Simultaneous Variations Research Articles

Synergistic effects of temporal variations in flow and chemistry on colloid retention and remobilization in saturated porous media

Rapid infiltration due to rainfall events, groundwater pumping, and artificial recharge of groundwater result in temporal variations in both flow and chemistry in the subsurface and may lead to remobilization of retained colloids, thereby re-contaminating the groundwater resources. Many researchers have studied the effects of temporal variations in water velocity and in water chemistry separately. These variations, however, almost always occur simultaneously. To the best knowledge of the authors, there are no studies reported in the literature where the effect of simultaneous temporal variations in flow velocity and ionic strength on colloid release is investigated. One cannot assume that those effects can be simply superimposed. In fact, in this study, we show that these effects are not simply additive. We have performed eight sets of saturated column experiments on the effects of temporal variations in flow velocity alone and simultaneous temporal variations in flow velocity and ionic strength on retention and remobilization of colloids. Temporal increases in average water velocity caused an instantaneous spike release of colloids in the measured breakthrough curve, with the time to peak coinciding with the instant of velocity increase. Further, the effect of temporal variations in average water velocity on remobilization of deposited colloids is ionic-strength dependent. The simultaneous temporal increases in flow and decreases in ionic strength caused a spike release of colloids followed by long tails. The release curve for every step-change in velocity and ionic strength was unimodal for deposition ionic strengths of 100 and 10 mM, with the peak coinciding with the instant of arrival of ionic strength front at the column outlet. However, the release curve was bimodal for deposition ionic strengths of 50 and 25 mM. There, the first instantaneous spike coincided with the instant of increase in flow velocity, and the second delayed one coincided with the passage of the ionic strength front. Temporal variations in both flow and ionic strength released more colloids in the effluent than when only ionic-strength or only flow velocity was varied. This is due to the combined effects of greater hydrodynamic torque exerted on attached particles together with smaller adhesive torque.

Clinicopathological and molecular genetic insights into EBV-positive inflammatory follicular dendritic cell sarcoma

Epstein-Barr virus (EBV)-positive inflammatory follicular dendritic cell (FDC) sarcoma (EBV + IFDCS) is a rare entity, and its histopathological characteristics have not been fully described. This study aimed to investigate the clinical characteristics, pathological features, and molecular genetic profiles of EBV + IFDCS to improve our understanding of these lesions. A total of 12 EBV + IFDCS specimens were obtained from patients in our pathology diagnostic center. The clinical data, morphology, immunohistochemistry, in situ hybridization, and high-throughput DNA-targeted sequencing data were collected, and follow-up data were analyzed. These data were compared with those of 6 patients with traditional FDCS. The patients with EBV + IFDCS ranged from 21 to 84 years old, with a mean age of 52.3 years and a male-to-female ratio of 1:5. At the last follow-up, all patients were alive, with 2 experiencing recurrence and metastasis. In these cases, four were classified as the classical subtype, four as the angiomatoid/sclerosing subtype, and four as the lymphoma-like subtype, with two cases also exhibiting epithelioid granulomas. All patients exhibited heterogeneous expression of follicular dendritic cell markers (CD21, CD23, CD35, and CXCL13) alongside the fibroblast marker SMA, with significantly higher expressions of IgG4, EBER, and SMA in EBV + IFDCS patients compared to FDCS patients (P < 0.05). Conversely, SSTR2, EGFR, and STAT3 expression were significantly lower in the EBV + IFDCS group (P < 0.05). The average value of EBER was significantly higher in the classical subtype group (P = 0.022). Among the four cases of EBV + IFDCS analyzed for molecular genetic features, one patient exhibited germline mutations in the CDKN1C, PDGFRA, MSH2, FANCG, MLH1, ALK, and RUNX1 genes; three exhibited simultaneous SNP variations in the MTHFR gene; and two exhibited simultaneous SNP variations in the NQO1 gene. We conducted KEGG pathway analysis on the mutant genes, revealing significant enrichment in the cAMP signaling pathway, which plays a crucial role in tumor development. Survival analysis demonstrated that the median PFS rates were not reached (NR) for EBV + IFDCS patients, compared to 5 months (HR = 7.76) for FDCS patients. The 3-year PFS rates were 66.67% and 16.67%, respectively. Compared with the FDCS group, EBV + IFDCS patients had a significantly longer median PFS time (p < 0.05). In conclusion, EBV + IFDCS represents a group of tumors with unique clinical, morphological, immunological, prognostic, and molecular cytogenetic characteristics.

