Light Engineering of the Polariton Landscape in Semiconductor Microcavities

We demonstrate a method to create potential barriers with polarized light beams for polaritons in semiconductor microcavities. The form of the barriers is engineered via the real space shape of a focalised beam on the sample. Their height can be determined by the visibility of the scattering waves generated in a polariton fluid interacting with them. This technique opens up the way to the creation of dynamical potentials and defects of any shape in semiconductor microcavities.Comment: 4 pages, 5 figure

Analysis of the start to the first hurdle in 110m hurdles at the IAAF World Athletics Championships Beijing 2015

The purpose of this study was to use observational analysis to evaluate the relationships between variables measured at the start of the men’s 110 hurdles event and race performance itself. Data were obtained for competitors in 2015 IAAF World Athletics Ch ampionships, in Beijing, China. The athletes’ start was quantified by reaction time and time to the first hurdle; their action over the first hurdle was quantified by the take - off distance (i.e., the distance from the last step to the first hurdle), the la nding distance, and the total distance in the air over the first hurdle. Regression analyses revealed that the combination of one measure of the start (either reaction time or time to the first hurdle) and the measure of propulsion over the first hurdle (d istance in air over the first hurdle) predicted performance (SEE = 0.23 s in the heats, SEE = 0.16 s in the semi - finals, SEE = 0.09 s in the finals). In addition, looking at performances in the finals, where all athletes with available data used a seven - st ep approach to the first hurdle, inclusion of stride length data improved the prediction somewhat (SEE = 0.07 s). The results demonstrate that a combination of a fast start, rapid acceleration, and strong drive over the first hurdle quantifiably explains a nd contributes to performance in the men’s 110 m hurdles at the highest level

Aspects of the biology of Ephestia cautella and Tribolium castaneum on fermented stored cocoa beans

 Ephestia cautella (Walker) (Lepidotera: Pyralidae) and Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) are pests associated with dried fermented stored cocoa beans that cause extensive damage. The biology of these pests on cocoa beans in Ghana has not been well documented, especially on T. castaneum. Due to climate changes and improved/hybrid seedlings being released to farmers, it has become necessary to re-evaluate the biology and damage of these pests on fermented stored cocoa beans. The experiments were conducted in the Insectary laboratory of the Department of Crop and Soil Sciences, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana. Paired 0-1 day old E. cautella adults were placed in Petri dishes and covered with Kilner jars. The eggs laid daily by each female were carefully transferred onto 15 g cocoa beans in Petri dishes. The egg incubation period was four days, 31 days larval period and the pupal period of seven days. Unmated adult males lived for 12.1 days and females 7.9; mated males lived for 10.9 days and females 5.5. Paired T. castaneum were introduced on 2.0 g broken cocoa beans in Petri dishes. The average incubation period was nine days, 40 days larval period, and pupal period of five days

Assessment of damage caused by Ephestia cautella (Walker) to stored cocoa beans

Ephestia cautella is one of the most common storage pests of stored cocoa beans. When left uncontrolled it can cause extensive damage to stored dried cocoa beans. Increased Free Fatty Acid levels (FFA) affect the fat structure and reduce the hardness of cocoa butter. Insects have been found to be a contributory factor to the increased levels of FFA. Inadequate studies have been done exclusively on the influence of E. cautella. The study was to evaluate extent of damage of E. cautella and its impact on the FFA levels, Experiments were conducted under temperature and relative humidity ranges of 27 °C – 36.5 °C and 40 – 85 percent, respectively, in the Insectary building of the Department of Crop and Soil Sciences, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana and Quality Control Division of COCOCBOD, Tema, Ghana. Thirty six mini sacks, each containing 400 g of cocoa beans stackes were grouped into four, and placed in a transparent cage measuring 65 cm length × 65 cm width and 75 cm high. Each group had a pile up stack of three, placed side by side, totaling nine mini sacks per group. Twenty newly emerged E. cautella were released into the cage and damaged assessed monthly up to a period of 4 months. The damage caused included significant decrease in weight loss and increase in Free Fatty Acid levels to stored cocoa beans over a period of 4 months. The mean percentage damage to cocoa beans by E. cautella were 10.31 and 29.05 in the first and fourth months, respectively, with corresponding percentage weight losses of 1.21 and 6.53. There were high levels of FFA in damaged beans caused by E. cautella as compared to the controlled beans. The FFA levels in the controlled beans were all below 1 percent, whilst the FFA levels in E. cautella infested beans were above the threshold of 1.75 percent aside month 1. Thus, E. cautella infestation caused increased levels of FFA within stored cocoa beans. There was a strong positive correlation among insect numbers monthly, percentage damage, weight loss and free fatty acid

Dynamics of formation and decay of coherence in a polariton condensate

We study the dynamics of formation and decay of a condensate of microcavity polaritons. We investigate the relationship between the number of particles, the emission's linewidth and its degree of linear polarization which serves as the order parameter. Tracking the condensate's formation, we show that, even when interactions are negligible, coherence is not determined only by occupation of the ground state. As a result of the competition between the coherent and thermal fractions of the condensate, the highest coherence is obtained some time after the particle number has reached its maximum

An acoustic black hole in a stationary hydrodynamic flow of microcavity polaritons

We report an experimental study of superfluid hydrodynamic effects in a one-dimensional polariton fluid flowing along a laterally patterned semiconductor microcavity and hitting a micron-sized engineered defect. At high excitation power, superfluid propagation effects are observed in the polariton dynamics, in particular, a sharp acoustic horizon is formed at the defect position, separating regions of sub- and super-sonic flow. Our experimental findings are quantitatively reproduced by theoretical calculations based on a generalized Gross-Pitaevskii equation. Promising perspectives to observe Hawking radiation via photon correlation measurements are illustrated.Comment: 5 pages Main + 5 pages Supplementary, 8 figure