Models for the 3-D axisymmetric gravitational potential of the Milky Way Galaxy - A detailed modelling of the Galactic disk

Aims. Galaxy mass models based on simple and analytical functions for the density and potential pairs have been widely proposed in the literature. Disk models constrained by kinematic data alone give information on the global disk structure only very near the Galactic plane. We attempt to circumvent this issue by constructing disk mass models whose three-dimensional structures are constrained by a recent Galactic star counts model in the near-infrared and also by observations of the hydrogen distribution in the disk. Our main aim is to provide models for the gravitational potential of the Galaxy that are fully analytical but also with a more realistic description of the density distribution in the disk component. Methods. From the disk model directly based on the observations (here divided into the thin and thick stellar disks and the HI and H$_2$ disks subcomponents), we produce fitted mass models by combining three Miyamoto-Nagai disk profiles of any "model order" (1, 2, or 3) for each disk subcomponent. The Miyamoto-Nagai disks are combined with models for the bulge and "dark halo" components and the total set of parameters is adjusted by observational kinematic constraints. A model which includes a ring density structure in the disk, beyond the solar Galactic radius, is also investigated. Results. The Galactic mass models return very good matches to the imposed observational constraints. In particular, the model with the ring density structure provides a greater contribution of the disk to the rotational support inside the solar circle. The gravitational potential models and their associated force-fields are described in analytically closed forms, and in addition, they are also compatible with our best knowledge of the stellar and gas distributions in the disk component. The gravitational potential models are suited for investigations of orbits in the Galactic disk.Comment: 22 pages, 13 figures, 11 tables, accepted for publication in A&

Modelling resonances and orbital chaos in disk galaxies. Application to a Milky Way spiral model

Context: Resonances in the stellar orbital motion under perturbations from spiral arms structure play an important role in the evolution of the disks of spiral galaxies. The epicyclic approximation allows the determination of the corresponding resonant radii on the equatorial plane (for nearly circular orbits), but is not suitable in general. Aims: We expand the study of resonant orbits by analysing stellar motions perturbed by spiral arms with Gaussian-shaped profiles without any restriction on the stellar orbital configurations, and we expand the concept of Lindblad (epicyclic) resonances for orbits with large radial excursions. Methods: We define a representative plane of initial conditions, which covers the whole phase space of the system. Dynamical maps on representative planes are constructed numerically, in order to characterize the phase-space structure and identify the precise location of resonances. The study is complemented by the construction of dynamical power spectra, which provide the identification of fundamental oscillatory patterns in the stellar motion. Results: Our approach allows a precise description of the resonance chains in the whole phase space, giving a broader view of the dynamics of the system when compared to the classical epicyclic approach, even for objects in retrograde motion. The analysis of the solar neighbourhood shows that, depending on the current azimuthal phase of the Sun with respect to the spiral arms, a star with solar kinematic parameters may evolve either inside the stable co-rotation resonance or in a chaotic zone. Conclusions: Our approach contributes to quantifying the domains of resonant orbits and the degree of chaos in the whole Galactic phase-space structure. It may serve as a starting point to apply these techniques to the investigation of clumps in the distribution of stars in the Galaxy, such as kinematic moving groups.Comment: 17 pages, 15 figures. Matches accepted version in A&

Disorder-induced double resonant Raman process in graphene

An analytical study is presented of the double resonant Raman scattering process in graphene, responsible for the D and D$^{\prime}$ features in the Raman spectra. This work yields analytical expressions for the D and D$^{\prime}$ integrated Raman intensities that explicitly show the dependencies on laser energy, defect concentration, and electronic lifetime. Good agreement is obtained between the analytical results and experimental measurements on samples with increasing defect concentrations and at various laser excitation energies. The use of Raman spectroscopy to identify the nature of defects is discussed. Comparison between the models for the edge-induced and the disorder-induced D band intensity suggests that edges or grain boundaries can be distinguished from disorder by the different dependence of their Raman intensity on laser excitation energy. Similarly, the type of disorder can potentially be identified not only by the intensity ratio $I_{\mathrm{D}}/I_{\mathrm{D}^{\prime}}$, but also by its laser energy dependence. Also discussed is a quantitative analysis of quantum interference effects of the graphene wavefunctions, which determine the most important phonon wavevectors and scattering processes responsible for the D and D$^{\prime}$ bands.Comment: 10 pages, 4 figure

Management control systems and innovation: A case study grounded in institutional theory

Drawing on the growing literature that has addressed the role of Management Control Systems in innovation and the literature on institutional theory, this study explores the case of Amorim Cork Composites to analyse how the situated rationalities within the company get reflected in the management control practices in use, and then how these practices are used to communicate and provide guidance when innovation is part of the strategy. The study uses a single case study approach at an innovative company, collecting data from 32 interviews, direct observations, and documentation of the company. Based on that data, this study is able to perceive the existence of a rationality that is constructed around the importance of innovation, which becomes a paramount part of the defined strategy and leaves signs on to the internal control practices of the company. After that, through a mix of strategic objectives, well-defined cascaded process of these objectives, values, mottos, objectives related to that situated rationality within the company, and with the commitment created within the “signing” of objectives contracts, managers are able to communicate strategically and provide guidance to the collaborators, driving them to action that makes them more aware.info:eu-repo/semantics/publishedVersio

