A storage and access architecture for efficient query processing in spatial database systems

Due to the high complexity of objects and queries and also due to extremely large data volumes, geographic database systems impose stringent requirements on their storage and access architecture with respect to efficient query processing. Performance improving concepts such as spatial storage and access structures, approximations, object decompositions and multi-phase query processing have been suggested and analyzed as single building blocks. In this paper, we describe a storage and access architecture which is composed from the above building blocks in a modular fashion. Additionally, we incorporate into our architecture a new ingredient, the scene organization, for efficiently supporting set-oriented access of large-area region queries. An experimental performance comparison demonstrates that the concept of scene organization leads to considerable performance improvements for large-area region queries by a factor of up to 150

Performance comparison of point and spatial access methods

In the past few years a large number of multidimensional point access methods, also called multiattribute index structures, has been suggested, all of them claiming good performance. Since no performance comparison of these structures under arbitrary (strongly correlated nonuniform, short "ugly") data distributions and under various types of queries has been performed, database researchers and designers were hesitant to use any of these new point access methods. As shown in a recent paper, such point access methods are not only important in traditional database applications. In new applications such as CAD/CIM and geographic or environmental information systems, access methods for spatial objects are needed. As recently shown such access methods are based on point access methods in terms of functionality and performance. Our performance comparison naturally consists of two parts. In part I we w i l l compare multidimensional point access methods, whereas in part I I spatial access methods for rectangles will be compared. In part I we present a survey and classification of existing point access methods. Then we carefully select the following four methods for implementation and performance comparison under seven different data files (distributions) and various types of queries: the 2-level grid file, the BANG file, the hB-tree and a new scheme, called the BUDDY hash tree. We were surprised to see one method to be the clear winner which was the BUDDY hash tree. It exhibits an at least 20 % better average performance than its competitors and is robust under ugly data and queries. In part I I we compare spatial access methods for rectangles. After presenting a survey and classification of existing spatial access methods we carefully selected the following four methods for implementation and performance comparison under six different data files (distributions) and various types of queries: the R-tree, the BANG file, PLOP hashing and the BUDDY hash tree. The result presented two winners: the BANG file and the BUDDY hash tree. This comparison is a first step towards a standardized testbed or benchmark. We offer our data and query files to each designer of a new point or spatial access method such that he can run his implementation in our testbed

Feed-forward Torque Control of Interior Permanent Magnet Brushless AC Drive for Traction Applications

This paper presents a feed-forward torque control (FTC) technique for interior permanent magnet (IPM) brushless AC (BLAC) drives in traction applications. It is shown that by adopting the Newton-Raphson iterative method for solving the proposed high-order nonlinear relationship between the torque demand, flux-linkage and desirable dq-axis currents, FTC with due account of nonlinear machine parameters can be achieved for IPM BLAC drives. It is also proven that the comparison between the reference voltage magnitudes under maximum torque per ampere (MTPA) and field-weakening (FW) operations together with online base speed determination can be utilized for FW operation activation to achieve full exploitation of the available DC-link voltage during the transition between the constant torque and FW operation regions. Since both the dqaxis current references and the base speed for FW operation activation are computed online, the proposed FTC technique provides flexibility for online parameter update or estimation and is able to cope with wide DC-link voltage variation. The proposed FTC strategy is experimentally validated by measurements on a 10kW wide constant power speed range (CPSR) IPM BLAC machine drive

Query processing of spatial objects: Complexity versus Redundancy

The management of complex spatial objects in applications, such as geography and cartography, imposes stringent new requirements on spatial database systems, in particular on efficient query processing. As shown before, the performance of spatial query processing can be improved by decomposing complex spatial objects into simple components. Up to now, only decomposition techniques generating a linear number of very simple components, e.g. triangles or trapezoids, have been considered. In this paper, we will investigate the natural trade-off between the complexity of the components and the redundancy, i.e. the number of components, with respect to its effect on efficient query processing. In particular, we present two new decomposition methods generating a better balance between the complexity and the number of components than previously known techniques. We compare these new decomposition methods to the traditional undecomposed representation as well as to the well-known decomposition into convex polygons with respect to their performance in spatial query processing. This comparison points out that for a wide range of query selectivity the new decomposition techniques clearly outperform both the undecomposed representation and the convex decomposition method. More important than the absolute gain in performance by a factor of up to an order of magnitude is the robust performance of our new decomposition techniques over the whole range of query selectivity

