Calculated Decay Constants Research Articles

Calibration of the Reynolds stress model for turbulent round free jets based on jet half-width

Reynolds stress model (RSM) turbulence models are expected to yield more accurate numerical results for flows with strong anisotropy, such as round free jets, because they directly solve Reynolds stresses rather than modeling them. However, when computational fluid dynamics (CFD) analyses were performed at moderate jet Reynolds numbers using the isotropization by production (IP) RSM model, it was observed that the calculated jet half-widths, decay constants, and spreading rates differed from experimental results due to uncertainties inherent in the turbulence model. In this study, the closure coefficients of the IP RSM turbulence model were calibrated using a variant of the Multi-Objective Genetic Algorithm based on jet half-width data obtained experimentally in the near-field region of the jet. With the use of appropriate discretization schemes and computational grids, the calibrated coefficient combination for the IP RSM turbulence model showed improved accuracy in modeling jet half-widths at Reynolds numbers of 10 000 and 20 000, reducing the errors of calculated decay constants and spreading rates approximately from 2% to 1% and from 16% to 5%, respectively. A detailed examination of the turbulence budget along the longitudinal axis in the self-similar region revealed that the new model coefficients enhanced the modeling of diffusion term but compromised the advection term. As a result of the altered advection term, increased error margins were observed in turbulence intensity (TI) and velocity distribution along the jet centerline, although dissipation along the axis was improved. Consequently, the modeling error in jet half-width calculations using the CFD method was decreased, enhancing the computational cost-effectiveness of the RSM turbulence model compared to more complex turbulence models.

Mass spectra and decay properties of the $c\bar{c}$ c c ¯ meson

In this article we present the result of $c\bar{c}$ meson mass calculation by solving the Schrodinger equation numerically considering the Coulomb plus linear potential. The spin-hyperfine, spin-orbit and tensor components of one-gluon-exchange interactions are employed to obtain the mass spectra of $c\bar{c}$ meson. The calculated mass spectra are compared with the latest results of PDG and are found to be in good accordance. The Regge trajectories of the calculated mass spectra have also been constructed. The values of the wave function are extracted and employed to calculate the leptonic decay constant, $\gamma\gamma$ , gg, $e^{+}e^{-}$ , light hadron (LH) and $\gamma\gamma\gamma$ decay widths of S-wave $0^{-+}$ and $1^{- -}$ states of $c\bar{c}$ meson, the widths have been calculated by Van Royen-Weisskopf formula and by NRQCD mechanism incorporating relativistic corrections of order $\nu^{2}$ . The $\gamma\gamma$ and gg decay widths of $\chi_{0}$ and $\chi_{2}$ states of $c\bar{c}$ meson have also been calculated. The calculated decay constants and widths have been compared with the experimental results.

Ultra-high-b radial diffusion-weighted imaging (UHb-rDWI) of human cervical spinal cord.

Injury in the cervical spinal cord (CSC) can lead to varying degrees of neurologic deficit and persistent disability. Diffusion tensor imaging (DTI) is a promising method to evaluate white matter integrity and pathology. However, the conventional DTI results are limited with respect to the specific details of neuropathology and microstructural architecture. In this study we used ultrahigh-b radial-DWI (UHb-rDWI) with b-values ranging from 0 to ∼7500 s/mm2 and calculated decay constant (DH ) at the high b-values, which gives much deeper insight about the microscopic environment of CSC white matter. To evaluate a novel diffusion MRI, UHb-rDWI technique for imaging of the CSC. Longitudinal. Four healthy controls, each scanned twice. 3T/2D single shot diffusion-weighted stimulated echo planar imaging with reduced field of view. The signal from each pixel of b0 (b = 0) and b-value (b ≠ 0) images were fitted to a biexponential function and normalized. The signal-b curve is obtained by dividing the latter curve by the former. DH was obtained from the curve at b >4000 s/mm2 . A Monte-Carlo Simulation (MCS) was performed to investigate how DH changes upon the increased water-exchange at the CSC. The signal-b curves plotted at multiple levels of healthy CSC are almost identical on two successive scans and show a biexponential decay behavior: fast exponential decay at lower b-values and much slower decay at UHb-values. The mean values of DH were measured as (0.0607 ± 0.02531) ×10-3 and (0.0357 ± 0.02072) ×10-3 s/mm2 at the lateral funiculus and posterior column, respectively. MCS of diffusion MRI shows that the DH is elevated by increased water exchange between the intra- and extraaxonal spaces. UHb-rDWI signal-b plots of the normal CSC were highly reproducible on successive scans and their biexponential decay behavior can be used to characterize normal spinal white matter. 2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;49:204-211.

