Heat release rate of wood-plastic composites

Science.gov (United States)

N. M. Stark; R. H. White; C. M. Clemons

1997-01-01

Wood-plastic composites are becoming more important as a material that fulfills recycling needs. In this study, fire performance tests were conducted on several compositions of wood and plastic materials using the Ohio State University rate of heat release apparatus. Test results included five-minute average heat release rate in kW/m2 (HRR avg) and maximum heat release...

Constant strain accumulation rate between major earthquakes on the North Anatolian Fault.

Science.gov (United States)

Hussain, Ekbal; Wright, Tim J; Walters, Richard J; Bekaert, David P S; Lloyd, Ryan; Hooper, Andrew

2018-04-11

Earthquakes are caused by the release of tectonic strain accumulated between events. Recent advances in satellite geodesy mean we can now measure this interseismic strain accumulation with a high degree of accuracy. But it remains unclear how to interpret short-term geodetic observations, measured over decades, when estimating the seismic hazard of faults accumulating strain over centuries. Here, we show that strain accumulation rates calculated from geodetic measurements around a major transform fault are constant for its entire 250-year interseismic period, except in the ~10 years following an earthquake. The shear strain rate history requires a weak fault zone embedded within a strong lower crust with viscosity greater than ~10 20  Pa s. The results support the notion that short-term geodetic observations can directly contribute to long-term seismic hazard assessment and suggest that lower-crustal viscosities derived from postseismic studies are not representative of the lower crust at all spatial and temporal scales.

The time dependence of rate constants of esub(aq)sup(-) reactions

International Nuclear Information System (INIS)

Burcl, R.; Byakov, V.M.; Grafutin, V.I.

1982-01-01

Published data about the time dependence of rate constants k(esub(aq)sup(-)+Ac) of esub(aq)sup(-) reactions with the acceptor Ac are analyzed, using the results of rate constant k(Ps+Ac) measurements for positronium reactions. It is shown that neither esub(aq)sup(-) nor Ps reaction rate constants depend on time in the observable range. Experimentally found concentration dependence of k(esub(aq)sup(-)+Ac) is due to other factors, connected with the existence of electric charge of esub(aq)sup(-), e.g. ionic strength, tunnelling effect etc. (author)

Determination of rate constants of N-alkylation of primary amines by 1H NMR spectroscopy.

Science.gov (United States)

Li, Chenghong

2013-09-05

Macromolecules containing N-diazeniumdiolates of secondary amines are proposed scaffolds for controlled nitrogen oxide (NO) release medical applications. Preparation of these compounds often involves converting primary amine groups to secondary amine groups through N-alkylation. However, N-alkylation results in not only secondary amines but tertiary amines as well. Only N-diazeniumdiolates of secondary amines are suitable for controlled NO release; therefore, the yield of secondary amines is crucial to the total NO load of the carrier. In this paper, (1)H NMR spectroscopy was used to estimate the rate constants for formation of secondary amine (k1) and tertiary amine (k2) for alkylation reagents such as propylene oxide (PO), methyl acrylate (MA), and acrylonitrile (ACN). At room temperature, the ratio of k2/k1 for the three reactions was found to be around 0.50, 0.026, and 0.0072.

Rate constant for reaction of hydroxyl radicals with bicarbonate ions

International Nuclear Information System (INIS)

Buxton, G.V.; Elliot, A.J.

1986-01-01

The rate constant for reaction of hydroxyl radicals with the bicarbonate ion has been determined to be 8.5 x 10 6 dm 3 mol -1 s -1 . This value was calculated from: the measured rate of formation of the CO 3 - radical in pulsed electron irradiation of bicarbonate solutions over the pH range 7.0 to 9.4; the pK for the equilibrium HCO 3 - = CO 3 2- + H + ; and the rate constant for hydroxyl radicals reacting with the carbonate ion. (author)

Reaction rate constant for radiative association of CF{sup +}

Energy Technology Data Exchange (ETDEWEB)

Öström, Jonatan, E-mail: jonatan.ostrom@gmail.com; Gustafsson, Magnus, E-mail: magnus.gustafsson@ltu.se [Applied Physics, Division of Materials Science, Department of Engineering Science and Mathematics, Luleå University of Technology, 97187 Luleå (Sweden); Bezrukov, Dmitry S. [Department of Chemistry, M. V. Lomonosov Moscow State University, Moscow, 119991 (Russian Federation); Nyman, Gunnar [Department of Chemistry and Molecular Biology, University of Gothenburg, 41296 Gothenburg (Sweden)

2016-01-28

Reaction rate constants and cross sections are computed for the radiative association of carbon cations (C{sup +}) and fluorine atoms (F) in their ground states. We consider reactions through the electronic transition 1{sup 1}Π → X{sup 1}Σ{sup +} and rovibrational transitions on the X{sup 1}Σ{sup +} and a{sup 3}Π potentials. Semiclassical and classical methods are used for the direct contribution and Breit–Wigner theory for the resonance contribution. Quantum mechanical perturbation theory is used for comparison. A modified formulation of the classical method applicable to permanent dipoles of unequally charged reactants is implemented. The total rate constant is fitted to the Arrhenius–Kooij formula in five temperature intervals with a relative difference of <3%. The fit parameters will be added to the online database KIDA. For a temperature of 10–250 K, the rate constant is about 10{sup −21} cm{sup 3} s{sup −1}, rising toward 10{sup −16} cm{sup 3} s{sup −1} for a temperature of 30 000 K.

Diffusion rates for elevated releases

International Nuclear Information System (INIS)

Ramsdell, J.V.

1983-11-01

A search of the literature related to diffusion from elevated sources has determined that an adequate data base exists for use in developing parameterizations for estimating diffusion rates for material released from free standing stacks at nuclear power plants. A review of published data analyses indicates that a new parameterization of horizontal diffusion rates specifically for elevated releases is not likely to significantly change the magnitudes of horizontal diffusion coefficients on the average. However, the uncertainties associated with horizontal diffusion coefficient estimates under any given set of atmospheric conditions could be reduced by a new parameterization. Similarly, a new parameterization of vertical diffusion rates would be unlikely to significantly alter the magnitudes of diffusion coefficients for unstable atmospheric conditons. However, for neutral and stable atmospheric conditions, a new parameterization of vertical diffusion rates might increase vertical diffusion coefficients significantly. The increase would move ground-level time-integrated concentration maxima closer to the plant and would increase the maxima. 55 references, 2 figures, 4 tables

Glucose consumption and rate constants for 18F-fluorodeoxyglucose in human gliomas

International Nuclear Information System (INIS)

Ishikawa, Masatsune; Kikuchi, Haruhiko; Nagata, Izumi; Yamagata, Sen; Taki, Waro; Yonekura, Yoshiharu; Nishizawa, Sadahiko; Iwasaki, Yasushi; Mukai, Takao

1990-01-01

To investigate the value of direct measurement of the rate constants by performing 18 F-labeled fluorodeoxyglucose (FDG) studies of glucose consumption in human gliomas in vivo, a kinetic method with 3- and 4-parameter rate constant models for FDG uptake was used to analyze data from dynamic scans obtained by positron emission tomography after injection of FDG into 14 patients with glioma. The results were compared with those obtained by the autoradiographic method using 3- and 4-parameter rate constant models. There were no significant differences in the glucose consumption calculated by the four different methods both in the gliomas and in the contralateral intact cortex. It was found that the rate constant k4 could be neglected in calculation of glucose consumption in gliomas as well as in the contralateral intact cortex. The rate constant k3, an index of hexokinase function, was higher in malignant gliomas than in benign gliomas and was close to that in the contralateral cortex. This study indicates that the 3-parameter autoradiographic method, which is the most common one used in clinical practice, is reliable for the calculation of glucose consumption in human gliomas. Furthermore, direct measurement of the regional rate constants for FDG by the kinetic method was found to be useful for evaluation of the biochemical and physiological characteristics of human gliomas in vivo. (author)

Reaction rate constants of H-abstraction by OH from large ketones: Measurements and site-specific rate rules

KAUST Repository

Badra, Jihad; Elwardani, Ahmed Elsaid; Farooq, Aamir

2014-01-01

-pentanone, and 4-methl-2-pentanone. Rate constants are measured under pseudo-first-order kinetics at temperatures ranging from 866 K to 1375 K and pressures near 1.5 atm. The reported high-temperature rate constant measurements are the first direct

Relationship among reaction rate, release rate and efficiency of nanomachine-based targeted drug delivery.

Science.gov (United States)

Zhao, Qingying; Li, Min; Luo, Jun

2017-12-04

In nanomachine applications towards targeted drug delivery, drug molecules released by nanomachines propagate and chemically react with tumor cells in aqueous environment. If the nanomachines release drug molecules faster than the tumor cells react, it will result in loss and waste of drug molecules. It is a potential issue associated with the relationship among reaction rate, release rate and efficiency. This paper aims to investigate the relationship among reaction rate, release rate and efficiency based on two drug reception models. We expect to pave a way for designing a control method of drug release. We adopted two analytical methods that one is drug reception process based on collision with tumors and another is based on Michaelis Menten enzymatic kinetics. To evaluate the analytical formulations, we used the well-known simulation framework N3Sim to establish simulations. The analytical results of the relationship among reaction rate, release rate and efficiency is obtained, which match well with the numerical simulation results in a 3-D environment. Based upon two drug reception models, the results of this paper would be beneficial for designing a control method of nanomahine-based drug release.

Determination of Biological Oxygen Demand Rate Constant and ...

African Journals Online (AJOL)

Determination of Biological Oxygen Demand Rate Constant and Ultimate Biological Oxygen Demand for Liquid Waste Generated from Student Cafeteria at Jimma University: A Tool for Development of Scientific Criteria to Protect Aquatic Health in the Region.

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

Science.gov (United States)

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.

Power consumption analysis of constant bit rate data transmission over 3G mobile wireless networks

DEFF Research Database (Denmark)

Wang, Le; Ukhanova, Ann; Belyaev, Evgeny

2011-01-01

This paper presents the analysis of the power consumption of data transmission with constant bit rate over 3G mobile wireless networks. Our work includes the description of the transition state machine in 3G networks, followed by the detailed energy consumption analysis and measurement results...... of the radio link power consumption. Based on these description and analysis, we propose power consumption model. The power model was evaluated on the smartphone Nokia N900, which follows a 3GPP Release 5 and 6 supporting HSDPA/HSPA data bearers. Further we propose method of parameters selection for 3GPP...... transition state machine that allows to decrease power consumption on the mobile device....

Rate constants for some electrophilic reactions of benzyl, benzhydryl, and trityl cations in solution

International Nuclear Information System (INIS)

Ujdak, R.J.; Jones, R.L.; Dorfman, L.M.

1976-01-01

Absolute rate constants have been determined by the pulse radiolysis technique for several electrophilic reactions of the benzyl, the benzhydryl, and the trityl cation in 1,2-dichloroethane solution. The rate constants for the reactions of these carbonium ions with chloride ion, with bromide ion, and with iodide ion are all very nearly the same, namely 6 x 10 10 M -1 s -1 at 24 0 C. The values very likely represent the diffusion controlled limit for the ion combination reactions. The rate constants for the reactions with triethylamine, tri-n-propylamine, and tri-n-butylamine range from 2.0 x 10 9 to 7 x 10 6 M -1 s -1 at 24 0 C. With increasing phenyl substitution, the decreasing trend in the magnitude of the rate constant is consistent with the combined electronic and steric effects. With increasing size of the amine, the decrease in the value of the rate constant seems to indicate that the steric effect predominates. The values of the rate constants for reactions of benzyl and benzhydryl cation with methanol, ethanol, and 2-propanol indicate the following. The rate constant is higher for reaction with the alcohol dimer in solution than with alcohol monomer. The rate constants for reaction with alcohol monomer have values of 1 x 10 8 M -1 s -1 or lower

VMATc: VMAT with constant gantry speed and dose rate

International Nuclear Information System (INIS)

Peng, Fei; Romeijn, H Edwin; Epelman, Marina A; Jiang, Steve B

2015-01-01

This article considers the treatment plan optimization problem for Volumetric Modulated Arc Therapy (VMAT) with constant gantry speed and dose rate (VMATc). In particular, we consider the simultaneous optimization of multi-leaf collimator leaf positions and a constant gantry speed and dose rate. We propose a heuristic framework for (approximately) solving this optimization problem that is based on hierarchical decomposition. Specifically, an iterative algorithm is used to heuristically optimize dose rate and gantry speed selection, where at every iteration a leaf position optimization subproblem is solved, also heuristically, to find a high-quality plan corresponding to a given dose rate and gantry speed. We apply our framework to clinical patient cases, and compare the resulting VMATc plans to idealized IMRT, as well as full VMAT plans. Our results suggest that VMATc is capable of producing treatment plans of comparable quality to VMAT, albeit at the expense of long computation time and generally higher total monitor units. (paper)

Impact of Constant Rate Factor on Objective Video Quality Assessment

Directory of Open Access Journals (Sweden)

Juraj Bienik

2017-01-01

Full Text Available This paper deals with the impact of constant rate factor value on the objective video quality assessment using PSNR and SSIM metrics. Compression efficiency of H.264 and H.265 codecs defined by different Constant rate factor (CRF values was tested. The assessment was done for eight types of video sequences depending on content for High Definition (HD, Full HD (FHD and Ultra HD (UHD resolution. Finally, performance of both mentioned codecs with emphasis on compression ratio and efficiency of coding was compared.

Reaction rate constants of H-abstraction by OH from large ketones: measurements and site-specific rate rules.

Science.gov (United States)

Badra, Jihad; Elwardany, Ahmed E; Farooq, Aamir

2014-06-28

Reaction rate constants of the reaction of four large ketones with hydroxyl (OH) are investigated behind reflected shock waves using OH laser absorption. The studied ketones are isomers of hexanone and include 2-hexanone, 3-hexanone, 3-methyl-2-pentanone, and 4-methl-2-pentanone. Rate constants are measured under pseudo-first-order kinetics at temperatures ranging from 866 K to 1375 K and pressures near 1.5 atm. The reported high-temperature rate constant measurements are the first direct measurements for these ketones under combustion-relevant conditions. The effects of the position of the carbonyl group (C=O) and methyl (CH3) branching on the overall rate constant with OH are examined. Using previously published data, rate constant expressions covering, low-to-high temperatures, are developed for acetone, 2-butanone, 3-pentanone, and the hexanone isomers studied here. These Arrhenius expressions are used to devise rate rules for H-abstraction from various sites. Specifically, the current scheme is applied with good success to H-abstraction by OH from a series of n-ketones. Finally, general expressions for primary and secondary site-specific H-abstraction by OH from ketones are proposed as follows (the subscript numbers indicate the number of carbon atoms bonded to the next-nearest-neighbor carbon atom, the subscript CO indicates that the abstraction is from a site next to the carbonyl group (C=O), and the prime is used to differentiate different neighboring environments of a methylene group):

Constrained least squares methods for estimating reaction rate constants from spectroscopic data

NARCIS (Netherlands)

Bijlsma, S.; Boelens, H.F.M.; Hoefsloot, H.C.J.; Smilde, A.K.

2002-01-01

Model errors, experimental errors and instrumental noise influence the accuracy of reaction rate constant estimates obtained from spectral data recorded in time during a chemical reaction. In order to improve the accuracy, which can be divided into the precision and bias of reaction rate constant

Estimating reaction rate constants: comparison between traditional curve fitting and curve resolution

NARCIS (Netherlands)

Bijlsma, S.; Boelens, H. F. M.; Hoefsloot, H. C. J.; Smilde, A. K.

2000-01-01

A traditional curve fitting (TCF) algorithm is compared with a classical curve resolution (CCR) approach for estimating reaction rate constants from spectral data obtained in time of a chemical reaction. In the TCF algorithm, reaction rate constants an estimated from the absorbance versus time data

Dissociative electron attachment to ozone: rate constant

International Nuclear Information System (INIS)

Skalny, J.D.; Cicman, P.; Maerk, T.D.

2002-01-01

The rate constant for dissociative electron attachment to ozone has been derived over the energy range of 0-10 eV by using previously measured cross section data revisited here in regards to discrimination effect occurring during the extraction of ions. The obtained data for both possible channels exhibit the maximum at mean electron energies close to 1 eV. (author)

Glucose consumption and rate constants for sup 18 F-fluorodeoxyglucose in human gliomas

Energy Technology Data Exchange (ETDEWEB)

Ishikawa, Masatsune; Kikuchi, Haruhiko; Nagata, Izumi; Yamagata, Sen; Taki, Waro; Yonekura, Yoshiharu; Nishizawa, Sadahiko; Iwasaki, Yasushi; Mukai, Takao [Kyoto Univ. (Japan). Faculty of Medicine

1990-06-01

To investigate the value of direct measurement of the rate constants by performing {sup 18}F-labeled fluorodeoxyglucose (FDG) studies of glucose consumption in human gliomas in vivo, a kinetic method with 3- and 4-parameter rate constant models for FDG uptake was used to analyze data from dynamic scans obtained by positron emission tomography after injection of FDG into 14 patients with glioma. The results were compared with those obtained by the autoradiographic method using 3- and 4-parameter rate constant models. There were no significant differences in the glucose consumption calculated by the four different methods both in the gliomas and in the contralateral intact cortex. It was found that the rate constant k4 could be neglected in calculation of glucose consumption in gliomas as well as in the contralateral intact cortex. The rate constant k3, an index of hexokinase function, was higher in malignant gliomas than in benign gliomas and was close to that in the contralateral cortex. This study indicates that the 3-parameter autoradiographic method, which is the most common one used in clinical practice, is reliable for the calculation of glucose consumption in human gliomas. Furthermore, direct measurement of the regional rate constants for FDG by the kinetic method was found to be useful for evaluation of the biochemical and physiological characteristics of human gliomas in vivo. (author).

High-temperature rate constant measurements for OH+xylenes

KAUST Repository

Elwardani, Ahmed Elsaid; Badra, Jihad; Farooq, Aamir

2015-01-01

The overall rate constants for the reactions of hydroxyl (OH) radicals with o-xylene (k 1), m-xylene (k 2), and p-xylene (k 3) were measured behind reflected shock waves over 890-1406K at pressures of 1.3-1.8atm using OH laser absorption near 306

Constant displacement rate testing at elevated temperatures

International Nuclear Information System (INIS)

Pepe, J.J.; Gonyea, D.C.

1989-01-01

A short time test has been developed which is capable of determining the long time notch sensitivity tendencies of CrMoV rotor forging materials. This test is based on Constant Displacement Rate (CDR) testing of a specific notch bar specimen at 1200 0 F at 2 mils/in/hour displacement rate. These data were correlated to conventional smooth and notch bar rupture behavior for a series of CrMoV materials with varying long time ductility tendencies. The purpose of this paper is to describe the details of this new test procedure and some of the relevant mechanics of material information generated during its development

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.

Science.gov (United States)

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

A calculation of the surface recombination rate constant for hydrogen isotopes on metals

International Nuclear Information System (INIS)

Baskes, M.J.

1980-01-01

The surface recombination rate constant for hydrogen isotopes on a metal has been calculated using a simple model whose parameters may be determined by direct experimental measurements. Using the experimental values for hydrogen diffusivity, solubility, and sticking coefficient at zero surface coverage a reasonable prediction of the surface recombination constant may be made. The calculated recombination constant is in excellent agreement with experiment for bcc iron. A heuristic argument is developed which, along with the rate constant calculation, shows that surface recombination is important in those metals in which hydrogen has an exothermic heat of solution. (orig.)

Microscopic Rate Constants of Crystal Growth from Molecular Dynamic Simulations Combined with Metadynamics

Directory of Open Access Journals (Sweden)

Dániel Kozma

2012-01-01

Full Text Available Atomistic simulation of crystal growth can be decomposed into two steps: the determination of the microscopic rate constants and a mesoscopic kinetic Monte Carlo simulation. We proposed a method to determine kinetic rate constants of crystal growth. We performed classical molecular dynamics on the equilibrium liquid/crystal interface of argon. Metadynamics was used to explore the free energy surface of crystal growth. A crystalline atom was selected at the interface, and it was displaced to the liquid phase by adding repulsive Gaussian potentials. The activation free energy of this process was calculated as the maximal potential energy density of the Gaussian potentials. We calculated the rate constants at different interfacial structures using the transition state theory. In order to mimic real crystallization, we applied a temperature difference in the calculations of the two opposite rate constants, and they were applied in kinetic Monte Carlo simulation. The novelty of our technique is that it can be used for slow crystallization processes, while the simple following of trajectories can be applied only for fast reactions. Our method is a possibility for determination of elementary rate constants of crystal growth that seems to be necessary for the long-time goal of computer-aided crystal design.

Power consumption analysis of constant bit rate video transmission over 3G networks

DEFF Research Database (Denmark)

Ukhanova, Ann; Belyaev, Evgeny; Wang, Le

2012-01-01

This paper presents an analysis of the power consumption of video data transmission with constant bit rate over 3G mobile wireless networks. The work includes the description of the radio resource control transition state machine in 3G networks, followed by a detailed power consumption analysis...... and measurements of the radio link power consumption. Based on this description and analysis, we propose our power consumption model. The power model was evaluated on a smartphone Nokia N900, which follows 3GPP Release 5 and 6 supporting HSDPA/HSUPA data bearers. We also propose a method for parameter selection...... for the 3GPP transition state machine that allows to decrease power consumption on a mobile device taking signaling traffic, buffer size and latency restrictions into account. Furthermore, we discuss the gain in power consumption vs. PSNR for transmitted video and show the possibility of performing power...

Convergence analysis of Chauvin's PCA learning algorithm with a constant learning rate

International Nuclear Information System (INIS)

Lv Jiancheng; Yi Zhang

2007-01-01

The convergence of Chauvin's PCA learning algorithm with a constant learning rate is studied in this paper by using a DDT method (deterministic discrete-time system method). Different from the DCT method (deterministic continuous-time system method), the DDT method does not require that the learning rate converges to zero. An invariant set of Chauvin's algorithm with a constant learning rate is obtained so that the non-divergence of this algorithm can be guaranteed. Rigorous mathematic proofs are provided to prove the local convergence of this algorithm

The surface-forming energy release rate versus the local energy release rate

OpenAIRE

Xiao, Si; Wang, He-ling; Landis, Chad M; Hwang, Keh-Chih; Liu, Bin

2016-01-01

This paper identifies two ways to extract the energy (or power) flowing into a crack tip during propagation based on the power balance of areas enclosed by a stationary contour and a comoving contour. It is very interesting to find a contradiction that two corresponding energy release rates (ERRs), a surface-forming ERR and a local ERR, are different when stress singularity exists at a crack tip. Besides a rigorous mathematical interpretation, we deduce that the stress singularity leads to an...

Determination of reaction rate constants for alkylation of 4-(p-nitrobenzyl) pyridine by different alkylating agents.

Science.gov (United States)

Walles, S A

1980-02-01

The rate constants have been determined for the reaction between some different alkylating agents and 4-(p-nitrobenzyl) pyridine (NBP) in methanol. These constants have been compared with those for alkylation of aniline in water. All the constants were lower in methanol than in water but in different degrees. The rate constants of the different alkylating agents have been calculated at a nucleophilic strength n=2. The genetic risk defined as the degree of alkylation of a nucleophile (n=2) is equivalent to the rate constant kn=2 and the target dose. The dependence of the genetic risk on the rate constant (kn=2) is discussed.

An atomistic methodology of energy release rate for graphene at nanoscale

International Nuclear Information System (INIS)

Zhang, Zhen; Lee, James D.; Wang, Xianqiao

2014-01-01

Graphene is a single layer of carbon atoms packed into a honeycomb architecture, serving as a fundamental building block for electric devices. Understanding the fracture mechanism of graphene under various conditions is crucial for tailoring the electrical and mechanical properties of graphene-based devices at atomic scale. Although most of the fracture mechanics concepts, such as stress intensity factors, are not applicable in molecular dynamics simulation, energy release rate still remains to be a feasible and crucial physical quantity to characterize the fracture mechanical property of materials at nanoscale. This work introduces an atomistic simulation methodology, based on the energy release rate, as a tool to unveil the fracture mechanism of graphene at nanoscale. This methodology can be easily extended to any atomistic material system. We have investigated both opening mode and mixed mode at different temperatures. Simulation results show that the critical energy release rate of graphene is independent of initial crack length at low temperature. Graphene with inclined pre-crack possesses higher fracture strength and fracture deformation but smaller critical energy release rate compared with the graphene with vertical pre-crack. Owing to its anisotropy, graphene with armchair chirality always has greater critical energy release rate than graphene with zigzag chirality. The increase of temperature leads to the reduction of fracture strength, fracture deformation, and the critical energy release rate of graphene. Also, higher temperature brings higher randomness of energy release rate of graphene under a variety of predefined crack lengths. The energy release rate is independent of the strain rate as long as the strain rate is small enough

Release rates from waste packages in a salt repository

International Nuclear Information System (INIS)

Chambre, P.L.; Hwang, Y.; Lee, W.W.L.; Pigford, T.H.

1987-06-01

In this report we present estimates of radionuclide release rates from waste packages into salt. This conservative and bounding analysis shows that release rates from waste packages in salt are well below the US Nuclear Regulatory Commission's performance objectives for the engineered barrier system. 2 refs., 2 figs

Reaction rate constants of HO2 + O3 in the temperature range 233-400 K

Science.gov (United States)

Wang, Xiuyan; Suto, Masako; Lee, L. C.

1988-01-01

The reaction rate constants of HO2 + O3 were measured in the temperature range 233-400 K using a discharge flow system with photofragment emission detection. In the range 233-253 K, the constants are approximately a constant value, and then increase with increasing temperature. This result suggests that the reaction may have two different channels. An expression representing the reaction rate constants is presented.

Heat release rate from the combustion of uranium

International Nuclear Information System (INIS)

Solbrig, C.W.

1995-01-01

Fuel treatment is planned at the Argonne National Laboratory on EBR-II spent fuel. The electrochemical treatment process is carried out in a cell with an argon atmosphere to prevent any reaction. The amount of fuel processed at any time is limited by the amount of energy which could be released by metal combustion if air is inadvertently allowed into the cell since the heat release would increase the cell pressure. The cell pressure is required to be below atmospheric even if combustion occurs to ensure no cell gas/aerosol is released to the environment. Metal fires can release large amounts of heat. In certain configurations such as fine particulate, metal can be pyrophoric at room temperature. When the metal is a nuclear fuel, it is important to be able to predict the reaction/heat release rate if the metal is inadvertently exposed to air. A realistic combustion model is needed to predict heat release rates for the many different flow and transport configurations which exist in the various fuel processing steps. A model for the combustion of uranium is developed here which compares satisfactorily to experimental data

Semiclassical Calculation of Reaction Rate Constants for Homolytical Dissociations

Science.gov (United States)

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.

Constant rate natural gas production from a well in a hydrate reservoir

International Nuclear Information System (INIS)

Ji Chuang; Ahmadi, Goodarz; Smith, Duane H.

2003-01-01

Using a computational model, production of natural gas at a constant rate from a well that is drilled into a confined methane hydrate reservoir is studied. It is assumed that the pores in the reservoir are partially saturated with hydrate. A linearized model for an axisymmetric condition with a fixed well output is used in the analysis. For different reservoir temperatures and various well outputs, time evolutions of temperature and pressure profiles, as well as the gas flow rate in the hydrate zone and the gas region, are evaluated. The distance of the decomposition front from the well as a function of time is also computed. It is shown that to maintain a constant natural gas production rate, the well pressure must be decreased with time. A constant low production rate can be sustained for a long duration of time, but a high production rate demands unrealistically low pressure at the well after a relatively short production time. The simulation results show that the process of natural gas production in a hydrate reservoir is a sensitive function of reservoir temperature and hydrate zone permeability

Effect of selecting a fixed dephosphorylation rate on the estimation of rate constants and rCMRGlu from dynamic [18F] fluorodeoxyglucose/PET data

International Nuclear Information System (INIS)

Dhawan, V.; Moeller, J.R.; Strother, S.C.; Evans, A.C.; Rottenberg, D.A.

1989-01-01

Several publications have discussed the estimation and physiologic significance of regional [ 18 F]fluorodeoxyglucose (FDG) rate constants and metabolic rates. Most of these studies analyzed dynamic data collected over 45-60 min; three rate constants (k1-k3) and blood volume (Vb) were estimated and the regional cerebral metabolic rate for glucose (rCMRGlu) was subsequently derived using the measured blood glucose value and a regionally invariant value of the lumped constant (LC). The dephosphorylation rate constant (k4) was either neglected, or a fixed value was used in the estimation procedure to obtain the remaining parameters. To compare the rate constants obtained by different authors using different values of k4 is impossible without knowledge of the effect of selecting different fixed values of k4 (including zero) on the estimated rate constants and rCMRGlu. Based on our analysis of FDG/PET data from nine normal volunteer subjects, we conclude that inclusion of a fixed value for k4, in spite of a scaling effect on the absolute values of model parameters, has no effect on the coefficient of variation (CV) of within- and between-subject parameter estimates and glucose metabolic rates

Impact of uncertainties in inorganic chemical rate constants on tropospheric composition and ozone radiative forcing

Directory of Open Access Journals (Sweden)

B. Newsome

2017-12-01

Full Text Available 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

Determination of the sterile release rate for stopping growing age-structured populations

International Nuclear Information System (INIS)

Barclay, Hugh John

2016-01-01

A freely-growing age-structured population was modelled for growth and control by sterile male releases. Equilibrium populations yield critical sterile male release rates that would hold the population at equilibrium. It is shown here that these rates may be different from the release rates required to stop a growing population and bring it to an equilibrium. A computer simulation was constructed of this population and a parameter sensitivity analysis graphed the effects on the required sterile male release rate of fertility, mating delay in adult females, net juvenile survivorship, three adult survivorship curves, the time spent in the juvenile stages, and total life span. The adult survivorship curves had the greatest effect on the required sterile release rate for population elimination. The required release rate was also determined for Ceratitis capitata (Wiedemann) using survivorship and fertility data from a laboratory strain. The concepts of over-flooding ratio and release ratio were discussed and quantified for the cases above. (author)

Extraction of elementary rate constants from global network analysis of E. coli central metabolism

Directory of Open Access Journals (Sweden)

Broderick Gordon

2008-05-01

Full Text Available Abstract Background As computational performance steadily increases, so does interest in extending one-particle-per-molecule models to larger physiological problems. Such models however require elementary rate constants to calculate time-dependent rate coefficients under physiological conditions. Unfortunately, even when in vivo kinetic data is available, it is often in the form of aggregated rate laws (ARL that do not specify the required elementary rate constants corresponding to mass-action rate laws (MRL. There is therefore a need to develop a method which is capable of automatically transforming ARL kinetic information into more detailed MRL rate constants. Results By incorporating proteomic data related to enzyme abundance into an MRL modelling framework, here we present an efficient method operating at a global network level for extracting elementary rate constants from experiment-based aggregated rate law (ARL models. The method combines two techniques that can be used to overcome the difficult properties in parameterization. The first, a hybrid MRL/ARL modelling technique, is used to divide the parameter estimation problem into sub-problems, so that the parameters of the mass action rate laws for each enzyme are estimated in separate steps. This reduces the number of parameters that have to be optimized simultaneously. The second, a hybrid algebraic-numerical simulation and optimization approach, is used to render some rate constants identifiable, as well as to greatly narrow the bounds of the other rate constants that remain unidentifiable. This is done by incorporating equality constraints derived from the King-Altman and Cleland method into the simulated annealing algorithm. We apply these two techniques to estimate the rate constants of a model of E. coli glycolytic pathways. The simulation and statistical results show that our innovative method performs well in dealing with the issues of high computation cost, stiffness, local

Extraction of elementary rate constants from global network analysis of E. coli central metabolism

Science.gov (United States)

Zhao, Jiao; Ridgway, Douglas; Broderick, Gordon; Kovalenko, Andriy; Ellison, Michael

2008-01-01

Background As computational performance steadily increases, so does interest in extending one-particle-per-molecule models to larger physiological problems. Such models however require elementary rate constants to calculate time-dependent rate coefficients under physiological conditions. Unfortunately, even when in vivo kinetic data is available, it is often in the form of aggregated rate laws (ARL) that do not specify the required elementary rate constants corresponding to mass-action rate laws (MRL). There is therefore a need to develop a method which is capable of automatically transforming ARL kinetic information into more detailed MRL rate constants. Results By incorporating proteomic data related to enzyme abundance into an MRL modelling framework, here we present an efficient method operating at a global network level for extracting elementary rate constants from experiment-based aggregated rate law (ARL) models. The method combines two techniques that can be used to overcome the difficult properties in parameterization. The first, a hybrid MRL/ARL modelling technique, is used to divide the parameter estimation problem into sub-problems, so that the parameters of the mass action rate laws for each enzyme are estimated in separate steps. This reduces the number of parameters that have to be optimized simultaneously. The second, a hybrid algebraic-numerical simulation and optimization approach, is used to render some rate constants identifiable, as well as to greatly narrow the bounds of the other rate constants that remain unidentifiable. This is done by incorporating equality constraints derived from the King-Altman and Cleland method into the simulated annealing algorithm. We apply these two techniques to estimate the rate constants of a model of E. coli glycolytic pathways. The simulation and statistical results show that our innovative method performs well in dealing with the issues of high computation cost, stiffness, local minima and uncertainty

Experimental determination of the high-temperature rate constant for the reaction of OH with sec-butanol.

Science.gov (United States)

Pang, Genny A; Hanson, Ronald K; Golden, David M; Bowman, Craig T

2012-10-04

The overall rate constant for the reaction of OH with sec-butanol [CH(3)CH(OH)CH(2)CH(3)] was determined from measurements of the near-first-order OH decay in shock-heated mixtures of tert-butylhydroperoxide (as a fast source of OH) with sec-butanol in excess. Three kinetic mechanisms from the literature describing sec-butanol combustion were used to examine the sensitivity of the rate constant determination to secondary kinetics. The overall rate constant determined can be described by the Arrhenius expression 6.97 × 10(-11) exp(-1550/T[K]) cm(3) molecule(-1) s(-1), valid over the temperature range of 888-1178 K. Uncertainty bounds of ±30% were found to adequately account for the uncertainty in secondary kinetics. To our knowledge, the current data represent the first efforts toward an experimentally determined rate constant for the overall reaction of OH with sec-butanol at combustion-relevant temperatures. A rate constant predicted using a structure-activity relationship from the literature was compared to the current data and previous rate constant measurements for the title reaction at atmospheric-relevant temperatures. The structure-activity relationship was found to be unable to correctly predict the measured rate constant at all temperatures where experimental data exist. We found that the three-parameter fit of 4.95 × 10(-20)T(2.66) exp(+1123/T[K]) cm(3) molecule(-1) s(-1) better describes the overall rate constant for the reaction of OH with sec-butanol from 263 to 1178 K.

A REVIEW ON CONTROLLED DRUG RELEASE FORMULATION: SPANSULES

OpenAIRE

Rinky Maurya; Dr. Pramod Kumar Sharma; Rishabha Malviya

2014-01-01

Spansules are a dosage form which was considered as one of the Advanced Drug Delivery System. Multidrug preparations can be delivered easily by spansules or granules in capsule technology. This type of delivery system designed to release a drug or a medicament at two or more different rates or in different span of time. A quick/slow release system provides an initial release of drug followed by a constant rate of drug release over a extended period or a defined period of time and in slow/quic...

Reaction rate constants of H-abstraction by OH from large ketones: Measurements and site-specific rate rules

KAUST Repository

Badra, Jihad

2014-01-01

Reaction rate constants of the reaction of four large ketones with hydroxyl (OH) are investigated behind reflected shock waves using OH laser absorption. The studied ketones are isomers of hexanone and include 2-hexanone, 3-hexanone, 3-methyl-2-pentanone, and 4-methl-2-pentanone. Rate constants are measured under pseudo-first-order kinetics at temperatures ranging from 866 K to 1375 K and pressures near 1.5 atm. The reported high-temperature rate constant measurements are the first direct measurements for these ketones under combustion-relevant conditions. The effects of the position of the carbonyl group (CO) and methyl (CH3) branching on the overall rate constant with OH are examined. Using previously published data, rate constant expressions covering, low-to-high temperatures, are developed for acetone, 2-butanone, 3-pentanone, and the hexanone isomers studied here. These Arrhenius expressions are used to devise rate rules for H-abstraction from various sites. Specifically, the current scheme is applied with good success to H-abstraction by OH from a series of n-ketones. Finally, general expressions for primary and secondary site-specific H-abstraction by OH from ketones are proposed as follows (the subscript numbers indicate the number of carbon atoms bonded to the next-nearest-neighbor carbon atom, the subscript CO indicates that the abstraction is from a site next to the carbonyl group (CO), and the prime is used to differentiate different neighboring environments of a methylene group):P1,CO = 7.38 × 10-14 exp(-274 K/T) + 9.17 × 10-12 exp(-2499 K/T) (285-1355 K)S10,CO = 1.20 × 10-11 exp(-2046 K/T) + 2.20 × 10-13 exp(160 K/T) (222-1464 K)S11,CO = 4.50 × 10-11 exp(-3000 K/T) + 8.50 × 10-15 exp(1440 K/T) (248-1302 K)S11′,CO = 3.80 × 10-11 exp(-2500 K/T) + 8.50 × 10-15 exp(1550 K/T) (263-1370 K)S 21,CO = 5.00 × 10-11 exp(-2500 K/T) + 4.00 × 10-13 exp(775 K/T) (297-1376 K) © 2014 the Partner Organisations.

Phototransformation rate constants of PAHs associated with soot particles

International Nuclear Information System (INIS)

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 (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. - Highlights: ► PAHs on soot were evaluated by a model of coupled photolysis and diffusion. ► Photodegradation rate at the surface, diffusion coefficient, and light penetration path were determined. ► Low MW PAHs were influenced by fast photodegradation and fast diffusion. ► High MW PAHs were controlled either by slow

A first-passage scheme for determination of overall rate constants for non-diffusion-limited suspensions

Science.gov (United States)

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.

Design of a new type of coating for the controlled release of heparin

NARCIS (Netherlands)

Hinrichs, W.L.J.; Hinrichs, W.L.J.; ten Hoopen, Hermina W.M.; Wissink, M.J.B.; Engbers, G.H.M.; Feijen, Jan

1997-01-01

Thrombus formation at the surface of blood contacting devices can be prevented by local release of heparin. Preferably, the release rate should be constant for prolonged periods of time. The minimum heparin release rate to achieve thromboresistance will be different for various applications and

Application of accelerated evaluation method of alteration temperature and constant dose rate irradiation on bipolar linear regulator LM317

International Nuclear Information System (INIS)

Deng Wei; Wu Xue; Wang Xin; Zhang Jinxin; Zhang Xiaofu; Zheng Qiwen; Ma Wuying; Lu Wu; Guo Qi; He Chengfa

2014-01-01

With different irradiation methods including high dose rate irradiation, low dose rate irradiation, alteration temperature and constant dose rate irradiation, and US military standard constant high temperature and constant dose rate irradiation, the ionizing radiation responses of bipolar linear regulator LM317 from three different companies were investigated under the operating and zero biases. The results show that compared with constant high temperature and constant dose rate irradiation method, the alteration temperature and constant dose rate irradiation method can not only very rapidly and accurately evaluate the dose rate effect of three bipolar linear regulators, but also well simulate the damage of low dose rate irradiation. Experiment results make the alteration temperature and constant dose rate irradiation method successfully apply to bipolar linear regulator. (authors)

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

Science.gov (United States)

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.

Macroscopic calculational model of fission gas release from water reactor fuels

International Nuclear Information System (INIS)

Uchida, Masaki

1993-01-01

Existing models for estimating fission gas release rate usually have fuel temperature as independent variable. Use of fuel temperature, however, often brings an excess ambiguity in the estimation because it is not a rigorously definable quantity as a function of heat generation rate and burnup. To derive a mathematical model that gives gas release rate explicitly as a function of design and operational parameters, the Booth-type diffusional model was modified by changing the character of the diffusion constant from physically meaningful quantity into a mere mathematical parameter, and also changing its temperature dependency into power dependency. The derived formula was found, by proper choice of arbitrary constants, to satisfactorily predict the release rates under a variety of irradiation histories up to a burnup of 60,000 MWd/t. For simple power histories, the equation can be solved analytically by defining several transcendental functions, which enables simple calculation of release rate using graphs. (author)

Endo- and exocytic rate constants for spontaneous and protein kinase C-activated T cell receptor cycling

DEFF Research Database (Denmark)

Menné, Charlotte; Møller Sørensen, Tine; Siersma, Volkert

2002-01-01

To determine the rate constants of spontaneous and activated TCR cycling, we examined TCR endo- and exocytosis in the human T cell line Jurkat by three different methods. Using a simple kinetic model for TCR cycling and non-linear regression analyses, we found that the spontaneous endocytic rate...... constant of the TCR was low (approximately 0.012 min(-1)) whereas the spontaneous exocytic rate constant was similar to that of other cycling receptors (approximately 0.055 min(-1)). Following protein kinase C activation (PKC) the endocytic rate constant was increased tenfold (to approximately 0.128 min(-1......)) whereas the exocytic rate constant was unaffected. Thus, the TCR becomes a rapidly cycling receptor with kinetics similar to classical cycling receptors subsequent to PKC activation. This results in a reduction of the half-life of cell surface expressed TCR from approximately 58 to 6 min and allows rapid...

Rate constants for the reaction of OH radicals with 1-chloroalkanes at 295 K

DEFF Research Database (Denmark)

Markert, F.; Nielsen, O.J.

1992-01-01

The rate constants for the reaction of OH radicals with a series of 1-chloroalkanes were measured at 295 K and at a total pressure of 1 atm. The rate constants were obtained by using the absolute technique of pulse radiolysis combined with kinetic UV-spectroscopy. The results are discussed in terms...

a comparative study of the drying rate constant, drying efficiency

African Journals Online (AJOL)

The drying rate constants for the solar dryer and open- air sun dried bitter leaf were 0.8 and ... of cost benefit but the poorest when other considerations ... J. I. Eze, National Centre for Energy Research and Development (NCERD), University of ...

Uniaxial tension test on Rubber at constant true strain rate

Directory of Open Access Journals (Sweden)

Sourne H.L.

2012-08-01

Full Text Available Elastomers are widely used for damping parts in different industrial contexts because of their remarkable dissipation properties. Indeed, they can undergo severe mechanical loading conditions, i.e., high strain rates and large strains. Nevertheless, the mechanical response of these materials can vary from purely rubber-like to glassy depending on the strain rate undergone. Classically, uniaxial tension tests are made in order to find a relation between the stress and the strain in the material at various strain rates. However, even if the strain rate is searched to be constant, it is the nominal strain rate that is considered. Here we develop a test at constant true strain rate, i.e. the strain rate that is experienced by the material. In order to do such a test, the displacement imposed by the machine is an exponential function of time. This test has been performed with a high speed hydraulic machine for strain rates between 0.01/s and 100/s. A specific specimen has been designed, yielding a uniform strain field (and so a uniform stress field. Furthermore, an instrumented aluminum bar has been used to take into account dynamic effects in the measurement of the applied force. A high speed camera enables the determination of strain in the sample using point tracking technique. Using this method, the stress-strain curve of a rubber-like material during a loading-unloading cycle has been determined, up to a stretch ratio λ = 2.5. The influence of the true strain rate both on stiffness and on dissipation of the material is then discussed.

Arrhenius Rate: constant volume burn

Energy Technology Data Exchange (ETDEWEB)

Menikoff, Ralph [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

2017-12-06

A constant volume burn occurs for an idealized initial state in which a large volume of reactants at rest is suddenly raised to a high temperature and begins to burn. Due to the uniform spatial state, there is no fluid motion and no heat conduction. This reduces the time evolu tion to an ODE for the reaction progress variable. With an Arrhenius reaction rate, two characteristics of thermal ignition are illustrated: induction time and thermal runaway. The Frank-Kamenetskii approximation then leads to a simple expression for the adiabatic induction time. For a first order reaction, the analytic solution is derived and used to illustrate the effect of varying the activation temperature; in particular, on the induction time. In general, the ODE can be solved numerically. This is used to illustrate the effect of varying the reaction order. We note that for a first order reaction, the time evolution of the reaction progress variable has an exponential tail. In contrast, for a reaction order less than one, the reaction completes in a nite time. The reaction order also affects the induction time.

Neural estimation of kinetic rate constants from dynamic PET-scans

DEFF Research Database (Denmark)

Fog, Torben L.; Nielsen, Lars Hupfeldt; Hansen, Lars Kai

1994-01-01

A feedforward neural net is trained to invert a simple three compartment model describing the tracer kinetics involved in the metabolism of [18F]fluorodeoxyglucose in the human brain. The network can estimate rate constants from positron emission tomography sequences and is about 50 times faster ...

Shock tube measurements of the rate constants for seven large alkanes+OH

KAUST Repository

Badra, Jihad

2015-01-01

Reaction rate constants for seven large alkanes + hydroxyl (OH) radicals were measured behind reflected shock waves using OH laser absorption. The alkanes, n-hexane, 2-methyl-pentane, 3-methyl-pentane, 2,2-dimethyl-butane, 2,3-dimethyl-butane, 2-methyl-heptane, and 4-methyl-heptane, were selected to investigate the rates of site-specific H-abstraction by OH at secondary and tertiary carbons. Hydroxyl radicals were monitored using narrow-line-width ring-dye laser absorption of the R1(5) transition of the OH spectrum near 306.7 nm. The high sensitivity of the diagnostic enabled the use of low reactant concentrations and pseudo-first-order kinetics. Rate constants were measured at temperatures ranging from 880 K to 1440 K and pressures near 1.5 atm. High-temperature measurements of the rate constants for OH + n-hexane and OH + 2,2-dimethyl-butane are in agreement with earlier studies, and the rate constants of the five other alkanes with OH, we believe, are the first direct measurements at combustion temperatures. Using these measurements and the site-specific H-abstraction measurements of Sivaramakrishnan and Michael (2009) [1,2], general expressions for three secondary and two tertiary abstraction rates were determined as follows (the subscripts indicate the number of carbon atoms bonded to the next-nearest-neighbor carbon): S20=1.58×10-11exp(-1550K/T)cm3molecule-1s-1(887-1327K)S30=2.37×10-11exp(-1850K/T)cm3molecule-1s-1(887-1327K)S21=4.5×10-12exp(-793.7K/T)cm3molecule-1s-1(833-1440K)T100=2.85×10-11exp(-1138.3K/T)cm3molecule-1s-1(878-1375K)T101=7.16×10-12exp(-993K/T)cm3molecule-1s-1(883-1362K) © 2014 The Combustion Institute.

Development of polymer film dosage forms of lidocaine for buccal administration. I. Penetration rate and release rate.

Science.gov (United States)

Okamoto, H; Taguchi, H; Iida, K; Danjo, K

2001-12-13

We examined the penetration rate of lidocaine (LC) through excised oral mucosa from hamster cheek pouch and the in vitro release rate of LC from film dosage forms with hydroxypropylcellulose (HPC) as a film base. Addition of glycyrrhizic acid (GL) to the HPC films increased the LC release rate almost GL-content-dependently, while an optimum GL content was observed for the LC penetration rate. No LC penetration was observed from an acidic aqueous solution (pH 3.4) of LC, suggesting only unionized LC can substantially penetrate through the mucosa. A significant relationship between the penetration rate of LC and the release rate of unionized LC was found, suggesting that the in vitro dissolution study is a useful tool to predict the penetration rate taking the unionized drug fraction into consideration.

The correlation schemes in calculations of the rate constants of some radiation chemical reactions

International Nuclear Information System (INIS)

Zagorets, P.A.; Shostenko, A.G.; Kim, V.

1983-01-01

The various correlation relationships of the evaluation of the rate constants of radiation chemical reactions of addition, abstraction and isomerization were considered. It was shown that neglection of the influence of solvent can result in errors in calculations of rate constants equalling two orders in magnitude. Several examples of isokinetic relationship are given. The methods of calculation of transmission coefficient of reaction addition have been discussed. (author)

Rate constant and reaction coordinate of Trp-cage folding in explicit water

NARCIS (Netherlands)

Juraszek, J.; Bolhuis, P.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

Exergy analysis of integrated photovoltaic thermal solar water heater under constant flow rate and constant collection temperature modes

NARCIS (Netherlands)

Tiwari, A.; Dubey, Swapnil; Sandhu, G.S.; Sodha, M.S.; Anwar, S.I.

