Collective cloaking of a cluster of electrostatically defined core-shell quantum dots in graphene

We study cloaking of a cluster of electrostatically defined core-shell quantum dots in graphene. Guided by the generalized multiparticle Mie theory, the Dirac electron scattering from a cluster of quantum dots is addressed. Indeed distant quantum dots may experience a sort of individual cloaking. But despite the multiple scattering of an incident electron from a set of adjacent quantum dots, collective cloaking may happen. Via a proper choice of the radii and bias voltages of shells, two most important scattering coefficients and hence the scattering efficiency of the cluster dramatically decrease. Energy-selective electron cloaks are realizable. More importantly, clusters simultaneously transparent to electrons of different energies, are achievable. Being quite sensitive to applied bias voltages, clusters of core-shell quantum dots may be used to develop switches with high on-off ratios.

Scattering efficiencies measurements of soft protons at grazing incidence from an Athena Silicon Pore Optics sample

Soft protons are a potential threat for X-ray missions using grazing incidence optics, as once focused onto the detectors they can contribute to increase the background and possibly induce radiation damage as well. The assessment of these undesired effects is especially relevant for the future ESA X-ray mission Athena, due to its large collecting area. To prevent degradation of the instrumental performance, which ultimately could compromise some of the scientific goals of the mission, the adoption of ad-hoc magnetic diverters is envisaged. Dedicated laboratory measurements are fundamental to understand the mechanisms of proton forward scattering, validate the application of the existing physical models to the Athena case and support the design of the diverters. In this paper we report on scattering efficiency measurements of soft protons impinging at grazing incidence onto a Silicon Pore Optics sample, conducted in the framework of the EXACRAD project. Measurements were taken at two different energies, $\sim $ ∼ 470 keV and $\sim $ ∼ 170 keV, and at four different scattering angles between 0.6∘ and 1.2∘. The results are generally consistent with previous measurements conducted on eROSITA mirror samples, and as expected the peak of the scattering efficiency is found around the angle of specular reflection.

Co-benefits of reducing PM2.5 and improving visibility by COVID-19 lockdown in Wuhan

The less improvement of ambient visibility suspects the government’s efforts on alleviating PM2.5 pollution. The COVID-19 lockdown reduced PM2.5 and increased visibility in Wuhan. Compared to pre-lockdown period, the PM2.5 concentration decreased by 39.0 μg m−3, dominated by NH4NO3 mass reduction (24.8 μg m−3) during lockdown period. The PM2.5 threshold corresponding to visibility of 10 km (PTV10) varied in 54–175 μg m−3 and an hourly PM2.5 of 54 μg m−3 was recommended to prevent haze occurrence. The lockdown measures elevated PTV10 by 9–58 μg m−3 as the decreases in PM2.5 mass scattering efficiency and optical hygroscopicity. The visibility increased by 107%, resulted from NH4NO3 extinction reduction. The NH4NO3 mass reduction weakened its mutual promotion with aerosol water and increased PM2.5 deliquescence humidity. Controlling TNO3 (HNO3 + NO3−) was more effective to reduce PM2.5 and improve visibility than NHx (NH3 + NH4+) unless the NHx reduction exceeded 11.7–17.5 μg m−3.

Size Effects of Closed Encounter Ag Nanoshell Pairs for SERS Application

Closed encounter Ag nanoshell pairs with remarkable improved plasmonic light enhancement in their gaps have been attracting much attention in the production of sensitivity SERS substrates. This work demonstrates the size effects of Ag nanoshell pairs on obtaining higher light intensity in their gaps. It is found that very complex light intensity changes occur in the gaps of Ag nanoshell pairs with their diameter enlargements ( diameters > 100 nm). By the calculation of scattering efficiency and electric field vectors, the size-related light intensity changes in the gaps have been revealed and been concluded systematically. This work fills in the gaps of application of nanoshell pairs with larger sizes in SERS detectors and could guide the design of some other Ag nanoshell pair-based optical devices.

Spectral Radiative Properties of a Liquid n-Octane Droplet in the Midinfrared Region

The optical constants of a liquid hydrocarbon such as liquid n-octane are basic material properties that may be used to evaluate their thermal radiation transfer capabilities. In this study, the ellipsometry method was used to measure the optical constants of liquid n-octane in the midinfrared wavelength range of 2.0–16.0 μm at temperatures of 20, 50, and 80°C. Experimental analyses indicate the significant effect of temperature on the refractive index, although it has little effect on the absorption index. With increasing temperature, the refractive index shows a linear decrease, and reduced density leads to weaker absorption intensities. The radiative properties of n-octane droplets, including the absorption and scattering efficiency factors of single droplets with droplet radii r = 10, 20, 50, and 100 μm and the absorption and scattering coefficients in a droplets-air system of droplet volume fractions fv = 2%, 3%, and 4%, were calculated using Mie theory. The numerical results indicate that, with increasing temperature, the absorption efficiency factor slightly decreases, and the variation trend of the scattering efficiency factor is more complicated. With increasing droplet radius, the absorption efficiency factor increases within the studied wavelength range, except for certain absorption peaks, but the scattering efficiency factor tends to decrease. While the absorption is greater, the scattering is weaker for a given droplet radius. With an increasing volume fraction of n-octane droplets, the absorption and scattering coefficients increase linearly within the studied wavelength range.

Scattering in graphene quantum dots under generalized uncertainty principle

In this article, the Dirac electron scattering problem on circular barrier of radius [Formula: see text] is studied under the generalized uncertainty principle (GUP). The expressions of scattering coefficients, scattering cross-section and scattering efficiency of massless Dirac particle are obtained by solving the massless Dirac equation under GUP and discussed by numerical methods. It shows that the scattering coefficient, the scattering cross-section, and the scattering efficiency depend explicitly on the GUP parameter [Formula: see text]. For the scattering coefficient [Formula: see text], GUP may cause slight shift in the oscillation position of [Formula: see text] and make some peaks value of [Formula: see text] smaller. For scattering cross-section and scattering efficiency, GUP may also lead to slight shift in their oscillation position and increase of amplitude when the GUP parameter increases.