526 research outputs found
A new experiment to search for the invisible decay of the orthopositronium
We propose an experiment to search for invisible decays of orthopositronium
(o-Ps) with a 90% confidence sensitivity in the branching ratio as low as
. Evidence for this decay mode would unambigously signal new physics:
either the existence of extra--dimensions or fractionally charged particles or
new light gauge bosons. The experimental approach and the detector components
of the proposed experiment are described.Comment: Based on a talk given at Workshop on Positronium Physics, Zurich,
Switzerland, 30-31 May 200
Why do Great White Pelican chicks die suddenly on Arel island, Banc d'Arguin, in Mauritania ?
Le statut du Pélican blanc en Afrique dans les années quatre-vingts est passé en revue. Pendant cette période la taille de la colonie de Pelecanus onocrotalus située sur la côte mauritanienne au Banc d'Arguin a été multipliée par
dix grâce à un afflux d'individus provenant des nouvelles colonies sénégalaises. Les Pélicans blancs sont absents de février à juin sur le banc d'Arguin. Les premiers s'installent sur le banc en juillet au moment où arrivent à ce niveau les eaux chaudes provenant du golfe de Guinée. Les
pélicans pondent leurs oeufs par vagues, de la mi-août à la fin novembr
Cardiac computed tomography radiomics: an emerging tool for the non-invasive assessment of coronary atherosclerosis
In the last decades, significant advances have been made in the preventive approaches to cardiovascular disease. Even so, coronary artery disease remains one of the main causes of morbidity and mortality worldwide. Invasive imaging modalities, such as intravascular ultrasound or optical coherence tomography, have played a key role in the comprehension of the pathological processes underlying myocardial infarction and cerebrovascular disease. These imaging techniques have contributed greatly to the identification and phenotyping of the culprit lesion, the so-called vulnerable plaque. Coronary computed tomographic angiography (CCTA) has emerged in more recent years as the non-invasive modality of choice in the study of coronary atherosclerosis, showing in many studies a diagnostic yield comparable to invasive approaches. Moreover, being able to describe extra-luminal characteristics of the affected vessel, CCTA has greatly contributed towards shifting the attention of researchers from the mere quantification of luminal stenosis to the identification of adverse plaque features, which appear to have a stronger prognostic value. However, the identification of some of the hallmarks of vulnerable plaques is qualitative in nature and, therefore, subject to some degree of inter-reader variability. Moreover, CCTA is still unable to identify some fine markers of plaque vulnerability which can be detected by invasive techniques, such as neovascularization and plaque erosion, among others. Nonetheless, radiological images can be viewed as vast 3-D datasets which, via the use of recent technology, allow for the extraction of numerous quantitative features that may be used to accurately phenotype a given lesion. Radiomics is the process of extrapolating innumerable parameters from a given region of interest, with the goal of establishing correlations between quantitative variables and clinical data. These datasets can then be manipulated to create predictive models via the use of automated algorithms in a process called machine learning. As a result of these approaches, radiological images may offer information regarding the characterization of a plaque which can go much beyond the boundaries of what can be qualitatively asserted by the human eye, contributing to expanding the knowledge of the disease and ultimately assist clinical decisions. Thus far, radiomics has found its more consistent area of application in the field of oncology; to present date, the amount of clinical data regarding coronary artery disease is still relatively small, partly due to the technical difficulties associated with the implementation of such techniques to the study of a small and geometrically complex lesion such as the coronary plaque. The present review, after a summary of the imaging modalities most commonly used nowadays in the study of coronary plaques, will provide a perspective on the application of radiomic analysis to coronary artery disease
Introductions de poissons d'eau douce et d'écrevisses en Camargue : historique, origines et modifications des peuplements
An Improved Limit on Invisible Decays of Positronium
The results of a new search for positronium decays into invisible final
states are reported. Convincing detection of this decay mode would be a strong
evid ence for new physics beyond the Standard Model (SM): for example the
existence of extra--dimensions, of milli-charged particles, of new light gauge
bosons or of mirror particles. Mirror matter could be a relevant dark matter
candidate.
In this paper the setup and the results of a new experiment are presented. In
a collected sample of about orthopositronium decay
s, no evidence for invisible decays in an energy window [0,80] keV was found
and an upper limit on the branching ratio of orthopositronium \invdecay could
be set: \binvdecay<4.2\times 10^{-7} (90% C.L.)
Our results provide a limit on the photon mirror-photon mixing strength
(90% C.L.) and rule out particles lighter
than the electron mass with a fraction of the
electron charge. Furthermore, upper limits on the branching ratios for the
decay of parapositronium (90%
C.L.) and the direct annihilation (90% C.L.) could be set.Comment: 17 pages, 7 figures, added references, fixed limit on millicharged
particles and changed two plots accordingl
Positronium Portal into Hidden Sector: A new Experiment to Search for Mirror Dark Matter
The understanding of the origin of dark matter has great importance for
cosmology and particle physics. Several interesting extensions of the standard
model dealing with solution of this problem motivate the concept of hidden
sectors consisting of SU(3)xSU(2)_LxU(1)_Y singlet fields. Among these models,
the mirror matter model is certainly one of the most interesting. The model
explains the origin of parity violation in weak interactions, it could also
explain the baryon asymmetry of the Universe and provide a natural ground for
the explanation of dark matter. The mirror matter could have a portal to our
world through photon-mirror photon mixing (epsilon). This mixing would lead to
orthopositronium (o-Ps) to mirror orthopositronium oscillations, the
experimental signature of which is the apparently invisible decay of o-Ps. In
this paper, we describe an experiment to search for the decay o-Ps -> invisible
in vacuum by using a pulsed slow positron beam and a massive 4pi BGO crystal
calorimeter. The developed high efficiency positron tagging system, the low
calorimeter energy threshold and high hermiticity allow the expected
sensitivity in mixing strength to be epsilon about 10^-9, which is more than
one order of magnitude below the current Big Bang Nucleosynthesis limit and in
a region of parameter space of great theoretical and phenomenological interest.
