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Interesting Problem (interesting + problem)

Distribution by Scientific Domains

Information Science and Computing	33%

Selected Abstracts

A framework for the transmission of streaming media to mobile devices

INTERNATIONAL JOURNAL OF NETWORK MANAGEMENT, Issue 1 2002
Kevin Curran
One interesting problem is the delay imposed upon mobile receivers when switching between wireless cells. We provide a solution to this in the form of an extension of Mobile IP's handoff algorithm. Our solution involves the exploitation of mobility prediction to predict a mobile terminal's future location based on its previous history (i.e. the last cell that it has been in) and for the media stream to be already present and cached by next cells base station ready for receiving by the mobile device. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Backstepping-based cascade control scheme for batch distillation columns

AICHE JOURNAL, Issue 9 2004
Rosendo Monroy-Loperena
Abstract Nonstationary dynamics, finite-time operation, large thermodynamical uncertainty and delayed composition measurements make the control of batch distillation processes a challenging and interesting problem. In this paper, a cascade control design to regulate the overhead composition of a batch distillation column is presented. The controller is designed within the framework of robust nonlinear control with modeling error compensation techniques in conjunction with a backstepping approach. The result is a cascade controller with a master loop that, driven by the composition regulation error, produces a time-varying set point for the temperature in a certain tray; and with a secondary controller that manipulates the internal reflux ratio to track the time-varying set point determined by the master composition loop. How to extend the controller design to have multiple slave temperature controllers, to improve the regulation of the overhead composition in a batch distillation column, is also presented. The proposed control approach is illustrated by numerical simulations on a full dynamical model. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2113,2129, 2004 [source]

An international and multidisciplinary drilling project into a young complex impact structure: The 2004 ICDP Bosumtwi Crater Drilling Project,An overview

METEORITICS & PLANETARY SCIENCE, Issue 4-5 2007
Christian KOEBERL
It is the source crater of the Ivory Coast tektites. The structure was excavated in 2.1,2.2 Gyr old metasediments and metavolcanics of the Birimian Supergroup. A drilling project was conceived that would combine two major scientific interests in this crater: 1) to obtain a complete paleoenvironmental record from the time of crater formation about one million years ago, at a near-equatorial location in Africa for which very few data are available so far, and 2) to obtain a complete record of impactites at the central uplift and in the crater moat, for ground truthing and comparison with other structures. Within the framework of an international and multidisciplinary drilling project led by the International Continental Scientific Drilling Program (ICDP), 16 drill cores were obtained from June to October 2004 at six locations within Lake Bosumtwi, which is 8.5 km in diameter. The 14 sediment cores are currently being investigated for paleoenvironmental indicators. The two impactite cores LB-07A and LB-08A were drilled into the deepest section of the annular moat (540 m) and the flank of the central uplift (450 m), respectively. They are the main subject of this special issue of Meteoritics & Planetary Science, which represents the first detailed presentations of results from the deep drilling into the Bosumtwi impactite sequence. Drilling progressed in both cases through the impact breccia layer into fractured bedrock. LB-07A comprises lithic (in the uppermost part) and suevitic impact breccias with appreciable amounts of impact melt fragments. The lithic clast content is dominated by graywacke, besides various metapelites, quartzite, and a carbonate target component. Shock deformation in the form of quartz grains with planar microdeformations is abundant. First chemical results indicate a number of suevite samples that are strongly enriched in siderophile elements and Mg, but the presence of a definite meteoritic component in these samples cannot be confirmed due to high indigenous values. Core LB-08A comprises suevitic breccia in the uppermost part, followed with depth by a thick sequence of graywacke-dominated metasediment with suevite and a few granitoid dike intercalations. It is assumed that the metasediment package represents bedrock intersected in the flank of the central uplift. Both 7A and 8A suevite intersections differ from suevites outside of the northern crater rim. Deep drilling results confirmed the gross structure of the crater as imaged by the pre-drilling seismic surveys. Borehole geophysical studies conducted in the two boreholes confirmed the low seismic velocities for the post-impact sediments (less than 1800 m/s) and the impactites (2600,3300 m/s). The impactites exhibit very high porosities (up to 30 vol%), which has important implications for mechanical rock stability. The statistical analysis of the velocities and densities reveals a seismically transparent impactite sequence (free of prominent internal reflections). Petrophysical core analyses provide no support for the presence of a homogeneous magnetic unit (= melt breccia) within the center of the structure. Borehole vector magnetic data point to a patchy distribution of highly magnetic rocks within the impactite sequence. The lack of a coherent melt sheet, or indeed of any significant amounts of melt rock in the crater fill, is in contrast to expectations from modeling and pre-drilling geophysics, and presents an interesting problem for comparative studies and requires re-evaluation of existing data from other terrestrial impact craters, as well as modeling parameters. [source]

