19,907 research outputs found
Inference in complex biological systems with Gaussian processes and parallel tempering
Parameter inference in mathematical models of complex biological
systems, expressed as coupled ordinary differential equations (ODEs), is a challenging problem. These depend on kinetic parameters, which cannot all be measured and have to be ascertained a different way. However, the computational
costs associated with repeatedly solving the ODEs are often staggering, making
many techniques impractical. Therefore, aimed at reducing this cost, new concepts using gradient matching have been proposed. This paper combines current
adaptive gradient matching approaches, using Gaussian processes, with a parallel tempering scheme, in order to compare 2 different paradigms using the same
nonlinear regression method. We use 2 ODE systems to assess our technique,
showing an improvement over the recent method in Calderhead et al. (2008)
Boron-oxygen defect imaging in p-type Czochralski silicon
In this work, we demonstrate an accurate method for determining the effective boron-oxygen (BO) related defect density on Czochralski-grown silicon wafers using photoluminescence imaging. Furthermore, by combining a recently developed dopant density imaging technique and microscopic Fourier transform infrared spectroscopy measurements of the local interstitial oxygen concentration [Oi ], the BO-related defect density, [Oi ], and the boron dopant density from the same wafer were determined, all with a spatial resolution of 160 μm. The results clearly confirm the established dependencies of the BO-related defect density on [Oi ] and the boron dopant density and demonstrate a powerful technique for studying this important defect.This work was supported by the Australian Research
Council (ARC) Future Fellowships program and the
Australian Renewable Energy Agency (ARENA) fellowships
program
Extracting Energy from a Black Hole through Its Disk
When some magnetic field lines connect a Kerr black hole with a disk rotating
around it, energy and angular momentum are transferred between them. If the
black hole rotates faster than the disk, for a thin Keplerian
disk, then energy and angular momentum are extracted from the black hole and
transferred to the disk ( is the mass and is the angular momentum
of the black hole). This way the energy originating in the black hole may be
radiated away by the disk.
The total amount of energy that can be extracted from the black hole spun
down from to by a thin Keplerian disk is
. This is larger than which can be
extracted by the Blandford-Znajek mechanism.Comment: 8 pages, 2 figure
Collective excitations in double-layer quantum Hall systems
We study the collective excitation spectra of double-layer quantum-Hall
systems using the single mode approximation. The double-layer in-phase density
excitations are similar to those of a single-layer system. For out-of-phase
density excitations, however, both inter-Landau-level and intra-Landau-level
double-layer modes have finite dipole oscillator strengths. The oscillator
strengths at long wavelengths for the latter transitions are shifted upward by
interactions by identical amounts proportional to the interlayer Coulomb
coupling. The intra-Landau-level out-of-phase mode has a gap when the ground
state is incompressible except in the presence of spontaneous inter-layer
coherence. We compare our results with predictions based on the
Chern-Simons-Landau-Ginzburg theory for double-layer quantum Hall systems.Comment: RevTeX, 21 page
Reading data stored in the state of metastable defects in silicon using band-band photoluminescence: Proof of concept and physical limits to the data storage density
The state of bistable defects in crystalline silicon such as iron-boron pairs or the boron-oxygen defect can be changed at room temperature. In this letter, we experimentally demonstrate that the chemical state of a group of defects can be changed to represent a bit of information. The state can then be read without direct contact via the intensity of the emitted band-band photoluminescence signal of the group of defects, via their impact on the carrier lifetime. The theoretical limit of the information density is then computed. The information density is shown to be low for two-dimensional storage but significant for three-dimensional data storage. Finally, we compute the maximum storage capacity as a function of the lower limit of the photoluminescence detector sensitivity.This work has been supported by the Australian
Research Council (ARC) Future Fellowships program and
the Australian Renewable Energy Agency (ARENA) fellowships
program
Effect of Edge Roughness on Electronic Transport in Graphene Nanoribbon Channel Metal Oxide Semiconductor Field-Effect Transistors
Results of quantum mechanical simulations of the influence of edge disorder
on transport in graphene nanoribbon metal oxide semiconductor field-effect
transistors (MOSFETs) are reported. The addition of edge disorder significantly
reduces ON-state currents and increases OFF-state currents, and introduces wide
variability across devices. These effects decrease as ribbon widths increase
and as edges become smoother. However the bandgap decreases with increasing
width, thereby increasing the band-to-band tunneling mediated subthreshold
leakage current even with perfect nanoribbons. These results suggest that
without atomically precise edge control during fabrication, MOSFET performance
gains through use of graphene will be difficult to achieve.Comment: 8 pages, 5 figure
Intrinsic Curie temperature bistability in ferromagnetic semiconductor resonant tunneling diodes
We predict bistability in the Curie temperature-voltage characteristic of
double barrier resonant-tunneling structures with dilute ferromagnetic
semiconductor quantum wells. Our conclusions are based on simulations of
electrostatics and ballistic quantum transport combined with a mean-field
theory description of ferromagnetism in dilute magnetic semiconductors.Comment: 10 pages, 3 figures, submitted to Phys. Rev. B; typo removed in
revised version - spurious eq.12 immediately after eq.1
Dynamical correlation functions in the Calogero-Sutherland model
We compute the dynamical Green function and density-density correlation in
the Calogero-Sutherland model for all integer values of the coupling constant.
An interpretation of the intermediate states in terms of quasi-particles is
found.Comment: 20pgs, (1 reference added
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