4,860 research outputs found
Resonant Interactions Between Protons and Oblique Alfv\'en/Ion-Cyclotron Waves
Resonant interactions between ions and Alfv\'en/ion-cyclotron (A/IC) waves
may play an important role in the heating and acceleration of the fast solar
wind. Although such interactions have been studied extensively for "parallel"
waves, whose wave vectors are aligned with the background magnetic
field , much less is known about interactions between ions and
oblique A/IC waves, for which the angle between and is nonzero. In this paper, we present new numerical results on resonant
cyclotron interactions between protons and oblique A/IC waves in collisionless
low-beta plasmas such as the solar corona. We find that if some mechanism
generates oblique high-frequency A/IC waves, then these waves initially modify
the proton distribution function in such a way that it becomes unstable to
parallel waves. Parallel waves are then amplified to the point that they
dominate the wave energy at the large parallel wave numbers at which the waves
resonate with the particles. Pitch-angle scattering by these waves then causes
the plasma to evolve towards a state in which the proton distribution is
constant along a particular set of nested "scattering surfaces" in velocity
space, whose shapes have been calculated previously. As the distribution
function approaches this state, the imaginary part of the frequency of parallel
A/IC waves drops continuously towards zero, but oblique waves continue to
undergo cyclotron damping while simultaneously causing protons to diffuse
across these kinetic shells to higher energies. We conclude that oblique A/IC
waves can be more effective at heating protons than parallel A/IC waves,
because for oblique waves the plasma does not relax towards a state in which
proton damping of oblique A/IC waves ceases
Non-adherence to eye care in people with diabetes
Objective Evaluate individual factors that impact adherence to eye care follow-up in patients with diabetes. Design and methods A 4-year retrospective chart review was conducted for 1968 patients with diabetes over age 40 from an urban academic center. Data collected included demographics, insurance, visual acuity, smoking status, medications, dates of dilated fundus examinations (DFE), and reported hemoglobin A1C and blood glucose levels. The primary outcome was timely DFE follow-up adherence following the initial eye exam visit. Results Overall, 41.6% of patients adhered to initial follow-up eye care recommendations. Multivariable analysis demonstrated that patients with severe diabetic retinopathy (DR) were more adherent than patients with mild DR (OR 1.86). Other variables associated with increased adherence were visual impairment and reported A1C or blood glucose. Smoking was associated with decreased adherence. Ethnicity and insurance were also significantly associated with adherence. Longitudinal follow-up rates were influenced by additional factors, including ethnicity and neighborhood deprivation index. Conclusions Patients with moderate to severe DR and/ or visual impairment were more likely to adhere to timely DFE follow-up. This could relate to the presence of visual symptoms and/or other systemic manifestations of diabetes. Smokers were less likely to adhere to timely DFE follow-up. One hypothesis is patients who smoke have other symptomatic health problems which patients prioritize over asymptomatic ocular disorders. In order to reduce vision loss from DR, practitioners should be aware that patients with mild and moderate DR, patients with normal vision, and smokers are at greater risk for poor follow-up eye care adherence. © Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2017. All rights reserved
A modified Oster-Murray-Harris mechanical model of morphogenesis
There are two main modeling paradigms for biological pattern formation in developmental biology: chemical prepattern models and cell aggregation models. This paper focuses on an example of a cell aggregation model, the mechanical model developed by Oster, Murray, and Harris [Development, 78 (1983), pp. 83--125]. We revisit the Oster--Murray--Harris model and find that, due to the infinitesimal displacement assumption made in the original version of this model, there is a restriction on the types of boundary conditions that can be prescribed. We derive a modified form of the model which relaxes the infinitesimal displacement assumption. We analyze the dynamics of this model using linear and multiscale nonlinear analysis and show that it has the same linear behavior as the original Oster--Murray--Harris model. Nonlinear analysis, however, predicts that the modified model will allow for a wider range of parameters where the solution evolves to a bounded steady state. The results from both analyses are verified through numerical simulations of the full nonlinear model in one and two dimensions. The increased range of boundary conditions that are well-posed, as well as a wider range of parameters that yield bounded steady states, renders the modified model more applicable to, and more robust for, comparisons with experiments
