22,960 research outputs found
Amplitude squeezed light from a laser
Intensity squeezed light was successfully generated using semiconductor lasers with sub-Poissonian pumping. Control of the pumping statistics is crucial and is achieved by a large series resistor which regulates the pump current; its sub-Poissonian statistics are then transferred to the laser output. The sub-Poissonian pumping of other laser systems is not so simple, however, and their potential as squeezed states sources is apparently diminished. We consider a conventional laser incoherently pumped well above threshold, and allow for pump depletion of the ground state. In this regime, sub-Poissonian photon statistics and squeezed amplitude fluctuations are produced
Experimental autoimmune encephalomyelitis in the common marmoset: a translationally relevant model for the cause and course of multiple sclerosis
Aging Western societies are facing an increasing prevalence of chronic
autoimmune-mediated inflammatory disorders (AIMIDs) for which treatments that are safe and effective are scarce. One of the
main reasons for this situation is the lack of animal models, which accurately replicate
clinical and pathological aspects of the human diseases. One important AIMID is the
neuroinflammatory disease multiple sclerosis (MS), for which the mouse experimental
autoimmune encephalomyelitis (EAE) model has been frequently used in preclinical
research. Despite some successes, there is a long list of experimental treatments that
have failed to reproduce promising effects observed in murine EAE models when they were
tested in the clinic. This frustrating situation indicates a wide validity gap between
mouse EAE and MS. This monography describes the development of an EAE model in nonhuman
primates, which may help to bridge the gap.</p
High power coupled CO2 waveguide laser array
A hollow-bore ridge waveguide technique for phase locking arrays of coupled CO2 rf excited waveguide lasers was demonstrated. Stable phase-locked operation of two- and three-channel arrays has been demonstrated at the 50 W output level. Preliminary experiments with a five-element array generated an output power of 95 W but phase-locked operation was not conclusively demonstrated
The monopole mass in the three-dimensional Georgi-Glashow model
We study the three-dimensional Georgi-Glashow model to demonstrate how
magnetic monopoles can be studied fully non-perturbatively in lattice Monte
Carlo simulations, without any assumptions about the smoothness of the field
configurations. We examine the apparent contradiction between the conjectured
analytic connection of the `broken' and `symmetric' phases, and the
interpretation of the mass (i.e., the free energy) of the fully quantised 't
Hooft-Polyakov monopole as an order parameter to distinguish the phases. We use
Monte Carlo simulations to measure the monopole free energy and its first
derivative with respect to the scalar mass. On small volumes we compare this to
semi-classical predictions for the monopole. On large volumes we show that the
free energy is screened to zero, signalling the formation of a confining
monopole condensate. This screening does not allow the monopole mass to be
interpreted as an order parameter, resolving the paradox.Comment: 12 pages, 7 figures, uses revtex. Minor changes made to the text to
match with the published version at
http://link.aps.org/abstract/PRD/v65/e12500
Casimir scaling of domain wall tensions in the deconfined phase of D=3+1 SU(N) gauge theories
We perform lattice calculations of the spatial 't Hooft k-string tensions in
the deconfined phase of SU(N) gauge theories for N=2,3,4,6. These equal (up to
a factor of T) the surface tensions of the domain walls between the
corresponding (Euclidean) deconfined phases. For T much larger than Tc our
results match on to the known perturbative result, which exhibits Casimir
Scaling, being proportional to k(N-k). At lower T the coupling becomes stronger
and, not surprisingly, our calculations show large deviations from the
perturbative T-dependence. Despite this we find that the behaviour proportional
to k(N-k) persists very accurately down to temperatures very close to Tc. Thus
the Casimir Scaling of the 't Hooft tension appears to be a `universal' feature
that is more general than its appearance in the low order high-T perturbative
calculation. We observe the `wetting' of these k-walls at T around Tc and the
(almost inevitable) `perfect wetting' of the k=N/2 domain wall. Our
calculations show that as T tends to Tc the magnitude of the spatial `t Hooft
string tension decreases rapidly. This suggests the existence of a (would-be)
't Hooft string condensation transition at some temperature which is close to
but below Tc. We speculate on the `dual' relationship between this and the
(would-be) confining string condensation at the Hagedorn temperature that is
close to but above Tc.Comment: 40 pages, 14 figure
Monopoles, vortices and confinement in SU(3) gauge theory
We compute, in SU(3) pure gauge theory, the vacuum expectation value (vev) of
the operator which creates a vortex wrapping the lattice through periodic
