Large Intensity Research Articles

Quasi-static optical parametric amplification

High-gain optical parametric amplification is an important nonlinear process used both as a source of coherent infrared light and as a source of nonclassical light. In this work, we experimentally demonstrate an approach to optical parametric amplification that enables extremely large parametric gains with low energy requirements. In conventional nonlinear media driven by femtosecond pulses, multiple dispersion orders limit the effective interaction length available for parametric amplification. Here, we use the dispersion engineering available in periodically poled thin-film lithium niobate nanowaveguides to eliminate several dispersion orders at once. The result is a quasi-static process; the large peak intensity associated with a short pump pulse can provide gain to signal photons without undergoing pulse distortion or temporal walk-off. We characterize the parametric gain available in these waveguides using optical parametric generation, where vacuum fluctuations are amplified to macroscopic intensities. In the unsaturated regime, we observe parametric gains as large as 71 dB (118 dB/cm) spanning 1700–2700 nm with pump energies of only 4 pJ. When driven with pulse energies > 10 p J , we observe saturated parametric gains as large as 88 dB ( > 146 d B / c m ). The devices shown here achieve saturated optical parametric generation with orders of magnitude less pulse energy than previous techniques.

The occurrence of adverse events following immunization after first and/or second dose of Covishield or Covaxin vaccine at a tertiary care hospital: An observational study

Background: With the introduction of the COVID-19 vaccine, many cities of India are reporting minor, mild, and severe AEFI cases during half an hour of observation and after that. No vaccine can protect everyone receiving it and is safe too for everyone. Effective vaccines could produce a few unwanted side effects mainly mild and clear up frequently.Methods: After the COVID-19 vaccination, everyone was asked to wait for 30 minutes in the observation room to check for any type of AEFI. While waiting, all second dose beneficiaries were asked to fill a printed case record form with all demographic details, including AEFI events experienced after their first dose of the COVID-19 vaccine. Phone calls were made to all 500 beneficiaries after seven days of vaccination to know about the type of AEFI experienced after the second dose.Results: Safety of product is of paramount importance and in this study, we actively captured adverse events post-vaccination. Fever, headache, weakness, body pain, were the most common adverse events along with pain at the injection site. In our study, the younger age group was associated with minor AEFIs. However, we did not find any supporting evidence for high reactogenicity among women, and this may be due to an almost similar proportion of men and women in our sample.Conclusions: The advantages of immunization in disease prevention have significantly exceeded the risks of immunization-associated adverse events. COVID vaccines have their largest potential to end the COVID-19 pandemic if they are widely accepted and used. As we all want to get rid of the diseases which are not curable easily and spread with very large intensity, now is the time to get vaccinated and control them.

Relative Impact of Climate Change and Grazing on NDVI Changes in Grassland in the Mt. Qomolangma Nature Reserve and Adjacent Regions during 2000–2018

As the roof of the world, the Mt. Qomolangma National Nature Reserve and adjacent regions have a fragile environment and are very sensitive to global climate change. Based on the MODIS and SPOT remote sensing data during 2000–2018, we aimed to explore the change trend and driving factors of grassland in this area under the dual influence of climate change and human activities. Here, temperature and precipitation data were enrolled as the main indicators of climate change, while the number of livestock at the end of the year was regarded as the key indicator of grazing. The results showed that: (1) during 2000–2018, the grassland NDVI reflected an overall increasing trend, and the impact of precipitation was more significant than those of temperature and grazing at both pixel and county levels; (2) probably due to the large population and high grazing intensity, the grassland NDVI in Tingri County was controlled by both precipitation and grazing. In general, precipitation exerts a greater impact on the NDVI changes since this region is characterized by arid and semiarid climates. In some areas, vegetation growth is simultaneously affected by both grazing and climate factors due to the relatively greater pressure of grazing. In the context of future warming, control of the number of tourists for Mt. Qomolangma, as well as that of livestock in Tingri County, will help improve sustainability development and to reduce the adverse effects of grassland degradation.

