Polarization control and sensing with two-dimensional coupled photonic crystal microcavity arrays

We have experimentally studied polarization properties of the two-dimensional coupled photonic crystal microcavity arrays, and observed a strong polarization dependence of the transmission and reflection of light from the structures - the effects that can be employed in building miniaturized polarizing optical components. Moreover, by combining these properties with a strong sensitivity of the coupled bands on the surrounding refractive index, we have demonstrated a detection of small refractive index changes in the environment, which is useful for construction of bio-chemical sensors.Comment: 8 pages text and 4 figures on 4 pages. Submitted for publication on 07/14/0

Constructing Minority Representation: Empirical-Theoretical Study

Performance and performativity are deeply entwined in political representation. This research explores the performance of minority representation – i.e., how representatives from ethnic minority backgrounds shape their positions and deliver their claims about and for minorities depending on the audience they address – and the performativity of their representative claims – i.e., how they contribute to the construction of ethnic identities and interests, which they purportedly merely describe or present. In doing so, the thesis reuses, tests and expands the increasingly influential theoretical understanding of representation as claim-making, while, at the same time, it effects a much-needed constructivist turn in the empirical study of the representation of ethnic minorities. In theoretical terms, the dissertation argues that the categories of descriptive and substantive representation remain essential to the study of minority representation. Its contribution to the theoretical literature is in reconceptualising these categories in line with the constructivist turn. The constructivist understanding of political representation has had considerable theoretical impact, but limited operationalization and empirical application. When applied to the study of group representation, the representation of gender has commanded attention. The thesis breaks new ground in applying it to the study of the representation of minority ethnic groups, a field in which the traditional understanding of representation as responsiveness to the pre-given demands and interests of constituents remains dominant. Focusing on two similar cases where ethnicity has been historically and institutionally constructed as a relevant feature to be represented in political forums, this thesis shows that rather than factors determining the behaviour of representatives, institutional and cultural backgrounds can be, and are often, deployed creatively as resources in the claim-making process whereby ethnic identifications are produced and reproduced over time

Modal analysis of waveguides based on a triangular photonic crystal lattice

We have performed modal analysis of both conventional single line defect waveguides and proposed "narrowed" waveguides. We have shown that the proposed structure has fewer guided modes than the conventional one, and based on the dispersion diagram-type analysis, we predict that it will have better coupling properties. At present we are working on the experimental verification of these properties. We are also engaged in the quantitative experimental verification of the predicted high transmission efficiency around sharp bends in the photonic crystal waveguides

The effect of mushroom culture filtrates on the inhibition of mycotoxins produced by Aspergillus flavus and Aspergillus carbonarius

Two of the mycotoxins of greatest agroeconomic significance are aflatoxin B-1 (AFB(1)), and ochratoxin A (OTA). It has been reported that extracts from some wood-decaying mushrooms, such as Lentinula edodes and Trametes versicolor showed the ability to inhibit AFB(1) or OTA biosynthesis. Therefore, in our study, a wide screening of 42 isolates of different ligninolytic mushrooms was assayed for their ability to inhibit the synthesis of OTA in Aspergillus carbonarius and AFB(1) in Aspergillus flavus, in order to find a metabolite that can simultaneously inhibit both mycotoxins. The results showed that four isolates produce metabolites able to inhibit the synthesis of OTA, and 11 isolates produced metabolites that inhibited AFB(1) by >50%. Two strains, the Trametes versicolor strain TV117 and the Schizophyllum commune strain S.C. Ailanto, produced metabolites able to significantly inhibit (>90%) the synthesis of both mycotoxins. Preliminary results suggest that the mechanism of efficacy of the S. commune rough and semipurified polysaccharides could be analogous to that found previously for Tramesan(R), by enhancing the antioxidant response in the target fungal cells. The overall results indicate that S. commune's polysaccharide(s) could be a potential agent(s) in biological control and/or a useful component of the integrated strategies able to control mycotoxin synthesis

Nanobeam photonic crystal cavity quantum dot laser

The lasing behavior of one dimensional GaAs nanobeam cavities with embedded InAs quantum dots is studied at room temperature. Lasing is observed throughout the quantum dot PL spectrum, and the wavelength dependence of the threshold is calculated. We study the cavity lasers under both 780 nm and 980 nm pump, finding thresholds as low as 0.3 uW and 19 uW for the two pump wavelengths, respectively. Finally, the nanobeam cavity laser wavelengths are tuned by up to 7 nm by employing a fiber taper in near proximity to the cavities. The fiber taper is used both to efficiently pump the cavity and collect the cavity emission.Comment: 8 pages; 6 figure

