Mean life predictions in respect of Kπ = 2+ collective excitations in deformed even nuclei

1982 ◽  
Vol 60 (10) ◽  
pp. 1461-1470 ◽  
Author(s):  
V. P. Varshney ◽  
K. K. Gupta ◽  
A. K. Chaubey ◽  
D. K. Gupta
Keyword(s):  
Branching Ratios ◽  
Collective Excitations ◽  
Medium Mass ◽  
Theoretical Predictions ◽  
Asymmetric Rotor ◽  
The Mean ◽  
The Asymmetry ◽  
Experimental Values ◽  
Life Predictions ◽  
Rotor Model

The figures of Gupta et al. (Nuovo Cimento B, 58, 101 (1980)) regarding the E2 transitions in heavy mass nuclei have been modified. Medium mass nuclei of range 20° < γ < 30°, which reflect the asymmetry of the nuclei, have been included. We have employed the asymmetric rotor model dependent Q0 for the sake of consistency in theoretical predictions instead of its experimental values. It is observed that theoretical values of B(E2) branching ratios viz. 2+′ → 2+/0+, 2+′ → 2+/2+ → 0+, and 2+′ → 0+/2+ → 0+ coincide excellently with experimental ones for the nuclei, which consistently show a low-lying second 2+ state at about the same energy as the first 4+ state. In general, the agreement with experimental values is found to be within a factor of two. On using absolute B(E2: 2+ → 0+) and γ data, the values of B(E2: 2+′ → 0+), B(E2: 2+′ → 2+), and the mean life of 2+′ states have been predicted.

Triaxiality in 146,148Sm nuclei

1989 ◽  
Vol 67 (2-3) ◽  
pp. 131-134 ◽  
Author(s):  
A. K. Varshney ◽  
K. K. Gupta ◽  
D. K. Gupta ◽  
R. K. Tyagi
Keyword(s):  
Energy Levels ◽  
Branching Ratios ◽  
Energy Ratio ◽  
Poor Agreement ◽  
Model Framework ◽  
Expansion Technique ◽  
Asymmetric Rotor ◽  
Boson Expansion ◽  
Spherical Nuclei ◽  
Rotor Model

Recently, attempts have been made to use the dynamic pairing plus quadrupole model to evaluate B(E2) values, B(E2) branching ratios, and low-lying energy levels for 146,148Sm nuclei, which are in poor agreement with experiment. Application of the boson expansion technique on 148Sm shows too much splitting and an incorrect order for the quintet states, while other properties have not been discussed. In the present work, 146,148Sm nuclei have been described using an asymmetric rotor model framework. The nonaxiality parameter (γ) has been evaluated using the energy ratio E2+′/E6+. Remarkable success has been achieved in explaining the correct ordering of known low-lying energy levels, B(E2) values, and B(E2) branching ratios, which indicate that the so-called spherical nuclei may be treated as triaxial.

DFT Benchmark Study of the O--O Bond Dissociation Energy in Peroxides Validated with High-Level Ab-Initio Calculations

2019 ◽  
Author(s):  
Danilo Carmona ◽  
Pablo Jaque ◽  
Esteban Vöhringer-Martinez
Keyword(s):  
Reference Value ◽  
Basis Set ◽  
Basis Sets ◽  
Mean Deviation ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
The Mean ◽  
Experimental Values ◽  
High Level ◽  
Almost All

<div><div><div><p>Peroxides play a central role in many chemical and biological pro- cesses such as the Fenton reaction. The relevance of these compounds lies in the low stability of the O–O bond which upon dissociation results in radical species able to initiate various chemical or biological processes. In this work, a set of 64 DFT functional-basis set combinations has been validated in terms of their capability to describe bond dissociation energies (BDE) for the O–O bond in a database of 14 ROOH peroxides for which experimental values ofBDE are available. Moreover, the electronic contributions to the BDE were obtained for four of the peroxides and the anion H2O2− at the CBS limit at CCSD(T) level with Dunning’s basis sets up to triple–ζ quality provid- ing a reference value for the hydrogen peroxide anion as a model. Almost all the functionals considered here yielded mean absolute deviations around 5.0 kcal mol−1. The smallest values were observed for the ωB97 family and the Minnesota M11 functional with a marked basis set dependence. Despite the mean deviation, order relations among BDE experimental values of peroxides were also considered. The ωB97 family was able to reproduce the relations correctly whereas other functionals presented a marked dependence on the chemical nature of the R group. Interestingly, M11 functional did not show a very good agreement with the established order despite its good performance in the mean error. The obtained results support the use of similar validation strategies for proper prediction of BDE or other molecular properties by DF Tmethods in subsequent related studies.</p></div></div></div>

