Investigation of flexoelectricity and ionic contamination in nematic liquid crystals

The work presented is a study of nematic liquid crystal physical properties. One of the phenomenon investigated is the bistability or in other words, the ability of the director of the material to rest in different orientations as function of the geometry of the sidewall. The main core of this research is the study of exoelectric effect and ionic contamination within the nematic layer. This can be split into three approaches. In the first part, the exoelectric coefficients are determined from the distortion of a nematic liquid crystal in response to non uniform electric fields created using an interdigitated electrode architecture. The distortion was deduced from the fringes movement in a Mach-Zhender interferometer built especially for this investigation. In the second part, the transient capacitance technique is used to measure the permittivity response of two homogeneous nematic materials subjected to different electric signal waveforms. The results remain to be fitted in order to give an alternative method to deduce the exoelectric coefficients values and a better understanding of the effect of ionic contamination. The last part of the work relates to the determination of the exoelectricity coefficients and ionic contamination and their effects on the Fréedericksz transition in homogeneous nematic liquid crystal using magnetic fields. The Mach-Zhender interferometer was also used to investigate two other phenomena, the first one is electrophoresis and the second is the resonance mode of insects

Flexoelectric polarisation effects in nematic liquid crystal phase gratings

Nematic phase gratings have been studied in which a planar nematic layer of thickness 17.2 μm is sandwiched between two glass substrates coated with an alignment polymer. The upper substrate is a continuous earth plane and the lower substrate has a patterned electrode of interdigitated stripes (electrodes and gaps are both 40 μm wide). Reorientation of the nematic liquid crystal occurs in response to d.c. electric fields applied between the interdigitated electrodes. These nematic reorientation regions have been used to investigate the influence of the flexoelectric polarisation in the nematic liquid crystal by observing the resultant (i) movement of tilt fringes in a Mach-Zehnder interferometer, and (ii) optical diffraction patterns. In the Mach-Zehnder interferometer the periodic variation of the refractive index resulting from the periodic distortion profile is measured directly from the displacement of the tilt fringes. The asymmetry in the response to positive and negative polarities of the d.c. voltage for both measurement techniques is directly related to the sum of the flexoelectric coefficients, e1 + e3

NMR-based metabonomics of bovine blood: an investigation into the effects of long term storage on plasma samples

Freezers in research institutions often contain a plethora of samples left over from studies performed years or even decades ago. Along with samples stored in biobanks, these could prove to be treasure troves for metabonomic research. Although the influence of sample handling and short to medium term storage on conventionally determined blood parameters has been reported, little is known about the effects of long term storage (years to decades) on plasma samples. The aim of this study was to investigate the influence of long term storage on the metabolite profile and to assess the value of archived samples for metabonomic studies. Heparinised plasma samples of 22 Holstein Friesian heifers that had been stored at -20°C for between 2 and 15 years were analysed using proton NMR spectroscopy and statistical analysis techniques. Lactate accounted for principal component one and explained 79.6% of variance between all spectra, but was not correlated with storage time. The highest correlation with storage time (R2 = 0.474) was found for betaine, with other metabolites (acetoacetate, histidines, glycerol, lipids and glucose) also showing moderate correlation (R2 values between 0.217 and 0.437). Our results indicate that samples stored for extended periods of time can potentially be used in metabolomics studies, if precautions are taken during data analysis

NMR CAPIBarA: proof of principle of a low-field unilateral magnetic resonance system for monitoring of the placenta during pregnancy

A growing body of literature shows that the transverse relaxation times of the placenta change during pregnancy and may be an early indicator of disease. Magnetic resonance imaging (MRI) of pregnant women is not, however, currently used frequently despite this evidence. One significant barrier to adoption is the cost of undertaking an MRI scan and the over utilization of existing equipment. Low-field nuclear magnetic resonance (NMR) offers a low-cost alternative, capable of measuring transverse relaxation in a single point in space. Ultrasound imaging (US) is routinely used at several points during pregnancy but is not capable of early detection of pre-eclampsia, for example. It does, however, provide a technique that is capable of locating the placenta with ease. In combination with a single point low-field measurement, localised with ultrasound imaging allows access to this exciting technique without the need for an expensive traditional MRI. In this work, we present a unilateral system (NMR CAPIBarA), operating at a magnetic field of only 18mT, which measures transverse relaxation times at distances from its surface equivalent to the positioning of a human placenta. Data are presented to characterise the system using relation time standards covering the full transverse relaxation time range relevant for the developing placenta, which are also measured on a 1.5 T clinical MRI scanner

