Multiple solutions for asteroid orbits: Computational procedure and applications

We describe the Multiple Solutions Method, a one-dimensional sampling of the six-dimensional orbital confidence region that is widely applicable in the field of asteroid orbit determination. In many situations there is one predominant direction of uncertainty in an orbit determination or orbital prediction, i.e., a ``weak'' direction. The idea is to record Multiple Solutions by following this, typically curved, weak direction, or Line Of Variations (LOV). In this paper we describe the method and give new insights into the mathematics behind this tool. We pay particular attention to the problem of how to ensure that the coordinate systems are properly scaled so that the weak direction really reflects the intrinsic direction of greatest uncertainty. We also describe how the multiple solutions can be used even in the absence of a nominal orbit solution, which substantially broadens the realm of applications. There are numerous applications for multiple solutions; we discuss a few problems in asteroid orbit determination and prediction where we have had good success with the method. In particular, we show that multiple solutions can be used effectively for potential impact monitoring, preliminary orbit determination, asteroid identification, and for the recovery of lost asteroids

Comparison of the fluctuation influence on the resistive properties of the mixed state of BiSrCaCuO and of thin films of conventional superconductor

The resistive properties of layered HTSC BiSrCaCuO in the mixed state are compared with those of thin films of conventional superconductors with weak disorders (amorphous Nb_{1-x}0_{x} films) and with strong disorders (Nb_{1-x}O_{x} films with small grain structure). The excess conductivity is considered as a function of superconducting electron density and phase coherence length. It is shown that the transition to the Abrikosov state differs from the ideal case both in BiSrCaCuO and Nb_{1-x}O_{x} films, i.e. the appearance of long-range phase coherence is continuous transition in both cases. The quantitative difference between thin films with weak and strong disorders is greater than the one between layered HTSC and conventional superconductors, showing that the dimensionality of the system, rather than the critical temperature, is the key factor ruling fluctuation effectsComment: 17 pages, 5 figure

A Clustering System for Dynamic Data Streams Based on Metaheuristic Optimisation

open access articleThis article presents the Optimised Stream clustering algorithm (OpStream), a novel approach to cluster dynamic data streams. The proposed system displays desirable features, such as a low number of parameters and good scalability capabilities to both high-dimensional data and numbers of clusters in the dataset, and it is based on a hybrid structure using deterministic clustering methods and stochastic optimisation approaches to optimally centre the clusters. Similar to other state-of-the-art methods available in the literature, it uses “microclusters” and other established techniques, such as density based clustering. Unlike other methods, it makes use of metaheuristic optimisation to maximise performances during the initialisation phase, which precedes the classic online phase. Experimental results show that OpStream outperforms the state-of-the-art methods in several cases, and it is always competitive against other comparison algorithms regardless of the chosen optimisation method. Three variants of OpStream, each coming with a different optimisation algorithm, are presented in this study. A thorough sensitive analysis is performed by using the best variant to point out OpStream’s robustness to noise and resiliency to parameter changes

Outcrop Lithostratigraphy and Petrophysics of the Middle Devonian Marcellus Shale in West Virginia and Adjacent States

A stratigraphic study of 15 partial outcrops of the Marcellus Shale in West Virginia, Pennsylvania, and Maryland has identified six distinct lithofacies. These include grey calcareous shale (Facies 1), limestone (Facies 2), black calcareous shale (Facies 3), black non-calcareous shale (Facies 4), grey non-calcareous shale (Facies 5) and K-bentonite (Facies 6). Packages of these facies have been organized into six vertically stacked units (A-F). Deposition of the facies resulted from the rise and fall of relative sea level, which in turn shifted the location of the thermocline and affected the amount of terrigenous sediment distributed from the eastern source. Facies 1 and 2 were deposited above the thermocline and just below wave base. Facies 3 and 5 were deposited both above and below the thermocline depending on seasonal mixing and storm events. Facies 4 was deposited under the thermocline in the deepest water (~60 meters). Facies 1 and 5 accumulated in response to increased sediment influx, whereas Facies 2, 3 and 4 accumulated at times of low sediment supply. A decrease in sediment supply corresponded to a rise in relative sea level that allowed for the storage of terrigenous sediment far landward and the deposition of carbonate and organic-rich sediment on the foreland ramp. The intimate stratigraphic relationship among the shale and limestone facies over time and space indicates a dynamic and complex shallow-water environment for the deposition of the Marcellus Shale, as opposed to the traditional deep-water, sediment starved and statically-anoxic model.;A spectral gamma-ray type log constructed for the Marcellus Shale in outcrop (Units AF) shows a good correlation with the formation in the nearby subsurface. Moreover, the outcrop units can be identified in terms of the subsurface nomenclature: Units A-C correspond to the Union Springs Formation; Unit D, the Cherry Valley Member; and Units E-F, the Oatka Creek Formation. Correlations indicate that the Marcellus becomes increasingly enriched in black shale (Facies 4) westward, resulting in an increased thickness of organic-rich condensed section. On the other hand, limestone and calcareous shale become less abundant westward into the basin due to the reduced sediment supply and greater water depth

