Decoherence and Quantum Interference assisted electron trapping in a quantum dot

We present a theoretical model for the dynamics of an electron that gets trapped by means of decoherence and quantum interference in the central quantum dot (QD) of a semiconductor nanoring (NR) made of five QDs, between 100 K and 300 K. The electron's dynamics is described by a master equation with a Hamiltonian based on the tight-binding model, taking into account electron-LO phonon interaction (ELOPI). Based on this configuration, the probability to trap an electron with no decoherence is almost 27%. In contrast, the probability to trap an electron with decoherence is 70% at 100 K, 63% at 200 K and 58% at 300 K. Our model provides a novel method of trapping an electron at room temperature.Comment: Revtex 4, 11 pages, 13 figure

Optical Parity Time Metasurface Structures

In the last few years, optics has witnessed the emergence of two fields namely metasurfaces and parity-time (PT) symmetry. Optical metasurfaces are engineered structures that provide unique responses to electromagnetic waves, absent in natural materials. Optical metasurfaces are known for their reduced dimensionality i.e. subwavelength and consequently lower losses are anticipated. The other paradigm is the PT symmetric materials, also known as photonic synthetic matter. PT symmetry has emerged from quantum mechanics when a new class of non-Hermitian Hamiltonian quantum systems was highlighted to have real eigenvalues, hence eradicating Hermiticity of the Hamiltonian as an essential condition to the existence of real eigenvalues. The first half of the thesis is focused on the experimental and numerical realization of PT symmetric metasurfaces. A systematic methodology is developed to implement this class of metasurfaces in both one-dimensional and two-dimensional geometries. In two dimensional systems, PT symmetry can be established by employing either H-like diffractive elements or diatomic oblique Bravais lattices. It is shown that the passive PT symmetric metasurfaces can be utilized to appropriately engineer the resulting far-field characteristics. Such PT-symmetric structures are capable of eliminating diffraction orders in specific directions, while maintaining or even enhancing the remaining orders. Later, it is shown a first ever attempt of PT metasurface fabricated on a flexible polymer (polyimide) substrate. The studied PT metasurface exhibits the ability to direct light, i.e. Poynting vector in a desired direction. Herein, the light scattered from the fabricated device in the undesired direction is attenuated by at least an order of magnitude. The proposed PT symmetric metasurface is essentially diatomic Honeycomb Bravais lattice, where both the passive and lossy elements exist side by side on each site separated by 50 nm. The unidirectionality of the studied metasurface is not limited to a single wavelength, on the contrary, it is observed to be effective on the entire visible band (400 – 600 nm). The PT symmetric meatsurface is also fabricated on a high strength substrate; sapphire (Al2O3). An excellent agreement between the experimental and numerical (COMSOL) results is found for both substrates. Customized modifications to the current design can open avenues to study the unidirectionality of metasurfaces to different optical bands, for example IR. The second part of the thesis deals with the theoretical modeling of the dynamics of an electron that gets trapped by means of decoherence and quantum interference in the central quantum dot (QD) of a semiconductor nanoring (NR) made of five QDs, between 100 and 300 K. The electron\u27s dynamics is described by a master equation with a Hamiltonian based on the tight-binding model, taking into account electron–LO phonon interaction. Based on this configuration, the probability to trap an electron with no decoherence is almost 27%. In contrast, the probability to trap an electron with decoherence is 70% at 100 K, 63% at 200 K and 58% at 300 K. Our model provides a novel method of trapping an electron at room temperature. This setup is then used to propose a theoretical model for an electrically driven single photon source operating at high temperatures. It is shown that the decoherence, which is usually the main obstacle for operating single photon sources at high temperatures, ensures an efficient operation of the presented electrically driven single photon source at high temperatures. The single-photon source is driven by a single electron source attached to a heterostructure semiconductor nanoring. The electron\u27s dynamics in the nanoring and the subsequent recombination with the hole is described by the generalized master equation with a Hamiltonian based on tight-binding model, taking into account the electron-LO phonon interaction. As a result of decoherence, an almost 100% single photon emission with a strong antibunching behavior i.e. g(2)(0) \u3c \u3c 1 at high temperature up to 300 K is achieved

Primary GC-MS chemical analysis of alcoholic extract of Emex spinosa (L.) Campd. and screening of their antioxidant, antibacterial, and cytotoxic characteristics

ABSTRACT. The chemical constituents of the methanolic extract of Emex spinosa shoots were primarily characterized by gas-chromatography-mass spectrometry analysis (GC-MS), forty components were identified. The major components were ethyl 2-hydroxycyclohexane-1-carboxylate (10.11%), 3,5-dihydroxy-6-methyl-2,3-dihydro-4H-pyran-4-one (38.09%), 2-propyltetrahydro-2H-pyran-3-ol (5.75%), oleic acid (8.02%), and methyl (E)-octadec-16-enoate (5.91%). The results of antioxidant activity of leaves extract presented the most potent activity (IC50 = 29.92 mg mL-1), followed by stem extract (IC50 = 41.17 mg mL-1), and root extract (IC50 = 50.14 mg mL-1), comparable to that of the standard ascorbic acid (IC50 = 13.3 mg mL-1). The antibacterial results revealed that leaves extract is the most potent (22.0 mm) antibacterial agent against the variety of the tested species. Stem and leaves extracts are more potent (20 and 20 mm, respectively) than azithromycin (13.0 mm) against Pseudomonas aeruginosa species, while root and leaves extracts displayed potent antibacterial activities than tetracycline (10 mm). The most potent activity was recorded for leaves extract against Bacillus cereus species (22.0 mm) higher than the standard antibiotics (5.0-20.0 mm). The cytotoxic activity of E. spinosa MeOH extract specified the EC50 value at 2.68 µg mL-1 attended by a cytotoxic effect on HepG2 cell lines with the effective dose of the plant extract at a higher concentration.                                                                      KEY WORDS: Emex spinosa, GC-MS, Antioxidant, Antibacterial, Cytotoxic activities   Bull. Chem. Soc. Ethiop. 2023, 37(1), 101-114.                                                              DOI: https://dx.doi.org/10.4314/bcse.v37i1.9                                                       &nbsp

