Antireflective nanotextures for monolithic perovskite silicon tandem solar cells

Recently, we studied the effect of hexagonal sinusoidal textures on the reflective properties of perovskite silicon tandem solar cells using the finite element method FEM . We saw that such nanotextures, applied to the perovskite top cell, can strongly increase the current density utilization from 91 for the optimized planar reference to 98 for the best nanotextured device period 500 nm and peak to valley height 500 nm , where 100 refers to the Tiedje Yablonovitch limit. [D. Chen et al., J. Photonics Energy 8, 022601, 2018 , doi 10.1117 1.JPE.8.022601] In this manuscript we elaborate on some numerical details of that work we validate an assumption based on the Tiedje Yablonovitch limit, we present a convergence study for simulations with the finite element method, and we compare different configurations for sinusoidal nanotexture

Electromechanical coupling in free-standing AlGaN/GaN planar structures

The strain and electric fields present in free-standing AlGaN/GaN slabs are examined theoretically within the framework of fully-coupled continuum elastic and dielectric models. Simultaneous solutions for the electric field and strain components are obtained by minimizing the electric enthalpy. We apply constraints appropriate to pseudomorphic semiconductor epitaxial layers and obtain closed-form analytic expressions that take into account the wurtzite crystal anisotropy. It is shown that in the absence of free charges, the calculated strain and electric fields are substantially differently from those obtained using the standard model without electromechanical coupling. It is also shown, however, that when a two-dimensional electron gas is present at the AlGaN/GaN interface, a condition that is the basis for heterojunction field-effect transistors, the electromechanical coupling is screened and the decoupled model is once again a good approximation. Specific cases of these calculations corresponding to transistor and superlattice structures are discussed.Comment: revte

The effect of electromechanical coupling on the strain in AlGaN/GaN heterojunction field effect transistors

The strain in AlGaN/GaN heterojunction field-effect transistors (HFETs) is examined theoretically in the context of the fully-coupled equation of state for piezoelectric materials. Using a simple analytical model, it is shown that, in the absence of a two-dimensional electron gas (2DEG), the out-of-plane strain obtained without electromechanical coupling is in error by about 30% for an Al fraction of 0.3. This result has consequences for the calculation of quantities that depend directly on the strain tensor. These quantities include the eigenstates and electrostatic potential in AlGaN/GaN heterostructures. It is shown that for an HFET, the electromechanical coupling is screened by the 2DEG. Results for the electromechanical model, including the 2DEG, indicate that the standard (decoupled) strain model is a reasonable approximation for HFET calculataions. The analytical results are supported by a self-consistent Schr\"odinger-Poisson calculation that includes the fully-coupled equation of state together with the charge-balance equation.Comment: 6 figures, revte

Popular support for military intervention and anti-establishment alternatives in Tunisia: Appraising outsider eclecticism

Popular attitudes in support of authoritarian alternatives and weak party systems constitute important threats to democratic consolidation and the stability of new democracies. This article explores popular alienation from established political actors in Tunisia. Under what conditions do citizens support alternatives to the elites in power and the institutional infrastructure of a new democracy? Drawing on an original, nationally representative survey in Tunisia administered in 2017, this article examines three categories of popular attitudes in support of political outsiders.Military interventionism appears in people’s preferences for anti-system politics—the most immediate challenge to the country’s stability and democratic transition. Anti-political establishment sentiments are shown in people’s preferences for an enhanced role of the country’s main trade union as a civil-society alternative to political party elites. Finally, outsider eclecticism is the seemingly incoherent phenomenon of concurrent support for a civil society actor and the military as an ‘authoritarian alternative.’ Anti-establishment sentiments will continue to be an important element in Tunisian post-authoritarian politics, evidenced by the rise to power of Kais Said in the 2019 presidential elections and his 2021 decision to dismiss parliament. In turn, popular support for military intervention may have implications for the country’s domestic security and peaceful transition

Improving Monolithic Perovskite Silicon Tandem Solar Cells From an Optical Viewpoint

