Fast Polarization Research Articles

Nonlinear dynamics of trions under strong optical excitation in monolayer MoSe2

By employing ultrafast transient reflection measurements based on two-color pump-probe spectroscopy, the population and valley polarization dynamics of trions in monolayer MoSe2 were investigated at relatively high excitation densities under near-resonant excitation. Both the nonlinear dynamic photobleaching of the trion resonance and the redshift of the exciton resonance were found to be responsible for the excitation-energy- and density-dependent transient reflection change as a result of many-body interactions. Furthermore, from the polarization-resolved measurements, it was revealed that the initial fast population and polarization decay process upon strong photoexcitation observed for trions was determined by trion formation, transient phase-space filling and the short valley lifetime of excitons. The results provide a basic understanding of the nonlinear dynamics of population and valley depolarization of trions, as well as exciton-trion correlation in atomically thin MoSe2 and other transition metal dichalcogenide materials.

SKS Splitting and the Scale of Vertical Coherence of the Taiwan Mountain Belt

AbstractMany continental orogens feature a pattern of SKS shear wave splitting with fast polarization directions parallel to the mountain fabrics and delay times of 1–2 s, implying that the crust and lithosphere deform consistently. In the Taiwan arc‐continent collision zone, similar pattern of SKS splitting exists, and thereby lithospheric scale deformation due to collision has been assumed. However, recent dynamic modeling demonstrated that the SKS splitting in Taiwan can be generated by the toroidal flow in the asthenosphere induced by the subduction of the Philippine Sea plate and the Eurasian plate. To further evaluate this hypothesis, we analyzed a new data set using a quantitative approach. The results show that models with slab geometries constrained by seismicity explain the observed fast splitting direction to within 25°, whereas the misfit grows to ~50–60° if the toroidal flow is disrupted by the presence of a sizable aseismic slab beneath central Taiwan as often suggested by tomographic imaging. However, small sized aseismic slab or detached slab fragment can potentially reconcile the splitting observations. We estimated the scale of vertical coherence to be 10–40 km in the lithosphere and 100–150 km in the asthenosphere, making the former unfavorable for accumulating large delay times. The low coherence is caused by the subduction of the Eurasian plate that creates complex deformation different from what characterizes the compressional tectonics above the plate. This suggests that the mountain building in Taiwan is a shallow process, rather than lithospheric in scale.

Room Temperature Polarization Phenomena in Nanocrystalline and Epitaxial Thin Films of Gd-Doped Ceria Studied by Kelvin Probe Force Microscopy

Thin films of the composition Ce0.9Gd0.1O2-δ and with a thickness of 200 nm were prepared on an Al2O3 (0001) substrate at 720°C or room temperature, to yield epitaxial or nanocrystalline materials. The effect of the microstructure on room temperature polarization were assessed by a combination of polarization with up to ±5 V using an AFM tip and a large silver back contact followed by surface potential mapping with Kelvin probe force microscopy. The nanocrystalline sample showed a low degree of polarization, which was reversible, and a fast relaxation process. The epitaxial thin film, in contrast, was already polarized at smaller biases and showed irreversible changes of the surface potential after polarization with +5 V. For lower biases, two distinct relaxation reactions were identified: a fast redistribution of charge over a large area in the first seconds after end of polarization and a slower process in the vicinity of the polarization contact, which took several minutes to relax. The slower polarization behavior is due to a bulk chemical diffusion process with a coefficient Dδ on the order of 10−17 m2·s−1, whereas the faster polarization can be assigned to a charge carrier redistribution within a space charge layer.

