Set Of Theoretical Values Research Articles

Synchrotron radiation induced X‐ray production cross sections of 66Dy at energies across its Li (i = 1–3) subshell absorption edges

The X‐ray production (XRP) cross sections for the 66Dy Lk (k = l, α, η, β2,6,7,15, β1,6, β1,3,4,6, β2,7,15, γ1,5, γ2,3) emission lines have been measured by tuning the incident synchrotron radiation at energies over the range 7.8–9.2 keV and ~10–370 eV above the respective Li (i = 1–3) absorption edges. These measurements aim to check the reliability of the independent particle approximation models used to generate the theoretical data sets of different physical parameters required to calculate the XRP cross sections and also investigate the influence of many body effects on the photoionization process. The measured values have been compared with 4 sets of XRP cross sections calculated using the Dirac–Fock model‐based X‐ray emission rates, 2 sets of the Li (i = 1–3) subshell photoionization cross sections deduced from the self‐consistent Dirac–Hartree–Fock model‐based values and the nonrelativistic Hartree–Fock–Slater model‐based values, and 2 sets of the fluorescence (ωi) and Coster–Kronig (fij) yields. The present measured Lγ2,3 (originating from decay of the L1 subshell vacancies) XRP cross sections are found to be significantly higher than different sets of theoretical values, whereas a good agreement is generally observed for the various other XRP cross sections and relative intensities.

Measurements of mass attenuation coefficients and determination of photoionization cross sections at energies across the Li (i=1–3) edges of 66Dy

The absolute values of the mass attenuation coefficients have been measured at sixty two photon energies across the Li (i=1–3) sub-shell absorption edges of 66Dy covering the region 7.6–14.0keV in order to investigate the influence of near-edge processes on the attenuation coefficients. The present measured attenuation coefficients are found to be higher by up to 10% than the theoretical values evaluated from the computer code XCOM (Berger et al., 2010) and the self-consistent Dirac-Hartree-Slater (DHS) model based values tabulated by Chantler (1995) over the energy region 7.6–14.0keV, except at energies in vicinity (few eV) of the Li (i=1–3) sub-shell absorption edge energies where the measured values are significantly higher (up to 37%) than both the sets of theoretical values. Further, the Li (i=1–3) sub-shell photoionization cross sections, (σLiP)exp, deduced from the present measured mass attenuation coefficients are compared with the non-relativistic Hartree-Fock-Slater (HFS) model based values tabulated by Scofield (1973) and those evaluated from the theoretical total photoionization attenuation coefficients tabulated by Chantler (1995). The deduced (σLiP)exp(i=1–3) values are found to be in better agreement with those evaluated from the tabulations given by Chantler (1995) than the values given by Scofield (1973) over the energy region 7.8 – 14.0keV included in this study. However, at photon energies up to few eV above the Li edges, the deduced (σLiP)exp(i=1–3) values are found to be significantly higher (up to 32%) than both the sets of theoretical values.

On-farm estimation of pig growth parameters from longitudinal data of live weight and feed consumption and the use of a mathematical model

Experimental data of feed consumption and composition, recorded over 5 consecutive short periods of growth from 30 crossbred male pigs divided 2 two groups and fed two restricted feeding regimes from 25 to 160 kg LW, were used to run a model in which a set of theoretical values, to describe the potential chemical growth of the pig, was preliminarily assumed. Simulated values of average daily gain (ADG) and feed conversion ratio (FCR) were the outputs. Estimates of protein mass at maturity (Pm, kg) and relative growth rate (B, d-1) for each feeding regimes where successively obtained through an optimization procedure which has minimized the coefficients of variation of the differences between the estimates and the measurements of ADG and FCR. The very similar values of Pm (33.7 and 33.2 kg), and B (0.0104 and 0.0105 d-1), obtained for the two feed treatments suggested that these values can be used as operational data to describe the growth parameters of the experimental pigs used.

Mean ranges of 209Bi ions in ZnP-glass detector

Mean ranges of 13.0 MeV/u 209Bi ions in ZnP-Glass detector have been measured using a nuclear track technique. Aluminium degrader foils were used in a stair-case configuration over a single ZnP glass plate in this experiment. Mean ranges have been measured as maximum etchable track lengths and are compared with three sets of theoretical values.

Solvent Effects upon the Electronic Absorption and Fluorescence Spectra of Pteridines and Riboflavin and Their Ground and First Excited Singlet State Dipole Moments

The electronic absorption. fluorescence excitation, and fluorescence emission spectra of a series of pteridines (lumazine, xanthopterin, isoxanthopterin, biopterin) and riboflavin (vitamin B2) were measured at room temperature (298 K) in a number of solvents covering a wide range of polarities (dioxane, ethyl ether, chloroform, ethyl acetate, 1-butanol. 2-propanol, ethanol, methanol, dimethylformamide, acetonitrile, and dimethyl sulfoxide). The effects of the solvent upon the spectral properties are discussed. Experimental groundstate dipole moments were measured for selected compounds and were used in combination with the spectral data to evaluate their first excited singlet-state dipole moments by means of the solvatochromic shift method (Bakhshiev's and Kawski-Chamma-Viallet's equations based on the variation of the Stokes shift with the solvent dielectric constant-refractive index term). The theoretical ground and excited singlet-state dipole moments for all pteridines and riboflavin were calculated as a vector sum of the π-component (obtained by the PPP method) and the a-component (obtained from a-bond moments). A second set of theoretical values was obtained by using the CNDO/2method. A good agreement was observed between the experimental and the theoretical values. Excited singlet-state dipole moments are higher than the ground state values by 1 to 6 Debye units for all the pteridines under study with the exception of xanthopterin.

