Determination of mechanical stress distribution in Drosophila wing discs using photoelasticity

Morphogenesis, the process by which all complex biological structures are formed, is driven by an intricate interplay between genes, growth, as well as intra- and intercellular forces. While the expression of different genes changes the mechanical properties and shapes of cells, growth exerts forces in response to which tissues, organs and more complex structures are shaped. This is exemplified by a number of recent findings for instance in meristem formation in Arabidopsis and tracheal tube formation in Drosophila. However, growth not only generates forces, mechanical forces can also have an effect on growth rates, as is seen in mammalian tissues or bone growth. In fact, mechanical forces can influence the expression levels of patterning genes, allowing control of morphogenesis via mechanical feedback. In order to study the connections between mechanical stress, growth control and morphogenesis, information about the distribution of stress in a tissue is invaluable. Here, we applied stress-birefringence to the wing imaginal disc of Drosophila melanogaster, a commonly used model system for organ growth and patterning, in order to assess the stress distribution present in this tissue. For this purpose, stress-related differences in retardance are measured using a custom-built optical set-up. Applying this method, we found that the stresses are inhomogeneously distributed in the wing disc, with maximum compression in the centre of the wing pouch. This compression increases with wing disc size, showing that mechanical forces vary with the age of the tissue. These results are discussed in light of recent models proposing mechanical regulation of wing disc growth

Dynamic roughening of the magnetic flux landscape in YBa2_2Cu3_3O7−x_{7-x}

We study the magnetic flux landscape in YBa$_2$Cu$_3$O$_{7-x}$ thin films as a two dimensional rough surface. The vortex density in the superconductor forms a self-affine structure in both space and time. This is characterized by a roughness exponent $\alpha = 0.76(3)$ and a growth exponent $\beta = 0.57(6)$. This is due to the structure and distribution of flux avalanches in the self-organized critical state, which is formed in the superconductor. We also discuss our results in the context of other roughening systems in the presence of quenched disorder.Comment: 13 pages, 7 figures, accepted for publication in Physica

Modeling and Satellite Remote Sensing of the Meteorological Impacts of Irrigation During the 2012 Central Plains Drought

As irrigation is increasingly needed for agricultural production, it is becoming progressively more important to understand not only how irrigation impacts water availability, but how the introduction of this water into the soil impacts weather and climate through land-atmosphere interactions. In the summer of 2012, the Central Plains of the United States experienced one of its most severe droughts on record. This study examines the meteorological impacts of irrigation during this drought through observations and model simulations using the Community Land Model (CLM) coupled to the Weather Research and Forecasting (WRF) model. A simple parameterization of irrigation processes is added into the WRF model. In addition to keeping soil moisture in irrigated areas at a minimum of 50% of soil moisture capacity, this irrigation scheme also has the following new features: (1) accurate representation of the spatial distribution of irrigation area in the study domain by using MODIS-based 250-m resolution land surface classification; and (2) improved representation of the time series of leaf area index (LAI) values derived from crop modeling and satellite observations in both irrigated and non-irrigated areas. Several numerical sensitivity experiments are conducted. The WRF-simulated temperature field when including soil moisture and LAI modification within the model is shown to be most consistent with ground and satellite observations, all indicating a 2-3 K decrease of temperature in irrigated areas compared to the control run. Modification of leaf area index in irrigated and dryland areas led to smaller changes, with a 0.2 K temperature decrease in irrigated areas and up to a 0.5 K temperature increase in dryland areas. Furthermore, the increased soil moisture and modified leaf area index is shown to lead to increases in surface divergence, increases in surface pressure, and decreases in planetary boundary layer height over irrigated areas. Advisor: Jun Wan

Threshing Dinner

It was threshing day at Frank Andrew\u27s place. The yard was filled with horses and racks and wagons..

Modeling and Satellite Remote Sensing of the Meteorological Impacts of Irrigation During the 2012 Central Plains Drought

As irrigation is increasingly needed for agricultural production, it is becoming progressively more important to understand not only how irrigation impacts water availability, but how the introduction of this water into the soil impacts weather and climate through land-atmosphere interactions. In the summer of 2012, the Central Plains of the United States experienced one of its most severe droughts on record. This study examines the meteorological impacts of irrigation during this drought through observations and model simulations using the Community Land Model (CLM) coupled to the Weather Research and Forecasting (WRF) model. A simple parameterization of irrigation processes is added into the WRF model. In addition to keeping soil moisture in irrigated areas at a minimum of 50% of soil moisture capacity, this irrigation scheme also has the following new features: (1) accurate representation of the spatial distribution of irrigation area in the study domain by using MODIS-based 250-m resolution land surface classification; and (2) improved representation of the time series of leaf area index (LAI) values derived from crop modeling and satellite observations in both irrigated and non-irrigated areas. Several numerical sensitivity experiments are conducted. The WRF-simulated temperature field when including soil moisture and LAI modification within the model is shown to be most consistent with ground and satellite observations, all indicating a 2-3 K decrease of temperature in irrigated areas compared to the control run. Modification of leaf area index in irrigated and dryland areas led to smaller changes, with a 0.2 K temperature decrease in irrigated areas and up to a 0.5 K temperature increase in dryland areas. Furthermore, the increased soil moisture and modified leaf area index is shown to lead to increases in surface divergence, increases in surface pressure, and decreases in planetary boundary layer height over irrigated areas. Advisor: Jun Wan

New developments and applications in sol-gel coatings

In this overview we describe some recent developments of technological interest realized at INM in the processing of sol-gel coatings. Nanoscale crystalline particles, fully redispersed in aqueous solutions, have been developed to produce thin ceramic layers at low temperature. As an example, antistatic optical coatings and conducting membranes based on SnO2:Sb material are reported. New wet chemical processes have been developed to extend the sol-gel basic principles for the coating of oxide compounds on plastic (biomimetic process) and sulfide materials (MoS2). Also ink-jet and pad printing processes, well established in other fields, have been adapted for the development of micro structured coatings. As examples, the realization of single and arrays of spherical and cylindrical refractive microlenses is presented. Finally non conventional sintering process using high power CO2 laser is exemplified for the obtention of optical quality transparent conducting coatings under high sintering rate (30 cm2/s)