146 research outputs found
Test of a Liquid Argon TPC in a magnetic field and investigation of high temperature superconductors in liquid argon and nitrogen
Tests with cosmic ray muons of a small liquid argon time projection chamber
(LAr TPC) in a magnetic field of 0.55 T are described. No effect of the
magnetic field on the imaging properties were observed. In view of a future
large, magnetized LAr TPC, we investigated the possibility to operate a high
temperature superconducting (HTS) solenoid directly in the LAr of the detector.
The critical current of HTS cables in an external magnetic field was
measured at liquid nitrogen and liquid argon temperatures and a small prototype
HTS solenoid was built and tested.Comment: 5 pages, 5 figures, to appear in Proc. of 1st International Workshop
towards the Giant Liquid Argon Charge Imaging Experiment (GLA2010), Tsukuba
(Japan), March 201
First operation of a liquid Argon TPC embedded in a magnetic field
We have operated for the first time a liquid Argon TPC immersed in a magnetic
field up to 0.55 T. We show that the imaging properties of the detector are not
affected by the presence of the magnetic field. The magnetic bending of the
ionizing particle allows to discriminate their charge and estimate their
momentum. These figures were up to now not accessible in the non-magnetized
liquid Argon TPC.Comment: 9 pages, 3 figure
Feasibility of high-voltage systems for a very long drift in liquid argon TPCs
Designs of high-voltage (HV) systems for creating a drift electric field in
liquid argon TPCs are reviewed. In ongoing experiments systems capable of
approx. 100 kV are realised for a drift field of 0.5-1 kV/cm over a length of
up to 1.5 m. Two of them having different approaches are presented: (1) the
ICARUS-T600 detector having a system consisting of an external power supply, HV
feedthroughs and resistive voltage degraders and (2) the ArDM-1t detector
having a cryogenic Greinacher HV multiplier inside the liquid argon volume. For
a giant scale liquid argon TPC, a system providing 2 MV may be required to
attain a drift length of approx. 20 m. Feasibility of such a system is
evaluated by extrapolating the existing designs.Comment: 8 pages, 13 figures, to appear in Proc. of 1st International Workshop
towards the Giant Liquid Argon Charge Imaging Experiment (GLA2010), Tsukuba
(Japan), March 201
High-Temperature Superconducting Level Meter for Liquid Argon Detectors
Capacitive devices are customarily used as probes to measure the level of
noble liquids in detectors operated for neutrino studies and dark matter
searches. In this work we describe the use of a high-temperature
superconducting material as an alternative to control the level of a cryogenic
noble liquid. Lab measurements indicate that the superconductor shows a linear
behaviour, a high degree of stability and offers a very accurate determination
of the liquid volume. This device is therefore a competitive instrument and
shows several advantages over conventional level meters.Comment: 13 pages, 11 figures. Accepted for publication in JINS
EMG-driven control in lower limb prostheses: a topic-based systematic review
Background The inability of users to directly and intuitively control their state-of-the-art commercial prosthesis contributes to a low device acceptance rate. Since Electromyography (EMG)-based control has the potential to address those inabilities, research has flourished on investigating its incorporation in microprocessor-controlled lower limb prostheses (MLLPs). However, despite the proposed benefits of doing so, there is no clear explanation regarding the absence of a commercial product, in contrast to their upper limb counterparts. Objective and methodologies This manuscript aims to provide a comparative overview of EMG-driven control methods for MLLPs, to identify their prospects and limitations, and to formulate suggestions on future research and development. This is done by systematically reviewing academical studies on EMG MLLPs. In particular, this review is structured by considering four major topics: (1) type of neuro-control, which discusses methods that allow the nervous system to control prosthetic devices through the muscles; (2) type of EMG-driven controllers, which defines the different classes of EMG controllers proposed in the literature; (3) type of neural input and processing, which describes how EMG-driven controllers are implemented; (4) type of performance assessment, which reports the performance of the current state of the art controllers. Results and conclusions The obtained results show that the lack of quantitative and standardized measures hinders the possibility to analytically compare the performances of different EMG-driven controllers. In relation to this issue, the real efficacy of EMG-driven controllers for MLLPs have yet to be validated. Nevertheless, in anticipation of the development of a standardized approach for validating EMG MLLPs, the literature suggests that combining multiple neuro-controller types has the potential to develop a more seamless and reliable EMG-driven control. This solution has the promise to retain the high performance of the currently employed non-EMG-driven controllers for rhythmic activities such as walking, whilst improving the performance of volitional activities such as task switching or non-repetitive movements. Although EMG-driven controllers suffer from many drawbacks, such as high sensitivity to noise, recent progress in invasive neural interfaces for prosthetic control (bionics) will allow to build a more reliable connection between the user and the MLLPs. Therefore, advancements in powered MLLPs with integrated EMG-driven control have the potential to strongly reduce the effects of psychosomatic conditions and musculoskeletal degenerative pathologies that are currently affecting lower limb amputees
First results from a Liquid Argon Time Projection Chamber in a Magnetic Field
A small liquid argon Time Projection Chamber (LAr TPC) was operated for the
first time in a magnetic field of 0.55 Tesla. The imaging properties of the
detector were not affected by the magnetic field. In a test run with cosmic
rays a sample of through going and stopping muons was collected. The chamber
with the readout electronics and the experimental setup are described. A few
selected events were reconstructed and analyzed and the results are presented.
The magnetic bending of the charged particle tracks allows the determination of
the electric charge and the momentum, even for particles not fully contained in
the drift chamber. These features are e.g. required for future neutrino
detectors at a neutrino factory.Comment: 35 pages, 25 figures, version with full resolution figures at
available at http://neutrino.ethz.ch/GLACIER
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