Investigating generation mechanisms of tyre/road noise by speed exponent analysis

The purpose of this study is to clarify the influence of air-pumping related noise sources on typical tyre/road noise. The aim is to increase the understanding of noise generation mechanisms and catalyse the development of existing tyre/road noise simulation tools. The speed dependency of measured and simulated tyre/road noise is analysed and the results show that a large part of the noise can be explained by a high speed exponent traditionally connected with air-pumping mechanisms. Surprisingly, this is also the case for rough road surfaces which are expected to mainly generate noise by tyre vibrations. It is also found that vehicle wind noise may have a strong influence on the pass-by noise and care must be taken when analysing measurement data of quiet tyre/road combinations. Even simulated tyre/road noise shows higher speed exponents than what is anticipated without the inclusion of any type of air-pumping mechanism in the model. It is concluded that it is unfeasible to separate noise created by tyre vibrations from noise created by air-pumping with a speed exponent analysis due to the overlap in the speed exponents connected with the different generation mechanisms.     

Electrospinning of complex oxide nanofibers

Electrospinning is a versatile process for drawing fibers of diverse materials including polymers, ceramics, and composites. We demonstrate here its application in the synthesis of complex ceramic oxide materials. The phase formation and morphology of BaTiO₃ nanofibers synthesized via electrospinning is investigated as a function of heat treatment conditions. Fully crystallized BaTiO₃ nanofibers with the perovskite structure are obtained after annealing at 750 °C and show an average grain size of about 30 nm. Tetragonal crystal structure of the fibers is indicated by XRD peak splitting (calculated c/a ratio=1.007), and confirmed by Raman spectroscopy. Furthermore, the advancement in heat treatment of the electrospun fibers yields single crystalline BaTiO₃ nanofibers with 50 nm in diameter and lengths up to 1 μm.     

Thermal stability of the cubic phase in Ba0.5Sr0.5Co0.8Fe0.2O3 - δ (BSCF)1

Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3 - δ (BSCF) is a material with excellent oxygen ionic and electronic transport properties reported by many research groups. In its cubic phase, this mixed ionic-electronic conducting (MIEC) perovskite is a promising candidate for oxygen permeation membranes. For this application, its long-term stability under operating conditions (especially temperature and oxygen partial pressure) is of crucial importance.The present work is focused on the thermal stability of the BSCF cubic phase in the targeted temperature range for applications (700…900 °C) in light of previous studies in literature reporting a reversible transition to a hexagonal phase somewhere below 900 °C.To this end, single phase cubic BSCF powders were annealed at different temperatures over varying periods of time. Phase composition was subsequently analysed by X-ray diffractometry (XRD) in order to determine both the temperature limit and the time-scale for the formation of the hexagonal phase. Additionally, the long-term behaviour of the electrical conductivity was examined on bulk samples at 700 °C, 800 °C and 900 °C over several hundreds of hours, showing a prolonged decrease at 800 °C. The decrease in electrical conductivity at this temperature was also examined on bulk samples with different grain sizes, showing a more pronounced decrease the smaller the average grain size.Coexistence of both phases (cubic and hexagonal) could also be shown for 700 °C, however with a different phase equilibrium than at 800 °C.     

Shear viscosity of the Quark–Gluon Plasma from a virial expansion

We calculate the shear viscosity η in the quark–gluon plasma (QGP) phase within a virial expansion approach with particular interest in the ratio of η to the entropy density s, i.e. η/s. The virial expansion approach allows us to include the interactions between the partons in the deconfined phase and to evaluate the corrections to a single-particle partition function. In the latter approach we start with an effective interaction with parameters fixed to reproduce thermodynamical quantities of QCD such as energy and/or entropy density. We also directly extract the effective coupling α _V for the determination of η. Our numerical results give a ratio η/s≈0.097 at the critical temperature T _c, which is very close to the theoretical bound of 1/(4π). Furthermore, for temperatures T≤1.8T _c the ratio η/s is in the range of the present experimental estimates 0.1–0.3 at RHIC. When combining our results for η/s in the deconfined phase with those from chiral perturbation theory or the resonance-gas model in the confined phase we observe a pronounced minimum of η/s close to the critical temperature T _c.     

Temporal weights in the level discrimination of time-varying sounds

To determine how listeners weight different portions of the signal when integrating level information, they were presented with 1-s noise samples the levels of which randomly changed every 100 ms by repeatedly, and independently, drawing from a normal distribution. A given stimulus could be derived from one of two such distributions, a decibel apart, and listeners had to classify each sound as belonging to the "soft" or "loud" group. Subsequently, logistic regression analyses were used to determine to what extent each of the ten temporal segments contributed to the overall judgment. In Experiment 1, a nonoptimal weighting strategy was found that emphasized the beginning, and, to a lesser extent, the ending of the sounds. When listeners received trial-by-trial feedback, however, they approached equal weighting of all stimulus components. In Experiment 2, a spectral change was introduced in the middle of the stimulus sequence, changing from low-pass to high-pass noise, and vice versa. The temporal location of the stimulus change was strongly weighted, much as a new onset. These findings are not accounted for by current models of loudness or intensity discrimination, but are consistent with the idea that temporal weighting in loudness judgments is driven by salient events.     

Bayesian estimation of Karplus parameters and torsion angles from three-bond scalar couplings constants

We apply Bayesian inference to analyze three-bond scalar coupling constants in an objective and consistent way. The Karplus curve and a Gaussian error law are used to model scalar coupling measurements. By applying Bayes' theorem, we obtain a probability distribution for all unknowns, i.e., the torsion angles, the Karplus parameters, and the standard deviation of the Gaussian. We infer all these unknowns from scalar coupling data using Markov chain Monte Carlo sampling and analytically derive a probability distribution that only involves the torsion angles.     

CAS-supported multiple representations in elementary linear algebra

Usually the Gaussian algorithm (GA) is presented at school as a method of solving a given system of linear equations by reducing it to a “triangular form”. In contrast to this technically oriented view, I will demonstrate a CAS-supported learning environment which includes a visual representation of GA and an activity-oriented «Gauss-game». This game stresses the concept of elementary matrices and leads directly to a partial, implementation of GA in the form of a «semi-automatic” functional CAS-program. These multiple representation of GA tries to take into consideration the research results on mental representations, to design rich variations of student activities and thereby to lead leading to webbeb concepts around GA. The CAS MuPAD is used.     

Induced product representations of extended Cuntz algebras

Let _H be the extended Cuntz algebra over the Hilbert space H. Since its zero grade part _H⁰ is the C^*-inductive limit of B(H^r), we look for some family of representations on an inductive limit of H^r as r. When such construction is shaped according to the structure of _H⁰, von Neumanns notion of a reference sequence of unit vectors for Hilbert infinite tensor products emerges; after a further Rieffel induction step, a class IPR[H] of representations of _H arises. For any two such representations, we describe explicitly their associated intertwiners. Any two representations in IPR[H] are either disjoint or unitarily equivalent. Actions of the group by translation on sequences of unit vectors are involved, as well as the ideals of .