Identification of surface urban heat versus cool islands for arid cities depends on the choice of urban and rural definitions

The urban heat island (UHI) effect in arid cities can be small or even negative, the latter known as the urban cool island (UCI) effect. Differences in defining urban and rural areas can introduce uncertainties in detecting UHI or UCI, especially when the UHI signal is small. Here, we compared the surface UHI intensity (SUHII) estimated by a dozen different methods (with multiple urban and/or rural definitions) across 104 arid cities globally, providing a comprehensive evaluation of the uncertainty in SUHII estimates. Results show that the absolute difference in annual average SUHII (∆SUHII) among methods exceeded 1 °C in about half of the arid cities during both daytime and nighttime. The overall annual mean ∆SUHII for all arid cities was 1.35 °C during daytime and 1.03 °C at night. The uncertainty arising from simultaneous variations in urban and rural definitions was generally higher than that resulting from their individual changes. It was observed that, with varying definitions of urban and rural areas, nearly 50 % of arid cities experienced a sign reversal in daytime SUHII estimates, while approximately 15 % exhibited a sign reversal in nighttime SUHII. Variations in urban-rural differences in surface properties, such as vegetation index and albedo, due to differing urban and rural definitions, contributed strongly to the observed SUHII uncertainties. Overall, our results offer new insights into the ongoing debate on heat and cold islands in arid cities, emphasizing a critical need to standardize SUHII estimation frameworks.

Most of the Long-Term Solar Radiation Forcing on the Climate Is Due to the Strong Feedback Mechanisms

The main interactions of the Total Solar Irradiance (TSI) variations with the climatic system are considered. This research introduced new physically based indexes for 11-year cycles: the integral relative energetic power of the cycles solar activity (SA) and TSI, as well as the cycle-weighted mean value both of the TSI and sunspot number. The observed cycle-average TSI value in cycles XXII–XXIV has decreased by more than 0.5 W/m2, indicating its quasi-bicentennial decline. The onset of the Maunder-type Grand minimum phase of the SA and TSI of the quasi-bicentennial cycle (BCC) is expected in the 27th or 28th 11-year cycle in 2042 or 2053. The Earth's thermal inertia will cause a temperature reduction of around 0.25 K due to the deficit in TSI during the declining phase of the bicentennial cycle due to its negative impact on Earth's energy imbalance. As a result, the Bond's albedo will increase, and the abundance of atmospheric water vapor and carbon dioxide will decrease as a response to a direct solar forcing. BCC feedback mechanisms will also continue operating during both its minimum and maximum phases. The feedback mechanisms will continue further in short periods (about 30 years) at the beginning of BCC's growth and decline phases. These long-term self-reinforcing feedback effects will act as a response to the TSI, forcing in such a way as to trigger a strong amplification of the initial direct input to the corresponding temperature changes. They will lead to a significant increasing cooling in 2070 or 2080. Variations of the galactic cosmic rays and cloud cover practically do not affect the climate. The quasi-bicentennial cyclicity of the TSI also provides simultaneous climate variations on all Solar system planets.

Probing Thermal Electrons in Gamma-Ray Burst Afterglows

Particle-in-cell simulations have unveiled that shock-accelerated electrons do not follow a pure power-law distribution, but have an additional low-energy “thermal” part, which owns a considerable portion of the total energy of the electrons. Investigating the effects of these thermal electrons on gamma-ray burst (GRB) afterglows may provide valuable insights into the particle acceleration mechanisms. We solve the continuity equation of electrons in energy space, from which multiwavelength afterglows are derived by incorporating processes including synchrotron radiation, synchrotron self-absorption, synchrotron self-Compton scattering, and γ–γ annihilation. First, there is an underlying positive correlation between the temporal and spectral indices due to the cooling of electrons. Moreover, thermal electrons result in simultaneous nonmonotonic variations of both the spectral and temporal indices at multiple wavelengths, which could be individually recorded by the 2.5 m Wide Field Survey Telescope and Vera Rubin Observatory Legacy Survey of Space and Time (LSST). The thermal electrons could also be diagnosed using afterglow spectra from synergistic observations in the optical (with LSST) and X-ray (with the Microchannel X-ray Telescope on board the Space Variable Objects Monitor) bands. Finally, we use Monte Carlo simulations to obtain the distribution of the peak flux ratio (R X) between the soft and hard X-rays, and of the time delay (Δt) between the peak times of the soft X-ray and optical light curves. The thermal electrons significantly raise the upper limits of both R X and Δt. Thus, the distribution of GRB afterglows with thermal electrons is more scattered in the R X−Δt plane.