Range and energy-loss of 16.34 Mev/u238U in kapton polyamide

Abstract The range and energy-loss of 16.34 MeV/u 238U in Kapton-polyamide plastic have been measured by the nuclear track technique. The experimental ranges are compared with two sets of theoretical values. It has been observed that ranges obtained from the computer code ‘DEDXT’ are found to be 5–8% lower as compared to measured ones whereas those from Northcliffe and Schilling are about 10–15% overestimated above 8 MeV/u.

On the origin of the observed distribution of toponymic substance (TOP) in avian retina

The present study takes as its basis the published data on the distribution of the substance TOP in embryonic chick retina; the data consists of TOP concentration values associated with retinal tissue fragments formed by dissecting retina in a number of different ways. These values are compared with corresponding sets of theoretical values obtained by the numerical evaluation of various alternative models. Each model assumes a hemispherical retina carrying a source of morphogen that may be TOP itself or a separate substance that prepatterns TOP distribution. The geometry of the morphogen source varies between models but in each case the morphogen is assumed to move within the retina by a diffusion-like process. The nature of morphogen loss from the retina also varies between models, this being alternatively attributed to a significant molecular half-life, removal at a sink of variable geometry, or removal by encounter with a diffusing antagonist that itself originates from a source of variable geometry. The free parameters of each model are adjusted to give best agreement with the measured concentrations and selection is then made between the models on the basis of their sets of residuals under best match conditions. It emerges that TOP is probably too large and slowly diffusing to be the postulated morphogen, and requires a separate, more mobile morphogen to prepattern its distribution. It is also found that the most probable source geometry for this morphogen is a wide spherical sector and this accords well with the idea of an initial small arc of morphogen-producing cells that grows naturally into a sector shape as the retina itself grows. It is not resolved whether morphogen loss should be attributed to a finite half-life or to removal by an antagonistic substance.

H and He II spectra of Of stars

view Abstract Citations (187) References (43) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS H and He II spectra of Of stars. Klein, R. I. ; Castor, J. I. Abstract Previously developed dynamical models of Of stars are used as the basis of a set of statistical equilibrium calculations for hydrogen and ionized helium, on the hypothesis of radiative equilibrium in the stellar envelope. A number of spectral lines of these species are observed in the expanding envelopes of Of stars, and thus they provide diagnostic information about the stellar wind. It is found that the H-alpha line has a strength that is quite sensitive to the rate of mass loss by the star, and comparison with observation indicates loss rates as high as 0.00001 solar mass/yr. The ratio H-alpha/He II 4686-A as observed is in agreement with one of the two sets of theoretical values that are computed; the choice is allowed by uncertainties in the treatment of He II 304-A. Other lines of He II, for which the data are more fragmentary, give only factor-of-2 agreement with theory. The computed profiles of H-alpha and 4686-A are in qualitative agreement with observation, but certain systematic differences exist; the effect of absorption on the violet side of the emission profile is generally more marked in the theoretical profile. The effect of assuming a higher electron temperature in the stellar wind is considered. The primary change would be an upward adjustment in the inferred rates of mass loss, with some worsening of agreement between theory and observation of the H-alpha/4686-A ratio in the later subclasses. Publication: The Astrophysical Journal Pub Date: March 1978 DOI: 10.1086/155980 Bibcode: 1978ApJ...220..902K Keywords: Helium Ions; Hydrogen Atoms; O Stars; Stellar Envelopes; Stellar Models; Stellar Spectra; Atomic Spectra; Dynamic Models; Line Spectra; Stellar Mass Ejection; Stellar Winds; Astrophysics; Envelopes:Of Stars; Mass Loss:Of Stars; Of Stars:Spectra; Of Stars:Stellar Winds full text sources ADS | data products SIMBAD (14)

Born model repulsive interactions in the alkali halides determined from ultrasonic data

Abstract Recent studies of the Born Model of the Li, Na, K and Rb halides using ultrasonic data are summarized. It is shown that, when ultrasonic values of the temperature and pressure derivatives of the bulk modulus are used in the Hildebrand approximation for vibrational terms in the free energy, the stiffness π = − r 2 W ″ R / rW ′ R of the net repulsive interaction, W R , exhibits a smooth and regular behavior when plotted against nearest neighbor distance, d o . This contrasts with the erratic behavior of the repulsive stiffnesses when hydrostatic compression data are employed. Numerical values of the ultrasonic W R and π are given. The experimental stiffnesses compare well in their pattern with a recent comprehensive set of theoretical values (exchange charge model) calculated by Hafemeister and Zahrt. A possible improvement of the theory is pointed out.