scholarly journals THE QUENCHING OF TRIPLET POSITRONIUM BY IONS IN AQUEOUS SOLUTIONS

1958 ◽  
Vol 36 (12) ◽  
pp. 1684-1695 ◽  
Author(s):  
R. E. Green ◽  
R. E. Bell
Keyword(s):  
Aqueous Solutions ◽  
Cross Sections ◽  
Pure Water ◽  
Experimental Results ◽  
Conversion Process ◽  
Fast Time ◽  
Unpaired Electrons ◽  
Positron Lifetimes ◽  
Paramagnetic Atoms

Measurements of positron lifetimes in aqueous solutions have been performed using a fast time-to-amplitude converter with a resolving time of ~10−9 sec. The lifetime, τ2, of the long-lived component of the complex decay observed in water has been found to decrease when paramagnetic salts are added. The experimental results are interpreted in terms of "pickoff" annihilation to explain the observed τ2 in pure water, and a rapid triplet ↔ singlet conversion process to account for the quenching of the τ2 component. The conversion is caused by the presence of unpaired electrons in the structure of the paramagnetic atoms. Triplet → singlet conversion cross sections have been calculated on the basis of this interpretation and they range from 4.0 × 10−20 cm2 for NdCl3 to 3.8 × 10−18 cm2 for FeCl3.

The viscosity of dilute aqueous nonelectrolyte solutions

1981 ◽  
Vol 34 (11) ◽  
pp. 2283 ◽  
Author(s):  
DM Alexander ◽  
DC Moy
Keyword(s):  
Aqueous Solutions ◽  
Temperature Dependence ◽  
Empirical Equation ◽  
Pure Water ◽  
Entropy Change ◽  
Aqueous System ◽  
Experimental Results ◽  
Dilute Solutions ◽  
Molar Entropy ◽  
B Coefficients

An equation is proposed to describe the viscosity B coefficients for dilute solutions of nonelectrolytes in water. It is based on an empirical equation developed for nonaqueous mixtures and an assumption that the entropy change on solution of the liquid solute affects the viscosity of the aqueous system in the same way as a change of molar entropy affects the viscosity of pure water. The equation is shown to represent experimental results well and is especially successful in representing the temperature dependence of the B coefficient for aqueous solutions of alcohols.

Experimental Study on the Specific Heat Capacity Measurement of Water-Based Al2O3-Cu Hybrid Nanofluid by using Differential Thermal Analysis Method

2019 ◽  
Vol 15 ◽  
Author(s):  
Andaç Batur Çolak ◽  
Oğuzhan Yıldız ◽  
Mustafa Bayrak ◽  
Ali Celen ◽  
Ahmet Selim Dalkılıç ◽  
...  
Keyword(s):  
Heat Capacity ◽  
Specific Heat ◽  
Specific Heat Capacity ◽  
Thermophysical Properties ◽  
Volume Concentration ◽  
Pure Water ◽  
Heat Capacity Measurement ◽  
Experimental Results ◽  
Hybrid Nanofluid ◽  
Capacity Measurement

Background: Researchers working in the field of nanofluid have done many studies on the thermophysical properties of nanofluids. Among these studies, the number of studies on specific heat are rather limited. In the study of the heat transfer performance of nanofluids, it is necessary to increase the number of specific heat studies, whose subject is one of the important thermophysical properties. Objective: The authors aimed to measure the specific heat values of Al2O3/water, Cu/water nanofluids and Al2O3-Cu/water hybrid nanofluids using the DTA method, and compare the results with those frequently used in the literature. In addition, this study focuses on the effect of temperature and volume concentration on specific heat. Method: The two-step method was used in the preparation of nanofluids. The pure water selected as the base fluid was mixed with the Al2O3 and Cu nanoparticles and Arabic Gum as the surfactant, firstly mixed in the magnetic stirrer for half an hour. It was then homogenized for 6 hours in the ultrasonic homogenizer. Results: After the experiments, the specific heat of nanofluids and hybrid nanofluid were compared and the temperature and volume concentration of specific heat were investigated. Then, the experimental results obtained for all three fluids were compared with the two frequently used correlations in the literature. Conclusion: Specific heat capacity increased with increasing temperature, and decreased with increasing volume concentration for three tested nanofluids. Cu/water has the lowest specific heat capacity among all tested fluids. Experimental specific heat capacity measurement results are compared by using the models developed by Pak and Cho and Xuan and Roetzel. According to experimental results, these correlations can predict experimental results within the range of ±1%.

scholarly journals Experimental study of the $ \gamma p \rightarrow K^{0}\Sigma^{+}$, $ \gamma n \rightarrow K^{0} \Lambda$, and $ \gamma n \rightarrow K^{0} \Sigma^{0}$ reactions at the Mainz Microtron

