785 research outputs found
Governance and Regulation of Ride-hailing Services in Emerging Markets: Challenges, Experiences and Implications
This paper seeks to shed some light on the different considerations for regulation and governance of ride-hailing platforms in emerging markets, highlighting their positive and negative externalities. Building on an extensive review of the literature and secondary sources, we outline Ride-hailing's identified and potential effects on users (providers and consumers), incumbents, and society. Based on the welfare impacts structure, we identify the significant challenges that regulators face in understanding, monitoring, evaluating, and regulating this type of transportation innovation. Finally, the paper proposes a framework for approaching such mobility innovations from governance and regulation perspectives. In a context of exponential growth in research and innovation in urban mobility in general and Ride-hailing, a rigorous review of the literature and a critical framework for understanding governance and regulation in such services in rapidly changing contexts is a timely contribution
Carbonation of alkaline paper mill waste to reduce CO2 greenhouse gas emissions into the atmosphere
International audienceThe global warming of Earth's near-surface, air and oceans in recent decades is a direct consequence of anthropogenic emission of greenhouse gases into the atmosphere such as CO2, CH4, N2O and CFCs. The CO2 emissions contribute approximately 60% to this climate change. This study investigates experimentally the aqueous carbonation mechanisms of an alkaline paper mill waste containing about 55 wt% portlandite (Ca(OH)2) as a possible mineralogical CO2 sequestration process. The overall carbonation reaction includes the following steps: (1) Ca release from portlandite dissolution, (2) CO2 dissolution in water and (3) CaCO3 precipitation. This CO2 sequestration mechanism was supported by geochemical modelling of final solutions using PHREEQC software, and observations by scanning electron microscope and X-ray diffraction of final reaction products. According to the experimental protocol, the system proposed would favour the total capture of approx. 218 kg of CO2 into stable calcite/ton of paper waste, independently of initial CO2 pressure. The final product from the carbonation process is a calcite (ca. 100 wt%)-water dispersion. Indeed, the total captured CO2 mineralized as calcite could be stored in degraded soils or even used for diverse industrial applications. This result demonstrates the possibility of using the alkaline liquidâsolid waste for CO2 mitigation and reduction of greenhouse effect gases into the atmosphere
Mineral sequestration of CO2 by aqueous carbonation of coal combustion fly-ash
International audienceThe increasing CO2 concentration in the Earth's atmosphere, mainly caused by fossil fuel combustion, has led to concerns about global warming. A technology that could possibly contribute to reducing carbon dioxide emissions is the in-situ mineral sequestration (long term geological storage) or the ex-situ mineral sequestration (controlled industrial reactors) of CO2. In the present study, we propose to use coal combustion fly-ash, an industrial waste that contains about 4.1 wt.% of lime (CaO), to sequester carbon dioxide by aqueous carbonation. The carbonation reaction was carried out in two successive chemical reactions, first, the irreversible hydration of lime. CaO + H2O â Ca(OH)2 second, the spontaneous carbonation of calcium hydroxide suspension. Ca(OH)2 + CO2 â CaCO3 + H2O A significant CaOâCaCO3 chemical transformation (approximately 82% of carbonation efficiency) was estimated by pressure-mass balance after 2 h of reaction at 30 °C. In addition, the qualitative comparison of X-ray diffraction spectra for reactants and products revealed a complete CaOâCaCO3 conversion. The carbonation efficiency of CaO was independent on the initial pressure of CO2 (10, 20, 30 and 40 bar) and it was not significantly affected by reaction temperature (room temperature â20â25â, 30 and 60 °C) and by fly-ash dose (50, 100, 150 g). The kinetic data demonstrated that the initial rate of CO2 transfer was enhanced by carbonation process for our experiments. The precipitate calcium carbonate was characterized by isolated micrometric particles and micrometric agglomerates of calcite (SEM observations). Finally, the geochemical modelling using PHREEQC software indicated that the final solutions (i.e. after reaction) are supersaturated with respect to calcium carbonate (0.7 †saturation index †1.1). This experimental study demonstrates that 1 ton of fly-ash could sequester up to 26 kg of CO2, i.e. 38.18 ton of fly-ash per ton of CO2 sequestered. This confirms the possibility to use this alkaline residue for CO2 mitigation
Generalized Heisenberg algebra coherent states for Power-law potentials
Coherent states for power-law potentials are constructed using generalized
Heisenberg algabras. Klauder's minimal set of conditions required to obtain
coherent states are satisfied. The statistical properties of these states are
investigated through the evaluation of the Mandel's parameter. It is shown that
