Transient Bands Research Articles

Research on Phase-to-phase Fault Location Method of Active Distribution Network

Due to the weak feed characteristic of active distribution networks, the sensitivity of the original fault phase selection method and the accuracy of fault location are decreased. Most of the existing fault section location methods focus on the phase selection and location of the earth fault, and there is a lack of relevant research on the location of the fault section to the phase-to-phase fault. Moreover, most of the methods need to install the signal measuring device in the system as large as possible, which is not economical. The operation condition of active distribution networks is complicated, the fault characteristics are weak, and the location result is easily affected by non-fault disturbances such as DG access capacity and location. In this paper, the phase-to-phase fault of active distribution networks is taken as the research object. Firstly, phase current and zero-sequence current combined criterion is used for fault phase selection, and then combined with the phase-frequency characteristics of mode impedance of distribution line and photovoltaic power line, a fault section location method based on transient characteristic frequency band is proposed, which is not affected by non-fault disturbance such as photovoltaic control strategy and DG access capacity and location. Simulation results show that the method is effective.

Transient band keratopathy associated with epithelial ingrowth treated with antimetabolites

Introduction: To report a case of visually significant band keratopathy associated with ocular inflammation in the setting of epithelial ingrowth, both of which resolved after repeated antimetabolite treatments. Patient and Clinical Findings: A 74-year-old woman with a history of uveitis–glaucoma–hyphema syndrome after complicated cataract surgery presented with epithelial ingrowth in the right eye and diffuse central band keratopathy after posterior chamber intraocular lens (IOL) removal and pars plana vitrectomy and anterior chamber IOL placement. Diagnosis, Intervention, and Outcomes: After multiple intraocular injections of antimetabolites, the epithelial ingrowth and visually significant band keratopathy resolved. Conclusions: Treating the underlying source of inflammation, such as epithelial ingrowth with antimetabolites, was associated with clearance of the band keratopathy without further intervention.

Uncovering the mechanisms of efficient upconversion in two-dimensional perovskites with anti-Stokes shift up to 220 meV.

Phonon-assisted photon upconversion holds great potential for numerous applications, e.g., optical refrigeration. However, traditional semiconductors face energy gain limitations due to thermal energy, typically achieving only ~25 milli-electron volts at room temperature. Here, we demonstrate that quasi-two-dimensional perovskites, with a soft hybrid organic-inorganic lattice, can efficiently upconvert photons with an anti-Stokes shift exceeding 200 milli-electron volts. By using microscopic transient absorption measurements and density functional theory calculations, we explicate that the giant energy gain stems from strong lattice fluctuation leading to a picosecond timescale transient band energy renormalization with a large energy variation of around ±180 milli-electron volts at room temperature. The motion of organic molecules drives the deformation of inorganic framework, providing energy and local states necessary for efficient upconversion within a time constant of around 1 ps. These results establish a deep understanding of perovskite-based photon upconversion and offer previously unknown insights into the development of various upconversion applications.

Burr Puzzle-Inspired Seismic Metamaterials

Two novel seismic metamaterials models, trophy and apple core, inspired by an ancient Chinese puzzle are proposed in this study. Bandgaps below 15[Formula: see text]Hz are achieved by exclusively using concrete as the base material in the designs. Vibration modes are investigated to clarify the bandgap formation. Through comparison, we found that under the same volume, the apple core model can provide a lower frequency bandgap than the trophy model. Results from transient simulations and band structures are in good agreement, validating the accuracy of the simulation results. To broaden the bandwidth, the radii of the apple core models are varied and arranged in a gradient pattern. Transient analyses using a Gaussian wave packet and Taiwan’s Chi-Chi earthquake dataset are conducted to verify the effectiveness of the gradient apple core seismic metamaterial.

Single-ended protection method for hybrid HVDC transmission line based on transient voltage characteristic frequency band

Hybrid high-voltage direct current (HVDC) transmission has the characteristic of long transmission distance, complex corridor environment, and rapid fault evolution of direct current (DC) lines. As high fault current can easily cause irreversible damage to power devices, rapid and reliable line protection and isolation are necessary to improve the security and reliability of hybrid HVDC transmission system. To address such requirement, this paper proposes a single-ended protection method based on transient voltage frequency band characteristics. First, the frequency characteristics of the smoothing reactor, DC filter, and DC line are analyzed, and the characteristic frequency band is defined. A fault criterion is then constructed based on the voltage characteristic frequency band energy, and faulty pole selection is performed according to the fault voltage characteristic frequency band energy ratio. The proposed protection method is verified by simulation, and the results show that it can rapidly and reliably identify internal and external faults, accurately select faulty poles without data communication synchronization, and has good fault-resistance and anti-interference performance.

