78 research outputs found
On Approaching the Ultimate Limits of Photon-Efficient and Bandwidth-Efficient Optical Communication
It is well known that ideal free-space optical communication at the quantum
limit can have unbounded photon information efficiency (PIE), measured in bits
per photon. High PIE comes at a price of low dimensional information efficiency
(DIE), measured in bits per spatio-temporal-polarization mode. If only temporal
modes are used, then DIE translates directly to bandwidth efficiency. In this
paper, the DIE vs. PIE tradeoffs for known modulations and receiver structures
are compared to the ultimate quantum limit, and analytic approximations are
found in the limit of high PIE. This analysis shows that known structures fall
short of the maximum attainable DIE by a factor that increases linearly with
PIE for high PIE.
The capacity of the Dolinar receiver is derived for binary coherent-state
modulations and computed for the case of on-off keying (OOK). The DIE vs. PIE
tradeoff for this case is improved only slightly compared to OOK with photon
counting. An adaptive rule is derived for an additive local oscillator that
maximizes the mutual information between a receiver and a transmitter that
selects from a set of coherent states. For binary phase-shift keying (BPSK),
this is shown to be equivalent to the operation of the Dolinar receiver.
The Dolinar receiver is extended to make adaptive measurements on a coded
sequence of coherent state symbols. Information from previous measurements is
used to adjust the a priori probabilities of the next symbols. The adaptive
Dolinar receiver does not improve the DIE vs. PIE tradeoff compared to
independent transmission and Dolinar reception of each symbol.Comment: 10 pages, 8 figures; corrected a typo in equation 3
A Schematic for Focusing on Youth in Investigations of Community Design and Physical Activity
This paper provides a first step in addressing special considerations for youth in a relatively new area of physical activity research. After reviewing the urgent need for novel approaches to increasing physical activity, the growing interest in the effects of community design are discussed. Although most discussion on this topic has focused on adults, there are important differences between youth and adults that warrant a special focus on youth and need to be accounted for. This article presents a schematic that accounts for how and where youth spend their time, decomposing the day into time spent in travel and time spent at destinations, and identifying portions of those times that are spent engaged in physical activity. By focusing on both spatial and behavioral dimensions of youth time, the schematic may help organize and advance scientific inquiry into the relationships between community design and physical activity specifically for youth
Progress in cavity QED with single trapped atoms
We report on recent progress in our lab involving cavity quantum electrodynamics with optically trapped atoms.
In particular, we will focus on a recent measurement of the Vacuum-Rabi splitting for one atom strongly coupled to the field of a high finesse optical resonator. This splitting is characteristic of the normal modes in the eigenvalue spectrum of the atom-cavity system. A new Raman scheme for cooling atomic motion along the cavity axis enables a complete spectrum to be recorded for an individual atom trapped within the cavity mode, in contrast to all previous measurements in cavity QED that have required averaging over many atoms
Killed but metabolically active Leishmania infantum as a novel whole-cell vaccine for visceral leishmaniasis
There are currently no effective vaccines for visceral leishmaniasis, the second most deadly parasitic infection in the world. Here, we describe a novel whole-cell vaccine approach using Leishmania infantum chagasi promastigotes treated with the psoralen compound amotosalen (S-59) and low doses of UV A radiation. This treatment generates permanent, covalent DNA cross-links within parasites and results in Leishmania organisms termed killed but metabolically active (KBMA). In this report, we characterize the in vitro growth characteristics of both KBMA L. major and KBMA L. infantum chagasi. Concentrations of S-59 that generate optimally attenuated parasites were identified. Like live L. infantum chagasi, KBMA L. infantum chagasi parasites were able to initially enter liver cells in vivo after intravenous infection. However, whereas live L. infantum chagasi infection leads to hepatosplenomegaly in mice after 6 months, KBMA L. infantum chagasi parasites were undetectable in the organs of mice at this time point. In vitro, KBMA L. infantum chagasi retained the ability to enter macrophages and induce nitric oxide production. These characteristics of KBMA L. infantum chagasi correlated with the ability to prophylactically protect mice via subcutaneous vaccination at levels similar to vaccination with live, virulent organisms. Splenocytes from mice vaccinated with either live L. infantum chagasi or KBMA L. infantum chagasi displayed similar cytokine patterns in vitro. These results suggest that KBMA technology is a potentially safe and effective novel vaccine strategy against the intracellular protozoan L. infantum chagasi. This approach may represent a new method for whole-cell vaccination against other complex intracellular pathogens
