Unimodal Distribution Research Articles

Experimental study on the concentration fluctuation of dust particles with different sizes during a dust storm

The particle size distribution (PSD) and concentration fluctuation were analyzed during different stages of a dust event. Our results show that dust smaller than 0.5 μm were dominant during the development stage; dust less than 0.5 μm decreased and dust from 0.5 μm to 10 μm increased in the high and low concentration stage; dust from 0.5 μm to 10 μm decreased and dust less than 0.5 μm increased in the dissipation stage. PSD of the first and fourth stages shows the unimodal distribution, but that of the other stages shows the distribution of 4 peaks. For large scale fluctuation with a period larger than 300 s, the concentration fluctuation of particles with size less than 0.4 μm and size larger than 0.4 μm has a high correlation. For small scale fluctuation with period less than 300 s, some particle size segments have high correlation at different stages, while some particle size segments have poor correlation at different stages. At the same stage, the size of the benchmark particle that is highly correlated in different particle size segments fluctuates with increasing particle size. In addition, the concentration fluctuation in 0.01276 Hz ∼ 0.02084 Hz and 0.00285 Hz ∼ 0.01096 Hz has significant contributions.

Machine learning analysis of the effects of COVID-19 on migration patterns

This study investigates the impact of the COVID-19 pandemic on European tourist mobility patterns from 2019 to 2021 by conceptualizing countries as monomers emitting radiation to model and analyze their patterns through the lens of socio-economics and machine learning. By incorporating perturbations into clustering, this work evaluates the stability of mobility flux clustering under variable conditions, offering insights into the dynamics of socio-economic corridors. The results highlight distinct shifts in tourist behavior, with bimodal clustering in 2019 reflecting heterogeneous mobility patterns, whereas unimodal distributions in 2020 and 2021 indicate increased global uniformity, driven by pandemic-induced restrictions and gradual recovery. The PCA and dendrograms of the perturbed clustering reveal that tourist preferences align with GDP, cultural, and linguistic similarities, explaining regional cohesion and fragility. This study demonstrates the fragility of emerging socio-economic corridors like the Red Octopus compared to the resilience of established ones like the Blue Banana. The findings emphasize the importance of targeted policy interventions, such as strengthening transport infrastructure and fostering small and medium-sized enterprises (SMEs), to mitigate disruptions and promote balanced regional development. By integrating perturbations into clustering, this research introduces a strong framework for assessing mobility patterns under realistic variability to enhance economic resilience and anticipate shifts in tourist behavior during global crises.

Detrital zircon provenance links between outcrop and subsurface, Rocas Verdes and Magallanes-Austral Basins, Patagonia

Analyzing how provenance signatures of tectonically complex ancient sedimentary basins vary between the outcrop and the subsurface provides a more complete sediment provenance history. The 500+-km-long outcrop belt of the Rocas Verdes and the Magallanes-Austral Basins in southern Patagonia and its subsurface to the east allow us to constrain relationships between longitudinal and transverse sediment sources feeding the basin. New detrital zircon U-Pb ages (n = 2558) from nine subsurface core samples from the Springhill, Piedra Clavada, and La Anita Formations along a 140 km E-W seismic reflection transect (50°S, 71.5°W–69.5°W) reveal the provenance of the basin’s eastern subsurface extent and the influence that tectonic activity can have on sediment capture. Detrital zircon ages (n = 1068) were also collected from four outcrop Springhill Formation samples 140 km NW from the transect near Lago San Martín. Maximum depositional ages (MDAs) from the Springhill Formation cores range from 159 to 157 Ma, which are older than correlative outcrop ages of 151–148 Ma. MDAs from the Piedra Clavada and La Anita Formations range from 93.7 to 91.5 Ma and from 79.3 to 78.3 Ma, respectively, and overlap in age or are slightly younger than outcrop ages. The unimodal Late Jurassic age distribution from the Springhill Formation suggests that it almost exclusively was sourced by recycling of the underlying El Quemado Complex. Early–Middle Jurassic ages in the Early Cretaceous Piedra Clavada Formation samples suggest the basin was either sourcing from the North Patagonian Massif to the N-NE and from the Deseado Massif to the NE or recycling exhumed volcaniclastic sequences in the northern margin of the basin. By the Late Cretaceous, the basin fill was more locally sourced, as suggested by the muted abundance of Early–Middle Jurassic ages in La Anita Formation samples and a second mode of Late Jurassic–Early Cretaceous ages locally derived from recycling of the exhumed El Quemado Complex from the Patagonian fold-and-thrust belt. We suggest that the latitudinal and local transverse drainages that sourced the Magallanes-Austral Basin outcrop belt also fed the eastern, subsurface extent of the basin. Results of this work highlight the importance of using several types of provenance methods and a three-dimensional approach to study the erosional history of sedimentary basins.

