264 research outputs found
Cosmic ray driven dynamo in barred and ringed galaxies
We study the global evolution of the magnetic field and interstellar medium (ISM) of the barred and ringed galaxies in the presence of non-axisymmetric components of the potential, i.e. the bar and/or the oval perturbations. The magnetohydrodynamical dynamo is driven by cosmic rays (CR), which are continuously supplied to the disk by supernova (SN) remnants. Additionally, weak, dipolar and randomly oriented magnetic field is injected to the galactic disk during SN explosions. To compare our results directly with the observed properties of galaxies we construct realistic maps of high-frequency polarized radio emission. The main result is that CR driven dynamo can amplify weak magnetic fields up to few G within few Gyr in barred and ringed galaxies. What is more, the modelled magnetic field configuration resembles maps of the polarized intensity observed in barred and ringed galaxies
Formation of gaseous arms in barred galaxies with dynamically important magnetic field : 3D MHD simulations
We present results of three-dimensional nonlinear MHD simulations of a
large-scale magnetic field and its evolution inside a barred galaxy with the
back reaction of the magnetic field on the gas. The model does not consider the
dynamo process. To compare our modeling results with observations, we construct
maps of the high-frequency (Faraday-rotation-free) polarized radio emission on
the basis of simulated magnetic fields. The model accounts for the effects of
projection and the limited resolution of real observations. We performed 3D MHD
numerical simulations of barred galaxies and polarization maps. The main result
is that the modeled magnetic field configurations resemble maps of the
polarized intensity observed in barred galaxies. They exhibit polarization
vectors along the bar and arms forming coherent structures similar to the
observed ones. In the paper, we also explain the previously unsolved issue of
discrepancy between the velocity and magnetic field configurations in this type
of galaxies. The dynamical influence of the bar causes gas to form spiral waves
that travel outwards. Each gaseous spiral arm is accompanied by a magnetic
counterpart, which separates and survives in the inter-arm region. Because of a
strong compression, shear of non-axisymmetric bar flows and differential
rotation, the total energy of modeled magnetic field grows constantly, while
the azimuthal flux grows slightly until 0.05\Gyr and then saturates.Comment: 4 pages, 4 figure
Simulations of galactic dynamos
We review our current understanding of galactic dynamo theory, paying
particular attention to numerical simulations both of the mean-field equations
and the original three-dimensional equations relevant to describing the
magnetic field evolution for a turbulent flow. We emphasize the theoretical
difficulties in explaining non-axisymmetric magnetic fields in galaxies and
discuss the observational basis for such results in terms of rotation measure
analysis. Next, we discuss nonlinear theory, the role of magnetic helicity
conservation and magnetic helicity fluxes. This leads to the possibility that
galactic magnetic fields may be bi-helical, with opposite signs of helicity and
large and small length scales. We discuss their observational signatures and
close by discussing the possibilities of explaining the origin of primordial
magnetic fields.Comment: 28 pages, 15 figure, to appear in Lecture Notes in Physics "Magnetic
fields in diffuse media", Eds. E. de Gouveia Dal Pino and A. Lazaria
Distributed physical sensors network for the protection of critical infrastractures against physical attacks
The SCOUT project is based on the use of multiple innovative and low impact technologies for the protection of space control ground stations and the satellite links against physical and cyber-attacks, and for intelligent reconfiguration of the ground station network (including the ground node of the satellite link) in the case that one or more nodes fail. The SCOUT sub-system devoted to physical attacks protection, SENSNET, is presented. It is designed as a network of sensor networks that combines DAB and DVB-T based passive radar, noise radar, Ku-band radar, infrared cameras, and RFID technologies. The problem of data link architecture is addressed and the proposed solution described
Nucleon density of 172Yb and 176Yb at the nuclear periphery determined with antiprotonic x rays
Towards transnational feminist queer methodologies
This article introduces the possibilities of transnational feminist queer research as seeking to conceptualise the transnational as a methodology composed of a series of flows that can augment feminist and queer research. Transnational feminist queer methodologies can contest long-standing configurations of power between researcher and researched, subject and object, academics and activists across places, typically those which are embedded in the hierarchies of the Global North/Global South. Beginning with charting our roots in, and routes through, the diverse arenas of transnational, feminist, participatory and queer methodologies, the article uses a transcribed and edited conversation between members of the Liveable Lives research team in Kolkata and Brighton, to start an exploration of transnational feminist queer methodologies. Understanding the difficult, yet constructive moments of collaborative work and dialogue, we argue for engagements with the multiplicities of ‘many-many' lives that recognise local specificities, and the complexities of lives within transnational research, avoiding creating a currency of comparison between places. We seek to work toward methodologies that take seriously the politics of place, namely by creating research that answers the same question in different places, using methods that are created in context and may not be ‘comparable'. Using a dialogue across the boundaries of activism/academia, as well as across geographical locations, the article contends that there are potentials, as well as challenges, in thinking ourselves through transnational research praxis. This seeks complexities and spatial nuances within as well as between places