Proximate Composition, Mineral Content and Secondary Metabolites of Three Medicinal Wild Fagonia Species

Proximate composition of the aerial parts of three Fagonia species (Fagonia arabica L., F. mollis Delile and F. cretica L.) collected from different habitats were analyzed. Macro- and micro-elements as well as some secondary metabolites were estimated. The obtained results revealed that F. creticus contains appreciable levels of nutritive components considering that its nutritional value (351.06 kcal/100g dry wt.) was remarkably higher than that of F. arabica and F. mollis (327.99 and 293.07 kcal/100g dry wt., respectively). The concentration of Na was relatively the highest among the other estimated macroelements in the studied species followed by K, Ca and Mg, respectively while Fe was the highest microelement followed by Cu, Mn and Zn, respectively. The phytochemical composition revealed that methanolic extract of F. creticus was the richest in total alkaloids and flavonoids, while F. arabica found to be the richest in total phenolics and tannins

HPLC-DAD-MS/MS profiling of phenolics from Securigera securidaca flowers and its anti-hyperglycemic and anti-hyperlipidemic activities

AbstractSecurigera securidaca (L.) Degen & Döefl., Fabaceae, has been widely used in the Iranian, Indian and Egyptian folk medicine as antidiabetic and anti-hyperlipidemic remedy. Phenolic profiling of the ethanolic extract (90%) of the flowers of S. securidaca was performed via HPLC-DAD-MS/MS analysis in the positive and negative ion modes. The total polyphenols and flavonoids in the flowers were determined colorimetrically, and the quantification of their components was carried out using HPLC-UV. Total phenolics and flavonoids estimated as gallic acid and rutin equivalents were 82.39±2.79mg/g and 48.82±1.95mg/g of the dried powdered flowers, respectively. HPLC-DAD-MS/MS analysis of the extract allowed the identification of 39 flavonoids and eight phenolic acids. Quantitative analysis of some flavonoids and phenolics (mg/100g powdered flowers) revealed the presence of isoquercetrin (3340±2.1), hesperidin (32.09±2.28), naringin (197.3±30.16), luteolin (10.247±0.594), chlorogenic acid (84.22±2.08), catechin (3.94±0.57) and protocatechuic acid (34.4±0.15), in the extract. Moreover, the acute toxicity, hypoglycemic and hypolipidemic effects of the extract were investigated using alloxan induced diabetes in rats in a dose of 100, 200, and 400mg/kgbwt. The ethanolic extract was safe up to a dose of 2000mg/kg. All tested doses of the flower extract showed marked decrease in blood glucose level by 31.78%, 66.41% and 63.8% at 100, 200 and 400mg/kgbwt, respectively, at p<0.05. Regarding the anti-hyperlipidemic effect, a dose of 400mg/kg of the flower extract showed the highest reduction in serum triacylglycerides and total cholesterol levels (68.46% and 51.50%, respectively at p<0.05). The current study proved the folk use of the flowers of S. securidaca as anti-diabetic and anti-hyperlipidemic agent which could be attributed to its high phenolic content

Spatial Distribution and Ecological Risk Assessment of Trace Metals in Surface Sediments of Lake Qarun Wetland, Egypt

Wetlands sediments could be critical indicators to control contamination in the aquatic ecosystem. Qarun Lake is regarded as the third biggest lake in Egypt that is not related to any sea. Twelve georeferenced sediment samples were gathered in September, 2020 from the different locations. Five heavy metals (Pb, Cd, Cr, Ni, and Co) were measures in the sediments estimated by Atomic Absorption Spectrophotometer. Grain size and content of organic matters in the sediment were estimated on the basis of standard assays, as well as the contamination factor, geoaccumulation index, ecological risk factor, contamination degree and potential ecological risk index in the sediment. Data revealed that the average concentration could be arranged as Ni (27.36 mg k g-1) > Pb (18.28 mg k g-1) > Cr (15.31 mg k g-1) > Co (11.16 mg k g-1) > Cd (23.31 mg k g-1). Cd, Co and Pb were estimated to be in the range of EU (2002) and the US EPA (1999), while Co and Ni in the range of EU (2002). The ecological risk index (Er) of the studied elements in sediments of lake could be arranged as: Ni > Pb > Co > Cd > Cr. In addition, the highest-integrated potential ecological risk was on the south side of the lake, which is subjected to huge amounts of drainage water composed of organic and inorganic pollutants