55,264 research outputs found
Torch kit for welding in difficult areas
Miniature tungsten inert gas welding torch, used with variously formed interchangeable soft copper tubing extensions, provides inexpensive, accurate welding capability for inaccessible joints. Kit effectively welds stainless steel tubing 0.089 cm thick. Other applications are cited
A solution procedure for behavior of thick plates on a nonlinear foundation and postbuckling behavior of long plates
Approximate solutions for three nonlinear orthotropic plate problems are presented: (1) a thick plate attached to a pad having nonlinear material properties which, in turn, is attached to a substructure which is then deformed; (2) a long plate loaded in inplane longitudinal compression beyond its buckling load; and (3) a long plate loaded in inplane shear beyond its buckling load. For all three problems, the two dimensional plate equations are reduced to one dimensional equations in the y-direction by using a one dimensional trigonometric approximation in the x-direction. Each problem uses different trigonometric terms. Solutions are obtained using an existing algorithm for simultaneous, first order, nonlinear, ordinary differential equations subject to two point boundary conditions. Ordinary differential equations are derived to determine the variable coefficients of the trigonometric terms
Earthquake modelling at the country level using aggregated spatio-temporal point processes
The goal of this paper is to derive a hazard map for earthquake occurrences in Pakistan from a catalogue that contains spatial coordinates of shallow earthquakes of magnitude 4.5 or larger aggregated over calendar years. We test relative temporal stationarity by the KPSS statistic and use the inhomogeneous J-function to test for inter-point interactions. We then formulate a cluster model, and de-convolve in order to calculate the hazard map, and verify that no particular year has an undue influence on the map. Within the borders of the single country, the KPSS test did not show any deviation from homogeneity in the spatial intensities. The inhomogeneous J-function indicated clustering that could not be attributed to inhomogeneity, and the analysis of aftershocks showed some evidence of two major shocks instead of one during the 2005 Kashmir earthquake disaster. Thus, the spatial point pattern analysis carried out for these data was insightful in various aspects and the hazard map that was obtained may lead to improved measures to protect the population against the disastrous effects of earthquakes
Infrared Continuum from HII Regions
Expected flux calculation for infrared free-free emission from planetary nebul
Issues of scale for environmental indicators
The value of environmental indicators largely depends upon the spatial and temporal scale that they represent. Environmental indicators are dependent upon data availability and also upon the scale for which statements are required. As these may not match, changes in scales may be necessary. In this paper a geostatistical approach to analyse quantitative environmental indicators has been used. Scales, defined in terms of resolution and procedures, are presented to translate data from one scale to another: upscaling to change from high resolution data towards a low resolution, and downscaling for the inverse process. The study is illustrated with three environmental indicators. The first concerns heavy metals in the environment, where the zinc content is used as the indicator. Initially, data were present at a 1km2 resolution, and were downscaled to 1m2 resolution. High resolution data collected later showed a reasonable correspondence with the downscaled data. Available covariates were also used. The second example is from the Rothamsted’s long-term experiments. Changes in scale are illustrated by simulating reduced data sets from the full data set on grass cuts. A simple regression model related the yield from these condcut to that of the first cut in the cropping season. Reducing data availability (upscaling) resulted in poor estimates of the regression coefficients. The final example is on nitrate surpluses on Danish farms. Data at the field level are upscaled to the farm level, and the dispersion variance indicates differences between different farms. Geostatistical methods were useful to define, change and determine the most appropriate scales for environmental variables in space and in time
Mechanism of spontaneous formation of stable magnetic structures on the Sun
One of the puzzling features of solar magnetism is formation of long-living
compact magnetic structures; such as sunspots and pores, in the highly
turbulent upper layer of the solar convective zone. We use realistic radiative
3D MHD simulations to investigate the interaction between magnetic field and
turbulent convection. In the simulations, a weak vertical uniform magnetic
field is imposed in a region of fully developed granular convection; and the
total magnetic flux through the top and bottom boundaries is kept constant. The
simulation results reveal a process of spontaneous formation of stable magnetic
structures, which may be a key to understanding of the magnetic
self-organization on the Sun and formation of pores and sunspots. This process
consists of two basic steps: 1) formation of small-scale filamentary magnetic
structures associated with concentrations of vorticity and whirlpool-type
motions, and 2) merging of these structures due to the vortex attraction,
caused by converging downdrafts around magnetic concentration below the
surface. In the resulting large-scale structure maintained by the converging
plasma motions, the magnetic field strength reaches ~1.5 kG at the surface and
~6 kG in the interior; and the surface structure resembles solar pores. The
magnetic structure remains stable for the whole simulation run of several hours
with no sign of decay.Comment: 13 pages, 4 figures, submitted to the Astrophysical Journa
Measurement-driven Quality Assessment of Nonlinear Systems by Exponential Replacement
We discuss the problem how to determine the quality of a nonlinear system
with respect to a measurement task. Due to amplification, filtering,
quantization and internal noise sources physical measurement equipment in
general exhibits a nonlinear and random input-to-output behaviour. This usually
makes it impossible to accurately describe the underlying statistical system
model. When the individual operations are all known and deterministic, one can
resort to approximations of the input-to-output function. The problem becomes
challenging when the processing chain is not exactly known or contains
nonlinear random effects. Then one has to approximate the output distribution
in an empirical way. Here we show that by measuring the first two sample
moments of an arbitrary set of output transformations in a calibrated setup,
the output distribution of the actual system can be approximated by an
equivalent exponential family distribution. This method has the property that
the resulting approximation of the statistical system model is guaranteed to be
pessimistic in an estimation theoretic sense. We show this by proving that an
equivalent exponential family distribution in general exhibits a lower Fisher
information measure than the original system model. With various examples and a
model matching step we demonstrate how this estimation theoretic aspect can be
exploited in practice in order to obtain a conservative measurement-driven
quality assessment method for nonlinear measurement systems.Comment: IEEE International Instrumentation and Measurement Technology
Conference (I2MTC), Taipei, Taiwan, 201
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