Nematic liquid crystal alignment on chemical patterns

Patterned Self-Assembled Monolayers (SAMs) promoting both homeotropic and planar degenerate alignment of 6CB and 9CB in their nematic phase, were created using microcontact printing of functionalised organothiols on gold films. The effects of a range of different pattern geometries and sizes were investigated, including stripes, circles and checkerboards. EvanescentWave Ellipsometry was used to study the orientation of the liquid crystal (LC) on these patterned surfaces during the isotropic-nematic phase transition. Pretransitional growth of a homeotropic layer was observed on 1 ¹m homeotropic aligning stripes, followed by a homeotropic mono-domain state prior to the bulk phase transition. Accompanying Monte-Carlo simulations of LCs aligned on nano-patterned surfaces were also performed. These simulations also showed the presence of the homeotropic mono-domain state prior to the transition.</p

Simultaneous detection and identification of pathogenic fungi in wheat using a DNA macroarray

The detection of economically important pathogens is a key element in sustainable wheat production and a prerequisite for crop protection. The objective of the project was to develop a DNA macroarray for fast and cost-effective detection of nine pathogenic fungi in wheat: Fusarium graminearum, Fusarium culmorum, Fusarium poae, Microdochium nivale var. majus, Microdochium nivale var. nivale, Puccinia recondita, Septoria tritici, Septoria nodorum and Pyrenophora tritici-repentis. Methodically, a macroarray is similar to a microarray but without the need for expensive equipment. PCR labelled samples of DNA are hybridized to pathogen-specific oligonucleotides (probes) anchored to a solid support. A positive reaction between an amplicon and a perfectly matched oligonucleotide generates a chemiluminescent signal which can be detected by a plate reader. The macroarray is sensitive enough to detect single nucleotide polymorphism (SNPs). Sample analysis is simple, fast, cost-effective, fully automated and suitable for high throughput screening. In this project, the nine wheat pathogens were detected within 6 hours simultaneously in a single sample using between one to four different species-specific probes for each pathogen. Species-specific detector oligonucleotides were designed based on the β-tubulin and/or succinate dehydrogenase region of fungal DNA. The detection limit of the DNA macroarray technique particularly depends on the pathogen-specific oligonucleotides deployed. The necessity for monitoring pathogenic fungi in wheat production and for prediction of crop yield has been recognized for a long time. The DNA macroarray responds very sensitively and has the potential to recognize pathogenic fungi earlier with reference to the cultivation period than a conventional PCR. This means that the DNA macroarray can detect genomic DNA from fungi in a lower potency than the conventional PCR. One benefit of the DNA macroarray for detection of fungal pathogens in wheat is its increased specificity and the other its application to a large number of microorganisms which can be detected in a single assay. This technology has been proven to be relatively cost-effective compared with real-time PCR or microarrays. This project was financially supported by the Commission of Technology and Innovation CTI in Berne, Switzerland

Large Coherence Area Thin-Film Photonic Stop-Band Lasers

We demonstrate that the shift of the stop band position with increasing oblique angle in periodic structures results in a wide transverse exponential field distribution corresponding to strong angular confinement of the radiation. The beam expansion follows an effective diffusive equation depending only upon the spectral mode width. In the presence of gain, the beam cross section is limited only by the size of the gain area. As an example of an active periodic photonic medium, we calculate and measure laser emission from a dye-doped cholesteric liquid crystal film

Deep asteroseismic sounding of the compact hot B subdwarf pulsator KIC02697388 from Kepler time series photometry

peer reviewedContext. Contemporary high precision photometry from space provided by the Kepler and CoRoT satellites generates significant breakthroughs in terms of exploiting the long-period, g-mode pulsating hot B subdwarf (sdBVs) stars with asteroseismology. Aims: We present a detailed asteroseismic study of the sdBVs star KIC02697388 monitored with Kepler, using the rich pulsation spectrum uncovered during the ~27-day-long exploratory run Q2.3. Methods: We analyse new high-S/N spectroscopy of KIC02697388 using appropriate NLTE model atmospheres to provide accurate atmospheric parameters for this star. We also reanalyse the Kepler light curve using standard prewhitening techniques. On this basis, we apply a forward modelling technique using our latest generation of sdB models. The simultaneous match of the independent periods observed in KIC02697388 with those of models leads objectively to the identification of the pulsation modes and, more importantly, to the determination of some of the parameters of the star. Results: The light curve analysis reveals 43 independent frequencies that can be associated with oscillation modes. All the modulations observed in this star correspond to g-mode pulsations except one high-frequency signal, which is typical of a p-mode oscillation. Although the presence of this p-mode is surprising considering the atmospheric parameters that we derive for this cool sdB star (Teff = 25 395 ± 227 K, log g = 5.500 ± 0.031 (cgs), and log N(He) /N(H) = -2.767 ± 0.122), we show that this mode can be accounted for particularly well by our optimal seismic models, both in terms of frequency match and nonadiabatic properties. The seismic analysis leads us to identify two model solutions that can both account for the observed pulsation properties of KIC02697388. Despite this remaining ambiguity, several key parameters of the star can be derived with stringent constraints, such as its mass, its H-rich envelope mass, its radius, and its luminosity. We derive the properties of the core proposing that it is a relatively young sdB star that has burnt less than ~34% (in mass) of its central helium and has a relatively large mixed He/C/O core. This latter measurement is in line with the trend already uncovered for two other g-mode sdB pulsators analysed with asteroseismology and suggests that extra mixing is occurring quite early in the evolution of He cores on the horizontal branch. Conclusions: Additional monitoring with Kepler of this particularly interesting sdB star should reveal the inner properties of KIC02697388 and provide important information about the mode driving mechanism and the helium core properties

