Victorian Research Laboratory

West Melbourne, Australia

Victorian Research Laboratory

West Melbourne, Australia
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Al-Dirini F.,University of Melbourne | Al-Dirini F.,Victorian Research Laboratory | Mohammed M.A.,Princess Sumaya University for Technology | Hossain F.M.,University of Melbourne | And 2 more authors.
IEEE Journal of the Electron Devices Society | Year: 2016

This paper proposes a new class of resonant tunneling diodes (RTDs) that are planar and realizable with a single graphene nanoribbon. Unlike conventional RTDs, which incorporate vertical quantum well regions, the proposed devices incorporate two confined planar quantum dots within the single graphene nanoribbon, giving rise to a pronounced negative differential resistance (NDR) effect. The proposed devices, termed here as planar double-quantum-dot RTDs, and their transport properties are investigated using quantum simulations based on nonequilibrium Green's function formalism and the extended Huckel method. The proposed devices exhibit a unique current-voltage waveform consisting of a single pronounced current peak with an extremely high, in the order of 104, peak-to-valley ratio. The position of the current peak can be tuned between discrete voltage levels, allowing digitized tunability, which is exploited to realize multi-peak NDR devices. © 2013 IEEE.

Al-Dirini F.,University of Melbourne | Al-Dirini F.,Victorian Research Laboratory | Mohammed M.A.,Princess Sumaya University for Technology | Hossain M.S.,University of Melbourne | And 4 more authors.
Nanoscale | Year: 2016

Solid-state nanopores are promising candidates for next generation DNA and protein sequencing. However, once fabricated, such devices lack tuneability, which greatly restricts their biosensing capabilities. Here we propose a new class of solid-state graphene-based nanopore devices that exhibit a unique capability of self-Tuneability, which is used to control their conductance, tuning it to levels comparable to the changes caused by the translocation of a single biomolecule, and hence, enabling high detection sensitivities. Our presented quantum simulation results suggest that the smallest amino acid, glycine, when present in water and in an aqueous saline solution can be detected with high sensitivity, up to a 90% change in conductance. Our results also suggest that passivating the device with nitrogen, making it an n-Type device, greatly enhances its sensitivity, and makes it highly sensitive to not only the translocation of a single biomolecule, but more interestingly to intramolecular electrostatics within the biomolecule. Sensitive detection of the carboxyl group within the glycine molecule, which carries a charge equivalent to a single electron, is achieved with a conductance change that reaches as high as 99% when present in an aqueous saline solution. The presented findings suggest that tuneable graphene nanopores, with their capability of probing intramolecular electrostatics, could pave the way towards a new generation of single biomolecule detection devices. © 2016 The Royal Society of Chemistry.

Close T.G.,Okinawa Institute of Science and Technology | Close T.G.,University of Melbourne | Close T.G.,Victorian Research Laboratory | Tournier J.-D.,Florey Institute of Neuroscience and Mental Health | And 8 more authors.
NeuroImage | Year: 2015

Diffusion MRI tractography algorithm development is increasingly moving towards global techniques to incorporate "downstream" information and conditional probabilities between neighbouring tracts. Such approaches also enable white matter to be represented more tangibly than the abstract lines generated by the most common approaches to fibre tracking. However, previously proposed algorithms still use fibre-like models of white matter corresponding to thin strands of white matter tracts rather than the tracts themselves, and therefore require many components for accurate representations, which leads to poorly constrained inverse problems. We propose a novel tract-based model of white matter, the 'Fourier tract', which is able to represent rich tract shapes with a relatively low number of parameters, and explicitly decouples the spatial extent of the modelled tract from its 'Apparent Connection Strength (ACS)'. The Fourier tract model is placed within a novel Bayesian framework, which relates the tract parameters directly to the observed signal, enabling a wide range of acquisition schemes to be used. The posterior distribution of the Bayesian framework is characterised via Markov-chain Monte-Carlo sampling to infer probable values of the ACS and spatial extent of the imaged white matter tracts, providing measures that can be directly applied to many research and clinical studies. The robustness of the proposed tractography algorithm is demonstrated on simulated basic tract configurations, such as curving, twisting, crossing and kissing tracts, and sections of more complex numerical phantoms. As an illustration of the approach in vivo, fibre tracking is performed on a central section of the brain in three subjects from 60 direction HARDI datasets. © 2015 Elsevier Inc.