A comprehensive stability-indicating HPLC method for determination of chloroquine in active pharmaceutical ingredient and tablets: Identification of oxidation impurities

Malaria is the most common parasitic disease in humans. It is estimated that 3 billion people live under the risk of contracting this disease in the world. Chloroquine (CQ) is the drug of choice to treat cases of non-complicated malaria. Forced degradation studies are important to know the drug’s potentials degradation products and to develop a stability indicating method. Thus, chloroquine active pharmaceutical ingredient (API), chloroquine tablets and placebo were submitted to a detailed forced degradation study, using several stressing agents. The results were used on the development of a stability indicating method, using high performance liquid chromatography. The method was validated showing selectivity, precision, accuracy, robustness and linearity in the range of 30–360μg/mL of chloroquine. Chloroquine API and tablets were susceptible to alkaline hydrolysis with NaOH 1mol/L, and to oxidation with H2O2 3.0%. Two degradation products were formed in oxidative test. Kinetics of chloroquine degradation in alkaline hydrolysis was performed for both API and tablets. The calculated decay constant (k1) was 0.223days−1 for API and 0.182days−1 for tablets, while the half-life (t1/2) was 3.1days for API and 3.8days for tablets. Chemical structures have been proposed for the two degradation products formed in the presence of H2O2, using an UHPLC-UV-MS/MS approach.

Theoretical Investigation on the Decaying Behavior of Exchange Interaction in Quinoid and Aromatic Molecular Wires

The difference in the decaying behavior of the exchange interaction between quinoid and aromatic molecular wires was investigated by means of density functional theory calculations. The biradical quinoid structure was realized when the molecular wire consists of thiophene-S,S-dioxide and allyl nitronyl nitroxide radical. While the calculated decay constant (β) for oligothiophene was 0.23 Å–1, the obtained β value for the quinoid structure of oligothiophene-S,S-dioxide was 0.09 Å–1; this finding suggested that the quinoid molecular wire had a smaller β value than the aromatic wire. It was also found that β decreases upon oxidation of the sulfur atom in the oligothiophene due to an increase in its olefinic nature. The quinoid molecular wire made of thiophene-S,S-dioxide can be thus considered as a suitable system for the charge and spin transport in molecular electronics and spintronics.

Modeling and assessment of long afterglow decay curves.

Multiple exponential equations have been successfully fitted to experimental long afterglow decay curve data for some phosphor materials by previous researchers. The calculated decay constants in such equations are used to assess the phosphorescence characteristics of an object. This study generates decay constants from experimental test data and from existing literature for comparison. It shows that the decay constants of an object may not be invariant and that they are dependent on phosphor material, temperature, irradiation intensity, sample thickness, and phosphor density for samples. In addition, the use of different numbers of exponential components in interpretation leads to different numerical results for decay constants. The relationship between the calculated decay constants and the afterglow characteristics of an object is studied and discussed in this paper. The appearance of the luminescence intensity is less correlated to the decay constants than to the time-invariant constants in an equation.

Prompt Neutron Decay for Delayed Critical Bare and Natural-Uranium-Reflected Metal Spheres of Plutonium and Highly Enriched Uranium

Prompt neutron decay at delayed criticality was measured by Oak Ridge National Laboratory for uranium-reflected highly enriched uranium (HEU) and Pu metal spheres (FLATTOP), for an unreflected Pu metal (4.5% 240Pu) sphere (JEZEBEL) at Los Alamos National Laboratory (LANL) and for an unreflected HEU metal sphere at Oak Ridge Critical Experiments Facility. The average prompt neutron decay constants from hundreds of Rossi-α and randomly pulsed neutron measurements with 252Cf at delayed criticality are as follows: 3.8458 ± 0.0016 × 105 s−1, 2.2139 ± 0.0022 × 105 s−1, 6.3126 ± 0.0100 × 105 s−1, and 1.1061 ± 0.0009 × 106 s−1, respectively. These values agree with previous measurements by LANL for FLATTOP, JEZEBEL, and GODIVA I as follows: 3.82 ± 0.02 × 105 s−1 for a uranium core; 2.14 ± 0.05 × 105 s−1 and 2.29 × 105 s−1 (uncertainty not reported) for a plutonium core; 6.4 ± 0.1 × 105 s−1, and 1.1 ± 0.1 × 106 s−1, respectively, but have smaller uncertainties because of the larger number of measurements. For the FLATTOP and JEZEBEL assemblies, the measurements agree with calculations. Traditionally, the calculated decay constants for the bare uranium metal sphere GODIVA I and the Oak Ridge Uranium Metal Sphere were higher than experimental by ~10%. Other energy-dependent quantities for the bare uranium sphere agree within 1%.

