Twist in the Tale: Exploring the Dielectric Screening Effect in Twisted Bilayer Graphene

Although the screening of an external electric field, strongly influences the electronic states of two-dimensional material stack, it is not well understood. Magnetotransport measurements of twisted double bilayer graphene uncovered the screening of atomic layers.

Self-Screening of the polarized electric field in Wurtzite Gallium Nitride along [0001] direction

The strong polarization effect of GaN-based materials is widely used in high-performance devices such as white-light-emitting diodes (white LEDs), high electron mobility transistors (HEMTs) and GaN Polarization SuperJunctions. However, the current researches on the polarization mechanism of GaN-based materials are not sufficient. In this paper, we studied the influence of polarization on electric field and energy band characteristics of Ga-face GaN bulk materials by using a combination of theoretical analysis and semiconductor technology computer-aided design (TCAD) simulation. The self-screening effect in Ga-face bulk GaN under ideal and non-ideal conditions is studied respectively. We believe that the formation of high-density two-dimensional electron gas (2DEG) in GaN is the accumulation of screening charges. So that, we also clarify the source and accumulation of the screening charges caused by the GaN self-screening effect in this paper and aim to guide the design and optimization of high-performance GaN-based devices.

Assessment and quantification of meteorological data for implementation of weather radar in mountainous regions

The scope of this paper is to improve observation and detection of hydro-meteorological hazard over the Grenoble region which is characterised by significant changes of terrain in altitude and geomorphology. The city of Grenoble is located at a height between 200 up to 500 m, installing the weather radar in this range of elevation leads to better quality measurements, but visibility and as well coverage capability will be reduced at the other sites of the affected region. Two locations are shortlisted for the implementation of the future weather radar in Grenoble; (i) Moucherotte (1920 m a.s.l.) and (ii) Saint Eynard (1365 m a.s.l.). Several simulation and data analysis are performed to get the clear picture about precipitation variability by considering meteorological data from individual ground stations and radio sounding data as well. Compared to previous work, in this study is considered climatology of the vertical structure of the rainfall. In this context, several statistical computations are done regarding 0°C isotherm altitude. Concerning rainfall error estimation, ground clutter and screening effect, statistical calculations by using VISHYDRO code, are performed by for different quintiles for several elevation angles in both shortlisted sites. The results obtained from calculations carried out on two locations are almost similar. Also, significant under and over-estimation of rainfall error due to screening and ground clutter effect are detected. To achieve more accurate results, other sites need to be tested for further simulation. On the other hand since ground clutter, and screening effect at the Moucherotte is not too high compare with Saint Eynard, this site may be considered for implementing the future weather radar for observation of the meteorological processes over the Grenoble region.

Screening current induced field characteristics of HTS quasi-isotropic and simply stacked strands in alternating magnetic field

The screening current induced field (SCIF) in the flat REBCO coated conductors (REBCO CCs) so called 2G HTS tapes cause undesirable effects in multiple applications. Their existence reduces the spatial uniformity and temporal stability of magnetic fields for applications of superconducting magnets. In this paper, we numerically and experimentally investigate the characterization of the screening current and SCIF of quasi-isotropic strand (Q-IS) and simply stacked strand (SSS) under external alternating magnetic field with various amplitudes, orientations, and excitation rates. The two-dimensional finite element method (2D FEM) based on T-A formulation is adopted for simulation, the Q-IS and SSS samples are fabricated for experiments. The field angle is in the range of 0° to 90° at intervals of 15°, the excitation rate varies from 20 mT/s to 800 mT/s. We display the distribution of screening current in both strands under various field amplitudes and orientations. Then the dependence of SCIF on the amplitude and orientation of external field is studied, respectively. The spatial distribution of SCIF of both strands with different amplitudes and angles of the external field are also discussed. Besides, we analyze the properties of SCIF under various excitation rates. As a result, the SCIF of Q-IS is much smaller and has quasi-isotropic distribution comparing with SSS, which represents that Q-IS has relative smaller screening effect. The spatial point with the largest SCIF of Q-IS locates at the corner of the strand and is independent of the external field, but the corresponding point in SSS varies with the angle and amplitude. The Q-IS is also less susceptible to the change of rate. Therefore, Q-IS has more advantages when the screening effect is considered in superconducting applications.

