Identifying Self-excited Vibrations with Evolutionary Computing

AbstractThis study uses differential evolution to identify the coeffic ients of second-order differentia l equations of self-e xc ited vibrations fro m a time signal. The motivation is found in the ample occurrence of this vibration type in engineering and physics, in particu lar in the real -life proble m of v ibrations of hydraulic structure gates. In the proposed method, an equation structure is assumed at the level of the ordinary differentia l equation and a population of candidate coefficient vectors undergoes evolutionary training. In this way the numerical constants of non-linear terms of various self-e xc ited vibration types were recovered fro m the time signal and the velocity value only at the initial t ime. Co mparisons are given regarding accuracy and computing time. Dependency of the test errors on the algorith m para meters is studied in a sensitivity analysis. The presented evolutionary method shows good promise for future applicat ion in engineering systems, in particular operational early -wa rning systems that recognise oscillations with negative damping before they can cause damage

More is different: 50 years of nuclear BCS

Many of the concepts which are at the basis of the development associated with a quantitative treatment of the variety of phenomena associated with the spontaneous breaking of gauge symmetry in nuclei have been instrumental in connection with novel studies of soft matter, namely of protein evolution and protein folding. Although the route to these subjects and associated development does not necessarily imply the nuclear physics connection, such a connection has proven qualitatively and quantitatively inspiring. In particular to model protein evolution in terms of the alignment of quasispins displaying twenty different projections, one for each of the twenty amino acids occurring in nature, and the associated symmetry breaking in information (sequence) space. Emergent properties of the corresponding phase transition are domain walls which stabilize local elementary structures (LES), few groups of 10-20 aminoacids which become structured already in the denatured state provide the molecular recognition directing protein folding. In fact, their docking is closely related to the transition state of the process. While the two-step, yes or no, folding process, does not provide direct information concerning LES, one can force LES from virtual to become real, observable final state entities. Getting again inspiration from the nuclear case (virtual processes contributing to pair correlations can be forced to become real with the help of a probe which itself changes particle number by two), one would expect that to make real virtual LES, that is segments of the protein which already at an early stage of the folding process flicker in and out of their native conformation, one needs a probe which itself displays a similar behaviour. Peptides displaying a sequence identical to LES are such probes.Comment: Contribution to the Volume 50 years of Nuclear BCS edited by World Scientifi

A molecular state of correlated electrons in a quantum dot

Correlation among particles in finite quantum systems leads to complex behaviour and novel states of matter. One remarkable example is predicted to occur in a semiconductor quantum dot (QD) where at vanishing density the Coulomb correlation among electrons rigidly fixes their relative position as that of the nuclei in a molecule. In this limit, the neutral few-body excitations are roto-vibrations, which have either rigid-rotor or relative-motion character. In the weak-correlation regime, on the contrary, the Coriolis force mixes rotational and vibrational motions. Here we report evidence of roto-vibrational modes of an electron molecular state at densities for which electron localization is not yet fully achieved. We probe these collective modes by inelastic light scattering in QDs containing four electrons. Spectra of low-lying excitations associated to changes of the relative-motion wave function -the analogues of the vibration modes of a conventional molecule- do not depend on the rotational state represented by the total angular momentum. Theoretical simulations via the configuration-interaction (CI) method are in agreement with the observed roto-vibrational modes and indicate that such molecular excitations develop at the onset of short-range correlation.Comment: PDF file only; 24 pages, 7 figures, 2 table. Supplementary Information include

Non-Markovian Quantum State Diffusion for Temperature-Dependent Linear Spectra of Light Harvesting Aggregates

Non-Markovian Quantum State Diffusion (NMQSD) has turned out to be an efficient method to calculate excitonic properties of aggregates composed of organic chromophores, taking into account the coupling of electronic transitions to vibrational modes of the chromophores. NMQSD is an open quantum system approach that incorporates environmental degrees of freedom (the vibrations in our case) in a stochastic way. We show in this paper that for linear optical spectra (absorption, circular dichroism) no stochastics is needed, even for finite temperatures. Thus, the spectra can be obtained by propagating a single trajectory. To this end we map a finite temperature environment to the zero temperature case using the so-called thermofield method. The resulting equations can then be solved efficiently by standard integrators.Comment: 14 pages, 4 figure

Chatter milling modeling of active magnetic bearing spindle in high-speed domain

A new dynamical modeling of Active Magnetic Bearing Spindle (AMBS) to identify machining stability of High Speed Milling (HSM) is presented. This original modeling includes all the minimum required parameters for stability analysis of AMBS machining. The stability diagram generated with this new model is compared to classical stability lobes theory. Thus, behavior’s specificities are highlighted, especially the major importance of forced vibrations for AMBS. Then a sensitivity study shows impacts of several parameters of the controller. For example, gain adjustment shows improvements on stability. Side milling ramp test is used to quickly evaluate the stability. Finally, the simulation results are then validated by HSM cutting tests on a 5 axis machining center with AMBS

Proceedings of the Thirteenth International Conference on Time-Resolved Vibrational Spectroscopy

The thirteenth meeting in a long-standing series of “Time-Resolved Vibrational Spectroscopy” (TRVS) conferences was held May 19th to 25th at the Kardinal Döpfner Haus in Freising, Germany, organized by the two Munich Universities - Ludwig-Maximilians-Universität and Technische Universität München. This international conference continues the illustrious tradition of the original in 1982, which took place in Lake Placid, NY. The series of meetings was initiated by leading, world-renowned experts in the field of ultrafast laser spectroscopy, and is still guided by its founder, Prof. George Atkinson (University of Arizona and Science and Technology Advisor to the Secretary of State). In its current format, the conference contributes to traditional areas of time resolved vibrational spectroscopies including infrared, Raman and related laser methods. It combines them with the most recent developments to gain new information for research and novel technical applications. The scientific program addressed basic science, applied research and advancing novel commercial applications. The thirteenth conference on Time Resolved Vibrational Spectroscopy promoted science in the areas of physics, chemistry and biology with a strong focus on biochemistry and material science. Vibrational spectra are molecule- and bond-specific. Thus, time-resolved vibrational studies provide detailed structural and kinetic information about primary dynamical processes on the picometer length scale. From this perspective, the goal of achieving a complete understanding of complex chemical and physical processes on the molecular level is well pursued by the recent progress in experimental and theoretical vibrational studies. These proceedings collect research papers presented at the TRVS XIII in Freising, German