4,771 research outputs found
Robust Near-Field 3D Localization of an Unaligned Single-Coil Agent Using Unobtrusive Anchors
The magnetic near-field provides a suitable means for indoor localization,
due to its insensitivity to the environment and strong spatial gradients. We
consider indoor localization setups consisting of flat coils, allowing for
convenient integration of the agent coil into a mobile device (e.g., a smart
phone or wristband) and flush mounting of the anchor coils to walls. In order
to study such setups systematically, we first express the Cram\'er-Rao lower
bound (CRLB) on the position error for unknown orientation and evaluate its
distribution within a square room of variable size, using 15 x 10cm anchor
coils and a commercial NFC antenna at the agent. Thereby, we find cm-accuracy
being achievable in a room of 10 x 10 x 3 meters with 12 flat wall-mounted
anchors and with 10mW used for the generation of magnetic fields. Practically
achieving such estimation performance is, however, difficult because of the
non-convex 5D likelihood function. To that end, we propose a fast and accurate
weighted least squares (WLS) algorithm which is insensitive to initialization.
This is enabled by effectively eliminating the orientation nuisance parameter
in a rigorous fashion and scaling the individual anchor observations, leading
to a smoothed 3D cost function. Using WLS estimates to initialize a
maximum-likelihood (ML) solver yields accuracy near the theoretical limit in up
to 98% of cases, thus enabling robust indoor localization with unobtrusive
infrastructure, with a computational efficiency suitable for real-time
processing.Comment: 7 pages, to be presented at IEEE PIMRC 201
Practical Accuracy Limits of Radiation-Aware Magneto-Inductive 3D Localization
The key motivation for the low-frequency magnetic localization approach is
that magnetic near-fields are well predictable by a free-space model, which
should enable accurate localization. Yet, limited accuracy has been reported
for practical systems and it is unclear whether the inaccuracies are caused by
field distortion due to nearby conductors, unconsidered radiative propagation,
or measurement noise. Hence, we investigate the practical performance limits by
means of a calibrated magnetoinductive system which localizes an active
single-coil agent with arbitrary orientation, using 4 mW transmit power at 500
kHz. The system uses eight single-coil anchors around a 3m x 3m area in an
office room. We base the location estimation on a complex baseband model which
comprises both reactive and radiative propagation. The link coefficients, which
serve as input data for location estimation, are measured with a multiport
network analyzer while the agent is moved with a positioner device. This
establishes a reliable ground truth for calibration and evaluation. The system
achieves a median position error of 3.2 cm and a 90th percentile of 8.3 cm.
After investigating the model error we conjecture that field distortion due to
conducting building structures is the main cause of the performance bottleneck.
The results are complemented with predictions on the achievable accuracy in
more suitable circumstances using the Cram\'er-Rao lower bound.Comment: To appear at the IEEE ICC 2019 Workshops. This work has been
submitted to the IEEE for possible publication. Copyright may be transferred
without notice, after which this version may no longer be accessibl
Tahap penguasaan, sikap dan minat pelajar Kolej Kemahiran Tinggi MARA terhadap mata pelajaran Bahasa Inggeris
Kajian ini dilakukan untuk mengenal pasti tahap penguasaan, sikap dan minat pelajar
Kolej Kemahiran Tinggi Mara Sri Gading terhadap Bahasa Inggeris. Kajian yang
dijalankan ini berbentuk deskriptif atau lebih dikenali sebagai kaedah tinjauan. Seramai
325 orang pelajar Diploma in Construction Technology dari Kolej Kemahiran Tinggi
Mara di daerah Batu Pahat telah dipilih sebagai sampel dalam kajian ini. Data yang
diperoleh melalui instrument soal selidik telah dianalisis untuk mendapatkan
pengukuran min, sisihan piawai, dan Pekali Korelasi Pearson untuk melihat hubungan
hasil dapatan data. Manakala, frekuensi dan peratusan digunakan bagi mengukur
penguasaan pelajar. Hasil dapatan kajian menunjukkan bahawa tahap penguasaan
Bahasa Inggeris pelajar adalah berada pada tahap sederhana manakala faktor utama yang
mempengaruhi penguasaan Bahasa Inggeris tersebut adalah minat diikuti oleh sikap.
