Aspiration of plosives in final position and word boundaries

Question

In a sentence like

It is a cat, is it?

I'm not sure what kind of aspiration the various /t/ should have. I guess the first one in "it" would be weakly aspirated, as it's followed by a stressed vowel but is in a word boundary, and the one in "cat" would likewise be weak – supposing I'm right, would the last one have no aspiration, non-audible release or weak aspiration?

Answer 1

My pronunciation of "It is a cat, is it?" is [ˌʔɪɾɪzəˈkʰæːɾɪzɪtʼ].

I don't know what it "should" be -- it's just my best shot at describing my own pronunciation. (I'm a pretty typical Midwesterner.) The diacritic on the last t is meant to represent closure of the glottis. The preceding /t/s have both been flapped because they are at the ends of syllables and are between vowels. They are at the ends of syllables because they are at the ends of words -- any stress on the following vowel doesn't matter to whether they flap. The lengthening of the vowel of "cat" reflects the following comma in the spelling.

Answer 2

I'll answer my own question, as I think I finally understood this.
It turns out that in British English Received Pronunciation, voiceless plosives /t, d, k/ are:

• Fully aspirated when followed by a vowel in a stressed syllable;
• Weakly aspirated when in unstressed syllable or word boundary (as every /t/ in the example sentence, except for the last one); and
• Not aspirated when preceded by an /s/ or in final position (as, obviously, the last /t/).