A finite element-discrete element approach for the analysis of the venice trans-lagoon railway bridge

In this paper, the feasibility of the utilization of a combined finite element/discrete element (FE-DE) approach to investigate the behavior of masonry arch bridges is proposed. Attention is paid to the assessment of the load carrying capacity by means of a suitable coupled FE-DE two-dimensional approach. This paper outlines the fields and limits of applicability of the FE-DE method to the study of masonry arch bridges. The main contribution is to evaluate the applicability of FE-DE, in particular its reliability to describe the nonlinear behavior of masonry arch bridges under increasing static loads, to catch kinematic failure mechanisms and collapse load multipliers, as well as to evaluate the role played by the backfill. A discussion on a possible approach to FE-DE modelling of the Venice trans-Lagoon masonry arch bridge is proposed. With such a purpose, a series of parametric analyses has been conducted in order to evaluate the influence of the different parameters involved on the behavior of the bridges. Pushover analyses have been performed to investigate the nonlinear behavior up to the collapse and up to a clear formation of a failure mechanism in the model

Low-frequency modes in the Raman spectrum of sp-sp2 nanostructured carbon

A novel form of amorphous carbon with sp-sp2 hybridization has been recently produced by supersonic cluster beam deposition showing the presence in the film of both polyynic and cumulenic species [L. Ravagnan et al. Phys. Rev. Lett. 98, 216103 (2007)]. Here we present a in situ Raman characterization of the low frequency vibrational region (400-800 cm-1) of sp-sp2 films at different temperatures. We report the presence of two peaks at 450 cm-1 and 720 cm-1. The lower frequency peak shows an evolution with the variation of the sp content and it can be attributed, with the support of density functional theory (DFT) simulations, to bending modes of sp linear structures. The peak at 720 cm-1 does not vary with the sp content and it can be attributed to a feature in the vibrational density of states activated by the disorder of the sp2 phase.Comment: 15 pages, 5 figures, 1 tabl

Implementation and validation of a total displacement non-linear homogenization approach for in-plane loaded masonry

Two simple homogenization models suitable for the non-linear analysis of masonry walls in-plane loaded are presented. A rectangular running bond elementary cell is discretized by means of twenty-four constant stress threenoded plane-stress triangular elements and linear two-noded interfaces. Non-linearity is concentrated on mortar reduced to interface, exhibiting a holonomic behavior with softening. The paper shows how the mechanical problem in the unit cell can be characterized by very few displacement/stress variables and how homogenized stress-strain behavior can be evaluated by means of a small-scale system of non-linear equations. At a structural level, it is therefore not necessary to solve a homogenization problem at each load step in each Gauss point and a direct implementation into commercial software as an external user supplied subroutine is straightforward. Nonlinear structural analyses are conducted on a variety of different problems, for which experimental and numerical data are available in the literature, in order to show that accurate results can be obtained with a limited computational effort

Challenges in Dental Statistics: Survey Methodology Topics

This paper gathers some contributions concerning survey methodology in dental research, as discussed during the first Workshop of the SISMEC STATDENT working group on statistical methods and applications in dentistry, held in Ancona on the 28th September 2011. The first contribution deals with the European Global Oral Health Indicators Development (EGOHID) Project which proposed a comprehensive and standardized system of epidemiological tools (questionnaires and clinical forms) for national data collection on oral health in Europe. The second contribution regards the design and conduct of trials to evaluate the clinical efficacy and safety of toothbrushes and mouthrinses. Finally, a flexible and effective tool used to trace dental age reference charts tailored to Italian children was presented

Challenges in Dental Statistics: Survey Methodology Topics

This paper gathers some contributions concerning survey methodology in dental research, as discussed during the first Workshop of the SISMEC STATDENT working group on statistical methods and applications in dentistry, held in Ancona on the 28th September 2011. The first contribution deals with the European Global Oral Health Indicators Development (EGOHID) Project which proposed a comprehensive and standardized system of epidemiological tools (questionnaires and clinical forms) for national data collection on oral health in Europe. The second contribution regards the design and conduct of trials to evaluate the clinical efficacy and safety of toothbrushes and mouthrinses. Finally, a flexible and effective tool used to trace dental age reference charts tailored to Italian children was presented