Broadband Rydberg atom-based radio-frequency field sensor

Significant progress has been made in atom-based measurements of length, time, gravity and electromagnetic fields in recently years. Rydberg atom-based microwave electric field measurement, using electromagnetically induced transparency (EIT) in room temperature alkali-metal vapors, has been extensively investigated and aroused the broad interest. This approach may establish a new standard for the measurements of microwave (MW) and radio frequency (RF) electric fields.In this review, we describe the work on a new method of measuring electric fields based on quantum interference by using either cesium or rubidium atoms contained in a dielectric vapor cell. Rydberg atoms with principal quantum number n >>1 have large direct current (DC) polarizabilities and microwave transition dipole moments, thereby making them extremely sensitive to external electric fields. Using the Rydberg three-level EIT to detect the level splitting and shift that is induced by the external field, we can realize a rapid and robust self-calibration method of measuring the electric field in a frequency range from 0.01 GHz to 1000 GHz. For the MW electric field (frequency range > 1 GHz), the MW field causes the Rydberg states to split, known as an Autler-Townes splitting (A-T) effect when the applied microwave can resonate with adjacent Rydberg states. The MW coupled A-T splitting is proportional to the applied electric field strength, from which the field strength is measured. Using the EIT window, a high sensitivity of 3 μV·cm-1·Hz-1/2 and small electric field of 1 μV/cm are expected to be achieved with a modest setup, and the limitations of the sensitivity are also addressed in the review. For the RF field at frequency mj EIT lines, and avoided crossings formed with the fine-structure levels of equal mj and different J's, which is used to calibrate and measure the RF field amplitude. On the other hand, the dependence of the EIT-line strength on the RF field polarization provides a fast and robust polarization measurement of RF fields based on matching experimental data with a theoretical simulation. The measurements of minimum strengths and sensitivity of RF fields based on Rydberg atoms are one order magnitude below the values obtained by traditional antenna methods. The atom-based field measurement paves the way for determining fields through calibration-free, invariable atomic properties and miniaturization. We also propose its various potential applications in the future.

针对电力悬空光缆量子密钥分发的高速偏振反馈算法

针对电力悬空光缆量子密钥分发的高速偏振反馈算法

Rapid screening and characterization of glutathione-trapped reactive metabolites using a polarity switch-based approach on a high-resolution quadrupole orbitrap mass spectrometer.

Formation of reactive metabolites that are capable to react with macromolecules could contribute to drug-induced toxicity. As part of early drug screening strategy to support small molecule structure-activity relationship analysis, glutathione (GSH) trapping is commonly used for the detection of reactive metabolites. When trapped, the GSH conjugates can be characterized using mass spectrometry (MS)-based methods. In the present study, an efficient method was developed for rapid identification and characterization of GSH-trapped metabolites with a single run using a quadrupole orbitrap high-resolution mass spectrometer. The selective ion monitoring of m/z 272.0888, a characteristic product ion corresponding to deprotonated γ-glutamic-dehydroalanyl-glycine in the negative ionization mode, was applied as a survey scan leveraging all ion fragmentation mode using in-source collision-induced dissociation. Detection of the extracted product ions within 5.0Δppm mass accuracy indicated the presence of putative GSH conjugates. Incorporation of fast polarity switching option and multiple data-dependent acquisition scans in a single cycle allowed the determination of accurate mass and multiple MS/MS spectra of GSH conjugates in both negative and positive ionization modes, which featured rich fragments for structural characterization. The effectiveness of this method was evaluated with four model compounds including acetaminophen, clozapine, diclofenac, and nefazodone in both liver microsome and cryopreserved hepatocyte incubations. Successful characterization of multiple GSH conjugates in each case validated this method. Overall, this approach provided a sensitive tool for rapid detection and characterization of GSH conjugates in vitro. Notably, this method could be suitable for high-throughput screening of reactive metabolites in the early drug discovery process. Graphical abstract Sensitive detection and characterization of glutatione conjugates using a high-resolution quadrupole orbitrap mass spectrometer.