2009-01-01

In this communication, an analytical expression for the water temperature of an integrated photovoltaic thermal solar (IPVTS) water heater under constant flow rate hot water withdrawal has been obtained. Analysis is based on basic energy balance for hybrid flat plate collector and storage tank,

Big bang nucleosynthesis with a varying fine structure constant and nonstandard expansion rate

International Nuclear Information System (INIS)

Ichikawa, Kazuhide; Kawasaki, Masahiro

2004-01-01

We calculate the primordial abundances of light elements produced during big bang nucleosynthesis when the fine structure constant and/or the cosmic expansion rate take nonstandard values. We compare them with the recent values of observed D, 4 He, and 7 Li abundances, which show a slight inconsistency among themselves in the standard big bang nucleosynthesis scenario. This inconsistency is not solved by considering either a varying fine structure constant or a nonstandard expansion rate separately but solutions are found by their simultaneous existence

Convergence analysis of Chauvin's PCA learning algorithm with a constant learning rate

Energy Technology Data Exchange (ETDEWEB)

Lv Jiancheng [Computational Intelligence Laboratory, School of Computer Science and Engineering, University of Electronic Science and Technology of China, Chengdu 610054 (China); Yi Zhang [Computational Intelligence Laboratory, School of Computer Science and Engineering, University of Electronic Science and Technology of China, Chengdu 610054 (China)]. E-mail: zhangyi@uestc.edu.cn

2007-05-15

The convergence of Chauvin's PCA learning algorithm with a constant learning rate is studied in this paper by using a DDT method (deterministic discrete-time system method). Different from the DCT method (deterministic continuous-time system method), the DDT method does not require that the learning rate converges to zero. An invariant set of Chauvin's algorithm with a constant learning rate is obtained so that the non-divergence of this algorithm can be guaranteed. Rigorous mathematic proofs are provided to prove the local convergence of this algorithm.

Controlling Object Heat Release Rate using Geometrical Features

OpenAIRE

Kraft, Stefan Marc

2017-01-01

An experimental study was conducted to determine the effect of complex geometries on the burning rate of materials made using additive manufacturing. Controlling heat release rate has applicability in limiting fire hazards as well as for designing fuels for optimal burning rate. The burning rate of a structure is a function of the material properties as well as the airflow through it, which is dictated by the geometry. This burning rate is generally proportional to the porosity for obj...

Helium release from radioisotope heat sources

Energy Technology Data Exchange (ETDEWEB)

Peterson, D.E.; Early, J.W.; Starzynski, J.S.; Land, C.C.

1984-05-01

Diffusion of helium in /sup 238/PuO/sub 2/ fuel was characterized as a function of the heating rate and the fuel microstructure. The samples were thermally ramped in an induction furnace and the helium release rates measured with an automated mass spectrometer. The diffusion constants and activation energies were obtained from the data using a simple diffusion model. The release rates of helium were correlated with the fuel microstructure by metallographic examination of fuel samples. The release mechanism consists of four regimes, which are dependent upon the temperature. Initially, the release is controlled by movement of point defects combined with trapping along grain boundaries. This regime is followed by a process dominated by formation and growth of helium bubbles along grain boundaries. The third regime involves volume diffusion controlled by movement of oxygen vacancies. Finally, the release at the highest temperatures follows the diffusion rate of intragranular bubbles. The tendency for helium to be trapped within the grain boundaries diminishes with small grain sizes, slow thermal pulses, and older fuel.

Helium release from radioisotope heat sources

International Nuclear Information System (INIS)

Peterson, D.E.; Early, J.W.; Starzynski, J.S.; Land, C.C.

1984-05-01

Diffusion of helium in 238 PuO 2 fuel was characterized as a function of the heating rate and the fuel microstructure. The samples were thermally ramped in an induction furnace and the helium release rates measured with an automated mass spectrometer. The diffusion constants and activation energies were obtained from the data using a simple diffusion model. The release rates of helium were correlated with the fuel microstructure by metallographic examination of fuel samples. The release mechanism consists of four regimes, which are dependent upon the temperature. Initially, the release is controlled by movement of point defects combined with trapping along grain boundaries. This regime is followed by a process dominated by formation and growth of helium bubbles along grain boundaries. The third regime involves volume diffusion controlled by movement of oxygen vacancies. Finally, the release at the highest temperatures follows the diffusion rate of intragranular bubbles. The tendency for helium to be trapped within the grain boundaries diminishes with small grain sizes, slow thermal pulses, and older fuel

Measurement of semiochemical release rates with a dedicated environmental control system

Science.gov (United States)

Heping Zhu; Harold W. Thistle; Christopher M. Ranger; Hongping Zhou; Brian L. Strom

2015-01-01

Insect semiochemical dispensers are commonly deployed under variable environmental conditions over a specified period. Predictions of their longevity are hampered by a lack of methods to accurately monitor and predict how primary variables affect semiochemical release rate. A system was constructed to precisely determine semiochemical release rates under...

Determination of rate constants for the oxygen reduction reaction

Energy Technology Data Exchange (ETDEWEB)

Racz, A.; Walter, T.; Stimming, U. [Munich Technical Univ., Garching (Germany). Dept. of Physics

2008-07-01

The oxygen reduction reaction (ORR) in fuel cells is a complex and fundamental electrochemical reaction. However, greater insight is needed into this multi-electron reaction in order to develop efficient and innovative catalysts. The rotating ring disc electrode (RRDE) is a useful tool for studying reaction intermediates of the ORR and to better understand the reaction pathway. Carbon materials such as carbon nanofilaments-platelets (CNF-PL) have high electrical conductivity and may be considered for fuel cells. In particular Pt and RuSe{sub x}, deposited on CNF-PL materials could act as efficient catalysts in fuel cells. This study used the RRDE to evaluate the oxygen reduction kinetics of these catalysts in oxygen-saturated, diluted sulphuric acid at room temperature. Kinetic data and hydrogen peroxide formation were determined by depositing a thin-film of the catalyst on the Au disc. The values for the constants k1, k2 and k3 were obtained using diagnostic criteria and expressions to calculate the rate constants of the cathodic oxygen reduction reaction for RuSe on new carbon supports. A potential dependency of the constants k1 and k2 for RuSe{sub x}/CNF-PL was observed. The transition of the Tafel slopes for this catalyst was obtained. 4 refs., 1 fig.

Reaction mechanisms and rate constants of waste degradation in landfill bioreactor systems with enzymatic-enhancement.

Science.gov (United States)

Jayasinghe, P A; Hettiaratchi, J P A; Mehrotra, A K; Kumar, S

2014-06-01

Augmenting leachate before recirculation with peroxidase enzymes is a novel method to increase the available carbon, and therefore the food supply to microorganisms at the declining phase of the anaerobic landfill bioreactor operation. In order to optimize the enzyme-catalyzed leachate recirculation process, it is necessary to identify the reaction mechanisms and determine rate constants. This paper presents a kinetic model developed to ascertain the reaction mechanisms and determine the rate constants for enzyme catalyzed anaerobic waste degradation. The maximum rate of reaction (Vmax) for MnP enzyme-catalyzed reactors was 0.076 g(TOC)/g(DS).day. The catalytic turnover number (k(cat)) of the MnP enzyme-catalyzed was 506.7 per day while the rate constant (k) of the un-catalyzed reaction was 0.012 per day. Copyright © 2014 Elsevier Ltd. All rights reserved.

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

Science.gov (United States)

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

Measuring Protein Synthesis Rate In Living Object Using Flooding Dose And Constant Infusion Methods

OpenAIRE

Ulyarti, Ulyarti

2018-01-01

Constant infusion is a method used for measuring protein synthesis rate in living object which uses low concentration of amino acid tracers. Flooding dose method is another technique used to measure the rate of protein synthesis which uses labelled amino acid together with large amount of unlabelled amino acid.  The latter method was firstly developed to solve the problem in determination of precursor pool arise from constant infusion method.  The objective of this writing is to com...

Frost heave susceptibility of saturated soil under constant rate of freezing

Science.gov (United States)

Ryokai, K.; Iguro, M.; Yoneyama, K.

Introduced are the results of experiments carried out to quantitatively obtain the frost heave pressure and displacement of soil subjected to artificial freezing or freezing around in-ground liquefied natural gas storage tanks. This experiment is conducted to evaluate the frost heave susceptibility of saturated soil under overconsolidation. In other words, this experiment was carried out to obtain the relation of the over-burden pressure and freezing rate to the frost heave ratio by observing the frost heave displacement and freezing time of specimens by freezing the specimens at a constant freezing rate under a constant overburden pressure, while letting water freely flow in and out of the system. Introduced are the procedures for frost heave test required to quantitatively obtain the frost heave displacement and pressure of soil. Furthermore, the relation between the frost heave susceptibility and physical properties of soil obtained by this test is reported.

Controlled release of insect sex pheromones from paraffin wax and emulsions.

Science.gov (United States)

Atterholt, C A; Delwiche, M J; Rice, R E; Krochta, J M

1999-02-22

Paraffin wax and aqueous paraffin emulsions can be used as controlled release carriers for insect sex pheromones for mating disruption of orchard pests. Paraffin can be applied at ambient temperature as an aqueous emulsion, adheres to tree bark or foliage, releases pheromone for an extended period of time, and will slowly erode from bark and biodegrade in soil. Pheromone emulsions can be applied with simple spray equipment. Pheromone release-rates from paraffin were measured in laboratory flow-cell experiments. Pheromone was trapped from an air stream with an adsorbent, eluted periodically, and quantified by gas chromatography. Pheromone release from paraffin was partition-controlled, providing a constant (zero-order) release rate. A typical paraffin emulsion consisted of 30% paraffin, 4% pheromone, 4% soy oil, 1% vitamin E, 2% emulsifier, and the balance water. Soy oil and vitamin E acted as volatility suppressants. A constant release of oriental fruit moth pheromone from paraffin emulsions was observed in the laboratory for more than 100 days at 27 degreesC, with release-rates ranging from 0.4 to 2 mg/day, depending on the concentration and surface area of the dried emulsion. The use of paraffin emulsions is a viable method for direct application of insect pheromones for mating disruption. Sprayable formulations can be designed to release insect pheromones to the environment at a rate necessary for insect control by mating disruption. At temperatures below 38 degreesC, zero-order release was observed. At 38 degreesC and higher, pheromone oxidation occurred. A partition-controlled release mechanism was supported by a zero-order pheromone release-rate, low air/wax partition coefficients, and pheromone solubility in paraffin.

Release rates of soluble species at Yucca Mountain

International Nuclear Information System (INIS)

Lee, W.W.-L.; Pigford, T.H.

1989-02-01

Experimental leaching of spent fuel shows that some fission product species are preferentially released upon contact with water. We analyze the conservative case of bare spent fuel in contact with saturated tuff using diffusional mass transfer analysis. For the parameter values used, the USNRC release rate limit is not exceeded, except for 99 Tc. The presence of a container and the distribution of water contact over time will assist in meeting this criterion. 6 figs., 2 tabs

Fission product release from defected nuclear reactor fuel elements

International Nuclear Information System (INIS)

Lewis, B.J.

1983-01-01

The release of gaseous (krypton and xenon) and iodine radioactive fission products from defective fuel elements is described with a semi-empirical model. The model assumes precursor-corrected 'Booth diffusional release' in the UO 2 and subsequent holdup in the fuel-to-sheath gap. Transport in the gap is separately modelled with a phenomenological rate constant (assuming release from the gap is a first order rate process), and a diffusivity constant (assuming transport in the gap is dominated by a diffusional process). Measured release data from possessing various states of defection are use in this analysis. One element (irradiated in an earlier experiment by MacDonald) was defected with a small drilled hole. A second element was machined with 23 slits while a third element (fabricated with a porous end plug) displayed through-wall sheath hydriding. Comparison of measured release data with calculated values from the model yields estimates of empirical diffusion coefficients for the radioactive species in the UO 2 (1.56 x 10 -10 to 7.30 x 10 -9 s -1 ), as well as escape rate constants (7.85 x 10 -7 to 3.44 x 10 -5 s -1 ) and diffusion coefficients (3.39 x 10 -5 to 4.88 x 10 -2 cm 2 /s) for these in the fuel-to-sheath gap. Analyses also enable identification of the various rate-controlling processes operative in each element. For the noble gas and iodine species, the rate-determining process in the multi-slit element is 'Booth diffusion'; however, for the hydrided element an additional delay results from diffusional transport in the fuel-to-heath gap. Furthermore, the iodine species exhibit an additional holdup in the drilled element because of significant trapping on the fuel and/or sheath surfaces. Using experimental release data and applying the theoretical results of this work, a systematic procedure is proposed to characterize fuel failures in commercial power reactors (i.e., the number of fuel failures and average leak size)

Biodegradation testing of chemicals with high Henry’s constants – separating mass and effective concentration reveals higher rate constants

DEFF Research Database (Denmark)

Birch, Heidi; Andersen, Henrik Rasmus; Comber, Mike

Microextraction (HS-SPME) was applied directly on the test systems to measure substrate depletion by biodegradation relative to abiotic controls. HS-SPME was also applied to determine air to water partitioning ratios. Water phase biodegradation rate constants, kwater, were up to 72 times higher than test system...

On the estimate of the rate constant in the homogeneous dissolution model

Czech Academy of Sciences Publication Activity Database

Čupera, Jakub; Lánský, Petr

2013-01-01

Roč. 39, č. 10 (2013), s. 1555-1561 ISSN 0363-9045 Institutional support: RVO:67985823 Keywords : dissolution * estimation * rate constant Subject RIV: FR - Pharmacology ; Medidal Chemistry Impact factor: 2.006, year: 2013

Rate constant measurements for the overall reaction of OH + 1-butanol → products from 900 to 1200 K.

Science.gov (United States)

Pang, Genny A; Hanson, Ronald K; Golden, David M; Bowman, Craig T

2012-03-15

The rate constant for the overall reaction OH + 1-butanol → products was determined in the temperature range 900 to 1200 K from measurements of OH concentration time histories in reflected shock wave experiments of tert-butyl hydroperoxide (TBHP) as a fast source of OH radicals with 1-butanol in excess. Narrow-linewidth laser absorption was employed for the quantitative OH concentration measurement. A detailed kinetic mechanism was constructed that includes updated rate constants for 1-butanol and TBHP kinetics that influence the near-first-order OH concentration decay under the present experimental conditions, and this mechanism was used to facilitate the rate constant determination. The current work improves upon previous experimental studies of the title rate constant by utilizing a rigorously generated kinetic model to describe secondary reactions. Additionally, the current work extends the temperature range of experimental data in the literature for the title reaction under combustion-relevant conditions, presenting the first measurements from 900 to 1000 K. Over the entire temperature range studied, the overall rate constant can be expressed in Arrhenius form as 3.24 × 10(-10) exp(-2505/T [K]) cm(3) molecule(-1) s(-1). The influence of secondary reactions on the overall OH decay rate is discussed, and a detailed uncertainty analysis is performed yielding an overall uncertainty in the measured rate constant of ±20% at 1197 K and ±23% at 925 K. The results are compared with previous experimental and theoretical studies on the rate constant for the title reaction and reasonable agreement is found when the earlier experimental data were reinterpreted.

Phenazopyridine-phthalimide nano-cocrystal: Release rate and oral bioavailability enhancement.

Science.gov (United States)

Huang, Yu; Li, Jin-Mei; Lai, Zhi-Hui; Wu, Jun; Lu, Tong-Bu; Chen, Jia-Mei

2017-11-15

Both cocrystal and nanocrystal technologies have been widely used in the pharmaceutical development for poorly soluble drugs. However, the synergistic effects due to the integration of these two technologies have not been well investigated. The aim of this study is to develop a nano-sized cocrystal of phenazopyridine (PAP) with phthalimide (PI) to enhance the release rate and oral bioavailability of PAP. A PAP-PI nano-cocrystal with particle diameter of 21.4±0.1nm was successfully prepared via a sonochemical approach and characterized by powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and dynamic light scattering (DLS) analysis. An in vitro release study revealed a significant release rate enhancement for PAP-PI nano-cocrystal as compared to PAP-PI cocrystal and PAP hydrochloride salt. Further, a comparative oral bioavailability study in rats indicated significant improvement in C max and oral bioavailability (AUC 0-∞ ) by 1.39- and 2.44-fold, respectively. This study demonstrated that this novel nano-cocrystal technology can be a new promising option to improve release rate and absorption of poorly soluble compounds in the pharmaceutical industry. Copyright © 2017 Elsevier B.V. All rights reserved.

Multi-target QSPR modeling for simultaneous prediction of multiple gas-phase kinetic rate constants of diverse chemicals

Science.gov (United States)

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.

Hindered disulfide bonds to regulate release rate of model drug from mesoporous silica.

Science.gov (United States)

Nadrah, Peter; Maver, Uroš; Jemec, Anita; Tišler, Tatjana; Bele, Marjan; Dražić, Goran; Benčina, Mojca; Pintar, Albin; Planinšek, Odon; Gaberšček, Miran

2013-05-01

With the advancement of drug delivery systems based on mesoporous silica nanoparticles (MSNs), a simple and efficient method regulating the drug release kinetics is needed. We developed redox-responsive release systems with three levels of hindrance around the disulfide bond. A model drug (rhodamine B dye) was loaded into MSNs' mesoporous voids. The pore opening was capped with β-cyclodextrin in order to prevent leakage of drug. Indeed, in absence of a reducing agent the systems exhibited little leakage, while the addition of dithiothreitol cleaved the disulfide bonds and enabled the release of cargo. The release rate and the amount of released dye were tuned by the level of hindrance around disulfide bonds, with the increased hindrance causing a decrease in the release rate as well as in the amount of released drug. Thus, we demonstrated the ability of the present mesoporous systems to intrinsically control the release rate and the amount of the released cargo by only minor structural variations. Furthermore, an in vivo experiment on zebrafish confirmed that the present model delivery system is nonteratogenic.

A new analytical method for estimating lumped parameter constants of linear viscoelastic models from strain rate tests

Science.gov (United States)

Mattei, G.; Ahluwalia, A.

2018-04-01

We introduce a new function, the apparent elastic modulus strain-rate spectrum, E_{app} ( \\dot{ɛ} ), for the derivation of lumped parameter constants for Generalized Maxwell (GM) linear viscoelastic models from stress-strain data obtained at various compressive strain rates ( \\dot{ɛ}). The E_{app} ( \\dot{ɛ} ) function was derived using the tangent modulus function obtained from the GM model stress-strain response to a constant \\dot{ɛ} input. Material viscoelastic parameters can be rapidly derived by fitting experimental E_{app} data obtained at different strain rates to the E_{app} ( \\dot{ɛ} ) function. This single-curve fitting returns similar viscoelastic constants as the original epsilon dot method based on a multi-curve global fitting procedure with shared parameters. Its low computational cost permits quick and robust identification of viscoelastic constants even when a large number of strain rates or replicates per strain rate are considered. This method is particularly suited for the analysis of bulk compression and nano-indentation data of soft (bio)materials.

Critical Review of rate constants for reacitons of hydrated electrons

International Nuclear Information System (INIS)

Buxton, G.V.; Greenstock, C.L.; Phillips Helman, W.; Ross, A.B.

1988-01-01

Kinetic data for the radicals Hx and xOH in aqueous solution,and the corresponding radical anions, xO - and e/sub =/, have been critically reviewed. Reactions of the radicals in aqueous solution have been studied by pulse radiolysis, flash photolysis and other methods. Rate constants for over 3500 reaction are tabulated, including reaction with molecules, ions and other radicals derived from inorganic and organic solutes

Dose rate constant and energy spectrum of interstitial brachytherapy sources

International Nuclear Information System (INIS)

Chen Zhe; Nath, Ravinder

2001-01-01

In the past two years, several new manufacturers have begun to market low-energy interstitial brachytherapy seeds containing 125 I and 103 Pd. Parallel to this development, the National Institute of Standards and Technology (NIST) has implemented a modification to the air-kerma strength (S K ) standard for 125 I seeds and has also established an S K standard for 103 Pd seeds. These events have generated a considerable number of investigations on the determination of the dose rate constants (Λ) of interstitial brachytherapy seeds. The aim of this work is to study the general properties underlying the determination of Λ and to develop a simple method for a quick and accurate estimation of Λ. As the dose rate constant of clinical seeds is defined at a fixed reference point, we postulated that Λ may be calculated by treating the seed as an effective point source when the seed's source strength is specified in S K and its source characteristics are specified by the photon energy spectrum measured in air at the reference point. Using a semi-analytic approach, an analytic expression for Λ was derived for point sources with known photon energy spectra. This approach enabled a systematic study of Λ as a function of energy. Using the measured energy spectra, the calculated Λ for 125 I model 6711 and 6702 seeds and for 192 Ir seed agreed with the AAPM recommended values within ±1%. For the 103 Pd model 200 seed, the agreement was 5% with a recently measured value (within the ±7% experimental uncertainty) and was within 1% with the Monte Carlo simulations. The analytic expression for Λ proposed here can be evaluated using a programmable calculator or a simple spreadsheet and it provides an efficient method for checking the measured dose rate constant for any interstitial brachytherapy seed once the energy spectrum of the seed is known

Extrapolation of rate constants of reactions producing H2 and O2 in radiolysis of water at high temperatures

International Nuclear Information System (INIS)

Leblanc, R.; Ghandi, K.; Hackman, B.; Liu, G.

2014-01-01

One target of our research is to extrapolate known data on the rate constants of reactions and add corrections to estimate the rate constants at the higher temperatures reached by the SCWR reactors. The focus of this work was to extrapolate known data on the rate constants of reactions that produce Hydrogen or Oxygen with a rate constant below 10 10 mol -1 s -1 at room temperature. The extrapolation is done taking into account the change in the diffusion rate of the interacting species and the cage effect with thermodynamic conditions. The extrapolations are done over a wide temperature range and under isobaric conditions. (author)

CONTROLLED-RELEASE OF PARACETAMOL FROM AMYLODEXTRIN TABLETS - IN-VITRO AND IN-VIVO RESULTS

NARCIS (Netherlands)

VANDERVEEN, J; EISSENS, AC; LERK, CF

Amylodextrin is a suitable excipient for the design of solid controlled-release systems. The release of paracetamol from tablets containing 30% drug and 70% amylodextrin was studied in vitro and in vivo. In vitro dissolution profiles showed almost-constant drug release rates during 8 hr, when

Site-specific reaction rate constant measurements for various secondary and tertiary H-abstraction by OH radicals

KAUST Repository

Badra, Jihad

2015-02-01

Reaction rate constants for nine site-specific hydrogen atom (H) abstraction by hydroxyl radicals (OH) have been determined using experimental measurements of the rate constants of Alkane+OH→Products reactions. Seven secondary (S 20, S 21, S 22, S 30, S 31, S 32, and S 33) and two tertiary (T 100 and T 101) site-specific rate constants, where the subscripts refer to the number of carbon atoms (C) connected to the next-nearest-neighbor (N-N-N) C atom, were obtained for a wide temperature range (250-1450K). This was done by measuring the reaction rate constants for H abstraction by OH from a series of carefully selected large branched alkanes. The rate constant of OH with four different alkanes, namely 2,2-dimethyl-pentane, 2,4-dimethyl-pentane, 2,2,4-trimethyl-pentane (iso-octane), and 2,2,4,4-tetramethyl-pentane were measured at high temperatures (822-1367K) using a shock tube and OH absorption diagnostic. Hydroxyl radicals were detected using the narrow-line-width ring-dye laser absorption of the R1(5) transition of OH spectrum near 306.69nm.Previous low-temperature rate constant measurements are added to the current data to generate three-parameter rate expressions that successfully represent the available direct measurements over a wide temperature range (250-1450. K). Similarly, literature values of the low-temperature rate constants for the reaction of OH with seven normal and branched alkanes are combined with the recently measured high-temperature rate constants from our group [1]. Subsequent to that, site-specific rate constants for abstractions from various types of secondary and tertiary H atoms by OH radicals are derived and have the following modified Arrhenius expressions:. S20=8.49×10-17T1.52exp(73.4K/T)cm3molecule-1s-1(250-1450K) S21=1.07×10-15T1.07exp(208.3K/T)cm3molecule-1s-1(296-1440K) S22=2.88×10-13T0.41exp(-291.5K/T)cm3molecule-1s-1(272-1311K) S30=3.35×10-18T1.97exp(323.1K/T)cm3molecule-1s-1(250-1366K) S31=1.60×10-18T2.0exp(500.0K/T)cm3

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

Directory of Open Access Journals (Sweden)

Sebastian Höhna

Full Text Available 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

Distance constant of the Risø cup anemometer

DEFF Research Database (Denmark)

Kristensen, L.; Frost Hansen, O.

2002-01-01

The theory for cup-anemometer dynamics is presented in some detail and two methods of obtaining the distance constant lo are discussed. The first method is based on wind tunnel measurements: with a constant wind speed the cup anemometer is released from alocked position of the rotor...... and the increasing rotation rate recorded. It is concluded that the rapid increase in rotation rate makes the method very inaccurate. The second method consists of an analysis of turbulent, atmospheric of wind speed asmeasured by the cup anemometer and a fast-responding sonic anemometer with a spatial eddy...... resolution which is significantly better than that which can be obtained by a cup anemometer. The ratio between the measured power spectra of the horizontal windspeed by the two instruments contains the necessary information for determining the response characteristics of the cup anemometer and thereby lo...

Kinetics of extracellular release of 14C-labelled organic carbon by submerged macrophytes

International Nuclear Information System (INIS)

Soendergaard, M.

1981-01-01

The release of extracellular organic carbon (EOC) by six submerged freswater macrophytes was measured in time course studies with a 14 C-technique. Incubation in light in an open water-flow system made it possible to assay the time courses of 14 C-fixation and the simultaneous release of labelled EOC. Heterotrophic utilization of the released products by epiphytic communities was measured. Two patterns of release kinetics were found: (1) Constant rates of release occurred during the incubations, (2) The rates still increased after 24 h of incubation. During the first hours of incubation the rates of release increased in all species. Elodea reached constant rates after 2-4 h and Littorella and Ceratophyllum demersum after about 20 h. In the experiments with C. submersum and Nitella the rates of release increased almost linearly during the entire incubation period. The kinetics of release were in agreement with the molecular weight distribution of the dissolved EOC measured with gel chromatography. Low molecular weight products ( 10000 Daltons) dominated the dissolved EOC released by C. submersum and Nitella. A large fraction (18-60%) of the total EOC could be recovered on filters with a pore size of 0.2 μm. This particulate fraction probably represents some abiotic removal. The quantities of relase were low in all species and did not exceed 0.9% of the photosynthetic carbon fixation. Heterotrophic uptake by the epiphytic communities was less than 10% of the EOC released. The results emphasize that the 14 C-labelling of extracellular products is a time dependent process. (author)

Free energy correlation of rate constants for electron transfer between organic systems in aqueous solutions

Energy Technology Data Exchange (ETDEWEB)

Meisel, D

1975-07-15

Recent experimental data concerning the rate constants for electron transfer reactions of organic systems in aqueous solutions and their equilibrium constants is examined for possible correlation. The data is correlated quite well by the Marcus theory, if a reorganization parameter, lambda, of 18 kcal/mole is used. Assuming that the only contribution to lambda is the free energy of rearrangement of the water molecules, an effective radius of 5 A for the reacting entities is estimated. For the zero free energy change reaction, i.e., electron exchange between a radical ion and its parent molecule, a rate constant of about 5 X 10/sup 7/ M/sup -1/ s/sup -1/ is predicted. (auth)

In situ release rates of Cu and Zn from commercial antifouling paints at different salinities.

Science.gov (United States)

Lagerström, Maria; Lindgren, J Fredrik; Holmqvist, Albin; Dahlström, Mia; Ytreberg, Erik

2018-02-01

Antifouling paints are environmentally risk assessed based on their biocidal release rates to the water phase. In situ release rates of copper (Cu) and zinc (Zn) were derived for five commercial paints in two recreational marinas with different salinities (5 and 14 PSU) using an X-Ray Fluorescence spectrometer (XRF). Salinity was found to significantly affect the Cu release, with twice the amount of Cu released at the higher salinity, while its influence on the Zn release was paint-specific. Site-specific release rates for water bodies with salinity gradients, e.g. the Baltic Sea, are therefore necessary for more realistic risk assessments of antifouling paints. Furthermore, the in situ release rates were up to 8 times higher than those generated using standardized laboratory or calculation methods. The environmental risk assessment repeated with the field release rates concludes that it is questionable whether the studied products should be allowed on the Swedish market. Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.

On the ambiguity of the reaction rate constants in multivariate curve resolution for reversible first-order reaction systems.

Science.gov (United States)

Schröder, Henning; Sawall, Mathias; Kubis, Christoph; Selent, Detlef; Hess, Dieter; Franke, Robert; Börner, Armin; Neymeyr, Klaus

2016-07-13

If for a chemical reaction with a known reaction mechanism the concentration profiles are accessible only for certain species, e.g. only for the main product, then often the reaction rate constants cannot uniquely be determined from the concentration data. This is a well-known fact which includes the so-called slow-fast ambiguity. This work combines the question of unique or non-unique reaction rate constants with factor analytic methods of chemometrics. The idea is to reduce the rotational ambiguity of pure component factorizations by considering only those concentration factors which are possible solutions of the kinetic equations for a properly adapted set of reaction rate constants. The resulting set of reaction rate constants corresponds to those solutions of the rate equations which appear as feasible factors in a pure component factorization. The new analysis of the ambiguity of reaction rate constants extends recent research activities on the Area of Feasible Solutions (AFS). The consistency with a given chemical reaction scheme is shown to be a valuable tool in order to reduce the AFS. The new methods are applied to model and experimental data. Copyright © 2016 Elsevier B.V. All rights reserved.

Determination of rate constants in second-order kinetics using UV-visible spectroscopy

NARCIS (Netherlands)

Bijlsma, S.; Boelens, H. F. M.; Smilde, A. R.

2001-01-01

A general method for estimating reaction rate constants of chemical reactions using ultraviolet-visible (UV-vis) spectroscopy is presented. The only requirement is that some of the chemical components involved be spectroscopically active. The method uses the combination of spectroscopic measurements

Bibliographies on radiation chemistry: Pt. 12; Rate constants for reactions of nonmetallic inorganic radicals in aqueous solution

Energy Technology Data Exchange (ETDEWEB)

Helman, W P; Ross, A B [Notre Dame Univ., IN (USA). Radiation Chemistry Data Center

1990-01-01

Rate constants have been determined by pulse radiolysis, flash photolysis, and other methods, for a wide variety of reactions involving transient radicals in aqueous solution. Reliable rate constants have been established for reactions of radicals from water (e{sub aq}{sup -}, {center dot}H, {center dot}OH/{center dot}O{sup -}) and the data have been tabulated (Buxton, 1988) through 1986. Kinetic data for HO{sub 2}{center dot}/O{sub 2}{center dot}{sup -} were tabulated. (Bielski, 1985) from papers published through 1983. A compilation of rate constants, from the literature through Mid-1987, for other nonmetallic inorganic radicals has also appeared recently (Neta, 1988). Together, these compilations contain rate constants for more than 6,000 different reactions, reported in about 2,000 references. The present bibliography provides a list of relevant references which have been collected since the publication of the above-mentioned compilations. The list contains references received through the end of December, 1989. (author).

Kinetics of immobilisation and release of tryptophan, riboflavin and peptides from whey protein microbeads.

Science.gov (United States)

O'Neill, Graham J; Egan, Thelma; Jacquier, Jean Christophe; O'Sullivan, Michael; Dolores O'Riordan, E

2015-08-01

This study investigated the kinetics of immobilisation and release of riboflavin, amino acids and peptides from whey microbeads. Blank whey microbeads were placed in solutions of the compounds. As the volume of microbeads added to the solution was increased, the uptake of the compounds increased, to a maximum of 95% for the pentapeptide and 56%, 57% and 45% for the dipeptide, riboflavin and tryptophan respectively, however, the rate of uptake remained constant. The rate of uptake increased with increasing molecule hydrophobicity. The opposite was observed in the release studies, the more hydrophobic compounds had lower release rate constants (kr). When whey microbeads are used as sorbents, they show excellent potential to immobilise small hydrophobic molecules and minimise subsequent diffusion, even in high moisture environments. Copyright © 2015 Elsevier Ltd. All rights reserved.

Rate constants for the reaction of CF3O radicals with hydrocarbons at 298 K

DEFF Research Database (Denmark)

Kelly, C.; Treacy, J.; Sidebottom, H.W.

1993-01-01

Rate constant ratios of the reactions of CF3O radicals with a number of hydrocarbons have been determined at 298 +/- 2 K and atmospheric pressure using a relative rate method. Using a previously determined value k(CF30 + C2H6) = 1.2 x 10(-12) cm3 molecule-1 s-1 these rate constant ratios provide...... estimates of the rate constants: k(CF3O + CH4) = (1.2 +/- 0.1) x 10(-14), k(CF3O + c-C3H6) = (3.6 +/- 0.2) x 10(-13), k(CF3O + C3H8) = (4.7 +/- 0.7) x 10(-12), k(CF3O + (CH3)3CH) = (7.2 +/- 0.5) x 10(-12), k(CF3O + C2H4) = (3.0 +/- 0.1) x 10(-11) and k(CF3O + C6H6) = (3.6 +/- 0.1) x 10(-11) cm3 molecule-1 s......-1. The importance of the reactions of CF3O radicals with hydrocarbons under atmospheric conditions is discussed....

Laser Measurements of the H Atom + Ozone Rate Constant at Atmospheric Temperatures

Science.gov (United States)

Liu, Y.; Smith, G. P.; Peng, J.; Reppert, K. J.; Callahan, S. L.

2015-12-01

The exothermic H + O3 reaction produces OH(v) Meinel band emissions, used to derive mesospheric H concentrations and chemical heating rates. We have remeasured its rate constant to reduce resulting uncertainties and the measurement extend to lower mesospheric temperatures using modern laser techniques. H atoms are produced by pulsed ultraviolet laser trace photolysis of O3, followed by reaction of O(D) with added H2. A second, delayed, frequency-mixed dye laser measures the reaction decay rate with the remaining ozone by laser induced fluorescence. We monitor either the H atom decay by 2 photon excitation at 205 nm and detection of red fluorescence, or the OH(v=9) product time evolution with excitation of the B-X (0,9) band at 237 nm and emission in blue B-A bands. By cooling the enclosed low pressure flow cell we obtained measurements from 146-305 K. Small kinetic modeling corrections are made for secondary regeneration of H atoms. The results fully confirm the current NASA JPL recommendation for this rate constant, and establish its extrapolation down to the lower temperatures of the mesosphere. This work was supported by the NSF Aeronomy Program and an NSF Physics summer REU student grant.

Rate constants for the reaction of e-aq with EDTA and some metal EDTA-complexes

International Nuclear Information System (INIS)

Buitenhuis, R.; Bakker, C.M.N.; Stock, F.R.; Louwrier, P.W.F.

1977-01-01

The rate constants for the reaction e - aq + EDTA were measured as a function of the pH by the pulse-radiolysis technique. Between pH = 6and pH = 10 this rate constant can be represented by the equation k = 4.7 x 10 6 x (fraction of HEDTA 3- )+1.0 x 10 8 x (fraction H 2 EDTA 2 -)M -1 s -1 . Also the rate constants for reactions of e - aq with the following metal-EDTA complexes were measured: CuEDTA 2- , HgEDTA 2- , CoEDTA 2- , InEDTA - , NiEDTA 2- , GaEDTA - , MnEDTA 2- , ZnEDTA 2- , CdEDTA 2- , PbEDTA 2- . Ionic strength variation indicates that the reacting ions are not hydrolized to an appreciable amount at pH = 11.5. It is found that some of the products show light absorption in the region between 300 and 400 nm. (orig.) [de

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

Science.gov (United States)

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.

Research on release rate of volatile organic compounds in typical vessel cabin

Directory of Open Access Journals (Sweden)

ZHANG Jinlan

2018-02-01

Full Text Available [Objectives] Volatile Organic Compounds (VOC should be efficiently controlled in vessel cabins to ensure the crew's health and navigation safety. As an important parameter, research on release rate of VOCs in cabins is required. [Methods] This paper develops a method to investigate this parameter of a ship's cabin based on methods used in other closed indoor environments. A typical vessel cabin is sampled with Tenax TA tubes and analyzed by Automated Thermal Desorption-Gas Chromatography-Mass Spectrometry (ATD-GC/MS. The lumped mode is used and the release rate of Benzene, Toluene, Ethylbenzene and Xylene (BTEX, the typical representatives of VOCs, is obtained both in closed and ventilated conditions. [Results] The results show that the content of xylene and Total Volatile Organic Compounds (TVOC exceed the indoor environment standards in ventilated conditions. The BTEX release rate is similar in both conditions except for the benzene. [Conclusions] This research builds a method to measure the release rate of VOCs, providing references for pollution character evaluation and ventilation and purification system design.

Measurement of very low release rates of corrosion products in high temperature water

International Nuclear Information System (INIS)

Hermansson, H.-P.; Falk, I.

1984-01-01

A radiotracer technique has been developed for the measurement of release rates from nuclear reactor materials and it has been tested in a number of experiments. THis article, which forms the first part in a series, describes the experimental loop, the experimental technique and the preliminary results. Experiments were carried out on 18Cr8Ni stainless steel and on Inconel X750 in BWR primary system and feed water environments. The result show that a steady state in the release rate is achieved after operation for approximately 600 h. The release rate depends on the elemental concentration in the material and on the chemical and physical environments. Typical release rates for an 18Cr8Ni stainless steel and Inconel X750 in a BWR primary system environment were found to be 5 mdm and 8 mdm respectively. (Authors)

Studies on the catalytic rate constant of ribosomal peptidyltransferase.

Science.gov (United States)

Synetos, D; Coutsogeorgopoulos, C

1987-02-20

A detailed kinetic analysis of a model reaction for the ribosomal peptidyltransferase is described, using fMet-tRNA or Ac-Phe-tRNA as the peptidyl donor and puromycin as the acceptor. The initiation complex (fMet-tRNA X AUG X 70 S ribosome) or (Ac-Phe-tRNA X poly(U) X 70 S ribosome) (complex C) is isolated and then reacted with excess puromycin (S) to give fMet-puromycin or Ac-Phe-puromycin. This reaction (puromycin reaction) is first order at all concentrations of S tested. An important asset of this kinetic analysis is the fact that the relationship between the first order rate constant kobs and [S] shows hyperbolic saturation and that the value of kobs at saturating [S] is a measure of the catalytic rate constant (k cat) of peptidyltransferase in the puromycin reaction. With fMet-tRNA as the donor, this kcat of peptidyltransferase is 8.3 min-1 when the 0.5 M NH4Cl ribosomal wash is present, compared to 3.8 min-1 in its absence. The kcat of peptidyltransferase is 2.0 min-1 when Ac-Phe-tRNA replaces fMet-tRNA in the presence of the ribosomal wash and decreases to 0.8 min-1 in its absence. This kinetic procedure is the best method available for evaluating changes in the activity of peptidyltransferase in vitro. The results suggest that peptidyltransferase is subjected to activation by the binding of fMet-tRNA to the 70 S initiation complex.

Constant Growth Rate Can Be Supported by Decreasing Energy Flux and Increasing Aerobic Glycolysis

Directory of Open Access Journals (Sweden)

Nikolai Slavov

2014-05-01

Full Text Available Fermenting glucose in the presence of enough oxygen to support respiration, known as aerobic glycolysis, is believed to maximize growth rate. We observed increasing aerobic glycolysis during exponential growth, suggesting additional physiological roles for aerobic glycolysis. We investigated such roles in yeast batch cultures by quantifying O2 consumption, CO2 production, amino acids, mRNAs, proteins, posttranslational modifications, and stress sensitivity in the course of nine doublings at constant rate. During this course, the cells support a constant biomass-production rate with decreasing rates of respiration and ATP production but also decrease their stress resistance. As the respiration rate decreases, so do the levels of enzymes catalyzing rate-determining reactions of the tricarboxylic-acid cycle (providing NADH for respiration and of mitochondrial folate-mediated NADPH production (required for oxidative defense. The findings demonstrate that exponential growth can represent not a single metabolic/physiological state but a continuum of changing states and that aerobic glycolysis can reduce the energy demands associated with respiratory metabolism and stress survival.

Rate Constants for the Reactions of Hydroxyl Radical with Several Alkanes, Cycloalkanes, and Dimethyl Ether

Science.gov (United States)

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.

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

Science.gov (United States)

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.

An Empirical Rate Constant Based Model to Study Capacity Fading in Lithium Ion Batteries

Directory of Open Access Journals (Sweden)

Srivatsan Ramesh

2015-01-01

Full Text Available A one-dimensional model based on solvent diffusion and kinetics to study the formation of the SEI (solid electrolyte interphase layer and its impact on the capacity of a lithium ion battery is developed. The model uses the earlier work on silicon oxidation but studies the kinetic limitations of the SEI growth process. The rate constant of the SEI formation reaction at the anode is seen to play a major role in film formation. The kinetics of the reactions for capacity fading for various battery systems are studied and the rate constants are evaluated. The model is used to fit the capacity fade in different battery systems.

Inverse modelling of radionuclide release rates using gamma dose rate observations

Science.gov (United States)

Hamburger, Thomas; Evangeliou, Nikolaos; Stohl, Andreas; von Haustein, Christoph; Thummerer, Severin; Wallner, Christian

2015-04-01

Severe accidents in nuclear power plants such as the historical accident in Chernobyl 1986 or the more recent disaster in the Fukushima Dai-ichi nuclear power plant in 2011 have drastic impacts on the population and environment. Observations and dispersion modelling of the released radionuclides help to assess the regional impact of such nuclear accidents. Modelling the increase of regional radionuclide activity concentrations, which results from nuclear accidents, underlies a multiplicity of uncertainties. One of the most significant uncertainties is the estimation of the source term. That is, the time dependent quantification of the released spectrum of radionuclides during the course of the nuclear accident. The quantification of the source term may either remain uncertain (e.g. Chernobyl, Devell et al., 1995) or rely on estimates given by the operators of the nuclear power plant. Precise measurements are mostly missing due to practical limitations during the accident. The release rates of radionuclides at the accident site can be estimated using inverse modelling (Davoine and Bocquet, 2007). The accuracy of the method depends amongst others on the availability, reliability and the resolution in time and space of the used observations. Radionuclide activity concentrations are observed on a relatively sparse grid and the temporal resolution of available data may be low within the order of hours or a day. Gamma dose rates, on the other hand, are observed routinely on a much denser grid and higher temporal resolution and provide therefore a wider basis for inverse modelling (Saunier et al., 2013). We present a new inversion approach, which combines an atmospheric dispersion model and observations of radionuclide activity concentrations and gamma dose rates to obtain the source term of radionuclides. We use the Lagrangian particle dispersion model FLEXPART (Stohl et al., 1998; Stohl et al., 2005) to model the atmospheric transport of the released radionuclides. The

Low-Temperature Experimental and Theoretical Rate Constants for the O(1D) + H2 Reaction.

Science.gov (United States)

Hickson, Kevin M; Suleimanov, Yury V

2017-03-09

In the present joint experimental and theoretical study, we report thermal rate constants for the O( 1 D) + H 2 reaction within the 50-300 K temperature range. Experimental kinetics measurements were performed using a continuous supersonic flow reactor coupled with pulsed laser photolysis for O( 1 D) production and pulsed laser-induced fluorescence in the vacuum ultraviolet wavelength range (VUV LIF) for O( 1 D) detection. Theoretical rate constants were obtained using the ring polymer molecular dynamics (RPMD) approach over the two lowest potential energy surfaces 1 1 A' and 1 1 A″, which possess barrierless and thermally activated energy profiles, respectively. Both the experimental and theoretical rate constants exhibit a weak temperature dependence. The theoretical results show the dominant role of the 1 1 A' ground state and that contribution of the 1 1 A″ excited state to the total thermal rate decreases dramatically at lower temperature. Agreement between the experimental and theoretical results is good, and the discrepancy does not exceed 25%. It is argued that these differences are likely to be due to nonadiabatic couplings between the 1 1 A' and 2 1 A' surfaces.

Determination of hydroxyl rate constants by a high-throughput fluorimetric assay: towards a unified reactivity scale for antioxidants

International Nuclear Information System (INIS)

Louit, G.; Renault, J.P.; Pin, S.; Coffigny, H.; Hanedanian, M.; Taran, F.; Renault, J.P.; Pin, S.

2009-01-01

We describe in this article the development of a new method for the determination of rate constants of reaction of the hydroxyl radical, generated by radiolysis of water, with almost any possible molecule. It has been designed to provide a fast and reliable screening of antioxidant banks using microplates. Our particular approach is based on the use of the coumarin molecule as a competitor against the tested molecules: after a fast pulse of low dose irradiation, the fluorescence of 7-hydroxycoumarin produced by the oxidation of coumarin is measured and is inversely proportional to the scavenging ability of the tested antioxidant. We have validated our protocol using 32 molecules whose rate constants with HO . had already been evaluated and found a good agreement between our rate constants and the latter ones. The scopes and limitations of our method, as well as those of other rate constant determination methods, are discussed. (authors)

Kinetics analysis for development of a rate constant estimation model for ultrasonic degradation reaction of methylene blue.

Science.gov (United States)

Kobayashi, Daisuke; Honma, Chiemi; Matsumoto, Hideyuki; Takahashi, Tomoki; Kuroda, Chiaki; Otake, Katsuto; Shono, Atsushi

2014-07-01

Ultrasound has been used as an advanced oxidation method for wastewater treatment. Sonochemical degradation of organic compounds in aqueous solution occurs by pyrolysis and/or reaction with hydroxyl radicals. Moreover, kinetics of sonochemical degradation has been proposed. However, the effect of ultrasonic frequency on degradation rate has not been investigated. In our previous study, a simple model for estimating the apparent degradation rate of methylene blue was proposed. In this study, sonochemical degradation of methylene blue was performed at various frequencies. Apparent degradation rate constant was evaluated assuming that sonochemical degradation of methylene blue was a first-order reaction. Specifically, we focused on effects of ultrasonic frequency and power on rate constant, and the applicability of our proposed model was demonstrated. Using this approach, maximum sonochemical degradation rate was observed at 490 kHz, which agrees with a previous investigation into the effect of frequency on the sonochemical efficiency value evaluated by KI oxidation dosimetry. Degradation rate increased with ultrasonic power at every frequency. It was also observed that threshold power must be reached for the degradation reaction to progress. The initial methylene blue concentration and the apparent degradation rate constant have a relation of an inverse proportion. Our proposed model for estimating the apparent degradation rate constant using ultrasonic power and sonochemical efficiency value can apply to this study which extended the frequency and initial concentration range. Copyright © 2013 Elsevier B.V. All rights reserved.

Deuterium isotope effects on toluene metabolism. Product release as a rate-limiting step in cytochrome P-450 catalysis

International Nuclear Information System (INIS)

Ling, K.H.; Hanzlik, R.P.

1989-01-01

Liver microsomes from phenobarbital-induced rats oxidize toluene to a mixture of benzyl alcohol plus o-, m- and p-cresol (ca. 69:31). Stepwise deuteration of the methyl group causes stepwise decreases in the yield of benzyl alcohol relative to cresols (ca. 24:76 for toluene-d3). For benzyl alcohol formation from toluene-d3 DV = 1.92 and D(V/K) = 3.53. Surprisingly, however, stepwise deuteration induces stepwise increases in total oxidation, giving rise to an inverse isotope effect overall (DV = 0.67 for toluene-d3). Throughout the series (i.e. d0, d1, d2, d3) the ratios of cresol isomers remain constant. These results are interpreted in terms of product release for benzyl alcohol being slower than release of cresols (or their epoxide precursors), and slow enough to be partially rate-limiting in turnover. Thus metabolic switching to cresol formation causes a net acceleration of turnover

Constant savings rates and quasi-arithmetic population growth under exhaustible resource constraints

NARCIS (Netherlands)

Asheim, G.B.; Buchholz, W.; Hartwick, J.M.; Mitra, T.; Withagen, C.A.A.M.

2007-01-01

In the Dasgupta–Heal–Solow–Stiglitz (DHSS) model of capital accumulation and resource depletion we show the following equivalence: if an efficient path has constant (gross and net of population growth) savings rates, then population growth must be quasi-arithmetic and the path is a maximin or a

Divided Saddle Theory: A New Idea for Rate Constant Calculation.

Science.gov (United States)

Daru, János; Stirling, András

2014-03-11

We present a theory of rare events and derive an algorithm to obtain rates from postprocessing the numerical data of a free energy calculation and the corresponding committor analysis. The formalism is based on the division of the saddle region of the free energy profile of the rare event into two adjacent segments called saddle domains. The method is built on sampling the dynamics within these regions: auxiliary rate constants are defined for the saddle domains and the absolute forward and backward rates are obtained by proper reweighting. We call our approach divided saddle theory (DST). An important advantage of our approach is that it requires only standard computational techniques which are available in most molecular dynamics codes. We demonstrate the potential of DST numerically on two examples: rearrangement of alanine-dipeptide (CH3CO-Ala-NHCH3) conformers and the intramolecular Cope reaction of the fluxional barbaralane molecule.

