400 research outputs found
Arrays of magnetized quantum dots at critical conditions
No full textKondratyev VN, Kadenko IM, Blanchard P. Arrays of magnetized quantum dots at critical conditions. JOURNAL OF MOLECULAR LIQUIDS. 2006;127(1-3, SI):148-150.Magnetodynamics of an array of ferromagnetically coupled quantum dots are analyzed when accounting for disorder effects, inter- and intra-dot structure. Particular attention is paid for specific features associated with sharp step-like change of a dot magnetic moment caused by the Zeeman splitting of energy levels. For an analysis of the system we employ the randomly jumping interacting moments model including quantum fluctuations due to the discrete level structure, inter-dot coupling and disorder. At the jump anomalies the magnetic state equation is found to indicate an existence of spinodal regions and critical points. In the vicinity of such points magnetization evolves as erratic jumps associated with avalanches of the moment steps in magnetized dots. The model predicts some universal scaling properties for magnetic noise. The considered magnetodynamics is similar to the well-known Barkhausen effect but occurs at conditions far from the magnetization reversal. Such an effect might be employed, therefore, as a tool to analyze the roughness and the disorder in magnetic dot arrays, which are of great importance for advanced electronic devices, nanoscale storage media and magnetic recording technology. (C) 2006 Elsevier B.V All rights reserved
Some features in experimental determination of subcriticality in nuclear reactor and accelerator driven system
No full textArticle is dedicated to the analysis of some terms and definitions of the normative document "General safety provisions for subcritical nuclear installation". The main attention is given to the discussion of such terms as effective multiplication factor, self-sustaining fission chain reaction, subcritical nuclear installation. For correct definition of these terms there should be considered the reactor kinetics equations, from which it follows that the stationary neutron flux can be realized both in the critical and subcritical reactor. Meanwhile, definitions in the corresponding normative document take into account only the critical state of the reactor, whereas other stationary states in "subcritical state" were not properly considered. It is offered "to clarify" corresponding definitions of these terms based on the analysis of nuclear reactor kinetics equations
Cross sections of (n, n'α) nuclear reaction on rear earth elements at 14.7 MeV neutron energy
No full textCross sections of nuclear reactions 159Tb(n, n'α)155Eu, 165Ho(n, n'α)161Tb, 169Tm(n, n'α)165Ho and 176Yb(n, n'α)172Er for incident neutron energy region (8 - 20) MeV are presented. Comparison of the nuclear cross sections data with available experimental information, evaluated nuclear data and theoretical calculation results with the variation of different parameters of the theoretical models was performed. Theoretical calculations were executed with TALYS-1.2 code
Nuclear reactions cross sections (n, x) on dysprosium and ytterbium isotopes
No full textCross sections of nuclear reactions 162,163Dy(n, x)162Tb, 163,164Dy(n, x)163Tb, 156Dy(n, 2n)155Dy, 158Dy(n, 2n)157(m+g)Dy, 166,167Er(n, x)166gHo, 170Er(n, p)170gHo were measured and presented for incident neutron energy (14.6 ± 0.2) MeV. The measurements were undertaken with neutron-activation technique. Samples of natural composition
of above mentioned elements were irradiated with (d-t) neutrons. Instrumental gamma-ray spectra of induced activities were measured using HPGe detectors. The main sources of uncertainties for cross section values were considered
and taken into account. Measured cross section for 162Er(n, p)162(m+g)Ho nuclear reaction is considered as original data.
