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phase coherence

Alice Odier, Anne Durécu, Jean-Michel Melkonian, Laurent Lombard, Michel Lefebvre, Pierre Bourdon
Coherent beam combining by active phase control could be useful for power scaling fiber-laser-pumped optical frequency converters. However, a fast phase modulator operating at the frequency-converted wavelength, a non-standard component, would be necessary. Fortunately, nonlinear conversion processes rely on a phase-matching condition allowing for indirect phase control using standard phase modulators. In this Letter, coherent combining of second-harmonic generators is demonstrated in both birefringent and quasi-phase-matching schemes in CW regime...
August 15, 2017: Optics Letters
Dan Nguyen, Ganesh L R Lokesh, David E Volk, Junji Iwahara
NMR spectroscopy is a powerful tool for research on protein dynamics. In the past decade, there has been significant progress in the development of NMR methods for studying charged side chains. In particular, NMR methods for lysine side-chain NH₃⁺ groups have been proven to be powerful for investigating the dynamics of hydrogen bonds or ion pairs that play important roles in biological processes. However, relatively low sensitivity has been a major practical issue in NMR experiments on NH₃⁺ groups. In this paper, we present a unique and simple approach to improve sensitivity in (15)N relaxation measurements for NH₃⁺ groups...
August 15, 2017: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
Andrius Zukauskas, Anne-Lise Viotti, Charlotte Liljestrand, Valdas Pasiskevicius, Carlota Canalias
Mirrorless optical parametric oscillators (MOPOs) are very attractive parametric devices that rely on the nonlinear interaction of counter-propagating photons to inherently establish distributed feedback, without the use of external mirrors or surface coatings. These devices offer unique spectral and coherence properties that will benefit a large variety of applications ranging from spectroscopy to quantum communications. The major obstacle in exploiting their full potential is ascribed to the difficulty in engineering a nonlinear material in which the generation of counter-propagating waves can be phase matched...
August 14, 2017: Scientific Reports
Yuan Zong, Huan Xu, Jian Yu, Chunhui Jiang, Xiangmei Kong, Yi He, Xinghuai Sun
The impairment of retinal vascular autoregulation can be an early manifestation of many systemic and ocular diseases. Therefore, quantifying retinal vascular autoregulation in a non-invasive manner is very important. This study evaluated the effects of a Valsalva maneuver (VM)-induced blood pressure increases on retinal vascular autoregulation. Parafoveal and peripapillary retinal vessel density were measured with optical coherence tomography angiography before (baseline) and 5 s after each subject completed a VM (Phase IV [VM-IV])...
2017: Frontiers in Physiology
Saskia Steinmann, Jan Meier, Guido Nolte, Andreas K Engel, Gregor Leicht, Christoph Mulert
Interhemispheric auditory connectivity via the corpus callosum has been demonstrated to be important for normal speech processing. According to the callosal relay model, directed information flow from the right to the left auditory cortex has been suggested, but this has not yet been proven. For this purpose, 33 healthy participants were investigated with 64-channel EEG while performing the dichotic listening task in which two different consonant-vowel syllables were presented simultaneously to the left (LE) and right ear (RE)...
August 12, 2017: Brain Topography
Jiayang Zhang, Jie Zhou, Ming Tang, Heng Guo, Michael Small, Yong Zou
A growing number of algorithms have been proposed to map a scalar time series into ordinal partition transition networks. However, most observable phenomena in the empirical sciences are of a multivariate nature. We construct ordinal partition transition networks for multivariate time series. This approach yields weighted directed networks representing the pattern transition properties of time series in velocity space, which hence provides dynamic insights of the underling system. Furthermore, we propose a measure of entropy to characterize ordinal partition transition dynamics, which is sensitive to capturing the possible local geometric changes of phase space trajectories...
August 10, 2017: Scientific Reports
Bilal Haj Najeeb, Christian Simader, Gabor Deak, Clemens Vass, Jutta Gamper, Alessio Montuoro, Bianca S Gerendas, Ursula Schmidt-Erfurth
Purpose: To determine the distribution of leakage on fluorescein angiography (FA) and explore the clinically protective role of astrocytes against damage to the inner blood retinal barrier (iBRB) in diabetic macular edema (DME). Methods: A consecutive case series of 87 eyes of 87 patients with DME was included. We measured the leakage area in each field of the Early Treatment Diabetic Retinopathy Study (ETDRS) grid on late-phase FA images. The normative thickness of the nerve fiber layer (NFL), in which the astrocytes are confined, was derived from a previous work using spectral-domain optical coherence tomography...
