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Purpose: This article introduces the Pentacam® Cornea OCT (optical coherence tomography). This advanced corneal imaging system combines rotating ultra-high-resolution spectral domain OCT with sub- 2-micron axial resolution and Scheimpflug photography. The purpose of this study is to present the first experience with the instrument and its potential for corneal diagnostics, including optical biopsy. Methods: In this prospective study, the Pentacam® Cornea OCT was used to image the corneas of seven patients. The novel wide-angle pericentric scan system enables optimal OCT imaging performance for the corneal layer structure over the entire width of the cornea, including the limbal regions. A detailed analysis of the resulting images assessed the synergism between the OCT and Scheimpflug photography. Results: The Pentacam® Cornea OCT demonstrated significantly improved image resolution and ability to individualize corneal layers with high quality. There is a synergism between the OCT high-definition signal to individualize details on the cornea and Scheimpflug photography to detect and quantify corneal scattering. The noncontact exam was proven safe, user-friendly, and effective for enabling optical biopsy. Conclusions: Pentacam® Cornea OCT is an advancement in corneal imaging technology. The ultra-high-resolution spectral domain OCT and Scheimpflug photography provide unprecedented detail and resolution, enabling optical biopsy and improving the understanding of corneal pathology. Further studies are necessary to compare and analyze the tomographic reconstructions of the cornea with the different wavelengths, which may provide helpful information for diagnosing and managing corneal diseases. [ABSTRACT FROM AUTHOR]

Due to resilience to background noise, avoidance of linear phase distortion, and stability of redundant representation, various simply symmetric frame scaling functions and derived framelets are becoming widely-used tools in data processing and transmission systems. In this study, we will reveal topological features (range, diameter, origin behavior, etc.) of spectral domain of fully symmetric frame scaling functions in the higher-dimensional space. Moreover, we present sufficient and necessary conditions for fully symmetric frame scaling functions with cube-shaped, sphere-shaped and ellipsoid-shape spectral domains. At the same time, we give the construction of fully symmetric frame scaling function and derived framelets with fully symmetry. [ABSTRACT FROM AUTHOR]

Optical Coherence Tomography (OCT) is a growing family of biophotonic imaging techniques, but in the literature there is a lack of easy-to-use tools to universally directly evaluate a device's theoretical performance for a given metric. Modern computing tools mean that direct numerical modeling can, from first principles, simulate the performance metrics of a specific device directly without relying on analytical approximations and/or complexities. Here, we present two different direct numerical models, along with the example MATLAB code for the reader to adapt to their own systems. The first model is of photo-electron shot noise at the detector, the primary noise source for OCT. We use this firstly to evaluate the amount of additional noise present (1.5 dB) for an experimental setup. Secondly, we demonstrate how to use it to precisely quantify the expected shot noise SNR limit difference between time-domain and Fourier-domain OCT systems in a given hypothetical experiment. The second model is used to demonstrate how USAF 1951 test chart images should be interpreted for a given lateral PSF shape. Direct numerical modeling is an easy and powerful basic tool for researchers and developers, the wider use of which may improve the rigor of the OCT literature. [ABSTRACT FROM AUTHOR]

Purpose: This article introduces the Pentacam® Cornea OCT (optical coherence tomography). This advanced corneal imaging system combines rotating ultra-high-resolution spectral domain OCT with sub- 2-micron axial resolution and Scheimpflug photography. The purpose of this study is to present the first experience with the instrument and its potential for corneal diagnostics, including optical biopsy. Methods: In this prospective study, the Pentacam® Cornea OCT was used to image the corneas of seven patients. The novel wide-angle pericentric scan system enables optimal OCT imaging performance for the corneal layer structure over the entire width of the cornea, including the limbal regions. A detailed analysis of the resulting images assessed the synergism between the OCT and Scheimpflug photography. Results: The Pentacam® Cornea OCT demonstrated significantly improved image resolution and ability to individualize corneal layers with high quality. There is a synergism between the OCT high-definition signal to individualize details on the cornea and Scheimpflug photography to detect and quantify corneal scattering. The noncontact exam was proven safe, user-friendly, and effective for enabling optical biopsy. Conclusions: Pentacam® Cornea OCT is an advancement in corneal imaging technology. The ultra-high-resolution spectral domain OCT and Scheimpflug photography provide unprecedented detail and resolution, enabling optical biopsy and improving the understanding of corneal pathology. Further studies are necessary to compare and analyze the tomographic reconstructions of the cornea with the different wavelengths, which may provide helpful information for diagnosing and managing corneal diseases.

