Search results for "Diagram"
showing 10 items of 795 documents
Analytic first and second derivatives for the CCSDT-n (n = 1–3) models: a first step towards the efficient calculation of CCSDT properties
2000
Analytic first and second derivatives of the energy are implemented for closed-shell systems described by the CCSDT-n (n=1, 1b, 2 and 3) and CC3 electron correlation models. A detailed discussion of the computational requirements of these calculations is given, along with diagrammatic formulas for all relevant quantities. The method is applied to calculate the nuclear magnetic shielding of H2O, CO and N2O and the structure and properties of propadienylidene.
Indispensability and Effectiveness of Diagrams in Molecular Biology
2019
Abstract: In this paper I aim to defend a twofold thesis. On one hand, I will support, against Perini (2005), the indispensability of diagrams when structurally complex biomolecules are concerned, since it is not possible to satisfactorily use linguistic-sentential representations at that domain. On the other hand, even when diagrams are dispensable I will defend than they will generally be more effective than other representations in encoding biomolecular knowledge, relying on Kulvicki-Shimojima’s diagrammatic effectiveness thesis. Finally, I will ground many epistemic virtues of biomolecular diagrams (understandability, explanatory power, prediction and hypothesis evaluation) on their cog…
Diagrammatic Gestures. Cognition, Mathematics, and Semiotics.
2021
here are words having an extraordinary evocative power. This is precisely the case of “Diagram” and “Gesture”. The frst term covers an interconnected network of concepts like “graph”, “schema”, “form”, “model”, “arrow”, and so on... And the same can be said of the second one: just think, for example, of the ideas of “movement”, “bodily action”, “practical activity” or, more generally, of “doing”. Accounting for them has been, over the last 50 years, the aim of signifcant portions of the work conduction in philosophy (Deleuze, Foucault, Merleau-Ponty), mathematics (Grothendieck, Lawvere, Thom), semiotics (Peirce), and theoretical linguistics (Culioli, Langacker, Pottier). The present issue a…
On the construction of lusternik-schnirelmann critical values with application to bifurcation problems
1987
An iterative method to construct Lusternik-Schnirelmann critical values is presented. Examples of its use to obtain numerical solutions to nonlinear eigenvalue problems and their bifurcation branches are given
Microscopic Origins of the Anomalous Melting Behavior of Sodium under High Pressure
2012
X-ray diffraction experiments have shown that sodium exhibits a dramatic pressure-induced drop in melting temperature, which extends from 1000 K at ~30 GPa to as low as room temperature at ~120 GPa. Despite significant theoretical effort to understand the anomalous melting, its origins are still debated. In this work, we reconstruct the sodium phase diagram by using an ab initio quality neural-network potential. Furthermore, we demonstrate that the reentrant behavior results from the screening of interionic interactions by conduction electrons, which at high pressure induces a softening in the short-range repulsion.
Melting of tantalum at high pressure determined by angle dispersive x-ray diffraction in a double-sided laser-heated diamond-anvil cell
2003
The high pressure and high temperature phase diagram of Ta has been studied in a laser-heated diamond-anvil cell (DAC) using x-ray diffraction measurements up to 52 GPa and 3800 K. The melting was observed at nine different pressures, being the melting temperature in good agreement with previous laser-heated DAC experiments, but in contradiction with several theoretical calculations and previous piston-cylinder apparatus experiments. A small slope for the melting curve of Ta is estimated (dTm/dP = 24 K/GPa at 1 bar) and a possible explanation for this behaviour is given. Finally, a P-V-T equation of states is obtained, being the temperature dependence of the thermal expansion coefficient an…
High-pressure phase transitions and compressibility of wolframite-type tungstates
2010
This paper reports an investigation on the phase diagram and compressibility of wolframite-type tungstates by means of x-ray powder diffraction and absorption in a diamond-anvil cell and ab initio calculations. The diffraction experiments show that monoclinic wolframite-type MgWO4 suffers at least two phase transitions, the first one being to a triclinic polymorph with a structure similar to that of CuWO4 and FeMoO4-II. The onset of each transition is detected at 17.1 and 31 GPa. In ZnWO4 the onset of the monoclinic-triclinic transition has been also found at 15.1 GPa. These findings are supported by density-functional theory calculations, which predict the occurrence of additional transiti…
Two-dimensional electrical ordering in physisorbed monolayers
1990
Abstract Monolayers of polar molecules CF3H, CF3Cl and CF2Cl2 have been physisorbed on the graphite (001) surface and studied by X-ray diffraction and dielectric measurements. The temperature-coverage phase diagrams of the quasitwodimensional crystalline phases are presented. The structures of the paraelectric and the electrically ordered phases have been determined. The phase transitions are discussed.
Ferroelasticity and glass-like behavior in alkali halide-alkali cyanide mixed crystals
1991
Abstract Single crystal neutron diffraction studies in (KBr)1-x(KCN)x are summarized. Mixed crystals with CN− concentrations x > 0.6 exhibit ferroelastic phase transitions from a high-temperature plastic phase into a low-temperature elastically ordered phase in which the CN− orientations show long range orientational order and the center of mass lattice exhibits shear distortions. For concentrations x ≤ 0.6 orientational disorder is frozen-in and transitions into an orientational glass state occur. Close to the critical concentration xc ∼ 0.6 the diffraction profiles at the transition temperatures are dominated by diffuse-scattering contributions. These results are compared to model calcula…
X-ray diffraction study of CF3Cl monolayers adsorbed on graphite (001)
1988
X-ray diffraction experiments have been performed on mono- and submonolayers of CF3Cl physisorbed on the (001) surfaces of exfoliated graphite. Five quasi-twodimensional solid phases including the commensurate 2×2 phase, an electrically ordered phase and a disordered incommensurate phase have been observed. A phase diagram is proposed and the various phase transitions are discussed.