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Chemical Basis of MethodWhen a solution containing molybdate ions is acidified, polymerisation occurs to give the so-called isopolymolybdate (Mo,~,,~-). If the solution also contains an 0x0 anion then on acidification this is also incorporated into the polymer, giving the so-called heteropolymolybdate (e.g., the phosphorus species PM0&4,,3-, dodecamolybdophosphate). The protonated forms of both these species can be extracted into a number of oxygen-containing organic solvents. Analytical useThe heteropoly formation reaction occurs with about 35 heteroatoms but has been applied analytically only to the following 10 : P, Si, As, Ge, V, Th, Ta, Ti, Nb and Ce. The analytical methods reported previously have used ultraviolet, visible and flame atomic-absorption spectrophotometry as the final measuring stage in a procedure that commences with addition of excess of molybdate to the sample solution followed by acidification and possibly reduction (to give the so-called "molybdenum blue" species). For separation from the excess of isopolymolybdate, a necessary step if atomic or ultraviolet absorption spectrophotometry are May, 1981 F I F T H INTERNATIONAL SAC CONFERENCE 185 being used, solvent extraction is used together with an appropriate washing procedure and sometimes followed by a back-extraction into basic aqueous solution. The analytical literature contains a large number of often contradictory papers describing the most appropriate conditions of formation, extraction, reduction and back-extraction for the analysis under consideration.The aim of the work described here was to decrease the detection limit of the atomicabsorption method by using an electrothermal atomiser instead of a flame. AttractionsThe proposed method has a number of attractions: (a) there is a 12: 1 molar amplification, which with P and As becomes a 37.2 and 15.4 mass amplification, respectively; (b) the determination of molybdenum by atomic-absorption spectrophotometry is more straightforward than that of phosphorus or arsenic in that the resonance line is in a more accessible part of the spectrum, a hollow-cathode rather than an electrodeless discharge lamp may be used and molybdenum has a higher oscillator strength for absorption; and (c) the use of an electrothermal atomiser, which only requires a few microlitres of solution, enables chlorinated solvents (which have toxic combustion products) to be used and, assuming the precision is satisfactory, gives lower detection limits because of the higher sensitivity. Fuller1 quotes values of 20 and 5 pg for the sensitivity and detection limit, respectively, for molybdenum, which correspond to 0.54 and 0.13 pg for phosphorus and 1.3 and 0.32 pg for arsenic. If the solvent extraction stage also provided pre-concentration, these values could be even lower. ApparatusThe instrument used in these studies was a Baird Atomic A3400 atomic-absorption spectrometer with an A3700 graphite rod atomiser. Experimental and ResultsFirstly, the determination of molybdenum using the carbon rod atomiser was prone to me...

Retake detection is useful for many applications of video summarization. It is a challenging task since different takes of the same scene are usually of different lengths; or have been recorded under different environment conditions. A general approach to solve this problem is to decompose the input video sequence into sub-sequences and then group these sub-sequences into clusters. By combining with temporal information, the clustering result is used to find take and scene boundaries. One of the most difficult steps in this approach is to cluster sub-sequences. Most of previous approaches only use one keyframe for representing one sub-sequence and extract features such as color and texture from this keyframe for clustering. We propose another approach to improve the performance by combining the motion feature extracted from each sub-sequence and the features extracted from each representing keyframe. Experiments evaluated on the standard benchmark dataset of TRECVID BBC Rushes 2007 show the effectiveness of the proposed method.

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