Management control systems and innovation: A levers of control analysis in an innovative company

Purpose: Building on the growing body of research that has addressed management control systems and innovation, the goal of this study is to assess the extent and nature of the use of controls in an innovative setting and how they work together unveiling the relationships and tensions amongst the Simons’ levers. Design/methodology/approach: This study resorts to an in-depth and single case study in a company that has both a strong orientation to innovation and stable control practices in place. Evidence was collected from 32 interviews, visits to the company, and internal documentation. Findings: At the case company it was possible to find the presence of controls according to all the levers of control. Likewise, joint effects of controls used according to interactive and beliefs approaches and diagnostic and boundary controls showed a consistent reinforcement that push the organization in a single direction. Signs of some countervailing reinforcement between these pairs were also detected, creating tensions. This in general shows that innovation can be weighed against the necessity of goal achievement taking place within fields in which the company can exploit the effort developed. Originality: This study documents the collective use of controls in a context in which innovation is needed, and how the combination of the levers of control with their inner workings and tensions allow the company to have a corporate environment of innovation that is friendly.info:eu-repo/semantics/acceptedVersio

Time-Reversal Symmetry Breaking and Decoherence in Chaotic Dirac Billiards

In this work, we perform a statistical study on Dirac Billiards in the extreme quantum limit (a single open channel on the leads). Our numerical analysis uses a large ensemble of random matrices and demonstrates the preponderant role of dephasing mechanisms in such chaotic billiards. Physical implementations of these billiards range from quantum dots of graphene to topological insulators structures. We show, in particular, that the role of finite crossover fields between the universal symmetries quickly leaves the conductance to the asymptotic limit of unitary ensembles. Furthermore, we show that the dephasing mechanisms strikingly lead Dirac billiards from the extreme quantum regime to the semiclassical Gaussian regime

Bridging management control systems and innovation: the evolution of the research and possible research directions

Purpose: The purpose of this study is to present the evolution of thinking on the role of management control systems (MCSs) in innovation, according to the development of control practices, and to provide a reflection on the achievements of the more recent literature. Design/methodology/approach: This paper assesses articles, books and book chapters that have explored MCSs in innovation, together with seminal works on management accounting and control. Findings: Moving from the traditional phase where MCSs were seen as detrimental to innovation, the literature has now reached a new consensus that attributes a positive role to control. In this recent phase, it arises from the literature that MCSs in the realm of innovation should embrace a multiplicity of controls; MCSs depend on the magnitude and innovation mode of a company; MCSs evolve over time; and that synergies and tensions are expected to arise. Adding these factors to the inherent complexity of innovation, the assertion is that qualitative approaches should be undertaken to infuse the field with more fine-grained evidence. It is also proposed that this methodological approach be used to address the following points: (1) the use of multiple controls; (2) synergies and tensions; and (3) behavioural aspects of controls in relation with innovation. Originality/value: The paper is of value for researchers who have an interest in studying the use of MCSs in innovation and in qualitative research and proposes some areas of research that could be explored.info:eu-repo/semantics/acceptedVersio

A new model for gravitational potential perturbations in disks of spiral galaxies. An application to our Galaxy

We propose a new, more realistic, description of the perturbed gravitational potential of spiral galaxies, with spiral arms having Gaussian-shaped groove profiles. We investigate the stable stellar orbits in galactic disks, using the new perturbed potential. The influence of the bulge mass on the stellar orbits in the inner regions of a disk is also investigated. The new description offers the advantage of easy control of the parameters of the Gaussian profile of its potential. We find a range of values for the perturbation amplitude from 400 to 800 km^2 s^{-2} kpc^{-1} which implies a maximum ratio of the tangential force to the axisymmetric force between 3% and 6%, approximately. Good self-consistency of arm shapes is obtained between the Inner Lindblad resonance (ILR) and the 4:1 resonance. Near the 4:1 resonance the response density starts to deviate from the imposed logarithmic spiral form. This creates bifurcations that appear as short arms. Therefore the deviation from a perfect logarithmic spiral in galaxies can be understood as a natural effect of the 4:1 resonance. Beyond the 4:1 resonance we find closed orbits which have similarities with the arms observed in our Galaxy. In regions near the center, in the presence of a massive bulge, elongated stellar orbits appear naturally, without imposing any bar-shaped potential, but only extending the spiral perturbation a little inward of the ILR. This suggests that a bar is formed with a half-size around 3 kpc by a mechanism similar to that of the spiral arms. The potential energy perturbation that we adopted represents an important step in the direction of self-consistency, compared to previous sine function descriptions of the potential. Our model produces a realistic description of the spiral structure, able to explain several details that were not yet understood.Comment: 12 pag., 11 fig. Accepted for publication in A&A, 2012 December 1