Théorie Économique, Modélisation et Applications

For Dirac electrons the Klein paradox implies that the confinement is difficult to achieve with an electrostatic potential although it can be of great importance for graphene-based devices. Here, ab initio and tight-binding approaches are combined and show that the wave function of Dirac electrons can be localized in rotated graphene bilayers due to the Moire pattern. This localization of wave function is maximum in the limit of the small rotation angle between the two layers.

Extensive scanning tunneling microscopy and spectroscopy experiments complemented by first-principles and parametrized tight binding calculations provide a clear answer to the existence, origin, and robustness of van Hove singularities (vHs) in twisted graphene layers. Our results are conclusive: vHs due to interlayer coupling are ubiquitously present in a broad range (from 1° to 10°) of rotation angles in our graphene on 6H-SiC(000-1) samples. From the variation of the energy separation of the vHs with the rotation angle we are able to recover the Fermi velocity of a graphene monolayer as well as the strength of the interlayer interaction. The robustness of the vHs is assessed both by experiments, which show that they survive in the presence of a third graphene layer, and by calculations, which test the role of the periodic modulation and absolute value of the interlayer distance. Finally, we clarify the role of the layer topographic corrugation and of electronic effects in the apparent moiré contrast measured on the STM images.

John Rawls's work (1971) has greatly contributed to rehabilitating equality as a basic social value, after decades of utilitarian hegemony,particularly in normative economics, but Rawls also emphasized that full equality of welfare is not an adequate goal either. This thesis was echoed in Dworkin's famous twin papers on equality (Dworkin 1981a,b), and it is now widely accepted that egalitarianism must be selective. The bulk of the debate on ‘Equality of What?’ thus deals with what variables ought to be submitted for selection and how this selection ought to be carried out.

The Internet of Things (IoT) is expected to be the next phase of the Internet revolution and to transform consumers’ service experience. It nevertheless raises challenges on innovation in services. Based on Ram and Sheth's ( ) theoretical framework, this work attempts to provide a better understanding of the barriers that lead to consumers’ resistance to smart services as an innovation. To this end, our research adopts an integrative framework that combines functional barriers, psychological barriers, and individual barriers to explain consumer resistance to smart services. Structural equation modeling was used to test this theoretical framework. Our research enriches the existing literature by (1) adapting Ram and Sheth's ( ) theoretical framework to the evolution of digital technologies (technological vulnerability barriers), (2) taking into account the ideological aspect of resistance (ideological barriers), and (3) considering dispositional variables (individual barriers). Moreover, it highlights the key role of skepticism toward IoT devices as a mediator between technological vulnerability barriers and individual barriers on the one hand and consumer resistance to smart services on the other.

Rotated graphene multilayers form a new class of graphene-related systems with electronic properties that drastically depend on the rotation angles. It has been shown that bilayers behave like two isolated graphene planes for large rotation angles. For smaller angles, states in the Dirac cones belonging to the two layers interact resulting in the appearance of two Van Hove singularities. States become localized as the rotation angle decreases and the two Van Hove singularities merge into one peak at the Dirac energy. Here we go further and consider bilayers with very small rotation angles. In this case, well-defined regions of AA stacking exist in the bilayer supercell and we show that states are confined in these regions for energies in the [$\ensuremath{-}{\ensuremath{\gamma}}_{t}$, $+{\ensuremath{\gamma}}_{t}$] range with ${\ensuremath{\gamma}}_{t}$ the interplane mean interaction. As a consequence, the local densities of states show discrete peaks for energies different from the Dirac energy.

The Internet of Things (IoT) market is set to grow rapidly. Although IoT offers new opportunities, it nevertheless raises challenges. The objective of this research is to develop a better understanding of the reasons underlying consumer resistance to smart and connected products. To this end, a quantitative survey was carried out to understand resistance to smartwatch. Structural equation modelling was used to test the conceptual model. The findings show that perceived uselessness, perceived price, intrusiveness, perceived novelty and self-efficacy have an impact on consumer resistance to smart products. Moreover, privacy concerns have an effect on intrusiveness and dependence impacts privacy concerns. To our best knowledge, this is the first research studying smart products through a resistance approach.

