Anisotropic colloids through non-trivial buckling

We present a study on buckling of colloidal particles, including experimental, theoretical and numerical developments. Oil-filled thin shells prepared by emulsion templating show buckling in mixtures of water and ethanol, due to dissolution of the core in the external medium. This leads to conformations with a single depression, either axisymmetric or polygonal depending on the geometrical features of the shells. These conformations could be theoretically and/or numerically reproduced in a model of homogeneous spherical thin shells with bending and stretching elasticity, submitted to an isotropic external pressure.Comment: submitted to EPJ

Digitally Assisted Transmitter Enhancement Techniques for Millimeter Wave Radio Systems

Wireless communication has become an integral part of life in a modern society. The data to be transmitted is modulated on radio frequency carrier signals for transmission where the bandwidth of the signal to be transmitted increases proportional to the speed at which the data is intended to be transmitted. The present generation cellular wireless communication systems employ channel bandwidths as wide as 20 MHz in multipole bands between 800 MHz and 3.5 GHz with digitally modulated multi-carrier transmission schemes and hybrid access schemes in time, frequency and spatial domains. The radio spectrum has stretched to occupy multiple bands below to meet the demand for volume and speed of the data to be communicated. Indoor short range wireless communications of present generation employ channel bandwidths as wide as 160 MHz and transmit at powers lesser than a tenth of that transmitted by cellular systems and employ similar access schemes as cellular wireless systems. There has been a similar evolution in the area of wireless communications through satellites. Next generation wireless communication systems such as 5G and High-Throughput-Satellite systems in the millimetre wave bands have promised a step increase in data rates in the order of several gigabits per second operating multiple frequency bands over and above those in use at present. This necessitates design of state of the art mm-wave transceivers capable of operating in millimetre wave bands with instantaneous bandwidths of several hundreds of MHz. The cost and complexity of implementation of the radio transmission system increases rapidly as the bandwidths increase. This work investigates digital enhancement techniques to enhance performance of wideband radio frequency transmitters. A section of the work focusses on characterizing wideband impairments in radio frequency hardware and mitigating them through digital signal processing. Another section devises digital signal processing operations to jointly enhance power efficiency in radio frequency transmitters along with providing an additional tier of security to the information being transmitted.The third section focusses on methods of transmission of wideband modulated signals by seamlessly interleaving multiple radio frequency transceivers of relatively narrow bandwidths in the frequency domain thereby presenting an architecture for scalable bandwidth transmitters. Overall this thesis presents innovative techniques to mitigate limitations in radio frequency hardware that hinder wideband operation and schemes to construct scalable bandwidth transceivers with scope to reuse legacy radio frequency hardware for next generation communication systems in part or whole

Structural changes of poly(butadiene)-poly(ethyleneoxide) diblock-copolymer micelles induced by a cationic surfactant: Scattering and cryogenic transmission electron microscopy studies

Nordskog A, Egger H, Findenegg GH, et al. Structural changes of poly(butadiene)-poly(ethyleneoxide) diblock-copolymer micelles induced by a cationic surfactant: Scattering and cryogenic transmission electron microscopy studies. Physical Review E. 2003;68(1): 11406.Micelles of the diblock copolymer poly(butadiene)-poly(ethyleneoxide) (B-40-b-EO62) and mixed micelles of this polymer with the cationic surfactant dodecyltrimethylammonium bromide (C(12)TAB) were investigated using static and dynamic light scattering and small-angle neutron scattering. It is shown that the surfactant induces a major structural change from large mainly rodlike aggregates to smaller spherical mixed micelles. The rodlike assemblies found in the absence of surfactant have a contour length L of ca. 500 nm and a diameter d approximate to30 nm. The spherical mixed micelles obtained upon addition of C(12)TAB possess a hydrodynamic radius of 15 nm and still contain several polymer molecules. The results of the scattering experiments are consistent with observations of the aggregates by cryogenic transmission electron microscopy