Separating the effect of respiration from the heart rate variability for cases of constant harmonic breathing

Directory of Open Access Journals (Sweden)

Kircher Michael

2015-09-01

Full Text Available Heart Rate Variability studies are a known measure for the autonomous control of the heart rate. In special situations, its interpretation can be ambiguous, since the respiration has a major influence on the heart rate variability. For this reason it has often been proposed to measure Heart Rate Variability, while the subjects are breathing at a constant respiration rate. That way the spectral influence of the respiration is known. In this work we propose to remove this constant respiratory influence from the heart rate and the Heart Rate Variability parameters to gain respiration free autonomous controlled heart rate signal. The spectral respiratory component in the heart rate signal is detected and characterized. Subsequently the respiratory effect on Heart Rate Variability is removed using spectral filtering approaches, such as the Notch filter or the Raised Cosine filter. As a result new decoupled Heart Variability parameters are gained, which could lead to new additional interpretations of the autonomous control of the heart rate.

H2S release rate assessment guidelines and audit forms

International Nuclear Information System (INIS)

Johnson, S.; Wilson, T.; Long, R.; Shewan, K.; Nchkalo, H.; Nelson, R.; Morand, M.

1998-01-01

Development of a process to evaluate and calculate potential hydrogen sulfide release has been recommended by the Canadian Association of Petroleum Producers' Drilling and Completion Committee, and the Alberta Energy and Utilities Board. To facilitate the process, CAPP has released guidelines describing a methodology and standard for the industry to calculate the potential hydrogen sulfide release rates of a well, and a standardized format for the documentation and retention of data. The Guidelines describe a four-step process, with each step having an increasing degree of complexity. Step One describes the zone hydrogen sulfide exclusion area maps, defining when reporting is to be used (based on well location and distance from inhabited areas). Step Two provides details of the recommended method for determining hydrogen sulfide release through a data search process. Step Three consists of a series of instructions in the use of geologic analogs, data editing and wellbore design to further refine the cumulative hydrogen sulfide release rate. Step Four contains information designed to assist in detailed geological and reservoir modeling. It is not necessary to use all four steps in all cases. The user, however, is advised to use sound engineering judgement and due diligence in the calculation decisions. Sample calculations are provided for a variety of different situations. Measurement techniques are described in an appendix. A completed example of an audit form is attached. 10 + 6 refs., tabs

The rate constant for the CO + H2O2 reaction

DEFF Research Database (Denmark)

Glarborg, Peter; Marshall, Paul

2009-01-01

The rate constant for the reaction CO + H2O2 -> HOCO + OH (R1) at 713 K is determined based on the batch reactor experiments of Baldwin et al. [ R. R. Baldwin, R. W. Walker, S. J. Webster, Combust. Flame 15 (1970) 167] on decomposition of H2O2 sensitized by CO. The value, k(1) (713 K) = 8.1 x 10...

The Rate Constant for the Reaction H + C2H5 at T = 295 - 150K

Science.gov (United States)

Pimentel, Andre S.; Payne, Walter A.; Nesbitt, Fred L.; Cody, Regina J.; Stief, Louis J.

2004-01-01

The reaction between the hydrogen atom and the ethyl (C2H3) radical is predicted by photochemical modeling to be the most important loss process for C2H5 radicals in the atmospheres of Jupiter and Saturn. This reaction is also one of the major sources for the methyl radicals in these atmospheres. These two simplest hydrocarbon radicals are the initial species for the synthesis of larger hydrocarbons. Previous measurements of the rate constant for the H + C2H5 reaction varied by a factor of five at room temperature, and some studies showed a dependence upon temperature while others showed no such dependence. In addition, the previous studies were at higher temperatures and generally higher pressures than that needed for use in planetary atmospheric models. The rate constant for the reaction H + C2H5 has been measured directly at T = 150, 202 and 295 K and at P = 1.0 Torr He for all temperatures and additionally at P = 0.5 and 2.0 Torr He at T = 202 K. The measurements were performed in a discharge - fast flow system. The decay of the C2H5 radical in the presence of excess hydrogen was monitored by low-energy electron impact mass spectrometry under pseudo-first order conditions. H atoms and C2H5 radicals were generated rapidly and simultaneously by the reaction of fluorine atoms with H2 and C2H6, respectively. The total rate constant was found to be temperature and pressure independent. The measured total rate constant at each temperature are: k(sub 1)(295K) = (1.02+/-0.24)x10(exp -10), k(sub 1)(202K) = (1.02+/-0.22)x10(exp -10) and k(sub 1)(150K) = (0.93+/-0.21)x10(exp -10), all in units of cu cm/molecule/s. The total rate constant derived from all the combined measurements is k(sub 1) = (l.03+/-0.17)x10(exp -10) cu cm/molecule/s. At room temperature our results are about a factor of two higher than the recommended rate constant and a factor of three lower than the most recently published study.

Release rate of diazinon from microcapsule based on melamine formaldehyde

Science.gov (United States)

Noviana Utami C., S.; Rochmadi

2018-04-01

The microcapsule containing diazinon as the core material and melamine formaldehyde as the membrane material have been synthesized by in situ polymerization method. The microcapsule membrane in this research is melamine formaldehyde (MF). This research aims to study the effect of pH and temperature on the release rate of diazinon from microcapsule based on melamine formaldehyde in aqueous medium. The results showed that pH and temperature has little effect on the release rate of diazinon from microcapsule based on melamine formaldehyde. This is due to the diffusion through the microcapsule membrane is not influenced by the pH and temperature of the solution outside of microcapsule.

The ATP hydrolysis and phosphate release steps control the time course of force development in rabbit skeletal muscle.

Science.gov (United States)

Sleep, John; Irving, Malcolm; Burton, Kevin

2005-03-15

The time course of isometric force development following photolytic release of ATP in the presence of Ca(2+) was characterized in single skinned fibres from rabbit psoas muscle. Pre-photolysis force was minimized using apyrase to remove contaminating ATP and ADP. After the initial force rise induced by ATP release, a rapid shortening ramp terminated by a step stretch to the original length was imposed, and the time course of the subsequent force redevelopment was again characterized. Force development after ATP release was accurately described by a lag phase followed by one or two exponential components. At 20 degrees C, the lag was 5.6 +/- 0.4 ms (s.e.m., n = 11), and the force rise was well fitted by a single exponential with rate constant 71 +/- 4 s(-1). Force redevelopment after shortening-restretch began from about half the plateau force level, and its single-exponential rate constant was 68 +/- 3 s(-1), very similar to that following ATP release. When fibres were activated by the addition of Ca(2+) in ATP-containing solution, force developed more slowly, and the rate constant for force redevelopment following shortening-restretch reached a maximum value of 38 +/- 4 s(-1) (n = 6) after about 6 s of activation. This lower value may be associated with progressive sarcomere disorder at elevated temperature. Force development following ATP release was much slower at 5 degrees C than at 20 degrees C. The rate constant of a single-exponential fit to the force rise was 4.3 +/- 0.4 s(-1) (n = 22), and this was again similar to that after shortening-restretch in the same activation at this temperature, 3.8 +/- 0.2 s(-1). We conclude that force development after ATP release and shortening-restretch are controlled by the same steps in the actin-myosin ATPase cycle. The present results and much previous work on mechanical-chemical coupling in muscle can be explained by a kinetic scheme in which force is generated by a rapid conformational change bracketed by two

Biotransformation of trace organic chemicals during groundwater recharge: How useful are first-order rate constants?

KAUST Repository

Regnery, J.

2015-05-29

This study developed relationships between the attenuation of emerging trace organic chemicals (TOrC) during managed aquifer recharge (MAR) as a function of retention time, system characteristics, and operating conditions using controlled laboratory-scale soil column experiments simulating MAR. The results revealed that MAR performance in terms of TOrC attenuation is primarily determined by key environmental parameters (i.e. redox, primary substrate). Soil columns with suboxic and anoxic conditions performed poorly (i.e. less than 30% attenuation of moderately degradable TOrC) in comparison to oxic conditions (on average between 70-100% attenuation for the same compounds) within a residence time of three days. Given this dependency on redox conditions, it was investigated if key parameter-dependent rate constants are more suitable for contaminant transport modeling to properly capture the dynamic TOrC attenuation under field-scale conditions. Laboratory-derived first-order removal kinetics were determined for 19 TOrC under three different redox conditions and rate constants were applied to MAR field data. Our findings suggest that simplified first-order rate constants will most likely not provide any meaningful results if the target compounds exhibit redox dependent biotransformation behavior or if the intention is to exactly capture the decline in concentration over time and distance at field-scale MAR. However, if the intention is to calculate the percent removal after an extended time period and subsurface travel distance, simplified first-order rate constants seem to be sufficient to provide a first estimate on TOrC attenuation during MAR.

Biotransformation of trace organic chemicals during groundwater recharge: How useful are first-order rate constants?

Science.gov (United States)

Regnery, J; Wing, A D; Alidina, M; Drewes, J E

2015-08-01

This study developed relationships between the attenuation of emerging trace organic chemicals (TOrC) during managed aquifer recharge (MAR) as a function of retention time, system characteristics, and operating conditions using controlled laboratory-scale soil column experiments simulating MAR. The results revealed that MAR performance in terms of TOrC attenuation is primarily determined by key environmental parameters (i.e., redox, primary substrate). Soil columns with suboxic and anoxic conditions performed poorly (i.e., less than 30% attenuation of moderately degradable TOrC) in comparison to oxic conditions (on average between 70-100% attenuation for the same compounds) within a residence time of three days. Given this dependency on redox conditions, it was investigated if key parameter-dependent rate constants are more suitable for contaminant transport modeling to properly capture the dynamic TOrC attenuation under field-scale conditions. Laboratory-derived first-order removal kinetics were determined for 19 TOrC under three different redox conditions and rate constants were applied to MAR field data. Our findings suggest that simplified first-order rate constants will most likely not provide any meaningful results if the target compounds exhibit redox dependent biotransformation behavior or if the intention is to exactly capture the decline in concentration over time and distance at field-scale MAR. However, if the intention is to calculate the percent removal after an extended time period and subsurface travel distance, simplified first-order rate constants seem to be sufficient to provide a first estimate on TOrC attenuation during MAR. Copyright © 2015 Elsevier B.V. All rights reserved.

Stress corrosion crack initiation of Zircaloy-4 cladding tubes in an iodine vapor environment during creep, relaxation, and constant strain rate tests

Science.gov (United States)

Jezequel, T.; Auzoux, Q.; Le Boulch, D.; Bono, M.; Andrieu, E.; Blanc, C.; Chabretou, V.; Mozzani, N.; Rautenberg, M.

2018-02-01

During accidental power transient conditions with Pellet Cladding Interaction (PCI), the synergistic effect of the stress and strain imposed on the cladding by thermal expansion of the fuel, and corrosion by iodine released as a fission product, may lead to cladding failure by Stress Corrosion Cracking (SCC). In this study, internal pressure tests were conducted on unirradiated cold-worked stress-relieved Zircaloy-4 cladding tubes in an iodine vapor environment. The goal was to investigate the influence of loading type (constant pressure tests, constant circumferential strain rate tests, or constant circumferential strain tests) and test temperature (320, 350, or 380 °C) on iodine-induced stress corrosion cracking (I-SCC). The experimental results obtained with different loading types were consistent with each other. The apparent threshold hoop stress for I-SCC was found to be independent of the test temperature. SEM micrographs of the tested samples showed many pits distributed over the inner surface, which tended to coalesce into large pits in which a microcrack could initiate. A model for the time-to-failure of a cladding tube was developed using finite element simulations of the viscoplastic mechanical behavior of the material and a modified Kachanov's damage growth model. The times-to-failure predicted by this model are consistent with the experimental data.

Photon spectrometry for the determination of the dose-rate constant of low-energy photon-emitting brachytherapy sources

International Nuclear Information System (INIS)

Chen, Zhe Jay; Nath, Ravinder

2007-01-01

Accurate determination of dose-rate constant (Λ) for interstitial brachytherapy sources emitting low-energy photons (<50 keV) has remained a challenge in radiation dosimetry because of the lack of a suitable absolute dosimeter for accurate measurement of the dose rates near these sources. Indeed, a consensus value of Λ taken as the arithmetic mean of the dose-rate constants determined by different research groups and dosimetry techniques has to be used at present for each source model in order to minimize the uncertainties associated with individual determinations of Λ. Because the dosimetric properties of a source are fundamentally determined by the characteristics of the photons emitted by the source, a new technique based on photon spectrometry was developed in this work for the determination of dose-rate constant. The photon spectrometry technique utilized a high-resolution gamma-ray spectrometer to measure source-specific photon characteristics emitted by the low-energy sources and determine their dose-rate constants based on the measured photon-energy spectra and known dose-deposition properties of mono-energetic photons in water. This technique eliminates many of the difficulties arising from detector size, the energy dependence of detector sensitivity, and the use of non-water-equivalent solid phantoms in absolute dose rate measurements. It also circumvents the uncertainties that might be associated with the source modeling in Monte Carlo simulation techniques. It was shown that the estimated overall uncertainty of the photon spectrometry technique was less than 4%, which is significantly smaller than the reported 8-10% uncertainty associated with the current thermo-luminescent dosimetry technique. In addition, the photon spectrometry technique was found to be stable and quick in Λ determination after initial setup and calibration. A dose-rate constant can be determined in less than two hours for each source. These features make it ideal to determine

Theoretical and Shock Tube Study of the Rate Constants for Hydrogen Abstraction Reactions of Ethyl Formate

KAUST Repository

Wu, Junjun; Khaled, Fathi; Ning, Hongbo; Ma, Liuhao; Farooq, Aamir; Ren, Wei

2017-01-01

We report a systematic chemical kinetics study of the H-atom abstractions from ethyl formate (EF) by H, O(3P), CH3, OH, and HO2 radicals. The geometry optimization and frequency calculation of all the species were conducted using the M06 method and the cc-pVTZ basis set. The one-dimensional hindered rotor treatment of the reactants and transition states and the intrinsic reaction coordinate analysis were also performed at the M06/cc-pVTZ level of theory. The relative electronic energies were calculated at the CCSD(T)/cc-pVXZ (where X = D, T) level of theory and further extrapolated to the complete basis set limit. Rate constants for the tittle reactions were calculated over the temperature range of 500‒2500 K by the transition state theory (TST) in conjunction with asymmetric Eckart tunneling effect. In addition, the rate constants of H-abstraction by hydroxyl radical were measured in shock tube experiments at 900‒1321 K and 1.4‒2.0 atm. Our theoretical rate constants of OH + EF → Products agree well with the experimental results within 15% over the experimental temperature range of 900‒1321 K. Branching ratios for the five types of H-abstraction reactions were also determined from their individual site-specific rate constants.

Theoretical and Shock Tube Study of the Rate Constants for Hydrogen Abstraction Reactions of Ethyl Formate

KAUST Repository

Wu, Junjun

2017-08-03

We report a systematic chemical kinetics study of the H-atom abstractions from ethyl formate (EF) by H, O(3P), CH3, OH, and HO2 radicals. The geometry optimization and frequency calculation of all the species were conducted using the M06 method and the cc-pVTZ basis set. The one-dimensional hindered rotor treatment of the reactants and transition states and the intrinsic reaction coordinate analysis were also performed at the M06/cc-pVTZ level of theory. The relative electronic energies were calculated at the CCSD(T)/cc-pVXZ (where X = D, T) level of theory and further extrapolated to the complete basis set limit. Rate constants for the tittle reactions were calculated over the temperature range of 500‒2500 K by the transition state theory (TST) in conjunction with asymmetric Eckart tunneling effect. In addition, the rate constants of H-abstraction by hydroxyl radical were measured in shock tube experiments at 900‒1321 K and 1.4‒2.0 atm. Our theoretical rate constants of OH + EF → Products agree well with the experimental results within 15% over the experimental temperature range of 900‒1321 K. Branching ratios for the five types of H-abstraction reactions were also determined from their individual site-specific rate constants.

Empirical correlation for prediction of the elutriation rate constant

Directory of Open Access Journals (Sweden)

Stojkovski Valentino

2003-01-01

Full Text Available In vessels containing fluidized solids, the gas leaving carries some suspended particles. This flux of solids is called entrainment, E or carryover and the bulk density of solids on this leaving gas stream is called the holdup. For design we need to know the rate of this entrainment and the size distribution of these entrained particles Rim in relation to the size distribution in the bed, Rib, as well as the variation of both these quantities with gas and solids properties, gas flow rate, bed geometry and location of the leaving gas stream. Steady-state elutriation experiments have been done in a fluidized bed 0,2 m diameter by 2,94 m high freeboard with superficial gas velocities up to 1 m/s using solids ranging in mean size from 0,15 to 0,58 mm and with particle density 2660 kg/m3. When the fine and coarse particles were mixed, the total entrainment flux above the freeboard was increased. None of the published correlations for estimating the elutriation rate constant were useful. A new simple equation, which is developed on the base of experimental results and theory of dimensional analyses, is presented.

Extrapolation of rate constants of reactions producing H{sub 2} and O{sub 2} in radiolysis of water at high temperatures

Energy Technology Data Exchange (ETDEWEB)

Leblanc, R.; Ghandi, K.; Hackman, B.; Liu, G. [Mount Allison Univ., Sackville, NB (Canada)

2014-07-01

One target of our research is to extrapolate known data on the rate constants of reactions and add corrections to estimate the rate constants at the higher temperatures reached by the SCWR reactors. The focus of this work was to extrapolate known data on the rate constants of reactions that produce Hydrogen or Oxygen with a rate constant below 10{sup 10} mol{sup -1} s{sup -1} at room temperature. The extrapolation is done taking into account the change in the diffusion rate of the interacting species and the cage effect with thermodynamic conditions. The extrapolations are done over a wide temperature range and under isobaric conditions. (author)

Determination of Methane and Carbon Dioxide Formation Rate Constants for Semi-Continuously Fed Anaerobic Digesters

Directory of Open Access Journals (Sweden)

Jan Moestedt

2015-01-01

Full Text Available To optimize commercial-scale biogas production, it is important to evaluate the performance of each microbial step in the anaerobic process. Hydrolysis and methanogenesis are usually the rate-limiting steps during digestion of organic waste and by-products. By measuring biogas production and methane concentrations on-line in a semi-continuously fed reactor, gas kinetics can be evaluated. In this study, the rate constants of the fermentative hydrolysis step (kc and the methanogenesis step (km were determined and evaluated in a continuously stirred tank laboratory-scale reactor treating food and slaughterhouse waste and glycerin. A process additive containing Fe2+, Co2+ and Ni2+ was supplied until day 89, after which Ni2+ was omitted. The omission resulted in a rapid decline in the methanogenesis rate constant (km to 70% of the level observed when Ni2+ was present, while kc remained unaffected. This suggests that Ni2+ mainly affects the methanogenic rather than the hydrolytic microorganisms in the system. However, no effect was initially observed when using conventional process monitoring parameters such as biogas yield and volatile fatty acid concentration. Hence, formation rate constants can reveal additional information on process performance and km can be used as a complement to conventional process monitoring tools for semi-continuously fed anaerobic digesters.

Reaction rate constant of HO2+O3 measured by detecting HO2 from photofragment fluorescence

Science.gov (United States)

Manzanares, E. R.; Suto, Masako; Lee, Long C.; Coffey, Dewitt, Jr.

1986-01-01

A room-temperature discharge-flow system investigation of the rate constant for the reaction 'HO2 + O3 yields OH + 2O2' has detected HO2 through the OH(A-X) fluorescence produced by photodissociative excitation of HO2 at 147 nm. A reaction rate constant of 1.9 + or - 0.3 x 10 to the -15th cu cm/molecule per sec is obtained from first-order decay of HO2 in excess O3; this agrees well with published data.

QSARs for phenols and phenolates: oxidation potential as a predictor of reaction rate constants with photochemically produced oxidants.

Science.gov (United States)

Arnold, William A; Oueis, Yan; O'Connor, Meghan; Rinaman, Johanna E; Taggart, Miranda G; McCarthy, Rachel E; Foster, Kimberley A; Latch, Douglas E

2017-03-22

Quantitative structure-activity relationships (QSARs) for prediction of the reaction rate constants of phenols and phenolates with three photochemically produced oxidants, singlet oxygen, carbonate radical, and triplet excited state sensitizers/organic matter, are developed. The predictive variable is the one-electron oxidation potential (E 1 ), which is calculated for each species using density functional theory. The reaction rate constants are obtained from the literature, and for singlet oxygen, are augmented with new experimental data. Calculated E 1 values have a mean unsigned error compared to literature values of 0.04-0.06 V. For singlet oxygen, a single linear QSAR that includes both phenols and phenolates is developed that predicts experimental rate constants, on average, to within a factor of three. Predictions for only 6 out of 87 compounds are off by more than a factor of 10. A more limited data set for carbonate radical reactions with phenols and phenolates also gives a single linear QSAR with prediction of rate constant being accurate to within a factor of three. The data for the reactions of phenols with triplet state sensitizers demonstrate that two sensitizers, 2-acetonaphthone and methylene blue, most closely predict the reactivity trend of triplet excited state organic matter with phenols. Using sensitizers with stronger reduction potentials could lead to overestimation of rate constants and thus underestimation of phenolic pollutant persistence.

Application of an Artificial Neural Network to the Prediction of OH Radical Reaction Rate Constants for Evaluating Global Warming Potential.

Science.gov (United States)

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.

Determination of photoformation rates and scavenging rate constants of hydroxyl radicals in natural waters using an automatic light irradiation and injection system

International Nuclear Information System (INIS)

Nakatani, Nobutake; Hashimoto, Norichika; Shindo, Hirotaka; Yamamoto, Masatoshi; Kikkawa, Megumi; Sakugawa, Hiroshi

2007-01-01

Photoformation rates and scavenging rate constants of hydroxyl radicals (·OH) in natural water samples were determined by an automatic determination system. After addition of benzene as a chemical probe to a water sample in a reaction cell, light irradiation and injection of irradiated water samples into an HPLC as a function of time were performed automatically. Phenol produced by the reaction between ·OH and the benzene added to the water sample was determined to quantify the ·OH formation rate. The rate constants of ·OH formation from the photolysis of nitrate ions, nitrite ions and hydrogen peroxide were comparable with those obtained in previous studies. The percent of expected ·OH photoformation rate from added nitrate ion were high in drinking water (97.4%) and river water (99.3%). On the other hand, the low percent (65.0%) was observed in seawater due to the reaction of ·OH with the high concentrations of chloride and bromide ions. For the automatic system, the coefficient of variance for the determination of the ·OH formation rate was less than 5.0%, which is smaller than that in the previous report. When the complete time sequence of analytical cycle was 40 min for one sample, the detection limit of the photoformation rate and the sample throughput were 8 x 10 -13 M s -1 and 20 samples per day, respectively. The automatic system successfully determined the photoformation rates and scavenging rate constants of ·OH in commercial drinking water and the major source and sink of ·OH were identified as nitrate and bicarbonate ions, respectively

Recent developments in semiclassical mechanics: eigenvalues and reaction rate constants

International Nuclear Information System (INIS)

Miller, W.H.

1976-04-01

A semiclassical treatment of eigenvalues for a multidimensional non-separable potential function and of the rate constant for a chemical reaction with an activation barrier is presented. Both phenomena are seen to be described by essentially the same semiclassical formalism, which is based on a construction of the total Hamiltonian in terms of the complete set of ''good'' action variables (or adiabatic invariants) associated with the minimum in the potential energy surface for the eigenvalue case, or the saddle point in the potential energy surface for the case of chemical reaction

Decomposition and nutrient release of leguminous plants in coffee agroforestry systems

Directory of Open Access Journals (Sweden)

Eduardo da Silva Matos

2011-02-01

Full Text Available Leguminous plants used as green manure are an important nutrient source for coffee plantations, especially for soils with low nutrient levels. Field experiments were conducted in the Zona da Mata of Minas Gerais State, Brazil to evaluate the decomposition and nutrient release rates of four leguminous species used as green manures (Arachis pintoi, Calopogonium mucunoides, Stizolobium aterrimum and Stylosanthes guianensis in a coffee agroforestry system under two different climate conditions. The initial N contents in plant residues varied from 25.7 to 37.0 g kg-1 and P from 2.4 to 3.0 g kg-1. The lignin/N, lignin/polyphenol and (lignin+polyphenol/N ratios were low in all residues studied. Mass loss rates were highest in the first 15 days, when 25 % of the residues were decomposed. From 15 to 30 days, the decomposition rate decreased on both farms. On the farm in Pedra Dourada (PD, the decomposition constant k increased in the order C. mucunoides < S. aterrimum < S. guianensis < A. pintoi. On the farm in Araponga (ARA, there was no difference in the decomposition rate among leguminous plants. The N release rates varied from 0.0036 to 0.0096 d-1. Around 32 % of the total N content in the plant material was released in the first 15 days. In ARA, the N concentration in the S. aterrimum residues was always significantly higher than in the other residues. At the end of 360 days, the N released was 78 % in ARA and 89 % in PD of the initial content. Phosphorus was the most rapidly released nutrient (k values from 0.0165 to 0.0394 d-1. Residue decomposition and nutrient release did not correlate with initial residue chemistry and biochemistry, but differences in climatic conditions between the two study sites modified the decomposition rate constants.

The burning and smoke release rates of sodium pool fires

International Nuclear Information System (INIS)

Newman, R.N.; Payne, J.F.B.

1976-10-01

The burning rates and smoke release fractions of sodium pool fires have been measured over the pool temperature range 250 0 C to 750 0 C. A theoretical model is derived which satisfactorily predicts the burning rate over the above temperature range. The theory further predicts that the burning rate should be independent of pool diameter, a prediction supported by a comparison of burning rate data from this study and available data from other studies. (author)

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

Science.gov (United States)

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

2012-04-28

The proton-transfer ground-state rate constants of the xanthenic dye 9-[1-(2-methyl-4-methoxyphenyl)]-6-hydroxy-3H-xanthen-3-one (TG-II), recovered by Fluorescence Lifetime Correlation Spectroscopy (FLCS), have proven to be useful to quantitatively reflect specific cation effects in aqueous solutions (J. M. Paredes, L. Crovetto, A. Orte, J. M. Alvarez-Pez and E. M. Talavera, Phys. Chem. Chem. Phys., 2011, 13, 1685-1694). Since these phenomena are more sensitive to anions than to cations, in this paper we have accounted for the influence of salts with the sodium cation in common, and the anion classified according to the empirical Hofmeister series, on the proton transfer rate constants of TG-II. We demonstrate that the presence of ions accelerates the rate of the ground-state proton-exchange reaction in the same order than ions that affect ion solvation in water. The combination of FLCS with a fluorophore undergoing proton transfer reactions in the ground state, along with the desirable feature of a pseudo-dark state when the dye is protonated, allows one unique direct determination of kinetic rate constants of the proton exchange chemical reaction. This journal is © the Owner Societies 2012

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

Science.gov (United States)

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 constants for the reactions of OH with HFC-134a (CF3CH2F) and HFC-134 (CHF2CHF2)

Science.gov (United States)

Demore, W. B.

1993-01-01

Measurements of rate constants for HFC-134 (CF2HCF2H) relative to CH3CCl3, HFC-125, and HFC-134a are reported. The measurements were made in a slow-flow, temperature controlled photochemical reactor, and were based on relative rates of disappearance of the parent compounds as measured by FTIR spectroscopy. Hydroxyl radicals were generated by 254-nm photolysis of O3 in the presence of water vapor. NASA/JPL rate constants for the reference compounds are used to derive temperature-dependent rate constants of both compounds. Rate constants obtained from the different reference compounds are in excellent agreement. The presently recommended rate constant for HFC-134a is about 25 percent too high.

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

Science.gov (United States)

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.

Radionuclide release rates from spent fuel for performance assessment modeling

International Nuclear Information System (INIS)

Curtis, D.B.

1994-01-01

In a scenario of aqueous transport from a high-level radioactive waste repository, the concentration of radionuclides in water in contact with the waste constitutes the source term for transport models, and as such represents a fundamental component of all performance assessment models. Many laboratory experiments have been done to characterize release rates and understand processes influencing radionuclide release rates from irradiated nuclear fuel. Natural analogues of these waste forms have been studied to obtain information regarding the long-term stability of potential waste forms in complex natural systems. This information from diverse sources must be brought together to develop and defend methods used to define source terms for performance assessment models. In this manuscript examples of measures of radionuclide release rates from spent nuclear fuel or analogues of nuclear fuel are presented. Each example represents a very different approach to obtaining a numerical measure and each has its limitations. There is no way to obtain an unambiguous measure of this or any parameter used in performance assessment codes for evaluating the effects of processes operative over many millennia. The examples are intended to suggest by example that in the absence of the ability to evaluate accuracy and precision, consistency of a broadly based set of data can be used as circumstantial evidence to defend the choice of parameters used in performance assessments

Variational transition-state theory study of the rate constant of the DMS·OH scavenging reaction by O2.

Science.gov (United States)

Ramírez-Anguita, Juan M; González-Lafont, Àngels; Lluch, José M

2011-07-30

The chemical tropospheric dimethyl sulfide (DMS, CH3SCH3) degradation involves several steps highly dependent on the environmental conditions. So, intensive efforts have been devoted during the last years to enhance the understanding of the DMS oxidation mechanism under different conditions. The reaction of DMS with OH is considered to be the most relevant process that initiates the whole oxidation process. The experimental observations have been explained by a two-channel mechanism consisting of a H-abstraction process leading to CH3S(O)CH3 and HO2 and an addition reaction leading to the DMS·OH adduct. In the presence of O2, the DMS·OH adduct is competitively scavenged increasing the contribution of the addition channel to the overall DMS oxidation. Recent experimental measurements have determined from a global fit that the rate constant of this scavenging process is independent of pressure and temperature but this rate constant cannot be directly measured. In this article, a variational transition-state theory calculation of the low- and high-pressure rate constants for the reaction between DMS·OH and O2 has been carried out as a function of temperature. Our proposal is that the slight temperature dependence of the scavenging rate constant can only be explained if the H-abstraction bottleneck is preceded by a dynamical bottleneck corresponding to the association process between the DMS·OH adduct and the O2 molecule. The agreement between the low-pressure and high-pressure rate constants confirms the experimental observations. Copyright © 2011 Wiley Periodicals, Inc.

[In vitro drug release behavior of carrier made of porous glass ceramics].

Science.gov (United States)

Wang, De-ping; Huang, Wen-hai; Zhou, Nai

2002-09-01

To conduct the in vitro test on drug release of rifampin encapsulated in a carrier made of porous phosphate glass ceramics and to analyze main factors which affect the drug release rate. A certain quantitative of rifampin was sealed in a hollow cylindrical capsule which consisted of chopped calcium phosphate crystal fiber obtained from glass crystallization. The rifampin concentration was measured in the simulated physiological solution in which the capsule soaked. Rifampin could be released in a constant rate from the porous glass ceramic carrier in a long time. The release rate was dependent on the size of crystal fiber and the wall thickness of the capsule. This kind of calcium phosphate glass ceramics can be a candidate of the carrier materials used as long term drug therapy after osteotomy surgery.

Formulation and in-vitro evaluation of directly compressed controlled release matrices of Losartan Potassium using Ethocel Grade 100 as rate retarding agent.

Science.gov (United States)

Khan, Kamran Ahmad; Khan, Gul Majid; Zeeshan Danish, Muhammad; Akhlaq; Khan, Haroon; Rehman, Fazal; Mehsud, Saifullah

2015-12-30

Current study was aimed to develop 200mg controlled release matrix tablets of Losartan Potassium using Ethocel 100 Premium and Ethocel 100 FP Premium as rate controlling polymer. In-vitro studies were performed according to USP Method-I in phosphate buffer (PH 6.8) using pharma test dissolution apparatus. The temperature of the dissolution medium was kept constant at 37±0.5°C at 100rpm. Flow properties, physical quality control tests, effect of polymer size and drug-to-polymers ratios were studied using different kinetics models such as 1st-order, zero-order, Hixon Crowell model, Highuchi model and Power law. Difference factor f1 and similarity factor f2 were applied for dissolution profiles against Cardaktin® tablets used as a reference formulation. The matrices with polymer ethocel 100 FP Premiums have prolonged the drug release rate as compared to polymer ethocel 100 Premiums. The n values matrices with polymer ethocel grade 100 ranged from 0.603 to 0.857 indicating that the drug release occurred by anomalous non fickian diffusion kinetics while then value of reference Cardaktin® tablet was measured as 0.125 indicating that these tablets do not follow power law. The dissolution profiles of test formulations were different than that of reference Cardaktin®. This suggests the polymer Ethocel grade 100 can be proficiently incorporated in fabrication and development of once a day controlled release matrix tablets. Copyright © 2015. Published by Elsevier B.V.

Gas chromatography/sniffing port analysis evaluated for aroma release from rehydrated French beans (Phaseolus vulgaris).

NARCIS (Netherlands)

Ruth, van S.M.; Roozen, J.P.; Cozijnsen, J.L.

1996-01-01

The technique of gas chromatography/sniffing port analysis was evaluated for studying the release of aroma compounds from rehydrated diced French beans. The aroma compounds 2-—methylbutanal and hexanal were released at a constant rate over time. An identical selection of odour active compounds was

Atmospheric fate of a series of carbonyl nitrates: photolysis frequencies and OH-oxidation rate constants.

Science.gov (United States)

Suarez-Bertoa, R; Picquet-Varrault, B; Tamas, W; Pangui, E; Doussin, J-F

2012-11-20

Multifunctional organic nitrates are potential NO(x) reservoirs whose atmospheric chemistry is somewhat little known. They could play an important role in the spatial distribution of reactive nitrogen species and consequently in ozone formation and distribution in remote areas. In this work, the rate constants for the reaction with OH radical and the photolysis frequencies of α-nitrooxyacetone, 3-nitrooxy-2-butanone, and 3-methyl-3-nitrooxy-2-butanone have been determined at room temperature at 1000 mbar total pressure of synthetic air. The rate constants for the OH oxidation were measured using the relative rate technique, with methanol as reference compound. The following rate constants were obtained for the reaction with OH: k(OH) = (6.7 ± 2.5) × 10(-13) cm(3) molecule(-1) s(-1) for α-nitrooxyacetone, (10.6 ± 4.1) × 10(-13) cm(3) molecule(-1) s(-1) for 3-nitrooxy-2-butanone, and (2.6 ± 0.9) × 10(-13) cm(3) molecule(-1) s(-1) for 3-methyl-3-nitrooxy-2-butanone. The corresponding photolysis frequencies extrapolated to typical atmospheric conditions for July first at noon at 40° latitude North were (4.8 ± 0.3) × 10(-5) s(-1), (5.7 ± 0.3) × 10(-5) s(-1), and (7.4 ± 0.2) × 10(-5) s(-1), respectively. The data show that photolysis is a major atmospheric sink for these organic nitrates.

Site-specific reaction rate constant measurements for various secondary and tertiary H-abstraction by OH radicals

KAUST Repository

Badra, Jihad; Farooq, Aamir

2015-01-01

absorption of the R1(5) transition of OH spectrum near 306.69nm.Previous low-temperature rate constant measurements are added to the current data to generate three-parameter rate expressions that successfully represent the available direct measurements over a

Radionuclide release rate inversion of nuclear accidents in nuclear facility based on Kalman filter

International Nuclear Information System (INIS)

Tang Xiuhuan; Bao Lihong; Li Hua; Wan Junsheng

2014-01-01

The rapidly and continually back-calculating source term is important for nuclear emergency response. The Gaussian multi-puff atmospheric dispersion model was used to produce regional environment monitoring data virtually, and then a Kalman filter was designed to inverse radionuclide release rate of nuclear accidents in nuclear facility and the release rate tracking in real time was achieved. The results show that the Kalman filter combined with Gaussian multi-puff atmospheric dispersion model can successfully track the virtually stable, linear or nonlinear release rate after being iterated about 10 times. The standard error of inversion results increases with the true value. Meanwhile extended Kalman filter cannot inverse the height parameter of accident release as interceptive error is too large to converge. Kalman filter constructed from environment monitoring data and Gaussian multi-puff atmospheric dispersion model can be applied to source inversion in nuclear accident which is characterized by static height and position, short and continual release in nuclear facility. Hence it turns out to be an alternative source inversion method in nuclear emergency response. (authors)

Extension of the master sintering curve for constant heating rate modeling

Science.gov (United States)

McCoy, Tammy Michelle

The purpose of this work is to extend the functionality of the Master Sintering Curve (MSC) such that it can be used as a practical tool for predicting sintering schemes that combine both a constant heating rate and an isothermal hold. Rather than just being able to predict a final density for the object of interest, the extension to the MSC will actually be able to model a sintering run from start to finish. Because the Johnson model does not incorporate this capability, the work presented is an extension of what has already been shown in literature to be a valuable resource in many sintering situations. A predicted sintering curve that incorporates a combination of constant heating rate and an isothermal hold is more indicative of what is found in real-life sintering operations. This research offers the possibility of predicting the sintering schedule for a material, thereby having advanced information about the extent of sintering, the time schedule for sintering, and the sintering temperature with a high degree of accuracy and repeatability. The research conducted in this thesis focuses on the development of a working model for predicting the sintering schedules of several stabilized zirconia powders having the compositions YSZ (HSY8), 10Sc1CeSZ, 10Sc1YSZ, and 11ScSZ1A. The compositions of the four powders are first verified using x-ray diffraction (XRD) and the particle size and surface area are verified using a particle size analyzer and BET analysis, respectively. The sintering studies were conducted on powder compacts using a double pushrod dilatometer. Density measurements are obtained both geometrically and using the Archimedes method. Each of the four powders is pressed into ¼" diameter pellets using a manual press with no additives, such as a binder or lubricant. Using a double push-rod dilatometer, shrinkage data for the pellets is obtained over several different heating rates. The shrinkage data is then converted to reflect the change in relative

Some chaotic behaviors in a MCA learning algorithm with a constant learning rate

International Nuclear Information System (INIS)

Lv Jiancheng; Yi Zhang

2007-01-01

Douglas's minor component analysis algorithm with a constant learning rate has both stability and chaotic dynamical behavior under some conditions. The paper explores such dynamical behavior of this algorithm. Certain stability and chaos of this algorithm are derived. Waveform plots, Lyapunov exponents and bifurcation diagrams are presented to illustrate the existence of chaotic behavior

Sensitivity of the engineered barrier system (EBS) release rate to alternative conceptual models of advective release from waste packages under dripping fractures

International Nuclear Information System (INIS)

Lee, J.H.; Atkins, J.E.; McNeish, J.A.; Vallikat, V.

1996-01-01

Simulations were conducted to analyze the sensitivity of the engineered barrier system (EBS) release rate to alternative conceptual models of the advective release from waste packages under dripping fractures. The first conceptual model assumed that dripping water directly contacts the waste form inside the 'failed' waste package, and radionuclides are released from the EBS by advection. The second conceptual model assumed that dripping water is diverted around the 'failed' waste package (because of the presence of corrosion products plugging the perforations) and dripping water is prevented from directly contacting the waste form. In the second model, radionuclides were assumed to transport through the perforations by diffusion, and, once outside the waste package, to be released from the EBS by advection. The second model was to incorporate more realism into the EBS release calculations. For the case with the second EBS release model, most radionuclides had significantly lower peak EBS release rates (from at least one to several orders of magnitude) than with the first EBS release model. The impacts of the alternative EBS release models were greater for the radionuclides with a low solubility (or solubility-limited radionuclides) than for the radionuclides with a high solubility (or waste form dissolution-limited radionuclides). The analyses indicated that the EBS release model representing advection through a 'failed' waste package (the first EBS release model) may be too conservative in predicting the EBS performance. One major implication from this sensitivity study was that a 'failed' waste package container with multiple perforations may still be able to perform effectively as an important barrier to radionuclide release. (author)

Accelerated Testing Methodology in Constant Stress-Rate Testing for Advanced Structural Ceramics: A Preloading Technique

Science.gov (United States)

Choi, Sung R.; Gyekenyesi, John P.; Huebert, Dean; Bartlett, Allen; Choi, Han-Ho

2001-01-01

Preloading technique was used as a means of an accelerated testing methodology in constant stress-rate (dynamic fatigue) testing for two different brittle materials. The theory developed previously for fatigue strength as a function of preload was further verified through extensive constant stress-rate testing for glass-ceramic and CRT glass in room temperature distilled water. The preloading technique was also used in this study to identify the prevailing failure mechanisms at elevated temperatures, particularly at lower test rates in which a series of mechanisms would be associated simultaneously with material failure, resulting in significant strength increase or decrease. Two different advanced ceramics including SiC whisker-reinforced composite silicon nitride and 96 wt% alumina were used at elevated temperatures. It was found that the preloading technique can be used as an additional tool to pinpoint the dominant failure mechanism that is associated with such a phenomenon of considerable strength increase or decrease.

Mechanisms of iodine release from iodoapatite in aqueous solution

Science.gov (United States)

Zhang, Z.; Wang, J.

2017-12-01

Immobilization of iodine-129 with waste forms in geological setting is challenging due to its extremely long half-life and high volatility in the environment. To evaluate the long-term performance of waste form, it is imperative to determine the release mechanism of iodine hosted in the waste form materials. This study investigated the iodine released from apatite structured waste form Pb9.85 (VO4)6 I1.7 to understand how diffusion and dissolution control the durability of apatite waste form. A standard semi-dynamic leach test was adopted in this study. Samples were exposed in fresh leachant periodically and the leachant was replaced after each interval. Each experiment was carried out in cap-sealed Teflon vessels under constant temperature (e.g. 90 °C). ICP-MS analysis on the reacted leachates shows that Pb and V were released constantly and congruently with the stoichiometric ratio of Pb/V. However, iodine release is incongruent and time dependent. The iodine release rate starts significantly higher than the corresponding stoichiometric value and gradually decreases, approaching the stoichiometric value. Therefore, a dual-mode mechanism is proposed to account for the iodine release from apatite, which is dominated by short-term diffusion and long-term dissolution processes. Additional tests show that the element release rates depend on a number of test parameters, including sample surface to solution volume ratio (m-1), interval (day), temperature (°C), and solution pH. This study provides a quantitative characterization of iodine release mechanism. The activation energy of iodine leaching 21±1.6 kJ/mol was obtained by varying the test temperature. At the test conditions of to neutral pH and 90 °C, the long-term iodine release rate 3.3 mg/(m2 • day) is projected by normalizing sample surface area to solution volume ratio (S/V) to 1.0 m-1 and interval to 1 day. These findings demonstrate i) the feasibility of our approach to quantify the release mechanism

Rate constant computation on some elementary reactions of Hg during combustion

Energy Technology Data Exchange (ETDEWEB)

Wang, Qing; Yang, Bo-wen; Bai, Jing-ru [Northeast Dianli Univ., Jilin (China). Inst. of Energy and Power Engineering

2013-07-01

The geometry optimizations of reactants, products and transition states were made by the quantum chemistry MP2 method at the SDD basis function level for Hg, and 6-311++G(3df, 3pd) for others. The properties of stable minimums were validated by vibration frequencies analysis. Furthermore, the microcosmic chemical reaction mechanisms of reactions were investigated by ab initio calculations of quantum chemistry. On the basis of the geometry optimization, reaction rate constants within 298-2,000 K are calculated neither from experimental data nor by estimated, but directly from Quantum Chemistry software-Khimera.

Validation of kinetic modeling of progesterone release from polymeric membranes

Directory of Open Access Journals (Sweden)

Analia Irma Romero

2018-01-01

Full Text Available Mathematical modeling in drug release systems is fundamental in development and optimization of these systems, since it allows to predict drug release rates and to elucidate the physical transport mechanisms involved. In this paper we validate a novel mathematical model that describes progesterone (Prg controlled release from poly-3-hydroxybutyric acid (PHB membranes. A statistical analysis was conducted to compare the fitting of our model with six different models and the Akaike information criterion (AIC was used to find the equation with best-fit. A simple relation between mass and drug released rate was found, which allows predicting the effect of Prg loads on the release behavior. Our proposed model was the one with minimum AIC value, and therefore it was the one that statistically fitted better the experimental data obtained for all the Prg loads tested. Furthermore, the initial release rate was calculated and therefore, the interface mass transfer coefficient estimated and the equilibrium distribution constant of Prg between the PHB and the release medium was also determined. The results lead us to conclude that our proposed model is the one which best fits the experimental data and can be successfully used to describe Prg drug release in PHB membranes.

Calcium release rates from tooth enamel treated with dentifrices containing whitening agents and abrasives.

Science.gov (United States)

Araujo, Danilo Barral; Silva, Luciana Rodrigues; de Araujo, Roberto Paulo Correia

2010-01-01

Tooth whitening agents containing hydrogen peroxide and carbamide peroxide are used frequently in esthetic dental procedures. However, lesions on the enamel surface have been attributed to the action of these products. Using conventional procedures for separating and isolating biological structures, powdered enamel was obtained and treated with hydrogen peroxide, carbamide peroxide, and sodium bicarbonate, ingredients typically found in dentifrices. The enamel was exposed to different pH levels, and atomic emission spectrometry was used to determine calcium release rates. As the pH level increased, the rate of calcium release from enamel treated with dentifrices containing whitening agents decreased. Carbamide peroxide produced the lowest amount of decalcification, while sodium bicarbonate produced the highest release rates at all pH levels.

Ion-neutral gas reactions in a collision/reaction cell in inductively coupled plasma mass spectrometry: Correlation of ion signal decrease to kinetic rate constants

Energy Technology Data Exchange (ETDEWEB)

Gray, Patrick J. [Trace Element Research Laboratory, School of Earth Sciences, The Ohio State University, 125 S. Oval Mall, Columbus, OH 43210 (United States); Department of Chemistry, The Ohio State University, 120 18th Avenue, Columbus, OH 43210 (United States); Olesik, John W., E-mail: olesik.2@osu.edu [Trace Element Research Laboratory, School of Earth Sciences, The Ohio State University, 125 S. Oval Mall, Columbus, OH 43210 (United States)

2015-03-01

Reaction gas flow rate dependent Ar{sub 2}{sup +} and Ar{sup +} signals are correlated to fundamental kinetic rate coefficients. A simple calculation, assuming that gas exits the reaction cell due only to effusion, is described to estimate the gas pressure in the reaction cell. The value of the product of the kinetic rate constant and the ion residence time in the reaction cell can be determined from experimental measurement of the decrease in an ion signal as a function of reaction gas flow rate. New kinetic rate constants are determined for the reaction of CH{sub 3}F with Ar{sup +} and Ar{sub 2}{sup +}. - Highlights: • How to determine pressure and the product of the kinetic rate constant times the ion residence time in reaction cell • Relate measured ICP-DRC-MS signals versus gas flow rate to kinetic rate constants measured previously using SIFT-MS • Describe how to determine previously unmeasured kinetic rate constants using ICP-DRC-MS.

Nonadiabatic rate constants for proton transfer and proton-coupled electron transfer reactions in solution: Effects of quadratic term in the vibronic coupling expansion.

Science.gov (United States)

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 high 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

Nonadiabatic rate constants for proton transfer and proton-coupled electron transfer reactions in solution: Effects of quadratic term in the vibronic coupling expansion

International Nuclear Information System (INIS)

Soudackov, Alexander V.; Hammes-Schiffer, Sharon

2015-01-01

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 high 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

The dissolution rate constant of magnetite in water at different temperatures and neutral or ammoniated chemistry conditions

International Nuclear Information System (INIS)

Mohajery, K.; Lister, D.H.

2012-01-01

In this study, the dissolution rate constants of magnetite were measured at various water chemistry conditions and different temperatures, corresponding to several feedwater conditions of water-cooled reactors. Sintered magnetite pellets were used as the dissolving material and these were mounted in a jet-impingement apparatus in a recirculating water loop. Exposures were carried out at temperatures of 25, 55 and 140 o C and pHs of neutral and 9.2 in which many FAC (Flow Accelerated Corrosion) studies have been conducted. Average dissolution rate constants were estimated by measuring the volume of lost material with a profilometry technique. The excellent correspondent between the calculated value of dissolution rate constant of 2.20 mm/s for the synthesized magnetite and 2.05 mm/s for the single crystal of magnetite at neutral condition shows that the particle removal from the synthesized pellets is not an obstruction in this technique. Also, good agreement between the values calculated in duplicated runs at neutral condition at room temperature supports the accuracy of the method. (author)

Translational and extensional energy release rates (the J- and M-integrals) for a crack layer in thermoelasticity

Science.gov (United States)

Chudnovsky, A.; Gommerstadt, B.