Measuring the intracluster medium velocity structure within the A3266 galaxy cluster

We present a detailed analysis of the velocity structure of the hot intracluster medium (ICM) within the A3266 galaxy cluster, including new observations taken between June and November 2023. Firstly, morphological structures within the galaxy cluster were examined using a Gaussian gradient magnitude (GGM) and an adaptively smoothed GGM filter applied to the EPIC-pn X-ray image. Then, we applied a novel XMM-Newton EPIC-pn energy scale calibration, which uses instrumental Cu Kalpha as a reference for the line emission, to measure the line-of-sight velocities of hot gas within the system. This approach enabled us to create two-dimensional projected maps for velocity, temperature, and metallicity, showing that the hot gas displays a redshifted systemic velocity relative to the cluster redshift across all fields of view. Further analysis of the velocity distribution through non-overlapping circular regions demonstrates consistent redshifted velocities extending up to 1125 kpc from the cluster core. Additionally, the velocity distribution was assessed along regions following surface brightness discontinuities, where we observed redshifted velocities in all regions, with the largest velocities reaching $768 km/s. Moreover, we computed the velocity probability density function (PDF) from the velocity map. We applied a normality test, finding that the PDF adheres to an unimodal normal distribution consistent with theoretical predictions. Lastly, we computed a velocity structure function for this system using the measured line-of-sight velocities. These insights advance our understanding of the dynamic processes within the A3266 galaxy cluster and contribute to our broader knowledge of ICM behavior in merging galaxy clusters.

Progressive changes in binocular perception from stereopsis to rivalry.

The binocular system provides a stereoscopic view from slightly different retinal images and produces perceptual alternations, namely, binocular rivalry, from significantly different retinal images. When we observe a stereogram in which the stimulus configurations induce stereopsis and rivalry simultaneously, the binocular system prefers stereopsis to rivalry. However, changes in visual perception are yet to be investigated by parametrically manipulating the components of a stereogram. We examined stereopsis preferences in stereograms with various horizontal disparities. The stereograms of our paradigms included horizontal and vertical bars in one eye and a vertical bar alone in the other. Under experimental conditions, the vertical bar superimposed on the horizontal bar varied its position relative to the opposite vertical bar: range of horizontal disparity, 0.0' to 42.3'. The superimposed vertical bar was absent under the control condition. Observers were instructed to indicate the disappearance of monocular horizontal bars, that is, targets, from their perception during the 30-s trials. The total disappearance duration decreased under experimental conditions compared with that under control conditions, and it gradually increased with an increase in the disparity of the stereoscopic vertical bars. These results indicate that the disparity in the stereoscopic components biases binocular perception away from the rivalry between the vertical and horizontal bars toward the stereopsis of the vertical bars. Furthermore, the disappearance duration showed a unimodal and asymmetric distribution across all disparity conditions. This suggests that rivalry processing occurs in parallel when stereopsis is dominant. We found that stereopsis preference is an outcome of binocular perception selection biased by disparity.

