Optically activated shutter using a photo-tunable short-pitch chiral nematic liquid crystal

We report the demonstration of an optically activated shutter based upon a short-pitch chiral nematic liquid crystal (LC) device sandwiched between crossed polarizers. This LC is comprised of photo-active chiral dopants. In the trans-state, the LC appears dark between crossed polarizers due to the very short pitch. As the pitch is extended through exposure to ultraviolet light, the device becomes transmissive reaching a maximum for a particular value of the pitch. As a result, it is possible to switch between the light and dark states by subjecting the device to visible light so as to cause a cis-trans photo-isomerisation. © 2013 AIP Publishing LLC.

Strength and drying shrinkage of reactive MgO modified alkali-activated slag paste

Conventional alkali-activated slag (AAS) cements suffer from significant drying shrinkage which hinders their widespread application. This paper investigates the potential of using commercial reactive MgO to reduce the drying shrinkage of AAS. Two different reactive MgOs were added at a content of 2.5-7.5 wt% of the slag, which was activated by sodium hydroxide and water-glass. The strength and the drying shrinkage of those reactive MgO modified AAS (MAAS) pastes were measured up to 90 days. It is found that MgO with high reactivity accelerated the early hydration of AAS, while MgO with medium reactivity had little effect. The drying shrinkage was significantly reduced by highly reactive MgO but it also generated severe cracking under the dry condition. On the other hand, medium-reactive MgO only showed observable shrinkage-reducing effect after one month, but the cement soundness was improved. The hydration products, analysed by X-ray diffraction, thermogravimetric analysis and scanning electron microscopy techniques, showed that Mg was mainly incorporated in the hydrotalcite-like phases. It is concluded that the curing conditions and the time of hydrotalcite-like phases formation and their quantity are crucial to the developed strength and shrinkage reduction properties of MAAS, which are highly dependent on the reactivity and content of reactive MgO. Crown Copyright © 2013 Published by Elsevier Ltd. All rights reserved.

Bacterial diversity in activated sludge from a consecutively aerated submerged membrane bioreactor treating domestic wastewater

The bacterial diversity of activated sludge from submerged membrane bioreactor (SMBR) was investigated. A 16S rDNA clone library was generated, and 150 clones were screened using restriction fragment length polymorphism (RFLP). Of the screened clones, almost full-length 16S rDNA sequences of 64 clones were sequenced. Phylogenetic tree was constructed with a database containing clone sequences from this study and bacterial rDNA sequences from NCB1 for identification purposes. The 90.6% of the clones were affiliated with the two phyla Bacteroidetes (50%) and Proteobacteria (40%), and beta-, -gamma-, and delta-Proteobacteria accounted for 7.8%, 28.1%, and 4.7%, respectively. Minor portions were affiliated with the Actinobacteria and Firmicutes (both 3.1%). Only 6 out of 64 16S rDNA sequences exhibited similarities of more than 97% to classified bacterial species, which indicated that a substantial fraction of the clone sequences were derived from unknown taxa. Rarefaction analysis of operational taxonomic units (orrUs) clusters demonstrated that 150 clones screened were still insufficient to describe the whole bacterial diversity. Measurement of water quality parameter demonstrated that performance of the SMBR maintained high level, and the SMBR system remained stable during this study.

Increasing the genetic uniformity of bighead carp [Aristichthys nobilis (Richardson)] by means of spontaneous diploidization of gynogenetically activated eggs

Three groups of gynogenetic diploid bighead carp were successfully obtained by means of artificial gynogenesis. The activation rates of gynogenesis varied from 75.9% to 98.8%, and the frequency of spontaneous diploidization was around 0.4%. Over 2000 normally gynogenetic diploid fry were obtained in three gynogenetic groups. The haploid karyotype consisted of nine metacentric, 12 submetacentric, three subtelocentric chromosomes and 45 arms. The chromosome number was 48 from gynogenetic diploid. The results showed that the genetic material of offspring was maternal. The aneuploid hybrid embryos of bighead carp and Xingguo red common carp with chromosome numbers ranging from 28 to 73 did not survive post hatch, likely the result of incompatibility between the nucleus and the cytoplasm of two parents. Sixty RAPD primers from three groups were used for total DNA amplification of gynogenetic offspring, maternal and 'paternal' fish. A total of 451 bands were amplified from three kinds of samples above. From maternal bighead carp, 256 bands were amplified; however, there were 251 shared bands between maternal and gynogenetic bighead carp. From artificial gynogenetic offspring, two 'paternal' DNA segments without an expression function were found. An UPGMA tree showed that gynogenetic offspring were closely clustered and the genetic identity among them was very high (0.956).

Vibration of pressurised, elastic, spherical shells

Balloons are one example of pressurised, elastic, spherical shells. Whilst analytical solutions exist for the vibration of pressurised spheres, these models only incorporate constant tension in the membrane. For elastic shells, changes in curvature will result in restoring forces that are proportional to the elasticity in the membrane; hence the assumption of constant tension is not valid. This paper describes an analytical solution for the natural frequencies of an elastic spherical shell subject to internal pressure. When the membrane tension is set to zero, the results are shown to converge to the analytical solution for a spherical shell, and when the skin elasticity is neglected, the results converge to the constant-tension solution. This analytical solution is used to predict the natural frequencies of a small balloon, based on a value for the elastic modulus that is determined using biaxial tensile testing. These predictions are compared to experimental measurements of balloon vibrations using impact hammer testing, and good agreement is seen.

