http://www.amolf.nl/ Latest news from AMOLF en http://www.amolf.nl/typo3conf/ext/tt_news/ext_icon.gif http://www.amolf.nl/ 18 16 Latest news from AMOLF TYPO3 - get.content.right http://blogs.law.harvard.edu/tech/rss Tue, 17 Apr 2012 14:54:00 +0200 http://www.amolf.nl/news/detailpage/article/a-microtubule-based-molecular-switch-determines-the-orientation-of-cell-divison-in-plant-stem-cells//chash/000df6b5617ced69404f1c28c75c5a9e/ In order to create an organ like the plant root from a single niche of pluripotent cells, plants...  
Studies on plants with mutant developmental patterns show that microtubule-associated proteins known as CLASPs are recruited to certain cell edges to facilitate the switch to a longitudinal orientation. If the activity of these proteins is incorporated in the simulations the switching indeed occurs in a robust manner.
The results of this research are published on the 13th of April in the scientific journal Cell. The results are also interesting for both engineering more efficient crops and cancer research. Reference
P. Dhonukshe, D.A. Weits, A. Cruz-Ramirez, E.E. Deinum, S.H. Tindemans, K.  Kakar, K. Prasad, A.P. Mähönen, C. Ambrose, M. Sasabe, G. Wachsmann, M. Luijten, T. Bennett, Y. Machida,R. Heidstra, G. Wasteneys, B.M. Mulder and B. Scheres
A PLETHORA-Auxin Transcription Module Controls Cell Division Plane Rotation through MAP65 and CLASP
Cell 149, 383–396 (2012) Contact
Prof.dr. Bela Mulder, +31-20-754 7100 More information
Utrecht University]]> News Theory of Biomolecular Matter Tue, 17 Apr 2012 14:54:00 +0200 http://www.amolf.nl/news/detailpage/article/nano-hole-scatters-captured-light-wave//chash/3acfa11d11fe579cfbcbcb39ae8070d6/ The interaction of light that is ‘stuck’ to the surface of a metal – such as a type of light wave... Reference
N. Rotenberg, M. Spasenovic, T. L. Krijger, B. le Feber, F. J. Garcia de Abajo, and  L. Kuipers
Plasmon scattering from single sub-wavelength holes
Phys. Rev. Lett. 108, 127402 (2012) Contact
Prof.dr. Kobus Kuipers
Tel. +31-20-754 7100]]> News Nano-Optics Fri, 30 Mar 2012 15:22:00 +0200 http://www.amolf.nl/news/detailpage/article/the-breakdown-of-the-single-active-electron-approximation-in-strong-field-laser-ionization//chash/a6f2d884f01630e9dad64c506861b495/ Ionization of atoms or molecules by an intense femtosecond (1 fs = 10-15 s) laser is at the basis...  
However, in the last few years this is beginning to change. A number of experiments were reported in the recent literature that have been difficult to reconcile with a simple single active electron picture, and where theoretical descriptions have invoked the participation of electrons originating from different molecular orbitals in the strong field ionization process. An example has been high harmonic generation in several small molecules like CO₂ and N₂O₄. Still, a direct experimental demonstration of the participation of multiple electronic orbitals in strong field ionization has been lacking until now. This feat has now been achieved in a paper that is published in the March 16th issue of Science.
 
When the most weakly-bound electron is removed from an atom or molecule, this produces an ion in the ground state. By contrast, removal of an electron from a different, deeper lying orbital produces an ion in an excited state. In the case of larger molecules like the 1,3-butadiene (C₄H₆) and butane (C₄H₁₀) molecules that were the subject of the present study, these excited ions are unstable and fall apart, producing lighter fragment ions, which can readily be distinguished from intact parent ions. The observation of these fragment ions does not yet prove, however, that they were formed directly during the ionization process. On the contrary, it is very common that ions absorb additional photons from an ionizing laser after they are formed, and this often leads to fragmentation.
 
