Electron wave and quantum optics in graphene.

In the last decade, graphene has become an exciting platform for electron optical experiments, in some aspects superior to conventional two-dimensional electron gases (2DEGs). A major advantage, besides the ultra-large mobilities, is the fine control over the electrostatics, which gives the possibility of realising gap-less and compact p-n interfaces with high precision. The latter host non-trivial states,e.g., snake states in moderate magnetic fields, and serve as building blocks of complex electron interferometers. Thanks to the Dirac spectrum and its non-trivial Berry phase, the internal (valley and sublattice) degrees of freedom, and the possibility to tailor the band structure using proximity effects, such interferometers open up a completely new playground based on novel device architectures. In this review, we introduce the theoretical background of graphene electron optics, fabrication methods used to realise electron-optical devices, and techniques for corresponding numerical simulations. Based on this, we give a comprehensive review of ballistic transport experiments and simple building blocks of electron optical devices both in single and bilayer graphene, highlighting the novel physics that is brought in compared to conventional 2DEGs. After describing the different magnetic field regimes in graphene p-n junctions and nanostructures, we conclude by discussing the state of the art in graphene-based Mach-Zender and Fabry-Perot interferometers.

Microfluidic Validation of the Diffusional Bridging Effect Suppressing Dispersion in Multicapillary Flow Systems.

The efficiency of liquid chromatography separations could be strongly improved by changing the current packed bed columns by a bundle of parallel capillary tubes. In practice, however, the polydispersity effect, which emanates from the inevitable small differences in capillary diameter, completely ruins this potential. The concept of diffusional bridging, introducing a diffusive cross talk between adjacent capillaries, has recently been proposed to resolve this. The present contribution provides the first experimental proof for this concept and quantitatively validates its underlying theory. This has been accomplished by measuring the dispersion of a fluorescent tracer in 8 different microfluidic channels with different degrees of polydispersity and diffusional bridging. The observed degree of dispersion reduction agrees very well with the theoretical predictions, hence opening the road to the use of this theory to design a new family of chromatographic beds, potentially offering unprecedented performance.

Effects of a New Soft Skills Metacognition Training Program on Self-Efficacy and Adaptive Performance.

Although soft skills training is called for by many scholars and managers, empirical studies on concrete training programs are scarce and do not always have the methodological rigor that is necessary to draw meaningful conclusions about their impact. In the present research, we investigate the effects of a new soft skills metacognition training program on self-efficacy and adaptive performance. To test these effects, we conducted an experiment with a sample of employees of a large firm (n = 180). The experiment included pre- and post-measurements and a control condition. The results suggested that participating in the training led to an increase in soft skills metacognition, self-efficacy, and four dimensions of adaptive performance, compared to a control condition. Mediation analyses suggested that an increase in soft skills metacognition led to an increase in self-efficacy, which led, in turn, to an increase in adaptive performance. Theoretical and practical implications are discussed, as well as limitations.

Transient Taylor-Aris dispersion in N-capillary systems: Convergence properties of the band broadening in polydisperse multi-capillary columns with diffusional bridging.

We report on a generic mathematical study of the transient plate height regime in bundles of polydisperse capillaries with diffusional bridging. I.e., we have investigated how the plate height in such systems can be expected to vary with the residence time, or equivalently, with the column length, before reaching a long-time limit wherein the plate height becomes constant. This is important because, in case of systems with a large number of capillaries (N), the transient regime solution is practically much more relevant than the long-time limit solution. The problem has been investigated using a simplified, yet representative geometry that is amenable to a semi-analytical solution, only requiring a numerical integration of the velocity field across a line (2D geometries) or a square or rectangle (3D geometries). The availability of this semi-analytical approach allows to consider the required large number of different random capillary diameter drawings (order of 10,000) needed to establish a sufficiently averaged result (deviation from true mean on the order of 1%). The general solution could be simplified into a set of two-parameter expressions describing either the long-time limit (τ→∞) as well as that of an infinite number of capillaries (N→∞). The combinations of N and τ where these expressions are valid to within an accuracy of 5% could be delimited with simple analytical expressions as well. It has also been observed that the long-time limit solution for the additional plate height (Δhτ→∞) remains dependant on the number of capillaries N, even when N tends to infinity. It is found that Δhτ→∞ can be expected to increase in proportion with N-1 (2D-case) or with ln(N-1) (3D-case). This dependency of Δhτ→∞ on N is a result that is not obtained when modelling the capillary bundle using a representative binary capillary system approach as has been done up-till-now in literature.

Exact analytical expressions for the band broadening in polydisperse 2-D multi-capillary columns with diffusional bridging.

Using a recent generalization of the Aris dispersion method, we have derived exact analytical expressions for the long-time limit dispersion in 2-D multi-capillary packings with diffusional bridging (binary channel system). Both the plug flow and the parabolic flow case are considered. The expressions are mathematically exact over the entire range of possible values of the degree of polydispersity (σ), the retention equilibrium constant K and the diffusion coefficients in the mobile and stationary zone. They are validated by comparing them to the dispersion data obtained by numerically solving the partial differential equation describing the general advection-diffusion mass balance. A correlation coefficient of R2 > 0.99995 is obtained. The form of the obtained analytical expression shows the dispersion arising from the polydispersity effect in multi-capillary systems can be split in two contributions, one related to the actual velocity difference between the adjacent channels and one related to the fact that the average of the intra-capillary C-term band broadening is larger in any σ≠0-case than in the σ=0-case. When leaving the small σ-assumption, a new factor ((1- σ2)/(1+3σ2)2) emerges, common to both the solution for the plug flow and the parabolic case. The analysis shows the parabolic flow not only leads to a larger intra-capillary dispersion (σ=0) than the plug flow case as known from literature but is also more sensitive to the polydispersity effect (up to some 10 to 20%).

Evolution and impact of self-efficacy during French COVID-19 confinement: a longitudinal study.

Based on social cognitive theory, we propose that self-efficacy is a personal resource that protects people from the impact of confinement in the context of the COVID-19 pandemic. In a longitudinal study where 197 French citizens were surveyed over 8 weeks of confinement (though only 25 participants responded each of these 8 weeks), we examined the relationships between general self-efficacy and positive affect, negative affect and adaptive performance at work. Consistent with theoretical expectations, self-efficacy was relatively stable during confinement and was positively related to positive affect and negatively related to negative affect. Self-efficacy was also positively correlated with all dimensions of adaptive performance at work during confinement. The role of self-efficacy as a protective factor against depressive risks induced by the stressful COVID-19 pandemic is discussed.

Electronic Wave-Packets in Integer Quantum Hall Edge Channels: Relaxation and Dissipative Effects.

We theoretically investigate the evolution of the peak height of energy-resolved electronic wave-packets ballistically propagating along integer quantum Hall edge channels at filling factor equal to two. This is ultimately related to the elastic scattering amplitude for the fermionic excitations evaluated at different injection energies. We investigate this quantity assuming a short-range capacitive coupling between the edges. Moreover, we also phenomenologically take into account the possibility of energy dissipation towards additional degrees of freedom-both linear and quadratic-in the injection energy. Through a comparison with recent experimental data, we rule out the non-dissipative case as well as a quadratic dependence of the dissipation, indicating a linear energy loss rate as the best candidate for describing the behavior of the quasi-particle peak at short enough propagation lengths.