A TPR-family membrane protein gene is required for light-activated heterotrophic growth of the cyanobacterium Synechocystis sp PCC 6803

The unicellular cyanobacterium Synechocystis sp. PCC6803 can grow heterotrophically in complete darkness, given that a brief period of illumination is supplemented every day (light-activated heterotrophic growth, LAHG), or under very weak ( < 0.5 mumol m(-2) s(-1)) but continuous light. By random insertion of the genome with an antibiotic resistance cassette, mutants defective in LAHG were generated. In two identical mutants, sll0886, a tetratricopeptide repeat (TPR)-family membrane protein gene, was disrupted. Targeted insertion of sll0886 and three downstream genes showed that the phenotype was not due to a polar effect. The sll0886 mutant shows normal photoheterotrophic growth when the light intensity is at 2.5 mumol m(-2) s(-1) or above, but no growth at 0.5 mumol m(-2) s(-1). Homologs to sll0886 are also present in cyanobacteria that are not known of LAHG. sll0886 and homologs may be involved in controlling different physiological processes that respond to light of low fluence. (C) 2003 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.

Electronic structure in GaAs/AlxGa1-xAs spherical quantum dots

In this paper, how the dots' radius, At concentration and external electric field affect the single electron energy states in GaAs/AlxGa1-xAs spherical quantum dots are discussed in detail. Furthermore, the modification of the energy states is calculated when the difference in effective electron mass in GaAs and AlxGa1-xAs are considered. In addition, both the analytical method and the plane wave method are used in calculation and the results are compared, showing that they are in good agreement with each other. The results and methods can provide useful information for the future research and potential applications of quantum dots.

Lasing of CdSSe quantum dots in glass spherical microcavity

Glass spherical microcavities containing CdSSe semiconductor quantum dots (QDs) of a few microns in diameter are fabricated using a physical method. When a single glass microspherical cavity is excited by a laser beam at room temperature, very strong and sharp whispering gallery modes are shown on the background of PL spectra of CdSSe QDs, which confirms that coupling between the optical emission of embedded QDs and spherical cavity modes is realized. For a glass microsphere only 4.6 mum in diameter, it was found that the energy separation is nearly up to 26 nm both for TE and TM modes. With the increasing excitation intensity, the excitation intensity dependence of the emission intensity is not linear in the double-logarithmic scale. Above the threshold value, the linewidths of resonance modes become narrower. The lasing behavior is achieved at relatively low excitation intensity at room temperature. High optical stability and low threshold value make this optical system promising in visible microlaser applications. (C) 2002 Elsevier Science B.V. All rights reserved.

Lasing of CdSexS1-x quantum dots in a glass spherical microcavity

A glass spherical microcavity only a few microns in diameter embedded with CdSexS1-x quantum dots (QDs) was fabricated using a physical method; it exhibited good optical stability under continuous-wave laser excitation with high power. We investigated the excitation power dependences of the emission intensity and the linewidth of both transverse electric and transverse magnetic resonance peaks of whispering gallery modes. Stimulated emission behaviour of multi-frequency modes is observed at room temperature. The low threshold value and large mode separation makes QD-containing microspheres promising for visible microlaser applications.

Photoluminescence behavior of quantum dots in spherical glass microcavity

Micrometer-sized spherical glass microspheres were fabricated. CdSeS semiconductor nanometer clusters were incorporated into spherical microcavities. When a single microsphere was excited by a laser beam, the whispering gallery mode resonance of the photoluminescence of CdSeS quantum dots in the spherical microcavities was realized by the multiple total internal reflections at the spherical interface. The coupling of restricted electronic and photonic states was realized.

Photoluminescence study of CdSexS1-x quantum dots in a glass spherical microcavity

The photoluminescence (PL) of CdSexS1-x semiconductor quantum dots (QDs) in a glass spherical microcavity is investigated. The CdSexS1-x semiconductor clusters embedded in a glass matrix are fabricated by using the heat treatment method. Periodical structures consisting of sharp spectral lines are observed in the PL spectra of CdSexS1-x QDs, which can be well explained by the coupling with the whispering gallery modes of the spherical microcavity based on Mie scattering theory.

Quantum dots in glass spherical microcavity

Glass spherical microcavities containing CdSexS1-x semiconductor quantum dots (QDs) are fabricated. The coupling between the optical emission of embedded CdSexS1-x QDs and spherical cavity modes is realized. When the luminescence of QDs is excited by a laser beam, the strong whispering gallery mode resonance with high Q factors is achieved in the photoluminescence spectra. (C) 2001 American Institute of Physics.

Different transfer paths for thermally activated electrons and holes in self-organized Ge/Si(001) islands in a multilayer structure

We investigated the temperature dependence (10-250 K) of the photoluminescence (PL) emission spectrum of self-organized Ge/Si(001) islands in a multilayer structure. With elevated temperature, we find that the thermally activated holes and electrons are gathered by the Ge islands in different ways. The holes drift from the wetting layer into the islands, while the electrons, confined in Si due to type-II band alignment, leak into the Ge islands by the electrostatic interaction with the holes accumulated there. It results in an increase of the integrated intensity of island-related PL at a certain temperature range and a reduction of the phonon energy in the phonon-assisted PL of the islands by involving a type-I transition into a type-II transition. (C) 2001 American Institute of Physics.