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This paper is a continuation of a recent investigation by Zhan and Dyachenko (2021) on the Hurwitz stability of monic matrix polynomials with algebraic techniques. By improving an inertia formula for matrix polynomials with respect to the imaginary axis, we show that, under some conditions, the quasi-stability of a monic matrix polynomial can be tested via the Hermitian nonnegative definiteness of two block Hankel matrices built from its matricial Markov parameters. Moreover, for the so-called doubly monic matrix polynomials, the quasi-stability criteria can be formulated in a much simpler form. In particular, the relationship between Hurwitz stable matrix polynomials and Stieltjes positive definite matrix sequences established in Zhan and Dyachenko (2021) is included as a special case. [ABSTRACT FROM AUTHOR]

A study about the effect of different configurations of stationary and movable appendages on the dynamic stability of an autonomous underwater vehicle (AUV) is presented. A new stability index that can be used to assess dynamic stability in the vertical plane is derived. It improves upon the vertical plane stability index by accurately accounting for the contribution of hydrostatic forces to dynamic stability, even at low speeds. The use of the new stability index is illustrated by applying it to a set of AUV configurations based on an AUV initially designed at Virginia Tech and built by Dive Technologies. The applicability of this index depends on the speed of the craft. The range of applicability in terms of speed is presented for the DIVE craft as an example. The baseline design of the DIVE craft has asymmetry in the vertical plane and symmetry in the horizontal plane. A virtual planar motion mechanism (VPMM) is used to obtain the hydrodynamic coefficients of the hull. Design iterations are performed on the baseline design by varying the appendages in shape and size, adding appendages and adding features on appendages. The best and the baseline design from this effort are incorporated in a 6 DOF lumped-parameter model (LPM) to compare results of a straight line maneuver. A computational fluid dynamic (CFD) tool is used to obtain the trajectory comparison of turn-circle maneuver for these two designs. A principal conclusion is the important contribution of a hydrostatic restoring force at low-moderate speeds by using GVgrav and the influence of design of control surfaces, both stationary and non-stationary, in the achievement of control-fixed course stability.

The seed yield in hemp (Cannabis sativa L.) is strongly influenced, besides by genotype, by environment and the genotype x environment interaction, so establishing the fitness and stability of hemp cultivars in multiple environments is necessary. The purpose of this study was to investigate the performance and degree of stability and variance of seed yield, the main related traits, and the correlation among the traits in five hemp monoecious cultivars cultivated in six different environments. The environments resulted from the combination of four locations, two years, and two delayed sowings in a Mediterranean area of north-eastern Italy, and the stability index of the weighted average of absolute scores (WAAS) was used in order to identify the most productive and stable genotypes on the basis of their deviation from the average performance across environments. In this studied area, early varieties, such as Fedora and Felina, proved to be the best performing and stable for seed yield and both increased their yield in correspondence to delayed sowing times, opening up the possibility of cultivating hemp as a second crop. Among the climate parameters, high temperatures during the early grain filling period led to a progressive decrease in seed yield. For a dual-purpose crop, a good compromise could be a late monoecious cultivar (like Futura, in the present experiment), which, if sown early, could certainly provide notable biomass production and acceptable seed yield.

The main regional factors of occurrence and activation of landslides within the mountain region were examined. As a result of study of recommendations made by experts, geologists, and gap analysis of existing methods of forecasting the landslide process, an algorithm of comprehensive assessment of landslide hazard areas based on the construction of models in a GIS environment was proposed. These models describe the spatial patterns of landslides. All factors determining the tendency of the studies area to the landslide process development were divided into actual factors, reflecting the regional peculiarities of the territory and forming the landslide-prone slopes (static model), as well as triggering factors, initiating the landslide process and determining its activity (dynamic model). The first cartographic model was built, showing the distribution of the deterministic indirect indicator of landslide hazard, i.e. stability index.

