3,079 research outputs found
Long memory and crude oil’s price predictability
This paper discusses the usefulness of the long term memory property in price prediction. In particular, the Hurst’s exponents related to a wide set of portfolios generated by three crude oils are estimated by using the detrended fluctuation analysis. To this aim, the daily empirical data on West Texas Intermediate, Brent crude oil and Dubai crude oil for a period of more than 10 years have been considered. It is shown that specific combinations are associated to persistence/antipersistence long-run behaviors, and this highlights the presence of statistical arbitrage opportunities. Such an outcome shows that long term memory can effectively serve as price predictor.
This is a post-peer-review, pre-copyedit version of an article published in Annals of Operations Research. The final authenticated version is available online at: http://dx.doi.org/10.1007/s10479-019-03376-y
ICE Second Halley radial: TDA mission support and DSN operations
The article documents the operations encompassing the International Cometary Explorer (ICE) second Halley radial experiment centered around March 28, 1986. The support was provided by the Deep Space Network (DSN) 64-meter subnetwork. Near continuous support was provided the last two weeks of March and the first two weeks of April to insure the collection of adequate background data for the Halley radial experiment. During the last week of March, plasma wave measurements indicate that ICE was within the Halley heavy ion pick-up region
Diffusion in a crowded environment
We analyze a pair of diffusion equations which are derived in the infinite
system--size limit from a microscopic, individual--based, stochastic model.
Deviations from the conventional Fickian picture are found which ultimately
relate to the depletion of resources on which the particles rely. The
macroscopic equations are studied both analytically and numerically, and are
shown to yield anomalous diffusion which does not follow a power law with time,
as is frequently assumed when fitting data for such phenomena. These anomalies
are here understood within a consistent dynamical picture which applies to a
wide range of physical and biological systems, underlining the need for clearly
defined mechanisms which are systematically analyzed to give definite
predictions.Comment: 4 pages, 3 figures, minor change
Managerial features and outcome in neonatal intensive care units: results from a cluster analysis
Background: Healthcare organisations differ in performance even if they are located in the same country or region. Suitable managerial practices and organisational processes can lead to better health outcomes. As a result, hospitals are constantly looking for managerial arrangements that can improve outcomes and keep costs down. This study aims to identify different managerial models in neonatal intensive care units (NICUs) and their impact on a large number of outcomes. Methods: The research was conducted in Italy, within the SONAR project. SONAR’s aim was to identify the characteristics of NICUs, monitor outcomes and promote best practices. This study includes 51 of the 63 NICUs that took part in the SONAR project. Questionnaires on the activities and managerial features were administered to doctors and nurses working in NICUs. A total of 643 questionnaires were analysed from doctors and a total of 1601 from nurses. A cluster analysis was performed to identify managerial models of NICUs. Results: Three managerial models emerged from cluster analysis: traditional, collaborative and individualistic. In the “traditional” model the doctor is above the nurse in the hierarchy, and the nurse therefore has exclusively operational autonomy. The “collaborative” model has as key elements professional specialisation and functional coordination. The “individualistic” model considers only individual professional skills and does not concern the organisational conditions necessary to generate organisational effectiveness. The results also showed that there is an association between managerial model and neonatal outcomes. The collaborative model shows best results in almost all outcomes considered, and the traditional model has the worst. The individualistic model is in the middle, although its values are very close to those of traditional model. Conclusions: Health management needs to assess NICU strategically in order to develop models to improve outcomes. This study provides insights for management useful for designing managerial characteristics of NICUs in order to achieve better results. NICUs characterised by a collaborative model in fact show better neonatal outcomes
Liquid-Liquid Phase Separation in an Elastic Network
Living and engineered systems rely on the stable coexistence of two
interspersed liquid phases. Yet surface tension drives their complete
separation. Here we show that stable droplets of uniform and tuneable size can
be produced through arrested phase separation in an elastic matrix. Starting
with an elastic polymer network swollen by a solvent mixture, we change the
temperature or composition to drive demixing. Droplets nucleate and grow to a
stable size that is tuneable by the network cross-linking density, the cooling
rate, and the composition of the solvent mixture. We discuss thermodynamic and
mechanical constraints on the process. In particular, we show that the
threshold for macroscopic phase separation is altered by the elasticity of the
polymer network, and we highlight the role of internuclear correlations in
determining the droplet size and polydispersity. This phenomenon has potential
applications ranging from colloid synthesis and structural colour to phase
separation in biological cells.Comment: 6 figure
A note on the fibres of Mori fibre spaces
In this note we consider the problem of determining which Fano manifolds can
be realised as fibres of a Mori fibre space. In particular, we study the case
of toric varieties, Fano manifolds with high index and some Fano manifolds with
high Picard rank
Intrinsic noise and discrete-time processes
A general formalism is developed to construct a Markov chain model that
converges to a one-dimensional map in the infinite population limit. Stochastic
fluctuations are therefore internal to the system and not externally specified.
For finite populations an approximate Gaussian scheme is devised to describe
the stochastic fluctuations in the non-chaotic regime. More generally, the
stochastic dynamics can be captured using a stochastic difference equation,
derived through an approximation to the Markov chain. The scheme is
demonstrated using the logistic map as a case study.Comment: Modified version accepted for publication in Phys. Rev. E Rapid
Communications. New figures adde
Far-Ultraviolet Color Gradients in Early-Type Galaxies
We discuss far-UV (1500 A) surface photometry and FUV-B color profiles for 8
E/S0 galaxies from images taken with the Ultraviolet Imaging Telescope,
primarily during the Astro-2 mission. In three cases, the FUV radial profiles
are more consistent with an exponential than a de Vaucouleurs function, but
there is no other evidence for the presence of a disk or of young, massive
stars. In all cases except M32 the FUV-B color becomes redder at larger radii.
There is a wide range of internal radial FUV-B color gradients. However, we
find no correlation between the FUV-B color gradients and internal metallicity
gradients based on Mg absorption features. We conclude that metallicity is not
the sole parameter controlling the "UV upturn component" in old populations.Comment: 11 pages; tar.gz file includes LaTeX text file, 3 PostScript figures.
Paper to be published in ApJ Letter
Structural assessment of the gripper interlock of the DEMO breeding blanket transporter
The maintenance of the DEMO Breeding Blanket (BB) remotely is a crucial aspect in development of the DEMO power plant. It is a challenge due to the huge mass of the BB segment of about 180 tons. A new concept for the BB transporter has recently been developed. To properly grip and manipulate each BB segment, the BB transporter has been equipped with a gripper interlock. Due to the geometry of the BB and the vacuum vessel, the attachment point on the BB segment is not aligned with its center of gravity. Hence in addition to the vertical lifting load, large moments about the horizontal axes need to be reacted.The work discussed here concerns the structural analysis conducted on the gripper interlock; its structural integrity has been checked against the most severe load conditions that include also seismic loads according to the EN13001. Elastic analyses were performed using a finite element model in accordance with EN 13001-3-1:2012 + A2:2018, Cranes - General Design - Part 3-1: Limit States and proof competence of steel structure. The effect of the gap sizes at the contact surfaces between gripper interlock and BB after engagement as well as the effect of different friction coefficients on the sliding areas were assessed. The improvements of the design based on the structural analysis are presented, too
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