Let X be an infinite-dimensional complex Banach space and let B (X) denote the algebra of all bounded linear operators on X. For an operator T ∈ B (X) the sets σ 1 (T) , σ 2 (T) , and σ 3 (T) are called, respectively, the semi-Fredholm domain, the Fredholm domain, and the Weyl domain, of T in the spectrum, σ (T) . Given i ∈ { 1 , 2 , 3 } , the goal of this article is to describe the general form of all surjective maps ϕ on B (X) which satisfy σ i (ϕ (A) ϕ (T) + ϕ (T) ϕ (A)) = σ i (A T + T A) for all A , T ∈ B (X) . [ABSTRACT FROM AUTHOR]

Abstract Let X $\mathcal {X}$ be an infinite-dimensional complex Banach space, B ( X ) $\mathcal {B}(\mathcal {X})$ the algebra of all bounded linear operators on X $\mathcal {X}$ . Denote the spectral domain by σ γ ( T ) = { λ ∈ σ a ( T ) : T that is semi-Fredholm and a s c ( T − λ I ) < ∞ } $\sigma _{\gamma}(T)=\{\lambda \in \sigma _{a}(T): T { \text{ that is semi-Fredholm and }} asc(T-\lambda I)

Let B (X) be the algebra of all bounded linear operators on an infinite dimensional complex Banach space X. For A ∈ B (X) , σ 1 (A) , σ 2 (A) , and σ 3 (A) are the semi-Fredholm domain, the Fredholm domain, and the Weyl domain of A in the spectrum σ (A) , respectively. For an integer k ≥ 2 , let (i 1 , … , i m) be a finite sequence with terms chosen from { 1 , … , k } and assume that at least one of the terms in (i 1 , … , i m) appears exactly once. The generalized product of k operators A 1 , … , A k ∈ B (X) is defined by A 1 ∗ A 2 ∗ ⋯ ∗ A k = A i 1 A i 2 ⋯ A i m , and includes the usual product and the triple product. In this paper we characterize the form of the map ϕ from B (X) into itself which satisfies σ i (A 1 ∗ ⋯ ∗ A k) = σ i (ϕ (A 1) ∗ ⋯ ∗ ϕ (A k)) , for all A 1 , … , A k ∈ B (X) and i ∈ 1 , 2 , 3 . [ABSTRACT FROM AUTHOR]

Let X be an infinite-dimensional complex Banach space, B (X) the algebra of all bounded linear operators on X . Denote the spectral domain by σ γ (T) = { λ ∈ σ a (T) : T that is semi-Fredholm and a s c (T − λ I) < ∞ } . In this paper, we characterize the structure of additive surjective maps φ : B (X) → B (X) with σ γ (φ (T)) = σ γ (T) for all T ∈ B (X) . [ABSTRACT FROM AUTHOR]

Purpose: To establish normative data on anterior scleral thickness using the spectral domain anterior segment optical coherence tomography (AS-OCT). Methods: In total, 200 eyes of 100 healthy subjects underwent AS-OCT scans in the temporal and nasal quadrants. The scleral + conjunctival complex thickness (SCT) was measured by a single examiner. Mean SCT was analyzed for differences across age groups, gender, and location (nasal versus temporal). Results: Mean age was 46.4 ± 18.3 (21–84) years; male to female ratio was 54:46. Mean SCT (nasal + temporal) of the right eye (RE) was 682.3 ± 64.2 μm in males and 660.6 ± 57.1 μm in females. In the left eye (LE), it was 684.6 ± 64.9 μm in males and 661.8 ± 49.3 μm in females. These differences between male and female for both eyes were statistically significant (P = 0.006 and P = 0.002). The mean SCT of temporal and nasal quadrants in the RE was 678.54 ± 57.50 and 666 ± 66.2 μm, respectively. In the LE, the temporal mean SCT quadrant was 679.6 ± 55.8 μm, and the nasal was 668.6 ± 63.6 μm. Age had a negative correlation with SCT (−0.62 μm/year; P = 0.03), and males had a higher temporal SCT than females (22 μm higher; P = 0.03). After adjusting for age and gender in a multivariate analysis, temporal SCT was significantly (P < 0.001) higher than nasal SCT. Conclusion: In our study, mean SCT decreased with age and males had a higher temporal SCT. This is the first study to evaluate scleral thickness in the Indian population, and the data can be used as a baseline for comparing variations in scleral thickness in disease.

The aim of this paper is to present an analytical study for the investigation of the reciprocal metamaterial gyro-bianisotropy effects on the input impedance of a dipole antenna. This study is based on the numerical resolution, using the spectral method of moments (SMoM), of the integral equation developed through the mathematical derivation of the appropriate spectral Green’s functions of the studied dipole configuration. The original obtained results are discussed and showed good agreements with the isotropic studied cases available in published literature. It is found that the imaginary valued magnetoelectric elements (chiral medium) exhibit an inverse effect on the resonant length compared to purely real elements (Tellegen medium), while negative elements decrease the input impedance. Combination of the two cases has led to more general complex media with further inspiring features.

Let H be an infinite dimensional Hilbert space and B (H) be the algebra of all bounded linear operators on H . For A ∈ B (H) , let σ ∗ (A) denote the semi-Fredholm domain, the Fredholm domain or the Weyl domain of A in the spectrum, σ(A). We characterize the form of a map ϕ from B (H) into itself with range contains the operators of rank at most two and satisfies σ ∗ (ϕ (A) ϕ (B) ∗) = σ ∗ (A B ∗) for all A , B ∈ B (H). We also describe those maps on B (H) preserving the same spectral set σ ∗ (.) 'but of Jordan skew-triple product' A B ∗ A 'of operators'. [ABSTRACT FROM AUTHOR]

