Article

1999 ◽  
Vol 77 (11) ◽  
pp. 1728-1733
Author(s):  
RED McClung ◽  
T T Nakashima ◽  
H Yamamoto ◽  
G Kotovych
Keyword(s):  
Density Matrix ◽  
Key Words ◽  
Rate Constants ◽  
Water Exchange ◽  
Experimental Measurements ◽  
Spin Lock ◽  
Solvent Water ◽  
Ph Values ◽  
Product Operator ◽  
Theoretical Predictions

A product operator description of the nuclei in an ensemble of molecules undergoing intermolecular exchange during the spin-lock period of TOCSY is presented. Experimental measurements of the transfer of magnetization from the CH2 protons in N-acetylglycine to the solvent water protons, via exchange of the NH proton with water protons during the spin-lock period in TOCSY, are shown to be in agreement with theoretical predictions at lower pH values (7.85-9.54) where the rate constants for NH-water exchange are known. Measurements at higher pH (up to 11.03) indicate that the highest rate constant for exchange that can be determined by this technique is τA-1 ~ 4000 s-1.Key words: product operator, density matrix, intermolecular exchange, TOCSY, NMR.

A kinetic modeling study of ethylene pyrolysis

2000 ◽  
Vol 78 (1) ◽  
pp. 16-25 ◽  
Author(s):  
John M Roscoe ◽  
Alain R Bossard ◽  
Margaret H Back
Keyword(s):  
Activation Energy ◽  
Kinetic Model ◽  
Temperature Dependence ◽  
Key Words ◽  
Kinetic Modeling ◽  
Rate Constants ◽  
Preexponential Factor ◽  
Isomerization Reaction ◽  
Experimental Measurements ◽  
Experimental Conditions

A kinetic model is presented for the pyrolysis of ethylene at pressures ranging from 0.8 to 27 kPa and temperatures from 774 to 1023 K. The model is based on experimental measurements of C2H2, C2H6, C3H6, 1-C4H8, and 1,3-C4H6. In this temperature range the reaction is initiated by the disproportionation of C2H4 and the observed products result from reactions of the C2H3 and C2H5 radicals produced in this process. The C2H2 and 1,3-C4H6 result from reactions of C2H3 while C2H6, C3H6, and 1-C4H8 result from reactions of C2H5. C2H2 is produced exclusively by the decomposition of the C2H3 radical. This process is in its falloff region throughout the range of experimental conditions examined and the yield of C2H2 provides a measure of the degree of falloff. The production of 1,3-C4H6 is controlled by the reaction C4H7 –> C4H6 + H. The rate constants for this reaction were independent of pressure and are given as a function of temperature by k = 2.2 × 1013 exp (-19.6 × 103/T). Production of C2H6 is controlled by the reaction C2H5 + C2H4 –> C2H6 + C2H3. The rate constant for this reaction is given as a function of temperature by k = 5.83 × 1011 exp (-14.6 × 103/T). C3H6 is produced by decomposition of 2-C4H9 and is controlled kinetically by the isomerization reaction 1-C4H9 –> 2-C4H9. The temperature dependence of the rate constants obtained for this reaction leads to a preexponential factor of approximately 3 × 1016 and an activation energy of approximately 200 kJ mol-1. The yield of 1-C4H8 is controlled by 1-C4H9 –> 1-C4H8 + H. The rate constants for this reaction were independent of pressure and are given as a function of temperature by k = 2.97 × 1012 exp (-17.1 × 103/T). Key words: kinetic modeling, ethylene pyrolysis.

Remarkable kinetic stability of α-thiocarbamoyl substituted 4-methoxybenzylcations

1998 ◽  
Vol 76 (12) ◽  
pp. 1910-1915 ◽  
Author(s):  
Robert A McClelland ◽  
Victoria E Licence ◽  
John P Richard ◽  
Kathleen B Williams ◽  
Shrong-Shi Lin
Keyword(s):  
Key Words ◽  
Strong Interaction ◽  
Rate Constants ◽  
Flash Photolysis ◽  
Visible Absorption ◽  
Methyl Group ◽  
Thioamide Group ◽  
Azide Ion ◽  
Uv Visible ◽  
Leaving Groups