P and S Velocity Structure in the Groningen Gas Reservoir From Noise Interferometry

AbstractNoise interferometry has proven to be a powerful tool to image seismic structure. In this study we used data from 10 geophones located in a borehole at ∼3 km depth within the Groningen gas reservoir in the Netherlands. The continuous data cross correlations show that noise predominantly comes in from above. The observed daily and weekly variations further indicate that the noise has an anthropogenic origin. The direct P wave emerges from the stacked vertical component cross correlations with frequencies up to 80 Hz and the direct S wave is retrieved from the horizontal components with frequencies up to 50 Hz. The measured intergeophone travel times were used to retrieve the P and S velocity structure along the borehole, and a good agreement was found with well log data. In addition, from the S wave polarizations, we determined azimuthal anisotropy with a fast direction of N65°W±18° and an estimated magnitude of (4±2)%. The fast polarization direction corresponds to the present direction of maximum horizontal stress measured at nearby boreholes but is also similar to the estimated paleostress direction.

A Simple Proof of Fast Polarization

Fast polarization is a key property of polar codes. It was proved for the binary polarizing $2 \times 2$ kernel by Arikan and Telatar. The proof was later adapted to the general case by Sasoglu. We give a simplified proof.

Fast polarization mechanisms in the uniaxial tungsten-bronze relaxor strontium barium niobate SBN-81

The high-frequency dielectric response of the uniaxial strontium barium niobate crystals with 81% of Sr has been studied from 1 kHz to 30 THz along the polar c axis by means of several techniques (far infrared, time domain terahertz, high-frequency and low-frequency dielectric spectroscopies) in a wide temperature interval 20–600 K. Relaxor properties were observed in the complex dielectric response and four main excitations were ascertained below the phonon frequencies. These fast polarization mechanisms take place at THz, GHz and MHz ranges and show different temperature evolution. The central mode excitation in the THz range, related to anharmonic dynamics of cations, slightly softens from high temperatures and then hardens below T ~ 400 K. Below the phase transition (at T ~ 330 K) an additional microwave excitation appears near 10 GHz related to micro domain wall oscillations. The strongest relaxation appears in the GHz range and slows down on cooling according to the Arrhenius law. Finally, another relaxation, present in the MHz range at high temperatures, also slows down on cooling at least to the kHz range. These two relaxations are due to polar fluctuations and nanodomains dynamics. Altogether, the four excitations explain the dielectric permittivity maximum in the kHz range.

Insights into asthenospheric anisotropy and deformation in Mainland China

Seismic anisotropy can provide direct constraints on asthenospheric deformation which also can be induced by the inherent mantle flow within our planet. Mantle flow calculations thus have been an effective tool to probe asthenospheric anisotropy. To explore the source of seismic anisotropy, asthenospheric deformation and the effects of mantle flow on seismic anisotropy in Mainland China, mantle flow models driven by plate motion (plate-driven) and by a combination of plate motion and mantle density heterogeneity (plate-density-driven) are used to predict the fast polarization direction of shear wave splitting. Our results indicate that: (1) plate-driven or plate-density-driven mantle flow significantly affects the predicted fast polarization direction when compared with simple asthenospheric flow commonly used in interpreting the asthenospheric source of seismic anisotropy, and thus new insights are presented; (2) plate-driven flow controls the fast polarization direction while thermal mantle flow affects asthenospheric deformation rate and local deformation direction significantly; (3) asthenospheric flow is an assignable contributor to seismic anisotropy, and the asthenosphere is undergoing low, large or moderate shear deformation controlled by the strain model, the flow plane/flow direction model or both in most regions of central and eastern China; and (4) the asthenosphere is under more rapid extension deformation in eastern China than in western China.

Seismic anisotropies of the Songshugou peridotites (Qinling orogen, central China) and their seismic implications