August 1, 2017: Investigative Ophthalmology & Visual Science
Chao Zuo, Jiasong Sun, Jiaji Li, Jialin Zhang, Anand Asundi, Qian Chen
For quantitative phase imaging (QPI) based on transport-of-intensity equation (TIE), partially coherent illumination provides speckle-free imaging, compatibility with brightfield microscopy, and transverse resolution beyond coherent diffraction limit. Unfortunately, in a conventional microscope with circular illumination aperture, partial coherence tends to diminish the phase contrast, exacerbating the inherent noise-to-resolution tradeoff in TIE imaging, resulting in strong low-frequency artifacts and compromised imaging resolution...
August 9, 2017: Scientific Reports
Mahmood Sayed Hoseini, Jeff Pobst, Nathaniel Caleb Wright, Wesley Clawson, Woodrow Shew, Ralf Wessel
Bursts of oscillatory neural activity have been hypothesized to be a core mechanism by which remote brain regions can communicate. Such hypothesis raises the question to what extent oscillations are coherent across spatially distant neural populations. To address this question, we obtained local field potential (LFP) and membrane potential recordings from the visual cortex of turtle in response to visual stimulation of the retina. The time-frequency analysis of these recordings revealed pronounced bursts of oscillatory neural activity and a large trial-to-trial variability in the spectral and temporal properties of the observed oscillations...
August 9, 2017: Journal of Neurophysiology
Joachim Bellet, Chih-Yang Chen, Ziad M Hafed
Microsaccades are tiny saccades that occur during gaze fixation. Even though visual processing has been shown to be strongly modulated close to the time of microsaccades, both at central and peripheral eccentricities, it is not clear how these eye movements might influence longer-term fluctuations in brain activity and behavior. Here we found that visual processing is significantly affected, and in a rhythmic manner, even several hundreds of milliseconds after a microsaccade. Human visual detection efficiency, as measured by reaction time, exhibited coherent rhythmic oscillations in the α and β frequency bands for up to ~650-700 ms after a microsaccade...
August 9, 2017: Journal of Neurophysiology
Cheng Guo, Qiang Li, Ce Wei, Jiubin Tan, Shutian Liu, Zhengjun Liu
As a coherent diffractive imaging technique, axial multi-image phase retrieval utilizes a series of diffraction patterns on the basis of axial movement diversity to reconstruct full object wave field. Theoretically, fast convergence and high-accuracy of axial multi-image phase retrieval are demonstrated. In experiment, its retrieval suffers from the tilt illumination, in which diffraction patterns will shift in the lateral direction as the receiver traverses along the axis. In this case, the reconstructed result will be blurry or even mistaken...
August 8, 2017: Scientific Reports
Paolo Bazzigaluppi, Tina L Beckett, Margaret M Koletar, Aaron Y Lai, Illsung L Joo, Mary E Brown, Peter L Carlen, JoAnne McLaurin, Bojana Stefanovic
Alzheimer's disease (AD) is pathologically characterized by amyloid-β peptide (Aβ) accumulation, neurofibrillary tangle formation, and neurodegeneration. Preclinical studies on neuronal impairments associated with progressive amyloidosis have demonstrated some Aβ-dependent neuronal dysfunction including modulation of GABAergic signalling. The present work focuses on the early stage of disease progression and uses TgF344-AD rats that recapitulate a broad repertoire of AD-like pathologies to investigate the neuronal network functioning using simultaneous intracranial recordings from the hippocampus (HPC) and the medial prefrontal cortex (mPFC), followed by pathological analyses of gamma-aminobutyric acid (GABAA ) receptors subunits α1, α5 and δ, and glutamic acid decarboxylases (GAD65 and GAD67)...
August 4, 2017: Journal of Neurochemistry
A Kantian, D S L Abergel
We theoretically predict that a true bilayer exciton condensate, characterized by off-diagonal long-range order and global phase coherence, can be created in one-dimensional solid state electron systems. The mechanism by which this happens is to introduce a single particle hybridization of electron and hole populations, which locks the phase of the relevant mode and hence invalidates the Mermin-Wagner theorem. Electron-hole interactions then amplify this tendency towards off-diagonal long-range order, enhancing the condensate properties by more than an order of magnitude over the noninteracting limit...
