Nacev A.,University of Maryland College Park |
Beni C.,California Institute of Technology |
Bruno O.,California Institute of Technology |
Shapiro B.,Institute for Systems Research |
Shapiro B.,University of Maryland College Park
Journal of Magnetism and Magnetic Materials | Year: 2011
In magnetic drug delivery, therapeutic magnetizable particles are typically injected into the blood stream and magnets are then used to concentrate them to disease locations. The behavior of such particles in-vivo is complex and is governed by blood convection, diffusion (in blood and in tissue), extravasation, and the applied magnetic fields. Using physical first-principles and a sophisticated vessel-membrane-tissue (VMT) numerical solver, we comprehensively analyze in detail the behavior of magnetic particles in blood vessels and surrounding tissue. For any blood vessel (of any size, depth, and blood velocity) and tissue properties, particle size and applied magnetic fields, we consider a Krogh tissue cylinder geometry and solve for the resulting spatial distribution of particles. We find that there are three prototypical behaviors (blood velocity dominated, magnetic force dominated, and boundary-layer formation) and that the type of behavior observed is uniquely determined by three non-dimensional numbers (the magnetic-Richardson number, mass Pclet number, and Renkin reduced diffusion coefficient). Plots and equations are provided to easily read out which behavior is found under which circumstances (Figs. 58). We compare our results to previously published in-vitro and in-vivo magnetic drug delivery experiments. Not only do we find excellent agreement between our predictions and prior experimental observations, but we are also able to qualitatively and quantitatively explain behavior that was previously not understood. © 2010 Elsevier B.V. All rights reserved.
Mathai P.P.,U.S. National Institute of Standards and Technology |
Mathai P.P.,University of Maryland University College |
Carmichael P.T.,U.S. National Institute of Standards and Technology |
Shapiro B.A.,U.S. National Institute of Standards and Technology |
And 3 more authors.
RSC Advances | Year: 2013
We present a material-property independent method for manipulating both the position and orientation of nanowires (NWs), by feedback control of flows. For example, the NWs need not be electromagnetically polarizable. Control of NWs in a microfluidic device is demonstrated across a 170 μm × 170 μm region with on-demand trapping, translation, and simultaneous rotation of dielectric, semiconducting, and metallic NWs. An average trapping precision of 0.6 μm in position and 5.4° in orientation is achieved for the NWs considered, making it attractive for sensing and directed assembly applications. This journal is © 2013 The Royal Society of Chemistry.
DeVries L.,U.S. Naval Academy |
Paley D.A.,University of Maryland University College |
Paley D.A.,Institute for Systems Research
Journal of Guidance, Control, and Dynamics | Year: 2016
The continued development of sophisticated aircraft with high-fidelity control systems will enable autonomous execution of challenging tasks such as aerial refueling and close-formation flight.To achieve such tasks autonomously, an aircraft must sense other aircraft in close proximity and position itself relative to them. For example, formationflying aircraft must position themselves strategically to realize benefits of aerodynamic efficiency; aerial refueling requires the follower aircraft to intercept the filling nozzle attached to the leader aircraft. This paper uses lifting-line theory to represent a two-aircraft formation and presents a grid-based, recursive Bayesian filter for estimating the wake parameters of the lead aircraft using noisy pressure measurements distributed along the trailing aircraft's wing; the estimator also uses a binary, relative-altitude measurement to break the vertical symmetry. The paper employs measures of observability to quantify spatial regions prone to degraded estimation performance. Optimal control strategies are presented to steer the follower aircraft to a desired lateral position relative to the leader while simultaneously optimizing the observability of the leader's relative position. The control algorithms guide the follower aircraft along trajectories that maintain adequate observability, thereby guaranteeing estimator performance. Theoretical results are illustrated using numerical examples of a two-aircraft formation.