1985-01-01

A number of papers have been presented on the evaluation of energy release rate for thermoelasticity and corresponding J integral. Two main approaches were developed to treat energy release rate in elasticity. The first is based on direct calculation of the potential energy rate with respect to crack length. The second makes use of Lagrangian formalism. The translational and expansional energy release rates in thermoelasticity are studied by employing the formalism of irreversible thermodynamics and the Crack Layer Approach.

Estimation of Anaerobic Debromination Rate Constants of PBDE Pathways Using an Anaerobic Dehalogenation Model.

Science.gov (United States)

Karakas, Filiz; Imamoglu, Ipek

2017-04-01

This study aims to estimate anaerobic debromination rate constants (k m ) of PBDE pathways using previously reported laboratory soil data. k m values of pathways are estimated by modifying a previously developed model as Anaerobic Dehalogenation Model. Debromination activities published in the literature in terms of bromine substitutions as well as specific microorganisms and their combinations are used for identification of pathways. The range of estimated k m values is between 0.0003 and 0.0241 d -1 . The median and maximum of k m values are found to be comparable to the few available biologically confirmed rate constants published in the literature. The estimated k m values can be used as input to numerical fate and transport models for a better and more detailed investigation of the fate of individual PBDEs in contaminated sediments. Various remediation scenarios such as monitored natural attenuation or bioremediation with bioaugmentation can be handled in a more quantitative manner with the help of k m estimated in this study.

Preliminary calculations of release rates from spent fuel in a tuff repository

International Nuclear Information System (INIS)

Apted, M.J.; O'Connell, W.J.; Lee, K.H.; MacIntyre, A.T.; Ueng, T.S.; Pigford, T.H.; Lee, W.W.L.

1991-01-01

Time-dependent release rates of Tc-99, I-129, Cs-135, and Np-237 have been calculated for wet-drip and moist-continuous release modes from the engineered barrier system of a potential nuclear waste repository in unsaturated tuff, representative of a possible repository at Yucca Mountain in southern Nevada. We describe the modes of water contact and of release of dissolved radionuclides to the surrounding intact rock, and the corresponding calculational models. We list the parameter values adopted, and then present numerical results, conclusions, and recommendations. 21 refs., 5 figs., 2 tabs

Ratiometric analysis in hyperpolarized NMR (I): test of the two-site exchange model and the quantification of reaction rate constants.

Science.gov (United States)

Li, Lin Z; Kadlececk, Stephen; Xu, He N; Daye, Dania; Pullinger, Benjamin; Profka, Harrilla; Chodosh, Lewis; Rizi, Rahim

2013-10-01

Conventional methods for the analysis of in vivo hyperpolarized (13) C NMR data from the lactate dehydrogenase (LDH) reaction usually make assumptions on the stability of rate constants and/or the validity of the two-site exchange model. In this study, we developed a framework to test the validity of the assumption of stable reaction rate constants and the two-site exchange model in vivo via ratiometric fitting of the time courses of the signal ratio L(t)/P(t). Our analysis provided evidence that the LDH enzymatic kinetics observed by hyperpolarized NMR are in near-equilibrium and satisfy the two-site exchange model for only a specific time window. In addition, we quantified both the forward and reverse exchange rate constants of the LDH reaction for the transgenic and mouse xenograft models of breast cancer using the ratio fitting method developed, which includes only two modeling parameters and is less sensitive to the influence of instrument settings/protocols, such as flip angles, degree of polarization and tracer dosage. We further compared the ratio fitting method with a conventional two-site exchange modeling method, i.e. the differential equation fitting method, using both the experimental and simulated hyperpolarized NMR data. The ratio fitting method appeared to fit better than the differential equation fitting method for the reverse rate constant on the mouse tumor data, with less relative errors on average, whereas the differential equation fitting method also resulted in a negative reverse rate constant for one tumor. The simulation results indicated that the accuracy of both methods depends on the width of the transport function, noise level and rate constant ratio; one method may be more accurate than the other based on the experimental/biological conditions aforementioned. We were able to categorize our tumor models into specific conditions of the computer simulation and to estimate the errors of rate quantification. We also discussed possible

Comments to "Analysis of constant rate period of spray drying of slurry" by Liang et al., 2001

DEFF Research Database (Denmark)

Jørgensen, Kåre; Jensen, Anker Degn; Sloth, Jakob

2006-01-01

In the study by Liang et al. [2001. Analysis of constant rate period of spray drying of slurry. Chemical Engineering Science 56, 2205-2213] the Darcy flow of liquid through a pore system of primary particles to the surface of a slurry droplet was applied for the constant rate period. Steep primary...... particle concentration gradients inside -25 mu m droplets with a primary particle size of 0.2 mu m were observed. Unfortunately, the boundary condition at the droplet surface for the parabolic second-order PDE did not conserve the solid mass in the droplet, and the plots for the primary particle...

Prediction of ozone tropospheric degradation rate constant of organic compounds by using artificial neural networks

International Nuclear Information System (INIS)

Fatemi, M.H.

2006-01-01

Ozone tropospheric degradation of organic compound is very important in environmental chemistry. The lifetime of organic chemicals in the atmosphere can be calculated from the knowledge of the rate constant of their reaction with free radicals such as OH and NO 3 or O 3 . In the present work, the rate constant for the tropospheric degradation of 137 organic compounds by reaction with ozone, the least widely and successfully modeled degradation process, are predicted by quantitative structure activity relationships modeling based on a variety of theoretical descriptors, which screened and selected by genetic algorithm variable subset selection procedure. These descriptors which can be used as inputs for generated artificial neural networks are; HOMO-LUMO gap, number of double bonds, number of single bonds, maximum net charge on C atom, minimum (>0.1) bond order of C atom and Minimum e-e repulsion of H atom. After generation, optimization and training of artificial neural network, network was used for the prediction of log KO 3 for the validation set. The root mean square error for the neural network calculated log KO 3 for training, prediction and validation set are 0.357, 0.460 and 0.481, respectively, which are smaller than those obtained by multiple linear regressions model (1.217, 0.870 and 0.968, respectively). Results obtained reveal the reliability and good predictivity of neural network model for the prediction of ozone tropospheric degradations rate constant of organic compounds

Estimation in adults of the glomerular filtration rate in [99mTc] DTPA renography - the rate constant method

International Nuclear Information System (INIS)

Carlsen, Ove

2004-01-01

The purpose of this study was to design an alternative and robust method for estimation of glomerular filtration rate (GFR) in [ 99 mTc]-diethylenetriaminepentaacetic acid ([ 99 mTc] -DTPA renography with a reliability not significantly lower than that of the conventional Gates' method. Methods: The method is based on renographies lasting 40 min in which regions of interest (ROIs) are manually created over selected parts of certain blood pools (e.g. heart, lungs, spleen, and liver). For each ROI the corresponding time-activity curve (TAC) was generated, decay corrected and exposed to a monoexponential fit in the time interval 10 to 40 min postinjection. The rate constant in min-1 of the monoexponential fit was denoted BETA. Following an iterative procedure comprising usually 5-10 manually created ROIs, the monoexponential fit with the maximum rate constant (BETA max ) was used for estimation of GFR. Results: In a patient material of 54 adult subjects in whom GFR was determined with multiple or one sample techniques with [ 51 Cr]-ethylenediaminetetraacetic acid ([ 51 Cr]-EDTA) the regression curve of standard GFR (GFR std ) (i.e. GFR adjusted to 1.73 m 2 body surface area) showed a close, non-linear relationship with BETA max with a correlation coefficient of 95%. The standard errors of estimate (SEE) were 6.6, 10.6 and 16.8 for GFR std equal to 30, 60, and 120 ml/(min .73 m 2 ), respectively. The corresponding SEE values for almost the same patient material using Gates' method were 8.4, 11.9, and 16.8 ml/(min 1.73 m 2 ). Conclusions: The alternative rate constant method yields estimates of GFR std with SEE values equal to or slightly smaller than in Gates' method. The two methods provide statistically uncorrelated estimates of GFR std . Therefore, pooled estimates of GFR std can be calculated with SEE values approximately 1.41 times smaller than those mentioned above. The reliabilities of the pooled estimate of GFR std separately and of the multiple samples method

Impaired sarcoplasmic reticulum Ca(2+) release rate after fatiguing stimulation in rat skeletal muscle

DEFF Research Database (Denmark)

Ørtenblad, Niels; Sjøgaard, G; Madsen, Klavs

2000-01-01

during the first 0.5-1 h the metabolic state recovered to resting levels, and a slow phase from 1-3 h characterized by a rather slow recovery of the mechanical properties. The recovery of SR Ca(2+) release rate was closely correlated to +dF/dt during the slow phase of recovery (r(2) = 0.51; P ... to 66% that persisted for 1 h, followed by a gradual recovery to 87% of prefatigue release rate at 3 h recovery. Tetanic force and rate of force development (+dF/dt) and relaxation (-dF/dt) were depressed by approximately 80% after stimulation. Recovery occurred in two phases: an initial phase, in which......The purpose of the study was to characterize the sarcoplasmic reticulum (SR) function and contractile properties before and during recovery from fatigue in the rat extensor digitorum longus muscle. Fatiguing contractions (60 Hz, 150 ms/s for 4 min) induced a reduction of the SR Ca(2+) release rate...

Addition and spin exchange rate constants by longitudinal field μSR: the Mu + NO reaction

International Nuclear Information System (INIS)

Senba, Masayoshi; Gonzalez, A.C.; Kempton, J.R.; Arseneau, D.J.; Pan, J.J.; Tempelmann, A.; Fleming, D.G.

1991-01-01

The addition reaction Mu + NO + M → MuNO + M and the spin exchange reaction Mu(↑) + NO(↓)→Mu(↓)+NO(↑) have been measured by longitudinal field μSR at room temperature in the presence of up to 58 atm of N 2 as inert collider. The pressure dependence of the longitudinal relaxation rate due to the addition reaction (λ c ) demonstrates that the system is still in the low pressure regime in this pressure range. The corresponding termolecular rate constant has been determined as k 0.Mu =(1.10±0.25)x10 -32 cm 6 molecules -2 s -1 , almost 4 times smaller than the corresponding H atom reaction k 0,H =3.90x10 -32 cm 6 molecules -2 s -1 . The average value of the spin exchange rate constants in the 2.5-58 atm pressure range, k SE = (3.16±0.06)x10 -10 cm 3 molecule -1 s -1 , is in good agreement with previous values obtained by transverse field μSR. (orig.)

Rate constants for a mechanism including intermediates in the interconversion of ternary complexes by horse liver alcohol dehydrogenase

International Nuclear Information System (INIS)

Sekhar, V.C.; Plapp, B.V.

1990-01-01

Transient kinetic data for partial reactions of alcohol dehydrogenase and simulations of progress curves have led to estimates of rate constants for the following mechanism, at pH 8.0 and 25 degrees C: E in equilibrium E-NAD+ in equilibrium *E-NAD+ in equilibrium E-NAD(+)-RCH2OH in equilibrium E-NAD+-RCH2O- in equilibrium *E-NADH-RCHO in equilibrium E-NADH-RCHO in equilibrium E-NADH in equilibrium E. Previous results show that the E-NAD+ complex isomerizes with a forward rate constant of 620 s-1. The enzyme-NAD(+)-alcohol complex has a pK value of 7.2 and loses a proton rapidly (greater than 1000 s-1). The transient oxidation of ethanol is 2-fold faster in D 2 O, and proton inventory results suggest that the transition state has a charge of -0.3 on the substrate oxygen. Rate constants for hydride ion transfer in the forward or reverse reactions were similar for short-chain aliphatic substrates (400-600 s-1). A small deuterium isotope effect for transient oxidation of longer chain alcohols is apparently due to the isomerization of the E-NAD+ complex. The transient reduction of aliphatic aldehydes showed no primary deuterium isotope effect; thus, an isomerization of the E-NADH-aldehyde complex is postulated, as isomerization of the E-NADH complex was too fast to be detected. The estimated microscopic rate constants show that the observed transient reactions are controlled by multiple steps

Tempo of Diversification of Global Amphibians: One-Constant Rate, One-Continuous Shift or Multiple-Discrete Shifts?

OpenAIRE

Youhua Chen

2014-01-01

In this brief report, alternative time-varying diversification rate models were fitted onto the phylogeny of global amphibians by considering one-constant-rate (OCR), one-continuous-shift (OCS) and multiplediscrete- shifts (MDS) situations. The OCS diversification model was rejected by γ statistic (γ=-5.556, p⁄ 0.001), implying the existence of shifting diversification rates for global amphibian phylogeny. Through model selection, MDS diversification model outperformed OCS and OCR...

[The effects of various factors on the in vitro velocity of drug release from repository tablets. Part 4: Isoniazid (Rimicid) respository tablets (author's transl)].

Science.gov (United States)

Tomassini, L; Michailova, D; Naplatanova, D; Slavtschev, P

1979-12-01

The authors investigated the release of isoniazid from repository tablets as related to form, processing technology, strength constant and storage for 5 years. On determining the diffusion coefficient (D), the initial dissolution rate (Vo) and the time required for the diffusion of the releasing medium to the middle of the tablet (t1/2), it was found that the difference in release rate between the flat and the biconvex tablets is small. Furthermore, it was stated that the three-layer tablets have very high D and Vo values and very low t1/2 values, for what reason they are unsuited for repository tablets of the composition under investigation. Moreover, it was found that an increase of the strength constant does not affect the D, t1/2 and Vo values, and that the release of isoniazid is retarded only in flat tablets with the highest strength constant. Storage exerts no effect on the drug release from these tablets. The industrial production of these tablets is under way.

Electron attachment rate constant measurement by photoemission electron attachment ion mobility spectrometry (PE-EA-IMS)

International Nuclear Information System (INIS)

Su, Desheng; Niu, Wenqi; Liu, Sheng; Shen, Chengyin; Huang, Chaoqun; Wang, Hongmei; Jiang, Haihe; Chu, Yannan

2012-01-01

Photoemission electron attachment ion mobility spectrometry (PE-EA-IMS), with a source of photoelectrons induced by vacuum ultraviolet radiation on a metal surface, has been developed to study electron attachment reaction at atmospheric pressure using nitrogen as the buffer gas. Based on the negative ion mobility spectra, the rate constants for electron attachment to tetrachloromethane and chloroform were measured at ambient temperature as a function of the average electron energy in the range from 0.29 to 0.96 eV. The experimental results are in good agreement with the data reported in the literature. - Highlights: ► Photoemission electron attachment ion mobility spectrometry (PE-EA-IMS) was developed to study electron attachment reaction. ► The rate constants of electron attachment to CCl 4 and CHCl 3 were determined. ► The present experimental results are in good agreement with the previously reported data.

Dynamic energy release rate in couple-stress elasticity

International Nuclear Information System (INIS)

Morini, L; Piccolroaz, A; Mishuris, G

2013-01-01

This paper is concerned with energy release rate for dynamic steady state crack problems in elastic materials with microstructures. A Mode III semi-infinite crack subject to loading applied on the crack surfaces is considered. The micropolar behaviour of the material is described by the theory of couple-stress elasticity developed by Koiter. A general expression for the dynamic J-integral including both traslational and micro-rotational inertial contributions is derived, and the conservation of this integral on a path surrounding the crack tip is demonstrated

A Unified Kinetics and Equilibrium Experiment: Rate Law, Activation Energy, and Equilibrium Constant for the Dissociation of Ferroin

Science.gov (United States)

Sattar, Simeen

2011-01-01

Tris(1,10-phenanthroline)iron(II) is the basis of a suite of four experiments spanning 5 weeks. Students determine the rate law, activation energy, and equilibrium constant for the dissociation of the complex ion in acid solution and base dissociation constant for phenanthroline. The focus on one chemical system simplifies a daunting set of…

Evaluation of rate of swelling and erosion of verapamil (VRP) sustained-release matrix tablets.

Science.gov (United States)

Khamanga, Sandile M; Walker, Roderick B

2006-01-01

Tablets manufactured in-house were compared to a marketed sustained-release product of verapamil to investigate the rate of hydration, erosion, and drug-release mechanism by measuring the wet and subsequent dry weights of the products. Swelling and erosion rates depended on the polymer and granulating fluid used, which ultimately pointed to their permeability characteristics. Erosion rate of the marketed product was highest, which suggests that the gel layer that formed around these tablets was weak as opposed to the robust and resistant layers of test products. Anomalous and near zero-order transport mechanisms were dominant in tests and commercial product, respectively.

Influence of the oil globule fraction on the release rate profiles from multiple W/O/W emulsions.

Science.gov (United States)

Bonnet, Marie; Cansell, Maud; Placin, Frédéric; Monteil, Julien; Anton, Marc; Leal-Calderon, Fernando

2010-06-15

Water-in-oil-in-water (W/O/W) double emulsions were prepared and the kinetics of release of magnesium ions from the internal to the external water phase was investigated as a function of the formulation and the globule volume fraction. All the emulsions were formulated using the same surface-active species (polyglycerol polyricinoleate and sodium caseinate). Also, the internal droplet and oil globule diameters were almost identical for all the systems. Two types of W/O/W emulsions were prepared based either on a synthetic oil (miglyol) or on an edible oil (olive oil). The globule volume fraction varied from 11% to 72%. At constant temperature (T=25 degrees C) and irrespective of the oil type, the percentage of magnesium released was lowered by increasing the globule fraction. In all cases, magnesium leakage occurred without film rupturing (no coalescence). Thus, the experimental data were interpreted within the frame of a model based on diffusion. The rate of release was determined by the permeation coefficient of magnesium across the oil phase and by the binding (chelation) of magnesium by caseinate molecules. The data could be adequately fitted by considering a time-dependant permeation coefficient. The better retention of magnesium at high globule fractions could account for two distinct phenomena: (i) the reduction of the relative volume of the outer phase, and (ii) the attenuation of the permeation coefficient over time induced by interfacial magnesium binding, all the more important than the globule fraction increased. Copyright 2010 Elsevier B.V. All rights reserved.

First-Principles Computed Rate Constant for the O + O2 Isotopic Exchange Reaction Now Matches Experiment.

Science.gov (United States)

Guillon, Grégoire; Honvault, Pascal; Kochanov, Roman; Tyuterev, Vladimir

2018-04-19

We show, by performing exact time-independent quantum molecular scattering calculations, that the quality of the ground electronic state global potential energy surface appears to be of utmost importance in accurately obtaining even as strongly averaged quantities as kinetic rate constants. The oxygen isotope exchange reaction, 18 O + 32 O 2 , motivated by the understanding of a complex long-standing problem of isotopic ozone anomalies in the stratosphere and laboratory experiments, is explored in this context. The thermal rate constant for this key reaction is now in quantitative agreement with all experimental data available to date. A significant recent progress at the frontier of three research domains, advanced electronic structure calculations, ultrasensitive spectroscopy, and quantum scattering calculations, has therefore permitted a breakthrough in the theoretical modeling of this crucial collision process from first principles.

Usefulness of radiatively obtained acrylamide polymers for production of drug forms with controlled release of the therapeutic component

International Nuclear Information System (INIS)

Mosiniak, T.; Switek, W.

1988-01-01

Using 60 Co gamma radiation as a factor initiating polymerization and cross-linking of polymers, polyacrylamide matrices were formed with the following therapeutic agents: aspirin, amidopyrin, sodium salicylate. Gamma radiation doses ranged from 3.5 to 22.5 kGy, dose rate was 0.138 Gy x s -1 . Kinetics of the therapeutic agent release from the matrix polymers was determined by measurement of per cent of the drug release in the course of time and calculations of release rate constants. The preparations containing slowly released drugs were obtained. 12 figs., 2 tabs., 11 refs. (author)

Estimation of rate constants of PCB dechlorination reactions using an anaerobic dehalogenation model.

Science.gov (United States)

Karakas, Filiz; Imamoglu, Ipek

2017-02-15

This study aims to estimate anaerobic dechlorination rate constants (k m ) of reactions of individual PCB congeners using data from four laboratory microcosms set up using sediment from Baltimore Harbor. Pathway k m values are estimated by modifying a previously developed model as Anaerobic Dehalogenation Model (ADM) which can be applied to any halogenated hydrophobic organic (HOC). Improvements such as handling multiple dechlorination activities (DAs) and co-elution of congeners, incorporating constraints, using new goodness of fit evaluation led to an increase in accuracy, speed and flexibility of ADM. DAs published in the literature in terms of chlorine substitutions as well as specific microorganisms and their combinations are used for identification of pathways. The best fit explaining the congener pattern changes was found for pathways of Phylotype DEH10, which has the ability to remove doubly flanked chlorines in meta and para positions, para flanked chlorines in meta position. The range of estimated k m values is between 0.0001-0.133d -1 , the median of which is found to be comparable to the few available published biologically confirmed rate constants. Compound specific modelling studies such as that performed by ADM can enable monitoring and prediction of concentration changes as well as toxicity during bioremediation. Copyright © 2016 Elsevier B.V. All rights reserved.

Flowing afterglow: construction of an apparatus, measurement of rate constants, and consideration of the diffusive behavior of charges

International Nuclear Information System (INIS)

Matsuoka, Shingo; Nakamura, Hirone; Tamura, Takaaki; Fujii, Toshihiro.

1984-01-01

A flowing afterglow apparatus was constructed and the operation of the afterglow system including data analysis was tested by measuring the rate constants for the reactions N + + NO, N 2 + + NO, He + + N 2 , and SF 6 + e; the results were 5.8 x 10 -10 , 3.9 x 10 -10 , 1.20 x 10 -9 , and 2.1 x 10 -7 cm 3 s -1 respectively. In the measurements an extraction voltage for ion sampling was not applied to the nose cone in order not to introduce an electric field into the reaction region. A ''non-ambipolar'' model developed by us was used for the data analysis of the ion/molecule reactions. For the data analysis of the electron attachment, a typical curve fit mehtod to the product ion signal was used. However, no theoretical curves fit the experimental points. This disagreement is attributed to a change of the ion-sampling efficiency through the nose-cone aperture arising from a change of the electron-dominated plasma to a negative-ion-dominated plasma with an increasing flow rate of SF 6 . Nevertheless, the attachment rate could be determined by fitting the theoretical and experimantal curves in the limited region of the SF 6 flow rate where the negative-ion-dominated plasma is established at the sampling aperture. All the rate constants obtained here agree reasonably well with literature values. Next, errors in the positive ion/molecule reaction rate constants, which would occur if the diffusion coefficients of the ions and neutrals each have a + 10 % error were calculated for the flow model to be -0.4 and +1.2 % respectively, demonstrating that these parameters are not important in the analysis of data. This insensitivity explains why the nose-cone voltage applied in a typical flowing afterglow operation has not caused a significant error in the published rate constants although it disturbs the ion diffusive behavior. (author)

An optimal policy for deteriorating items with time-proportional deterioration rate and constant and time-dependent linear demand rate

Science.gov (United States)

Singh, Trailokyanath; Mishra, Pandit Jagatananda; Pattanayak, Hadibandhu

2017-12-01

In this paper, an economic order quantity (EOQ) inventory model for a deteriorating item is developed with the following characteristics: (i) The demand rate is deterministic and two-staged, i.e., it is constant in first part of the cycle and linear function of time in the second part. (ii) Deterioration rate is time-proportional. (iii) Shortages are not allowed to occur. The optimal cycle time and the optimal order quantity have been derived by minimizing the total average cost. A simple solution procedure is provided to illustrate the proposed model. The article concludes with a numerical example and sensitivity analysis of various parameters as illustrations of the theoretical results.

Radioisotopic composition of yellowcake: an estimation of stack release rates

International Nuclear Information System (INIS)

Momeni, M.H.; Kisieleski, W.E.; Rayno, D.R.; Sabau, C.S.

1979-12-01

Uranium concentrate (yellowcake) composites from four mills (Anaconda, Kerr-McGee, Highland, and Uravan) were analyzed for U-238, U-235, U-234, Th-230, Ra-226, and Pb-210. The ratio of specific activities of U-238 to U-234 in the composites suggested that secular radioactive equilibrium exists in the ore. The average activity ratios in the yellowcake were determined to be 2.7 x 10 -3 (Th-230/U-238), 5 x 10 -4 (Ra-226/U-238) and 2 x 10 -4 (Pb-210/U-238). Based on earlier EPA measurements of the release rates from the stacks, the amount of yellowcake released was determined to be 0.1% of the amount processed

Utilization of ''CONTACT'' experiments to improve the fission gas release knowledge in PWR fuel rods

Energy Technology Data Exchange (ETDEWEB)

Charles, M; Abassin, J J; Bruet, M; Baron, D; Melin, P

1983-03-01

The CONTACT experiments, which were carried out by the French CEA, within the framework of a CEA-FRAMATOME collaboration agreement, bear on the behaviour of in-pile irradiated PWR fuel rods. We will focus here upon their results dealing with fission gas release. The experimental device is briefly described, then the following results are given: the kinetics of stable fission gas release for various linear ratings; the instantaneous fractional release rates of radioactive gases versus their decay constant in the range 1.5 10/sup -6/-3.6 10/sup -3/s/sup -1/, for various burnups, as also the influence of fuel temperature. Moreover, the influence of the nature and the pressure of the filling gas upon the release is presented for various linear ratings. The experimental results are discussed and analysed with the purpose to model various physical phenomena involved in the release (low-temperature mechanisms, diffusion).

Utilization of ''CONTACT'' experiments to improve the fission gas release knowledge in PWR fuel rods

International Nuclear Information System (INIS)

Charles, M.; Abassin, J.J.; Bruet, M.

1983-01-01

The CONTACT experiments, which were carried out by the French CEA, within the framework of a CEA-FRAMATOME collaboration agreement, bear on the behaviour of in-pile irradiated PWR fuel rods. We will focus here upon their results dealing with fission gas release. The experimental device is briefly described, then the following results are given: the kinetics of stable fission gas release for various linear ratings; the instantaneous fractional release rates of radioactive gases versus their decay constant in the range 1.5 10 -6 -3.6 10 -3 s -1 , for various burnups, as also the influence of fuel temperature. Moreover, the influence of the nature and the pressure of the filling gas upon the release is presented for various linear ratings. The experimental results are discussed and analysed with the purpose to model various physical phenomena involved in the release (low-temperature mechanisms, diffusion)

A new method for calculating energy release rate in tunnel excavation subjected to high in situ stress

Directory of Open Access Journals (Sweden)

Xiao Qinghua

2016-03-01

Full Text Available Based on energy theory, energy release rate (EER and local energy release rate (LEER, a new index called FERR (Fractional Energy Release Rate is proposed, and this method can not only evaluate the risk of rock burst, but also can point out the location of high risk and the scale of rockburst. The FERR index is applied to the TBM assembling tunnel in Jinping Hydro Power Station II to evaluate the scale and intensity of rockburst, as well as the location where rockburst occurs. With FDM method adopted, the energy release rate of 3 excavation plans are calculated and the scale and risk of rockburst is evaluated, and the location of high risk of rockburst is also mapped. With FERR used in the evaluation, the rockburst is nicely controlled which ensured the safety and construction schedule of the project.

Influence of Strain Rate on Heat Release under Quasi-Static Stretching of Metals. Experiment

Science.gov (United States)

Zimin, B. A.; Sventitskaya, V. E.; Smirnov, I. V.; Sud'enkov, Yu. V.

2018-04-01

The paper presents the results of experimental studies of energy dissipation during a quasi-static stretching of metals and alloys at room temperature. The strain rates varied in the range of 10-3-10-2 s-1. Samples of M1 copper, AZ31B magnesium alloy, BT6 titanium, 12Cr18Ni10Ti steel, and D16AM aluminum alloy were analyzed. The experimental results demonstrated a significant dependence of the heat release on the strain rate in the absence of its influence on stress-strain diagrams for all the metals studied in this range of strain rates. The correlation of the changes in the character of heat release with the processes of structural transformations at various stages of plastic flow is shown on the qualitative level. A difference in the nature of the processes of heat release in materials with different ratios of the plasticity and strength is noted.

Effect of crack-microcracks interaction on energy release rates

Science.gov (United States)

Chudnovsky, A.; Wu, Shaofu

1990-01-01

The energy release rates associated with the main crack advancing into its surrounding damage zone, and the damage zone translation relative to the main crack, as well as the energy of interaction between the crack and the damage zone are analyzed. The displacement and stress fields for this crack-damage interaction problem are reconstructed by employing a semi-empirical stress analysis which involves experimental evaluation of the average microcrack density in the damage zone.

USE OF ROUGH SETS AND SPECTRAL DATA FOR BUILDING PREDICTIVE MODELS OF REACTION RATE CONSTANTS

Science.gov (United States)

A model for predicting the log of the rate constants for alkaline hydrolysis of organic esters has been developed with the use of gas-phase min-infrared library spectra and a rule-building software system based on the mathematical theory of rough sets. A diverse set of 41 esters ...

Gas-phase reaction rate constants for atmospheric pressure ionization in ion-mobility spectrometry

International Nuclear Information System (INIS)

Vandiver, V.J.

1987-01-01

Ion-mobility spectrometry (IMS) is an instrumental technique in which gaseous ions are formed from neutral molecules by proton and charge transfer from reactant ions through collisional ionization. An abbreviated rate theory has been proposed for atmospheric pressure ionization (API) in IMS, but supporting experimental measurements have not been reported. The objectives of this thesis were (1) assessment of existing API rate theory using positive and negative product ions in IMS, (2) measurement of API equilibria and kinetics for binary mixtures, and (3) investigating of cross-ionizations with multiple-product ions in API reactions. Although IMS measurements and predictions from rate theory were comparable, shapes and slopes of response curves for both proton transfer and electron capture were not described exactly by existing theory. In particular, terms that are needed for calculation of absolute rate constants were unsuitable in the existing theory. These included recombination coefficients,initial number of reactant ions, and opposing ion densities

Effects of Sediment Chemical Properties on Phosphorus Release Rates in the Sediment-Water Interface of the Steppe Wetlands.

Science.gov (United States)

He, Jing; Su, Derong; Lv, Shihai; Diao, Zhaoyan; Xie, Jingjie; Luo, Yan

2017-11-22

Rising temperature causes a process of phosphorus release, which can be characterized well using phosphorus release rates (V P ). The objective of the present study was to investigate the major factors affecting sediment phosphorus release rates through a wetland habitat simulation experiment. The results showed that the V P of different wetland sediments were different and changed with the order of W-R (river wetland) > W-L (lake wetland) > W-M (grassy marsh wetland) > W-A (reservoir wetland). The main driving factors which influenced sediment phosphorus flux velocity in the sediment-water interface were sediment B-SO₄ 2- , B-MBN and A-MBP content. Path analysis and determination coefficient analysis indicated the standard multiple regression equation for sediment phosphorus release rates in the sediment-water interface, and each main factor was Y = -0.105 + 0.096X₁ + 0.275X₂ - 0.010X₃ ( r = 0.416, p phosphorus release rates; X₁ is sediment B-SO₄ 2- content; X₂ is sediment B-MBN; and X₃ is sediment A-MBP content. Sediment B-SO₄ 2- , B-MBN and A-MBP content and the interaction between them were the main factors affecting sediment phosphorus release rates in the sediment-water interface. Therefore, these results suggest that soil chemical properties and microbial activities likely play an important role in phosphorus release rates in the sediment-water interface. We hope to provide effective scientific management and control methods for relevant environmental protection departments.

Electron transfer rates and energy releases during denitrification of municipal wastewater

DEFF Research Database (Denmark)

Abdul-Talib, S.; Ujang, Z; Vollertsen, J.

2004-01-01

could be simplified by a two-stage process. In the first stage, nitrate was utilised with significant accumulation of nitrite. In the second stage nitrite was utilised when nitrate depleted. Denitrification rates during the two stages were expressed in terms of electron equivalents (e-eq.) in order...... to compare the process when differennt electron acceptors namlely, nitrate and nitrite were utilised. The energy release rates during the two stages were calculated and compared....

Computerized data base of the fundamental constants of nature

International Nuclear Information System (INIS)

Henry, E.A.; Hampel, V.E.

1975-01-01

Fifty-seven fundamental constants of nature were computerized from the up-to-date evaluations of E. R. Cohen and B. N. Taylor. The constants are annotated with regard to symbol, value, uncertainty, and scaling factor. This computerization is part of the scientific data base project of the Information Research Group at Lawrence Livermore Laboratory. The MASTER CONTROL data base management system is used. The computerized fundamental constants can be requested from the ERDA Computer Program Exchange and Information Center of the Argonne National Laboratory or from the National Technical Information Service of the U. S. Department of Commerce. This is the first of a series of releases on preparation of computerized scientific and technological data banks. The next release is a data bank of conversion factors for different units of measurements. 3 figures

Sensitivity of the engineered barrier system (EBS) release rate to alternative conceptual models of advective release from waste packages under dripping fractures

International Nuclear Information System (INIS)

Lee, J.H.; Atkins, J.E.; McNeish, J.A.; Vallikat, V.

1996-01-01

The first model assumed that dripping water directly contacts the waste form inside the ''failed'' waste package and radionuclides are released from the EBS by advection. The second model assumed that dripping water is diverted around the package (because of corrosion products plugging the perforations), thereby being prevented from directly contacting the waste form. In the second model, radionuclides were assumed to diffuse through the perforations, and, once outside the waste package, to be released from the EBS by advection. For the case with the second EBS release model, most radionuclides had lower peak EBS release rates than with the first model. Impacts of the alternative EBS release models were greater for the radionuclides with low solubility. The analysis indicated that the EBS release model representing advection through a ''failed'' waste package (the first model) may be too conservative; thus a ''failed'' waste package container with multiple perforations may still be an important barrier to radionuclide release

Rate constant of free electrons and holes recombination in thin films CdSe

International Nuclear Information System (INIS)

Radychev, N.A.; Novikov, G.F.

2006-01-01

Destruction kinetics of electrons generated in thin films CdSe by laser impulse (wave length is 337 nm, period of impulse - 8 nc) is studied by the method of microwave photoconductivity (36 GHz) at 295 K. Model of the process was suggested using the analysis of kinetics of photo-responses decay, and it allowed determination of rate constant of recombination of free electrons and holes in cadmium selenide - (4-6)x10 -11 cm 3 s -1 [ru

Propargyl Recombination: Estimation of the High Temperature, Low Pressure Rate Constant from Flame Measurements

DEFF Research Database (Denmark)

Rasmussen, Christian Lund; Skjøth-Rasmussen, Martin Skov; Jensen, Anker

2005-01-01

The most important cyclization reaction in hydrocarbon flames is probably recombination of propargyl radicals. This reaction may, depending on reaction conditions, form benzene, phenyl or fulvene, as well as a range of linear products. A number of rate measurements have been reported for C3H3 + C3H......3 at temperatures below 1000 K, while data at high temperature and low pressure only can be obtained from flames. In the present work, an estimate of the rate constant for the reaction at 1400 +/- 50 K and 20 Torr is obtained from analysis of the fuel-rich acetylene flame of Westmoreland, Howard...

Low-molecular-weight organoiodine and organobromine compounds released by polar macroalgae--the influence of abiotic factors.

Science.gov (United States)

Laturnus, F; Giese, B; Wiencke, C; Adams, F C

2000-01-01

The influence of temperature, light, salinity and nutrient availability on the release of volatile halogenated hydrocarbons was investigated in the Antarctic red macroalgal species Gymnogongrus antarcticus Skottsberg. Compared to standard culture condition, an increase in the release rates of iodocompounds was generally found for the exposure of the alga to altered environmental conditions. Macroalgae exhibited higher release rates after adaptation for two months to the changed factors, than after short-term exposure. Monitoring the release rates during a 24 h incubation period (8.25 h light, 15.75 h darkness) showed that changes between light and dark periods had no influence on the release of volatile halocarbons. Compounds like bromoform and 1-iodobutane exhibited constant release rates during the 24 h period. The formation mechanisms and biological role of volatile organohalogens are discussed. Although marine macroalgae are not considered to be the major source of biogenically-produced volatile organohalogens, they contribute significantly to the bromine and iodine cycles in the environment. Under possible environmental changes like global warming and uncontrolled entrophication of the oceans their significance may be increase.

Methane combustion kinetic rate constants determination: an ill-posed inverse problem analysis

Directory of Open Access Journals (Sweden)

Bárbara D. L. Ferreira

2013-01-01

Full Text Available Methane combustion was studied by the Westbrook and Dryer model. This well-established simplified mechanism is very useful in combustion science, for computational effort can be notably reduced. In the inversion procedure to be studied, rate constants are obtained from [CO] concentration data. However, when inherent experimental errors in chemical concentrations are considered, an ill-conditioned inverse problem must be solved for which appropriate mathematical algorithms are needed. A recurrent neural network was chosen due to its numerical stability and robustness. The proposed methodology was compared against Simplex and Levenberg-Marquardt, the most used methods for optimization problems.

Effects of Sediment Chemical Properties on Phosphorus Release Rates in the Sediment-Water Interface of the Steppe Wetlands

Directory of Open Access Journals (Sweden)

Jing He

2017-11-01

Full Text Available Rising temperature causes a process of phosphorus release, which can be characterized well using phosphorus release rates (VP. The objective of the present study was to investigate the major factors affecting sediment phosphorus release rates through a wetland habitat simulation experiment. The results showed that the VP of different wetland sediments were different and changed with the order of W–R (river wetland > W–L (lake wetland > W–M (grassy marsh wetland > W–A (reservoir wetland. The main driving factors which influenced sediment phosphorus flux velocity in the sediment–water interface were sediment B-SO42−, B-MBN and A-MBP content. Path analysis and determination coefficient analysis indicated the standard multiple regression equation for sediment phosphorus release rates in the sediment–water interface, and each main factor was Y = −0.105 + 0.096X1 + 0.275X2 − 0.010X3 (r = 0.416, p < 0.01, n = 144, where Y is sediment phosphorus release rates; X1 is sediment B-SO42− content; X2 is sediment B-MBN; and X3 is sediment A-MBP content. Sediment B-SO42−, B-MBN and A-MBP content and the interaction between them were the main factors affecting sediment phosphorus release rates in the sediment–water interface. Therefore, these results suggest that soil chemical properties and microbial activities likely play an important role in phosphorus release rates in the sediment–water interface. We hope to provide effective scientific management and control methods for relevant environmental protection departments.

Encapsulation of Volatile Citronella Essential Oil by Coacervation: Efficiency and Release Study

Science.gov (United States)

Manaf, M. A.; Subuki, I.; Jai, J.; Raslan, R.; Mustapa, A. N.

2018-05-01

The volatile citronella essential oil was encapsulated by simple coacervation and complex coacervation using Arabic gum and gelatin as wall material. Glutaraldehyde was used in the methodology as crosslinking agent. The citronella standard calibration graph obtained with R2 of 0.9523 was used for the accurate determination of encapsulation efficiency and release study. The release kinetic was analysed based on Fick"s law of diffusion for polymeric system and linear graph of Log fraction release over Log time was constructed to determine the release rate constant, k and diffusion coefficient, n. Both coacervation methods in the present study produce encapsulation efficiency around 94%. The produced capsules for both coacervation processes were discussed based on the capsules morphology and release kinetic mechanisms.

Marrow stem cell release in the autorepopulation assay

Energy Technology Data Exchange (ETDEWEB)

Maloney, M A; Patt, H M [California Univ., San Francisco (USA). Lab. of Radiobiology

1978-01-01

The early migration of stem cells from shielded marrow to an irradiated spleen has been re-evaluated, and the findings have been compared with the results of earlier studies. The composite data reveal a constant rate during the first 24 h after irradiation, with a slope of 1.6 cells per h and an intercept of 2.4. The positive intercept is interpreted to signify an immediate brief perturbation of CFU/sub s/ release. The low concentration of CFU/sub s/ in the bloodstream, despite their continuous migration from the shielded marrow, is indicative of a rapid, and probably greatly increased, blood turnover. Despite the constancy of stem cell seeding, it is not yet possible to determine whether the rate of stem cell release is different in shielded marrow than in normal marrow. The resolution of this question requires more precise information about spleen seeding efficiency in the autorepopulation assay and about the normal turnover rate of stem cells in the bloodstream.

Applications of energy-release-rate techniques to part-through cracks in experimental pressure vessels

International Nuclear Information System (INIS)

Bass, B.R.; Bryan, R.H.; Bryson, J.W.; Merkle, J.G.

1982-01-01

In nonlinear applications of computational fracture mechanics, energy release rate techniques are used increasingly for computing stress intensity parameters of crack configurations. Recently, deLorenzi used the virtual-crack-extension method to derive an analytical expression for the energy release rate that is better suited for three-dimensional calculations than the well-known J-integral. Certain studies of fracture phenomena, such as pressurized-thermal-shock of cracked structures, require that crack tip parameters be determined for combined thermal and mechanical loads. A method is proposed here that modifies the isothermal formulation of deLorenzi to account for thermal strains in cracked bodies. This combined thermo-mechanical formulation of the energy release rate is valid for general fracture, including nonplanar fracture, and applies to thermo-elastic as well as deformation plasticity material models. Two applications of the technique are described here. In the first, semi-elliptical surface cracks in an experimental test vessel are analyzed under elastic-plastic conditions using the finite element method. The second application is a thick-walled test vessel subjected to combined pressure and thermal shock loadings

Analysis of drug effects on neurotransmitter release

International Nuclear Information System (INIS)

Rowell, P.; Garner, A.

1986-01-01

The release of neurotransmitter is routinely studied in a superfusion system in which serial samples are collected and the effects of drugs or other treatments on the amount of material in the superfusate is determined. With frequent sampling interval, this procedure provides a mechanism for dynamically characterizing the release process itself. Using automated data collection in conjunction with polyexponential computer analysis, the equation which describes the release process in each experiment is determined. Analysis of the data during the nontreated phase of the experiment allows an internal control to be used for accurately assessing any changes in neurotransmitter release which may occur during a subsequent treatment phase. The use of internal controls greatly improves the signal to noise ratio and allows determinations of very low concentrations of drugs on small amounts of tissue to be made. In this presentation, the effects of 10 μM nicotine on 3 H-dopamine release in rat nucleus accumbens is described. The time course, potency and efficacy of the drug treatment is characterized using this system. Determinations of the exponential order of the release as well as the rate constants allow one to study the mechanism of the release process. A description of 3 H-dopamine release in normal as well as Ca ++ -free medium is presented

On the Ni-Ion release rate from surfaces of binary NiTi shape memory alloys

Science.gov (United States)

Ševčíková, Jana; Bártková, Denisa; Goldbergová, Monika; Kuběnová, Monika; Čermák, Jiří; Frenzel, Jan; Weiser, Adam; Dlouhý, Antonín

2018-01-01

The study is focused on Ni-ion release rates from NiTi surfaces exposed in the cell culture media and human vascular endothelial cell (HUVEC) culture environments. The NiTi surface layers situated in the depth of 70 μm below a NiTi oxide scale are affected by interactions between the NiTi alloys and the bio-environments. The finding was proved with use of inductively coupled plasma mass spectrometry and electron microscopy experiments. As the exclusive factor controlling the Ni-ion release rates was not only thicknesses of the oxide scale, but also the passivation depth, which was two-fold larger. Our experimental data strongly suggested that some other factors, in addition to the Ni concentration in the oxide scale, admittedly hydrogen soaking deep below the oxide scale, must be taken into account in order to rationalize the concentrations of Ni-ions released into the bio-environments. The suggested role of hydrogen as the surface passivation agent is also in line with the fact that the Ni-ion release rates considerably decrease in NiTi samples that were annealed in controlled hydrogen atmospheres prior to bio-environmental exposures.

Controlled release of 1-methylcyclopropene from its functionalised electrospun fibres under constant and linearly ramped humidity.

Science.gov (United States)

Neoh, Tze Loon; Ariyanto, Hermawan Dwi; Menéndez Galvan, Patricia; Yoshii, Hidefumi

2017-10-01

The methodology to electrospin polystyrene (PS) fibres functionalised with the inclusion complex between 1-methylcyclopropene (1-MCP) and α-cyclodextrin (α-CD) has been developed successfully. Due to limited availability, α-CD crystals instead of 1-MCP/α-CD complex were suspended in the electrospinning (ES) solutions to investigate the ES process. The ES solutions were characterised in terms of viscosity, conductivity and surface tension. Meanwhile, the fibres were subjected to scanning electron microscopy. The average fibre diameter was proportional to approximately one-sixth power of the capillary number of the ES solution. Viscosity, which was a function of PS concentration and α-CD loading, was the main property that dictated the spin ability of the ES solutions. ES fibres with 1.5-4.4 μm in diameter were produced with 12.5-20.0% (w/w) PS in ES solution and an equal amount of the inclusion complex for PS. In the case of the ES solutions of 20 wt% PS loaded with the inclusion complex from 0 to 100% (w/w) to PS, all the ES solutions were electrospinnable with the average diameter ranging from 3.8 to 4.6 μm. X-ray diffractometry indicated that the α-CD crystals were homogeneously suspended on the fibre mats. Confocal laser scanning microscopy showed that the crystals were suspended on the fibre mats while being coated with a layer of PS. The complex-functionalised fibre was formed from the ES solution of 20% PS and 50% (w/w) inclusion complex with the ES. The release characteristics of 1-methylcyclopropene (1-MCP) from the functionalised fibre and the inclusion complex were investigated real time under linearly ramping humidity conditions at constant temperatures with a home-built humidity regulating system coupled with gas chromatography. The irregular release profiles were successfully modelled and the activation energies of release for the functionalised fibre and inclusion complex were about 128 and 69 kJ/mol, respectively..

Development of novel diclofenac potassium controlled release tablets by wet granulation technique and the effect of co-excipients on in vitro drug release rates.

Science.gov (United States)

Shah, Shefaatullah; Khan, Gul Majid; Jan, Syed Umer; Shah, Kifayatullah; Hussain, Abid; Khan, Haroon; Khan, Haroon; Khan, Haroon; Khan, Kamran Ahmad

2012-01-01

The aim of the present study was the formulation and evaluation of controlled release polymeric tablets of Diclofenac Potassium by wet granulation method for the release rate, release pattern and the mechanism involved in drug release. Formulations having three grades of polymer Ethocel (7P; 7FP, 10P, 10FP, 100P, 100FP) in several drugs to polymer ratios (10:3 and 10:1) were compressed into tablets using wet granulation method. Co-excipients were added to some selected formulations to investigate their enhancement effect on in vitro drug release patterns. In vitro drug release studies were performed using USP Method-1 (Rotating Basket method) and Phosphate buffer (pH 7.4) was used as a dissolution medium. The similarities and dissimilarities of release profiles of test formulations with reference standard were checked using f2 similarity factor and f1 dissimilarity factor. Mathematical/Kinetic models were employed to determine the release mechanism and drug release kinetics.

Evaluation of olibanum and its resin as rate controlling matrix for controlled release of diclofenac

OpenAIRE

Chowdary KPR; Mohapatra P; Murali Krishna M

2006-01-01

Olibanum and its resin and carbohydrate fractions were evaluated as rate controlling matrix materials in tablets for controlled release of diclofenac. Diclofenac matrix tablets were formulated employing olibanum and its resin and carbohydrate fractions in different concentrations and the tablets were evaluated for various tablet characters including drug release kinetics and mechanism. Olibanum and its resin component exhibited excellent retarding effect on drug release from the matrix tablet...

Rate Constants for Reactions of Radiation-Produced Transients in Aqueous Solutions of Actinides

International Nuclear Information System (INIS)

Gordon, S.; Sullivan, J.C.; Ross, A.B.

1986-01-01

Rate constants have been critically compiled for reactions of ions of the actinides Am, Cf, Cm, Np, Pu, Th, and U, as well as the element Tc, in different oxidation states with various chemical species in aqueous solution. The reactants include products of the radiolysis of water (hydrated electrons, hydrogen atoms, hydroxyl radicals, hydrogen peroxide) and transient species derived from other solutes (e.g., carbonate radical). The data are useful in the estimation of migration properties of actinides, which are relevant to waste management studies

Fraction of organic carbon predicts labile desorption rates of chlorinated organic pollutants in laboratory-spiked geosorbents.

Science.gov (United States)

Ginsbach, Jake W; Killops, Kato L; Olsen, Robert M; Peterson, Brittney; Dunnivant, Frank M

2010-05-01

The resuspension of large volumes of sediments that are contaminated with chlorinated pollutants continues to threaten environmental quality and human health. Whereas kinetic models are more accurate for estimating the environmental impact of these events, their widespread use is substantially hampered by the need for costly, time-consuming, site-specific kinetics experiments. The present study investigated the development of a predictive model for desorption rates from easily measurable sorbent and pollutant properties by examining the relationship between the fraction of organic carbon (fOC) and labile release rates. Duplicate desorption measurements were performed on 46 unique combinations of pollutants and sorbents with fOC values ranging from 0.001 to 0.150. Labile desorption rate constants indicate that release rates predominantly depend upon the fOC in the geosorbent. Previous theoretical models, such as the macro-mesopore and organic matter (MOM) diffusion model, have predicted such a relationship but could not accurately predict the experimental rate constants collected in the present study. An empirical model was successfully developed to correlate the labile desorption rate constant (krap) to the fraction of organic material where log(krap)=0.291-0.785 . log(fOC). These results provide the first experimental evidence that kinetic pollution releases during resuspension events are governed by the fOC content in natural geosorbents. Copyright (c) 2010 SETAC.

