Dispersion Region Research Articles

Frequency-dependent and capacitive tissue electrical properties in spinal cord stimulation models.

Models of spinal cord stimulation (SCS) simulate the electric fields (E-fields) generated in targeted tissues, which in turn can predict physiological and then behavioral outcomes. Notwithstanding increasing sophistication and use in optimizing therapy, SCS models typically calculate E-fields using the quasi-static approximation (QSA). QSA, as implemented in neuromodulation models, neglects the frequency dispersion of tissue conductivity, as well as propagation, capacitive, and inductive effects on the E-field. The reliability of QSA specifically for SCS has not been considered in detail, especially for higher-frequency SCS. We implemented a frequency-dependent finite element method (FEM) and solved a high- resolution RADO-SCS model with voltage-controlled (VC) and current-controlled (CC) stimulation to assess the impact of frequency-dependent conductivity (dispersion) and permittivity of spinal tissues on E-fields generated at three different spinal column locations (epidural space, spinal cord, and root) for frequencies spanning from 1 Hz to 10 MHz. Results were compared with predictions of QSA method, with varied conductivity values of purely resistive tissues. We further assessed the impact of frequency-dependent and capacitive tissue properties on spinal heating and distortion of the E-field waveform. Tissue-specific electric properties around the energized leads and mode of stimulation-control impacted the magnitude of E-fields. In the spinal cord, the VC-SCS E-field generated with the frequency-dependent and capacitive properties was comparable to the QSA with 2X epidural fat conductivity, whereas the CC-SCS generated E-field was minimally impacted by frequency- dependent and capacitive properties up to 10 kHz. Spinal cord heating predicted by frequency- dependent and capacitive tissue properties was comparable to the QSA conditions with VC-SCS, whereas with CC-SCS, there was no impact of the frequency-dependent and capacitive tissue properties in spinal cord heating. E-field waveform distortion in the spinal cord, with CC-SCS at 1 kHz-specific electrical properties, was significant when fat capacitance (permittivity) was increased by 10X, whereas with VC-SCS, there was no effect of tissue capacitance. Regardless of the mode of SCS, QSA was still valid in predicting SCS-induced E-field and heating at the spinal tissues- across α and β dispersion region of spinal tissue's dielectric spectrum for VC-SCS and up to 10 kHz for CC-SCS.

Multi-octave two-color soliton frequency comb in integrated chalcogenide microresonators

Mid-infrared (MIR) Kerr microcombs are of significant interest for portable dual-comb spectroscopy and precision molecular sensing due to strong molecular vibrational absorption in the MIR band. However, achieving a compact, octave-spanning MIR Kerr microcomb remains a challenge due to the lack of suitable MIR photonic materials for the core and cladding of integrated devices and appropriate MIR continuous-wave (CW) pump lasers. Here, we propose a novel slot concentric dual-ring (SCDR) microresonator based on an integrated chalcogenide glass chip, which offers excellent transmission performance and flexible dispersion engineering in the MIR band. This device achieves both phase-matching and group velocity matching in two separated anomalous dispersion regions, enabling phase-locked, two-color solitons in the MIR region with a commercial 2-μm CW laser as the pump source. Moreover, the spectral locking of the two-color soliton enhances pump wavelength selectivity, providing precise control over soliton dynamics. By leveraging the dispersion characteristics of the SCDR microresonator, we have demonstrated a multi-octave-spanning, two-color soliton microcomb, covering a spectral range from 1156.07 to 5054.95 nm (200 THz) at a −40 dB level, highlighting the versatility and broad applicability of our approach. And the proposed multi-octave MIR frequency comb is relevant for applications such as dual-comb spectroscopy and trace-gas sensing.Graphical

Optical properties of a hollow cylindrical quantum wire in a parallel applied magnetic field