Theoretical Investigation of Dual-Mode Gradient Elution Chromatography Considering Simultaneous Variations in the Column Temperature and Solvent Composition

Theoretical Investigation of Dual-Mode Gradient Elution Chromatography Considering Simultaneous Variations in the Column Temperature and Solvent Composition

Development of a Genetic Algorithm – Artificial Neural Network model to optimize the Dimensional Accuracy of parts printed by FFF

PurposeFused Filament Fabrication (FFF) is one of the growing technologies in additive manufacturing, that can be used in a number of applications. In this method, process parameters can be customized and their simultaneous variation has conflicting impacts on various properties of printed parts such as dimensional accuracy (DA) and surface finish. These properties could be improved by optimizing the values of these parameters.Design/methodology/approachIn this paper, four process parameters, namely, print speed, build orientation, raster width, and layer height which are referred to as “input variables” were investigated. The conflicting influence of their simultaneous variations on the DA of printed parts was investigated and predicated. To achieve this goal, a hybrid Genetic Algorithm – Artificial Neural Network (GA-ANN) model, was developed in C#.net, and three geometries, namely, U-shape, cube and cylinder were selected. To investigate the DA of printed parts, samples were printed with a central through hole. Design of Experiments (DoE), specifically the Rotational Central Composite Design method was adopted to establish the number of parts to be printed (30 for each selected geometry) and also the value of each input process parameter. The dimensions of printed parts were accurately measured by a shadowgraph and were used as an input data set for the training phase of the developed ANN to predict the behavior of process parameters. Then the predicted values were used as input to the Desirability Function tool which resulted in a mathematical model that optimizes the input process variables for selected geometries. The mean square error of 0.0528 was achieved, which is indicative of the accuracy of the developed model.FindingsThe results showed that print speed is the most dominant input variable compared to others, and by increasing its value, considerable variations resulted in DA. The inaccuracy increased, especially with parts of circular cross section. In addition, if there is no need to print parts in vertical position, the build orientation should be set at 0° to achieve the highest DA. Finally, optimized values of raster width and layer height improved the DA especially when the print speed was set at a high value.Originality/valueBy using ANN, it is possible to investigate the impact of simultaneous variations of FFF machines’ input process parameters on the DA of printed parts. By their optimization, parts of highly accurate dimensions could be printed. These findings will be of significant value to those industries that need to produce parts of high DA on FFF machines.

Configurable SNAP microresonators induced by axial pre-strain-assisted CO2 laser exposure.

Flexible engineering of the complex shapes of the surface nanoscale axial photonics (SNAP) bottle microresonators (SBMs) is challenging for future nanophotonic technology applications. Here, we experimentally propose a powerful approach for the one-step fabrication of SBMs with simultaneous negative and positive radius variations, exhibiting a distinctive "bump-well-bump" profile. It is executed by utilizing two focused and symmetrical CO2 laser beams exposed on the fiber surface for only several hundred milliseconds. The spectral characteristics of different eigenmodes are analyzed, providing deep insights into the complex physical processes during the CO2 laser exposure. The shapes of the SBMs can be flexibly adjusted by the exposure time, laser power, and applied pre-strains. As a proof of this technique, the developed approach enables the efficient production of a bat SBM, ensuring a uniform field amplitude of the bat mode over the length exceeding 120 µm with 7% deviation. Our proposed technique provides a powerful technique for the efficient fabrication of SBMs with predetermined shapes, laying the groundwork for its applications on microscale optical signal processing, quantum computing, and so on.

