Coherent Reflection Research Articles

A quantitative assessment approach of feasible optical mechanisms contributing to structural color of golden-like Chrysina aurigans scarab beetles

Under normal incidence of non-polarized light, reflection spectra from the cuticle of golden-like C. aurigans scarabs shows a broad band displayed from 525 to 950nm, with a spectral ripple structure that consists of a uniform sequence of peaks superimposed on the main reflection band. Cross sectional Scanning Electron Microscope (SEM) images of the cuticle initially suggest the presence of a multilayered structure. A radiative transfer matrix formalism is first applied to describe as much as possible the main features of coherent reflection spectra, by assuming optically homogenous layers distributed through the exocuticle, with chitin as the major constituent material. Additional non-coherent multiple reflections due to layers in the endocuticle are also evaluated from this approach. The presence of a pigmented micron sized structure beneath the procuticle requires the evaluation of a diffuse light contribution to the reflection. This was carried out from a four-flux radiative transfer model. Optical anisotropy is introduced by interpreting the SEM images in terms of a twisted Bouligand-type structure, and reflection spectra are evaluated from an implementation of the so-called 4×4 Berreman׳s formalism. We have been able to approach the main features characterizing the reflection spectra of C. aurigans׳ elytra following this progressive way.

Non‐invasive diagnosis of sweat gland dysplasia using optical coherence tomography and reflectance confocal microscopy in a family with anhidrotic ectodermal dysplasia (Christ–Siemens–Touraine syndrome)

Anhidrotic ectodermal dysplasia (AED) is an inherited syndrome, which originates mainly from genetic alteration of the ectodysplasin A (EDA) gene. It regularly affects the adnexa of the skin which results in a characteristic phenotype of the patients including hypo- or anhidrosis leading to severe disturbances in the regulation of body temperature. To prevent the development of the symptoms in early childhood promising therapeutic approaches are currently under clinical investigation. In this context, timely diagnosis of this genetic syndrome is crucial. The purpose of our study was the investigation of modern non-invasive imaging methods such as optical coherence tomography (OCT) and reflectance confocal microscopy (RCM) in the immediate diagnosis of AED. We examined a 3-year-old boy with the suspicion for an AED syndrome and his family members with RCM and OCT to document presence and characteristic features of sweat glands in comparison to non-affected individuals. The patient and the affected brother showed significantly reduced sweat glands in the imaging compared to the controls. The genetic analysis revealed a mutation of the EDA gene for hemizygosity previously associated with AED and the mother was revealed as the conductor of the genetic alteration. With the help of non-invasive imaging, we were able to detect sweat gland dysplasia in the affected family members without performing a biopsy which led us to the diagnosis of an AED. The application of modern dermatological imaging techniques might serve as valuable supplementary tools in the immediate, non-invasive diagnosis of genetic syndromes especially in newborns when early therapeutic approaches are planned.

Salient features of otoacoustic emissions are common across tetrapod groups and suggest shared properties of generation mechanisms

Otoacoustic emissions (OAEs) are faint sounds generated by healthy inner ears that provide a window into the study of auditory mechanics. All vertebrate classes exhibit OAEs to varying degrees, yet the biophysical origins are still not well understood. Here, we analyzed both spontaneous (SOAE) and stimulus-frequency (SFOAE) otoacoustic emissions from a bird (barn owl, Tyto alba) and a lizard (green anole, Anolis carolinensis). These species possess highly disparate macromorphologies of the inner ear relative to each other and to mammals, thereby allowing for novel insights into the biomechanical mechanisms underlying OAE generation. All ears exhibited robust OAE activity, and our chief observation was that SFOAE phase accumulation between adjacent SOAE peak frequencies clustered about an integral number of cycles. Being highly similar to published results from human ears, we argue that these data indicate a common underlying generator mechanism of OAEs across all vertebrates, despite the absence of morphological features thought essential to mammalian cochlear mechanics. We suggest that otoacoustic emissions originate from phase coherence in a system of coupled oscillators, which is consistent with the notion of "coherent reflection" but does not explicitly require a mammalian-type traveling wave. Furthermore, comparison between SFOAE delays and auditory nerve fiber responses for the barn owl strengthens the notion that most OAE delay can be attributed to tuning.

