493 research outputs found
Critical behavior of a non-equilibrium interacting particle system driven by an oscillatory field
First- and second-order temperature driven transitions are studied, in a
lattice gas driven by an oscillatory field. The short time dynamics study
provides upper and lower bounds for the first-order transition points obtained
using standard simulations. The difference between upper and lower bounds is a
measure for the strength of the first-order transition and becomes negligible
small for densities close to one half. In addition, we give strong evidence on
the existence of multicritical points and a critical temperature gap, the
latter induced by the anisotropy introduced by the driving field.Comment: 12 pages, 4 figures; to appear in Europhys. Let
Surrogates with random Fourier Phases
The method of surrogates is widely used in the field of nonlinear data
analysis for testing for weak nonlinearities. The two most commonly used
algorithms for generating surrogates are the amplitude adjusted Fourier
transform (AAFT) and the iterated amplitude adjusted Fourier transfom (IAAFT)
algorithm. Both the AAFT and IAAFT algorithm conserve the amplitude
distribution in real space and reproduce the power spectrum (PS) of the
original data set very accurately. The basic assumption in both algorithms is
that higher-order correlations can be wiped out using a Fourier phase
randomization procedure. In both cases, however, the randomness of the Fourier
phases is only imposed before the (first) Fourier back tranformation. Until
now, it has not been studied how the subsequent remapping and iteration steps
may affect the randomness of the phases. Using the Lorenz system as an example,
we show that both algorithms may create surrogate realizations containing
Fourier phase correlations. We present two new iterative surrogate data
generating methods being able to control the randomization of Fourier phases at
every iteration step. The resulting surrogate realizations which are truly
linear by construction display all properties needed for surrogate data.Comment: To appear in: "Topics on Chaotic Systems: Selected Papers from Chaos
2008 International Conference", World Scientifi
Experimental study of consistency degradation of different greases in mixed neutron and gamma radiation
Many of the moving components in accelerator and target environments require lubrication. Lubricants in such environments are exposed to high fluxes of secondary radiation, which originates from beam interactions with the target and from beam losses. The secondary radiation is a mix of components, which can include significant fractions of neutrons. Lubricants are radiation-sensitive polymeric materials. The radiation-induced modifications of their structure reduce their service lifetime and impose additional facility maintenance, which is complicated by the environmental radioactivity. The study of the lubricants radiation resistance is therefore necessary for the construction of new generation accelerators and target systems. Nevertheless, data collected in mixed radiation fields are scarce. Nine commercial greases were irradiated at a TRIGA Mark II Research Reactor to serve for the construction of new accelerator projects like the European Spallation Source (ESS) at Lund (Sweden) and Selective Production of Exotic Species (SPES) at Legnaro, (Italy). Mixed neutron and gamma doses ranging from 0.1MGy to 9.0MGy were delivered to the greases. For an experimental quantification of their degradation, consistency was measured. Two of the greases remained stable, while the others became fluid. Post-irradiation examinations evidence the cleavage of the polymeric structure as the dominant radiation effect. Dose and fluence limits for the use of each product are presented. Apart from the scientific significance, the results represent an original and useful reference in selecting radiation resistant greases for accelerator and target applications
Running head: IMPROVING STUDENT ACHIEVEMENT 1 A Systems-based Synthesis of Research Related to Improving Students ’ Academic Performance
This paper addresses the issue of school improvement by looking to research on both the variables that should be the focus of school improvement efforts as well as factors that make it more likely that the organization will actually implement research findings. Issues of transformational leadership, instructional leadership, and high functioning teams are addressed; Hattie’s (2009) review of over 800 meta-analyses of variables related to school achievement is the primary source of identifying classroom and school variables that can be addressed by educators. As developed nations move out of the industrial age into the information/conceptual age, there is an ongoing debate about how to best prepare children and youth for adult success in the twenty-first century (Huitt, 1999b, 2007). While there is a consensus that schools should play a major role in this process, there is less agreement about exactly what that role should be. Some believe that the primary focus of schools should be academic preparation of students (Hirsch, 1987, 1996; Tienken, & Wilson, 2001), that classroom teachers are primarily responsible for student academic achievement (Darling-Hammond, 2000), and schools should efficiently and effectively organize themselves towards that task (Engelmann & Carnine, 1991). These effort
Application of a renormalization group algorithm to nonequilibrium cellular automata with one absorbing state
We improve a recently proposed dynamically driven renormalization group
algorithm for cellular automata systems with one absorbing state, introducing
spatial correlations in the expression for the transition probabilities. We
implement the renormalization group scheme considering three different
approximations which take into account correlations in the stationary
probability distribution. The improved scheme is applied to a probabilistic
cellular automaton already introduced in the literature.Comment: 7 pages, 4 figures, to be published in Phys. Rev.
PMS66 Determinants of Non-Persistence to Antiosteoporotic Drugs by Using Administrative Database
Osteoporosis treatment involves several therapeutic tools, including long-term drug therapy. Subjects with chronic disorders are more likely to be non-adherent and/or non-persistent to treatment than those with other diseases. Adherence is the extent to which patients take medication as prescribed by their physicians, whereas persistence is the time from treatment initiation to discontinuation. Lack of persistence is common among subjects using oral anti-osteoporotic drugs, and leads to increased risk of fragility fracture
Long term persistence in the sea surface temperature fluctuations
We study the temporal correlations in the sea surface temperature (SST)
fluctuations around the seasonal mean values in the Atlantic and Pacific
oceans. We apply a method that systematically overcome possible trends in the
data. We find that the SST persistence, characterized by the correlation
of temperature fluctuations separated by a time period , displays two
different regimes. In the short-time regime which extends up to roughly 10
months, the temperature fluctuations display a nonstationary behavior for both
oceans, while in the asymptotic regime it becomes stationary. The long term
correlations decay as with for both
oceans which is different from found for atmospheric land
temperature.Comment: 14 pages, 5 fiure
Una procedura per la valutazione dei limiti di utilizzo di O-Ring sottoposti ad intensi fasci di neutroni
Si presenta una procedura per la previsione della durata di utilizzo di O-ring in materiale polimerico impiegati nei bersagli per la produzione di fasci di ioni radioattivi. Si sono dapprima condotte prove di tenuta a vuoto e analisi a elementi finiti di un O-ring di riferimento operante con diversi livelli di interferenza con la cava, identificando la precompressione limite per la tenuta e la corrispondente pressione di contatto con la cava. Si sono poi effettuate prove di trazione e di Compression Set su campioni di O-ring in EPDM, preventivamente sottoposti a diversi livelli di irraggiamento in campi misti di neutroni e gamma, analizzando l’effetto della dose assorbita sul comportamento meccanico del materiale e sulle corrispondenti proprietà resistenziali, e definendo opportune leggi costitutive. Si sono infine simulate le progressive modifiche di comportamento della guarnizione indotte dall’irraggiamento, prevedendone la durata in esercizio in termini di tenuta e di resistenza strutturale
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