Setting accelerated dissolution test for PLGA microspheres containing peptide, investigation of critical parameters affecting drug release rate and mechanism.

Science.gov (United States)

Tomic, I; Vidis-Millward, A; Mueller-Zsigmondy, M; Cardot, J-M

2016-05-30

The objective of this study was development of accelerated in vitro release method for peptide loaded PLGA microspheres using flow-through apparatus and assessment of the effect of dissolution parameters (pH, temperature, medium composition) on drug release rate and mechanism. Accelerated release conditions were set as pH 2 and 45°C, in phosphate buffer saline (PBS) 0.02M. When the pH was changed from 2 to 4, diffusion controlled phases (burst and lag) were not affected, while release rate during erosion phase decreased two-fold due to slower ester bonds hydrolyses. Decreasing temperature from 45°C to 40°C, release rate showed three-fold deceleration without significant change in release mechanism. Effect of medium composition on drug release was tested in PBS 0.01M (200 mOsm/kg) and PBS 0.01M with glucose (380 mOsm/kg). Buffer concentration significantly affected drug release rate and mechanism due to the change in osmotic pressure, while ionic strength did not have any effect on peptide release. Furthermore, dialysis sac and sample-and-separate techniques were used, in order to evaluate significance of dissolution technique choice on the release process. After fitting obtained data to different mathematical models, flow-through method was confirmed as the most appropriate for accelerated in vitro dissolution testing for a given formulation. Copyright © 2016 Elsevier B.V. All rights reserved.

The ruin probability of a discrete time risk model under constant interest rate with heavy tails

NARCIS (Netherlands)

Tang, Q.

2004-01-01

This paper investigates the ultimate ruin probability of a discrete time risk model with a positive constant interest rate. Under the assumption that the gross loss of the company within one year is subexponentially distributed, a simple asymptotic relation for the ruin probability is derived and

Rate constant for the reaction of O(3P) with diacetylene from 210 to 423 K

Science.gov (United States)

Mitchell, M. B.; Nava, D. F.; Stief, L. J.

1986-01-01

The absolute rate constant for the reaction of O(3P) with diacetylene (C4H2) has been measured as a function of pressure and temperature by the flash-photolysis/resonance-fluorescence method. At 298 K and below, no pressure dependence of the rate constant was observed, but at 423 K a moderate (factor-of-2) increase was detected in the range 3 to 75 torr Ar.Results at or near the high-pressure limit are represented by an Arrhenius expression over the temperature range 210 to 423 K. The results are compared with previous determinations, all of which employed the discharge-flow/mass-spectrometry technique. The mechanism of the reaction is considered, including both primary and secondary processes. The heats of formation of the reactants, adducts, and products for the O(3P) + C4H2 reaction are discussed and contrasted with those for O(3P) + C2H2.

Comodulation masking release in bit-rate reduction systems

DEFF Research Database (Denmark)

Vestergaard, Martin David; Rasmussen, Karsten Bo; Poulsen, Torben

1999-01-01

It has been suggested that the level dependence of the upper masking slope be utilized in perceptual models in bit-rate reduction systems. However, comodulation masking release (CMR) phenomena lead to a reduction of the masking effect when a masker and a probe signal are amplitude modulated...... with the same frequency. In bit-rate reduction systems the masker would be the audio signal and the probe signal would represent the quantization noise. Masking curves have been determined for sinusoids and 1-Bark-wide noise maskers in order to investigate the risk of CMR, when quantizing depths are fixed...... in accordance with psycho-acoustical principles. Masker frequencies of 500 Hz, 1 kHz, and 2 kHz have been investigated, and the masking of pure tone probes has been determined in the first four 1/3 octaves above the masker. Modulation frequencies between 6 and 20 Hz were used with a modulation depth of 0...

Rate constant for reaction of vitamin C with protein radicals in γ-irradiated aqueous albumin solution at 295K

International Nuclear Information System (INIS)

Miyazaki, Tetsuo; Yoshimura, Toru; Mita, Kazuya; Suzuki, Keiji; Watanabe, Masami

1995-01-01

When an aqueous solution of albumin (0.1 kg dm -3 ) is irradiated by γ-rays at 295 K, albumin radicals with a long lifetime are observed by ESR. The reaction of vitamin C with the albumin radicals has been studied at 295 K in the albumin solution, which is considered as a model of cells. The rate constant for the reaction of vitamin C with the albumin radicals was measured as 0.014 dm 3 mol -1 S -1 , which is much smaller than the reported constants (10 6 -10 10 dm 3 mol -1 s -1 ) for the reaction of vitamin C with radicals in a dilute aqueous solution. The small rate constant for the reaction of vitamin C is ascribed to the reaction in polymer coils in the albumin solution, since vitamin C and albumin radicals diffuse very slowly in the coils. (author)

Tritium and helium release from beryllium pebbles neutron-irradiated up to 230appm tritium and 3000appm helium

Directory of Open Access Journals (Sweden)

Vladimir Chakin

2016-12-01

Full Text Available Study of tritium and helium release from beryllium pebbles with diameters of 0.5 and 1mm after high-dose neutron irradiation at temperatures of 686–968K was performed. The release rate always has a single peak, and the peak temperatures at heating rates of 0.017K/s and 0.117K/s lie in the range of 1100–1350K for both tritium and helium release. The total tritium release from 1mm pebbles decreases considerably by increasing the irradiation temperature. The total tritium release from 0.5mm pebbles is less than that from 1mm pebbles and remains constant regardless of the irradiation temperature. At high irradiation temperatures, open channels are formed which contribute to the enhanced tritium release.

The dissolution rate constant of magnetite in water at different temperatures and pH conditions

International Nuclear Information System (INIS)

Mohajery, Khatereh; Deydier de Pierrefeu, Laurent; Lister, Derek H.

2012-09-01

chemistry. For most determinations, a jet of water conditioned to the required chemistry but stripped of dissolved iron with ion-exchange is directed onto a pellet of magnetite and the dissolution monitored; the high velocity of the jet ensures that mass transfer effects are minimised. The magnetite is synthesised by a solid-state method involving heating a mixture of haematite and iron under vacuum at 600 deg. C, compacting under pressure and sintering into a pellet under argon at 1,100 deg. C. The product has an appropriate consistency and resistance to erosion. Most experiments have measured the average dissolution rate by estimating the amount of magnetite lost from the pellet by surface analysis and profilometry after exposure for a given time. Concomitant electrochemical information is obtained by electrically isolating the pellet from the loop and connecting it to a potentiostat, along with a counter-electrode and reference electrode strategically mounted in the loop test section. Detailed kinetic data are obtained by irradiating the magnetite before installation in the loop and monitoring on-line with gamma spectrometry the transport of dissolved, radioactive 59 Fe. Preliminary determinations had used radioactive magnetite precipitated under galvanostatic conditions from a solution of irradiated FeSO 4 in EDTA onto a platinum coupon. The coupon was then mounted axially in the loop test section and subjected to a range of imposed potentials during exposure; however, this coupon technique gave dissolution results confounded by the release of magnetite crystallites, so we concentrated on the pellet technique. The paper presents the results of exposures carried out over a range of temperatures and alkalinities at oxygen concentrations between 0 and 20 ppb. It shows how dissolution rate constants obtained under CANDU primary coolant conditions of 310 deg. C and pH 25C 10.5 (with LiOH) fall between published values, which were obtained with a different technique under

Determination of rate constants and branching ratios for TCE degradation by zero-valent iron using a chain decay multispecies model.

Science.gov (United States)

Hwang, Hyoun-Tae; Jeen, Sung-Wook; Sudicky, Edward A; Illman, Walter A

2015-01-01

The applicability of a newly-developed chain-decay multispecies model (CMM) was validated by obtaining kinetic rate constants and branching ratios along the reaction pathways of trichloroethene (TCE) reduction by zero-valent iron (ZVI) from column experiments. Changes in rate constants and branching ratios for individual reactions for degradation products over time for two columns under different geochemical conditions were examined to provide ranges of those parameters expected over the long-term. As compared to the column receiving deionized water, the column receiving dissolved CaCO3 showed higher mean degradation rates for TCE and all of its degradation products. However, the column experienced faster reactivity loss toward TCE degradation due to precipitation of secondary carbonate minerals, as indicated by a higher value for the ratio of maximum to minimum TCE degradation rate observed over time. From the calculated branching ratios, it was found that TCE and cis-dichloroethene (cis-DCE) were dominantly dechlorinated to chloroacetylene and acetylene, respectively, through reductive elimination for both columns. The CMM model, validated by the column test data in this study, provides a convenient tool to determine simultaneously the critical design parameters for permeable reactive barriers and natural attenuation such as rate constants and branching ratios. Copyright © 2015 Elsevier B.V. All rights reserved.

Rapid release of 42K and 86Rb from an occluded state of the Na,K-pump in the presence of ATP or ADP

International Nuclear Information System (INIS)

Forbush, B. III

1987-01-01

We have measured the time course of release of 42 K and 86 Rb from an occluded state of the Na,K-pump using a rapid filtration apparatus. We have found that at 20 degrees C and in the presence of ATP, 42 K is released with a rate constant of approximately 45 s-1 and 86 Rb with a rate constant of approximately 20 s-1; both ATP and ADP are effective at a low affinity site (Kd approximately 0.3 and 1 mM, respectively) with the rate of deocclusion being only half as great in ADP as in ATP. Mg2+ stimulates 2-fold at low concentrations probably by forming MgATP, and free Mg2+ is strongly inhibitory at high concentrations (Kd approximately 10 mM). Mg2+ also decreases the affinity for ATP, and the data are consistent with mixed type inhibition; from the analysis the dissociation constant is approximately 1 mM for the inhibitory Mg2+ and the Rb+-occluded form without ATP. The rate of 42 K or 86 Rb release increases monotonically with pH while ATPase activity decreases above pH 8, so that deocclusion is not rate-limiting in the overall cycle at high pH. This is reflected by a convergence of the rate of Na,K-ATPase and Na,Rb-ATPase activities at high pH and by a decrease in the observed steady-state level of the occluded 86 Rb intermediate at high pH. K+, Rb+, Na+, and Cs+, but not Li+, increase the rate of 42 K and 86 Rb release at constant ionic strength, presumably at sites other than the transport sites. The spontaneous rate of deocclusion is only approximately 0.1 s-1 at low ionic strength in the absence of nucleotides, and it is increased markedly by all cations tested except Li+. Overall the data are consistent with deocclusion as a rate-limiting step in the Na,K-pump cycle

A photon spectrometric dose-rate constant determination for the Advantage™ Pd-103 brachytherapy source

OpenAIRE

Chen, Zhe Jay; Bongiorni, Paul; Nath, Ravinder

2010-01-01

Purpose: Although several dosimetric characterizations using Monte Carlo simulation and thermoluminescent dosimetry (TLD) have been reported for the new Advantage™ Pd-103 source (IsoAid, LLC, Port Richey, FL), no AAPM consensus value has been established for the dosimetric parameters of the source. The aim of this work was to perform an additional dose-rate constant (Λ) determination using a recently established photon spectrometry technique (PST) that is independent of the published TLD and ...

Constant Leverage And Constant Cost Of Capital: A Common Knowledge Half-Truth

Directory of Open Access Journals (Sweden)

Ignacio Vélez–Pareja

2008-04-01

In this document we show that for finite cash flows, Ke and hence WACC depend on the discount rate that is used to value the tax shield, TS and as expected, Ke and WACC are not constant with Kd as the discount rate for the tax shield, even if the leverage is constant. We illustrate this situation with a simple example. We analyze five methods: DCF using APV, FCF and traditional and general formulation for WACC, present value of CFE plus debt and Capital Cash Flow, CCF.

Tritium sorption by cement and subsequent release

International Nuclear Information System (INIS)

Ono, F.; Yamawaki, M.

1995-01-01

In a fusion reactor or tritium-handling facilities, contamination of concrete by tritium and subsequent release from it to the reator or experimental room is a matter of problem for safe control of tritium and management of operational environment. In order to evaluate this tritium behavior, interaction of tritiated water with concrete or cement should be clarified. In the present study, HTO sorption and subsequent release from cement were experimentally studied.(1)Sorption experiments were conducted using columns packed with cement particles of different sizes. From the analysis of the breakthrough curve, tritium diffusivity in macropores and microparticles were evaluated.(2)From the short-term tritium release experiments, effective desorption rate constants were evaluated and the effects of temperature and moisture were studied.(3)In the long-term tritium release experiments to 6000h, the tritium release mechanism was found to be composed of three kinds of water: initially from capillary water, and in the second stage from gel water and from the water in the cement crystal.(4)Tritium release behavior by heat treatment to 800 C was studied. A high temperature above 600 C was required for the tritium trapped in the crystal water to be released. (orig.)

Basic study on relationship between estimated rate constants and noise in FDG kinetic analysis

International Nuclear Information System (INIS)

Kimura, Yuichi; Toyama, Hinako; Senda, Michio.

1996-01-01

For accurate estimation of the rate constants in 18 F-FDG dynamic study, the shape of the estimation function (Φ) is crucial. In this investigation, the relationship between the noise level in tissue time activity curve and the shape of the least squared estimation function which is the sum of squared error between a function of model parameters and a measured data is calculated in 3 parameter model of 18 F-FDG. In the first simulation, by using actual plasma time activity curve, the true tissue curve was generated from known sets of rate constants ranging 0.05≤k 1 ≤0.15, 0.1≤k 2 ≤0.2 and 0.01≤k 3 ≤0.1 in 0.01 step. This procedure was repeated under various noise levels in the tissue time activity curve from 1 to 8% of the maximum value in the tissue activity. In the second simulation, plasma and tissue time activity curves from clinical 18 F-FDG dynamic study were used to calculate the Φ. In the noise-free case, because the global minima is separated from neighboring local minimums, it was easy to find out the optimum point. However, with increasing noise level, the optimum point was buried in many neighboring local minima. Making it difficult to find out the optimum point. The optimum point was found within 20% of the convergence point by standard non-linear optimization method. The shape of Φ for the clinical data was similar to that with the noise level of 3 or 5% in the first simulation. Therefore direct search within the area extending 20% from the result of usual non-linear curve fitting procedure is recommended for accurate estimation of the constants. (author)

Rate Constant of the Reaction between CH3O2 Radicals and OH Radicals Revisited.

Science.gov (United States)

Assaf, Emmanuel; Song, Bo; Tomas, Alexandre; Schoemaecker, Coralie; Fittschen, Christa

2016-11-17

The reaction between CH 3 O 2 and OH radicals has been studied in a laser photolysis cell using the reaction of F atoms with CH 4 and H 2 O for the simultaneous generation of both radicals, with F atoms generated through 248 nm photolysis of XeF 2 . An experimental setup combining cw-Cavity Ring Down Spectroscopy (cw-CRDS) and high repetition rate laser-induced fluorescence (LIF) to a laser photolysis cell has been used. The absolute concentration of CH 3 O 2 was measured by cw-CRDS, while the relative concentration of OH(v = 0) radicals was determined by LIF. To remove dubiety from the quantification of CH 3 O 2 by cw-CRDS in the near-infrared, its absorption cross section has been determined at 7489.16 cm -1 using two different methods. A rate constant of k 1 = (1.60 ± 0.4) × 10 -10 cm 3 s -1 has been determined at 295 K, nearly a factor of 2 lower than an earlier determination from our group ((2.8 ± 1.4) × 10 -10 cm 3 s -1 ) using CH 3 I photolysis as a precursor. Quenching of electronically excited I atoms (from CH 3 I photolysis) in collision with OH(v = 0) is suspected to be responsible for a bias in the earlier, fast rate constant.

Alternative approach to estimate the hydrolysis rate constant of particulate material from batch data

International Nuclear Information System (INIS)

Koch, Konrad; Drewes, Jörg E.

2014-01-01

Highlights: • An alternative to the commonly used first-order approach is presented. • A relationship between k h and the 1% criterion of the VDI 4630 is deduced. • Equation is proposed to directly calculate k h without the need for data fitting. • Hydrolysis constant k h can then easily be read-off from a table. - Abstract: As anaerobic batch tests are easy to conduct, they are commonly used to assess the effects of different operational factors on the anaerobic digestion process. Hydrolysis of particulate material is often assumed to be the rate limiting step in anaerobic digestion. Its velocity is often estimated by data fitting from batch tests. In this study, a Monod-type alternative to the commonly used first-order approach is presented. The approach was adapted from balancing a continuously stirred-tank reactor and better accommodates the fact that even after a long incubation time, some of the methane potential of the substrate remains untapped in the digestate. In addition, an equation is proposed to directly calculate the hydrolysis constant from the time when the daily gas production is less than 1% of the total gas production. The hydrolysis constant can then easily be read-off from a table when the batch test duration is known

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

Science.gov (United States)

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.

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

Energy Technology Data Exchange (ETDEWEB)

Aima, M; Culberson, W; Hammer, C; Micka, J; DeWerd, L [Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI (United States)

2016-06-15

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 analog 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

Stress relaxation of entangled polystyrene solution after constant-rate, uniaxial elongation

DEFF Research Database (Denmark)

Matsumiya, Yumi; Masubuchi, Yuichi; Watanabe, Hiroshi

For an entangled solution of linear polystyrene (PS 545k; M = 545k) in dibutyl phthalate (DBP), the stress relaxation after constant-rate uniaxial elongation was examined with an extensional viscosity fixture mounted on ARES (TA Instruments). The PS concentration, c = 52 wt%, was chosen in a way...... that the entanglement density M/Me of the solution coincided with that of PS 290k melt (M = 290k). After the elongation at the Rouse-based Weissenberg number Wi(R) ~ 3 up to the Hencky strain of 3, the short time stress relaxation of the solution was accelerated by a factor of ~4, which was less significant compared...... and the lack of monotonic thinning observed for the semidilute solutions. Results for less concentrated solutions will be also presented on site....

A photon spectrometric dose-rate constant determination for the Advantage Pd-103 brachytherapy source

International Nuclear Information System (INIS)

Chen, Zhe Jay; Bongiorni, Paul; Nath, Ravinder

2010-01-01

Purpose: Although several dosimetric characterizations using Monte Carlo simulation and thermoluminescent dosimetry (TLD) have been reported for the new Advantage Pd-103 source (IsoAid, LLC, Port Richey, FL), no AAPM consensus value has been established for the dosimetric parameters of the source. The aim of this work was to perform an additional dose-rate constant (Λ) determination using a recently established photon spectrometry technique (PST) that is independent of the published TLD and Monte Carlo techniques. Methods: Three Model IAPD-103A Advantage Pd-103 sources were used in this study. The relative photon energy spectrum emitted by each source along the transverse axis was measured using a high-resolution germanium spectrometer designed for low-energy photons. For each source, the dose-rate constant was determined from its emitted energy spectrum. The PST-determined dose-rate constant ( PST Λ) was then compared to those determined by TLD ( TLD Λ) and Monte Carlo ( MC Λ) techniques. A likely consensus Λ value was estimated as the arithmetic mean of the average Λ values determined by each of three different techniques. Results: The average PST Λ value for the three Advantage sources was found to be (0.676±0.026) cGyh -1 U -1 . Intersource variation in PST Λ was less than 0.01%. The PST Λ was within 2% of the reported MC Λ values determined by PTRAN, EGSnrc, and MCNP5 codes. It was 3.4% lower than the reported TLD Λ. A likely consensus Λ value was estimated to be (0.688±0.026) cGyh -1 U -1 , similar to the AAPM consensus values recommended currently for the Theragenics (Buford, GA) Model 200 (0.686±0.033) cGyh -1 U -1 , the NASI (Chatsworth, CA) Model MED3633 (0.688±0.033) cGyh -1 U -1 , and the Best Medical (Springfield, VA) Model 2335 (0.685±0.033) cGyh -1 U -1 103 Pd sources. Conclusions: An independent Λ determination has been performed for the Advantage Pd-103 source. The PST Λ obtained in this work provides additional information

An exclusion process on a tree with constant aggregate hopping rate

International Nuclear Information System (INIS)

Mottishaw, Peter; Waclaw, Bartlomiej; Evans, Martin R

2013-01-01

We introduce a model of a totally asymmetric simple exclusion process (TASEP) on a tree network where the aggregate hopping rate is constant from level to level. With this choice for hopping rates the model shows the same phase diagram as the one-dimensional case. The potential applications of our model are in the area of distribution networks, where a single large source supplies material to a large number of small sinks via a hierarchical network. We show that mean-field theory (MFT) for our model is identical to that of the one-dimensional TASEP and that this MFT is exact for the TASEP on a tree in the limit of large branching ratio, b (or equivalently large coordination number). We then present an exact solution for the two level tree (or star network) that allows the computation of any correlation function and confirm how mean-field results are recovered as b → ∞. As an example we compute the steady-state current as a function of branching ratio. We present simulation results that confirm these results and indicate that the convergence to MFT with large branching ratio is quite rapid. (paper)

The Reaction Mechanism and Rate Constants in the Radiolysis of Fe2+-Cu2+ Solutions

DEFF Research Database (Denmark)

Bjergbakke, Erling; Sehested, Knud; Rasmussen, O. Lang

1976-01-01

Pulse radiolysis and gamma radiolysis have been used to study the reaction mechanism in the radiolysis of aqueous solutions of Fe2+ and Cu2+. A reaction scheme has been developed and confirmed by computation of the corresponding complete set of differential equations. The rate constants for some ...... 10^{8}$ and $1.3\\times 10^{8}\\ {\\rm mol}^{-1}\\ {\\rm sec}^{-1}$ in pH 2.1 H2 SO4 and HClO4, respectively.......Pulse radiolysis and gamma radiolysis have been used to study the reaction mechanism in the radiolysis of aqueous solutions of Fe2+ and Cu2+. A reaction scheme has been developed and confirmed by computation of the corresponding complete set of differential equations. The rate constants for some...... of the reactions have been determined at different pH's. $k_{{\\rm Cu}^{+}+{\\rm O}_{2}}=4.6\\times 10^{5}$ and $1.0\\times 10^{6}\\ {\\rm mol}^{-1}\\ {\\rm sec}^{-1}$, $k_{{\\rm Cu}^{+}+{\\rm Fe}^{3+}}=5.5\\times 10^{6}$ and $1.3\\times 10^{7}\\ {\\rm mol}^{-1}\\ {\\rm sec}^{-1}$, $k_{{\\rm Cu}({\\rm III)}+{\\rm Fe}^{2+}}=3.3\\times...

Stress intensity factors and constant stress terms for interface cracks

International Nuclear Information System (INIS)

Fett, T.; Rizzi, G.

2004-01-01

In bi-material joints cracks can propagate along the interface or kink into one of the two materials. Whereas the energy release rate can be applied for interface cracks in the same way as usual for homogeneous materials, the computation of stresses in the vicinity of the crack tip is significantly more complicated. In order to assess crack kinking, it is necessary to know the mixed-mode stress intensity factor contributions K I and K II as well as the constant stress terms in the two materials. Whereas the stress intensity factors are available for a large number of infinite and semi-infinite bodies, there is experimental interest in practically used test specimens. This especially holds for the constant x-stress terms. Finite element computations are performed for the special case of a disappearing second Dundurs parameter, i.e. β=0. The fracture mechanics parameters K I , K II , σ 0 for the interface crack are reported in the form of diagrams and approximate relations. (orig.)

Quantification of Kinetic Rate Law Parameters of Uranium Release from Sodium Autunite as a Function of Aqueous Bicarbonate Concentrations

Energy Technology Data Exchange (ETDEWEB)

Gudavalli, Ravi; Katsenovich, Yelena; Wellman, Dawn M.; Lagos, Leonel; Tansel, Berrin

2013-09-05

ABSTRACT: Hydrogen carbonate is one of the most significant components within the uranium geochemical cycle. In aqueous solutions, hydrogen carbonate forms strong complexes with uranium. As such, aqueous bicarbonate may significantly increase the rate of uranium release from uranium minerals. Quantifying the relationship of aqueous hydrogen carbonate solutions to the rate of uranium release during dissolution is critical to understanding the long-term fate of uranium within the environment. Single-pass flow-through (SPTF) experiments were conducted to estimate the rate of uranium release from Na meta-autunite as a function of bicarbonate solutions (0.0005-0.003 M) under the pH range of 6-11 and temperatures of 5-60oC. Consistent with the results of previous investigation, the rate of uranium release from sodium autunite exhibited minimal dependency on temperature; but were strongly dependent on pH and increasing concentrations of bicarbonate solutions. Most notably at pH 7, the rate of uranium release exhibited 370 fold increases relative to the rate of uranium release in the absence of bicarbonate. However, the effect of increasing concentrations of bicarbonate solutions on the release of uranium was significantly less under higher pH conditions. It is postulated that at high pH values, surface sites are saturated with carbonate, thus the addition of more bicarbonate would have less effect on uranium release. Results indicate the activation energies were unaffected by temperature and bicarbonate concentration variations, but were strongly dependent on pH conditions. As pH increased from 6 to 11, activation energy values were observed to decrease from 29.94 kJ mol-1 to 13.07 kJ mol-1. The calculated activation energies suggest a surface controlled dissolution mechanism.

Rate constants and mechanisms for the crystallization of Al nano-goethite under environmentally relevant conditions

Science.gov (United States)

Bazilevskaya, Ekaterina; Archibald, Douglas D.; Martínez, Carmen Enid

2012-07-01

Mobile inorganic and organic nanocolloidal particles originate-from and interact-with bulk solid phases in soil and sediment environments, and as such, they contribute to the dynamic properties of environmental systems. In particular, ferrihydrite and (nano)goethite are the most abundant of nanocolloidal Fe oxy(hydr)oxides in these environments. We therefore investigated the ferrihydrite to goethite phase transformation using experimental reaction conditions that mimicked environmental conditions where the formation of nanocolloidal Fe oxy(hydr)oxides may occur: slow titration of dilute solutions to pH 5 at 25 °C with and without 2 mol% Al. Subsequently, the rate constants from 54-d nano-goethite aging/crystallization experiments at 50 °C were determined using aliquots pulled for vibrational spectroscopy (including multivariate curve resolution, MCR, analyses of infrared spectra) and synchrotron-based X-ray diffraction (XRD). We also present a mechanistic model that accounts for the nano-goethite crystallization observed by the aforementioned techniques, and particle structural characteristics observed by dynamic light scattering (DLS) and transmission electron microscopy (TEM). In contrast to the common assumption that metastable ferrihydrite precipitates first, before it transforms to goethite, the presence of characteristic infrared bands in freshly synthesized nanoparticle suspensions indicate goethite can precipitate directly from solution under environmentally relevant conditions: low Fe concentration, ambient temperature, and pH maintained at 5. However, the presence of 2 mol% Al prevented direct goethite precipitation. Rate constants obtained by fitting the contributions from the MCR-derived goethite-like component to the OH-stretching region were (7.4 ± 1.1) × 10-7 s-1 for 0% Al and (4.2 ± 0.4) × 10-7 s-1 for 2 mol% Al suspensions. Rate constants derived from intensities of OH-bending infrared vibrations (795 and 895 cm-1) showed similar values

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

Science.gov (United States)

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

Sustained-release progesterone vaginal suppositories 1--development of sustained-release granule--.

Science.gov (United States)

Nakayama, Ayako; Sunada, Hisakazu; Okamoto, Hirokazu; Furuhashi, Kaoru; Ohno, Yukiko; Ito, Mikio

2009-02-01

Progesterone (P) is an important hormone for the establishment of pregnancy, and its administration is useful for luteal insufficiency. Considering the problems of commercially available oral and injection drugs, hospital-formulated vaginal suppositories are clinically used. However, since the half-life of P suppositories is short, it is difficult to maintain its constant blood concentration. To sustain drug efficacy and prevent side-effects, we are attempting to develop sustained-release suppositories by examining the degree of sustained-release of active ingredients. In this study, we examined the combinations of granulation methods and release systems for the preparation of sustained-release granules of P, and produced 13 types of sustained-release granules. We also examined the diameter, content, and dissolution of each type of granules, and confirmed that the sustained-release of all types of granules was satisfactory. Among the sustained-release granules, we selected granules with a content and a degree of sustained-release suitable for sustained-release suppositories.

Variable temperature effects on release rates of readily soluble nuclides

International Nuclear Information System (INIS)

Kim, C.-L.; Light, W.B.; Lee, W.W.-L.; Chambre, P.L.; Pigford, T.H.

1988-09-01

In this paper we study the effect of temperature on the release rate of readily soluble nuclides, as affected by a time-temperature dependent diffusion coefficient. In this analysis ground water fills the voids in the waste package at t = 0 and one percent of the inventories of cesium and iodine are immediately dissolved into the void water. Mass transfer resistance of partly failed container and cladding is conservatively neglected. The nuclides move through the void space into the surrounding rock under a concentration gradient. We use an analytic solution to compute the nuclide concentration in the gap or void, and the mass flux rate into the porous rock. 8 refs., 4 figs

Evaluation of fuel release rate and mechanism tests under RBCB conditions

International Nuclear Information System (INIS)

Adamson, M.G.

1981-09-01

This task includes theoretical evaluation of fuel/fission product release behavior from failed LMFBR fuel elements as well as an on-going experimental investigation of the mechanism of oxide fuel dispersal into flowing liquid sodium. The primary objectives of this work are to develop a fuel source term that can be used in predictive models for primary heat transfer system contamination and to understand the separate influences of important system variables (such as flow rate, oxygen impurity level) on this source term. The present report is written in two parts: the first, in condensed form, is an updated evaluation of fuel (U,Pu) and fission product release data, and the second describes the current status of supporting experimental work at General Electric's Vallecitos Laboratory

Sedative and cardiorespiratory effects of detomidine constant rate infusion in sheep.

Science.gov (United States)

de Moura, Rauane Sousa; Bittar, Isabela Plazza; da Silva, Luiz Henrique; Villela, Ana Carolina Vasquez; Dos Santos Júnior, Marcelo Borges; Borges, Naida Cristina; Franco, Leandro Guimarães

2018-02-01

The use of sheep in experiments is widespread and is increasing worldwide, and so is the need to develop species-specific anaesthetic techniques to ensure animal safety. Previous studies have mentioned several protocols involving the administration of alpha-2 adrenergic agonists in sheep; however, assessment of the efficacy and safety of these infusion techniques is still relatively new. Thus, the aim of the present study is to assess the effectiveness of detomidine constant rate infusion (CRI) in sheep by measuring the cardiovascular and respiratory parameters, blood gas variables and sedation scores. Eight adult female Santa Inês sheep received 20 µg/kg of detomidine hydrochloride intravenously as a bolus loading dose, followed by an infusion rate of 60 µg/kg/h. The heart rates and respiratory rates changed continuously during the CRI period. No arrhythmias were observed. The reduction in arterial partial pressure of oxygen (PaO 2 ) was not significant, but one animal showed signs of hypoxaemia (minimum PaO 2 of 66.9 mmHg). The arterial partial pressure of carbon dioxide (PaCO 2 ) increased, but the animals did not become hypercapnic. The bicarbonate (HCO 3- ), pH and base excess (BE) tended towards metabolic alkalosis. The cardiac output (CO), stroke volume (SV), cardiac index (CI) and ejection fraction (EF%) showed no significant changes. The fractional shortening (FS%) decreased slightly, starting at T 45min . Sedation scores varied between 3 (0/10) after sedation and during recovery and 7 (0/10) during CRI. We concluded that administering detomidine at an infusion rate of 60 µg/kg/h in Santa Inês sheep is a simple technique that produces satisfactory sedation for minimally invasive procedures.

Evaluating Steam Generator Tubing Corrosion through Shutdown Nickel and Cobalt Releases

International Nuclear Information System (INIS)

Marks, Chuck; Little, Mike; Krull, Peter; Dennis Hussey; Kenny Epperson

2012-09-01

During power operation in PWRs, steam generator tubing corrodes. In PWRs with nickel alloy steam generator tubing this leads to the release of nickel into the coolant. While not structurally significant, this process leads to corrosion product deposition on the fuel surfaces that can threaten fuel integrity, provide a site for boron precipitation, and, through activation and subsequent release, lead to increased out-of-core radiation fields. During shutdown, decreases in temperature and pH and an increase in the oxidation potential lead to dissolution of some corrosion products from the core. This work evaluated the masses of corrosion products released during shutdown as a proxy for steam generator tubing corrosion rates. The masses were evaluated for trends with time (e.g., the number of cycles) and for the influence of design and operating features such as tubing manufacturer, plant design (e.g., three loop versus four loop), and operating chemistry program. This project utilized the EPRI PWR Chemistry Monitoring and Assessment database. Data from over 20 units, many over several cycles, were assessed. The focus was on corrosion product release from Alloy 690TT tubing and all data were from units that had replaced steam generators. Data were analyzed using models developed from corrosion rate test data reported in the literature with a heavy reliance on data from the EDF BOREAL testing. The most striking result of this analysis was a clear division between plants that exhibited corrosion with a falling rate (i.e., following an exponential decay as has been observed, for example, in the BOREAL testing) and those that showed a constant corrosion rate, sustained for many outages. This difference appears to be most closely correlated with the manufacturer of the tubing. Within the two distinct plant groups (decaying corrosion rate and constant corrosion rate), details of the trends were evaluated for correlation with zinc addition history, plant type, and operating

Kinetic, spectroscopic and chemical modification study of iron release from transferrin; iron(III) complexation to adenosine triphosphate

International Nuclear Information System (INIS)

Thompson, C.P.

1985-01-01

Amino acids other than those that serve as ligands have been found to influence the chemical properties of transferrin iron. The catalytic ability of pyrophosphate to mediate transferrin iron release to a terminal acceptor is largely quenched by modification non-liganded histine groups on the protein. The first order rate constants of iron release for several partially histidine modified protein samples were measured. A statistical method was employed to establish that one non-liganded histidine per metal binding domain was responsible for the reduction in rate constant. These results imply that the iron mediated chelator, pyrophosphate, binds directly to a histidine residue on the protein during the iron release process. EPR spectroscopic results are consistent with this interpretation. Kinetic and amino acid sequence studies of ovotransferrin and lactoferrin, in addition to human serum transferrin, have allowed the tentative assignment of His-207 in the N-terminal domain and His-535 in the C-terminal domain as the groups responsible for the reduction in rate of iron release. The above concepts have been extended to lysine modified transferrin. Complexation of iron(II) to adenosine triphosphate (ATP) was also studied to gain insight into the nature of iron-ATP species present at physiological pH. 31 P NMR spectra are observed when ATP is presented in large excess

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

Science.gov (United States)

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

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

Science.gov (United States)

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

In situ and laboratory determined first-order degradation rate constants of specific organic compounds in an aerobic aquifer

DEFF Research Database (Denmark)

Nielsen, P.H.; Bjerg, P.L.; Nielsen, P.

1996-01-01

In situ microcosms (ISM) and laboratory batch microcosms (LBM) were used for determination of the first-order degradation rate constants of benzene, toluene, o-xylene, nitrobenzene, naphthalene, biphenyl, o- and p-dichlorobenzene, 1,1,1 -trichloroethane, tetrachlorometane, trichloroethene......, tetrachloroethene, phenol, o-cresol, 2,4- and 2,6-dichlorophenol, 4,6-o-dichlorocresol, and o- and p-nitrophenol in an aerobic aquifer, All aromatic hydrocarbons were degraded in ISM and LBM experiments. The phenolic hydrocarbons were ail degraded in ISM experiments, but some failed to degrade in LBM experiments....... Chlorinated aliphatic hydrocarbons were degraded neither in ISM nor LBM experiments. Degradation rate constants were determined by a model accounting for kinetic sorption (bicontinuum model), lag phases, and first-order degradation. With a few exceptions, lag phases were less than 2 weeks in both ISM and LBM...

Direct measurements of methoxy removal rate constants for collisions with CH4, Ar, N2, Xe, and CF4 in the temperature range 673--973K

International Nuclear Information System (INIS)

Wantuck, P.J.; Oldenborg, R.C.; Baugchum, S.L.; Winn, K.R.

1988-01-01

Removal rate constants for CH 3 O by CH 4 , Ar, N 2 , Xe, and CF 4 were measured over a 400K temperature range using a laser photolysis/laser-induced fluorescence technique. Rapid methoxy removal rates are observed for the non-reactive collision partners (Ar, N 2 , Xe, and CF 4 ) at elevated temperatures showing that the dissociation and isomerization channels for CH 3 O are indeed important. The total removal rate constant (reaction /plus/ dissociation and/or isomerization) for CH 4 exhibits a linear dependence on temperature and has a removal rate constant, k/sub r/ /equals/ (1.2 +- 0.6) /times/ 10/sup /minus/8/exp[(/minus/101070 +- 350)/T]cm 3 molecule/sup /minus/1/s/sup /minus/1/. Assuming that the removal rate constant due to dissociation and/or isomerization are similar for CH 4 and CF 4 , the reaction rate constant for CH 3 O /plus/ CH 4 is equal to (1.7 +- 1.0) /times/ 10/sup /minus/10/exp[(/minus/7480 +- 1100)/T]cm 3 molecule/sup /minus/1/s/sup /minus/1/. 7 refs., 4 figs

Rate constant for the reaction of OH with CH3CCl2F (HCFC-141b) determined by relative rate measurements with CH4 and CH3CCl3

Science.gov (United States)

Huder, Karin; Demore, William B.

1993-01-01

Determination of accurate rate constants for OH abstraction is of great importance for the calculation of lifetimes for HCFCs and their impact on the atmosphere. For HCFC-141b there has been some disagreement in the literature for absolute measurements of this rate constant. In the present work rate constant ratios for HCFC-141b were measured at atmospheric pressure in the temperature range of 298-358 K, with CH4 and CH3CCl3 as reference gases. Ozone was photolyzed at 254 nm in the presence of water vapor to produce OH radicals. Relative depletions of 141b and the reference gases were measured by FTIR. Arrhenius expressions for 141b were derived from each reference gas and found to be in good agreement with each other. The combined expression for HCFC-141b which we recommend is 1.4 x 10 exp -12 exp(-1630/T) with k at 298 K being 5.9 x 10 exp -15 cu cm/molec-s. This value is in excellent agreement with the JPL 92-20 recommendation.

Unexpectedly high catch-and-release rates in European marine recreational fisheries: implications for science and management

DEFF Research Database (Denmark)

Ferter, Keno; Weltersbach, Marc Simon; Strehlow, Harry Vincent

2013-01-01

Unexpectedly high catch-and-release rates in European marine recreational fisheries: implications for science and management. – ICES Journal of Marine Science, 70: .While catch-and-release (C&R) is a well-known practice in several European freshwater recreational fisheries, studies on the magnitu...

Competitive kinetics as a tool to determine rate constants for reduction of ferrylmyoglobin by food components

DEFF Research Database (Denmark)

Jongberg, Sisse; Lund, Marianne Nissen; Pattison, David I.

2016-01-01

Competitive kinetics were applied as a tool to determine apparent rate constants for the reduction of hypervalent haem pigment ferrylmyoglobin (MbFe(IV)=O) by proteins and phenols in aqueous solution of pH 7.4 and I = 1.0 at 25 °C. Reduction of MbFe(IV)=O by a myofibrillar protein isolate (MPI) f...

Inflation with a smooth constant-roll to constant-roll era transition

Science.gov (United States)

Odintsov, S. D.; Oikonomou, V. K.

2017-07-01

In this paper, we study canonical scalar field models, with a varying second slow-roll parameter, that allow transitions between constant-roll eras. In the models with two constant-roll eras, it is possible to avoid fine-tunings in the initial conditions of the scalar field. We mainly focus on the stability of the resulting solutions, and we also investigate if these solutions are attractors of the cosmological system. We shall calculate the resulting scalar potential and, by using a numerical approach, we examine the stability and attractor properties of the solutions. As we show, the first constant-roll era is dynamically unstable towards linear perturbations, and the cosmological system is driven by the attractor solution to the final constant-roll era. As we demonstrate, it is possible to have a nearly scale-invariant power spectrum of primordial curvature perturbations in some cases; however, this is strongly model dependent and depends on the rate of the final constant-roll era. Finally, we present, in brief, the essential features of a model that allows oscillations between constant-roll eras.

Absolute rate constants for the reaction of NO with a series of peroxy radicals in the gas at 295 K

DEFF Research Database (Denmark)

Sehested, J.; Nielsen, O.J.; Wallington, T.J.

1993-01-01

The rate constants for the reaction of NO with a series of peroxy radicals: CH3O2, C2H5O2, (CH3)3CCH2O2, (CH3)3CC(CH3)2CH2O2, CH2FO2, CH2ClO2, CH2BrO2, CHF2O2, CF2ClO2, CHF2CF2O2, CF3CF2O2, CFCl2CH2O2 and CF2ClCH2O2 were measured at 298 K and a total pressure of 1 atm. The rate constants were...

Aerosol material release rates from zircaloy-4 at temperatures from 2000 to 22000C

International Nuclear Information System (INIS)

Mulpuru, S.R.; Wren, D.J.; Rondeau, R.K.

1987-01-01

During some postulated severe accidents involving loss of coolant and loss of emergency coolant injection, the temperatures in a CANDU reactor fuel channel become high enough to cause failure and melting of the Zircaloy fuel cladding. At such high temperatures, vapors of fission products and structural (fuel and cladding) materials will be released into the coolant steam and hydrogen mixture. These vapors will condense as cooler conditions are encountered downstream. The vapors from structural materials are relatively involatile; therefore, they will condense readily into aerosol particles. These particles, in turn, will provide sites for the condensation of the more volatile fission products. The aerosol transport of fission products in the primary heat transport system (PHTS) will thus be influenced by the structural material release rates. As part of an ongoing program to develop predictive tools for aerosol and associated fission product transport through the PHTS, experiments have been conducted to measure the vapor mass release rates of the alloying elements from Zircaloy-4 at high temperatures. The paper presents the results and analysis of these experiments

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

Science.gov (United States)

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.

TOXRISK, Toxic Gas Release Accident Analysis

International Nuclear Information System (INIS)

Bennett, D.E.; Chanin, D.I.; Shiver, A.W.

1993-01-01

1 - Description of program or function: TOXRISK is an interactive program developed to aid in the evaluation of nuclear power plant control room habitability in the event of a nearby toxic material release. The program uses a model which is consistent with the approach described in the NRC Regulatory Guide 1.78. Release of the gas is treated as an initial puff followed by a continuous plume. The relative proportions of these as well as the plume release rate are supplied by the user. Transport of the gas is modeled as a Gaussian distribution and occurs through the action of a constant velocity, constant direction wind. Great flexibility is afforded the user in specifying the release description, meteorological conditions, relative geometry of the accident and plant, and the plant ventilation system characteristics. Two types of simulation can be performed: multiple case (parametric) studies and probabilistic analyses. Upon execution, TOXRISK presents a menu, and the user chooses between the Data Base Manager, the Multiple Case program, and the Probabilistic Study Program. The Data Base Manager provides a convenient means of storing, retrieving, and modifying blocks of data required by the analysis programs. The Multiple Case program calculates resultant gas concentrations inside the control room and presents a summary of information that describes the event for each set of conditions given. Optimally, a time history profile of inside and outside concentrations can also be produced. The Probabilistic Study program provides a means for estimating the annual probability of operator incapacitation due to toxic gas accidents on surrounding transportation routes and storage sites. 2 - Method of solution: Dispersion or diffusion of the gas during transport is described by modified Pasquill-Gifford dispersion coefficients

A photon spectrometric dose-rate constant determination for the Advantage Pd-103 brachytherapy source

Energy Technology Data Exchange (ETDEWEB)

Chen, Zhe Jay; Bongiorni, Paul; Nath, Ravinder [Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, Connecticut 06520 (United States)

2010-02-15

Purpose: Although several dosimetric characterizations using Monte Carlo simulation and thermoluminescent dosimetry (TLD) have been reported for the new Advantage Pd-103 source (IsoAid, LLC, Port Richey, FL), no AAPM consensus value has been established for the dosimetric parameters of the source. The aim of this work was to perform an additional dose-rate constant ({Lambda}) determination using a recently established photon spectrometry technique (PST) that is independent of the published TLD and Monte Carlo techniques. Methods: Three Model IAPD-103A Advantage Pd-103 sources were used in this study. The relative photon energy spectrum emitted by each source along the transverse axis was measured using a high-resolution germanium spectrometer designed for low-energy photons. For each source, the dose-rate constant was determined from its emitted energy spectrum. The PST-determined dose-rate constant ({sub PST}{Lambda}) was then compared to those determined by TLD ({sub TLD}{Lambda}) and Monte Carlo ({sub MC}{Lambda}) techniques. A likely consensus {Lambda} value was estimated as the arithmetic mean of the average {Lambda} values determined by each of three different techniques. Results: The average {sub PST}{Lambda} value for the three Advantage sources was found to be (0.676{+-}0.026) cGyh{sup -1} U{sup -1}. Intersource variation in {sub PST}{Lambda} was less than 0.01%. The {sub PST}{Lambda} was within 2% of the reported {sub MC}{Lambda} values determined by PTRAN, EGSnrc, and MCNP5 codes. It was 3.4% lower than the reported {sub TLD}{Lambda}. A likely consensus {Lambda} value was estimated to be (0.688{+-}0.026) cGyh{sup -1} U{sup -1}, similar to the AAPM consensus values recommended currently for the Theragenics (Buford, GA) Model 200 (0.686{+-}0.033) cGyh{sup -1} U{sup -1}, the NASI (Chatsworth, CA) Model MED3633 (0.688{+-}0.033) cGyh{sup -1} U{sup -1}, and the Best Medical (Springfield, VA) Model 2335 (0.685{+-}0.033) cGyh{sup -1} U{sup -1} {sup 103}Pd

Short-term Outcomes following Concussion in the NFL: An 11-year Retrospective Study of Player Release Rate and Financial Loss

Science.gov (United States)

Ramkumar, Prem; Navarro, Sergio Michael

2017-01-01

Objectives: The primary goal of this study was to assess the short-term outcomes among National Football League (NFL) players following concussion in terms of: (1) DNP protocol activation, (2) release rate at one and three years, and (3) mean salary reduction. A secondary goal of the study was to stratify the post-concussive release rate by franchise and player position. Methods: NFL player transaction records and publicly available weekly injury reports from August 2005 to January 2016 for NFL players were analyzed. All players immediately sustaining recorded concussions were evaluated for a change to inactive or do-not-play (DNP) status. The one-year and three-year release rate following concussion was defined as any player transitioning to inactivation, retirement, free agency, or any failure to return for a successive season on the same team’s active roster after one or three years from the initial concussion. Student’s t-test was used to compare release rates between non-concussed and concussed players at one and three years. Mean salary reduction per year following concussion was calculated using publicly available player contracts. Additionally, franchise-level and position-based analyses of the release rate were performed. Results: Of the total 5,451 NFL players retrospectively analyzed over the 11-year period, 373 sustained publicly reported concussions resulting in DNP protocol activation. The release rate of the post-concussive versus non-concussive player was 26% vs. 20% at 1 year (pfranchise to release an athlete following concussion within one and three years. Table 1 reports a position-based analysis in terms of concussion rate, mean salary reduction, and NFL career longevity. Conclusion: Our retrospective study demonstrates that NFL concussions resulting in DNP protocol activation leads to a statistically greater release rate among concussed NFL players than non-concussed players. Released players suffered reduction in year-over-year accumulated

Differentiating inflamed and normal lungs by the apparent reaction rate constants of lactate dehydrogenase probed by hyperpolarized (13)C labeled pyruvate.