The aim was to assess the association between fetal growth restriction (FGR) and fetal heart rate variability (FHRV) in relation to fetal movements. A prospective observational cohort study was performed. Non‐invasive fetal electrocardiography (NI‐FECG) allowed beat‐to‐beat assessments with <5% corrections of RR intervals. FHRV analyses included: Root mean square of successive RR interval differences (RMSSD), high frequency power (HF power), and low frequency power (LF power). Fetal movements were categorized by continuous ultrasound scanning. We enrolled 36 singleton pregnant women expecting a small fetus (< the 2.3 percentile of mean weight for gestational age) diagnosed by ultrasound, of whom 25 presented with a birthweight < the 2.3 percentile. Among these, 11 were excluded due to low quality NI‐FECG recordings, leaving 14 women with 28 recordings eligible for inclusion in the analyses. The control group consisted of 22 healthy fetuses with birthweights between the 10th and the 90th percentile (average for gestational age [AGA]). In FGR fetuses the HRV response to respiratory activity was comparable to that of AGA fetuses. RMSSD (Ratio 1.54 [95% CI: 1.33; 1.79]) and HF power (Ratio 2.88 [95% CI: 2.12; 3.91]) increased, whereas LF/HF power (Ratio: 0.44 [95% CI: 0.31;0.63]) decreased. However, during fetal quiescence, FGR fetuses differed significantly from AGA fetuses. Compared to AGA fetuses, FGR fetuses displayed lower RMSSD (Ratio 0.77 (95% CI: 0.58; 1.02)) and HF power (Ratio 0.56 (95% CI:0.32; 0.98)). This reduction was associated with the severity of the FGR. In conclusion, FGR fetuses displayed a respiratory sinus arrhythmia (RSA) comparable to AGA fetuses; however, more important, parameters representing cardiac vagal activity were impaired in FGR fetuses during quiescence. RSA may constitute an intrinsic function of the cardiovascular system, which is unaffected by fetal compromise. However, the basic cardiac outflow assessed during fetal quiescence indicates a suppressed cardiac vagal activity in the FGR fetuses. [ABSTRACT FROM AUTHOR]

A semianalytic single-level fast direct solver (FDS) is presented for the method-of-moments (MoM) analysis of large planar antenna arrays with up to few thousands of complex elements on current desktop computers. Assuming a partition of the impedance matrix, the proposed scheme factorizes the near-field blocks via a singular value decomposition (SVD)-based low-rank approximation and the intermediate-field blocks via an analytical inhomogeneous plane-wave (IPW) expansion. The near- and intermediate-field bases are then unified to leverage the Woodbury formula for the inversion. The solutions for the excitation of each array ports are obtained at once with $O(N^{15/7} \ln ^{3} N)$ computational cost and $O(N^{11/7} \ln N)$ memory for array problems with $N$ basis functions. The complexities are traced precisely and the error is controlled by means of analytical formulas for the required number of IPWs. The FDS is also combined with a macrobasis function (MBF) approach to deal with antenna geometries containing many subwavelength details. This article includes simulations of regular arrays of about $169^{2}~3$ -D dipoles and an irregular array composed of seven stations of the low-frequency square kilometer array (SKA) telescope comprising each 256 log-periodic (LP) antennas. The proposed FDS allows the analysis of the coupling effect both within any one station but also between the stations of the telescope, a size and complexity of problem which has not been possible with existing published techniques. [ABSTRACT FROM AUTHOR]

In this paper a generalized formulation for the spectral domain Green's functions of unit current sources embedded within a multilayer stack is presented. The current source can be either electric or magnetic. It can be oriented either parallel to the layers or perpendicular to them. The electric and magnetic fields due to these generalized sources are calculated. The proposed technique utilizes inward and outward recurrence processes in order to solve for the desired quadruple-dyadic Green's functions. It requires the calculation of 6 spectral coefficients only, from which all types of spectral Green's functions can be calculated. The proposed formulation is written such that the electromagnetic fields are directly obtained in terms of the current sources rather than the vector and scalar potentials with no explicit analogy with transmission lines. The dependencies on the z-coordinates of the source and field points are expressed explicitly, which is important for Volume Integral Equation (VIE) formulation. The proposed generalized formulation is applied on a number of plasmonic layer structures such as Insulator/Metal/Insulator (IMI), Metal/Insulator/Metal (MIM), and five-layer plasmonic/dielectric layer structure. The poles of the spectral domain Green's functions are linked to the Surface Plasmon Polaritons (SPPs), i.e., surface wave modes, associated with the source-free layer structure. The spectral Green's functions calculated using the proposed generalized technique are also used by an in-house Method of Moments (MoM) solver. The results of this solver are compared with those obtained by a full-wave commercial software.

Abstract The aim was to assess the association between fetal growth restriction (FGR) and fetal heart rate variability (FHRV) in relation to fetal movements. A prospective observational cohort study was performed. Non‐invasive fetal electrocardiography (NI‐FECG) allowed beat‐to‐beat assessments with

Recently, as the science of materials has greatly advanced, the achieved results have changed the conventional vision of the intrinsic properties of materials such as chiral and metamaterial. An important class of existing microwave devices takes advantage of the bianisotropic materials phenomena and properties for the development of innovative devices that respond to the needs of modern technologies. In this scope, we have investigated the bianisotropic Tellegen medium used as a substrate for a printed dipole antenna; a complex material that is less addressed in the literature. Numerical studies are based on the development of the spectral Green's functions and the method of moments is used to solve for the electromagnetic field components and the dipole input impedance. The behavior of the magnetoelectric elements of the Tellegen medium is highlighted by analyzing their effect on the electromagnetic field distribution and input impedance. Initial results reveal a negative real part of the dipole input impedance for some values of the magnetoelectric elements. A result that should be viewed in the light of unusual behavior of synthetic materials such as negative refractive index in metamaterials. An elementary explanation for this behavior is presented based on the analysis of the electromagnetic field distribution. [ABSTRACT FROM AUTHOR]

