You should approach the professors directly over email along with your CV, a motivation and relevant documents. More likely than not, they respond promptly in case they find you an appropriate match to their work. The interview takes place in a few rounds spanning over 2-3 weeks. The preliminary interview is a basic 'get to know you' kinda interview. The senior scientist will then ask for your referees to recommend you in her email. A technical interview round then follows based on your research area (for example presenting/discussing a paper the interviewer provided to you). While you may not be fully expected to know everything, try to be absolutely thorough with your fundamental subject concepts and thoroughly learn your previous projects, the rationale, why you did the project. The same goes for paper presentation, try to understand the rationale and future course of research as the researcher is actually trying to learn if you can build on his ongoing research. Also, be aware and enthusiastic about the interviewers research works, at least in a broad way. Ask questions at the end. Let them know your preferences

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