Simulation of Coherent X-Ray Imaging of Tilted Objects in the Fourier Space

Coherent reflection imaging is a new imaging technology allowing X-ray study of upper surface layers of thick and opaque samples or nanostructures and thin samples fixed on a reflecting substrate. We develop the diffraction theory and calculations relevant to coherent reflection imaging of tilted objects illuminated below critical angles of X-ray reflection.

On the spatial distribution of the reflection sources of different latency components of otoacoustic emissions.

The experimental observation of long- and short-latency components in both stimulus-frequency and transient-evoked otoacoustic emissions admits a comprehensive explanation within the coherent reflection mechanism, in a linear active transmission-line cochlear model. A local complex reflectivity function associated with roughness was defined and analyzed by varying the tuning factor of the model, systematically showing, for each frequency, a multiple-peak spatial structure, compatible with the observed multiple-latency structure of otoacoustic emissions. Although this spatial pattern and the peak relative intensity changes with the chosen random roughness function, the multiple-peak structure is a reproducible feature of different "digital ears," in good agreement with experimental data. If one computes the predicted transmission delays as a function of frequency and position for each source, one gets a good match to the latency-frequency patterns that are directly computed from synthesized otoacoustic spectra using time-frequency analysis. This result clarifies the role of the spatial distribution of the otoacoustic emission sources, further supporting the interpretation of different-latency otoacoustic components as due to reflection sources localized at different places along the basilar membrane.

Reflection of a plane wave from a two-layered seafloor with non-parallel interface between the layers.

This work studies the reflection coefficient of a plane wave incident on a seafloor consisting of two layers (sediment and substrate), whose interface is linear but not parallel to the water-sediment interface. This is an extension of the well-established and studied reflection coefficient concept for seafloors with parallel layers. Moreover this study introduces the concept of the Coherent Reflection Coefficient (CRC) that extends the usual Rayleigh reflection coefficient definition not only at the water-sediment interface but inside the water column as well. The mathematical formulation of the CRC is derived and its numerical implementation is explained. Based on this implementation a numerical code is developed and incorporated-among other codes-in a user-friendly graphics toolbox that was built to facilitate CRC calculations. Numerical examples for realistic seafloors are presented and the derived results are compared to similar ones for parallel layers, indicating that even for small inclination angles the reflection coefficient difference between parallel and slanted interface layers is substantial, hence cannot be ignored. An imminent application of the extended seafloor model and the CRC introduced in this work is the enhancement of geophysics inversion schemes for the estimation of the seafloor parameters.

D.C. Josephson transport by quartets and other Andreev resonances in superconducting bijunctions

Bijunctions are three-terminal Josephson junctions where three superconductors are connected by a single weak link made of a metallic region or of quantum dots. Biasing two of the superconductors with commensurate voltages yields Andreev resonances that produce d.c. Josephson currents made of correlated Cooper pairs. For instance with applied voltages (0, V, - V), quartets formed by two entangled Cooper pairs are emitted by one reservoir towards the two others. Theory involving non-equilibrium Green's functions reveal the microsopic mechanism at play, e.g multiple coherent Andreev reflections that provide an energy-conserving and fully coherent channel. Recent experiments on diffusive Aluminum-Copper bijunctions show transport anomalies that are interpreted in terms of quartet resonances.