Hasil dapatan menggunakan pekali Korelasi Pearson juga menunjukkan bahawa terdapat
hubungan yang signifikan antara sikap dengan penguasaan Bahasa Inggeris dan antara
minat dengan penguasaan Bahasa Inggeris. Kajian menunjukkan bahawa semakin positif
sikap dan minat pelajar terhadap pengajaran dan pembelajaran Bahasa Inggeris semakin
tinggi pencapaian mereka. Hasil daripada kajian ini diharapkan dapat membantu pelajar
dalam meningkatkan penguasaan Bahasa Inggeris dengan memupuk sikap positif dalam
diri serta meningkatkan minat mereka terhadap Bahasa Inggeris dengan lebih baik. Oleh
itu, diharap kajian ini dapat memberi panduan kepada pihak-pihak yang terlibat dalam
membuat kajian yang akan datang
Design analysis of levitation facility for space processing applications
Containerless processing facilities for the space laboratory and space shuttle are defined. Materials process examples representative of the most severe requirements for the facility in terms of electrical power, radio frequency equipment, and the use of an auxiliary electron beam heater were used to discuss matters having the greatest effect upon the space shuttle pallet payload interfaces and envelopes. Improved weight, volume, and efficiency estimates for the RF generating equipment were derived. Results are particularly significant because of the reduced requirements for heat rejection from electrical equipment, one of the principal envelope problems for shuttle pallet payloads. It is shown that although experiments on containerless melting of high temperature refractory materials make it desirable to consider the highest peak powers which can be made available on the pallet, total energy requirements are kept relatively low by the very fast processing times typical of containerless experiments and allows consideration of heat rejection capabilities lower than peak power demand if energy storage in system heat capacitances is considered. Batteries are considered to avoid a requirement for fuel cells capable of furnishing this brief peak power demand
IMag:Accurate and Rapidly Deployable Inertial Magneto-Inductive Localisation
Localisation is of importance for many applications. Our motivating scenarios are short-term construction work and emergency rescue. Not only is accuracy necessary, these scenarios also require rapid setup and robustness to environmental conditions. These requirements preclude the use of many traditional methods e.g. vision-based, laser-based, Ultra-wide band (UWB) and Global Positioning System (GPS)-based localisation systems. To solve these challenges, we introduce iMag, an accurate and rapidly deployable inertial magneto-inductive (MI) localisation system. It localises monitored workers using a single MI transmitter and inertial measurement units with minimal setup effort. However, MI location estimates can be distorted and ambiguous. To solve this problem, we suggest a novel method to use MI devices for sensing environmental distortions, and use these to correctly close inertial loops. By applying robust simultaneous localisation and mapping (SLAM), our proposed localisation method achieves excellent tracking accuracy, and can improve performance significantly compared with only using an inertial measurement unit (IMU) and MI device for localisation
Non-conventional geoelectric arrays : practical results of the OTKA project K49604
In this paper we provide a comprehensive summary about the practical results
of the OTKA project K49604. 1. We calculated the consequences of incorrect positioning
of the electrodes for various multielectrode systems. In practice these effects
were found to be negligible. The only exception is the case of rocky surface, where it
is impossible to put the electrodes in the desired positions. The errors can however
be kept within an acceptable range, if the electrodes of the linear arrays are put
off-set, at right angles from the measuring line. A five-six times larger off-set has less
effect than a certain mis-position along the line, connecting the electrodes. 2. We
carried out tensorial geoelectric measurements around the Cistercian Monastery at
Pilisszentkereszt. Areal measurements provide much more detailed and unambiguous
anomalies than 2D profile measurements, and the tensor invariant representation of
apparent resistivity anomalies provides a realistic picture about the lateral variation
of the subsurface resistivity, even in field circumstances. 3. We tested the applicability
of 3D electrical resistivity tomography (ERT) technique to detect landmines
in different soil conditions and at various depths. Metallic and non-metallic landmines
buried in wet and dry soils had been synthetically modeled. According to the
inverted resistivity data using the dipole axial array in wet environment, it was possible
to locate the metallic and non-metallic landmines as long as the noise level was
about 5%. 4. We elaborated moreover a geoelectrical procedure which is able to map
multidirectional fissure systems by combining geoelectrical profiling and geoelectrical
azimuthal measurements. Results received by using both the so-called null-, and
traditional arrays were jointly interpreted. The humidity of the fissures affects the
measured results significantly, and in a meaningful way. 5. We presented the socalled
standardized pricking probe (PP) surveying technique and demonstrated its
usefulness in an archaeological study. The PP images proved to be definitely more
close to the realistic shape of the buried chapel than the geoelectric and magnetic
measurements, and they also revealed more details about the subsurface than the
georadar. The optimum PP parameters: horizontal interval, pricking depth, observable
quantity and its way of presentation were optimized through field experiments.
For more details see the cited publications. The figures ever published in Hungarian
journals are not reproduced here.
Keywords: 3D ERT; geometric nois
A bacterial cytolinker couples positioning of magnetic organelles to cell shape control
Magnetotactic bacteria maneuver within the geomagnetic field by means of intracellular magnetic organelles, magnetosomes, which are aligned into a chain and positioned at midcell by a dedicated magnetosome-specific cytoskeleton, the "magnetoskeleton." However, how magnetosome chain organization and resulting magnetotaxis is linked to cell shape has remained elusive. Here, we describe the cytoskeletal determinant CcfM (curvature-inducing coiled-coil filament interacting with the magnetoskeleton), which links the magneto-skeleton to cell morphology regulation in Magnetospirillum gryphiswaldense. Membrane-anchored CcfM localizes in a filamentous pattern along regions of inner positive-cell curvature by its coiled-coil motifs, and independent of the magnetoskeleton. CcfM overexpression causes additional circumferential localization patterns, associated with a dramatic increase in cell curvature, and magnetosome chain mislocalization or complete chain disruption. In contrast, deletion of ccfM results in decreased cell curvature, impaired cell division, and predominant formation of shorter, doubled chains of magnetosomes. Pleiotropic effects of CcfM on magnetosome chain organization and cell morphology are supported by the finding that CcfM interacts with the magnetoskeleton-related MamY and the actin-like MamK via distinct motifs, and with the cell shape-related cytoskeleton via MreB. We further demonstrate that CcfM promotes motility and magnetic alignment in structured environments, and thus likely confers a selective advantage in natural habitats of magnetotactic bacteria, such as aquatic sediments. Overall, we unravel the function of a prokaryotic cytoskeletal constituent that is widespread in magnetic and nonmagnetic spirilla-shaped Alphaproteobacteria
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