988 research outputs found
Emergence of time-horizon invariant correlation structure in financial returns by subtraction of the market mode
We investigate the emergence of a structure in the correlation matrix of
assets' returns as the time-horizon over which returns are computed increases
from the minutes to the daily scale. We analyze data from different stock
markets (New York, Paris, London, Milano) and with different methods. Result
crucially depends on whether the data is restricted to the ``internal''
dynamics of the market, where the ``center of mass'' motion (the market mode)
is removed or not. If the market mode is not removed, we find that the
structure emerges, as the time-horizon increases, from splitting a single large
cluster. In NYSE we find that when the market mode is removed, the structure of
correlation at the daily scale is already well defined at the 5 minutes
time-horizon, and this structure accounts for 80 % of the classification of
stocks in economic sectors. Similar results, though less sharp, are found for
the other markets. We also find that the structure of correlations in the
overnight returns is markedly different from that of intraday activity.Comment: 12 pages, 17 figure
Propeller blade stress estimates using lifting line theory
OpenProp, an open-source computational tool for the design and analysis of propellers and horizontal-axis turbines, is extended to provide estimates of normal stresses in the blades for both on- and off-design operating conditions. The numerical model is based on propeller lifting theory, and the present implementation of the code includes an analysis capability to estimate the off-design performance of the propeller or turbine and to make blade stress predictions.
As an example, we present the design and performance of a two-bladed propeller. Experimental measurements of the propeller performance over a wide range of off-design operating conditions agree with performance predictions. Estimates of the blade stress are given for on-design and off-design operating states of the propeller.United States. Office of Naval Research (N000140810080)United States. National Oceanic and Atmospheric Administration (NOAA NSG NA060AR4170019)Project Ocean (Robert Damus
Multiscaled Cross-Correlation Dynamics in Financial Time-Series
The cross correlation matrix between equities comprises multiple interactions
between traders with varying strategies and time horizons. In this paper, we
use the Maximum Overlap Discrete Wavelet Transform to calculate correlation
matrices over different timescales and then explore the eigenvalue spectrum
over sliding time windows. The dynamics of the eigenvalue spectrum at different
times and scales provides insight into the interactions between the numerous
constituents involved.
Eigenvalue dynamics are examined for both medium and high-frequency equity
returns, with the associated correlation structure shown to be dependent on
both time and scale. Additionally, the Epps effect is established using this
multivariate method and analyzed at longer scales than previously studied. A
partition of the eigenvalue time-series demonstrates, at very short scales, the
emergence of negative returns when the largest eigenvalue is greatest. Finally,
a portfolio optimization shows the importance of timescale information in the
context of risk management
A New Solution for the Dispersive Element in Astronomical Spectrographs
We present a new solution for the dispersive element in astronomical spectrographs that, in many cases, can provide an upgrade path to enhance the spectral resolution of existing moderate-resolution reflection-grating spectrographs. We demonstrate that in the case of LRIS-R at the Keck 1 Telescope, a spectral resolution of 18,000 can be achieved with reasonable throughput under good seeing conditions
Science and Technology Libraries Partnering with Knovel
The engineering library plays a critical role in initiating and maintaining the conduit between vendors of engineering information and the users of that informationâfaculty, students, and researchers. Likewise, vendors play a key role in supporting library and faculty efforts to promote engineering information resources, beyond just supplying content and interface. Engineering libraries and vendors can effectively work together to get the most from electronic engineering resources for both large and small institutions. The case studies here show how Knovel Corporation, a sci-tech e-book vendor, has worked with engineering librarians at large and small institutions and with faculty members to promote awareness and usage of Knovelâs interactive library of electronic books for engineering education
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Considering the switch: Challenges of transitioning to non-lead hunting ammunition
