On this first morning in San Francisco we visited Lentinklab, which is founded by David Lentink. The first paper was published in 2004. The Lentinklab is mostly driven by the interests of David himself. With the students he brainstorms about new research projects, of which he has a broad spectrum of ideas. The main interest of the lab is to find out more about the flight and behaviour of birds, insects, bats, maple leaves, and how to apply this knowledge to robots. Over the years the research shifted from more fluid mechanics oriented research to more biomechanical types of research. David Lentink has a number of 48 publications on his name. The research group, situated at Stanford University, has approximately a dozen students working under David, doing all kinds of research, related to robotics and the flight of birds. Because David has done research on a lot of universities, he knows the difference between the working of several research groups over the world  quite well. During the visit he pointed out that in the United States, it was much more important to write proposals and to find money to do the research. However, it is also a bit easier at Stanford, because the name of the university is big worldwide.

An interesting aspect of birds is their flight. It is possible for birds to fly through a difficult environment with for example skyscrapers, trees or busy traffic without hitting something. This would be an interesting feature for delivering packages or looking ahead in a traffic jam for an accident. To research this, Lentinklab uses real birds on which tiny laser goggles are put, to protect  them. When shooting high speed X-rays, the wing movement of the birds could be tracked.

An unexplored research field is that of the navigation of birds. It is unclear how birds navigate, especially in the dark. It could be with the eyes, with their hearing, or the organ of balance. There are even theories that involve quantum mechanics.

The Lentinklab also has the possibility to inject particles to track the airflow, especially around the wings of birds. In fluid mechanics classes we learn to take all the boundaries into account when doing control volume analysis. This is however not really possible in practice, because during the measurements, the cameras are only pointed at one side of the bird. In the Lentinklab, this problem is solved by putting multiple cameras around the bird.

The wind tunnel has multiple pressure sensors, which detect the pressure waves caused by the wing movement of the birds. With this method, the researchers can understand the movement, the lift and the drag of the birds.

The newest research involved a self-made robot with real bird feathers. One of the advantages of using feathers is the strength and the flexibility of the material. The wings consist of the highest number of parts contributing to the shape of the wing ever produced in this lab. The robot is tested in the wind tunnel and currently the sixth generation is being tested.

Furthermore, we visited the neighboring lab shortly to see how sticky robots are made. The research that we saw involved a flying robot which could hit the wall, whereafter it made a majestic climb upon a beautiful wall. This sticking is due to the microstructure underneath the ‘paws’ of the robot in combination with the PDMS that it was applied on.

As far as we know, there is no such research group in the Netherlands. Lentinklab has collaborations with universities in the United States, but also with the Wageningen University. David Lentink himself went to the United States to do this research, because it was easier to start with a new research area in the United States using grants.

After a quick lunch in the cars, we arrived at SLAC: Stanford Linear Accelerator Complex. It was founded in the 1960s and the goal was to accelerate electrons for groundbreaking experiments in creating and identifying subatomic particles. Over the years, the role of the complex changed. After some major discoveries, like the existence of the J/Psi-particle, SLAC began using the accelerator for making X-rays. The X-rays are used to study a wide variety of specimens. They can be used in different research areas, such as photosynthesis, drug development, electronics, customizing chemical reactions and designing new materials. SLAC is used by many institutions and companies, because of the uniqueness and the size of this type of accelerator. For a company it costs $30,000 dollars per hour to do experiments. It is one of the longest buildings in the world with its 3 kilometers. Furthermore, the experiments generated more than 600 papers in the first six years of operation.

In the Netherlands we don’t have a linear accelerator, so it’s hard to compare the organizational structure to a Dutch equivalent. At SLAC, there is one boss, with three deputies. Under this boss and deputies, there are sub-teams, which are not that big.

The accelerator is able to create beam energies between 250 eV to 2 keV for soft X-rays and 4 keV to 25 keV for hard X-rays. Soft X-rays can be used to study the electronic structure of the sample, while hard X-rays are used to study the atomic structure. The customer can specify the energy that is needed for their experiment. X-rays are created in multiple steps. First, lasers are used to kick electrons out of copper. These electrons are then accelerated in the linear accelerator, up to a fraction off of the speed of light. In the undulator, these electrons are shaken such that they emit X-rays. The electrons are bent such that they are absorbed in some metal, while the X-rays continue to the experimental halls. These X-rays are then used in various machines, in various ways. They can be scattered to determine length scales in the sample material. Secondly, it is possible to use them in imaging to determine the texture, and lastly they can be used for spectroscopy, to determine the atomic elements and chemical composition. Spectroscopy is also the newest technique. X-rays are mainly useful because they can be fired in short pulses in the order of 10 femtoseconds, allowing for observation of the material before it is damaged by the X-rays, and to observe fast dynamics in the sample. Currently, SLAC is being upgraded. The accelerator is expanded by a long superconducting accelerator. This will allow for continuous operation because the superconducting accelerator does not have downtime due to heat dissipation that is present in the copper accelerator magnets. Therefore, there will be an enormous increase in data output of at least a thousand times. This is more than the data acquisition system can process, but this may change in the future, such that the upgrade will be useful for a long time.

Due to the success of SLAC, other countries are also interested in building linear accelerators. As of now, there is not really another institution which allows for a fair comparison.

Categories: San Francisco


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