Broadband enhancement of light harvesting in luminescent solar concentrator

Luminescent solar concentrator (LSC) can absorb large-area incident sunlight, then emit luminescence with high quantum efficiency, which finally be collected by a small photovoltaic (PV) system. The light-harvesting area of the PV system is much smaller than that of the LSC system, potentially improving the efficiency and reducing the cost of solar cells. Here, based on Fermi-golden rule, we present a theoretical description of the luminescent process in nanoscale LSCs where the conventional ray-optics model is no longer applicable. As an example calculated with this new model, we demonstrate that a slot waveguide consisting of a nanometer-sized low-index slot region sandwiched by two high-index regions provides a broadband enhancement of light harvesting by the luminescent centers in the slot region. This is because the slot waveguide can (1) greatly enhance the spontaneous emission due to the Purcell effect, (2) dramatically increase the effective absorption cross-section of luminescent centers, and (3) strongly improve the quantum efficiency of luminescent centers. It is found that about 80% solar photons can be ultimately converted to waveguide-coupled luminescent photons even for a low luminescent quantum efficiency of 0.5. This LSC is potential to construct a tandem structure which can absorb nearly full-spectrum solar photons, and also may be of special interest for building integrated nano-PV applications

Polypropylene based anion exchange fiber for enrichment and determination of trace indium by GFAAS

Indium was enriched and separated by a new polypropylene based anion exchange fiber before determined by graphite furnace atomic absorption spectrometry (GFAAS). Indium can be enriched quantitatively by 0.1 g of fiber at the flow rate within 6 mL·min-1 in the pH 4 and can be desorbed quantitatively with 10 mL of 1.0 M nitric acid from the fiber column. The fibers were soaked in 2 M sodium hydroxide sodium hydroxide solution for activation and were washed with distilled water at least thirty times until neutral for regeneration, The saturated capacity of the fiber for In(III) was 1.32 mg·g-1. The activation energy (Ea) of the fiber adsorption In(III) was 89.3 kJ·mol-1. The method was used to enrich trace In(III) in artificial samples solution and zinc concentrate solution before determination. The method detection limit was 0.08 ng·mL-1, the recoveries were 96.8-101%, and the relative standard deviations (RSD) were 0.1-2.1%. KEY WORDS: Anion exchange fiber, Separation, Enrichment, Indium, GFAAS Bull. Chem. Soc. Ethiop. 2011, 25(2), 295-298

Dependence of the decoherence of polarization states in phase-damping channels on the frequency spectrum envelope of photons

We consider the decoherence of photons suffering in phase-damping channels. By exploring the evolutions of single-photon polarization states and two-photon polarization-entangled states, we find that different frequency spectrum envelopes of photons induce different decoherence processes. A white frequency spectrum can lead the decoherence to an ideal Markovian process. Some color frequency spectrums can induce asymptotical decoherence, while, some other color frequency spectrums can make coherence vanish periodically with variable revival amplitudes. These behaviors result from the non-Markovian effects on the decoherence process, which may give rise to a revival of coherence after complete decoherence.Comment: 7 pages, 4 figures, new results added, replaced by accepted versio

Quantum electrodynamics in a whispering-gallery microcavity coated with a polymer nanolayer

Quasi-transverse-electric and -transverse-magnetic fundamental whispering gallery modes in a polymer-coated silica microtoroid are theoretically investigated and demonstrated to possess very high-quality factors. The existence of a nanometer-thickness layer not only evidently reduces the cavity mode volume but also draws the maximal electric field's position of the mode to the outside of the silica toroid, where single quantum dots or nanocrystals are located. Both effects result in a strongly enhanced coherent interaction between a single dipole (for example, a single defect center in a diamond crystal) and the quantized cavity mode. Since the coated microtoroid is highly feasible and robust in experiments, it may offer an excellent platform to study strong-coupling cavity quantum electrodynamics, quantum information, and quantum computation

High-Q exterior whispering gallery modes in a metal-coated microresonator

We propose a kind of plasmonic whispering gallery modes highly localized on the exterior surface of a metal-coated microresonator. This exterior (EX) surface mode possesses high quality factors at room temperature, and can be efficiently excited by a tapered fiber. The EX mode can couple to an interior (IN) mode and this coupling produces a strong anti-crossing behavior, which not only allows conversion of IN to EX modes, but also forms a long-lived anti-symmetric mode. As a potential application, the EX mode could be used for a biosensor with a sensitivity high up to 500 nm per refraction index unit, a large figure of merit, and a wide detection range