Extraction of P Wave From Ambient Seafloor Noise Observed by Distributed Acoustic Sensing

AbstractSeismic wave extractions have been performed using ambient noise records observed by distributed acoustic sensing (DAS) technology. Extractions of microseisms can be investigated at a local scale using such DAS records observed in the ocean. Here, we show P and Scholte wave extractions from ambient seafloor noise observed by DAS along a submarine cable deployed off Cape Muroto in the Nankai subduction zone, Japan. The P waves can be observed at a frequency band of 0.1–0.3 Hz and up to a distance of 8 km. The distance at which the P waves can be observed is controlled by the P incident angle and the DAS sensitivity to the observable apparent velocity. Effective extractions of P and Scholte waves, corresponding to large intensity of wave‐wave interaction at the sea surface, are performed, indicating that the waves are originated from pressure field at the sea surface.

A voxel-based three-dimensional framework for flash drought identification in space and time

Flash drought (FD) is an extreme event causing severe impacts on ecosystems and agriculture due to its fast velocity of evolution and high frequency. Here, we develop a voxel-based three-dimensional FD (V3DFD) method to track the spatio-temporal dynamics of FD based on the soil moisture (SM) decline method proposed by Yuan et al. (2019). The key idea of V3DFD is that FD is identified in terms of the connectivity of drought voxels (i.e., cubes with width, length and height representing latitude, longitude and time, respectively) in 3D space instead of directly forming the drought events by merging drought clusters. The V3DFD is systematically evaluated and compared with the commonly used 3D severity-area-duration (SAD) method in four provinces in China: Guangdong (GD), Guangxi (GX), Guizhou (GZ), and Yunnan (YN). Results show that V3DFD can better reflect the dynamic development and recovery of FD events compared with SAD. Regional analyses indicate that FD occurs more frequent with a larger intensity and longer duration in GD and GX than YN and GZ. The onset (terminal) of FD in YN occurs mostly in April-May (April-June). The onset of FD in GX and GD is scattered at the intra-annual scale, but the terminal occurs mostly in November. In addition, the first FD event in a year is mostly located during April-May in YN and GZ, while the last FD event of a year occurs mostly during October-November in GX and GD.

Daytime Ionospheric Large‐Scale Plasma Density Depletion Structures Detected at Low Latitudes Under Relatively Quiet Geomagnetic Conditions

AbstractThe ionospheric electron density is expected to enhance after sunrise during geomagnetic quiet days. In this paper, we report an anomalous large‐scale ionospheric TEC depletion structure occurring in morning hours over low latitudes in China under relatively quiet geomagnetic conditions. The depletion structure, which occurred over a wide longitude range of >35°, developed toward higher latitudes at the speed of ∼250 m/s. A statistical analysis using the data in 2018–2020 showed that such large‐scale daytime TEC depletion mainly occurred in summer (mostly with Kp < 3), with large intensities at ∼16–30°N. The geomagnetic ΔH measurements at the stations near and away from the magnetic dip equator showed positive values, which rules out the possible contribution from a westward electric field. Observations from multiple ionosondes revealed a net downward plasma transport during the TEC depletion. An enhanced poleward neutral wind during the early morning hours, which may induce downward plasma transport, was surmised to play a leading role in driving the large‐scale morning TEC depletion.

