists a correlation between the surface area or band-gap of the sonocatalysts and the degradation kinetic constants of RhB. In addition, the reusability of TiO 2 -GR composites was also investigated. Overall, the performance of TiO 2 -GRs prepared by the hydrothermal method was better than that of calcined TiO 2 -CNTs. Among TiO 2 -GRs, 5% GR incorporated media (TiO 2 -GR-5) showed the best performance. Interestingly, the kinetic constants of sonocatalysts prepared under hydrothermal conditions had a negative linear relationship with the band-gap energy for the corresponding media. Furthermore, the strongest SL intensity and highest degradation rates of RhB for both carbonaceous composites were observed at 500 kHz. The kinetic constants of calcined media decreased linearly as the specific area of the media decreased, while the band-gap energy could not be correlated with the kinetic constants. The GR combined TiO 2 composite might be a good sonocatalyst in wastewater treatment using ultrasound-based oxidation because of its high stability. Copyright © 2018 Elsevier B.V. All rights reserved.

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.

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.

Examining (239+240)Pu, (210)Pb and historical events to determine carbon, nitrogen and phosphorus burial in mangrove sediments of Moreton Bay, Australia.

PubMed

Sanders, Christian J; Santos, Isaac R; Maher, Damien T; Breithaupt, Joshua L; Smoak, Joseph M; Ketterer, Michael; Call, Mitchell; Sanders, Luciana; Eyre, Bradley D

2016-01-01

Two sediment cores were collected in a mangrove forest to construct geochronologies for the previous century using natural and anthropogenic radionuclide tracers. Both sediment cores were dated using (239+240)Pu global fallout signatures as well as (210)Pb, applying both the Constant Initial Concentration (CIC) and the Constant Rate of Supply (CRS) models. The (239+240)Pu and CIC model are interpreted as having comparable sediment accretion rates (SAR) below an apparent mixed region in the upper ∼5 to 10 cm. In contrast, the CRS dating method shows high sediment accretion rates in the uppermost intervals, which is substantially reduced over the lower intervals of the 100-year record. A local anthropogenic nutrient signal is reflected in the high total phosphorus (TP) concentration in younger sediments. The carbon/nitrogen molar ratios and δ(15)N values further support a local anthropogenic nutrient enrichment signal. The origin of these signals is likely the treated sewage discharge to Moreton Bay which began in the early 1970s. While the (239+240)Pu and CIC models can only produce rates averaged over the intervals of interest within the profile, the (210)Pb CRS model identifies elevated rates of sediment accretion, organic carbon (OC), nitrogen (N), and TP burial from 2000 to 2013. From 1920 to 2000, the three dating methods provide similar OC, N and TP burial rates, ∼150, 10 and 2 g m(-2) year(-1), respectively, which are comparable to global averages. Copyright © 2015 Elsevier Ltd. All rights reserved.

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

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.

A model for the kinetics of a solar-pumped long path laser experiment

NASA Technical Reports Server (NTRS)

Stock, L. V.; Wilson, J. W.; Deyoung, R. J.

1986-01-01

A kinetic model for a solar-simulator pumped iodine laser system is developed and compared to an experiment in which the solar simulator output is dispersed over a large active volume (150 cu cm) with low simulator light intensity (approx. 200 solar constants). A trace foreign gas which quenches the upper level is introduced into the model. Furthermore, a constant representing optical absorption of the stimulated emission is introduced, in addition to a constant representing the scattering at each of the mirrors, via the optical cavity time constant. The non-uniform heating of the gas is treated as well as the pressure change as a function of time within the cavity. With these new phenomena introduced into the kinetic model, a best reasonable fit to the experimental data is found by adjusting the reaction rate coefficients within the range of known uncertainty by numerical methods giving a new bound within this range of uncertainty. The experimental parameters modeled are the lasing time, laser pulse energy, and time to laser threshold.

H0, q0 and the local velocity field. [Hubble and deceleration constants in Big Bang expansion

NASA Technical Reports Server (NTRS)

Sandage, A.; Tammann, G. A.

1982-01-01

An attempt is made to find a systematic deviation from linearity for distances that are under the control of the Virgo cluster, and to determine the value of the mean random motion about the systematic flow, in order to improve the measurement of the Hubble and the deceleration constants. The velocity-distance relation for large and intermediate distances is studied, and type I supernovae are calibrated relatively as distance indicators and absolutely to obtain a new value for the Hubble constant. Methods of determining the deceleration constant are assessed, including determination from direct measurement, mean luminosity density, virgocentric motion, and the time scale test. The very local velocity field is investigated, and a solution is preferred with a random peculiar radial velocity of very nearby field galaxies of 90-100 km/s, and a Virgocentric motion of the local group of 220 km/s, leading to an underlying expansion rate of 55, in satisfactory agreement with the global value.

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.

An ab initio/Rice-Ramsperger-Kassel-Marcus study of the hydrogen-abstraction reactions of methyl ethers, H(3)COCH(3-x)(CH(3))(x), x = 0-2, by OH; mechanism and kinetics.

PubMed

Zhou, Chong-Wen; Simmie, John M; Curran, Henry J

2010-07-14

A theoretical study of the mechanism and kinetics of the H-abstraction reaction from dimethyl (DME), ethylmethyl (EME) and iso-propylmethyl (IPME) ethers by the OH radical has been carried out using the high-level methods CCSD(T)/CBS, G3 and G3MP2BH&H. The computationally less-expensive methods of G3 and G3MP2BH&H yield results for DME within 0.2-0.6 and 0.7-0.9 kcal mol(-1), respectively, of the coupled cluster, CCSD(T), values extrapolated to the basis set limit. So the G3 and G3MP2BH&H methods can be confidently used for the reactions of the higher ethers. A distinction is made between the two different kinds of H-atoms, classified as in/out-of the symmetry plane, and it is found that abstraction from the out-of-plane H-atoms proceeds through a stepwise mechanism involving the formation of a reactant complex in the entrance channel and product complex in the exit channel. The in-plane H-atom abstractions take place through a more direct mechanism and are less competitive. Rate constants of the three reactions have been calculated in the temperature range of 500-3000 K using the Variflex code, based on the weak collision, master equation/microcanonical variational RRKM theory including tunneling corrections. The computed total rate constants (cm(3) mol(-1) s(-1)) have been fitted as follows: k(DME) = 2.74 xT(3.94) exp (1534.2/T), k(EME) = 20.93 xT(3.61) exp (2060.1/T) and k(IPME) = 0.55 xT(3.93) exp (2826.1/T). Expressions of the group rate constants for the three different carbon sites are also provided.

Dynamic Monitoring of Blood-Brain Barrier Integrity using Water Exchange Index (WEI) During Mannitol and CO2 Challenges in Mouse Brain

PubMed Central

Huang, Shuning; Farrar, Christian T.; Dai, Guangping; Kwon, Seon Joo; Bogdanov, Alexei A.; Rosen, Bruce R.; Kim, Young R.

2012-01-01

The integrity of the blood-brain barrier (BBB) is critical to normal brain function. Traditional techniques for assessing BBB disruption rely heavily on the spatiotemporal analysis of extravasating contrast agents. But such methods based on the leakage of relatively large molecules are not suitable to detect subtle BBB impairment or to perform repeated measurements in a short time frame. Quantification of the water exchange rate constant (WER) across the BBB using strictly intravascular contrast agents could provide a much more sensitive method for quantifying the BBB integrity. For estimating the WER, we have recently devised a powerful new method using a water exchange index (WEI) biomarker and demonstrated BBB disruption in an acute stroke model. Here we confirm that the WEI is sensitive to even very subtle changes in the integrity of the BBB caused by (1) systemic hypercapnia and (2) low doses of a hyperosmolar solution. In addition, we have examined the sensitivity and accuracy of the WEI as a biomarker of the WER using computer simulation. In particular, the dependence of the WEI-WER relation on changes in vascular blood volume, T1 relaxation of cellular magnetization, and transcytolemmal water exchange was explored. The simulated WEI was found to vary linearly with the WER for typically encountered exchange rate constants (1–4 Hz) regardless of the blood volume. However, for very high WER (>5 Hz) the WEI became progressively more insensitive to increasing WER. The incorporation of transcytolemmal water exchange, using a three-compartment tissue model, helped to extend the linear WEI regime to slightly higher WER, but had no significant effect for most physiologically important water exchange rate constants (WER<4 Hz). Variation in the cellular T1 had no effect on the WEI. Using both theoretical and experimental approaches, our study validates the utility of the WEI biomarker for monitoring BBB integrity. PMID:23055278

Estimating time-based instantaneous total mortality rate based on the age-structured abundance index

NASA Astrophysics Data System (ADS)

Wang, Yingbin; Jiao, Yan

2015-05-01

The instantaneous total mortality rate ( Z) of a fish population is one of the important parameters in fisheries stock assessment. The estimation of Z is crucial to fish population dynamics analysis, abundance and catch forecast, and fisheries management. A catch curve-based method for estimating time-based Z and its change trend from catch per unit effort (CPUE) data of multiple cohorts is developed. Unlike the traditional catch-curve method, the method developed here does not need the assumption of constant Z throughout the time, but the Z values in n continuous years are assumed constant, and then the Z values in different n continuous years are estimated using the age-based CPUE data within these years. The results of the simulation analyses show that the trends of the estimated time-based Z are consistent with the trends of the true Z, and the estimated rates of change from this approach are close to the true change rates (the relative differences between the change rates of the estimated Z and the true Z are smaller than 10%). Variations of both Z and recruitment can affect the estimates of Z value and the trend of Z. The most appropriate value of n can be different given the effects of different factors. Therefore, the appropriate value of n for different fisheries should be determined through a simulation analysis as we demonstrated in this study. Further analyses suggested that selectivity and age estimation are also two factors that can affect the estimated Z values if there is error in either of them, but the estimated change rates of Z are still close to the true change rates. We also applied this approach to the Atlantic cod ( Gadus morhua) fishery of eastern Newfoundland and Labrador from 1983 to 1997, and obtained reasonable estimates of time-based Z.

