Phase Increment Research Articles

Kinetic theory of nonrelativistic electron beam–inhomogeneous plasma system instability

On the basis of kinetic theory, the stability of an electron beam interacting with inhomogeneous plasma is investigated at Knudsen numbers of the order of 1. The theory has been tested on the example of a low-voltage beam discharge in a rear gas. It is shown that in the case of an inhomogeneous plasma even if the attenuation of a beam is neglected, several perturbations can propagate simultaneously at the same frequency, but with different phase and group velocities and increments. The case of a linear dependence of the plasma density on the coordinate is investigated in detail. In this case, there are two solutions: n- and p-waves, only the n-wave having a physical meaning. It is found that an increase in the plasma density gradient leads to a decrease in the increment and an increase in the phase and group velocities of propagation of perturbations with a frequency of the order of plasma frequency. A system with a growing plasma density along the beam direction is more stable than that with a constant density. For a significant change in the growth rate of the disturbance, the relative gradient of plasma density by an amount of about 10% at the wavelength is sufficient. All the observed features of the perturbation parameters depending on the plasma density gradient are physically interpreted. The calculations are confirmed by experimental data.

Phase-based fast 3D high-resolution quantitative T2 MRI in 7 T human brain imaging

Magnetic resonance imaging (MRI) is a powerful and versatile technique that offers a range of physiological, diagnostic, structural, and functional measurements. One of the most widely used basic contrasts in MRI diagnostics is transverse relaxation time (T2)-weighted imaging, but it provides only qualitative information. Realizing quantitative high-resolution T2 mapping is imperative for the development of personalized medicine, as it can enable the characterization of diseases progression. While ultra-high-field (≥ 7 T) MRI offers the means to gain new insights by increasing the spatial resolution, implementing fast quantitative T2 mapping cannot be achieved without overcoming the increased power deposition and radio frequency (RF) field inhomogeneity at ultra-high-fields. A recent study has demonstrated a new phase-based T2 mapping approach based on fast steady-state acquisitions. We extend this new approach to ultra-high field MRI, achieving quantitative high-resolution 3D T2 mapping at 7 T while addressing RF field inhomogeneity and utilizing low flip angle pulses; overcoming two main ultra-high field challenges. The method is based on controlling the coherent transverse magnetization in a steady-state gradient echo acquisition; achieved by utilizing low flip angles, a specific phase increment for the RF pulses, and short repetition times. This approach simultaneously extracts both T2 and RF field maps from the phase of the signal. Prior to in vivo experiments, the method was assessed using a 3D head-shaped phantom that was designed to model the RF field distribution in the brain. Our approach delivers fast 3D whole brain images with submillimeter resolution without requiring special hardware, such as multi-channel transmit coil, thus promoting high usability of the ultra-high field MRI in clinical practice.

An alternative Coulomb correction method for numerical study on spiderlike photoelectron momentum distributions

We formulate an analytically-corrected semiclassical rescattering model (AC-SRM) by including analytical correction terms of Coulomb interaction into the standard SRM theory. By using the simple but effective AC-SRM, we perform extensive numerical simulation of the spiderlike photoelectron momentum distributions (PMDs) of hydrogen atom ionized by intense laser pulse. It is shown that the spiderlike structure in the PMDs manifests a systematic shift along the transverse momentum direction upon considering the Coulomb action. This shift is deciphered with a phase map scheme and trajectory analysis, with the former being particularly powerful for the most important first interference minimum of the spiderlike feature. The simulation reveals that the proposed AC-SRM is physically transparent and its computational implementation is economical. In addition, we propose a physical picture of the Coulomb action as a phase increment of the initial longitudinal momentum of the ionized electron.