In this paper a generalized formulation for the spectral domain Green's functions of unit current sources embedded within a multilayer stack is presented. The current source can be either electric or magnetic. It can be oriented either parallel to the layers or perpendicular to them. The electric and magnetic fields due to these generalized sources are calculated. The proposed technique utilizes inward and outward recurrence processes in order to solve for the desired quadruple-dyadic Green's functions. It requires the calculation of 6 spectral coefficients only, from which all types of spectral Green's functions can be calculated. The proposed formulation is written such that the electromagnetic fields are directly obtained in terms of the current sources rather than the vector and scalar potentials with no explicit analogy with transmission lines. The dependencies on the z-coordinates of the source and field points are expressed explicitly, which is important for Volume Integral Equation (VIE) formulation. The proposed generalized formulation is applied on a number of plasmonic layer structures such as Insulator/Metal/Insulator (IMI), Metal/Insulator/Metal (MIM), and five-layer plasmonic/dielectric layer structure. The poles of the spectral domain Green's functions are linked to the Surface Plasmon Polaritons (SPPs), i.e., surface wave modes, associated with the source-free layer structure. The spectral Green's functions calculated using the proposed generalized technique are also used by an in-house Method of Moments (MoM) solver. The results of this solver are compared with those obtained by a full-wave commercial software. [ABSTRACT FROM AUTHOR]

Spectral-domain resonances for cavities formed by two distributed Bragg reflectors (DBRs) were analyzed theoretically and experimentally. We model the reflectance and transmittance spectra of the cavity at the normal incidence of light when DBRs are represented by a one-dimensional photonic crystal (1DPhC) comprising six bilayers of TiO 2 /SiO 2 with a termination layer of TiO 2 . Using a new approach based on the reference reflectance, we model the reflectance ratio as a function of both the cavity thickness and its refractive index (RI) and show that narrow dips within the 1DPhC band gap can easily be resolved. We revealed that the sensitivity and figure of merit (FOM) are as high as 610 nm/RIU and 938 RIU − 1 , respectively. The transmittance spectra include narrow peaks within the 1DPhC band gap and their amplitude and spacing depend on the cavity's thickness. We experimentally demonstrated the sensitivity to variations of relative humidity (RH) of moist air and FOM as high as 0.156 nm/%RH and 0.047 %RH − 1 , respectively. In addition, we show that, due to the transmittance spectra, the DBRs with air cavity can be employed as spectral filters, and this is demonstrated for two LED sources for which their spectra are filtered at wavelengths 680 nm and 780 nm, respectively, to widths as narrow as 2.3 nm. The DBR-based resonators, thus, represent an effective alternative to both sensors and optical filters, with advantages including the normal incidence of light and narrow-spectral-width resonances. [ABSTRACT FROM AUTHOR]

The aim of this paper is to present an analytical study for the investigation of the reciprocal metamaterial gyro-bianisotropy effects on the input impedance of a dipole antenna. This study is based on the numerical resolution, using the spectral method of moments (SMoM), of the integral equation developed through the mathematical derivation of the appropriate spectral Green's functions of the studied dipole configuration. The original obtained results are discussed and showed good agreements with the isotropic studied cases available in published literature. It is found that the imaginary valued magnetoelectric elements (chiral medium) exhibit an inverse effect on the resonant length compared to purely real elements (Tellegen medium), while negative elements decrease the input impedance. Combination of the two cases has led to more general complex media with further inspiring features. [ABSTRACT FROM AUTHOR]

• We develop a method to integrate GNSS and GRACE data within the spectral domain. • We detect 80 % of Yangtze River Basin floods using joint water mass change estimates. • Hydrologic changes in the Yangtze River Basin respond to different climate patterns. We develop a joint inversion method in the spectral domain that accounts for different signal characteristics in Global Navigation Satellite System (GNSS) and Gravity Recovery and Climate Experiment (GRACE) observations for quantifying terrestrial water storage (TWS) changes in the Yangtze River Basin (YRB). The method seamlessly integrates these geodetic datasets with distinct spatial scales and coverages. We exploit the Slepian basis functions, being spectrally band-limited and spatially concentrated, to put these datasets together in the regional TWS modeling. Our integrated geodetic results reveal variable spatiotemporal patterns of water storage changes within the YRB, hydrological extremes, and their linkage to interannual climate variability. The results indicate that annual precipitation in the middle and lower YRB is twice of that in the Jinsha River Basin (the uppermost basin of YRB), yet the TWS change is less than a half. This large discrepancy in the ratio of water storage and precipitation can be attributed to substantial runoff in the middle and lower YRB. The joint geodetic inversion identifies extreme droughts and flood events in the basin, consistent with the assessments from precipitation anomalies and Global Flood Awareness System. We also find that interannual TWS variations in the Jinsha River Basin are modulated by Indian Ocean Dipole, while those in the upper YRB and middle and lower YRB are modulated by El Niño-Southern Oscillation. Our findings highlight the potential use of geodetic data combination to advance hydrological variabilities in the region and inform water resource management strategies in response to climate change. [ABSTRACT FROM AUTHOR]

