The latent potential of YouTube - Will it become the 21st Century lecturer's film archive?

YouTube (http://www.youtube.com) is an online, public-access video-sharing site that allows users to post short streaming-video submissions for open viewing. Along with Google, MySpace, Facebook, etc. it is one of the great success stories of the Internet, and is widely used by many of today's undergraduate students. The higher education sector has recently realised the potential of YouTube for presenting teaching resources/material to students, and publicising research. This article considers another potential use for online video archiving websites such as YouTube and GoogleVideo in higher education - as an online video archive providing thousands of hours of video footage for use in lectures. In this article I will discuss why this might be useful, present some examples that demonstrate the potential for YouTube as a teaching resource, and highlight some of the copyright and legal issues that currently impact on the effective use of new online video websites, such as YouTube, for use as a teaching resource.Comment: To be published in October 2008 issue of CAL-laborate (http://science.uniserve.edu.au/pubs/callab/index.html

Tracking the energies of one-dimensional subband edges in quantum point contacts using dc conductance measurements

The semiconductor quantum point contact has long been a focal point for studies of one-dimensional electron transport. Their electrical properties are typically studied using ac conductance methods, but recent work has shown that the dc conductance can be used to obtain additional information, with a density-dependent Land\'{e} effective g-factor recently reported [T.-M. Chen et al, Phys. Rev. B 79, 081301 (2009)]. We discuss previous dc conductance measurements of quantum point contacts, demonstrating how valuable additional information can be extracted from the data. We provide a comprehensive and general framework for dc conductance measurements that provides a path to improving the accuracy of existing data and obtaining useful additional data. A key aspect is that dc conductance measurements can be used to map the energy of the 1D subband edges directly, giving new insight into the physics that takes place as the spin-split 1D subbands populate. Through a re-analysis of the data obtained by Chen et al, we obtain two findings. The first is that the 2-down subband edge closely tracks the source chemical potential when it first begins populating before dropping more rapidly in energy. The second is that the 2-up subband populates more rapidly as the subband edge approaches the drain potential. This second finding suggests that the spin-gap may stop opening, or even begin to close again, as the 2-up subband continues populating, consistent with recent theoretical calculations and experimental studies.Comment: Published version available at http://iopscience.iop.org/0953-8984/23/36/362201 15 pages, 3 figure

What lurks below the last plateau: Experimental studies of the 0.7 x 2e^2/h conductance anomaly in one-dimensional systems

The integer quantized conductance of one-dimensional electron systems is a well understood effect of quantum confinement. A number of fractionally quantized plateaus are also commonly observed. They are attributed to many-body effects, but their precise origin is still a matter of debate, having attracted considerable interest over the past 15 years. This review reports on experimental studies of fractionally quantized plateaus in semiconductor quantum point contacts and quantum wires, focusing on the 0.7 x 2e^2/h conductance anomaly, its analogs at higher conductances, and the zero bias peak observed in the d.c. source-drain bias for conductances less than 2e^2/h.Comment: Topical Review for J. Phys.: Condens. Matter, published version available at http://iopscience.iop.org/0953-8984/23/44/443201/ Document is 131 pages, 43 figure

Near-thermal limit gating in heavily-doped III-V semiconductor nanowires using polymer electrolytes

Doping is a common route to reducing nanowire transistor on-resistance but has limits. High doping level gives significant loss in gate performance and ultimately complete gate failure. We show that electrolyte gating remains effective even when the Be doping in our GaAs nanowires is so high that traditional metal-oxide gates fail. In this regime we obtain a combination of sub-threshold swing and contact resistance that surpasses the best existing p-type nanowire MOSFETs. Our sub-threshold swing of 75 mV/dec is within 25% of the room-temperature thermal limit and comparable with n-InP and n-GaAs nanowire MOSFETs. Our results open a new path to extending the performance and application of nanowire transistors, and motivate further work on improved solid electrolytes for nanoscale device applications.Comment: 6 pages, 2 figures, supplementary available at journa

A study of transport suppression in an undoped AlGaAs/GaAs quantum dot single-electron transistor