Effect of phase interface on stretch-flangeability of metastable ferrous medium-entropy alloys

The demand for high-strength, lightweight structural materials has been increasing; however, alloys with high mechanical performance often have limitations such as unfavorable bendability and stretch-flangeability. In terms of stretch-flangeability, an unexpected crack occurring on the trim line during sheet metal forming has recently been considered as an issue of concern by the industry and academia, but its cause and solution have not been determined yet. This study investigated the effect of the phase interface generated by deformation-induced martensitic transformation on the stretch-flangeability of metastable ferrous medium-entropy alloys. We prepared three alloys that exhibited different transformation-induced plasticity behaviors by controlling their grain sizes and chemical compositions. It was observed that the transformation activity, which is dependent on the microstructure and phase stability, considerably affects the hole expansion ratio obtained from the hole expansion test. Microstructural analyses revealed that deformation-induced martensite formed a layered structure and the phase interface between the face-centered cubic (FCC) and body-centered cubic (BCC) phases served as a site vulnerable to cracking during stretch-flanging. The decreased transformation activity by grain refinement resulted in an increase in the hole expansion ratio (HER) from 8.6% to 28.4%. On the other hand, when the phase stability is low enough to form athermal martensite during quenching, most of the FCC grains are easily transformed into BCC phase and the phase interface is also decreased during stretch-flanging, resulting in the HER of 22.9%. Therefore, the increment of phase interfaces leads to lower stretch-flangeability. This study sheds lights on expanding the applicability of TRIP-utilized materials to industry by suggesting ways to improve stretch-flangeability.

A joint linear reconstruction for multishot diffusion weighted non-Carr-Purcell-Meiboom-Gill fast spin echo with full signal.

Diffusion weighted Fast Spin Echo (DW-FSE) is a promising approach for distortionless DW imaging that is robust to system imperfections such as eddy currents and off-resonance. Due to non-Carr-Purcell-Meiboom-Gill (CPMG) magnetization, most DW-FSE sequences discard a large fraction of the signal ( ), reducing signal-to-noise ratio (SNR) efficiency compared to DW-EPI. The full FSE signal can be preserved by quadratically incrementing the transmit phase of the refocusing pulses, but this method of resolving non-CPMG magnetization has only been applied to single-shot DW-FSE due to challenges associated with image reconstruction. We present a joint linear reconstruction for multishot quadratic phase increment data that addresses these challenges and corrects ghosting from both shot-to-shot phase and intrashot signal oscillations. Multishot imaging reduces T2 blur and joint reconstruction of shots improves g-factor performance. A thorough analysis on the condition number of the proposed linear system is described. A joint multishot reconstruction is derived from the non-CPMG signal model. Multishot quadratic phase increment DW-FSE was tested in a standardized diffusion phantom and compared to single-shot DW-FSE and DW-EPI in vivo in the brain, cervical spine, and prostate. The pseudo multiple replica technique was applied to generate g-factor and SNR maps. The proposed joint shot reconstruction eliminates ghosting from shot-to-shot phase and intrashot oscillations. g-factor performance is improved compared to previously proposed reconstructions, permitting efficient multishot imaging. apparent diffusion coefficient estimates in phantom experiments and in vivo are comparable to those obtained with conventional methods. Multi-shot non-CPMG DW-FSE data with full signal can be jointly reconstructed using a linear model.

Design and Implementation of a Subnanometer Heterodyne Interference Signal Processing Algorithm with a Dynamic Filter.

In this study, a subnanometer heterodyne interference signal processing algorithm with a dynamic filter is proposed. The algorithm can effectively reduce the measurement error caused by the noise introduced in the optical path and circuit. Because of the low signal−to−noise ratio of the measurement signal, a dynamic filter with variable coefficients is designed. The role of the bi−quadrature lock−in amplifier algorithm in the problem of different amplitudes among the measurement signal, reference signal, and uncertainty of the frequency difference of the dual−frequency laser is analyzed. With the aid of the heterodyne interferometry platform, the error in the solution results of the proposed algorithm and the conventional algorithm is compared. The results indicate that the maximum deviation of the phase increment of the algorithm does not exceed 6 mrad, the single−cycle phase difference can be subdivided by 1024, and the system resolution reaches 0.15 nm.

