High-pressure study of the non-Fermi liquid material U_2Pt_2In

The effect of hydrostatic pressure (p<= 1.8 GPa) on the non-Fermi liquid state of U_2Pt_2In is investigated by electrical resistivity measurements in the temperature interval 0.3-300 K. The experiments were carried out on single-crystals with the current along (I||c) and perpendicular (I||a) to the tetragonal axis. The pressure effect is strongly current-direction dependent. For I||a we observe a rapid recovery of the Fermi-liquid T^2-term with pressure. The low-temperature resistivity can be analysed satisfactorily within the magnetotransport theory of Rosch, which provides strong evidence for the location of U_2Pt_2In at an antiferromagnetic quantum critical point. For I||c the resistivity increases under pressure, indicating the enhancement of an additional scattering mechanism. In addition, we have measured the pressure dependence of the antiferromagnetic ordering temperature (T_N= 37.6 K) of the related compound U_2Pd_2In. A simple Doniach-type diagram for U_2Pt_2In and U_2Pd_2In under pressure is presented.Comment: 21 pages (including 5 figures); pdf forma

Twisted Open Strings from Closed Strings: The WZW Orientation Orbifolds

Including {\it world-sheet orientation-reversing automorphisms} $\hat{h}_{\sigma} \in H_-$ in the orbifold program, we construct the operator algebras and twisted KZ systems of the general WZW {\it orientation orbifold} $A_g (H_-) /H_-$. We find that the orientation-orbifold sectors corresponding to each $\hat{h}_{\sigma} \in H_-$ are {\it twisted open} WZW strings, whose properties are quite distinct from conventional open-string orientifold sectors. As simple illustrations, we also discuss the classical (high-level) limit of our construction and free-boson examples on abelian $g$.Comment: 65 pages, typos correcte

The coupling of a hearing aid loudspeaker membrane to visco-thermal air layers

Hearing aids and their components are becoming smaller. This presents new problems for the acoustical components, such as the loudspeaker. A circular membrane of a hearing aid loudspeaker is modeled in this paper. Neglecting air influences, the membrane and its suspension behave as a mass spring system. However, under operating conditions, thin layers of air on both sides of the membrane influence its behavior. Air can enter and leave these layers at certain locations on the circular edge of the layer. Since these air layers are thin, visco-thermal effects may have to be taken into account. Therefore, the air layers are not modeled by the wave equation, but by the low reduced frequency model that takes these visco-thermal effects into account. The equations of this model are solved in a polar coordinate system, using a wave-based method. The other acoustical parts of the hearing aid loudspeaker, and the membrane itself are modeled by simple lumped models. The emphasis in this paper is on the coupling of the viscothermal air layer model to the mechanical model of the membrane. Coupling of the air layer to other acoustical parts by using an impedance as boundary condition for the layer model, is also described. The resulting model is verified by experiments. The model and the measurements match reasonably well, considering the level of approximation with lumped parts

Quantum models related to fouled Hamiltonians of the harmonic oscillator

We study a pair of canonoid (fouled) Hamiltonians of the harmonic oscillator which provide, at the classical level, the same equation of motion as the conventional Hamiltonian. These Hamiltonians, say $K_{1}$ and $K_{2}$, result to be explicitly time-dependent and can be expressed as a formal rotation of two cubic polynomial functions, $H_{1}$ and $H_{2}$, of the canonical variables (q,p). We investigate the role of these fouled Hamiltonians at the quantum level. Adopting a canonical quantization procedure, we construct some quantum models and analyze the related eigenvalue equations. One of these models is described by a Hamiltonian admitting infinite self-adjoint extensions, each of them has a discrete spectrum on the real line. A self-adjoint extension is fixed by choosing the spectral parameter $\epsilon$ of the associated eigenvalue equation equal to zero. The spectral problem is discussed in the context of three different representations. For $\epsilon =0$, the eigenvalue equation is exactly solved in all these representations, in which square-integrable solutions are explicity found. A set of constants of motion corresponding to these quantum models is also obtained. Furthermore, the algebraic structure underlying the quantum models is explored. This turns out to be a nonlinear (quadratic) algebra, which could be applied for the determination of approximate solutions to the eigenvalue equations.Comment: 24 pages, no figures, accepted for publication on JM

Modelling actors’ influence on land use change: a dynamic systems approach

In this paper we show how the dynamic behavior of human actors and their influence on land use change can be modeled to produce spatially explicit simulations of future land use. An actor-based dynamic systems approach is integrated with the existing APoLUS (Actor, Policy and Land Use Simulator) cellular automata land use model. Previous versions of APoLUS determined final total land use amounts, (land use claims), by entering estimated growth tendencies by hand. The values of actor state variables, representing the influence of actor behaviour on land use change, were also input at the start of a simulation and did not vary throughout the model run-time. The present paper overcomes these limitations by applying a dynamic systems approach to model both land use claims and the dynamic evolution of actor behaviour over time. We apply the modified model to the case of the Navarre region, Spain, for the example of land use dedicated to solar energy. Three different cases are considered: (i) the case of ‘actor statics’ (the actor variables are static parameters); and also ‘actor dynamics’ under two long-term regional economic scenarios: (ii) the ‘no-growth’ scenario (no long-term economic growth in the region) and (ii) the ‘growth’ scenario (exponential long-term economic growth in the region). Simulation results demonstrate the much faster development of solar energy in the region under study in both ‘actor dynamics’ cases, as compared to the ‘actor statics’ approximation, with regional economic growth further facilitating the solar energy development, as compared to the ‘no-growth’ scenario. Keywords: policy implementation, Contextual Interaction Theory, actor dynamics, land use models, cellular automata, dynamic system

The inner environment of Z~CMa: High-Contrast Imaging Polarimetry with NaCo

Context. Z\,CMa is a binary composed of an embedded Herbig Be and an FU Ori class star separated by $\sim100$ au. Observational evidence indicate a complex environment in which each star has a circumstellar disk and drives a jet, and the whole system is embedded in a large dusty envelope. Aims. We aim to probe the circumbinary environment of Z\,CMa in the inner 400 au in scattered light. Methods. We use high contrast imaging polarimetry with VLT/NaCo at $H$ and $K_s$ bands. Results. The central binary is resolved in both bands. The polarized images show three bright and complex structures: a common dust envelope, a sharp extended feature previously reported in direct light, and an intriguing bright clump located 0\farcs3 south of the binary, which appears spatially connected to the sharp extended feature. Conclusions.We detect orbital motion when compared to previous observations, and report a new outburst driven by the Herbig star. Our observations reveal the complex inner environment of Z\,CMa with unprecedented detail and contrast.Comment: Accepted for publication in A&A Letter