This paper deals with the mathematical expressions called Sommerfeld integrals. Introduced by A. Sommerfeld in 1909, they are mathematically equivalent to inverse Hankel transforms. The original historical goal of these integrals was to provide an accurate mathematical description of the electromagnetic phenomena involved in long-distance wireless radio and telegraphy. However, their scope was quickly enlarged thanks to the so-called spectral-domain stratified theory, and now they are ubiquitous in the mathematical models associated to many electromagnetic technologies, ranging from EMC lightning modelization and ground penetrating radar to optical and plasmonic integrated devices and going through the familiar microwave and millimeter-wave planar structures using printed circuit technology. In all these areas, Sommerfeld integrals can provide direct evaluations of the involved electromagnetic fields or they can be used as Green's functions in the frame of integral equation formulations. Other disciplines involving stratified media, like seismology and geological prospection, also benefit from these integrals. After discussing the most canonical Sommerfeld integral, appearing in the so-called Sommerfeld identity, this paper reviews three classical structures, namely, the original Sommerfeld problem involving two semi-infinite media, and the microstrip and stripline geometries. It is shown that Sommerfeld integrals provide a unifying treatment of these three problems and that their mathematical features have a direct translation in terms of the physical properties exhibited by the electromagnetic fields that can exist in them.

Fetal heart rate variability (FHRV) reflects autonomic cardiac regulation. The autonomic nervous system constantly adjusts the heart rate to maintain homeostasis. By providing insight into the fetal autonomic state, FHRV has the potential to become an investigational and clinical instrument. However, the method needs standardization and the influence of fetal movements, including fetal respiratory movements, is not well explored. Therefore, in a highly standardized setting, the aim was to evaluate the association between fetal movements and fetal heart rate variability (FHRV) including their impact on reliability. Fetal heart rate was obtained by noninvasive fetal electrocardiography (NI‐FECG) and fetal movements by simultaneous ultrasound scanning in 30 healthy singleton pregnant women on two occasions with a maximum interval of 7 days. The standard deviation of normal‐to‐normal RR‐intervals (SDNN), root mean square of successive RR‐interval differences (RMDDS), high‐frequency power (HF‐power), low‐frequency power (LF‐power), and LF/HF were measured. A multivariate mixed model was used and reliability was defined as acceptable by a coefficient of variance (CV) ≤15% and an intraclass correlation coefficient (ICC) ≥0.80. During time periods with fetal respiratory movements, the highest reliability was achieved. Intra‐ and inter‐observer reliability measurements were very high (CV: 0–9%; ICC ≧ 0.86). Within the same recording, SDNN and RMSSD achieved acceptable reliability (CV: 14–15%; ICC ≧ 0.80). However, day‐to‐day reliability displayed high CV's. In time periods with fetal respiratory movements, as compared to periods with quiescence RMSSD and HF‐power were higher (Ratio: 1.33–2.03) and LF/HF power lower (Ratio: 0.54). In periods with fetal body movements SDNN, RMSSD and HF‐power were higher (Ratio: 1.27–1.65). In conclusion, time periods with fetal respiratory movements were associated with high reliability of FHRV analyses and the highest values of parameters supposed to represent vagal activity. [ABSTRACT FROM AUTHOR]

In this work, we introduce a general method to deduce spectral functional equations in elasticity and thus, the generalized Wiener-Hopf equations (GWHEs), for the wave motion in angular regions filled by arbitrary linear homogeneous media and illuminated by sources localized at infinity. The work extends the methodology used in electromagnetic applications and proposes for the first time a complete theory to get the GWHEs in elasticity. In particular, we introduce a vector differential equation of firstorder characterized by a matrix that depends on the medium filling the angular region. The functional equations are easily obtained by a projection of the reciprocal vectors of this matrix on the elastic field present on the faces of the angular region. The application of the boundary conditions to the functional equations yields GWHEs for practical problems. This paper extends and applies the general theory to the challenging canonical problem of elastic scattering in angular regions. [ABSTRACT FROM AUTHOR]

Anomalies in remote sensing images are generally reflected in two aspects of spatial and spectral ones, as for the anomaly detection of sea surface using multispectral or hyperspectral images, spectral information is more important. To this end, a novel spectral anomaly detection method based on dictionary optimization is proposed in this letter. More specifically, the normal scene is first defined to distinguish the anomaly. Then, without any assumption about the distribution of anomaly, a spectral dictionary is formulated and derived theoretically with optimization to express the normal scenes. Using the sparse and low-rank constraints, the alternating direction method of multiplier (ADMM) is employed to solve the above optimization in the spectral domain. Finally, for a given sea-surface image to be detected, the error matrix that cannot be fully expressed by the optimized spectral dictionary is regarded as anomalies. It shows certain generality for various kinds of spectral anomalies on the sea surface. Taking multispectral images obtained by the HY-1C satellite as an example, comparisons with related state-of-the-art methods demonstrate that our proposed method achieves the best anomaly detection performance not only for oil-spill pollution but also for algae pollution. [ABSTRACT FROM AUTHOR]