Science.gov (United States)

Xu, He N; Kadlececk, Stephen; Shaghaghi, Hoora; Zhao, Huaqing; Profka, Harilla; Pourfathi, Mehrdad; Rizi, Rahim; Li, Lin Z

2016-02-01

Clinically translatable hyperpolarized (HP) (13)C-NMR can probe in vivo enzymatic reactions, e.g., lactate dehydrogenase (LDH)-catalyzed reaction by injecting HP (13)C-pyruvate into the subject, which is converted to (13)C labeled lactate by the enzyme. Parameters such as (13)C-lactate signals and lactate-to-pyruvate signal ratio are commonly used for analyzing the HP (13)C-NMR data. However, the biochemical/biological meaning of these parameters remains either unclear or dependent on experimental settings. It is preferable to quantify the reaction rate constants with a clearer physical meaning. Here we report the extraction of the kinetic parameters of the LDH reaction from HP (13)C-NMR data and investigate if they can be potential predictors of lung inflammation. Male Sprague-Dawley rats (12 controls, 14 treated) were used. One dose of bleomycin (2.5 U/kg) was administered intratracheally to the treatment group. The lungs were removed, perfused, and observed by the HP-NMR technique, where a HyperSense dynamic nuclear polarization system was used to generate the HP (13)C-pyruvate for injecting into the lungs. A 20 mm (1)H/(13)C dual-tuned coil in a 9.4-T Varian vertical bore NMR spectrometer was employed to acquire the (13)C spectral data every 1 s over a time period of 300 s using a non-selective, 15-degree radiofrequency pulse. The apparent rate constants of the LDH reaction and their ratio were quantified by applying ratiometric fitting analysis to the time series data of (13)C labeled pyruvate and lactate. The apparent forward rate constant kp =(3.67±3.31)×10(-4) s(-1), reverse rate constant kl =(4.95±2.90)×10(-2) s(-1), rate constant ratio kp /kl =(7.53±5.75)×10(-3) for the control lungs; kp =(11.71±4.35)×10(-4) s(-1), kl =(9.89±3.89)×10(-2) s(-1), and kp /kl =(12.39±4.18)×10(-3) for the inflamed lungs at the 7(th) day post treatment. Wilcoxon rank-sum test showed that the medians of these kinetic parameters of the 7-day cohort were significantly

Rate constant for the H˙ + H2O → ˙OH + H2 reaction at elevated temperatures measured by pulse radiolysis.

Science.gov (United States)

Muroya, Y; Yamashita, S; Lertnaisat, P; Sanguanmith, S; Meesungnoen, J; Jay-Gerin, J-P; Katsumura, Y

2017-11-22

Maintaining the structural integrity of materials in nuclear power plants is an essential issue associated with safe operation. Hydrogen (H 2 ) addition or injection to coolants is a powerful technique that has been widely applied such that the reducing conditions in the coolant water avoid corrosion and stress corrosion cracking (SCC). Because the radiation-induced reaction of ˙OH + H 2 → H˙ + H 2 O plays a crucial role in these systems, the rate constant has been measured at operation temperatures of the reactors (285-300 °C) by pulse radiolysis, generating sufficient data for analysis. The reverse reaction H˙ + H 2 O → ˙OH + H 2 is negligibly slow at ambient temperature; however, it accelerates considerably quickly at elevated temperatures. Although the reverse reaction reduces the effectiveness of H 2 addition, reliable rate constants have not yet been measured. In this study, the rate constants have been determined in a temperature range of 250-350 °C by pulse radiolysis in an aqueous I - solution.

Theoretical growth rates, periods, and pulsation constants for long-period variables

International Nuclear Information System (INIS)

Fox, M.W.; Wood, P.R.

1982-01-01

Theoretical values of the growth rate, period, and pulsation constant for the first three radial pulsation modes in red giants (Population II and galactic disk) and supergiants have been derived in the linear, nonadiabatic approximation. The effects of altering the surface boundary conditions, the effective temperature (or mixing length), and the opacity in the outer layers have been explored. In the standard models, the Q-value for the first overtone can be much larger (Q 1 1 roughly-equal0.04); in addition, the Q-value for the fundamental mode is reduced from previous values, as is the period ratio P 0 /P 1 . The growth rate for the fundamental mode is found to increase with luminosity on the giant branch while the growth rate for the first overtone decreases. Dynamical instabilities found in previous adiabatic models of extreme red giants do not occur when nonadiabatic effects are included in the models. In some massive, luminous models, period ratios P 0 /P 1 approx.7 occur when P 0 approx.2000--5000 days; it is suggested that the massive galactic supergiants and carbon stars which have secondary periods Papprox.2000--7000 days and primary periods Papprox.300--700 days are first-overtone pulsators in which the long secondary periods are due to excitation of the fundamental mode. Some other consequences of the present results are briefly discussed, with particular emphasis on the mode of pulsation of the Mira variables. Subject headings: stars: long-period variables: stars: pulsation: stars: supergiants

Dynamic Monte Carlo rate constants for magnetic Hamiltonians coupled to a phonon bath

Science.gov (United States)

Solomon, Lazarus; Novotny, Mark

2007-03-01

For quantitative comparisons between experimental time- dependent measurements and dynamic Monte Carlo simulations, a relation between the time constant in the simulation and real time is necessary. We calculate the transition rate for spin S system using the lattice frame method for a rigid spin cluster in an elastic medium [1]. We compare this with the transition rate for an Ising spin 12 system using the quantum- mechanical density-matrix method [2] with the results of ref [1,3]. These transition probabilities are different from those of either the Glauber or the Metropolis dynamics, and reflect the properties of the bosonic bath. Comparison with recent experiments [4] will be discussed. [1] E. M. Chudnovsky, D. A. Garanin, and R. Schilling (PRB 72, 2006) [2] K. Park, M. A. Novotny, and P. A. Rikvold (PRE 66, 2002) [3] K Saito, S. Takesue, and S. Miyashita, (PRE 61, 2002) [4] T. Meunier et al (Condensed Matter, 2006)

Rate constant for the reaction of atomic oxygen with phosphine at 298 K

Science.gov (United States)

Stief, L. J.; Payne, W. A.; Nava, D. F.

1987-01-01

The rate constant for the reaction of atomic oxygen with phosphine has been measured at 298 K using flash photolysis combined with time-resolved detection of O(3P) via resonance fluorescence. Atomic oxygen was produced by flash photolysis of N2O or NO highly diluted in argon. The results were shown to be independent of (PH3), (O), total pressure and the source of O(3P). The mean value of all the experiments is k1 = (3.6 + or -0.8) x 10 to the -11th cu cm/s (1 sigma). Two previous measurements of k1 differed by more than an order of magnitude, and the results support the higher value obtained in a discharge flow-mass spectrometry study. A comparison with rate data for other atomic and free radical reactions with phosphine is presented, and the role of these reactions in the aeronomy or photochemistry of Jupiter and Saturn is briefly considered.

Dynamic Characteristics of The DSI-Type Constant-Flow Valves

Science.gov (United States)

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.

Metal release profiles of orthodontic bands, brackets, and wires: an in vitro study.

Science.gov (United States)

Wendl, B; Wiltsche, H; Lankmayr, E; Winsauer, H; Walter, A; Muchitsch, A; Jakse, N; Wendl, M; Wendl, T

2017-11-01

The present study evaluated the temporal release of Co Cr, Mn, and Ni from the components of a typical orthodontic appliance during simulated orthodontic treatment. Several commercially available types of bands, brackets, and wires were exposed to an artificial saliva solution for at least 44 days and the metals released were quantified in regular intervals using inductively coupled plasma quadrupole mass spectrometry (ICP-MS, Elan DRC+, Perkin Elmer, USA). Corrosion products encountered on some products were investigated by a scanning electron microscope equipped with an energy dispersive X-ray microanalyzer (EDX). Bands released the largest quantities of Co, Cr, Mn, and Ni, followed by brackets and wires. Three different temporal metal release profiles were observed: (1) constant, though not necessarily linear release, (2) saturation (metal release stopped after a certain time), and (3) an intermediate release profile that showed signs of saturation without reaching saturation. These temporal metal liberation profiles were found to be strongly dependent on the individual test pieces. The corrosion products which developed on some of the bands after a 6-month immersion in artificial saliva and the different metal release profiles of the investigated bands were traced back to different attachments welded onto the bands. The use of constant release rates will clearly underestimate metal intake by the patient during the first couple of days and overestimate exposure during the remainder of the treatment which is usually several months long. While our data are consistent with heavy metal release by orthodontic materials at levels well below typical dietary intake, we nevertheless recommend the use of titanium brackets and replacement of the band with a tube in cases of severe Ni or Cr allergy.

Influence of ionic complexation on release rate profiles from multiple water-in-oil-in-water (W/O/W) emulsions.

Science.gov (United States)

Bonnet, Marie; Cansell, Maud; Placin, Frédéric; David-Briand, Elisabeth; Anton, Marc; Leal-Calderon, Fernando

2010-07-14

Water-in-oil-in-water (W/O/W) double emulsions were prepared, and the kinetics of release of magnesium ions from the internal to the external water phase was followed. Different chelating agents (phosvitin and gluconate) were used to bind magnesium within the prospect of improving the ion retention in the internal aqueous droplets. Magnesium release was monitored for 1 month of storage, for each formulation, with and without chelation, at two storage temperatures (4 and 25 degrees C). Leakage occurred without film rupturing (coalescence) and was mainly due to entropically driven diffusion/permeation phenomena. The experimental results revealed a clear correlation between the effectiveness of chelating agents to delay the delivery and their binding capacity characterized by the equilibrium affinity constant. The kinetic data (percent released versus time curves) were interpreted within the framework of a kinetic model based on diffusion and taking into account magnesium chelation.

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

Science.gov (United States)

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.

Isopleths of surface concentration and surface exposure rate due to a radioactive cloud released from a stack

International Nuclear Information System (INIS)

Kobayashi, Hideo; Yabuta, Hajimu; Katagiri, Hiroshi; Obata, Kazuichi; Kokubu, Morinobu

1982-03-01

Various calculations are made to estimate the distributions of concentration and γ-exposure rate due to a radioactive cloud released from a point source to the atmosphere. In this report, the isopleths of concentration and γ-exposure rate which were calculated are given in graphs to enable rapid prediction of the influence of released radioactive material in the emergency situation. Recently there are facilities which are equipped with a system to display the calculation results on CRT; but such practice is rather rare. By placing the calculated isopleths of reduction scale 1/25000 or 1/50000 on the usual map, any facilities without the CRT system can readily estimate the influence of an accidental release. The graphs of isopleths are given with the release height (11 values of 0 to 200 m at about 20 m intervals) and the atmospheric stability (6 classes) as parameters. Calculations of γ-exposure rates were made using the computer code GAMPUL developed by T. Hayashi and T. Shiraishi. In the calculation of radioactive concentrations and γ-exposure rates, the vertical diffusion depths, σsub(z), exceeding 1000 m are taken to be 1000 m according to the Meteorological Guide for the Safety Analysis of Power Reactor (J.AEC). The comparison between with and without this limitation in σsub(z) is made in the case of downwind axial surface distributions. (author)

Airborne release fractions/rates and respirable fractions for nonreactor nuclear facilities. Volume 2, Appendices

International Nuclear Information System (INIS)

1994-12-01

This document contains compiled data from the DOE Handbook on Airborne Release Fractions/Rates and Respirable Fractions for Nonreactor Nuclear facilities. Source data and example facilities utilized, such as the Plutonium Recovery Facility, are included

Additive effects on the energy barrier for synaptic vesicle fusion cause supralinear effects on the vesicle fusion rate

DEFF Research Database (Denmark)

Schotten, Sebastiaan; Meijer, Marieke; Walter, Alexander Matthias

2015-01-01

supralinear effects on the fusion rate. To test this prediction experimentally, we developed a method to assess the number of releasable vesicles, rate constants for vesicle priming, unpriming, and fusion, and the activation energy for fusion by fitting a vesicle state model to synaptic responses induced......-linear effects of genetic/pharmacological perturbations on synaptic transmission and a novel interpretation of the cooperative nature of Ca2+-dependent release....

Bimolecular Rate Constants for FAD-Dependent Glucose Dehydrogenase from Aspergillus terreus and Organic Electron Acceptors.

Science.gov (United States)

Tsuruoka, Nozomu; Sadakane, Takuya; Hayashi, Rika; Tsujimura, Seiya

2017-03-10

The flavin adenine dinucleotide-dependent glucose dehydrogenase (FAD-GDH) from Aspergillus species require suitable redox mediators to transfer electrons from the enzyme to the electrode surface for the application of bioelectrical devices. Although several mediators for FAD-GDH are already in use, they are still far from optimum in view of potential, kinetics, sustainability, and cost-effectiveness. Herein, we investigated the efficiency of various phenothiazines and quinones in the electrochemical oxidation of FAD-GDH from Aspergillus terreus . At pH 7.0, the logarithm of the bimolecular oxidation rate constants appeared to depend on the redox potentials of all the mediators tested. Notably, the rate constant of each molecule for FAD-GDH was approximately 2.5 orders of magnitude higher than that for glucose oxidase from Aspergillus sp. The results suggest that the electron transfer kinetics is mainly determined by the formal potential of the mediator, the driving force of electron transfer, and the electron transfer distance between the redox active site of the mediator and the FAD, affected by the steric or chemical interactions. Higher k ₂ values were found for ortho-quinones than for para-quinones in the reactions with FAD-GDH and glucose oxidase, which was likely due to less steric hindrance in the active site in the case of the ortho-quinones.

Bimolecular Rate Constants for FAD-Dependent Glucose Dehydrogenase from Aspergillus terreus and Organic Electron Acceptors

Directory of Open Access Journals (Sweden)

Nozomu Tsuruoka

2017-03-01

Full Text Available The flavin adenine dinucleotide-dependent glucose dehydrogenase (FAD-GDH from Aspergillus species require suitable redox mediators to transfer electrons from the enzyme to the electrode surface for the application of bioelectrical devices. Although several mediators for FAD-GDH are already in use, they are still far from optimum in view of potential, kinetics, sustainability, and cost-effectiveness. Herein, we investigated the efficiency of various phenothiazines and quinones in the electrochemical oxidation of FAD-GDH from Aspergillus terreus. At pH 7.0, the logarithm of the bimolecular oxidation rate constants appeared to depend on the redox potentials of all the mediators tested. Notably, the rate constant of each molecule for FAD-GDH was approximately 2.5 orders of magnitude higher than that for glucose oxidase from Aspergillus sp. The results suggest that the electron transfer kinetics is mainly determined by the formal potential of the mediator, the driving force of electron transfer, and the electron transfer distance between the redox active site of the mediator and the FAD, affected by the steric or chemical interactions. Higher k2 values were found for ortho-quinones than for para-quinones in the reactions with FAD-GDH and glucose oxidase, which was likely due to less steric hindrance in the active site in the case of the ortho-quinones.

Theoretical prediction of energy release rate for interface crack initiation by thermal stress in environmental barrier coatings for ceramics

Science.gov (United States)

Kawai, E.; Umeno, Y.

2017-05-01

As weight reduction of turbines for aircraft engines is demanded to improve fuel consumption and curb emission of carbon dioxide, silicon carbide (SiC) fiber reinforced SiC matrix composites (SiC/SiC) are drawing enormous attention as high-pressure turbine materials. For preventing degradation of SiC/SiC, environmental barrier coatings (EBC) for ceramics are deposited on the composites. The purpose of this study is to establish theoretical guidelines for structural design which ensures the mechanical reliability of EBC. We conducted finite element method (FEM) analysis to calculate energy release rates (ERRs) for interface crack initiation due to thermal stress in EBC consisting of Si-based bond coat, Mullite and Ytterbium (Yb)-silicate layers on a SiC/SiC substrate. In the FEM analysis, the thickness of one EBC layer was changed from 25 μm to 200 μm while the thicknesses of the other layers were fixed at 25 μm, 50 μm and 100 μm. We compared ERRs obtained by the FEM analysis and a simple theory for interface crack in a single-layered structure where ERR is estimated as nominal strain energy in the coating layers multiplied by a constant factor (independent of layer thicknesses). We found that, unlike the case of single-layered structures, the multiplication factor is no longer a constant but is determined by the combination of consisting coating layer thicknesses.

Theoretical prediction of energy release rate for interface crack initiation by thermal stress in environmental barrier coatings for ceramics

International Nuclear Information System (INIS)

Kawai, E; Umeno, Y

2017-01-01

As weight reduction of turbines for aircraft engines is demanded to improve fuel consumption and curb emission of carbon dioxide, silicon carbide (SiC) fiber reinforced SiC matrix composites (SiC/SiC) are drawing enormous attention as high-pressure turbine materials. For preventing degradation of SiC/SiC, environmental barrier coatings (EBC) for ceramics are deposited on the composites. The purpose of this study is to establish theoretical guidelines for structural design which ensures the mechanical reliability of EBC. We conducted finite element method (FEM) analysis to calculate energy release rates (ERRs) for interface crack initiation due to thermal stress in EBC consisting of Si-based bond coat, Mullite and Ytterbium (Yb)-silicate layers on a SiC/SiC substrate. In the FEM analysis, the thickness of one EBC layer was changed from 25 μm to 200 μm while the thicknesses of the other layers were fixed at 25 μm, 50 μm and 100 μm. We compared ERRs obtained by the FEM analysis and a simple theory for interface crack in a single-layered structure where ERR is estimated as nominal strain energy in the coating layers multiplied by a constant factor (independent of layer thicknesses). We found that, unlike the case of single-layered structures, the multiplication factor is no longer a constant but is determined by the combination of consisting coating layer thicknesses. (paper)

Uranium geochemistry in estuarine sediments: Controls on removal and release processes

International Nuclear Information System (INIS)

Barnes, C.E.; Cochran, J.K.

1993-01-01

Porewater uranium profiles from Long Island Sound (LIS) and Amazon shelf sediments and LIS sediment incubation experiments indicate that both removal and release processes control U geochemistry in estuarine sediments. Release of U from sediments occurs in association with Fe reduction. A correlation between U and Fe (and Mn) observed in sediment incubation experiments suggests that there is release of U from Fe-Mn-oxides as they are reduced, consistent with data from the Amazon shelf. In both sediment porewater profiles (LIS and Amazon) and sediment incubation experiments (LIS), there is removal of U from porewater under conditions of sulfate reduction. Sediment incubation experiments indicate that the removal rate is first-order with respect to U concentration, and the rate constant is linearly correlated to sulfate reduction rates. The link between U removal and sulfate reduction (a measure of diagenetic microbial activity) is consistent with a microbial mediation of U reduction. The diffusion flux of U into LIS sediments is estimated from porewater profiles. The inclusion of this estuarine removal term in the oceanic U balance increases the importance of the sediment sink. 62 refs., 12 figs., 2 tabs

The constant failure rate model for fault tree evaluation as a tool for unit protection reliability assessment

International Nuclear Information System (INIS)

Vichev, S.; Bogdanov, D.

2000-01-01

The purpose of this paper is to introduce the fault tree analysis method as a tool for unit protection reliability estimation. The constant failure rate model applies for making reliability assessment, and especially availability assessment. For that purpose an example for unit primary equipment structure and fault tree example for simplified unit protection system is presented (author)

Hysteresis behaviour of silver sputtered in different plasma atmospheres at constant flow rates

International Nuclear Information System (INIS)

Rizk, A.; Makar, L.N.; Rizk, N.S.; Shinoda, R.

1990-01-01

The effects of ion bombardment on sputtering behaviour of pure silver targets in inert and active gas atmospheres were investigated, using a dc planar magnetron sputtering system. The obtained current-voltage characteristics showed the formation of hysteresis loops without noticeable sharp transitions. Redeposited layers of silver nitride or silver oxide on the target surface when using nitrogen or oxygen in the glow discharge, residual ionization when using dry argon atmosphere were considered the main reasons for the occurrence of these loops. The results indicate that films of AgN x and AgO x can be deposited with controlled x in the range 0 ≤ x ≤ 1 using voltage control at constant gas flow rates. (author)

Constant strain rate and peri-implant bone modeling: an in vivo longitudinal micro-CT analysis.

Science.gov (United States)

De Smet, Els; Jaecques, Siegfried V N; Wevers, Martine; Sloten, Jos Vander; Naert, Ignace E

2013-06-01

Strain, frequency, loading time, and strain rate, among others, determine mechanical parameters in osteogenic loading. We showed a significant osteogenic effect on bone mass (BM) by daily peri-implant loading at 1.600µε.s(-1) after 4 weeks. To study the peri-implant osteogenic effect of frequency and strain in the guinea pig tibia by in vivo longitudinal micro-computed tomography (CT) analysis. One week after implant installation in both hind limb tibiae, one implant was loaded daily for 10' during 4 weeks, while the other served as control. Frequencies (3, 10, and 30Hz) and strains varied alike in the three series to keep the strain rate constant at 1.600µε.s(-1) . In vivo micro-CT scans were taken of both tibiae: 1 week after implantation but before loading (v1) and after 2 (v2) and 4 weeks (v3) of loading as well as postmortem (pm). BM (BM (%) bone-occupied area fraction) was calculated as well as the difference between test and control sides (delta BM) RESULTS: All implants (n=78) were clinically stable at 4 weeks. Significant increase in BM was measured between v1 and v2 (pimplant marrow 500 Region of Interest already 2 weeks after loading (p=.01) and was significantly larger (11%) in series 1 compared with series 2 (p=.006) and 3 (p=.016). Within the constraints of constant loading time and strain rate, the effect of early implant loading on the peri-implant bone is strongly dependent on strain and frequency. This cortical bone model has shown to be most sensitive for high force loading at low frequency. © 2011 Wiley Periodicals, Inc.

Direct quantum mechanical calculation of the F + H{sub 2} {yields} HF + H thermal rate constant

Energy Technology Data Exchange (ETDEWEB)

Moix, Marc [Computer Simulation and Modeling (COSMO) Lab, Parc Cientific de Barcelona, Josep Samitier 5, 08028 Barcelona (Spain); Institut de Quimica Teorica i Computacional de la UB (IQTCUB), Universitat de Barcelona (Spain); Huarte-Larranaga, Fermin [Computer Simulation and Modeling (COSMO) Lab, Parc Cientific de Barcelona, Josep Samitier 5, 08028 Barcelona (Spain); Institut de Quimica Teorica i Computacional de la UB (IQTCUB), Universitat de Barcelona (Spain)], E-mail: fhuarte@pcb.ub.es

2008-07-03

Accurate full-dimensional quantum mechanical thermal rate constant values have been calculated for the F+H{sub 2}{yields}HF+H reaction on the Stark-Werner ab initio potential energy surface. These calculations are based on a flux correlation functions and employ a rigorous statistical sampling scheme to account for the overall rotation and the MCTDH scheme for the wave packet propagation. Our results shed some light on discrepancies on the thermal rate found for previous flux correlation based calculations with respect to accurate reactive scattering results. The resonance pattern of the all-J cumulative reaction probability is analyzed in terms of the partial wave contributions.

Aqueous studies of hydrogen sulfide releases from a heavy water extraction facility

International Nuclear Information System (INIS)

Kiser, D.L.

1979-03-01

Upsets in the operation of the wastewater strippers in the 400 Area of the Savannah River Plant have released hydrogen sulfide in quantities as large as 1800 kg to the effluent stream. Fish kills in the swamp area of Beaver Dam Creek have occurred following the large releases. A literature survey revealed volatilization and oxidation as the major loss mechanisms of H 2 S. Laboratory investigations supported the literature survey. The computer code for pollutant transport in a stream, LODIPS, has an option to account for sink-source effects in a stream. Volatilization and oxidation rate constants were developed for the sink option from two H 2 S releases (18 kg and 118 kg) and results were predicted with LODIPS. Based on the predicted concentration-time profiles for various hypothetical cases, releases as small as 568 kg if discharged over a 30-minute period or releases as large as 1818 kg if discharged over a 360-minute period or less are lethal to swamp fish

Tempo of Diversification of Global Amphibians: One-Constant Rate, One-Continuous Shift or Multiple-Discrete Shifts?

Directory of Open Access Journals (Sweden)

Youhua Chen

2014-01-01

Full Text Available In this brief report, alternative time-varying diversification rate models were fitted onto the phylogeny of global amphibians by considering one-constant-rate (OCR, one-continuous-shift (OCS and multiplediscrete- shifts (MDS situations. The OCS diversification model was rejected by γ statistic (γ=-5.556, p⁄ 0.001, implying the existence of shifting diversification rates for global amphibian phylogeny. Through model selection, MDS diversification model outperformed OCS and OCR models using “laser” package under R environment. Moreover, MDS models, implemented using another R package “MEDUSA”, indicated that there were sixteen shifts over the internal nodes for amphibian phylogeny. Conclusively, both OCS and MDS models are recommended to compare so as to better quantify rate-shifting trends of species diversification. MDS diversification models should be preferential for large phylogenies using “MEDUSA” package in which any arbitrary numbers of shifts are allowed to model.

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

Science.gov (United States)

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.

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

Science.gov (United States)

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

Constant conditional entropy and related hypotheses

International Nuclear Information System (INIS)

Ferrer-i-Cancho, Ramon; Dębowski, Łukasz; Moscoso del Prado Martín, Fermín

2013-01-01

Constant entropy rate (conditional entropies must remain constant as the sequence length increases) and uniform information density (conditional probabilities must remain constant as the sequence length increases) are two information theoretic principles that are argued to underlie a wide range of linguistic phenomena. Here we revise the predictions of these principles in the light of Hilberg’s law on the scaling of conditional entropy in language and related laws. We show that constant entropy rate (CER) and two interpretations for uniform information density (UID), full UID and strong UID, are inconsistent with these laws. Strong UID implies CER but the reverse is not true. Full UID, a particular case of UID, leads to costly uncorrelated sequences that are totally unrealistic. We conclude that CER and its particular cases are incomplete hypotheses about the scaling of conditional entropies. (letter)

Estimating reaction rate constants from a two-step reaction: a comparison between two-way and three-way methods

NARCIS (Netherlands)

Bijlsma, S.; Smilde, A. K.

2000-01-01

In this paper, two different spectral datasets are used in order to estimate reaction rate constants using different algorithms. Dataset 1 consists of short-wavelength near-infrared (SW NIR) spectra taken in time of the two-step epoxidation of 2,5-di-tert-butyl-1,4-benzoquinone using tert-butyl

Regional Distribution of Epifascial Swelling and Epifascial Lymph Drainage Rate Constants in Breast Cancer-Related Lymphedema

OpenAIRE

MODI, STEPHANIE; STANTON, ANTHONY W. B.; MELLOR, RUSSELL H.; MICHAEL PETERS, A.; RODNEY LEVICK, J.; MORTIMER, PETER S.

2005-01-01

Background: The view that breast cancer-related lymphedema (BCRL) is a simple, direct mechanical result of axillary lymphatic obstruction (‘stopcock’ mechanism) appears incomplete, because parts of the swollen limb (e.g., hand) can remain nonswollen. The lymph drainage rate constant (k) falls in the swollen forearm but not in the spared hand, indicating regional differences in lymphatic function. Here the generality of the hypothesis that regional epifascial lymphatic failure underlies region...

On the energy release rate in a turbulent current sheet on the Sun

International Nuclear Information System (INIS)

Bardakov, V.M.

1986-01-01

It is shown that turbulent current sheets on the Sun, realizing in the form of the Parker - Sweet flow, are in quasilinear regime of turbulence (or in the regime of instability threshold). The energy release rate in such sheets does not exceed 10 26 erg/s for typical plasma parameters in active regions

Evaluation of Ocimum basilicum L. seed mucilage as rate controlling matrix for sustained release of propranolol HCl

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Majid Saeedi

2015-01-01

Full Text Available Polysaccharide mucilage derived from the seeds of Ocimum basilicum L. (family Lamiaceae was investigated for use in matrix formulations containing propranolol hydrochloride. Basil mucilage was extracted and several tablets were formulated. The effect of mucilage on drug release rate was evaluated in comparison with tablets containing two kinds of hydroxypropyl methylcellulose (HPMC K4M and HPMC K100M as standard polymer. The release data were fitted to several models for kinetic evaluation. The results showed that hardness decreased and friability of tablets increased as the concentration of mucilage increased. The rate of release of propranolol HCl from O. basilicm mucilage matrices was mainly controlled by the drug: mucilage ratio. Drug release was slower from the HPMC K4M and HPMCK100M containing tablets compared to the mucilage containing matrices than the drug release from matrices containing O. basilicum seed mucilage in similar ratios.  Formulations containing O. basilicm mucilage were found to exhibit suitable release pattern. The results of kinetic analysis showed that in tablets containing O. basilicm mucilage the highest correlation coefficient was achieved with the zero order model. The swelling and erosion studies revealed that, as the proportion of mucilage in tablets was increased, there was a corresponding increase in percent swelling and a decrease in percent erosion of tablets.

Fission gas release from UO2 pellet fuel at high burn-up

International Nuclear Information System (INIS)

Vitanza, C.; Kolstad, E.; Graziani, U.

1979-01-01

Analysis of in-reactor measurements of fuel center temperature and rod internal pressure at the OECD Halden Reactor Project has led to the development of an empirical fission gas release model, which is described. The model originally derived from data obtained in the low and intermediate burn-up range, appears to give good predictions for rods irradiated to high exposures as well. PIE puncturing data from seven fuel rods, operated at relatively constant powers and peak center temperatures between 1900 and 2000 0 C up to approx. 40,000 MWd/t UO 2 , did not exhibit any burn-up enhancement on the fission gas release rate

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

Energy Technology Data Exchange (ETDEWEB)

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 [Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ (United Kingdom)

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.

Poly(dimethylsiloxane) coatings for controlled drug release--polymer modifications.

Science.gov (United States)

Schulze Nahrup, J; Gao, Z M; Mark, J E; Sakr, A

2004-02-11

Modifications of endhydroxylated poly(dimethylsiloxane) (PDMS) formulations were studied for their ability to be applied onto tablet cores in a spray-coating process and to control drug release in zero-order fashion. Modifications of the crosslinker from the most commonly used tetraethylorthosilicate (TEOS) to the trifunctional 3-(2,3-epoxypropoxy)propyltrimethoxysilane (SIG) and a 1:1 mixture of the two were undertaken. Addition of methylpolysiloxane-copolymers were studied. Lactose, microcrystalline cellulose (MCC) and polyethylene glycol 8000 (PEG) were the channeling agents applied. The effects on dispersion properties were characterized by particle size distribution and viscosity. Mechanical properties of resulting free films were studied to determine applicability in a pan-coating process. Release of hydrochlorothiazide (marker drug) was studied from tablets coated in a lab-size conventional coating pan. All dispersions were found suitable for a spray-coating process. Preparation of free films showed that copolymer addition was not possible due to great decline in mechanical properties. Tablets coated with formulations containing PEG were most suitable to control drug release, at only 5% coating weight. Constant release rates could be achieved for formulations with up to 25% PEG; higher amounts resulted in a non-linear release pattern. Upon adding 50% PEG, a drug release of 63% over 24 h could be achieved.

Employment of the porous particles for preparation of the capsules containing aspirin and drug release property

International Nuclear Information System (INIS)

Hosoi, Fumio; Makuuchi, Keizo; Saito, Kenji; Koishi, Masumi.

1985-01-01

Polymer-coated porous particles containing aspirin as a drug were prepared and the rate of release of aspirin was studied. The impregnation of aspirin was carried out by post-graft polymerization, where methyl methacrylate or methacrylic acid was treated with porous particles, pre-irradiated with γ-ray from 60 Co, in the presence of aspirin. Release of aspirin from modified particles was tested with 50 % methanol solution and/or pH 5.2 buffer solution of acetic acid. The amount of aspirin released from capsules increased with time and reached a constant values after 140 h. The amount of aspirin absorbed in porous particles was increased with graft polymerization. In addition, absorption of aspirin in porous particles was significantly enhanced by treating the particle surface with TiO 2 before irradiation. The amount of aspirin released was linearly to the square root of time. It was concluded that the diffusion of aspirin through the polymer matrix was the rate limiting step. (author)

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.

Science.gov (United States)

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.

Selective attenuation of norepinephrine release and stress-induced heart rate increase by partial adenosine A1 agonism.

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Lorenz Bott-Flügel

Full Text Available The release of the neurotransmitter norepinephrine (NE is modulated by presynaptic adenosine receptors. In the present study we investigated the effect of a partial activation of this feedback mechanism. We hypothesized that partial agonism would have differential effects on NE release in isolated hearts as well as on heart rate in vivo depending on the genetic background and baseline sympathetic activity. In isolated perfused hearts of Wistar and Spontaneously Hypertensive Rats (SHR, NE release was induced by electrical stimulation under control conditions (S1, and with capadenoson 6 · 10(-8 M (30 µg/l, 6 · 10(-7 M (300 µg/l or 2-chloro-N(6-cyclopentyladenosine (CCPA 10(-6 M (S2. Under control conditions (S1, NE release was significantly higher in SHR hearts compared to Wistar (766+/-87 pmol/g vs. 173+/-18 pmol/g, p<0.01. Capadenoson led to a concentration-dependent decrease of the stimulation-induced NE release in SHR (S2/S1  =  0.90 ± 0.08 with capadenoson 6 · 10(-8 M, 0.54 ± 0.02 with 6 · 10(-7 M, but not in Wistar hearts (S2/S1  =  1.05 ± 0.12 with 6 · 10(-8 M, 1.03 ± 0.09 with 6 · 10(-7 M. CCPA reduced NE release to a similar degree in hearts from both strains. In vivo capadenoson did not alter resting heart rate in Wistar rats or SHR. Restraint stress induced a significantly greater increase of heart rate in SHR than in Wistar rats. Capadenoson blunted this stress-induced tachycardia by 45% in SHR, but not in Wistar rats. Using a [(35S]GTPγS assay we demonstrated that capadenoson is a partial agonist compared to the full agonist CCPA (74+/-2% A(1-receptor stimulation. These results suggest that partial adenosine A(1-agonism dampens stress-induced tachycardia selectively in rats susceptible to strong increases in sympathetic activity, most likely due to a presynaptic attenuation of NE release.

Controlled release from aspirin based linear biodegradable poly(anhydride esters) for anti-inflammatory activity.

Science.gov (United States)

Dasgupta, Queeny; Movva, Sahitya; Chatterjee, Kaushik; Madras, Giridhar

2017-08-07

This work reports the synthesis of a novel, aspirin-loaded, linear poly (anhydride ester) and provides mechanistic insights into the release of aspirin from this polymer for anti-inflammatory activity. As compared to conventional drug delivery systems that rely on diffusion based release, incorporation of bioactives in the polymer backbone is challenging and high loading is difficult to achieve. In the present study, we exploit the pentafunctional sugar alcohol (xylitol) to provide sites for drug (aspirin) attachment at its non-terminal OH groups. The terminal OH groups are polymerized with a diacid anhydride. The hydrolysis of the anhydride and ester bonds under physiological conditions release aspirin from the matrix. The resulting poly(anhydride ester) has high drug loading (53%) and displays controlled release kinetics of aspirin. The polymer releases 8.5 % and 20%, of the loaded drug in one and four weeks, respectively and has a release rate constant of 0.0035h -0.61 . The release rate is suitable for its use as an anti-inflammatory agent without being cytotoxic. The polymer exhibits good cytocompatibility and anti-inflammatory properties and may find applications as injectable or as an implantable bioactive material. The physical insights into the release mechanism can provide development of other drug loaded polymers. Copyright © 2017 Elsevier B.V. All rights reserved.

Operational control of material release and discharges from nuclear power plant

International Nuclear Information System (INIS)

Szabo, I. C.; Ranga, T.; Daroczi, L.; Deme, S.; Kerekes, A.

2003-01-01

were received from overall investigation release limit based on measured dose fraction of different component. Dose due to operational release control levels in case of constant release rate is 15 times lower than the investigation dose limits giving very high safety factor. (authors)

Investigating the feasibility of temperature-controlled accelerated drug release testing for an intravaginal ring.

Science.gov (United States)

Externbrink, Anna; Clark, Meredith R; Friend, David R; Klein, Sandra

2013-11-01

The objective of the present study was to investigate if temperature can be utilized to accelerate drug release from Nuvaring®, a reservoir type intravaginal ring based on polyethylene vinyl acetate copolymer that releases a constant dose of contraceptive steroids over a duration of 3 weeks. The reciprocating holder apparatus (USP 7) was utilized to determine real-time and accelerated etonogestrel release from ring segments. It was demonstrated that drug release increased with increasing temperature which can be attributed to enhanced drug diffusion. An Arrhenius relationship of the zero-order release constants was established, indicating that temperature is a valid parameter to accelerate drug release from this dosage form and that the release mechanism is maintained under these accelerated test conditions. Accelerated release tests are particularly useful for routine quality control to assist during batch release of extended release formulations that typically release the active over several weeks, months or even years, since they can increase the product shelf life. The accelerated method should therefore be able to discriminate between formulations with different release characteristics that can result from normal manufacturing variance. In the case of Nuvaring®, it is well known that the process parameters during the extrusion process strongly influence the polymeric structure. These changes in the polymeric structure can affect the permeability which, in turn, is reflected in the release properties. Results from this study indicate that changes in the polymeric structure can lead to a different temperature dependence of the release rate, and as a consequence, the accelerated method can become less sensitive to detect changes in the release properties. When the accelerated method is utilized during batch release, it is therefore important to take this possible restriction into account and to evaluate the accelerated method with samples from non

Ab initio calculation of the transition-state properties and addition rate constants for H + C2H2 and selected isotopic analogues

International Nuclear Information System (INIS)

Harding, L.B.; Wagner, A.F.; Bowman, J.M.; Schatz, G.C.; Christoffel, K.

1982-01-01

GVB-POL-CI ab initio calculations of the geometries, energetics, and normal mode frequencies of C 2 H 2 , C 2 H 3 , and the transition state for the addition reaction of H + C 2 H 2 are presented. In addition, normal mode frequencies for the isotopic variants D + C 2 D 2 , D + C 2 H 2 , and H + C 2 D 2 are preented. These results are compared to experimental values for C 2 H 2 and to ab initio values of Hagase and Kern, and semiempirical values of Keil, Lynch, Cowfer, and Michael. The results are also used to calculate the apparent bimolecular addition rate constant using conventional RRKM theory for chemical activation. The calculated rate constants and their isotopic variants are compared as a function of temperature and pressure to available experimental information. The agreement is little different from that obtained by Keil et al. with a similar calculation using semiempirical values for acetylene, transition-state, and vinyl radical properties. In particular, the calculated high-pressure limit of the rate constant appears to be at least 1 order of magnitude higher than the experimental limit. Several possible reasons for this discrepancy are discussed

Hydrogen retention and release from uranium dioxide

International Nuclear Information System (INIS)

Sherman, D.F.

1987-08-01

The ceramic samples (UO 2 ) are exposed to high pressure hydrogen gas at a fixed temperature for a time sufficient to achieve equilibrium. After rapid quenching, the hydrogen-saturated sample is transferred to a vacuum-outgassing furnace. The sample is outgassed in a linear temperature ramp and the released hydrogen is detected by an in-situ mass spectrometer. This technique measures the rate of release of hydrogen with a sensitivity level of about 2 ng of hydrogen (as D 2 ) per hour. In this study, experiments were conducted on both polycrystalline and single-crystal UO 2 . Experimental variables included temperature (1000 to 1600 0 C) and infusion pressure (5 to 32 atm D 2 ), and for the polycrystalline specimen, stoichiometry. Dissolution of H 2 in both single-crystal and polycrystalline UO 2 was found to obey Seivert's law. The Sievert's law constant of deuterium in single-crystal UO 2 was determined to be: 3.0 x 10 7 exp(-235 kJ/RT) ppM atomic/√atm and for polycrystalline UO 2 : 5.5 x 10 4 exp(-100 kJ/RT) ppM atomic/√atm. The solubility of hydrogen in hypostoichiometric urania was found to be up to three orders of magnitude greater than in stoichiometric UO 2 depending on the O/U ratios, implying the anion vacancy is the primary solution site in the UO 2 lattice. The release-rate curves for the single crystal and polycrystalline UO 2 specimens exhibited multiple peaks, with most of the deuterium released between 600 and 1200 0 C for the polycrystalline samples, and between 700 and 1800 0 C in the single-crystal specimens. This release of hydrogen from UO 2 could not be adequately modeled as diffusion or diffusion with trapping and resolution. It was determined that release was governed by release from traps in both the polycrystalline and single crystal UO 2 specimens. 40 refs., 72 figs., 6 tabs

Assessment of volumetric-modulated arc therapy for constant and variable dose rates

Directory of Open Access Journals (Sweden)

Mariluz De Ornelas-Couto

2017-01-01

Full Text Available Purpose: The aim of this study is to compare the effects of dose rate on volumetric-modulated arc therapy plans to determine optimal dose rates for prostate and head and neck (HN cases. Materials and Methods: Ten prostate and ten HN cases were retrospectively studied. For each case, seven plans were generated: one variable dose rate (VDR and six constant dose rate (CDR (100–600 monitor units [MUs]/min plans. Prescription doses were: 80 Gy to planning target volume (PTV for the prostate cases, and 70, 60, and 54 Gy to PTV1, PTV2, and PTV3, respectively, for HN cases. Plans were normalized to 95% of the PTV and PTV1, respectively, with the prescription dose. Plans were assessed using Dose-Volume-Histogram metrics, homogeneity index, conformity index, MUs, and delivery time. Results: For the prostate cases, significant differences were found for rectum D35 between VDR and all CDR plans, except CDR500. Furthermore, VDR was significantly different than CDR100 and 200 for bladder D50. Delivery time for all CDR plans and MUs for CDR400–600 were significantly higher when compared to VDR. HN cases showed significant differences between VDR and CDR100, 500 and 600 for D2 to the cord and brainstem. Significant differences were found for delivery time and MUs for all CDR plans, except CDR100 for number of MUs. Conclusion: The most significant differences were observed in delivery time and number of MUs. All-in-all, the best CDR for prostate cases was found to be 300 MUs/min and 200 or 300 MUs/min for HN cases. However, VDR plans are still the choice in terms of MU efficiency and plan quality.

The Dynamics of Pheromone Gland Synthesis and Release: a Paradigm Shift for Understanding Sex Pheromone Quantity in Female Moths.

Science.gov (United States)

Foster, Stephen P; Anderson, Karin G; Casas, Jérôme

2018-05-10

Moths are exemplars of chemical communication, especially with regard to specificity and the minute amounts they use. Yet, little is known about how females manage synthesis and storage of pheromone to maintain release rates attractive to conspecific males and why such small amounts are used. We developed, for the first time, a quantitative model, based on an extensive empirical data set, describing the dynamical relationship among synthesis, storage (titer) and release of pheromone over time in a moth (Heliothis virescens). The model is compartmental, with one major state variable (titer), one time-varying (synthesis), and two constant (catabolism and release) rates. The model was a good fit, suggesting it accounted for the major processes. Overall, we found the relatively small amounts of pheromone stored and released were largely a function of high catabolism rather than a low rate of synthesis. A paradigm shift may be necessary to understand the low amounts released by female moths, away from the small quantities synthesized to the (relatively) large amounts catabolized. Future research on pheromone quantity should focus on structural and physicochemical processes that limit storage and release rate quantities. To our knowledge, this is the first time that pheromone gland function has been modeled for any animal.

Controlled release of ketorolac through nanocomposite films of hydrogel and LDH nanoparticles

International Nuclear Information System (INIS)

Xu Zhiping; Gu Zi; Cheng Xiaoxi; Rasoul, Firas; Whittaker, Andrew K.; Lu Gaoqing Max

2011-01-01

A novel nanocomposite film for sustained release of anionic ophthalmic drugs through a double-control process has been examined in this study. The film, made as a drug-loaded contact lens, consists principally of a polymer hydrogel of 2-hydroxyethyl methacrylate (HEMA), in whose matrix MgAl-layered double hydroxide (MgAl-LDH) nanoparticles intercalated with the anionic drug are well dispersed. Such nanocomposite films (hydrogel-LDH-drug) contained 0.6–0.8 mg of MgAl-LDH and 0.08–0.09 mg of the ophthalmic drug (ketorolac) in 1.0 g of hydrogel. MgAl-drug-LDH nanoparticles were prepared with the hydrodynamic particle size of 40–200 nm. TEM images show that these nanoparticles are evenly dispersed in the hydrogel matrix. In vitro release tests of hydrogel-LDH-drug in pH 7.4 PBS solution at 32 °C indicate a sustained release profile of the loaded drug for 1 week. The drug release undergoes a rapid initial burst and then a monotonically decreasing rate up to 168 h. The initial burst release is determined by the film thickness and the polymerization conditions, but the following release rate is very similar, with the effective diffusion coefficient being nearly constant (3.0 × 10 −12 m 2 /s). The drug release from the films is mechanistically attributed to anionic exchange and the subsequent diffusion in the hydrogel matrix.

Detection of low-level environmental exposure rates due to noble gas releases from the Muehleberg nuclear power plant

International Nuclear Information System (INIS)

Czarnecki, J.; Volkle, H.; Pretre, S.

1980-01-01

The increase of radiation doses in the vicinity of the Swiss Nuclear Power Stations due to airborne releases is generally expected to be below one mrem/year (about one percent of the natural radiation dose). To prove this expected rate, long term measurements with pressure ionization chambers in the vicinity of the Muhleberg plant (BWR) were conducted. Two of these chambers were installed at places where the greatest dose rates from the noble gas plumes were expected in the two prevailing wind directions. The local dose rates were continuously registered on magnetic tape to allow minicomputer evaluation. After the fuel change in the summer of 1976 the noble gas releases from Muhleberg dropped considerably. From that time the noble gas releases consisted of a very low continuous component and some rare short-time spike compoments resulting from turbine and reactor trips. The dose due to the low continuous component was determined by correlating the dose rates at the measuring points with the release measure--ments at the stack and with weather conditions, and by subtracting the natural background. The short noble gas spikes lasted from minutes to some hours and caused small dose rate increases which were easily measured with the ionization chambers, and usually amounted to doses of some microroentgens. By further correlating these dose peaks with wind direction and stack emission measurements, determination of short time atmospheric dilution factors for existing weather situations became possible. By this process, the very low annual environmental doses in the range of 1 mrem per year were determined. (author)

In-vitro Release Study of Carvedilol Phosphate Matrix Tablets ...

African Journals Online (AJOL)

decreased while Starch 1500 and lactose monohydrate increased drug release. Drug release mechanism ... case of antihypertensive agents to maintain constant blood levels ... systems because of their low toxicity, pH- independent swelling ...

Effect of detention basin release rates on flood flows - Application of a model to the Blackberry Creek Watershed in Kane County, Illinois

Science.gov (United States)

Soong, David T.; Murphy, Elizabeth A.; Straub, Timothy D.

2009-01-01

The effects of stormwater detention basins with specified release rates are examined on the watershed scale with a Hydrological Simulation Program - FORTRAN (HSPF) continuous-simulation model. Modeling procedures for specifying release rates from detention basins with orifice and weir discharge configurations are discussed in this report. To facilitate future detention modeling as a tool for watershed management, a chart relating watershed impervious area to detention volume is presented. The report also presents a case study of the Blackberry Creek watershed in Kane County, Ill., a rapidly urbanizing area seeking to avoid future flood damages from increased urbanization, to illustrate the effects of various detention basin release rates on flood peaks and volumes and flood frequencies. The case study compares flows simulated with a 1996 land-use HSPF model to those simulated with four different 2020 projected land-use HSPF model scenarios - no detention, and detention basins with release rates of 0.08, 0.10, and 0.12 cubic feet per second per acre (ft3/s-acre), respectively. Results of the simulations for 15 locations, which included the downstream ends of all tributaries and various locations along the main stem, showed that a release rate of 0.10 ft3/s-acre, in general, can maintain postdevelopment 100-year peak-flood discharge at a similar magnitude to that of 1996 land-use conditions. Although the release rate is designed to reduce the 100-year peak flow, reduction of the 2-year peak flow is also achieved for a smaller proportion of the peak. Results also showed that the 0.10 ft3/s-acre release rate was less effective in watersheds with relatively high percentages of preexisting (1996) development than in watersheds with less preexisting development.

Computational study of the rate constants and free energies of intramolecular radical addition to substituted anilines

Directory of Open Access Journals (Sweden)

Andreas Gansäuer

2013-08-01

Full Text Available The intramolecular radical addition to aniline derivatives was investigated by DFT calculations. The computational methods were benchmarked by comparing the calculated values of the rate constant for the 5-exo cyclization of the hexenyl radical with the experimental values. The dispersion-corrected PW6B95-D3 functional provided very good results with deviations for the free activation barrier compared to the experimental values of only about 0.5 kcal mol−1 and was therefore employed in further calculations. Corrections for intramolecular London dispersion and solvation effects in the quantum chemical treatment are essential to obtain consistent and accurate theoretical data. For the investigated radical addition reaction it turned out that the polarity of the molecules is important and that a combination of electrophilic radicals with preferably nucleophilic arenes results in the highest rate constants. This is opposite to the Minisci reaction where the radical acts as nucleophile and the arene as electrophile. The substitution at the N-atom of the aniline is crucial. Methyl substitution leads to slower addition than phenyl substitution. Carbamates as substituents are suitable only when the radical center is not too electrophilic. No correlations between free reaction barriers and energies (ΔG‡ and ΔGR are found. Addition reactions leading to indanes or dihydrobenzofurans are too slow to be useful synthetically.

Time-Dependent Quantum Wave Packet Study of the Si + OH → SiO + H Reaction: Cross Sections and Rate Constants.