July 21, 2017: Physical Review Letters
James Keeley, Joshua Freeman, Karl Bertling, Yah L Lim, Reshma A Mohandas, Thomas Taimre, Lianhe H Li, Dragan Indjin, Aleksandar D Rakić, Edmund H Linfield, A Giles Davies, Paul Dean
The effects of optical feedback (OF) in lasers have been observed since the early days of laser development. While OF can result in undesirable and unpredictable operation in laser systems, it can also cause measurable perturbations to the operating parameters, which can be harnessed for metrological purposes. In this work we exploit this 'self-mixing' effect to infer the emission spectrum of a semiconductor laser using a laser-feedback interferometer, in which the terminal voltage of the laser is used to coherently sample the reinjected field...
August 3, 2017: Scientific Reports
Claudio Sbarufatti, Alessio Beligni, Andrea Gilioli, Maddalena Ferrario, Marco Mattarei, Mario Martinelli, Marco Giglio
A novel fiber optic sensing technology for high frequency dynamics detection is proposed in this paper, specifically tailored for structural health monitoring applications based on strain wave analysis, for both passive impact identification and active Lamb wave monitoring. The sensing solution relies on a fiber optic-based interferometric architecture associated to an innovative coherent detection scheme, which retrieves in a completely passive way the high-frequency phase information of the received optical signal...
July 13, 2017: Materials
Mostafa A Ellabban, Gašper Glavan, Jürgen Klepp, Martin Fally
A detailed investigation of the recording, as well as the readout of transmission gratings in composites of poly(ethylene glycol) dimethacrylate (PEGDMA) and ionic liquids is presented. Gratings with a period of about 5.8 micrometers were recorded using a two-wave mixing technique with a coherent laser beam of a 355-nm wavelength. A series of samples with grating thicknesses d 0 = 10 … 150 micrometers, each for two different exposure times, was prepared. The recording kinetics, as well as the post-exposure properties of the gratings were monitored by diffracting a low intensity probe beam at a wavelength of 633 nm for Bragg incidence...
December 24, 2016: Materials
T Hensgens, T Fujita, L Janssen, Xiao Li, C J Van Diepen, C Reichl, W Wegscheider, S Das Sarma, L M K Vandersypen
Interacting fermions on a lattice can develop strong quantum correlations, which are the cause of the classical intractability of many exotic phases of matter. Current efforts are directed towards the control of artificial quantum systems that can be made to emulate the underlying Fermi-Hubbard models. Electrostatically confined conduction-band electrons define interacting quantum coherent spin and charge degrees of freedom that allow all-electrical initialization of low-entropy states and readily adhere to the Fermi-Hubbard Hamiltonian...
August 2, 2017: Nature
Gerald Hefferman, Zhen Chen, Tao Wei
This article details the generation of an extended-bandwidth frequency sweep using a single, communication grade distributed feedback (DFB) laser. The frequency sweep is generated using a two-step technique. In the first step, injection current modulation is employed as a means of varying the output frequency of a DFB laser over a bandwidth of 99.26 GHz. A digital optical phase lock loop is used to lock the frequency sweep speed during current modulation, resulting in a linear frequency chirp. In the second step, the temperature of the DFB laser is modulated, resulting in a shifted starting laser output frequency...
July 2017: Review of Scientific Instruments
Keunhwa Lee, Woojae Seong, Seongil Kim
This paper proposes a roll-angle estimation method for the triplet towed array using the oceanic ambient noise recorded in the mid-frequency range of 1 to 10 kHz. Here, the dominance of oceanic surface-generated noises such as wind-driven and shipping noises is expected. The ratio between the approximated phase parts of the noise-coherence function regarding the triplet hydrophones is used for the roll estimation. Advantage of this technique is that explicit input regarding the oceanic environment is not required, especially for an ocean with an azimuthally uniform noise field or dominant noise sources at the end-fire direction of the horizontal array...
July 2017: Journal of the Acoustical Society of America
Bidesh K Bera, Dibakar Ghosh, Punit Parmananda, G V Osipov, Syamal K Dana
We report the emergence of coexisting synchronous and asynchronous subpopulations of oscillators in one dimensional arrays of identical oscillators by applying a self-feedback control. When a self-feedback is applied to a subpopulation of the array, similar to chimera states, it splits into two/more sub-subpopulations coexisting in coherent and incoherent states for a range of self-feedback strength. By tuning the coupling between the nearest neighbors and the amount of self-feedback in the perturbed subpopulation, the size of the coherent and the incoherent sub-subpopulations in the array can be controlled, although the exact size of them is unpredictable...
July 2017: Chaos
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