For the past several decades, we have been able to directly probe the motion of atoms that is associated with chemical transformations and which occurs on the femtosecond (10−15-s) timescale. ...However, studying the inner workings of atoms and molecules on the electronic timescale has become possible only with the recent development of isolated attosecond (10−18-s) laser pulses. Such pulses have been used to investigate atomic photoexcitation and photoionization and electron dynamics in solids, and in molecules could help explore the prompt charge redistribution and localization that accompany photoexcitation processes. In recent work, the dissociative ionization of H2 and D2 was monitored on femtosecond timescales and controlled using few-cycle near-infrared laser pulses. Here we report a molecular attosecond pump-probe experiment based on that work: H2 and D2 are dissociatively ionized by a sequence comprising an isolated attosecond ultraviolet pulse and an intense few-cycle infrared pulse, and a localization of the electronic charge distribution within the molecule is measured that depends-with attosecond time resolution-on the delay between the pump and probe pulses. The localization occurs by means of two mechanisms, where the infrared laser influences the photoionization or the dissociation of the molecular ion. In the first case, charge localization arises from quantum mechanical interference involving autoionizing states and the laser-altered wavefunction of the departing electron. In the second case, charge localization arises owing to laser-driven population transfer between different electronic states of the molecular ion. These results establish attosecond pump-probe strategies as a powerful tool for investigating the complex molecular dynamics that result from the coupling between electronic and nuclear motions beyond the usual Born-Oppenheimer approximation.
This book provides an accessible and self-contained introduction to the theory of algebraic curves over a finite field, a subject that has been of fundamental importance to mathematics for many years ...and that has essential applications in areas such as finite geometry, number theory, error-correcting codes, and cryptology. Unlike other books, this one emphasizes the algebraic geometry rather than the function field approach to algebraic curves.
The authors begin by developing the general theory of curves over any field, highlighting peculiarities occurring for positive characteristic and requiring of the reader only basic knowledge of algebra and geometry. The special properties that a curve over a finite field can have are then discussed. The geometrical theory of linear series is used to find estimates for the number of rational points on a curve, following the theory of Stöhr and Voloch. The approach of Hasse and Weil via zeta functions is explained, and then attention turns to more advanced results: a state-of-the-art introduction to maximal curves over finite fields is provided; a comprehensive account is given of the automorphism group of a curve; and some applications to coding theory and finite geometry are described. The book includes many examples and exercises. It is an indispensable resource for researchers and the ideal textbook for graduate students.
SignificanceContemporary social sciences aim to be diverse and inclusive, but traces of the historical dominance of Western European and North American academic institutions persist in scientific ...practices. One such practice is the phrasing of article titles. Our analysis shows that articles studying the global North are systematically less likely to mention the name of the country they study in their title compared to articles on the global South. This constitutes, potentially, an unwarranted claim on universality and may lead to lesser recognition of global South studies. Social and behavioral scientists must reflect on the phrasing of their article titles to avoid reproducing harmful relations of intellectual domination which limit inclusivity and constitute a barrier to the generalizability of scientific knowledge.
Satellite remote sensing is an effective way to monitor vast extents of global glaciers and snowfields. However, satellite remote sensing is limited by spatial and temporal resolutions and the high ...costs involved in data acquisition. Unmanned aerial vehicle (UAV)-based glaciological studies are gaining pace in recent years due to their advantages over conventional remote sensing platforms. UAVs are easy to deploy, with the option of alternating the sensors working in visible, infrared, and microwave wavelengths. The high spatial resolution remote sensing data obtained from these UAV-borne sensors are a significant improvement over the data obtained by traditional remote sensing. The cost involved in data acquisition is minimal and researchers can acquire imagery according to their schedule and convenience. We discuss significant glaciological studies involving UAV as remote sensing platforms. This is the first review work, exclusively dedicated to highlight UAV as a remote sensing platform in glaciology. We examine polar and alpine applications of UAV and their future prospects in separate sections and present an extensive reference list for the readers, so that they can delve into their topic of interest. Because the technology is still widely unexplored for snow and glaciers, we put a special emphasis on discussing the future prospects of utilising UAVs for glaciological research.
•First review exclusively to highlight UAV as remote sensing platform in glaciology.•Separate sections discuss polar and alpine applications of UAV and future prospects.•An extensive reference list is very useful for the readers.•All published research papers on the topic have been included in this paper.•Most recent research articles are also included.
The ability to predict short-term electric energy demand would provide several benefits, both at the economic and environmental level. For example, it would allow for an efficient use of resources in ...order to face the actual demand, reducing the costs associated to the production as well as the emission of CO 2 . To this aim, in this paper we propose a strategy based on ensemble learning in order to tackle the short-term load forecasting problem. In particular, our approach is based on a stacking ensemble learning scheme, where the predictions produced by three base learning methods are used by a top level method in order to produce final predictions. We tested the proposed scheme on a dataset reporting the energy consumption in Spain over more than nine years. The obtained experimental results show that an approach for short-term electricity consumption forecasting based on ensemble learning can help in combining predictions produced by weaker learning methods in order to obtain superior results. In particular, the system produces a lower error with respect to the existing state-of-the art techniques used on the same dataset. More importantly, this case study has shown that using an ensemble scheme can achieve very accurate predictions, and thus that it is a suitable approach for addressing the short-term load forecasting problem.