scholarly journals An Additive Model to Predict the Rheological and Mechanical Properties of Polypropylene Blends Made by Virgin and Reprocessed Components

Recycling ◽  
2021 ◽  
Vol 6 (1) ◽  
pp. 2
Author(s):  
Francesco Paolo La Mantia ◽  
Maria Chiara Mistretta ◽  
Vincenzo Titone
Keyword(s):  
Experimental Data ◽  
Mechanical Properties ◽  
Additive Model ◽  
Industrial Process ◽  
Theoretical Predictions ◽  
Experimental Values ◽  
Polypropylene Blends ◽  
Polypropylene Sample

In this work, an additive model for the prediction of the rheological and mechanical properties of monopolymer blends made by virgin and reprocessed components is proposed. A polypropylene sample has been reprocessed more times in an extruder and monopolymer blends have been prepared by simulating an industrial process. The scraps are exposed to regrinding and are melt reprocessed before mixing with the virgin polymer. The reprocessed polymer is, then, subjected to some thermomechanical degradation. Rheological and mechanical experimental data have been compared with the theoretical predictions. The results obtained showed that the values of this simple additive model are a very good fit for the experimental values of both rheological and mechanical properties.

Infrared spectra, rotational correlation functions, and intermolecular mean squared torques in compressed gaseous methane

1968 ◽  
Vol 46 (11) ◽  
pp. 1331-1340 ◽  
Author(s):  
R. L. Armstrong ◽  
S. M. Blumenfeld ◽  
C. G. Gray
Keyword(s):  
Correlation Functions ◽  
Theoretical Calculations ◽  
Dominant Contribution ◽  
Dispersion Interactions ◽  
Fundamental Vibration ◽  
Order Of Magnitude ◽  
The Mean ◽  
Vibration Rotation ◽  
Experimental Values ◽  
Rotational Correlation

Extensive measurements of the methane ν3 and ν4 fundamental vibration–rotation bands in CH4–He mixtures and the ν3 band in CH4–He, CH4–N2, and CD4–He mixtures have been carried out in infrared absorption at 295 °K to pressures of 3000 atm. Some profiles of the ν3 band in CH4–Ar mixtures and in pure CH4 have also been obtained. Rotational correlation functions, band moments, and intermolecular mean squared torques have been determined from the ν3 band profiles. Theoretical calculations of the mean squared torque due to anisotropic multipolar, induction and dispersion interactions have been carried out. The theoretical and experimental torques are in order-of-magnitude agreement for the CH4–N2 and CH4–CH4 systems; for CH4–He, CD4–He, and CH4–Ar the theoretical values are two to three orders of magnitude too small to account for the experimental values, indicating that in these cases the dominant contribution to the torques is given by the anisotropic overlap forces.

Ignition and flame quenching of quiescent fuel mists

1978 ◽  
Vol 364 (1717) ◽  
pp. 277-294 ◽  
Keyword(s):  
Reaction Rates ◽  
Ignition Energy ◽  
Minimum Ignition Energy ◽  
Proposed Model ◽  
Theoretical Predictions ◽  
Quenching Distance ◽  
Experimental Values ◽  
Sole Criterion ◽  
Fuel Vapour ◽  
Level Of Agreement