4-Methoxybenzyl cations bearing α-(N,N-dimethylcarbamoyl) and α-(N,N-dimethylthiocarbamoyl) substituents have been generated photochemically upon irradiation of precursors with pentafluorobenzoate or 4-methoxybenzoate leaving groups. The ions have been observed with flash photolysis in 40:60 acetonitrile:water and in 50:50 methanol:water, and rate constants were measured for their decay in solvent alone and for their capture by azide ion. The cations so studied and their lifetimes in 40% acetonitrile are 6, ArC+H-CONMe2, 0.6 μs; 2, ArC+H-CSNMe2, 7 ms; and 4, ArC+(CH3)-CSMe2, 6 ms, where Ar = 4-MeOC6H4. The cation 4 reacts with solvent by elimination of a proton from the α-methyl group, and the rate constant for solvent addition must be less than 1 s-1. The CSNMe2 substituted cations are 105-107-fold longer lived than analogs where the thioamide group has been replaced with an α-methyl. The UV-visible absorption spectra of these two cations also show significant differences from those of typical 4-methoxybenzyl cations. Thus, both the lifetimes and spectra point to a strong interaction of the benzylic centre with the thioamide group. Key words: flash photolysis, thiocarbamoyl stabilized carbocation, photosolvolysis.

scholarly journals Optical Analysis of Ball Bearing Starvation

1971 ◽  
Vol 93 (3) ◽  
pp. 349-361 ◽  
Author(s):  
L. D. Wedeven ◽  
D. Evans ◽  
A. Cameron
Keyword(s):  
Film Thickness ◽  
Ball Bearing ◽  
Point Contact ◽  
Experimental Measurements ◽  
Line Contact ◽  
Optical Analysis ◽  
Grease Lubrication ◽  
Theoretical Predictions ◽  
Pressure Stress ◽  
Starvation Conditions

Elastohydrodynamic oil film measurements for rolling point contact under starvation conditions are obtained using optical interferometry. The experimental measurements present a reasonably clear picture of the starvation phenomenon and are shown to agree with theoretical predictions. Starvation inhibits the generation of pressure and, therefore, reduces film thickness. It also causes the overall pressure, stress, and elastic deformation to become more Hertzian. Additional experiments using interferometry illustrate: the cavitation pattern, lubricant entrapment, grease lubrication, ball spin, and edge effects in line contact.

Soil acidity in 1970 and 1989 in a coniferous forest in southwest Finland

1998 ◽  
Vol 78 (3) ◽  
pp. 477-479 ◽  
Author(s):  
C. J. Westman ◽  
S. Jauhiainen
Keyword(s):  
Key Words ◽  
Soil Ph ◽  
Soil Acidity ◽  
Mineral Soil ◽  
Coniferous Forest ◽  
Soil Layers ◽  
Water Suspension ◽  
Ph Values ◽  
Humus Layer ◽  
Repeated Sampling

Forest soil pH in southwest Finland was measured with identical sampling and analysing methods in 1970 and 1989. The acidity of the organic humus layer increased significantly as pH values measured on water and on salt suspensions decreased between the two sampling dates. For the mineral soil layers, no unambiguous trend was found. pH values measured on salt suspension tended to be unchanged or lower, while pH on water suspension in some soil layers were even higher in 1989 than in 1970. Key words: pH, repeated sampling

An ICR mass spectrometry study of ion/molecule reactions between ethyl chloride and alkylamines

1991 ◽  
Vol 69 (2) ◽  
pp. 363-367
Author(s):  
Guoying Xu ◽  
Jan A. Herman
Keyword(s):  
Mass Spectrometry ◽  
Key Words ◽  
Rate Constant ◽  
Rate Constants ◽  
Ethyl Chloride ◽  
Ion Molecule Reactions ◽  
Mass Spectrometry Study ◽  
Ethyl Cation

Ion/molecule reactions in mixtures of ethyl chloride with C1–C4 alkylamines were studied by ICR mass spectrometry. Ethyl cation transfer to C1–C4 alkylamines proceeds mainly through diethylchloronium ions with rate constants ~3 × 10−10cm3 s−1. In the case of s-butylamine the corresponding rate constant is 0.5 × 10−10 cm3 s−1. Key words: ICR mass spectrometry, ion/molecule reactions, ethylchloride, methylamine, ethylamine, propylamines, butylamines

scholarly journals The Effect of Attenuation from Fish on Passive Detection of Sound Sources in Ocean Waveguide Environments