In recent years some studies have been done on the moment rredistribution in buildings and new methods offered for calculating of redistribution. Observations demonstrated that the combination of moment and shear force is important in analysis of reinforced concrete structures. But little research is done about the effect of redistribution by using moding in software. In order to study the effect of moment redistribution on the stability of RC moment resisting frame structures, four buildings with 4, 7, 10 and 13 story have been considered. In these models, the nonlinear behavior of elements (beam and column) is considered by the use of interaction PMM hinges. The average plastic rotation was calculated by performing pushover analysis and storing stiffness matrix for 5 points and then the buckling coefficients were obtained by conducting buckling analysis. By the use of modal analysis natural frequency was calculated and it was attempted to be related the average plastic rotation with the buckling coefficients and the natural frequency. It could be concluded that increase in the plastic rotation reduce the buckling coefficients to about 96% which this amount of reduction is related to the average plastic rotation. Moreover, the buildings experience instability state when the average plastic rotation reached to 0.006 radian.

Objective: To detect the effect of combined oral contraceptive pills (COC) on dynamic postural balance in healthy middle aged women. Materials and methods: A prospective randomized controlled study included 200 patients classified into two groups. Group I received COC containing 30 μg of EE and 3 mg of drospirenone for 12 consecutive cycles and Group II received no treatment. Overall, medio-lateral and antero-posterior stability were measured using Biodex system after 12 months. Results: There was a highly statistically significant difference between the 2 study groups regarding estradiol level (12.84 ± 1.96 vs. 38.86 ± 3.99, P value

We suggest a new, parsimonious, method to fit financial data with a stable distribution. As a result of a stable fitting via maximum likelihood estimation (MLE), we find that some assets have similar values as stability indices, independently of the time interval considered. This fact can be exploited to pool the assets in groups and to choose a parameter α as an ex ante stability index, valid for every asset in the pool sector. With this fixed parameter, MLE is used again to obtain the other stable parameters. We discuss an innovative risk measure, based on the Expected Shortfall, which exploits the above procedure. We show that it gives a good estimation of risk even when only short time series are available. Finally, we introduce the notion of Risk Class, which allows us to classify assets according to their risk exposition and to compare different methods for the computation of the Expected Shortfall. [ABSTRACT FROM AUTHOR]

Background/Objectives: Trampolines are rehabilitative methods that can enhance one's ability to stimulate and balance inherent capacities, which have a significant effect on sensory organs, nervous system, and physical strength. Methods/Statistical analysis: In this study, 45 healthy subjects were recruited. Subjects were randomly assigned to walking, tiptoeing, or jumping groups. Each group of trampoline interventions was performed for 10 minutes. In all three groups, balance and proprioceptive sensory tests were performed before exercise, immediately after exercise, and 5 and 10 minutes after exercise. Findings: There was a significant difference in SI data between pre- and post-intervention (p<0.05). According to the SI results in the NO condition, the stability was reduced immediately after exercise and restored after 5 minutes in all groups (p<0.05). According to SI results in NC condition, there was a significant difference between immediately after exercise and after 5 minutes in all groups (p<0.05). Improvements/Applications: Trampolines are effective for posture stability. A rest time of 5 minutes is required to restore posture stability after trampoline exercise. [ABSTRACT FROM AUTHOR]

Incomplete data sampling, bias, and like properties of distribution datasets that potentially introduce uncertainty in biogeographical analyses and blur biogeographical patterns; therefore, it is important to understand their influence. Despite their relevance, these problems have been largely overlooked in biogeography, where concepts such as ambiguity, stability or support have not even been defined. Here, we propose two stability measures for hypotheses of areas of endemism (AEs) and use them to explore the degree to which different structural qualities of data affect the results of analyses of endemism. Our findings suggest that different types of data incompleteness have different effects on the recovery of the species composition and the geographical or spatial structure of AEs, showing that distinct levels of sampling coverage affect the stability of results in different ways. We show that a small proportion of poorly sampled species may have a stronger impact on AEs stability than many species with medium sampling and that excluding poorly sampled species from the analyses does not guarantee more stable results. These results highlight the importance of planning data collection and indicate that, in order to obtain more stable results, focusing on completing the distribution of strongly undersampled species might be preferable to adding records of any species randomly. [ABSTRACT FROM AUTHOR]

