30,180 research outputs found
Standards for material handling and facilities equipment proofload testing
Document provides information on verifying the safety of material handling and facilities equipment /MH/FE/, ranging from monorail systems to ladders and non-powered mobile equipment. Seven catagories of MH/FE equipment are defined
The Effects of High Skilled Immigration in a Dual Labour Market with Union Wage Setting and Fiscal Redistribution
We study the effects of high skilled immigration on employment and net income in the receiving economy where the market for low skilled labour is distorted by union wage setting and a redistributive unemployment benefit scheme. Based on the empirical fact that high and low skilled workers are close albeit imperfect substitutes, we show that high skilled immigration can either be beneficial or harmful, both in terms of employment and net income. More precisely, we conclude that a Pareto improvement can be achieved if the unemployment benefit level remains unaffected by high skilled immigration whereas an overall loss in net income cannot be ruled out if we suggest unemployment benefits to be funded by an exogenous egalitarian tax rate.Immigration, Imperfect Labour Markets, Fiscal Redistribution
Search for a new Resonance decaying into Top-Antitop at Tevatron
In this report a new search for a narrow-width heavy resonance decaying into
top quark pairs (X -> ttbar) in ppbar collisions at sqrt(s)=1.96 TeV has been
performed using data collected by the D0 detector at the Fermilab Tevatron
collider. The analysis considers ttbar candidate events in the lepton+jets
channel using a lifetime tag to identify b-jets and the ttbar invariant mass
distribution to search for evidence of resonant production. The analyzed
dataset corresponds to an integrated luminosity of approximately 370 pb^-1.
Since no evidence for a ttbar resonance X is found, upper limits on sigma(X) x
B(X -> ttbar) for different hypothesized resonance masses using a Bayesian
approach are set. Within a topcolor-assisted technicolor model, the existence
of a leptophobic Z' boson with M(Z') < 680 GeV and width Gamma(Z') = 0.012
M(Z') can be excluded at 95% C.L..Comment: Talk given at the "International Europhysics Conference on High
Energy Physics", July 21st - 27th 2005, Lisboa, Portuga
Damage in porous media due to salt crystallization
We investigate the origins of salt damage in sandstones for the two most
common salts: sodium chloride and sulfate. The results show that the observed
difference in damage between the two salts is directly related to the kinetics
of crystallization and the interfacial properties of the salt solutions and
crystals with respect to the stone. We show that, for sodium sulfate, the
existence of hydrated and anhydrous crystals and specifically their dissolution
and crystallization kinetics are responsible for the damage. Using magnetic
resonance imaging and optical microscopy we show that when water imbibes sodium
sulfate contaminated sandstones, followed by drying at room temperature, large
damage occurs in regions where pores are fully filled with salts. After partial
dissolution, anhydrous sodium sulfate salt present in these regions gives rise
to a very rapid growth of the hydrated phase of sulfate in the form of clusters
that form on or close to the remaining anhydrous microcrystals. The rapid
growth of these clusters generates stresses in excess of the tensile strength
of the stone leading to the damage. Sodium chloride only forms anhydrous
crystals that consequently do not cause damage in the experiments
Measurement of the Pressure induced by salt crystallization in confinement
Salt crystallization is a major cause of weathering of artworks, monuments
and rocks. Damage will occur if crystals continue to grow in confinement, i.e.
within the pore space of these materials generating mechanical stresses. We
report on a novel method that allows to directly measure, at the microscale,
the resulting pressure while visualizing the spontaneous nucleation and growth
of alkali halide salts. The experiments reveal the crucial role of the wetting
films between the growing crystal and the confining walls for the development
of the pressure. The results suggest that the pressure originates from a charge
repulsion between the similarly charged wall and the crystal separated by a
~1.5 nm salt solution film. Consequently, if the walls are made hydrophobic, no
film and no crystallization pressure are detected. The magnitude of the
pressure is system-specific and explains how a growing crystal exerts stresses
at the scale of individual grains in porous materials
Forming blocks speed production of strain gage grids
A tool is designed which facilitates the forming of wire grids used in manufacturing strain gage grids. Flattening the grid wire by a cold working process produces a stabilized grid which can be readily handled for storage or shipment
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