4,488 research outputs found
Fermion vacuum energies in brane world models
The fermion representations and boundary conditions in five dimensional anti
de Sitter space are described in detail. In each case the one loop effective
action is calculated for massless fermions. The possibility of topological or
Wilson loop symmetry breaking is discussed.Comment: 6 pages, no figures, one correctio
Photo-thermal tuning of graphene oxide coated integrated optical waveguides
We experimentally investigate power sensitive photothermal tuning (PTT) of
two dimensional (2D) graphene oxide (GO) films coated on integrated optical
waveguides. We measure the light power thresholds for reversible and permanent
GO reduction in silicon nitride (SiN) waveguides integrated with 1 and 2 layers
of GO. Raman spectra at different positions of a hybrid waveguide with
permanently reduced GO are characterized, verifying the inhomogeneous GO
reduction along the direction of light propagation through the waveguide. The
differences between the PTT induced by a continuous wave laser and a pulsed
laser are also compared, confirming that the PTT mainly depend on the average
input power. These results reveal interesting features for 2D GO films coated
on integrated optical waveguides, which are of fundamental importance for the
control and engineering of GO properties in hybrid integrated photonic devices.Comment: 12 pages, 6 figures, 99 reference
Theory for the Accuracy of Microcomb Photonic Microwave Transversal Signal Processors
Photonic RF transversal signal processors, which are equivalent to
reconfigurable electrical digital signal processors but implemented with
photonic technologies, have been widely used for modern high-speed information
processing. With the capability of generating large numbers of wavelength
channels with compact micro-resonators, optical microcombs bring new
opportunities for realizing photonic RF transversal signal processors that have
greatly reduced size, power consumption, and complexity. Recently, a variety of
signal processing functions have been demonstrated using microcomb-based
photonic RF transversal signal processors. Here, we provide detailed analysis
for quantifying the processing accuracy of microcomb-based photonic RF
transversal signal processors. First, we investigate the theoretical
limitations of the processing accuracy determined by tap number, signal
bandwidth, and pulse waveform. Next, we discuss the practical error sources
from different components of the signal processors. Finally, we analyze the
contributions of the theoretical limitations and the experimental factors to
the overall processing inaccuracy both theoretically and experimentally. These
results provide a useful guide for designing microcomb-based photonic RF
transversal signal processors to optimize their accuracy.Comment: 17 pages, 12 figures, 103 reference
Towards a lightweight generic computational grid framework for biological research
Background: An increasing number of scientific research projects require access to large-scale computational resources. This is particularly true in the biological field, whether to facilitate the analysis of large high-throughput data sets, or to perform large numbers of complex simulations – a characteristic of the emerging field of systems biology. Results: In this paper we present a lightweight generic framework for combining disparate computational resources at multiple sites (ranging from local computers and clusters to established national Grid services). A detailed guide describing how to set up the framework is available from the following URL: http://igrid-ext.cryst.bbk.ac.uk/portal_guide/. Conclusion: This approach is particularly (but not exclusively) appropriate for large-scale biology projects with multiple collaborators working at different national or international sites. The framework is relatively easy to set up, hides the complexity of Grid middleware from the user, and provides access to resources through a single, uniform interface. It has been developed as part of the European ImmunoGrid project
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