In this issue of The Condor: Ornithological Applications, Haig et al. (2014) summarize negative impacts of lead ammunition and fishing tackle on birds and discuss strategies for mitigating risks to wildlife and human health. Their Review raises an important set of questions for hunters, wildlife managers, and conservation scientists. Effective mitigation will require careful understanding of technical, economic, and social dimensions of the problem. Here, I focus on challenges specific to adopting non-lead ammunition for hunting, particularly for large game animals. I discuss limitations of using the ban on lead ammunition for waterfowl hunting as an analog for reducing lead use for other types of hunting, explain important technical considerations in design and use of non-lead ammunition, and point out areas where effective non-lead alternatives are still lacking. I suggest that currently available economic analyses of the cost of non-lead alternatives are inadequate and do not recognize wide variation in hunter behavior. These considerations have strong implications for designing effective outreach and predicting responses of hunters asked to consider non-lead alternatives. Enforcing outright bans on using lead ammunition for all types of hunting, as recently enacted in California, may prove even more challenging than similar restrictions for waterfowl hunting. Despite this, I propose that major reductions in exposure of wildlife and people to lead bullet fragments are achievable, particularly through outreach and incentive programs that focus on the most commonly used types of firearms for big game huntingâhigh velocity modern rifles. Bullets from these widely used rifles typically produce the most lead fragments and have the best selection of effective non-lead options available at this time. Efforts to change hunter behavior must recognize the true costs and challenges of changing to non-lead ammunition. Likewise, hunters should recognize and accept their important role in wildlife conservation and work to embrace effective alternatives to lead as they become available.Keywords: hunting, lead, hunter outreach, bullets, ammunitio
The Cryogenic Refractive Indices of S-FTM16, a Unique Optical Glass for Near-Infrared Instruments
The Ohara glass S-FTM16 is of considerable interest for near-infrared optical
designs because it transmits well through the K band and because negative
S-FTM16 elements can be used to accurately achromatize positive calcium
fluoride elements in refractive collimators and cameras. Glass manufacturers
have sophisticated equipment to measure the refractive index at room
temperature, but cannot typically measure the refractive index at cryogenic
temperatures. Near-infrared optics, however, are operated at cryogenic
temperatures to reduce thermal background. Thus we need to know the temperature
dependence of S-FTM16's refractive index. We report here our measurements of
the thermal dependence of S-FTM16's refractive index between room temperature
and ~77 K. Within our measurement errors we find no evidence for a wavelength
dependence or a nonlinear temperature term so our series of measurements can be
reduced to a single number. We find that Delta n_{abs} / Delta T = -2.4x10^{-6}
K^{-1} between 298 K and ~77 K and in the wavelength range 0.6 micron to 2.6
micron. We estimate that the systematic error (which dominates the measurement
error) in our measurement is 10%, sufficiently low for most purposes. We also
find the integrated linear thermal expansion of S-FTM16 between 298 K and 77 K
is -0.00167 m m^{-1}.Comment: 8 pages, including 9 figures. Uses emulateapj.cls. Accepted for
publication in PAS
The SIDE dual VIS-NIR fiber fed spectrograph for the 10.4 m Gran Telescopio Canarias
SIDE (Super Ifu Deployable Experiment) is proposed as second-generation,
common-user instrument for the GTC. It will be a low and intermediate
resolution fiber fed spectrograph, highly efficient in multi-object and 3D
spectroscopy. The low resolution part (R = 1500, 4000) is called Dual VIS-NIR
because it will observe in the VIS and NIR bands (0.4 ~V 1.7 microns)
simultaneously. Because of the large number of fibers, a set of ~10 identical
spectrographs is needed, each with a mirror collimator, a dichroic and two
refractive cameras. The cameras are optimized for 0.4 - 0.95 microns (VIS) and
0.95 - 1.7 microns (NIR) respectively.Comment: To appear in "Advanced Optical and Mechanical Technologies in
Telescopes and Instrumentation" SPIE conference Proc. 7018, Marseille, 23-28
June 200
Very Isolated Early-Type Galaxies
We use the Karachentseva (1973) ``Catalogue of Very Isolated Galaxies'' to
investigate a candidate list of >100 very isolated early-type galaxies.
Broad-band imaging and low resolution spectroscopy are available for a large
fraction of these candidates and result in a sample of 102 very isolated
early-type galaxies, including 65 ellipticals and 37 S0 galaxies. Many of these
systems are quite luminous and the resulting optical luminosity functions of
the Es and early-types (E+S0s) show no statistical differences when compared to
luminosity functions dominated by group and cluster galaxies. However, whereas
S0s outnumber Es 4:1 in the CfA survey, isolated Es outnumber S0s by nearly
2:1. We conclude that very isolated elliptical galaxies show no evidence for a
different formation and/or evolution process compared to Es formed in groups or
clusters, but that most S0s are formed by a mechanism (e.g., gas stripping)
that occurs only in groups and rich clusters. Our luminosity function results
for ellipticals are consistent with very isolated ellipticals being formed by
merger events, in which no companions remain.
CHANDRA observations were proposed to test specifically the merger hypothesis
for isolated ellipticals. However, this program has resulted in the observation
of only one isolated early-type galaxy, the S0 KIG 284, which was not detected
at a limit well below that expected for a remnant group of galaxies. Therefore,
the hypothesis remains untested that very isolated elliptical galaxies are the
remains of a compact group of galaxies which completely merged.Comment: 19 pages, 3 figures; AJ in pres
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