Evaluation of Species Invasiveness: A Case Study with Acacia dealbata Link. on the Slopes of Cabeça (Seia-Portugal)

One of the main causes of biodiversity loss in the world is the uncontrolled expansion of invasive plants. According to the edaphoclimatic conditions of each region, plants acquire different invasion behaviors. Thus, to better understand the expansion of invasive plants with radial growth, it is proposed to use two equations, the Annual Linear Increment (ALI) and the Annual Invasiveness Rate (AIR). These equations are applied using spatiotemporal data obtained from the analysis of orthophotomaps referring populations of Acacia dealbata Link. in areas located in Serra da Estrela, Portugal. As a result, the area occupied by this species in the parish of Cabeça was evaluated and a 20-year projection was carried out. The data produced by these equations contributed to improving the knowledge about the invasion behavior of exotic species in a rigorous and detailed way according to local ecological conditions. This study may serve as the basis for the application of other similar situations concerning invasive species in other territories, to improve the efficiency of future projections for these species. Local technical and scientific knowledge will contribute to improving spatial and management planning, enabling a better adequacy and effectiveness of the control measures to be adopted.

Activity-determined Steps on the Growth of Atmospheric CO2 Concentration Environmental Kuznets Curve (EKC) at the Country Level: Taiwan’s Empirical Evidence

Taiwan’s atmospheric CO2 concentration is half in compliance on the formation of a environmental Kuznets curve (EKC), and the major contributor of direct CO2 emissions in Taiwan is from the power generation sector using coal and natural gas as fuel. Atmospheric CO2 concentration has been found to have the linear increment with stepwise fluctuations every five years during the period 2001-2018. Activity-determined steps were proposed noting that there is a proportion process for the increase of CO2 coming directly from the emission source of power plants and the source from the marginal sea sink to atmosphere sink due to memory delay-releasing. The alternative occurring events of EI Nino and La Nina in the West-Pacific region exactly match the fluctuations every five years, and the difference between the monitored atmospheric CO2 concentration with an empirical equation of calculated atmospheric CO2 concentration from the electricity structure in a single country level is a new indictor for the occurrences of EI Nino and La Nina phenomena in this region. Results also showed that the atmospheric CO2 concentration in Taiwan for the year 2035 is predicted to be as high as 430 ppm, due to a 50% natural gas energy policy. Our study provides a causal explanation for why atmospheric CO2 concentration has a linear increase shape with stepwise fluctuations for a single country. Our study has also proved that the linear increment with stepwise fluctuations also exhibits a EKC pattern.

Design and Fabrication of Non-Uniform Spacing Multiple Floating Field Limiting Rings for 6500V 4H-SiC JBS Diodes

Designed for 6500V 4H-SiC JBS diodes, a highly-efficient termination structure of a non-uniform multiple floating field limiting rings (MFFLR) featuring with a non-uniform ring spacing and a multiple region division is studied and purposed. For each region, ring spacing is modulated independently by a multiplication factor and a linear increment factor. The non-uniform MFFLR structure is simulated and optimized for a better electric field distribution and a higher breakdown voltage. Based on the simulation results, 4H-SiC JBS diodes with the optimized non-uniform termination designs are fabricated. Experimental results show that the SiC JBS diode with optimized non-uniform MFFLR termination structure can achieve a breakdown voltage of up to 7800 V, and its termination efficiency is about 94% of an ideal parallel-plane junction’s. Our results demonstrate that the optimized non-uniform MFFLR termination structure is capable for SiC JBS diodes with breakdown voltage of 6500V and above. Our results can provide a valuable design methodology of edge termination structures for other high-voltage SiC devices.

Numerical study on the limit of quasi-static approximation for plasmonic nanosphere

Plasmonic nanospheres are often employed as resonant substrates in many nanophotonic applications, like in enhanced spectroscopy, near-field microscopy, photovoltaics, and sensing. Accurate calculation and tuning of optical responses of such nanospheres are essential to achieve optimal performance. Mie theory is widely used to calculate optical properties of spherical particles. Although, an approximated version of Mie approach, the quasi-static approximation (QSA) can also be used to determine the very same properties of those spheres with a lot simpler formulations. In this work, we report our numerical study on the limit and accuracy of QSA with respect to the rigorous Mie approach. We calculated scattering, absorption and extinction spectra of silver and gold nanospheres in air with varying sizes using both QSA and Mie theory. Then, we extracted spectral positions of the resonance peaks from their calculated optical responses and defined the error present in QSA as the difference between the spectral positions of the resonance peaks calculated by QSA and Mie method. Our error analysis reveals that QSA approach yields nonlinear increment in error with linear increment in size of the nanosphere and that the amount of error is significantly less in the case of gold spheres compared to the silver ones. We also provide a polynomial-fitted error function that resembles the qualitative trend in error.

Effect of NaOH treatment on mechanical strength of banana/epoxy laminates

The present study is focused on studying the effect of alkali treatment on the mechanical properties of banana fiber-reinforced epoxy composites. Four batches of samples were prepared with respect to the percentage of sodium hydroxide (NaOH) in the treatment solution (0%, 2.5%, 4.5%, and 6.5%). Later mechanical tests such as tensile, compressive, and interlaminar shear tests were conducted on the prepared composite specimens to determine the influence of alkali treatment on the mechanical characteristics. The test results indicate an overall improvement in all the mechanical properties due to the fiber treatment. Moreover, the samples made from the fiber treated with 4.5% of NaOH solution indicated the highest tensile strength and compressive strength, with an overall increment of 24.2% and 34.8% in tensile and compressive strengths, respectively, when compared with the untreated sample. A linear increment in interlaminar strength is observed with a maximum value of 25.4 N/mm2 for the sample made from the fiber treated with 6.5% of NaOH solution. This increase is due to the fiber flattening process which increases the bonding surface at the interface.

Diffusion of elements during reflow ageing of Sn-Zn solder in liquid state on Ni/Cu substrate – theoretical and experimental study

Purpose This paper aims to study the diffusion of Zn, Ni and Sn in the liquid state during the reflow ageing of the Sn-Zn solder above its melting point on an Ni/Cu substrate in relation to the formation of intermetallic compounds (IMCs). Design/methodology/approach The Sn-Zn solder is reflowed on Ni/Cu substrates and is aged at 503 K. The formation of IMCs and their composition is characterized using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). Diffusion coefficients and diffusion distances of Zn, Ni and Sn in the liquid state during reflow and ageing are theoretically calculated. Both experimental and theoretical behaviours for Ni and Zn diffusions are compared. Findings Calculations show a linear increment in the liquid-state diffusion coefficients of Ni, Zn and Sn in the solder matrix with a rise in temperature, but they remained constant during ageing. However, diffusion distances increased slowly with temperature but manifold with ageing time. The experimental results revealed segregation of Zn and Ni at the interface in the as-reflow aged specimens. The Zn was concentrated at the solder–substrate interface and it reacted with Ni diffusing from the substrate to form Ni-Sn-Zn IMCs. The rapid diffusion of Zn and Ni with the increase in ageing time increased their atomic concentrations in the IMCs against the reduction in Sn concentration owing to a comparatively slower diffusion. Originality/value The novelty of the paper is the detailed study of theoretical diffusion of Zn, Sn and Ni in the liquid state during reflow ageing of Sn-Zn above its melting points on a Ni/Cu substrate. This is compared with values obtained experimentally and related to the mechanisms of IMC formation.