Analytical Evaluation of Coverage-Oriented Femtocell Network Deployment

This paper proposes a coverage-oriented femtocell network deployment scheme, in which the femtocell base stations (BSs) can decide whether to be active or inactive depending on their distances from the macrocell BSs. Specifically, as the areas close to the macrocell BSs already have satisfactory cellular coverage, the femtocell BSs located inside such areas are kept to be inactive. Thus, all the active femtocells are located in the poor macrocell coverage areas. Based on a stochastic geometric framework, the coverage probability can be analyzed with tractable results. Surprisingly, the results show that the proposed scheme, although with a lower defacto femtocell density, can achieve better coverage performance than that keeping all femtocells in the entire network to be active. The analytical results further identify the achievable optimal performance of the new scheme, which provides mobile operators a guideline for femtocell deployment and operation.Comment: 6 pages, 7 figures, published in IEEE International Conference on Communications (ICC'13

QuAC : Question Answering in Context

We present QuAC, a dataset for Question Answering in Context that contains 14K information-seeking QA dialogs (100K questions in total). The dialogs involve two crowd workers: (1) a student who poses a sequence of freeform questions to learn as much as possible about a hidden Wikipedia text, and (2) a teacher who answers the questions by providing short excerpts from the text. QuAC introduces challenges not found in existing machine comprehension datasets: its questions are often more open-ended, unanswerable, or only meaningful within the dialog context, as we show in a detailed qualitative evaluation. We also report results for a number of reference models, including a recently state-of-the-art reading comprehension architecture extended to model dialog context. Our best model underperforms humans by 20 F1, suggesting that there is significant room for future work on this data. Dataset, baseline, and leaderboard available at http://quac.ai.Comment: EMNLP Camera Read

Exploring the Atmosphere of Neoproterozoic Earth: The Effect of O2_{2} on Haze Formation and Composition

Previous studies of haze formation in the atmosphere of the Early Earth have focused on N$_{2}$/CO$_{2}$/CH$_{4}$ atmospheres. Here, we experimentally investigate the effect of O$_{2}$ on the formation and composition of aerosols to improve our understanding of haze formation on the Neoproterozoic Earth. We obtained in situ size, particle density, and composition measurements of aerosol particles produced from N$_{2}$/CO$_{2}$/CH$_{4}$/O$_{2}$ gas mixtures subjected to FUV radiation (115-400 nm) for a range of initial CO$_{2}$/CH$_{4}$/O$_{2}$ mixing ratios (O$_{2}$ ranging from 2 ppm to 0.2\%). At the lowest O$_{2}$ concentration (2 ppm), the addition increased particle production for all but one gas mixture. At higher oxygen concentrations (20 ppm and greater) particles are still produced, but the addition of O$_{2}$ decreases the production rate. Both the particle size and number density decrease with increasing O$_{2}$, indicating that O$_{2}$ affects particle nucleation and growth. The particle density increases with increasing O$_{2}$. The addition of CO$_{2}$ and O$_{2}$ not only increases the amount of oxygen in the aerosol, but it also increases the degree of nitrogen incorporation. In particular, the addition of O$_{2}$ results in the formation of nitrate bearing molecules. The fact that the presence of oxygen bearing molecules increases the efficiency of nitrogen fixation has implications for the role of haze as a source of molecules required for the origin and evolution of life. The composition changes also likely affect the absorption and scattering behavior of these particles but optical properties measurements are required to fully understand the implications for the effect on the planetary radiative energy balance and climate.Comment: 15 pages, 3 tables, 8 figures, accepted in Astrophysical Journa

Translating Cognitive and Linguistic Metaphors in Popular Science: A Case Study of Scientific Discoveries

Since the cognitive turn in metaphor studies in the late 1970s, metaphor has been seen as a cognitive phenomenon reflecting how we think, alongside its classic role as a powerful literary device. This ‘cognitive turn’ in metaphor studies makes it possible to investigate metaphor in two facets: the cognitive one and the linguistic one. In this tenet, the notion of metaphor features two intertwined parts: conceptual metaphors which resemble mental connections between different knowledge packets (e.g., LIFE IS A BOOK), and their linguistic manifestations known as metaphorical expressions or linguistic metaphors (e.g., They are starting a new chapter of their life). This opens a window for metaphor translation research, for it allows researchers to examine metaphor translation from the two complementary facets. Building on conceptual metaphor theory (Lakoff and Johnson 1980, 2003) and conceptual blending theory (Fauconnier and Turner 2002), our case study discusses the translation of cognitive and linguistic metaphors identified in source and target texts. Metaphorical expressions were handpicked from seven popular cosmological articles published in Scientific American between 2017 and 2018, and their official Chinese translations published in Huanqiukexue (‘global science,’ Beijing) and Kexueren (‘science person,’ Taipei). The findings lend support to the joint application of two metaphor theories to descriptive translation studies, for it not only facilitates the analysis of translation examples but also enhances the feasibility of comparing metaphor translation research across languages pinned by metaphor parameters waiting to be explored

On the physical layer security in large scale cellular networks

This paper studies the information-theoretic secrecy performance in large-scale cellular networks based on a stochastic geometry framework. The locations of both base stations and the mobile users are modeled as independent two-dimensional Poisson point processes. We consider a key feature of the cellular network, namely, information exchange between base stations, and characterize its impact on the achievable secrecy rate of an arbitrary downlink transmission with a certain portion of the mobile users acting as potential eavesdroppers. In particular, analytical results are presented under diverse assumptions on the availability of eavesdroppers' location information at the serving base station, which captures the benefit from the exchange of mobile users' location information between base stations.H. Wang is with the Australian National University and NICTA. NICTA is funded by the Australian Government as represented by the Department of Broadband, Communications and the Digital Economy and the Australian Research Council through the ICT Centre of Excellence program. This work was supported by the Australian Research Councils Discovery Projects funding scheme (Project No. DP110102548 and Project No. DP130101760)