Lack of investment in nuclear physics, says IOP

Current funding of nuclear physics research is insufficient for the UK to take advantage of developing technologies needed in such areas as healthcare, the nuclear industry and defense, according to an international panel of nuclear physicists.

IOP website

A new report by the Institute of Physics, A Review of UK Nuclear Physics Research, has been published to help produce a strategy to help guide nuclear physics in the UK for the next decade [1].


[1] A Review of UK Nuclear Physics Research (PDF, 10 MB)


Nuclear physics ‘compromised by lack of investment’, IOP News

Cauliflower and fractals

Researchers have published a mathematical formula to describe the processes that dictate how cauliflower-like fractals form [1].


The team grew thin films using a technique known as chemical vapour deposition (CVD). They adapted the CVD process so that the film would grow into shapes similar to those seen on a cauliflower. These structures were on the submicron scale.

From this work the team were able to derive the formula which describes how the cauliflower-like patterns develop over time.

Theory verses Experiment

Below are some graphics comparing the theory with experimental observations. The close agreement is clear.


Taken from the paper [1], courtesy of IOP publishing


[1] Mario Castro et al (2012) Universality of cauliflower-like fronts: from nanoscale thin films to macroscopic plants New J. Phys. 14 103039 (online here)


IOP News

One step closer to a Star Trek tractor beam

Professor David Grier and David Ruffner (graduate student), working at the Department of Physics and Centre for Soft Matter Research have published a paper announcing that they have experimentally demonstrated a class of tractor beams[1]. They were able to move microscopic spheres of silica suspended in water over distances of about 30 micrometres.


David G. Grier

The definition of a tractor beam (quoted from the paper) is: A tractor beam is a traveling wave that can transport illuminated material along its length back to its source.

By this definition things like optical tweezers or optical conveyor belts are not technically tractor beams.

The problem

If you think about it, in order for a particle to be pulled by a beam of light, rather than pushed, it has to redirect the momentum of enough photons to overcome the force due to the radiation pressure of the beam.

This can happen if the intensity of light beam changes sufficiently along the axis of the beam. For example, one can use a beam with tightly focused areas.

The method

The tractor beam demonstrated by Ruffner and Grier uses a special kind of laser beam called a Bessel beam laser– the amplitude is given by a Bessel function of the first kind. A perfect Bessel beam would not diffract and spread out as it propagates. (For those that are interested, there is a lot of classical mathematical physics behind Bessel functions)

The team produced two Bessel beams side by side using a lens to angle them so they overlapped. Then by varying the relative phase of the two beams, the particle becomes trapped in an “optical conveyor” which allows the particle to be transported in three dimensions.


Cross-section of the Bessel beam and graph of intensity


No-one is about to start pulling space craft about using this technique. However, it may find applications in biology rather quickly.


[1] Optical conveyors: A class of active tractor beams, D. B. Ruffner and D. G. Grier, Physical Review Letters, in press (2012) (download)


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