Age-related differences in transient gamma band activity during working memory maintenance through adolescence

Adolescence is a stage of development characterized by neurodevelopmental specialization of cognitive processes. In particular, working memory continues to improve through adolescence, with increases in response accuracy and decreases in response latency continuing well into the twenties. Human electroencephalogram (EEG) studies indicate that gamma oscillations (35-65Hz) during the working memory delay period support the maintenance of mnemonic information guiding subsequent goal-driven behavior, which decrease in power with development. Importantly, recent electrophysiological studies have shown that gamma events, more so than sustained activity, may underlie working memory maintenance during the delay period. However, developmental differences in gamma events during working memory have not been studied. Here, we used EEG in conjunction with a novel spectral event processing approach to investigate age-related differences in transient gamma band activity during a memory guided saccade (MGS) task in 164 10- to 30-year-olds. Total gamma power was found to significantly decrease through adolescence, replicating prior findings. Results from the spectral event pipeline showed age-related decreases in the mean power of gamma events and trial-by-trial power variability across both the delay period and fixation epochs of the MGS task. In addition, we found that while event number decreased with age during the fixation period, the developmental decrease during the delay period was more dramatic, resulting in an increase in event spiking from fixation to delay in adolescence but not adulthood. While average power of the transient gamma events was found to mediate age-related differences in total gamma power in the fixation and delay periods, the number of gamma events was related to total power in only the delay period, suggesting that the power of gamma events may underlie the sustained gamma activity seen in EEG literature while the number of events may directly support age-related improvements in working memory maintenance. Our findings provide compelling new evidence for mechanistic changes in neural processing characterized by refinements in neural function as behavior becomes optimized in adulthood.

Gradient V-Shaped and N-Shaped Seismic Metamaterials.

Seismic metamaterials provide an innovative alternative in earthquake engineering by reducing the hazards from seismic waves without modifying the existing structures. Although many seismic metamaterials have been proposed, a design for a broad bandgap at low frequencies is still in demand. In this study, two novel seismic metamaterials, V- and N-shaped designs, are proposed. We found that by adding a line to the letter V, turning the V-shaped design into an N-shaped design, the bandgap can be broadened. Both the V- and N-shaped designs are arranged in a gradient pattern to combine the bandgaps from metamaterials with different heights. Using only concrete as the base material for the design makes the proposed seismic metamaterial cost effective. Finite element transient analysis and band structures are in good agreement, validating the accuracy of the numerical simulations. Surface waves are effectively attenuated over a broad range of low frequencies using the gradient V- and N-shaped seismic metamaterials.

Build-up and dephasing of Floquet-Bloch bands on subcycle timescales.

Strong light fields have created opportunities to tailor novel functionalities of solids1-5. Floquet-Bloch states can form under periodic driving of electrons and enable exotic quantum phases6-15. On subcycle timescales, lightwaves can simultaneously drive intraband currents16-29 and interband transitions18,19,30,31, which enable high-harmonic generation16,18,19,21,22,25,28-30 and pave the way towards ultrafast electronics. Yet, the interplay of intraband and interband excitations and their relation to Floquet physics have been key open questions as dynamical aspects of Floquet states have remained elusive. Here we provide this link by visualizing the ultrafast build-up of Floquet-Bloch bands with time-resolved and angle-resolved photoemission spectroscopy. We drive surface states on a topological insulator32,33 with mid-infrared fields-strong enough for high-harmonic generation-and directly monitor the transient band structure with subcycle time resolution. Starting with strong intraband currents, we observe how Floquet sidebands emerge within a single optical cycle; intraband acceleration simultaneously proceeds in multiple sidebands until high-energy electrons scatter into bulk states and dissipation destroys the Floquet bands. Quantum non-equilibrium calculations explain the simultaneous occurrence of Floquet states with intraband and interband dynamics. Our joint experiment and theory study provides a direct time-domain view of Floquet physics and explores the fundamental frontiers of ultrafast band-structure engineering.