When atoms or molecules are ionized by a strong near-infrared laser field, they absorb a large number of photons, typically more than the minimum number that is required to remove an electron. As a result the photoelectron kinetic energy distribution contains a series of discrete peaks, where each peak corresponds to a specific number of absorbed photons. To prove that excited ions were formed immediately accompanying the electron removal (in other words, to prove that the electron was not removed from the outermost orbital, but from a deeper lying one), experiments were performed where both the kinetic energy of the electrons and the mass of the ions produced in the ionization process were measured in a correlated way.  
 
If the fragmentation occurred by the absorption of additional photons after ionization, then we would expect that the photoelectron kinetic energy distribution accompanying the formation of parent and fragment ions would be identical (see Figure). On the other hand, if directly-formed excited parent ions would be the precursor to fragmentation, then we would expect an offset between the photoelectron kinetic energy distributions accompanying the formation of parents and fragments. This turned out to be the case in the experiments on 1,3-butadiene and butane, proving unambiguously that in strong field ionization of mid-size molecules electrons can not only be removed from the most weakly-bound outer orbital, but also from more strongly-bound deeper-lying orbitals. This result has important implications for future studies in attosecond science. It suggests that ionization by a strong laser field can be used to prepare ions in multiple ionic states where the hole left behind as a result of the ionization process can be transported along the molecular frame on an attosecond to few-femtosecond timescale. And these ultrafast changes in the electronic density may pave the way to the realization of charge-directed reactivity, representing a novel paradigm for chemical reactivity where the reactivity is controlled by the motion of electrons rather than that of atomic nuclei.

Part of this research was done at AMOLF by the group of Marc Vrakking. This group has moved to the Max-Born-Institute for Nonlinear Optics and Short–Pulse spectroscopy in Berlin, Germany.

Reference
Andrey E. Boguslavskiy, Jochen Mikosch, Arjan Gijsbertsen, Michael Spanner, Serguei Patchkovskii, Niklas Gador, Marc J.J. Vrakking, Albert Stolow
The multielectron ionization dynamics underlying attosecond strong field spectroscopies
Science 335, 6074 (2012)

Contact
Max-Born-Institute for Nonlinear Optics and Short-Pulse Spectroscopy (MBI)
Prof. Dr. Marc Vrakking
Tel.: +49(030) 6392-1200]]> News Extreme-Ultraviolet (XUV) Fri, 16 Mar 2012 00:00:00 +0100 http://www.amolf.nl/news/detailpage/article/albert-polman-appointed-professor-at-the-university-of-amsterdam//chash/aa31b586c20fdf2d0788d5fa1b51d20b/ AMOLF director Albert Polman has been appointed professor at the Faculty of Science of the... Before, Polman was professor at Utrecht University.]]> News Photonic Materials Fri, 09 Mar 2012 09:00:00 +0100 http://www.amolf.nl/news/detailpage/article/oscillations-enhance-signaling-fidelity//chash/5fc782c00388c6146e6fdcbf4dee5ee1/ Cells often encode information about their environment in oscillations or pulses in the...
Arguably the most important mechanism for regulating cellular activity is the expression of genes,  which is regulated by the binding of gene regulatory proteins to the DNA. The researchers studied using a mathematical model how a gene responds to either an oscillating or a constant input signal - the concentration of a gene regulatory protein. Surprisingly, they found that an oscillating input can lead to a more constant output - the gene-expression level - than a constant input signal. These results suggest that oscillating signals may be used to minimize noise in gene regulation. Reference
Filipe Tostevin, Wiet de Ronde, and Pieter Rein ten Wolde
Reliability of Frequency and Amplitude Decoding in Gene Regulation
Phys. Rev. Lett. 108, 108104 (2012)]]> News Biochemical networks Thu, 08 Mar 2012 00:00:00 +0100 http://www.amolf.nl/news/detailpage/article/nanoscatterers-render-silicon-solar-cells-black//chash/f43e26d5051120fbba5da71e57658db1/ AMOLF researchers, together with colleagues at Philips Research have developed a new type of... Using an array of silicon nanoparticles, thereflection of a silicon wafer, the base material for solar cells, is reduced from 40% to 1%. This can significantly increase the efficiency of solar cells.  The new anti-reflection coating can also find applications in coatings for lenses, cameras and photo detectors. The work is published on February 21st in the journal Nature Communications.
 
