• Open Access close
• 02 engineering and technology close

International audience; We develop in this paper a trend detection algorithm , designed to find trendy topics being disseminated in a social network. We assume that the broadcasts of messages in the social network is governed by a self-exciting point process, namely a Hawkes process, which takes into consideration the real broadcasting times of messages and the interaction between users and topics. We formally define trendiness and derive trend indices for each topic being disseminated in the social network. These indices take into consideration the time between the detection and the message broadcasts, the distance between the real broadcast intensity and the maximum expected broadcast intensity, and the social network topology. The proposed trend detection algorithm is simple and uses stochastic control techniques in order to calculate the trend indices. It is also fast and aggregates all the information of the broadcasts into a simple one-dimensional process, thus reducing its complexity and the quantity of data necessary to the detection.

Optoelectronic measurements of carbon nanotube transistors have shown a wide variety of sensitivites to the incident light. Direct photocurrent processes compete with a number of extrinsic mechanisms. Here we show that visible light absorption in the silicon substrate generates a photovoltage that can electrically gate the nanotube device. The photocurrent induced by the changing gate voltage can be significantly larger than that due to direct electron-hole pair generation in the nanotube. The dominance of photogating in these devices is confirmed by the power and position dependence of the resulting photocurrent. The power dependence is strongly non-linear and photocurrents are measured through the device even when the laser illuminates up to 1~mm from the nanotube. Comment: 18 pages, 7 figures

An assessment is made here of the role played by the micropolar continuum theory on the cracked Brazilian disc test used for determining rock fracture toughness. By analytically solving the corresponding mixed boundary-value problems and employing singular-perturbation arguments, we provide closed-form expressions for the energy release rate and the corresponding stress-intensity factors for both mode I and mode II loading. These theoretical results are augmented by a set of fracture toughness experiments on both sandstone and marble rocks. It is further shown that the morphology of the fracturing process in our centrally pre-cracked circular samples correlates very well with discrete element simulations.

The accessibility impacts of transport projects ex-post implementation are generally evaluated using cumulative opportunity measures based on a single travel time threshold. Fewer studies have explored how accessibility appraisal of transport plans can be used to evaluate policy scenarios and their impacts for different social groups or examined whether the results of project appraisals are sensitive to the time threshold of choice. This paper analyzes how different scenarios of full and partial implementation of the TransBrasil BRT project in Rio de Janeiro (Brazil) will likely impact the number of jobs accessible to the population of different income levels. The analysis is conducted under various travel time thresholds of 30, 60, 90 and 120 minutes to test whether the results are sensitive to the boundary effect of the modifiable temporal unit problem (MTUP). Compared to a partial operation scenario, the full implementation of TransBrasil that extends this corridor into the city center would lead to higher accessibility gains due to network effects of connecting this BRT to other transport modes. Nonetheless, the size of the accessibility impacts of the proposed BRT as well as its distribution across income classes would significantly change depending on the time threshold chosen for the accessibility analysis. Considering cut-off times of 30 or 60 minutes, both scenarios of TransBrasil would lead to higher accessibility impacts in general and particularly for low-income groups, moving Rio towards a more equitable transportation system. However, under longer thresholds of 90 and 120 minutes, an evaluation of this project would find much smaller accessibility gains more evenly distributed by income levels. The paper highlights how time threshold choice in cumulative opportunity measures can have important but overlooked implications for policy evaluation and it calls for further research on the MTUP in future transport and mobility studies.

This paper presents a prototype of a telemonitoring system, based on a BAN (Body Area Network) that is integrated by a Bluetooth (BT) pulse oximeter, a GPS (Global Positioning System) unit, and a smartphone. The smartphone is the hardware platformfor running a Python software thatmanages the Bluetooth piconet formed by the sensors. Thus the smartphone forwards the data received from the Bluetooth devices, encoded into JSON (JavaScript Object Notation), to a central server. This server provides universal access to the information of the patient’s location and health status through a web application based on AJAX (Asynchronous JavaScript and XML) technology. Additionally, for the described prototype, the study presents some performance analyses about several topics that are of great interest for the applicability of the prototype: (i) the technique used to forward the patient’s location and health status, (ii) the power consumption of the smartphone (which is compared with the measurements of an equivalent software developed for Java Micro Edition platform), and (iii) the web browser compatibility of the web application developed for the control and monitoring of the patients. Ministerio de Educación y Ciencia TEC2009-13763-C02-01

Cryptocurrencies like Bitcoin are offering new avenues for economic empowerment to individuals around the world. However, they also provide a powerful tool that facilitates criminal activities such as human trafficking and illegal weapons sales that cause great harm to individuals and communities. Cryptocurrency advocates have argued that the ethical dimensions of cryptocurrency are not qualitatively new, insofar as money has always been understood as a passive instrument that lacks ethical values and can be used for good or ill purposes. In this paper, we challenge such a presumption that money must be ‘value-neutral.’ Building on advances in artificial intelligence, cryptography, and machine ethics, we argue that it is possible to design artificially intelligent cryptocurrencies that are not ethically neutral but which autonomously regulate their own use in a way that reflects the ethical values of particular human beings – or even entire human societies. We propose a technological framework for such cryptocurrencies and then analyse the legal, ethical, and economic implications of their use. Finally, we suggest that the development of cryptocurrencies possessing ethical as well as monetary value can provide human beings with a new economic means of positively influencing the ethos and values of their societies.

Patch-based image inpainting methods iteratively fill the missing region via searching the best sample patch from the source region. However, most of the existing approaches basically use the fixed size of patch regardless of content features nearby, which may lead to inpainting defects. Also, global match is needed for searching the best sample patch, but only to fill one target patch in each iteration, resulting in low efficiency. To handle the issues above, we first evaluate the nonuniformity in an image, by which the patch size is adaptively determined. Moreover, we divide the source region into multiple non-overlapping subregions with different nonuniformity levels, and the patch match proceeds in every subregion, respectively. This strategy not only saves the match time for single target patch, but also reduces the mismatch, and enables the simultaneous filling of multiple target patches in a single iteration. Experimental results show that in comparison to previous patch-based works, our method has achieved further improvement both in quality and efficiency. We believe our method could provide a new way for patch match with better accuracy and efficiency in image inpainting tasks.

The orthorhombically distorted perovskite NaMnF$_{3}$ has been predicted to become ferroelectric if an $a=c$ distortion of the bulk $Pnma$ structure is imposed. In order to test this prediction, NaMnF$_{3}$ thin films were grown on SrTiO$_{3}$ (001) single crystal substrates via molecular beam epitaxy. The best films were smooth and single phase with four different twin domains. In-plane magnetization measurements revealed the presence of antiferromagnetic ordering with weak ferromagnetism below the N\'eel temperature $T_N=66$ K. For the dielectric studies, NaMnF$_{3}$ films were grown on a 30 nm SrRuO$_{3}$ (001) layer used as a bottom electrode grown via pulsed laser deposition. The complex permittivity as a function of frequency indicated a strong Debye-like relaxation contribution characterized by a distribution of relaxation times. A power-law divergence of the characteristic relaxation time revealed an order-disorder phase transition at 8 K. The slow relaxation dynamics indicated the formation of super-dipoles (superparaelectric moments) that extend over several unit cells, similar to polar nanoregions of relaxor ferroelectrics. Comment: 4 pages, 3 figures