Experimental data

Experimental data in science and engineering is data produced by a measurement, test method, experimental design or quasi-experimental design. In clinical research any data produced are the result of a clinical trial. Experimental data may be qualitative or quantitative, each being appropriate for different investigations. Generally speaking, qualitative data are considered more descriptive and can be subjective in comparison to having a continuous measurement scale that produces numbers. Whereas quantitative data are gathered in a manner that is normally experimentally repeatable, qualitative information is usually more closely related to phenomenal meaning and is, therefore, subject to interpretation by individual observers. Experimental data can be reproduced by a variety of different investigators and mathematical analysis may be performed on these data. See also

Accuracy and precision
Computer science
Data analysis
Empiricism
Epistemology
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Ab initio study of the work functions of elemental metal crystals

This thesis is concerned with the theoretical study of the physical characteristics of metallic surfaces. Ab initio quantum calculations are performed to determine the electronic properties of clean elemental metal surfaces, fully accounting for the material's atomic structure. We aim to understand the atomicscale mechanisms responsible for the dependence of the work function on the surface geometry, including the crystallographic orientation of the surface, the atomic relaxation and reconstruction, as well as the effect of surface edges. We present an accurate method to derive work functions from self-consistent thin-film calculations. By applying a technique based on a macroscopic average, we filter the atomic oscillations in the electronic density to measure precisely the electrostatic potential step at the crystal surface. Combining this quantity with the Fermi energy of a bulk crystal is shown to reduce size effects on the work functions and to yield very precise values. The microscopic origin of the work function anisotropy is studied in sodium, aluminium, copper and gold. For these metals, we find that the trends of increasing work functions for the principal surface orientations reproduce the experimental data and that the trend in aluminium is different from most other metals. The origin of the work function anisotropy is discussed in relation with the orbital character of the electronic states at the Fermi energy. Our study of metal surfaces is extended to the facets of a finite crystal. First-principles studies of the electronic structure of nanowires enable us to obtain the electrostatic potential outside a variety of infinitely-long facet edges. In particular, we determine the microscopic mechanism that allows two different work functions to coexist on either side of a facet edge.

EPFL1999

Too big to grow

Vladislav Mantic Lugo

Open flows, such as wakes, jets, separation bubbles, mixing layers, boundary layers, etc., develop in domains where fluid particles are continuously advected downstream. They are encountered in a wide variety of situations, ranging from nature to technology. Such configurations are characterised by the development of strong instabilities resulting in observable unsteady dynamics. They can be categorised as oscillators which present intrinsic dynamics through self-sustained oscillations, or as amplifiers, which exhibit a strong sensitivity to external disturbances through extrinsic dynamics. Over the years, different linear and nonlinear approaches have been adopted to describe the dynamics of oscillators and amplifiers. However, a simplified physical description that accurately accounts for the nonlinear saturation of instabilities in oscillators as well as that of the response to disturbances in stable amplifier flows is still missing. In this thesis, this question is addressed by introducing a self-consistent semi-linear model. The model is formally constructed by a set of equations where the mean flow is coupled to a linear perturbation equation through the Reynolds stress. The full nonlinear fluctuating motion is thus approximated by a linear equation. The nonlinear dynamics of oscillators is studied in the cylinder wake, where the most unstable eigenmode of finite amplitude is coupled to the instantaneous mean flow for different oscillation amplitudes. This family of solutions provides an instantaneous mean flow evolution as a function of an equivalent slow time. A transient physical picture is formalised, wherein a harmonic perturbation grows and changes the amplitude, frequency, growth-rate and structure due to the modification of the instantaneous mean flow by the Reynolds stress forcing. Eventually this perturbation saturates when the flow is marginally stable. In contrast to standard linear stability analysis around the mean flow, the iterative solution of the model provides a priori an accurate prediction of the instantaneous amplitude, frequency and growth rate, as well as the flow fields, without resorting to any input from numerical or experimental data. Regarding noise amplifiers, the nonlinear saturation of the large linear amplification to external disturbances is studied in the framework of the receptivity analysis of the backward facing step flow. The self-consistent model is first introduced for harmonic forcing and later generalised to stochastic forcing by reformulating it conveniently in frequency domain. The results show an accurate prediction of the response energy as well as the flow fields. Hence, a similar picture is revealed, wherein the Reynolds stress dominates the saturation process. Despite the difference in the dynamics of the described flows, they share the same nonlinear saturation mechanism: the mean flow distortion.

EPFL2015

Too big to grow

Vladislav Mantic Lugo

EPFL2015

Assessment of soil compaction using soil shrinkage modelling : Experimental data and perspectives

Ab initio study of the work functions of elemental metal crystals

Too big to grow

Assessment of soil compaction using soil shrinkage modelling : Experimental data and perspectives

Too big to grow

Ab initio study of the work functions of elemental metal crystals