Al-Dirini F.,University of Melbourne | Al-Dirini F.,Victorian Research Laboratory | Skafidas E.,University of Melbourne | Skafidas E.,Victorian Research Laboratory | And 2 more authors.
Proceedings of the IEEE Conference on Nanotechnology | Year: 2013

This paper presents a new Graphene nanodevice that acts as a two terminal nanorectifier with a high rectification ratio, without the need for a p-n junction or a third gate terminal. The device's operation is similar to that of Self-Switching Diodes (SSD) and is therefore named here as a Graphene Self-Switching Diode (G-SSD). Graphene's 2D structure and its interesting electronic properties make it very well suited for building SSDs, while the simple planar architecture of SSDs simplifies the fabrication process of these devices on Graphene and avoids most processes that deteriorate Graphene's excellent electronic properties, especially its high charge carrier mobility. Atomistic quantum simulation results, based on the Extended Huckel method and Nonequilibrium Green's Function, are presented confirming the operation of G-SSDs as nanorectifiers, and achieving forward/reverse current rectification ratios greater than one order of magnitude. © 2013 IEEE.

Al-Dirini F.,University of Melbourne | Al-Dirini F.,Victorian Research Laboratory | Hossain F.M.,University of Melbourne | Nirmalathas A.,University of Melbourne | Skafidas E.,University of Melbourne
IEEE Journal of the Electron Devices Society | Year: 2014

In this work, we propose an atomically-thin all-graphene planar double barrier resonant tunneling diode that can be realized within a single graphene nanoribbon. The proposed device does not require any doping or external gating and can be fabricated using minimal process steps. The planar architecture of the device allows a simple in-plane connection of multiple devices in parallel without any extra processing steps during fabrication, enhancing the current driving capabilities of the device. Quantum mechanical simulation results, based on non-equilibrium Green's function formalism and the extended Huckel method, show promising device performance with a high reverse-to-forward current rectification ratio exceeding 50 000, and confirm the presence of negative differential resistance within the device's current-voltage characteristics. © 2014 IEEE.

Siekmann I.,Victorian Research Laboratory | Siekmann I.,University of Melbourne | Sneyd J.,University of Auckland | Crampin E.J.,Victorian Research Laboratory | Crampin E.J.,University of Melbourne
Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2014

Ion channels regulate the concentrations of ions within cells. By stochastically opening and closing its pore, they enable or prevent ions from crossing the cell membrane. However, rather than opening with a constant probability, many ion channels switch between several different levels of activity even if the experimental conditions are unchanged. This phenomenon is known as modal gating: instead of directly adapting its activity, the channel seems to mix sojourns in active and inactive modes in order to exhibit intermediate open probabilities. Evidence is accumulating that modal gating rather than modulation of opening and closing at a faster time scale is the primary regulatory mechanism of ion channels. However, currently, no method is available for reliably calculating sojourns in different modes. In order to address this challenge, we develop a statistical framework for segmenting singlechannel datasets into segments that are characteristic for particular modes. The algorithm finds the number of mode changes, detects their locations and infers the open probabilities of the modes. We apply our approach to data from the inositoltrisphosphate receptor. Based upon these results, we propose that mode changes originate from alternative conformational states of the channel protein that determine a certain level of channel activity. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

Hossain M.S.,University of Melbourne | Hossain M.S.,Victorian Research Laboratory | Al-Dirinil F.,University of Melbourne | Al-Dirinil F.,Victorian Research Laboratory | And 2 more authors.
14th IEEE International Conference on Nanotechnology, IEEE-NANO 2014 | Year: 2014

