40 research outputs found
Exact General Relativistic Disks with Magnetic Fields
The well-known ``displace, cut, and reflect'' method used to generate cold
disks from given solutions of Einstein equations is extended to solutions of
Einstein-Maxwell equations. Four exact solutions of the these last equations
are used to construct models of hot disks with surface density, azimuthal
pressure, and azimuthal current. The solutions are closely related to Kerr,
Taub-NUT, Lynden-Bell-Pinault and to a one-soliton solution. We find that the
presence of the magnetic field can change in a nontrivial way the different
properties of the disks. In particular, the pure general relativistic
instability studied by Bicak, Lynden-Bell and Katz [Phys. Rev. D47, 4334, 1993]
can be enhanced or cured by different distributions of currents inside the
disk. These currents, outside the disk, generate a variety of axial symmetric
magnetic fields. As far as we know these are the first models of hot disks
studied in the context of general relativity.Comment: 21 pages, 11 figures, uses package graphics, accepted in PR
End-User Development in Industry 4.0: Challenges and Opportunities
This position paper aims to discuss challenges and opportunities related to human-computer interaction technologies for Industry 4.0 and to explore the role that end-user development can play in new industrial scenarios. The paper highlights the gap between what Industry 4.0 and related enabling technologies promise and how the Operator 4.0 will be called on to change his/her work practice. End-user development and meta-design are here proposed as suitable methods to fill this gap and improve operators’ quality of work
Europe
Forests and other wooded lands cover about a third of the European land area and are therefore a characteristic element of the continent’s natural and cultural landscape. Woodland has always provided people with economic, social and environmental products and services. Indeed the history of Western civilisation would be dramatically different without the multiple benefits forests provided to society. However, the current distribution and composition of forests in most parts of Europe reflect the profound cumulative impacts of many centuries of land use change and forest management. While in many cases the loss of biodiversity of cultural landscapes we observe today is closely related to modern exploitation strategies, very often this situation is connected with changes in traditional agricultural systems and the abandonment of traditional land management practices.In this chapter, we examine the principal factors responsible for the development of locally adapted technologies and traditional forest management practices used historically to sustain the long-term availability of forest resources through generations. The chapter also considers the influences of science and modern forestry on the development of cultural landscapes. A central part of the chapter considers the relevance of traditional forest-related knowledge to current debates about sustainable forest management. Inclusion of traditional forest-related knowledge within formal scientific forestry is considered a necessary step to maintain an important part of the European cultural heritage. Such knowledge is also regarded vital for the development of an effective approach to maintaining the ecological balance of European forests and for securing the sustainable development of rural areas in Europe