Yacon (Smallanthus sonchifolius) is a tuber with a high content of active compounds that offer health benefits, so its productive chain seeks new alternatives to generate yacon products with added value; however, it tends to be a perishable product due to its high aw, chemical composition, and enzymatic activity. The influence of both composition and homogenization in the colloidal stability of yacon suspensions was evaluated for later use in spray drying. Response surface methodology and a central composite design were used, considering three independent variables: homogenization time (TH) (4-6 min), xanthan gum (XG) (0.1-0.2%), and acidity (0.1-0.3%); and the following dependent variables: zeta potential (ζ), color (CIELab), viscosity (µ), stability index by spectral absorption (R), and particle size (D10, D50, and D90). The values of the independent variables that best fit the experimental optimization criteria were: XG=0.16%, acid=0.3%, and TH=4.8 min. The values of the experimental dependent variables and the variables predicted by the quadratic model were ζ=-33.8±4.0 and -37.6 mV, µ=1143.0±93.4 and 1000 cP, R=0.45±0.1 and 0.48, D10=127.8±8.2 and 138.1 µm, D50=251.2±16.3 and 267.7 µm, D90=424.3±28.7 µm and 463.9 µm, L*=41.7±1.4 and 41.8, a*=0.02±0.85 and 1.6, and b*=15.0±1.3 and 14.8, respectively. The colloidal suspension showed adequate physicochemical stability, favored mainly by repulsive forces, homogenization, and rheology of the continuous phase; reaching a content of total solids of 12.5%. [ABSTRACT FROM AUTHOR]

Oilseed rape seed yield has increased in the last 40 years in most countries, but this yield gain has not been accompanied by greater yield stability. The current study aimed to quantify the genotype by environment (G × E) interaction on oilseed rape yield, identify genotypes with broad adaptability and the main environmental drivers related to seed yield. A weighted two-stage mixed-model analysis was applied to official multi-environment trials of nine spring genotypes (G), in three locations (L) during 6 years (Y) on central and southern Argentine Pampas under rainfed conditions. Best linear unbiased prediction of seed yield ranged from 0.37 to 3.73 kg/ha. Fixed effect L × Y was highly significant and G variability was estimated as 130 kg/ha of standard deviation. Contrasting genotypes were identified by Shukla's stability index and two of those showed the best yield performance in the wettest year. Factor analysis explained 0.75 of total variation and discriminated genotypes with broad and specific adaptability, as well as combined environments according to the similarities in seed yield of the evaluated genotypes. Environmental loadings of Factor 2 were linearly associated with cumulative rainfall in the post-flowering period (up to 230 mm). It is concluded that (i) a significant G × L × Y interaction underlies the high variability of seed yield, (ii) two genotypes (G6 and G7) with high yield stability were identified, and (iii) G × E effects are associated with post-flowering rainfall. [ABSTRACT FROM AUTHOR]

The objective of the study was to investigate, which gender group was at risk of falling, using stability index as a fall-risk predictor. A total number of 58 institutionalized elderly persons were invited to participate in the study. Stability index was assessed on the Biodex Balance System SD. Difference in stability index between males and females were noted, females had a mean rank score of 26.83, whilst males had a mean rank score of 33.02, however, there was no significance difference among the two gender groups (U =324.5, z = 1.382, p =.167, r = 0.17). Elderly female participants had an elevated body mass index (M = 27.67 kg/m2, SD = ±7.41) compared to male participants (M = 26.43kg/m2, SD = ±5.62). Overall, the mean stability score for elderly women was 3.58 (±1.21) and elderly men was 4.72(±3.03) respectively. The results suggest that elderly males are at higher risk of falling compared to their female counterparts. [ABSTRACT FROM AUTHOR]

