31,764 research outputs found
A Multi-Code Analysis Toolkit for Astrophysical Simulation Data
The analysis of complex multiphysics astrophysical simulations presents a
unique and rapidly growing set of challenges: reproducibility, parallelization,
and vast increases in data size and complexity chief among them. In order to
meet these challenges, and in order to open up new avenues for collaboration
between users of multiple simulation platforms, we present yt (available at
http://yt.enzotools.org/), an open source, community-developed astrophysical
analysis and visualization toolkit. Analysis and visualization with yt are
oriented around physically relevant quantities rather than quantities native to
astrophysical simulation codes. While originally designed for handling Enzo's
structure adaptive mesh refinement (AMR) data, yt has been extended to work
with several different simulation methods and simulation codes including Orion,
RAMSES, and FLASH. We report on its methods for reading, handling, and
visualizing data, including projections, multivariate volume rendering,
multi-dimensional histograms, halo finding, light cone generation and
topologically-connected isocontour identification. Furthermore, we discuss the
underlying algorithms yt uses for processing and visualizing data, and its
mechanisms for parallelization of analysis tasks.Comment: 18 pages, 6 figures, emulateapj format. Resubmitted to Astrophysical
Journal Supplement Series with revisions from referee. yt can be found at
http://yt.enzotools.org
Regularization, Renormalization and Range: The Nucleon-Nucleon Interaction from Effective Field Theory
Regularization and renormalization is discussed in the context of low-energy
effective field theory treatments of two or more heavy particles (such as
nucleons). It is desirable to regulate the contact interactions from the outset
by treating them as having a finite range. The low energy physical observables
should be insensitive to this range provided that the range is of a similar or
greater scale than that of the interaction. Alternative schemes, such as
dimensional regularization, lead to paradoxical conclusions such as the
impossibility of repulsive interactions for truly low energy effective theories
where all of the exchange particles are integrated out. This difficulty arises
because a nonrelativistic field theory with repulsive contact interactions is
trivial in the sense that the matrix is unity and the renormalized coupling
constant zero. Possible consequences of low energy attraction are also
discussed. It is argued that in the case of large or small scattering lengths,
the region of validity of effective field theory expansion is much larger if
the contact interactions are given a finite range from the beginning.Comment: 7 page
In good company: risk, security and choice in young people's drug decisions
This article draws on original empirical research with young people to question the degree to which 'individualisation of risk', as developed in the work of Beck and Giddens, adequately explains the risks young people bear and take. It draws on alternative understandings and critiques of 'risk' not to refute the notion of the reflexive individual upon which 'individualisation of risk' is based but to re-read that reflexivity in a more hermeneutic way. It explores specific risk-laden moments â young people's drug use decisions â in their natural social and cultural context of the friendship group. Studying these decisions in context, it suggests, reveals the meaning of 'risk' to be not given, but constructed through group discussion, disagreement and consensus and decisions taken to be rooted in emotional relations of trust, mutual accountability and common security. The article concludes that 'the individualisation of risk' fails to take adequate account of the significance of intersubjectivity in risk-decisions. It argues also that addressing the theoretical overemphasis on the individual bearer of risk requires not only further empirical testing of the theory but appropriate methodological reflection
Electron Removal Self Energy and its application to Ca2CuO2Cl2
We propose using the self energy defined for the electron removal Green's
function. Starting from the electron removal Green's function, we obtained
expressions for the removal self energy Sigma^ER (k,omega) that are applicable
for non-quasiparticle photoemission spectral functions from a single band
system. Our method does not assume momentum independence and produces the self
energy in the full k-omega space. The method is applied to the angle resolved
photoemission from Ca_2CuO_2Cl_2 and the result is found to be compatible with
the self energy value from the peak width of sharp features. The self energy is
found to be only weakly k-dependent. In addition, the Im Sigma shows a maximum
at around 1 eV where the high energy kink is located.Comment: 5 pages, 3 figure
Narrow Band Chandra X-ray Analysis of Supernova Remnant 3C391
We present the narrow-band and the equivalent width (EW) images of the
thermal composite supernova remnant (SNR) 3C391 for the X-ray emission lines of
elements Mg, Si, & S using the Chandra ACIS Observational data. These EW images
reveal the spatial distribution of the emission of the metal species Mg, Si, &
S in the remnant. They have clumpy structure similar to that seen from the
broadband diffuse emission, suggesting that they are largely of interstellar
origin. We find an interesting finger-like feature protruding outside the
southwestern radio border of the remnant, which is somewhat similar to the
jet-like Si structure found in the famous SNR Cas A. This feature may possibly
be the debris of the jet of ejecta which implies an asymmetrical supernova
explosion of a massive progenitor star.Comment: 9 pages, 4 embedded figures, Chinese Journal of Astronomy and
Astrophysics (ChJAA), in pres
A Hard X-Ray View of Two Distant VHE Blazars: 1ES 1101-232 and 1ES 1553+113
TeV blazars are known as prominent nonthermal emitters across the entire
electromagnetic spectrum with their photon power peaking in the X-ray and TeV
bands. If distant, absorption of gamma-ray photons by the extragalactic
