Self-propelled micromotors for cleaning polluted water

We describe the use of catalytically self-propelled microjets (dubbed micromotors) for degrading organic pollutants in water via the Fenton oxidation process. The tubular micromotors are composed of rolled-up functional nanomembranes consisting of Fe/Pt bilayers. The micromotors contain double functionality within their architecture, i.e., the inner Pt for the self-propulsion and the outer Fe for the in situ generation of ferrous ions boosting the remediation of contaminated water.The degradation of organic pollutants takes place in the presence of hydrogen peroxide, which acts as a reagent for the Fenton reaction and as main fuel to propel the micromotors. Factors influencing the efficiency of the Fenton oxidation process, including thickness of the Fe layer, pH, and concentration of hydrogen peroxide, are investigated. The ability of these catalytically self-propelled micromotors to improve intermixing in liquids results in the removal of organic pollutants ca. 12 times faster than when the Fenton oxidation process is carried out without catalytically active micromotors. The enhanced reaction-diffusion provided by micromotors has been theoretically modeled. The synergy between the internal and external functionalities of the micromotors, without the need of further functionalization, results into an enhanced degradation of nonbiodegradable and dangerous organic pollutants at small-scale environments and holds considerable promise for the remediation of contaminated water

Wireless magnetic-based closed-loop control of self-propelled microjets

In this study, we demonstrate closed-loop motion control of self-propelled microjets under the influence of external magnetic fields. We control the orientation of the microjets using external magnetic torque, whereas the linear motion towards a reference position is accomplished by the thrust and pulling magnetic forces generated by the ejecting oxygen bubbles and field gradients, respectively. The magnetic dipole moment of the microjets is characterized using the U-turn technique, and its average is calculated to be 1.3x10-10 A.m2 at magnetic field and linear velocity of 2 mT and 100 μm/s, respectively. The characterized magnetic dipole moment is used in the realization of the magnetic force-current map of the microjets. This map in turn is used for the design of a closed-loop control system that does not depend on the exact dynamical model of the microjets and the accurate knowledge of the parameters of the magnetic system. The motion control characteristics in the transient- and steady-states depend on the concentration of the surrounding fluid (hydrogen peroxide solution) and the strength of the applied magnetic field. Our control system allows us to position microjets at an average velocity of 115 μm/s, and within an average region-of-convergence of 365 μm

Planning, art, and Post-WWII urban history in New York, Berlin, and Tokyo

Thesis: Ph. D. in Architecture: History and Theory of Architecture, Massachusetts Institute of Technology, Department of Architecture, 2017.Cataloged from PDF version of thesis. "For copyright reasons, images in this dissertation have been redacted"--Disclaimer Notice page.Includes bibliographical references (pages 234-244).Thinking about cities became increasingly global during and after WWII. 'Global' here refers to how, in the context of the war, the roles and meanings of cities in the world were beginning to be understood differently. This dissertation investigates urban histories since the 1940s in their connection to changing imaginaries of the world that were shaped by the experience of war, and that have received little attention in historical literature. The dominant narratives of postwar urban history are focused on issues such as destruction and reconstruction, and the ideological divides between East and West. Global history is here employed as a non-hegemonic methodology for going beyond these larger narratives, and to demonstrate that in an age of global war, cities were becoming global long before economic discourses on globalization labeled them as such. New York City, West Berlin, and Tokyo are used as case studies because they are the principal cities of three industrialized nations that were heavily affected by WWII. New York became a center of the US war industry and beacon of the proclaimed Western values of freedom and democracy. However, the hypocrisy of fighting for freedom and democracy abroad, while racial violence and injustice was experienced at home, led to housing and segregation in New York being seen in global context. Discourses on fighting fascism at home and abroad, and artistic representations of the city illuminate these narratives. In Berlin-especially with the founding of the two German states in 1949 and the building of the Berlin Wall in 1961-urban planning and development are most easily understood to be part of East-West ideological divides. Visions for the city of the future that were produced in secluded West Berlin demonstrate, however, that the city was also imagined in ways that transcended its local conflict and positioned it as a democratic tool for a global urban society. Tokyo's destruction during WWII, and its subsequent reconstruction, dominates the city's postwar history, but Japan's experience of war and nuclear bombings led to the creation of urban models that were more global in scope. An analysis of Japanese involvement in world's fairs and of architectural and urban thought in response to the nuclear bombings connects these threads. In different ways, these case studies substantiate the connection between global war and global cities and introduce global history methodology into the analysis of global thinking in urbanism during and after WWII.by Sebastian Schmidt.Ph. D. in Architecture: History and Theory of Architectur