A First Comparison of Kepler Planet Candidates in Single and Multiple Systems

In this letter we present an overview of the rich population of systems with multiple candidate transiting planets found in the first four months of Kepler data. The census of multiples includes 115 targets that show 2 candidate planets, 45 with 3, 8 with 4, and 1 each with 5 and 6, for a total of 170 systems with 408 candidates. When compared to the 827 systems with only one candidate, the multiples account for 17 percent of the total number of systems, and a third of all the planet candidates. We compare the characteristics of candidates found in multiples with those found in singles. False positives due to eclipsing binaries are much less common for the multiples, as expected. Singles and multiples are both dominated by planets smaller than Neptune; 69 +2/-3 percent for singles and 86 +2/-5 percent for multiples. This result, that systems with multiple transiting planets are less likely to include a transiting giant planet, suggests that close-in giant planets tend to disrupt the orbital inclinations of small planets in flat systems, or maybe even to prevent the formation of such systems in the first place.Comment: 13 pages, 13 figures, submitted to ApJ Letter

Determination of the director profile in a nematic cell from guided wave data: an inverse problem

Copyright © 2007 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. This is the published version of an article published in New Journal of Physics Vol. 9, article 166. DOI: 10.1088/1367-2630/9/6/166We consider an inverse problem: the estimation of the nematic director profile from experimental fully leaky guided mode data. This inverse problem is ill-posed in that small changes in the data may lead to large changes in the estimates of the director profile. The continuum equations for a nematic are exploited to stabilize the problem. We use experimental data drawn from a study of the dynamics of a hybrid-aligned nematic cell as an example

TESS Discovery of a Transiting Super-Earth in the π\pi Mensae System

We report the detection of a transiting planet around $\pi$ Mensae (HD 39091), using data from the Transiting Exoplanet Survey Satellite (TESS). The solar-type host star is unusually bright (V=5.7) and was already known to host a Jovian planet on a highly eccentric, 5.7-year orbit. The newly discovered planet has a size of $2.04\pm 0.05$ $R_\oplus$ and an orbital period of 6.27 days. Radial-velocity data from the HARPS and AAT/UCLES archives also displays a 6.27-day periodicity, confirming the existence of the planet and leading to a mass determination of $4.82\pm 0.85$ $M_\oplus$. The star's proximity and brightness will facilitate further investigations, such as atmospheric spectroscopy, asteroseismology, the Rossiter--McLaughlin effect, astrometry, and direct imaging.Comment: Accepted for publication ApJ Letters. This letter makes use of the TESS Alert data, which is currently in a beta test phase. The discovery light curve is included in a table inside the arxiv submissio

A uniform asteroseismic analysis of 22 solar-type stars observed by Kepler

Asteroseismology with the Kepler space telescope is providing not only an improved characterization of exoplanets and their host stars, but also a new window on stellar structure and evolution for the large sample of solar-type stars in the field. We perform a uniform analysis of 22 of the brightest asteroseismic targets with the highest signal-to-noise ratio observed for 1 month each during the first year of the mission, and we quantify the precision and relative accuracy of asteroseismic determinations of the stellar radius, mass, and age that are possible using various methods. We present the properties of each star in the sample derived from an automated analysis of the individual oscillation frequencies and other observational constraints using the Asteroseismic Modeling Portal (AMP), and we compare them to the results of model-grid-based methods that fit the global oscillation properties. We find that fitting the individual frequencies typically yields asteroseismic radii and masses to \sim1% precision, and ages to \sim2.5% precision (respectively 2, 5, and 8 times better than fitting the global oscillation properties). The absolute level of agreement between the results from different approaches is also encouraging, with model-grid-based methods yielding slightly smaller estimates of the radius and mass and slightly older values for the stellar age relative to AMP, which computes a large number of dedicated models for each star. The sample of targets for which this type of analysis is possible will grow as longer data sets are obtained during the remainder of the mission.Comment: 13 pages, 5 figures in the main text, 22 figures in Appendix. Accepted for publication in Ap