Transient “cis-Peak” Is Present in Excited-State Absorption of Central-cis Isomers of Carotenoids

Application of femtosecond time-resolved transient absorption spectroscopy on all-trans and central-cis isomers of two exemplary carotenoids, lutein and spirilloxanthin, performed at room and cryogenic temperatures in the spectral range expanded toward UV revealed new spectroscopic transient features for the cis isomers. Notably, particularly for the central-cis spirilloxanthin, a very distinct additional transient absorption band is observed on the short wavelength side of the main excited-state absorption band of the S1 state, having the same temporal characteristics as the latter one. This band is absent in transient absorption spectra of all-trans isomers, suggesting it could be assigned to "transient cis-peak." Overall, the results show that the "transient" counterpart of the spectral marker of cis-isomers of carotenoids, or the so-called cis-peak, is detectable in the excited-state absorption spectrum and could be attributed to electronic transition from the S1 state. This new transient spectral band could be very useful for spectroscopic experiments targeting the dynamics of carotenoid isomers and their severely distorted forms.

Unmasking of a Relapsing Encephalomyelitis After SARS-CoV-2 Infection and COVID-19 Vaccination

Objective NA. Background Prior case studies suggest that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its vaccines may unmask neuroinflammatory conditions. We present a case of relapsing steroid-responsive encephalomyelitis after SARS-CoV-2 infection and subsequent COVID-19 vaccination. Design/Methods NA. Results A 47-year-old man with a history COVID-19 presented with subacute lower extremity weakness, erectile dysfunction, and gait instability with falls. His symptoms started several weeks after COVID-19 vaccination which he underwent 3 months after COVID-19 infection. His initial exam demonstrated weakness at the knees and ankles and extensor plantar responses. MRI demonstrated innumerable enhancing lesions involving the subcortical white matter, basal ganglia, thalami, brainstem, cerebellum, and the entire spinal cord parenchyma. CSF testing revealed a lymphocytic pleocytosis (10 WBC, 88% lymphocytes), and transient matched serum and CSF oligoclonal bands. Testing was unremarkable for infections, malignancies, primary demyelinating conditions, etc. He responded dramatically to five days of high dose methylprednisolone but had recurrence of symptoms with weaning of oral prednisone, requiring another pulse of IV steroids. After 2 months, his steroids were weaned again, with clinical and radiographic recurrence, requiring another course of IV steroids. He was subsequently transitioned to mycophenolate as a steroid-sparing agent. Literature review identified 20 additional cases of CNS neuroinflammatory disease after either SARS-CoV-2 infection or vaccination (11 transverse myelitis, 6 optic neuritis, 3 encephalomyelitis). Conclusions Our patient's steroid-dependency and relapsing course suggests unmasking of an underlying CNS neuroinflammatory condition. Temporal associations of neurological conditions with vaccinations or infections do not prove causality despite previous reports of such sequelae. Vaccines containing SARS-CoV-2 antigens may enhance autoimmunity by mechanisms including polyclonal activation, epitope spreading, or molecular mimicry. This case highlights that the resulting inflammation may be insidious and extensive, though treatable. As COVID-19 constitutes a life-threatening infection in some patients, the benefits of vaccination outweigh the smaller risk of unmasking an immune-related condition.

Spectral shift of solid high-order harmonics from different channels in a combined laser field

We investigate theoretically the spectral shift of the high-order harmonic generation (HHG) in ZnO driven by a combined laser field by solving the two-band semiconductor Bloch equations (SBEs) in the velocity gauge. The combined laser field is synthesized by a fundamental laser pulse and its seventh-frequency laser pulse. When the seventh-frequency laser pulse is added to the rising or falling parts of the fundamental laser field, we find that the spectral blueshift or redshift appears, which is due to the unequal contribution of the rising and falling parts in the fundamental laser field to the harmonics. By analyzing the time-dependent conduction band population in k space, we found that, in addition to the tunneling ionization channel, there is also the resonant electron injection channels which is induced by the seventh-frequency laser pulse. The harmonics generated by the different channels show the spectral redshift or the spectral blueshift, respectively. Through analyzing the k -integrated transient conduction band population of the electrons from different channels, we found that if there is a certain delay in the process of the electron excitation, it will lead to the delay in the harmonic emission, which results in the spectral redshift of the harmonics.