Nanophotonics based on planar photonic crystals

By creating different types of defects in the photonic crystal lattice, various nanophotonics components, such as cavities and waveguides, can be realized. The quest for a compact and efficient nano-cavity, with high quality factor (Q) and small mode volume (V/sub mode/), has been a central part of research in integrated optics. Recently, we have proposed a systematic method to design optical nano-cavities that satisfy both of these requirements. The cavity consists of a defect hole that is smaller than surrounding holes arranged in the triangular lattice photonic crystal. In order to test our design we have fabricated high-Q cavities in the InGaAsP material system

Electrically controlled modulation in a photonic crystal nanocavity

We describe a compact modulator based on a planar photonic crystal nanocavity whose resonance is electrically controlled. A forward bias applied across a p-i-n diode shifts the cavity into and out of resonance with a continuous-wave laser field in a waveguide. The sub-micron size of the nanocavity promises extremely low capacitance, high bandwidth, and efficient on-chip integration in optical interconnects.Comment: 9 pages, 4 figure

Political Representation of National Minorities: A Case Study of Minority Parties in Serbia

This thesis explores the relationship between descriptive and substantive representation of national minorities. Previous studies have emphasized the importance of descriptive representation and justified the need for affirmative action measures such as reserved seats or a lower electoral threshold to achieve descriptive representation. However, this thesis differs in claiming that substantive representation of minority interests is equally, if not more, important than descriptive representation. It is argued throughout the thesis that an equal right to political representation consists of the right to be present (descriptive representation) and the right to representation of interests and perspectives (substantive representation). Although mere presence of minority representatives might have some symbolic benefits, members of minority groups primarily need the representatives to act in their interests and attempt to influence public policies. Hence, this thesis provides an answer to two important and yet insufficiently researched questions: is descriptive representation a sufficient condition for substantive and if not, in what conditions can descriptive representatives act as substantive? In aim to understand in what conditions can descriptive representatives act as substantive, this research provides an empirical analysis of the behaviour of the representatives of minority parties in the VIII National Assembly of the Republic of Serbia. More particularly, the analysis includes content analysis of all interventions in plenary parliamentary debates of the 12 national minority MPs in the period between June 2008 and May 2012. The research shows that the relationship between descriptive and substantive representation differs across minority parties. Two groups of MPs can be distinguished from the data: MPs elected on minority electoral lists creating parliamentary group of national minorities in parliament and those who were elected through pre-electoral arrangements with mainstream political parties. It is concluded that minority political parties are not a priori substantive representatives of national minorities and that descriptive representatives elected on minority electoral lists perform better as substantive representatives than descriptive representatives elected on electoral list of mainstream parties. Finally, some institutional changes are suggested which could enhance substantive representation of national minorities

Mushroom exo-polysaccharides as control agents of aflatoxin and ochratoxin. A biosynthesis