Direct numerical simulation of a stationary spherical particle in fluctuating inflows

Fully resolved direct numerical simulations are conducted to study the effects of fluctuating freestream flow on the drag force and wake characteristics of a stationary spherical particle. Sinusoidal fluctuation around a mean value is adopted as the freestream velocity. The interaction between the particle and fluctuating flow is computed by the direct-forcing immersed boundary method. We principally consider the relative difference between the computed mean drag and the drag law of a uniform flow past the particle and the properties of drag fluctuation in different freestream fluctuation directions. For the influence of streamwise fluctuating inflow, the relative mean drag difference increases with the particle Reynolds number. At small or intermediate particle scale ratios, the relative mean drag difference is very close to zero, indicating that the classical drag law can be used in these cases, while a large particle scale ratio can induce a notable increase in the relative mean drag difference at a large particle Reynolds number and high fluctuation intensity. For the transverse fluctuating inflow, generally, there is an evident increase in the mean drag coefficient when the particle scale ratio is small. Compared with the streamwise fluctuation case, the drag fluctuation intensity is a little smaller with the transverse fluctuating inflow. An explicit empirical drag fluctuation law is obtained by fitting the data for streamwise fluctuating inflow. The wake characteristics are also analyzed, and they are found to be strongly dependent on the direction of inflow fluctuation.

LPSO: Multi-Source Image Matching Considering the Description of Local Phase Sharpness Orientation

To solve the matching problems caused by the large intensity difference between the multi-source images and the nonlinear radiation distortion, we present a multi-source image matching approach that considers the orientation of the phase sharpness. First, the scale-space of the image pyramid was constructed, and the phase consistency of the image frequency domain was solved to obtain the maximum moment feature, and the KAZE operator is used to extract the feature points. Next, the Log-Gabor even symmetric filter was used to perform Fourier transform, and the improved local phase sharpness feature and phase orientation feature were constructed respectively to replace the gradient amplitude and gradient direction feature of the image. A descriptor of local phase sharpness orientation (LPSO) was established through the log-polar description template, and finally the Euclidean distance was used to measure the similarity to obtain the corresponding points. Multiple sets of typical multi-source images were used as data sources, and the LPSO algorithm was compared with SIFT, LGHD, RIFT and HAPCG algorithms in datasets. Evaluation of the algorithm performances indicates that the proposed method is more accurate and robust in the task of multi-source image matching.

Ecological Risk Assessment using Satellite Derived NDVI, HFP and Rainfall Erosivity in Nepal

Understanding vegetation dynamics is becoming increasingly crucial to maintain ecosystem in the Himalaya region. An assessment of the normalized difference vegetation index (NDVI) and human footprint pressure indicates the ecological risk scenario of Nepal. The original NOAA NDVI product available from 1981-2015 were used. Similarly, Human footprint pressure data for 1993 and 2009 were used. The study purpose was to develop ecological risk map based on NDVI dynamics and human pressure to natural resources. The result showed that the intensity of vegetation dynamics was 0.065 yr-1 with large positive and negative intensities observed in 2006 and 1984, respectively. Both of the intensity of vegetation changes and variance of NDVI showed increased ecological fragility in the Tran-Himalayan region. However, negative correlation between NDVI and rainfall erosivity showed reduced soil erosion and ecological risk in the region. The human footprint pressure has increased up to 43 which together with increasing annual population growth trend (1.35 yr-1) has exerted pressure on the natural system and created ecological risk. The results have important implications for a better understanding of the vegetation dynamics in response to ongoing climatic variability and associated ecological risks in Nepal.

A Semi-Lagrangian Computation of Front Speeds of G-equation in ABC and Kolmogorov Flows with Estimation via Ballistic Orbits

The Arnold-Beltrami-Childress (ABC) flow and the Kolmogorov flow are three dimensional periodic divergence free velocity fields that exhibit chaotic streamlines. We are interested in front speed enhancement in G-equation of turbulent combustion by large intensity ABC and Kolmogorov flows. We give a quantitative construction of the ballistic orbits of ABC and Kolmogorov flows, namely those with maximal large time asymptotic speeds in a coordinate direction. Thanks to the optimal control theory of G-equation (a convex but non-coercive Hamilton-Jacobi equation), the ballistic orbits serve as admissible trajectories for front speed estimates. To study the tightness of the estimates, we compute the front speeds of G-equation based on a semi-Lagrangian (SL) scheme with Strang splitting and weighted essentially non-oscillatory (WENO) interpolation. Time step size is chosen so that the Courant number grows sublinearly with the flow intensity. Numerical results show that the front speed growth rate in terms of the flow intensity may approach the analytical bounds from the ballistic orbits.