In this paper we study the thermoelectric (TE) properties of graphene nano-ribbons (GNRs) with incorporated nanopores (NPs), and present a nanopore-engineering approach for enhancing their TE properties. The nearest neighbor tight binding (TB) model and Non equilibrium Green's function (NEGF) method were employed to obtain the electron transmission spectra. For phonon calculations, Tersoff potential along with Landaur formalism were used. We found a direct relationship between pore width and phononic thermal conductivity. The dependence of other parameters like Seebeck coefficient and electrical conductance on pore width was not so straight forward, and showed a clear dependence on the number of atoms in the side channel (NS). By optimizing NS we achieved a significant improvement in the thermoelectric figure of merit of GNRs-NPs. This research can be a route towards enhancing the TE properties of GNRs, making them potential candidates for future thermoelectronics. © 2014 IEEE.

Hossain M.S.,University of Melbourne | Hossain M.S.,Victorian Research Laboratory | Al-Dirini F.,University of Melbourne | Al-Dirini F.,Victorian Research Laboratory | And 4 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2015

It has been well established that delta-like transport distribution of electron gives the best thermoelectric performance. On another front, it has been experimentally verified that graphene nano-ribbon with nano-break in the channel region exhibits tunnelling. Here, we utilize the tunnelling phenomena observed in graphene break junctions to achieve delta like transport distribution. Indeed our device exhibit record ZT ranging from 10 to 100. This high ZT can be attributed to complete blockage of phonon transport due to the break. The electrical conductance also goes very low, however, near the tunnelling energy it becomes significant, giving rise to an enhanced ZT value. In this report we investigate the effect edge orientation and the width of the ribbon on thermoelectric property. Moreover, we investigate the effect of temperature on tunnelling and how it affect thermoelectric performance. We find that there is an optimal temperature at which the device performs best. In the simulations, we assumed ballistic transport and used first principle approach to obtain the electrical properties. The phononic system was characterized by a Tersoff empirical potential model. The proposed device structure has potential applications as a two-dimensional nanoscale local cooler and as a thermoelectric power generator when connected in arrays. © 2015 SPIE.

Ekanayake S.W.,Deakin University | Pathirana P.N.,Victorian Research Laboratory | Caelli T.,Victorian Research Laboratory
2012 IEEE International Conference on Robotics and Biomimetics, ROBIO 2012 - Conference Digest | Year: 2012

This paper proposes a constrained optimization approach to improve the accuracy of a Time-of-Arrival (ToA) based multiple target localization system. Instead of using an overdetermined measurement system, this paper uses local distance measurements between the targets/emitters as the geometric constraint. Computer simulations are used to evaluate the performance of the geometrically constrained optimization method. © 2012 IEEE.

Siekmann I.,Victorian Research Laboratory | Siekmann I.,University of Melbourne
Ecological Complexity | Year: 2014

Individual-based models (IBMs) enable us to investigate the effects of inter-individual differences within a population much more easily than traditional modelling approaches based on differential equations. However, the greater flexibility of IBMs makes it difficult to systematically analyse the parameter dependency of the model behaviour so that an IBM may be hard to interpret. In this article, bifurcation analysis techniques for investigating models based on ordinary differential equations (ODE) are transferred to IBMs. For this purpose, we infer stationary solutions of the IBM from the asymptotic dynamics. The stability of these stationary solutions can then be studied depending on model parameters. As shown previously for ODE models (Siekmann et al., 2010; Siekmann, 2013), stationary solutions Si S can be used as bifurcation parameters which allows us to predict survival or extinction of populations by simple algebraic relationships. This is demonstrated with the example of a simple two-strain infection IBM. Moreover, analysing model behaviour based on stationary solutions provides a unified representation of different models that allows us to rigorously compare IBMs with other modelling frameworks like, for example, ODE models. A comparison of the IBM to a population-based ODE model of a two-strain infection leads to similar predictions although both models were built with very different modelling approaches. © 2014 Elsevier B.V. All rights reserved.

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