A novel framework for debris flow susceptibility assessment considering the uncertainty of sample selection

The uncertainty arising from random sampling of non-debris flow samples significantly impacts the accuracy of debris flow susceptibility assessments (DFSA). This study introduces a novel uncertainty elimination method, Kernel Density Estimation (KDE), and compares it with Mean and Maximum Probability Analysis (MPA) methods. Furthermore, we investigate the responses of four commonly used machine learning models to sampling uncertainty, comparing two structurally similar models (Random Forest (RF) and Extremely Randomized Trees (ERT)) with two structurally different models (Support Vector Machine (SVM) and Multilayer Perceptron (MLP)). The results indicate that the application of these uncertainty elimination methods can significantly enhance AUC values and zoning accuracy, with the KDE method outperforming the others. Specifically, the AUC values based on KDE for RF, ERT, SVM, and MLP are 0.995, 0.999, 0.999, and 0.853, respectively. The corresponding zoning accuracy for these models is 1.00, 1.00, 1.00, and 0.78, respectively. The study further reveals that the responses to sampling uncertainty vary by model architecture: RF, ERT, and SVM typically exhibit bimodal normal distributions, while the MLP model shows a unimodal distribution. Additionally, MLP is more sensitive to variations in negative samples, whereas RF and ERT are less affected due to the ensemble structure.

Paclitaxel loaded Capmul MCM and tristearin based nanostructured lipid carriers (NLCs) for glioblastoma treatment: screening of formulation components by quality by design (QbD) approach.

Paclitaxel (PTX), a naturally occurring diterpenoid isolated from Taxus brevifolia, is a first-line drug for the treatment of glioblastoma; however, it suffers from the disadvantages of poor water solubility and nonspecific biodistribution, which cause serious side effects in the human body. The marketed formulation suffers from serious side effects, such as allergic reactions, neutropenia, and neuropathy, which require safe and effective formulations of PTX. In the present study, PTX was entrapped in a solid-liquid lipid mixture with the aid of a surfactant using a modified solvent evaporation technique. Higher entrapment of the impressive stability of the formulation was achieved by employing quality design-based strategies. Optimized levels by employing a numerical optimization technique for each factor, that is, surfactant concentration (X1), lipid concentration (X2), and amount of organic solvent (X3) were 0.3%, 0.76% & 8.3 ml respectively. The resultant formulation exhibited a particle size of 121.44 nm, entrapment efficiency of 94.27%, and zeta potential of -20.21 mV with unimodal size distribution. A reduction in the % crystalline index from 48 to 3.4% ensured the amorphous form of the entrapped drug inside the formulation, which precludes the fear of leakage and instability of the formulation. Cell line studies conducted on U87MG Cell lines also suggested that the NLC of paclitaxel are more effective than those of pure PTX. In summary, PTXNLC seem to be a superior alternative carrier system for the formulation industry to obtain higher entrapment with excellent stability.

Chemical structure and hydrocarbon generation potentials of cyanobacteria Schizothrix calcicole and its resistant biopolymer

Microalgae have attracted much attention because of their great potential in the development of sustainable biofuel. In this study, cyanobacteria Schizothrix calcicole was fractionated into different fractions and characterized by elemental analyses, Rock-Eval pyrolysis, and 13C NMR. Closed pyrolysis experiments were carried out on the bulk (BL) sample of S. calcicole and its nonhydrolyzable organic matter (NHOM) fraction. The results suggested the NHOM fraction was composed of a saturated and unbranched or weakly branched hydrocarbon chain with a chain length up to 32, which was highly aliphatic resistant biopolymer similar to algaenan in structure, and exhibited higher oil yield (58.1 %) and oil and gas production potentials (OGPs, 63.9 %) than the BL sample did. Moreover, the n-alkanes for the NHOM fraction showed bimodal distribution and were dominated by long chains higher than C15. On the contrary, the BL sample exhibited unimodal distribution of n-alkanes, in which middle- and short-chain n-alkanes with chain length <17 were more abundant. In addition, the results indicated 13C NMR is an effective approach to evaluate hydrocarbon generation potentials. Our investigation identifies aliphatic biopolymers in cyanobacteria S. calcicole and improves the understanding of hydrocarbon generation of its different fractions.