Characterization of Casirivimab Plus Imdevimab, Sotrovimab, and Bamlanivimab Plus Etesevimab-Derived Interference in Serum Protein Electrophoresis and Immunofixation Electrophoresis.

BackgroundTherapeutic monoclonal antibodies can be a source of assay interference in clinical serum protein electrophoresis (SPEP) and immunofixation electrophoresis (IFE), producing monoclonal bands that can be misinterpreted as a monoclonal gammopathy related to a B-cell or plasma cell neoplasm. The extent to which new anti-COVID-19 monoclonal antibodies produce this interference is unknown.MethodsCasirivimab plus imdevimab, sotrovimab, and bamlanivimab plus etesevimab were spiked into patient serum samples to evaluate for SPEP/IFE interference, to characterize the position of therapy-derived bands relative to a reference band (either combined beta band or beta 1 band, depending on instrument platform), and to confirm heavy and light chain utilization of each medication. Serum samples from patients who had recently received casirivimab plus imdevimab or sotrovimab were also evaluated for comparison.ResultsWhen spiked into serum samples, all tested anti-COVID-19 monoclonal antibodies generated interference in SPEP/IFE. Importantly, the patterns of interference differed between spiked serum samples and serum from patients who had recently received casirivimab plus imdevimab or sotrovimab.ConclusionsImdevimab can be added to the growing list of therapeutic monoclonal antibodies that produce sustained interference in SPEP/IFE. Although casirivimab and sotrovimab also produce assay interference in vitro, these antibodies are not reliably detected in serum from recently infused patients. The value of relative band position in recognizing bands that may represent therapeutic monoclonal antibodies is also emphasized. Clinicians and laboratorians should consider therapeutic monoclonal antibody interference in diagnostic SPEP/IFE and review a patient’s medication list when new or transient monoclonal bands are identified.

Probing topological Floquet states in WSe2 using circular dichroism in time- and angle-resolved photoemission spectroscopy

Observing signatures of light-induced topological Floquet states in materials has been shown to be very challenging. Angle-resolved photoemission spectroscopy (ARPES) is well suited for the investigation of Floquet physics, as it allows to directly probe the dressed electronic states of driven solids. Depending on the system, scattering and decoherence can play an important role, hampering the emergence of Floquet states. Another challenge is to disentangle Floquet side bands from laser-assisted photoemission (LAPE), since both lead to similar signatures in ARPES spectra. Here, we investigate the emergence of Floquet state in the transition metal dichalcogenide 2H-WSe2, one of the most promising systems for observing Floquet physics. We discuss how the topological Floquet state manifests in characteristic features in the circular dichroism in photoelectron angular distributions (CDAD) that is determined by the transient band structure modifications and the associated texture of the orbital angular momentum. Combining highly accurate modeling of the photoemission matrix elements with an ab initio description of the light-matter interaction, we investigate regimes which can be realized in current state-of-the-art experimental setups. The predicted features are robust against scattering effects and are expected to be observed in forthcoming experiments.

Spectroscopic view of ultrafast charge carrier dynamics in single- and bilayer transition metal dichalcogenide semiconductors

The quasiparticle spectra of atomically thin semiconducting transition metal dichalcogenides (TMDCs) and their response to an ultrafast optical excitation critically depend on interactions with the underlying substrate. Here, we present a comparative time- and angle-resolved photoemission spectroscopy (TR-ARPES) study of the transient electronic structure and ultrafast carrier dynamics in the single- and bilayer TMDCs MoS2 and WS2 on three different substrates: Au(111), Ag(111) and graphene/SiC. The photoexcited quasiparticle bandgaps are observed to vary over the range of 1.9–2.5 eV between our systems. The transient conduction band signals decay on a sub-50 fs timescale on the metals, signifying an efficient removal of photoinduced carriers into the bulk metallic states. On graphene, we instead observe a fast timescale on the order of 170 fs, followed by a slow dynamics for the conduction band decay in MoS2. These timescales are explained by Auger recombination involving MoS2 and in-gap defect states. In bilayer TMDCs on metals we observe a complex redistribution of excited holes along the valence band that is substantially affected by interactions with the continuum of bulk metallic states.

