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Last night, I was reading this article:

The article

Ok, probably you cannot download the paper then I toke a screenshot and uploaded it here for you:

image1

Please read this paragraph(Highlighted in the above screenshot):

Park et al. [3] investigated sonic nozzles that are applied to gas flow rate measurements and determined that the critical pressure ratio is highly dependent on the Reynolds number rather than area ratio, especially in the cases with low flow velocity. Variation of discharge coefficients for sonic nozzles with flow geometry and Reynolds number was reported by Paik et al. [4], who determined higher discharge coefficients with increase of mass flow rate. Spotts et al. [5] performed a CFD study of the compressible flow through convergent–conical nozzles to investigate the effect of the nozzle pressure ratio and nozzle angle on the nozzle performance. They confirmed that for smaller nozzle angles, the discharge coefficient increases and the choked nozzle pressure ratio will be reduced.

Why didn't the bold words or phrases get any definite article "the"? Totally some parts of this paragraph is odd. e.g. There are two "Reynolds number" and the first one has got a definite article but the last one didn't get. Is it okay?

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The author could have used the definite article with the sonic nozzles since the reference is to specific nozzles (i.e. those "that are applied to gas flow measurements"). But the author chose to present those nozzles generically using the plural, referring to a type of nozzle, and then rely upon the that-clause to do the specifying.

gas flow rate measurements, another plural, refers generically to a kind of measurement, not to specific instances of measuring.

area ratio is again a generality, area ratio as factor, rather than a specific set of area ratios.

low flow velocity is again a generality, that kind of velocity as factor, rather than actual instances of low flow velocities.

Speed is a significant factor when shopping for a striker.

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  • How about Reynolds number?
    – Roh
    Commented Dec 10, 2018 at 13:18
  • That's a term of art, here used as a category of information. Your medical record shows height, weight, and age.
    – TimR
    Commented Dec 10, 2018 at 13:18
  • Other bold phrases? e.g. Variation, discharge coefficients, flow geometry,...
    – Roh
    Commented Dec 10, 2018 at 14:42
  • 1
    @Roh: Can you not extrapolate from the explanation already provided to you? Or do you prefer to be spoon-fed?
    – TimR
    Commented Dec 10, 2018 at 15:15

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