Scalable distributed event detection for Twitter

Social media streams, such as Twitter, have shown themselves to be useful sources of real-time information about what is happening in the world. Automatic detection and tracking of events identified in these streams have a variety of real-world applications, e.g. identifying and automatically reporting road accidents for emergency services. However, to be useful, events need to be identified within the stream with a very low latency. This is challenging due to the high volume of posts within these social streams. In this paper, we propose a novel event detection approach that can both effectively detect events within social streams like Twitter and can scale to thousands of posts every second. Through experimentation on a large Twitter dataset, we show that our approach can process the equivalent to the full Twitter Firehose stream, while maintaining event detection accuracy and outperforming an alternative distributed event detection system

Can twitter replace newswire for breaking news?

Twitter is often considered to be a useful source of real-time news, potentially replacing newswire for this purpose. But is this true? In this paper, we examine the extent to which news reporting in newswire and Twitter overlap and whether Twitter often reports news faster than traditional newswire providers. In particular, we analyse 77 days worth of tweet and newswire articles with respect to both manually identified major news events and larger volumes of automatically identified news events. Our results indicate that Twitter reports the same events as newswire providers, in addition to a long tail of minor events ignored by mainstream media. However, contrary to popular belief, neither stream leads the other when dealing with major news events, indicating that the value that Twitter can bring in a news setting comes predominantly from increased event coverage, not timeliness of reporting

NON–FAR-BASED CONTRACTS AND ACQUISITION ENVIRONMENTAL FACTOR ANALYSIS

Strategic competitors like China have the ability to sprint through technological hurdles by disregarding intellectual property laws, and can decide when contractors will work with the government. Meanwhile the U.S. remains tied down by regulation, laws, and bureaucracy. To help alleviate these barriers, acquisition offices are turning to non– Federal Acquisition Regulation- (FAR) based procurement. Other transactions and additional non–FAR-based acquisition represent an area of contracting that personnel are seeking out but do not understand. The environmental factors that lead these non–FAR-based acquisition offices to success are also shrouded in mystery. Interviews of personnel in organizations that do FAR-based acquisition and in organizations that do non–FAR-based acquisition brought to light environmental factors at play. The interviews produced quantifiable data highlighting a large gap in training with fewer than half of non–FAR-based contracting respondents having training available to them and fewer than half of finance and requirement owners knowing non–FAR-based acquisition laws and regulations. Data also showed a drive from leadership for legal, finance, and contracting personnel to work together as a team. Continued importance must be placed on acquisition teams to find risk-appropriate deregulated solutions. Training and education should also be a main priority to educate personnel on what non–FAR-based procurement and contracting is how to do it properly.Captain, United States Air ForceCaptain, United States Air ForceApproved for public release. Distribution is unlimited

Water waves over a rough bottom in the shallow water regime

This is a study of the Euler equations for free surface water waves in the case of varying bathymetry, considering the problem in the shallow water scaling regime. In the case of rapidly varying periodic bottom boundaries this is a problem of homogenization theory. In this setting we derive a new model system of equations, consisting of the classical shallow water equations coupled with nonlocal evolution equations for a periodic corrector term. We also exhibit a new resonance phenomenon between surface waves and a periodic bottom. This resonance, which gives rise to secular growth of surface wave patterns, can be viewed as a nonlinear generalization of the classical Bragg resonance. We justify the derivation of our model with a rigorous mathematical analysis of the scaling limit and the resulting error terms. The principal issue is that the shallow water limit and the homogenization process must be performed simultaneously. Our model equations and the error analysis are valid for both the two- and the three-dimensional physical problems.Comment: Revised version, to appear in Annales de l'Institut Henri Poincar\'

