109,313 research outputs found
Experimental demonstration of an isotope-sensitive warhead verification technique using nuclear resonance fluorescence
Future nuclear arms reduction efforts will require technologies to verify
that warheads slated for dismantlement are authentic without revealing any
sensitive weapons design information to international inspectors. Despite
several decades of research, no technology has met these requirements
simultaneously. Recent work by Kemp et al. [Kemp RS, Danagoulian A, Macdonald
RR, Vavrek JR (2016) Proc Natl Acad Sci USA 113:8618--8623] has produced a
novel physical cryptographic verification protocol that approaches this treaty
verification problem by exploiting the isotope-specific nature of nuclear
resonance fluorescence (NRF) measurements to verify the authenticity of a
warhead. To protect sensitive information, the NRF signal from the warhead is
convolved with that of an encryption foil that contains key warhead isotopes in
amounts unknown to the inspector. The convolved spectrum from a candidate
warhead is statistically compared against that from an authenticated template
warhead to determine whether the candidate itself is authentic. Here we report
on recent proof-of-concept warhead verification experiments conducted at the
Massachusetts Institute of Technology. Using high-purity germanium (HPGe)
detectors, we measured NRF spectra from the interrogation of proxy 'genuine'
and 'hoax' objects by a 2.52 MeV endpoint bremsstrahlung beam. The observed
differences in NRF intensities near 2.2 MeV indicate that the physical
cryptographic protocol can distinguish between proxy genuine and hoax objects
with high confidence in realistic measurement times.Comment: 38 pages, 19 figures; revised for peer review and copy editing;
addition to SI for realistic scenario projections; minor length reduction for
journal requirement
A Review of Prosthetic Interface Stress Investigations
Over the last decade, numerous experimental and numerical analyses have been conducted to investigate the stress distribution between the residual limb and prosthetic socket of persons with lower limb amputation. The objectives of these analyses have been to improve our understanding of the residual limb/prosthetic socket system, to evaluate the influence of prosthetic design parameters and alignment variations on the interface stress distribution, and to evaluate prosthetic fit. The purpose of this paper is to summarize these experimental investigations and identify associated limitations. In addition, this paper presents an overview of various computer models used to investigate the residual limb interface, and discusses the differences and potential ramifications of the various modeling formulations. Finally, the potential and future applications of these experimental and numerical analyses in prosthetic design are presented
Evaluation of resistive-plate-chamber-based TOF-PET applied to in-beam particle therapy monitoring
Particle therapy is a highly conformal radiotherapy technique which reduces the dose deposited to the surrounding normal tissues. In order to fully exploit its advantages, treatment monitoring is necessary to minimize uncertainties related to the dose delivery. Up to now, the only clinically feasible technique for the monitoring of therapeutic irradiation with particle beams is Positron Emission Tomography (PET). In this work we have compared a Resistive Plate Chamber (RPC)-based PET scanner with a scintillation-crystal-based PET scanner for this application. In general, the main advantages of the RPC-PET system are its excellent timing resolution, low cost, and the possibility of building large area systems. We simulated a partial-ring scannerbeam monitoring, which has an intrinsically low positron yield compared to diagnostic PET. In addition, for in-beam PET there is a further data loss due to the partial ring configuration. In order to improve the performance of the RPC-based scanner, an improved version of the RPC detector (modifying the thickness of the gas and glass layers), providing a larger sensitivity, has been simulated and compared with an axially extended version of the crystal-based device. The improved version of the RPC shows better performance than the prototype, but the extended version of the crystal-based PET outperforms all other options. based on an RPC prototype under construction within the Fondazione per Adroterapia Oncologica (TERA). For comparison with the crystal-based PET scanner we have chosen the geometry of a commercially available PET scanner, the Philips Gemini TF. The coincidence time resolution used in the simulations takes into account the current achievable values as well as expected improvements of both technologies. Several scenarios (including patient data) have been simulated to evaluate the performance of different scanners. Initial results have shown that the low sensitivity of the RPC hampers its application to hadro
Critical Casimir Interactions and Percolation: the quantitative description of critical fluctuations
Casimir forces in a critical media are produced by spatial suppression of
order parameter fluctuations. In this paper we address the question how
fluctuations of a critical media relates the magnitude of critical Casimir
interactions. Namely, for the Ising model we express the potential of critical
Casimir interactions in terms of Fortuin-Kasteleyn site-bond correlated
percolation clusters. These clusters are quantitative representation of
fluctuations in the media. New Monte Carlo method for the computation of the
Casimir force potential which is based on this relation is proposed. We verify
this method by computation of Casimir interactions between two disks for 2D
Ising model. The new method is also applied to the investigation of
non-additivity of the critical Casimir potential. The non-additive contribution
to three-particles interaction is computed as a function of the temperature.Comment: 13 pages, 4 figure
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