Assessment of modernized GPS L5 SNR for ground-based multipath reflectometry applications

Global Positioning System (GPS) signal-to-noise ratio (SNR) measurements can be employed to retrieve environmental variables in multipath reception conditions, whereby direct or line-of-sight transmission is received simultaneously with coherent reflections thereof. Previous GPS SNR multipath studies of soil moisture and snow depth have focused on the legacy GPS L1 and L2 bands. In the present paper, short-delay, near-grazing incidence multipath from the L5-band GPS SNR is assessed for its value in detecting soil moisture and snow depth. The L5 signal will become more important in the future because of compatibility and interoperability among the different global satellite navigation systems. The L5 results are compared with L2C estimates to determine whether the L2C–L5 differences (given their differing power budgets and their modulation properties) are significant. To address these questions, measurements and simulations were employed. A physically-based multipath simulator was enhanced to investigate the differences between parameter retrievals for the L2C and the L5 GPS signals. Parameter retrievals from synthetic observations for different scenarios were compared. Comparisons included varying reflector height, surface material, and surface roughness. Measurements from two GPS stations in Colorado, USA, were used to retrieve soil moisture and snow depth conditions. Over a 153-day period that encompassed the catastrophic 2013 Colorado flooding event, L2-derived volumetric soil moisture had an RMS difference of 0.042cm3/cm3 while the L5 RMS difference was 0.034cm3/cm3 with respect to in-situ data (values of volumetric soil moisture range between 0.04 and 0.34cm3/cm3). In a separate 483-day campaign, L5-derived snow depth estimates were compared to L2C-derived values and found strongly correlated, deviating from a one-to-one relationship by only 0.00001±0.0064cm/cm. These results indicate the absence of any detectable biases in L5 as compared to L2C for retrieving soil moisture and snow depth from GPS SNR multipath observations.

Phase Coherence and Andreev Reflection in Topological Insulator Devices

Topological insulators (TIs) have attracted immense interest because they host helical surface states. Protected by time-reversal symmetry, they are robust to non-magnetic disorder. When superconductivity is induced in these helical states, they are predicted to emulate p-wave pairing symmetry, with Majorana states bound to vortices. Majorana bound states possess non-Abelian exchange statistics which can be probed through interferometry. Here, we take a significant step towards Majorana interferometry by observing pronounced Fabry-Perot oscillations in a TI sandwiched between a superconducting and normal lead. For energies below the superconducting gap, we observe a doubling in the frequency of the oscillations, arising from the additional phase accumulated from Andreev reflection. When a magnetic field is applied perpendicular to the TI surface, a number of very sharp and gate-tunable conductance peaks appear at or near zero energy, which has consequences for interpreting spectroscopic probes of Majorana fermions. Our results demonstrate that TIs are a promising platform for exploring phase-coherent transport in a solid-state system.

Scattershot: A look at designing, integrating, and measuring diffusion

A primary goal of the small-scale performance venue is to provide the audience with supportive, well-timed reflections and to energize the space adequately without overpowering the room volume. The judicious use of sound-diffusive elements in such venues can lend a pleasing sense of body and space while avoiding undesirable reflections that disrupt the listener experience. However, while working with architects to develop a space that is pleasing to both the ear and the eye, it is often necessary to reconcile these needs with each other. Diffusive elements must integrate seamlessly within the space visually as well as architecturally. While developing interior room acoustics for three small spaces for performance/worship, with audience size ranging from 150 to 299, an exploration of diffusive elements was conducted. As each project required a different method and frequency range of diffusion, scale models were constructed and tested under varied conditions, using sometimes unorthodox methods to determine the acoustic effect. These efforts were focused on limiting coloration caused by the “picket fence effect,” reducing harsh reflections without rendering a space excessively sound-absorptive, and maintaining coherent reflections from discrete sections of a prominent wall while leaving other sections diffusive. Methods, experiences, and results will be presented.

All that Jazz Coming Out of My Ears

All that Jazz Coming Out of My Ears

Bias error of source level estimate in submerged vessel’s radiated noise measurement

Two standards, the American National Standards Institute/the Acoustical Society of America (ANSI/ASA) and the International Organization for Standardization/Publicly Available Specification (ISO/PAS) have been published for surface vessel radiated noise assessment but not for a submerged vessel. Their measurement uncertainties of random and bias error are addressed for components of the measurement system. In this study, the bias error for a submerged vessel source level estimate is interpreted on the basis of the sea surface coherent reflection coefficient and transmission anomaly as functions of frequency, grazing angle, and effective wave height. It is found that the bias error using the mean intensity in a vertical hydrophone array is approximately 3 dB at frequencies less than 2 kHz, but 1 dB at frequencies higher than 2 kHz for effective wave heights of 0.3 and 0.6 m. This result will contribute a future standard for submerged vessel radiated noise assessment.

