960 research outputs found
Non-properly Embedded H-Planes in H^2xR
For any in (0,1/2), we construct complete, non-proper, stable,
simply-connected surfaces embedded in with constant mean curvature .Comment: Details added at referee's request. To appear in Mathematische
Annale
Phase-conjugate optical coherence tomography
Quantum optical coherence tomography (Q-OCT) offers a factor-of-two
improvement in axial resolution and the advantage of even-order dispersion
cancellation when it is compared to conventional OCT (C-OCT). These features
have been ascribed to the non-classical nature of the biphoton state employed
in the former, as opposed to the classical state used in the latter.
Phase-conjugate OCT (PC-OCT), introduced here, shows that non-classical light
is not necessary to reap Q-OCT's advantages. PC-OCT uses classical-state signal
and reference beams, which have a phase-sensitive cross-correlation, together
with phase conjugation to achieve the axial resolution and even-order
dispersion cancellation of Q-OCT with a signal-to-noise ratio that can be
comparable to that of C-OCT.Comment: 4 pages, 3 figure
Gaussian-State Theory of Two-Photon Imaging
Biphoton states of signal and idler fields--obtained from spontaneous
parametric downconversion (SPDC) in the low-brightness, low-flux regime--have
been utilized in several quantum imaging configurations to exceed the
resolution performance of conventional imagers that employ coherent-state or
thermal light. Recent work--using the full Gaussian-state description of
SPDC--has shown that the same resolution performance seen in quantum optical
coherence tomography and the same imaging characteristics found in quantum
ghost imaging can be realized by classical-state imagers that make use of
phase-sensitive cross correlations. This paper extends the Gaussian-state
analysis to two additional biphoton-state quantum imaging scenarios: far field
diffraction-pattern imaging; and broadband thin-lens imaging. It is shown that
the spatial resolution behavior in both cases is controlled by the nonzero
phase-sensitive cross correlation between the signal and idler fields. Thus,
the same resolution can be achieved in these two configurations with
classical-state signal and idler fields possessing a nonzero phase-sensitive
cross correlation.Comment: 14 pages, 5 figure
Signal-to-noise ratio of Gaussian-state ghost imaging
The signal-to-noise ratios (SNRs) of three Gaussian-state ghost imaging
configurations--distinguished by the nature of their light sources--are
derived. Two use classical-state light, specifically a joint signal-reference
field state that has either the maximum phase-insensitive or the maximum
phase-sensitive cross correlation consistent with having a proper
representation. The third uses nonclassical light, in particular an entangled
signal-reference field state with the maximum phase-sensitive cross correlation
permitted by quantum mechanics. Analytic SNR expressions are developed for the
near-field and far-field regimes, within which simple asymptotic approximations
are presented for low-brightness and high-brightness sources. A high-brightness
thermal-state (classical phase-insensitive state) source will typically achieve
a higher SNR than a biphoton-state (low-brightness, low-flux limit of the
entangled-state) source, when all other system parameters are equal for the two
systems. With high efficiency photon-number resolving detectors, a
low-brightness, high-flux entangled-state source may achieve a higher SNR than
that obtained with a high-brightness thermal-state source.Comment: 12 pages, 4 figures. This version incorporates additional references
and a new analysis of the nonclassical case that, for the first time,
includes the complete transition to the classical signal-to-noise ratio
asymptote at high source brightnes
A Diffusion Model of Dynamic Participant Inflow Management
This paper studies a diffusion control problem motivated by challenges faced
by public health agencies who run clinics to serve the public. A key challenge
for these agencies is to motivate individuals to participate in the services
provided. They must manage the flow of (voluntary) participants so that the
clinic capacity is highly utilized, but not overwhelmed. The organization can
deploy costly promotion activities to increase the inflow of participants.
Ideally, the system manager would like to have enough participants waiting in a
queue to serve as many individuals as possible and efficiently use clinic
capacity. However, if too many participants sign up, resulting in a long wait,
participants may become irritated and hesitate to participate again in the
future. We develop a diffusion model of managing participant inflow mechanisms.
Each mechanism corresponds to choosing a particular drift rate parameter for
the diffusion model. The system manager seeks to balance three different costs
optimally: i) a linear holding cost that captures the congestion concerns; ii)
an idleness penalty corresponding to wasted clinic capacity and negative impact
on public health, and iii) costs of promotion activities. We show that a
nested-threshold policy for deployment of participant inflow mechanisms is
optimal under the long-run average cost criterion. In this policy, the system
manager progressively deploys mechanisms in increasing order of cost, as the
number of participants in the queue decreases. We derive explicit formulas for
the queue length thresholds that trigger each promotion activity, providing the
system manager with guidance on when to use each mechanism
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