Frequency Of Degeneration Research Articles

Prototype optical enhancement cavity for steady-state microbunching.

The innovative mechanism of steady-state microbunching (SSMB) promises a potent light source, featuring high repetition rate and coherent radiation. The laser modulator, comprising an undulator and an optical enhancement cavity, is pivotal in SSMB. A high-finesse prototype optical enhancement cavity for SSMB with an average power of 55 kW is described in this paper. Preliminary design of the laser modulator, experimental setup, and methods to address frequency degeneracy and power coupling issues are discussed. D-shaped mirrors are utilized to successfully suppress the modal instability. This study is the first to illustrate the finesse reduction caused by high-order mode damping during experiments. The experimental and simulation results match closely. A cavity power coupling model is established, and the experimental results verify the correctness of the coupling model. A method for estimating the absorption coefficient through thermal-induced evolution of cavity mode has been implemented. Experimental results demonstrate a high-average-power enhancement cavity with a finesse of 16 518 ± 103 and an estimated average absorption coefficient of 12 ppm for the cavity mirrors. The findings contribute to the advancement of SSMB by providing insights into the design and operation of high-power optical enhancement cavities.

On separability of semigroups: application to models of physics and discrete optimization

Nilpotent semigroups are used in various fields of physics to model processes like system decay in quantum mechanics, state transitions in statistical mechanics, and simplifying dynamical systems. They also assist in optimizing control processes. The set of nilpotent matrices forms a semigroup and plays a key role in Jordan decomposition, which has many physical applications. In quantum mechanics, the Jordan form helps analyze linear operators on Hilbert spaces, especially with systems involving eigenvalue multiplicities. In vibration analysis, it aids in studying normal modes of mechanical systems with degenerate frequencies. Additionally, Jordan decomposition simplifies control theory for linear time-invariant systems, stability analysis in dynamical systems, and the behavior of coupled oscillators, as well as solving systems of linear differential equations. Certainly, the semigroup theory has even more applications in theoretical computer science: suffice it to say, for example, that some authors identify semigroups and finite automata. In this paper, we address the problem of P-separability of semigroups with respect to three key predicates: equality-separability, divisibility-separability, and subsemigroup-separability, achieved through homomorphisms into a nilpotent semigroup. We present some significant results that advance the understanding of these concepts.

Persistence of Multiscale Degenerate Invariant Tori in Reversible Systems with Degenerate Frequency Mapping

Persistence of Multiscale Degenerate Invariant Tori in Reversible Systems with Degenerate Frequency Mapping

Estimation of Frequencies and Splitting of <sub>2</sub>S<sub>1</sub> and <sub>3</sub>S<sub>1</sub> Modes from the IGETS Superconducting Gravimeter Network Data after the 2013 Sea of Okhotsk Earthquake

For the first time, the 2S1 and 3S1 modes of the Earth’s free oscillations following the largest deep-focus earthquake in the Sea of Okhotsk on May 24, 2013, have been analyzed using the maximum likelihood method. Data from 14 superconducting gravimeters of the IGETS network deployed in the central part of Europe were used for the analysis. Estimates of the time of mode excitation after the earthquake origin time, degenerate frequencies, and mode splitting parameters are obtained.

Band flipping and bandgap closing in a photonic crystal ring and its applications

The size of the bandgap in a photonic crystal ring is typically intuitively considered to monotonically grow as the modulation amplitude of the grating increases, causing increasingly large frequency splittings between the "dielectric" and "air" bands. In contrast, here we report that as the modulation amplitude in a photonic crystal ring increases, the bandgap does not simply increase monotonically. Instead, after the initial increase, the bandgap closes and then reopens again with the two bands flipped in energy. The air and dielectric band edges are degenerate at the bandgap closing point. We demonstrate this behavior experimentally in silicon nitride photonic crystal microrings, where we show that the bandgap is closed to within the linewidth of the optical cavity mode, whose intrinsic quality factor remains unperturbed with a value ≈ 1×106. Moreover, through finite-element simulations, we show that such bandgap closing and band flipping phenomena exist in a variety of photonic crystal rings with varying unit cell geometries and cladding layers. At the bandgap closing point, the two standing wave modes with a degenerate frequency are particularly promising for single-frequency lasing applications. Along this line, we propose a compact self-injection locking scheme that integrates many core functionalities in one photonic crystal ring. Additionally, the single-frequency lasing might be applicable to distributed-feedback (DFB) lasers to increase their manufacturing yield.