A model is proposed for the ignition of quiescent multidroplet fuel mists which assumes that chemical reaction rates are infinitely fast, and that the sole criterion for successful ignition is the generation, by the spark, of an adequate concentration of fuel vapour in the ignition zone. From analysis of the relevant heat transfer and evaporation processes involved, ex­pressions are derived for the prediction of quenching distance and minimum ignition energy. Support for the model is demonstrated by a close level of agreement between theoretical predictions of minimum ignition energy and the corresponding experimental values obtained using a specially designed ignition apparatus in which ignition energies are measured for several different fuels, over wide ranges of pressure, mixture composition and mean drop size. The results show that both quenching distance and mini­mum ignition energy are strongly dependent on droplet size, and are also dependent, but to a lesser extent, on air density, equivalence ratio and fuel volatility. An expression is derived to indicate the range of drop sizes over which the proposed model is valid.

scholarly journals Quantum Calculations to Estimate the Heat of Hydrogenation Theoretically

2020 ◽  
Author(s):  
Ali Amir Khairbek
Keyword(s):  
Unsaturated Hydrocarbon ◽  
Experimental Results ◽  
Basis Set ◽  
Good Linear ◽  
Complete Basis ◽  
Complete Basis Set ◽  
Complete Basis Set Limit ◽  
The Mean ◽  
Experimental Values ◽  
Linear Correlations

Standard enthalpies of hydrogenation of 29 unsaturated hydrocarbon compounds were calculated in the gas phase by CCSD(T) theory with complete basis set cc-pVXZ, where X = DZ, TZ, as well as by complete basis set limit extrapolation. Geometries of reactants and products were optimized at the M06-2X/6-31g(d) level. This M06-2X geometries were used in the CCSD(T)/cc-pVXZ//M06-2X/6-31g(d) and cc-pV(DT)Z extrapolation calculations. (MAD) the mean absolute deviations of the enthalpies of hydrogenation between the calculated and experimental results that range from 8.8 to 3.4 kJ mol−1 based on the Comparison between the calculation at CCSD(T) and experimental results. The MAD value has improved and decreased to 1.5 kJ mol−1 after using complete basis set limit extrapolation. The deviations of the experimental values are located inside the “chemical accuracy” (±1 kcal mol−1 ≈ ±4.2 kJ mol−1) as some results showed. A very good linear correlations between experimental and calculated enthalpies of hydro-genation have been obtained at CCSD(T)/cc-pVTZ//M06-2X/6-31g(d) level and CCSD(T)/cc-pV(DT)Z extrapolation levels (SD =2.11 and 2.12 kJ mol−1, respectively).

scholarly journals Asteroseismology of the β Cephei Star 12 (DD) Lacertae

1998 ◽  
Vol 185 ◽  
pp. 379-382
Author(s):  
W.A. Dziembowski ◽  
M. Jerzykiewicz
Keyword(s):  
Frequency Spectrum ◽  
Recent Analysis ◽  
Central Frequency ◽  
The Mean ◽  
The Asymmetry

The frequency spectrum in Fig. 1 shows that at least five pulsation modes are excited in DD Lac. Three frequencies, f1, f4, and f3, form an equidistant triplet. In addition to the value of the central frequency, f4, the triplet can be characterized by the mean separation, S = (f3 − f1)/2, and the asymmetry, Δf = f4 − (f1 + f3)/2. Taking the values of the frequencies from a recent analysis of all available data (Pigulski 1994), we get S = 0.15544 ± 0.00021 and Δf = −0.00014 ± 0.00029 d−1.

scholarly journals The ionospheric heating beneath the magnetospheric cleft revisited

2005 ◽  
Vol 23 (3) ◽  
pp. 827-830 ◽  
Author(s):  
G. W. Prölss
Keyword(s):  
Magnetic Activity ◽  
Topside Ionosphere ◽  
Ionospheric Heating ◽  
Superposed Epoch Analysis ◽  
Theoretical Predictions ◽  
Northern Winter ◽  
The Mean ◽  
Epoch Analysis ◽  
Winter Hemisphere ◽  
Prominent Peak