Formation and thermal stability of ω-Ti(Fe) in α-phase-based Ti(Fe) alloys

In this work, the formation and thermal stability of the ω-Ti(Fe) phase that were produced by the high-pressure torsion (HPT) were studied in two-phase α-Ti + TiFe alloys containing 2 wt.%, 4 wt.% and 10 wt.% iron. The two-phase microstructure was achieved by annealing the alloys at 470 °C for 4000 h and then quenching them in water. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were utilized to characterize the samples. The thermal stability of the ω-Ti(Fe) phase was investigated using differential scanning calorimetry (DSC) and in situ high-temperature XRD. In the HPT process, the high-pressure ω-Ti(Fe) phase mainly formed from α-Ti. It started to decompose by a cascade of exothermic reactions already at temperatures of 130 °C. The decomposition was finished above ~320 °C. Upon further heating, the phase transformation proceeded via the formation of a supersaturated α-Ti(Fe) phase. Finally, the equilibrium phase assemblage was established at high temperatures. The eutectoid temperature and the phase transition temperatures measured in deformed and heat-treated samples are compared for the samples with different iron concentrations and for samples with different phase compositions prior to the HPT process. Thermodynamic calculations were carried out to predict stable and metastable phase assemblages after heat-treatments at low (α-Ti + TiFe) and high temperatures (α-Ti + β-(Ti,Fe), β-(Ti,Fe))

Promoting abnormal grain growth in Fe-based shape memory alloys through compositional adjustments

Iron-based shape memory alloys are promising candidates for large-scale structural applications due to their cost efficiency and the possibility of using conventional processing routes from the steel industry. However, recently developed alloy systems like Fe–Mn–Al–Ni suffer from low recoverability if the grains do not completely cover the sample cross-section. To overcome this issue, here we show that small amounts of titanium added to Fe–Mn–Al–Ni significantly enhance abnormal grain growth due to a considerable refinement of the subgrain sizes, whereas small amounts of chromium lead to a strong inhibition of abnormal grain growth. By tailoring and promoting abnormal grain growth it is possible to obtain very large single crystalline bars. We expect that the findings of the present study regarding the elementary mechanisms of abnormal grain growth and the role of chemical composition can be applied to tailor other alloy systems with similar microstructural features

Considerations about multistep community detection

The problem and implications of community detection in networks have raised a huge attention, for its important applications in both natural and social sciences. A number of algorithms has been developed to solve this problem, addressing either speed optimization or the quality of the partitions calculated. In this paper we propose a multi-step procedure bridging the fastest, but less accurate algorithms (coarse clustering), with the slowest, most effective ones (refinement). By adopting heuristic ranking of the nodes, and classifying a fraction of them as `critical', a refinement step can be restricted to this subset of the network, thus saving computational time. Preliminary numerical results are discussed, showing improvement of the final partition.Comment: 12 page

Personhood, consciousness, and god : how to be a proper pantheist

© Springer Nature B.V. 2018In this paper I develop a theory of personhood which leaves open the possibility of construing the universe as a person. If successful, it removes one bar to endorsing pantheism. I do this by examining a rising school of thought on personhood, on which persons, or selves, are understood as identical to episodes of consciousness. Through a critique of this experiential approach to personhood, I develop a theory of self as constituted of qualitative mental contents, but where these contents are also capable of unconscious existence. On this theory, though we can be conscious of our selves, consciousness turns out to be inessential to personhood. This move, I then argue, provides resources for responding to the pantheist’s problem of God’s person.Peer reviewedFinal Accepted Versio