I am doing a M.S. degree in a mechanical engineering program. I sent to over 20 professors, whose lab's website clearly showed Ph.D. position information, a letter for an opportunity in the previous three weeks, while only 4 rejected letter responses, the others chose to not reply, is there any reason? If possible, can you put forward your opinion? Is there any way to solve this problem? Should I send to them again in the later time? Thanks in advance.

The format of my letter like this:

attachment-1:my transcript

attachment-2:my cv

Hello Professor,

Paragraph-1: Personal information, like my name, graduate school, my thesis topic, my publication condition.

Paragraph-2: Where I found your position information, why I chose your labs(I indicated the interesting topics they listed in their page)

Paragraph-3: My qualification, like my programming level, practical experience of simulation, related courses I ever took.

Paragraph-4: An ending sentence, like: looking forward to your reply, have a nice day.

I searched for reasons and found listed potential reasons to account for my undergoes: 1) Now is summer vacation. 2) I have a weak academic background. 3) Professors do not think my research field can match theirs. 4) The content of the letter is not unique, professors may think this letter can be sent for everyone. 5) I didn't put the professor's name at the start.

I am doing a M.S. degree in a mechanical engineering program. In the previous three weeks I sent a letter inquiring for an opportunity to over 20 professors whose lab's website clearly showed Ph.D. position information. I received only 4 rejections, the others did not reply, is there any reason? Is there any way to solve this problem? Should I resend them my letter at a later time?

The format of my letter like this:

attachment-1:my transcript

attachment-2:my cv

Hello Professor,

Paragraph-1: Personal information, like my name, graduate school, my thesis topic, my publication condition. Paragraph-2: Where I found your position information, why I chose your labs(I indicated the interesting topics they listed in their page)

Paragraph-3: My qualification, like my programming level, practical experience of simulation, related courses I ever took.

Paragraph-4: An ending sentence, like: looking forward to your reply, have a nice day.

I found potential reasons to account for the lack of replies:

1. Its summer vacation.
2. I have a weak academic background.
3. Professors do not think my research field can match theirs.
4. The content of my letter is not unique, professors may think this letter can be sent by everyone.
5. I didn't put the professor's name at the start.