Variable carbon isotope fractionation of photosynthetic communities over depth in an open-ocean euphotic zone

Marine particulate organic carbon (POC) contributes to carbon export, food webs, and sediments, but uncertainties remain in its origins. Globally, variations in stable carbon isotope ratios (δ13C values) of POC between the upper and lower euphotic zones (LEZ) indicate either varying aspects of photosynthetic communities or degradative alteration of POC. During summertime in the subtropical north Atlantic Ocean, we find that δ13C values of the photosynthetic product phytol decreased by 6.3‰ and photosynthetic carbon isotope fractionation (εp) increased by 5.6‰ between the surface and the LEZ-variation as large as that found in the geologic record during major carbon cycle perturbations, but here reflecting vertical variation in δ13C values of photosynthetic communities. We find that simultaneous variations in light intensity and phytoplankton community composition over depth may be important factors not fully accounted for in common models of photosynthetic carbon isotope fractionation. Using additional isotopic and cell count data, we estimate that photosynthetic and non-photosynthetic material (heterotrophs or detritus) contribute relatively constant proportions of POC throughout the euphotic zone but are isotopically more distinct in the LEZ. As a result, the large vertical differences in εp result in significant, but smaller, differences in the δ13C values of total POC across the same depths (2.7‰). Vertical structuring of photosynthetic communities and export potential from the LEZ may vary across current and past ocean ecosystems; thus, LEZ photosynthesis may influence the exported and/or sedimentary δ13C values of both phytol and total organic carbon and affect interpretations of εp over geologic time.

Diverse spatiotemporal patterns of vapor pressure deficit and soil moisture across China

Study regionChina and the different climatic zones. Study focusVapor pressure deficit (VPD) and soil moisture (SM) are vital for the land-atmosphere hydrological cycle and vegetation growth. Understanding the spatiotemporal variations of VPD and SM is essential for exploring vegetation dynamics and ecosystem changes. However, our current understanding of the simultaneous variations of VPD and SM within specific regions remains limited. This study utilized Empirical Orthogonal Function (EOF) methods to analyze the spatiotemporal variability of VPD, surface SM (SMsurf), and root-zone SM (SMroot), respectively. We then investigated the synchronous and asynchronous variations of VPD and SM and examined their relationships with climatic factors. New hydrologic insights for the regionFrom 1980–2020, VPD exhibited a significant upward trend across China and in various climate zones, indicating an increase in atmospheric dryness. However, the trends of SMsurf and SMroot showed a slight upward trend across China but divergent patterns in different climate zones. In summary, approximately 43% of China experiences a significant simultaneous increase in both VPD and SM, mainly in semi-arid and arid regions. Conversely, about 4% of China shows contrasting changes in VPD and SM, primarily in humid tropical and subtropical regions. These findings enhance our understanding of VPD and SM patterns in various climates, emphasizing the significance of soil drought in humid and semi-humid regions.

Two simultaneous anatomical variations of the cervical spine - a case report discussing the concept of tandem anomalies.

forming a bony opening through which the vertebral artery (VA) enters the vertebral canal. Block vertebra is a synostosis of at least two vertebral bodies that did not separate during the embryological development. It is worth distinguishing it from the Klippel-Feil syndrome, as the latter oftentimes involves other abnormalities (namely skeletal) and is typically diagnosed in childhood. Both variants could potentially lead to an impairment of the blood flow through the VA. Case report: The following case report presents a finding of two anomalies of the cervical spine, found in a 38 y.o. female patient suffering from dizziness. A synostosis of the C4 and C5 vertebral bodies, arches and zygapophysial (facet) joint, was noted by the examining radiologist, with marked narrowing of the intervertebral foramen. Furthermore, second anatomical variation in the form of the complete bilateral arcuate foramen was identified superior to the groove for the VA on the upper surface of the posterior arch of the atlas. Conclusions: To the best knowledge of the authors, this case report is the first to present a co-existing block vertebra and bilateral complete arcuate foramen. Common presence of at least two anatomical variations that could have a synergistic clinical effect could possibly be termed 'tandem anomaly.' Notwithstanding, identification of a single anomaly explaining a patient's symptoms does not absolve the medical professionals from searching for any other potential variations that could also be present and could further influence the clinical picture.