Preliminary results of the influence of Schizophyllum commune polysaccharides on the inhibition of mycotoxin synthesis in Aspergillus flavus and Aspergillus carbonarius Jelena Loncar1,3, Slaven Zjalić1 , Paola Cescutti2 Alice Motola 3, Massimo Reverberi3 1) Department of Ecology, Aquaculture and Agriculture, University of Zadar, Mihovila Pavlinovića 1, 23 000 Zadar, Croatia 2) Department of Life Sciences, University of Trieste, Via Licio Giorgieri 1, 34127 Trieste, Italy 3) Department of Environmental Biology, Sapienza University of Rome, P.le Aldo Moro 5, 00185 Rome, Italy Abstract There has been interest in the use of mushroom polysaccharides to control the synthesis of key mycotoxins in staple commodities. Tramesan(c), an exo-polysaccharide produced by Trametes versicolor, is among the most efficient and studied ones. The objective of the present study were to analyse the effects of secreted polysaccharides of Schizophyllum commune on production of aflatoxin B1 (AFB1) and ochratoxin A (OTA) produced by Aspergillus flavus and Aspergillus carbonarius respectively. Comparison of the effects of commercial schizophyllan and partialy purified S. commune polysaccharides indicated that the inhibition of AFB1 and OTA synthesis may be due to other types of polysaccharide(s) rather than schizophyllan. Preliminary results suggest that the mechanism of efficacy of the S. commune polysaccharides could be analogous to that found previously for Tramesan®, i.e., by enhancing the antioxidant response in the target fungal cells.Oligosaccharides derived from Tramesan: their structure and activity on mycotoxin inhibition in Aspergillus flavus and Aspergillus carbonarius Jelena Loncar1,3, Barbara Bellich2, Paola Cescutti2, Roberto Rizzo2, Slaven Zjalić1, Alessia Parroni3, Massimo Reverberi3 1) Department of Ecology, Aquaculture and Agriculture, University of Zadar, Mihovila Pavlinovića 1, 23 000 Zadar, Croatia 2) Deptartment of Life Sciences, University of Trieste, Via Licio Giorgieri 1, 34127 Trieste, Italy 3) Department of Environmental Biology, Sapienza University of Rome, P.le Aldo Moro 5, 00185 Rome, Italy Abstract Food and feed safety, due to its direct influence on human health, has acquired a paramount relevance in everyday life. The awareness that different chemicals, e.g., those largely used in agriculture to control pests, could present both environmental problems and health hazards, has led to a large limitation of their use. Since 2014, the European Community (EC) has banned about 50% of crop protection chemicals used in agriculture. In plant cultivation, chemicals were also the main tool used against fungal pathogens and against the contamination of food/feed stuff with toxic secondary metabolites, mycotoxins. There is thus a drive to develop more environmentally friendly “green” approaches and eco-compatible tools to control mycotoxigenic fungi and toxin contamination of staple foodstuffs. Different mushroom metabolites showed the potential to act as control agents against fungal growth and mycotoxin production. This study has examined the use of a polysaccharide Tramesan, extracted from the basidiomycete Trametes versicolor for controlling mycotoxin biosynthesis by Aspergillus flavus (aflatoxin B1) and Aspergillus carbonarius (ochratoxin A). This study evaluated component of the repeating unit of the polysaccharide produced by T. versicolor which was active in inhibition of aflatoxin B1 synthesis. The purified exopolysaccharide of T. versicolor was partially hydrolyzed and separated by column chromatography into fractions from disaccharides to heptasaccharides. Each fraction was individually tested for mycotoxin inhibition in A. flavus and A. carbonarius. Although fragments smaller than seven units showed no significant effect on mycotoxin inhibition, heptasaccharides showed inhibitory activity of up to 90% in both fungi. These results indicated that these compounds could be used as natural alternatives to crop protection chemicals for control of these two mycotoxins in economically important commodities.Effect of mushroom culture filtrates on inhibition of mycotoxins produced by Aspergillus flavus and Aspergillus carbonarius Jelena Loncar1,3, Barbara Bellich2, Paola Cescutti2, Alice Motola3, Slaven Zjalić1, Massimo Reverberi3 1) Department of Ecology, Aquaculture and Agriculture, University of Zadar, Mihovila Pavlinovića 1, 23 000 Zadar, Croatia 2) Deptartment of Life Sciences, University of Trieste, Via Licio Giorgieri 1, 34127 Trieste, Italy 3) Department of Environmental Biology, Sapienza University of Rome, P.le Aldo Moro 5, 00185 Rome, Italy Abstract Mycotoxins are secondary metabolites produced by certain fungi that have hazardous effects on humans and animals, which in turn result in disease and economic losses. Two of the mycotoxins of greatest public health and agroeconomic significance are aflatoxin B1 (AFB1), and ochratoxin A (OTA). There is a need for the development of natural compounds for the control of these mycotoxins in food and feed. There has been interest in the use of mushroom polysaccharides for controlling mycotoxins. In this study 42 isolates of different ligninolytic mushrooms were assayed for their ability to inhibit the synthesis of OTA and AFB1. The results showed that 23 strains produce metabolites able to inhibit the synthesis of OTA by >20%, and 32 strains that produced metabolites that inhibited AFB1. Only two strains, Trametes versicolor strain TV117 and Schizophyllum commune strain S.C. Ailanto, produced metabolites able to significantly inhibit (>90%) the synthesis of both mycotoxins. It is known that T. versicolor produces a polysaccharide Tramesan, able to inhibit the synthesis of AFB1 and was probably responsible for mycotoxin inhibition. The results suggest that S. commune metabolites were able to inhibit both OTA and AFB1 synthesis may be based on polysaccharides