7,026 research outputs found
Etching of High Purity Zinc
A method of etching high purity zinc to reveal various etch figures on {101ÂŻ0} planes is presented in this
paper. Etch figures are formed by polishing in a dichromic acid solution after the introduction of mercury
to the crystal surface. No measurable aging time is required to form etch figures at newly formed dislocation
sites when mercury is on the surface prior to deformation. The mercury concentrates at the sites
where etch figures form and may be removed by vacuum distillation and chemical polishing before it appreciably
affects the purity of the bulk of the crystal
Dislocations and etch figures in high purity zinc
A method of etching high purity zinc single crystals to reveal various etch figures on {1010} planes is presented in the preceding paper. The procedure involves the introduction of mercury to the crystal surface prior to a chemical polish with dichromic acid. The mercury was found to be concentrated at the etch figures. This paper presents the results of several experiments which support the conclusion that there exists a one-to-one correspondence between etch figures and dislocations. Some observations of slip on (0001) basal planes and {1212} pyramidal planes, and of twinning in zinc are also presented
Interdisciplinary, Translational, and Community-Based Participatory Research: Finding a Common Language to Improve Cancer Research
Preventing cancer, downstaging disease at diagnosis, and reducing mortality require that relevant research findings be translated across scientific disciplines and into clinical and public health practice. Interdisciplinary research focuses on using the languages of different scientific disciplines to share techniques and philosophical perspectives to enhance discovery and development of innovations; (i.e., from the âleft endâ of the research continuum). Community-based participatory research (CBPR), whose relevance often is relegated to the âright endâ (i.e., delivery and dissemination) of the research continuum, represents an important means for understanding how many cancers are caused as well as for ensuring that basic science research findings affect cancer outcomes in materially important ways. Effective interdisciplinary research and CBPR both require an ability to communicate effectively across groups that often start out neither understanding each otherâs worldviews nor even speaking the same language. Both demand an ability and willingness to treat individuals from other communities with respect and understanding. We describe the similarities between CBPR and both translational and interdisciplinary research, and then illustrate our points using squamous cell carcinoma of the esophagus as an example of how to deepen understanding and increase relevance by applying techniques of CBPR and interdisciplinary engagement
Efficient Multigrid Preconditioners for Atmospheric Flow Simulations at High Aspect Ratio
Many problems in fluid modelling require the efficient solution of highly
anisotropic elliptic partial differential equations (PDEs) in "flat" domains.
For example, in numerical weather- and climate-prediction an elliptic PDE for
the pressure correction has to be solved at every time step in a thin spherical
shell representing the global atmosphere. This elliptic solve can be one of the
computationally most demanding components in semi-implicit semi-Lagrangian time
stepping methods which are very popular as they allow for larger model time
steps and better overall performance. With increasing model resolution,
algorithmically efficient and scalable algorithms are essential to run the code
under tight operational time constraints. We discuss the theory and practical
application of bespoke geometric multigrid preconditioners for equations of
this type. The algorithms deal with the strong anisotropy in the vertical
direction by using the tensor-product approach originally analysed by B\"{o}rm
and Hiptmair [Numer. Algorithms, 26/3 (2001), pp. 219-234]. We extend the
analysis to three dimensions under slightly weakened assumptions, and
numerically demonstrate its efficiency for the solution of the elliptic PDE for
the global pressure correction in atmospheric forecast models. For this we
compare the performance of different multigrid preconditioners on a
tensor-product grid with a semi-structured and quasi-uniform horizontal mesh
and a one dimensional vertical grid. The code is implemented in the Distributed
and Unified Numerics Environment (DUNE), which provides an easy-to-use and
scalable environment for algorithms operating on tensor-product grids. Parallel
scalability of our solvers on up to 20,480 cores is demonstrated on the HECToR
supercomputer.Comment: 22 pages, 6 Figures, 2 Table
AMRA: An Adaptive Mesh Refinement Hydrodynamic Code for Astrophysics
Implementation details and test cases of a newly developed hydrodynamic code,
AMRA, are presented. The numerical scheme exploits the adaptive mesh refinement
technique coupled to modern high-resolution schemes which are suitable for
relativistic and non-relativistic flows. Various physical processes are
incorporated using the operator splitting approach, and include self-gravity,
nuclear burning, physical viscosity, implicit and explicit schemes for
conductive transport, simplified photoionization, and radiative losses from an
optically thin plasma. Several aspects related to the accuracy and stability of
the scheme are discussed in the context of hydrodynamic and astrophysical
flows.Comment: 41 pages, 21 figures (9 low-resolution), LaTeX, requires elsart.cls,
