797 research outputs found
Object-Oriented Paradigms for Modelling Vascular\ud Tumour Growth: a Case Study
Motivated by a family of related hybrid multiscale models, we have built an object-oriented framework for developing and implementing multiscale models of vascular tumour growth. The models are implemented in our framework as a case study to highlight how object-oriented programming techniques and good object-oriented design may be used effectively to develop hybrid multiscale models of vascular tumour growth. The intention is that this paper will serve as a useful reference for researchers modelling complex biological systems and that these researchers will employ some of the techniques presented herein in their own projects
Vacuum-stimulated cooling of single atoms in three dimensions
Taming quantum dynamical processes is the key to novel applications of
quantum physics, e.g. in quantum information science. The control of
light-matter interactions at the single-atom and single-photon level can be
achieved in cavity quantum electrodynamics, in particular in the regime of
strong coupling where atom and cavity form a single entity. In the optical
domain, this requires permanent trapping and cooling of an atom in a
micro-cavity. We have now realized three-dimensional cavity cooling and
trapping for an orthogonal arrangement of cooling laser, trap laser and cavity
vacuum. This leads to average single-atom trapping times exceeding 15 seconds,
unprecedented for a strongly coupled atom under permanent observation.Comment: 4 pages, 4 figure
A broadband stripline technique for characterizing relative permittivity and permeability (article)
This is the author accepted manuscript. The final version is available from IEEE via the DOI in this record.The dataset associated with this article is located in ORE at: https://doi.org/10.24378/exe.503We present a stripline design and calibration method
allowing the extraction of relative permittivity of single dielectric
samples in the 200 MHz – 50 GHz range. The simultaneous
extraction of relative permittivity and permeability is also illustrated
by characterizing a set of samples comprising magnetic
inclusions over the same frequency range. The calibration
method involves the use of seven measurements of the stripline
scattering parameters (S-parameters) with different length shorts
inserted. From these measurements, it is possible to determine
the reflections at the transition regions of the stripline to correct
the measured S-parameters for characterization. By quantifying
a range of samples with increasing percentage volume filling
of barium titanate in polyurethane for the case of dielectric
samples, and carbonyl iron powder (CIP) for magnetic samples,
this work demonstrates a reliable method for the broadband
characterization of composite materials.This work was supported by The Engineering and Physical Sciences
Research Council (EPSRC) of the United Kingdom and The Defence
Science and Technology Laboratory (DSTL) of The United Kingdom,
via the EPSRC Center for Doctoral Training in Metamaterials
(Grant No. EP/L015331/1
Cystic Cervical Intramedullary Ependymoma with Previous lntracyst Hemorrhage: Magnetic Resonance Imaging at 1.5 T
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/117483/1/jon199442111.pd
Theory of Photon Blockade by an Optical Cavity with One Trapped Atom
In our recent paper [1], we reported observations of photon blockade by one
atom strongly coupled to an optical cavity. In support of these measurements,
here we provide an expanded discussion of the general phenomenology of photon
blockade as well as of the theoretical model and results that were presented in
Ref. [1]. We describe the general condition for photon blockade in terms of the
transmission coefficients for photon number states. For the atom-cavity system
of Ref. [1], we present the model Hamiltonian and examine the relationship of
the eigenvalues to the predicted intensity correlation function. We explore the
effect of different driving mechanisms on the photon statistics. We also
present additional corrections to the model to describe cavity birefringence
and ac-Stark shifts. [1] K. M. Birnbaum, A. Boca, R. Miller, A. D. Boozer, T.
E. Northup, and H. J. Kimble, Nature 436, 87 (2005).Comment: 10 pages, 6 figure
Cavity cooling of a single atom
All conventional methods to laser-cool atoms rely on repeated cycles of
optical pumping and spontaneous emission of a photon by the atom. Spontaneous
emission in a random direction is the dissipative mechanism required to remove
entropy from the atom. However, alternative cooling methods have been proposed
for a single atom strongly coupled to a high-finesse cavity; the role of
spontaneous emission is replaced by the escape of a photon from the cavity.
Application of such cooling schemes would improve the performance of atom
cavity systems for quantum information processing. Furthermore, as cavity
cooling does not rely on spontaneous emission, it can be applied to systems
that cannot be laser-cooled by conventional methods; these include molecules
(which do not have a closed transition) and collective excitations of Bose
condensates, which are destroyed by randomly directed recoil kicks. Here we
demonstrate cavity cooling of single rubidium atoms stored in an intracavity
dipole trap. The cooling mechanism results in extended storage times and
improved localization of atoms. We estimate that the observed cooling rate is
at least five times larger than that produced by free-space cooling methods,
for comparable excitation of the atom
Comparison of Theory and Experiment for a One-Atom Laser in a Regime of Strong Coupling
Our recent paper reports the experimental realization of a one-atom laser in
a regime of strong coupling (Ref. [1]). Here we provide the supporting
theoretical analysis relevant to the operating regime of our experiment. By way
of a simplified four-state model, we investigate the passage from the domain of
conventional laser theory into the regime of strong coupling for a single
intracavity atom pumped by coherent external fields. The four-state model is
also employed to exhibit the vacuum-Rabi splitting and to calculate the optical
spectrum. We next extend this model to incorporate the relevant Zeeman
hyperfine states as well as a simple description of the pumping processes in
the presence of polarization gradients and atomic motion. This extended model
is employed to make quantitative comparisons with the measurements of Ref. [1]
for the intracavity photon number versus pump strength and for the photon
statistics as expressed by the intensity correlation function g2(tau).Comment: 19 pages, 14 figures. Added sections on: scaling properties,
vacum-Rabi splitting, and optical spectru
Reducing multi-photon rates in pulsed down-conversion by temporal multiplexing
We present a simple technique to reduce the emission rate of higher-order
photon events from pulsed spontaneous parametric down-conversion. The technique
uses extra-cavity control over a mode locked ultrafast laser to simultaneously
increase repetition rate and reduce the energy of each pulse from the pump
beam. We apply our scheme to a photonic quantum gate, showing improvements in
the non-classical interference visibility for 2-photon and 4-photon
experiments, and in the quantum-gate fidelity and entangled state production in
the 2-photon case.Comment: 8 pages, 6 figure
An optical fibre rereadable radiation dosimeter for use at high doses and at elevated temperature
A new type of radiation dosimeter for large radiation doses is described, which is based on silica fibre material. Conventional radioluminescence or thermoluminescence of silica produces emission in the blue region of the spectrum. However, in this new material irradiation, in conjunction with a heat treatment, generates a green emission band. The intensity of the green band can be monitored by either radioluminescence or thermoluminescence using a test dose. The signals are directly related to the total irradiation history of the material. The dosimeter is therefore rereadable. The production mechanism of the green emission centre requires a thermal processing stage, with an activation energy of 0.52 eV. Further, the dosimeter is effective at recording radiation during high-temperature exposure, to at least 400°C, with the subsequent dosimetry being performed below 200°C
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