Axion-photon conversion caused by dielectric interfaces: quantum field calculation

Axion-photon conversion at dielectric interfaces, immersed in a near-homogeneous magnetic field, is the basis for the dielectric haloscope method to search for axion dark matter. In analogy to transition radiation, this process is possible because the photon wave function is modified by the dielectric layers ("Garibian wave function") and is no longer an eigenstate of momentum. A conventional first-order perturbative calculation of the transition probability between a quantized axion state and these distorted photon states provides the microwave production rate. It agrees with previous results based on solving the classical Maxwell equations for the combined system of axions and electromagnetic fields. We argue that in general the average photon production rate is given by our result, independently of the detailed quantum state of the axion field. Moreover, our result provides a new perspective on axion-photon conversion in dielectric haloscopes because the rate is based on an overlap integral between unperturbed axion and photon wave functions, in analogy to the usual treatment of microwave-cavity haloscopes.Comment: 15 pages, 2 figures; v2: minor changes to match published versio

Restrained Shrinkage of Fly Ash Based Geopolymer Concrete and Analysis of Long Term Shrinkage Prediction Models

The research presented in this manuscript describes the procedure to quantify the restrained shrinkage of geopolymer concrete (GPC) using ring specimen. Massive concrete structures are susceptible to shrinkage and thermal cracking. This cracking can increase the concrete permeability and decrease the strength and design life. This test is comprised of evaluating geopolymer concrete of six different mix designs including different activator solution to fly ash ratio and subjected to both restrained and free shrinkage. Test results obtained from this experimental setup was plotted along with the available empirical equation to observe the shrinkage strain of GPC and a model was suggested to predict the shrinkage strain of GPC. It was found from this study that along with activator solution to fly ash ratio the final compressive strength of GPC plays an important role on shrinkage strai

Culture practices of freshwater giant prawn in some selected areas of Mymensingh

A study was conducted to examine the culture practices of freshwater giant prawn, Macrobrachium rosenbergii in some selected areas of Mymensingh. Based on a sample of 100 farmers from three different upazila, namely Phulpur, Gouripur and Ishwargonj in Mymensingh district, 94% of farmers cultured prawn with fish in their pond. Only 6% of farmers cultured prawn, fish and dike crops for higher economic return. The culture period is typically nine months; hatchery produced post-larvae were stocked from May to June and harvested from November to January. Per hectare production of prawn, 375 kg/yr was very low because the farmers followed simple culture method. Most of the farmers made a profit of Tk. 68,403/ha/yr and the major costs incurred were for purchasing prawn seed and feed. The culture of prawn in pond system is technically possible under different conditions though expansion of small-scale prawn farming mainly depends on reduction of production costs. Future targets could be integration of pond prawn culture with other agricultural activities especially dike cropping and rice production in the monsoon

Cell migration directionality and speed are independently regulated by RasG and Gβ in Dictyostelium cells in electrotaxis.

Motile cells manifest increased migration speed and directionality in gradients of stimuli, including chemoattractants, electrical potential and substratum stiffness. Here, we demonstrate that Dictyostelium cells move directionally in response to an electric field (EF) with specific acceleration/deceleration kinetics of directionality and migration speed. Detailed analyses of the migration kinetics suggest that migration speed and directionality are separately regulated by Gβ and RasG, respectively, in EF-directed cell migration. Cells lacking Gβ, which is essential for all chemotactic responses in Dictyostelium, showed EF-directed cell migration with the same increase in directionality in an EF as wild-type cells. However, these cells failed to show induction of the migration speed upon EF stimulation as much as wild-type cells. Loss of RasG, a key regulator of chemoattractant-directed cell migration, resulted in almost complete loss of directionality, but similar acceleration/deceleration kinetics of migration speed as wild-type cells. These results indicate that Gβ and RasG are required for the induction of migration speed and directionality, respectively, in response to an EF, suggesting separation of migration speed and directionality even with intact feedback loops between mechanical and signaling networks

Electropermanent magnetic connectors and actuators : devices and their application in programmable matter