Testing the simultaneity of Forbush decreases with algorithm-selected Forbush event catalogue

Accurate detection and precise timing of transient events such as X-ray photons, $$\gamma $$ -ray burst, coronal mass ejections (CMEs), ground-level enhancements (GLEs) and Forbush decreases (FDs) frequently raise issues that remain on the cutting edge of research in astrophysics. In an attempt to automate FD event selection, a combination of Fast Fourier transform as well as FD detection algorithms implemented in the statistical computing software R was developed and recently used to calculate the magnitude and FD event timing. The R-FD code implemented in the present study includes several different calculations. Some subroutines detect both small and large transient intensity reductions (minima/pits) as well as increases (maxima/peaks) in cosmic ray (CR) data. Others calculate event amplitude, timing and cataloguing of the events identified. As the current work focuses on reductions in CR flux (FDs), the subroutine that identifies increases was disabled. Totals of 229 FDs at Magadan neutron monitor (NM), 230 (Oulu NM) and 224 (Inuvick NM) were identified with daily averaged data, while 4032 (Magadan), 4144 (Oulu) and 4055 (Inuvick) were detected with hourly averages. FDs identified as simultaneous at the three stations totaled 99 for the daily and 261 for the hourly CR averages respectively.

Light Emission Enhancement of (C3H10N)4Pb1-xMnxBr6 Metal-Halide Powders by the Dielectric Confinement Effect of a Nanosized Water Layer.

Organic-inorganic hybrid metal halides have been widely studied as a kind of phosphor materials for high-performance white light-emitting diodes. In this paper, a series of organic-inorganic metal-halide (C3H10N)4Pb1-xMnxBr6 powders with different Mn2+ ion doping concentrations were synthesized by mechanochemical methods, giving broadband white light emission with a photoluminescence quantum yield of 36.1% at room temperature, which turn green with a much larger intensity at 80 K. Interestingly, its emission converted from white to red after 100 °C treatments and turned back to white again when exposed to moist air for a while. This emission variation was caused by the adsorbed water layer on the surface of product powders via the dielectric confinement. The red emission from no water powders is identified to occur from the Mn ferromagnetic pair in point-shared octahedral sites, while the broadband white emission originated from the surface water-assisted dielectric confinement and surface polarization which combine the self-trapped excitons and d-d transitions of Mn ions and Mn pairs in the product. Moreover, this white emission can transform into green color at 80 K with a much stronger intensity, caused by the even efficient surface dielectric confinement by the adsorbed frozen water layer. This special compound has the advantages of simple preparation, low cost, and good stability and even contains water molecule in the air, giving a near-perfect white emission, with CIE of (0.33, 0.35) and correlated color temperatures at around 5733 K, which may be used for different applications such as sensing, solid-state lighting, and display.

Averaging of magnetic fields and applications

In this paper, we estimate the magnetic Laplacian energy norm in appropriate planar domains under a weak regularity hypothesis on the magnetic field. Our main contribution is an averaging estimate, valid in small cells, allowing us to pass from non-uniform to uniform magnetic fields. As a matter of application, we derive new upper and lower bounds of the lowest eigenvalue of the Dirichlet Laplacian which match in the regime of large magnetic field intensity. Furthermore, our averaging technique allows us to estimate the nonlinear Ginzburg–Landau energy, and as a byproduct, yields a non-Gaussian trial state for the Dirichlet magnetic Laplacian.