Though extensively studied, the roles of olivine crystal preferred orientations (CPOs or fabrics) in affecting the seismic anisotropies in the Earth's upper mantle are rather complicated and still not fully known. In this study, we attempted to address this issue by analyzing the seismic anisotropies [e.g., P-wave anisotropy (AVp), S-wave polarization anisotropy (AVs), radial anisotropy (ξ), and Rayleigh wave anisotropy (G)] of the Songshugou peridotites (dunite dominated) in the Qinling orogen in central China, based on our previously reported olivine CPOs. The seismic anisotropy patterns of olivine aggregates in our studied samples are well consistent with the prediction for their olivine CPO types; and the magnitude of seismic anisotropies shows a striking positive correlation with equilibrium pressure and temperature (P–T) conditions. Significant reductions of seismic anisotropies (AVp, max. AVs, and G) are observed in porphyroclastic dunite compared to coarse- and fine-grained dunites, as the results of olivine CPO transition (from A-/D-type in coarse-grained dunite, through AG-type-like in porphyroclastic dunite, to B-type-like in fine-grained dunite) and strength variation (weakening: A-/D-type → AG-type-like; strengthening: AG-type-like → B-type-like) during dynamic recrystallization. The transition of olivine CPOs from A-/D-type to B-/AG-type-like in the forearc mantle may weaken the seismic anisotropies and deviate the fast velocity direction and the fast S-wave polarization direction from trench-perpendicular to trench-oblique direction with the cooling and aging of forearc mantle. Depending on the size and distribution of the peridotite body such as the Songshugou peridotites, B- and AG-type-like olivine CPOs can be an additional (despite minor) local contributor to the orogen-parallel fast velocity direction and fast shear-wave polarization direction in the orogenic crust such as in the Songshugou area in Qinling orogen.

Large-scale trench-normal mantle flow beneath central South America

We investigate the anisotropic properties of the fore-arc region of the central Andean margin between 17–25°S by analyzing shear-wave splitting from teleseismic and local earthquakes from the Nazca slab. With partly over ten years of recording time, the data set is uniquely suited to address the long-standing debate about the mantle flow field at the South American margin and in particular whether the flow field beneath the slab is parallel or perpendicular to the trench. Our measurements suggest two anisotropic layers located within the crust and mantle beneath the stations, respectively. The teleseismic measurements show a moderate change of fast polarizations from North to South along the trench ranging from parallel to subparallel to the absolute plate motion and, are oriented mostly perpendicular to the trench. Shear-wave splitting measurements from local earthquakes show fast polarizations roughly aligned trench-parallel but exhibit short-scale variations which are indicative of a relatively shallow origin. Comparisons between fast polarization directions from local earthquakes and the strike of the local fault systems yield a good agreement. To infer the parameters of the lower anisotropic layer we employ an inversion of the teleseismic waveforms based on two-layer models, where the anisotropy of the upper (crustal) layer is constrained by the results from the local splitting. The waveform inversion yields a mantle layer that is best characterized by a fast axis parallel to the absolute plate motion which is more-or-less perpendicular to the trench. This orientation is likely caused by a combination of the fossil crystallographic preferred orientation of olivine within the slab and entrained mantle flow beneath the slab. The anisotropy within the crust of the overriding continental plate is explained by the shape-preferred orientation of micro-cracks in relation to local fault zones which are oriented parallel to the overall strike of the Andean range. Our results do not provide any evidence for a significant contribution of trench-parallel mantle flow beneath the subducting slab.

Sensing Characteristics of Arc-Induced Long Period Gratings in Polarization-Maintaining Panda Fiber

We present and discuss an investigation of the sensing features of long period gratings fabricated in a polarization-maintaining Panda optical fiber, by means of the electric arc discharge technique. In particular, the investigation regards the resonant wavelength shift of first three cladding modes as function of three environmental parameters, such as strain, temperature, and surrounding medium refractive index. We also investigate and discuss the variations of the sensing behavior as a function of the polarization input state. The achieved results show that the sensitivity of each resonant wavelength to environmental parameters is modulated by the cladding mode order and by polarization input light, with some appealing characteristics. For instance, the lowest order cladding mode in slow polarization state is practically insensitive to temperature and surrounding refractive index, but sensitive to strain. Temperature and strain sensitivities show opposite signs with the input light polarization. Sensitivity to surrounding refractive index is higher in the case of fast polarization state. These results represent a concrete perspective of the possibility that this device can act as a 3-parameter sensor.