Damping and acoustic properties of nanosilica filled poly(styrene-acrylate) interpenetrating polymer networks (IPNs): Effect of nanocomposite preparation method

Research on noise pollution reduction has focused on utilizing damping coatings and polymer nanocomposites to enhance sound absorption. Nanosilica/poly(styrene-acrylate) nanocomposites as a water-based coating were prepared through in-situ emulsion polymerization and direct mixing methods at varying concentrations of 1, 2, and 3 wt% of nanosilica. Fourier transform infrared (FTIR) spectroscopy revealed that the inclusion of surfactant-containing micelles and a more extended synthesis period in the in-situ synthesis technique enhanced the interaction between silica nanoparticles and polymer chains. Dynamic light scattering (DLS) analysis showed a unimodal distribution and an acceptable range of polydispersity index (PDI) for neat and nanocomposite latexes. The addition of silica nanoparticles enhanced the stability of latex particles, especially evident in the direct mixing method. The field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) images confirmed the better dispersion of nanoparticles within the polymer matrix in the in-situ method. The addition of nanosilica resulted in a significant increase in pseudoplastic behavior and viscosity, notably in the in-situ synthesis. In both the in-situ synthesis and direct mixing techniques, the addition of 1 wt% of nanosilica resulted in an increase in the damping factor of nanocomposite films to about 2. However, when the nanosilica content was further increased to 3 wt%, the damping factor decreased. Acoustic tests demonstrated improved sound absorption with silica nanoparticles, yielding noise reduction coefficient (NRC) values of 0.49 and 0.46 for in-situ synthesis and direct mixing. The direct mixing method notably enhanced tensile properties at all nanoparticle content levels. Dried nanocomposite films exhibited superior UV-blocking capabilities compared to neat polymer films.

VEGAS-SSS: Tracing globular cluster populations in the interacting NGC 3640 galaxy group

Context. Globular clusters (GCs) are among the oldest stellar systems in the universe. As such, GC populations are valuable fossil tracers of galaxy formation and interaction history. This paper is part of the VEGAS-SSS series, which focuses on studying the properties of small stellar systems (SSSs) in and around bright galaxies. Aims. We used the multiband wide-field images obtained with the VST to study the properties of the GC population in an interacting pair of galaxies. Methods. We derived ugri photometry over 1.5 × 1.5 sq. degrees centered on the galaxy group composed of two elliptical galaxies: NGC 3640 and its fainter companion NGC 3641. We studied the GC system properties from both the ugri and gri matched catalogs. GC candidates were identified based on a combination of photometric properties (colors and magnitudes) and morphometric criteria (concentration index, elongation, FWHM, etc.), using sources with well-defined classifications from spectroscopic or imaging data available in the literature and numerical simulations as references. The selection criteria were also applied to empty fields to determine a statistical background correction for the number of identified GC candidates. Results. The 2D density maps of GCs appear to align with the diffuse light patches resulting from the merging events of the galaxies. The highest density peak of GCs is observed to be on NGC 3641 rather than NGC 3640, despite the latter being the more massive galaxy. The azimuthal averaged radial density profiles in both galaxies reveal that the GC population extends beyond the galaxy light profile and this indicates the likely presence of an intra-group GC component. A color bimodality in (u − r) and (g − i) is observed for NGC 3641, whereas NGC 3640 shows a broad unimodal distribution. Analysis of the GC luminosity function indicates that both galaxies are roughly located at the same distance (∼27 Mpc). We provide an estimate of the total number of GCs, and determine the specific frequency for NGC 3640, SN = 2.0 ± 0.6, which aligns with expectations, while for NGC 3641 we find a large SN = 4.5 ± 1.6.