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...

Theoretical study of thermodynamic properties and reaction rates of importance in the high-speed research program

NASA Technical Reports Server (NTRS)

Langhoff, Stephen; Bauschlicher, Charles; Jaffe, Richard

1992-01-01

One of the primary goals of NASA's high-speed research program is to determine the feasibility of designing an environmentally safe commercial supersonic transport airplane. The largest environmental concern is focused on the amount of ozone destroying nitrogen oxides (NO(x)) that would be injected into the lower stratosphere during the cruise portion of the flight. The limitations placed on NO(x) emission require more than an order of magnitude reduction over current engine designs. To develop strategies to meet this goal requires first gaining a fundamental understanding of the combustion chemistry. To accurately model the combustor requires a computational fluid dynamics approach that includes both turbulence and chemistry. Since many of the important chemical processes in this regime involve highly reactive radicals, an experimental determination of the required thermodynamic data and rate constants is often very difficult. Unlike experimental approaches, theoretical methods are as applicable to highly reactive species as stable ones. Also our approximation of treating the dynamics classically becomes more accurate with increasing temperature. In this article we review recent progress in generating thermodynamic properties and rate constants that are required to understand NO(x) formation in the combustion process. We also describe our one-dimensional modeling efforts to validate an NH3 combustion reaction mechanism. We have been working in collaboration with researchers at LeRC, to ensure that our theoretical work is focused on the most important thermodynamic quantities and rate constants required in the chemical data base.

Heating rate effects in simulated liquid Al2O_3

NASA Astrophysics Data System (ADS)

van Hoang, Vo

2006-01-01

The heating rate effects in simulated liquid Al{2}O{3} have been investigated by Molecular Dynamics (MD) method. Simulations were done in the basic cube under periodic boundary conditions containing 3000 ions with Born-Mayer type pair potentials. The temperature of the system was increasing linearly in time from the zero temperature as T(t)=T0 +γ t, where γ is the heating rate. The heating rate dependence of density and enthalpy of the system was found. Calculations show that static properties of the system such as the coordination number distributions and bond-angle distributions slightly depend on γ . Structure of simulated amorphous Al{2}O{3} model with the real density at the ambient pressure is in good agreement with Lamparter's experimental data. The heating rate dependence of dynamics of the system has been studied through the diffusion constant, mean-squared atomic displacement and comparison of partial radial distribution functions (PRDFs) for 10% most mobile and immobile particles with the corresponding mean ones. Finally, the evolution of diffusion constant of Al and O particles and structure of the system upon heating for the smallest heating rate was studied and presented. And we find that the temperature dependence of self-diffusion constant in the high temperature region shows a crossover to one which can be described well by a power law, D∝ (T-Tc )^γ . The critical temperature Tc is about 3500 K and the exponent γ is close to 0.941 for Al and to 0.925 for O particles. The glass phase transition temperature Tg for the Al{2}O{3} system is at anywhere around 2000 K.

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

Unimolecular reaction of acetone oxide and its reaction with water in the atmosphere.

PubMed

Long, Bo; Bao, Junwei Lucas; Truhlar, Donald G

2018-05-29

Criegee intermediates (i.e., carbonyl oxides with two radical sites) are known to be important atmospheric reagents; however, our knowledge of their reaction kinetics is still limited. Although experimental methods have been developed to directly measure the reaction rate constants of stabilized Criegee intermediates, the experimental results cover limited temperature ranges and do not completely agree well with one another. Here we investigate the unimolecular reaction of acetone oxide [(CH 3 ) 2 COO] and its bimolecular reaction with H 2 O to obtain rate constants with quantitative accuracy comparable to experimental accuracy. We do this by using CCSDT(Q)/CBS//CCSD(T)-F12a/DZ-F12 benchmark results to select and validate exchange-correlation functionals, which are then used for direct dynamics calculations by variational transition state theory with small-curvature tunneling and torsional and high-frequency anharmonicity. We find that tunneling is very significant in the unimolecular reaction of (CH 3 ) 2 COO and its bimolecular reaction with H 2 O. We show that the atmospheric lifetimes of (CH 3 ) 2 COO depend on temperature and that the unimolecular reaction of (CH 3 ) 2 COO is the dominant decay mode above 240 K, while the (CH 3 ) 2 COO + SO 2 reaction can compete with the corresponding unimolecular reaction below 240 K when the SO 2 concentration is 9 × 10 10 molecules per cubic centimeter. We also find that experimental results may not be sufficiently accurate for the unimolecular reaction of (CH 3 ) 2 COO above 310 K. Not only does the present investigation provide insights into the decay of (CH 3 ) 2 COO in the atmosphere, but it also provides an illustration of how to use theoretical methods to predict quantitative rate constants of medium-sized Criegee intermediates.

Real-Time Monitoring of Azo Dye Interfacial Adsorption at Silica-Water Interface by Total Internal Reflection-Induced Surface Evanescent Wave.

PubMed

Xiong, Yan; Wang, Qing; Duan, Ming; Tan, Jun; Fang, Shenwen; Wu, Jiayi

2018-06-19

An interface research method based on total internal reflection induced evanescent wave (TIR-EW) is developed to monitor the adsorption behavior of azo dye at the silica-water interface. The monitoring system is constructed by employing silica optical fiber (SOF) as both charged substrate for dye adsorption and light transmission waveguide for evanescent wave production. According to the change of evanescent wave intensity and followed by Beer's law, the methylene blue (MB) adsorption behavior can be real-time monitored at the silica-water interface. Langmuir adsorption model and pseudo-first-order model are applied to obtain the related thermodynamic and kinetic data. The adsorption equilibrium constant ( K ads ) and adsorption free energy (Δ G) of MB at the silica-water interface are determined to be (3.3 ± 0.5) × 10 4 M -1 and -25.7 ± 1.7 kJ mol -1 . Meanwhile, this method is highlighted to isolate elementary processes of adsorption and desorption under steady-state conditions, and gives adsorption rate constant ( k a ) and desorption rate constant ( k d ) of 8585 ± 19.8 min -1 and 0.26 ± 0.0006 min -1 for 15 r/min flow rate. The surface interaction process is revealed and adsorption mechanism is proposed, indicating MB first adsorbed on Si-O - sites through electrostatic attraction and then on Si-OH sites through hydrogen bond with increasing MB concentrations. Our findings from this study provided molecular-level interpretation of azo dye adsorption at silica-water interface, and the results provide important insight into how MB adsorption can be controlled at the interface.

Nonadiabatic dynamics of electron transfer in solution: Explicit and implicit solvent treatments that include multiple relaxation time scales

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

Schwerdtfeger, Christine A.; Soudackov, Alexander V.; Hammes-Schiffer, Sharon, E-mail: shs3@illinois.edu

2014-01-21

The development of efficient theoretical methods for describing electron transfer (ET) reactions in condensed phases is important for a variety of chemical and biological applications. Previously, dynamical dielectric continuum theory was used to derive Langevin equations for a single collective solvent coordinate describing ET in a polar solvent. In this theory, the parameters are directly related to the physical properties of the system and can be determined from experimental data or explicit molecular dynamics simulations. Herein, we combine these Langevin equations with surface hopping nonadiabatic dynamics methods to calculate the rate constants for thermal ET reactions in polar solvents formore » a wide range of electronic couplings and reaction free energies. Comparison of explicit and implicit solvent calculations illustrates that the mapping from explicit to implicit solvent models is valid even for solvents exhibiting complex relaxation behavior with multiple relaxation time scales and a short-time inertial response. The rate constants calculated for implicit solvent models with a single solvent relaxation time scale corresponding to water, acetonitrile, and methanol agree well with analytical theories in the Golden rule and solvent-controlled regimes, as well as in the intermediate regime. The implicit solvent models with two relaxation time scales are in qualitative agreement with the analytical theories but quantitatively overestimate the rate constants compared to these theories. Analysis of these simulations elucidates the importance of multiple relaxation time scales and the inertial component of the solvent response, as well as potential shortcomings of the analytical theories based on single time scale solvent relaxation models. This implicit solvent approach will enable the simulation of a wide range of ET reactions via the stochastic dynamics of a single collective solvent coordinate with parameters that are relevant to experimentally accessible systems.« less

Determining the elastic properties of aptamer-ricin single molecule multiple pathway interactions

NASA Astrophysics Data System (ADS)

Wang, Bin; Park, Bosoon; Kwon, Yongkuk; Xu, Bingqian

2014-05-01

We report on the elastic properties of ricin and anti-ricin aptamer interactions, which showed three stable binding conformations, each of which has its special elastic properties. These different unbinding pathways were investigated by the dynamic force spectroscopy. A series-spring model combining the worm-like-chain model and Hook's law was used to estimate the apparent spring constants of the aptamer and linker molecule polyethylene glycol. The aptamer in its three different unbinding pathways showed different apparent spring constants. The two reaction barriers in the unbinding pathways also influence the apparent spring constant of the aptamer. This special elastic behavior of aptamer was used to distinguish its three unbinding pathways under different loading rates. This method also offered a way to distinguish and discard the non-specific interactions in single molecule experiments.