Quantum optical signal processing in diamond
Controlling the properties of single photons is essential for a wide array of
emerging optical quantum technologies spanning quantum sensing, quantum
computing, and quantum communications. Essential components for these
technologies include single photon sources, quantum memories, waveguides, and
detectors. The ideal spectral operating parameters (wavelength and bandwidth)
of these components are rarely similar; thus, frequency conversion and spectral
control are key enabling steps for component hybridization. Here we perform
signal processing of single photons by coherently manipulating their spectra
via a modified quantum memory. We store 723.5 nm photons, with 4.1 nm
bandwidth, in a room-temperature diamond crystal; upon retrieval we demonstrate
centre frequency tunability over 4.2 times the input bandwidth, and bandwidth
modulation between 0.5 to 1.9 times the input bandwidth. Our results
demonstrate the potential for diamond, and Raman memories in general, to be an
integrated platform for photon storage and spectral conversion.Comment: 6 pages, 4 figure
Storage and retrieval of ultrafast single photons using a room-temperature diamond quantum memory
We report the storage and retrieval of single photons, via a quantum memory,
in the optical phonons of room-temperature bulk diamond. The THz-bandwidth
heralded photons are generated by spontaneous parametric downconversion and
mapped to phonons via a Raman transition, stored for a variable delay, and
released on demand. The second-order correlation of the memory output is
, demonstrating preservation of non-classical
photon statistics throughout storage and retrieval. The memory is low-noise,
high-speed and broadly tunable; it therefore promises to be a versatile
light-matter interface for local quantum processing applications.Comment: 6 pages, 4 figure
Storage of polarization-entangled THz-bandwidth photons in a diamond quantum memory
Bulk diamond phonons have been shown to be a versatile platform for the
generation, storage, and manipulation of high-bandwidth quantum states of
light. Here we demonstrate a diamond quantum memory that stores, and releases
on demand, an arbitrarily polarized 250 fs duration photonic qubit. The
single-mode nature of the memory is overcome by mapping the two degrees of
polarization of the qubit, via Raman transitions, onto two spatially distinct
optical phonon modes located in the same diamond crystal. The two modes are
coherently recombined upon retrieval and quantum process tomography confirms
that the memory faithfully reproduces the input state with average fidelity
with a total memory efficiency of . In an
additional demonstration, one photon of a polarization-entangled pair is stored
in the memory. We report that entanglement persists in the retrieved state for
up to 1.3 ps of storage time. These results demonstrate that the diamond phonon
platform can be used in concert with polarization qubits, a key requirement for
polarization-encoded photonic processing
A diverse repertoire of human immunoglobulin variable genes in a chicken B cell line is generated by both gene conversion and somatic hypermutation
Chicken immune responses to human proteins are often more robust than rodent responses because of the phylogenetic relationship between the different species. For discovery of a diverse panel of unique therapeutic antibody candidates, chickens therefore represent an attractive host for human-derived targets. Recent advances in monoclonal antibody technology, specifically new methods for the molecular cloning of antibody genes directly from primary B cells, has ushered in a new era of generating monoclonal antibodies from non-traditional host animals that were previously inaccessible through hybridoma technology. However, such monoclonals still require post-discovery humanization in order to be developed as therapeutics. To obviate the need for humanization, a modified strain of chickens could be engineered to express a human-sequence immunoglobulin variable region repertoire. Here, human variable genes introduced into the chicken immunoglobulin loci through gene targeting were evaluated for their ability to be recognized and diversified by the native chicken recombination machinery that is present in the B-lineage cell line DT40. After expansion in culture the DT40 population accumulated genetic mutants that were detected via deep sequencing. Bioinformatic analysis revealed that the human targeted constructs are performing as expected in the cell culture system, and provide a measure of confidence that they will be functional in transgenic animals
- …