2,801 research outputs found
Price Discovery and the Accuracy of Consolidated Data Feeds in the U.S. Equity Markets
Both the scientific community and the popular press have paid much attention
to the speed of the Securities Information Processor, the data feed
consolidating all trades and quotes across the US stock market. Rather than the
speed of the Securities Information Processor, or SIP, we focus here on its
accuracy. Relying on Trade and Quote data, we provide various measures of SIP
latency relative to high-speed data feeds between exchanges, known as direct
feeds. We use first differences to highlight not only the divergence between
the direct feeds and the SIP, but also the fundamental inaccuracy of the SIP.
We find that as many as 60 percent or more of trades are reported out of
sequence for stocks with high trade volume, therefore skewing simple measures
such as returns. While not yet definitive, this analysis supports our
preliminary conclusion that the underlying infrastructure of the SIP is
currently unable to keep pace with the trading activity in today's stock
market.Comment: 18 pages, 20 figures, 2 table
Seasonal Movements and Distribution of Stellerâs Eiders (Polysticta stelleri) Wintering at Kodiak Island, Alaska
We used satellite telemetry in 2004â06 to describe the annual movements and habitat use of a segment of the Pacific population of Stellerâs Eiders (Polysticta stelleri) that winters at Kodiak Island, Alaska. Information about broad-scale patterns of seasonal distribution and links among annual cycle stages is critical for interpreting population trends and developing conservation strategies. We captured birds in Chiniak Bay at Kodiak Island in late February and early March and monitored the movements after departure from Kodiak Island of 24 satellite-tagged birds: 16 after-second-year (ASY) age class females, one second-year age class female, and seven ASY males. All birds used the same intercontinental migration corridor during spring, but routes and chronology of spring migration appeared to vary by year and among individuals. Sixteen of the 24 birds that were tracked migrated to breeding areas along the Arctic coast of Russia from the Chukotka Peninsula to the Taymyr Peninsula; five birds, assumed to be non-breeding, spent the summer in nearshore waters of Russia and Alaska; and the remaining three birds either died during spring migration or had failed transmitters. Thirteen birds were tracked to molt sites that were broadly distributed along the coast of Alaska. Molt sites included St. Lawrence Island, the Kuskokwim Shoals, Kamishak Bay, and three sites along the Alaska Peninsula. Twelve of these 13 birds returned to Kodiak Island to winter, and a single male wintered on the Alaska Peninsula. Stellerâs Eiders marked during winter at Kodiak Island were widely distributed during the breeding season, but a large proportion of marked birds returned to molting and wintering areas in two years of the study.De 2004 Ă 2006, nous avons recouru Ă la tĂ©lĂ©mĂ©trie satellitaire pour dĂ©crire lâutilisation de lâhabitat et les mouvements annuels dâun segment de la population dâeiders de Steller (Polysticta stelleri) dans la rĂ©gion du Pacifique, eiders qui hivernent sur lâĂźle Kodiak, en Alaska. Il est essentiel dâobtenir des donnĂ©es sur les tendances Ă grande Ă©chelle de la rĂ©partition saisonniĂšre et des liens entre les divers stades du cycle annuel de ces oiseaux afin dâĂȘtre en mesure dâinterprĂ©ter leurs tendances dĂ©mographiques et dâĂ©laborer des stratĂ©gies de conservation. Nous avons capturĂ© des oiseaux