Reflection is a natural phenomenon that occurs when light passes the interface between two different materials. For example, at a glass window, 5-10% of the sunlight is reflected at the interface between glass and air. A silicon wafer, the base material for solar cells, reflects even 40% of the light. For solar cells this is a problem, because the reflected light is not converted to electricity. Ideally, a solar cell has no reflection and is completely black. The fact that most solar panels have a blue colour implies that they do not function optimally.

Catching light by scattering
Now, there is a solution to this problem, which at first glance seems quite unnatural. It was found that when the solar cell is covered with a pattern of tiny silicon nanoparticles, the silicon wafer becomes completely black. The surprise is that 99% of the light disappears into the silicon wafer. Only 1% of the light bounces back.
 
This effect is so strong because the size of the nanoparticles was chosen such that exactly one or more wavelengths of light fit inside the nanoparticles. The particles act as tiny cavities that capture light very efficiently, and then transfer it into the silicon substrate. The light is first trapped in nano-cavities, runs a few laps inside, and thendisappears into the silicon. By properly choosing the geometry of the nano-cavities, this principle works simultaneously for all colours of light from the ultraviolet to the infrared spectral region.
 
Printing nanoparticles
This new discovery was made using a new technique developed at Philips Research that allows to very accurately "stamp" nanoparticles on a large surface area. Normally these small structures would be manufactured with expensive cleanroom machines, but with a newly developed stamping technique, that uses a rubber stamp with the desired pattern which is rolled on the Si wafer to reproduce the pattern, it is now possible to do it in an inexpensive way.
 
Albert Polman, the leader of the team: "This new method makes it possible to fabricate solar cells that are perfectly absorbing. And it works not only for silicon, but for all highly reflective materials. The stamping technique can be easily integrated in a roll-to-roll production process. And what I find most interesting is that we had never thought that by scattering light you can control it better. Usually we relate to disorder, but here it actually leads to exceptional control over light."

Reference
P. Spinelli, M.A. Verschuuren & A. Polman
Broadband omnidirectional antireflection coating based on subwavelength surface Mie resonators
Nature Communications 3, Article number: 692 doi:10.1038/ncomms1691. Published 21 February 2012 Contact
Albert Polman, tel.  (020) 754 7100, e-mail: polmanATamolf.nl]]> News Photonic Materials Tue, 21 Feb 2012 17:00:00 +0100 http://www.amolf.nl/news/detailpage/article/light-management-leads-to-ultra-efficient-solar-cells//chash/7ece18f9a69a891cddf38b40498927a1/ It has long been thought that conversion efficiency of solar cells cannot exceed 34 percent. A... How this can be done is described by AMOLF director Albert Polman and his colleague Harry Atwater from the California Institute of Technology in a commentary article in Nature Materials that appears on Tuesday, February 21.

A solar cell is a device that converts sunlight into electrical power. This conversion process, however, is not very efficient: in a conventional solar cell a large fraction of the energy of the sunlight is lost. Blue and green light are converted to electricity with an efficiency less than 50%, while infrared light is not absorbed by a solar cell at all. The highest efficiency realized by a silicon solar cell is only 27 percent.

Light that is not converted in the solar cell leads to thermodynamic disorder and therefore a reduced voltage. As a result, the maximum achievable efficiency is limited to 34%, the so-called Shockley-Queisser limit. Also the incomplete trapping of light inside the solar cell and defects in the solar cell material’s crystal structure cause a loss in efficiency.

