Research Highlights (AY2009 - 2010)

Transition dynamics and selection of the distinct S-DNA and strand unpeeling modes of double helix overstretching

The mechanism of DNA overstretching has been a mystery for 15 years. Recently a group of scientists from National University of Singapore and Northwestern University has shown that there exist two distinct pathways for the DNA overstretching transition near 65 pN: 'unpeeling' of one strand from the other, and a "B-to-S" transition from B-DNA to an elongated double-stranded 'S-DNA' form (Fu et al., Nucleic Acids Research 2011: 38, 5594-5600). More recently, the same group of authors has found answers to basic questions concerning the dynamics of these transitions, relative stability of the two competing overstretched states, the biophysical properties of S-DNA, and whether the "B-to-S" transition requires nicks and free DNA ends. In addition to solving the mystery of DNA overstretching transition, these results have provided the most complete understanding of the response of DNA to large tension.

Supramolecular Materials

Supramolecular materials containing three-dimensional fiber network are designed and constructed in the micro-/nanometer scale to deliver different benefis for applications in many fields, such as drug delivery, tissue engineering, nanocrystallite synthesis, etc.

Roll-to-roll production of 30-inch graphene films for transparent electrodes

The efforts to make transparent conducting films from graphene have been hampered by the lack of efficient methods for the synthesis, transfer and doping of graphene at the scale and quality required for applications. Here, we report the roll-to-roll production and wet-chemical doping of predominantly monolayer 30-inch graphene films grown by chemical vapour deposition onto flexible copper substrates.

Two distinct overstretched DNA states

The DNA double helix undergoes an 'overstretching' transition in a narrow force range near 65 pN. We show that overstretching in fact involves two distinct types of double-helix reorganization: slow hysteretic 'unpeeling' of one strand off the other; and a fast, non-hysteretic transition to an elongated double-stranded form.

Noise Bridges Dynamical Correlation and Topology in Coupled Oscillator Networks

We study the relationship between dynamical properties and interaction patterns in complex oscillator networks in the presence of noise.

Berry-Phase-Induced Heat Pumping and Its Impact on the Fluctuation Theorem

Applying adiabatic, cyclic two-parameter modulations we investigate quantum heat transfer across an anharmonic molecular junction contacted with two heat baths.

Semiconductors: Plastic electronics

Organic, carbon-based and soft materials crosslinking compounds help to build polymer electronic devices faster.

A divalent switch drives H-NS/DNA-binding conformations between stiffening and bridging modes

Heat-stable nucleoid structuring protein (H-NS) is an abundant prokaryotic protein that plays important roles in organizing chromosomal DNA and gene silencing.

Simultaneous phase and size control of upconversion nanocrystals through lanthanide doping

Singapore scientists from NUS, the Agency for Science, Technology and Research (A*STAR), NTU and King Abdullah University of Science and Technology (KAUST) have discovered a new synthetic strategy for controlling the properties of ultra-small luminescent nanocrystals. Their findings have been published in the prestigious Nature journal on 25 February 2010.

Capillarity-Assisted Assembly of Carbon Nanotube Microstructures with Organized Initiations

In this work, detailed studies of three different capillary-assisted techniques for the formations of large-scale multiwalled carbon-nanotube (MWNT)-based microstructures were presented. These new insights and techniques presented could further encourage the use of self-organized MWNT structures with initiation as a flexible and viable route for the implementations of carbon-nanotube-based electronic devices.

Universal dynamical decoupling: Two-qubit states and beyond

Uhrig's dynamical decoupling pulse sequence has emerged as a universal and highly promising approach to decoherence suppression. So far, both the theoretical and experimental studies have examined single-qubit decoherence only. This work extends Uhrig's universal dynamical decoupling from one-qubit to two-qubit systems and even to general multilevel quantum systems.

Polymer semiconductors become sophisticated

News Release (31 Dec 2009, Singapore): NUS scientists from the departments of physics and chemistry, in collaboration with Cambridge scientists, have announced their success in creating high-quality heterostructures that make polymer organic semiconductors more functional and energy-efficient. The report was carried online by Nature Materials. Heterostructures are interfaces of two or more materials with carefully selected energy-level, bandgap or refractive-index differences that enable charge-carriers, excitons and photons to be manipulated within layers as thin as a few nanometers.

Tunable Two-Dimensional Binary Molecular Networks

A novel approach to constructing tunable and robust 2D binary molecular nanostructures on an inert graphite surface is presented. The guest molecules are embedded into a host molecular matrix and constrained via the formation of multiple intermolecular hydrogen bonds.

A Rotational DNA Nanomotor Driven by an Externally Controlled Electric Field

Continuous rotation of DNA around its phosphate backbone is achieved with a simple nanomotor, which is driven by an electric field oscillated between four orientations (see image). The motor consists of a DNA rotor and a partially single-stranded DNA axle held between a surface and a magnetic bead. Rotation is caused by realignment of the rotor DNA with the oscillated electric field.

A new physical principle behind quantum physics

Tomasz Paterek, Dagomir Kaszliskowski, Valerio Scarani and Andreas Winter from CQT, together with co-workers of the University of Gdansk (Poland), propose a new physical principle called "information causality" in a paper published in Nature. If this principle is enforced, the number of theories that can describe our world is drastically reduced. This might explain why no phenomenon has ever been observed that would go beyond quantum physics.