boundary conditions (dual Polyakov line). The technique used is the same
already tested in the SU(2) case. The dual Polyakov line proves to be a good
disorder parameter for confinement, and has a similar behaviour to the monopole
condensate. The new features which characterise the construction of the
disorder operator in SU(3) are emphasised.Comment: 8 pages, 4 eps figures, typed with elsart.cl
Ground-layer wavefront reconstruction from multiple natural guide stars
Observational tests of ground layer wavefront recovery have been made in open
loop using a constellation of four natural guide stars at the 1.55 m Kuiper
telescope in Arizona. Such tests explore the effectiveness of wide-field seeing
improvement by correction of low-lying atmospheric turbulence with ground-layer
adaptive optics (GLAO). The wavefronts from the four stars were measured
simultaneously on a Shack-Hartmann wavefront sensor (WFS). The WFS placed a 5 x
5 array of square subapertures across the pupil of the telescope, allowing for
wavefront reconstruction up to the fifth radial Zernike order. We find that the
wavefront aberration in each star can be roughly halved by subtracting the
average of the wavefronts from the other three stars. Wavefront correction on
this basis leads to a reduction in width of the seeing-limited stellar image by
up to a factor of 3, with image sharpening effective from the visible to near
infrared wavelengths over a field of at least 2 arc minutes. We conclude that
GLAO correction will be a valuable tool that can increase resolution and
spectrographic throughput across a broad range of seeing-limited observations.Comment: 25 pages, 8 figures, to be published in Astrophys.
Theory of Networked Minority Games based on Strategy Pattern Dynamics
We formulate a theory of agent-based models in which agents compete to be in
a winning group. The agents may be part of a network or not, and the winning
group may be a minority group or not. The novel feature of the present
formalism is its focus on the dynamical pattern of strategy rankings, and its
careful treatment of the strategy ties which arise during the system's temporal
evolution. We apply it to the Minority Game (MG) with connected populations.
Expressions for the mean success rate among the agents and for the mean success
rate for agents with neighbors are derived. We also use the theory to
estimate the value of connectivity above which the Binary-Agent-Resource
system with high resource level goes into the high-connectivity state.Comment: 24 pages, 3 figures, submitted to PR
Childhood and the politics of scale: Descaling children's geographies?
This is the post-print version of the final published paper that is available from the link below. Copyright @ 2008 SAGE Publications.The past decade has witnessed a resurgence of interest in the geographies of children's lives, and particularly in engaging the voices and activities of young people in geographical research. Much of this growing body of scholarship is characterized by a very parochial locus of interest â the neighbourhood, playground, shopping mall or journey to school. In this paper I explore some of the roots of children's geographies' preoccupation with the micro-scale and argue that it limits the relevance of research, both politically and to other areas of geography. In order to widen the scope of children's geographies, some scholars have engaged with developments in the theorization of scale. I present these arguments but also point to their limitations. As an alternative, I propose that the notion of a flat ontology might help overcome some difficulties around scalar thinking, and provide a useful means of conceptualizing sociospatiality in material and non-hierarchical terms. Bringing together flat ontology and work in children's geographies on embodied subjectivity, I argue that it is important to examine the nature and limits of children's spaces of perception and action. While these spaces are not simply `local', they seldom afford children opportunities to comment on, or intervene in, the events, processes and decisions that shape their own lives. The implications for the substance and method of children's geographies and for geographical work on scale are considered
Periprosthetic acetabular fractures as a complication of total hip arthroplasty
Periprosthetic acetabular fractures are rare but potentially devastating complications of total hip arthroplasty. As the number of total hip arthroplasties performed annually increases, so has the incidence of periprosthetic fractures, with the topic being spotlighted more frequently in the orthopaedic community. There is a particular sparsity of literature regarding periprosthetic acetabular fractures, with periprosthetic femoral fractures after total hip arthroplasty being traditionally far more commonly reported. This article aims to provide an up-to-date review of the epidemiology, risk factors, diagnostic challenges, classifications, and management strategies for periprosthetic acetabular fractures after total hip arthroplasty
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