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.

Effect of dissolved organic matter on pre-equilibrium passive sampling: A predictive QSAR modeling study.

PubMed

Lin, Wei; Jiang, Ruifen; Shen, Yong; Xiong, Yaxin; Hu, Sizi; Xu, Jianqiao; Ouyang, Gangfeng

2018-04-13

Pre-equilibrium passive sampling is a simple and promising technique for studying sampling kinetics, which is crucial to determine the distribution, transfer and fate of hydrophobic organic compounds (HOCs) in environmental water and organisms. Environmental water samples contain complex matrices that complicate the traditional calibration process for obtaining the accurate rate constants. This study proposed a QSAR model to predict the sampling rate constants of HOCs (polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and pesticides) in aqueous systems containing complex matrices. A homemade flow-through system was established to simulate an actual aqueous environment containing dissolved organic matter (DOM) i.e. humic acid (HA) and (2-Hydroxypropyl)-β-cyclodextrin (β-HPCD)), and to obtain the experimental rate constants. Then, a quantitative structure-activity relationship (QSAR) model using Genetic Algorithm-Multiple Linear Regression (GA-MLR) was found to correlate the experimental rate constants to the system state including physicochemical parameters of the HOCs and DOM which were calculated and selected as descriptors by Density Functional Theory (DFT) and Chem 3D. The experimental results showed that the rate constants significantly increased as the concentration of DOM increased, and the enhancement factors of 70-fold and 34-fold were observed for the HOCs in HA and β-HPCD, respectively. The established QSAR model was validated as credible (R Adj. 2 =0.862) and predictable (Q 2 =0.835) in estimating the rate constants of HOCs for complex aqueous sampling, and a probable mechanism was developed by comparison to the reported theoretical study. The present study established a QSAR model of passive sampling rate constants and calibrated the effect of DOM on the sampling kinetics. Copyright © 2018 Elsevier B.V. All rights reserved.

HO + CO reaction rates and H/D kinetic isotope effects: master equation models with ab initio SCTST rate constants.

PubMed

Weston, Ralph E; Nguyen, Thanh Lam; Stanton, John F; Barker, John R

2013-02-07

Ab initio microcanonical rate constants were computed using Semi-Classical Transition State Theory (SCTST) and used in two master equation formulations (1D, depending on active energy with centrifugal corrections, and 2D, depending on total energy and angular momentum) to compute temperature-dependent rate constants for the title reactions using a potential energy surface obtained by sophisticated ab initio calculations. The 2D master equation was used at the P = 0 and P = ∞ limits, while the 1D master equation with centrifugal corrections and an empirical energy transfer parameter could be used over the entire pressure range. Rate constants were computed for 75 K ≤ T ≤ 2500 K and 0 ≤ [He] ≤ 10(23) cm(-3). For all temperatures and pressures important for combustion and for the terrestrial atmosphere, the agreement with the experimental rate constants is very good, but at very high pressures and T ≤ 200 K, the theoretical rate constants are significantly smaller than the experimental values. This effect is possibly due to the presence in the experiments of dimers and prereactive complexes, which were not included in the model calculations. The computed H/D kinetic isotope effects are in acceptable agreement with experimental data, which show considerable scatter. Overall, the agreement between experimental and theoretical H/D kinetic isotope effects is much better than in previous work, and an assumption of non-RRKM behavior does not appear to be needed to reproduce experimental observations.

Testing for variation in taxonomic extinction probabilities: a suggested methodology and some results

USGS Publications Warehouse

Conroy, M.J.; Nichols, J.D.

1984-01-01

Several important questions in evolutionary biology and paleobiology involve sources of variation in extinction rates. In all cases of which we are aware, extinction rates have been estimated from data in which the probability that an observation (e.g., a fossil taxon) will occur is related both to extinction rates and to what we term encounter probabilities. Any statistical method for analyzing fossil data should at a minimum permit separate inferences on these two components. We develop a method for estimating taxonomic extinction rates from stratigraphic range data and for testing hypotheses about variability in these rates. We use this method to estimate extinction rates and to test the hypothesis of constant extinction rates for several sets of stratigraphic range data. The results of our tests support the hypothesis that extinction rates varied over the geologic time periods examined. We also present a test that can be used to identify periods of high or low extinction probabilities and provide an example using Phanerozoic invertebrate data. Extinction rates should be analyzed using stochastic models, in which it is recognized that stratigraphic samples are random varlates and that sampling is imperfect

Absolute protein-protein association rate constants from flexible, coarse-grained Brownian dynamics simulations: the role of intermolecular hydrodynamic interactions in barnase-barstar association.

PubMed

Frembgen-Kesner, Tamara; Elcock, Adrian H

2010-11-03

Theory and computation have long been used to rationalize the experimental association rate constants of protein-protein complexes, and Brownian dynamics (BD) simulations, in particular, have been successful in reproducing the relative rate constants of wild-type and mutant protein pairs. Missing from previous BD studies of association kinetics, however, has been the description of hydrodynamic interactions (HIs) between, and within, the diffusing proteins. Here we address this issue by rigorously including HIs in BD simulations of the barnase-barstar association reaction. We first show that even very simplified representations of the proteins--involving approximately one pseudoatom for every three residues in the protein--can provide excellent reproduction of the absolute association rate constants of wild-type and mutant protein pairs. We then show that simulations that include intermolecular HIs also produce excellent estimates of association rate constants, but, for a given reaction criterion, yield values that are decreased by ∼35-80% relative to those obtained in the absence of intermolecular HIs. The neglect of intermolecular HIs in previous BD simulation studies, therefore, is likely to have contributed to the somewhat overestimated absolute rate constants previously obtained. Consequently, intermolecular HIs could be an important component to include in accurate modeling of the kinetics of macromolecular association events. Copyright © 2010 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Measurement of the Dissociation-Equilibrium Constants for Low Affinity Antibiotic Binding Interaction with Bacterial Ribosomes by the T2 (CPMG) and Line-Broadening Methods

NASA Astrophysics Data System (ADS)

Verdier, L.; Gharbi-Benarous, J.; Bertho, G.; Mauvais, P.; Girault, J.-P.

1999-10-01

In this study the dissociation constants of the low antibiotic-ribosomes interaction were determined by the T2 (CPMG), the Carr-Purcell-Meiboom-Gill spin-echo decay rate and the line-broadening methods. Three MLSB antibiotics were studied, a macrolide roxithromycin, a ketolide HMR 3647 and a lincosamide clindamycin for their weak interaction with three bacterial ribosomes, E. coli, Staphylococcus aureus sensitive and resistant to erythromycin. Nous avons mesuré la constante de dissociation, Kd correspondant à l'interaction faible antibiotique-ribosome bactérien pour des antibiotiques de différentes classes, un macrolide (roxithromycine), un kétolide (HMR 3647) et une lincosamide (clindamycine) avec des ribosomes de différentes souches bactériennes (E. coli, Staphylococcus aureus sensible ou résistant à l'erythromycin) par deux méthodes : l'une basée sur la variation des largeurs de raies et l'autre sur les temps de relaxation transversaux T2 en utilisant une séquence CPMG.

METHOD FOR SENSING DEGREE OF FLUIDIZATION IN FLUIDIZED BED

DOEpatents

Levey, R.P. Jr.; Fowler, A.H.

1961-12-12

A method is given for detecting, indicating, and controlling the degree of fluidization in a fluid-bed reactor into which powdered material is fed. The method comprises admitting of gas into the reactor, inserting a springsupported rod into the powder bed of the reactor, exciting the rod to vibrate at its resonant frequency, deriving a signal responsive to the amplitude of vibi-ation of the rod and spring, the signal being directiy proportional to the rate of flow of the gas through the reactor, displaying the signal to provide an indication of the degree of fluidization within the reactor, and controlling the rate of gas flow into the reactor until said signal stabilizes at a constant value to provide substantially complete fluidization within the reactor. (AEC)

Reactive Coevaporation Synthesis and Characterization of SrTiO3 Thin Films

NASA Astrophysics Data System (ADS)

Yamaguchi, Hiromu; Matsubara, Shogo; Miyasaka, Yoichi

1991-09-01

SrTiO3 thin films were prepared by the reactive coevaporation method, where the Ti and Sr metals were evaporated in oxygen ambient with an E-gun and K-cell, respectively. A uniform depth profile in composition was achieved by altering the Ti evaporation rate according to the Sr evaporation rate change. A typical dielectric constant of 170 was measured on films of 75 nm in thickness. The in-situ annealing in oxygen plasma reduced the leakage current.

Vapors-liquid phase separator. [infrared telescope heat sink

NASA Technical Reports Server (NTRS)

Frederking, T. H. K.; Brown, G. S.; Chuang, C.; Kamioka, Y.; Kim, Y. I.; Lee, J. M.; Yuan, S. W. K.