A Markovian Gauss inequality for asymmetric deviations from the mode of symmetric unimodal distributions

For a random variable with a unimodal distribution and finite second moment Gauß (1823) proved a sharp bound on the probability of the random variable to be outside a symmetric interval around its mode. An alternative proof for it under the assumption of a finite r r -th absolute moment is given ( r ≥ 1 r\geq 1 ), based on the Khintchine representation of unimodal random variables. A special instance of the resulting Narumi–Gauß inequality is the one with finite first absolute moment, which might be called a Markovian Gauß inequality. For symmetric unimodal distributions with finite second moment Semenikhin (2019) generalized the Gauß inequality to arbitrary intervals. For the class of symmetric unimodal distributions with finite first absolute moment we construct a Markovian version of it. Related inequalities of Volkov (1969) and Sellke and Sellke (1997) will be discussed as well.

Investigation of the Influence of Spoiler and Maintenance Track on Second-Order Heaving Vortex-Induced Vibration

To improve the guidance for the wind tunnel test, this study initially conducted thorough research on the wind environment at a coastal bridge site to ascertain the characteristics of the wind parameters varying along the bridge span. Subsequently, the measured results were utilized to steer wind tunnel test research, focusing on analyzing the influence of the spoiler and maintenance track on the second-order heaving vortex-induced vibration of the flat steel box girder. This investigation uncovered two distinct distributions in the angle of attack along the span: bimodal distribution and asymmetric unimodal distribution. The angle of attack of the incoming flow was primarily concentrated within ±5°. Both the two-side and the windward spoiler were found to exert similar effects on the second-order heaving vortex-induced vibration, primarily impacting the second lock-in region. Furthermore, the outer maintenance track could effectively suppress the vortex-induced vibration, while the spacing of the inner maintenance track significantly affected the vortex-induced vibration at high wind speeds.

High-concentrated synthesis of surface modified iron oxide nanoparticles using ethanol-enhanced supercritical CO2 media

In the synthesis of surface modified metal oxide nanoparticles (NPs), supercritical CO2 is an attractive medium to achieve a simple and green chemistry approach without waster liquor. However, the mass production of surface-modified NPs is still a serious challenge for their industrial utilization. In this work, we aimed to demonstrate the high-concentrated synthesis of surface-modified iron oxide NPs in ethanol-enhanced supercritical CO2. The synthesis and phase observation were performed at 30.0 ± 0.8 MPa of CO2, 100 °C and 18 h, while changing the total concentration of iron(Ⅲ) acetylacetonate, water and oleic acid and ethanol ratio. As a result, lower total concentration gave single nano-sized α-Fe2O3 nanocrystal under uniform phase while higher one gave aggregated α-FeOOH under ununiform phase. However, ethanol entrainer successfully homogenized the reaction field by drastically raising the solubilities of components, allowing the high-concentrated synthesis of single nano-sized α-Fe2O3 nanocrystal. Furthermore, synthesized nanocrystal had chemically and densely modified surface, showing the unimodal size distribution in cyclohexane. These results conclusively show that supercritical CO2 with ethanol entrainer is a promising medium to allow the mass production of densely modified nanocrystal and subsequent their industrial utilization in thin film fabrication and drug delivery system.

Numerical and experimental study of TIG welding arc in high frequency longitudinal magnetic field

The phenomenon of arc compression in TIG welding with high-frequency longitudinal magnetic field (HF-LMF) has been observed. However, its mechanism remains unclear, and there is a lack of numerical investigation. This work presents a two-dimension axisymmetrical model of arc plasma in high-frequency longitudinal magnetic field based on the magnetohydrodynamics (MHD). The distributions of temperature, velocity and pressure of arc plasma in HF-LMF are investigated at different applied LMF frequencies ranging from 0 to 5000 Hz. In order to make the simulation results more convincing, the induced current and the electric force were considered. The results show that the HF-LMF could generate a circumferential electric field, causing particles rotating. However, since HF-LMF is variable, the direction of the electric field also changes, which causes the arc to rotate back and forth. When the frequency of HF-LMF reaches 2000 Hz, the negative pressure zone above the center of the anode disappeared and the arc was compressed. Thus, as the frequency of LMF increases, the distribution of current density, anodic heat flux, and arc pressure changes from a bimodal distribution to a unimodal distribution, and the peak value increases. The theoretical predictions were in good agreement with the experimental results.