Challenges in the Measurement of Passive Dissolution of Steel in Concrete

The corrosion rate of the steel reinforcement of concrete is measured and monitored by various techniques that include galvanostatic pulses and linear polarization resistance, among others. However, few studies have evaluated techniques for measurements of passive steel with very low corrosion rates, typically lower than 10-8 A/cm2. The measurement of such low corrosion rates is a challenging goal as it is difficult to separate polarization currents due to interfacial charge storage to those related to the anodic metal dissolution. A modeling approach is presented treating the time-domain small amplitude linear-regime behavior of a Constant Phase Element as if it were valid over a broad potential range. Application of that approach rapidly yielded corrosion rates similar to those of much more time consuming tests. The findings suggest fast scan rate cyclic polarization with model fitting as a promising alternative to other methods for monitoring structures in the field.

Joint polarization tracking and channel equalization based on radius-directed linear Kalman filter

We propose a joint polarization tracking and channel equalization scheme based on radius-directed linear Kalman filter (RD-LKF) by introducing the butterfly finite-impulse-response (FIR) filter in our previously proposed RD-LKF method. Along with the fast polarization tracking, it can also simultaneously compensate the inter-symbol interference (ISI) effects including residual chromatic dispersion and polarization mode dispersion. Compared with the conventional radius-directed equalizer (RDE) algorithm, it is demonstrated experimentally that three times faster convergence speed, one order of magnitude better tracking capability, and better BER performance is obtained in polarization division multiplexing 16 quadrature amplitude modulation system. Besides, the influences of the algorithm parameters on the convergence and the tracking performance are investigated by numerical simulation.

Shear-Wave Splitting and Crustal Anisotropy in the Shillong–Mikir Plateau of Northeast India

Seismic anisotropy of crust beneath the Shillong–Mikir Plateau and the surrounding regions of northeast India have been investigated with the help of splitting analysis of S-wave of local earthquakes. We estimate a total 83 pairs of splitting parameters (Φ and δt) from 67 local shallow focus earthquakes (depth ≤ 32 km) recorded by the 10 broadband seismological stations operated in the study region. The results show delay times ranging from 0.02 to 0.2 s, which correspond to anisotropy up to 4%, suggesting significant strength of anisotropy in the study region. Fast polarization direction (Φ) in the Shillong Plateau shows mostly NW–SE trend in the western part and NE–SW trend in the northern part. Φs near Kopili fault (KF) follows NW–SE trend. Φ at most of the stations in the study region is consistent with the local stress orientation, suggesting that the anisotropy is mainly caused by preferentially aligned cracks responding to the stress field. On the other hand, anisotropy observed near the KF is due to aligned macroscopic fracture related to strike-slip movement in the fault zone.

Asymmetric ferroelectric switching characteristics of ferroelectric poly(vinylidene fluoride-ran-trifluoroethylene) thin films grown on highly-oriented pyrolytic graphite substrates

Abstract Ferroelectric poly(vinylidene fluoride-ran-trifluoroethylene)(PVDF-TrFE) thin films were deposited on highly-oriented pyrolytic graphite (HOPG) substrates by spin coating. The PVDF-TrFE thin films on HOPG substrates exhibited good ferroelectric properties, with a remnant polarization of 10.2 μC/cm 2 (2Pr ∼20.4 μC/cm 2 ) and a coercive electric field of approximately 1.0 MV/cm. A Pt/PVDF-TrFE/HOPG capacitor had an asymmetric ferroelectric hysteresis loop and asymmetric switching speeds. The fast switching speed of a Pt/PVDF-TrFE/Pt capacitor from downward polarization to upward polarization supported the conclusion that HOPG or graphene electrodes provided fast polarization switching when used as one electrode of a ferroelectric PVDF-TrFE capacitor.

