Study of resonances in 1 x 25 kV AC traction systems with external balancing equipment

© 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.AC traction systems are 1 × 25 or 2 × 25 kV/50 Hz single-phase, nonlinear, time-varying loads that can cause power-quality problems, such as unbalanced or distorted voltages. To reduce unbalance, external balancing equipment is usually connected to these systems, forming the Steinmetz circuit. Parallel resonances can occur in these types of circuits, exciting the harmonic emissions (below 2 kHz) of railway-adjustable speed drives. This paper studies these resonances at pantograph terminals and provides analytical expressions to determine their harmonic frequencies. The expressions are validated from several traction systems in the literature and PSCAD simulations.Postprint (author's final draft

Exploration of flowering control in Lolium perenne L.

End of project reportFlowering or heading in Lolium perenne (perennial ryegrass) is induced by a period of vernalization, followed by long days at higher temperatures. When heading occurs there is a reduction in the feed quality of the forage and therefore extending the period of vegetative growth or eliminating heading during the growing season will improve the potential of perennial ryegrass in agriculture. Conversely, a better control of flowering time and increased heading will lead to higher seed yield for commercial producers. The aim of this project was to investigate the underlying genetic control of flowering time in perennial ryegrass. An F1 population was created by crosspollinating two lines with different heading dates and a genetic linkage map was constructed using Simple Sequence Repeat (SSR) markers. The population and genetic linkage map was then used to identify Quantitative Trait Loci (QTL) associated with heading date, spike length and spikelets per spike. A number of QTL were identified for all traits, some of which had not previously been identified in perennial ryegrass. A Suppression Subtractive Hybridization (SSH) study was also employed to identify genes differentially expressed between an extremely late flowering line and earlier flowering sibling line. Expression analysis of a number of identified genes through floral induction was performed using real time RT-PCR. This revealed a number of transcripts with expression profiles indicative of a role to play in floral induction

A robust comparison of dynamical scenarios in a glass-forming liquid

We use Bayesian inference methods to provide fresh insights into the sub-nanosecond dynamics of glycerol, a prototypical glass-forming liquid. To this end, quasielastic neutron scattering data as a function of temperature have been analyzed using a minimal set of underlying physical assumptions. On the basis of this analysis, we establish the unambiguous presence of three distinct dynamical processes in glycerol, namely, translational diffusion of the molecular centre of mass and two additional localized and temperature-independent modes. The neutron data also provide access to the characteristic length scales associated with these motions in a model-independent manner, from which we conclude that the faster (slower) localized motions probe longer (shorter) length scales. Careful Bayesian analysis of the entire scattering law favors a heterogeneous scenario for the microscopic dynamics of glycerol, where molecules undergo either the faster and longer or the slower and shorter localized motions.Peer ReviewedPostprint (author's final draft

Study of resonances in 1 x 25 kV AC traction systems

AC traction systems are 1 x 25 or 2 x 25 kV 50-Hz single-phase, non-linear, time-varying loads that can cause power quality problems. One of the main concerns about these systems is voltage distortion, because adjustable-speed drives for trains may inject harmonic currents of frequencies below 2kHz. Since the presence of parallel resonances in the contact feeder section of the traction circuit worsens the scenario, traction system resonance phenomena should be analyzed to prevent problems. Several works addressed these phenomena, but they only drew weak numerical conclusions based on the frequency scan method. This article studies 1 x 25 kV traction system resonances at pantograph terminals and provides more effective analytical expressions to locate them and determine the impact of traction system parameters on them. These expressions are validated from several traction systems in the literature.Postprint (author's final draft

Orientational relaxations in solid (1,1,2,2)tetrachloroethane

We employ dielectricspectroscopy and molecular dynamic simulations to investigate the dipolar dynamics in the orientationally disordered solid phase of (1,1,2,2)tetrachloroethane. Three distinct orientational dynamics are observed as separate dielectric loss features, all characterized by a simply activated temperature dependence. The slower process, associated to a glassytransition at 156 ± 1 K, corresponds to a cooperative motion by which each molecule rotates by 180° around the molecular symmetry axis through an intermediate state in which the symmetry axis is oriented roughly orthogonally to the initial and final states. Of the other two dipolar relaxations, the intermediate one is the Johari-Goldstein precursor relaxation of the cooperative dynamics, while the fastest process corresponds to an orientational fluctuation of single molecules into a higher-energy orientation. The Kirkwood correlation factor of the cooperative relaxation is of the order of one tenth, indicating that the molecular dipoles maintain on average a strong antiparallel alignment during their collective motion. These findings show that the combination of dielectricspectroscopy and molecular simulations allows studying in great detail the orientational dynamics in molecular solids.Peer ReviewedPostprint (author's final draft

