منابع مشابه
on the equivalence of constructed-response and multiple-choice : stem-equivalent, stem non-equivalent but content equivalent, and stem and content non-equivalent items in reading comprehension using multifaceted rasch
the present study investigated construct equivalence of multiple choice (mc) and constructed response (cr) item types across stem and content equivalent mc and cr items (item type ‘a’), non-stem-equivalent but content equivalent mc and cr items (item type ‘b’), and non-stem and non-content equivalent mc and cr items (item type ‘c’). one hundred seventy english-major undergraduates completed mc ...
Chromium and Chromium Compounds
Chromium is present in the environment in several different forms. The most common forms are chromium(0), chromium(III) (or trivalent chromium) and chromium(VI) (or hexavalent chromium). Chromium(III) occurs naturally in the environment and is an essential nutrient that helps the human body utilize sugar, protein and fat. Chromium(VI) and chromium(0) are generally produced by industrial process...
متن کاملPlasma spraying and characterization of chromium carbide – nickel chromium coatings
Chromium carbide – nickel chromium powder Cr3C2-25wt.NiCr was plasma sprayed by a water-stabilized system WSP®. A series of experiments with variable feeding distance was carried out. Basic characterization of coatings was done by XRD, SEM and light microscopy plus image analysis. Microhardness was measured on polished cross sections. The main focus of investigation was on resistances against w...
متن کاملSpectroscopic Determination of Chromium(Vl) during the Reduction of Chromium(VI) to Chromium(III)
Reduction of chromium(VI) to chromium(Ill) by thiourea between pH 3.0 and 5.5 is a key aspect of the chrominm(VI)/thiourea/polyacrylamide gel polymer system used in enhanced oil recovery processes. A method has been developed to determine chromium(Vl) concentration during the reduction of chromium(VI) to chromium(III) in this pH range. The reduction reaction is run in the presence of an acetic ...
متن کاملReaction of chromium(VI) with ascorbate produces chromium(V), chromium(IV), and carbon-based radicals.
Reaction of potassium dichromate with sodium ascorbate was studied by EPR spectroscopy at room temperature, in 0.10 M N-[2-hydroxyethyl]piperazine-N'-[2-ethanesulfonic acid] (HEPES), phosphate, cacodylate, and tris(hydroxymethyl)aminomethane hydrochloride (Tris.HCl) buffers at pH 7.0, in the presence of 0.10 M spin trap [5,5-dimethyl-1-pyrroline 1-oxide or 2-methyl-N-(4-pyridinylmethylene)-2-pr...
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ژورنال
عنوان ژورنال: The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science
سال: 1850
ISSN: 1941-5966,1941-5974
DOI: 10.1080/14786445008646512