Theoretical calculations of excitation functions for all reactions in specified energy range were performed with TALYS-1.2 code
Alert Alchemy: SOC Workflows and Decisions in the Management of NIDS Rules
No full textSignature-based network intrusion detection systems (NIDSs) and network intrusion prevention systems (NIPSs) remain at the heart of network defense, along with the rules that enable them to detect threats. These rules allow Security Operation Centers (SOCs) to properly defend a network, yet we know almost nothing about how rules are created, evaluated and managed from an organizational standpoint. In this work, we analyze the processes surrounding the creation, management, and acquisition of rules for network intrusion detection. To understand these processes, we conducted interviews with 17 professionals who work at Managed Security Service Providers (MSSPs) or other organizations that provide network monitoring as a service or conduct their own network monitoring internally. We discovered numerous critical factors, such as rule specificity and total number of alerts and false positives, that guide SOCs in their rule management processes. These lower-level aspects of network monitoring processes have generally been regarded as immutable by prior work, which has mainly focused on designing systems that handle the resulting alert flows by dynamically reducing the number of noisy alerts SOC analysts need to sift through. Instead, we present several recommendations that address these lower-level aspects to help improve alert quality and allow SOCs to better optimize workflows and use of available resources. These recommendations include increasing the specificity of rules, explicitly defining feedback loops from detection to rule development, and setting up organizational processes to improve the transfer of tacit knowledge.Organisation & Governanc
Di-electron spectroscopy in HADES and CBM : from p + p and n + p collisions at GSI to Au + Au collisions at FAIR
No full textThe study of the electromagnetic structure of hadrons plays an important role in understanding the nature of matter. In particular the emission of lepton pairs out of the hot and dense collision zone in heavy-ion reactions is a promising probe to investigate in-medium properties of hadrons and in general the properties of matter under such extreme conditions. The first experimental observation of an enhanced di-electron yield in the invariant-mass region 0:3 - 0:7 GeV/c2 in p+Be collisions at 4:9 GeV/u beam energy [2] was announced by the DLS collaboration [1]. Recent results of the HADES collaboration show a moderate enhancement above n Dalitz decay contributions for 12C+12C at 1 and 2 GeV/u [3, 4] confirming the DLS results. There are several theoretical explanations of this observation, most of them focusing on possible in-medium modifications of the properties of vector mesons. At low beam energies the question whether the observed excess is related to any in-medium effects remains open because of uncertainties in the description of elementary di-electron sources. In this work the di-electron production in p+p and d+p reactions at a kinetic beam energy of 1:25 GeV/u measured by the HADES spectrometer is discussed. At Ekin = 1:25 GeV/u, i.e. below the n meson production threshold in proton-proton reactions, the delta Dalitz decay is expected to be the most abundant source above the pi 0 Dalitz decay region. The observed large difference in di-electron production in p+p and d+p collisions suggests that di-electron production in the d+p system is dominated by the n+p interaction. In order to separate delta Dalitz decays and np bremsstrahlung the di-electron yield observed in p+p and n+p reactions, both measured at the same beam energy, has been compared. The main interest here is the investigation of iso-spin effects in baryonic resonance excitations and the off-shell production of vector mesons [5]. We indeed observe a large difference in di-electron production in p+p and n+p reactions. Results of these studies will be compared to recent calculations. We will also present our experimentally defined cocktail for heavy-ion data. At much higher beam energies experimental results of the CERES [6] and NA60 [7] collaborations also show an enhancement in the invariant mass region 0:3 - 0:7 GeV/c2, in principle similar to the situation in DLS. A strong excess of lepton pairs observed by recent high energy