48,254 research outputs found
Measuring the Hidden Aspects of Solar Magnetism
2008 marks the 100th anniversary of the discovery of astrophysical magnetic
fields, when George Ellery Hale recorded the Zeeman splitting of spectral lines
in sunspots. With the introduction of Babcock's photoelectric magnetograph it
soon became clear that the Sun's magnetic field outside sunspots is extremely
structured. The field strengths that were measured were found to get larger
when the spatial resolution was improved. It was therefore necessary to come up
with methods to go beyond the spatial resolution limit and diagnose the
intrinsic magnetic-field properties without dependence on the quality of the
telescope used. The line-ratio technique that was developed in the early 1970s
revealed a picture where most flux that we see in magnetograms originates in
highly bundled, kG fields with a tiny volume filling factor. This led to
interpretations in terms of discrete, strong-field magnetic flux tubes embedded
in a rather field-free medium, and a whole industry of flux tube models at
increasing levels of sophistication. This magnetic-field paradigm has now been
shattered with the advent of high-precision imaging polarimeters that allow us
to apply the so-called "Second Solar Spectrum" to diagnose aspects of solar
magnetism that have been hidden to Zeeman diagnostics. It is found that the
bulk of the photospheric volume is seething with intermediately strong, tangled
fields. In the new paradigm the field behaves like a fractal with a high degree
of self-similarity, spanning about 8 orders of magnitude in scale size, down to
scales of order 10 m.Comment: To appear in "Magnetic Coupling between the Interior and the
Atmosphere of the Sun", eds. S.S. Hasan and R.J. Rutten, Astrophysics and
Space Science Proceedings, Springer-Verlag, Heidelberg, Berlin, 200
Toward a Formal Semantics for Autonomic Components
Autonomic management can improve the QoS provided by parallel/ distributed
applications. Within the CoreGRID Component Model, the autonomic management is
tailored to the automatic - monitoring-driven - alteration of the component
assembly and, therefore, is defined as the effect of (distributed) management
code. This work yields a semantics based on hypergraph rewriting suitable to
model the dynamic evolution and non-functional aspects of Service Oriented
Architectures and component-based autonomic applications. In this regard, our
main goal is to provide a formal description of adaptation operations that are
typically only informally specified. We contend that our approach makes easier
to raise the level of abstraction of management code in autonomic and adaptive
applications.Comment: 11 pages + cover pag
How people find videos
At present very little is known about how people locate and view videos 'in the wild'. This study draws a rich picture of everyday video seeking strategies and video information needs, based on an ethnographic study of New Zealand university students. These insights into the participants' activities and motivations suggest potentially useful facilities for a video digital library
Exploring social music behaviour: An investigation of music selection at parties
This paper builds an understanding how music is currently listened to by small (fewer than 10 individuals) to medium-sized (10 to 40 individuals) gatherings of peopleâ how songs are chosen for playing, how the music fits in with other activities of group members, who supplies the music, the hardware/software that supports song selection and presentation. This fine-grained context emerges from a qualitative analysis of a rich set of participant observations and interviews focusing on the selection of songs to play at social gatherings. We suggest features for software to support music playing at parties
Online legacy preservation for humanities researchers
As researchers retire or pass away, the online record of their work and their research careers begins to fragment and fade away. We begin with case studies of four New Zealand Humanities researchers, nearing or at the ends of their active careers. What materials currently exist that they believe are essential to detail the results of their research, and that convey the âstoryâ of their work
The use of paper in everyday student life
The information we encounter in modern life, in developed countries, is a hybrid of the physical and the digital. Personal archiving tools allow users to capture and retrieve aspects of their everyday lives in digital form. In this paper we use a diary study of studentsâ interactions with paper-based information to inform the design of such archiving tools
Finding video on the web
At present very little is known about how people locate and view videos. This study draws a rich picture of everyday video seeking strategies and video information needs, based on an ethnographic study of New Zealand university students. These insights into the participantsâ activities and motivations suggest potentially useful facilities for a video digital library
Heavy oil production with energy effective steam-assisted gravity drainage
In reservoirs with extra heavy oil and bitumen, thermal methods are used to reduce the viscosity, in order to extract the oil. Steam-assisted gravity drainage (SAGD) is a thermal method where continuous steam injection is used. In this method, two horizontal wells are placed in parallel. The upper well injects steam and the lower well produces oil and condensed water. The continuous steam injection creates a chamber with uniform temperature. Heavy oil and bitumen reserves in Western Canada, which exceed 175 billion barrels, are becoming increasingly important petroleum sources due to the technical success of the SAGD processes. This study includes Computational fluid dynamics (CFD) modelling and simulations of a horizontal oil well with SAGD. The simulations are performed with inflow control devices (ICD) and autonomous inflow control valves (AICV) completion. In the SAGD processes, it is important that the residence time for steam in the reservoir is high enough to ensure that all the injected steam condenses in the reservoir to reduce the amount of steam injection and thereby making the SAGD process more energy effective. The simulations are carried out with ICD completion to delay the steam breakthrough and with AICV completion to prevent breakthrough of steam and water to the well. The numerical results showed that a most of the steam was produced together with the oil when ICD completion was used. AICV was able to close for steam and water, and the steam was thereby forced to condense in the reservoir, resulting in better utilization of the condensation energy
Connection between a possible fifth force and the direct detection of Dark Matter
If there is a fifth force in the dark sector and dark sector particles
interact non-gravitationally with ordinary matter, quantum corrections
generically lead to a fifth force in the visible sector. We show how the strong
experimental limits on fifth forces in the visible sector constrain the direct
detection cross section, and the strength of the fifth force in the dark
sector. If the latter is comparable to gravity, the spin-independent direct
detection cross section must typically be <~ 10^{-55} cm^2. The anomalous
acceleration of ordinary matter falling towards dark matter is also
constrained: \eta_{OM-DM} <~ 10^{-8}.Comment: 4 pages, 2 figures. v3: contains a more detailed treatment of the
spin-dependence of the effective interaction between dark matter and ordinary
matte
- âŠ