Characterization of gap-plasmon-based metasurfaces with scanning white-light interferometry

Subject of study. The possibility of using the well-established method of scanning white-light interferometry (SWLI), implemented as a commercially available device, is studied for characterizing promising metasurfaces based on third-order plasmon resonance. The characteristics of the samples were determined for two types of experimental metasurfaces, namely, for a binary grating with a period of 12.6 µm and a phase gradient grating with a period of 6.75 µm. Objective. The main goals of this study were to test the fundamental possibility of using a commercially available white-light interferometer to determine the phase characteristics of plasmonic metasurfaces and to estimate experimentally the lateral optical resolution in the phase image of metasurfaces. Main results. Although the method of SWLI was originally intended for measuring a geometric microrelief, it was found that it can be used to determine the phase increment of the optical radiation reflected from the studied metasurfaces in the range of 10°–100° with a relative accuracy of approximately 50% without any modification of the signal processing algorithm. The possibility of obtaining a phase mapping of the surface with such accuracy in this configuration is not obvious because the metasurface is a matrix of nanoelements with the same height of 50 nm, and the phase shift in the reflected optical radiation is created due to third-order gap plasmon resonance. On the obtained optical phase images of metasurfaces, unit (single) cells of the metasurface are reliably resolved owing to a sufficiently high lateral resolution (approximately 450 nm). The results of the characterization of metasurfaces obtained using SWLI are compared with those obtained in a laboratory setup using scanning differential heterodyne microscopy (SDHM). Although the SWLI method demonstrates better lateral resolution compared with the SDHM method, it is less accurate in restoring the phase characteristics of metasurfaces with a phase gradient. Practical significance. The results obtained allow us to conclude that the evaluation of the phase optical characteristics of nanostructured plasmonic metasurfaces by the method of SWLI is possible and requires further experimental and theoretical studies.

Quantum Dot Hybridization of Piezoelectric Polymer Films for Non-Transfer Integration of Flexible Biomechanical Energy Harvesters.

This work presents a low-temperature engineering strategy, from quantum dot (QD) synthesis to fabrication of a hybrid from a homogeneous dispersion to thermal annealing with elaborate use of a small organic molecule dopamine, for achieving a kind of ZnO QD-hybridized piezoelectric polymer film directly integrated into a flexible electrode and a plastic substrate. This strategy is the key for non-transfer assembly of flexible piezoelectric nanogenerators (FPENGs) with both mechanical robustness and high electrical performance via direct lamination. The rational addition of dopamine plays multiple roles of (1) significantly decreasing the size of ZnO particles to a QD level (3.77 nm), (2) formation of a stable and homogeneous dispersion of a ZnO QDs/piezoelectric polyvinylidene fluoride-co-hexafluoropropylene copolymer for uniform hybridization of a piezoelectric film, and (3) increment of the piezoelectric phase via induced crystallization at a low annealing temperature. This dopamine-assisted low-temperature annealing strategy for a hybrid piezoelectric film with a high d33 value (∼31.56 pC/N, 30.56% larger than that of a pure piezoelectric polymer film) required no additional high-voltage polarization treatment and effectively avoided the delamination, distortion, or melt phenomenon between the piezoelectric layer, flexible electrode, and plastic protective layer caused by the high temperature and thermal stress. The obtained FPENGs showed significantly enhanced output performance and mechanical robustness under repeated impact and large amounts of strain conditions. Their specific output voltage and charge density were stably maintained at 7.16 V and 2.40 nC/cm2, which were 30.7 and 50.0% higher than those of FPENGs based on a pure piezoelectric polymer film, respectively. They were further used as biomechanical energy harvesters for generating electricity to charge capacitor energy storage devices for power electronics and self-powered sensors for visual motion-detecting systems, indicating their promising applications in both wearable technology and smart homes.

High-accuracy ultrasonic method for in-situ monitoring of oil film thickness in a thrust bearing

The ultrasonic method has been widely applied to measure the oil film thickness – a critical variable that reflects lubrication conditions. However, due to the thermal dependence of ultrasonic signals, significant deviations in film thickness measurements are introduced, hindering the in-situ application of the ultrasonic technique. To address this issue, a real-time temperature compensation method that can accurately obtain the frequency domain information of the reference signal is proposed. Specifically, the reflection from the substrate-coating interface compensates for the thermal effect on the phase increment and amplitude attenuation – this is noted as “self-calibration”. An extra experimental test with a substrate-coating-air structure is performed to calibrate the thermal effect on the coating-induced phase shift – this part is denoted as “pre-calibration”. The combination of “self-calibration” and “pre-calibration” enables the overall temperature compensation strategy. After the effectiveness validation with a temperature-controlled experiment, the proposed method is implemented in a thrust bearing in a heavy-duty hydropower generator with full running conditions, including loading and unloading, normal speed and shut-down. The largely ranged oil film thickness (3–330 μm) is ultrasonically measured and compared with the theoretical value, showing a higher measurement accuracy than the eddy current method.