Macromolecular crowding induced elongation and compaction of single DNA molecules confined in a nanochannel

The effect of dextran nanoparticles on the conformation and compaction of single DNA molecules confined in a nanochannel was investigated with fluorescence microscopy. It was observed that the DNA molecules elongate and eventually condense into a compact form with increasing volume fraction of the crowding agent.

The security of practical quantum key distribution

Quantum key distribution (QKD) is the first quantum information task to reach the level of mature technology, already fit for commercialization. It aims at the creation of a secret key between authorized partners connected by a quantum channel and a classical authenticated channel.

Doping graphene: Molecular tuning

An article "Tuning the Electronic Structure of Graphene by an Organic Molecule" that originally appeared in J. Phys. Chem. B which Professor Feng Yuan Ping and Dr Lu Yunhaocollaborated with researchers from Zhejiang University has been highlighted in the Sept issue of NPG Asia Materials. Professor Feng and colleagues in Singapore and China report that the adsorption of organic molecules onto graphene could allow the electronic properties of graphene to be controlled and tuned. Their first-principles calculations show that a charge-transfer complex is created with the electron–acceptor molecule tetracyanoethylene (TCNE), allowing the electronic properties of graphene to be tuned by adjusting the coverage of adsorbed molecules.

Stretching Single Talin Rod Molecules Activates Vinculin Binding

"To solve the mystery of how a mechanical stimulus is translated into a chemical response in biological systems, Asst. Prof. Liu Ruchuan has collaborated with researchers at Columbia University to examine vinculin binding of talin rods under mechanical forces by single-molecule techniques, and proved a hypothesis of mechano-activation of talin for vinculin recruitment. As talin and vinculin play important roles between focal adhesion and the cytoskeleton, such a mechanism as proposed in their recent Science paper [Science 323, p638-641] may exist more generally in biological systems as a mechanism for force transduction."

A viewpoint on: Atom interferometry tests of local Lorentz invariance in gravity and electrodynamics

An article which Asst/Prof Chung Keng Yeow collaborated with researchers from UC Berkeley, Stanford University and Bremen University has been highlighted in the July issue of Physical Review D ( ). It was also selected for a viewpoint in Physics, an online publication of APS started last year that "highlights exceptional papers from the Physical Review journals" (quoted from the website).
Measuring quantum interference of atomic matter waves may help detect experimental signatures of a fundamental theory of physics. [Viewpoint on Phys. Rev. D 80, 016002 (2009)].

An omnidirectional retroreflector based on the transmutation of dielectric singularities

Cyclists and runners may one day have perfect reflecting devices to keep them safe in night-time traffic. Scientists here, working with theortical physicists from Scotland and the Czeh Republic, have married a theory of bending light with practical engineering. The team of Prof Ong Chong Kim and his collaborator Dr Ma Yun-Gui of the Temasek Laboratories and theoreticians aboard have designed a retroreflector which have potential use from road safety to radar target tracking.Their paper was published online 28 June 2009 in materials-science journal Nature Materials and in Straits Times, 4 July 2009 titled "Bright idea for bend theory".

Magnonic Spin-offs

Magnonic crystals, a lesser known analog of photonic crystals, form the basis of magnonics. It is an emerging field which aims to control the generation and propagation of information-carrying spin waves by means analogous to the control of light in photonic crystals. The Laser Brillouin Group has designed a nanostructured magnonic crystal comprising two different magnetic materials and mapped out its dispersion relations. Its frequency bandgaps exhibit magnetic-field tunability, an important property which could find applications in magnonic devices. This work published in Appl. Phys. Lett. Vol. 94 (2009) has been highlighted in Nature Materials Vol. 8 May (2009) as an article entitled Magnonic Spin-offs.

A Step Toward Superfast Carbon Memory - Graphene could make computer hard drives denser and speedier

Graphene memory can have significant advantages over today's magnetic memory. Bits can be read 30 times faster because electrons move through graphene quickly. With graphene, bits can also shrink to 10 nanometers or even smaller thus making the memory denser. In the Technology Review published by MIT on Wednesday, April 01, 2009, the work of Dr Özyilmaz Barbarosand histeam onferroelectric RAM was publicized in the article titled "A Step Toward Superfast Carbon Memory - Graphene could make computer hard drives denser and speedier" by Prachi Patel.

Graphene gets ready for the big time

Work on graphene heated up quickly since five years ago as researchers realized that the material's two-dimensionality caused it to show unusual quantum behaviours. In the recent American Physical Society meeting in Pittsburgh, Pennsylvania, physicist were deliberating on how to bring this laboratory curiosity to the commercial. In the article of the meeting published on Natures News, a STM grapheme image due to the recent work of Prof Andrew Wee and Dr Chen Wei of Physics department (A. WEE, NATL UNIV. SINGAPORE/H. HUANG ET AL. ACS NANO 2, 2513–2518 (2008) 390 Vol 458|26 March 2009) was cited in the report.

Having fun with dumpling skin: material physics made alive in the kitchen

Abstract. We report a school project which equips students with both theoretical and practical knowledge in material physics. We construct dumpling skins from a mixture of flour and water. A series of experiments is then conducted to quantify the toughness, hardness, and tensile strength of the skins, and how they are affected by adding other materials into the original material to form composite materials.
Print publication: Issue 2 (March 2009) Received 25 November 2008, in final form 11 December 2008

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