Hester Bijl recalls spending a rigorous and thrilling afternoon back in the mid-1990s working on a difficult mathematical problem with her doctoral adviser. They threw ideas through the air and equations on paper and ultimately emerged victorious: Problem solved. Bijl also recalls her adviser's amazed and somewhat befuddled reaction: "Huh, that's interesting," he said. "I never really believed in working together, but this time it really worked."
In Bijl's mind, that moment epitomises just how opposite their personalities were: Whereas her adviser avoided human interaction, she thrived on it. So when Bijl, an applied mathematician, landed an appointment in the aerodynamics department  in the Faculty of Aerospace Engineering  at Delft University of Technology  (TU Delft) in the Netherlands in 1999, she was keen to be more actively involved in her students' personal and professional development than her own adviser had been in hers.
As it happened, Bijl found another opposite in her first doctoral student, Sander van Zuijlen. Upon meeting them, their differences are immediately apparent. Pixyish Bijl, 37, has an infectious smile and a throw-her-head-back laugh. On the other hand, van Zuijlen, 32, speaks reticently and in a soft voice and slouches to minimise his height. The pairing might have reprised Bijl's own doctoral experience, with the roles reversed. Instead, with Bijl's insightful mentoring, these two opposites found strength in their differences and developed into an effective scientific team.
Now, more than a year after van Zuijlen's graduation, the pair continues to work closely together as colleagues. "They are quite different" but complementary, observes Peter Bakker, head of van Zuijlen and Bijl's department at TU Delft. "They both see that. They both benefit from that relationship."
When van Zuijlen started his Ph.D. in aerospace engineering in July 2001, the student and adviser met weekly to discuss his progress in learning the fundamentals behind the development of mathematical models for the flow of air around wind turbines and aeroplane wings. Van Zuijlen remembers these first months as being a tough time of "struggling to find a direction," although he hid it well behind his consistently stoic front. "I never really noticed any major doubt," Bijl recalls.
Nonetheless, Bijl reassured him, reaffirming her belief in his abilities and telling him that he wasn't expected to understand everything just yet. The first year of a Ph.D. can be especially trying for young scientists, Bijl says. "I think it's necessary to be supportive, stimulating … because when they're in this doubt period, they doubt everything, you know. 'Should I do a Ph.D.?' and 'Why am I on Earth?' " After their regular meetings, van Zuijlen says he "would feel [his confidence] coming back. [I] would always have a positive feeling after."
As is important in a mentoring relationship, they soon learned about their differences. Bijl wanted van Zuijlen to write out a schedule for his studies, outlining what actions he would take during the next few years to graduate on time--"a sort of reality check," she says. But van Zuijlen didn't believe in making plans that were sure to change. Again and again, he failed to bring the requested schedule to their meetings. Finally, Bijl says, "he did it after a long nagging."
Increasingly, however, van Zuijlen learned that Bijl had strengths where he had weaknesses and that Bijl was happy to help him develop in those areas. When it came to writing and presenting, for example, Bijl had a knack for describing why her results were important--as Bijl explains, "not just that [something is] 10 times faster, but … why should people be interested in the fact that we found that it's 10 times faster." Whereas van Zuijlen was pretty good at stating the "what" of his research, he admitted that he wasn't very good at explaining the "why." Bijl would talk him through that part, asking, "What is the reasoning behind it? Why did you do certain things?" With this coaching, his confidence in his papers and presentations rose dramatically.
Bijl also started to benefit from mentoring van Zuijlen. "I freak out more often than Sander does," Bijl says. While she works herself into a frenzy, van Zuijlen manages to remain preternaturally calm, showing, says Bijl, "no outer signs of nervousness." In 2002, the first time van Zuijlen and Bijl both presented at an international scientific meeting, they stayed up late refining their presentations together. As would happen many times, van Zuijlen's attitude calmed Bijl. "I think that was sort of special," she recalls.
About a year after van Zuijlen started his Ph.D. with Bijl, their mentoring relationship began to evolve into a scientific partnership as the pair started getting into the meat of van Zuijlen's thesis project. When designing wind turbine blades or aeroplane wings, engineers traditionally had to use two different models, one to calculate how the structure would displace the air and another to calculate how the structure would distort in response to the airflow. But this two-model approach has not been very accurate or fast, so Bijl and Zuijlen's work was to combine the two models into one.
Together, the pair had made progress in solving one major problem in combining the models, but they were struggling with another. Bijl then left on an extended work trip abroad, and when she returned, van Zuijlen presented her with the answer. "He said, 'What if we combine that algorithm with that?' And it worked," Bijl recalls. She was elated.
After that, their working relationship was less of a mentor to a student and more of "an equal partnership," Bijl says. "The ideas came from Sander instead of from me." Their closeness in age also helped. Only 5 years apart, Bijl and van Zuijlen have always called each other by their first names, something van Zuijlen wouldn't have done with older professors.
But van Zuijlen would need Bijl's advice one last time, when it came time to write his thesis. "I've tried to block it out of my memory," he jokes. Not a writer by nature, "I just kept on going with the research, when I should have stopped and started writing." Bijl noticed his delaying tactics, regularly asking, "Have you written a sentence yet?" Finally, she advised him to do what always worked for her: Stay away from the temptations of the office. "Scratch out whole days and go home," she advised. "Don't answer the phone."
It worked. In a triumph for both mentor and student, his thesis was a finalist for best 2006 Ph.D. theses from the European Community on Computational Methods in Applied Sciences .
As a result of mentoring van Zuijlen, Bijl has had the chance to develop her mentoring style with 10 other Ph.D. students. Bakker describes Bijl's mentoring approach as attentive but not overbearing. "She helps students to find their own way," he says. "She leaves room for creativity."
This ability to adapt to her students' personalities, which may be changing over time, is a key aspect in her mentoring. "You have to figure out along the way which kind of support they need," Bijl says. "If you're all the same, you start repeating each other, and you don't really learn from each other. If you have different personalities, you sort of add on to each other."
For a start, Bijl had to adjust to and respect van Zuijlen's differences, which in some cases she found hard to understand, she admits. For example, she has encouraged him to work abroad, "to see other approaches and other methods." But his resistance has been firm: He's happy where he is. "If I like something," he explains, "I don't have the urge to change it." After earning his Ph.D., he stayed on for a postdoctoral and then a staff appointment in the aerodynamics department. Although disappointed that he won't have the same eye-opening experiences that she had, Bijl concedes, "If he stays here, I'm very happy, of course."
Bijl's mentoring has made inroads in other areas where van Zuijlen was once intractable. Although van Zuijlen never took to making the sort of long-term schedule that Bijl requested at the start of his studies, he now makes prioritised to-do lists. "And sometimes it works," he admits. At the same time, Bijl admits that van Zuijlen's practical, if somewhat casual, approach to deadlines has rubbed off on her, too.
In what may be the biggest compliment, van Zuijlen has adopted Bijl's open-door mentoring style. He now tells his students that "they can always come around when they have problems or need some advice." He is also sensitive to what they need from him and not just what he wants from them. "Everyone is different," he says, sounding a lot like Bijl. "You have to adapt."
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Images. Top: John Wigham. Middle: Marcel Krijger, LENS! Fotografie. Bottom: courtesy of Sander van Zuijlen