these coherent states are useful for describing the states of real and ideal
lasers.Comment: 13 pages, 2 figure
Seasonal adaptation of the thermalâbased twoâsource energy balance model for estimating evapotranspiration in a semiarid treeâgrass ecosystem
© 2020 by the authors.The thermal-based two-source energy balance (TSEB) model has accurately simulated energy fluxes in a wide range of landscapes with both remote and proximal sensing data. However, tree-grass ecosystems (TGE) have notably complex heterogeneous vegetation mixtures and dynamic phenological characteristics presenting clear challenges to earth observation and modeling methods. Particularly, the TSEB modeling structure assumes a single vegetation source, making it difficult to represent the multiple vegetation layers present in TGEs (i.e., trees and grasses) which have different phenological and structural characteristics. This study evaluates the implementation of TSEB in a TGE located in central Spain and proposes a new strategy to consider the spatial and temporal complexities observed. This was based on sensitivity analyses (SA) conducted on both primary remote sensing inputs (local SA) and model parameters (global SA). The model was subsequently modified considering phenological dynamics in semi-arid TGEs and assuming a dominant vegetation structure and cover (i.e., either grassland or broadleaved trees) for different seasons (TSEB-2S). The adaptation was compared against the default model and evaluated against eddy covariance (EC) flux measurements and lysimeters over the experimental site. TSEB-2S vastly improved over the default TSEB performance decreasing the mean bias and root-mean-square-deviation (RMSD) of latent heat (LE) from 40 and 82 W mâ2 to â4 and 59 W mâ2, respectively during 2015. TSEB-2S was further validated for two other EC towers and for different years (2015, 2016 and 2017) obtaining similar error statistics with RMSD of LE ranging between 57 and 63 W mâ2. The results presented here demonstrate a relatively simple strategy to improve water and energy flux monitoring over a complex and vulnerable landscape, which are often poorly represented through remote sensing models.The research received funding from the European Unionâs Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 721995. It was also funded by Ministerio de EconomĂa y Competitividad through FLUXPEC CGL2012-34383 and SynerTGE CGL2015-G9095-R (MINECO/FEDER, UE) projects. The research infrastructure at the measurement site in Majadas de TiĂ©tar was partly funded through the Alexander von Humboldt Foundation, ELEMENTAL (CGL 2017-83538-C3-3-R, MINECO-FEDER) and IMAGINA (PROMETEU 2019; Generalitat Valenciana).Peer reviewe
Comparison of retinal nerve fiber layer thinning and retinal ganglion cell loss after optic nerve transection in adult albino rats
We compared the time-course and magnitude of retinal nerve fiber layer (RNFL) thinning with that of retinal ganglion cell (RGC) loss after intraorbital optic nerve transection (IONT) in adult rats
Worldwide impact of economic cycles on suicide trends over 3 decades: Differences according to level of development. A mixed effect model study
Objectives: To investigate the trends and correlations
of gross domestic product (GDP) adjusted for
purchasing power parity (PPP) per capita on suicide
rates in 10 WHO regions during the past 30 years.
Design: Analyses of databases of PPP-adjusted GDP
per capita and suicide rates. Countries were grouped
according to the Global Burden of Disease regional
classification system.
Data sources: World Bankâs official website and
WHOâs mortality database.
Statistical analyses: After graphically displaying
PPP-adjusted GDP per capita and suicide rates, mixed
effect models were used for representing and
analysing clustered data.
Results: Three different groups of countries, based on
the correlation between the PPP-adjusted GDP per
capita and suicide rates, are reported: (1) positive
correlation: developing (lower middle and upper
middle income) Latin-American and Caribbean
countries, developing countries in the South East Asian
Region including India, some countries in the Western
Pacific Region (such as China and South Korea) and
high-income Asian countries, including Japan; (2)
negative correlation: high-income and developing
European countries, Canada, Australia and New
Zealand and (3) no correlation was found in an African
country.
Conclusions: PPP-adjusted GDP per capita may offer
a simple measure for designing the type of preventive
interventions aimed at lowering suicide rates that can
be used across countries. Public health interventions
might be more suitable for developing countries. In
high-income countries, however, preventive measures
based on the medical model might prove more usefulAll authors have completed the Unified Competing Interest form. Dr.
Blasco-Fontecilla acknowledges the Spanish Ministry of Health (Rio Hortega
CMO8/00170; SAF2010-21849), Alicia Koplowitz Foundation and Conchita
Rabago Foundation for funding his post-doctoral stage at CHRU, Montpellier,
France
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