2.degrees of energy in terms of intensity of sound of the vowel or syllable. ə is weakest ʌ is stronger 3.open or closed syllables ə could be open or closed syllables ʌ only in closed syllables

there are 4 degrees of stress

1. main stress 2.sub stress 3.unstressed syllbles retaining the full quality of the vowels without any reduction into schwas. Eg undone. Verb advocate. End syllable of city. Purpose of this is to retain the clarity (and meaning represented by) of the syllables
2. Weakest schwaed syllables

So there’s always more or less some stress on ʌ syllables even in the absence of “‘“ markings.

In “append”, the first syllable is open one with the weakest schwa while in “upend”, 1st syllable is closed, thereby reducing the need of aspiration of “p” in 2nd syllable. There’s also a need to retain the meanings in “up” and “end” as 2 words, by shutting the lips immediately after ʌ and by reducing the aspiration of “p” in a linkage Hope this answers the original question.

3 @JohnLawler Or phonemic stress. For me, "upend" has stress vaguely on the first syllable, "append" firmly on the second. – No Name yesterday

I believe this last answer got the the point. When the symbols schwa ə and ʌ were created, it was meant that ə should represent 3 shades of meanings:

1.Tongue positions: It’s a strictly a middle vowel when the tongue is at a totally relaxed position, while ʌ would represent a vowel somewhere between back & middle. Because certain accents especially in US give a rendition of ʌ closer to the middle than to the back, sometimes even coincide with ə in terms of tongue position, some dictionaries adopt ə in place of ʌ.

2.Intensity of sound of the vowel or energy to be expended in the production of the vowel: ə is weakest in terms energy used to produce the intensity of sound. ʌ is stronger in use of energy in sound production.

3.Open or closed syllables: ə could be in an open or closed syllable while ʌ could only occur in closed syllables.

There are 4 degrees of stress in descending order:

1. main stress.

2. sub stress.

3. unstressed syllbles retaining the full quality of the vowels without any reduction into schwas. Eg 1st syllable in “undone” & 3rd syllable in the verb form of “advocate” as well as the ending syllable of “city”. The purpose of this is to retain some clarity of (and meaning represented by) the syllables.

4. Weakest schwaed syllables.

So there’s always more or less some stress on ʌ syllables even in the absence of ‘ markings.

In “append”, the first syllable is an open one with the weakest schwa while in “upend”, 1st syllable is closed, thereby reducing the need of aspiration of “p” in 2nd syllable. There’s also a need to retain the meanings in “up” and “end” as 2 separate words before being combined to form the aggregate new word “upend”, by shutting the lips immediately after ʌ and by reducing the aspiration of “p” in a linkage with “end”. Hope this answers the original question.