Minimizing Seed Set Selection with Probabilistic Coverage Guarantee in a Social Network

A topic propagating in a social network reaches its tipping point if the number of users discussing it in the network exceeds a critical threshold such that a wide cascade on the topic is likely to occur. In this paper, we consider the task of selecting initial seed users of a topic with minimum size so that with a guaranteed probability the number of users discussing the topic would reach a given threshold. We formulate the task as an optimization problem called seed minimization with probabilistic coverage guarantee (SM-PCG). This problem departs from the previous studies on social influence maximization or seed minimization because it considers influence coverage with probabilistic guarantees instead of guarantees on expected influence coverage. We show that the problem is not submodular, and thus is harder than previously studied problems based on submodular function optimization. We provide an approximation algorithm and show that it approximates the optimal solution with both a multiplicative ratio and an additive error. The multiplicative ratio is tight while the additive error would be small if influence coverage distributions of certain seed sets are well concentrated. For one-way bipartite graphs we analytically prove the concentration condition and obtain an approximation algorithm with an $O(\log n)$ multiplicative ratio and an $O(\sqrt{n})$ additive error, where $n$ is the total number of nodes in the social graph. Moreover, we empirically verify the concentration condition in real-world networks and experimentally demonstrate the effectiveness of our proposed algorithm comparing to commonly adopted benchmark algorithms.Comment: Conference version will appear in KDD 201

Effect of using full inversion tillage at pasture renewal on soil and plant cadmium concentrations : a thesis presented in partial fulfilment of the requirements for the degree of Master of Environmental Management, Massey University, Palmerston North, New Zealand

Cadmium (Cd) accumulation in New Zealand (NZ) agricultural soils has been recognised as a potential concern for food safety, which can limit the exports of some agricultural products. In NZ, elevated soil Cd concentrations in long-term pastures is mainly because of the historic application of Cd-rich phosphate fertiliser. Similar to the strong vertical stratification of soil organic carbon (SOC), total soil Cd concentration also shows a decreasing trend with soil depth. Recently, one-off full inversion tillage (FIT, or deeper ploughing below 25 cm soil depth) at pasture renewal is being investigated in NZ, due to the potential positive impact of this cultivation method on long-term soil C storage. By burying topsoil under the 10–25 cm soil depth, FIT potentially influences soil Cd vertical stratification, but there is no previous research that quantifies the impacts of this practice on soil and plant Cd. Hence, the aim of the current study was to assess the effect of using FIT at pasture renewal on soil and plant Cd concentrations in two contrasting grazed pasture soils. The current study involved the analysis of Cd in soil and plant samples taken from two on-going field trials in the North Island of NZ (Trial 1: Pallic Soil; Trial 2: Allophanic Soil). At both trial sites, three contrasting tillage treatments (i.e. FIT, shallow tillage-ST and no tillage-NT) were used in spring to establish a summer forage crop (leafy turnip), followed by sowing new ryegrass/white clover pasture in autumn. Soil cores were collected to a soil depth of 40 cm before the establishment of tillage treatments (i.e. pre-tillage: PT) and again at the end of the grazing of leafy turnip (i.e. post-tillage: FIT, ST and NT). Changes in soil total Cd (0–40 cm soil depth) and extractable Cd (0–15 cm soil depth) concentrations and soil pH (0–15 cm soil depth) were analysed. In addition, Cd concentration in herbage samples was monitored during both the summer crop and early new pasture growth phases. At both trial sites, FIT modified the vertical stratification of total soil Cd, thus helping reduce topsoil (0–5 cm soil depth) Cd concentration, without changing the total mass of soil Cd to 40 cm soil depth. However, the extent of its effect was different between the two field trials, which was influenced by the pre-tillage total soil Cd concentrations, and its degree of vertical stratification above the 25 cm soil depth. At the Trial 1 site, average total soil Cd concentration in the 0–5 cm soil depth for the FIT treatment was about 24% lower (0.16 mg Cd/kg) than the pre-tillage value (0.21 mg Cd/kg); however, at the Trial 2 site, the average total soil Cd concentration in this soil depth for the FIT treatment was about 40% lower (0.25 mg Cd/kg) than the pre-tillage value (0.42 mg Cd/kg). In terms of extractable Cd concentration, FIT also resulted in a different influence between the two trial sites, because of the contrasting pre-tillage extractable Cd distribution with soil depth. At the Trial 1 site, the FIT treatment had about 52% higher (0.024 mg Cd/kg) average extractable Cd concentration in the 0–5 cm soil depth than the pre-tillage value (0.016 mg Cd/kg), while it had about 57% lower (0.013 mg Cd/kg) average extractable Cd in this soil depth at the Trial 2 site than the pre-tillage value (0.031 mg Cd/kg). Tillage treatments caused contrasting effects on plant Cd concentrations between the two trial sites. In addition, there was also a strong plant species influence on herbage Cd concentrations. In general, the new pasture Cd concentrations were less than 10% of the summer turnip crop at both trial sites. At the Trial 1 site, tillage practices did not significantly (P > 0.05) affect tissue Cd concentrations in either turnip leaves (on average: 0.92, 0.79 and 0.95 mg Cd/kg DM for the FIT, ST and NT treatment, respectively) or new grass (on average: 0.05 mg Cd/kg DM for all tillage treatments). In contrast, at the Trial 2 site, the FIT treatment resulted in lower Cd concentrations for both summer forage crop (on average: 0.69, 0.76 and 0.80 mg Cd/kg DM for the FIT, ST and NT treatment, respectively) and new pasture (on average: 0.04, 0.06 and 0.05 mg Cd/kg DM for the FIT, ST and NT treatment, respectively). Lower Cd uptake by plants sampled for the FIT treatment is likely to be the result of FIT-induced lower total soil Cd and extractable Cd concentrations in the topsoil at this trial site. This field study demonstrated that the use of FIT during pasture renewal can be effective at decreasing total topsoil Cd concentrations in NZ pasture soils, particularly in those soils where there is a high degree of stratification in total soil Cd with soil depth. However, other management practices may also further reduce soil Cd bioavailability after tillage. In particular, any future accumulation of soil organic matter under the new pasture is expected to improve the topsoil’s capacity to bind and immobilise Cd. Further work is required to evaluate the long-term influence of tillage treatments on soil chemical properties (e.g. soil Cd, organic matter and pH), and their effects on Cd bioavailability and uptake by plants

