Reflectivity Modelling of All-Porous-Silicon Distributed Bragg Reflectors and Fabry-Perot Microcavities

Herein, the problem of nanocrystaline silicon laser and its importance in microelectronics are discussed upon. The features of vertical Fabry-Perot microcavities made on the base of porous silicon are described. The responses of the reflectivity of the distributed reflection Bragg mirrors and Fabry-Perot microcavities were found using transfer matrixes method for this purpose. Inherent optical parameters of porous silicon, deposited by electrochemical etch, were used in the calculations. The calculation of the reflectivity of the distributed reflection Bragg mirrors with front active layer of nanostructural porous silicon had been examined. In the second part, the features of Fabry-Perot microcavities on variation of the number of layers of the front or rear mirrors are described. The impact of the thickness of the active nanocrystaline silicon spacer between two distributed reflection Bragg mirrors upon the spectra of optical reflectivity of Fabry-Perot microcavities in the wavelength range of 0.4–0.9 µm had been examined as well. The made conclusions are important for improvement of the thickness of the active porous silicon spacer in front of Bragg mirror and the features of Fabry-Perot microcavities

Effect of planting scheme on photosynthetic activity and dry matter accumulation in apple leaves

This study aims to identify changes photosynthetic rate and dry matter accumulation in apple leaves with decreasing plant to plant distance of the trees. Apple tree Auksis' was grafted on dwaring P60 rootstock and planted at different in distances: 0.5 m, 0.75 m, I m and 1.25 m between plant to plant distance in rows. Photosynthetic indices were measured at 1.00-1.20 m above ground inside the canopy. 20 randomly selected leaves from the whole apple tree canopy were used to determine leaf area, fresh and dry weight. Measurements were made in three different stages in May, June and September. By decreasing the distance between apple trees irom 1.5 m to 0.5 m, photosynthetic rate decreases correspondingly, decreasing by 23% in spring, and decreasing by 31% in autumn. Distance between trees has no significant impact on leave mass per area (LMA), however in spring is higher by 33-51% compared to summer and 42-78% compared to autumn. Dry and fresh weight ratio (DW/FW) significantly increased in summer by 27%% and in autumn - by 37% compared to spring, also DW/W significantly decreased by the decreasing distance from 1.5 m to 0.5 m by 4-6%. In summary, the decreasing distance reduces the photosynthetic rate, the accumulation of dry matter. Also, photosynthetic rate decreases from spring to harvest time, and on the contrary, the accumulation of dry matter increases as autumn approaches. After evaluating the obtained results, the aim is to further delve into the use and transpiration of water and the impact of the planting scheme on fruit quality

Oxidative discolouration in whole-head and cut lettuce: biochemical and environmental influences on a complex phenotype and potential breeding strategies to improve shelf-life

Lettuce discolouration is a key post-harvest trait. The major enzyme controlling oxidative discolouration has long been considered to be polyphenol oxidase (PPO) however, levels of PPO and subsequent development of discolouration symptoms have not always correlated. The predominance of a latent state of the enzyme in plant tissues combined with substrate activation and contemporaneous suicide inactivation mechanisms are considered as potential explanations for this phenomenon. Leaf tissue physical properties have been associated with subsequent discolouration and these may be influenced by variation in nutrient availability, especially excess nitrogen and head maturity at harvest. Mild calcium and irrigation stress has also been associated with a reduction in subsequent discolouration, although excess irrigation has been linked to increased discolouration potentially through leaf physical properties. These environmental factors, including high temperature and UV light intensities, often have impacts on levels of phenolic compounds linking the environmental responses to the biochemistry of the PPO pathway. Breeding strategies targeting the PALand PPOpathway biochemistry and environmental response genes are discussed as a more cost-effective method of mitigating oxidative discolouration then either modified atmosphere packaging or post-harvest treatments, although current understanding of the biochemistry means that such programs are likely to be limited in nature and it is likely that they will need to be deployed alongside other methods for the foreseeable future