Control of Self-Propelled Microjets Inside a Microchannel With Time-Varying Flow Rates

We demonstrate the closed-loop motion control of self-propelled microjets inside a fluidic microchannel. The motion control of the microjets is achieved in hydrogen peroxide solution with time-varying flow rates, under the influence of the controlled magnetic fields and the self-propulsion force. Magnetic dipole mo- ment of the microjets is characterized using the U-turn and the rotating field techniques. The characterized magnetic dipole mo- ment has an average of 1.4 × 10 − 13 A.m 2 at magnetic field, linear velocity, and boundary frequency of 2 mT, 100 μ m/s, and 25 rad/s, respectively. We implement a closed-loop control system that is based on the characterized magnetic dipole moment of the mi- crojets. This closed-loop control system positions the microjets by directing the magnetic field lines toward the reference position. Experiments are done using a magnetic system and a fluidic mi- crochannel with a width of 500 μ m. In the absence of a fluid flow, our control system positions the microjets at an average velocity and within an average region-of-convergence (ROC) of 119 μ m/s and 390 μ m, respectively. As a representative case, we observe that our control system positions the microjets at an average velocity and within an average ROC of 90 μ m/s and 600 μ m and 120 μ m/s and 600 μ m when a flow rate of 2.5 μ l/min is applied against and along the direction of the microjets, respectively. Furthermore, the average velocity and ROC are determined throughout the flow range (0 to 7.5 μ l/min) to characterize the motion of the microjets inside the microchanne

Wireless Magnetic-Based Closed-Loop Control of Self- Propelled Microjets

In this study, we demonstrate closed-loop motion control of self-propelled microjets under the influence of external magnetic fields. We control the orientation of the microjets using external magnetic torque, whereas the linear motion towards a reference position is accomplished by the thrust and pulling magnetic forces generated by the ejecting oxygen bubbles and field gradients, respectively. The magnetic dipole moment of the microjets is characterized using the U-turn technique, and its average is calculated to be 1.3|10210 A.m2 at magnetic field and linear velocity of 2 mT and 100 mm/s, respectively. The characterized magnetic dipole moment is used in the realization of the magnetic force-current map of the microjets. This map in turn is used for the design of a closed-loop control system that does not depend on the exact dynamical model of the microjets and the accurate knowledge of the parameters of the magnetic system. The motion control characteristics in the transient- and steady-states depend on the concentration of the surrounding fluid (hydrogen peroxide solution) and the strength of the applied magnetic field. Our control system allows us to position microjets at an average velocity of 115 mm/s, and within an average region-of-convergence of 365 mm

Biocompatible, accurate, and fully autonomous: a sperm-driven micro-bio-robot

We study the magnetic-based motion control of a sperm-flagella driven Micro-Bio-Robot (MBR), and demonstrate precise point-to-point closed-loop motion control under the influence of the controlled magnetic field lines. This MBR consists of a bovine spermatozoon that is captured inside Ti/Fe nanomembranes. The nanomembranes are rolled-up into a 50 μm long microtube with a diameter of 5-8 μm. Our MBR is self-propelled by the sperm cell and guided using the magnetic torque exerted on the magnetic dipole of its rolled-up microtube. The self-propulsion force provided by the sperm cell allows the MBR to move at an average velocity of 25 ±10 μm/s towards a reference position, whereas the magnetic dipole moment and the controlled weak magnetic fields (approximately 1.39 mT) allow for the localization of the MBR within the vicinity of reference positions with an average region-of-convergence of 90 ±40μm. In addition, we experimentally demonstrate the guided motion of the MBR towards a magnetic microparticle with applications towards targeted drug delivery and microactuation