Search results for "Total energy"
showing 10 items of 26 documents
Levels of self-consistency in the GW approximation
2009
We perform $GW$ calculations on atoms and diatomic molecules at different levels of self-consistency and investigate the effects of self-consistency on total energies, ionization potentials and on particle number conservation. We further propose a partially self-consistent $GW$ scheme in which we keep the correlation part of the self-energy fixed within the self-consistency cycle. This approximation is compared to the fully self-consistent $GW$ results and to the $G W_0$ and the $G_0W_0$ approximations. Total energies, ionization potentials and two-electron removal energies obtained with our partially self-consistent $GW$ approximation are in excellent agreement with fully self-consistent $…
A standard calculation methodology for human doubly labeled water studies.
2021
Summary The doubly labeled water (DLW) method measures total energy expenditure (TEE) in free-living subjects. Several equations are used to convert isotopic data into TEE. Using the International Atomic Energy Agency (IAEA) DLW database (5,756 measurements of adults and children), we show considerable variability is introduced by different equations. The estimated rCO2 is sensitive to the dilution space ratio (DSR) of the two isotopes. Based on performance in validation studies, we propose a new equation based on a new estimate of the mean DSR. The DSR is lower at low body masses (<10 kg). Using data for 1,021 babies and infants, we show that the DSR varies non-linearly with body mass betw…
Study of a medium-size biological molecular association by means of a pair potential semiempirical approach: β-carboline-lumiflavin
1985
The molecular association between some substituted β-carbolines and a model flavin, lumiflavin, has been studied by means of a semiempirical approach proposed by Fraga based on a 1/R expansion of atom-atom pair potentials. Only stacked minima have been considered because of their possible biological interest. The calculations characterize 15 different minimum stacked conformations, most of them occurring in the complexes considered. The structural and energetic effects of 1–Me, 6–OH and 7–OH substituents of β-carboline are discussed. An equilibrium conformation involving geometric overlap between the pteridinic portion of flavin and the indole group of β-carboline is predicted to be the mos…
Nonequilibrium Green's function approach to strongly correlated few-electron quantum dots
2009
The effect of electron-electron scattering on the equilibrium properties of few-electron quantum dots is investigated by means of nonequilibrium Green's function theory. The ground and equilibrium states are self-consistently computed from the Matsubara (imaginary time) Green's function for the spatially inhomogeneous quantum dot system whose constituent charge carriers are treated as spin-polarized. To include correlations, the Dyson equation is solved, starting from a Hartree-Fock reference state, within a conserving (second-order) self-energy approximation where direct and exchange contributions to the electron-electron interaction are included on the same footing. We present results for…
Data-Driven Clustering Approach to Derive Taste Perception Profiles from Sweet, Salt, Sour, Bitter, and Umami Perception Scores: An Illustration amon…
2021
BACKGROUND Current approaches to studying relations between taste perception and diet quality typically consider each taste-sweet, salt, sour, bitter, umami-separately or aggregately, as total taste scores. Consistent with studying dietary patterns rather than single foods or total energy, an additional approach may be to study all 5 tastes collectively as "taste perception profiles." OBJECTIVE We developed a data-driven clustering approach to derive taste perception profiles from taste perception scores and examined whether profiles outperformed total taste scores for capturing individual variability in taste perception. METHODS The cohort included 367 community-dwelling adults [55-75 y; 5…
Polyphenol intake and cardiovascular risk in the PREDIMED-Plus trial. A comparison of different risk equations
2022
Abstract Introduction and objectives Quantification of cardiovascular risk has been based on scores such as Framingham, Framingham-REGICOR, SCORE or Life's Simple 7 (LS7). In vitro, animal, and randomized clinical studies have shown that polyphenols may provide benefits to the vascular system and reduce the inflammatory response. However, some clinical-epidemiological studies have yielded inconsistent results. Our aim was to assess the possible association between intake of the various polyphenol classes and established cardiovascular scores. Methods This cross-sectional analysis involved 6633 PREDIMED-Plus study participants. Food polyphenol content was estimated by a semiquantitative food…
HAPEX-Sahel
1997
The variation in evaporative fraction and actual evaporation is examined for three sample days in the HAPEX-Sahel Intensive Observation Period (IOP), including data from all the vegetation types and sites. The trends in evaporative fraction over the IOP are also presented for eight sites. The high rate of evaporation from bare soil in the days following rainfall produces a variability in evaporation which makes differences between sites difficult to interpret on a day-to-day basis, but over the whole IOP it is shown that the millet uses a smaller proportion of the available energy for evaporation than the tiger bush or fallow savannah. The combined effect of differences in the total energy …
Diagram technique for nonorthogonal electron group functions. II. Reduced density matrices and total energy
1992
In part I, both the arrow diagram (AD) and expanded AD decompositions of the antisymmetrization operator A for an N‐electron system with wave function represented by the product of mutually nonorthogonal group functions have been considered. Based on them, new diagrams for decompositions of normalization and overlap integrals, reduced density matrices, as well as for total electronic energy of the system are proposed and discussed in detail in the present part. The rules for evaluation of the contribution of each diagram in the form of an analytical expression are obtained. Both the strong and p‐orthogonality approximations are discussed.
First tests of the applicability of gamma-ray imaging for background discrimination in time-of-flight neutron capture measurements
2015
In this work we explore for the first time the applicability of using $\gamma$-ray imaging in neutron capture measurements to identify and suppress spatially localized background. For this aim, a pinhole gamma camera is assembled, tested and characterized in terms of energy and spatial performance. It consists of a monolithic CeBr$_3$ scintillating crystal coupled to a position-sensitive photomultiplier and readout through an integrated circuit AMIC2GR. The pinhole collimator is a massive carven block of lead. A series of dedicated measurements with calibrated sources and with a neutron beam incident on a $^{197}$Au sample have been carried out at n_TOF, achieving an enhancement of a factor…
Negative pressures in CaWO4 nanocrystals
2009
Tetragonal scheelite-type CaWO4 nanocrystals recently prepared by a hydrothermal method show an enhancement of its structural symmetry with the decrease in nanocrystal size. The analysis of the volume dependence of the structural parameters in CaWO4 nanocrystals with the help of ab initio total-energy calculations shows that the enhancement of the symmetry in the scheelite-type nanocrystals is a consequence of the negative pressure exerted on the nanocrystals; i.e., the nanocrystals are under tension. Besides, the behavior of the structural parameters in CaWO4 nanocrystals for sizes below 10 nm suggests an onset of a scheelite-to-zircon phase transformation in good agreement with the predic…