143 research outputs found
A fast pneumatic sample-shuttle with attenuated shocks
We describe a home-built pneumatic shuttle suitable for the fast displacement
of samples in the vicinity of a highly sensitive atomic magnetometer. The
samples are magnetized at 1 T using a Halbach assembly of magnets. The device
enables the remote detection of free induction decay in ultra-low-field and
zero-field NMR experiments, in relaxometric measurements and in other
applications involving the displacement of magnetized samples within time
intervals as short as a few tens of milliseconds. Other possible applications
of fast sample shuttling exist in radiological studies, where samples have to
be irradiated and then analyzed in a 'cold' environment.Comment: 3 pages and 3 figures; 2 additional pages (2 figures) as a
supplemental materia
Self-adaptive loop for external disturbance reduction in differential measurement set-up
We present a method developed to actively compensate common-mode magnetic
disturbances on a multi-sensor device devoted to differential measurements. The
system uses a field-programmable-gated-array card, and operates in conjunction
with a high sensitivity magnetometer: compensating the common-mode of magnetic
disturbances results in a relevant reduction of the difference-mode noise. The
digital nature of the compensation system allows for using a numerical approach
aimed at automatically adapting the feedback loop filter response. A common
mode disturbance attenuation exceeding 50 dB is achieved, resulting in a final
improvement of the differential noise floor by a factor of 10 over the whole
spectral interval of interest.Comment: 7 pages, 8 figures, 26 ref
Restoring Narrow Linewidth to a Gradient-Broadened Magnetic Resonance by Inhomogeneous Dressing
We study the possibility of counteracting the line-broadening of atomic
magnetic resonances due to inhomogeneities of the static magnetic field by
means of spatially dependent magnetic dressing, driven by an alternating field
that oscillates much faster than the Larmor precession frequency. We
demonstrate that an intrinsic resonance linewidth of 25~Hz that has been
broadened up to hundreds Hz by a magnetic field gradient, can be recovered by
the application of an appropriate inhomogeneous dressing field. The findings of
our experiments may have immediate and important implications, because they
facilitate the use of atomic magnetometers as robust, high sensitivity
detectors in ultra-low-field NMR imaging.Comment: 9 pages, 7 figures, 33 refs. This is the unedited versio
Multichannel optical atomic magnetometer operating in unshielded environment
A multi-channel atomic magnetometer operating in an unshielded environment is
described and characterised. The magnetometer is based on D1 optical pumping
and D2 polarimetry of Cs vapour contained in gas-buffered cells. Several
technical implementations are described and discussed in detail. The
demonstrated sensitivity of the setup is 100fT/Hz^1/2 when operating in the
difference mode.Comment: 9 pages, 5 figures, appearing in Appl.Phys.
Selective coronary angiogrphy: care for patients during the preparation for and after the procedure
Introduction: Selective coronary angiography is a highly specialized diagnostic test, which provides accurate information about potential stenosis and/or occlusion of coronary arteries, as well as about pathologic alterations of heart chambers and valves. Cardiovascular diseases are a key factor for high mortality and disability in Bulgaria and globally. Fast and accurate diagnosis is critical for patients with cardiac symptoms, such as chest pain. Nurses working in cardiology units must have specific knowledge and professional skills in providing quality care, in order to lower the risk for complications.Aim: To describe the main activities nurses accomplish when preparing patients for selective coronary angiography, and during recovery after the procedure.Materials and methods: Research based on invasive cardiology literature, official medical information and legal documentation. Targeted observation and surveillance of the activities of healthcare specialists in a cardiology unit.Results and considerations: Providing student nurses with a technical checklist card related to activities before and after selective coronary angiography would help them expand their knowledge and professional skills
Microtesla NMR J-coupling spectroscopy with an unshielded atomic magnetometer
We present experimental data and theoretical interpretation of NMR spectra of
remotely magnetized samples, detected in an unshielded environment by means of
a differential atomic magnetometer. The measurements are performed in an
ultra-low-field at an intermediate regime, where the J-coupling and the Zeeman
energies have comparable values and produce rather complex line sets, which are
satisfactorily interpreted.Comment: 8 pages, 8 figs, appearing in JMR (2016
Stray Magnetic Field Compensation with a Scalar Atomic Magnetometer
We describe a system for the compensation of time-dependent stray magnetic
fields using a dual channel scalar magnetometer based on non-linear Faraday
rotation in synchronously optically pumped Cs vapour. We detail the active
control strategy, with an emphasis on the electronic circuitry, based on a
simple phase-locked-loop integrated circuit. The performance and limits of the
system developed are tested and discussed. The system was applied to
significantly improve the detection of free induction decay signals from
protons of remotely magnetized water precessing in an ultra-low magnetic field.Comment: 8 pages, 6 figures, 31 refs, v2 (with minor improvements) appearing
in Rev.Sc.Instr. June 201
Cloud benchmarking and performance analysis of an HPC application in Amazon EC2
Cloud computing platforms have been continuously evolving. Features such as the Elastic Fabric Adapter (EFA) in the Amazon Web Services (AWS) platform have brought yet another revolution in the High Performance Computing (HPC) world, further accelerating the convergence of HPC and cloud computing. Other public clouds also support similar features further fueling this change. In
this paper, we show how and why the performance of a large-scale computational fluid dynamics (CFD) HPC application on AWS competes very closely with the one on Beskow - a Cray XC40 supercomputer at the PDC Center for High-Performance Computing - in terms of cost-efficiency with strong scaling up to 2304 processes. We perform an extensive set of micro and macro bench-
marks in both environments and conduct a comparative analysis. Until as recently as 2020 these benchmarks have notoriously yielded unsatisfactory results for the cloud platforms compared with on-premise infrastructures. Our aim is to access the HPC capabilities of the cloud, and in general to demonstrate how researchers can scale and evaluate the performance of their application in the cloud.ENABL
A room-temperature alternating current susceptometer - Data analysis, calibration, and test
An AC susceptometer operating in the range of 10 Hz to 100 kHz and at room
temperature is designed, built, calibrated and used to characterize the
magnetic behaviour of coated magnetic nanoparticles. Other weakly magnetic
materials (in amounts of some millilitres) can be analyzed as well. The setup
makes use of a DAQ-based acquisition system in order to determine the amplitude
and the phase of the sample magnetization as a function of the frequency of the
driving magnetic field, which is powered by a digital waveform generator. A
specific acquisition strategy makes the response directly proportional to the
sample susceptibility, taking advantage of the differential nature of the coil
assembly. A calibration method based on conductive samples is developed.Comment: 8 pages, 7 figures, 19 ref
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