have been developed vs were developed

[Smithereens]

Hi everybody,

I am writing a research paper and having problem deciding which tense to use (and why) when describing methods, processes or techniques. Past simple tense is usually used in this context but sometimes present perfect too.
For instance, I don’t understand what is the difference (in meaning) between the sentences (a) and (b) below.

(a) Thin-film Ta2N resistors have been developed and deposited on polyimide flex using a horizontal batch process.

(b) Thin-film Ta2N resistors were developed and deposited on polyimide flex using a horizontal batch process .

Would you please let me know what meaning is implied in (a) and (b) by the use of the respective tense?

Thank you for your consideration.

[Smithereens]

Here, I am posting one more example that confuses me:

"Scanning electron microscopy (SEM) on the fibre composite has been performed on a Philips XL 20 SEM. The sample was embedded in epoxy resin and polished with water using sandpaper and a very fine polishing paste, followed by cleaning in an ultrasonic bath."

I don’t understand why the paragraph starts with present perfect and continues with past simple tense. Would you please explain me?

[Alan]

Hi,

The main difference between past simple and present perfect simple is that the ps contains within it, even if it's not stated, a suggestion of a definite time in the past. Your examples/was embedded/ was polished/were developed all tell us that these actions took place and if you wanted to know ( the use of the tense indicates this) you could find out.

The pps on the other hand is not so precise

Your other examples have been developed/has been performed tell us that these actions took place but when exactly we don't know.

When someone starts a conversation in the past simple, your ear is waiting to hear when something happened. When someone starts a conversation in the present perfect, you are more interested to know that this happened and you're not so interested exactly when.

For example:

A I went to Paris ..
B Did you? When was that?

A I have been to Paris.
B Yes, so have I. It's beautiful isn't it?

Alan
_________________
English as a Second Language
You can read my ESL story A day in the life of a policeman

[Smithereens]

Alan, thank you very much for the prompt answer!
I still don’t understand why someone would prefer to write the second of my examples* the way it is written… Having in mind your explanation, I wander, could I reason like that:
(1) SEM was performed by somebody but most probably this wasn’t the author of the sentence; or - the action was performed by somebody else and the result was delivered to the author therefore the author doesn’t know (from his own experience) all the details about what has been performed.
(2) The one who embedded and polished the sample could be the author of the sentence; or – the author of the sentence knows all that is necessary about the embedment and the polishing of the sample.

Does this reading make sense?

* "(1) Scanning electron microscopy (SEM) on the fibre composite has been performed on a Philips XL 20 SEM. (2)The sample was embedded in epoxy resin and polished with water using sandpaper and a very fine polishing paste, followed by cleaning in an ultrasonic bath."