The frequency degeneracy range of transverse mode in an off-axis end-pumped solid-state lasers

The frequency degeneracy range of transverse mode in an off-axis end-pumped solid-state lasers

Scattering matrix for chiral harmonic generation and frequency mixing in nonlinear metasurfaces

We generalize the concept of optical scattering matrix (S-matrix) to characterize harmonic generation and frequency mixing in planar metasurfaces in the limit of undepleted pump approximation. We show that the symmetry properties of such nonlinear S-matrix are determined by the metasurface symmetries at the macroscopic and microscopic scale. We demonstrate that for description of degenerate frequency mixing processes such as optical harmonic generation, the multidimensional S-matrix can be replaced with a reduced two-dimensional S-matrix. We show that for metasurfaces possessing specific point group symmetries, the selection rules determining the transformation of the reduced nonlinear S-matrix are simplified substantially and can be expressed in a compact form. We apply the developed approach to analyze chiral harmonic generation in nonlinear metasurfaces with various symmetries including rotational, inversion, in-plane mirror, and out-of-plane mirror symmetries. For each of those symmetries, we confirm the results of the developed analysis by full-wave numerical calculations. We believe our results provide a new paradigm for engineering nonlinear optical properties of metasurfaces which may find applications in active and nonlinear optics, biosensing, and quantum information processing.

Исследование отражения и прохождения волны через планарный слой кирального метаматериала, расположенного в прямоугольном волноводе с учетом материальной дисперсии

The work analyzes the diffraction of the fundamental wave of a rectangular waveguide on a planar layer of a chiral metamaterial located in a transverse plane. The mathematical model of the metamaterial takes into account its chirality and dispersion of material parameters. To connect the electromagnetic field vectors through the parameters of the chiral layer, two-sided approximate boundary conditions are used. Cross-polarization of the field is taken into account in the work. A system of linear algebraic equations for the reflection and transmission coefficients of the fundamental and cross-polarized waves was obtained in the work. It is shown that at the cutoff frequencies of the fundamental and cross-polarized waves are also excited in the waveguide. It is shown that at different levels of attenuation in the waveguide, situations arise when the degeneracy of resonant frequencies arises and disappears. It has been proven that the reflection and transmission of the fundamental wave at low attenuation values is of a frequency-selective resonant nature.

Higher-order fractal transverse modes observed in microlasers

Two classes of higher-order, fractal spatial eigenmodes have been predicted computationally and observed experimentally in microlasers. The equatorial plane of a close-packed array of microspheres, lying on one mirror within a Fabry-Pérot resonator and immersed in the laser gain medium, acts as a refractive slit array in a plane transverse to the optical axis. Edge diffraction from the slit array generates the high spatial frequencies (>104 cm−1) required for the formation of high-order laser fractal modes, and fractal transverse modes are generated, amplified, and evolve within the active medium. With a quasi-rectangular (4-microsphere) aperture, the fundamental mode and several higher-order eigenmodes (m = 2,4,5) are observed in experiments, whereas only the m = 1,2 modes are observed experimentally for the higher-loss resonators defined by triangular (3-microsphere) apertures. The fundamental and 2nd-order modes (m = 1,2) for the 4-sphere aperture are calculated to have qualitatively similar intensity profiles and nearly degenerate resonant frequencies that differ by less than <0.1% of the free-spectral range (375 GHz) but exhibit even and odd parity, respectively. For all of the observed fractal modes, the fractal dimension (D) rises rapidly beyond the intracavity aperture array as a result of the high spatial frequencies introduced into the mode profile. Elsewhere, D varies gradually along the resonator axis and 2.2 < D < 2.5. Generating fractal laser modes in an equivalent optical waveguide is expected to allow the realization of new optical devices and imaging protocols based on the spatial frequencies and variable D values available.