Abstract The description of quantized collective excitations stands as a landmark in the quantum theory of condensed matter. A prominent example occurs in conventional magnets, which support bosonic magnons—quantized harmonic fluctuations of the ordered spins. In striking contrast is the recent discovery that strongly spin-orbital-coupled magnets, such as α-RuCl 3 , may display a broad excitation continuum inconsistent with conventional magnons. Due to incomplete knowledge of the underlying interactions unraveling the nature of this continuum remains challenging. The most discussed explanation refers to a coherent continuum of fractional excitations analogous to the celebrated Kitaev spin liquid. Here, we present a more general scenario. We propose that the observed continuum represents incoherent excitations originating from strong magnetic anharmonicity that naturally occurs in such materials. This scenario fully explains the observed inelastic magnetic response of α-RuCl 3 and reveals the presence of nontrivial excitations in such materials extending well beyond the Kitaev state.

While most of the world has enjoyed exponential economic growth, more than one-sixth of the world is today roughly as poor as their ancestors were many generations ago. Widely accepted general explanations for the persistence of such poverty have been elusive and are needed by the international development community. Building on a well-established model of human infectious diseases, we show how formally integrating simple economic and disease ecology models can naturally give rise to poverty traps, where initial economic and epidemiological conditions determine the long-term trajectory of the health and economic development of a society. This poverty trap may therefore be broken by improving health conditions of the population. More generally, we demonstrate that simple human ecological models can help explain broad patterns of modern economic organization.

From its very beginning, quantum theory has been revealing extraordinary and counter-intuitive phenomena, such as wave-particle duality, Schrödinger cats and quantum non-locality. Another paradoxical phenomenon found within the framework of quantum mechanics is the 'quantum Cheshire Cat': if a quantum system is subject to a certain pre- and postselection, it can behave as if a particle and its property are spatially separated. It has been suggested to employ weak measurements in order to explore the Cheshire Cat's nature. Here we report an experiment in which we send neutrons through a perfect silicon crystal interferometer and perform weak measurements to probe the location of the particle and its magnetic moment. The experimental results suggest that the system behaves as if the neutrons go through one beam path, while their magnetic moment travels along the other.

We demonstrate that stacking layered materials allows a strain engineering where each layer is strained independently, which we call heterostrain. We combine detailed structural and spectroscopic measurements with tight-binding calculations to show that small uniaxial heterostrain suppresses Dirac cones and leads to the emergence of flat bands in twisted graphene layers (TGLs). Moreover, we demonstrate that heterostrain reconstructs, much more severely, the energy spectrum of TGLs than homostrain for which both layers are strained identically, a result which should apply to virtually all van der Waals structures opening exciting possibilities for straintronics with 2D materials.

We investigate spectral statistics in spatially extended, chaotic many-body quantum systems with a conserved charge. We compute the spectral form factor K(t) analytically for a minimal Floquet circuit model that has a U(1) symmetry encoded via spin-1/2 degrees of freedom. Averaging over an ensemble of realizations, we relate K(t) to a partition function for the spins, given by a Trotterization of the spin-1/2 Heisenberg ferromagnet. Using Bethe ansatz techniques, we extract the "Thouless time" t_{Th} demarcating the extent of random matrix behavior, and find scaling behavior governed by diffusion for K(t) at t≲t_{Th}. We also report numerical results for K(t) in a generic Floquet spin model, which are consistent with these analytic predictions.

The outbreak of SARS-COV-2 has led to the COVID-19 pandemic in March 2020 and caused over 4.5 million deaths worldwide by September 2021. Besides the public health crisis, COVID-19 affected the global economy and development significantly. It also led to changes in people's mobility and lifestyle during the COVID-19 pandemic. In addition to short-term changes, the drastic transformation of the world may account for the potentially disruptive long-term impacts. Recognizing the adverse effects of the COVID-19 pandemic is crucial in mitigating the negative behavioral changes that directly relate to people's psychological and social well-being. It is important to stress that citizens and governments face an uncertain situation since nobody knows exactly how the viruses and cures will develop. Better understanding uncertainties and evaluating behavioral changes contribute to addressing the future of urban development, public transportation, and behavioral strategies to tackle COVID-19 negative consequences. The major sources of impacts on short-term (route, departure time, mode, teleshopping, and teleworking) and medium and long-term (car ownership, work location, choice of job, and residential location) mobility decisions are mostly reviewed and discussed in this paper.