Interferometric method for determining the sum of the flexoelectric coefficients (e1+e3) in an ionic nematic material

The time-dependent periodic distortion profile in a nematic liquid crystal phase grating has been measured from the displacement of tilt fringes in a Mach-Zehnder interferometer. A 0.2 Hz squarewave voltage was applied to alternate stripe electrodes in an interdigitated electrode geometry. The time-dependent distortion profile is asymmetric with respect to the polarity of the applied voltage and decays with time during each half period due to ionic shielding. This asymmetry in the response allows the determination of the sum of the flexoelectric coefficients (e1+e3) using nematic continuum theory since the device geometry does not possess inherent asymmetry

Effet de trois légumineuses de couverture sur l’assemblage des termites (Isoptera : Termitidae) dans les jachères au Centre Ouest de Côte d’Ivoire (Oumé)

Les termites contribuent pour beaucoup dans le recyclage de la matière organique des sols. Toutefois, avec le raccourcissement des cycles de jachère, on assiste à une diminution des espèces sur ces milieux. L’objectif de cette étude était d’apprécier l’effet de trois (3) plantes de couverture (Cajanus cajan, Mucuna pruriens et Pueraria phaseoloides) sur le mode d’assemblage des termites dans des jachères de 2 ans dans la région d’Oumé. Des mesures de la biodiversité des termites ont été effectuées sur des jachères non traitées en plantes légumineuses (témoin) et des jachères qui contiennent des légumineuses (traitée) selon la méthode d’estimation rapide des termites. Les résultats, obtenus montrent l’effet de la variabilité des plantes de couverture (P. phaseoloides et C. cajan) sur la richesse spécifique et l’abondance des termites. Aussi, la qualité de la litière en relation avec la composition du groupe trophique des termites a-t-elle été mise en évidence. Ceci par la présence de l’espèce Astalotermes sp1 fortement liée à la matière organique du sol. Ces observations révèlent que les jachères peuvent constituer des milieux de conservation de la biodiversité selon la durée de la mise en repos de ces sols.Mots clés: Plante de couverture, termite, jachèreEnglish Title:  Effect of tree land cover plants on termites (isoptera : termitidae) assembling in fallow : case of Cajanus cajan, Mucuna pruriens and Pueraria phaseoloides (fabaceae)English AbstractTermites contribute significantly in the recycling of organic matter in soils. However, with shorter of fallow cycles there is a decrease in the number of their species. The objective of this study was to evaluate the effect of three (3) land cover plants (Cajanus cajan, Mucuna pruriens and Pueraria phaseoloides) on the assembling of termites in 2 years fallow area in the region of Oumé. Measures of biodiversity for termites were performed on untreated fallows with land cover plants (control) and fallow which were also treated with land cover plants (processed) by the rapid method of termites’ estimation. The results obtained show the effect of the variability of the land cover plants (P. phaseoloides and C. cajan) on species richness and abundance of termites. Besides the quality of the litter in connection with the composition of the food group of termites has been demonstrated by the presence of the species of Astalotermes sp1 strongly related to soil organic matter. In sum, these observations show that fallow land may consist of shelter areas for the conservation of biodiversity depending on the time of the rest of these soils.Keywords: Land cover plant, termite, Fallo

A study of thermistor performance within a textile structure

Textiles provide an ideal structure for embedding sensors for medical devices. Skin temperature measurement is one area in which a sensor textile could be particularly beneficial; pathological skin is normally very sensitive, making the comfort of anything placed on that skin paramount. Skin temperature is an important parameter to measure for a number of medical applications, including for the early detection of diabetic foot ulcer formation. To this end an electronic temperature-sensor yarn was developed by embedding a commercially available thermistor chip into the fibres of a yarn, which can be used to produce a textile or a garment. As part of this process a resin was used to encapsulate the thermistor. This protects the thermistor from mechanical and chemical stresses, and also allows the sensing yarn to be washed. Building off preliminary work, the behaviour and performance of an encapsulated thermistor has been characterised to determine the effect of encapsulation on the step response time and absolute temperature measurements. Over the temperature range of interest only a minimal effect was observed, with step response times varying between 0.01–0.35 s. A general solution is presented for the heat transfer coefficient compared to size of the micro-pod formed by the encapsulation of the thermistor. Finally, a prototype temperature-sensing sock was produced using a network of sensing yarns as a demonstrator of a system that could warn of impending ulcer formation in diabetic patients

