burns_2018 ========== R\. A\. Burns, C\. J\. Peters and P\. M\. Danehy, "Unseeded velocimetry in nitrogen for high\-pressure, cryogenic wind tunnels\: part I\. Femtosecond\-laser tagging", Meas\. Sci\. Technol\. 29, 115302 \(2018\) `Source record `__ · :doc:`Catalogue ` · :doc:`Review register ` DOI: `10\.1088/1361\-6501/aade1b `__ **Source kind:** measurement **Recorded technique:** Femtosecond laser electronic excitation tagging \(FLEET\) velocimetry in the NASA Langley 0\.3 m Transonic Cryogenic Tunnel \(nitrogen\)\: a regeneratively amplified Ti\:sapphire laser \(800 nm, 20 nm bandwidth, 1 kHz, about 1\.2 mJ of which about half reaches the flow\) focused by an f = 200 mm lens; the N2 first\-positive emission of the tagged spot imaged by an intensified high\-speed camera; 89\-275 K, 85\-400 kPa, Mach 0\.2\-0\.75 \(PDF pp\. 3\-6\)\. **Materials in structured entries:** None recorded. **Dataset quantities:** None recorded. **Contents:** 0 datasets; 0 formulas. Curation notes -------------- Context only, no datasets\. Identity checked on the article's first page \(PDF page 2; PDF page 1 is a cover sheet\)\: Burns, Peters and Danehy, Meas\. Sci\. Technol\. 29, 115302 \(2018\); page numbers are the PDF's\. The pulse duration is not stated\. What it shows\: the FLEET signal \(nitrogen emission that follows the femtosecond pulse, from N\-atom recombination and excited N2\) scales linearly with the gas density, and its lifetimes fall with density, 'with little independent sensitivity to the other thermodynamic conditions' \(abstract\)\. Table 1 \(PDF p\. 9\) fits the two lifetimes of a tri\-exponential decay as tau / tau\_ref = C1 \(rho / rho\_ref \+ C2\)^C3 \(Eq\. 2\)\: tau\_1, tau\_ref = 21\.6 us, rho\_ref = 1\.15 kg m^\-3, C1 = 2\.42, C2 = 0\.395, C3 = \-1\.57; tau\_2, 69\.1 us, 1\.15, 1\.30, 0\.013, \-1\.27; 'purely empirical in nature' \(PDF p\. 9\)\. Why nothing is taken\: the lifetimes describe the decay of the tagged spot's emission in a flowing, laser\-heated gas, not a property of a molecule \(not a dissociation time or a rate coefficient\), and the authors give no physical attribution to the fit \(PDF p\. 9\)\. The kinetics behind the signal are modelled in peters\_2019 \(C\. J\. Peters is an author of both\)\. The velocity accuracy and precision results are outside optmat's scope\. Register\: TC\-981\. **Recorded bibliographic identity status:** VALIDATED. This concerns identification of the source; it does not establish the scientific correctness of its contents. Datasets -------- No datasets are recorded. Formulas -------- No formulas are recorded. Corrections ----------- No dataset errata are recorded in this source record. Formula corrections, where recorded, appear with their formulas above. Curation notes may also discuss corrections or unresolved interpretation. Consult the :doc:`review register ` for the checks and decisions.