Gauge‐Flux‐Induced Anti‐Pt Phase Transitions for Extreme Control of Channel‐Drop Tunneling

AbstractParity‐time (PT) and anti‐parity‐time (anti‐PT) symmetries have provided important guiding principles in the research of non‐Hermitian physics. However, realizations of anti‐PT symmetry in photonic systems usually rely on optical nonlinearities and indirect‐coupling approaches. Here, they apply the channel interference principle mediated by synthetic gauge‐flux biasing in open‐cavity systems to construct anti‐PT symmetries. It is shown that a specific π‐flux biasing into a looped‐resonator array can force a frequency degeneracy between pairwise Bloch modes therein. By further coupling the array into two external waveguides with tailored positions of ports, the system near the degeneracy point can be described by an anti‐PT‐symmetric Hamiltonian. When a real gauge‐flux detuning is introduced, the system undergoes a spontaneous transition between anti‐PT and anti‐PT‐broken phases, through which the two extreme cases of complete channel‐drop tunneling and complete tunneling suppression can be switched. Finally, by superimposing a PT‐symmetric term onto the anti‐PT‐symmetric Hamiltonian via applying an imaginary gauge‐flux biasing, extreme channel‐drop amplifying effects can be further realized by exciting the “lasing” mode under the critical‐coupling condition. The work bridges the physical connection between synthetic gauge field and anti‐PT symmetry. This paradigm may also find many applications from optical routing, and switching to buffering and amplifying on a chip–scale platform.

Clinicopathological correlates in the frontotemporal lobar degeneration-motor neuron disease spectrum.

Amyotrophic lateral sclerosis (ALS) is a devastating motor neuron disease (MND) that shares a common clinical, genetic and pathologic spectrum with frontotemporal dementia (FTD). It is highly heterogeneous in its presentation and features. Up to 50% of patients with MND develop cognitive-behavioural symptoms during the course of the disease, meeting criteria for FTD in 10%-15% of cases. In the absence of a precise biomarker, neuropathology is still a valuable tool to understand disease nosology, reach a definite diagnostic confirmation and help define specific subgroups of patients with common phenotypic, genetic and biomarker profiles. However, few neuropathological series have been published, and the frequency of frontotemporal lobar degeneration (FTLD) in MND is difficult to estimate. In this work we describe a large clinicopathological series of MND patients, analysing the frequency of concurrent FTLD changes and trying to define specific subgroups of patients based on their clinical, genetic and pathological characteristics. We performed an observational, retrospective, multicentre case study. We included all cases meeting neuropathological criteria for MND from the Neurological Tissue Bank of the FRCB-IDIBAPS-Hospital Clínic Barcelona Biobank between 1994 and 2022, regardless of their last clinical diagnosis. While brain donation is encouraged in all patients, it is performed in very few, and representativeness of the cohort might not be precise for all patients with MND. We retrospectively reviewed clinical and neuropathological data and describe the main clinical, genetic and pathogenic features, comparing neuropathologic groups between MND with and without FTLD changes and aiming to define specific subgroups. We included brain samples from 124 patients, 44 of whom (35.5%) had FTLD neuropathologic features (i.e. FTLD-MND). Pathologic TDP-43 aggregates were present in 93.6% of the cohort and were more extensive (higher Brettschneider stage) in those with concurrent FTLD (P < 0.001). Motor symptom onset was more frequent in the bulbar region in FTLD-MND cases than in those with isolated MND (P = 0.023), with no differences in survival. We observed a better clinicopathological correlation in the MND group than in the FTLD-MND group (93.8% versus 61.4%; P < 0.001). Pathogenic genetic variants were more common in the FTLD-MND group, especially C9orf72. We describe a frequency of FTLD of 35.5% in our series of neuropathologically confirmed cases of MND. The FTLD-MND spectrum is highly heterogeneous in all aspects, especially in patients with FTLD, in whom it is particularly difficult to define specific subgroups. In the absence of definite biomarkers, neuropathology remains a valuable tool for a definite diagnosis, increasing our knowledge in disease nosology.