Perovskite silicon tandem solar cells are the most promising concept for a future photovoltaic technology. We report on recent progress from an optical viewpoint and disucss how we achieved more than 25 device efficienc

Differences in Dopamine Function in Fibromyalgia

poster abstractObjective: Fibromyalgia (FM) is a debilitating pain disorder that affects 2% of the population. Many of the drugs prescribed to fibromyalgia sufferers are highly addictive, have limited clinical efficacy, and do not treat the cognitive symptoms of fibromyalgia. The neurobiological substrates of fibromyalgia are unknown, but there is evidence for involvement of altered dopaminergic transmission in pain disorders. Given that dopamine is essential for proper cognitive function, it is possible that fibromyalgia symptoms are partly mediated by abnormal dopaminergic functioning. However, the in vivo dopamine system in fibromyalgia patients has not been assessed. Thus, the objective of the current study was to ascertain how the dopamine system in fibromyalgia differs from healthy controls. Methods: [18F]-Fallypride (FAL) PET scanning was used to assess DA changes during a working memory task relative to a baseline task. Twelve patients with FM and twelve controls completed study procedures. Subjects received one FAL PET scan during a 2-back working-memory condition and one during a 0-back (attentional control) task. Results: Fibromyalgia subjects had higher baseline FAL binding potential (BPND) in the right amygdala and ventral pallidum relative to controls. FM subjects had lower baseline FAL BPND in frontal, temporal, and cingulate cortices. Voxel-wise paired t-tests were used to infer increases or decreases in FAL BPND (indicative of decreases or increases in dopamine, respectively) during 2-back performance. Fibromyalgia subjects had significant dopamine release in the ACC, left insula, OFC, and bilateral hippocampus during the 2-back task. Conversely, decreases in DA were detected in the posterior parietal cortex and vmPFC. In controls, dopamine appeared to decrease in the posterior parietal lobe, left hippocampus, and vmPFC during the 2-back task. No significant DA release was detected in controls. Self-reported pain ratings in fibromyalgia subjects were significantly associated with baseline FAL BPND in the ACC, bilateral ventral pallidum, amygdalae, and PAG. Conclusion: These data suggest that in fibromyalgia, abnormalities in dopamine function may be associated with both working memory and pain perception. Further studies are needed to further explore the potential associations between dopamine and cognitive performance and pain perception in FM

Direct Photon Production in Heavy Ion Reactions at SPS and RHIC

A review on experimental results for direct photon production in heavy ion reactions is given. A brief survey of early direct photon limits from SPS experiments is presented. The first measurement of direct photons in heavy ion reactions from the WA98 collaboration is discussed and compared to theoretical calculations. An outlook on the perspective of photon measurements at RHIC is given.Comment: 12 pages, 8 figures, invited talk at ICPA-QGP 2001, Jaipur, India, to be published in PRAMAN

Stationary Points of Scalar Fields Coupled to Gravity

We investigate the dynamics of gravity coupled to a scalar field using a non-canonical form of the kinetic term. It is shown that its singular point represents an attractor for classical solutions and the stationary value of the field may occur distant from the minimum of the potential. In this paper properties of universes with such stationary states are considered. We reveal that such state can be responsible for modern dark energy density.Comment: H. Kroger, invited talk, FFP6, Udine (2004), revised version with corrected author lis

Advances in Corrosion Casting Methods

This paper briefly discusses the concept of corrosion cast preparation (primarily of blood vessels), the use of the scanning electron microscope (SEM) to study these casts and the observations which can be made, together with the merits and the limitations in various applications. A number of reviews and surveys are quoted in which the different injection media, injection methods, animal preparations and corrosion procedures are described. A new procedure of cleaning the corrosion casts with sodium hydroxide and Triton X-100 is described. The observations which can be made are listed and illustrated both on the cellular level as well as in organ systems as a whole. The discussion centers around some common misconceptions, the feasibility in various applications and the limitations of the method. The conclusion is that the method has proven to be useful especially in conjunction with other methods. Moreover, while the concept of the method may be very straight-forward the approach and the interpretation often need careful consideration and might not be as straight-forward as one tends to expect from the simple sounding principle