1,375 research outputs found
Viscoresistive MHD Configurations of Plasma in Accretion Disks
We present a discussion of two-dimensional magneto-hydrodynamics (MHD)
configurations, concerning the equilibria of accretion disks of a strongly
magnetized astrophysical object. We set up a viscoresistive scenario which
generalizes previous two-dimensional analyses by reconciling the ideal MHD
coupling of the vertical and the radial equilibria within the disk with the
standard mechanism of the angular momentum transport, relying on dissipative
properties of the plasma configuration. The linear features of the considered
model are analytically developed and the non-linear configuration problem is
addressed, by fixing the entire disk profile at the same order of
approximation. Indeed, the azimuthal and electron force balance equations are
no longer automatically satisfied when poloidal currents and matter fluxes are
included in the problem. These additional components of the equilibrium
configuration induce a different morphology of the magnetic flux surface, with
respect to the ideal and simply rotating disk.Comment: 19 pages, 4 figures. To appear on the Proceedings of the Second
Italian-Pakistani Workshop on Relativistic Astrophysic
An Overview of Video Shot Clustering and Summarization Techniques for Mobile Applications
The problem of content characterization of video programmes is of great interest because video appeals to large audiences and its efficient distribution over various networks should contribute to widespread usage of multimedia services. In this paper we analyze several techniques proposed in literature for content characterization of video programmes, including movies and sports, that could be helpful for mobile media consumption. In particular we focus our analysis on shot clustering methods and effective video summarization techniques since, in the current video analysis scenario, they facilitate the access to the content and help in quick understanding of the associated semantics. First we consider the shot clustering techniques based on low-level features, using visual, audio and motion information, even combined in a multi-modal fashion. Then we concentrate on summarization techniques, such as static storyboards, dynamic video
skimming and the extraction of sport highlights. Discussed summarization methods can be employed in the development of tools that would be greatly useful to most mobile users: in fact these algorithms automatically shorten the original video while preserving most events by highlighting only the important content. The effectiveness of each approach has been analyzed, showing that it mainly depends on the kind of video programme it relates to, and the type of summary or highlights we are focusing on
Radiative observables for linearized gravity on asymptotically flat spacetimes and their boundary induced states
We discuss the quantization of linearized gravity on globally hyperbolic,
asymptotically flat, vacuum spacetimes and the construction of distinguished
states which are both of Hadamard form and invariant under the action of all
bulk isometries. The procedure, we follow, consists of looking for a
realization of the observables of the theory as a sub-algebra of an auxiliary,
non-dynamical algebra constructed on future null infinity . The
applicability of this scheme is tantamount to proving that a solution of the
equations of motion for linearized gravity can be extended smoothly to .
This has been claimed to be possible provided that a suitable gauge fixing
condition, first written by Geroch and Xanthopoulos, is imposed. We review its
definition critically showing that there exists a previously unnoticed
obstruction in its implementation leading us to introducing the concept of
radiative observables. These constitute an algebra for which a Hadamard state
induced from null infinity and invariant under the action of all spacetime
isometries exists and it is explicitly constructed.Comment: 31 pages, added reference
Interactive Video Mashup Based on Emotional Identity
The growth of new multimedia technologies has provided the user with the ability to become a videomaker, instead of being merely part of a passive audience. In such a scenario, a new generation of audiovisual content, referred to as video mashup, is gaining consideration and popularity. A mashup is created by editing and remixing pre-existing material to obtain a product which has its own identity and, in some cases, an artistic value itself. In this work we propose an emotional-driven interactive framework for the creation of video mashup. Given a set of feature movies as primary material, during the mixing task the user is supported by a selection of sequences belonging to different movies which share a similar emotional identity, defined through the investigation of cinematographic techniques used by directors to convey emotions
Using Content Analysis for Video Compression
This paper suggests the idea to model video information as a concatenation of different recurring sources. For each source a different tailored compressed representation can be optimally designed so as to best match the intrinsic characteristics of the viewed scene. Since in a video, a shot or scene with similar visual content recurs more than once, even at distant intervals in time, this enables to build a more compact representation of information. In a specific implementation of this idea, we suggest a content-based approach to structure video sequences into hierarchical summaries, and have each such summary represented by a tailored set of dictionaries of codewords. Vector quantization techniques, formerly employed for compression purposes only, have been here used ïŹrst to represent the visual content of video shots and then to exploit visual-content redundancy inside the video. The depth in the hierarchy determines the precision in the representation both from a structural point of view and from a quality level in reproducing the video sequence. The eïŹectiveness of the proposed method is demonstrated by preliminary tests performed on a limited collection of video-data excerpted from a feature movie. Some additional functionalities such as video skimming may remarkably benefit from this type of representation
A Connotative Space for Supporting Movie Affective Recommendation
The problem of relating media content to usersâaffective responses is here addressed. Previous work suggests that a direct mapping of audio-visual properties into emotion categories elicited by films is rather difficult, due to the high variability of individual reactions. To reduce the gap between the objective level of video features and the subjective sphere of emotions, we propose to shift the representation towards the connotative properties of movies, in a space inter-subjectively shared among users. Consequently, the connotative space allows to define, relate and compare affective descriptions of film videos on equal footing. An extensive test involving a significant number of users watching famous movie scenes, suggests that the connotative space can be related to affective categories of a single user. We apply this finding to reach high performance in meeting userâs emotional preferences
Text Driven Recognition of Multiple Faces in Newspapers
Face recognition is still a hard task when performed on newspaper images, since they often show faces in non-frontal poses, prohibitive lighting conditions, and too poor quality in terms of resolution. In these cases, combining textual information derived from the page articles with visual information proves to be advantageous for improving the recognition performance. In this work, we extract charactersâ names from articles and captions to restrict facial recognition to a limited set of candidates. To solve the difficulties derived from having multiple faces in the same image, we also propose a solution that enables a joint assignment of faces to charactersâ names. Extensive tests in both ideal and real scenarios confirm the soundness of the proposed approach
Gauge/gravity duality and the interplay of various fractional branes
We consider different types of fractional branes on a Z_2 orbifold of the
conifold and analyze in detail the corresponding gauge/gravity duality. The
gauge theory possesses a rich and varied dynamics, both in the UV and in the
IR. We find the dual supergravity solution which contains both untwisted and
twisted 3-form fluxes, related to what are known as deformation and N=2
fractional branes respectively. We analyze the resulting RG flow from the
supergravity perspective, by developing an algorithm to easily extract it. We
find hints of a generalization of the familiar cascade of Seiberg dualities due
to a non-trivial interplay between the different types of fractional branes. We
finally consider the IR behavior in several limits, where the dominant
effective dynamics is either confining, in a Coulomb phase or runaway, and
discuss the resolution of singularities in the dual geometric background.Comment: 38 pages + appendices, 15 figures; v2: refs added and typos correcte
Identifying Video Content Consistency by Vector Quantization
Many post-production videos such as movies and cartoons present well structured story-lines organized in separated visual scenes. Accurate grouping of shots into these logical segments could lead to semantic indexing of scenes for interactive multimedia retrieval and video summaries. In this paper we introduce a novel shot-based analysis approach which aims to cluster together shots with similar visual content. We demonstrate how the use of codebooks of visual codewords (generated by a vector quantization process) represents an effective method to identify clusters containing shots with similar long-term consistency of chromatic compositions. The clusters, obtained by a single-link clustering algorithm, allow the further use of the well-known scene transition graph framework for logical story unit detection and pattern investigation
- âŠ