Towards Distributed Convoy Pattern Mining

Mining movement data to reveal interesting behavioral patterns has gained attention in recent years. One such pattern is the convoy pattern which consists of at least m objects moving together for at least k consecutive time instants where m and k are user-defined parameters. Existing algorithms for detecting convoy patterns, however do not scale to real-life dataset sizes. Therefore a distributed algorithm for convoy mining is inevitable. In this paper, we discuss the problem of convoy mining and analyze different data partitioning strategies to pave the way for a generic distributed convoy pattern mining algorithm.Comment: SIGSPATIAL'15 November 03-06, 2015, Bellevue, WA, US

Anomalies in non-stoichiometric uranium dioxide induced by pseudo-phase transition of point defects

A uniform distribution of point defects in an otherwise perfect crystallographic structure usually describes a unique pseudo phase of that state of a non-stoichiometric material. With off-stoichiometric uranium dioxide as a prototype, we show that analogous to a conventional phase transition, these pseudo phases also will transform from one state into another via changing the predominant defect species when external conditions of pressure, temperature, or chemical composition are varied. This exotic transition is numerically observed along shock Hugoniots and isothermal compression curves in UO2 with first-principles calculations. At low temperatures, it leads to anomalies (or quasi-discontinuities) in thermodynamic properties and electronic structures. In particular, the anomaly is pronounced in both shock temperature and the specific heat at constant pressure. With increasing of the temperature, however, it transforms gradually to a smooth cross-over, and becomes less discernible. The underlying physical mechanism and characteristics of this type of transition are encoded in the Gibbs free energy, and are elucidated clearly by analyzing the correlation with the variation of defect populations as a function of pressure and temperature. The opportunities and challenges for a possible experimental observation of this phase change are also discussed.Comment: 11 pages, 5 figure

An investigation on the use of copulas when calculating general cash flow distributions.

In a paper of 2000, Kaas, Dhaene and Goovaerts investigate the present value of a rather general cash flow as a special case of sums of dependent risks. Making use of comonotonic risks, they derive upper and lower bounds for the distribution of the present value, in the sense of convex ordering. These bounds are very close to the real distribution in case all payments have the same sign; however, if there are both positive and negative payments, the upper bounds perform rather badly. In the present contribution we show what happens when solving this problem by means of copulas. The idea consists of splitting up the total present value in the difference of two present values with positive payments. Making use of a copula as an approximation for the joint distribution of the two sums, an approximation for the distribution of the original present value can be derived.Approximation; Cash flow; Convex order; copulas; Dependent risk; Distribution; Lower bounds; present value; Research; Risk; Sign; Value;

On the use of copula for calculating the present value of a general cash flow.

present value; Value;

Internal corrosion of carbon steel pipelines for dense phase CO₂ transport in Carbon Capture and Storage (CCS) - A review

Carbon Capture and Storage (CCS) has been highlighted as a potential method to enable the continued use of fossil-fuelled power stations through the abatement of carbon dioxide (CO2). A complete CCS cycle requires safe, reliable and cost effective solutions for the transmission of CO2 from the capturing facility to the location of permanent storage. This publication presents a detailed review of the integrity risks posed to dense-phase CO2 pipelines in the form of internal corrosion. To begin, the current worldwide experience in handling dense-phase CO2 and the anthropogenic stream compositions expected from the different combustion techniques currently available are discussed. The anticipated compositions are then related to a number of tentative CO2 stream compositions available in open literature proposed by research institutes and pipeline operators. In subsequent sections, early laboratory and field corrosion experience relating to natural dense-phase CO2 transport for the purposes of enhanced oil recovery (EOR) are summarised along with more recent research efforts which focus on identifying the role of anthropogenic impurities in the degradation processes. For each system impurity, the reaction rates, mechanisms and corrosion product composition/morphology expected at the steel surfaces are discussed, as well as each component’s ability to influence the critical water content required to initiate corrosion. Potential bulk phase reactions between multiple impurities are also evaluated in an attempt to help understand how the impurity content may evolve along a long-distance pipeline. The likelihood of stress-corrosion cracking and hydrogen-induced cracking is discussed and the various corrosion mitigation techniques which exist to control degradation to acceptable levels are reviewed. Based on the current research performed in the context of impure dense-phase CO2 corrosion, issues associated with performing laboratory experiments to replicate field conditions and the challenges such limitations present in terms of defining the safe operating window for CO2 transport are considered