Science.gov (United States)

Rivero Santamaría, Alejandro; Dayou, Fabrice; Rubayo-Soneira, Jesus; Monnerville, Maurice

2017-03-02

The dynamics of the Si( 3 P) + OH(X 2 Π) → SiO(X 1 Σ + ) + H( 2 S) reaction is investigated by means of the time-dependent wave packet (TDWP) approach using an ab initio potential energy surface recently developed by Dayou et al. ( J. Chem. Phys. 2013 , 139 , 204305 ) for the ground X 2 A' electronic state. Total reaction probabilities have been calculated for the first 15 rotational states j = 0-14 of OH(v=0,j) at a total angular momentum J = 0 up to a collision energy of 1 eV. Integral cross sections and state-selected rate constants for the temperature range 10-500 K were obtained within the J-shifting approximation. The reaction probabilities display highly oscillatory structures indicating the contribution of long-lived quasibound states supported by the deep SiOH/HSiO wells. The cross sections behave with collision energies as expected for a barrierless reaction and are slightly sensitive to the initial rotational excitation of OH. The thermal rate constants show a marked temperature dependence below 200 K with a maximum value around 15 K. The TDWP results globally agree with the results of earlier quasi-classical trajectory (QCT) calculations carried out by Rivero-Santamaria et al. ( Chem. Phys. Lett. 2014 , 610-611 , 335 - 340 ) with the same potential energy surface. In particular, the thermal rate constants display a similar temperature dependence, with TDWP values smaller than the QCT ones over the whole temperature range.

Bioaccessibility of metal cations in soil is linearly related to its water exchange rate constant.

Science.gov (United States)

Laird, Brian D; Peak, Derek; Siciliano, Steven D

2011-05-01

Site-specific risk assessments often incorporate the concepts of bioaccessibility (i.e., contaminant fraction released into gastrointestinal fluids) or bioavailability (i.e., contaminant fraction absorbed into systemic circulation) into the calculation of ingestion exposure. We evaluated total and bioaccessible metal concentrations for 19 soil samples under simulated stomach and duodenal conditions using an in vitro gastrointestinal model. We demonstrated that the median bioaccessibility of 23 metals ranged between exchange rates of metal cations (k(H₂O)) indicated that desorption kinetics may influence if not control metal bioaccessibility.

A simple method to evaluate the fission gas release at fuel grain boundary including the grain growth both at constant and at transient power histories

International Nuclear Information System (INIS)

Paraschiv, M.; Paraschiv, A.

1991-01-01

A method to rewrite Fick's second law for a region with a moving boundary when the moving law in time of this boundary is known, has been proposed. This method was applied to Booth's sphere model for radioactive and stable fission product diffusion from the oxide fuel grain in order to take into account the grain growth. The solution of this new equation was presented in the mathematical formulation for power histories from ANS 5.4 model for the stable species. It is very simple to apply and very accurate. The results obtained with this solution for constant and transient temperatures show that the fission gas release (FGR) at grain boundary is strongly dependent on kinetics of grain growth. The utilization of two semiempirical grain growth laws, from published information, shows that the fuel microstructural properties need to be multicitly considered in the fission gas release for every manufacturer of fuel. (orig.)

Combustion Heat Release Rate Comparison of Algae Hydroprocessed Renewable Diesel to F-76 in a Two-Stroke Diesel Engine

Science.gov (United States)

2013-06-01

was recorded. Figure 14 shows the gauge on the rocker arm during calibration . Figure 14. Mechanical Injector Rocker Arm Strain Gauge. D. DATA...RELEASE RATE COMPARISON OF ALGAE HYDROPROCESSED RENEWABLE DIESEL TO F-76 IN A TWO-STROKE DIESEL ENGINE by John H. Petersen June 2013 Thesis...RELEASE RATE COMPARISON OF ALGAE HYDROPROCESSED RENEWABLE DIESEL TO F-76 IN A TWO-STROKE DIESEL ENGINE 5. FUNDING NUMBERS 6. AUTHOR(S) John H

Variational RRKM calculation of thermal rate constant for C–H bond fission reaction of nitro methane

Directory of Open Access Journals (Sweden)

Afshin Taghva Manesh

2017-02-01

Full Text Available The present work provides quantitative results for the rate constants of unimolecular C–H bond fission reactions in the nitro methane at elevated temperatures up to 2000 K. In fact, there are three different hydrogen atoms in the nitro methane. The potential energy surface for each C–H bond fission reaction of nitro methane was investigated by ab initio calculations. The geometry and vibrational frequencies of the species involved in this process were optimized at the MP2 level of theory, using the cc-pvdz basis set. Since C–H bond fission channel is a barrierless reaction, we have used variational RRKM theory to predict rate coefficients. By means of calculated rate coefficients at different temperatures, the Arrhenius expression of the channel over the temperature range of 100–2000 K is k(T = 5.9E19∗exp(−56274.6/T.

Reaction kinetics aspect of U3O8 kernel with gas H2 on the characteristics of activation energy, reaction rate constant and O/U ratio of UO2 kernel

International Nuclear Information System (INIS)

Damunir

2007-01-01

The reaction kinetics aspect of U 3 O 8 kernel with gas H 2 on the characteristics of activation energy, reaction rate constant and O/U ratio of UO 2 kernel had been studied. U 3 O 8 kernel was reacted with gas H 2 in a reduction furnace at varied reaction time and temperature. The reaction temperature was varied at 600, 700, 750 and 850 °C with a pressure of 50 mmHg for 3 hours in gas N 2 atmosphere. The reation time was varied at 1, 2, 3 and 4 hours at a temperature of 750 °C using similar conditions. The reaction product was UO 2 kernel. The reaction kinetic aspect between U 3 O 8 and gas H 2 comprised the minimum activation energy (ΔE), the reaction rate constant and the O/U ratio of UO 2 kernel. The minimum activation energy was determined from a straight line slope of equation ln [{D b . R o {(1 - (1 - X b ) ⅓ } / (b.t.Cg)] = -3.9406 x 10 3 / T + 4.044. By multiplying with the straight line slope -3.9406 x 10 3 , the ideal gas constant (R) 1.985 cal/mol and the molarity difference of reaction coefficient 2, a minimum activation energy of 15.644 kcal/mol was obtained. The reaction rate constant was determined from first-order chemical reaction control and Arrhenius equation. The O/U ratio of UO 2 kernel was obtained using gravimetric method. The analysis result of reaction rate constant with chemical reaction control equation yielded reaction rate constants of 0.745 - 1.671 s -1 and the Arrhenius equation at temperatures of 650 - 850 °C yielded reaction rate constants of 0.637 - 2.914 s -1 . The O/U ratios of UO 2 kernel at the respective reaction rate constants were 2.013 - 2.014 and the O/U ratios at reaction time 1 - 4 hours were 2.04 - 2.011. The experiment results indicated that the minimum activation energy influenced the rate constant of first-order reaction and the O/U ratio of UO 2 kernel. The optimum condition was obtained at reaction rate constant of 1.43 s -1 , O/U ratio of UO 2 kernel of 2.01 at temperature of 750 °C and reaction time of 3

Building shielding effects on radiation doses from routine radionuclide releases

International Nuclear Information System (INIS)

Kocher, D.C.

1977-01-01

In calculating population doses from the release of radionuclides to the atmosphere, it is usually assumed that man spends all of his time outdoors standing on a smooth infinite plane. Realistically, however, man spends most of the time indoors, so that substantial reductions in radiation doses may result compared with the usual estimates. Calculational models were developed to study the effects of building structures on radiation doses from routine releases of radionuclides to the atmosphere. Both internal dose from inhaled radionuclides and external photon dose from airborne and surface-deposited radionuclides are considered. The effect of building structures is described quantitatively by a dose reduction factor, which is the ratio of the dose inside a structure to the corresponding dose with no structure present. The internal dose from inhaled radionuclides is proportional to the radionuclide concentration in the air. Assuming that the outdoor airborne concentration is constant with time, the time-dependence of the indoor airborne concentration in terms of the structure air ventilation rate, the deposition velocities for radionuclides on the inside floor, walls, and ceiling, and the radioactive decay constant, were calculated

FLECHT low flooding rate cosine test series data report

International Nuclear Information System (INIS)

Rosal, E.R.; Hochreiter, L.E.; McGuire, M.F.; Krepinevich, M.C.

1975-12-01

The FLECHT Low Flooding Rate Tests were conducted in an improved original FLECHT Test Facility to provide heat transfer coefficient and entrainment data at forced flooding rates of 1 in./sec and below. In addition these tests were performed to supplement parametric effects studied in the original FLECHT program, provide data for reflood model development, repeat original FLECHT tests with new instrumentation and data processing techniques, and to provide data to establish test repeatability. These tests examined the effects of low initial clad temperature, variable stepped and continuously variable flooding rates, housing heat release, run peak power, constant low flooding rates, coolant subcooling, hot and cold channel entrainment, and bundle stored and generated power. Data obtained in sixty four runs which met the test specifications are reported, and include rod clad temperatures, turn around and quench times, heat transfer coefficients, inlet flooding rates, overall mass balances, differential pressures and calculated void fractions in the test section, thimble wall and steam temperatures, exhaust steam and liquid carryover rates, and housing total and rate of heat release

QSAR models for oxidation of organic micropollutants in water based on ozone and hydroxyl radical rate constants and their chemical classification

KAUST Repository

Sudhakaran, Sairam

2013-03-01

Ozonation is an oxidation process for the removal of organic micropollutants (OMPs) from water and the chemical reaction is governed by second-order kinetics. An advanced oxidation process (AOP), wherein the hydroxyl radicals (OH radicals) are generated, is more effective in removing a wider range of OMPs from water than direct ozonation. Second-order rate constants (kOH and kO3) are good indices to estimate the oxidation efficiency, where higher rate constants indicate more rapid oxidation. In this study, quantitative structure activity relationships (QSAR) models for O3 and AOP processes were developed, and rate constants, kOH and kO3, were predicted based on target compound properties. The kO3 and kOH values ranged from 5 * 10-4 to 105 M-1s-1 and 0.04 to 18 * (109) M-1 s-1, respectively. Several molecular descriptors which potentially influence O3 and OH radical oxidation were identified and studied. The QSAR-defining descriptors were double bond equivalence (DBE), ionisation potential (IP), electron-affinity (EA) and weakly-polar component of solvent accessible surface area (WPSA), and the chemical and statistical significance of these descriptors was discussed. Multiple linear regression was used to build the QSAR models, resulting in high goodness-of-fit, r2 (>0.75). The models were validated by internal and external validation along with residual plots. © 2012 Elsevier Ltd.

Parametric imaging of the rate constant K[sub i] using 18Fluoro-L-dopa positron emission tomography in progressive supranuclear palsy

Energy Technology Data Exchange (ETDEWEB)

Cordes, M. (Neurodegenerative Disorders Centre, Univ. Hospital, Univ. of British Columbia, Vancouver, BC (Canada) Strahlenklinik und Poliklinik, Universitaetsklinikum Rudolf-Virchow, Berlin (Germany)); Snow, B.J. (Neurodegenerative Disorders Centre, Univ. Hospital, Univ. of British Columbia, Vancouver, BC (Canada)); Morrison, S. (TRIUMF, Univ. of British Columbia, Vancouver, BC (Canada)); Sossi, V. (TRIUMF, Univ. of British Columbia, Vancouver, BC (Canada)); Ruth, T.J. (TRIUMF, Univ. of British Columbia, Vancouver, BC (Canada)); Calne, D.B. (Neurodegenerative Disorders Centre, Univ. Hospital, Univ. of British Columbia, Vancouver, BC (Canada))

1993-01-01

Positron emission tomography (PET) studies using 18F-L-dopa were carried out in 9 patients with supranuclear palsy and 13 controls. For quantification of PET data a rate constant K[sub i] was calculated for the radiotracer using a graphical method. Corrections for nonspecific activity were performed in both arterial plasma and brain tissue. The purpose of this study was to test the hypothesis that parametric images of the rate constant K mapping can be obtained on a pixel-by-pixel basis using an appropriate mathematical algorithm. K[sub i] values from these parametric images and the graphical approach were compared. Both correlated closely, with y=0.013+0.947[sup *]x, r=0.992 and y=-0.052+1.048[sup *]x, r=0.965 in patients and controls, respectively. Contrast measurements were also performed and showed a striking increase in contrast on parametric images. K mapping offers several advantages over the graphical approach, since parametric images are time-independent, i.e. one image represents the quantitative result of the study. In addition, parmetric images of the rate constant are normalized to arterial plasma radioactivity and corrected for tissue metabolites. Thus, parametric images of K[sub i] in different individuals can be compared directly without further processing in order to assess the nigrostriatal integrity. (orig.)

Prediction of ion-exchange column breakthrough curves by constant-pattern wave approach.

Science.gov (United States)

Lee, I-Hsien; Kuan, Yu-Chung; Chern, Jia-Ming

2008-03-21

The release of heavy metals from industrial wastewaters represents one of major threats to environment. Compared with chemical precipitation method, fixed-bed ion-exchange process can effectively remove heavy metals from wastewaters and generate no hazardous sludge. In order to design and operate fixed-bed ion-exchange processes successfully, it is very important to understand the column dynamics. In this study, the column experiments for Cu2+/H+, Zn2+/H+, and Cd2+/H+ systems using Amberlite IR-120 were performed to measure the breakthrough curves under varying operating conditions. The experimental results showed that total cation concentration in the mobile-phase played a key role on the breakthrough curves; a higher feed concentration resulted in an earlier breakthrough. Furthermore, the column dynamics was also predicted by self-sharpening and constant-pattern wave models. The self-sharpening wave model assuming local ion-exchange equilibrium could provide a simple and quick estimation for the breakthrough volume, but the predicted breakthrough curves did not match the experimental data very well. On the contrary, the constant-pattern wave model using a constant driving force model for finite ion-exchange rate provided a better fit to the experimental data. The obtained liquid-phase mass transfer coefficient was correlated to the flow velocity and other operating parameters; the breakthrough curves under varying operating conditions could thus be predicted by the constant-pattern wave model using the correlation.

Conditions affecting the release of phosphorus from surface lake sediments.

Science.gov (United States)

Christophoridis, Christophoros; Fytianos, Konstantinos

2006-01-01

Laboratory studies were conducted to determine the effect of pH and redox conditions, as well as the effect of Fe, Mn, Ca, Al, and organic matter, on the release of ortho-phosphates in lake sediments taken from Lakes Koronia and Volvi (Northern Greece). Results were evaluated in combination with experiments to determine P fractionation in the sediment. The study revealed the major effect of redox potential and pH on the release of P from lake sediments. Both lakes showed increased release rates under reductive conditions and high pH values. The fractionation experiments revealed increased mobility of the reductive P fraction as well as of the NaOH-P fraction, indicating participation of both fractions in the overall release of sediment-bound P, depending on the prevailing environmental conditions. The results were assessed in combination with the release patterns of Fe, Mn, Ca, Al, and organic matter, enabling the identification of more specific processes of P release for each lake. The basic release patterns included the redox induced reductive dissolution of P-bearing metal oxides and the competitive exchange of phosphate anions with OH- at high pH values. The formation of an oxidized surface microlayer under oxic conditions acted as a protective film, preventing further P release from the sediments of Lake Volvi, while sediments from Lake Koronia exhibited a continuous and increased tendency to release P under various physicochemical conditions, acting as a constant source of internal P loading.

Drug release kinetic analysis and prediction of release data via polymer molecular weight in sustained release diltiazem matrices.

Science.gov (United States)

Adibkia, K; Ghanbarzadeh, S; Mohammadi, G; Khiavi, H Z; Sabzevari, A; Barzegar-Jalali, M

2014-03-01

This study was conducted to investigate the effects of HPMC (K4M and K100M) as well as tragacanth on the drug release rate of diltiazem (DLTZ) from matrix tablets prepared by direct compression method.Mechanism of drug transport through the matrices was studied by fitting the release data to the 10 kinetic models. 3 model independent parameters; i. e., mean dissolution time (MDT), mean release rate (MRR) and release rate efficacy (RE) as well as 5 time point approaches were established to compare the dissolution profiles. To find correlation between fraction of drug released and polymer's molecular weight, dissolution data were fitted into two proposed equations.All polymers could sustain drug release up to 10 h. The release data were fitted best to Peppas and Higuchi square root kinetic models considering squared correlation coefficient and mean percent error (MPE). RE and MRR were decreased when polymer to drug ratio was increased. Conversely, t60% was increased with raising polymer /drug ratio. The fractions of drug released from the formulations prepared with tragacanth were more than those formulated using the same amount of HPMC K4M and HPMC K100M.Preparation of DLTZ matrices applying HPMCK4M, HPMC K100M and tragacanth could effectively extend the drug release. © Georg Thieme Verlag KG Stuttgart · New York.

Radionuclide mass transfer rates from a pinhole in a waste container for an inventory-limited and a constant concentration source

International Nuclear Information System (INIS)

LeNeveu, D.M.

1996-03-01

Analytical solutions for transient and steady state diffusive mass transfer rates from a pinhole in a waste container are developed for constant concentration and inventory-limited source conditions. Mass transport in three media are considered, inside the pinhole (medium 2), outside the container (medium 3) and inside the container (medium 1). Simple equations are developed for radionuclide mass transfer rates from a pinhole. It is shown that the medium with the largest mass transfer resistance need only be considered to provide a conservative estimate of mass transfer rates. (author) 11 refs., 3 figs

Reaction of H2 with O2 in Excited Electronic States: Reaction Pathways and Rate Constants.

Science.gov (United States)

Pelevkin, Alexey V; Loukhovitski, Boris I; Sharipov, Alexander S

2017-12-21

Comprehensive quantum chemical analysis with the use of the multireference state-averaged complete active space self-consistent field approach was carried out to study the reactions of H 2 with O 2 in a 1 Δ g , b 1 Σ g + , c 1 Σ u - , and A' 3 Δ u electronically excited states. The energetically favorable reaction pathways and possible intersystem crossings have been revealed. The energy barriers were refined employing the extended multiconfiguration quasi-degenerate second-order perturbation theory. It has been shown that the interaction of O 2 (a 1 Δ g ) and O 2 (A' 3 Δ u ) with H 2 occurs through the H-abstraction process with relatively low activation barriers that resulted in the formation of the HO 2 molecule in A″ and A' electronic states, respectively. Meanwhile, molecular oxygen in singlet sigma states (b 1 Σ g + and c 1 Σ u - ) was proved to be nonreactive with respect to the molecular hydrogen. Appropriate rate constants for revealed reaction and quenching channels have been estimated using variational transition-state theory including corrections for the tunneling effect, possible nonadiabatic transitions, and anharmonicity of vibrations for transition states and reactants. It was demonstrated that the calculated reaction rate constant for the H 2 + O 2 (a 1 Δ g ) process is in reasonable agreement with known experimental data. The Arrhenius approximations for these processes have been proposed for the temperature range T = 300-3000 K.

Measurement of nucleotide exchange rate constants in single rabbit soleus myofibrils during shortening and lengthening using a fluorescent ATP analog.

Science.gov (United States)

Shirakawa, I; Chaen, S; Bagshaw, C R; Sugi, H

2000-02-01

The kinetics of displacement of a fluorescent nucleotide, 2'(3')-O-[N[2-[[Cy3]amido]ethyl]carbamoyl]-adenosine 5'-triphosphate (Cy3-EDA-ATP), bound to rabbit soleus muscle myofibrils were studied using flash photolysis of caged ATP. Use of myofibrils from this slow twitch muscle allowed better resolution of the kinetics of nucleotide exchange than previous studies with psoas muscle myofibrils (, Biophys. J. 73:2033-2042). Soleus myofibrils in the presence of Cy3-EDA-nucleotides (Cy3-EDA-ATP or Cy3-EDA-ADP) showed selective fluorescence staining of the A-band. The K(m) for Cy3-EDA-ATP and the K(d) for Cy3-EDA-ADP binding to the myofibril A-band were 1.9 microM and 3.8 microM, respectively, indicating stronger binding of nucleotide to soleus cross-bridges compared to psoas cross-bridges (2.6 microM and 50 microM, respectively). After flash photolysis of caged ATP, the A-band fluorescence of the myofibril in the Cy3-EDA-ATP solution under isometric conditions decayed exponentially with a rate constant of 0.045 +/- 0.007 s(-1) (n = 32) at 10 degrees C, which was about seven times slower than that for psoas myofibrils. When a myofibril was allowed to shorten with a constant velocity, the nucleotide displacement rate constant increased from 0.066 s(-1) (isometric) to 0.14 s(-1) at 20 degrees C with increasing shortening velocity up to 0.1 myofibril length/s (V(max), the shortening velocity under no load was approximately 0. 2 myofibril lengths/s). The rate constant was not significantly affected by an isovelocity stretch of up to 0.1 myofibril lengths/s. These results suggest that the cross-bridge kinetics are not significantly affected at higher strain during lengthening but depend on the lower strain during shortening. These data also indicate that the interaction distance between a cross-bridge and the actin filament is at least 16 nm for a single cycle of the ATPase.

The Relationship between Toxics Release Inventory Discharges and Mortality Rates in Rural and Urban Areas of the United States

Science.gov (United States)

Hendryx, Michael; Fedorko, Evan

2011-01-01

Background: Potential environmental exposures from chemical manufacturing or industrial sites have not been well studied for rural populations. The current study examines whether chemical releases from facilities monitored through the Toxics Release Inventory (TRI) program are associated with population mortality rates for both rural and urban…

Self-assembled nanoparticles of modified-chitosan conjugates for the sustained release of dl-α-tocopherol

DEFF Research Database (Denmark)

Quinones, Javier Perez; Gothelf, Kurt Vesterager; Kjems, Jørgen

2013-01-01

Synthetic O6-succinylated chitosan and commercial glycol chitosan were covalently linked to dl-α-tocopheryl monoesters for controlled release of vitamin E. These conjugates formed self-assembled nanoparticles in aqueous solution with 254–496 nm mean diameters and dl-α-tocopherol contents between 27...... and 39% (w/w). The particles appeared as 40–75 nm almost spherical nanoparticles when studied by scanning and transmission electron microscopy upon drying. Drug linking to chitosan matrix was confirmed by FTIR spectroscopy and proton NMR. Conjugates were also characterized by differential scanning...... calorimetry and wide-angle X-ray diffraction. In vitro tocopherol release studies performed in water at acid pH indicated a drug release dependence on drug content, hydrated particle sizes and employed chitosan derivative. Almost constant release rates were observed the first 7 h. The obtained nanoparticles...

Time-integrated thyroid dose for accidental releases from Pakistan Research Reactor-1

International Nuclear Information System (INIS)

Raza, S Shoaib; Iqbal, M; Salahuddin, A; Avila, R; Pervez, S

2004-01-01

The two-hourly time-integrated thyroid dose due to radio-iodines released to the atmosphere through the exhaust stack of Pakistan Research Reactor-1 (PARR-1), under accident conditions, has been calculated. A computer program, PAKRAD (which was developed under an IAEA research grant, PAK/RCA/8990), was used for the dose calculations. The sensitivity of the dose results to different exhaust flow rates and atmospheric stability classes was studied. The effect of assuming a constant activity concentration (as a function of time) within the containment air volume and an exponentially decreasing air concentration on the time-integrated dose was also studied for various flow rates (1000-50,000 m 3 h -1 ). The comparison indicated that the results were insensitive to the containment air exhaust rates up to or below 2000 m 3 h -1 , when the prediction with the constant activity concentration assumption was compared to an exponentially decreasing activity concentration model. The results also indicated that the plume touchdown distance increases with increasing atmospheric stability. (note)

Multivariate Metal-Organic Frameworks for Dialing-in the Binding and Programming the Release of Drug Molecules.

Science.gov (United States)

Dong, Zhiyue; Sun, Yangzesheng; Chu, Jun; Zhang, Xianzheng; Deng, Hexiang

2017-10-11

We report the control of guest release profiles by dialing-in desirable interactions between guest molecules and pores in metal-organic frameworks (MOFs). The interactions can be derived by the rate constants that were quantitatively correlated with the type of functional group and its proportion in the porous structure; thus the release of guest molecules can be predicted and programmed. Specifically, three probe molecules (ibuprofen, rhodamine B, and doxorubicin) were studied in a series of robust and mesoporous MOFs with multiple functional groups [MIL-101(Fe)-(NH 2 ) x , MIL-101(Fe)-(C 4 H 4 ) x , and MIL-101(Fe)-(C 4 H 4 ) x (NH 2 ) 1-x ]. The release rate can be adjusted by 32-fold [rhodamine from MIL-101(Fe)-(NH 2 ) x ], and the time of release peak can be shifted by up to 12 days over a 40-day release period [doxorubicin from MIL-101(Fe)-(C 4 H 4 ) x (NH 2 ) 1-x ], which was not obtained in the physical mixture of the single component MOF counterparts nor in other porous materials. The corelease of two pro-drug molecules (ibuprofen and doxorubicin) was also achieved.

Effective Anti-miRNA Oligonucleotides Show High Releasing Rate of MicroRNA from RNA-Induced Silencing Complex.

Science.gov (United States)

Ariyoshi, Jumpei; Matsuyama, Yohei; Kobori, Akio; Murakami, Akira; Sugiyama, Hiroshi; Yamayoshi, Asako

2017-10-01

MicroRNAs (miRNAs) regulate gene expression by forming RNA-induced silencing complexes (RISCs) and have been considered as promising therapeutic targets. MiRNA is an essential component of RISC for the modulation of gene expression. Therefore, the release of miRNA from RISC is considered as an effective method for the inhibition of miRNA functions. In our previous study, we reported that anti-miRNA oligonucleotides (AMOs), which are composed of the 2'-O-methyl (2'-OMe) RNA, could induce the release of miRNA from RISC. However, the mechanisms underlying the miRNA-releasing effects of chemically modified AMOs, which are conventionally used as anti-cancer drugs, are still unclear. In this study, we investigated the relationship between the miRNA releasing rate from RISC and the inhibitory effect on RISC activity (IC 50 ) using conventional chemically modified AMOs. We demonstrated that the miRNA-releasing effects of AMOs are directly proportional to the IC 50 values, and AMOs, which have an ability to promote the release of miRNA from RISC, can effectively inhibit RISC activity in living cells.

Effects of nutrient enrichment on the release of dissolved organic carbon and nitrogen by the scleractinian coral Montipora digitata

Science.gov (United States)

Tanaka, Y.; Ogawa, H.; Miyajima, T.

2010-09-01

The effects of nutrient enrichment on the release of dissolved organic carbon and nitrogen (DOC and DON, respectively) from the coral Montipora digitata were investigated in the laboratory. Nitrate (NO3 -) and phosphate (PO4 3-) were supplied to the aquarium to get the final concentrations of 10 and 0.5 μmol l-1, respectively, and the corals were incubated for 8 days. The release rate of DON per unit coral surface area significantly decreased after the nutrient enrichment, while the release rate of DOC was constant. Because the chlorophyll a (chl a) content of zooxanthellae per unit surface area increased, the release rate of DOC significantly decreased when normalized to unit chl a. These results suggested that the incorporation of NO3 - and PO4 3- stimulated the synthesis of new cellular components in the coral colonies and consequently, reduced extracellular release of DOC and DON. Actually, significant increase in N and P contents relative to C content was observed in the coral’s tissue after the nutrient enrichment. The present study has concluded that inorganic nutrient enrichment not only affects coral-algal metabolism inside the colony but also affects a microbial community around the coral because the organic matter released from corals functions as energy carrier in the coral reef ecosystem.

The chemistry of bromine in the stratosphere: Influence of a new rate constant for the reaction BrO + HO2

Science.gov (United States)

Pirre, Michel; Marceau, Francois J.; Lebras, Georges; Maguin, Francoise; Poulet, Gille; Ramaroson, Radiela

1994-01-01

The impact of new laboratory data for the reaction BrO + HO2 yields HOBr + O2 in the depletion of global stratospheric ozone has been estimated using a one-dimensional photochemical model taking into account the heterogeneous reaction on sulphate aerosols which converts N2O5 into HNO3. Assuring an aerosol loading 2 times as large as the 'background' and a reaction probability of 0.1 for the above heterogeneous reaction, the 6 fold increase in the measured rate constant for the reaction of BrO with HO2 increases the computed depletion of global ozone produced by 20 ppt of total bromine from 2.01 percent to 2.36 percent. The use of the higher rate constant increases the HOBr mixing ratio and makes the bromine partitioning and the ozone depletion very sensitive to the branching ratio of the potential channel forming HBr in the BrO + HO2 reaction.

Influence of the rate of conversion of HT and HTO on projected radiation doses from release of molecular tritium

International Nuclear Information System (INIS)

Jacobs, D.G.; Easterly, C.E.; Phillips, J.E.

1979-01-01

Releases of tritium in the past have been largely in the form of tritiated water, and the projected radiation doses could be estimated by assuming tritium behaviour to parallel that of water. There is increasing interest in potential releases of tritium in the form of HT because of significant recent advances in fusion reactor research. Several recent studies have shown that bacteria containing the enzyme hydrogenase can catalyse the conversion of HT to HTO at rates several orders of magnitude faster than the rates measured in atmospheric systems. Rates of conversion in the soil have been combined with estimates of rates of permeation of HT into the soil and with global and local models depicting tritium transport and cycling. The results suggest that for the expected conversion rates, the impact on projected radiation doses should be relatively minor. (author)

Determination of acidity constants and ionic mobilities of polyprotic peptide hormones by CZE

Czech Academy of Sciences Publication Activity Database

Šolínová, Veronika; Kašička, Václav

2013-01-01

Roč. 34, č. 18 (2013), s. 2655-2665 ISSN 0173-0835 R&D Projects: GA ČR(CZ) GAP206/12/0453; GA ČR(CZ) GA13-17224S Institutional support: RVO:61388963 Keywords : acid dissociation constant * gonadotropin-releasing hormones * ionization constant * peptides * pK(a) Subject RIV: CB - Analytical Chemistry, Separation Impact factor: 3.161, year: 2013

Evaluating release alternatives for a long-lived bird species under uncertainty about long-term demographic rates

Science.gov (United States)

Moore, Clinton T.; Converse, Sarah J.; Folk, Martin J.; Runge, Michael C.; Nesbitt, Stephen A.

2012-01-01

The release of animals to reestablish an extirpated population is a decision problem that is often attended by considerable uncertainty about the probability of success. Annual releases of captive-reared juvenile Whooping Cranes (Grus americana) were begun in 1993 in central Florida, USA, to establish a breeding, non-migratory population. Over a 12-year period, 286 birds were released, but by 2004, the introduced flock had produced only four wild-fledged birds. Consequently, releases were halted over managers' concerns about the performance of the released flock and uncertainty about the efficacy of further releases. We used data on marked, released birds to develop predictive models for addressing whether releases should be resumed, and if so, under what schedule. To examine the outcome of different release scenarios, we simulated the survival and productivity of individual female birds under a baseline model that recognized age and breeding-class structure and which incorporated empirically estimated stochastic elements. As data on wild-fledged birds from captive-reared parents were sparse, a key uncertainty that confronts release decision-making is whether captive-reared birds and their offspring share the same vital rates. Therefore, we used data on the only population of wild Whooping Cranes in existence to construct two alternatives to the baseline model. The probability of population persistence was highly sensitive to the choice of these three models. Under the baseline model, extirpation of the population was nearly certain under any scenario of resumed releases. In contrast, the model based on estimates from wild birds projected a high probability of persistence under any release scenario, including cessation of releases. Therefore, belief in either of these models suggests that further releases are an ineffective use of resources. In the third model, which simulated a population Allee effect, population persistence was sensitive to the release decision

Study on crack propagation of adhesively bonded DCB for aluminum foam using energy release rate

Energy Technology Data Exchange (ETDEWEB)

Bang, Hye Jin; Lee, Sang Kyo; Cho, Chong Du [Inha University, Incheon (Korea, Republic of); Cho, Jae Ung [Kongju National University, Choenan (Korea, Republic of)

2015-01-15

Aluminum foam with initial crack, which has a closed cell form adhesively bonded, is studied to compare and analyze the crack propagation behavior by using both experimental and finite element analysis techniques. The specimen is loaded in Mode I type of fracture as 15 mm/min speed of a displacement control method. The experimental results were used to accommodate the finite element analysis performed with commercial software ABAQUS 6.10. First, using a video recording, five steps of experiment were selected at random and then the energy release rate was calculated. The estimated energy release rate was then used as fracture energy into the finite element analysis. Comparing the experimental axial load-displacement graphs and the finite element analysis results, roughly equivalent peak values were observed in the cohesive strength of the aluminum foam double cantilever beam. However, force versus displacement patterns showed somewhat different: little deformation was observed in aluminum foam, whereas adhesive parts in double cantilever beam were significantly deformed.

Rate constants and temperature effects for reactions of Cl2sm-bullet- with unsaturated alcohols and hydrocarbons in aqueous and acetonitrile/water solutions

International Nuclear Information System (INIS)

Padmaja, S.; Neta, P.; Huie, R.E.

1992-01-01

Absolute rate constants for reactions of the dichlorine radical anion, Cl 2 sm-bullet- , with unsaturated alcohols and hydrocarbons have been measured at various temperatures. The alcohol reactions were measured in aqueous solutions and the hydrocarbon reactions in 1:1 aqueous acetonitirle (ACN) solutions. The rate constants for two alcohols and one hydrocarbon were also examined as a function of solvent composition. The room temperature rate constants varied between 10 6 and 10 9 M -1 s -1 . The pre-exponential factors, A, were about (1-5) x 10 9 M -1 s -1 for the alcohols in aqueous solutions and about (0.1-1) x 10 9 M -1 s -1 for the hydrocarbons in aqueous ACN solutions. The activation energies, E a , varied considerably, between 4 and 12 kJ mol -1 for the alcohols and between 2 and 8 kJ mol -1 for the hydrocarbons. The rate constants, k 298 , decrease with increasing ionization potential (IP) of the unsaturated compound, in agreement with an electrophilic addition mechanism. The activation energies for the unsaturated alcohols decrease when the IP decreases from 9.7 to 9.1 eV but appear to level off at lower IP. Most alkenes studied had IP a . Upon addition of ACN to the aqueous solution, the values of log k 298 decreased linearly by more than 1 order of magnitude with increasing ACN mole fraction. This decrease appears to result from a combination of changes in the activation energy and in the pre-exponential factor. The reason for these changes may lie in changes in the solvation shell of the Cl 2 sm-bullet- radical, which will affect the A factor, in combination with changes in solvation of Cl - , which will affect the energetics of the reactions as well. 20 refs., 7 figs., 6 tabs

Reactor group constants and benchmark test

Energy Technology Data Exchange (ETDEWEB)

Takano, Hideki [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment

2001-08-01

The evaluated nuclear data files such as JENDL, ENDF/B-VI and JEF-2 are validated by analyzing critical mock-up experiments for various type reactors and assessing applicability for nuclear characteristics such as criticality, reaction rates, reactivities, etc. This is called Benchmark Testing. In the nuclear calculations, the diffusion and transport codes use the group constant library which is generated by processing the nuclear data files. In this paper, the calculation methods of the reactor group constants and benchmark test are described. Finally, a new group constants scheme is proposed. (author)

Kinetics of selenium release in mine waste from the Meade Peak Phosphatic Shale, Phosphoria Formation, Wooley Valley, Idaho, USA

Science.gov (United States)

Stillings, Lisa L.; Amacher, Michael C.

2010-01-01

Phosphorite from the Meade Peak Phosphatic Shale member of the Permian Phosphoria Formation has been mined in southeastern Idaho since 1906. Dumps of waste rock from mining operations contain high concentrations of Se which readily leach into nearby streams and wetlands. While the most common mineralogical residence of Se in the phosphatic shale is elemental Se, Se(0), Se is also an integral component of sulfide phases (pyrite, sphalerite and vaesite–pyritess) in the waste rock. It may also be present as adsorbed selenate and/or selenite, and FeSe2 and organo-selenides.Se release from the waste rock has been observed in field and laboratory experiments. Release rates calculated from waste rock dump and column leachate solutions describe the net, overall Se release from all of the possible sources of Se listed above. In field studies, Se concentration in seepage water (pH 7.4–7.8) from the Wooley Valley Unit 4 dump ranges from 3600 µg/L in May to 10 µg/L by Sept. Surface water flow, Q, from the seep also declines over the summer, from 2 L/s in May to 0.03 L/s in Sept. Se flux ([Se] ⁎ Q) reaches a steady-state of Laboratory experiments were performed with the waste shale in packed bed reactors; residence time varied from 0.09 to 400 h and outlet pH ∼ 7.5. Here, Se concentration increased with increasing residence time and release was modeled with a first order reaction with k = 2.19e−3 h− 1 (19.2 yr− 1).Rate constants reported here fall within an order of magnitude of reported rate constants for oxidation of Se(0) formed by bacterial precipitation. This similarity among rate constants from both field and laboratory studies combined with the direct observation of Se(0) in waste shales of the Phosphoria Formation suggests that oxidation of Se(0) may control steady-state Se concentration in water draining the Wooley Valley waste dump.

Modeling the downward transport of 210Pb in Peatlands: Initial Penetration‐Constant Rate of Supply (IP-CRS) model

International Nuclear Information System (INIS)

Olid, Carolina; Diego, David; Garcia-Orellana, Jordi; Cortizas, Antonio Martínez; Klaminder, Jonatan

2016-01-01

The vertical distribution of 210 Pb is commonly used to date peat deposits accumulated over the last 100–150 years. However, several studies have questioned this method because of an apparent post-depositional mobility of 210 Pb within some peat profiles. In this study, we introduce the Initial Penetration–Constant Rate of Supply (IP-CRS) model for calculating ages derived from 210 Pb profiles that are altered by an initial migration of the radionuclide. This new, two-phased, model describes the distribution of atmospheric-derived 210 Pb ( 210 Pb xs ) in peat taking into account both incorporation of 210 Pb into the accumulating peat matrix as well as an initial flushing of 210 Pb through the uppermost peat layers. The validity of the IP-CRS model is tested in four anomalous 210 Pb peat records that showed some deviations from the typical exponential decay profile not explained by variations in peat accumulation rates. Unlike the most commonly used 210 Pb-dating model (Constant Rate of Supply (CRS)), the IP-CRS model estimates peat accumulation rates consistent with typical growth rates for peatlands from the same areas. Confidence in the IP-CRS chronology is also provided by the good agreement with independent chronological markers (i.e. 241 Am and 137 Cs). Our results showed that the IP-CRS can provide chronologies from peat records where 210 Pb mobility is evident, being a valuable tool for studies reconstructing past environmental changes using peat archives during the Anthropocene. - Highlights: • Accurate age dating of peat and sediment cores is critical for evaluating change. • A new 210 Pb dating model that includes vertical transport of 210 Pb was developed. • The IP-CRS model provided consistent peat accumulation rates. • The IP-CRS ages were consistent with independent chronological markers. • The IP-CRS model derives peat ages where downward 210 Pb transport is evidenced.

Fitting the elementary rate constants of the P-gp transporter network in the hMDR1-MDCK confluent cell monolayer using a particle swarm algorithm.

Directory of Open Access Journals (Sweden)

Deep Agnani

Full Text Available 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

Site-Specific Rate Constant Measurements for Primary and Secondary H- and D-Abstraction by OH Radicals: Propane and n -Butane

KAUST Repository

Badra, Jihad; Nasir, Ehson F.; Farooq, Aamir

2014-01-01

Site-specific rate constants for hydrogen (H) and deuterium (D) abstraction by hydroxyl (OH) radicals were determined experimentally by monitoring the reaction of OH with two normal and six deuterated alkanes. The studied alkanes include propane (C3H8), propane 2,2 D2 (CH 3CD2CH3), propane 1,1,1-3,3,3 D6 (CD 3CH2CD3), propane D8 (C3D 8), n-butane (n-C4H10), butane 2,2-3,3 D4 (CH3CD2CD2CH3), butane 1,1,1-4,4,4 D6 (CD3CH2CH2CD3), and butane D10 (C4D10). Rate constant measurements were carried out over 840-1470 K and 1.2-2.1 atm using a shock tube and OH laser absorption. Previous low-temperature data were combined with the current high-temperature measurements to generate three-parameter fits which were then used to determine the site-specific rate constants. Two primary (P1,H and P 1,D) and four secondary (S00,H, S00,D, S 01,H, and S01,D) H- and D-abstraction rate constants, in which the subscripts refer to the number of C atoms connected to the next-nearest-neighbor C atom, are obtained. The modified Arrhenius expressions for the six site-specific abstractions by OH radicals are P1,H = 1.90 × 10-18T2.00 exp(-340.87 K/T) cm 3molecule-1s-1 (210-1294 K); P1,D= 2.72 × 10-17 T1.60 exp(-895.57 K/T) cm 3molecule-1s-1 (295-1317 K); S00,H = 4.40 × 10-18 T1.93 exp(121.50 K/T) cm 3molecule-1s-1 (210-1294 K); S00,D = 1.45 × 10-20 T2.69 exp(282.36 K/T) cm 3molecule-1s-1 (295-1341 K); S01,H = 4.65 × 10-17 T1.60 exp(-236.98 K/T) cm 3molecule-1s-1 (235-1407 K); S01,D = 1.26 × 10-18 T2.07 exp(-77.00 K/T) cm 3molecule-1s-1 (294-1412 K). © 2014 American Chemical Society.

Theoretical study and rate constant calculation for the reactions of SH (SD) with Cl2, Br2, and BrCl.

Science.gov (United States)

Wang, Li; Liu, Jing-Yao; Li, Ze-Sheng; Sun, Chia-Chung

2005-01-30

The mechanisms of the SH (SD) radicals with Cl2 (R1), Br2 (R2), and BrCl (R3) are investigated theoretically, and the rate constants are calculated using a dual-level direct dynamics method. The optimized geometries and frequencies of the stationary points are calculated at the MP2/6-311G(d,p) and MPW1K/6-311G(d,p) levels. Higher-level energies are obtained at the approximate QCISD(T)/6-311++G(3df, 2pd) level using the MP2 geometries as well as by the multicoefficient correlation method based on QCISD (MC-QCISD) using the MPW1K geometries. Complexes with energies less than those of the reactants or products are located at the entrance or the exit channels of these reactions, which indicate that the reactions may proceed via an indirect mechanism. The enthalpies of formation for the species XSH/XSD (X = Cl and Br) are evaluated using hydrogenation working reactions method. By canonical variational transition-state theory (CVT), the rate constants of SH and SD radicals with Cl2, Br2, and BrCl are calculated over a wide temperature range of 200-2000 K at the a-QCISD(T)/6-311++G(3df, 2pd)//MP2/6-311G(d, p) level. Good agreement between the calculated and experimental rate constants is obtained in the measured temperature range. Our calculations show that for SH (SD) + BrCl reaction bromine abstraction (R3a or R3a') leading to the formation of BrSH (BrSD) + Cl in a barrierless process dominants the reaction with the branching ratios for channels 3a and 3a' of 99% at 298 K, which is quite different from the experimental result of k3a'/k3' = 54 +/- 10%. Negative activation energies are found at the higher level for the SH + Br2 and SH + BrCl (Br-abstraction) reactions; as a result, the rate constants show a slightly negative temperature dependence, which is consistent with the determination in the literature. The kinetic isotope effects for the three reactions are "inverse". The values of kH/kD are 0.88, 0.91, and 0.69 at room temperature, respectively, and they increase

Site-Specific Rate Constant Measurements for Primary and Secondary H- and D-Abstraction by OH Radicals: Propane and n -Butane

KAUST Repository

Badra, Jihad

2014-07-03

Site-specific rate constants for hydrogen (H) and deuterium (D) abstraction by hydroxyl (OH) radicals were determined experimentally by monitoring the reaction of OH with two normal and six deuterated alkanes. The studied alkanes include propane (C3H8), propane 2,2 D2 (CH 3CD2CH3), propane 1,1,1-3,3,3 D6 (CD 3CH2CD3), propane D8 (C3D 8), n-butane (n-C4H10), butane 2,2-3,3 D4 (CH3CD2CD2CH3), butane 1,1,1-4,4,4 D6 (CD3CH2CH2CD3), and butane D10 (C4D10). Rate constant measurements were carried out over 840-1470 K and 1.2-2.1 atm using a shock tube and OH laser absorption. Previous low-temperature data were combined with the current high-temperature measurements to generate three-parameter fits which were then used to determine the site-specific rate constants. Two primary (P1,H and P 1,D) and four secondary (S00,H, S00,D, S 01,H, and S01,D) H- and D-abstraction rate constants, in which the subscripts refer to the number of C atoms connected to the next-nearest-neighbor C atom, are obtained. The modified Arrhenius expressions for the six site-specific abstractions by OH radicals are P1,H = 1.90 × 10-18T2.00 exp(-340.87 K/T) cm 3molecule-1s-1 (210-1294 K); P1,D= 2.72 × 10-17 T1.60 exp(-895.57 K/T) cm 3molecule-1s-1 (295-1317 K); S00,H = 4.40 × 10-18 T1.93 exp(121.50 K/T) cm 3molecule-1s-1 (210-1294 K); S00,D = 1.45 × 10-20 T2.69 exp(282.36 K/T) cm 3molecule-1s-1 (295-1341 K); S01,H = 4.65 × 10-17 T1.60 exp(-236.98 K/T) cm 3molecule-1s-1 (235-1407 K); S01,D = 1.26 × 10-18 T2.07 exp(-77.00 K/T) cm 3molecule-1s-1 (294-1412 K). © 2014 American Chemical Society.

Kinetic Analysis of the Uptake and Release of Fluorescein by Metal-Organic Framework Nanoparticles

Directory of Open Access Journals (Sweden)

Tobias Preiß

2017-02-01

Full Text Available Metal-organic framework nanoparticles (MOF NPs are promising guest-host materials with applications in separation, storage, catalysis, and drug delivery. However, on- and off-loading of guest molecules by porous MOF nanostructures are still poorly understood. Here we study uptake and release of fluorescein by two representative MOF NPs, MIL-100(Fe and MIL-101(Cr. Suspensions of these MOF NPs exhibit well-defined size distributions and crystallinity, as verified by electron microscopy, dynamic light scattering, and X-ray diffraction. Using absorbance spectroscopy the equilibrium dissociation constants and maximum numbers of adsorbed fluorescein molecules per NP were determined. Time-resolved fluorescence studies reveal that rates of release and loading are pH dependent. The kinetics observed are compared to theoretical estimates that account for bulk diffusion into NPs, and retarded internal diffusion and adsorption rates. Our study shows that, rather than being simple volumetric carriers, MOF-NPs are dominated by internal surface properties. The findings will help to optimize payload levels and develop release strategies that exploit varying pH for drug delivery.

WATER HYACINTH: A POSSIBLE ALTERNATIVE RATE RETARDING NATURAL POLYMER USED IN SUSTAINED RELEASE TABLET DESIGN

Directory of Open Access Journals (Sweden)

Sabera eKhatun

2014-06-01

Full Text Available In recent years natural polymers have been widely used, because of their effectiveness and availability over synthetic polymers. In this present investigation matrix tablets of Metformin hydrochloride were formulated using Water hyacinth powder and its rate retardant activity was studied. Tablets were prepared using wet granulation method with 8% starch as granulating agent and 5%, 10%, 15%, 20%, 25% and 30% of Water hyacinth powder to the drug. In preformulation study, angle of repose, Carr’s Index and Hausner ratio were calculated. Fourier Transform Infrared Spectroscopy (FTIR, Differential Scanning Calorimetry (DSC and Scanning Electron Microscopy (SEM studies were performed and no interactions were found between drug and excipients. Weight variation, friability, hardness, thickness, diameter, and in vitro release study were performed with the prepared matrix tablets. Dissolution studies were conducted using USP type II apparatus at a speed of 100 rpm at 37oC ± 0.5 temperature, for 8 hours. All the formulations comply with both BP and USP requirements, but among all the formulations F-1 (5% of Water hyacinth was the best fitted formula. The drug release patterns were explained in different kinetic models such as Zero order, First order, Higuchi, Hixson Crowell and Korsmeyer-Peppas equations. The current investigation implies that Water hyacinth has the potential to be used as a rate-retarding agent in sustained release drug formulations.

Water hyacinth: a possible alternative rate retarding natural polymer used in sustained release tablet design.