Antimicrobial susceptibility of Clostridium botulinum group III field strains isolated in Europe from animal outbreaks

Neurotoxins produced by Clostridium (C.) botulinum group III are responsible for the majority of botulism outbreaks occurring in animals and in this study we report the drug susceptibility of 71 field strains. The minimum inhibitory concentration (MIC) of 13 antimicrobials was established through the agar dilution method. The MIC50 matched or differed for one or two dilutions from MIC90 of the same antimicrobial, showing a unimodal distribution of the MIC values, irrespective of the geographical origin, the animal source and the toxinotype of the strain. Beta-lactams and rifampin showed the lowest MIC values, while gentamicin, polymyxin B and sulfamethoxazole showed the highest MICs. As for similar studies conducted in human botulism, the results could be helpful to avoid the administration of antimicrobials that could worsen the health condition of the affected animals and to develop selective media for the isolation of these fastidious anaerobes. Indeed, the isolation of the strain from affected animals and from environmental samples is important to perform epidemiological studies based on the genetic characterization and to produce tailor-made vaccines.

Hydrological Modeling to Unravel the Spatiotemporal Heterogeneity and Attribution of Baseflow in the Yangtze River Source Area, China

Revealing the spatiotemporal variation in baseflow and its underlying mechanisms is critical for preserving the health and ecological functions of alpine rivers, but this has rarely been conducted in the source region of the Yangtze River (SRYR). Our study employed the Soil and Water Assessment Tool (SWAT) model coupled with two-parameter digital filtering and geostatistical approaches to obtain a visual representation of the spatiotemporal heterogeneity characteristics of the baseflow and baseflow index (BFI) in the SRYR. The SWAT model and multiple linear regression model (MLR) were used to quantitatively estimate the contribution of climate change and human activities to baseflow and BFI changes. The results underscore the robust applicability of the SWAT model within the SRYR. Temporally, the precipitation, temperature, and baseflow exhibited significant upward trends, and the baseflow and BFI showed contrasting intra-annual distribution patterns, which were unimodal and bimodal distribution, respectively. Spatially, the baseflow increased from northwest to southeast, and from the watershed perspective, the Tongtian River exhibited higher baseflow values compared to other regions of the SRYR. The baseflow and BFI values of the Dangqu River were greater than those of other tributaries. More than 50% of the entire basin had an annual BFI value greater than 0.7, which indicates that baseflow was the major contributor to runoff generation. Moreover, the contributions of climate change and human activities to baseflow variability were 122% and −22%, and to BFI variability, 60% and 40%. Specifically, precipitation contributed 116% and 60% to the baseflow and BFI variations, while the temperature exhibited contributions of 6% and 8%, respectively. Overall, it was concluded that the spatiotemporal distributions of baseflow and the BFI are controlled by various factors, and climate change is the main factor of baseflow variation. Our study offers valuable insights for the management and quantitative assessment of groundwater resources within the SRYR amidst climate change.