Screening effect for excitonic spectrum of Coulomb coupling between two Dirac particles

The properties of screening effect for energy spectrum of excitons in monolayer transition metal dichalcogenides are investigated using a multiband model. The excitonic hamiltonian in the product base of the Dirac single-particle is used. The corresponding energy eigenvalue system of the first order ODE (radial equations) was solved using the finite difference method. This enables to determine the energy eigenvalues of the discrete excitonic spectrum and the wave functions. We compare the results for the energy spectrum and the corresponding eigen-functions forms for WS 2 and WSe 2 computed for two different potentials: pure Coulomb and screened Coulomb (Keldysh potential). It is demonstrated that excitonic energy levels for unscreened potential lie dipper, and the corresponding eigen-functions’ forms differ from those obtained for screened one.

The Impact of Guarantees on Peer-to-Peer Lending Platform: Evolutionary Game Analysis and Empirical Evidence from China

The peer-to-peer lending market has developed rapidly over the past decade and reveals a severe problem of information asymmetry. This research constructed a four-party evolutionary game model to analyze the influence pathway of the guarantee mechanism on the users’ participation of the peer-to-peer lending platform and conducted an empirical study applying the mediating effect model and simultaneous equation model based on data of China’s peer-to-peer lending platform. The theoretical model shows that the guarantee mechanism reduced the participation of borrowers of the peer-to-peer lending platform through a screening effect, but increased the participation of investors through a signal effect. In the case of the platform self-guarantee, there existed a self-screening effect, whose influence on the participation of investors depended on the strength of external constraints imposed on the platform enterprises. Further, the empirical study shows that during the sample period, the platform self-guarantee mechanism reduced the scale of borrowers and investors of the peer-to-peer lending platform at the same time, thus reducing the transaction volume of the platform. Although the third-party guarantee mechanism reduced the scale of borrowers, it increased the scale of investors, and the comprehensive effect was to increase the transaction volume of the platform. On this basis, this research puts forward suggestions such as strengthening the qualification examination of the platform enterprises, transforming the platform self-guarantee mechanism into the third-party guarantee mechanism, and introducing more signal mechanisms.

Densification of Carbon Nanotubes During Growth

Carbon nanotubes are highly attractive for research purposes due to their field emission properties. However, when the nanotubes are vertically aligned on a substrate to form a continuous film, screening effect is observed, which reduces the efficiency. To densify the tubes into bundles and eliminate this screening effect, costly lithography patterning of catalysts and post-growth chemical treatments have been previously reported. In this work, we report a novel, cheap, and reproducible technique of densifying the growth of carbon nanotubes by utilizing a colloidal catalyst and microwave plasma-enhanced chemical vapor deposition. A qualitative investigation was carried out, and a possible densification mechanism was proposed.

Do the prices of a preventive animal health product affect dairy farmers’ willingness to pay and product use? Evidence from an experimental study

Should we distribute preventive animal health products for free or charge a positive price? The decision depends on the price sensitivity of the product and the effect prices have on product use. We explore this idea through a field experiment in which we randomize the price a farmer faces for an animal health product. We find that the demand for the product is highly sensitive to prices; willingness to pay (WTP) decreased from 44% at ₹ 100 to 18% at ₹ 500. Further, among farmers who were willing to pay, the product usage rate was 71% and usage did not increase in prices (lack of screening effect). Furthermore, we find that farmers whose animals were sick in the baseline had a higher WTP. These findings support the human capital model relating to demand for human health products. We argue that individuals behave in a similar way when the decisions concern their own health or the health of an animal they rear for commercial purposes. A highly subsidized distribution of the product is recommended due to high price sensitivity, lack of screening effect, equitable distribution among poor and lesser implementation costs found in this study.