In this theoretical study, we investigate optical properties of a hollow cylindrical quantum wire in the presence of a homogeneous magnetic field. The magnetic field is applied parallel to the axis of the quantum wire. The investigations were achieved by solving the Schrödinger equation within the effective mass approximation. The optical properties studied were absorption coefficient (AC) of electromagnetic radiation and changes in refractive index (CRI) of the hollow cylinder. The parallel applied magnetic field lifts the degeneracy of states of opposite angular momentum (the ±|m|\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\pm |m |$$\\end{document} states, m being the angular momentum quantum number) known as the Zeeman splitting. As such, in the presence of magnetic field, AC splits into two branches, one corresponding to a transition involving the positive m states and the other corresponding to a transition involving the negative m states. Increase in intensity of the electromagnetic radiation reduces the magnitude of the AC. Presence of inner radius of the hollow cylindrical wire lowers transition energies. Apart from absorption due to the (m=0→±1)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(m=0 \\rightarrow \\pm 1)$$\\end{document} transitions, the presence of the inner radius also facilitates absorption due the (m=-1→0)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(m=-1\\rightarrow 0)$$\\end{document} transition as the magnetic field strength increases, a phenomenon that does not happen in solid cylindrical quantum wires. The presence of the inner radius also enhances AC in strong magnetic field. Increase in intensity of the electromagnetic radiation affects the CRI (here considered up to third order), introducing a normal dispersion region in an otherwise anomalous region. The parallel magnetic field also splits the CRI depending on the sign of the m states involved in the transitions.

Analytical Spectral Semi-quantitative Dating Method of Printed Text Toner Using Raman Spectroscopy and the Fluorescence signal of Paper Sheet Cellulose

Abstract: The chemical processes that occur during the surface degradation of document paper under the influence of external factors were studied by Raman spectroscopy. The possibility of comparing the same processes occurring on clean free paper and under printed text toner letters is of interest. It is assumed that the transformation of cellulose can occur at different rates in the areas of paper exposed to direct atmospheric and light exposure and in the areas containing an intermediate layer of the toner. The most stable temporal changes occur in the region of C–C–C and C– C–O vibrations of glycosidic rings in the short-wavelength region of the Raman spectrum. Background: The main areas of research in the field of document dating, mainly focused on chromatographic methods. These methods are based on studying the dynamics of evaporation of volatile ink components. There is also a variety of chromatography techniques, including gas chromatography, ion chromatography, high performance liquid chromatography, thin layer chromatography and gas chromatography-mass spectrometry. This indicates the wide range of approaches and techniques used to determine the age of written materials. However, all these methods are used mainly during the first two years after writing the document details, which does not allow examining documents that are more than two years old. Methods: Raman spectroscopy was used as the main research method. The object of the study was sheets of white A4 paper with printed text printed on them, produced on a laser printer. The subject of the study was areas of paper free of text, as well as areas of paper under toner. The integrated fluorescence of a paper optical brightener based on stilbene was studied in the wavelength range of 400–500 nm. Also, all objects were studied using optical microscopy. Results: The comparison of peak intensity values averaged over 10 brands over the years made it possible to reveal the following regularities: – the ratio of peaks in the paper spectra from which the toner was removed is greater than in the blank paper spectra, and the difference becomes less noticeable as the age of the paper decreases. The ratio of the intensity of the 330 cm-1 peak to the intensity of the 1603 cm-1 peak: the older the document becomes, the lower the average ratios of these peaks in both the blank paper spectra and in the spectra of paper from which the toner has been removed. –the intensity of the peak in the region of 280 cm-1 and 1 086 cm-1 of the Raman shift increases with decreasing the age of the toner-free paper.– a gradual increase in the intensity of the 380 cm-1 peak is observed when comparing the paper samples from which the toner was removed for 2016, 2018, 2020, and 2022. Regularity was also found in the change in the ratio of the average statistical values of the peak at 280 cm-1 in the spectra of the paper under the toner to a similar peak in the spectra of the paper free from text: the value of this ratio decreases with decreasing the paper age. At the same time, the paper fluorescence signal is an informative parameter that makes it possible to establish some facts from the document’s history. With artificial document aging, a significant broadening of the dispersion region and the appearance of its “splitting” into two or three strata are observed in the distribution of the fluorescence signal level of a paper sheet relative to the average value. The average fluorescence signal of a naturally aged sheet decreases with the age of the document. Conclusion: As a result of research, it has been established that Raman spectroscopy can be successfully used as a method for dating documents. When comparing the degree of degradation of the surface of open areas of paper and areas protected by toner of printed text, different effects of external factors on these areas were established, leading to different rates of degradation processes. The use of Raman peak intensity ratios for paper components in exposed areas compared to peaks under printed text further expands the methodology. The emphasis on spectral methods, in particular fluorescence signal distribution and Raman spectroscopy, to detect surface changes is well justified. It demonstrates a holistic approach to document analysis, taking into account both the chemical changes observed using Raman spectroscopy and the fluorescence signal distribution that may indicate signs of artificial aging through light exposure. This combination of methods appears to be reliable for assessing the age of documents and can make significant contributions to the field of forensic document examination.

