154 research outputs found
Response of the topological surface state to surface disorder in TlBiSe
Through a combination of experimental techniques we show that the topmost
layer of the topo- logical insulator TlBiSe as prepared by cleavage is
formed by irregularly shaped Tl islands at cryogenic temperatures and by mobile
Tl atoms at room temperature. No trivial surface states are observed in
photoemission at low temperatures, which suggests that these islands can not be
re- garded as a clear surface termination. The topological surface state is,
however, clearly resolved in photoemission experiments. This is interpreted as
a direct evidence of its topological self-protection and shows the robust
nature of the Dirac cone like surface state. Our results can also help explain
the apparent mass acquisition in S-doped TlBiSe.Comment: 16 pages, 5 figure
Application of the Compress Sensing Theory for Improvement of the TOF Resolution in a Novel J-PET Instrument
Nowadays, in Positron Emission Tomography (PET) systems, a Time of Flight
information is used to improve the image reconstruction process. In Time of
Flight PET (TOF-PET), fast detectors are able to measure the difference in the
arrival time of the two gamma rays, with the precision enabling to shorten
significantly a range along the line-of-response (LOR) where the annihilation
occurred. In the new concept, called J-PET scanner, gamma rays are detected in
plastic scintillators. In a single strip of J-PET system, time values are
obtained by probing signals in the amplitude domain. Owing to Compress Sensing
theory, information about the shape and amplitude of the signals is recovered.
In this paper we demonstrate that based on the acquired signals parameters, a
better signal normalization may be provided in order to improve the TOF
resolution. The procedure was tested using large sample of data registered by a
dedicated detection setup enabling sampling of signals with 50 ps intervals.
Experimental setup provided irradiation of a chosen position in the plastic
scintillator strip with annihilation gamma quanta
Arthroscopic meniscal surgery: a national society treatment guideline and consensus statement.
AIMS: The aim of the British Association for Surgery of the Knee (BASK) Meniscal Consensus Project was to develop an evidence-based treatment guideline for patients with meniscal lesions of the knee. MATERIALS AND METHODS: A formal consensus process was undertaken applying nominal group, Delphi, and appropriateness methods. Consensus was first reached on the terminology relating to the definition, investigation, and classification of meniscal lesions. A series of simulated clinical scenarios was then created and the appropriateness of arthroscopic meniscal surgery or nonoperative treatment in each scenario was rated by the group. The process was informed throughout by the latest published, and previously unpublished, clinical and epidemiological evidence. Scenarios were then grouped together based upon the similarity of clinical features and ratings to form the guideline for treatment. Feedback on the draft guideline was sought from the entire membership of BASK before final revisions and approval by the consensus group. RESULTS: A total of 45 simulated clinical scenarios were refined to five common clinical presentations and six corresponding treatment recommendations. The final guideline stratifies patients based upon a new, standardized classification of symptoms, signs, radiological findings, duration of symptoms, and previous treatment. CONCLUSION: The 2018 BASK Arthroscopic Meniscal Surgery Treatment Guidance will facilitate the consistent identification and treatment of patients with meniscal lesions. It is hoped that this guidance will be adopted nationally by surgeons and help inform healthcare commissioning guidance. Validation in clinical practice is now required and several areas of uncertainty in relation to treatment should be a priority for future high-quality prospective studies. Cite this article: Bone Joint J 2019;101-B:652-659
Novel method for hit-position reconstruction using voltage signals in plastic scintillators and its application to Positron Emission Tomography
Currently inorganic scintillator detectors are used in all commercial Time of
Flight Positron Emission Tomograph (TOF-PET) devices. The J-PET collaboration
investigates a possibility of construction of a PET scanner from plastic
scintillators which would allow for single bed imaging of the whole human body.
This paper describes a novel method of hit-position reconstruction based on
sampled signals and an example of an application of the method for a single
module with a 30 cm long plastic strip, read out on both ends by Hamamatsu
R4998 photomultipliers. The sampling scheme to generate a vector with samples
of a PET event waveform with respect to four user-defined amplitudes is
introduced. The experimental setup provides irradiation of a chosen position in
the plastic scintillator strip with an annihilation gamma quanta of energy
511~keV. The statistical test for a multivariate normal (MVN) distribution of
measured vectors at a given position is developed, and it is shown that signals
sampled at four thresholds in a voltage domain are approximately normally
distributed variables. With the presented method of a vector analysis made out
of waveform samples acquired with four thresholds, we obtain a spatial
resolution of about 1 cm and a timing resolution of about 80 p
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