Determination of the In-Plane Optical Conductivity of Multilayer Graphene Supported on a Transparent Substrate of Finite Thickness from Normal-Incidence Transmission Spectra

Normal-incidence transmission measurements are commonly used for determining the real part of the in-plane optical conductivities σ1(ω) of graphene layers. We present an accurate expression for σ1 (ω) in a closed form for a multilayer graphene film supported on a finite-thickness transparent substrate. This form takes into account the coherent and incoherent multiple reflections of the system, whereas the traditional method assumes a semi-infinite substrate. The simulated results for graphene sheets with a layer number N ≤ 10 show that no matter what the transparent substrate is, the accuracy to which σ1(ω) is determined by applying this expression is improved with no systematic error. Moreover, the layer number N can be exactly determined by simply dividing the σ1(ωp) value of N-layer graphene by the corresponding σ1(ωp) of monolayer graphene, where ωp is the peak frequency of the ordinary dielectric function's imaginary part ε2(ω) of graphene.

Arrival-time fluctuations of coherent reflections from surface gravity water waves.

Arrival time fluctuations of coherent reflections from surface gravity waves are examined. A two-dimensional ray model with an evolving rough sea surface is used to explain the mechanism and formation of the deterministic striation patterns due to the surface reflection. Arrival time predictions from the ray model match qualitatively well with the measurements from bidirectional acoustic transmissions in a water depth of 100 m.

Efficiency of complex trace analysis to attenuate ground-roll noise from seismic data

Abstract Ground-roll, characterized by low frequency and high amplitude, is one of the most important issues in seismic data processing. Common methods to eliminate ground-roll noise from seismic data include frequency-based methods which pose filtering the whole signal. In addition, assuming being stationary signal which attended in filter is another disadvantage of those methods; however, in this paper a new method based on using Hilbert transform to address high-amplitude, low-frequency coherent noise is proposed. In this respect the conventional seismic trace can be viewed as the real component of a complex trace. Therefore, its envelope and normalized phase, as the input of running average, are easily calculated. On the other hand, complex trace-based filtering is approached to be a method distinguishing between coherent noise and reflections overlapping each other. This is done by setting a suitable length of window on running average in order to extract low frequency components from data.

Cavity-Enhanced Real-Time Monitoring of Single-Charge Jumps at the Microsecond Time Scale

We use fast coherent reflectivity measurements, in a strongly-coupled quantum dot-micropillar device, to monitor in real-time single-charge jumps at the microsecond timescale. Thanks to the strong enhancement of light-matter interaction inside the cavity, the measurement rate is five orders of magnitude faster than with previous experiments of direct single-charge sensing with quantum dots. The monitored transitions, identified at any given time with a less than 0.2% error probability, correspond to a carrier being captured and then released by a single material defect. This high-speed technique opens the way for the real-time monitoring of other rapid single quantum events, such as the quantum jumps of a single spin.

Approximation of a physics-based model of surface reflection loss

A model of coherent acoustic reflection loss at the ocean surface had been prepared by the authors by combining a model of surface roughness loss with a description of surface incidence angle which accounted for the refractive effects of a uniformly stratified distribution of wind-driven bubbles. Here, surface roughness loss was based on a second-order small-slope approximation, and the surface incidence angle was obtained using a formulation for stratified media from Brekhovskikh applied to the sound speed variation resulting from the bubble distribution used by Ainslie [JASA 118, (2005)]. More recent work by the authors has shown that the analyses for each of surface roughness loss, and surface incidence angle, may be approximated adequately by relatively simple expressions, and that the complete model of surface reflection loss inclusive of the refractive effects of bubbles may be approximated in expressions suitable for hand calculations. Results from the use of this approximated model with a Gaussian-beam acoustic propagation code are compared with results obtained from the authors' more complete model for several surface ducted transmission scenarios. Both sets of results are also compared with predictions based on Monte Carlo parabolic equation (PE) transmission calculations.