Benefits and Cost-effectiveness Analysis of Exhaust Energy Recovery System Using Low and High Boiling Temperature Working Fluids in Rankine Cycle

AbstractIn this paper, six attactive working fluids, including low boiling refrigerants such as R123, R141b and R245fa (Group L) and high boiling substances such as cyclohexane, ethanal and water (Group H), are applied on Rankine cycle, in order to examine the potential of these two categories of working fluids in high temperature exhaust energy recovery system (EERs) from a gasoline engine. The influences of engine speed at full load and evaporating pressure on the EERs performances are analyzed. The results reveal that water in Group H and R141b in Group L contribute the peak improvement in system benefits, while fluids in Group H show better cost-effectiveness. The EERs performances would be influenced strongly by evaporating pressure at high engine speed, while it also requires high pressure to enhance the performances at low speed. Besides, when the evaporating pressure is low, selection of working fluid should be emphasized

The SpeakIn System Description for CNSRC2022

This report describes our speaker verification systems for the tasks of the CN-Celeb Speaker Recognition Challenge 2022 (CNSRC 2022). This challenge includes two tasks, namely speaker verification(SV) and speaker retrieval(SR). The SV task involves two tracks: fixed track and open track. In the fixed track, we only used CN-Celeb.T as the training set. For the open track of the SV task and SR task, we added our open-source audio data. The ResNet-based, RepVGG-based, and TDNN-based architectures were developed for this challenge. Global statistic pooling structure and MQMHA pooling structure were used to aggregate the frame-level features across time to obtain utterance-level representation. We adopted AM-Softmax and AAM-Softmax combined with the Sub-Center method to classify the resulting embeddings. We also used the Large-Margin Fine-Tuning strategy to further improve the model performance. In the backend, Sub-Mean and AS-Norm were used. In the SV task fixed track, our system was a fusion of five models, and two models were fused in the SV task open track. And we used a single system in the SR task. Our approach leads to superior performance and comes the 1st place in the open track of the SV task, the 2nd place in the fixed track of the SV task, and the 3rd place in the SR task.Comment: 4 page

Isotopic dynamics of precipitation and its regional and local drivers in a plateau inland lake basin, Southwest China

Shrinkage of plateau lakes under climate strength has drawn growing attention. Because of its intricate implication to hydro-meteorological condition and climate system, stable isotopes in precipitation (e.g. delta H-2(p) and delta O-18(p)) provide us a powerful tool to understand the climate-hydrologic dynamics in shrinking lakes. However, how the regional atmospheric circulation, moisture sources and local fractionation processes drive isotopic variability from temporal to spatial scale has rarely been reported for remote plateau lakes. Hence, we collected a total of 98 rainfall samples at the south and the north shores of Chenghai lake, Yunnan-Guizhou Plateau to study the potential driving forces of precipitation isotope variability during the wet season of 2019. Based on backward trajectories of air masses obtained from HYSPLIT model, 68% of moisture came from delta O-18 depleted ocean (Indian Ocean, Bay of Bengal, South China Sea and Pacific Ocean), and the rainout process promoted the isotopic depletion when moisture arrived at the study basin. Evapotranspiration increased the heavy isotope ratios in precipitation originated from continents (northern China inland and western continents). The temporal dynamics of delta O-18(p) and delta H-2(p) were in phase with the convection activities intensity underlined the influence from large-scale atmospheric circulation. Local meteorological factors played a secondary role in isotope variability. Precipitation amount-effect strongly affected isotope ratios while mild anti-temperature effect was observed at daily scale. Interestingly, the rainfall isotope ratios showed different mechanisms in govern at lake south shore and north shore, with a distance of 19 km in between. This south-to-north difference can be explained by either lower 1.03% sub-evaporation in the south shore or 7% of recycled moisture contributing to precipitation in the north shore. Our findings discover the driving forces for delta O-18(p) variation and provide solid interpretations for hydro-climate change in Southwest China. (C) 2020 Elsevier B.V. All rights reserved.Peer reviewe