Epidemiological characteristics and toxicant type of acute poisoning cases in China, 2016-2022

Objective: To analyze the acute poison epidemic and provide evidence for developing prevention and control strategies for acute poisoning. Methods: A retrospective analysis was conducted on acute poisoning cases collected from 2016 to 2022 in a health emergency information platform for acute poisoning accidents. The cases were grouped according to the distribution of poisoning occurrence time, geographic distribution, demographic distribution, types of toxicants, poisoning causes, and outcomes. Data were organized and analyzed using Excel 2016 and R 4.2.3. Results: A total of 95 754 acute poisoning cases were included in this study. The primary toxicants were pesticides, drugs, and industrial/household chemicals, accounting for 30.4%, 22.4%, and 20.4% of the total cases, respectively. Acute poisoning occurred throughout the year, with the highest frequency from June to August, accounting for 31.9%. The seasonal distribution varied among different types of toxicants. Except for plant poisoning, which showed a bimodal distribution, the other poisonings showed an unimodal distribution. There was a strong seasonality in fungal poisoning, which peaked in July. There was an obvious seasonality in animal poisoning, with a peak in August. The proportion of biological poisonings in the southwest region was higher than in other regions, including plants, animals, and fungi. There were more females than males, and their education level was mainly junior high school and below (35.2%). The main occupation was farmers (34.2%), and the main causes of poisoning were accidents and suicides. The case fatality rate of all poisoning cases was 1.24%. Pesticide poisoning was the most common type, and chlorfenapyr (11.68%), Diquat (7.23%), and paraquat (7.05%) ranked as the top three toxicants. Conclusions: The occurrence of acute poisoning has an obvious seasonal trend, and the toxicant spectrum of different regions and populations is different. A comprehensive poisoning surveillance system can provide a better understanding of the occurrence of poisonings, and facilitate the formulation of more scientifically precise poisoning prevention and control strategies.

Spatial and historical patterns of sedimentary organic matter sources and environmental changes in the Ross Sea, Antarctic: implication from bulk and n-alkane proxies

Organic carbon (OC) burial in the Antarctic marginal seas is essential for regulating global climate, particularly due to its association with ice shelf retreat. Here, we analyzed total OC (TOC), total nitrogen (TN), radiocarbon isotope, n-alkanes and relative indicators in surface and core sediments from the Ross Sea, West Antarctica. Our aim was to investigate spatial and historical changes in OC sources, and to explore the influencing factors and implications for ice shelf retreat since the last glacial maximum (LGM). Our results revealed distinct spatial patterns of OC sources as indicated by n-alkane indicators in surface sediments. In the Western Ross Sea, n-alkanes predominantly originated from phytoplankton and bacteria, as evidenced by their unimodal distribution, low carbon preference index (CPI) of short-chain n-alkanes (CPIL = 1.41 ± 0.30), and low terrestrial/aquatic ratio (TAR = 0.22 ± 0.14). In the Southwest Ross Sea, n-alkanes were derived from marine algae and terrestrial bryophytes, indicated by bimodal distribution, low ratio of low/high molecular-weight n-alkanes (L/H = 0.62 ± 0.21), low CPI of long-chain n-alkanes (CPIH = 1.18 ± 0.16), and high TAR (1.26 ± 0.66). In contrast, the Eastern Ross Sea exhibited n-alkanes that were a combination of phytoplankton and dust from Antarctic soils and/or leaf waxes from mid-latitude higher plant, as suggested by both unimodal and bimodal distributions, high L/H (1.60 ± 0.58) and CPIH (2.04 ± 0.28), and medium TAR (0.61 ± 0.30). Geologically, during the LGM (27.3 – 21.0 ka before present (BP)), there was an increased supply of terrestrial OC (TOC/TN = 13.63 ± 1.29, bimodal distribution of n-alkanes with main carbon peaks at nC17/nC19 and nC27). From 21.0 to 8.2 ka BP, as glaciers retreated and temperatures rose, the proportion of marine n-alkanes significantly increased (TOC/TN = 9.09 ± 1.82, bimodal distribution of n-alkanes with main carbon peaks at nC18/nC19 and nC25). From 8.2 ka BP to the present, as the ice shelf continued to retreat to its current position, the marine contribution became dominant (TOC/TN = 8.18 ± 0.51, unimodal distribution of n-alkanes with main carbon peak at nC17/nC18/nC19, and low TAR (0.41 ± 0.32)). This research has significant implications for understanding the variations in Antarctic OC sources and their climatic impacts in the context of accelerated glacier melting.

