Search results for "rare event"
showing 10 items of 14 documents
Development of low-diffusion techniques for a high pressure xenon electroluminescent TPC
2022
El neutrino es una partícula que ha despertado un gran interés en las últimas décadas. Su existencia fue conjeturada por W. Pauli en 1930 para explicar el espectro continuo de la desintegración beta. El descubrimiento inequívoco de la oscilación de neutrinos en 1998 demostró que los neutrinos tienen una masa que no desaparece. Por lo tanto, es necesario acomodar un neutrino masivo en la teoría expandiendo el Modelo Estándar y eso se puede hacer suponiendo que el neutrino es una partícula de Majorana, que se define como un fermión que es su propia antipartícula. El mecanismo que da su masa a un neutrino Majorana podría explicar la leptogénesis y parte de la asimetría materia-antimateria obse…
A Generic Approach to Scheduling and Checkpointing Workflows
2018
This work deals with scheduling and checkpointing strategies to execute scientific workflows on failure-prone large-scale platforms. To the best of our knowledge, this work is the first to target fail-stop errors for arbitrary workflows. Most previous work addresses soft errors, which corrupt the task being executed by a processor but do not cause the entire memory of that processor to be lost, contrarily to fail-stop errors. We revisit classical mapping heuristics such as HEFT and MinMin and complement them with several checkpointing strategies. The objective is to derive an efficient trade-off between checkpointing every task (CkptAll), which is an overkill when failures are rare events, …
Epistemic uncertainty in fault tree analysis approached by the evidence theory
2012
Abstract Process plants may be subjected to dangerous events. Different methodologies are nowadays employed to identify failure events, that can lead to severe accidents, and to assess the relative probability of occurrence. As for rare events reliability data are generally poor, leading to a partial or incomplete knowledge of the process, the classical probabilistic approach can not be successfully used. Such an uncertainty, called epistemic uncertainty, can be treated by means of different methodologies, alternative to the probabilistic one. In this work, the Evidence Theory or Dempster–Shafer theory (DST) is proposed to deal with this kind of uncertainty. In particular, the classical Fau…
Cross-entropy-based adaptive optimization of simulation parameters for Markovian-driven service systems
2005
Abstract Markov fluid models represent a general description of the process of service request arrivals to service systems. The solution of performance analysis problems incorporating them often calls for a simulation approach, for which a reference methodology is Importance Sampling. However, in this case the appropriate choice of the biasing conditions is a problem in itself. In this paper an iterative method based on the cross-entropy is proposed for this choice. The equations are given that allow to derive the biasing conditions from the simulation itself. The application of the proposed method to three different sample cases, referring to one transient scenario (finite time horizon and…
Discerning the Origins of the Amplitude Fluctuations in Dynamic Raman Nanospectroscopy
2012
International audience; We introduce a novel experimental and analytical method for discerning rare surface-enhanced Raman scattering (SERS) events observable at the nanoscale. We show that the kinetics of the Raman activity recorded on an isolated nanostructure is punctuated by intense and rare events of large amplitude and spectral variations. The fluctuations of thousands of SERS spectra were analyzed statistically in terms of power density functions, and the occurrence of the rare events was quantified by a wavenumber statistics. Our analysis enables one to extract valuable and unique spectroscopic signature of Raman variations usually hidden in time-average or space-average measurement…
Low-diffusion Xe-He gas mixtures for rare-event detection: electroluminescence yield
2020
[EN] High pressure xenon Time Projection Chambers (TPC) based on secondary scintillation (electroluminescence) signal amplification are being proposed for rare event detection such as directional dark matter, double electron capture and double beta decay detection. The discrimination of the rare event through the topological signature of primary ionisation trails is a major asset for this type of TPC when compared to single liquid or double-phase TPCs, limited mainly by the high electron diffusion in pure xenon. Helium admixtures with xenon can be an attractive solution to reduce the electron diffu- sion significantly, improving the discrimination efficiency of these optical TPCs. We have m…
Future axion searches with the International Axion Observatory (IAXO)
2013
Çetin, Serkant Ali (Dogus Author) -- Conference full title: 6th Symposium on Large TPCs for Low Energy Rare Event Detection; Paris; France; 17 December 2012 through 19 December 2012. The International Axion Observatory (IAXO) is a new generation axion helioscope aiming at a sensitivity to the axion-photon coupling of gaγ ∼ few × 10-12 GeV-1, i.e. 1-1.5 orders of magnitude beyond the one achieved by CAST, currently the most sensitive axion helioscope. The main elements of IAXO are an increased magnetic field volume together with extensive use of x-ray focusing optics and low background detectors, innovations already successfully tested in CAST. Additional physics cases of IAXO could include …
Quantification of Competing Magnetic States and Switching Pathways in Curved Nanowires by Direct Dynamic Imaging.
2020
For viable applications, spintronic devices based, for example, on domain wall motion need to be highly reliable with stable magnetization states and highly reproducible switching pathways transforming one state to another. The existence of multiple stable states and switching pathways in a system is a definitive barrier for device operation, yet rare and stochastic events are difficult to detect and understand. We demonstrate an approach to quantify competing magnetic states and stochastic switching pathways based on time-resolved scanning electron microscopy with polarization analysis, applied to the technologically relevant control of vortex domain wall chirality via field and curvature …
A heavy-ion identification system for the detection of rare events
1990
Abstract A large area detection system is described which consists of twelve low-pressure multi-wire proportional counters and is used in the search for exotic super-massive nuclei. The experiments are based on Rutherford backscattering of heavy ions, preferably 208Pb or 238U, from various target samples. The measured parameters of a detected particle are its time-of-flight, scattering angle, and specific ionization. From this information the mass of the target nucleus can be inferred. The present experimental sensitivity for the detection of exotic nuclei with at least twice the mass of the projectile is about 10−12 relative to the number of nucleons.
Rare events and scaling properties in field-induced anomalous dynamics
2012
We show that, in a broad class of continuous time random walks (CTRW), a small external field can turn diffusion from standard into anomalous. We illustrate our findings in a CTRW with trapping, a prototype of subdiffusion in disordered and glassy materials, and in the L\'evy walk process, which describes superdiffusion within inhomogeneous media. For both models, in the presence of an external field, rare events induce a singular behavior in the originally Gaussian displacements distribution, giving rise to power-law tails. Remarkably, in the subdiffusive CTRW, the combined effect of highly fluctuating waiting times and of a drift yields a non-Gaussian distribution characterized by long sp…