Spacetime quasiperiodic solutions to a nonlinear Schrödinger equation on Z

We consider a discrete non-linear Schrödinger equation on Z and show that, after adding a small potential localized in the time-frequency space, one can construct a three-parametric family of non-decaying spacetime quasiperiodic solutions to this equation. The proof is based on the Craig–Wayne–Bourgain method combined with recent techniques of dealing with Anderson localization for two-dimensional quasiperiodic operators with degenerate frequencies.

Genotypic and allelic frequencies of progressive rod-cone degeneration and other main variants associated with progressive retinal atrophy in Italian dogs.

Progressive retinal atrophy (PRA) is a group of canine inherited retinal disorders affecting up to 100 breeds. Genetic tests are available. The aim of this study was to retrospectively evaluate the genetic variants associated with PRA among dogs residing in Italy. Genetic data of 20 variants associated with different forms of PRA were collected through DNA tests over a 10-year period for several dog breeds in the Italian canine population. Allelic and genotypic frequencies were calculated. A total of 1467 DNA tests were conducted for 1180 dogs. Progressive rod-cone degeneration (PRCD) was the most tested form of PRA, with 58.15% (n = 853) of the DNA tests. Among the widespread breeds in Italy, Labrador retrievers and toy poodles showed a prevalence of heterozygous carriers higher than 15%. Among the others, 175 DNA tests for golden retrievers (GR) showed a prevalence of heterozygous carriers of 13.04% (n = 12) for GR-PRA1 and 8.43% (n = 7) for GR-PRA2. The zwergschnauzer breed was tested for the type B and/or the type B1 forms of PRA with 25.32% (n = 20) heterozygous carriers and 0%, respectively. The study offers an overview of the prevalence of PRCD and other PRA forms within some of the most popular breeds in Italy.

Chirality reversal of resonant modes in GdFe ferrimagnets

Chirality of antiferromagnetic spin waves as an intrinsic degree of freedom has been attracting considerable attention due to its potential applications for magnonic devices. In this paper, atomistic-scale dynamics simulations were conducted to investigate the chirality of spin wave resonant modes in ferrimagnetic alloy GdxFe1−x (0 &amp;lt; x &amp;lt;1) under different proportion x and external magnetic fields near the angular momentum compensation point. Simulation results reveal that as the proportion of Gd increases, the resonance mode of spin waves undergoes two distinct handedness flipping at magnetization compensation point and angular momentum compensation point. When the proportion x deviates from the magnetization compensation point, a frequency degeneracy point emerges at a non-zero magnetic field, indicating that the chirality of spin waves can also be switched by an external magnetic field. A theoretical analysis is developed to explain the observed phenomena. These findings provide valuable insights into the control and manipulation of spin wave chirality in ferrimagnetic alloys, with potential implications for the development of spin-based devices and technologies.

Noise resilient exceptional-point voltmeters enabled by oscillation quenching phenomena

Exceptional point degeneracies (EPD) of linear non-Hermitian systems have been recently utilized for hypersensitive sensing. This proposal exploits the sublinear response that the degenerate frequencies experience once the system is externally perturbed. The enhanced sensitivity, however, might be offset by excess (fundamental and/or technical) noise. Here, we developed a self-oscillating nonlinear platform that supports transitions between two distinct oscillation quenching mechanisms – one having a spatially symmetric steady-state, and the other with an asymmetric steady-state – and displays nonlinear EPDs (NLEPDs) that can be employed for noise-resilient sensing. The experimental setup incorporates a nonlinear electronic dimer with voltage-sensitive coupling and demonstrates two-orders signal-to-noise enhancement of voltage variation measurements near NLEPDs. Our results resolve a long-standing debate on the efficacy of EPD-sensing in active systems above self-oscillating threshold.