Phase-cycled balanced SSFP imaging for non-contrast-enhanced functional lung imaging.

To introduce phase-cycled balanced SSFP (bSSFP) acquisition as an alternative in Fourier decomposition MRI for improved robustness against field inhomogeneities. Series 2D dynamic lung images were acquired in 5 healthy volunteers at 1.5 T and 3T using bSSFP sequence with multiple RF phase increments and compared with conventional single RF phase increment acquisitions. The approach was evaluated based on functional map homogeneity analysis, while ensuring image and functional map quality by means of SNR and contrast-to-noise ratio analyses. At both field strengths, functional maps obtained with phase-cycled acquisitions displayed improved robustness against local signal losses compared with single-phase acquisitions. The coefficient of variation (mean± SD, across volunteers) measured in the ventilation maps resulted in 29.7 ± 2.6 at 1.5T and 37.5 ± 3.1 at 3T for phase-cycled acquisitions, compared with 39.9 ± 5.2 at 1.5T and 49.5 ± 3.7 at 3T for single-phase acquisitions, indicating a significant improvement ( ) in ventilation map homogeneity. Phase-cycled bSSFP acquisitions improve robustness against field inhomogeneity artifacts and significantly improve ventilation map homogeneity at both field strengths. As such, phase-cycled bSSFP may serve as a robust alternative in lung function assessments.

Effect of Cardiac Phase on Cardiac Output Index Derived from Dynamic CT Myocardial Perfusion Imaging.

Purpose: The aortic time-enhancement curve obtained from dynamic CT myocardial perfusion imaging can be used to derive the cardiac output (CO) index based on the indicator dilution principle. The objective of this study was to investigate the effect of cardiac phase at which CT myocardial perfusion imaging is triggered on the CO index measurement with this approach. Methods: Electrocardiogram (ECG) gated myocardial perfusion imaging was performed on farm pigs with consecutive cardiac axial scans using a large-coverage CT scanner (Revolution, GE Healthcare) after intravenous contrast administration. Multiple sets of dynamic contrast-enhanced (DCE) cardiac images were reconstructed retrospectively from 30% to 80% R-R intervals with a 5% phase increment. The time-enhancement curve sampled from above the aortic orifice in each DCE image set was fitted with a modified gamma variate function (MGVF). The fitted curve was then normalized to the baseline data point unaffected by the streak artifact emanating from the contrast solution in the right heart chamber. The Stewart–Hamilton equation was used to calculate the CO index based on the integral of the fitted normalized aortic curve, and the results were compared among different cardiac phases. Results: The aortic time-enhancement curves sampled at different cardiac phases were different from each other, especially in the baseline portion of the curve where the effect of streak artifact was prominent. After properly normalizing and denoising with a MGVF, the integrals of the aortic curve were minimally different among cardiac phases (0.228 ± 0.001 Hounsfield Unit × second). The corresponding mean CO index was 4.031 ± 0.028 L/min. There were no statistical differences in either the integral of the aortic curve or CO index among different cardiac phases (p > 0.05 for all phases).

Theta:gamma phase coupling and evoked gamma activity reflect the fidelity of mental templates during memory matching in visual perception.