Activation of dinitrogen plays an important role in daily anthropogenic life, and the processes by which this fixation occurs have been a longstanding and significant research focus within the ...community. One of the major fields of dinitrogen activation research is the use of multimetallic compounds to reduce and/or activate N2 into a more useful nitrogen-atom source, such as ammonia. Here we report a comprehensive review of multimetallic-dinitrogen complexes and their utility toward N2 activation, beginning with the d-block metals from Group 4 to Group 11, then extending to Group 13 (which is exclusively populated by B complexes), and finally the rare-earth and actinide species. The review considers all polynuclear metal aggregates containing two or more metal centers in which dinitrogen is coordinated or activated (i.e., partial or complete cleavage of the N2 triple bond in the observed product). Our survey includes complexes in which mononuclear N2 complexes are used as building blocks to generate homo- or heteromultimetallic dinitrogen species, which allow one to evaluate the potential of heterometallic species for dinitrogen activation. We highlight some of the common trends throughout the periodic table, such as the differences between coordination modes as it relates to N2 activation and potential functionalization and the effect of polarizing the bridging N2 ligand by employing different metal ions of differing Lewis acidities. By providing this comprehensive treatment of polynuclear metal dinitrogen species, this Review aims to outline the past and provide potential future directions for continued research in this area.
Electricity demand and its typical load pattern are usually affected by many endogenous and exogenous factors to which the generation system must accordingly respond through utility operators. ...Lockdown measures to prevent the spread of COVID-19 imposed by many countries have led to sudden changes in socioeconomic habits which have had direct effects on the electricity systems. Therefore, a detailed analysis of how confinement measures have modified the electricity consumption in Spain, one of the countries most affected by this pandemic, has been performed in this work. Its electricity consumption has decreased by 13.49% from March 14 to April 30, compared to the average value of five previous years. Daily power demand profiles, especially morning and evening peaks, have been modified at homes, hospitals, and in the total power demand. These changes generate a greater uncertainty for the System Operator when making demand forecasts, but production deviations have increased by only 0.1%, thanks to the presence of a diversified generation mix, which has been modified during this period, increasing the proportion of renewable sources and decreasing CO2 emissions.
•Power demand in Spain has decreased by 13.49% due to lockdown measures by COVID-19.•Power demand profiles have changed its usual form on weekdays and weekends.•Average daily deviations in power predictions have only increased by 0.1%.•Renewable power generation has increased during the lockdown.•In March and April 2020, CO2 emissions have decreased by 32.61% compared to 2019.
Studies of the seasonal and annual patterns of glacier velocities improve our understanding of the ice volume, topography, responses to climate change, and surge events of glaciers. Such studies are ...especially relevant and equally rare for the Himalayan glaciers, which supply many rivers that sustain some of the most heavily populated mountainous regions in the world. In particular, the control of the hypsometric distribution of geomorphometric parameters, such as slope, aspect, and curvature, on the dynamics of Himalayan glaciers have never been studied so far, at the river basin scale. Here, we present the degree to which topographic and hypsometric parameters affect the seasonal and annual average flow velocities of 112 glaciers in the Baspa River basin in the Western Indian Himalaya by analysing Global Land Ice Velocity Extraction from Landsat 8 (GoLIVE) datasets for the years 2013-2017. We observe, (i) significant heterogeneity in topographic controls on the velocities of these glaciers, (ii) elevation and the seasons play important roles in regulating the degree to which morphometric parameters (slope, aspect, and curvature) affect these velocities, (iii) a possible polythermal regime promoting both sliding and deformational forms of motion in a majority of these glaciers, and (iv) a detailed analysis of complex topographic controls within various elevation zones using a novel hypso-morphometric approach. These findings can help us to better model the dynamics of Himalayan glaciers and their responses to the future climatic scenarios. The inferences also suggest the need to incorporate dynamic topography in glacio-hydrological models in the wake of constant glacial evolutions.
•A general class of fractional optimal control problems was considered, which contains the bang-bang, free final time and path constraints problems.•Fractional integration matrices of ...Grünwald–Letnikov, trapezoidal and Simpson’s formulas are derived.•Using the fractional integration matrix, the fractional optimal control problems are reduced to a finite-dimensional optimization problem.•In order to improve the speed and accuracy, the gradient of objective function and the Jacobian of constraints are supplied to the optimization solver.•Numerical simulations are provided to illustrate the presented method on different types of fractional optimal control problems.
This paper presents three direct methods based on Grünwald–Letnikov, trapezoidal and Simpson fractional integral formulas to solve fractional optimal control problems (FOCPs). At first, the fractional integral form of FOCP is considered, then the fractional integral is approximated by Grünwald–Letnikov, trapezoidal and Simpson formulas in a matrix approach. Thereafter, the performance index is approximated either by trapezoidal or Simpson quadrature. As a result, FOCPs are reduced to nonlinear programming problems, which can be solved by many well-developed algorithms. To improve the efficiency of the presented method, the gradient of the objective function and the Jacobian of constraints are prepared in closed forms. It is pointed out that the implementation of the methods is simple and, due to the fact that there is no need to derive necessary conditions, the methods can be simply and quickly used to solve a wide class of FOCPs. The efficiency and reliability of the presented methods are assessed by ample numerical tests involving a free final time with path constraint FOCP, a bang-bang FOCP and an optimal control of a fractional-order HIV-immune system.
A wind nebula generating extended X-ray emission was recently detected surrounding Swift J1834.9-0846. This is the first magnetar for which such a wind nebula was found. Here, we investigate whether ...there is a plausible scenario where the pulsar wind nebula (PWN) can be sustained without the need of advocating for additional sources of energy other than rotational. We do this by using a detailed radiative and dynamical code that studies the evolution of the nebula and its particle population in time. We find that such a scenario indeed exists: Swift J1834.9-0846's nebula can be explained as being rotationally powered, as all other known PWNe are, if it is currently being compressed by the environment. The latter introduces several effects, the most important of which is the appearance of adiabatic heating, being increasingly dominant over the escape of particles as reverberation goes by. The need of reverberation naturally explains why this is the only magnetar nebula detected and provides estimates for Swift 1834.9-0846's age.
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