Ab initio study of electric field effects on phonon vibrations in tetragonal ZrO2

The effects of external electric fields on phonon-associated phenomena, such as phase transformation and diffusion in ZrO2 ceramics, have been reported from recent experiments. This study examined the effects of external direct current (DC) electric fields on the phonon vibration properties in a tetragonal ZrO2 unit cell based on the density-functional perturbation theory. Phonon dispersions and densities of states were analyzed with optimized structures under varying external DC electric fields up to 45 mV/Å. The field sensitivities of phonon characteristics exhibited significant orientation dependence and were attributed to ionic polarization associated with symmetry breaking in dielectric properties. Optical phonons showed considerable field sensitivities particularly near the Brillouin zone boundaries, such as in the M (π/a, π/a, 0) to X (0, π/a, 0) and A (π/a, π/a, π/c) to R (0, π/a, π/c) directions, where doubly degenerate phonon frequencies exhibited splitting behaviors associated with the symmetry breaking between two unique oxygen atoms in the original unit cell. In contrast, transversal acoustic phonons demonstrated a softening trend with increasing field strengths around the Z (0, 0, π/c) point, where imaginary and splitting frequencies were obtained under electric fields of &amp;gt;40 mV/Å, indicating the potential phase transformation from the tetragonal to orthorhombic symmetries under strong external electric fields.

Mucinous Degeneration on MRI After Neoadjuvant Therapy in Patients With Rectal Adenocarcinoma: Frequency and Association With Clinical Outcomes.

BACKGROUND. Patients with nonmucinous rectal adenocarcinoma may develop mucinous changes after neoadjuvant chemoradiotherapy, which are described as mucinous degeneration. The finding's significance in earlier studies has varied. OBJECTIVE. The purpose of this study was to assess the frequency of mucinous degeneration on MRI after neoadjuvant therapy for rectal adenocarcinoma and to compare outcomes among patients with nonmucinous tumor, mucinous tumor, and mucinous degeneration on MRI. METHODS. This retrospective study included 201 patients (83 women, 118 men; mean age, 61.8 ± 2.2 [SD] years) with rectal adenocarcinoma who underwent neoadjuvant chemoradiotherapy followed by total mesorectal excision from October 2011 to November 2015, underwent baseline and restaging rectal MRI examinations, and had at least 2 years of follow-up. Two radiologists independently evaluated MRI examinations for mucin content, which was defined as T2 hyperintensity in the tumor or tumor bed, and resolved differences by consensus. Patients were classified into three groups on the basis of mucin status: those with nonmucinous tumor (≤ 50% mucin content on baseline and restaging examinations), those with mucinous tumor (> 50% mucin content on baseline and restaging examinations), and those with mucinous degeneration (≤ 50% mucin content on baseline examination and > 50% content on restaging examination). The three groups were compared. RESULTS. Interreader agreement for mucin content, expressed as a kappa coefficient, was 0.893 on baseline MRI and 0.890 on restaging MRI. Of the 201 patients, 156 (77.6%) had nonmucinous tumor, 34 (16.9%) had mucinous tumor, and 11 (5.5%) had mucinous degeneration. Mucin status was not significantly associated with complete pathologic response (p = .41) or local or distant recurrence (both p > .05). The death rate during follow-up was not significantly different (p = .21) between patients with nonmucinous tumor (23.1%), those with mucinous tumor (29.4%), and those with mucinous degeneration (9.1%). In adjusted Cox regression analysis, with mucinous degeneration used as reference, the HR for the overall survival rate for the mucinous tumor group was 4.7 (95% CI, 0.6-38.3; p = .14), and that for the nonmucinous tumor group was 8.0 (95% CI, 0.9-59.9; p = .06). On histopathologic assessment, all 11 patients with mucinous degeneration showed acellular mucin, yet 10 of 11 patients showed viable tumor (i.e., in nonmucinous portions of the tumors). CONCLUSION. Mucinous degeneration on MRI is not significantly associated with pathologic complete response, recurrence, or survival. CLINICAL IMPACT. Mucinous degeneration on MRI is uncommon and should not be deemed an indicator of pathologic complete response.