1980-01-01

The use of porous plugs, mostly with in the form of passive devices with constant area were considered as vapor-liquid phase separators for helium 2 storage vessels under reduced gravity. The incorporation of components with variable cross sectional area as a method of flow rate modification was also investigated. A particular device which uses a shutter-type system for area variation was designed and constructed. This system successfully permitted flor rate changes of up to plus or minus 60% from its mean value.

Unimolecular decomposition reactions at low-pressure: A comparison of competitive methods

NASA Technical Reports Server (NTRS)

Adams, G. F.

1980-01-01

The lack of a simple rate coefficient expression to describe the pressure and temperature dependence hampers chemical modeling of flame systems. Recently developed simplified models to describe unimolecular processes include the calculation of rate constants for thermal unimolecular reactions and recombinations at the low pressure limit, at the high pressure limit and in the intermediate fall-off region. Comparison between two different applications of Troe's simplified model and a comparison between the simplified model and the classic RRKM theory are described.

ESTIMATION OF PHOSPHATE ESTER HYDROLYSIS RATE CONSTANTS. I. 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...

MICROBIAL TRANSFORMATION RATE CONSTANTS OF STRUCTURALLY DIVERSE MAN-MADE CHEMICALS

EPA Science Inventory

To assist in estimating microbially mediated transformation rates of man-made chemicals from their chemical structures, all second order rate constants that have been measured under conditions that make the values comparable have been extracted from the literature and combined wi...

To Model Chemical Reactivity in Heterogeneous Emulsions, Think Homogeneous Microemulsions.

PubMed

Bravo-Díaz, Carlos; Romsted, Laurence Stuart; Liu, Changyao; Losada-Barreiro, Sonia; Pastoriza-Gallego, Maria José; Gao, Xiang; Gu, Qing; Krishnan, Gunaseelan; Sánchez-Paz, Verónica; Zhang, Yongliang; Dar, Aijaz Ahmad

2015-08-25

Two important and unsolved problems in the food industry and also fundamental questions in colloid chemistry are how to measure molecular distributions, especially antioxidants (AOs), and how to model chemical reactivity, including AO efficiency in opaque emulsions. The key to understanding reactivity in organized surfactant media is that reaction mechanisms are consistent with a discrete structures-separate continuous regions duality. Aggregate structures in emulsions are determined by highly cooperative but weak organizing forces that allow reactants to diffuse at rates approaching their diffusion-controlled limit. Reactant distributions for slow thermal bimolecular reactions are in dynamic equilibrium, and their distributions are proportional to their relative solubilities in the oil, interfacial, and aqueous regions. Our chemical kinetic method is grounded in thermodynamics and combines a pseudophase model with methods for monitoring the reactions of AOs with a hydrophobic arenediazonium ion probe in opaque emulsions. We introduce (a) the logic and basic assumptions of the pseudophase model used to define the distributions of AOs among the oil, interfacial, and aqueous regions in microemulsions and emulsions and (b) the dye derivatization and linear sweep voltammetry methods for monitoring the rates of reaction in opaque emulsions. Our results show that this approach provides a unique, versatile, and robust method for obtaining quantitative estimates of AO partition coefficients or partition constants and distributions and interfacial rate constants in emulsions. The examples provided illustrate the effects of various emulsion properties on AO distributions such as oil hydrophobicity, emulsifier structure and HLB, temperature, droplet size, surfactant charge, and acidity on reactant distributions. Finally, we show that the chemical kinetic method provides a natural explanation for the cut-off effect, a maximum followed by a sharp reduction in AO efficiency with increasing alkyl chain length of a particular AO. We conclude with perspectives and prospects.

The Effect of Electric Field on the Explosive Sensitivity of Silver Azide

NASA Astrophysics Data System (ADS)

Rodzevich, A. P.; Gazenaur, E. G.; Kuzmina, L. V.; Krasheninin, V. I.; Gazenaur, N. V.

2017-05-01

The effect of a constant contactless electric field on the rate of a chemical reaction in silver azide is explored in this paper. The technology of growing and processing silver azide whiskers in the constant contactless electric field (field intensity was varied in the range from 10-3 V/m to 100 V/m) allows supervising their explosive sensitivity, therefore, the results of experiments can be relevant for purposeful controlling the resistance of explosive materials. This paper is one of the first attempts to develop efficient methods to affect the explosive sensitivity of energy-related materials in a weak electric field (up to 10-3 V/m).

Dissociative electron attachment to C{sub 2}F{sub 5} radicals

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

Haughey, Sean A.; Field, Thomas A.; Langer, Judith

Dissociative electron attachment to the reactive C{sub 2}F{sub 5} molecular radical has been investigated with two complimentary experimental methods; a single collision beam experiment and a new flowing afterglow Langmuir probe technique. The beam results show that F{sup -} is formed close to zero electron energy in dissociative electron attachment to C{sub 2}F{sub 5}. The afterglow measurements also show that F{sup -} is formed in collisions between electrons and C{sub 2}F{sub 5} molecules with rate constants of 3.7 Multiplication-Sign 10{sup -9} cm{sup 3} s{sup -1} to 4.7 Multiplication-Sign 10{sup -9} cm{sup 3} s{sup -1} at temperatures of 300-600 K. Themore » rate constant increases slowly with increasing temperature, but the rise observed is smaller than the experimental uncertainty of 35%.« less

High-temperature tensile-hold crack-growth behavior of HASTELLOY® X alloy compared to HAYNES® 188 and HAYNES® 230® alloys

NASA Astrophysics Data System (ADS)

Lee, S. Y.; Lu, Y. L.; Liaw, P. K.; Choo, H.; Thompson, S. A.; Blust, J. W.; Browning, P. F.; Bhattacharya, A. K.; Aurrecoechea, J. M.; Klarstrom, D. L.

2008-03-01

The creep-fatigue crack-growth tests of HASTELLOY® X alloy were carried out at the temperatures of 649°C, 816°C, and 927°C in laboratory air. The experiments were conducted under a constant stress-intensity-factor-range (Δ K) control mode with a R-ratio of 0.05. In the constant Δ K tests, a Δ K of 27.5 MPa sqrt{m} and a triangular waveform with a frequency of 0.333 Hz were used. Various tensile hold times at the maximum load were imposed to study fatigue and creep-fatigue interactions. Crack lengths were measured by a direct current potential drop method. In this paper, effects of hold time and temperature on the crack-growth rates are discussed. Furthermore, the crack-growth rates of the HASTELLOY® X alloy are compared to those of the HAYNES® 188 and HAYNES® 230® superalloys.

Perchlorate reduction by autotrophic bacteria in the presence of zero-valent iron.

PubMed

Yu, Xueyuan; Amrhein, Christopher; Deshusses, Marc A; Matsumoto, Mark R

2006-02-15

A series of batch experiments were performed to study the combination of zero-valent iron (ZVI) with perchlorate-reducing microorganisms (PRMs) to remove perchlorate from groundwater. In this method, H2 produced during the process of iron corrosion by water is used by PRMs as an electron donor to reduce perchlorate to chloride. Perchlorate degradation rates followed Monod kinetics, with a normalized maximum utilization rate (rmax) of 9200 microg g(-1) (dry wt) h(-1) and a half-velocity constant (Ks) of 8900 microg L(-1). The overall rate of perchlorate reduction was affected by the biomass density within the system. An increase in the OD600 from 0.025 to 0.08 led to a corresponding 4-fold increase of perchlorate reduction rate. PRM adaptation to the local environment and initiation of perchlorate reduction was rapid under neutral pH conditions. At the initial OD600 of 0.015, perchlorate reduction followed pseudo-first-order reaction rates with constants of 0.059 and 0.033 h(-1) at initial pH 7 and 8, respectively. Once perchlorate reduction was established, the bioreductive process was insensitive to the increases of pH from near neutral to 9.0. In the presence of nitrate, perchlorate reduction rate was reduced, but not inhibited completely.

Radiative corrections to quantum sticking on graphene

NASA Astrophysics Data System (ADS)

Sengupta, Sanghita; Clougherty, Dennis P.

2017-07-01

We study the sticking rate of atomic hydrogen to suspended graphene using four different methods that include contributions from processes with multiphonon emission. We compare the numerical results of the sticking rate obtained by: (i) the loop expansion of the atom self-energy; (ii) the noncrossing approximation (NCA); (iii) the independent boson model approximation (IBMA); and (iv) a leading-order soft-phonon resummation method (SPR). The loop expansion reveals an infrared problem, analogous to the infamous infrared problem in QED. The two-loop contribution to the sticking rate gives a result that tends to diverge for large membranes. The latter three methods remedy this infrared problem and give results that are finite in the limit of an infinite membrane. We find that for micromembranes (sizes ranging 100 nm to 10 μ m ), the latter three methods give results that are in good agreement with each other and yield sticking rates that are mildly suppressed relative to the lowest-order golden rule rate. Lastly, we find that the SPR sticking rate decreases slowly to zero with increasing membrane size, while both the NCA and IBMA rates tend to a nonzero constant in this limit. Thus, approximations to the sticking rate can be sensitive to the effects of soft-phonon emission for large membranes.