Highly efficient persistent luminescent nanozymes-based luminescence-colorimetric dual-mode sensor for total antioxidant capacity assay

Total antioxidant capacity (TAC) is a vital parameter to assess the gross antioxidant activity in biological and food matrices. Accurate determination of TAC has become increasingly important for health monitoring and dietary guidance. Here, we report a persistent luminescent nanozyme (ZGO-Pt) based luminescence-colorimetric dual-mode sensor for selective determination of TAC. ZGO-Pt was fabricated based on ZnGa2O4:Cr nanoparticles (ZGO) with platinum nanoflower as synthetic additive. The prepared ZGO-Pt exhibited fascinating peroxidase-mimetic activity and persistent luminescence, and enabled effectively catalysis of the oxidation of colorless 3,3′,5,5′-tetramethylbenzidine (TMB) to blue oxTMB. Meanwhile, the generated oxTMB gave strong absorption at 652 nm to quench the luminescence of ZGO-Pt at 700 nm via the inner filter effect. Antioxidants could compete with the oxidable TMB or reduce oxTMB to TMB, resulting in the simultaneous variations of blue color and luminescence to provide the basis for dual-mode assay for TAC. The highly efficient catalysis of ZGO-Pt (Km, 3.12 mM for H2O2, 0.592 mM for TMB) allows the dual-mode sensor to realize precise determination of TAC with a wide linear range (0.5–200 μM and 1–300 μM for colorimetric and luminescence mode, respectively) and low limit of detection (LOD, 0.05 μM and 0.78 μM for colorimetric and luminescence mode, respectively). The developed dual-mode sensor was successfully applied to the determination of TAC in vitamin tablet, beverages and fruits. This work provides an efficient persistent luminescent nanoparticle-based nanozyme for a facile TAC assay with further vision in biosensing and food technology.

Magnetic field properties inside the jet of Mrk 421

Aims. We aim to probe the magnetic field geometry and particle acceleration mechanism in the relativistic jets of supermassive black holes. Methods. We conducted a polarimetry campaign from radio to X-ray wavelengths of the high-synchrotron-peak (HSP) blazar Mrk 421, including Imaging X-ray Polarimetry Explorer (IXPE) measurements from 2022 December 6–8. During the IXPE observation, we also monitored Mrk 421 using Swift-XRT and obtained a single observation with XMM-Newton to improve the X-ray spectral analysis. The time-averaged X-ray polarization was determined consistently using the event-by-event Stokes parameter analysis, spectropolarimetric fit, and maximum likelihood methods. We examined the polarization variability over both time and energy, the former via analysis of IXPE data obtained over a time span of 7 months. Results. We detected X-ray polarization of Mrk 421 with a degree of ΠX = 14 ± 1% and an electric-vector position angle ψX = 107 ± 3° in the 2–8 keV band. From the time variability analysis, we find a significant episodic variation in ψX. During the 7 months from the first IXPE pointing of Mrk 421 in 2022 May, ψX varied in the range 0° to 180°, while ΠX remained relatively constant within ∼10–15%. Furthermore, a swing in ψX in 2022 June was accompanied by simultaneous spectral variations. The results of the multiwavelength polarimetry show that ΠX was generally ∼2–3 times greater than Π at longer wavelengths, while ψ fluctuated. Additionally, based on radio, infrared, and optical polarimetry, we find that the rotation of ψ occurred in the opposite direction with respect to the rotation of ψX and over longer timescales at similar epochs. Conclusions. The polarization behavior observed across multiple wavelengths is consistent with previous IXPE findings for HSP blazars. This result favors the energy-stratified shock model developed to explain variable emission in relativistic jets. We considered two versions of the model, one with linear and the other with radial stratification geometry, to explain the rotation of ψX. The accompanying spectral variation during the ψX rotation can be explained by a fluctuation in the physical conditions, for example in the energy distribution of relativistic electrons. The opposite rotation direction of ψ between the X-ray and longer wavelength polarization accentuates the conclusion that the X-ray emitting region is spatially separated from that at longer wavelengths. Moreover, we identify a highly polarized knot of radio emission moving down the parsec-scale jet during the episode of ψX rotation, although it is unclear whether there is any connection between the two events.