While most of the world is thought to be on long-term economic growth paths, more than one-sixth of the world is roughly as poor today as their ancestors were hundreds of years ago. The majority of the extremely poor live in the tropics. The latitudinal gradient in income is highly suggestive of underlying biophysical drivers, of which disease conditions are an especially salient example. However, conclusions have been confounded by the simultaneous causality between income and disease, in addition to potentially spurious relationships. We use a simultaneous equations model to estimate the relative effects of vector-borne and parasitic diseases (VBPDs) and income on each other, controlling for other factors. Our statistical model indicates that VBPDs have systematically affected economic development, evident in contemporary levels of per capita income. The burden of VBDPs is, in turn, determined by underlying ecological conditions. In particular, the model predicts it to rise as biodiversity falls. Through these positive effects on human health, the model thus identifies measurable economic benefits of biodiversity.

Purpose Consumers are increasingly connected to, and make use of, a multitude of technologies in their daily lives. The exponential growth in the use of Internet of Things (IoT)-based services is ushering in a new era of e-services, in which the service experience is becoming autonomous (intelligence), devices are intercommunicating (connectivity) and consumers can access the service anytime, anywhere and using any device (ubiquity). However, a number of challenges have arisen. The purpose of this paper is to investigate factors that reduce consumer resistance to smart services (factors against resistance) and factors that promote this resistance (factors for resistance), by means of a dual-factor approach. Design/methodology/approach To test this theoretical model, the authors developed a Web-based survey and used structural equation modeling. Findings Results show that consumer-lifestyle factors (individual “mobiquity” and self-image congruence) reduce consumer resistance to smart services (factors against resistance). Conversely, innovation-related factors (perceived security, perceived complexity) and ecosystem-related factors (perceived government surveillance and general skepticism toward IoT) promote consumer resistance to smart services (factors for resistance). In addition, general skepticism toward IoT has a significant positive effect on perceived complexity, perceived security risk and perceived government surveillance. Originality/value This research investigates consumer resistance to smart services using a dual-factor perspective (Cenfetelli, 2004; Claudy et al. , 2015): factors reducing resistance versus factors promoting resistance. This paper provides evidence for the importance of consumer lifestyle-related factors, innovation-related factors and ecosystem-related factors in explaining consumer resistance to smart services. This work enriches previous studies of consumer resistance to innovation (Ram and Sheth, 1989; Ram, 1987) by studying original variables (individual mobiquity, technological innovativeness, government surveillance).

BACKGROUND: Friedreich ataxia (FA) is the most frequent autosomal recessive cerebellar ataxia. Although the phenotype is well known, disease progression has not been evaluated in a prospective manner. OBJECTIVE: To perform a long-term prospective follow-up of neurological, cardiological, and oculomotor function in patients with FA (FA patients). DESIGN: In this open-labeled prospective survey, we examined 104 FA patients every 6 months during a median period of 5 years (range, 6 months to 7 years), with a systematic standardized protocol. Data are reported as mean +/- SD. SETTING: Neurological examinations were performed at the Federation of Neurology and the Department of Genetics of the Salpêtrière Hospital, Paris, France. Cardiological follow-up was performed at the Department of Cardiology; oculomotor examinations were performed at the Institut National de la Santé et de la Récherche Médicale Unit 679, at the same hospital. Patients We studied 104 FA patients with a confirmed molecular diagnosis. None were receiving antioxidant therapy at baseline; 88 accepted treatment with the coenzyme Q(10) analogue idebenone (5 mg/kg per day). Sixteen preferred not to be treated. INTERVENTIONS: Neurological status was evaluated with the International Cooperative Ataxia Rating Scale (ICARS) and a quantitative writing test. Cardiological evaluations included echocardiography, electrocardiography, and Holter monitoring. Oculomotor function was evaluated by electro-oculography to determine the frequency of square wave jerks. RESULTS: The total ICARS score worsened during follow-up, whether or not the patients were treated with idebenone (1.93 +/- 0.25 and 4.43 +/- 1.56 points per year, respectively). The total ICARS score increased faster in patients with onset before age 15 years compared with the others (2.6 +/- 0.4 [n = 51] vs 1.1 +/- 0.3 [n = 37]; P = .05). The posture subscore increased faster in patients able to stand at baseline, who also had shorter disease durations than patients unable to stand (1.25 +/- 0.12 vs 0.47 +/- 0.22 point per year; P<.001). Neurological progression was underestimated, however, by the ICARS scores, which reached a plateau in patients with long disease durations. Oculomotor function slightly deteriorated (0.09 +/- 0.02 Hz per year; P<.001). Left ventricular mass index decreased (-4.1 +/- 1.5 g/m(2) per year; P = .008), as did ejection fraction (-1.32% +/- 0.29% per year; P<.001). CONCLUSIONS: The neurological condition of FA patients deteriorated slowly over time, even with idebenone treatment. Although cardiac hypertrophy decreased under treatment, cardiac function did not improve. The ICARS scale is not appropriate to evaluate the progression of FA in patients with long disease durations. Additional quantitative measures may improve the reliability of this scale.