2019 ◽  
Vol 55 (11) ◽  
Author(s):  
C. S. Akondi ◽  
K. Bantawa ◽  
D. M. Manley ◽  
S. Abt ◽  
P. Achenbach ◽  
...  
Keyword(s):  
Experimental Study ◽  
Cross Sections ◽  
Differential Cross ◽  
Legendre Polynomials ◽  
Neutral Kaon ◽  
Experimental Results ◽  
Differential Cross Sections ◽  
Theoretical Predictions ◽  
Photoproduction Reactions ◽  
Insight Into

Abstract.This work measured $ \mathrm{d}\sigma/\mathrm{d}\Omega$dσ/dΩ for neutral kaon photoproduction reactions from threshold up to a c.m. energy of 1855MeV, focussing specifically on the $ \gamma p\rightarrow K^0\Sigma^+$γp→K0Σ+, $ \gamma n\rightarrow K^0\Lambda$γn→K0Λ, and $ \gamma n\rightarrow K^0 \Sigma^0$γn→K0Σ0 reactions. Our results for $ \gamma n\rightarrow K^0 \Sigma^0$γn→K0Σ0 are the first-ever measurements for that reaction. These data will provide insight into the properties of $ N^{\ast}$N* resonances and, in particular, will lead to an improved knowledge about those states that couple only weakly to the $ \pi N$πN channel. Integrated cross sections were extracted by fitting the differential cross sections for each reaction as a series of Legendre polynomials and our results are compared with prior experimental results and theoretical predictions.

K shell X-ray intensity ratios, K-Li, K-L, and K-M vacancy transfer probabilities of Ba and Tl following internal conversion process

2014 ◽  
Vol 92 (11) ◽  
pp. 1489-1493 ◽  
Author(s):  
P.V. Sreevidya ◽  
S.B. Gudennavar ◽  
Daisy Joseph ◽  
S.G. Bubbly
Keyword(s):  
Beta Decay ◽  
Internal Conversion ◽  
Experimental Results ◽  
Conversion Process ◽  
X Rays ◽  
X Ray ◽  
Multichannel Analyser ◽  
Intensity Ratios

K shell X-rays of barium and thallium following internal conversion decay in Cs137 and Hg203, respectively, were detected using a Si(Li) X-ray detector coupled to PC-based 8k multichannel analyser employing the method suggested earlier by our group. The K shell X-ray intensity ratios and vacancy transfer probabilities for thallium and barium were calculated. The obtained results are compared with theoretical, semiempirical, and others’ experimental results obtained via photoionization as well as decay processes. The effects of beta decay and internal conversion on X-ray emission probabilities are discussed.

Multiple ionization of argon by positron impact

1996 ◽  
Vol 74 (7-8) ◽  
pp. 373-375 ◽  
Author(s):  
R. Hippler ◽  
S. Helms ◽  
U. Brinkmann ◽  
J. Deiwiks ◽  
H. Schneider ◽  
...  
Keyword(s):  
Electron Impact ◽  
Cross Sections ◽  
Experimental Results ◽  
Positronium Formation ◽  
Positron Impact ◽  
Single Ionization ◽  
Multiple Ionization

Recent experimental results for the multiple ionization of argon by positron impact have been reanalysed. Absolute cross sections for the double and triple ionization of argon were obtained from measured ratios of double-to-single and triple-to-single ionization, using known cross sections for single ionization and for positronium formation. Distinct differences compared to similar results for electron impact are noted.

scholarly journals Valorization of Spent Coffee by Caffeine Extraction Using Aqueous Solutions of Cholinium-Based Ionic Liquids

2021 ◽  
Vol 13 (13) ◽  
pp. 7509
Author(s):  
Ana M. Ferreira ◽  
Hugo M. D. Gomes ◽  
João A. P. Coutinho ◽  
Mara G. Freire
Keyword(s):  
Ionic Liquids ◽  
Aqueous Solutions ◽  
Pure Water ◽  
Waste Product ◽  
Weight Ratio ◽  
Extraction Yield ◽  
Operational Conditions ◽  
Coffee Grounds ◽  
Extractable Compounds ◽  
Nutraceutical Products

Spent coffee grounds (SCGs) are a waste product with no relevant commercial value. However, SCGs are rich in extractable compounds with biological activity. To add value to this coffee byproduct, water and aqueous solutions of cholinium-based ionic liquids (ILs) were studied to extract caffeine from SCGs. In general, all IL aqueous solutions lead to higher extraction efficiencies of caffeine than pure water, with aqueous solutions of cholinium bicarbonate being the most efficient. A factorial planning was applied to optimize operational conditions. Aqueous solutions of cholinium bicarbonate, at a temperature of 80 °C for 30 min of extraction, a biomass–solvent weight ratio of 0.05 and at an IL concentration of 1.5 M, made it possible to extract 3.29 wt% of caffeine (against 1.50 wt% obtained at the best conditions obtained with pure water). Furthermore, to improve the sustainability of the process, the same IL aqueous solution was consecutively applied to extract caffeine from six samples of fresh biomass, where an increase in the extraction yield from 3.29 to 13.10 wt% was achieved. Finally, the cholinium bicarbonate was converted to cholinium chloride by titration with hydrochloric acid envisioning the direct application of the IL-caffeine extract in food, cosmetic and nutraceutical products. The results obtained prove that aqueous solutions of cholinium-based ILs are improved solvents for the extraction of caffeine from SCGs, paving the way for their use in the valorization of other waste rich in high-value compounds.