2 Looking Beyond Gender Hierarchy: Rethinking Gender at Teotihuacan, Mexico

ARCHEOLOGICAL PAPERS OF THE AMERICAN ANTHROPOLOGICAL ASSOCIATION, Issue 1 2008
Kristin De Lucia
ABSTRACT The absence of gender inequality in art and burials at Teotihuacan, Mexico, poses an interesting problem that has been largely ignored by archaeologists. Archaeologists' lack of attention to gender at Teotihuacan perhaps derives from expectations of gender hierarchies in state societies, resulting in misguided conclusions and unexplored alternative interpretations. In this chapter, I ask how eliminating assumptions about gender hierarchies might help us to gain a better understanding of social relations at Teotihuacan. By incorporating multiple lines of evidence including art, burials, and households, I argue that group identity superseded the importance of the individual, foregrounding "house" identity over gender. Social solidarity may have been particularly necessary at Teotihuacan since a large percentage of male and female residents were foreigners. While socially constructed genders may have been an important component of social identity, I suggest that it was largely an unimportant factor in determining social status. [source]

Acoustic communication in crocodilians: from behaviour to brain

BIOLOGICAL REVIEWS, Issue 3 2009
A. L. Vergne
ABSTRACT Crocodilians and birds are the modern representatives of Phylum Archosauria. Although there have been recent advances in our understanding of the phylogeny and ecology of ancient archosaurs like dinosaurs, it still remains a challenge to obtain reliable information about their behaviour. The comparative study of birds and crocodiles represents one approach to this interesting problem. One of their shared behavioural features is the use of acoustic communication, especially in the context of parental care. Although considerable data are available for birds, information concerning crocodilians is limited. The aim of this review is to summarize current knowledge about acoustic communication in crocodilians, from sound production to hearing processes, and to stimulate research in this field. Juvenile crocodilians utter a variety of communication sounds that can be classified into various functional categories: (1) "hatching calls", solicit the parents at hatching and fine-tune hatching synchrony among siblings; (2) "contact calls", thought to maintain cohesion among juveniles; (3) "distress calls", induce parental protection; and (4) "threat and disturbance calls", which perhaps function in defence. Adult calls can likewise be classified as follows: (1) "bellows", emitted by both sexes and believed to function during courtship and territorial defence; (2) "maternal growls", might maintain cohesion among offspring; and (3) "hisses", may function in defence. However, further experiments are needed to identify the role of each call more accurately as well as systematic studies concerning the acoustic structure of vocalizations. The mechanism of sound production and its control are also poorly understood. No specialized vocal apparatus has been described in detail and the motor neural circuitry remains to be elucidated. The hearing capabilities of crocodilians appear to be adapted to sound detection in both air and water. The ear functional anatomy and the auditory sensitivity of these reptiles are similar in many respects to those of birds. The crocodilian nervous system likewise shares many features with that of birds, especially regarding the neuroanatomy of the auditory pathways. However, the functional anatomy of the telencephalic auditory areas is less well understood in crocodilians compared to birds. [source]

Kinematics, Dynamics, Biomechanics: Evolution of Autonomy in Game Animation

COMPUTER GRAPHICS FORUM, Issue 3 2005
Steve Collins
The believeable portrayal of character performances is critical in engaging the immersed player in interactive entertainment. The story, the emotion and the relationship between the player and the world they are interacting within are hugely dependent on how appropriately the world's characters look, move and behave. We're concerned here with the character's motion; with next generation game consoles like Xbox360TM and Playstation®3 the graphical representation of characters will take a major step forward which places even more emphasis on the motion of the character. The behavior of the character is driven by story and design which are adapted to game context by the game's AI system. The motion of the characters populating the game's world, however, is evolving to an interesting blend of kinematics, dynamics, biomechanics and AI drivenmotion planning. Our goal here is to present the technologies involved in creating what are essentially character automata, emotionless and largely brainless character shells that nevertheless exhibit enough "behavior" to move as directed while adapting to the environment through sensing and actuating responses. This abstracts the complexities of low level motion control, dynamics, collision detection etc. and allows the game's artificial intelligence system to direct these characters at a higher level. While much research has already been conducted in this area and some great results have been published, we will present the particular issues that face game developers working on current and next generation consoles, and how these technologies may be integrated into game production pipelines so to facilitate the creation of character performances in games. The challenges posed by the limited memory and CPU bandwidth (though this is changing somewhat with next generation) and the challenges of integrating these solutions with current game design approaches leads to some interesting problems, some of which the industry has solutions for and some others which still remain largely unsolved. [source]