This article provides a simple model that explains the choice between permanent and temporary jobs. This model, which incorporates important features of actual employment protection legislations neglected by the economic literature so far, reproduces the main stylized facts about entries into permanent and temporary jobs observed in Continental European countries. We find that job protection has very small effects on total employment but induces large substitution of temporary jobs for permanent jobs, which significantly reduces aggregate production.

We review two important non-perturbative approaches for extracting the physics of low-dimensional strongly correlated quantum systems. Firstly, we start by providing a comprehensive review of non-Abelian bosonization. This includes an introduction to the basic elements of conformal field theory as applied to systems with a current algebra, and we orient the reader by presenting a number of applications of non-Abelian bosonization to models with large symmetries. We then tie this technique into recent advances in the ability of cold atomic systems to realize complex symmetries. Secondly, we discuss truncated spectrum methods for the numerical study of systems in one and two dimensions. For one-dimensional systems we provide the reader with considerable insight into the methodology by reviewing canonical applications of the technique to the Ising model (and its variants) and the sine-Gordon model. Following this we review recent work on the development of renormalization groups, both numerical and analytical, that alleviate the effects of truncating the spectrum. Using these technologies, we consider a number of applications to one-dimensional systems: properties of carbon nanotubes, quenches in the Lieb-Liniger model, 1 + 1D quantum chromodynamics, as well as Landau-Ginzburg theories. In the final part we move our attention to consider truncated spectrum methods applied to two-dimensional systems. This involves combining truncated spectrum methods with matrix product state algorithms. We describe applications of this method to two-dimensional systems of free fermions and the quantum Ising model, including their non-equilibrium dynamics.

We estimate the wage penalty associated with working in the South African informal sector. To this end we use a rich data set on non‐self‐employed males that allows one to accurately distinguish workers employed in the informal sector from those employed in the formal sector and link individuals over time. Implementing various econometric approaches we find that there is a gross wage penalty of a little over 18% for working in the informal sector. However, once we reduce our sample to a group for which we can reasonably calculate earnings net of taxes and control for time‐invariant unobservables, the wage penalty disappears.

The aim of this study is to provide a better understanding of the factors that explain consumer resistance to smart services from a privacy perspective. To this end, an exploratory qualitative study and a quantitative study were carried out. 653 French consumers answered an online questionnaire regarding smart services in the banking sector. Structural equation modelling was used to test the conceptual model. The findings show that information privacy, the unauthorised secondary use of personal information and perceived intrusion have an impact on consumer resistance to smart services. Moreover, our research highlights the major role of the ‘Big Brother effect’ as an antecedent to these various privacy concerns.

We study a simple model of $N$-component fermions with contact interactions which describes fermionic atoms with $N=2F+1$ hyperfine states loaded into a one-dimensional optical lattice. We show by means of analytical and numerical approaches that, for attractive interaction, a quasi-long-range molecular superfluid phase emerges at low density. In such a phase, the pairing instability is strongly suppressed and the leading instability is formed from bound states made of $N$ fermions. At small density, the molecular superfluid phase is generic and exists for a wide range of attractive contact interactions without an $\mathrm{SU}(N)$ symmetry between the hyperfine states.