Cell-by-cell dissection of phloem development links a maturation gradient to cell specialization
Publisher Copyright: Copyright © 2021 The Authors, some rights reserved;In the plant meristem, tissue-wide maturation gradients are coordinated with specialized cell networks to establish various developmental phases required for indeterminate growth. Here, we used single-cell transcriptomics to reconstruct the protophloem developmental trajectory from the birth of cell progenitors to terminal differentiation in the Arabidopsis thaliana root. PHLOEM EARLY DNA-BINDING-WITH-ONE-FINGER (PEAR) transcription factors mediate lineage bifurcation by activating guanosine triphosphatase signaling and prime a transcriptional differentiation program. This program is initially repressed by a meristem-wide gradient of PLETHORA transcription factors. Only the dissipation of PLETHORA gradient permits activation of the differentiation program that involves mutual inhibition of early versus late meristem regulators. Thus, for phloem development, broad maturation gradients interface with cell-type-specific transcriptional regulators to stage cellular differentiation.Peer reviewe
Ultrafast all-optical switching by single photons
An outstanding goal in quantum optics is the realization of fast optical
non-linearities at the single-photon level. Such non-linearities would allow
for the realization of optical devices with new functionalities such as a
single-photon switch/transistor or a controlled-phase gate, which could form
the basis of future quantum optical technologies. While non-linear optics
effects at the single-emitter level have been demonstrated in different
systems, including atoms coupled to Fabry-Perot or toroidal micro-cavities,
super-conducting qubits in strip-line resonators or quantum dots (QDs) in
nano-cavities, none of these experiments so far has demonstrated single-photon
switching on ultrafast timescales. Here, we demonstrate that in a strongly
coupled QD-cavity system the presence of a single photon on one of the
fundamental polariton transitions can turn on light scattering on a transition
from the first to the second Jaynes-Cummings manifold with a switching time of
20 ps. As an additional device application, we use this non-linearity to
implement a single-photon pulse-correlator. Our QD-cavity system could form the
building-block of future high-bandwidth photonic networks operating in the
quantum regime
Meeting Report: Moving Upstream—Evaluating Adverse Upstream End Points for Improved Risk Assessment and Decision-Making
Background Assessing adverse effects from environmental chemical exposure is integral to public health policies. Toxicology assays identifying early biological changes from chemical exposure are increasing our ability to evaluate links between early biological disturbances and subsequent overt downstream effects. A workshop was held to consider how the resulting data inform consideration of an “adverse effect” in the context of hazard identification and risk assessment. Objectives Our objective here is to review what is known about the relationships between chemical exposure, early biological effects (upstream events), and later overt effects (downstream events) through three case studies (thyroid hormone disruption, antiandrogen effects, immune system disruption) and to consider how to evaluate hazard and risk when early biological effect data are available. Discussion Each case study presents data on the toxicity pathways linking early biological perturbations with downstream overt effects. Case studies also emphasize several factors that can influence risk of overt disease as a result from early biological perturbations, including background chemical exposures, underlying individual biological processes, and disease susceptibility. Certain effects resulting from exposure during periods of sensitivity may be irreversible. A chemical can act through multiple modes of action, resulting in similar or different overt effects. Conclusions For certain classes of early perturbations, sufficient information on the disease process is known, so hazard and quantitative risk assessment can proceed using information on upstream biological perturbations. Upstream data will support improved approaches for considering developmental stage, background exposures, disease status, and other factors important to assessing hazard and risk for the whole population
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