This letter considers a nonlinear piezomagnetoelastic energy harvester driven by stationary Gaussian white noise. The increase in the energy generated by this device has been demonstrated for harmonic excitation with slowly varying frequency in simulation and validated by experiment. This paper considers the simulated response of this validated model to random base excitation and shows that the system exhibits a stochastic resonance. If the variance of the excitation were known then the device may be optimized to maximize the power harvested, even under random excitation.

A common energy harvesting device uses a piezoelectric patch on a cantilever beam with a tip mass. The usual configuration exploits the linear resonance of the system; this works well for harmonic excitation and when the natural frequency is accurately tuned to the excitation frequency. A new configuration is proposed, consisting of a cantilever beam with a tip mass that is mounted vertically and excited in the transverse direction at its base. This device is highly non-linear with two potential wells for large tip masses, when the beam is buckled. The system dynamics may include multiple solutions and jumps between the potential wells, and these are exploited in the harvesting device. The electromechanical equations of motion for this system are developed, and its response for a range of parameters is investigated using phase portraits and bifurcation diagrams. The model is validated using an experimental device with three different tip masses, representing three interesting cases: a linear system; a low natural frequency, non-buckled beam; and a buckled beam. The most practical configuration seems to be the pre-buckled case, where the proposed system has a low natural frequency, a high level of harvested power and an increased bandwidth over a linear harvester.

On the basis of a three orbital model and an effective attractive interaction between electrons we investigate the possible superconducting states, with p and f -wave internal symmetry, of Sr2RuO4. For an orbital dependent interaction which acts between in plane and out of plane nearest neighbour Ruthenium atoms we find a state for which the gap in the quasi-particle spectra has a line node on the α and β sheets of the Fermi Surface, but it is complex with no nodes on the γ-sheet. We show that this state is consistent with all the available experimental data. In particular, we present the results of our calculations of the specific heat and penetration depth as functions of the temperature.PACS numbers: 74.70. Pq, 74.20.Rp, 74.25.Bt Ever since triplet pairing was discovered in superfluid 3 He [1], during the early seventies, there has been a constant search for the superconducting analogue of this intriguing macroscopic quantum phenomenon. Although, as yet, there is no metal for which triplet paring has been definitively demonstrated there are a number of good candidates. The evidence that Sr 2 RuO 4 is a triplet superconductor is particularly strong [2,3]. Nevertheless, even in this case the full symmetry of the equilibrium state below T c remains open to debate [2][3][4][5][6][7][8][9][10][11][12].One of the puzzles currently at the centre of attention is the apparent incompatibility between experimental evidence for broken time-reversal symmetry in the superconducting state [13,10] and equally convincing measurements indicating that the order parameter d(k) has a line of nodes on the Fermi Surface [14,15]. The reason why this state of affairs represents a dilemma is that for all odd parity spin triplet pairing states in tetragonal crystals, group theory does not require the simultaneous presence of both broken time-reversal symmetry and line nodes [16]. Consequently, due to their lower condensation energy, line nodes are unlikely. For instance, the pairing state d(k) ∼ (k x + ik y )ê z , proposed by Agterberg et al.[4] on the grounds that it minimizes the free energy, obviously breaks time reversal invariance and has no line nodes. Of course, such states as Graf and Balatsky [7] and other f-wave states [8,9,11] are allowed by symmetry considerations but, the point is that, the nodes are not required by symmetry and hence it is not very attractive ansatz to build a theory on. Under these circumstances it is more advantageous to study physically motivated microscopic models even if the question of the actual mechanism of pairing is to be avoided. In this letter we propose and investigate one such physically motivated model. Our model is prompted by the observation, of Hasegawa et al. [11], that coupling between the Ruthenium layers in Sr 2 RuO 4 leads to convenient, horizontal, k z = ± π c lines of zeros on the Fermi Surface. It features two, intra and inter plane, interaction constants U and U ⊥ respectively, which describe the attraction between electrons each occupying one of three, t 2g , orbitals on Ru...

A coherent-potential approximation CPA is developed for s-wave and d-wave superconductivity in disordered systems. We show that the CPA formalism reproduces the standard pair breaking formula, the selfconsistent Born approximation and the self-consistent T-matrix approximation in the appropriate limits. We implement the theory and compute T c for s-wave and d-wave pairing using an attractive nearest-neighbor Hubbard model featuring both binary-alloy disorder and a uniform distribution of scattering site potentials. We determine the density of states and examine its consequences for low-temperature heat capacity.

The Melnikov criterion is used to examine a global homoclinic bifurcation and transition to chaos in the case of a quarter car model excited kinematically by the road surface profile. By analyzing the potential an analytic expression is found for the homoclinic orbit. By introducing an harmonic excitation term and damping as perturbations, the critical Melnikov amplitude of the road surface profile is found, above which the system can vibrate chaotically.

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