Insight into NE Tibetan Plateau expansion from crustal and upper mantle anisotropy revealed by shear-wave splitting

The northeastern Tibetan plateau margin is the current expansion border, where growth of the plateau is ongoing. We analyze shear-wave splitting at ChinArray stations in the NE Tibetan Plateau and its margin with the stable North Chine Craton. The measurements provide important information on the seismic anisotropy and deformations patterns in the crust and upper mantle, which can be used to constrain the expansion mechanism of the plateau. Along the margin and within the craton, the dominant NW–SE fast polarization direction (FPD) is NW–SE, subparallel to the boundary between the plateau and the North China Craton. The shear-wave splitting measurements on the NE Tibetan Plateau itself generally reflect two-layer anisotropy. The lower-layer anisotropy (with NW–SE FPDs) is consistent in the whole region and FPDs are the same as those in the North China Craton. The upper-layer FPDs are parallel to crustal motion rather than surface structures within the high plateau. The two-layer anisotropy implies the presence of deformed Tibetan lithosphere above the underthrusting North China Craton. The NE Tibetan shows similar deformation patterns at the surface (inferred from GPS) and within the mantle (inferred from shear-wave splitting), but significant crustal anisotropy (parallel to crustal motion) requires mid-lower crustal channel flow or detachment to drive further tectonic uplift of the plateau.

Simple, high efficiency detection of microcystins and nodularin-R in water by fluorescence polarization immunoassay

This manuscript describes the development of a sensitive, fast and easily-performed fluorescence polarization immunoassay (FPIA) for detection of microcystins (MCs) and nodularin-R (NOD) in water. MCs and NOD, the most widespread cyanobacterial toxin are hepatotoxins and tumor promoters, and their acute exposure may result in severe health problems in animals and humans. The fluorescein-based tracers were synthesized, and for the first time preparative high performance liquid chromatography (HPLC) was employed for their purification. Optimal tracers for the analysis were selected by evaluating the immunochemical activity. Under the optimal conditions, the achieved limits of detection (LODs) for MC-LR and NOD were 0.86 and 0.95 μg L−1, respectively, providing a sufficient sensitivity to meet the provisional guideline value recommended by the World Health Organization (WHO). An ultra-performance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS) method was developed to confirm the accuracy and precision of the FPIA, and no obvious difference in recovery between these two methods was found. The correlation coefficients (R2) were higher than 0.968. The developed FPIA was easy-to-operate and could be completed within 10 min after simple filtration and adjustment of pH for water samples. The method can be easily extended for screening of other cyanotoxins, representing a versatile strategy for environmental sample analysis.

Hadamard-Encoded Multipulses for Contrast-Enhanced Ultrasound Imaging

The development of contrast-enhanced ultrasound (CEUS) imaging offers great opportunities for new ultrasound clinical applications such as myocardial perfusion imaging and abdominal lesion characterization. In CEUS imaging, the contrast agents (i.e., microbubbles) are utilized to improve the contrast between blood and tissue based on their high nonlinearity under low ultrasound pressure. In this paper, we propose a new CEUS pulse sequence by combining Hadamard-encoded multipulses (HEM) with fundamental frequency bandpass filter (i.e., filter centered on transmit frequency). HEM consecutively emits multipulses encoded by a second-order Hadamard matrix in each of the two transmission events (i.e., pulse-echo events), as opposed to conventional CEUS methods which emit individual pulses in two separate transmission events (i.e., pulse inversion (PI), amplitude modulation (AM), and PIAM). In HEM imaging, the microbubble responses can be improved by the longer transmit pulse, and the tissue harmonics can be suppressed by the fundamental frequency filter, leading to significantly improved contrast-to-tissue ratio (CTR) and signal-to-noise ratio (SNR). In addition, the fast polarity change between consecutive coded pulse emissions excites strong nonlinear microbubble echoes, further enhancing the CEUS image quality. The spatial resolution of HEM image is compromised as compared to other microbubble imaging methods due to the longer transmit pulses and the lower imaging frequency (i.e., fundamental frequency). However, the resolution loss was shown to be negligible and could be offset by the significantly enhanced CTR, SNR, and penetration depth. These properties of HEM can potentially facilitate robust CEUS imaging for many clinical applications, especially for deep abdominal organs and heart.