Research on Particle Emissions of Light-duty Hybrid Electric Vehicles in Real Driving

Real driving emission (RDE) assessments were conducted on light-duty hybrid electric vehicles (HEVs) compliant with China-VI standards across various altitudes, including Kaiyuan, Jianshui, and Kunming. Portable Emission Measurement Systems (PEMS) were utilized to analyze instantaneous particulate number (PN) emissions. At the same time, a particle trap was used to collect primary particulate matter (PM). High-resolution Transmission Electron Microscopy (TEM) was employed to capture the micro-morphology and nano-structure of PM. The findings revealed a positive correlation between PN emission factors and altitude, suggesting more stringent regulations are necessary in high-altitude regions. Cold-start conditions exhibited heightened PN emissions, surpassing regulatory thresholds (primarily when the coolant temperature is below 30°C). Notably, the PN emission rate increases when the vehicle is under light acceleration (0 ≤ a ≤ 0.5 m/s2) and the coolant temperature is within the range of 20∼30°C. The PM emitted by HEVs exhibited an unimodal distribution across different driving conditions, with cold-start yielding finer particles. In contrast, urban and rural driving conditions showed enhanced PM aggregation due to more complete fuel combustion. Urban driving conditions, characterized by coolant temperatures exceeding 70°C and speeds below 60 km/h, produced PM with the largest average particle size (32.68 nm) and the broadest size distribution range (8.99 nm to 77.60 nm). Furthermore, increased engine speed and load resulted in elevated average outer shell fringe lengths of primary nanoparticles. The average inner core fringe lengths initially increased, peaked in urban environments (1.04 nm), and then decreased. Fringe separation distances gradually increased, predominantly between 0.2 nm and 0.8 nm. The increase in engine load is the primary factor influencing the growth of microcrystal tortuosity. The study underscores the significance of HEVs in PM emissions, which pose potential risks to both human health and environmental sustainability, emphasizing the need for effective mitigation strategies.

Modified Low-Field NMR Method for Improved Pore Space Analysis in Tight Fe-Bearing Siliciclastic and Extrusive Rocks

Abstract Understanding the filtration and storage properties of tight reservoirs is crucial for efficient resource exploitation, particularly in unconventional formations. This study presents two low-field nuclear magnetic resonance (LF-NMR) techniques: standard cut-off and modified differential approaches combined with mercury injection capillary pressure (MICP) and X-ray diffraction (XRD) studies to evaluate porosity and pore size distribution (PSD) in such formations. The differential technique involves subtracting the dry sample signal from a 100% water-saturated one, allowing the chemically bound water compound to be eliminated and facilitating PSD analysis. Through the application of the percolation theory, we established a power–law relationship between LF-NMR transverse relaxation time (T2) and MICP pore-throat diameter, enabling the derivation of PSD and pseudo capillary pressure curves. Our methodology was validated on a sample set representing tight sandstones, conglomerates, and extrusive rocks with high clay and iron mineral content, demonstrating the superior accuracy of the modified differential method in estimating effective porosity and absolute PSD in comparison with the standard approach. While the use of the percolation theory in PSD conversion was successful for rocks with unimodal distributions, it often failed for rocks with larger voids. The study also revealed that the relationship between the LF-NMR transverse relaxation times and MICP pore sizes is both nonlinear and challenging to describe with a universal equation, especially in the presence of para- and ferro-magnetic elements in the rock matrix. Despite obstacles to the complete elimination of the influence of these minerals on the T2 distribution, employing the modified differential LF-NMR method significantly mitigated this effect and offered a precise and noninvasive way of characterizing the petrophysical properties of tight reservoir rocks. Consequently, our studies offer a significant step toward a more precise assessment of pore structures in unconventional reservoirs that could be translated into more efficient strategies for locating geothermal heat and hydrocarbon resources.