Clever nanostructures
By managing the light in a clever way a large portion of these problems can be solved. By using specially engineered nanostructures, printed on the solar cells surface, the light can be better trapped. In their article, Polman en Atwater describe several recipes with which these improvements can be realized. They are based on the integration of photonic nanostructures and circuits on the solar cell. The inspiration for some of these ideas comes from the optical integrated circuit technology, where structures to guide and control light
are routinely made.

Albert Polman: "The solar cell community is very conservative. It is often assumed that only extremely simple solar cells can be made at low costs. But if you can reach an efficiency larger than 50% a much higher cost of the solar cell is acceptable. Solar panels with a high efficiency take up much less space, because you need fewer panels to generate the same amount of power. That saves costs of land, installation and infrastructure. With a slightly more complex solar cell it becomes possible to convert all colors of the light from the sun to electricity. An efficiency of 70% is achievable.

Reference
Albert Polman & Harry A. Atwater
Photonic design principles for ultrahigh-efficiency photovoltaics
Nature Materials 11, 174–177 (2012). Published online 21 February 2012]]> News Photonic Materials Tue, 21 Feb 2012 17:00:00 +0100 http://www.amolf.nl/news/detailpage/article/nanomachines-organise-the-cells-skeleton//chash/bb66be0d461eb903e31a4ff967e19d9c/ Researchers from the FOM Institute AMOLF in Amsterdam have reconstituted the dynamic cell skeleton... They have demonstrated how the organisation of the skeleton is determined by small nanomachines, so-called dynein motor proteins.  An understanding of this process is important for explaining phenomena such as cell division and cell movement, for example. The group of Marileen Dogterom worked together with biologists from the University of California, San Francisco (UCSF) and Harvard University, and theoreticians from the Max Planck Institute for the Physics of Complex Systems (MPI-PKS) in Dresden. The results of the research will be published 3 February online in the scientific journal Cell.

The cell’s skeleton largely consists of microtubules. These long, stiff protein polymers grow into the cell from the centrosome, a structure in the vicinity of the cell nucleus. The position of the centrosome in the cell determines the cell’s internal organisation to a large extent and is therefore vitally important. However, how do centrosomes ‘measure’ the distance to the edge of the cell (the cell cortex) and how do they adjust their position if necessary? Liedewij Laan and Marileen Dogterom from AMOLF, together with their colleagues, have devised a way to answer this question.

Molecular motors
Up until now it was known that the position of the centrosome depends on the forces that arise when the ends of the microtubules come into contact with the edge of the cell and that the motor protein dynein plays a role in this. The researchers have simulated the situation in the cell by attaching dynein molecules to small walls and allowing microtubules to grow towards these walls. With the help of fluorescence microscopy and optical tweezers the behaviour of individual microtubules could be studied in this set-up.

The researchers saw that the ends of microtubules stop growing when they come into contact with dynein molecules. However, if the ends come into contact with small walls that do not contain dynein then they simply carry on growing. As a result of the contact with dynein, microtubules switch from a growing (pushing) state to a shrinking (pulling) state. This results in a well-controlled length of the microtubules but also in a stable contact between the ends of the microtubules and the cortex (the walls). This is how a centrosome ‘measures’ the distance to the edge of the cell.

Three-dimensional confinement
To simulate the actual organisation process in the cell, the researchers finally placed a centrosome within a three-dimensional chamber the size of the living cell. If there was no dynein on the walls then the centrosome in these experiments could rarely find the centre of the chamber. However, with dynein on the walls the centrosome’s behaviour radically changed. At high dynein densities, the centrosomes positioned themselves exactly in the middle of the chamber almost without exception. This result is supported by a mathematical model. The researchers have thus shown how the interaction between microtubules and dynein at the edge of the cell determines the position of the centrosome and hence the organisation of the living cell.

This research was financed by NWO, the FOM Foundation, HFSP, the EU, and the Volkswagen Foundation.

