A non-Gaussian continuous state space model for asset degradation

The degradation model plays an essential role in asset life prediction and condition based maintenance. Various degradation models have been proposed. Within these models, the state space model has the ability to combine degradation data and failure event data. The state space model is also an effective approach to deal with the multiple observations and missing data issues. Using the state space degradation model, the deterioration process of assets is presented by a system state process which can be revealed by a sequence of observations. Current research largely assumes that the underlying system development process is discrete in time or states. Although some models have been developed to consider continuous time and space, these state space models are based on the Wiener process with the Gaussian assumption. This paper proposes a Gamma-based state space degradation model in order to remove the Gaussian assumption. Both condition monitoring observations and failure events are considered in the model so as to improve the accuracy of asset life prediction. A simulation study is carried out to illustrate the application procedure of the proposed model

China’s Sharing Mobility Economy

Evolution in the urban landscape is key for sustainable development in the world because people have progressively moved from rural areas to live in urban cities. The mobility and transport industry offer the greatest potential to reduce carbon emissions in cities. The arrival of application-based and intelligent-sharing systems into the shores of China has been disruptive to local and international businesses. These has led to a liberation of an automobile sharing economy at a much deeper and greater level: a rise in the use of electric vehicles (EVs), car-pooling, and the utilization of bike-sharing models. Integrating the pre-existing but under-utilized low-carbon transportation vehicles in urban cities, such as public transportation, with the various application-based mobility sharing business systems surfacing, we see immense potential in the transformation of urban transportation to long-term viability. However, the accelerated expansions of businesses and innovation in the sharing economy have been challenging pre-existing sources of knowledge, socio-economic ties, and physical and geographical urban infrastructures. This research investigates the relationship between the continual progress of urban structures and the socio-ecological innovations in the sharing mobility economy, utilizing observational statistics from three studies that focus on sharing transportation industry -- in particular, the sharing of rides, EVs, and bicycles in China. These statistics show that there is a robust evolutionary system that integrates the increasingly sustainable macro-level urban landscape and the innovative business structures to form a meso-level intelligent and green transport framework. Namely, these two levels of evolutionary change in urban landscapes and business structures generated by the disruptive technologies of the sharing mobility sector and brought forth by the urban changes towards increasing sustainability, both subsequently shape one another and reinforce sustainable practices and principles in the swift-changing urban sector and corporate innovation sectors in Shanghai, China

Extensions of an Empirical Automated Tuning Framework

Empirical auto-tuning has been successfully applied to scientific computing applications and web-based cluster servers over the last few years. However, few studies are focused on applying this method on optimizing the performance of database systems. In this thesis, we present a strategy that uses Active Harmony, an empirical automated tuning framework to optimize the throughput of PostgreSQL server by tuning its settings such as memory and buffer sizes. We used Nelder-Mead simplex method as the search engine, and we showed how our strategy performs compared to the hand-tuned and default results. Another part of this thesis focuses on using data from prior runs of auto-tuning. Prior data has been proved to be useful in many cases, such as modeling the search space or finding a good starting point for hill-climbing. We present several methods that were developed to manage the prior data in Active Harmony. Our intention was to provide tuners a complete set of information for their tuning tasks

Two-tier Spatial Modeling of Base Stations in Cellular Networks

Poisson Point Process (PPP) has been widely adopted as an efficient model for the spatial distribution of base stations (BSs) in cellular networks. However, real BSs deployment are rarely completely random, due to environmental impact on actual site planning. Particularly, for multi-tier heterogeneous cellular networks, operators have to place different BSs according to local coverage and capacity requirement, and the diversity of BSs' functions may result in different spatial patterns on each networking tier. In this paper, we consider a two-tier scenario that consists of macrocell and microcell BSs in cellular networks. By analyzing these two tiers separately and applying both classical statistics and network performance as evaluation metrics, we obtain accurate spatial model of BSs deployment for each tier. Basically, we verify the inaccuracy of using PPP in BS locations modeling for either macrocells or microcells. Specifically, we find that the first tier with macrocell BSs is dispersed and can be precisely modelled by Strauss point process, while Matern cluster process captures the second tier's aggregation nature very well. These statistical models coincide with the inherent properties of macrocell and microcell BSs respectively, thus providing a new perspective in understanding the relationship between spatial structure and operational functions of BSs