Spectroscopic variability of massive pre-main-sequence stars in M17

Context. It is a challenge to study the formation process of massive stars: their formation time is short, there are only few of them, they are often deeply embedded, and they lie at relatively large distances. Our strategy is to study the outcome of the star formation process and to search for signatures that remain of the formation. We have access to a unique sample of (massive) pre-main-sequence (PMS) stars in the giant H II region M17. These PMS stars can be placed on PMS tracks in the Hertzsprung–Russell diagram (HRD) as we can detect their photospheric spectrum, and they exhibit spectral features indicative of the presence of a circumstellar disk. These stars are most likely in the final stage of formation. Aims. The aim is to use spectroscopic variability as a diagnostic tool to learn about the physical nature of these massive PMS stars. More specifically, we wish to determine the variability properties of the hot gaseous disks to understand the physical origin of the emission lines, identify dominant physical processes in these disks, and to find out about the presence of an accretion flow and/or jet. Methods. We obtained multiple-epoch (four to five epochs) VLT/X-shooter spectra of six young stars in M17 covering about a decade. Four of these stars are intermediate to massive PMS stars with gaseous disks. Using stacked spectra, we updated the spectral classification and searched for the presence of circumstellar features. With the temporal variance method (TVS), we determined the extent and amplitude of the spectral line variations in velocity space. The double-peaked emission lines in the PMS stars with gaseous disks were used to determine peak-to-peak velocities, V/R ratios, and the radial velocity of the systems. Simultaneous photometric variations were studied using VLT acquisition images. Results. From detailed line identification in the PMS stars with gaseous disks, we identify many (double-peaked) disk features, including a new detection of CO bandhead and CI emission. In three of these stars, we detect significant spectral variability, mainly in lines originating in the circumstellar disk, in a velocity range up to 320 km s−1, which exceeds the rotational velocity of the central sources. The shortest variability timescale is about one day. We also detect long-term (months, years) variability. The ratio of the blue and red peaks in two PMS stars shows a correlation with the peak-to-peak velocity, which might be explained by a spiral-arm structure in the disk. Conclusions. The variable PMS stars lie at similar positions in the HRD, but show significant differences in disk lines and variability. The extent and timescale of the variability differs for each star and line (sets), showing the complexity of the region where the lines are formed. We find indications for an accretion flow, slow disk winds, and/or disk structures in the hot gaseous inner disks. We find no evidence for close companions or strong accretion bursts as the cause of the variability in these PMS stars.

Optimizing water electrolysis activity in Mo-doped Sr2FeCoO6-δ perovskites by balancing oxygen vacancies and structural stability

Perovskite-based solid oxide electrolysis cells (SOECs) are promising for efficacious hydrogen production. This work explored how varying molybdenum (Mo) content impacts the structure and performance of Sr2FeCo1-xMoxO6-δ (SFCMx) perovskites for SOEC water electrolysis. SFCMx (x = 0.1–0.5) were synthesized via sol-gel method and incorporated into symmetrical cells. Electrolysis testing showed SFCM0.3 had the highest activity, achieving 2.09 A cm−2 at 2.0 V and 800 °C, compared to 0.964 and 0.847 A cm−2 for SFCM0.1 and SFCM0.5 respectively. This optimal performance with 0.3 Mo doping was put down to simultaneous variations in oxygen vacancy concentration and crystalline structure stability. Lower Mo doping accelerated charge transfer but destabilized the structure, while higher doping stabilized the cubic perovskite structure but reduced vacancies and electrocatalytic activity. This work demonstrates that balancing activity and stability by optimizing dopant concentration is critical to maximize SOEC performance. This provides new insights for enhancing water electrolysis through controlled doping and tuning of the perovskite structure.

The Sound of Swarm. Auditory Description of Swarm Robotic Movements

Movements of robots in a swarm can be mapped to sounds, highlighting the group behavior through the coordinated and simultaneous variations of musical parameters across time. The vice versa is also possible: Sound parameters can be mapped to robotic motion parameters, giving instructions through sound. In this article, we first develop a theoretical framework to relate musical parameters such as pitch, timbre, loudness, and articulation (for each time) with robotic parameters such as position, identity, motor status, and sensor status. We propose a definition of musical spaces as Hilbert spaces and musical paths between parameters as elements of bigroupoids, generalizing existing conceptions of musical spaces. The use of Hilbert spaces allows us to build up quantum representations of musical states, inheriting quantum computing resources, already used for robotic swarms. We present the theoretical framework and then some case studies as toy examples. In particular, we discuss a 2D video and matrix simulation with two robo-caterpillars; a 2D simulation of 10 robo-ants with Webots; a 3D simulation of three robo-fish in an underwater search-and-rescue mission.