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

Isotalo, Aarno

A method referred to as tally nuclides is presented for accurately and efficiently calculating the time-step averages and integrals of any quantities that are weighted sums of atomic densities with constant weights during the step. The method allows all such quantities to be calculated simultaneously as a part of a single depletion solution with existing depletion algorithms. Some examples of the results that can be extracted include step-average atomic densities and macroscopic reaction rates, the total number of fissions during the step, and the amount of energy released during the step. Furthermore, the method should be applicable with several depletionmore » algorithms, and the integrals or averages should be calculated with an accuracy comparable to that reached by the selected algorithm for end-of-step atomic densities. The accuracy of the method is demonstrated in depletion calculations using the Chebyshev rational approximation method. Here, we demonstrate how the ability to calculate energy release in depletion calculations can be used to determine the accuracy of the normalization in a constant-power burnup calculation during the calculation without a need for a reference solution.« less

Calculating Time-Integral Quantities in Depletion Calculations

DOE PAGES

Isotalo, Aarno

2016-06-02

A method referred to as tally nuclides is presented for accurately and efficiently calculating the time-step averages and integrals of any quantities that are weighted sums of atomic densities with constant weights during the step. The method allows all such quantities to be calculated simultaneously as a part of a single depletion solution with existing depletion algorithms. Some examples of the results that can be extracted include step-average atomic densities and macroscopic reaction rates, the total number of fissions during the step, and the amount of energy released during the step. Furthermore, the method should be applicable with several depletionmore » algorithms, and the integrals or averages should be calculated with an accuracy comparable to that reached by the selected algorithm for end-of-step atomic densities. The accuracy of the method is demonstrated in depletion calculations using the Chebyshev rational approximation method. Here, we demonstrate how the ability to calculate energy release in depletion calculations can be used to determine the accuracy of the normalization in a constant-power burnup calculation during the calculation without a need for a reference solution.« less

Distance dependence in photoinduced intramolecular electron transfer. Additional remarks and calculations

NASA Astrophysics Data System (ADS)

Larsson, Sven; Volosov, Andrey

1987-12-01

Rate constants for photoinduced intramolecular electron transfer are calculated for four of the molecules studied by Hush et al. The electronic factor is obtained in quantum chemical calculations using the CNDO/S method. The results agree reasonably well with experiments for the forward reaction. Possible reasons for the disagreement for the charge recombination process are offered.

Dropout Rates, Student Momentum, and Course Walls: A New Tool for Distance Education Designers

ERIC Educational Resources Information Center

Christensen, Steven S.; Spackman, Jonathan S.

2017-01-01

This paper explores a new tool for instructional designers. By calculating and graphing the Student Momentum Indicator (M) for 196 university-level online courses and by employing the constant comparative method within the grounded theory framework, eight distinct graph shapes emerged as meaningful categories of dropout behavior. Several of the…

Slow Crack Growth Analysis of Advanced Structural Ceramics Under Combined Loading Conditions: Damage Assessment in Life Prediction Testing

NASA Technical Reports Server (NTRS)

Choi, S. R.; Gyekenyesi, J. P.

2001-01-01

Slow crack growth analysis was performed with three different loading histories including constant stress- rate/constant stress-rate testing (Case I loading), constant stress/constant stress-rate testing (Case II loading), and cyclic stress/constant stress-rate testing (Case III loading). Strength degradation due to slow crack growth and/or damage accumulation was determined numerically as a function of percentage of interruption time between the two loading sequences for a given loading history. The numerical solutions were examined with the experimental data determined at elevated temperatures using four different advanced ceramic materials, two silicon nitrides, one silicon carbide and one alumina for the Case I loading history, and alumina for the Case II loading history. The numerical solutions were in reasonable agreement with the experimental data, indicating that notwithstanding some degree of creep deformation presented for some test materials slow crack growth was a governing mechanism associated with failure for all the rest materials.

Slow Crack Growth Analysis of Advanced Structural Ceramics Under Combined Loading Conditions: Damage Assessment in Life Prediction Testing

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Gyekenyesi, John P.

2000-01-01

Slow crack growth analysis was performed with three different loading histories including constant stress-rate/constant stress-rate testing (Case 1 loading), constant stress/constant stress-rate testing (Case 2 loading), and cyclic stress/constant stress-rate testing (Case 2 loading). Strength degradation due to slow crack growth and/or damage accumulation was determined numerically as a function of percentage of interruption time between the two loading sequences for a given loading history. The numerical solutions were examined with the experimental data determined at elevated temperatures using four different advanced ceramic materials, two silicon nitrides, one silicon carbide and one alumina for the Case 1 loading history, and alumina for the Case 3 loading history. The numerical solutions were in reasonable agreement with the experimental data, indicating that notwithstanding some degree of creep deformation presented for some test materials slow crack growth was a governing mechanism associated with failure for all the test materials.

Slow Crack Growth Analysis of Advanced Structural Ceramics Under Combined Loading Conditions: Damage Assessment in Life Prediction Testing

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Gyekenyesi, John P.

2000-01-01

Slow crack growth analysis was performed with three different loading histories including constant stress-rate/constant stress-rate testing (Case I loading), constant stress/constant stress-rate testing (Case II loading), and cyclic stress/constant stress-rate testing (Case III loading). Strength degradation due to slow crack growth arid/or damage accumulation was determined numerically as a Function of percentage of interruption time between the two loading sequences for a given loading history. The numerical solutions were examined with the experimental data determined at elevated temperatures using four different advanced ceramic materials, two silicon nitrides, one silicon carbide and one alumina for the Case I loading history, and alumina for the Case II loading history. The numerical solutions were in reasonable agreement with the experimental data, indicating that notwithstanding some degree of creep deformation presented for some test materials slow crack growth was a governing mechanism associated with failure for all the test material&

Method and apparatus for producing pyrolysis oil having improved stability

DOEpatents

Baird, Lance A.; Brandvold, Timothy A.; Muller, Stefan

2016-12-27

Methods and apparatus to improve hot gas filtration to reduce the liquid fuel loss caused by prolonged residence time at high temperatures are described. The improvement can be obtained by reducing the residence time at elevated temperature by reducing the temperature of the pyrolysis vapor, by reducing the volume of the pyrolysis vapor at the elevated temperature, by increasing the volumetric flow rate at constant volume of the pyrolysis vapor, or by doing a combination of these.

Frost Susceptibility of Soil, Review of Index Tests,

DTIC Science & Technology

1981-12-01

contained in the CAA ( 1948 ) speci- used for both subgrade and base/subbase materi- fications for the construction of airports. Ac- als. An additional...Texas. Details of the Texas method for deter- t Percentage of portion smaller than mining FS were reported by Carothers ( 1948 ) and 20mm were taken...material. pies are frozen from the bottom up at a constant rate of heat flow, similar to the method sug- Switzerland gested by Penner and Ueda (1978

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

Greene, Samuel M., E-mail: samuel.greene@chem.ox.ac.uk; Shan, Xiao, E-mail: xiao.shan@chem.ox.ac.uk; Clary, David C., E-mail: david.clary@chem.ox.ac.u

Semiclassical Transition State Theory (SCTST), a method for calculating rate constants of chemical reactions, offers gains in computational efficiency relative to more accurate quantum scattering methods. In full-dimensional (FD) SCTST, reaction probabilities are calculated from third and fourth potential derivatives along all vibrational degrees of freedom. However, the computational cost of FD SCTST scales unfavorably with system size, which prohibits its application to larger systems. In this study, the accuracy and efficiency of 1-D SCTST, in which only third and fourth derivatives along the reaction mode are used, are investigated in comparison to those of FD SCTST. Potential derivatives aremore » obtained from numerical ab initio Hessian matrix calculations at the MP2/cc-pVTZ level of theory, and Richardson extrapolation is applied to improve the accuracy of these derivatives. Reaction barriers are calculated at the CCSD(T)/cc-pVTZ level. Results from FD SCTST agree with results from previous theoretical and experimental studies when Richardson extrapolation is applied. Results from our implementation of 1-D SCTST, which uses only 4 single-point MP2/cc-pVTZ energy calculations in addition to those for conventional TST, agree with FD results to within a factor of 5 at 250 K. This degree of agreement and the efficiency of the 1-D method suggest its potential as a means of approximating rate constants for systems too large for existing quantum scattering methods.« less

Dissolution process analysis using model-free Noyes-Whitney integral equation.

PubMed

Hattori, Yusuke; Haruna, Yoshimasa; Otsuka, Makoto

2013-02-01

Drug dissolution process of solid dosages is theoretically described by Noyes-Whitney-Nernst equation. However, the analysis of the process is demonstrated assuming some models. Normally, the model-dependent methods are idealized and require some limitations. In this study, Noyes-Whitney integral equation was proposed and applied to represent the drug dissolution profiles of a solid formulation via the non-linear least squares (NLLS) method. The integral equation is a model-free formula involving the dissolution rate constant as a parameter. In the present study, several solid formulations were prepared via changing the blending time of magnesium stearate (MgSt) with theophylline monohydrate, α-lactose monohydrate, and crystalline cellulose. The formula could excellently represent the dissolution profile, and thereby the rate constant and specific surface area could be obtained by NLLS method. Since the long time blending coated the particle surface with MgSt, it was found that the water permeation was disturbed by its layer dissociating into disintegrant particles. In the end, the solid formulations were not disintegrated; however, the specific surface area gradually increased during the process of dissolution. The X-ray CT observation supported this result and demonstrated that the rough surface was dominant as compared to dissolution, and thus, specific surface area of the solid formulation gradually increased. Copyright © 2012 Elsevier B.V. All rights reserved.

