160 research outputs found
On the Boolean dimension of a graph and other related parameters
We present the Boolean dimension of a graph, we relate it with the notions of
inner, geometric and symplectic dimensions, and with the rank and minrank of a
graph. We obtain an exact formula for the Boolean dimension of a tree in terms
of a certain star decomposition. We relate the Boolean dimension with the
inversion index of a tournament.Comment: 13 pages, 2 figure
Haematoma detection using EIT in a sheep model
Performance evaluation of a portable digital electrical impedance tomography system to detect haematomas using a sheep model is presented. Two different experiments have been performed using 8-electrode full array configuration. Artificial haematomas were introduced in the first experiment by injecting blood-like conductivity solution via the brainstem, and in the second by placing blood-like conductivity gel at a certain position on top of the parietal lobes of the brain on the left and right sides. For the first experiment, the Electrical Impedance Tomography (EIT) images were reconstructed sequentially for different injection volumes and the quantity index (QI) was calculated as a function of the injected solution volume. The results show a linear relationship of QI to the injected volume. For the second experiment, the images were successfully reconstructed and haematoma was clearly detected and localised using our developed system. The promising results of sheep experiments prove that our developed EIT system is able to detect and quantify small haematomas in head
Robust contact force controller for slip prevention in a robotic gripper
Grasping a soft or fragile object requires the use of minimum contact force to prevent damage or deformation. Without precise knowledge of object parameters, real-time feedback control must be used with a suitable slip sensor to regulate the contact force and prevent slip. Furthermore, the controller must be designed to have good performance characteristics to rapidly modulate the fingertip contact force in response to a slip event. In this paper, a fuzzy sliding mode controller combined with a disturbance observer is proposed for contact force control and slip prevention. The controller is based on a system model that is suitable for a wide class of robotic gripper configurations. The robustness of the controller is evaluated through both simulation and experiment. The control scheme was found to be effective and robust to parameter uncertainty. When tested on a real system, however, chattering phenomena, well known to sliding mode research, was induced by the unmodelled suboptimal components of the system (filtering, backlash, and time delays), and the controller performance was reduced
Performance evaluation of a digital electrical impedance tomography system
Performance evaluation of a portable digital multi-frequency electrical impedance tomography system is presented. The instrumentation hardware and image reconstruction are assessed according to a systematic methodology using a practical phantom. The phantom is equipped with eight electrodes in a ring configuration and a sinusoidal current of constant amplitude is injected using an adjacent current injection protocol. Artificial anomalies are introduced as inhomogeneity targets and the boundary potential data is collected. The images are reconstructed from the boundary data using Comsol Multiphysics and Matlab. Signal to noise ratio (SNR) and accuracy of the measurements are calculated. The limits of detectability and distinguishability of contrasts are measured from the collected potential data set for single and double inhomogeneities. The conductivity of the targets is successfully reconstructed from the potential data measurements. The detectability value is found to be high when a single target is close to the electrodes, while the values are less for the target in the centre. Also, the value of distinguishability increases when the targets move further away from each other
Designing UHF RFID tag antennas with Barcode shape for dual-technology identification
In this paper, a novel methodology to design Ultra High Frequency Radio-Frequency IDentification (UHF RFID) tag antennas with Barcode layout is proposed with the challenging goal of "fusing" both technologies in a single device. Specifically, after a brief recall of the well-known barcode standard, a procedure to design meandered barcode-shaped UHF RFID tags is introduced and discussed leveraging on electromagnetic evidence. The main steps of the proposed method are described by highlighting the constraints inherited by both the adopted technologies, as well as the useful opportunities to automatise the entire antenna design process after a preliminary simulation campaign through a full-wave simulator. Different RFID-Barcode tag antennas are designed, manufactured, and characterised in terms of maximum reading range and tag sensitivity. Obtained results demonstrate the validity of the proposed approach
A methodology for design and appraisal of surgical robotic systems
Surgical robotics is a growing discipline, continuously
expanding with an influx of new ideas and research.
However, it is important that the development of new devices
take account of past mistakes and successes. A structured
approach is necessary, as with proliferation of such research,
there is a danger that these lessons will be obscured,
resulting in the repetition of mistakes and wasted effort
and energy. There are several research paths for surgical
robotics, each with different risks and opportunities and
different methodologies to reach a profitable outcome. The
main emphasis of this paper is on a methodology for ‘applied
research’ in surgical robotics. The methodology sets out a
hierarchy of criteria consisting of three tiers, with the most
important being the bottom tier and the least being the top tier.
It is argued that a robotic system must adhere to these criteria
in order to achieve acceptability. Recent commercial systems
are reviewed against these criteria, and are found to conform
up to at least the bottom and intermediate tiers, the most
important first two tiers, and thus gain some acceptability.
However, the lack of conformity to the criteria in the top
tier, and the inability to conclusively prove increased clinical
benefit, is shown to be hampering their potential in gaining
wide establishment
Competing phases in the high field phase diagram of (TMTSF)ClO
A model is presented for the high field phase diagram of (TMTSF)ClO,
taking into account the anion ordering, which splits the Fermi surface in two
bands. For strong enough field, the largest metal-SDW critical temperature
corresponds to the N=0 phase, which originates from two intraband nesting
processes. At lower temperature, the competition between these processes puts
at disadvantage the N=0 phase vs. the N=1 phase, which is due to interband
nesting. A first order transition takes then place from the N=0 to N=1 phase.
We ascribe to this effect the experimentally observed phase diagrams.Comment: 5 pages, 3 figures (to appear in Phys. Rev. Lett.
Velocity autocorrelation function of a Brownian particle
In this article, we present molecular dynamics study of the velocity
autocorrelation function (VACF) of a Brownian particle. We compare the results
of the simulation with the exact analytic predictions for a compressible fluid
from [6] and an approximate result combining the predictions from hydrodynamics
at short and long times. The physical quantities which determine the decay were
determined from separate bulk simulations of the Lennard-Jones fluid at the
same thermodynamic state point.We observe that the long-time regime of the VACF
compares well the predictions from the macroscopic hydrodynamics, but the
intermediate decay is sensitive to the viscoelastic nature of the solvent.Comment: 7 pages, 6 figure
Field-induced confinement in (TMTSF)2ClO4 under accurately aligned magnetic fields
We present transport measurements along the least conducting c direction of
the organic superconductor (TMTSF)2ClO4, performed under an accurately aligned
magnetic field in the low temperature regime. The experimental results reveal a
two-dimensional confinement of the carriers in the (a,b) planes which is
governed by the magnetic field component along the b' direction. This 2-D
confinement is accompanied by a metal-insulator transition for the c axis
resistivity. These data are supported by a quantum mechanical calculation of
the transverse transport taking into account in self consistent treatment the
effect of the field on the interplane Green function and on the intraplane
scattering time
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