A comprehensive study on geometric shape optical soliton solutions to the time-factional nonlinear Schrödinger-Hirota equation

In this study, we investigate the analytical soliton solutions of a fundamental model, namely the nonlinear Schrödinger-Hirota equation, in the context of beta time-fractional derivative. We adopt the (ω′/ω, 1/ω)-expansion method, which is a reliable and straightforward approach to extract fresh and general soliton solutions in terms of hyperbolic, trigonometric, and rational functions. The solitons include anti-kink, anti-bell-shaped, bell-shaped, and periodic solitons. These solitons have significant applications in various scientific fields, such as optical fiber communications, signal processing, plasma physics, and trans-oceanic data transfer. This study demonstrates the significance of fractional-order differentiation in revealing new solitons. We also provide a comprehensive comparison with existing literature in normal and anomalous dispersion regions, highlighting the uniqueness of the solutions. Moreover, the graphical representations are used to illustrate the properties and potential applications of these solitons. This research might contribute to the advancement of nonlinear optical research and technology.

On the dependence of the thermal module of elasticity of a two-component magnetic fluid on frequency, concentration and magnetic field

Purpose. Study of the dependence of the thermal modulus of elasticity of a two-component magnetic fluid on the magnitude of the magnetic field strength, the frequency of external disturbance and the volumetric concentration of magnetic particles.Method. The research method is based on the kinetic theory of liquid systems. Based on previously constructed kinetic equations for one-particle and two-particle distribution functions and a microscopic expression for the heat flux vector, an explicit dynamic expression for the thermal modulus of elasticity of magnetic fluids is obtained. In fast processes in liquids, heat transfer occurs in waves and their propagation is similar to the propagation of second sound in helium II. The thermal modulus of elasticity in liquids appears at high frequencies and ensures the propagation of second sound. The expression for the thermal modulus of elasticity consists of potential and kinetic parts, taking into account structural and translational relaxation processes, respectively. To study the thermoelastic properties of magnetic fluids, appropriate expressions of potential interaction energies were selected for each subsystem, allowing for numerical calculations.Results. Numerical calculations of the frequency and concentration dependence of the dynamic thermal modulus of elasticity in the presence of an external magnetic field in a kerosene-based magnetic fluid were carried out. The calculation results show that an increase in the influence of external disturbances leads to a nonlinear increase in the thermal modulus of elasticity in the magnetic fluid. An increase in the volume concentration of magnetic particles and an increase in the magnetic field strength also led to a nonlinear increase in the thermal modulus of elasticity in the magnetic fluid.Conclusion. It has been established that, due to taking into account translational and structural relaxation processes, the region of frequency dispersion of the thermal elastic modulus is wide. Numerical calculations carried out at different values of the external magnetic field and the volume concentration of magnetic particles showed that although an increase in the magnetic field and concentration of magnetic particles leads to an increase in the thermal modulus of elasticity, their increase does not affect the change in the frequency dispersion region.