We report a study of transport blockade features in a quantum dot single-electron transistor, based on an undoped AlGaAs/GaAs heterostructure. We observe suppression of transport through the ground state of the dot, as well as negative differential conductance at finite source-drain bias. The temperature and magnetic field dependence of these features indicate the couplings between the leads and the quantum dot states are suppressed. We attribute this to two possible mechanisms: spin effects which determine whether a particular charge transition is allowed based on the change in total spin, and the interference effects that arise from coherent tunneling of electrons in the dot

Piezoelectric rotator for studying quantum effects in semiconductor nanostructures at high magnetic fields and low temperatures

We report the design and development of a piezoelectric sample rotation system, and its integration into an Oxford Instruments Kelvinox 100 dilution refrigerator, for orientation-dependent studies of quantum transport in semiconductor nanodevices at millikelvin temperatures in magnetic fields up to 10T. Our apparatus allows for continuous in situ rotation of a device through >100deg in two possible configurations. The first enables rotation of the field within the plane of the device, and the second allows the field to be rotated from in-plane to perpendicular to the device plane. An integrated angle sensor coupled with a closed-loop feedback system allows the device orientation to be known to within +/-0.03deg whilst maintaining the sample temperature below 100mK.Comment: 8 pages, 5 figure

Electrometry using the quantum Hall effect in a bilayer 2D electron system

We discuss the development of a sensitive electrometer that utilizes a two-dimensional electron gas (2DEG) in the quantum Hall regime. As a demonstration, we measure the evolution of the Landau levels in a second, nearby 2DEG as the applied perpendicular magnetic field is changed, and extract an effective mass for electrons in GaAs that agrees within experimental error with previous measurements.Comment: 3.5 pages, 3 figures, submitted to APL

The influence of atmosphere on the performance of pure-phase WZ and ZB InAs nanowire transistors

We compare the characteristics of phase-pure MOCVD grown ZB and WZ InAs nanowire transistors in several atmospheres: air, dry pure N$_2$ and O$_2$, and N$_2$ bubbled through liquid H$_2$O and alcohols to identify whether phase-related structural/surface differences affect their response. Both WZ and ZB give poor gate characteristics in dry state. Adsorption of polar species reduces off-current by 2-3 orders of magnitude, increases on-off ratio and significantly reduces sub-threshold slope. The key difference is the greater sensitivity of WZ to low adsorbate level. We attribute this to facet structure and its influence on the separation between conduction electrons and surface adsorption sites. We highlight the important role adsorbed species play in nanowire device characterisation. WZ is commonly thought superior to ZB in InAs nanowire transistors. We show this is an artefact of the moderate humidity found in ambient laboratory conditions: WZ and ZB perform equally poorly in the dry gas limit yet equally well in the wet gas limit. We also highlight the vital role density-lowering disorder has in improving gate characteristics, be it stacking faults in mixed-phase WZ or surface adsorbates in pure-phase nanowires.Comment: Accepted for publication in Nanotechnolog

Comment on "Drip Paintings and Fractal Analysis", arXiv:0710.4917v2, by K. Jones-Smith, H. Mathur and L.M. Krauss

In a recent manuscript (arXiv:0710.4917v2), Jones-Smith et al. attempt to use the well-established box-counting technique for fractal analysis to "demonstrate conclusively that fractal criteria are not useful for authentication". Here, in response to what we view to be an extremely simplistic misrepresentation of our earlier work by Jones-Smith et al., we reiterate our position regarding the potential of fractal analysis for artwork authentication. We also point out some of the flaws in the analysis presented in by Jones-Smith et al.Comment: Comment on arXiv:0710.4917v2 [cond-mat.stat-mech

Origin of the hysteresis in bilayer 2D systems in the quantum Hall regime

The hysteresis observed in the magnetoresistance of bilayer 2D systems in the quantum Hall regime is generally attributed to the long time constant for charge transfer between the 2D systems due to the very low conductivity of the quantum Hall bulk states. We report electrometry measurements of a bilayer 2D system that demonstrate that the hysteresis is instead due to non-equilibrium induced current. This finding is consistent with magnetometry and electrometry measurements of single 2D systems, and has important ramifications for understanding hysteresis in bilayer 2D systems.Comment: 4 pages, 3 figs. Accepted for publication in PR