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Flash Physics: Vibrots tumble and turn, string theorists bag Breakthrough Prize, microwave chip is a first

05 Dec 2016 Hamish Johnston

Flash Physics is our daily pick of the latest need-to-know developments from the global physics community selected by Physics World‘s team of editors and reporters

Twisted motion: vibrot converts vertical motion to rotation


Vibrots tumble and turn

Vibrots are tiny devices that convert linear vibrations into rotational motion and are of great interest to scientists studying the collective motions of particles in physics, biology and chemistry. In this latest study, Christian Scholz, Sean D’Silva and Thorsten Pöschel of Friedrich-Alexander-Universität Erlangen-Nürnberg in Germany have created a vibrot that is powered by a vibrating floor – something that is common in the processing of granular materials, where collective motion can emerge. The cylindrical device is about 1 cm in diameter and is supported by seven legs, which are all bent at the same angle (see figure). The legs are springy and this causes the vibrot to rotate when subjected to vertical vibrations. In this latest work, Scholz and colleagues identified two distinct ways in which this motion occurs: “ratcheting” and “tumbling”. The ratcheting mode occurs at relatively low amplitudes of vibration. The legs of the vibrot move in synchrony as the floor vibrates up and down, with the device getting a rotational kick once every vibrational cycle – much like a ratchet. The tumbling mode occurs at higher vibrational amplitudes and does not involve the synchronous motion of the legs. In this mode, the legs tend to remain in the air for longer than one cycle of the vibration. Although the vibrot does rotate in tumbling mode, it does so in a very irregular manner with chaotic fluctuations. The research is described in New Journal of Physics.

String theorists bag 2017 Breakthrough Prize

The 2017 Breakthrough Prize in Fundamental Physics has been awarded to Joseph Polchinski of the University of California, Santa Barbara and Harvard University’s Andrew Strominger and Cumrun Vafa. The trio won for making “transformative advances in quantum field theory, string theory, and quantum gravity”. The three physicists share £3m in prize money. The Breakthrough Prize was inaugurated in 2012 by the Russian venture-capitalist Yuri Milner, who had studied theoretical physics. This is the third year that the prize has been awarded to string theorists. The award was presented yesterday at a gala ceremony at the NASA Ames Research Center in California, where celebrities such as actor Morgan Freeman rubbed shoulders with Breakthrough Prize funders including Facebook founder Mark Zuckerberg. A special prize was also given to LIGO founders Ronald Drever and Kip Thorne of Caltech and Rainer Weiss of the Massachusetts Institute of Technology. This prize was shared with more than 1000 physicists who worked on LIGO when it made the first-ever detection of a gravitational wave in 2015. Also awarded was the 2017 New Horizons in Physics Prize, which was given to five early career physicists.

Fully integrated microwave communications device is a first

The first photonic device for microwave signals with all of the necessary components fully integrated on a single chip has been produced by researchers in Spain. The design could have important implications for the next generation of wireless communication technology, where the increased requirements for data capacity will require the use of higher-frequency, multiplexed signals that traditional electronics cannot process effectively at the speeds required. Optical signal processing provides an obvious solution, but the cost of the components required has so far proved prohibitive to telecommunications applications. Researchers have attempted to bring down the costs, as well as the physical size and power requirements, by integrating more and more components onto single chips, although this has proved challenging. Now, José Capmany Francoy and colleagues at the Polytechnic University of Valencia have squeezed all of the components necessary for a microwave filter onto a single piece of indium phosphide – including a laser, a tunable optical filter and photodetectors. The optical filter is tuned by changing its temperature – which can be achieved by applying voltages to specific pins of the chip to power an internal heater. The device suffered severe problems: for example, the researchers had to measure the output optically because of interference when measuring the output as an electrical signal. Nevertheless, they believe technical design improvements and elimination of manufacturing imperfections should correct these problems, allowing the researchers to push on towards their goal of a fully integrated, programmable photonic microwave signal processor. The chip is described in Nature Photonics.


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