Dynamics of charge carriers in La2CuO4 cuprates: Conductivity variation, scaling formalisms, and electric modulus study

In this work, we conducted a detailed investigation of the structural properties and the dynamics of the charges in the La2CuO4 Ruddlesden–Popper system that is prepared via the conventional solid-state process. Via the X-ray diffraction data and using the Rietveld refinement, we found that the compound exhibits a single crystallographic phase with a Bmab space group. The DC-conductivity investigation shows that the studied ceramic exhibits two electrical behaviors. Below 460 °C, the occurrence of a semiconductor behavior is attributed to the effect of the Variable range hopping conduction process. At high temperatures, the electrical nature of the material is linked to the thermally activated small polaron hopping conduction process via an activation energy Ea = 1.40 eV. Over the explored temperature range, conductivity spectra of the Ruddlesden–Popper are analyzed using the universal Double Jonscher power law. The dispersion region can be attributed to the coexistence of both hopping and tunneling processes. The conductivity spectra of the La2CuO4 Ruddlesden–Popper nicely follow the time-temperature superposition (TTSP) principle. This confirms that similar sources are responsible for relaxation and conduction processes. Using the Summerfield scaling approach, the superposition of the conductivity spectra into a single master curve confirms that the relaxation process is the microstructure's response independent. From the electrical modulus investigation, we found that the studied compound exhibits a non-Debye relaxation nature, over the explored temperature interval. Contribution of grain and grain boundary were resolved by complex modulus spectroscopy analysis. In addition, we found the absence of the electrode contribution at low frequencies. The correlation between both Z″ and the M″ peaks indicates that the conduction and relaxation processes are not related to the same origins.

Mitigation of the microbunching instability through transverse Landau damping

The microbunching instability has been a long-standing issue for high-brightness free-electron lasers (FELs) and is a significant showstopper to achieve full longitudinal coherence in the x-ray regime. This paper reports the first experimental demonstration of microbunching instability mitigation through transverse Landau damping, based on linear optics control in a dispersive region. Analytical predictions for the microbunching content are supported by numerical calculations of the instability gain. The effect is confirmed through the experimental characterization of the spectral brightness of the FERMI FEL under different transverse optics configurations of the transfer line between the linear accelerator and the FEL. Published by the American Physical Society 2024

Prostate tissue ablation and drug delivery by an image-guided injectable ionic liquid in ex vivo and in vivo models.

Benign prostatic hyperplasia and prostate cancer are often associated with lower urinary tract symptoms, which can severely affect patient quality of life. To address this challenge, we developed and optimized an injectable compound, prostate ablation and drug delivery agent (PADA), for percutaneous prostate tissue ablation and concurrently delivered therapeutic agents. PADA is an ionic liquid composed of choline and geranic acid mixed with anticancer therapeutics and a contrast agent. The PADA formulation was optimized for mechanical properties compatible with hand injection, diffusion capability, cytotoxicity against prostate cells, and visibility of an x-ray contrast agent. PADA also exhibited antibacterial properties against highly resistant clinically isolated bacteria in vitro. Ultrasound-guided injection, dispersion of PADA in the tissue, and tissue ablation were tested ex vivo in healthy porcine, canine, and human prostates and in freshly resected human tumors. In vivo testing was conducted in a murine subcutaneous tumor model and in the canine prostate. In all models, PADA decreased the number of viable cells in the region of dispersion and supported the delivery of nivolumab throughout a portion of the tissue. In canine survival experiments, there were no adverse events and no impact on urination. The injection approach was easy to perform under ultrasound guidance and produced a localized effect with a favorable safety profile. These findings suggest that PADA is a promising therapeutic prostate ablation strategy to treat lower urinary tract symptoms.