Science.gov (United States)

Khatun, Sabera; Sutradhar, Kumar B

2014-01-01

In recent years natural polymers have been widely used because of their effectiveness and availability over synthetic polymers. In this present investigation matrix tablets of Metformin hydrochloride were formulated using Water hyacinth powder and its rate retardant activity was studied. Tablets were prepared using wet granulation method with 8% starch as granulating agent and 5, 10, 15, 20, 25 and 30% of Water hyacinth powder to the drug. In preformulation study, angle of repose, Carr's Index and Hausner ratio were calculated. Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), and Scanning Electron Microscopy (SEM) studies were performed and no interactions were found between drug and excipients. Weight variation, friability, hardness, thickness, diameter, and in vitro release study were performed with the prepared matrix tablets. Dissolution studies were conducted using USP type II apparatus at a speed of 100 rpm at 37°C ± 0.5 temperature for 8 h. Though all the formulations comply with both BP and USP requirements, formulation F-1 (5% of Water hyacinth) was the best fitted formula. The drug release patterns were explained in different kinetic models such as Zero order, First order, Higuchi, Hixson Crowell, and Korsmeyer-Peppas equations. The current investigation implies that Water hyacinth has the potential to be used as a rate-retarding agent in sustained release drug formulations.

Surface hopping, transition state theory, and decoherence. II. Thermal rate constants and detailed balance

Energy Technology Data Exchange (ETDEWEB)

Jain, Amber; Subotnik, Joseph E., E-mail: subotnik@sas.upenn.edu [Department of Chemistry, University of Pennsylvania, 231 South 34th Street, Philadelphia, Pennsylvania 19104 (United States)

2015-10-07

We investigate a simple approach to compute a non-adiabatic thermal rate constant using the fewest switches surface hopping (FSSH) dynamics. We study the effects of both decoherence (using our augmented-FSSH (A-FSSH) algorithm) and forbidden hops over a large range of parameters, including high and low friction regimes, and weak and strong electronic coupling regimes. Furthermore, when possible, we benchmark our results against exact hierarchy equations of motion results, where we usually find a maximum error of roughly a factor of two (at reasonably large temperatures). In agreement with Hammes-Schiffer and Tully, we find that a merger of transition state theory and surface hopping can be both accurate and efficient when performed correctly. We further show that detailed balance is followed approximately by A-FSSH dynamics.

Maximum permissible continuous release rates of phosphorus-32 and sulphur-35 to atmosphere in a milk producing area

Energy Technology Data Exchange (ETDEWEB)

Bryant, P M

1963-01-01

A method is given for calculating, for design purposes, the maximum permissible continuous release rates of phosphorus-32 and sulphur-35 to atmosphere with respect to milk contamination. In the absence of authoritative advice from the Medical Research Council, provisional working levels for the concentration of phosphorus-32 and sulphur-35 in milk are derived, and details are given of the agricultural assumptions involved in the calculation of the relationship between the amount of the nuclide deposited on grassland and that to be found in milk. The agricultural and meteorological conditions assumed are applicable as an annual average to England and Wales. The results (in mc/day) for phosphorus-32 and sulphur-35 for a number of stack heights and distances are shown graphically; typical values, quoted in a table, include 20 mc/day of phosphorus-32 and 30 mc/day of sulfur-35 as the maximum permissible continuous release rates with respect to ground level releases at a distance of 200 metres from pastureland.

Rates and equilibrium constants of the ligand-induced conformational transition of an HCN ion channel protein domain determined by DEER spectroscopy.

Science.gov (United States)

Collauto, Alberto; DeBerg, Hannah A; Kaufmann, Royi; Zagotta, William N; Stoll, Stefan; Goldfarb, Daniella

2017-06-14

Ligand binding can induce significant conformational changes in proteins. The mechanism of this process couples equilibria associated with the ligand binding event and the conformational change. Here we show that by combining the application of W-band double electron-electron resonance (DEER) spectroscopy with microfluidic rapid freeze quench (μRFQ) it is possible to resolve these processes and obtain both equilibrium constants and reaction rates. We studied the conformational transition of the nitroxide labeled, isolated carboxy-terminal cyclic-nucleotide binding domain (CNBD) of the HCN2 ion channel upon binding of the ligand 3',5'-cyclic adenosine monophosphate (cAMP). Using model-based global analysis, the time-resolved data of the μRFQ DEER experiments directly provide fractional populations of the open and closed conformations as a function of time. We modeled the ligand-induced conformational change in the protein using a four-state model: apo/open (AO), apo/closed (AC), bound/open (BO), bound/closed (BC). These species interconvert according to AC + L ⇌ AO + L ⇌ BO ⇌ BC. By analyzing the concentration dependence of the relative contributions of the closed and open conformations at equilibrium, we estimated the equilibrium constants for the two conformational equilibria and the open-state ligand dissociation constant. Analysis of the time-resolved μRFQ DEER data gave estimates for the intrinsic rates of ligand binding and unbinding as well as the rates of the conformational change. This demonstrates that DEER can quantitatively resolve both the thermodynamics and the kinetics of ligand binding and the associated conformational change.

A constant velocity Moessbauer spectrometer free of long-term instrumental drifts in the count rate

International Nuclear Information System (INIS)

Sarma, P.R.; Sharma, A.K.; Tripathi, K.C.

1979-01-01

Two new control circuits to be used with a constant velocity Moessbauer spectrometer with a loud-speaker drive have been described. The wave-forms generated in the circuits are of the stair-case type instead of the usual square wave-form, so that in each oscillation of the source it remains stationary for a fraction of the time-period. The gamma-rays counted during this period are monitored along with the positive and negative velocity counts and are used to correct any fluctuation in the count rate by feeding these pulses into the timer. The associated logic circuits have been described and the statistical errors involved in the circuits have been computed. (auth.)

A survey of the reaction rate constants for the thermal dissociation and recombination of nitrogen and oxygen

Science.gov (United States)

Marraffa, Lionel; Dulikravich, George S.; Keeney, Timothy C.; Deiwert, George S.

1988-01-01

The objective of the present report is to survey the various values of forward and backward reaction rate constants used by investigators in the field of high-temperature (T greater than 2000 K) gas reactions involving nitrogen and oxygen only. The objective is to find those values that correlate well so that they can be used for the studies of hypersonic flow and supersonic combustion with reasonable confidence. Relatively good agreement among these various values is observed for temperatures lower than 10,000 K.

Fine-structure constant: Is it really a constant

International Nuclear Information System (INIS)

Bekenstein, J.D.

1982-01-01

It is often claimed that the fine-structure ''constant'' α is shown to be strictly constant in time by a variety of astronomical and geophysical results. These constrain its fractional rate of change alpha-dot/α to at least some orders of magnitude below the Hubble rate H 0 . We argue that the conclusion is not as straightforward as claimed since there are good physical reasons to expect alpha-dot/α 0 . We propose to decide the issue by constructing a framework for a variability based on very general assumptions: covariance, gauge invariance, causality, and time-reversal invariance of electromagnetism, as well as the idea that the Planck-Wheeler length (10 -33 cm) is the shortest scale allowable in any theory. The framework endows α with well-defined dynamics, and entails a modification of Maxwell electrodynamics. It proves very difficult to rule it out with purely electromagnetic experiments. In a cosmological setting, the framework predicts an alpha-dot/α which can be compatible with the astronomical constraints; hence, these are too insensitive to rule out α variability. There is marginal conflict with the geophysical constraints: however, no firm decision is possible because of uncertainty about various cosmological parameters. By contrast the framework's predictions for spatial gradients of α are in fatal conflict with the results of the Eoetvoes-Dicke-Braginsky experiments. Hence these tests of the equivalence principle rule out with confidence spacetime variability of α at any level

Temperature dependence of the rate constant for reactions of hydrated electrons with H, OH and H2O2

DEFF Research Database (Denmark)

Christensen, H.; Sehested, K.; Løgager, T.

1994-01-01

The temperature dependence of the rate constants, for the reactions of hydrated electrons with H atoms, OH radicals and H2O2 has been determined. The reaction with H atoms, studied in the temperature range 20-250-degrees-C gives k(20-degrees-C) = 2.4 x 10(10) M-1 s-1 and the activation energy E......-1 and E(A) = 15.6 kJ mol-1 (3.7 kcal mol-1) measured from 5-150-degrees-C. Thus, the activation energy for all three fast reactions is close to that expected for diffusion controlled reactions. As phosphates were used as buffer system, the rate constant and activation energy for the reaction......(A) = 14.0 kJ mol-1 (3.3 kcal mol-1). For reaction with OH radicals the corresponding values are, k(20-degrees-C) = 3.1 x 10(10) M-1 s-1 and E(A) = 14.7 kJ mol-1 (3.5 kcal mol-1) determined in the temperature range 5-175-degrees-C. For reaction with H2O2 the values are, k(20-degrees-C) = 1.2 x 10(10) M-1 s...

New perspectives on constant-roll inflation

Science.gov (United States)

Cicciarella, Francesco; Mabillard, Joel; Pieroni, Mauro

2018-01-01

We study constant-roll inflation using the β-function formalism. We show that the constant rate of the inflaton roll is translated into a first order differential equation for the β-function which can be solved easily. The solutions to this equation correspond to the usual constant-roll models. We then construct, by perturbing these exact solutions, more general classes of models that satisfy the constant-roll equation asymptotically. In the case of an asymptotic power law solution, these corrections naturally provide an end to the inflationary phase. Interestingly, while from a theoretical point of view (in particular in terms of the holographic interpretation) these models are intrinsically different from standard slow-roll inflation, they may have phenomenological predictions in good agreement with present cosmological data.

Comparison of the rate constants for energy transfer in the light-harvesting protein, C-phycocyanin, calculated from Foerster`s theory and experimentally measured by time-resolved fluorescence spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Debreczeny, Martin Paul [Univ. of California, Berkeley, CA (United States)

1994-05-01

We have measured and assigned rate constants for energy transfer between chromophores in the light-harvesting protein C-phycocyanin (PC), in the monomeric and trimeric aggregation states, isolated from Synechococcus sp. PCC 7002. In order to compare the measured rate constants with those predicted by Fdrster`s theory of inductive resonance in the weak coupling limit, we have experimentally resolved several properties of the three chromophore types ({beta}{sub 155} {alpha}{sub 84}, {beta}{sub 84}) found in PC monomers, including absorption and fluorescence spectra, extinction coefficients, fluorescence quantum yields, and fluorescence lifetimes. The cpcB/C155S mutant, whose PC is missing the {beta}{sub 155} chromophore, was, useful in effecting the resolution of the chromophore properties and in assigning the experimentally observed rate constants for energy transfer to specific pathways.

Absolute rate constants for the reaction of NO₃ radicals with a series of dienes at 295 K

DEFF Research Database (Denmark)

Ellermann, T.; Nielsen, O.J.; Skov, H.

1992-01-01

The rate constants for the reaction of NO3 radicals with a series of 7 dienes, 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, trans-1,3-pentadiene, cis-1,3-pentadiene, trans,trans-2,4-hexadiene, and 1,3-cyclohexadiene, were measured at 295 K and at a total pressure of 1 atm. The rate consta...... were obtained using the absolute technique of pulse radiolysis combined with kinetic UV-VIS spectroscopy. The results are discussed in terms of reactivity trends and previous literature data....

Constant mortality and fertility over age in Hydra

DEFF Research Database (Denmark)

Schaible, R.; Scheuerlein, A.; Danko, M. J.

2015-01-01

that 2,256 Hydra from two closely related species in two laboratories in 12 cohorts, with cohort age ranging from 0 to more than 41 y, have extremely low, constant rates of mortality. Fertility rates for Hydra did not systematically decline with advancing age. This falsifies the universality......Senescence, the increase in mortality and decline in fertility with age after maturity, was thought to be inevitable for all multicellular species capable of repeated breeding. Recent theoretical advances and compilations of data suggest that mortality and fertility trajectories can go up or down......, or remain constant with age, but the data are scanty and problematic. Here, we present compelling evidence for constant age-specific death and reproduction rates in Hydra, a basal metazoan, in a set of experiments comprising more than 3.9 million days of observations of individual Hydra. Our data show...

USING IN VIVO GAS UPDATE STUDIES TO ESTIMATE METABOLIC RATE CONSTANTS FOR CCL CHEMICALS: 1,1-DICHLOROPROPANE AND 2,2-DICHLOROPROPANE

Science.gov (United States)

USING IN VIVO GAS UPTAKE STUDIES TO ESTIMATE METABOLIC RATE CONSTANTS FOR CCL CHEMICALS: 1,1-DICHLOROPROPENE AND 2,2-DICHLOROPROPANE. Mitchell, C T, Evans, M V, Kenyon, E M. NHEERL, U.S. EPA, ORD, ETD, RTP, NC The Safe Drinking Water Act Amendments of 1996 required ...

The influence of Metolose structure on the free volume and the consequent metoprolol tartrate release of patches.

Science.gov (United States)

Papp, József; Marton, Sylvia; Süvegh, Károly; Zelkó, Romána

2009-01-01

Matrix-type patches containing Metoprolol tartrate were prepared from two types of Metolose and acrylate polymers. Metolose SM 4000 and Metolose 90SH 100.000SR were applied in different proportions in the patches where the total polymer content was kept constant in each sample. The purpose of the study was to investigate the effect of Metolose structure on the free volume of the patches and the consequent drug release profile. The drug release profiles were characterized by zero-order and first-order models. The results indicate that Metolose, containing hydroxypropyl ether groups and methyl ether groups, enables the formation of H-bonds, thus increasing the free volume holes and the consequent extent and rate of drug release of patches.

Direct Dynamics Simulation of the Thermal 3CH2 + 3O2 Reaction. Rate Constant and Product Branching Ratios.

Science.gov (United States)

Lakshmanan, Sandhiya; Pratihar, Subha; Machado, Francisco Bolivar Correto; Hase, William Louis

2018-04-26

The reaction of 3CH2 with 3O2 is of fundamental importance in combustion and the reaction is complex as a result of multiple extremely exothermic product channels. In the present study, direct dynamics simulations were performed to study the reaction on both the singlet and triplet potential energy surfaces (PESs). The simulations were performed at the UM06/6-311++G(d,p) level of theory. Trajectories were calculated at a temperature of 300 K and all reactive trajectories proceeded through the carbonyl oxide Criegee intermediate, CH2OO, on both the singlet and triplet PESs. The triplet surface leads to only one product channel, H2CO + O(3P), while the singlet surface leads to 8 product channels with their relative importance as: CO + H2O > CO + OH + H ~ H2CO + O(1D) > HCO + OH ~ CO2 + H2 ~ CO + H2 + O(1D) > CO2 + H + H > HCO + O(1D) + H. Reaction on the singlet PES is barrierless, consistent with experiment and the total rate constant on the singlet surface is 0.93 ± 0.22 x 10-12 cm3molecule-1s-1 in comparison to the recommended experimental rate constant of 3.3 x 10-12 cm3molecule-1s-1. The simulation product yields for the singlet PES are compared with experiment and the most significant differences are for H, CO2, and H2O. Reaction on the triplet surface is also barrierless, inconsistent with experiment. A discussion is given of the need for future calculations to address the: (1) barrier on the triplet PES for 3CH2 + 3O2 → 3CH2OO; (2) temperature dependence of the 3CH2 + 3O2 reaction rate constant and product branching ratios; and (3) possible non-RRKM dynamics of the 1CH2OO Criegee intermediate.

Sustained release of radioprotective agents

International Nuclear Information System (INIS)

Shani, J.

1980-11-01

New pharmaceutical formulations for the sustained release into the G.I. tract of radioprotective agents have been developed by the authors. The experimental method initially consisted in the production of methylcellulose microcapsules. This method failed apparently because of the premature ''explosion'' of the microcapsules and the consequent premature release of massive amounts of the drug. A new method has been developed which consists in drying and pulverising cysteamine and cysteine preparations, mixing them in various proportions with stearic acid and ethylcellulose as carriers. The mixture is then compressed into cylindrical tablets at several pressure values and the leaching rate of the radioprotective agents is then measured by spectrophotometry. The relation between the concentration of the active drug and its rate of release, and the effect on the release rate of the pressure applied to the tablet during its formation were also investigated. Results indicating that the release rate was linearly related to the square root of ''t'' seem to be in agreement with what is predictable, according to Higuchi's equation, save for the very initial and terminal phases. A clear correlation was also established between the stearic acid/ethylcellulose ratios and the release of 20% cysteine, namely a marked decrease in the rate of cysteine release was observed with increasing concentrations of stearic acid. Finally, it was observed that a higher formation pressure results in quicker release of the drug

Structural and functional analysis of a FeoB A143S G5 loop mutant explains the accelerated GDP release rate.

Science.gov (United States)

Guilfoyle, Amy P; Deshpande, Chandrika N; Vincent, Kimberley; Pedroso, Marcelo M; Schenk, Gerhard; Maher, Megan J; Jormakka, Mika

2014-05-01

GTPases (G proteins) hydrolyze the conversion of GTP to GDP and free phosphate, comprising an integral part of prokaryotic and eukaryotic signaling, protein biosynthesis and cell division, as well as membrane transport processes. The G protein cycle is brought to a halt after GTP hydrolysis, and requires the release of GDP before a new cycle can be initiated. For eukaryotic heterotrimeric Gαβγ proteins, the interaction with a membrane-bound G protein-coupled receptor catalyzes the release of GDP from the Gα subunit. Structural and functional studies have implicated one of the nucleotide binding sequence motifs, the G5 motif, as playing an integral part in this release mechanism. Indeed, a Gαs G5 mutant (A366S) was shown to have an accelerated GDP release rate, mimicking a G protein-coupled receptor catalyzed release state. In the present study, we investigate the role of the equivalent residue in the G5 motif (residue A143) in the prokaryotic membrane protein FeoB from Streptococcus thermophilus, which includes an N-terminal soluble G protein domain. The structure of this domain has previously been determined in the apo and GDP-bound states and in the presence of a transition state analogue, revealing conformational changes in the G5 motif. The A143 residue was mutated to a serine and analyzed with respect to changes in GTPase activity, nucleotide release rate, GDP affinity and structural alterations. We conclude that the identity of the residue at this position in the G5 loop plays a key role in the nucleotide release rate by allowing the correct positioning and hydrogen bonding of the nucleotide base. © 2014 FEBS.

Mineralization Rate Constants, Half-Lives and Effects of Two Organic

African Journals Online (AJOL)

INTRODUCTION. Low soil fertility is one the ... important for maintenance of fertility of tropical soils. ... soil N. Thus, total N in the soil and the amount released for plant uptake depend on its content of organic ... capacity for productivity, nutrient cycling, filtering and buffering ... (Steel and Torrie, 1981) and, thereafter, Fischer's.

Joint release rate estimation and measurement-by-measurement model correction for atmospheric radionuclide emission in nuclear accidents: An application to wind tunnel experiments.

Science.gov (United States)

Li, Xinpeng; Li, Hong; Liu, Yun; Xiong, Wei; Fang, Sheng

2018-03-05

The release rate of atmospheric radionuclide emissions is a critical factor in the emergency response to nuclear accidents. However, there are unavoidable biases in radionuclide transport models, leading to inaccurate estimates. In this study, a method that simultaneously corrects these biases and estimates the release rate is developed. Our approach provides a more complete measurement-by-measurement correction of the biases with a coefficient matrix that considers both deterministic and stochastic deviations. This matrix and the release rate are jointly solved by the alternating minimization algorithm. The proposed method is generic because it does not rely on specific features of transport models or scenarios. It is validated against wind tunnel experiments that simulate accidental releases in a heterogonous and densely built nuclear power plant site. The sensitivities to the position, number, and quality of measurements and extendibility of the method are also investigated. The results demonstrate that this method effectively corrects the model biases, and therefore outperforms Tikhonov's method in both release rate estimation and model prediction. The proposed approach is robust to uncertainties and extendible with various center estimators, thus providing a flexible framework for robust source inversion in real accidents, even if large uncertainties exist in multiple factors. Copyright © 2017 Elsevier B.V. All rights reserved.

Influence of the ionic character of a drug on its release rate from hydrogels based on 2-hydroxyethylmethacrylate and acrylamide synthesized by photopolymerization

Directory of Open Access Journals (Sweden)

M. L. Gomez

2012-03-01

Full Text Available The influence of the ionic character of a specific drug on its release rate from a hydrogel based on 2-hydroxyethylmethacrylate (HEMA and acrylamide (AAm is analyzed. The hydrogel was synthesized by photopolymerization employing visible light, safranine O (Saf, as sensitizer, and a silsesquioxane functionalized with amine and methacrylate groups (SFMA, as co-initiator and crosslinker. Safranine O (Saf was employed as a model of a cationic drug and the anionic form of resorufin (Rf as a model of an anionic drug. Saf exhibited a larger affinity with functional groups of the hydrogel than that of Rf. This produced a lower loading and a faster release rate of Rf with respect to Saf. Besides, the release rate of Rf followed a Fickian behavior, while that of Saf exhibited a non-Fickian behavior. By hydrolyzing the hydrogel at pH = 13, amide groups supplied by AAm were irreversibly converted into carboxylic acid groups. Higher loadings and slower release rates of Saf from the hydrolyzed hydrogels were observed, making them particularly suitable for the slow drug-delivery of cationic drugs.

Atmospheric dispersion of radionuclides released by a nuclear plant

International Nuclear Information System (INIS)

Barboza, A.A.

1989-01-01

A numerical model has been developed to simulate the atmospheric dispersion of radionuclides released by a nuclear plant operating under normal conditions. The model, based on gaussian plume representation, accouts for and evaluates several factors which affect the concentraction of effluents in the atmosphere, such as: ressuspension, deposition, radioactive decay, energy and type of the radiation emitted, among others. The concentraction of effluents in the atmosphere is calculated for a uniform mesh of points around the plant, allowing the equivalent doses to be then evaluated. Simulations of the atmosphere dispersion of radioactive plumes of Cs 137 and Ar 41 have been performed assuming a constant rate of release, as expected from the normal operation of a nuclear plant. Finally, this work analyzes the equivalent doses at ground level due to the dispersion of Cs 137 and Ar 41 , accumulated over one year and determines the isodose curves for a hypothetical site. (author) [pt

Release rates of Al from inorganic and organic compounds in a sandy podzol, during laboratory experiments

NARCIS (Netherlands)

Salm, van der C.; Westerveld, J.W.; Verstraten, J.M.

2000-01-01

Research with respect to release rates of Al and Al concentrations in the soil solution has led to two contrasting hypotheses, stressing either the importance of kinetically constrained dissolution reactions or the role of complexation of Al to soil organic matter. The existence of two contrasting

Electrochemical examination of ability of dsDNA/PAM composites for storing and releasing of doxorubicin.

Science.gov (United States)

Zabost, Ewelina; Liwinska, Wioletta; Karbarz, Marcin; Kurek, Eliza; Lyp, Marek; Donten, Mikolaj; Stojek, Zbigniew

2016-06-01

Composites consisting of ss- and ds-DNA strands and polyacrylamide (PAM) hydrogel have been synthesized. DNA was entrapped non-covalently. The obtained DNA biomaterial exhibited a strong increase in guanine and adenine anodic currents when temperature reached the physiological level. This increase was related to the unique oligonucleotide structural changes in the composite. The structural alterations in the PAM lattices were employed for the release of the drug accumulated in the composite. Doxorubicin (Dox) was selected as the drug; it was accumulated by intercalation to dsDNA and was slowly released from the dsDNA/PAM system by using a minor temperature increase (up to 40÷45 °C) as it is routinely done in hyperthermia. The applied release temperature was either constant or oscillating. The binding strength, the rate of Dox release and the properties of the composite were examined using voltammetry, SEM and ICP-MS. Copyright © 2015 Elsevier B.V. All rights reserved.

Consideration of demand rate in overall equipment effetiveness (OEE on equipment with constant process time

Directory of Open Access Journals (Sweden)

Perumal Puvanasvaran

2013-06-01

research should be conducted to test the possibility and to verify the definition of such performance ratio including Takt time on those processes of which its operating time is possibly to be reduced, especially those are not constant and fixed. This piece of research is temporarily done on the process where its operating time is constant from time to time and there is no ideal cycle time possible.Practical implications: The awareness of the overproduction should be emphasized and raised in the intention of pursuing higher OEE value. As the definition proposed such, the process with constant cycle time could even be defined in different performance ratio from time to time regarding to the customer demands and corresponding production rate. These two variables can be adjusted and balanced to increase the OEE value through optimization of average cycle time. Over this, optimization of average cycle time on equipment with constant operating time can be achieved through the optimization of loading number per each processing.Originality/value: The novelty of the paper is the inclusion of customer demand in obtaining OEE value of any particular equipment. Besides that, the equipment without ideal cycle time, which means those processes carried out in constant cycle time are possibly to be evaluated with performance ratio. As consequence of that, the machine utilization and capability used could be quantified and visualized using the performance ratio data of the OEE proposed.

The WiggleZ Dark Energy Survey: constraining the evolution of Newton's constant using the growth rate of structure

International Nuclear Information System (INIS)

Nesseris, Savvas; Blake, Chris; Davis, Tamara; Parkinson, David

2011-01-01

We constrain the evolution of Newton's constant using the growth rate of large-scale structure measured by the WiggleZ Dark Energy Survey in the redshift range 0.1 m (assuming General Relativity), and use this to construct a diagnostic to detect the presence of an evolving Newton's constant. Secondly we directly measure the evolution of Newton's constant, G eff , that appears in Modified Gravity theories, without assuming General Relativity to be true. The novelty of these approaches are that, contrary to other methods, they do not require knowledge of the expansion history of the Universe, H(z), making them model independent tests. Our constraints for the second derivative of Newton's constant at the present day, assuming it is slowly evolving as suggested by Big Bang Nucleosynthesis constraints, using the WiggleZ data is G double-dot eff (t 0 ) = −1.19 ± 0.95·10 −20 h 2 yr −2 , where h is defined via H 0 = 100 h km s −1 Mpc −1 , while using both the WiggleZ and the Sloan Digital Sky Survey Luminous Red Galaxy (SDSS LRG) data is G double-dot eff (t 0 ) = −3.6 ± 6.8·10 −21 h 2 yr −2 , both being consistent with General Relativity. Finally, our constraint for the rms mass fluctuation σ 8 using the WiggleZ data is σ 8 = 0.75 ± 0.08, while using both the WiggleZ and the SDSS LRG data σ 8 = 0.77 ± 0.07, both in good agreement with the latest measurements from the Cosmic Microwave Background radiation

Enhancement of flame development by microwave-assisted spark ignition in constant volume combustion chamber

KAUST Repository

Wolk, Benjamin

2013-07-01

The enhancement of laminar flame development using microwave-assisted spark ignition has been investigated for methane-air mixtures at a range of initial pressures and equivalence ratios in a 1.45. l constant volume combustion chamber. Microwave enhancement was evaluated on the basis of several parameters including flame development time (FDT) (time for 0-10% of total net heat release), flame rise time (FRT) (time for 10-90% of total net heat release), total net heat release, flame kernel growth rate, flame kernel size, and ignitability limit extension. Compared to a capacitive discharge spark, microwave-assisted spark ignition extended the lean and rich ignition limits at all pressures investigated (1.08-7.22. bar). The addition of microwaves to a capacitive discharge spark reduced FDT and increased the flame kernel size for all equivalence ratios tested and resulted in increases in the spatial flame speed for sufficiently lean flames. Flame enhancement is believed to be caused by (1) a non-thermal chemical kinetic enhancement from energy deposition to free electrons in the flame front and (2) induced flame wrinkling from excitation of flame (plasma) instability. The enhancement of flame development by microwaves diminishes as the initial pressure of the mixture increases, with negligible flame enhancement observed above 3. bar. © 2013 The Combustion Institute.

Constant strain rate experiments and constitutive modeling for a class of bitumen

Science.gov (United States)

Reddy, Kommidi Santosh; Umakanthan, S.; Krishnan, J. Murali

2012-08-01

The mechanical properties of bitumen vary with the nature of the crude source and the processing methods employed. To understand the role of the processing conditions played in the mechanical properties, bitumen samples derived from the same crude source but processed differently (blown and blended) are investigated. The samples are subjected to constant strain rate experiments in a parallel plate rheometer. The torque applied to realize the prescribed angular velocity for the top plate and the normal force applied to maintain the gap between the top and bottom plate are measured. It is found that when the top plate is held stationary, the time taken by the torque to be reduced by a certain percentage of its maximum value is different from the time taken by the normal force to decrease by the same percentage of its maximum value. Further, the time at which the maximum torque occurs is different from the time at which the maximum normal force occurs. Since the existing constitutive relations for bitumen cannot capture the difference in the relaxation times for the torque and normal force, a new rate type constitutive model, incorporating this response, is proposed. Although the blended and blown bitumen samples used in this study correspond to the same grade, the mechanical responses of the two samples are not the same. This is also reflected in the difference in the values of the material parameters in the model proposed. The differences in the mechanical properties between the differently processed bitumen samples increase further with aging. This has implications for the long-term performance of the pavement.

Modeling the downward transport of {sup 210}Pb in Peatlands: Initial Penetration‐Constant Rate of Supply (IP-CRS) model

Energy Technology Data Exchange (ETDEWEB)

Olid, Carolina, E-mail: olid.carolina@gmail.com [Department of Ecology and Environmental Science, Umeå University, SE-90187, Umeå (Sweden); Diego, David [Department of Earth Science, University of Bergen, NO-5020 Bergen (Norway); Garcia-Orellana, Jordi [Departament de Física, Universitat Autònoma de Barcelona, E-08193 Bellaterra (Spain); Institut de Ciència i Tecnologia Ambientals (ICTA), Universitat Autònoma de Barcelona, E-08193 Bellaterra (Spain); Cortizas, Antonio Martínez [Departamento de Edafoloxía e Química Agrícola, Universidade de Santiago de Compostela, E-15782 Santiago de Compostela (Spain); Klaminder, Jonatan [Department of Ecology and Environmental Science, Umeå University, SE-90187, Umeå (Sweden)

2016-01-15

The vertical distribution of {sup 210}Pb is commonly used to date peat deposits accumulated over the last 100–150 years. However, several studies have questioned this method because of an apparent post-depositional mobility of {sup 210}Pb within some peat profiles. In this study, we introduce the Initial Penetration–Constant Rate of Supply (IP-CRS) model for calculating ages derived from {sup 210}Pb profiles that are altered by an initial migration of the radionuclide. This new, two-phased, model describes the distribution of atmospheric-derived {sup 210}Pb ({sup 210}Pb{sub xs}) in peat taking into account both incorporation of {sup 210}Pb into the accumulating peat matrix as well as an initial flushing of {sup 210}Pb through the uppermost peat layers. The validity of the IP-CRS model is tested in four anomalous {sup 210}Pb peat records that showed some deviations from the typical exponential decay profile not explained by variations in peat accumulation rates. Unlike the most commonly used {sup 210}Pb-dating model (Constant Rate of Supply (CRS)), the IP-CRS model estimates peat accumulation rates consistent with typical growth rates for peatlands from the same areas. Confidence in the IP-CRS chronology is also provided by the good agreement with independent chronological markers (i.e. {sup 241}Am and {sup 137}Cs). Our results showed that the IP-CRS can provide chronologies from peat records where {sup 210}Pb mobility is evident, being a valuable tool for studies reconstructing past environmental changes using peat archives during the Anthropocene. - Highlights: • Accurate age dating of peat and sediment cores is critical for evaluating change. • A new {sup 210}Pb dating model that includes vertical transport of {sup 210}Pb was developed. • The IP-CRS model provided consistent peat accumulation rates. • The IP-CRS ages were consistent with independent chronological markers. • The IP-CRS model derives peat ages where downward {sup 210}Pb transport is

A Simulation Analysis of Errors in the Measurement of Standard Electrochemical Rate Constants from Phase-Selective Impedance Data.

Science.gov (United States)

1987-09-30

RESTRICTIVE MARKINGSC Unclassif ied 2a SECURIly CLASSIFICATION ALIIMOA4TY 3 DIS1RSBj~jiOAVAILAB.I1Y OF RkPORI _________________________________ Approved...of the AC current, including the time dependence at a growing DME, at a given fixed potential either in the presence or the absence of an...the relative error in k b(app) is ob relatively small for ks (true) : 0.5 cm s-, and increases rapidly for ob larger rate constants as kob reaches the

Multiscale approach to link red blood cell dynamics, shear viscosity, and ATP release.

Science.gov (United States)

Forsyth, Alison M; Wan, Jiandi; Owrutsky, Philip D; Abkarian, Manouk; Stone, Howard A

2011-07-05

RBCs are known to release ATP, which acts as a signaling molecule to cause dilation of blood vessels. A reduction in the release of ATP from RBCs has been linked to diseases such as type II diabetes and cystic fibrosis. Furthermore, reduced deformation of RBCs has been correlated with myocardial infarction and coronary heart disease. Because ATP release has been linked to cell deformation, we undertook a multiscale approach to understand the links between single RBC dynamics, ATP release, and macroscopic viscosity all at physiological shear rates. Our experimental approach included microfluidics, ATP measurements using a bioluminescent reaction, and rheology. Using microfluidics technology with high-speed imaging, we visualize the deformation and dynamics of single cells, which are known to undergo motions such as tumbling, swinging, tanktreading, and deformation. We report that shear thinning is not due to cellular deformation as previously believed, but rather it is due to the tumbling-to-tanktreading transition. In addition, our results indicate that ATP release is constant at shear stresses below a threshold (3 Pa), whereas above the threshold ATP release is increased and accompanied by large cellular deformations. Finally, performing experiments with well-known inhibitors, we show that the Pannexin 1 hemichannel is the main avenue for ATP release both above and below the threshold, whereas, the cystic fibrosis transmembrane conductance regulator only contributes to deformation-dependent ATP release above the stress threshold.

Systematics of constant roll inflation

Science.gov (United States)

Anguelova, Lilia; Suranyi, Peter; Wijewardhana, L. C. R.

2018-02-01

We study constant roll inflation systematically. This is a regime, in which the slow roll approximation can be violated. It has long been thought that this approximation is necessary for agreement with observations. However, recently it was understood that there can be inflationary models with a constant, and not necessarily small, rate of roll that are both stable and compatible with the observational constraint ns ≈ 1. We investigate systematically the condition for such a constant-roll regime. In the process, we find a whole new class of inflationary models, in addition to the known solutions. We show that the new models are stable under scalar perturbations. Finally, we find a part of their parameter space, in which they produce a nearly scale-invariant scalar power spectrum, as needed for observational viability.

Size-fractionated characterization and quantification of nanoparticle release rates from a consumer spray product containing engineered nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Hagendorfer, Harald, E-mail: Harald.Hagendorfer@empa.c [EMPA, Swiss Federal Laboratories for Materials Testing and Research (Switzerland); Lorenz, Christiane, E-mail: Christiane.Lorenz@chem.ethz.c [ETHZ, Swiss Federal Institute of Technology Zurich (Switzerland); Kaegi, Ralf, E-mail: Ralf.Kaegi@eawag.ch; Sinnet, Brian, E-mail: Brian.Sinnet@eawag.c [EAWAG, Swiss Federal Institute of Aquatic Science and Technology (Switzerland); Gehrig, Robert, E-mail: Robert.Gehrig@empa.c [EMPA, Swiss Federal Laboratories for Materials Testing and Research (Switzerland); Goetz, Natalie V., E-mail: Natalie.vonGoetz@chem.ethz.ch; Scheringer, Martin, E-mail: Martin.Scheringer@chem.ethz.c [ETHZ, Swiss Federal Institute of Technology Zurich (Switzerland); Ludwig, Christian, E-mail: Christian.Ludwig@psi.c [PSI, Paul Scherrer Institue (Switzerland); Ulrich, Andrea, E-mail: Andrea.Ulrich@empa.c [EMPA, Swiss Federal Laboratories for Materials Testing and Research (Switzerland)

2010-09-15

This study describes methods developed for reliable quantification of size- and element-specific release of engineered nanoparticles (ENP) from consumer spray products. A modified glove box setup was designed to allow controlled spray experiments in a particle-minimized environment. Time dependence of the particle size distribution in a size range of 10-500 nm and ENP release rates were studied using a scanning mobility particle sizer (SMPS). In parallel, the aerosol was transferred to a size-calibrated electrostatic TEM sampler. The deposited particles were investigated using electron microscopy techniques in combination with image processing software. This approach enables the chemical and morphological characterization as well as quantification of released nanoparticles from a spray product. The differentiation of solid ENP from the released nano-sized droplets was achieved by applying a thermo-desorbing unit. After optimization, the setup was applied to investigate different spray situations using both pump and gas propellant spray dispensers for a commercially available water-based nano-silver spray. The pump spray situation showed no measurable nanoparticle release, whereas in the case of the gas spray, a significant release was observed. From the results it can be assumed that the homogeneously distributed ENP from the original dispersion grow in size and change morphology during and after the spray process but still exist as nanometer particles of size <100 nm. Furthermore, it seems that the release of ENP correlates with the generated aerosol droplet size distribution produced by the spray vessel type used. This is the first study presenting results concerning the release of ENP from spray products.

Size-fractionated characterization and quantification of nanoparticle release rates from a consumer spray product containing engineered nanoparticles

International Nuclear Information System (INIS)

Hagendorfer, Harald; Lorenz, Christiane; Kaegi, Ralf; Sinnet, Brian; Gehrig, Robert; Goetz, Natalie V.; Scheringer, Martin; Ludwig, Christian; Ulrich, Andrea

2010-01-01

This study describes methods developed for reliable quantification of size- and element-specific release of engineered nanoparticles (ENP) from consumer spray products. A modified glove box setup was designed to allow controlled spray experiments in a particle-minimized environment. Time dependence of the particle size distribution in a size range of 10-500 nm and ENP release rates were studied using a scanning mobility particle sizer (SMPS). In parallel, the aerosol was transferred to a size-calibrated electrostatic TEM sampler. The deposited particles were investigated using electron microscopy techniques in combination with image processing software. This approach enables the chemical and morphological characterization as well as quantification of released nanoparticles from a spray product. The differentiation of solid ENP from the released nano-sized droplets was achieved by applying a thermo-desorbing unit. After optimization, the setup was applied to investigate different spray situations using both pump and gas propellant spray dispensers for a commercially available water-based nano-silver spray. The pump spray situation showed no measurable nanoparticle release, whereas in the case of the gas spray, a significant release was observed. From the results it can be assumed that the homogeneously distributed ENP from the original dispersion grow in size and change morphology during and after the spray process but still exist as nanometer particles of size <100 nm. Furthermore, it seems that the release of ENP correlates with the generated aerosol droplet size distribution produced by the spray vessel type used. This is the first study presenting results concerning the release of ENP from spray products.

QSAR models for oxidation of organic micropollutants in water based on ozone and hydroxyl radical rate constants and their chemical classification

KAUST Repository

Sudhakaran, Sairam; Amy, Gary L.

2013-01-01

. In this study, quantitative structure activity relationships (QSAR) models for O3 and AOP processes were developed, and rate constants, kOH and kO3, were predicted based on target compound properties. The kO3 and kOH values ranged from 5 * 10-4 to 105 M-1s-1

Rate constants for the slow Mu + propane abstraction reaction at 300 K by diamagnetic RF resonance.

Science.gov (United States)

Fleming, Donald G; Cottrell, Stephen P; McKenzie, Iain; Ghandi, Khashayar

2015-08-14

The study of kinetic isotope effects for H-atom abstraction rates by incident H-atoms from the homologous series of lower mass alkanes (CH4, C2H6 and, here, C3H8) provides important tests of reaction rate theory on polyatomic systems. With a mass of only 0.114 amu, the most sensitive test is provided by the rates of the Mu atom. Abstraction of H by Mu can be highly endoergic, due to the large zero-point energy shift in the MuH bond formed, which also gives rise to high activation energies from similar zero-point energy corrections at the transition state. Rates are then far too slow near 300 K to be measured by conventional TF-μSR techniques that follow the disappearance of the spin-polarised Mu atom with time. Reported here is the first measurement of a slow Mu reaction rate in the gas phase by the technique of diamagnetic radio frequency (RF) resonance, where the amplitude of the MuH product formed in the Mu + C3H8 reaction is followed with time. The measured rate constant, kMu = (6.8 ± 0.5) × 10(-16) cm(3) s(-1) at 300 K, is surprisingly only about a factor of three slower than that expected for H + C3H8, indicating a dominant contribution from quantum tunneling in the Mu reaction, consistent with elementary transition state theory calculations of the kMu/kH kinetic isotope effect.

A new variable interval schedule with constant hazard rate and finite time range.

Science.gov (United States)

Bugallo, Mehdi; Machado, Armando; Vasconcelos, Marco

2018-05-27

We propose a new variable interval (VI) schedule that achieves constant probability of reinforcement in time while using a bounded range of intervals. By sampling each trial duration from a uniform distribution ranging from 0 to 2 T seconds, and then applying a reinforcement rule that depends linearly on trial duration, the schedule alternates reinforced and unreinforced trials, each less than 2 T seconds, while preserving a constant hazard function. © 2018 Society for the Experimental Analysis of Behavior.

Modified gum Arabic hydrogels as matrices for controlled release of curcumin supramolecular complexes

International Nuclear Information System (INIS)

Gerola, Adriana P.; Silva, Danielle C.; Rubira, Adley F.; Muniz, Edvani C.

2015-01-01

Modified gum Arabic (GA) hydrogels show a pH-responsive behavior making them excellent matrices to be used for oral administration of drugs. Our goal is to study the behavior of those matrices in simulated gastric and intestinal fluids. In this work we will present how the methacrylation degree of GA, by using glycidyl methacrylate, can affect the properties of these hydrogels for controlled release. The drug used in this work is the curcumin (Cur). Cur is associated with numerous pharmacological activities, but their application is limited by the low water solubility. We will present some studies involving the formation of host-guest complexes between Cur and natural cyclodextrins. Both modified GA and hydrogels were characterized by different techniques. The kinetics release of Cur complex-containing modified GA hydrogels was studied to have an insight on the release mechanism and rate constants. Toxicity studies on undifferentiated and differentiated Caco-2 were also carried out. (author)

Diclofenac sodium sustained release hot melt extruded lipid matrices.

Science.gov (United States)

Vithani, K; Cuppok, Y; Mostafa, S; Slipper, I J; Snowden, M J; Douroumis, D

2014-08-01

Sustained release diclofenac sodium (Df-Na) solid lipid matrices with Compritol® 888 ATO were developed in this study. The drug/lipid powders were processed via cold and hot melt extrusion at various drug loadings. The influence of the processing temperatures, drug loading and the addition of excipients on the obtained dissolution rates was investigated. The physicochemical characterization of the extruded batches showed the existence of crystalline drug in the extrudates with a small amount being solubilized in the lipid matrix. The drug content and uniformity on the tablet surface were also investigated by using energy dispersive X-ray microanalysis. The dissolution rates were found to depend on the actual Df-Na loading and the nature of the added excipients, while the effect of the processing temperatures was negligible. The dissolution mechanism of all extruded formulations followed Peppas-Korsemeyer law, based on the estimated determination coefficients and the dissolution constant rates, indicating drug diffusion from the lipid matrices.

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.

Science.gov (United States)

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

Quantum mechanical calculations of state-to-state cross sections and rate constants for the F + DCl → Cl + DF reaction.

Science.gov (United States)

Bulut, Niyazi; Kłos, Jacek; Roncero, Octavio

2015-06-07

We present accurate state-to-state quantum wave packet calculations of integral cross sections and rate constants for the title reaction. Calculations are carried out on the best available ground 1(2)A' global adiabatic potential energy surface of Deskevich et al. [J. Chem. Phys. 124, 224303 (2006)]. Converged state-to-state reaction cross sections have been calculated for collision energies up to 0.5 eV and different initial rotational and vibrational excitations, DCl(v = 0, j = 0 - 1; v = 1, j = 0). Also, initial-state resolved rate constants of the title reaction have been calculated in a temperature range of 100-400 K. It is found that the initial rotational excitation of the DCl molecule does not enhance reactivity, in contract to the reaction with the isotopologue HCl in which initial rotational excitation produces an important enhancement. These differences between the isotopologue reactions are analyzed in detail and attributed to the presence of resonances for HCl(v = 0, j), absent in the case of DCl(v = 0, j). For vibrational excited DCl(v = 1, j), however, the reaction cross section increases noticeably, what is also explained by another resonance.

131I release from a HTGR during the LOFC accident

International Nuclear Information System (INIS)

Foley, J.E.

1975-03-01

The time-dependent release of 131 I from both the core and the containment building of a high temperature gas-cooled (HTGR) reactor during the loss of forced coolant (LOFC) accident is studied. A simplified core release model is combined with a containment building release model so that the total amount of the isotope released to the environment can be calculated. The time-dependent release of 131 I from the core during the LOFC accident is primarily a function of the time-dependent core temperatures and the failed fuel release constants. The most important factor in calculating the amount of the isotope released to the environment is the total amount released into the containment building. (U.S.)

Constant extension rate testing of Type 304L stainless steel in simulated waste tank environments

International Nuclear Information System (INIS)

Wiersma, B.J.

1992-01-01

New tanks for storage of low level radioactive wastes will be constructed at the Savannah River Site (SRS) of AISI Type 304L stainless steel (304L). The presence of chlorides and fluorides in the wastes may induce Stress Corrosion Cracking (SCC) in 304L. Constant Extension Rate Tests (CERT) were performed to determine the susceptibility of 304L to SCC in simulated wastes. In five of the six tests conducted thus far 304L was not susceptible to SCC in the simulated waste environments. Conflicting results were obtained in the final test and will be resolved by further tests. For comparison purposes the CERT tests were also performed with A537 carbon steel, a material similar to that utilized for the existing nuclear waste storage tanks at SRS

Quantifying MTBE biodegradation in the Vandenberg Air Force Base ethanol release study using stable carbon isotopes

Science.gov (United States)

McKelvie, Jennifer R.; Mackay, Douglas M.; de Sieyes, Nicholas R.; Lacrampe-Couloume, Georges; Sherwood Lollar, Barbara

2007-12-01

Compound-specific isotope analysis (CSIA) was used to assess biodegradation of MTBE and TBA during an ethanol release study at Vandenberg Air Force Base. Two continuous side-by-side field releases were conducted within a preexisting MTBE plume to form two lanes. The first involved the continuous injection of site groundwater amended with benzene, toluene and o-xylene ("No ethanol lane"), while the other involved the continuous injection of site groundwater amended with benzene, toluene and o-xylene and ethanol ("With ethanol lane"). The δ 13C of MTBE for all wells in the "No ethanol lane" remained constant during the experiment with a mean value of - 31.3 ± 0.5‰ ( n = 40), suggesting the absence of any substantial MTBE biodegradation in this lane. In contrast, substantial enrichment in 13C of MTBE by 40.6‰, was measured in the "With ethanol lane", consistent with the effects of biodegradation. A substantial amount of TBA (up to 1200 μg/L) was produced by the biodegradation of MTBE in the "With ethanol lane". The mean value of δ 13C for TBA in groundwater samples in the "With ethanol lane" was - 26.0 ± 1.0‰ ( n = 32). Uniform δ 13C TBA values through space and time in this lane suggest that substantial anaerobic biodegradation of TBA did not occur during the experiment. Using the reported range in isotopic enrichment factors for MTBE of - 9.2‰ to - 15.6‰, and values of δ 13C of MTBE in groundwater samples, MTBE first-order biodegradation rates in the "With ethanol lane" were 12.0 to 20.3 year - 1 ( n = 18). The isotope-derived rate constants are in good agreement with the previously published rate constant of 16.8 year - 1 calculated using contaminant mass-discharge for the "With ethanol lane".

Kinetics of N-Glycan Release from Human Immunoglobulin G (IgG) by PNGase F: All Glycans Are Not Created Equal.

Science.gov (United States)

Huang, Yining; Orlando, Ron

2017-12-01

The biologic activity of IgG molecules is modulated by its crystallizable fragment N-glycosylation, and thus, the analysis of IgG glycosylation is critical. A standard approach to analyze glycosylation of IgGs involves the release of the N-glycans by the enzyme peptide N-glycosidase F, which cleaves the linkage between the asparagine residue and innermost N-acetylglucosamine (GlcNAc) of all N-glycans except those containing a 3-linked fucose attached to the reducing terminal GlcNAc residue. The importance of obtaining complete glycan release for accurate quantitation led us to investigate the kinetics of this de-glycosylation reaction for IgG glycopeptides and to determine the effect of glycan structure and amino acid sequence on the rate of glycan release from glycopeptides of IgGs. This study revealed that the slight differences in amino acid sequences did not lead to a statistically different deglycosylation rate. However, statistically significant differences in the deglycosylation rate constants were observed between glycopeptides differing only in glycan structure ( i.e. , nonfucosylated, fucosylated, bisecting-GlcNAc, sialylated, etc .). For example, a single sialic acid residue was found to decrease the rate by a factor of 3. Similar reductions in rate were associated with the presence of a bisecting-GlcNAc. We predict the differences in release kinetics can lead to significant quantitative variations of the glycosylation study of IgGs.

Development and evaluation of a new prototype P&T system to determine in-heading gas release rate.

CSIR Research Space (South Africa)

Van Zyl, FJ

2001-11-01