2021 ◽  
Vol 13 (21) ◽  
pp. 4369
Author(s):  
Daniel Duane ◽  
Chenyang Zhu ◽  
Felix Piavsky ◽  
Olav Rune Godø ◽  
Nicholas C. Makris
Keyword(s):  
Remote Sensing ◽  
Propagation Path ◽  
Experimental Measurements ◽  
Sound Sources ◽  
Detection Range ◽  
Acoustic Waveguide ◽  
Passive Sensing ◽  
Surface Vessels ◽  
Theoretical Predictions ◽  
Radiated Sound

Attenuation from fish can reduce the intensity of acoustic signals and significantly decrease detection range for long-range passive sensing of manmade vehicles, geophysical phenomena, and vocalizing marine life. The effect of attenuation from herring shoals on the Passive Ocean Acoustic Waveguide Remote Sensing (POAWRS) of surface vessels is investigated here, where concurrent wide-area active Ocean Acoustic Waveguide Remote Sensing (OAWRS) is used to confirm that herring shoals occluding the propagation path are responsible for measured reductions in ship radiated sound and corresponding detection losses. Reductions in the intensity of ship-radiated sound are predicted using a formulation for acoustic attenuation through inhomogeneities in an ocean waveguide that has been previously shown to be consistent with experimental measurements of attenuation from fish in active OAWRS transmissions. The predictions of the waveguide attenuation formulation are in agreement with measured reductions from attenuation, where the position, size, and population density of the fish groups are characterized using OAWRS imagery as well as in situ echosounder measurements of the specific shoals occluding the propagation path. Experimental measurements of attenuation presented here confirm previous theoretical predictions that common heuristic formulations employing free space scattering assumptions can be in significant error. Waveguide scattering and propagation theory is found to be necessary for accurate predictions.

scholarly journals GROUNDWATER SELF-CLEARING FROM 90SR WITHIN BACKGROUND AREA AND OWING TO ARTIFICIAL CONTAMINATION

2018 ◽  
pp. 100-106
Author(s):  
O. Shevchenko ◽  
V. Dolin
Keyword(s):  
Rate Constants ◽  
Water Exchange ◽  
Main Idea ◽  
Exclusion Zone ◽  
Well Drilling ◽  
90Sr Content ◽  
Waste Storage ◽  
Formal Kinetic ◽  
Unstable Process ◽  
Water Saturated

The main idea of the presented results is the determination of spatial-temporal regularities of 90Sr content in groundwaters within Chornobyl Exclusion Zone. Utilization of formal kinetic regularities (of I order for irreversible process) for monitoring data analyses has been substantiated. Rate constants of groundwater self-clearing from 90Sr in dependence of type of contamination are calculated by iteration method. Graphic interpretation of data has been realized using package for analysis of Microsoft Excel and Statistica software. Self-clearing of groundwaters is carried out owing to three main processes: sorption as function of water containing medium dispercity, dispersion due to water exchange, concentration dilution (dissolving) of radionuclides in specified volume, and physical decay. considered Self-clearing is considered to be an important element both for the security and vulnerability of groundwaters. Data on 90Sr content in groundwater of background areas, in affected zone of radioactive waste storage, zone of groundwater nutrition from cooling pond of Chornobyl NPP, spots of primarily radioactive contamination, and of groundwater secondary contamination owing to well drilling are discussed. Rate constants for groundwater self-clearing from 90Sr are calculated from experimental data both for non-stationary (rapid) and stationary (slow) processes. The “half-decontamination” period (in analogy to half-life) is less than 0.5 year. The rate constant for unstable process two times, and for established one time exceeds the decay constant. The rates of groundwater self-clearing from strontium-90 owing to water exchange and geochemically immobilization are determined. The equilibrium of sorption-desorption within water saturated zone is generally depended on the rate of water exchange and radionuclides concentration in upper stream, i.e. from concentration gradient.