Fabrication of copper decorated tungsten oxide-titanium oxide nanotubes by photochemical deposition technique and their photocatalytic application under visible light

NASA Astrophysics Data System (ADS)

Momeni, Mohamad Mohsen

2015-12-01

Copper decorated WO3-TiO2 nanotubes (Cu/WTNs) with a high photocatalytic activity were prepared by anodizing and photochemical deposition. Highly ordered WO3-TiO2 nanotubes (WTNs) on pure titanium foils were successfully fabricated by electrochemical anodizing and copper deposited on these nanotubes (Cu/WTNs) by photoreduction method. The resulting samples were characterized by various methods. Only the anatase phase was detected by X-ray diffraction analysis. The presence of copper in the structure of thin films was confirmed by energy dispersive X-ray spectrometry and X-ray diffraction. The extension of optical absorption into the visible region of as-prepared films was indicated by UV/Vis spectroscopy. The degradation of methylene blue was used as a model reaction to evaluate the photocatalytic activity of the obtained samples. Results showed that the photocatalytic activity of Cu/WTNs samples is higher than bare WTNs sample. Kinetic research showed that the reaction rate constant of Cu/WTNs is approximately 2.5 times higher than the apparent reaction rate constant of bare WTNs. These results not only offer an economical method for constructing Cu/WTNs photocatalysts, but also shed new insight on the rational design of a low cost and high-efficiency photocatalyst for environmental remediation.

Deriving in vivo biotransformation rate constants and metabolite parent concentration factor/stable metabolite factor from bioaccumulation and bioconcentration experiments: An illustration with worm accumulation data.

PubMed

Kuo, Dave Ta Fu; Chen, Ciara Chun

2016-12-01

Growing concern for the biological fate of organic contaminants and their metabolites and the urge to connect in vitro and in vivo toxicokinetics have prompted researchers to characterize the biotransformation behavior of organic contaminants in biota. The whole body biotransformation rate constant (k M ) is currently determined by the difference approach, which has significant methodological limitations. A new approach for determining k M from the kinetic observations of the parent contaminant and its intermediate metabolites is proposed. In this method, k M can be determined by fitting kinetic data of the parent contaminant and the metabolites to analytical equations that depict the bioaccumulation kinetics. The application of the proposed method is illustrated using worm bioaccumulation-biotransformation data collected from the literature. Furthermore, a metabolite parent concentration factor (MPCF) is also proposed to characterize the persistence of the metabolite in biota. Because both the proposed k M method and MPCF build on the existing theoretical framework for bioaccumulation, they can be readily incorporated into standard experimental bioaccumulation protocols or risk assessment procedures or frameworks. Possible limitations, implications, and future directions are elaborated. Environ Toxicol Chem 2016;35:2903-2909. © 2016 SETAC. © 2016 SETAC.

Seedless synthesis and efficient recyclable catalytic activity of Ag@Fe nanocomposites towards methyl orange

NASA Astrophysics Data System (ADS)

Alzahrani, Salma Ahmed; Malik, Maqsood Ahmad; Al-Thabaiti, Shaeel Ahmed; Khan, Zaheer

2018-03-01

This work demonstrates a competitive reduction method of synthesis of nanomaterials. In this method along cetyltrimethylammonium bromide (CTAB), the reduction of Ag+ and Fe3+ ions is achieved by ascorbic acid-to-bimetallic Ag@Fe yellow-colored nanomaterials. The shape of UV-visible spectra and wavelengths absorbed of Ag@Fe can be tuned from ca. 290-600 nm by controlling [CTAB] and [Ag+]. The apparent first-order rate constants were calculated within the approximation of 6.1 × 10-3 s-1. The as-prepared Ag@Fe NPs have been found to be very important catalyst in terms of depredate methyl orange in vicinity of sodium borohydride (NaBH4), which exhibits excellent efficiency and re-usability in the prototypical reaction. The cmc of cationic surfactant CTAB has been determined by conductivity method under different experimental conditions. In the presence of CTAB, Ag+ and Fe3+ ions reduce to Ag@Fe core/shell nanoparticles, comprehend a change in wavelength and intensity of SRP band. The apparent first-order rate constant, activation energy, and turnover frequency for the methyl orange reduction catalyzed by Ag@Fe NPs were found to be 1.6 × 10-3 s-1, 58.2 kJ mol-1, and 1.1 × 10-3 s-1, respectively.

Bioconcentration kinetics of hydrophobic chemicals in different densities of Chlorella pyrenoidosa

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

Sijm, D.T.H.M.; Broersen, K.W.; Roode, D.F. de

1998-09-01

Algal density-dependent bioconcentration factors and rate constants were determined for a series of hydrophobic compounds in Chlorella pyrenoidosa. The apparent uptake rate constants of the hydrophobic compounds in algae varied between 200 and 710,000 L/kg/d, slightly increased with hydrophobicity within an experiment, were relatively constant for each algal density, and fitted fairly within existing allometric relationships. The bioavailability of the hydrophobic test compounds was significantly reduced by sorption by algal exudates. The sorption coefficients of the hydrophobic compounds to the algal exudates were between 80 and 1,200 L/kg, and were for most algal densities in the same order of magnitudemore » as the apparent bioconcentration factors to the algae, that is, between 80 and 60,200 L/kg. In typical field situations, however, no significant reduction in bioavailability due to exudates is expected. The apparent elimination rate constants of the hydrophobic compounds were high and fairly constant for each algal density and varied between 2 and 190/d. Because the apparent elimination rate constants were higher than the growth rate constant, and were independent of hydrophobicity, the authors speculated that other factors dominate excretion, such as exudate excretion-enhanced elimination. Bioconcentration factors increased less than proportional with hydrophobicity, i.e., the octanol-water partition coefficient [K{sub ow}]. The role of algal composition in bioconcentration is evaluated. Bioconcentrations (kinetics) of hydrophobic compounds that are determined at high algal densities should be applied with caution to field situations.« less

Discovery of a Significant Acetone•Hydroperoxy Adduct Chaperone Effect and Its Impact on the Determination of Room Temperature Rate Constants for Acetonylperoxy/Hydroperoxy Self-Reactions and Cross Reaction Via Infrared Kinetic Spectroscopy.

NASA Astrophysics Data System (ADS)

Grieman, F. J.; Hui, A. O.; Okumura, M.; Sander, S. P.

2017-12-01

In order to model the upper troposphere/lower stratosphere in regions containing acetone properly, the kinetics of the acetonylperoxy/hydroperoxy self-reactions and cross reaction have been studied over a wide temperature range using Infrared Kinetic Spectroscopy. We report here the determination of different rate constants for the acetonylperoxy chemistry that we obtained at 298 K compared to currently accepted values. A considerable increase in the observed HO2 self-reaction rate constant due to rate enhancement via the chaperone effect from the reaction between HO2 and the (CH3)2CO•HO2 hydrogen-bonded adduct, even at room temperature, was discovered that was previously ignored. Correct determination of the acetonylperoxy and hydroperoxy kinetics must include this dependence of the HO2 self-reaction rate on acetone concentration. Via excimer laser flash photolysis to create the radical reactants, HO2 absorption was monitored in the infrared by diode laser wavelength modulation detection simultaneously with CH3C(O)CH2O2absorption monitored in the ultraviolet at 300 nm as a function of time. Resulting decay curves were fit concurrently first over a short time scale to obtain the rate constants minimizing subsequent product reactions. Modeling/fitting with a complete reaction scheme was then performed to refine the rate constants and test their veracity. Experiments were carried out over a variety of concentrations of acetone and methanol. Although no effect due to methanol concentration was found at room temperature, the rate constant for the hydroperoxy self-reaction was found to increase linearly with acetone concentration which is interpreted as the adduct being formed and resulting in a chaperone mechanism that enhances the self-reaction rate: (CH3)2CO·HO2 + HO2 → H2O2 + O2 + (CH3)2CO Including this effect, the resulting room temperature rate constants for the cross reaction and the acetonylperoxy self-reaction were found to be 2-3 times smaller than previously reported. This complex formation/chaperone mechanism is similar to that found for methanol, but different in that it occurs at room temperature. No precursor concentration dependence was found for the acetonylperoxy radical reactions. The equilibrium constant for the complex formation will also be presented.

Quantitative In Vitro and In Vivo Evaluation of Intestinal and Blood-Brain Barrier Transport Kinetics of the Plant N-Alkylamide Pellitorine.

PubMed

Veryser, Lieselotte; Bracke, Nathalie; Wynendaele, Evelien; Joshi, Tanmayee; Tatke, Pratima; Taevernier, Lien; De Spiegeleer, Bart

2016-01-01

Objective. To evaluate the gut mucosa and blood-brain barrier (BBB) pharmacokinetic permeability properties of the plant N-alkylamide pellitorine. Methods. Pure pellitorine and an Anacyclus pyrethrum extract were used to investigate the permeation of pellitorine through (1) a Caco-2 cell monolayer, (2) the rat gut after oral administration, and (3) the BBB in mice after intravenous and intracerebroventricular administration. A validated bioanalytical UPLC-MS(2) method was used to quantify pellitorine. Results. Pellitorine was able to cross the Caco-2 cell monolayer from the apical-to-basolateral and from the basolateral-to-apical side with apparent permeability coefficients between 0.6 · 10(-5) and 4.8 · 10(-5) cm/h and between 0.3 · 10(-5) and 5.8 · 10(-5) cm/h, respectively. In rats, a serum elimination rate constant of 0.3 h(-1) was obtained. Intravenous injection of pellitorine in mice resulted in a rapid and high permeation of pellitorine through the BBB with a unidirectional influx rate constant of 153 μL/(g·min). In particular, 97% of pellitorine reached the brain tissue, while only 3% remained in the brain capillaries. An efflux transfer constant of 0.05 min(-1) was obtained. Conclusion. Pellitorine shows a good gut permeation and rapidly permeates the BBB once in the blood, indicating a possible role in the treatment of central nervous system diseases.