Prevalence and Predictive Factors of Early Degeneration of Bioprosthetic Mitral Valves: A Single-Center Cohort Study

Background. Bioprosthetic mitral valves (MV) have limited durability. Dysfunction and degeneration of these valves can lead to reoperation and progressive heart failure. We investigated the frequency and predictors of MV bioprosthesis early degeneration within three years following MV replacement surgery. Methods. In this retrospective cohort study, we retrieved the data of consecutive patients who underwent bioprosthetic MV replacement through midsternotomy at Tehran Heart Center between 2013 and 2019. Based on the reviewed parameters of the bioprosthetic MV in the follow-up echocardiography, the patients were divided into two groups to compare the variables respecting early degeneration. Finally, the predictors of early degeneration were recognized using the Cox regression hazards model. Results. We reviewed and analyzed data of 177 patients from our hospital database. The mean age of the patients was 63.9 ± 11.7 years and 100 (56.5%) were women. 39 (22.0%) patients had experienced early degeneration and two (1.1% of the total) had died during the follow-up period. Patients in the degeneration group tended to have a history of stroke and renal failure, although not statistically significant. The sole independent predictor of early degeneration of bioprosthetic MV was a high MV mean gradient in the first postoperative echocardiography study (HR = 11.01, 95% CI: 4.80–25.24; P &lt; 0.001 ). Conclusion. About 22.0% of our patients had echocardiographic criteria for early degeneration, and according to our results, increased MV gradients (without considering the reason) in the first postoperative echocardiography were the sole independent predictor for it. Careful valve selection can be essential in reducing early degeneration.

Is coronal imbalance in degenerative lumbar scoliosis patients associated with the number of degenerated discs? A retrospective imaging cross-sectional study

BackgroundDegenerative lumbar scoliosis (DLS) is a common degenerative disease of the spine, that predominates in the elderly, and causes spinal deformities along with severe pain and reduced quality of life. The relationship between DLS and degenerated discs is now a new direction of research. Our study aimed to the relationship between the imaging parameters of coronal imbalance and the number of degenerated discs in patients with degenerative lumbar scoliosis and analyzed the segmental distribution of the degenerated discs in patients with DLS.MethodsWe performed a retrospective analysis of the imaging of 40 patients who met the inclusion criteria who attended our outpatient clinic between April 2021 and July 2021, measuring the intervertebral space height of the AV (high side and low side), Cobb angle, and AVT (Apical vertebral translation) from coronal X-ray. Degenerated discs were evaluated by the Pfirrmann score based on T2-weighted magnetic resonance images. We record the number of degenerated discs (Graded as Grade III, Grade IV or Grade V by the Pfirrmann score) and the segments in which they are located. Finally, we explore the relationship between the imaging parameters of coronal imbalance and the number of degenerated discs in patients with DLS.ResultAmong the 40 patients with DLS in our study, all patients had degenerated discs in the lumbar spine, 95% of patients had degenerated discs(Pfirrmann score Grade III, Grade IV or Grade V) in 2 or more segments, with the L4-L5 segment being the most involved segment with the most degenerated discs, followed by the L3-L4 segment and the L5-S1 segment. There was no statistically significant relationship between the number of degenerated discs and the coronal imbalance in patients with DLS.ConclusionOur results showed an association between DLS and degenerated discs, but there was no statistically significant relationship between imbalance in the coronal plane of the lumbar spine and the number of degenerated discs in patients with DLS. The distribution of degenerated disc segments in patients with DLS showed a higher likelihood of disc degeneration in 2 or more segments, and a higher frequency of disc degeneration in the inferior disc and in the adjacent segments of the AV.

Kidney-Related Function of Mitochondrial Protein Mitoregulin.

A small protein, Mitoregulin (Mtln), localizes in mitochondria and contributes to oxidative phosphorylation and fatty acid metabolism. Mtln knockout mice develop obesity on a high-fat diet, demonstrating elevated cardiolipin damage and suboptimal creatine kinase oligomerization in muscle tissue. Kidneys heavily depend on the oxidative phosphorylation in mitochondria. Here we report kidney-related phenotypes in aged Mtln knockout mice. Similar to Mtln knockout mice muscle mitochondria, those of the kidney demonstrate a decreased respiratory complex I activity and excessive cardiolipin damage. Aged male mice carrying Mtln knockout demonstrated an increased frequency of renal proximal tubules' degeneration. At the same time, a decreased glomerular filtration rate has been more frequently detected in aged female mice devoid of Mtln. An amount of Mtln partner protein, Cyb5r3, is drastically decreased in the kidneys of Mtln knockout mice.