19,858 research outputs found
Optimization of Analytic Window Functions
Analytic functions represent the state-of-the-art way of performing complex
data analysis within a single SQL statement. In particular, an important class
of analytic functions that has been frequently used in commercial systems to
support OLAP and decision support applications is the class of window
functions. A window function returns for each input tuple a value derived from
applying a function over a window of neighboring tuples. However, existing
window function evaluation approaches are based on a naive sorting scheme. In
this paper, we study the problem of optimizing the evaluation of window
functions. We propose several efficient techniques, and identify optimization
opportunities that allow us to optimize the evaluation of a set of window
functions. We have integrated our scheme into PostgreSQL. Our comprehensive
experimental study on the TPC-DS datasets as well as synthetic datasets and
queries demonstrate significant speedup over existing approaches.Comment: VLDB201
The Photonic Band theory and the negative refraction experiment of metallic helix metamaterials
We develop a theory to compute and interpret the photonic band structure of a
periodic array of metallic helices for the first time. Interesting features of
band structure include the ingenuous longitudinal and circularly polarized
eigenmodes, the wide polarization gap [Science 325, 1513 (2009)], and the
helical symmetry guarantees the existence of negative group velocity bands at
both sides of the polarization gap and band crossings pinned at the zone
boundary with fixed frequencies. A direct proof of negative refraction via a
chiral route [Science 306, 1353 (2004)] is achieved for the first time by
measuring Gooshanchen shift through a slab of three dimensional bona fide helix
metamaterial
Don’t Forget Your Supplier When Remanufacturing
A popular assumption in the current literature on remanufacturing is that the whole new product is produced by an integrated manufacturer, which is inconsistent with most industries. In this paper, we model a decentralised closed-loop supply chain consisting of a key component supplier and a non-integrated manufacturer, and demonstrate that the interaction between these players significantly impacts the economic and environmental implications of remanufacturing. In our model, the non-integrated manufacturer can purchase new components from the supplier to produce new products, and remanufacture used components to produce remanufactured products. Thus, the non-integrated manufacturer is not only a buyer but also a rival to the supplier. In a steady state period, we analyse the performances of an integrated manufacturer and the decentralised supply chain. We find that, although the integrated manufacturer always benefits from remanufacturing, the remanufacturing opportunity may constitute a lose-lose situation to the supplier and the non-integrated manufacturer, making their profits be lower than in an identical supply chain without remanufacturing. In addition, the non-integrated manufacturer may be worse off with a lower remanufacturing cost or a larger return rate of used products due to the interaction with the supplier. We further demonstrate that the government-subsidised remanufacturing in the non-integrated (integrated) manufacturer is detrimental (beneficial) to the environment
Structural insights into the gating of DNA passage by the topoisomerase II DNA-gate.
Type IIA topoisomerases (Top2s) manipulate the handedness of DNA crossovers by introducing a transient and protein-linked double-strand break in one DNA duplex, termed the DNA-gate, whose opening allows another DNA segment to be transported through to change the DNA topology. Despite the central importance of this gate-opening event to Top2 function, the DNA-gate in all reported structures of Top2-DNA complexes is in the closed state. Here we present the crystal structure of a human Top2 DNA-gate in an open conformation, which not only reveals structural characteristics of its DNA-conducting path, but also uncovers unexpected yet functionally significant conformational changes associated with gate-opening. This structure further implicates Top2's preference for a left-handed DNA braid and allows the construction of a model representing the initial entry of another DNA duplex into the DNA-gate. Steered molecular dynamics calculations suggests the Top2-catalyzed DNA passage may be achieved by a rocker-switch-type movement of the DNA-gate
Sustainability, space and supply chains: the role of bamboo in Anji County, China
Rural modernization in China has been profound as the countryside has moved from agricultural production to industrial and tertiary industry development. Within rural areas these changes can have enormous significance for how we think about their sustainability. One rural county that vividly illustrates both the challenges and opportunities of rural development is Anji in Zhejiang Province in Eastern China. Anji is held up as a model of rural sustainable development. In this paper we analyse the basis for the sustainability claims made of Anji and to do so, we examine how the production and processing of bamboo materials transformed Anji into a place-specific bamboo-making locality that is lauded for its sustainability. We analyse how thinking on a place and a material (bamboo) come together to reinforce thinking on sustainability in rural China. We then go on to critically question the politico-economic arrangements that construct Anji and bamboo as models of sustainability. We argue that whilst both Anji and bamboo do have notable features that characterise them as sustainable and together can make an even more persuasive case for rural sustainability, a more detailed analysis allows us to uncover the deep-rooted tensions that persist in Chinese rural development between environmental protection and economic growth. The paper draws on a mixture of published and unpublished material to provide a detailed examination of the ways in which bamboo supply chains operate within and through Anji. The paper concludes that local constructions of sustainability are driven by economic rather than environmental values
Linear Structure of the Oligosaccharide Chains in α_1-Protease Inhibitor Isolated from Human Plasma
Two glycopeptides present in equal amounts were isolated from a pronase digest of alpha1-protease inhibitor of human plasma by gel filtration on Sephadex G-50 and chromatography on DEAE-cellulose. The carbohydrate side chains in both glycopeptides are linked through asparaginyl residues. The glycopeptides were digested sequentially with specific glycosidases; and after each step, the released sugars as well as the composition of the residual peptides were determined. The linear structures of these glycopeptides deduced from these data are shown below. Based on the total carbohydrate content of the intact protein and with these structural data, it is postulated that 4 oligosaccharide units are attached to 1 molecule of the protein; 2 of these were represented as in Equation 1, the other 2 as in Equation 2
Universal sheet resistance and revised phase diagram of the cuprate high-temperature superconductors
Upon introducing charge carriers into the copper-oxygen sheets of the
enigmatic lamellar cuprates the ground state evolves from an insulator into a
superconductor, and eventually into a seemingly conventional metal (a Fermi
liquid). Much has remained elusive about the nature of this evolution and about
the peculiar metallic state at intermediate hole-carrier concentrations (p).
The planar resistivity of this unconventional metal exhibits a linear
temperature dependence (\rho T) that is disrupted upon cooling toward
the superconducting state by the opening of a partial gap (the pseudogap) on
the Fermi surface. Here we first demonstrate for the quintessential compound
HgBaCuO a dramatic switch from linear to purely quadratic
(Fermi-liquid-like, \rho T) resistive behavior in the pseudogap
regime. Despite the considerable variation in crystal structures and disorder
among different compounds, our result together with prior work gives new
insight into the p-T phase diagram and reveals the fundamental resistance per
copper-oxygen sheet in both linear (\rho_S = A_{1S} T) and quadratic (\rho_S =
A_{2S} T) regimes, with A_{1S} A_{2S} 1/p. Theoretical
models can now be benchmarked against this remarkably simple universal
behavior. Deviations from this underlying behavior can be expected to lead to
new insights into the non-universal features exhibited by certain compounds
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