Photocatalytic removal of doxycycline from aqueous solution using ZnO nano-particles: a comparison between UV-C and visible light.

PubMed

Pourmoslemi, Shabnam; Mohammadi, Ali; Kobarfard, Farzad; Amini, Mohsen

2016-10-01

Zinc oxide nano-particles were synthesized, characterized and used for photocatalytic degradation of doxycycline using UV-C and visible light. Effects of several operational factors including initial pH of antibiotic solution, initial antibiotic concentration and ZnO nano-particles loading amount were investigated. Comparing photocatalytic degradation and mineralization of doxycycline under UV-C and visible light showed successful application of the method under both light sources. However, reaction rate was higher under UV-C irradiation, which degraded doxycycline almost completely in 5 hours, and 68% mineralization was achieved. Synthesized ZnO nano-particles were successfully applied for photocatalytic degradation of doxycycline in a pharmaceutical wastewater sample. The process was fitted to the pseudo first order kinetic model with rate constants in the range of 6-22(×10 -3 ) mg L -1 min -1 with respect to initial concentration of doxycycline under UV-C irradiation. The Langmuir-Hinshelwood model was also employed for describing the photocatalytic reaction with surface reaction kinetic constant k c and equilibrium adsorption constant K LH values calculated as 0.12 mg L -1 min -1 and 2.2 L mg -1 , respectively. Degradation of doxycycline was followed by UV-visible spectroscopy and a validated stability indicating high-performance liquid chromatography method that was developed using stressed samples of doxycycline and could selectively determine doxycycline in the presence of its degradation products. Mass spectrometry was used for determining final degradation products.

Mercury methylation and demethylation in Hg-contaminated lagoon sediments (Marano and Grado Lagoon, Italy)

NASA Astrophysics Data System (ADS)

Hines, Mark E.; Poitras, Erin N.; Covelli, Stefano; Faganeli, Jadran; Emili, Andrea; Žižek, Suzana; Horvat, Milena

2012-11-01

Mercury (Hg) transformation activities and sulfate (SO42-) reduction were studied in sediments of the Marano and Grado Lagoons in the Northern Adriatic Sea region as part of the "MIRACLE" project. The lagoons, which are sites of clam (Tapes philippinarum) farming, have been receiving excess Hg from the Isonzo River for centuries. Marano Lagoon is also contaminated from a chlor-alkali plant. Radiotracer methods were used to measure mercury methylation (230Hg, 197Hg), methylmercury (MeHg) demethylation (14C-MeHg) and SO42- reduction (35S) in sediment cores collected in autumn, winter and summer. Mercury methylation rate constants ranged from near zero to 0.054 day-1, generally decreased with depth, and were highest in summer. Demethylation rate constants were much higher than methylation reaching values of ˜0.6 day-1 in summer. Demethylation occurred via the oxidative pathway, except in winter when the reductive pathway increased in importance in surficial sediments. Sulfate reduction was also most active in summer (up to 1600 nmol mL-1 day-1) and depth profiles reflected seasonally changing redox conditions near the surface. Methylation and demethylation rate constants correlated positively with SO42- reduction and pore-water Hg concentrations, and inversely with Hg sediment-water partition coefficients indicating the importance of SO42- reduction and Hg dissolution on Hg cycling. Hg transformation rates were calculated using rate constants and concentrations of Hg species. In laboratory experiments, methylation was inhibited by amendments of the SO42--reduction inhibitor molybdate and by nitrate. Lagoon sediments displayed a dynamic seasonal cycle in which Hg dissolution in spring/summer stimulated Hg methylation, which was followed by a net loss of MeHg in autumn from demethylation. Sulfate-reducing bacteria (SRB) tended to be responsible for methylation of Hg and the oxidative demethylation of MeHg. However, during winter in surficial sediments, iron-reducing bacteria seemed to contribute to methylation and Hg-resistant bacteria increased in importance in the reductive demethylation of MeHg. The high rates of MeHg demethylation in lagoon sediments may diminish the accumulation of MeHg.

Selecting for Fast Protein-Protein Association As Demonstrated on a Random TEM1 Yeast Library Binding BLIP.

PubMed

Cohen-Khait, Ruth; Schreiber, Gideon

2018-04-27

Protein-protein interactions mediate the vast majority of cellular processes. Though protein interactions obey basic chemical principles also within the cell, the in vivo physiological environment may not allow for equilibrium to be reached. Thus, in vitro measured thermodynamic affinity may not provide a complete picture of protein interactions in the biological context. Binding kinetics composed of the association and dissociation rate constants are relevant and important in the cell. Therefore, changes in protein-protein interaction kinetics have a significant impact on the in vivo activity of the proteins. The common protocol for the selection of tighter binders from a mutant library selects for protein complexes with slower dissociation rate constants. Here we describe a method to specifically select for variants with faster association rate constants by using pre-equilibrium selection, starting from a large random library. Toward this end, we refine the selection conditions of a TEM1-β-lactamase library against its natural nanomolar affinity binder β-lactamase inhibitor protein (BLIP). The optimal selection conditions depend on the ligand concentration and on the incubation time. In addition, we show that a second sort of the library helps to separate signal from noise, resulting in a higher percent of faster binders in the selected library. Fast associating protein variants are of particular interest for drug development and other biotechnological applications.

Clustering and flow around a sphere moving into a grain cloud.

PubMed

Seguin, A; Lefebvre-Lepot, A; Faure, S; Gondret, P

2016-06-01

A bidimensional simulation of a sphere moving at constant velocity into a cloud of smaller spherical grains far from any boundaries and without gravity is presented with a non-smooth contact dynamics method. A dense granular "cluster" zone builds progressively around the moving sphere until a stationary regime appears with a constant upstream cluster size. The key point is that the upstream cluster size increases with the initial solid fraction [Formula: see text] but the cluster packing fraction takes an about constant value independent of [Formula: see text]. Although the upstream cluster size around the moving sphere diverges when [Formula: see text] approaches a critical value, the drag force exerted by the grains on the sphere does not. The detailed analysis of the local strain rate and local stress fields made in the non-parallel granular flow inside the cluster allows us to extract the local invariants of the two tensors: dilation rate, shear rate, pressure and shear stress. Despite different spatial variations of these invariants, the local friction coefficient μ appears to depend only on the local inertial number I as well as the local solid fraction, which means that a local rheology does exist in the present non-parallel flow. The key point is that the spatial variations of I inside the cluster do not depend on the sphere velocity and explore only a small range around the value one.

Theoretical study of the vibrational relaxation of the methyl radical in collisions with helium

NASA Astrophysics Data System (ADS)

Ma, Qianli; Dagdigian, Paul J.; Alexander, Millard H.

2013-03-01

We report a theoretical investigation of the relaxation of the umbrella vibrational mode (the ν2 mode) of the CH3 molecule in its ground tilde{X}^2A_2^' ' } electronic state in collisions with helium. We have calculated a four-dimensional potential energy surface (PES) for the interaction between CH3 with different umbrella displacements and a helium atom, using a restricted open-shell coupled-cluster method with inclusion of all single, double, and (perturbatively) triple excitations [RCCSD(T)]. With this PES we carried out full close-coupling scattering calculations including all CH3 umbrella-rotational levels with v2 ⩽ 3. To our knowledge, this work represents the first fully quantum calculations of ro-vibrational relaxation of a polyatomic. In more detail, we investigate propensities in the calculated ro-vibrational cross sections and the dependence on initial rotational excitation, as well as determining thermal rate constants. Overall, ro-vibrational relaxation is nearly two orders of magnitude less efficient than pure-rotational relaxation, with a noticeable dependence on the initial rotational level. We predict the room temperature v2 = 1 vibrational relaxation rate constant to be 5.4 × 10-12 cm3 molecule-1 s-1, compared to the rate constants for pure-rotational relaxation of the lower rotational levels (˜2.0 × 10-10 cm3 molecule-1 s-1).

Oxidative decomposition of propylene carbonate in lithium ion batteries: a DFT study.

PubMed

Leggesse, Ermias Girma; Lin, Rao Tung; Teng, Tsung-Fan; Chen, Chi-Liang; Jiang, Jyh-Chiang

2013-08-22

This paper reports an in-depth mechanistic study on the oxidative decomposition of propylene carbonate in the presence of lithium salts (LiClO4, LiBF4, LiPF6, and LiAsF6) with the aid of density functional theory calculations at the B3LYP/6-311++G(d,p) level of theory. The solvent effect is accounted for by using the implicit solvation model with density method. Moreover, the rate constants for the decompositions of propylene carbonate have been investigated by using transition-state theory. The shortening of the original carbonyl C-O bond and a lengthening of the adjacent ethereal C-O bonds of propylene carbonate, which occurs as a result of oxidation, leads to the formation of acetone radical and CO2 as a primary oxidative decomposition product. The termination of the primary radical generates polycarbonate, acetone, diketone, 2-(ethan-1-ylium-1-yl)-4-methyl-1,3-dioxolan-4-ylium, and CO2. The thermodynamic and kinetic data show that the major oxidative decomposition products of propylene carbonate are independent of the type of lithium salt. However, the decomposition rate constants of propylene carbonate are highly affected by the lithium salt type. On the basis of the rate constant calculations using transition-state theory, the order of gas volume generation is: [PC-ClO4](-) > [PC-BF4](-) > [PC-AsF6](-) > [PC-PF6](-).