Implanted muon spin spectroscopy on 2-O-adamantane: a model system that mimics the liquid

The transition taking place between two metastable phases in 2-O-adamantane, namely the [Formula: see text] cubic, rotator phase and the lower temperature P21/c, Z  =  4 substitutionally disordered crystal is studied by means of muon spin rotation and relaxation techniques. Measurements carried out under zero, weak transverse and longitudinal fields reveal a temperature dependence of the relaxation parameters strikingly similar to those exhibited by structural glass[Formula: see text]liquid transitions (Bermejo et al 2004 Phys. Rev. B 70 214202; Cabrillo et al 2003 Phys. Rev. B 67 184201). The observed behaviour manifests itself as a square root singularity in the relaxation rates pointing towards some critical temperature which for amorphous systems is located some tens of degrees above that shown as the characteristic transition temperature if studied by thermodynamic means. The implications of such findings in the context of current theoretical approaches concerning the canonical liquid-glass transition are discussed.Postprint (author's final draft

Giant reversible barocaloric response of (MnNiSi)(1-x)(FeCoGe)(x) (x=0.39, 0.40, 0.41)

MnNiSi-based alloys and isostructural systems have traditionally demonstrated impressive magnetocaloric properties near room temperature associated with a highly tunable first-order magnetostructural transition that involves large latent heat. However, these materials are limited by a small field-sensitivity of the transition, preventing significant reversible effects usable for cooling applications. Instead, the concomitant large transition volume changes prompt a high pressure-sensitivity, and therefore, promise substantial barocaloric performances, but they have been sparsely studied in these materials. Here, we study the barocaloric response in a series of composition-related (MnNiSi)1-x(FeCoGe)x (x = 0.39, 0.40, 0.41) alloys that span continuously over a wide temperature range around ambient. We report on giant reversible effects of ~40 J K-1 kg-1 and up to ~4 K upon application of ~2 kbar and find a degradation of the first-order transition properties with pressure that limits the barocaloric effects at high pressures. Our results confirm the potential of this type of alloys for barocaloric applications, where multicaloric and composite possibilities, along with the high density and relatively high thermal conductivity, constructively add to the magnitude of the caloric effects.Peer ReviewedPostprint (published version

Disentangling a and ß relaxation in orientationally disordered crystals with theory and experiments

We use a microscopically motivated Generalized Langevin Equation (GLE) approach to link the vibrational density of states (VDOS) to the dielectric response of orientational glasses (OGs). The dielectric function calculated based on the GLE is compared with experimental data for the paradigmatic case of two OGs: Freon 112 and Freon 113, around and just above Tg. The memory function is related to the integral of the VDOS times a spectral coupling function Y(¿p), which tells the degree of dynamical coupling between molecular degrees of freedom at different eigenfrequencies. The comparative analysis of the two Freons reveals that the appearance of a secondary ß relaxation in Freon 112 is due to cooperative dynamical coupling in the regime of mesoscopic motions caused by stronger anharmonicity (absent in Freon 113), and is associated with comparatively lower boson peak in the VDOS. The proposed framework brings together all the key aspects of glassy physics (VDOS with boson peak, dynamical heterogeneity, dissipation, anharmonicity) into a single model.Peer ReviewedPostprint (published version

Ultrastable glasses portray similar behaviour to ordinary glasses at high pressure

Pressure experiments provide a unique opportunity to unravel new insights into glass-forming liquids by exploring its effect on the dynamics of viscous liquids and on the evolution of the glass transition temperature. Here we compare the pressure dependence of the onset of devitrification, Ton, between two molecular glasses prepared from the same material but with extremely different ambient-pressure kinetic and thermodynamic stabilities. Our data clearly reveal that, while both glasses exhibit different dTon/dP values at low pressures, they evolve towards closer calorimetric devitrification temperature and pressure dependence as pressure increases. We tentatively interpret these results from the different densities of the starting materials at room temperature and pressure. Our data shows that at the probed pressures, the relaxation time of the glass into the supercooled liquid is determined by temperature and pressure similarly to the behaviour of liquids, but using stability-dependent parametersPostprint (published version