3,590 research outputs found
Radiocarbon positive-ion mass spectrometry
Proof-of-principle of a new mass spectrometric technique for radiocarbon measurement is demonstrated. Interfering nitrogen and hydrocarbon molecules are largely eliminated in a charge-exchange cell operating on non-metallic gas. The positive-to-negative ion conversion is the reverse of that conventionally used in accelerator mass spectrometry (AMS) and is compatible with plasma ion sources that may be significantly more efficient and capable of greater output than are AMS sputter ion sources. The Nanogan electron cyclotron resonance (ECR) ion source employed exhibited no sample memory and the >50 kyrs age range of AMS was reproduced. A bespoke prototype new instrument is now required to optimise the plasma and cell physics and to realise hypothetical performance gains over AMS
MIMO In Vivo
We present the performance of MIMO for in vivo environments, using ANSYS HFSS
and their complete human body model, to determine the maximum data rates that
can be achieved using an IEEE 802.11n system. Due to the lossy nature of the in
vivo medium, achieving high data rates with reliable performance will be a
challenge, especially since the in vivo antenna performance is strongly
affected by near field coupling to the lossy medium and the signals levels will
be limited by specified specific absorption rate (SAR) levels. We analyzed the
bit error rate (BER) of a MIMO system with one pair of antennas placed in vivo
and the second pair placed inside and outside the body at various distances
from the in vivo antennas. The results were compared to SISO simulations and
showed that by using MIMO in vivo, significant performance gain can be
achieved, and at least two times the data rate can be supported with SAR
limited transmit power levels, making it possible to achieve target data rates
in the 100 Mbps.Comment: WAMICON 201
Consistent Inversion of Noisy Non-Abelian X-Ray Transforms
For a simple surface, the non-linear statistical inverse problem of
recovering a matrix field from discrete, noisy
measurements of the -valued scattering data of a solution of a
matrix ODE is considered (). Injectivity of the map was established by [Paternain, Salo, Uhlmann; Geom.Funct.Anal. 2012].
A statistical algorithm for the solution of this inverse problem based on
Gaussian process priors is proposed, and it is shown how it can be implemented
by infinite-dimensional MCMC methods. It is further shown that as the number
of measurements of point-evaluations of increases, the statistical
error in the recovery of converges to zero in -distance at a
rate that is algebraic in , and approaches for smooth matrix
fields . The proof relies, among other things, on a new stability
estimate for the inverse map .
Key applications of our results are discussed in the case to
polarimetric neutron tomography, see [Desai et al., Nature Sc.Rep. 2018] and
[Hilger et al., Nature Comm. 2018
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