Degradation of diazinon contaminated waters by ionizing radiation

Study of degradation of diazinon pesticide by 60Co gamma irradiation in a single aqueous solution was conducted on a laboratory scale and the effect of ionizing radiation on the removal efficiency of diazinon residues was investigated. Distilled water solutions at three different concentrations of targeted compound (i.e. 0.329, 1.643 and 3.286 μmol dm −3) were irradiated over the range 0.1–6 kGy. The initial concentration of contaminant and irradiation doses play a significant role in the rate of destruction; this was evident from the calculated decay constants of diazinon residue. Gamma radiolysis showed that the absorbed doses from 1.5 to 5.6 kGy at a dose rate of 4.79 kGy h −1 achieved 90% destruction for diazinon with initial concentrations over the range 0.329–3.286 μmol dm −3. The radiolytic degradation by-products and their mass balances were qualitative determined with good confidence by using GC/quadrupole mass spectrometry (GC/MS) with EI + or CI in positive and negative ionization mode and diazinon degradation pathways were proposed. Additionally, the final products of irradiation were identified by ion chromatography (IC) to be acetic and formic acid.

Does the calculated decay constant for 7Be vary significantly with chemical form and/or applied pressure?

It has recently been reported that the electron capture decay constant for 7Be varies by as much as 1.5% in different oxidic compounds of Be and that application of 400 kbar pressure to a Be(OH) 2 gel increases its 7Be decay constant by about 1%. Differences of such magnitude in decay rate might be useful in determining the speciation of Be in glasses, gels and aqueous solutions. We have recently calculated structures, 9Be NMR shieldings and IR/Raman spectra for both monomeric and oligomeric species of Be to assist in determining Be speciation. We here use similar methods to calculate the electron densities at the Be nucleus, which determine the rates of electron capture decay. We find that variations in the electron density at the Be nucleus in a number of oxidic compounds are only at the 0.1–0.4% level, as had been concluded in the 1970s. This raises doubts about the recent experimental results which show larger variations from one oxidic compound to another. The calculated 9Be NMR shifts of these species differ by only a few ppm, but such changes are readily measurable by NMR spectroscopy, and they depend systematically on the degree of hydrolysis and the degree of oligomerization. Rough estimates of the effects of Be–O bond compression in Be(OH) 4 2− on the energy and the electron density at the nucleus indicate that several hundred kbar of pressure could increase the electron density by 1% or more, qualitatively consistent with the experimental results.

Length-dependence of intramolecular electron transfer in σ-bonded rigid molecular rods: an ab initio molecular orbital study

The dependence of electron transfer (ET) coupling element, V AB, on the length of rigid-rod-like systems consisting of bicyclo[1.1.1]pentane (BCP), cubane (CUB), and bicyclo[2.2.2]octane (BCO) monomers, has been investigated with the use of ab initio Hartree–Fock (HF) method employing Marcus–Hush two-state (TS) model. The value of V AB decreases exponentially with increase in the number of the cage units of the σ-bonded molecules. The calculated decay constant, β, shows good agreement with previously reported data. For molecular length⩾15 A ̊ , the value of V AB becomes negligibly small, suggesting complete suppression of the through bond direct tunneling contribution to ET process.

Pulsed-source experiments in a reflected coupled-core reactor-I. reactivity measurements

The behaviour has been studied of the Universities Research Reactor (URR) at Risley, Lancs., when subjected to pulses of fast neutrons. The URR is an enriched-uranium, water-cooled and moderated, graphite-reflected system, the core consisting of two coupled fuel slabs spaced 1 ft apart and containing approximately 3300 g of 235U. The work is reported in two parts. In the work reported in this first section the pulsed source was located symmetrically relative to the core slabs (so that the coupled-core nature of the reactor was suppressed) and the results analysed using the more conventional point-reactor models. A reflector decay mode, as predicted by a three-region Cohn model was not observed. The delayed critical prompt decay constant of the URR was found to be 33·5 ± 0·6 sec −1. The experiments showed that, for sub-critical core loadings in a highly reflected system such as the URR, the data is analysed most readily and reliably by the Simmons-King method supplemented by calculated changes in the generation time. For this reactor, the Gozani method corrected for kinetic distortion was found to be the most suitable of the modified pulse techniques. METHUSELAH II—GOG multigroup-diffusion poison-removal calculations gave prompt and delayed flux distributions which accounted well for the observed spatial dependence of the modified-pulse-technique reactivities. The experimental and calculated decay constants, although substantially in agreement at critical, diverged by as much as 15–25 per cent for the subcritical core loadings. Part 11 of this work will examine the coupled, two-slab, nature of the URR.