52 research outputs found
A Fast MOSFET RF Switch for TRASE MRI at Low Magnetic Field
International audienceTRansmit Array Spatial Encoding (TRASE) MRI uses trains of B1 pulses alternatively produced by distinct transmit coils. Commonly used coil switching involving PIN diodes is too slow for low-field MRI and would introduce wait times between pulses typically as long as each individual pulse (hence, significant diffusion-induced resolution loss in TRASE MRI of gas samples). A MOSFET-based RF switch is described and characterised. Up to 200 kHz, it allows for sub-µs switching of RF currents from a single amplifier to several coils with sufficient isolation ratio and no delay between pulses
Inside Out: Transforming Images of Lab-Grown Plants for Machine Learning Applications in Agriculture
Machine learning tasks often require a significant amount of training data
for the resultant network to perform suitably for a given problem in any
domain. In agriculture, dataset sizes are further limited by phenotypical
differences between two plants of the same genotype, often as a result of
differing growing conditions. Synthetically-augmented datasets have shown
promise in improving existing models when real data is not available. In this
paper, we employ a contrastive unpaired translation (CUT) generative
adversarial network (GAN) and simple image processing techniques to translate
indoor plant images to appear as field images. While we train our network to
translate an image containing only a single plant, we show that our method is
easily extendable to produce multiple-plant field images. Furthermore, we use
our synthetic multi-plant images to train several YoloV5 nano object detection
models to perform the task of plant detection and measure the accuracy of the
model on real field data images. Including training data generated by the
CUT-GAN leads to better plant detection performance compared to a network
trained solely on real data.Comment: 35 pages, 23 figure
CeCoIn5 - a quantum critical superfluid
We have made the first complete measurements of the London penetration depth
of CeCoIn5, a quantum-critical metal where superconductivity
arises from a non-Fermi-liquid normal state. Using a novel tunnel diode
oscillator designed to avoid spurious contributions to , we have
established the existence of intrinsic and anomalous power-law behaviour at low
temperature. A systematic analysis raises the possibility that the unusual
observations are due to an extension of quantum criticality into the
superconducting state.Comment: 5 pages, 3 figure
Effect of Impurity Scattering on the Nonlinear Microwave Response in High-Tc Superconductors
We theoretically investigate intermodulation distortion in high-Tc
superconductors. We study the effect of nonmagnetic impurities on the real and
imaginary parts of nonlinear conductivity. The nonlinear conductivity is
proportional to the inverse of temperature owing to the dependence of the
damping effect on energy, which arises from the phase shift deviating from the
unitary limit. It is shown that the final-states interaction makes the real
part predominant over the imaginary part. These effects have not been included
in previous theories based on the two-fluid model, enabling a consistent
explanation for the experiments with the rf and dc fields
Theory of Nonlinear Meissner Effect in High-Tc Superconductors
We investigate the nonlinear Meissner effect microscopically. Previous
studies did not consider a certain type of interaction effect on the nonlinear
phenomena. The scattering amplitude barely appears without being renormalized
into the Fermi-liquid parameter. With this effect we can solve the outstanding
issues (the quantitative problem, the temperature and angle dependences). The
quantitative calculation is performed with use of the fluctuation-exchange
approximation on the Hubbard model. It is also shown that the perturbation
expansion on the supercurrent by the vector potential converges owing to the
nonlocal effect
Phenomenology of a-axis and b-axis charge dynamics from microwave spectroscopy of highly ordered YBa2Cu3O6.50 and YBa2Cu3O6.993
Extensive measurements of the microwave conductivity of highly pure and
oxygen-ordered \YBCO single crystals have been performed as a means of
exploring the intrinsic charge dynamics of a d-wave superconductor. Broadband
and fixed-frequency microwave apparatus together provide a very clear picture
of the electrodynamics of the superconducting condensate and its thermally
excited nodal quasiparticles. The measurements reveal the existence of very
long-lived excitations deep in the superconducting state, as evidenced by sharp
cusp-like conductivity spectra with widths that fall well within our
experimental bandwidth. We present a phenomenological model of the microwave
conductivity that captures the physics of energy-dependent quasiparticle
dynamics in a d-wave superconductor which, in turn, allows us to examine the
scattering rate and oscillator strength of the thermally excited quasiparticles
as functions of temperature. Our results are in close agreement with the
Ferrell-Glover-Tinkham sum rule, giving confidence in both our experiments and
the phenomenological model. Separate experiments for currents along the and directions of detwinned crystals allow us to isolate the role
of the CuO chain layers in \YBCO, and a model is presented that incorporates
both one-dimensional conduction from the chain electrons and two-dimensional
transport associated with the \cuplane plane layers.Comment: 17 pages, 13 figure
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