dans la baie Chiniak de lâĂźle Kodiak vers la fin fĂ©vrier et le dĂ©but mars. AprĂšs notre dĂ©part de lâĂźle Kodiak, nous avons surveillĂ© les mouvements de 24 oiseaux pistĂ©s par satellite : 16 femelles de plus de deux ans, une femelle de deux ans et sept mĂąles de plus de deux ans. Tous les oiseaux ont empruntĂ© le mĂȘme couloir de migration intercontinental au printemps, mais les routes et la chronologie de la migration printaniĂšre semblaient varier dâune annĂ©e Ă lâautre et dâun individu Ă lâautre. Seize des24 oiseaux pistĂ©s ont migrĂ© vers des aires de reproduction situĂ©es le long de la cĂŽte arctique de la Russie, depuis la presquâĂźle de Tchoukotkae jusquâĂ la presquâĂźle de TaĂŻmyr; cinq oiseaux, probablement non reproducteurs, ont passĂ© lâĂ©tĂ© dans les eaux cĂŽtiĂšres de la Russie et de lâAlaska, tandis que les trois autres oiseaux sont morts pendant la migration printaniĂšre ou Ă©taient dotĂ©s de transmetteurs dĂ©fectueux. Treize oiseaux ont Ă©tĂ© repĂ©rĂ©s Ă des sites de mue largement rĂ©partis le long de la cĂŽte de lâAlaska. Parmi ces sites, notons ceux de lâĂźle Saint-Laurent, du haut-fond de Kuskokwim, de la baie de Kamishak et de trois autres sites le long de la pĂ©ninsule de lâAlaska. Douze de ces 13 oiseaux sont retournĂ©s Ă lâĂźle Kodiak pour passer lâhiver, et un seul mĂąle a hivernĂ© dans la pĂ©ninsule de lâAlaska. Les eiders de Steller qui ont Ă©tĂ© marquĂ©s Ă lâĂźle Kodiak pendant lâhiver Ă©taient largement rĂ©partis pendant la saison de reproduction, mais une grande proportion dâoiseaux pistĂ©s sont retournĂ©s aux aires de mue et dâhivernage au cours des deux annĂ©es visĂ©es par lâĂ©tude
Geologic controls on submarine slope failure along the central U.S. Atlantic margin : insights from the Currituck Slide Complex
© The Author(s), 2016. This is the author's version of the work and is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Marine Geology 385 (2017): 114-130, doi:10.1016/j.margeo.2016.10.007.Multiple styles of failure, ranging from densely spaced, mass transport driven canyons to
the large, slab-type slope failure of the Currituck Slide, characterize adjacent sections of
the central U.S. Atlantic margin that appear to be defined by variations in geologic
framework. Here we use regionally extensive, deep penetration multichannel seismic
(MCS) profiles to reconstruct the influence of the antecedent margin physiography on
sediment accumulation along the central U.S. Atlantic continental shelf-edge, slope, and
uppermost rise from the Miocene to Present. These data are combined with highresolution
sparker MCS reflection profiles and multibeam bathymetry data across the
Currituck Slide complex. Pre-Neogene allostratigraphic horizons beneath the slope are
generally characterized by low gradients and convex downslope profiles. This is followed
by the development of thick, prograded deltaic clinoforms during the middle Miocene.
Along-strike variations in morphology of a regional unconformity at the top of this
middle Miocene unit appear to have set the stage for differing styles of mass transport
along the margin. Areas north and south of the Currituck Slide are characterized by
oblique margin morphology, defined by an angular shelf-edge and a relatively steep
(>8°), concave slope profile. Upper slope sediment bypass, closely spaced submarine
canyons, and small, localized landslides confined to canyon heads and sidewalls characterize these sectors of the margin. In contrast, the Currituck region is defined by a
sigmoidal geometry, with a rounded shelf-edge rollover and gentler slope gradient (<6°).