Exploring the Coordination Modes of a Keggin-Type [ZnW12O40]6- Anionic Cluster: Bonding Patterns, Crystal Structure, and Semiconducting Properties.

Polyoxometalate-based organic-inorganic hybrid compounds (POIHCs) have been greatly developed due to their wide application prospects, but the pursuit of their directed synthesis via molecular design still remains a challenge. Herein, we demonstrate that the coordination modes of the Keggin-type [ZnW12O40]6- anion can be tuned, which leads to different semiconductor characteristics. Using the same building block, ligand, and metal ion (ZnW12, phen, Cu2+), we synthesized three new POIHCs with different bonding patterns by means of different coordination modes of ZnW12. The three POIHCs (H2phen){ZnW12O40[Cu(phen)2]2}·3H2O (1), {ZnW12O40[Cu(phen)(H2O)2]2[Cu(phen)(H2O)]}n·3H2O (2), and (Me4N)2{ZnW12O40[Cu(phen)(H2O)]2}n·5H2O (3) (phen = 1,10-phenanthroline) have been structurally characterized by single-crystal X-ray diffraction. Compound 1 appears as a zero-dimensional coordination complex cluster, while compounds 2 and 3 are both 1D chain structures with different Cu2+ bridge linkages. Although these three POIHCs possess the same chemical components, their semiconductor properties are different, which is demonstrated by measurements of transient photocurrent and band gap (Eg) values. Furthermore, we carried out comparative experiments on the photoconductivity performance of compounds 1-3 and their photocatalytic reduction from O2 to H2O2, indicating the significant influence of the energy level matching on the photocatalytic activity.

The oxidation of guanine by photoionized 2-aminopurine

2-Aminopurine (2AP) is a fluorescent nucleobase analogue of the DNA nucleobase adenine and can be inserted in place of adenine into nucleic acids with minimal structural perturbation. The inserted 2-aminopurine can be selectively excited, and the fluorescence observed used as a sensitive probe for local structure, in addition selective ionization of 2-aminopurine within a nucleic acid is possible and once formed the ionized 2-aminopurine will oxidize nearby guanine bases, providing a route to study charge transfer within nucleic acids. Time resolved infrared spectroscopy is a powerful tool to study oxidation processes on picosecond, and longer timescales. There is a lack of availability of high quality IR spectra in the literature of the individual, short lived, photoproducts, required to fully elucidate the mechanism of the interaction of photoionized 2-aminopurine with guanine. Density functional theory (DFT) methods (B3LYP/6–31G+(d) and EDF1/6–31G+(d)) have been used to calculate the energies and infrared spectra of 2-aminopurine, guanine and potential photoproducts that may result from photoionization reactions between 2-aminopurine and guanine. Direct comparison can therefore be made between areas of bleaching of bands in the IR spectra of 2-aminopurine or guanine and the appearance of new transient bands of potential photoproducts. These potential photoproducts could include deprotonated neutral radical species, deprotonated anion species, radical cations and radical anions. It was found in the current work that the key intermediates in the oxidation reaction between photoionized 2-aminopurine and guanine were: 2AP•(− H ,N2) (formed from deprotonation from the 2AP •+ amino group); G•(− H ) (formed from deprotonation from the N1 nitrogen, or possibly the amino group, of the initially formed G •+ ), and 2AP − (− H ,N2) (formed from the reduction of 2AP•(− H ,N2) by guanine).

Enhanced photocatalytic performance through the ferroelectric synergistic effect of p-n heterojunction BiFeO3/TiO2 under visible-light irradiation

A BiFeO3/TiO2 p-n heterojunction photocatalyst with ferroelectric synergistic effect under visible-light irradiation was developed through facile hydrolysis and precipitation by forming nanospheres of TiO2 on BiFeO3 nanocube to improve the photocatalytic efficiency. Analyses of the microstructure, optical properties, and photoelectrochemical performance indicate the formation of a core–shell heterostructure of BiFeO3/TiO2 with excellent energy band matching. The BiFeO3/TiO2 p-n heterojunction has enlarged specific surface area, higher sensitivity to visible-light, and improved separation and transfer efficiency of photoelectron-hole pairs than single TiO2 and BiFeO3. Moreover, the composite exhibits superior photocatalytic degradation performance for methylene blue (MB) and common antibiotic tetracycline (TC) under UV and visible-light irradiation. The MB degradation rate within 180 min reaches 78.4% and 90.4% under UV and visible-light irradiation, respectively. Furthermore, the enhanced photocatalytic mechanism of BiFeO3/TiO2 is explored by photoluminescence (PL), electrochemical impedance spectroscopy (EIS), transient photocurrent analysis, radical quenching, and band structure characterization.

