Quench dynamics of one-dimensional interacting bosons in a disordered potential: Elastic dephasing and critical speeding-up of thermalization

The dynamics of interacting bosons in one dimension following the sudden switching on of a weak disordered potential is investigated. On time scales before quasiparticles scatter (prethermalized regime), the dephasing from random elastic forward scattering causes all correlations to decay exponentially fast, but the system remains far from thermal equilibrium. For longer times, the combined effect of disorder and interactions gives rise to inelastic scattering and to thermalization. A novel quantum kinetic equation accounting for both disorder and interactions is employed to study the dynamics. Thermalization turns out to be most effective close to the superfluid-Bose glass critical point where nonlinearities become more and more important. The numerically obtained thermalization times are found to agree well with analytic estimates.Comment: 10 pages, 3 figures, published versio

Nulla dies sine linea: fragmentos de una conversación con Fernando Tavora

Peer Reviewe

An Algorithm to Estimate Suspended Particulate Matter Concentrations and Associated Uncertainties from Remote Sensing Reflectance in Coastal Environments

Suspended Particulate Matter (SPM) is a major constituent in coastal waters, involved in processes such as light attenuation, pollutant propagation, and waterways blockage. The spatial distribution of SPM is an indicator of deposition and erosion patterns in estuaries and coastal zones and a necessary input to estimate the material fluxes from the land through rivers to the sea. In-situ methods to estimate SPM provide limited spatial data in comparison to the coverage that can be obtained remotely. Ocean color remote sensing complements field measurements by providing estimates of the spatial distributions of surface SPM concentration in natural waters, with high spatial and temporal resolution. Existing methods to obtain SPM from remote sensing vary between purely empirical ones to those that are based on radiative transfer theory together with empirical inputs regarding the optical properties of SPM. Most algorithms use a single satellite band that is switched to other bands for different ranges of turbidity. The necessity to switch bands is due to the saturation of reflectance as SPM concentration increases. Here we propose a multi-band approach for SPM retrievals that also provides an estimate of uncertainty, where the latter is based on both uncertainties in reflectance and in the assumed optical properties of SPM. The approach proposed is general and can be applied to any ocean color sensor or in-situ radiometer system with red and near-infra-red bands. We apply it to six globally distributed in-situ datasets of spectral water reflectance and SPM measurements over a wide range of SPM concentrations collected in estuaries and coastal environments (the focus regions of our study). Results show good performance for SPM retrieval at all ranges of concentration. As with all algorithms, better performance may be achieved by constraining empirical assumptions to specific environments. To demonstrate the flexibility of the algorithm we apply it to a remote sensing scene from an environment with highly variable sediment concentrations

Economic feasibility of second generation ethanol with and without indirect greenhouse gas reduction benefits : a simulation for Brazil

The aim of this study is to determine the economic feasibility of second generation ethanol from sugar cane, whereby traditional ethanol production is combined with the use of lignocellulosic biomass for ethanol production. By applying cost-benefit analysis, this study evaluated the viability of the second generation ethanol technology as an alternative to conventional sugarcaneto- ethanol, both in terms of processing technology, and of land use impacts. Furthermore, an attempt is made to analyze impacts on CO2 mitigation and land use in economic. The research results indicate that: i) from an economic point of view, the first generation plant is clearly preferable. With IRR of 18.7%, Minimum selling price of US$0.31 per liter, and NPV of US$ 213.0 million, first generation ethanol production from sugar cane has a large economic advantage compared to the second generation plant (IRR of 13.5%, Minimum selling price of US$0.40 per liter and NPV of US$ 78.5 million). ii) from an environmental point of view, a second generation biofuel that makes use of lignocellulosic biomass plant is clearly preferable. The second generation plant uses 49.6% less land and avoids a CO2 debt average of 942,282 ton per year throughout the life of the project. iii) Productivity gains improve profitability (IRR) and reduce biofuel prices (Minimum selling prices). Increasing the yearlt Ethanol and sugar cane productivity’s growth rate from 0.5% to 4.0% leads to a range of IRR from 17.5% to 21.5%, and of price from 0.29 US$/l to 0.32 US$/l for first generation plant, and from 13.2% to 14.2% and of price from 0.39 US$/l to 0.40 US$/l for second generation plant. iv) Process improvement shows little economic impact but matters on environmental side because less land is needed. Up to 10% more land can be saved compared to least advanced technology. v) Energy conversion development can improve income of the plant, especially for the first generation plant. Each 5% improvement can lead to 0.6% change in IRR project, and a reduction of 1.1% in the Minimum selling price. vi) Equipment investment is the most sensitive parameter to alter biofuel prices and profitability. The conventional plant is more sensitive to equipment investment, land prices and trash costs in this order while second generation plant is sensitive to equipment investment and almost insensitive to land prices and trash costs changes. vii) Assuming an average payment of US$29.43 or higher per ton CO2 debt, the second generation plant may become a competing alternative to conventional, first generation plant. On average, the technology could be paid at reasonable cost (Revenue average of US$ 27.7 million). viii) Productivity gains reduce the repayment time of CO2 debt, with ethanol productivity having a stronger contribution. Besides, from a growth rate of ethanol and sugar cane productivity from 0.5% to 4.0% per year, the repayment time changes from 11.8 years to a range between 6.5 years and 5.5 years and 13 and 9.5, respectively. In conclusion, the appraisal model represents a useful tool for analyzing many issues related with the dilemmas involved in biofuel production