Thick (>800 m), regionally continuous stratified slope deposits suggest the low gradient
Currituck region was a primary depocenter for fluvial inputs during multiple sea level
lowstands. These results imply that the rounded, gentle slope physiography developed
during the middle Miocene allowed for a relatively high rate of subsequent sediment
accumulation, thus providing a mechanism for compactionâinduced overpressure that
preconditioned the Currituck region for failure. Detailed examination of the regional
geological framework illustrates the importance of both sediment supply and antecedent
slope physiography in the development of large, potentially unstable depocenters along
passive margins.The U.S. Geological Survey, the
U.S. Nuclear Regulatory Commission and Coastal Carolina University funded this
research
The Effect of 12-Weeks Recreational Football (Soccer) for Health Intervention on Functional Movement in Older Adults
There is growing evidence that recreational football offers health benefits for older adults
and an important pathway for physical activity for older adult groups. Despite anecdotal evidence that recreational football is beneficial for older adults, no empirical data are available to support this assertion. This study addressed this issue and examined the effects of a 12âweek recreational football intervention on the functional fitness of older adults. Using a preâpost caseâcontrol design, thirteen males, aged 61â73 years (mean age ± SD = 66 ± 4 years) undertook a twiceâweekly, 12âweek recreational football for health intervention, and were matched with a control group, comprising thirteen males, aged 62â78 years (mean age ± SD = 66 ± 4 years) who maintained their typical exercise habits during the intervention period. Preâ and postintervention, participants underwent assessment of functional fitness, using the Rikli and Jones functional fitness battery as well as an assessment of body fatness, via bioelectrical impedance analysis and dominant handgrip strength using handgrip dynamometry. Results from a series of 2 (preâpost) X 2 (intervention vs. control) repeatedâmeasures ANOVAs indicate significant preâpost X group interactions for the 30âsecond chair stand (p = 0.038, PÆ2 = 0.168), 8âfoot timed up and go (p = 0.001, PÆ2 = 0.577) and 6 min walk test (p = 0.036, PÆ2 = 0.171). In all cases, performance improved significantly after the intervention for the football intervention group but not the control group. There were no significant differences in the 30 s arm curl
test or dominant handgrip strength (p > 0.05). There was a nonâsignificant trend (p = 0.07, PÆ2 = 0.127) towards a preâpost X group interaction for body fatness, showing a decreased percent body fat for the intervention group over the control group. The results of the present study demonstrate the utility of recreational football as a physical activity intervention in older adults to improve functional movement
Seabed fluid expulsion along the upper slope and outer shelf of the U.S. Atlantic continental margin
Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 41 (2014): 96-101, doi:10.1002/2013GL058048.Identifying the spatial distribution of seabed fluid expulsion features is crucial for understanding the substrate plumbing system of any continental margin. A 1100âkm stretch of the U.S. Atlantic margin contains more than 5000 pockmarks at water depths of 120âm (shelf edge) to 700âm (upper slope), mostly updip of the contemporary gas hydrate stability zone (GHSZ). Advanced attribute analyses of high-resolution multichannel seismic reflection data reveal gas-charged sediment and probable fluid chimneys beneath pockmark fields. A series of enhanced reflectors, inferred to represent hydrate-bearing sediments, occur within the GHSZ. Differential sediment loading at the shelf edge and warming-induced gas hydrate dissociation along the upper slope are the proposed mechanisms that led to transient changes in substrate pore fluid overpressure, vertical fluid/gas migration, and pockmark formation.The U.S.
