1,591 research outputs found
Exact solutions for hydrodynamic interactions of two squirming spheres
We provide exact solutions of the Stokes equations for a squirming sphere
close to a no-slip surface, both planar and spherical, and for the interactions
between two squirmers, in three dimensions. These allow the hydrodynamic
interactions of swimming microscopic organisms with confining boundaries, or
each other, to be determined for arbitrary separation and, in particular, in
the close proximity regime where approximate methods based on point singularity
descriptions cease to be valid. We give a detailed description of the circular
motion of an arbitrary squirmer moving parallel to a no-slip spherical boundary
or flat free surface at close separation, finding that the circling generically
has opposite sense at free surfaces and at solid boundaries. While the
asymptotic interaction is symmetric under head-tail reversal of the swimmer, in
the near field microscopic structure can result in significant asymmetry. We
also find the translational velocity towards the surface for a simple model
with only the lowest two squirming modes. By comparing these to asymptotic
approximations of the interaction we find that the transition from near- to
far-field behaviour occurs at a separation of about two swimmer diameters.
These solutions are for the rotational velocity about the wall normal, or
common diameter of two spheres, and the translational speed along that same
direction, and are obtained using the Lorentz reciprocal theorem for Stokes
flows in conjunction with known solutions for the conjugate Stokes drag
problems, the derivations of which are demonstrated here for completeness. The
analogous motions in the perpendicular directions, i.e. parallel to the wall,
currently cannot be calculated exactly since the relevant Stokes drag solutions
needed for the reciprocal theorem are not available.Comment: 27 pages, 7 figure
A Review of Smart Materials in Tactile Actuators for Information Delivery
As the largest organ in the human body, the skin provides the important
sensory channel for humans to receive external stimulations based on touch. By
the information perceived through touch, people can feel and guess the
properties of objects, like weight, temperature, textures, and motion, etc. In
fact, those properties are nerve stimuli to our brain received by different
kinds of receptors in the skin. Mechanical, electrical, and thermal stimuli can
stimulate these receptors and cause different information to be conveyed
through the nerves. Technologies for actuators to provide mechanical,
electrical or thermal stimuli have been developed. These include static or
vibrational actuation, electrostatic stimulation, focused ultrasound, and more.
Smart materials, such as piezoelectric materials, carbon nanotubes, and shape
memory alloys, play important roles in providing actuation for tactile
sensation. This paper aims to review the background biological knowledge of
human tactile sensing, to give an understanding of how we sense and interact
with the world through the sense of touch, as well as the conventional and
state-of-the-art technologies of tactile actuators for tactile feedback
delivery
Wheel Slip Avoidance through a Nonlinear Model Predictive Control for Object Pushing with a Mobile Robot
Wheel slip may cause a significative worsening of control performance during the movement of a mobile robot. A method to avoid wheel slip is proposed in this paper through a nonlinear model predictive control. The constraints included within the optimization problem limit the force exchanged between each wheel and the ground. The approach is validated in a dynamic simulation environment through a Pioneer 3-DX wheeled mobile robot performing a pushing manipulation of a box. (C) 2019, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved
Nanoantennas for visible and infrared radiation
Nanoantennas for visible and infrared radiation can strongly enhance the
interaction of light with nanoscale matter by their ability to efficiently link
propagating and spatially localized optical fields. This ability unlocks an
enormous potential for applications ranging from nanoscale optical microscopy
and spectroscopy over solar energy conversion, integrated optical
nanocircuitry, opto-electronics and density-ofstates engineering to
ultra-sensing as well as enhancement of optical nonlinearities. Here we review
the current understanding of optical antennas based on the background of both
well-developed radiowave antenna engineering and the emerging field of
plasmonics. In particular, we address the plasmonic behavior that emerges due
to the very high optical frequencies involved and the limitations in the choice
of antenna materials and geometrical parameters imposed by nanofabrication.
Finally, we give a brief account of the current status of the field and the
major established and emerging lines of investigation in this vivid area of
research.Comment: Review article with 76 pages, 21 figure
Linear Time-Varying MPC for Nonprehensile Object Manipulation with a Nonholonomic Mobile Robot
This paper proposes a technique to manipulate an object with a nonholonomic
mobile robot by pushing, which is a nonprehensile manipulation motion
primitive. Such a primitive involves unilateral constraints associated with the
friction between the robot and the manipulated object. Violating this
constraint produces the slippage of the object during the manipulation,
preventing the correct achievement of the task. A linear time-varying model
predictive control is designed to include the unilateral constraint within the
control action properly. The approach is verified in a dynamic simulation
environment through a Pioneer 3-DX wheeled robot executing the pushing
manipulation of a package
Magnetic force imaging and handling of cancer cells on the nanoscale
A thesis submitted to the University of Bedfordshire in partial fulfilment of the requirements for the degree of Doctor of PhilosophyCancer treatment has become one of the top priorities in health. Great efforts have been devoted to the diagnosis and therapy of cancers. Culturing cells with drugs is a common method used to investigate cancer therapy in experiments. However, this method has limitations in cancer treatment because of the lack of capabilities of handling cells, targeting specific cells and measuring the nanoscale changes in cell structures. Magnetic nanoparticles (MNPs) and magnetic force microscopes (MFMs) have been used to study biological samples due to their advantages in tracing, manipulating and measuring, which has motivated to research the method for implanting MNPs into cancer cells, to target the cancer cells and to measure their changes during the treatment. Research reported in this thesis focuses on magnetic force imaging and handling of targeted cancer cells on the nanoscale for possible new cancer therapies.