Impact ionization and multiple photon absorption in the two-dimensional photoexcited Hubbard model

We study the non-equilibrium response of a 4x3 Hubbard model at U=8 under the influence of a short electric field pulse, with the main focus on multiple photon excitations and on the change of double occupancy after the pulse. The behavior mainly depends on the driving frequency of the electric field. The largest change of double occupancy occurs during the pulse. For frequencies below the Mott gap, we observe multiphoton excitations at large field intensities. For frequencies beyond the gap energy, there is a region where Auger recombination reduces the double occupancy after the pulse. Impact ionization (Multi Exciton Generation), namely a growing double occupancy after the pulse, occurs for frequencies larger than twice the Mott gap. From the Loschmidt amplitude we compute the eigenstate spectrum of the quantum state after the pulse, observing multiple distinct photon excitation peaks, in line with expectations from a quasiparticle picture. We introduce a technique with which we analyze the time evolution of double occupancy in each peak individually. The long-term behavior of the double occupancy almost only depends on the absorbed energy, and we explore the connection of this property to the Eigenstate Thermalization Hypothesis.

The Fragmented Glueball: A Personal View

A coupled-channel analysis has been performed to identify the spectrum of scalar mesons. The data include BESIII data on radiative J/ψ decays into π0π0, KS KS, ηη, and ωϕ, 15 Dalitz plots from ¯N annihilation at rest at LEAR, the CERN-Munich multipoles for ππ elastic scattering, the S-wave from BNL data on ππ scattering into KS KS, from GAMS data on ππ π0π0; ηη, and ηη', and NA48/2 data on low-mass ππ interactions from K± → ππe±v decays. The analysis reveals the existence of ten scalar isoscalar resonances. The resonances can be grouped into two classes: resonances with a large SU(3) singlet component and those with a large octet component. The production of isoscalar resonances with a large octet component should be suppressed in radiative J/ψ decays. However, in a limited mass range centered at 1900MeV, these mesons are produced abundantly. Mainly-singlet scalar resonances are produced over the full mass range but with larger intensity at 1900MeV. The total scalar isoscalar yield in radiative decays into scalar mesons shows a clear peak which is interpreted as the scalar glueball of lowest mass.

Analysis of Rainstorm Flood Induced Flash Flood in Wende River Basin

Due to the joint influence of climate and topography, flash flood disasters in the Wende River Basin of Jilin Province occurred repeatedly, causing serious casualties and huge economic losses; in July 2017, three floods with large rainfall intensity and profound influence occurred in a row in the main stream of Wende River. Based on official measured data of the Wende River basin, three typical rainfall processes (“July 13”, “July 20” and “, “August 3 “) are selected to discuss the rainfall characteristics. The triggered characteristics, induced factors and the disaster mechanism of the basin are preliminarily explored from the aspects of rainfall weather system, temporal and spatial distribution of rainstorm and flood, geographical factors to analyze the best countermeasures for flash flood prevention. The above will provide reference for the non-engineering measure project of flash flood prevention currently under construction.

Investigation of indoor environment and thermal comfort of building installed with bifacial PV modules

In comparison with common PV module, bifacial PV module can increase energy output by installing cells on both sides of the module. Due to the thermoelectric effect in the rear, the impact of bifacial PV module on indoor environment is more complex. To study indoor environment of bifacial PV module as building envelope, a building integrated bifacial PV module was established. Through the experiments and simulation of the PV building, it is found that thermal stratification is obvious at noon in summer, which indicates the bifacial PV module causes a large influence on the indoor temperature. PMV is between -1 and +1 in summer nights and winter days but it becomes poor in sunny days due to the large solar radiation intensity. Additionally, the indoor light environment is studied. The indoor lighting is ideal in general but overlarge when the solar radiation is too strong. For the purpose of improving the indoor comfort, the coverage of PV module was changed and the heat insulation reflective layer was installed behind the PV modules. With the optimization design, the indoor environment has been significantly improved, and the period of annual thermal comfort has increased by 8%.