Geological Survey and the U.S. Nuclear Regulatory Commission funded this
research.2014-07-0
Frequency Tracking and Parameter Estimation for Robust Quantum State-Estimation
In this paper we consider the problem of tracking the state of a quantum
system via a continuous measurement. If the system Hamiltonian is known
precisely, this merely requires integrating the appropriate stochastic master
equation. However, even a small error in the assumed Hamiltonian can render
this approach useless. The natural answer to this problem is to include the
parameters of the Hamiltonian as part of the estimation problem, and the full
Bayesian solution to this task provides a state-estimate that is robust against
uncertainties. However, this approach requires considerable computational
overhead. Here we consider a single qubit in which the Hamiltonian contains a
single unknown parameter. We show that classical frequency estimation
techniques greatly reduce the computational overhead associated with Bayesian
estimation and provide accurate estimates for the qubit frequencyComment: 6 figures, 13 page
Final Report of the AFIT Quality Initiative External Discovery Committee
This report summarizes the findings of the Air Force Institute of Technologyâs (AFITâs) Quality Initiative - External Discovery Team. The overarching purpose of the Quality Initiative is to create a detailed, executable investment strategy for modernizing AFITâs instructional capabilities across five thrust areas. These activities were completed over the course of one year, beginning in June of 2016 and concluding in June of 2017. The data gathered were evaluated and several recommendations for further review were decided upon by the External Discovery Team. The following report briefly covers those recommendations and provides sources from which the recommendations were gleaned. These recommendations are meant to serve as a baseline for ways in which AFIT could begin to program resources to help improve teaching and instruction across the institution as a whole. The data presented here are meant to serve as a compliment to the Internal Discovery Teamâs report that focuses on data and feedback gathered from institutions internal to AFIT
The neuroblast and angioblast chemotaxic factor SDF-1 (CXCL12) expression is briefly up regulated by reactive astrocytes in brain following neonatal hypoxic-ischemic injury
BACKGROUND: Stromal cell-derived factor 1 (SDF-1 or CXCL12) is chemotaxic for CXCR4 expressing bone marrow-derived cells. It functions in brain embryonic development and in response to ischemic injury in helping guide neuroblast migration and vasculogenesis. In experimental adult stroke models SDF-1 is expressed perivascularly in the injured region up to 30 days after the injury, suggesting it could be a therapeutic target for tissue repair strategies. We hypothesized that SDF-1 would be expressed in similar temporal and spatial patterns following hypoxic-ischemic (HI) injury in neonatal brain. RESULTS: Twenty-five 7-day-old C57BL/J mice underwent HI injury. SDF-1 expression was up regulated up to 7 days after the injury but not at the later time points. The chief sites of SDF-1 up regulation were astrocytes, their foot processes along blood vessels and endothelial cells. CONCLUSION: The localization of SDF-1 along blood vessels in the HI injury zone suggests that these perivascular areas are where chemotaxic signaling for cellular recruitment originates and that reactive astrocytes are major mediators of this process. The associated endothelium is likely to be the site for vascular attachment and diapedesis of CXCR4 receptor expressing cells to enter the injured tissue. Here we show that, relative to adults, neonates have a significantly smaller window of opportunity for SDF-1 based vascular chemotaxic recruitment of bone marrow-derived cells. Therefore, without modification, following neonatal HI injury there is only a narrow period of time for endogenous SDF-1 mediated chemotaxis and recruitment of reparative cells, including exogenously administered stem/progenitor cells
Deterministic mechanical model of T-killer cell polarization reproduces the wandering of aim between simultaneously engaged targets
T-killer cells of the immune system eliminate virus-infected and tumorous cells through direct cell-cell interactions. Reorientation of the killing apparatus inside the T cell to the T-cell interface with the target cell ensures specificity of the immune response. The killing apparatus can also oscillate next to the cell-cell interface. When two target cells are engaged by the T cell simultaneously, the killing apparatus can oscillate between the two interface areas. This oscillation is one of the most striking examples of cell movements that give the microscopist an unmechanistic impression of the cell's fidgety indecision. We have constructed a three-dimensional, numerical biomechanical model of the molecular-motor-driven microtubule cytoskeleton that positions the killing apparatus. The model demonstrates that the cortical pulling mechanism is indeed capable of orienting the killing apparatus into the functional position under a range of conditions. The model also predicts experimentally testable limitations of this commonly hypothesized mechanism of T-cell polarization. After the reorientation, the numerical solution exhibits complex, multidirectional, multiperiodic, and sustained oscillations in the absence of any external guidance or stochasticity. These computational results demonstrate that the strikingly animate wandering of aim in T-killer cells has a purely mechanical and deterministic explanation. © 2009 Kim, Maly
Prospectus, January 27, 1992
https://spark.parkland.edu/prospectus_1992/1001/thumbnail.jp
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