Kinetic analysis of potassium transport in bullfrog kidney

1977 ◽  
Vol 233 (5) ◽  
pp. F464-F480 ◽  
Author(s):  
L. P. Sullivan ◽  
D. J. Welling ◽  
D. G. Deeds ◽  
J. H. Simone
Keyword(s):  
Rate Constants ◽  
Vena Cava ◽  
Potassium Transport ◽  
Experimental Measurements ◽  
Luminal Surface ◽  
Portal Circulation ◽  
Tubular Cells ◽  
Rate Constants For Efflux ◽  
Kidney Tubular Cells ◽  
Made In

Techniques have been developed for studying the distribution and the rates of exchange of K among urine, the tubular cells, and the circulation in the isolated, pump-perfused, bullfrog kidney. Tubular cells were loaded with 42K via the portal circulation, and the subsequent washout of the tracer into the vena cava and into urine was measured. Analysis of the data indicated the existence of at least three cellular pools of K. Pools a and b have half times of exchange of 1.1 and 4.1 min and contain about 25 and 40% of tissue K, respectively. The remainder of cellular K is contained in one or more very slowly exchanging pools. The rate of exchange of K at the basolateral surface of tubular cells is 50-fold greater than at the luminal surface. A pulse-washout method was also devised to permit control and experimental measurements to be made in the same kidney. With this technique, we found that portal perfusion with 10 mM K increased the rate of uptake into pools a and b from the circulation and the rate constants for efflux into the urine from both pools, Acetazolamide increased uptake into pool a and the rate constants for efflux into the urine from both pools.

scholarly journals Bioinspired aerofoil adaptations: the next steps for theoretical models

2019 ◽  
Vol 377 (2159) ◽  
pp. 20190070 ◽  
Author(s):  
Lorna J. Ayton
Keyword(s):  
Experimental Data ◽  
Theoretical Models ◽  
Theoretical Modelling ◽  
Experimental Measurements ◽  
Far Field ◽  
Acoustic Analogy ◽  
Trailing Edge ◽  
Trailing Edge Noise ◽  
Theoretical Predictions ◽  
Field Noise

The extended introduction in this paper reviews the theoretical modelling of leading- and trailing-edge noise, various bioinspired aerofoil adaptations to both the leading and trailing edges of blades, and how these adaptations aid in the reduction of aerofoil–turbulence interaction noise. Attention is given to the agreement between current theoretical predictions and experimental measurements, in particular, for turbulent interactions at the trailing edge of an aerofoil. Where there is a poor agreement between theoretical models and experimental data the features neglected from the theoretical models are discussed. Notably, it is known that theoretical predictions for porous trailing-edge adaptations do not agree well with experimental measurements. Previous works propose the reason for this: theoretical models do not account for surface roughness due to the porous material and thus omit a key noise source. The remainder of this paper, therefore, presents an analytical model, based upon the acoustic analogy, to predict the far-field noise due to a rough surface at the trailing edge of an aerofoil. Unlike previous roughness noise models which focus on roughness over an infinite wall, the model presented here includes diffraction by a sharp edge. The new results are seen to be in better agreement with experimental data than previous models which neglect diffraction by an edge. This new model could then be used to improve theoretical predictions for far-field noise generated by turbulent interactions with a (rough) porous trailing edge. This article is part of the theme issue ‘Frontiers of aeroacoustics research: theory, computation and experiment’.

Analytic Calculations of the Branching Ratio and CP Violation in Bs0 → Ds+Ds− Decay

2020 ◽  
Vol 35 (15) ◽  
pp. 2050122
Author(s):  
H. R. Khan ◽  
E. H. Raslan ◽  
R. A. Reem
Keyword(s):  
Cp Violation ◽  
Decay Width ◽  
Branching Ratio ◽  
Gluon Condensate ◽  
Analytic Calculation ◽  
Experimental Measurements ◽  
Meson Decays ◽  
First Order ◽  
Theoretical Predictions ◽  
Charge Parity

We present an analytic calculation of Branching Ratio (BR) and Charge-Parity (CP) violating asymmetries of the [Formula: see text] meson decays to [Formula: see text] by calculating the amplitude and the decay width of the process including the chiral loop and gluon condensate to first-order. We find the BR of [Formula: see text] which is in agreement with other experimental measurements and theoretical predictions. We also calculate the direct CP violation, CP violation in mixing and CP violation due to interference which are [Formula: see text], [Formula: see text] and [Formula: see text], respectively.

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