16 research outputs found
Field quantization for open optical cavities
We study the quantum properties of the electromagnetic field in optical
cavities coupled to an arbitrary number of escape channels. We consider both
inhomogeneous dielectric resonators with a scalar dielectric constant
and cavities defined by mirrors of arbitrary shape. Using
the Feshbach projector technique we quantize the field in terms of a set of
resonator and bath modes. We rigorously show that the field Hamiltonian reduces
to the system--and--bath Hamiltonian of quantum optics. The field dynamics is
investigated using the input--output theory of Gardiner and Collet. In the case
of strong coupling to the external radiation field we find spectrally
overlapping resonator modes. The mode dynamics is coupled due to the damping
and noise inflicted by the external field. For wave chaotic resonators the mode
dynamics is determined by a non--Hermitean random matrix. Upon including an
amplifying medium, our dynamics of open-resonator modes may serve as a starting
point for a quantum theory of random lasing.Comment: 16 pages, added references, corrected typo
FORTE satellite constraints on ultra-high energy cosmic particle fluxes
The FORTE (Fast On-orbit Recording of Transient Events) satellite records
bursts of electromagnetic waves arising from near the Earth's surface in the
radio frequency (RF) range of 30 to 300 MHz with a dual polarization antenna.
We investigate the possible RF signature of ultra-high energy cosmic-ray
particles in the form of coherent Cherenkov radiation from cascades in ice. We
calculate the sensitivity of the FORTE satellite to ultra-high energy (UHE)
neutrino fluxes at different energies beyond the Greisen-Zatsepin-Kuzmin (GZK)
cutoff. Some constraints on supersymmetry model parameters are also estimated
due to the limits that FORTE sets on the UHE neutralino flux. The FORTE
database consists of over 4 million recorded events to date, including in
principle some events associated with UHE neutrinos. We search for candidate
FORTE events in the period from September 1997 to December 1999. The candidate
production mechanism is via coherent VHF radiation from a UHE neutrino shower
in the Greenland ice sheet. We demonstrate a high efficiency for selection
against lightning and anthropogenic backgrounds. A single candidate out of
several thousand raw triggers survives all cuts, and we set limits on the
corresponding particle fluxes assuming this event represents our background
level.Comment: added a table, updated references and Figure 8, this version is
submitted to Phys. Rev.
Assessment of algorithms for mitosis detection in breast cancer histopathology images
The proliferative activity of breast tumors, which is routinely estimated by counting of mitotic figures in hematoxylin and eosin stained histology sections, is considered to be one of the most important prognostic markers. However, mitosis counting is laborious, subjective and may suffer from low inter-observer agreement. With the wider acceptance of whole slide images in pathology labs, automatic image analysis has been proposed as a potential solution for these issues.
In this paper, the results from the Assessment of Mitosis Detection Algorithms 2013 (AMIDA13) challenge are described. The challenge was based on a data set consisting of 12 training and 11 testing subjects, with more than one thousand annotated mitotic figures by multiple observers. Short descriptions and results from the evaluation of eleven methods are presented. The top performing method has an error rate that is comparable to the inter-observer agreement among pathologists
Luminescence spectra and kinetics of disordered solid solutions
We have studied both theoretically and experimentally the luminescence spectra and kinetics of crystalline, disordered solid solutions after pulsed excitation. First, we present the model calculations of the steady-state luminescence band shape caused by recombination of excitons localized in the wells of random potential induced by disorder. Classification of optically active tail states of the main exciton band into two groups is proposed. The majority of the states responsible for the optical absorption corresponds to the group of extended states belonging to the percolation cluster, whereas only a relatively small group of “radiative” states forms the steady-state luminescence band. The continuum percolation theory is applied to distinguish the “radiative” localized states, which are isolated in space and have no ways for nonradiative transitions along the tail states. It is found that the analysis of the exciton-phonon interaction gives the information about the character of the localization of excitons. We have shown that the model used describes quite well the experimental cw spectra of CdS(1−c)Sec and ZnSe(1−c)Tec solid solutions. Further, the experimental results are presented for the temporal evolution of the luminescence band. It is shown that the changes of band shape with time come from the interplay of population dynamics of extended states and spatially isolated “radiative” states. Finally, the measurements of the decay of the spectrally integrated luminescence intensity at long delay times are presented. It is shown that the observed temporal behavior can be described in terms of relaxation of separated pairs followed by subsequent exciton formation and radiative recombination. Electron tunneling processes are supposed to be responsible for the luminescence in the long-time limit at excitation below the exciton mobility edge. At excitation by photons with higher energies the diffusion of electrons can account for the observed behavior of the luminescence
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