Top-down predictions of future events shaped by prior experience are an important control mechanism to allocate limited attentional resources more efficiently and are thought to be implemented as mental templates stored in memory. Increased evoked gamma activity and theta:gamma phase-phase coupling over parieto-occipital areas have previously been observed when mental templates meet matching visual stimuli. Here, we investigated how these signatures evolve during the formation of new mental templates and how they relate to the fidelity of such. Based on single-trial feedback, participants learned to classify target shapes as matching or mismatching with preceding cue sequences. In the end of the experiment, they were asked to freely reproduce targets as means of template fidelity. We observed fidelity-dependent increments of matching-related gamma phase locking and theta:gamma phase coupling in early visual areas around 100-200-ms poststimulus over time. Theta:gamma phase synchronization and evoked gamma activity might serve as complementary signatures of memory matching in visual perception; theta:gamma phase synchronization seemingly most important in early phases of learning and evoked gamma activity being essential for transition of mental templates into long-term memory.

Loading during Midstance of Gait Is Associated with Magnetic Resonance Imaging of Cartilage Composition Following Anterior Cruciate Ligament Reconstruction.

ObjectiveA complex association exists between aberrant gait biomechanics and posttraumatic knee osteoarthritis (PTOA) development. Previous research has primarily focused on the link between peak loading during the loading phase of stance and joint tissue changes following anterior cruciate ligament reconstruction (ACLR). However, the associations between loading and cartilage composition at other portions of stance, including midstance and late stance, is unclear. The objective of this study was to explore associations between vertical ground reaction force (vGRF) at each 1% increment of stance phase and tibiofemoral articular cartilage magnetic resonance imaging (MRI) T1ρ relaxation times following ACLR.DesignTwenty-three individuals (47.82% female, 22.1 ±4.1 years old) with unilateral ACLR participated in a gait assessment and T1ρ MRI collection at 12.25 ± 0.61 months post-ACLR. T1ρ relaxation times were calculated for the articular cartilage of the weightbearing medial and lateral femoral (MFC, LFC) and tibial (MTC, LTC) condyles. Separate bivariate, Pearson product moment correlation coefficients (r) were used to estimate strength of associations between T1ρ MRI relaxation times in the medial and lateral tibiofemoral articular cartilage with vGRF across the entire stance phase.ResultsGreater vGRF during midstance (46%-56% of stance phase) was associated with greater T1ρ MRI relaxation times in the MFC (r ranging between 0.43 and 0.46).ConclusionsBiomechanical gait profiles that include greater vGRF during midstance are associated with MRI estimates of lesser proteoglycan density in the MFC. Inability to unload the ACLR limb during midstance may be linked to joint tissue changes associated with PTOA development.

Optimization of pseudo-continuous arterial spin labeling using off-resonance compensation strategies at 7T.

The sensitivity of pseudo-continuous arterial spin labeling (PCASL) to off-resonance effects (ΔB0 ) is a major limitation at ultra-high field (≥7T). The aim of this study was to assess the effectiveness of different PCASL ΔB0 compensation methods at 7T and measure the labeling efficiency with off-resonance correction. Phase offset errors induced by ΔB0 at the feeding arteries can be compensated by adding an extra radiofrequency (RF) phase increment and transverse gradient blips into the PCASL RF pulse train. The effectiveness of an average field correction (AVGcor), a vessel-specific field-map-based correction (FMcor) and a vessel-specific prescan-based correction (PScor) were compared at 7T. After correction, the PCASL labeling efficiency was directly measured in feeding arteries downstream from the labeling location. The perfusion signal was more uniform throughout the brain after off-resonance correction. Whole-brain average perfusion signal increased by a factor of 2.4, 2.5, and 2.1, respectively, with AVGcor, FMcor and PScor compared to acquisitions without correction. With off-resonance correction, the maximum labeling efficiency was ~0.68 at mean B1 (B1mean ) of 0.70 µT when using a mean gradient (Gmean ) of 0.25 mT/m. Either a prescan or a field map can be used to correct for off-resonance effects and retrieve a good brain perfusion signal at 7T. Although the three methods performed well in this study, FMcor may be better suited for patient studies because it accounted for vessel-specific ΔB0 variations. Further improvements in image quality will be possible by optimizing the labeling efficiency with advanced hardware and software while satisfying specific absorption rate constraints.

Pure balanced steady-state free precession imaging (purebSSFP).