Continuous Rating for Diggability Assessment in Surface Mines

NASA Astrophysics Data System (ADS)

IPHAR, Melih

2016-10-01

The rocks can be loosened either by drilling-blasting or direct excavation using powerful machines in opencast mining operations. The economics of rock excavation is considered for each method to be applied. If blasting operation is not preferred and also the geological structures and rock mass properties in site are convenient (favourable ground conditions) for ripping or direct excavation method by mining machines, the next step is to determine which machine or excavator should be selected for the excavation purposes. Many researchers have proposed several diggability or excavatability assessment methods for deciding on excavator type to be used in the field. Most of these systems are generally based on assigning a rating for the parameters having importance in rock excavation process. However, the sharp transitions between the two adjacent classes for a given parameter can lead to some uncertainties. In this paper, it has been proposed that varying rating should be assigned for a given parameter called as “continuous rating” instead of giving constant rating for a given class.

Rapid and accurate prediction of degradant formation rates in pharmaceutical formulations using high-performance liquid chromatography-mass spectrometry.

PubMed

Darrington, Richard T; Jiao, Jim

2004-04-01

Rapid and accurate stability prediction is essential to pharmaceutical formulation development. Commonly used stability prediction methods include monitoring parent drug loss at intended storage conditions or initial rate determination of degradants under accelerated conditions. Monitoring parent drug loss at the intended storage condition does not provide a rapid and accurate stability assessment because often <0.5% drug loss is all that can be observed in a realistic time frame, while the accelerated initial rate method in conjunction with extrapolation of rate constants using the Arrhenius or Eyring equations often introduces large errors in shelf-life prediction. In this study, the shelf life prediction of a model pharmaceutical preparation utilizing sensitive high-performance liquid chromatography-mass spectrometry (LC/MS) to directly quantitate degradant formation rates at the intended storage condition is proposed. This method was compared to traditional shelf life prediction approaches in terms of time required to predict shelf life and associated error in shelf life estimation. Results demonstrated that the proposed LC/MS method using initial rates analysis provided significantly improved confidence intervals for the predicted shelf life and required less overall time and effort to obtain the stability estimation compared to the other methods evaluated. Copyright 2004 Wiley-Liss, Inc. and the American Pharmacists Association.

Ultraslow myosin molecular motors of placental contractile stem villi in humans.

PubMed

Lecarpentier, Yves; Claes, Victor; Lecarpentier, Edouard; Guerin, Catherine; Hébert, Jean-Louis; Arsalane, Abdelilah; Moumen, Abdelouahab; Krokidis, Xénophon; Michel, Francine; Timbely, Oumar

2014-01-01

Human placental stem villi (PSV) present contractile properties. In vitro mechanics were investigated in 40 human PSV. Contraction of PSV was induced by both KCl exposure (n = 20) and electrical tetanic stimulation (n = 20). Isotonic contractions were registered at several load levels ranging from zero-load up to isometric load. The tension-velocity relationship was found to be hyperbolic. This made it possible to apply the A. Huxley formalism for determining the rate constants for myosin cross-bridge (CB) attachment and detachment, CB single force, catalytic constant, myosin content, and maximum myosin ATPase activity. These molecular characteristics of myosin CBs did not differ under either KCl exposure or tetanus. A comparative approach was established from studies previously published in the literature and driven by mean of a similar method. As compared to that described in mammalian striated muscles, we showed that in human PSV, myosin CB rate constants for attachment and detachment were about 103 times lower whereas myosin ATPase activity was 105 times lower. Up to now, CB kinetics of contractile cells arranged along the long axis of the placental sheath appeared to be the slowest ever observed in any mammalian contractile tissue.

Interaction of dihydrofolate reductase with methotrexate: Ensemble and single-molecule kinetics

NASA Astrophysics Data System (ADS)

Rajagopalan, P. T. Ravi; Zhang, Zhiquan; McCourt, Lynn; Dwyer, Mary; Benkovic, Stephen J.; Hammes, Gordon G.

2002-10-01

The thermodynamics and kinetics of the interaction of dihydrofolate reductase (DHFR) with methotrexate have been studied by using fluorescence, stopped-flow, and single-molecule methods. DHFR was modified to permit the covalent addition of a fluorescent molecule, Alexa 488, and a biotin at the N terminus of the molecule. The fluorescent molecule was placed on a protein loop that closes over methotrexate when binding occurs, thus causing a quenching of the fluorescence. The biotin was used to attach the enzyme in an active form to a glass surface for single-molecule studies. The equilibrium dissociation constant for the binding of methotrexate to the enzyme is 9.5 nM. The stopped-flow studies revealed that methotrexate binds to two different conformations of the enzyme, and the association and dissociation rate constants were determined. The single-molecule investigation revealed a conformational change in the enzyme-methotrexate complex that was not observed in the stopped-flow studies. The ensemble averaged rate constants for this conformation change in both directions is about 2-4 s1 and is attributed to the opening and closing of the enzyme loop over the bound methotrexate. Thus the mechanism of methotrexate binding to DHFR involves multiple steps and protein conformational changes.

Non-equilibrium reaction rates in chemical kinetic equations

NASA Astrophysics Data System (ADS)

Gorbachev, Yuriy

2018-05-01

Within the recently proposed asymptotic method for solving the Boltzmann equation for chemically reacting gas mixture, the chemical kinetic equations has been derived. Corresponding one-temperature non-equilibrium reaction rates are expressed in terms of specific heat capacities of the species participate in the chemical reactions, bracket integrals connected with the internal energy transfer in inelastic non-reactive collisions and energy transfer coefficients. Reactions of dissociation/recombination of homonuclear and heteronuclear diatomic molecules are considered. It is shown that all reaction rates are the complex functions of the species densities, similarly to the unimolecular reaction rates. For determining the rate coefficients it is recommended to tabulate corresponding bracket integrals, additionally to the equilibrium rate constants. Correlation of the obtained results with the irreversible thermodynamics is established.

The computational analysis and modelling of substitution effects on hydrolysis of formanilides in acidic aqueous solutions

NASA Astrophysics Data System (ADS)

Lukeš, Vladimír; Škorňa, Peter; Michalík, Martin; Klein, Erik

2017-11-01

Various para, meta and ortho substituted formanilides have been theoretically studied. For trans and cis-isomers of non-substituted formanilide, the calculated B3LYP vibration normal modes were analyzed. Substituent effect on the selected normal modes was described and the comparison with the available experimental data is presented. The calculated B3LYP proton affinities were correlated with Hammett constants, Fujita-Nishioka equation and the rate constants of the hydrolysis in 1 M HCl. Found linear dependences allow predictions of dissociation constants (pKBH+) and hydrolysis rate constants. Obtained results indicate that protonation of amide group may represent the rate determining step of acid catalyzed hydrolysis.

Decomposition rates for hand-piled fuels

Treesearch

Clinton S. Wright; Alexander M. Evans; Joseph C. Restaino

2017-01-01

Hand-constructed piles in eastern Washington and north-central New Mexico were weighed periodically between October 2011 and June 2015 to develop decay-rate constants that are useful for estimating the rate of piled biomass loss over time. Decay-rate constants (k) were determined by fitting negative exponential curves to time series of pile weight for each site. Piles...

Constant pressure mode extended simple gradient liquid chromatography system for micro and nanocolumns.

PubMed

Šesták, Jozef; Kahle, Vladislav

2014-07-11

Performing gradient liquid chromatography at constant pressure instead of constant flow rate has serious potential for shortening the analysis time and increasing the productivity of HPLC instruments that use gradient methods. However, in the constant pressure mode the decreasing column permeability during a long period of time negatively affects the repeatability of retention time. Thus a volume-based approach, in which the detector signal is plotted as a function of retention volume, must be taken into consideration. Traditional HPLC equipment, however, requires quite complex hardware and software modifications in order to work at constant pressure and in the volume-based mode. In this short communication, a low cost and easily feasible pressure-controlled extension of the previously described simple gradient liquid chromatography platform is proposed. A test mixture of four nitro esters was separated by 10-60% (v/v) acetone/water gradient and a high repeatability of retention volumes at 20MPa (RSD less than 0.45%) was realized. Separations were also performed at different values of pressure (20, 25, and 31MPa), and only small variations of the retention volumes (up to 0.8%) were observed. In this particular case, the gain in the analysis speed of 7% compared to the constant flow mode was realized at a constant pressure. Copyright © 2014 Elsevier B.V. All rights reserved.

Rapid-Equilibrium Enzyme Kinetics

ERIC Educational Resources Information Center

Alberty, Robert A.

2008-01-01

Rapid-equilibrium rate equations for enzyme-catalyzed reactions are especially useful because if experimental data can be fit by these simpler rate equations, the Michaelis constants can be interpreted as equilibrium constants. However, for some reactions it is necessary to use the more complicated steady-state rate equations. Thermodynamics is…