Abstract. A prominent peak in the electron temperature of the topside ionosphere is observed beneath the magnetospheric cleft. The present study uses DE-2 data obtained in the Northern Winter Hemisphere to investigate this phenomenon. First, the dependence of the location and magnitude of the temperature peak on the magnetic activity is determined. Next, using a superposed epoch analysis, the mean latitudinal profile of the temperature enhancement is derived. The results of the present study are compared primarily with those obtained by Titheridge (1976), but also with more recent observations and theoretical predictions.

scholarly journals Measuring precise radial velocities and cross-correlation function line-profile variations using a Skew Normal density

2019 ◽  
Vol 622 ◽  
pp. A131 ◽  
Author(s):  
U. Simola ◽  
X. Dumusque ◽  
J. Cisewski-Kehe
Keyword(s):  
Correlation Function ◽  
Cross Correlation ◽  
Cross Correlation Function ◽  
Normal Density ◽  
Inverse Slope ◽  
Stellar Activity ◽  
New Model ◽  
The Mean ◽  
The Asymmetry ◽  
Skew Normal

Context. Stellar activity is one of the primary limitations to the detection of low-mass exoplanets using the radial-velocity (RV) technique. Stellar activity can be probed by measuring time-dependent variations in the shape of the cross-correlation function (CCF). It is therefore critical to measure with high-precision these shape variations to decorrelate the signal of an exoplanet from spurious RV signals caused by stellar activity. Aims. We propose to estimate the variations in shape of the CCF by fitting a Skew Normal (SN) density which, unlike the commonly employed Normal density, includes a Skewness parameter to capture the asymmetry of the CCF induced by stellar activity and the convective blueshift. Methods. We compared the performances of the proposed method to the commonly employed Normal density using both simulations and real observations with different levels of activity and signal-to-noise ratios. Results. When considering real observations, the correlation between the RV and the asymmetry of the CCF and between the RV and the width of the CCF are stronger when using the parameters estimated with the SN density rather than those obtained with the commonly employed Normal density. In particular, the strongest correlations have been obtained when using the mean of the SN as an estimate for the RV. This suggests that the CCF parameters estimated using a SN density are more sensitive to stellar activity, which can be helpful when estimating stellar rotational periods and when characterizing stellar activity signals. Using the proposed SN approach, the uncertainties estimated on the RV defined as the median of the SN are on average 10% smaller than the uncertainties calculated on the mean of the Normal. The uncertainties estimated on the asymmetry parameter of the SN are on average 15% smaller than the uncertainties measured on the Bisector Inverse Slope Span (BIS SPAN), which is the commonly used parameter to evaluate the asymmetry of the CCF. We also propose a new model to account for stellar activity when fitting a planetary signal to RV data. Based on simple simulations, we were able to demonstrate that this new model improves the planetary detection limits by 12% compared to the model commonly used to account for stellar activity. Conclusions. The SN density is a better model than the Normal density for characterizing the CCF since the correlations used to probe stellar activity are stronger and the uncertainties of the RV estimate and the asymmetry of the CCF are both smaller.

Experimental and theoretical fatigue-crack propagation lives of variously notched plates

1974 ◽  
Vol 9 (2) ◽  
pp. 61-66 ◽  
Author(s):  
R A Smith ◽  
K Jerram ◽  
K J Miller
Keyword(s):  
Fatigue Life ◽  
Crack Propagation ◽  
Finite Element Analyses ◽  
Intensity Factors ◽  
Complex Profile ◽  
Propagation Law ◽  
Theoretical Predictions ◽  
Life Predictions ◽  
Theoretical Results

The fatigue lives of variously notched plates have been determined theoretically and experimentally. Theoretical predictions of fatigue lives involved the determination of stress-intensity factors from finite-element analyses. By invoking a crack propagation law, fatigue-life predictions were made for four specimens. Fatigue experiments were conducted on four notched plates subjected to end load plus bending. Comparison with theoretical results shows that the experimental lives were greater by factors of 1.30 to 1.54. These results are most satisfactory since (1) a safe prediction of fatigue life has been made for a complex profile subjected to non-simple loading conditions, and (2) a theoretical elastic analysis has sufficed for a situation involving plastic strains.

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