A new differential MFM imaging method and a new compensation MFM imaging method were developed in this research to improve the MFM imaging quality. The former reverses the magnetized direction of probe from upward to downward and the latter scans the samples with three scanning directions of 0°, 45° and 90°. With these methods, the obtained MFM images achieve a high resolution, SNR, image contrast and accuracy.
A pair of innovative MNPs picking up method and MNPs releasing method were developed in this research to achieve flexible MNPs picking up and releasing. The picking up method handles the magnetic tip following a helical structure as the capture path when approaching to the target MNPs. The MNPs releasing method uses a biaxiably-oriented polypropylene (BOPP) film together with a magnet allowing MNPs to separate from the MFM tip surface. With these methods, the target MNPs can be picked up by the MFM tip and released from the tip surface successfully.
This research discovered, for the first time in the world to the author knowledge, the differences in morphological features (height, length, width and roughness) and mechanical properties (adhesive force and Young‟s modulus) between multinuclear and mononuclear colon cancer cells after treating the cells with fullerenol. This discovery provides guidance to the selection of cells for target treatment. The results indicate that the mononuclear SW480 cells are more sensitive to fullerenol than the multinuclear SW480 cells and the multinuclear SW480 cells exhibit a stronger drug-resistance than the mononuclear SW480 cells.
A new MNPs implantation method was developed in this research, which enables the FITC-MNPs functioned tip to insert into cells so that MNPs are implanted into the target cells. Fluorescence microscope images show that the FITC-MNPs are released into the cells successfully. Cells being treated with MNPs (Cell-MNPs) manipulation III
methods are explored by magnet and controllable electromagnets to manipulate the target cancer cells. The results show that the cell-MNPs have magnetic force manipulated capability and they can be manipulated to have the leftward, rightward, upward and downward flexibilities
Bending and positioning of nanoparticles with light
Die Wechselwirkung von Nanopartikeln mit Licht ist seit Jahrzehnten ein intensives Forschungsgebiet im Bereich der Nanowissenschaften. Dabei rücken insbesondere Methoden die es erlauben einzelne Nanopartikel mit Licht zu verändern und präzise zu positionieren immer mehr in den Fokus des wissenschaftlichen Interesses. Eine der größten Herausforderungen in diesem Zusammenhang ist es, neue und zuverlässige Wege zu finden, um einzelne Nanopartikel mit hoher Kontrolle zeitlich und räumlich exakt zu manipulieren. Zwei Beispiele, nämlich die Möglichkeit der kontrollierten Deformation einzelner Gold-Nanostäbchen mit Licht und die Verwendung plasmonischer Nanoantennenfelder für das optische Einfangen von Nanoobjekten mit hoher lateraler Präzession werden im Rahmen dieser Arbeit präsentiert.
Zunächst wurde untersucht, wie einzelne Gold-Nanostäbchen in Lösung mit Licht durch eine Kombination aus plasmonischem Heizen und der Wechselwirkung von optischen und hydrodynamischen Kräften in eine V-Form gebogen werden können. Dabei kann der Biegewinkel in Abhängigkeit der verwendeten Laserintensität kontrolliert werden. Derartige V-förmige Nanoantennen aus Gold haben ein großes Anwendungspotential bei der Herstellung von Metamaterialien. Die Möglichkeit einzelne, V-förmige Nanostäbchen mit Licht zu positionieren und auf einem Substrat zu orientieren ist eine Grundvorausetzung zur Verwirklichung derartiger Oberflächen und wurde in dieser Arbeit näher untersucht.
Im zweiten Teil dieser Arbeit wird die Eigenschaft von plasmonisch gekoppelten Nanoantennen, Licht in ein kleines Volumen zu bündeln ausgenutzt, um das optische Einfangen von Nanoobjekten auf plasmonischen Oberflächen zu ermöglichen. Mikro-nanostrukturierte Anordnungen von Gold-Nanodreiecken wurden durch eine Kombination aus kolloidaler Lithographie und Plasmabehandlung hergestellt. Die Anwendbarkeit dieser Nanoantennenstrukturen für das optische Einfangen von Siliziumdioxid-Partikeln wurde erforscht und die Abhängigkeit der Partikelgröße von der Nanoantennengeometrie genau untersucht. Als Erweiterung dieses Verfahrens wurde eine Kombination aus optischer Nah- und Fernfeldfalle angewendet, um einzelne Nanoobjekte wie Goldnanopartikel und Nanodiamanten präzise an einzelnen plasmonischen „Hot -Spots“ mit einer Genauigkeit von wenigen Nanometern exakt zu positionieren.Exploiting the interaction of nanoparticles with light has been a vivid area of research in nanoscience for decades. Recently, the possibility of transforming and precisely positioning nano-objects with light has increasingly come into focus. One of the biggest challenges in this regard is finding new and robust ways of manipulating single nanoparticles with high spatio-temporal control. Two methods of addressing this demanding task - namely controlling the melting and shape transformations of individual gold nanorods, and the use of plasmonic nanoantenna arrays for the enhanced optical trapping of nano-sized objects - are the subject of this thesis.