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 199-206).Programmable matter is a digital material having computation, sensing, and actuation capabilities as continuous properties active over its whole extent. To make programmable matter economical to fabricate, we want to use electromagnetic direct drive, rather than clockwork, to actuate the particles. Previous attempts to fabricate small scale (below one centimeter) robotic systems with electromagnetic direct-drive have typically run into problems with insufficient force or torque, excessive power consumption and heat generation (for magnetic-drive systems), or high-voltage requirements, humidity sensitivity, and air breakdown. (for electrostatic-drive systems) The electropermanent magnet is a solid-state device whose external magnetic flux can be stably switched on and off by a discrete electrical pulse. Electropermanent magnets can provide low-power connection and actuation for programmable matter and other small-scale robotic systems. The first chapter covers the electropermanent magnet, its physics, scaling, fabrication, and our experimental device performance data. The second introduces the idea of electropermanent actuators, covers their fundamental limits and scaling, and shows prototype devices and performance measurements. The third chapter describes the smart pebbles system, which consists of 12-mm cubes that can form shapes by stochastic self-assembly and self-disassembly. The fourth chapter describes the millibot, a continuous chain of programmable matter which forms shapes by folding.by Ara Nerses Knaian.Ph.D

Design of programmable matter

Thesis (S.M.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2008.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (leaves 115-119).Programmable matter is a proposed digital material having computation, sensing, actuation, and display as continuous properties active over its whole extent. Programmable matter would have many exciting applications, like paintable displays, shape-changing robots and tools, rapid prototyping, and sculpture-based haptic interfaces. Programmable matter would be composed of millimeter-scale autonomous microsystem particles, without internal moving parts, bound by electromagnetic forces or an adhesive binder. Particles can dissipate 10 mW heat, and store 6 J energy in an internal zinc-air battery. Photovoltaic cells provide 300 [mu]W outdoors and 3.0 [mu]W indoors. Painted systems can store battery reactants in the paint binder; 6 J / mm3 can be stored, and diffusion is fast enough to transport reactants to the particles. Capacitive power transfer is an efficient method to transfer power to sparse, randomly placed particles. Power from capacitive transfer is proportional to VDD 2: 100[mu]W at 3.3V and 12 mW at 35V. Inter-particle communication is possible via optical, near-field, and far-field electromagnetic systems. Optical systems allow communication with low area (sub-mm) particles, and 24 pJ/bit. Near-field electromagnetic gives precisely controlled neighborhoods, localization capability, and 37 pJ/bit. Far-field radio communication between widely spaced particles may be possible at 60 GHz; antennas that fit inside 1 mm3 exist; complete transceivers do not. A 32-bit CPU uses less than 0.26 mm2 die area, 256K x 8 SRAM uses 1.1 mm2, and 256K x 8 FLASH uses 0.32 mm2. Direct-drive electric and magnetic field systems allow actuation without moving parts inside the particles. Magnetic surface-drive motors designed for operation without bearings are not power-efficient, and parasitic interactions between permanent magnets may limit their usefulness at millimeter particle dimensions. Electrostatic surface-drive motors are power-efficient, but practical only at particle dimensions below a few millimeters. We constructed a prototype paintable display; a distributed PostScript rendering system with 1000 randomly-placed 3.4 cm nodes, each with a CPU, IR communications, and LED. The system is used to render the letter "A." We present a design, not yet constructed, for a literal paintable display, with 1.0 mm rendering particles, each with a microprocessor and memory, and 110 [mu]m display particles, with tri-color LED's and simpler circuitry. Storage of zinc-air battery reactants in the paint binder would provide an 8 hour battery life, and capacitive power distribution would allow continuous operation. We constructed a prototype sliding-cube modular robot, with 3.4 cm nodes. The system uses magnetic surface-drive actuation. We demonstrate horizontal lattice-unit translation. We describe a design, not yet constructed, for a sliding-cube modular robot with 2 mm nodes. The cubes use standard-process CMOS IC's, inserted into a cubic space frame and wire-bonded together. Arrays of passivated electrodes, 1 [mu]m from the surface of the cubes, are used for electrostatic surface-drive actuation, zero-power latching, power transfer, localization, and communication. The design allows actuation from any contacting position. Energy is stored in a standard SMT capacitor inside each node, which is recharged by power transfer through chains of contacting nodes.by Ara N. Knaian.S.M