Solid State Structures and Transport Properties of Selenazyl Radicals

The synthetic routes to the salts of the 3H-naphtho[1,2-d][1,2,3]dithiazolylium cation and its three selenium containing variants are described. The most efficient approach involves the condensation of bis-acetylated aminoselenolates and aminothiolates with sulfur and selenium halides. Cyclic voltammetry experiments illustrate that the four cations can be reduced to their neutral radical state and are stable in solution. The EPR spectra of all four radicals have been recorded and the spin distributions have been compared with those obtained from DFT calculations. It has been found that the selenium containing radicals are thermally unstable at room temperature, but the all sulfur species has been isolated and characterized by X-ray crystallography. In the solid state, the radicals associate into cofacial dimers and short interdimer S---Sʹ, S---Nʹ and C---Hʹ contacts are observed. The all-selenium species has been characterized in its oxidized state by X-ray crystallography. A series of four challenging crystallographic projects are presented. (1) 8-Phenyl-4-methyl-4H-bis[1,2,3]thiaselenazolo[4,5-b:5ʹ,4ʹ-e]pyridinyl has been prepared and its solid-state structure determined by powder X-ray diffraction methods. The radical crystallizes in the space group P3121 and is isostructural with its ethylated derivative and its all-sulfur containing analogue. Variable-temperature magnetic measurements confirm that the radical is an undimerized S = ½ system with weak intermolecular antiferromagnetic coupling. Pressed pellet variable-temperature electrical conductivity measurements provide a room-temperature conductivity (σRT) of 3.3 ×10-5 S cm-1 and an activation energy (Eact) of 0.29 eV. The results of Extended Hückel Theory (EHT) band structure calculations are presented. (2) Single-crystal and powder X-ray diffraction methods on a family of selenium-containing radicals based the 4-methyl-3H,4H-bis[1,2,3]dithiazolo[4,5-b:5ʹ,4ʹ-e]pyridin-3-yl radical are presented. All three radicals (SSN, SSeN and SeSeN) are isostructural, crystallizing in the space group P212121, and form slipped π-stacks of undimerized radicals with close E---Eʹ contacts. Pressed pellet variable-temperature electrical conductivity measurements of the systems provide σRT = 3 × 10-4 and 1 × 10-3 S cm-1 and Eact of 0.24 eV and 0.17 eV for the SSeN and SeSeN radicals respectively. (3) The crystal structures of 4-methyl-4H-bis[1,2,3]dithiazolo[4,5-b:5ʹ,4ʹ-e]pyrazin-3-yl at 298 K, 123 K and 88 K are presented. At 298 K the radicals remain undimerized, crystallizing in the space group Cmca and forming evenly-spaced π stacks. Upon cooling to 123 K the space group symmetry is lowered by loss of C-centering to Pccn such that the radicals are not evenly spaced within the π-stack. At 88 K a further lowering of space group symmetry to P21/c is observed. (4) [1,3,2]Dithiazolo[4,5-b]pyridin-2-yl is polymorphic, crystallizing in P21 and P21/n. A non-merohedral twin law is required to model the P21 system. The structures of both crystals are comprised of layers of head-to-head π dimers and the two structures differ in the orientation of the π dimers along the stacks. Variable-temperature magnetic data reveal that both phases are essentially diamagnetic at low temperatures and form weak π dimers at higher temperatures. Synthetic methods have been developed to generate the complete series of resonance stabilized heterocyclic thia/selenazyl radicals based on 8-chloro-4-ethyl-4H-bis[1,2,3]dithiazolo[4,5-b:5ʹ,4ʹ-e]pyridin-3-yl. X-ray crystallographic studies confirm that all four radicals are isostructural, belonging to the tetragonal space group P21m. The crystal structures consist of slipped π-stack arrays of undimerized radicals. Variable temperature conductivity measurements reveal an increase in conductivity with increasing selenium content, with σRT reaching a maximum of 3.0 × 10-4 S cm-1 with an Eact of 0.19 eV for the all-selenium containing variant. Variable temperature magnetic susceptibility measurements indicate that all four radicals exhibit S = ½ Curie-Weiss behaviour over the temperature range 20 - 300 K. At lower temperatures, the three selenium-based radicals display magnetic ordering. The first radical with selenium positioned at the E1 site, undergoes a phase transition at 14 K to a weakly spin-canted (φ = 0.010̊) antiferromagnetic state. By contrast, the radical containing the apical selenium and the all-selenium variant, which both possess selenium in the E2 position, order ferromagnetically, with Curie temperatures (Tc) = 12.8 K and 17.0 K respectively and coercive fields Hc at 2 K of 250 Oe and 1370 Oe respectively. The transport properties of the entire series of radicals are discussed in the light of EHT band-structure calculations. A series of bis-thiaselenazolyl radicals (R2BPTSR1) based on the bis-[1,2,3]-thiaselenazolo[4,5-b:5',4'-e]pyridin-3-yl (R1 = Et, Pr and CF3CH2, R2 = Cl; R1 = Et, R2 = Me and Br) have been prepared and characterized by X-ray crystallography. The radicals are formally isostructural, all belonging to the tetragonal space group P21m. The crystal structures consist of slipped π-stack arrays of undimerized radicals packed about centers. Variations in R1 (Et, Pr, CF3CH2) with R2 = Cl lead to significant changes in the degree of slippage of the π-stacks and hence the proximity of the Se---Seʹ contacts. By contrast, variations in R2 (Cl, Br, Me) with R1 = Et induce very little change in either the slippage angle or the Se---Seʹ contacts. Variable temperature conductivity measurements show relatively constant values for σRT (10-5 - 10-4 S cm-1) and Eact (0.27 - 0.31 eV) across the entire series. Variable temperature magnetic susceptibility measurements indicate major differences in the magnetic behaviour. Radicals with R1 = Pr, CH2CF3, R2 = Cl behave as weakly antiferromagnetically coupled Curie-Weiss paramagnets, but radicals with R1 = Et; R2 = Cl, Me, Br demonstrate ferromagnetic ordering, with Tc values of 12.8 K (R2 = Cl), 13.6 K (R2 = Me), and 14.1 K (R2 = Br)

为赔付金额辩护

Investor-state dispute settlement (ISDS) has come under intense criticism from some quarters, in part due to perceived “mega” quantum claims that strain both credulity and states’ ability to pay. The author describes these contentions as largely overblown, from the perspective of a practitioner representing ISDS claimants

Probing the Evaporation Dynamics of Ethanol/Gasoline Biofuel Blends Using Single Droplet Manipulation Techniques

Peer reviewedPublisher PD