Characterizing Spatial Patterns of Base Stations in Cellular Networks

The topology of base stations (BSs) in cellular networks, serving as a basis of networking performance analysis, is considered to be obviously distinctive with the traditional hexagonal grid or square lattice model, thus stimulating a fundamental rethinking. Recently, stochastic geometry based models, especially the Poisson point process (PPP), attracts an ever-increasing popularity in modeling BS deployment of cellular networks due to its merits of tractability and capability for capturing nonuniformity. In this study, a detailed comparison between common stochastic models and real BS locations is performed. Results indicate that the PPP fails to precisely characterize either urban or rural BS deployment. Furthermore, the topology of real data in both regions are examined and distinguished by statistical methods according to the point interaction trends they exhibit. By comparing the corresponding real data with aggregative point process models as well as repulsive point process models, we verify that the capacity-centric deployment in urban areas can be modeled by typical aggregative processes such as the Matern cluster process, while the coverage-centric deployment in rural areas can be modeled by representativ

Integer colorings with forbidden rainbow sums

For a set of positive integers $A \subseteq [n]$, an $r$-coloring of $A$ is rainbow sum-free if it contains no rainbow Schur triple. In this paper we initiate the study of the rainbow Erd\H{o}s-Rothchild problem in the context of sum-free sets, which asks for the subsets of $[n]$ with the maximum number of rainbow sum-free $r$-colorings. We show that for $r=3$, the interval $[n]$ is optimal, while for $r\geq8$, the set $[\lfloor n/2 \rfloor, n]$ is optimal. We also prove a stability theorem for $r\geq4$. The proofs rely on the hypergraph container method, and some ad-hoc stability analysis.Comment: 20 page

A Physical Model-based Correction for Charge Traps in the Hubble Space Telescope's Wide Field Camera 3 Near-IR Detector and Applications to Transiting Exoplanets and Brown Dwarfs

The Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) near-IR channel is extensively used in time-resolved observations, especially for transiting exoplanet spectroscopy and brown dwarf and directly imaged exoplanet rotational phase mapping. The ramp effect is the dominant source of systematics in the WFC3 for time-resolved observations, which limits its photometric precision. Current mitigation strategies are based on empirical fits and require additional orbits "to help the telescope reach a thermal equilibrium". We show that the ramp effect profiles can be explained and corrected with high fidelity using charge trapping theories. We also present a model for this process that can be used to predict and to correct charge trap systematics. Our model is based on a very small number of parameters that are intrinsic to the detector. We find that these parameters are very stable between the different datasets, and we provide best-fit values. Our model is tested with more than 120 orbits ($\sim40$ visits) of WFC3 observations and is proved to be able to provide near photon noise limited corrections for observations made with both staring and scanning modes of transiting exoplanets as well as for starting-mode observations of brown dwarfs. After our model correction, the light curve of the first orbit in each visit has the same photometric precision as subsequent orbits, so data from the first orbit need no longer be discarded. Near IR arrays with the same physical characteristics (e.g., JWST/NIRCam) may also benefit from the extension of this model, if similar systematic profiles are observed.Comment: 16 pages, 13 figures, accepted to Astronomical Journa

The Newly Discovered Graphic-text Combined Study of Liushui Genglubu in the South China Sea

The newly discovered Hainan fisherman Zheng Changmei s copy of the South China Sea Liushui Genglubu is divided into two parts Liushui Record and Mountain Water Potential Map It is the only complete graphic-text combination of the South China Sea Genglubu found so far This book records the tide situation in the western sea area of Hainan Island the route around Hainan Island the route distance from Hainan Island to Guangdong province Guangxi province of China Vietnam and other places and 24 mountain water potential diagram The discovery of this book proves the use of Genglubu by merchant ships in Hainan Island the 24 sea charts are the continuation and development of the rare mountain shape and water potential maps in the literature of the past dynasties The drawing of the mountain shape and water potential has the characteristics of integrity which makes up for the rare sea charts in the Genglubu of the South China Sea In addition the record writing rules and drawing characteristics of the Six Collision Flow Methods in this book have the writing of Hainan Island dialect which has important reference value for the study of Hainan Fishermen s Island s navigation knowledge folk trade and local knowledg