Recently, super-resolution has been intensively studied only on upscaling models with integer magnification. However, the need to expand arbitrary magnification is emerging in representative application fields of actual super-resolution, such as object recognition and display image quality improvement. In this paper, we propose a model that can support arbitrary magnification by using the weights of the existing integer magnification model. This model converts super-resolution results into the DCT spectral domain to expand the space for arbitrary magnification. To reduce the loss of high-frequency information in the image caused by the expansion by the DCT spectral domain, we propose a high-frequency attention network for arbitrary magnification so that this model can properly restore high-frequency spectral information. To recover high-frequency information properly, the proposed network utilizes channel attention layers. This layer can learn correlations between RGB channels, and it can deepen the model through residual structures. [ABSTRACT FROM AUTHOR]

Introduction: Optical coherence tomography (OCT) is used to study retinal structure in schizophrenia. Changes in retinal structure, especially the retinal nerve fiber layer (RNFL) has been correlated with psychotic disorders. Measurement variability is a concern since there are various generations of OCT devices. We investigated the inter- and intra-device agreement of macular thickness between spectral domain (SD−OCT) and swept source−OCT (SS−OCT), and compared macula and peripapillary group differences in schizophrenia using SS−OCT. Methods: Macular OCT thickness was obtained for schizophrenia (SZ, n = 30) and healthy controls (HC, n = 22) subjects using SD−OCT (Heidelberg Spectralis) and SS−OCT (DRI Topcon Triton). Peripapillary thickness was obtained using SS−OCT. RNFL, ganglion cell-inner plexiform complex (GCL+), RNFL plus GCL+ (GCL++), and macular thickness were collected. Clinical and cognitive data were gathered. All statistical analyses were performed using R software. Results: There was excellent inter-scanner agreement for GCL + and GCL++ with ICC’s between r = 0.92−0.99. Good-to-excellent intra-scanner (OD vs OS) agreement was present except for macular RNFL in the SS−OCT device. No significant peripapillary group differences were identified. Poorer GAF scores were correlated with thinner macular layers and thinner overall peripapillary retinal layer. Greater mania symptoms were associated with smaller peripapillary GCL + thickness (r=-0.43, p = 0.03). Poor overall cognition (Brief Assessment of Cognition in Schizophrenia) was associated with smaller overall peripapillary retinal thickness (r = 0.36, p = 0.02). Conclusion: While there is RNFL variability, GCL + and GCL++ are comparable between scanners SD−OCT and SS−OCT. Given that RNFL thinning is strongly implicated in psychotic disorders, the use of OCT scanners should not be interchanged due to increased RNFL measurement variability.

In this paper, we introduce a novel time-averaged sampling method that can be used in a low-cost, camera-based, line-field, spectral domain optical coherence tomography (SD-OCT) device. We demonstrate that when used with an automated subtraction and magnitude based averaging scheme that is analogous to lock-in detection, this method can enhance the usually poor dynamic range and SNR. The technique is unique as it effectively eliminates arbitrarily located, arbitrarily strong autocorrelation artifacts, and is robust against blemishes in the camera or the reference mirror. We show through experiment, theory and simulations that a judicious choice of the Fourier transform window function, and one of the two proposed variants of the averaging scheme can enhance the final image. B-scan images of a variety of samples, and facile 3D tomograms, acquired with a device built from off-the-shelf components, demonstrate the potential of making OCT devices for niche applications, at much reduced costs.

In this work, we introduce a general method to deduce spectral functional equations and, thus, the generalized Wiener–Hopf equations (GWHEs) for wave motion in angular regions filled by arbitrary linear homogeneous media and illuminated by sources localized at infinity with application to electromagnetics. The functional equations are obtained by solving vector differential equations of first order that model the problem. The application of the boundary conditions to the functional equations yields GWHEs for practical problems. This paper shows the general theory and the validity of GWHEs in the context of electromagnetic applications with respect to the current literature. Extension to scattering problems by wedges in arbitrarily linear media in different physics will be presented in future works. [ABSTRACT FROM AUTHOR]

Many physical datasets are generated by collections of instruments that make measurements at regular time intervals. For such regular monitoring data, we extend the framework of half‐spectral covariance functions to the case of nonstationarity in space and time and demonstrate that this method provides a natural and tractable way to incorporate complex behaviors into a covariance model. Further, we use this method with fully time‐domain computations to obtain bona fide maximum likelihood estimators—as opposed to using Whittle‐type likelihood approximations, for example—that can still be computed conveniently. We apply this method to very high‐frequency Doppler LIDAR vertical wind velocity measurements, demonstrating that the model can expressively capture the extreme nonstationarity of dynamics above and below the atmospheric boundary layer and, more importantly, the interaction of the process dynamics across it. [ABSTRACT FROM AUTHOR]

PurposeThe outer nuclear layer (ONL) contains photoreceptor nuclei, and its thickness is an important biomarker for retinal degenerations. Accurate ONL thickness measurements are obscured in standard optical coherence tomography (OCT) images because of Henle fiber layer (HFL). Improved differentiation of the ONL and HFL boundary is made possible by using directional OCT, a method that purposefully varies the pupil entrance position of the OCT beam.MethodsFifty-seven normal eyes were imaged using multiple pupil entry positions with a commercial spectral domain OCT system. Cross-sectional image sets were registered to each other and segmented at the top of HFL, the border of HFL and the ONL and at the external limiting membrane. Thicknesses of the ONL and HFL were measured and analyzed.ResultsThe true ONL and HFL thicknesses varied substantially by eccentricity and between individuals. The true macular ONL thickness comprised an average of 54.6% of measurements that also included HFL. The ONL and HFL thicknesses at specific retinal eccentricities were poorly correlated.ConclusionAccurate ONL and HFL thickness measurements are made possible by the optical contrast of directional OCT. Distinguishing these individual layers can improve clinical trial endpoints and assessment of disease progression.