Reference
Liedewij Laan, Nenad Pavin, Julien Husson, Guillaume Romet-Lemonne, Martijn van Duijn, Magdalena Preciado López, Ronald D. Vale, Frank Jülicher, Samara L. Reck-Peterson, and Marileen Dogterom
Cortical Dynein Controls Microtubule Dynamics to Generate Pulling Forces that Position Microtubule Asters
Cell (2012). Online February 3, 2012. DOI:10.1016/j.cell.2012.01.007

Contact
Marileen Dogterom +31 20 754 7135
Liedewij Laan ]]> News Bio-organization Fri, 03 Feb 2012 09:59:00 +0100 http://www.amolf.nl/news/detailpage/article/vici-grant-for-sander-tans-1//chash/fc0f434d99be8df01f4d8b2ca7ce0fcc/ AMOLF group leader prof.dr. Sander Tans received a VICI grant by NWO. He receives his grant of 1.5...
About the vici grants
The Innovational Research Incentives Scheme has been set up in 2000 by NWO, KNAW and the universities jointly. The aim is to promote innovation in the academic research field. The scheme is directed at providing encouragement for individual researchers and gives talented, creative researchers the opportunity to conduct their own research programme independently and promote talented researchers to enter and remain committed to the scientific profession. It includes three forms of grant: Veni (for researchers who have recently completed their doctorates), Vidi (for experienced researchers) and Vici (for researchers of professorial quality).]]> News Biophysics Wed, 01 Feb 2012 10:33:00 +0100 http://www.amolf.nl/news/detailpage/article/amolf-and-ecn-enter-collaboration-agreement//chash/466801634bc8198a364ead7436af5e81/ The FOM Institute AMOLF and ECN signed an agreement to consolidate their collaboration. With this...
Robert Kleiburg, COO at ECN: “With this agreement we expand our research field to more fundamental research. It offers us the opportunity to evaluate new technologies at an early stage and to more quickly (or faster) realize technology transfer to industry.

Albert Polman, AMOLF director: “In fundamental energy research it is essential to be able to test new concepts directly in high quality solar cells. The collaboration with ECN makes this possible.”

In 2011 AMOLF started a major solar cells research program, Light management in new photovoltaic materials. This program aims at light management: the control of the collection, guiding, concentration and conversion of light at the nano scale. The research focus lies on the development of new materials and new solar cell architectures, with the final goal of creating solar cells that transfer sunlight in an efficient and inexpensive manner into electricity.

ECN works at the development of new technologies and their implementation in large scale production of solar cells and panels. The agreement brings extensive synergy advantages and new opportunities arise to strengthen the patent portfolio.

About AMOLF
The FOM Institute AMOLF is one of the three institutes of the Foundation for Fundamental Research on Matter (FOM). FOM is part of the Netherlands Organisation for Scientific Research (NWO). AMOLF carries out fundamental research in the field of physics of biomolecular systems and nanophotonics, two topics that hold great promises for technological innovations. In these two themes threeprograms are carried out: nanophotonics, molecular biophysics, and systems biophysics. In addition, a new program will be started: photovoltaics. The institute contributes to the transfer of knowledge to industry and society and trains young and highly talented scientists and technicians.

About ECN
ECN is the largest energy research institute in the Netherlands. It has a strong international position in the areas of Solar Energy, Wind Energy, Policy Studies and Biomass & Energy Efficiency. With and for the market, we develop knowledge and technology that enable a transition to a sustainableenergy system. ECN focuses its research on sustainable energy generation to develop safe, efficient, reliable and environmentally friendly energy systems. ECN also conducts research on future opportunities and economic backgrounds related to energy.

Contact
For more information, please contact:  
AMOLF, Prof.dr. Albert Polman, a.polmanATamolf.nl, +31 20 7547100
ECN, Dr Arthur Weeber, weeberATecn.nl, +31 224 56 4113]]> News Fri, 27 Jan 2012 15:07:00 +0100