heavy-ion dilepton experiments hint to a strong influence of baryons, however no data exist at highly compressed baryonic matter, achievable in heavy-ion collisions from 8 - 45 GeV/u beam energy. These conditions would allow to study the expected restoration of chiral symmetry by measuring in-medium modifications of hadronic properties, an experimental program which is foreseen by the future CBM experiment at FAIR. The experimental challenge is to suppress the large physical background on the one hand and to provide a clean identification of electrons on the other hand. In this work, strategies to reduce the combinatorial background in electron pair measurements with the CBM detector are discussed. The main goal is to study the feasibility of effectively reducing combinatorial background with the currently foreseen experimental setup, which does not provide electron identification in front of the magnetic field.Untersuchungen der elektromagnetischen Struktur von Hadronen spielen eine wichtige Rolle um die Eigenschaften von stark wechselwirkender Materie zu verstehen. Insbesondere die Emission von Leptonenpaare aus der heißen und dichten Phase in Schwerionenkollisionen stellt eine vielversprechende Probe in der Untersuchung von veränderten Eigenschaften der Hadronen im Medium und der Eigenschaften von Materie unter extremen Bedingungen dar. Das DLS Experiment [1] beobachtete einen Überschuss der Elektronenpaarausbeute über die Erwartungen im invarianten Massenbereich von 0:3 - 0:7 GeV/c2 in p+Be-Kollisionen bei 4:9 GeV/u Strahlenergie [2]. Neuere Ergebnisse des HADES Experimentes bestätigen diese DLS Resultate und zeigen einen Überschuss von Elektronenpaare über den erwarteten Beiträgen von n Dalitz-Zerfällen für 12C+12C-Reaktionen bei 1 und 2 GeV/u Strahlenergie [3, 4]. Diese Beobachtung wird in verschiedenen theoretischen Ansätzen unterschiedlich erklärt, die meisten Deutungen konzentrieren sich auf Veränderungen der Eigenschaften der Vektormesonen im Medium. Allerdings bleibt diese Interpretation insbesondere bei diesen niedrigen Strahlenergien wegen der großen Unsicherheiten in den elementaren Elektronenpaarquellen unsicher. In dieser Arbeit wurde die mit dem HADES Experiment gemessene Produktion von Elektronenpaare in p+p und in aus d+p extrahierten n+p-Reaktionen bei Strahlenergien von 1:25 GeV/u untersucht. Bei Energien von Ekin = 1:25 GeV/u befindet man sich in Proton-Proton Stößen noch unterhalb der Schwelle für n-Mesonproduktion, daher ist der delta Dalitz-Zerfall die dominante Quelle für Elektronenpaare oberhalb der pi 0 Dalitz-Zerfallsregion. Man beobachtet einen großen Unterschied in den Spektren aus p+p und n+p Reaktionen bei derselben Strahlenergie. Dieser Vergleich ermöglicht es, die Beiträge der delta Dalitz-Zerfälle von denen aus np-Bremsstrahlung zu trennen. Das wesentliche Interesse liegt hier auf der Untersuchung von Isospin-Effekten in der Anregung baryonischer Resonanzen Produktion von Vektormesonen jenseits der Massenschale [5]. Ergebnisse der hier vorgestellten Analyse werden mit neueren Rechnungen verglichen. Ein experimentell bestimmter Cocktail zum Vergleich mit der Elektronenpaar-Produktion in C+C wird vorgestellt. Auch Ergebnnisse der CERES [6] und NA60 [7] Kollaborationen bei höherer Strahlenergie einen Überschuss der Elektronenpaar-Produktion über den Erwartungen im invarianten Massenbereich von 0:3 - 0:7 GeV/c2 zeigen. Erklärungen dieses Überschusses weisen auf einen starken Einfluss von Baryonen auf die Leptonenpaar-Emission hin. Es existieren allerdings noch keine Messungen im Bereich höchster Kompression von baryonischer Materie bzw. höchster Netto-Baryonendichte, die mit Schwerionenkollisionen bei 8 - 45 GeV/u Strahlenergie erreicht werden können. Solche Bedingungen erlauben die Untersuchung der erwarteten Wiederherstellung der spontan gebrochenen Chiralen Symmetrie durch die Messung von Modifikationen der hadronischen Eigenschaften im Medium. Ein solches experimentelles Programm ist einer der Kernpunkte des geplanten CBM-Experimentes an FAIR. Die experimentelle Herausforderung besteht darin, den großen physikalischen Untergrund zu unterdrücken sowie eine saubere Elektronen Identifizierung zu erhalten. In dieser Arbeit wurden detaillierte Machbarkeitsstudien hierzu durchgeführt und es wurde gezeigt, dass mit der entwickelten Strategie der kombinatorische Untergrund mit der vorgeschlagenen Detektoranordnung hinreichend unterdrückt werden kann
- …