Use of social media: empirical comparison between Europe And Middle East

Dissertation presented as the partial requirement for obtaining a Master's degree in Information Management, specialization in Marketing IntelligenceSocial media as an amazing active and fast-moving domain, is playing an important role shaping our lives. The purpose of this research is to understand the drivers of social media use in the West and Arab world. Societies are incessantly changing through social media, which is helping spreading the creation, modification and discussion of multiple contents. Yet, different cultures might present dissimilar behaviours towards this vehicle of communication for diverse reasons such as, among others, their access to technology and contents, or cultural influence. Studies about social media use combining two cultures are scarce conducing us to an undiscovered research field to explore. We developed the contents of knowledge on social media use by proposing an innovative comparison between Europe and Middle East, which integrates Venkatesh´s extended unified theory of acceptance and use of technology (UTAUT2). An online questionnaire was created to collect data from users within both cultures. Structural equation modelling (SEM) was used to analyse the outcome. The results revealed a significant disparity on what triggers social media behaviour in those two different regions. At the time that performance expectancy influences on the European side, the effort expectancy was found to be the most predominant trigger into use of social media in the Middle East, by affecting behaviour intention. The results underline the importance of social media nowadays and enriches the knowledge of the subject into different cultures. The present study contributes with new insights into factors that might be determinant regarding acceptance and use behaviour and continues on the discussion on why and how people engage in social media, independently on nation or culture

Equilibrium-Based Force and Torque Control for an Aerial Manipulator to Interact with a Vertical Surface

In this paper, a force and torque controller for aerial manipulation is developed using an unmanned aerial vehicle equipped with a robotic arm to interact near or on a vertical surface such as a wall. Control of aerial manipulators interacting with the environment is a challenging task due to dynamic interactions between aerial vehicles, robotic arms, and environment. To achieve this, modeling of aerial manipulators is first investigated and presented considering interaction with the environment. Nonlinear models of generic aerial manipulators, as well as of a prototype aerial manipulator composed of a hexacopter with a three-joint robotic arm, are established. An equilibrium-based force and torque controller is developed to conduct tasks that require the aerial manipulator to exert forces and torques on a wall. Simulations and experiments validate the performance of the controller that successfully applies desired forces and torques to an object fixed on a wall while flying near the wall

Monte Carlo studies of a novel X-ray tube anode design

When energetic electrons are incident on high atomic number absorbers, a substantial fraction is back-scattered. This phenomenon is responsible for several undesirable effects in X-ray tubes, in particular a reduction in the X-ray output. The extent of this shortfall has been estimated by using Monte Carlo simulation to start electrons at increasing depth inside the anode, the results indicating that an output enhancement of nearly 50% could be achieved in principle if the electrons wasted in back-scatter events could be trapped inside a tungsten anode. To test this idea a further set of simulations were done for a novel anode geometry. Results showed that X-ray tube efficiencies might be substantially enhanced by this approach.http://www.sciencedirect.com/science/article/B6TVT-43P41Y7-30/1/526566f6ea15332c302cdad2886e583