Gerdes J.W.,University of Maryland University College |
Gupta S.K.,Institute for Systems Research |
Wilkerson S.A.,U.S. Army
Proceedings of the ASME Design Engineering Technical Conference | Year: 2010
Physical and aerodynamic characteristics of the bird in flight may offer benefits over typical propeller or rotor driven miniature air vehicle (MAV) locomotion designs in certain types of scenarios. A number of research groups and companies have developed flapping wing vehicles that attempt to harness these benefits. The purpose of this paper is to report different types of flapping wing designs and compare their salient characteristics. For each category, advantages and disadvantages will be discussed. The discussion presented will be limited to miniature-sized flapping wing air vehicles, defined as 10-100 grams total weight. The discussion will be focused primarily on ornithopters which have performed at least one successful test flight. Additionally, this paper is intended to provide a representation of the field of current technology, rather than providing a comprehensive listing of all possible designs. This paper will familiarize a newcomer to the field with existing designs and their distinguishing features. By studying existing designs, future designers will be able to adopt features from other successful designs. This paper also summarizes the design challenges associated with the further advancement of the field and deploying flapping wing vehicles in practice. © 2010 by ASME.
Galloway K.S.,U.S. Naval Academy |
Justh E.W.,U.S. Navy |
Krishnaprasad P.S.,Institute for Systems Research |
Krishnaprasad P.S.,University of Maryland University College
Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2013
We specify and analyse models that capture the geometry of purposeful motion of a collective of mobile agents, with a focus on planar motion, dyadic strategies and attention graphs which are static, directed and cyclic. Strategies are formulated as constraints on joint shape space and are implemented through feedback laws for the actions of individual agents, here modelled as self-steering particles. By reduction to a labelled shape space (using a redundant parametrization to account for cycle closure constraints) and a further reduction through time rescaling, we characterize various special solutions (relative equilibria and pure shape equilibria) for cyclic pursuit with a constant bearing (CB) strategy. This is accomplished by first proving convergence of the (nonlinear) dynamics to an invariantmanifold (the CB pursuit manifold), and then analysing the closedloop dynamics restricted to the invariant manifold. For illustration, we sketch some low-dimensional examples. This formulation-involving strategies, attention graphs and sensor-driven steering laws- and the resulting templates of collective motion, are part of a broader programme to interpret the mechanisms underlying biological collective motion. © 2013 The Author(s).
Dykstra P.H.,Institute for Systems Research |
Roy V.,University of Maryland University College |
Byrd C.,Institute for Systems Research |
Byrd C.,University of Maryland University College |
And 3 more authors.
Analytical Chemistry | Year: 2011
We present a unique microfluidic platform to allow for quick and sensitive probing of protein adsorption to various functionalized surfaces. The ability to tailor a sensor surface for a specific analyte is crucial for the successful application of portable gas and fluid sensors and is of great interest to the drug screening community. However, choosing the correct surface chemistry to successfully passivate against nonspecific binding typically requires repeated trial and error experiments. The presented device incorporates an array of integrated electrochemical sensors for fast, sensitive, label-free detection of these binding interactions. The layout of the electrodes allows for loading various surface chemistries in one direction while sensing their interactions with particular compounds in another without any cross-contamination. Impedance data is collected for three commonly used passivation compounds (mercaptohexanol, polyethylene glycol, and bovine serum albumin) and demonstrates their interaction with three commonly studied proteins in genetic and cancer research (cAMP receptor protein, tumor necrosis factor α, and tumor necrosis factor β). The ability to quickly characterize various surface interactions provides knowledge for selecting optimal functionalization for any biosensor. © 2011 American Chemical Society.
Sarwar A.,University of Maryland University College |
Sarwar A.,University of Maryland College Park |
Nemirovski A.,Georgia Institute of Technology |
Shapiro B.,University of Maryland University College |
And 2 more authors.