Strongly enhanced light-matter interaction in a hybrid photonic-plasmonic resonator

We propose a hybrid photonic-plasmonic resonant structure which consists of a metal nanoparticle (MNP) and a whispering gallery mode (WGM) microcavity. It is found that the hybrid mode enables a strong interaction between the light and matter, and the single-atom cooperativity is enhanced by more than two orders of magnitude compared to that in a bare WGM microcavity. This remarkable improvement originates from two aspects: (1) the MNP offers a highly enhanced local field in the vicinity of an emitter, and (2), surprisingly, the high-\textit{Q} property of WGMs can be maintained in the presence of the MNP. Thus the present system has great advantages over a single microcavity or a single MNP, and holds great potential in quantum optics, nonlinear optics and highly sensitive biosening.Comment: 5 pages, 4 figure

Benzoxazolinones: Novel Bioactive Phytochemicals in Wheat with Potential Hypoglycemic Activity

Benzoxazolinones (BXs) are a group of natural compounds with biological activity. In recent years, benzoxazolinones have been identified in cereal grains and bakery foods. The most common BXs are 6-methoxy-benzoxazolin-2-one (MBOA) and 2-benzoxazolin-2-one (BOA). In this study, the contents of MBOA and BOA in 13varieties of wheat harvested in Henan Province were analyzed by LC-MS technology. Meanwhile, the inhibitory effects of MBOA and BOA on α-glucosidase and α-amylase were evaluated. The results showed that the contents of MBOA and BOA in wheat varied from 4.30 to 5.02 ng/g and 1.62 to 7.98 ng/g respectively. Interestingly, the contents of MBOA and BOA in whole wheat flour increased significantly after hot drying and germination by 1.5~2.0 and 500~1 000 times, respectively. In the aspect of hypoglycemic activity, MBOA and BOA showed reversible competitive inhibition on α-glucosidase and α-amylase. The IC50 of MBOA and BOA to α-glucosidase were 13.73 and 73.9 mg/mL, the IC50 to α-amylase were 64.98 and 17.68 mg/mL. These results revealed that BXs have the potential contribution to the hypoglycemic activity associated with whole wheat consumption. Food processing technologies such as germination can be used to enhance the concentration of BXs in the cereal food products that allow the intake of higher amounts of BXs. This study provides a new theoretical basis for the research on the health effects of whole wheat and its processed products

The efficacy of the Hiline gas permeable contact lens for the management of Keratoconus

Purpose: To investigate the efficacy of the Hiline® gas permeable contact lens (Hiline® GP) for keratoconus in clinical practice in correcting visual acuity. Methods: 218 eyes of 126 patients with keratoconus were fitted with Hiline® lenses. The fit of the lenses was evaluated. Visual acuity measurements were taken with spectacle lenses and with the Hiline lenses. The period of follow-up to observe for complications ranged from 3 to 27 months. Results: In all eyes, the Hiline® GP provided acceptable vision. There was a statistically significant improvement in vision with the Hiline® GP compared with spectacle lenses (t=10.90, p<0.0001). Initial evaluation showed that 169 lenses (77.52%) demonstrated a three-pointtouch relationship with the cornea 38 lenses (17.43%) had an apical clearance relationship with the cornea and 11 lenses (5.05%) had an apical bearing relationship. No severe complications were observed. Conclusions: Using corneal topography as a guide, a high success rate was achieved with the Hiline® GP design. It is easy to reach the ideal fit and to improve the visual acuity. These indicate the usefulness of Hiline® lens in clinical practice

1,3-Bis(4-methyl­benz­yl)pyrimidine-2,4(1H,3H)-dione

In the title mol­ecule, C20H20N2O2, the central pyrimidine ring forms dihedral angles of 71.9 (1) and 69.8 (1)° with the two benzene rings. In the crystal, weak inter­molecular C—H⋯O hydrogen bonds link mol­ecules into centrosymmetric dimers. The crystal packing exhibits also π–π inter­actions as indicated by short distances of 3.674 (2) Å between the centroids of the pyrimidine rings of neighbouring mol­ecules