submitted to Comp. Phys. Comm.; additional documentation and high-resolution
figures available from http://www.camk.edu.pl/~tomek/AMRA/index.htm
The association between threat and politics simultaneously depends on the type of threat, the political domain, and the country
Theories link threat with right-wing political beliefs. We use the World Values Survey (60,378 participants) to explore how six types of threat (e.g., economic, violence, and surveillance) are associated with multiple political beliefs (e.g., cultural, economic, and ideological identification) in 56 countries/territories. Multilevel models with individuals nested in countries revealed that the threat-political belief association depends on the type of threat, the type of political beliefs, and the country. Economic-related threats tended to be associated with more left-wing economic political beliefs and violence-related threats tended to be associated with more cultural right-wing beliefs, but there were exceptions to this pattern. Additional analyses revealed that the associations between threat and political beliefs were different across countries. However, our analyses identified few country characteristics that could account for these cross-country differences. Our findings revealed that political beliefs and perceptions of threat are linked, but that the relationship is not simple. Keywords: Ideology, Belief Systems, Threat, Cultur
Coherent QCD multiple scattering in proton-nucleus collisions
We argue that high energy proton-nucleus (p+A) collisions provide an
excellent laboratory for studying nuclear size enhanced parton multiple
scattering where power corrections to the leading twist perturbative QCD
factorization approach can be systematically computed. We identify and resum
these corrections and calculate the centrality and rapidity dependent nuclear
suppression of single and double inclusive hadron production at moderate
transverse momenta. We demonstrate that both spectra and dihadron correlations
in p+A reactions are sensitive measures of such dynamical nuclear attenuation
effectsComment: 5 pages, 3 figures. Updated figures and reference
A multidomain spectral method for solving elliptic equations
We present a new solver for coupled nonlinear elliptic partial differential
equations (PDEs). The solver is based on pseudo-spectral collocation with
domain decomposition and can handle one- to three-dimensional problems. It has
three distinct features. First, the combined problem of solving the PDE,
satisfying the boundary conditions, and matching between different subdomains
is cast into one set of equations readily accessible to standard linear and
nonlinear solvers. Second, touching as well as overlapping subdomains are
supported; both rectangular blocks with Chebyshev basis functions as well as
spherical shells with an expansion in spherical harmonics are implemented.
Third, the code is very flexible: The domain decomposition as well as the
distribution of collocation points in each domain can be chosen at run time,
and the solver is easily adaptable to new PDEs. The code has been used to solve
the equations of the initial value problem of general relativity and should be
useful in many other problems. We compare the new method to finite difference
codes and find it superior in both runtime and accuracy, at least for the
smooth problems considered here.Comment: 31 pages, 8 figure
Initial data for a head on collision of two Kerr-like black holes with close limit
We prove the existence of a family of initial data for the Einstein vacuum
equation which can be interpreted as the data for two Kerr-like black holes in
arbitrary location and with spin in arbitrary direction. This family of initial
data has the following properties: (i) When the mass parameter of one of them
is zero or when the distance between them goes to infinity, it reduces exactly
to the Kerr initial data. (ii) When the distance between them is zero, we
obtain exactly a Kerr initial data with mass and angular momentum equal to the
sum of the mass and angular momentum parameters of each of them. The initial
data depends smoothly on the distance, the mass and the angular momentum
parameters.Comment: 15 pages, no figures, Latex2
On the Nature of X-ray Variability in Ark 564
We use data from a recent long ASCA observation of the Narrow Line Seyfert 1
Ark 564 to investigate in detail its timing properties. We show that a thorough
analysis of the time series, employing techniques not generally applied to AGN
light curves, can provide useful information to characterize the engines of
these powerful sources.We searched for signs of non-stationarity in the data,
but did not find strong evidences for it. We find that the process causing the
variability is very likely nonlinear, suggesting that variability models based
on many active regions, as the shot noise model, may not be applicable to Ark
564. The complex light curve can be viewed, for a limited range of time scales,
as a fractal object with non-trivial fractal dimension and statistical
self-similarity. Finally, using a nonlinear statistic based on the scaling
index as a tool to discriminate time series, we demonstrate that the high and
low count rate states, which are indistinguishable on the basis of their
autocorrelation, structure and probability density functions, are intrinsically
different, with the high state characterized by higher complexity.Comment: 13 pages, 13 figures, accepted for publication in A&
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