Femtosecond dynamics of stepwise two-photon ionization in solutions as revealed by pump-repump-probe detection with a burst mode of photoexcitation.

Pump-repump-probe spectroscopy with a burst mode of photoexcitation was applied to the direct observation of the photoionization dynamics of perylene in the solution phase. Irradiation of a pump pulse train generated with birefringent crystals effectively accumulated an intermediate S1 state and a repump pulse triggered photoionization in the higher excited state, ensuring sufficiently large signal intensity to probe. Two-photon excitation to the energy level, which is 0.7 eV lower than the ionization potential in the gas phase, results in instantaneous formation of the radical cation of perylene in acetonitrile, unlike aromatic amines in previous reports. In addition, subsequent recombination dynamics between the radical cation and ejected electron was monitored in polar and nonpolar solvents. The ultrafast recombination in nonpolar solvents suggests that the distribution of the distance in the cation-ejected electron pair largely evolves even in acetonitrile in the femtosecond timescale, in which the solvation is not completed and the dielectric constant is still low. The recombination process in acetonitrile was well reproduced with simulations based on the Smoluchowski equation taking account of the transient change in the dielectric constant by solvation.

Single-shot experiments at the soft X-FEL FERMI using a back-side-illuminated scientific CMOS detector.

The latest Complementary Metal Oxide Semiconductor (CMOS) 2D sensors now rival the performance of state-of-the-art photon detectors for optical application, combining a high-frame-rate speed with a wide dynamic range. While the advent of high-repetition-rate hard X-ray free-electron lasers (FELs) has boosted the development of complex large-area fast CCD detectors in the extreme ultraviolet (EUV) and soft X-ray domains, scientists lacked such high-performance 2D detectors, principally due to the very poor efficiency limited by the sensor processing. Recently, a new generation of large back-side-illuminated scientific CMOS sensors (CMOS-BSI) has been developed and commercialized. One of these cost-efficient and competitive sensors, the GSENSE400BSI, has been implemented and characterized, and the proof of concept has been carried out at a synchrotron or laser-based X-ray source. In this article, we explore the feasibility of single-shot ultra-fast experiments at FEL sources operating in theEUV/soft X-ray regime with an AXIS-SXR camera equipped with the GSENSE400BSI-TVISB sensor. We illustrate the detector capabilities by performing a soft X-ray magnetic scattering experiment at the DiProi end-station of the FERMI FEL. These measurements show the possibility of integrating this camera for collecting single-shot images at the 50 Hz operation mode of FERMI with a cropped image size of 700× 700 pixels. The efficiency of the sensor at a working photon energy of 58 eV and the linearity over the large FEL intensity have been verified. Moreover, on-the-fly time-resolved single-shot X-ray resonant magnetic scattering imaging from prototype Co/Pt multilayer films has been carried out with a time collection gain of 30 compared to the classical start-and-stop acquisition method performed with the conventional CCD-BSI detector available at the end-station.

UAV Remote Sensing Image Dehazing Based on Double-Scale Transmission Optimization Strategy

Current dehazing methods for unmanned aerial vehicle (UAV) remote sensing images often have texture detail loss and color distortion problems, especially in highlighted regions. This is mainly due to the rich texture and low intensity of UAV remote sensing images being ignored, which results in incorrect transmission estimation. In this paper, we propose a UAV remote sensing image dehazing method based on double-scale transmission optimization strategy. First, we propose a double-scale optimization strategy to estimate the transmission map with more accurate texture details and color preservation, especially in highlighted regions of hazy UAV images that are most severely distorted. Second, a UAV-adaptive haze-line prior algorithm is proposed to address the large scene depth and low intensity of UAV remote sensing images. Finally, we introduce a luminance-weighted frequency domain saliency model to avoid texture detail loss and color distortions for better transmission optimization, especially in highlighted regions. Compared with state-of-the-art methods, our method shows better detail performance and visual effects, especially for UAV images with highlighted regions.