The vacuum experiment with such sensitivity is particularly timely in light of
the recent DAMA/LIBRA observations of the annual modulation signal consistent
with a mirror type dark matter interpretation.Comment: 40 pages, 29 Figures 2 Tables v2: Ref. added, Fig. 29 and some text
added to explain idea for backscattering e+ background suppression, corrected
typos v3: minor corrections: Eq 2.1 corrected (6 lines-> 5 lines), Eq.2.17:
two extra "-" signs remove
Particle physics applications of the AWAKE acceleration scheme
The AWAKE experiment had a very successful Run 1 (2016-8), demonstrating
proton-driven plasma wakefield acceleration for the first time, through the
observation of the modulation of a long proton bunch into micro-bunches and the
acceleration of electrons up to 2 GeV in 10 m of plasma. The aims of AWAKE Run
2 (2021-4) are to have high-charge bunches of electrons accelerated to high
energy, about 10 GeV, maintaining beam quality through the plasma and showing
that the process is scalable. The AWAKE scheme is therefore a promising method
to accelerate electrons to high energy over short distances and so develop a
useable technology for particle physics experiments. Using proton bunches from
the SPS, the acceleration of electron bunches up to about 50 GeV should be
possible. Using the LHC proton bunches to drive wakefields could lead to
multi-TeV electron bunches, e.g. with 3 TeV acceleration achieved in 4 km of
plasma. This document outlines some of the applications of the AWAKE scheme to
particle physics and shows that the AWAKE technology could lead to unique
facilities and experiments that would otherwise not be possible. In particular,
experiments are proposed to search for dark photons, measure strong field QED
and investigate new physics in electron-proton collisions. The community is
also invited to consider applications for electron beams up to the TeV scale.Comment: 12 pages, 8 figures, submitted to the European Particle Physics
Strategy Update process. arXiv admin note: substantial text overlap with
arXiv:1810.1225
Structural analysis of IPC zeolites and related materials using positron annihilation spectroscopy and high-resolution argon adsorption
ETH authors thanks for the grant ETH 33 15-1. PE and JČ acknowledge the financial support from the Czech Science Foundation (P106/12/0189). JPR and JČ gratefully acknowledge the financial support from the European Union Seventh Framework Programme (FP7/ 2007-2013) under grant agreement no. 604307. HRTEM characterization was performed at the Advanced Microscopy Laboratory (LMA) and the research leading to these results has received funding from the European Union Seventh Framework Programme under Grant Agreement 312483 – ESTEEM2 (Integrated Infrastructure Initiative-I3).The advanced investigation of pore networks in isoreticular zeolites and mesoporous materials related to the IPC family was performed using high-resolution argon adsorption experiments coupled with the development of a state-of-the-art non-local density functional theory approach. The optimization of a kernel for model sorption isotherms for materials possessing the same layer structure, differing only in the interlayer connectivity (e.g. oxygen bridges, single- or double-four-ring building units, mesoscale pillars etc.) revealed remarkable differences in their porous systems. Using high-resolution adsorption data, the bimodal pore size distribution consistent with crystallographic data for IPC-6, IPC-7 and UTL samples is shown for the first time. A dynamic assessment by positron annihilation lifetime spectroscopy (PALS) provided complementary insights, simply distinguishing the enhanced accessibility of the pore network in samples incorporating mesoscale pillars and revealing the presence of a certain fraction of micropores undetected by gas sorption. Nonetheless, subtle differences in the pore size could not be discriminated based on the widely-applied Tao-Eldrup model. The combination of both methods can be useful for the advanced characterization of microporous, mesoporous and hierarchical materials.PostprintPeer reviewe
Piezo-electric thick films for sensing
Monolithic piezoelectric sensors commonly used for acoustic emission and ultrasonic inspection are non-conforming, bulky, costly and heavy. This means they do not fit well to complex geometries, they can be susceptible to damage, and on larger structures their cost and weight can be prohibitive. An alternative to this is the use of piezo-electric thick films, which comprise of piezo-electric particles suspended in a matrix material. Such materials could provide "paint on" or "printable" sensors and sensor networks that are low profile, easy to mount and very cheap. In this work we explore the potential of piezo-electric thick films to sense and actuate for Acoustic Emission and ultrasonic applications. Sensors were produced by dispersing PZT 5a particles within water based acrylic and epoxy matrix materials with up to 70% fill by weight. The PZT films were applied to steel and their responses to artificial AE sources (Hsu-Nielson) were assessed and three-dimensional laser vibrometry was used to study the frequency response and mode shapes of the sensors under excitation. The results showed that although less sensitive than monolithic piezoelectric transducers, the thick film sensors can excite and detect ultrasonic waves for SHM applications and there is great potential for the development of a low cost, printed sensor network for SHM
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