Pulsed photothermal laser deflection for low-level smoke and NO2 measurements in engine exhausts

Pulsed Photothermal Laser Deflection (PLD) is developed to make temporally and spatially resolved measurements of NO₂ and smoke. The rapid response PLD signal is produced when a HeNe probe beam is deflected by a thermal lens produced by a pulsed XeCl-excimer laser pumped dye laser. The fast time response (30 ns) and good spatial resolution make the PLD method a candidate for future in situ measurements in turbulent engine exhausts. The PLD signals, measured in a sample cell, exhibit a linear response for NO₂ concentrations from 3 ppm to 208 ppm and for smoke concentrations from 0.3 mg/m³ to 10 mg/m³. With a low pulse energy of 4 mJ, single-shot PLD measurements in a sample cell have accuracies of ± 14 ppm for NO₂ indicating accuracies of ±0.7 mg/m³ for smoke. With increased pulse energy and multi-shot averaging, sensitivities of ± 0.4 ppm of NO₂ or ± 20 µg/m³ of smoke are expected.     

The nilpotence height of

A 20-year-old conjecture about the mod 2 Steenrod algebra The method of Walker and Wood is used to completely determine the nilpotence height of the elements in the Steenrod algebra at the prime 2. In particular, it is shown that for all , . In addition, several interesting relations in are developed in order to carry out the proof.