Anomalous to normal dispersion nonlinear optical dephasing switch in electromagnetically induced transparency using a Kerr effect

The atomic decoherence effect (DE) on a Kerr nonlinear (KNL) electromagnetically induced transparency (EIT)is studied in a Δ system. The DE between the ground state hyperfine levels is caused by the dephasing rate γ d which dramatically modifies the medium response. It controls the normal dispersive region which shows steep positive slopes for linear response at the line center while the nonlinear response experiences steep negative slopes for low γ d . The microwave field strength and γ d modify the nonlinear response from the anomalous dispersion to normal dispersion. The calculations show that room-temperature atoms are used to quantify the quantum interference (QI) on linear and nonlinear absorption with γ d . The EIT spectrum explores the understanding of the subluminal and superluminal wave propagation of probe signal and this study opens a new pathway for the understanding of the QI devices and their nonlinearities based on EIT.

Polarization-Dependent Formation of Extremely Compressed Femtosecond Wave Packets and Supercontinuum Generation in Fused Silica

Previous studies of formation of extremely compressed wave packets during femtosecond filamentation in the region of anomalous group velocity dispersion in solid dielectrics mostly considered the case of linearly polarized laser pulses. However, recent results suggest potential applications of polarization state manipulation for ultrafast laser writing of optical structures in bulk solid-state media. In the present work, evolution of radiation polarization parameters during formation of such extreme wave packets at the pump wavelength of 1900 nm in fused silica is studied numerically on the basis of the carrier-resolved unidirectional pulse propagation equation (UPPE). It was revealed that initial close-to-circular polarization leads to higher intensity of the anti-Stokes wing in the spectrum of the generated supercontinuum. Numerical simulations indicate a complex, space–time variant polarization state, and the resulting spatiotemporal electric field distribution exhibits a strong dependence on the initial polarization of the femtosecond pulse. At the same time, electric field polarization tends to linear one in the region with the highest field strength regardless of the initial parameters. The origin of this behavior is attributed to the properties of the supercontinuum components generation during filament-induced plasma formation.

Photonic crystal fiber temperature sensor based on self-phase modulation and solitons

In this paper, we investigated the temperature sensing properties of self-phase modulation (SPM) combined with solitons in photonic crystal fibers by experimental verification. Pumped in the normal dispersion region close to the zero-dispersion point, SPM allows the resulting spectrum to extend into the normal dispersion region, generating solitons. By detecting the wavelength shift of the soliton at 900 nm, 2.366 W, the maximum sensitivity is 0.98 nm/°C. To the best of our knowledge, this is the first study of temperature sensing using SPM in combination with solitons, which broadens the boundaries of nonlinear-based sensors and holds considerable promise for high-performance temperature detection in a variety of demanding scenarios, such as railway safety and national security.

439 MHz, 94 fs, low-threshold mode-locked all fiber ring laser

Pulsed fiber lasers with high repetition rates play a crucial role in applications such as high-efficiency processing and bio-optical imaging. However, many ring fiber mode-locked lasers primarily focus on shortening the cavity length to achieve high repetition rate pulse output. Attention is often directed towards the gain fiber and cavity structure, with less consideration given to the challenge of increasing mode-locking threshold power. In this study, we present a high-repetition-rate annular all-fiber laser system with dispersion management. Through strategic adjustment of the intracavity dispersion away from the near-zero dispersion region and careful control of the intracavity gain strength, we have successfully lowered the mode-locking threshold power. This approach can generate pulses with a repetition rate of 439.71 MHz and a mode-locking threshold power of approximately 600 mW. Following pulse compression, the achieved pulse width is 94.8 fs. Its time-bandwidth product is 0.368. To our knowledge, this represents the highest fundamental repetition rate currently attained using a ring all-fiber resonator, accompanied by the lowest mode-locking threshold. Our work introduces a ring fiber laser system characterized by a low mode-locking threshold and a high repetition rate, offering a valuable method for achieving higher fundamental repetition rate pulses.