Ergodic mutual information of full-duplex MIMO radios with residual self-interference

We study the theoretical performance of a full duplex multiple-input multiple-output (MIMO) bi-directional communication system. We focus on the effect of the residual self-interference due to channel estimation errors and transmitter impairments. We assume that the instantaneous channel state information (CSI) at the transmitting nodes is not known and the CSI at the receiving nodes is imperfect. To maximize the system ergodic mutual information, which is a non-convex function of power allocation vectors at the nodes, a gradient projection (GP) algorithm is developed to optimize the power allocation vectors. This algorithm exploits both spatial and temporal freedoms of the source covariance matrices of the MIMO links between the nodes to achieve higher sum ergodic mutual information. It is observed through the simulations that the algorithm reduces to a full-duplex scheme when the nominal residual self-interference is low, or to a half-duplex scheme when the nominal residual self-interference is high

Pulsars in FIRST Observations

We identified 16 pulsars from the Faint Images of the Radio Sky at Twenty-cm (FIRST) at 1.4 GHz. Their positions and total flux densities are extracted from the FIRST catalog. Comparing the source positions with those in the PSRcatalog, we obtained better determined positions of PSRs J1022+1001, J1518+4904, J1652+2651, and proper motion upper limits of another three pulsars PSRs J0751+1807, J1012+5307, J1640+2224. Proper motions of the other 10 pulsars are consistent with the values in the catalog.Comment: 6 pages, 2 figures, 3 tables, submited to CJA

Space-time power schedule for distributed MIMO links without instantaneous channel state information at the transmitting nodes

A space-time optimal power schedule for multiple distributed multiple-input multiple-output (MIMO) links without the knowledge of the instantaneous channel state information (CSI) at the transmitting nodes is proposed. A readily computable expression for the ergodic sum capacity of the MIMO links is derived. Based on this expression, which is a non-convex function of power allocation vectors, a projected gradient algorithm is developed to optimize the power allocation. For a symmetric set of MIMO links with independent identically distributed channels, it is observed that the space-time optimal power schedule reduces to a uniform isotropic power schedule when nominal interference is low, or to an orthogonal isotropic power schedule when nominal interference is high. Furthermore, the transition region between the latter two schedules is seen to be very sharp in terms of nominal interference-to-noise ratio (INR). For MIMO links with correlated channels, the corresponding space-time optimal power schedule is developed based on the knowledge of the channel correlation matrices. It is shown that the channel correlation has a great impact on the ergodic capacity and the optimality of different power scheduling approaches

Electrical and Structural Analysis of CNT-Metal Contacts in Via Interconnects

Vertically aligned carbon nanotubes grown by plasmaenhanced chemical vapor deposition offer a potentially suitable material for via interconnects in next-generation integrated circuits. Key performance-limiting factors include high contact resistance and low carbon nanotube packing density, which fall short of meeting the requirements delineated in the ITRS roadmap for interconnects. For individual carbon nanotube s, contact resistance is a major performance hurdle since it is the dominant component of carbon nanotube interconnect resistance, even in the case of vertically aligned carbon nanotube arrays. In this study, we correlate the carbon nanotube-metal interface nanostructure to their electrical properties in order to elucidate growth parameters that can lead to high density and low contact resistance and resistivity

Super-soft symmetry energy encountering non-Newtonian gravity in neutron stars

Considering the non-Newtonian gravity proposed in the grand unification theories, we show that the stability and observed global properties of neutron stars can not rule out the super-soft nuclear symmetry energies at supra-saturation densities. The degree of possible violation of the Inverse-Square-Law of gravity in neutron stars is estimated using an Equation of State (EOS) of neutron-rich nuclear matter consistent with the available terrestrial laboratory data.Comment: Version accepted by Physical Review Letter