Early diagnosis and treatment of glaucoma is important to reduce the risk of progressive and irreversible visual loss. The key to diagnosis is recognition of morphological changes to the optic nerve head and retinal nerve fiber layer, but in some patients, functional abnormalities are detected first. This review describes recent innovations with the potential to improve the early detection of glaucoma. Developments in imaging include novel optic nerve head metrics such as Bruch's membrane opening-minimum rim width, enhanced ability to quantify inner layers of the glaucomatous macula, and ability to image deep optic nerve head structures, including the lamina cribrosa. Developments in detection of early glaucomatous functional loss include novel perimetric tests using frequency-doubling technology and flicker-defined form stimuli. Methods to combine results of structural and functional assessments are also presented that may improve early detection of glaucoma.

Early diagnosis and treatment of glaucoma is important to reduce the risk of progressive and irreversible visual loss. The key to diagnosis is recognition of morphological changes to the optic nerve head and retinal nerve fiber layer, but in some patients, functional abnormalities are detected first. This review describes recent innovations with the potential to improve the early detection of glaucoma. Developments in imaging include novel optic nerve head metrics such as Bruch's membrane opening-minimum rim width, enhanced ability to quantify inner layers of the glaucomatous macula, and ability to image deep optic nerve head structures, including the lamina cribrosa. Developments in detection of early glaucomatous functional loss include novel perimetric tests using frequency-doubling technology and flicker-defined form stimuli. Methods to combine results of structural and functional assessments are also presented that may improve early detection of glaucoma.

Superconducting microwave circuits are composed of components made from superconducting microstrip transmission lines (SMTLs). The spatial features of the superconductors provide the system operation at high speed and low noise floor. However, coupling the external electromagnetic field in these systems reduces or nullifies their performance. This article presents a general solution for evaluating the electromagnetic behavior of multiconductor SMTLs under plane wave excitation. The analysis is portrayed in the spectral domain. Using the proposed approach, the electromagnetic susceptibility of the lines is evaluated for two proximity SMTLs. It is then investigated in different scenarios where the effect of film thickness, film spacing, and operating temperature is investigated. The study reveals that by increasing the film thickness or film spacing or decreasing the operating temperature, the lines’ susceptibility is increased. Further, it is shown that for small film spacing, the susceptibility dependency on temperature or film thickness of one line can affect the susceptibility of the other line. [ABSTRACT FROM AUTHOR]

The early detection of glaucoma is important in order to enable appropriate monitoring and treatment, and to minimize the risk of irreversible visual field loss. Although advances in ocular imaging offer the potential for earlier diagnosis, the best method is likely to involve a combination of information from structural and functional tests. Recent studies have shown it is possible to estimate the number of retinal ganglion cells from optical coherence tomography and standard automated perimetry, and to then pool the results to produce a combined structure-function index (CSFI). The CSFI represents the estimated percentage of retinal ganglion cells lost compared to an age-matched healthy eye. Previous studies have suggested that the CSFI is better able to detect glaucoma than isolated measures of structure and function, and that it performs well even in preperimetric glaucoma. The purpose of this review is to describe new strategies, such as the CSFI, that have the potential to improve the early detection of glaucoma. We also describe how our ability to detect early glaucoma may be further enhanced by incorporating demographic risk factors, clinical examination findings, and imaging and functional test results into intuitive models that provide estimates of disease probability.

Abstract Background This comparative study aimed to demonstrate the differences between swept source OCT (SS-OCT) (1310 nm) and spectral domain OCT (SD-OCT) (840 nm) for the identification and measurement of anterior chamber angle (ACA) structures. Methods Sixty seven eyes from 67 healthy subjects underwent ACA imaging at the nasal and temporal sides using SS-OCT and SD-OCT with different wavelength (Tomey, 1310 nm and RTvue, 840 nm). Images were evaluated for the ability to distinguish angle structures including the Schwalbe’s line (SL), the Schlemm’s canal (SC) and the scleral spur (SS). The length of trabecular meshwork (LTM), the angle-opening distance (AOD500 and AOD750) and the length of Schlemm’s canal (LSC) were also measured. Results The nasal identification rate for SL, SC and SS were 91.04%/89.55%, 50.75%/40.30% and 100.0%/74.63% (SS-OCT/SD-OCT), respectively. The temporal identification rate for SL, SC and SS were 86.57%/91.04%, 68.66%/70.15% and 100.0%/65.67% (SS-OCT/SD-OCT), respectively. Differences between SS-OCT and SD-OCT were found in terms of the visualization of the SS. With respect to the measurements of angle, the evaluation of LTM at the nasal side, LSC at the temporal side and AOD500/750 at both sides showed significant difference between the two devices. However, there existed good correlation between the AOD500/750 measured by SS-OCT and SD-OCT (Spearman’s rank correlation coefficient > 0.8, p