Achieving high fatigue endurance of nanocrystalline Ni/Ni-W layered composites through thermally and mechanically-induced relaxations

Stabilizing non-equilibrium nanograin boundaries has been shown to enhance the strength of nanocrystalline metals. Nevertheless, a thorough comprehension of how these stable grain boundaries impact the fatigue behavior in nanocrystalline metallic layered composites with heterogeneous interfaces is currently lacking. Here, aiming to develop high-performance small components in microelectromechanical systems, we prepared nanocrystalline Ni/Ni-W layered composites that underwent various degrees of annealing treatment. Our results reveal that the Ni/Ni-W layered composites annealed at 200 °C exhibit significantly higher fatigue strength, surpassing that of the as-prepared composites by 40 % and the Pt-10 at.% Au alloy by 17 % which is one of the best candidates for the microelectromechanical systems switches at present. The enhanced fatigue strength is primarily attributed to the annealing-induced grain boundary relaxation and mechanically-induced structural relaxation. Grain boundary relaxation enhances the strength by improving GB stability, while the mechanically-induced structural relaxation results in the coarsening and expansion of triangular columnar grains towards the Ni-W layer during fatigue loading. As a result, the dispersive strain localized regions triggered by the triangular columnar grains undertook cyclic strain accumulation and weakened localized damage accumulation in Ni layers, and thus further improved the fatigue resistance. The finding of the underlying mechanisms may offer a promising approach for designing high-performance materials for microelectromechanical systems switches operating at elevated temperatures.

Transient instability characteristics of fluid film bearings induced by bubble inclusion

Bubble inclusion in the tribo-pair leads to two-phase fluid lubrication. Upon the initial introduction of air bubbles to the tribo-pair, it can lead to instability in the operational state. A numerical model is formulated by coupling the fluid Reynolds equation, bubble dynamics equation, and rotor dynamics equation. Various parameters, such as hydrodynamic pressure, fluid carrying capacity, rotor trajectory, and equilibrium position, are employed to characterize the impact of operational and fluid interface parameters on the bubble entrainment process. The findings reveal that the hydrodynamic pressure plays a crucial role in establishing the correlation between velocity and fluctuations in kinetic parameters. Surface tension predominantly influences bubbles within the dispersion region, while surface dilatational viscosity affects the entire domain. Lower surface dilatational viscosity or neglecting surface tension can trigger larger fluctuations in the rotor trajectory. Changes in liquid-phase viscosity result in fluctuations in bubble behavior and dynamics parameters, influenced by the equilibrium position and the effect of hydrodynamic pressure. Higher initial gas-phase volume fractions lead to a more pronounced reduction in fluid-carrying capacity and increased system instability.

Tailoring the optical properties of dye–polymer composite films based on polyvinyl alcohol doped with phenol red toward flexible optoelectronic applications

The composite films of polyvinyl alcohol (PVA) incorporating varying concentrations of phenol red (PR) dye were fabricated using the solution casting method. Structural characteristics of the prepared films were explored through XRD and FTIR spectroscopy analyses. The inclusion of PR dye within the PVA matrix induced cross-linking, enhancing the amorphous nature of the doped PVA samples, as evidenced by XRD patterns. In the presence of PR dopants, the FTIR peaks for PVA exhibited altered intensities and increased width, indicating physical interactions between the functional groups of PVA and PR dopants. The impact of PR additives on the optical properties of PVA was investigated across the spectral range of 190–2500 nm. The PVA/phenol red composite demonstrated enhanced UV blocking in the 190–400 nm wavelength range, rendering it suitable for applications such as UV notch filters, including laser blocking filters. The indirect and direct optical band-gaps of PVA polymer films were reduced from 5.20 eV and 5.78 eV to 4.30 eV and 5.28 eV, respectively, with an increase in the PR filling ratio from 0 wt% to 1.8 wt%. The dispersion region of the refractive index was analyzed using the single oscillator model (Wemple-DiDomenico). Calculation and discussion of values such as dispersion and oscillation energies (Ed and Eo), permittivity at infinite frequency (ε ∞), and lattice contribution to the dielectric function (ε L) of PVA/PR composite films were conducted. These advancements position PVA/PR composite films for potential applications in flexible optoelectronic devices, including light-emitting diodes and photodetectors.