Synthesis of CPVC-modified SnS2/TiO2 composite with improved visible light-driven photocatalysis

Synthesis of heterojunctions is very effective in increasing the photocatalytic activity of photocatalysts. Considering conjugated polyvinyl chloride derivative (CPVC) is capable of constituting heterojunctions with both SnS2 and TiO2, this study used CPVC to modify SnS2/TiO2 composite to develop a new high-efficiency visible light-driven ternary photocatalyst (CPVC/SnS2/TiO2). CPVC/SnS2/TiO2 was synthesized by a convenient and practical method, and its composition and structure were characterized using many means. The photocatalytic tests manifested that CPVC/SnS2/TiO2 not only had higher activity than TiO2/SnS2 and SnS2 in photocatalytic reduction of aqueous Cr(VI), but also was efficient in photocatalytic degradation of methylene blue under visible light irradiation. Besides, the effect of the dosage of CPVC/SnS2/TiO2 on its photocatalytic reduction of Cr(VI) was investigated. Also, the photocatalytic improvement mechanism of CPVC/SnS2/TiO2 was put forward, based on the results of the electrochemical impedance, transient photocurrent response and energy band structure measurements.

A generic electroluminescent device for emission from infrared to ultraviolet wavelengths

The range of luminescent materials that can be used in electroluminescent devices is limited due to material processing challenges and band alignment issues. This impedes the development of electroluminescent devices at extreme wavelengths and hinders the use of electroluminescence spectroscopy as an analytical technique. Here, we show that a two-terminal device that uses an array of carbon nanotubes as the source contact can excite electroluminescence from various materials independent of their chemical composition. Transient band bending, created by applying an a.c. gate voltage, is used to achieve charge injection across different band alignments. As a result, the device can produce electroluminescence from long-wave infrared (0.13 eV) to ultraviolet (3.3 eV) wavelengths depending on the emitting material drop-casted on top of the nanotube array, and with onset voltages approaching the optical energy gap of the emitting material. We show that our device can be used to probe a chemical reaction in a liquid droplet via electroluminescence spectroscopy and can be used as an electroluminescence sensor for detecting organic vapours. A two-terminal device that uses an array of carbon nanotubes as the source contact can excite electroluminescence from a variety of materials, producing electroluminescence from long-wave infrared to ultraviolet wavelengths, with onset voltages approaching the optical energy gap of the emitting material.

Solvent-dependent photochemical dynamics of a phenoxazine-based photoredox catalyst

Abstract Organic substitutes for ruthenium and iridium complexes are increasingly finding applications in chemical syntheses involving photoredox catalysis. However, the performance of these organic compounds as electron-transfer photocatalysts depends on their accessible photochemical pathways and excited state lifetimes. Here, the UV-induced dynamics of N-phenyl phenoxazine, chosen as a prototypical N-aryl phenoxazine organic photoredox catalyst, are explored in three solvents, N,N-dimethyl formamide, dichloromethane and toluene, using ultrafast transient absorption spectroscopy. Quantum chemistry calculations reveal the locally excited or charge-transfer electronic character of the excited states, and are used to assign the transient electronic and vibrational bands observed. In toluene-d8, complete ground-state recovery is (31 ± 3) % by internal conversion (IC) from the photo-excited state (or from S1 after IC but before complete vibrational relaxation), (13 ± 2) % via direct decay from vibrationally relaxed S1 (most likely radiative decay, with an estimated radiative lifetime of 13 ns) and (56 ± 3) % via the T1 state (with intersystem crossing (ISC) rate coefficient k ISC = (3.3 ± 0.2) × 108 s−1). In dichloromethane, we find evidence for excited state N-phenyl phenoxazine reaction with the solvent. Excited state lifetimes, ISC rates, and ground-state recovery show only modest variation with changes to the solvent environment because of the locally excited character of the S1 and T1 states.