Cochlear reflectance: Measurements and modeling

Cochlear reflectance (CR), the cochlear contribution to ear-canal reflectance (ECR), has theoretical advantages for cochlear modeling. Comparisons between measurements and models may lead to improved interpretation of cochlear status and provide a basis for making improvements to the models. Previous evaluation of clinical utility of CR measurements showed that CR did not predict auditory status or behavioral threshold as accurately as other otoacoustic emission measurements. Strategies for improving the quality of CR measurements were assessed in ECR measurements from 27 participants. Results indicate that the quality of CR measurements can be improved by (1) increased averaging time and (2) adjustment to the methods for extracting CR from ECR. Simulation of ECR was performed using a combination of a middle-ear model and a one-dimensional cochlear model. Simulated CR was the ECR difference between active and passive conditions of the model. The model simulation results were compared with measurements of ECR and CR in both the time and frequency domains. Minor disparities between measurements and model will provide a basis for improvements in the model. Substantial agreement between measurements and model suggest that CR is consistent with linear coherent reflection due to random impedance perturbations along the cochlear partition.

Investigating Construction History, Labour Investment and Social Change at Ocmulgee National Monument's Mound A, Georgia, USA, Using Ground‐penetrating Radar

ABSTRACTPrehistoric societies from around the world constructed monumental mounded architecture (earthen pyramids) for a variety of functions, including the foundation for temples or a leader's residence, community stages and cemeteries. Flat‐topped earthen mounds often have complicated histories where the function, size, orientation and summit architecture varied throughout time. This paper presents the results from a ground‐penetrating radar (GPR) survey conducted on the summit of Mound A, the largest prehistoric Native American mound at Ocmulgee National Monument located in central Georgia, USA. Our study indicates that performing depth‐slice analyses of flat‐topped mounds can effectively map successive construction stages over distinct periods of archaeological prehistory. The GPR data show distinctive low‐amplitude, discontinuous stratigraphic variations that we interpret to be related to mound fill, which are interrupted by high‐amplitude coherent summit reflections. We also maintain sufficient vertical and horizontal resolution to identify summit architecture on earlier mound‐use episodes, which is imaged by distinct reflection geometry as patterned linear, square and circular high‐amplitude events in GPR depth‐slices. The authors recorded four possible mound summits, the western expansion of the mound, and the shifting location and shape of summit architecture; in addition to resolving a discrepancy regarding the location of early excavation units from the 1930s. Shallow geophysical data indicate a decline in the volume of material used over the course of mound construction, and by inference, a decline in the size of the labour force used to construct each stage. We conclude that the power and influence of Ocmulgee's early leadership subsided over the course of Mound A's use, and may have been contested by an emerging faction. Copyright © 2014 John Wiley & Sons, Ltd.

High‐definition optical coherence tomography and reflectance confocal microscopy in the in vivo visualization of a reaction to permanent make‐up

After permanent make-up treatments, eczematous and granulomatous reactions may occur which need anti-inflammatory treatment. For the definite diagnosis oftentimes biopsies are recommended. In vivo imaging such as reflectance confocal microscopy (RCM) and high-definition optical coherence tomography (HD-OCT) has been successfully used in the non-invasive diagnosis of various dermatoses before. Here, we report on non-invasive imaging of a reaction towards permanent make-up in a 40-year-old woman by using HD-OCT and RCM. Both in HD-OCT and in RCM subepidermal pigment and granulomatous changes could be visualized and correlated with the histopathological findings. Regression of the lesions in response to topical steroids and intralesional injections of steroids and 5-fluorouracil is reported and treatment options are discussed. Non-invasive imaging techniques such as HD-OCT and RCM allow the visualization and localization of exogenous pigment and help in the evaluation of adverse reactions due to permanent make-up tattooing.