Nauman Hashmani, Sharif Hashmani, Asif Murad, Natasha Baig Department of Ophthalmology and Visual Sciences, Hashmanis Hospital, Karachi, Pakistan Purpose: The aim of this study was to assess the effects of age, gender, axial length and retinal thickness on the vascular density in a normal population using the Optovue optical coherence tomography angiography (OCT-A). Methods: A total of 209 eyes of 209 healthy subjects were scanned using the OCT-A on an outpatient basis. Patients were 20–75 years of age. The built-in software covered a 3×3 mm circle centered at the macula. The circle was divided into five sectors: a 1 mm central foveal circle and an upper, lower, nasal and temporal sector each spanning 1–3 mm away from the central circle. The vascular density (VD) at the superficial capillary plexus was measured, which spanned from the inner limiting membrane to the inner plexiform layer. Results: The fovea was the least dense area (32.5%±5.9%), and the temporal area was the densest (52.4%± 4.4%). Similarly, the fovea was the thinnest part of the retina (237.8±20.7 µm); however, the nasal sector was the thickest (308.5±15.1 µm). We found a correlation of the retinal thickness (r=0.541, P

Spectral-domain resonances for cavities formed by two distributed Bragg reflectors (DBRs) were analyzed theoretically and experimentally. We model the reflectance and transmittance spectra of the cavity at the normal incidence of light when DBRs are represented by a one-dimensional photonic crystal (1DPhC) comprising six bilayers of TiO2/SiO2 with a termination layer of TiO2. Using a new approach based on the reference reflectance, we model the reflectance ratio as a function of both the cavity thickness and its refractive index (RI) and show that narrow dips within the 1DPhC band gap can easily be resolved. We revealed that the sensitivity and figure of merit (FOM) are as high as 610 nm/RIU and 938 RIU−1, respectively. The transmittance spectra include narrow peaks within the 1DPhC band gap and their amplitude and spacing depend on the cavity’s thickness. We experimentally demonstrated the sensitivity to variations of relative humidity (RH) of moist air and FOM as high as 0.156 nm/%RH and 0.047 %RH−1, respectively. In addition, we show that, due to the transmittance spectra, the DBRs with air cavity can be employed as spectral filters, and this is demonstrated for two LED sources for which their spectra are filtered at wavelengths 680 nm and 780 nm, respectively, to widths as narrow as 2.3 nm. The DBR-based resonators, thus, represent an effective alternative to both sensors and optical filters, with advantages including the normal incidence of light and narrow-spectral-width resonances.

The method of analytical preconditioning combines the discretization and the analytical regularization of a singular integral equation in a single step. In a recent paper by the author, such a method has been applied to a spectral domain integral equation formulation devised to analyze the propagation in polygonal cross-section microstrip lines, which are widely used as high-speed interconnects in monolithic microwave and millimeter waves integrated circuits. By choosing analytically Fourier transformable expansion functions reconstructing the behavior of the fields on the wedges, fast convergence is achieved, and the convolution integrals are expressed in closed form. However, the coefficient matrix elements are one-dimensional improper integrals of oscillating and, in the worst cases, slowly decaying functions. In this paper, a novel technique for the efficient evaluation of such kind of integrals is proposed. By means of a procedure based on Cauchy integral theorem, the general coefficient matrix element is written as a linear combination of fast converging integrals. As shown in the numerical results section, the proposed technique always outperforms the analytical asymptotic acceleration technique, especially when highly accurate solutions are required. [ABSTRACT FROM AUTHOR]

PurposeTo report the results of imaging using high-resolution, Fourier domain anterior segment optical coherence tomography (AS-OCT) to evaluate patients with a type 1 Boston Keratoprosthesis (KPro).MethodsWe performed a retrospective comparative study of patients in whom we implanted the Boston KPro. A total of 26 eyes of 23 patients from the Cornea Service at the University of California Davis Eye Center were included. Subjects were evaluated with the Spectralis AS-OCT (Heidelberg Engineering GmbH).ResultsPreoperative diagnoses for KPro surgery included failed corneal transplant (69%), chemical burn (23%), and aniridia (8%). The average age of patients was 63.2 years (range, 17-88 years). Fifty-four percent of the patients were female. The mean duration between the KPro surgery and the acquisition of high-resolution AS-OCT imaging was 35.8 months (range, 2-90 months). The most commonly observed finding was retroprosthetic membrane formation, which we found in 77% of KPro eyes. In 65% of KPro eyes, we identified epithelium behind the front plate, and in 54%, we identified an epithelial lip over the anterior surface of the KPro front plate. In 31% of KPro eyes, we identified periprosthetic cysts, gaps or spaces, and thinning in the corneal carrier graft.ConclusionsFourier domain AS-OCT is a useful noninvasive imaging technique in patients with a KPro and provides the ability to identify changes that are sometimes difficult to appreciate by clinical evaluation. The higher resolution Fourier domain systems may aid in the clinical diagnosis and management of pathology that might not be imaged with instruments of lower resolution. AS-OCT has the potential for monitoring the anatomic stability of an implanted KPro and may also help to monitor for complications. Moreover, high-resolution imaging may enhance our understanding of periprosthetic anatomy.