L X-ray fluorescence cross sections in the atomic region 59 ≤ Z ≤ 82 excited by 16.58 keV photons

1996 ◽  
Vol 74 (5-6) ◽  
pp. 230-235 ◽  
Author(s):  
D. V. Rao ◽  
R. Cesareo ◽  
G. E. Gigante
Keyword(s):  
Excitation Energy ◽  
Least Squares ◽  
Cross Sections ◽  
Experimental Results ◽  
X Ray ◽  
Experimental Cross ◽  
Average Fluorescence ◽  
Good Agreement

LL, Lα, Lβ, and Lγ X-ray fluorescence cross sections for Pr, Sm, Gd, Dy, Ho, Er, Yb, Pt Au, and Pb were measured at the excitation energy 16.58 keV. An X-ray tube and a secondary excitor system was used instead of radioisotopes for the measurements. Experimental cross sections are compared with the theoretical estimates based on relativistic Dirac–Hartree–Slater theory. Average L-shell fluorescence yields [Formula: see text] are deduced using the present experimental cross sections and the theoretical subshell photoionization cross sections. The derived average fluorescence yields are fitted by least squares to polynomials in Z of the form ΣnanZn and compared with theoretical and earlier fitted values. Good agreement is observed ' between the experimental results and the theoretical estimates based on relativistic Dirac–Hartree–Slater theory.

scholarly journals Photoreduction of Cr(VI) Ions in Aqueous Solutions by UV/ Photocatalytic Processes

2012 ◽  
Vol 2012 ◽  
pp. 1-7 ◽  
Author(s):  
Chih Ming Ma ◽  
Yung Shuen Shen ◽  
Po Hsiang Lin
Keyword(s):  
Aqueous Solutions ◽  
Reaction Rate ◽  
Removal Rate ◽  
Experimental Results ◽  
Order Kinetic ◽  
Solution Ph ◽  
Relationship Of ◽  
The Relationship ◽  
Photocatalytic Processes ◽  
Order Kinetic Equation

This study discussed the photoreduction of Cr(VI) ions in aqueous solutions by UV/TiO2photocatalytic processes under various operational factors. Experimental results showed that the removal rate of Cr(VI) increased with decreasing solution pH values and with increasing dosages of organic compounds, indicating that the recombination rate of electrons and h+can be retarded in the reaction systems by the addition of the scavenger, thus raising the reaction rate of Cr(VI). The relationship of the chemical reaction rate of Cr(VI), TiO2dosage, and changes of Cr(VI) concentration was expressed by the pseudo-first-order kinetic equation. Comparing the experimental results of two different doping metals in modified TiO2photoreduction systems, the removal rate of Cr(VI) by the Ag/TiO2process is larger, possibly because the electron transferring ability of Ag is superior to that of Cu. However, the photoreduction rates of Cr(VI) by modified UV/TiO2processes are worse than those by a nonmodified commercial UV/TiO2process.

Numerical Analysis on Nanofluid Forced Convection in Ducts With Triangular Cross Sections

2011 ◽  
Author(s):  
O. Manca ◽  
S. Nardini ◽  
D. Ricci ◽  
S. Tamburrino
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Forced Convection ◽  
Cross Sections ◽  
Fluid Dynamic ◽  
Pure Water ◽  
Convection Flow ◽  
Uniform Heat Flux ◽  
Surface Shear Stress ◽  
Surface Shear

Heat transfer of fluids is very important to many industrial heating or cooling equipments. Convective heat transfer can be enhanced passively by changing flow geometry, boundary conditions or by enhancing the thermal conductivity of the working fluids. An innovative way of improving the fluid thermal conductivity is to introduce suspended small solid nanoparticles in the base fluids. In this paper a numerical investigation on laminar forced convection flow of a water–Al2O3 nanofluid in a duct having an equilateral triangular cross section is performed. The hydraulic diameter is set equal to 1.0×10−2 m. A constant and uniform heat flux on the external surfaces has been applied and the single-phase model approach has been employed. The analysis has been run in steady state regime for a nanoparticle size equal to 38 nm, considering different volume particle concentrations. The CFD code Fluent has been employed in order to solve the tri-dimensional numerical model. Results are presented in terms of temperature and velocity distributions, surface shear stress and heat transfer convective coefficient, Nusselt number and required pumping power profiles. Comparison with results related to the fluid dynamic and thermal behaviors in pure water are carried out in order to evaluate the enhancement due to the presence of nanoparticles in terms of volumetric concentration.

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