Photoresponse of Porous Silicon Structures to Infrared Radiation

Photoresponse of silicon samples containing porous structures have been studied under the action of $CO_2$ laser radiation. The signal shape and its behavior under the applied bias voltage revealed the existence of two heterojunctions on the border of porous-crystalline silicon and on the border between the porous layers of different porosity. The photosignal is recognized to be composed of hot hole photoemfs induced across the heterojunctions

Uprawa rozsady papryki słodkiej pod światłem lamp HPS i LED

In greenhouses, artificial lighting is applied in winter and early spring as sup-plementary light source to increase photosynthesis and plant growth. The objective of this study was to evaluate the cultivation of sweet pepper transplants under LED lamps that were developed to supplement HPS lamps used in greenhouses. The experiments were carried out in the greenhouses at the Lithuanian Research Centre for Agriculture and For-estry Institute of Horticulture. Sweet peppers (Capsicum annuum) L. cultivar ‘Reda’ and the hybrid ‘Figaro’ F1 were used for investigation. Four types of solid-state lamps were used with light-emitting diodes (LEDs) with peak emissions at blue 455 nm and 470 nm, cyan 505 nm, and green 530 nm. PPFD of each type of LED lamp was 15 μmol m-2 s-1, and the PPFD of HPS lamps was 90 μmol m-2 s-1. The reference transplants were grown under the illumination of HPS lamps (110 μmol m-2 s-1). The photoperiod of artificial lighting was maintained at 18 hours. Our experiments revealed different responses to sup-plemental LED lightings between the cultivar and the hybrid. The supplemental 470 nm illumination with HPS lamps mostly resulted in increases in the following areas: leaf area, fresh and dry weight, and the photosynthetic pigment content of the sweet pepper ‘Reda’ transplants. A similar positive effect was determined using supplemental 455 and 505 nm LED lights. However, the supplemental green 530 nm LED lights had no effect on growth, and they inhibited the development of the sweet pepper ‘Reda’ transplants. The HPS light had a positive effect on the growth parameters of the ‘Figaro’ F1 transplants, but all of the supplemental LED lights suppressed their growth and developmentW szklarniach sztuczne oświetlenie stosowane jest zimą i wczesną wiosną jako dodatkowe źródło światła, aby zwiększyć fotosyntezę i wzrost roślin. Celem pracy była ocena możliwości uprawy rozsady papryki słodkiej w szklarni pod lampami HPS z dodatkiem LED. Badania przeprowadzono w Instytucie Ogrodnictwa Litewskiego Centrum Nauk Rolniczych i Leśnych. Przebadano dwie odmiany papryki słodkiej (Capsicum annuum L.): ‘Reda’ i ‘Figaro F1’. Jako dodatkowe światło, oprócz lamp HPS, zastosowano cztery rodzaje lamp LED o długościach fal: niebieskie 455 i 470 nm, zielono-niebieskie 505 nm oraz zielone 530 nm. PPFD LED wynosiło 15 μmol m-2 s-1, a lamp HPS – 90 μmol m-2 s-1. Długość dnia – 18 godzin. Na podstawie wyników stwierdzono, że dodatkowe światło LED miało różny wpływ na wzrost odmian papryki. Po dodaniu do światła lamp HPS LED-470 w rozsadzie papryki słodkiej odmiany ‘Reda’ stwierdzono największą powierzchnię liści, najwięcej świeżej i suchej masy roślin oraz największą zawartość barwników foto syntetycznych. Podobny wpływ wywierało dodatkowe światło LED 455 i 505 nm. Natomiast dodatkowe zielone światło LED-530 nie miało wpływu na wzrost, a hamowało rozwój rozsady odmiany ‘Reda’. Światło HPS miało korzystny wpływ na parametry wzrostu siewek ‘Figaro F1’, zaś dodatek światła LED hamował ich wzrost i rozwój