First, individual gold nanorods in a solution can be bent into a V-shaped geometry upon laser irradiation through a combination of plasmonic heating, optical forces, and hydrodynamic interactions. The bending angle can be controlled within small margins by adjusting the laser intensity. Such V-shaped antennas hold great application potential for the design of metasurfaces if the precise alignment of individual antennas on a flat surface is achieved. To work toward this application, a method for optically printing and orienting bent nanorods on a surface with respect to the laser power density and polarization is presented.
Second, the ability of plasmonically coupled nanostructures or nanoantennas to concentrate light into a small volume is employed for the enhanced near-field trapping of nanosized objects at plasmonic interfaces. Micro-nanopatterned arrays of plasmonic nanoantennas were synthesized via plasma-enhanced colloidal lithography. The applicability of these nanoantenna arrays for the near-field trapping of silica beads with respect to the antenna geometry and the irradiation intensities was investigated. In an extension of this general approach, a combination of optical far-field and near-field trapping was used to actively deliver individual nano-objects, such as gold nanoparticles or nanodiamonds, precisely to individual plasmonic “hot spots” with the accuracy of a few nanometers
Vocal fold vibratory and acoustic features in fatigued Karaoke singers
Session 3aMU - Musical Acoustics and Speech Communication: Singing Voice in Asian CulturesKaraoke is a popular singing entertainment particularly in Asia and is gaining more popularity in the rest of world. In Karaoke, an amateur singer sings with the background music and video (usually guided by the lyric captions on the video screen) played by Karaoke machine, using a microphone and an amplification system. As the Karaoke singers usually have no formal training, they may be more vulnerable to vocal fatigue as they may overuse and/or misuse their voices in the intensive and extensive singing activities. It is unclear whether vocal fatigue is accompanied by any vibration pattern or physiological changes of vocal folds. In this study, 20 participants aged from 18 to 23 years with normal voice were recruited to participate in an prolonged singing task, which induced vocal fatigue. High speed laryngscopic imaging and acoustic signals were recorded before and after the singing task. Images of /i/ phonation were quantitatively analyzed using the High Speed Video Processing (HSVP) program (Yiu, et al. 2010). It was found that the glottis became relatively narrower following fatigue, while the acoustic signals were not sensitive to measure change following fatigue. © 2012 Acoustical Society of Americapublished_or_final_versio
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MEASURED CAPILLARY FORCES ON SPHERES AT LIQUID INTERFACES AND THE MECHANICS OF INTERFACIAL PARTICULATE ASSEMBLIES
Particle-laden interfaces have promising potentials in many fields because the particulate nature can endow the surface with physical properties that are not readily obtained from molecular-scale surfactants. In this dissertation, we first focus on measuring capillary forces on particles at fluid interfaces in order to assess the key parameters that yield effective stabilizing particles. In experiment, the force and the displacement of a millimeter-scale particle passing through a liquid interface were recorded. We find that the peak force needed to detach a particle from an interface crowded with other particles is consistently smaller than the force at a clean interface. By ruling out other possibilities, we attribute the force reduction to the perturbation of interface shape due to the constraints imposed by free particles. Then we study the mechanics of particulate assemblies by measuring the force response under a normal indentation. We find that there exist two linear regions with different slopes. The small-slope regime starts at the beginning and persists over a range of indentations much less than capillary length. Once the system entered the higher plateau region, it has the same stiffness as a pure liquid interface. Further, from top-view images, we showed that, as long as the indenter was larger than the size of a single particle, the azimuthal compression can be relaxed through the in-plane rearrangement of particles. These features are independent of the difference in fluid mass densities, the radius of the indenter and the species of particles. Although the presence of floating particles at an interface does not change its capillary nature under a wide range of poking depth, we show that the existence of the particle raft makes the original interface tougher in terms of both the maximum force it can sustain and the largest indentation an indenter can reach. These results provide an important step toward understanding the mechanics of particulate assemblies at interfaces.
Finally, we study the formation of organic 2D material in aqueous media for the purpose of potential applications in passivating objects in suspension. We optimized the conditions for the self-assembly of bola-amphiphilic molecules, and directly observed 2D sheets in optical microscope under dark-field illumination. We find that stacking is not preferred by sheets because of the likely electrostatic repulsion. Our method provides an effective way to better understand the properties of those sheets
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