PurposeTo show that for tissues the conspicuous asymmetries in the frequency response function of bSSFP can be mitigated by using a short enough TR.Theory and MethodsConfiguration theory indicates that bSSFP becomes apparently “pure” (i.e., exhibiting a symmetric profile) in the limit of TR →0. To this end, the frequency profile of bSSFP was measured as a function of the TR using a manganese‐doped aqueous probe, as well as brain tissue that was shown to exhibit a pronounced asymmetry due to its microstructure. The frequency response function was sampled using N=72 (phantom) and N=36 (in vivo) equally distributed linear RF phase increments in the interval [0,2π). Imaging was performed with 2.0 mm isotropic resolution over a TR range of 1.5–8 ms at 3 and 1.5 T.ResultsAs expected, pure substances showed a symmetric TR‐independent frequency profile, whereas brain tissue revealed a pronounced asymmetry. The observed asymmetry for the tissue, however, decreases with decreasing TR and gives strong evidence that the frequency response function of bSSFP becomes symmetric in the limit of TR →0, in agreement with theory. The limit of apparently pure bSSFP imaging can thus be achieved for a TR ∼ 1.5 ms at 1.5 T, whereas at 3 T, tissues still show some residual asymmetry.ConclusionIn the limit of short enough TR, tissues become apparently pure for bSSFP. This limit can be reached for brain tissue at 1.5 T with TR ∼ 1–2 ms at clinically relevant resolutions.

Effect of Leg Extension Angle on Knee Flexion Angle during Swing Phase in Post-Stroke Gait.

Background and Objectives: Leg extension angle is important for increasing the propulsion force during gait and is a meaningful indicator for evaluating gait quality in stroke patients. Although leg extension angle during late stance might potentially also affect lower limb kinematics during the swing phase, the relationship between these two remains unclear. This study aimed to investigate the relationship between leg extension angle and knee flexion angle during pre-swing and swing phase in post-stroke gait. Materials and Methods: Twenty-nine stroke patients walked along a 16 m walkway at a self-selected speed. Tilt angles and acceleration of pelvis and paretic lower limb segments were measured using inertial measurement units. Leg extension angle, consisting of a line connecting the hip joint with the ankle joint, hip and knee angles, and increments of velocity during pre-swing and swing phase were calculated. Correlation analysis was conducted to examine the relationships between these parameters. Partial correlation analysis adjusted by the Fugl-Meyer assessment-lower limb (FMA-LL) was also performed. Results: On the paretic side, leg extension angle was positively correlated with knee flexion angle during the swing phase (r = 0.721, p < 0.001) and knee flexion angle and increments of velocity during the pre-swing phase (r = 0.740–0.846, p < 0.001). Partial correlation analysis adjusted by the FMA-LL showed significant correlation between leg extension angle and knee flexion angle during the swing phase (r = 0.602, p = 0.001) and knee flexion angle and increments of velocity during the pre-swing phase (r = 0.655–0.886, p < 0.001). Conclusions: Leg extension angle affected kinematics during the swing phase in post-stroke gait regardless of the severity of paralysis, and was similar during the pre-swing phase. These results would guide the development of effective gait training programs that enable a safe and efficient gait for stroke patients.

Simultaneous T1 -weighted and T2 -weighted 3D MRI using RF phase-modulated gradient echo imaging.

T1 -weighted and T2 -weighted (T1w and T2w) imaging are essential sequences in routine clinical practice to detect and characterize a wide variety of pathologies. Many approaches have been proposed to obtain T1w and T2w contrast, although many challenges still remain, including long acquisition time and limitations that favor 2D imaging. In this study, we propose a novel method for simultaneous T1w and T2w imaging using RF phase-modulated 3D gradient-echo imaging. Configuration theory is used to derive closed-form equations for the steady state of RF phase-modulated gradient-echo signal. These equations suggest the use of small RF phase increments to provide orthogonal signal contrast with T2w and T1w in the real and imaginary components, respectively. Background phase can be removed using a two-pass acquisition with opposite RF phase increments. Simulation and phantom experiments were performed to validate our proposed method. Volunteer images of the brain and knee were acquired to demonstrate the clinical feasibility. The proposed method was compared with T1w and T2w fast spin-echo imaging. The relative signal intensity of images acquired using the proposed method agreed closely with simulations and fast spin-echo imaging in phantoms. Images from volunteer imaging showed very similar contrast compared to conventional fast spin-echo imaging. Radiofrequency phase-modulated gradient-echo with small RF phase increments is an alternative method that provides simultaneous T1w and T2w contrast in short scan times with 3D volumetric coverage.

