Aalto University

About: Aalto University is a education organization based out in Espoo, Finland. It is known for research contribution in the topics: Population & Carbon nanotube. The organization has 9969 authors who have published 32648 publications receiving 829626 citations. The organization is also known as: TKK & Aalto-korkeakoulu.

Designing river flows to improve food security futures in the Lower Mekong Basin

Abstract: INTRODUCTION The Mekong River provides renewable energy and food security for a population of more than 60 million people in six countries: China, Myanmar, Lao PDR, Thailand, Vietnam, and Cambodia. Seasonal rains flood the river’s floodplain and delta. This flood pulse fuels what is likely the world’s largest freshwater fishery in Cambodia’s Tonle Sap Lake, with >2 million tonnes of annual harvest valued at ~$2 billion. Hydropower development is crucial to the region’s economic prosperity and is simultaneously a threat to fisheries and agriculture that thrived in the natural-flow regime. The Mekong is testament to the food, energy, and water challenges facing tropical rivers globally. RATIONALE We hypothesized that high fisheries yields are driven by measurable attributes of hydrologic variability, and that these relationships can be used to design and implement future flow regimes that improve fisheries yield through control of impending hydropower operations. Hydrologic attributes that drive strong fisheries yields were identified using a data-driven approach that combined 17 years of discharge and standardized harvest data with several time-series methods in the frequency and time domains. We then analyzed century-scale time series of discharge data on the Mekong and associated hydroclimate data sets to understand how current dams, independent of climate, have changed key drivers of the fishery since the early 1960s. Finally, we used estimated hydrologic drivers of the historical bag net, or “Dai,” fishery on the Tonle Sap River—the largest commercial fishery in the Mekong—to design better fisheries futures by comparing designed flows to current and pre-dam (natural-flow) regimes. RESULTS Our analysis identified several features of hydrologic variability that portend strong fisheries yield. These include two “high-level” descriptors: flood pulse extent (FPExt) and net annual anomaly (NAA). FPExt, which combines flood magnitude and duration, has long been hypothesized to drive fisheries yield in ecosystems subject to flood pulses, such as the Mekong. NAA is the annual sum of daily residual flows standardized to the long-term average hydrograph. Hence, NAA is a compact measure of hydrologic variance and can be further decomposed into nine shape “components.” Several of these components drive high fisheries yields, including a long low-flow period followed by a short, strong flood pulse with multiple peaks. All essential drivers of the flood pulse fishery have been changing since the closure of the first Mekong tributary dam and are independent of changes associated with climate observed over the past century. The direction of these changes is consistent with declining fisheries yield in the Tonle Sap. Projection of the fishery driven by a hypothetical “designer” hydrograph capturing the key shape features associated with strong yield improved harvest relative to current conditions; yield was projected to exceed that of the natural-flow regime by a factor of 3.7. This result was robust to the inclusion of density-dependent recruitment in our time-series model. CONCLUSION A data-driven approach reveals a new perspective on hydrologic drivers of fishery productivity in the Mekong. The extent of the flood pulse is paramount, as previous literature suggests, but so are other descriptors of hydrologic variation, including anomalous low flows. Variance is key—specifically, the sequence and timing of within-year anomalous high and low flows. A focus on variance shifts the conversation from “How much water do we need?” to “When do we need it the most, and when can we spare it?” Beneficial components of variance in the hydrograph can be described by a simple Fourier series—an asymmetric rectangular pulse train. A quantitative ecological objective function fills a critical gap in the balancing of fisheries harvest with other important objective functions including hydropower generation, rice production, and transportation. This opens the possibility of specifying and implementing flow regimes to manage rivers to satisfice trade-offs between fishery productivity and other ecosystem services provided by tropical rivers subject to flood pulses.

Multiwavelength Evidence for Quasi-periodic Modulation in the Gamma-Ray Blazar PG 1553+113

Abstract: We report for the first time a γ-ray and multiwavelength nearly periodic oscillation in an active galactic nucleus. Using the Fermi Large Area Telescope we have discovered an apparent quasi-periodicity in the γ-ray flux (E > 100 MeV) from the GeV/TeV BL Lac object PG 1553+113. The marginal significance of the 2.18 ± 0.08 year period γ-ray cycle is strengthened by correlated oscillations observed in radio and optical fluxes, through data collected in the Owens Valley Radio Observatory, Tuorla, Katzman Automatic Imaging Telescope, and Catalina Sky Survey monitoring programs and Swift-UVOT. The optical cycle appearing in ~10 years of data has a similar period, while the 15 GHz oscillation is less regular than seen in the other bands. Further long-term multiwavelength monitoring of this blazar may discriminate among the possible explanations for this quasi-periodicity.

Searchable Attribute-Based Mechanism With Efficient Data Sharing for Secure Cloud Storage

Abstract: To date, the growth of electronic personal data leads to a trend that data owners prefer to remotely outsource their data to clouds for the enjoyment of the high-quality retrieval and storage service without worrying the burden of local data management and maintenance. However, secure share and search for the outsourced data is a formidable task, which may easily incur the leakage of sensitive personal information. Efficient data sharing and searching with security is of critical importance. This paper, for the first time, proposes a searchable attribute-based proxy reencryption system. When compared with the existing systems only supporting either searchable attribute-based functionality or attribute-based proxy reencryption, our new primitive supports both abilities and provides flexible keyword update service. In particular, the system enables a data owner to efficiently share his data to a specified group of users matching a sharing policy and meanwhile, the data will maintain its searchable property but also the corresponding search keyword(s) can be updated after the data sharing. The new mechanism is applicable to many real-world applications, such as electronic health record systems. It is also proved chosen ciphertext secure in the random oracle model.

Joint Device Positioning and Clock Synchronization in 5G Ultra-Dense Networks

Abstract: In this paper, we address the prospects and key enabling technologies for highly efficient and accurate device positioning and tracking in fifth generation (5G) radio access networks. Building on the premises of ultra-dense networks as well as on the adoption of multicarrier waveforms and antenna arrays in the access nodes (ANs), we first formulate extended Kalman filter (EKF)-based solutions for computationally efficient joint estimation and tracking of the time of arrival (ToA) and direction of arrival (DoA) of the user nodes (UNs) using uplink reference signals. Then, a second EKF stage is proposed in order to fuse the individual DoA and ToA estimates from one or several ANs into a UN position estimate. Since all the processing takes place at the network side, the computing complexity and energy consumption at the UN side are kept to a minimum. The cascaded EKFs proposed in this article also take into account the unavoidable relative clock offsets between UNs and ANs, such that reliable clock synchronization of the access-link is obtained as a valuable by-product. The proposed cascaded EKF scheme is then revised and extended to more general and challenging scenarios where not only the UNs have clock offsets against the network time, but also the ANs themselves are not mutually synchronized in time. Finally, comprehensive performance evaluations of the proposed solutions on a realistic 5G network setup, building on the METIS project based outdoor Madrid map model together with complete ray tracing based propagation modeling, are provided. The obtained results clearly demonstrate that by using the developed methods, sub-meter scale positioning and tracking accuracy of moving devices is indeed technically feasible in future 5G radio access networks operating at sub-6 GHz frequencies, despite the realistic assumptions related to clock offsets and potentially even under unsynchronized network elements.