Intermittent aeration to improve wastewater treatment efficiency in pilot-scale constructed wetland

Forced aeration of horizontal subsurface flow constructed wetlands (HSSF CWs) is nowadays a recognized method to improve treatment efficiency, mainly in terms of ammonium removal. While numerous investigations have been reported testing constant aeration, scarce information can be found about the efficiency of intermittent aeration. This study aims at comparing continuous and intermittent aeration, establishing if there is an optimal regime that will increase treatment efficiency of HSSF CWs whilst minimizing the energy requirement. Full and intermittent aeration were tested in a pilot plant of three HSSF CWs (2.64 m2 each) fed with primary treated wastewater. One unit was fully aerated; one intermittently aerated (i.e. by setting a limit of 0.5 mg/L dissolved oxygen within the bed) with the remaining unit not aerated as a control. Results indicated that intermittent aeration was the most successful operating method. Indeed, the coexistence of aerobic and anoxic conditions promoted by the intermittent aeration resulted in the highest COD (66%), ammonium (99%) and total nitrogen (79%) removals. On the other hand, continuous aeration promotes ammonium removal (99%), but resulted in nitrate concentrations in the effluent of up to 27 mg/L. This study demonstrates the high potential of the intermittent aeration to increase wastewater treatment efficiency of CWs providing an extreme benefit in terms of the energy consumption

Phenotypic Correlation and Path Coefficient and Relative Importance Studies in Okra Abelmoschus esculentus (L.) Moench.

The experiment was undertaken to study correlation and path coefficient and relatively importance to yield and its components traits in Okra. The experimental material consisted of six generations (P1, P2, F1, F2, BC1 and BC2) through two crosses, which were evaluated in Completely Randomized Block Design (RCBD) with three replications at the Agriculture Scientific Center in Latakia during the summer of 2020. The result of phenotypic correlation revealed that yield per plant had positively significant correlation with fruit diameter (0.53), positively highly significant correlation with fruit weight (0.65), and negatively highly significant correlation with days for first flowering and days to 50% flowering (-0.56, -0.63), respectively in the first hybrid (Lathkani 6× Lathkani 10). In the second hybrid (Lathkani 7× Lathkani 9), yield per plant has exhibited positively and highly significant correlation with numbers of fruit per plant, numbers of flowers per plant, fruit length, fruit diameter and fruit weight (0.95, 0.96, 0.76, 0.65, 0.64), respectively. The high positively direct effect on yield per plant was contributed by fruit weight followed by days to 50% flowering in the first hybrid. Numbers of fruits per plant had desirably direct effect on yield per plant in the second hybrid. Hence, direct selection based on these traits would result in simultaneous improvement of previously mentioned traits and yield in Okra

Phenotypic Correlation and Path Coefficient and Relative Importance Studies in Okra Abelmoschus esculentus (L.) Moench.

The experiment was undertaken to study correlation and path coefficient and relatively importance to yield and its components traits in Okra. The experimental material consisted of six generations (P1, P2, F1, F2, BC1 and BC2) through two crosses, which were evaluated in Completely Randomized Block Design (RCBD) with three replications at the Agriculture Scientific Center in Latakia during the summer of 2020. The result of phenotypic correlation revealed that yield per plant had positively significant correlation with fruit diameter (0.53), positively highly significant correlation with fruit weight (0.65), and negatively highly significant correlation with days for first flowering and days to 50% flowering (-0.56, -0.63), respectively in the first hybrid (Lathkani 6× Lathkani 10). In the second hybrid (Lathkani 7× Lathkani 9), yield per plant has exhibited positively and highly significant correlation with numbers of fruit per plant, numbers of flowers per plant, fruit length, fruit diameter and fruit weight (0.95, 0.96, 0.76, 0.65, 0.64), respectively. The high positively direct effect on yield per plant was contributed by fruit weight followed by days to 50% flowering in the first hybrid. Numbers of fruits per plant had desirably direct effect on yield per plant in the second hybrid. Hence, direct selection based on these traits would result in simultaneous improvement of previously mentioned traits and yield in Okra