Approach and landing guidance using constrained model predictive static programming

The paper proposes a guidance scheme during the approach and landing phase of an unpowered vehicle to achieve high precision at touchdown by limiting the control inputs within allowable bounds using constrained Model Predictive Static Programming. The advantages of a single flight phase are incorporated into the design since the guess control history is obtained from a single segment based guidance approach. The requirement of ensuring continuity in states and guidance commands are hence avoided leading to minimization of control deviations using a simple cost function. Constrained input commands are used for determining control surface deflection based on dynamic inversion considering the longitudinal pitch rate dynamics. Comparison is carried out between the results obtained for constrained as well as unconstrained schemes for the nominal trajectory. Comparisons of load factor, dynamic pressure and flight path angle for three segment, two segment, single segment guidance strategies have been carried out with MPSP based guidance to evaluate the relative advantages offered by the scheme. Performance analysis of the proposed scheme is done based on numerous simulations with simultaneous variations in initial states, vehicle parameters and aerodynamic parameter variations. Simulation results indicate that the proposed scheme is suitable for landing on runways of shorter lengths due to minimal touchdown errors.

Texture recognition under scale and illumination variations

ABSTRACT Visual scene recognition is predominantly based on visual textures representing an object's material properties. However, the single material texture varies in scale and illumination angles due to mapping an object's shape. We present a comparative study of the colour histogram, Gabor, opponent Gabor, Local Binary Pattern (LBP), and wide-sense Markovian textural features concerning their sensitivity to simultaneous scale and illumination variations. Due to their application dominance, these textural features are selected from more than 50 published textural features. Markovian features are information preserving, and we demonstrate their superior performance for scale and illumination variable observation conditions over the standard alternative textural features. We bound the scale variation by double size, and illumination variation includes illumination spectra, acquisition devices, and 35 illumination directions spanned above a sample hemisphere. Recognition accuracy is tested on textile patterns from the University of East Anglia and wood veneers from UTIA BTF databases.

Theoretical Study of Non-Isothermal Gradient Elution Liquid Chromatography.

A two-component model of gradient elution chromatography is investigated to theoretically study the effects of simultaneous variations in temperature and solvent strength on the retention behaviors of elution profiles in thermally insulated liquid chromatographic columns. The gradient elution technique is based on the gradual increase or decrease in eluent strength during the chromatographic operation by varying the composition of the mobile phase. The enthalpy of adsorption is primarily responsible for internal temperature variations inside the column, as heat adsorbs during the adsorption process and releases in the desorption phase. Both types of variations change the propagation speeds of moving pulses inside the column which can lead to better separation of the components and a reduction in the recycling time for the next injection. The equilibrium dispersive model (EDM) coupled with the energy balance equation for temperature and transport equation for the volume fraction of the solvent is utilized to simulate this complex process. The resulting nonlinear model equations are approximated by applying a semi-discrete second-order finite volume scheme. The numerical solutions are used to study the impact of a gradient starting and ending times, volume-fraction of the solvent, solvent strength parameter, the slope of gradient, enthalpy of adsorption, injection temperature, and the ratio of specific heats on the concentration profiles.

An Optimized Switching Strategy Based on Gate Drivers with Variable Voltage to Improve the Switching Performance of SiC MOSFET Modules

This paper proposes an optimized switching strategy (OSS) based on a silicon carbide (SiC) MOSFET gate driver with variable voltage, which allows simultaneous variations in several different parameters to optimize the switching performance of semiconductor devices. As a relatively new device, the SiC MOSFET shines in the field of high power density and high-frequency switching; it has become a popular solution for electric vehicles and renewable energy conversion systems. However, the increase in voltage and current slope caused by high switching speeds inevitably increases the overshoot and oscillation in a circuit and can even generate additional losses. The principle of this new control strategy is to change the voltage and current in the turn-on and turn-off stages by changing the gate driver’s voltage. That is, we reduced the drive’s voltage after a certain time delay and maintained it for a period of time, thus directly controlling the slopes of di/dt and dv/dt. This study focused on the optimization of the SiC MOSFET by changing the time delay preceding the decrease in the voltage of the gate driver, analyzing and calculating the optimal time delay before the decrease in the voltage of the gate driver, and verifying the findings using LTspice simulation software. The simulated results were compared and analyzed with hard-switching strategies. The results showed that the proposed OSS can improve the switching performance of SiC MOSFETs.