Attitudes towards the ‘stranger’: negotiating encounters with difference in the UK and Poland
Due to recent intensification in international mobility in Europe, its citizens are exposed to a much wider range of lifestyles and competing attitudes towards difference. Individuals are, therefore, increasingly likely to encounter ‘strangers’ and are, therefore, required to negotiate discontinuities and contradictions between the values that are transmitted through different sites. In response, the article explores the concept of the ‘stranger’ through original data collected in the UK and Poland. The article highlights that the construction of who is a stranger depends on national historical contexts, core values and related visions of the society. The UK and Poland have very different histories and experiences with social diversity, impacting on the ways in which individuals negotiate strange encounters. In both countries, the ‘stranger’ is often seen in a negative way and in relation to the minority groups that are perceived to be visibly different, distinct or ‘unknown’ in contemporary times. In Poland, this is now largely articulated through sexual prejudice (homophobia), whilst in the UK, attitudes towards the ‘stranger’ are largely conveyed through religious prejudice (Islamophobia). As such, the article offers a means of understanding how encounters with difference ‘produce’ strangers in different contexts
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High-resolution x-ray imaging for microbiology at the Advanced Photon Source
Exciting new applications of high-resolution x-ray imaging have emerged recently due to major advances in high-brilliance synchrotrons sources and high-performance zone plate optics. Imaging with submicron resolution is now routine with hard x-rays: the authors have demonstrated 150 run in the 6--10 keV range with x-ray microscopes at the Advanced Photon Source (APS), a third-generation synchrotrons radiation facility. This has fueled interest in using x-ray imaging in applications ranging from the biomedical, environmental, and materials science fields to the microelectronics industry. One important application they have pursued at the APS is a study of the microbiology of bacteria and their associated extracellular material (biofilms) using fluorescence microanalysis. No microscopy techniques were previously available with sufficient resolution to study live bacteria ({approx}1 {micro}m x 4 {micro}m in size) and biofilms in their natural hydrated state with better than part-per-million elemental sensitivity and the capability of determining g chemical speciation. In vivo x-ray imaging minimizes artifacts due to sample fixation, drying, and staining. This provides key insights into the transport of metal contaminants by bacteria in the environment and potential new designs for remediation and sequestration strategies
Theory and Applications of Non-Relativistic and Relativistic Turbulent Reconnection
Realistic astrophysical environments are turbulent due to the extremely high
Reynolds numbers. Therefore, the theories of reconnection intended for
describing astrophysical reconnection should not ignore the effects of
turbulence on magnetic reconnection. Turbulence is known to change the nature
of many physical processes dramatically and in this review we claim that
magnetic reconnection is not an exception. We stress that not only
astrophysical turbulence is ubiquitous, but also magnetic reconnection itself
induces turbulence. Thus turbulence must be accounted for in any realistic
astrophysical reconnection setup. We argue that due to the similarities of MHD
turbulence in relativistic and non-relativistic cases the theory of magnetic
reconnection developed for the non-relativistic case can be extended to the
relativistic case and we provide numerical simulations that support this
conjecture. We also provide quantitative comparisons of the theoretical
predictions and results of numerical experiments, including the situations when
turbulent reconnection is self-driven, i.e. the turbulence in the system is
generated by the reconnection process itself. We show how turbulent
reconnection entails the violation of magnetic flux freezing, the conclusion
that has really far reaching consequences for many realistically turbulent
astrophysical environments. In addition, we consider observational testing of
turbulent reconnection as well as numerous implications of the theory. The
former includes the Sun and solar wind reconnection, while the latter include
the process of reconnection diffusion induced by turbulent reconnection, the
acceleration of energetic particles, bursts of turbulent reconnection related
to black hole sources as well as gamma ray bursts. Finally, we explain why
turbulent reconnection cannot be explained by turbulent resistivity or derived
through the mean field approach.Comment: 66 pages, 24 figures, a chapter of the book "Magnetic Reconnection -
Concepts and Applications", editors W. Gonzalez, E. N. Parke
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