Journal of Magnetism and Magnetic Materials | Year: 2012
Optimization methods are presented to design Halbach arrays to maximize the forces applied on magnetic nanoparticles at deep tissue locations. In magnetic drug targeting, where magnets are used to focus therapeutic nanoparticles to disease locations, the sharp fall off of magnetic fields and forces with distances from magnets has limited the depth of targeting. Creating stronger forces at a depth by optimally designed Halbach arrays would allow treatment of a wider class of patients, e.g. patients with deeper tumors. The presented optimization methods are based on semi-definite quadratic programming, yield provably globally optimal Halbach designs in 2 and 3-dimensions, for maximal pull or push magnetic forces (stronger pull forces can collect nanoparticles against blood forces in deeper vessels; push forces can be used to inject particles into precise locations, e.g. into the inner ear). These Halbach designs, here tested in simulations of Maxwells equations, significantly outperform benchmark magnets of the same size and strength. For example, a 3-dimensional 36 element 2000 cm3 volume optimal Halbach design yields a 5× greater force at a 10 cm depth compared to a uniformly magnetized magnet of the same size and strength. The designed arrays should be feasible to construct, as they have a similar strength (≤1 T), size (≤2000 cm3), and number of elements (≤36) as previously demonstrated arrays, and retain good performance for reasonable manufacturing errors (element magnetization direction errors ≤5°), thus yielding practical designs to improve magnetic drug targeting treatment depths. © 2011 Elsevier B.V.
Mallik A.,College Park |
Mallik A.,Institute for Systems Research |
Faulkner B.,Virginia Polytechnic Institute and State University |
Khaligh A.,College Park |
Khaligh A.,Institute for Systems Research
Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC | Year: 2016
Advances in power electronics are enabling More Electric Aircrafts (MEAs) to replace pneumatic systems with electrical systems. Active power factor correction (PFC) rectifiers are used in MEAs to rectify the output voltage of the three-phase AC-DC boost converter, while maintaining a unity input power factor. Many existing control strategies implement PI compensators, with slow response times, in their voltage and current loops. Alternatively, computationally expensive nonlinear controllers can be chosen to generate input currents with high power factor and low total harmonic distortion (THD), but they may need to be operated at high switching frequencies due to relatively slower execution of control loop. In this work, a novel control strategy is proposed for a three-phase, single-stage boost-type rectifier that is capable of tight and fast regulation of the output voltage, while simultaneously achieving unity input power factor, without constraining the operating switching frequency. The proposed control strategy is implemented, using one voltage-loop PI controller and a linearized transfer function of duty-ratio to input current, for inner loop current control. A 1.5 kW three-phase boost PFC prototype is designed and developed to validate the proposed control algorithm. The experimental results show that an input power factor of 0.992 and a tightly regulated DC link voltage with 3% ripple can be achieved. © 2016 IEEE.
Vogtmann D.E.,Institute for Systems Research |
Gupta S.K.,Institute for Systems Research |
Bergbreiter S.,Institute for Systems Research
Proceedings - IEEE International Conference on Robotics and Automation | Year: 2011
This paper describes a new process for fabricating planar, multi-material, compliant mechanisms, intended for use in small scale robotics. The process involves laser cutting the mechanism geometry from a rigid material, and refilling the joint areas with a second, elastomeric material. This method allows for a large set of potential materials, with a wide range of material properties, to be used in combination to create mechanisms with highly tailored mechanical properties. These multi-material compliant mechanisms have minimum feature sizes of approximately 100 μm and have demonstrated long lifetimes, easily surviving 100,000 bending cycles. We also present the first use of these compliant mechanisms in a 2.5cm × 2.5cm × 7.5cm, 6g hexapod. This hexapod has been demonstrated moving at speeds up to 6 cm/s, with a predicted maximum speed of up to 17 cm/s. © 2011 IEEE.
News Article | November 29, 2016
Abstract: Deepa Sritharan and Elisabeth Smela Department of Mechanical Engineering, University of Maryland, College Park, MD 20742, USA Institute for Systems Research, University of Maryland, College Park, MD 20742, USA Abstract : A voltage-controlled hydraulic actuator is presented that employs electroosmotic fluid flow (EOF) in paper microchannels within an elastomeric structure. The microfluidic device was fabricated using a new benchtop lamination process. Flexible embedded electrodes were formed from a conductive carbon-silicone composite. The pores in the layer of paper placed between the electrodes served as the microchannels for EOF, and the pumping fluid was propylene carbonate. A sealed fluid-filled chamber was formed by film-casting silicone to lay an actuating membrane over the pumping liquid. Hydraulic force generated by EOF caused the membrane to bulge by hundreds of micrometers within fractions of a second. Potential applications of these actuators include soft robots and biomedical devices. For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.