11,387 research outputs found
Giant Leaps and Minimal Branes in Multi-Dimensional Flux Landscapes
There is a standard story about decay in multi-dimensional flux landscapes:
that from any state, the fastest decay is to take a small step, discharging one
flux unit at a time; that fluxes with the same coupling constant are
interchangeable; and that states with N units of a given flux have the same
decay rate as those with -N. We show that this standard story is false. The
fastest decay is a giant leap that discharges many different fluxes in unison;
this decay is mediated by a 'minimal' brane that wraps the internal manifold
and exhibits behavior not visible in the effective theory. We discuss the
implications for the cosmological constant.Comment: Minor updates to agree with published version. 9 pages, 4 figure
The design and implementation of a system for the automatic generation of narrative debriefs for AUV Missions
Increased autonomy allows autonomous underwater vehicles to act without direct
support or supervision. This requires increased complexity, however, and a deficit
of trust may form between operators and these complex machines, though previous
research has shown this can be reduced through repeated experience with the system
in question. Regardless of whether a mission is performed with real vehicles or their
simulated counterparts, effective debrief represents the most efficient method for
performing an analysis of the mission.
A novel system is presented to maximise the effectiveness of a debrief by ordering
the mission events using a narrative structure, which has been shown to be the
quickest and most effective way of communicating information and building a situation
model inside a person’s mind. Mission logs are de-constructed and analysed,
then optimisation algorithms used to generate a coherent discourse based on the
events of the missions with any required exposition. This is then combined with
a timed mission playback and additional visual information to form an automated
mission debrief.
This approach was contrasted with two alternative techniques: a simpler chronological
ordering; and a facsimile of the current state of the art. Results show
that participant recall accuracy was higher and the need for redundant delivery of
information was lower when compared to either of the baselines. Also apparent is
a need for debriefs to be adapted to individual users and scenarios. Results are
discussed in full, along with suggestions for future avenues of research
Abundant variation in microsatellites of the parasitic nematode Trichostrongylus tenuis and linkage to a tandem repeat
An understanding of how genes move between and within populations of parasitic nematodes is important in combating the evolution and spread of anthelmintic resistance. Much has been learned by studying mitochondrial DNA markers, but autosomal markers such as microsatellites have been applied to only a few nematode species, despite their many advantages for studying gene flow in eukaryotes. Here, we describe the isolation of 307 microsatellites from Trichostrongylus tenuis, an intestinal nematode of red grouse. High levels of variation were revealed at sixteen microsatellite loci (including three sex-lined loci) in 111 male T. tenuis nematodes collected from four hosts at a single grouse estate in Scotland (average He = 0.708; mean number of alleles = 12.2). A population genetic analysis detected no deviation from panmixia either between (F(ST) = 0.00) or within hosts (F(IS) = 0.015). We discuss the feasibility of developing microsatellites in parasitic nematodes and the problem of null alleles. We also describe a novel 146-bp repeat element, TteREP1, which is linked to two-thirds of the microsatellites sequenced and is associated with marker development failure. The sequence of TteREP1 is related to the TcREP-class of repeats found in several other trichostrongyloid species including Trichostrongylus colubriformis and Haemonchus contortus
Opportunities for CO2 equivalent emissions reductions via flare and vent mitigation: A case study for Alberta, Canada
AbstractGlobal flaring and venting of gas associated with petroleum production is a significant source of greenhouse gas emissions and airborne pollutants that has proven difficult to mitigate. This work examines the technical and economic potential for flaring and venting mitigation in a mature oil and gas producing region of the world. Using detailed monthly production data spanning the years 2002–2008 for 18,203 active production facilities, combined with geographic information system pipeline data, reservoir gas composition data, and cost data derived from industry sources, a case study was constructed to explore the technical and economic viability of further mitigation of flaring and venting associated with upstream oil and gas production in Alberta, Canada. Calculations were performed to evaluate the feasibility of mitigation via collection and compression of gas into pipelines to connect into existing pipeline networks. Four main calculation scenarios were considered, and for each, a series of Monte-Carlo analyses were performed to evaluate uncertainties and sensitivities to key calculation parameters. In all scenarios, the results reveal potentially significant opportunities for economically viable flare and vent mitigation that would yield substantial reductions in CO2 equivalent emissions. Because of the highly skewed distribution of gas volumes flared and vented at individual facilities, the results also show that solutions for comparatively small numbers of the largest facilities can offer large reductions in overall emissions from the sector. These results suggest that in a concerted effort to minimize carbon emissions in the upstream oil and gas industry, there is potential for significant near-term reductions using existing technology while research and development continues on more advanced methods such as carbon capture and storage
Travelling Salesman Problem with a Center
We study a travelling salesman problem where the path is optimized with a
cost function that includes its length as well as a certain measure of
its distance from the geometrical center of the graph. Using simulated
annealing (SA) we show that such a problem has a transition point that
separates two phases differing in the scaling behaviour of and , in
efficiency of SA, and in the shape of minimal paths.Comment: 4 pages, minor changes, accepted in Phys.Rev.
Reversible tuning of the surface state in a psuedo-binary Bi2(Te-Se)3 topological insulator
We use angle-resolved photoemission spectroscopy to study non-trivial surface
state in psuedobinary Bi2Se0.6Te2.3 topological insulator. We show that unlike
previously studied binaries, this is an intrinsic topological insulator with
conduction bulk band residing well above the chemical potential. Our data
indicates that under good vacuum condition there are no significant aging
effects for more then two weeks after cleaving. We also demonstrate that shift
of the Kramers point at low temperature is caused by UV assisted absorption of
molecular hydrogen. Our findings pave the way for applications of these
materials in devices and present an easy scheme to tune their properties.Comment: 4 pages, 4 figure
Preventing Isolated Perioperative Reintubation: Who is at highest risk?
Objectives:
1. We aim to characterize IPR nationally through a retrospective review of the National Surgical Quality Improvement Program participant user file (NSQIP PUF).
2.Identify risk factors for IPR including analysis of procedure type and preoperative characteristics.https://jdc.jefferson.edu/patientsafetyposters/1041/thumbnail.jp
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