Effect of solution pH on as-synthesized and calcined WO3 nanoparticles synthesized using sol-gel method

Tungsten oxide nanoparticles are particularly suitable for a wide range of applications like non-invasive cancer treatment, water treatment, gas sensing, and so on. In this paper, the effect of the solution pH on as-synthesized WO 3 nanoparticles and calcined WO 3 nanostructures at 500 °C is investigated to achieve appropriate WO 3 nanoparticles with a simple and low-price sol-gel method. The results declare that solution pH significantly affects the morphology, crystallinity, chemical bonds, and optical properties of WO 3 nanoparticles. Increasing solution pH from 1 to 2 with the step of 0.5 leads to crystal phase transition and increment of the hexagonal phase percentage. The size of nanoparticles increases with increasing the solution pH in as-synthesized. So, it turns out that solution pH affects the particles growth process. In addition, the results reveal that increasing the solution pH leads to a blue shift at the optical absorption edges. Also, the indirect energy bandgap of WO 3 particles increases/decreases with increasing pH in the case of as-synthesized/calcined samples. The energy bandgaps of calcined samples were generally lower than as-synthesized ones. The sample prepared at pH = 1 shows the highest absorption (about ten times higher than other samples at λ = 300 nm) and low reflection in the whole range of the spectrum that makes it a worthy candidate for photocatalysis applications. • Synthesis of WO 3 NPs by simple and low-price sol-gel method. • WO 3 NPs as excellent photocatalysis and photodynamic agent. • Study the effects of the solution pH on as-synthesized and calcined WO 3 NPs. • Significant effect of pH on structural and optical properties of WO 3 NPs. • Producing of high absorption/low reflection WO 3 NPs for photocatalysis application.

Influence of ageing time on microstructure, hardness and corrosion of UNS Zeron 100 super duplex stainless steel

The present study is to investigate the influence of ageing time on the microstructure, hardness and corrosion properties of UNS Zeron 100 super duplex stainless steel. The material was solution treated at 1050°C and water quenched, further the ageing has been carried out at 850°C for 30, 60 and 90 minutes. Hardness test and corrosion test were carried out for both solution treated as well as aged specimens for different ageing period. Results of hardness test indicate an increase in hardness as the ageing period increases. Corrosion test results showed good resistance to corrosion as the ageing time increases. Changes in mechanical properties were observed due to sigma phase formation. Scanning electron microscope (SEM) analysis showed the sigma phase precipitation in duplex stainless steel. EDX analysis shows the consumption of ferrite and formation of chromium which indicates the formation of sigma phase. Optical image analysis showed the increment of sigma phase as the ageing time is increased.

Characterization of mass transfer study in a Kühni continuous extractor for rare earth processing using axial dispersion and backflow models

An experimental and modeling approach is presented to study the impact of operating parameters on mass transfer rate during reactive extraction in the Kühni continuous extractor. Three mathematical models were implemented to calculate the column's concentration profile. For case studies, D2EHPA extractant diluted in kerosene as an organic solvent and the aqueous solution containing lanthanum and cerium ions were utilized as the reactive solutions to provoke chemical reactions forcing desirable physical changes. Increasing rotation speed from 75 to 195 rpm generated the highest mass transfer and interfacial area and smaller drop sizes at all phase flow rates and ion concentrations. The results showed that axial dispersion and backflow coefficients of the dispersed phase increment as the solvent flow rate and agitation speed increase. These coefficients decrease with the increment in the aqueous flow rate. The AARE values (11–15%) in two extraction and stripping stages showed that the axial dispersion model is the most accurate among the three assessed mass transfer models. The modeling presented in this paper can be used as an engineering tool to design high performance for rare earth processing.