Bidirectional Raman soliton-like combs with unidirectional pump in a spherical microresonator.

We experimentally demonstrate bidirectional Raman soliton-like combs in a whispering gallery mode microresonator with a unidirectional pump for the first time, to the best of our knowledge. We develop a relatively simple theoretical model and find an analytical solution for forward- and backward-propagating Raman sech2-shaped solitons in an anomalous dispersion region under unidirectional pumping in a normal dispersion region. Raman solitons exist, thanks to the balance between losses and Raman gain from a CW wave (which is equal in both directions) as well as between dispersion and Kerr nonlinearity.

Contribution of strong electron-phonon interaction in the transport properties of La0.8Ca0.2Mn0.5Ni0.5O3 system

La0.8Ca0.2Mn0.5Ni0.5O3 NTC (negative thermal coefficient) thermo-sensitive material was prepared using a conventional solid-state reaction method. From the structural results, we found that the material is pure and crystallizes in the orthorhombic structure with a Pnma space group. It is found that the La0.8Ca0.2Mn0.5Ni0.5O3 ceramic can be used as an NTC thermistor compound in specific temperature sensors and attenuators. Based on Holsten's theory, detailed electrical investigations concerning the nature of the activated small polaron hopping mechanism were reported. The temperature dependence of the DC conductance was used to determine the electrical conduction processes that govern the transport properties of La0.8Ca0.2Mn0.5Ni0.5O3. Hence, the DC mechanisms exhibit changes from the variable range hopping at very low temperatures to the non-adiabatic small polaronic hopping at T = 210 K. In the intermediate temperature range, the semiconductor behavior of La0.8Ca0.2Mn0.5Ni0.5O3 was attributed to the contribution of the tunneling transport process. At various temperatures, the conductance spectra were discussed based on Jonscher and Bruce's laws. Contributions of the overlapping-large-polaron-tunneling, the correlated barrier hopping, the quantum mechanical tunneling, and the non-overlapping small polaron tunneling mechanisms to the transport properties were observed in the dispersive region of the conductance spectra. In addition, Summerfield scaling and corrected Summerfield scaling approaches prove that the charge mobility is temperature-dependent. The positive value of the correction parameter α = 1.2 confirms the presence of interactions in the studied sample.

Noise-like pulse generation by amplified well-defined pulse in an optical fiber with negative group velocity dispersion

We experimentally and numerically demonstrate that noise-like pulses (NLPs) can be generated by pumping well-defined pulses (WDPs) into an optical fiber amplifier at a wavelength in the region of negative group velocity dispersion. Through investigating the evolution of the optical pulses, it is realized that the output pulses consist of NLPs at the pump wavelength and split solitons at Stokes wavelengths, due to intrapulse Raman scattering followed by the process of soliton fission. Such process of pulse breakup results in the generation of sub-pulses that have peak powers much higher than the unbroken WDPs have, enabling WDPs to strongly induce nonlinear effects. This finding resolves the discrepancy between the experiment and simulation results of supercontinuum generation by using picosecond WDPs in previous research.

Formation of an O-Shaped Structure in the Red Wing of the Frequency–Angular Spectrum During Filamentation on a Long Atmospheric Path

An O-shaped structure at wavelengths of 930–960 nm in the frequency–angular spectrum of the supercontinuum generated during the filamentation of a femtosecond laser pulse with a central wavelength of 740 nm on a 75-m path in air has been observed experimentally. This feature of the frequency–angular spectrum is due to the presence of the absorption band of water vapor in the range of 930–960 nm and the anomalous dispersion region associated with this absorption. This result opens prospects for the remote single-pulse detection of impurities in air.