background light (EBL) alters the intrinsic TeV spectral shape, thereby
affecting the overall interpretation. Suzaku observations for two of the more
distant TeV blazars known to date, 1ES 1101-232 and 1ES 1553+113, were carried
out in 2006 May and July, respectively, including a quasi-simultaneous coverage
with the state-of-the-art Cerenkov telescope facilities. We report on the
resulting data sets with emphasis on the X-ray band and set in context to their
historical behavior. During our campaign, we did not detect any significant
X-ray or gamma-ray variability. 1ES 1101-232 was found in a quiescent state
with the lowest X-ray flux ever measured. The combined XIS and HXD PIN data for
1ES 1101-232 and 1ES 1553+113 clearly indicate spectral curvature up to the
highest hard X-ray data point (~30 keV), manifesting as softening with
increasing energy. We describe this spectral shape by either a broken power law
or a log-parabolic fit with equal statistical goodness of fits. The combined
1ES 1553+113 very high energy spectrum (90-500 GeV) did not show any
significant changes with respect to earlier observations. The resulting
contemporaneous broadband spectral energy distributions of both TeV blazars are
discussed in view of implications for intrinsic blazar parameter values, taking
into account the gamma-ray absorption in the EBL.Comment: 9 pages, 10 figure
Generating Function for Particle-Number Probability Distribution in Directed Percolation
We derive a generic expression for the generating function (GF) of the
particle-number probability distribution (PNPD) for a simple reaction diffusion
model that belongs to the directed percolation universality class. Starting
with a single particle on a lattice, we show that the GF of the PNPD can be
written as an infinite series of cumulants taken at zero momentum. This series
can be summed up into a complete form at the level of a mean-field
approximation. Using the renormalization group techniques, we determine
logarithmic corrections for the GF at the upper critical dimension. We also
find the critical scaling form for the PNPD and check its universality
numerically in one dimension. The critical scaling function is found to be
universal up to two non-universal metric factors.Comment: (v1,2) 8 pages, 5 figures; one-loop calculation corrected in response
to criticism received from Hans-Karl Janssen, (v3) content as publishe
Summative evaluation of climate application activities with pastoralists in western Queensland
Survey methods were engaged to measure the change in use and knowledge of climate information by pastoralists in western Queensland. The initial mail survey was undertaken in 2000/2001 (n=43) and provided a useful benchmark of pastoralists climate knowledge. Two years of climate applications activities were completed and clients were re-surveyed in 2003 (n=49) to measure the change in knowledge and assess the effectiveness of the climate applications activities. Two methods were used to assess changes in client knowledge, viz., self-assessment and test questions. We found that the use of seasonal climate forecasts in decision making increased from 36% in 2001 (n=42) to 51% in 2003 (n=49) (P=0.07). We found that the self-assessment technique was unsatisfactory as a measure of changing knowledge over short periods (1-3 years), but the test question technique was successful and indicated an improvement in climate knowledge among respondents. The increased levels of use of seasonal climate forecasts in management and improved knowledge was partly attributed to the climate applications activities of the project.
We found that those who used seasonal forecasting (n=25) didnât understand key components of forecasts (e.g. probability, median) better than those who didnât use seasonal forecasts (n=24) (P>0.05). This identifies the potential for misunderstanding and misinterpretation of forecasts among users and highlights the need for providers of forecasts to understand the difficulties and prepare simply written descriptions of forecasts and disseminate these with the maps showing probabilities.
The most preferred means of accessing climate information were internet, email, The Season Ahead newsletter and newspaper. The least preferred were direct contact with extension officers and attending field days and group meetings. Eighty-six percent of respondents used the internet and 67% used ADSL Broadband Internet (April 2003). Despite these findings Extension Officers play a key role in preparing and publishing the information on the web, in emails and newsletters. We also believe that direct contact with Extension Officers trained in climate applications is desirable in workshop-like events to improve knowledge of the difficult concepts underpinning climate forecasts, which may then stimulate further adoption
Selection of Optimized Retaining Wall Technique Using Self-Organizing Maps
Construction projects in urban areas tend to be associated with high-rise buildings and are of very large-scales; hence, the importance of a projectâs underground construction work is significant. In this study, a rational model based on machine learning (ML) was developed. ML algorithms are programs that can learn from data and improve from experience without human intervention. In this study, self-organizing maps (SOMs) were utilized. An SOM is an alternative to existing ML methods and involves a subjective decision-making process because a developed model is used for data training to classify and effectively recognize patterns embedded in the input data space. In addition, unlike existing methods, the SOM can easily create a feature map by mapping multidimensional data to simple two-dimensional data. The objective of this study is to develop an SOM model as a decision-making approach for selecting a retaining wall technique. N-fold cross-validation was adopted to validate the accuracy of the SOM model and evaluate its reliability. The findings are useful for decision-making in selecting a retaining wall method, as demonstrated in this study. The maximum accuracy of the SOM was 81.5%, and the average accuracy was 79.8%
- âŠ