309 research outputs found
Shaping and transporting diamagnetic sessile drops
Electromagnetic fields are commonly used to control small quantities of fluids in microfluidics and digital microfluidics. Magnetic control techniques are less well studied than their electric counterparts, with only a few investigations into liquid diamagnetism. The ratio of magnetic to surface energy (magnetic Bond number B m) is an order of magnitude smaller for diamagnetic drops (B m ≈-0.3 at 1.2 T applied field) than for paramagnetic drops (B m ≈ 9.0 at 1.2 T applied field). This weaker interaction between the magnetic field and the diamagnetic drop has led to the phenomenon being overlooked in digital microfluidics. Here, we investigate shaping and transport of diamagnetic drops using magnetostatic fields. Our findings highlight how diamagnetic fluids can be used as a novel tool in the toolbox of microfluidics and digital microfluidics
Field-induced shaping of sessile paramagnetic drops
We use the electromagnetic stress tensor to describe the elongation of paramagnetic drops in uniform magnetic fields. This approach implies a linear relationship between the shape of the drops and the square of the applied field, which we confirm experimentally. We show that this effect scales with the volume and susceptibility of the drops. By using this unified electromagnetic approach, we highlight the potential applications of combining electric and magnetic techniques for controlled shaping of drops in liquid displays, liquid lenses, and chemical mixing of drops in microfluidics
Review on the development of truly portable and in-situ capillary electrophoresis systems
Capillary electrophoresis (CE) is a technique which uses an electric field to separate a mixed sample into its constituents. Portable CE systems enable this powerful analysis technique to be used in the field. Many of the challenges for portable systems are similar to those of autonomous in-situ analysis and therefore portable systems may be considered a stepping stone towards autonomous in-situ analysis. CE is widely used for biological and chemical analysis and example applications include: water quality analysis; drug development and quality control; proteomics and DNA analysis; counter-terrorism (explosive material identification) and corrosion monitoring. The technique is often limited to laboratory use, since it requires large electric fields, sensitive detection systems and fluidic control systems. All of these place restrictions in terms of: size, weight, cost, choice of operating solutions, choice of fabrication materials, electrical power and lifetime. In this review we bring together and critique the work by researchers addressing these issues. We emphasize the importance of a holistic approach for portable and in-situ CE systems and discuss all the aspects of the design. We identify gaps in the literature which require attention for the realization of both truly portable and in-situ CE systems
Measuring atomic NOON-states and using them to make precision measurements
A scheme for creating NOON-states of the quasi-momentum of ultra-cold atoms
has recently been proposed [New J. Phys. 8, 180 (2006)]. This was achieved by
trapping the atoms in an optical lattice in a ring configuration and rotating
the potential at a rate equal to half a quantum of angular momentum . In this
paper we present a scheme for confirming that a NOON-state has indeed been
created. This is achieved by spectroscopically mapping out the anti-crossing
between the ground and first excited levels by modulating the rate at which the
potential is rotated. Finally we show how the NOON-state can be used to make
precision measurements of rotation.Comment: 14 preprint pages, 7 figure
Using thermodynamics to identify quantum subsystems
There are many ways to decompose the Hilbert space ℋ of a composite quantum system into tensor product subspaces. Different subsystem decompositions generally imply different interaction Hamiltonians V, and therefore different expectation values for subsystem observables. This means that the uniqueness of physical predictions is not guaranteed, despite the uniqueness of the total Hamiltonian H and the total Hilbert space ℋ. Here we use Clausius’ version of the second law of thermodynamics (CSL) and standard identifications of thermodynamic quantities to identify possible subsystem decompositions. It is shown that agreement with the CSL is obtained, whenever the total Hamiltonian and the subsystem-dependent interaction Hamiltonian commute (i.e. [H,V]=0). Not imposing this constraint can result in the transfer of heat from a cooler to a hotter subsystem, in conflict with thermodynamics. We also investigate the status of the CSL with respect to non-standard definitions of thermodynamic quantities and quantum subsystems
Feed-forward Disturbance Compensation for Station Keeping in Wave-dominated Environments
When deploying robots in shallow ocean waters, wave disturbances can be significant, highly dynamic and pose problems when operating near structures; this is a key limitation of current control strategies, restricting the range of conditions in which subsea vehicles can be deployed. To improve dynamic control and offer a higher level of robustness, this work proposes a Cascaded Proportional-Derivative (C-PD) with Feed-forward (FF) control scheme for disturbance mitigation, exploring the concept of explicitly using disturbance estimations to counteract state perturbations. Results demonstrate that the proposed controller is capable of higher performance in contrast to a standard C-PD controller, with an average reduction of ~48% witnessed across various sea states. Additional analysis also investigated performance when considering coarse estimations featuring inaccuracies; average improvements of ~17% demonstrate the effectiveness of the proposed strategy to handle these uncertainties. The proposal in this work shows promise for improved control without a drastic increase in required computing power; if coupled with sufficient sensors, state estimation techniques and prediction algorithms, utilising feed-forward compensating control actions offers a potential solution to improve vehicle control under wave-induced disturbances
Feed-forward Disturbance Compensation for Station Keeping in Wave-dominated Environments
When deploying robots in shallow ocean waters, wave disturbances can be
significant, highly dynamic and pose problems when operating near structures;
this is a key limitation of current control strategies, restricting the range
of conditions in which subsea vehicles can be deployed. To improve dynamic
control and offer a higher level of robustness, this work proposes a Cascaded
Proportional-Derivative (C-PD) with Feed-forward (FF) control scheme for
disturbance mitigation, exploring the concept of explicitly using disturbance
estimations to counteract state perturbations. Results demonstrate that the
proposed controller is capable of higher performance in contrast to a standard
C-PD controller, with an average reduction of ~48% witnessed across various sea
states. Additional analysis also investigated performance when considering
coarse estimations featuring inaccuracies; average improvements of ~17%
demonstrate the effectiveness of the proposed strategy to handle these
uncertainties. The proposal in this work shows promise for improved control
without a drastic increase in required computing power; if coupled with
sufficient sensors, state estimation techniques and prediction algorithms,
utilising feed-forward compensating control actions offers a potential solution
to improve vehicle control under wave-induced disturbances.Comment: To published in proceedings of Oceans 2023: Limeric
Noncovariant gauge fixing in the quantum Dirac field theory of atoms and molecules
Starting from the Weyl gauge formulation of quantum electrodynamics (QED),
the formalism of quantum-mechanical gauge fixing is extended using techniques
from nonrelativistic QED. This involves expressing the redundant gauge degrees
of freedom through an arbitrary functional of the gauge-invariant transverse
degrees of freedom. Particular choices of functional can be made to yield the
Coulomb gauge and Poincar\'{e} gauge representations. The Hamiltonian we derive
therefore serves as a good starting point for the description of atoms and
molecules by means of a relativistic Dirac field. We discuss important
implications for the ontology of noncovariant canonical QED due to the gauge
freedom that remains present in our formulation.Comment: 8 pages, 0 figure
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