Flame stability assessment is essential for optimizing combustion operation and improving combustion quality. However, an accurate and reliable assessment of stability is difficult, heavily relying on prior expert knowledge and massive labeled data. This study proposes a novel method for flame stability assessment through flame images and deep learning techniques. In this method, the deep image features are extracted by an unsupervised convolutional denoising autoencoder (CDAE), and then quantitatively analyzed by a stability index. In particular, the CDAE introduces a new loss function composed of denoising coding constraints and reconstruction similarity to improve its training efficiency. The stability index is established based on clustering analysis and statistical analysis of the deep image features, with a numerical interval of [0, 1]. The effectiveness of the proposed method is verified by the flame images obtained from ethylene-air diffusion combustion conditions. Results show that the proposed method extracts representative flame features accurately and quantifies the flame stability with strong robustness and generalization ability. [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel materials for simultaneous dedusting and explosion prevention are studied. • Remarkable reduction on dust concentration and explosion risk has been achieved. • The materials are also effective when curing coal particle with high oil content. • Better performance is due to the optimized wetting and agglomerating behaviour. • The mechanisms have been investigated from both macro and micro perspectives. The fully mechanized mining faces in underground oil-rich coal mines are exposed to the serious dust pollution and the high risk of dust explosion. Traditional materials cannot effectively realize the removal and inerting of coal particles with high oil content. Thus, this paper innovated new materials to eliminate the occupational disasters and explosion accident in underground coal mines by achieving simultaneous dedusting and explosion prevention of coal particles with high oil content. Compare with traditional materials, the presence of short-chain fluorocarbon surfactants and electrolytes achieved 76.30–84.92% improvement on dedusting rate, a maximum 22 times improvement on MIE, 4.20–8.90% improvement on MIT, and 50% improvement of MEC. Mechanism analysis revealed the better performance is attributed to the optimized wetting and agglomerating behaviour. Kinetic analysis showed that the new materials reduced the heat release and inhibit combustion process. The NaCl outperforms NaHCO 3 in achieving better dedusting and explosion suppression performance in most cases for its higher TSI and more efficient explosion prevention mechanisms. Studies also demonstrated that the oil content could moderate the dedusting and explosion prevention performance due to the reduction of static liquid bridge force in terms of the increased proportion of saturated hydrocarbons and aromatic hydrocarbons, the reduced concentration of polar functional group, and the corresponding increased contact angle "θ". The Findings of this paper provide an efficient and environmental-friendly choice for ensuring occupational health and safe production in underground oil-rich coal mines by achieving simultaneous dedusting and explosion prevention. It will also guide the innovation and development of multiple protective materials for coal mine safety protection. [ABSTRACT FROM AUTHOR]

Studying and modeling the effects of soil properties and management on soil structure and near saturation water retention is vital for the development of effective soil and water conservation practices. The contribution of soil intrinsic properties and extrinsic conditions to structure stability was inferred, in quantitative terms, from changes in water retention curves near saturation (low matric potential, 0-50 cm, macropores > 60 µm) that were obtained by the high energy moisture characteristic (HEMC) method. The S-shaped water retention curves were characterized by the modified van Genuchten model that provided: (i) the model parameters α and n, which represent the location of the inflection point and the steepness of the water retention curve, respectively; and (ii) the soil structure index, SI=VDP/MS, where VDP is the volume of drainable pores, and MS is the modal suction. Model parameters, claculated by the soil-HEMC model, were related to soil properties and hence soil water retention properties were linked to measured characteristics in several field and laboratory experiments. Soil SI increased exponentially with the increase in α and the decrease in n, while the relationship between SI and α/n was linear. An improved description of the water retention and its link to pore and apparent aggregate size distribution, by using the model parameters α and n, could potentially assist in the selection of management practices for obtaining the most suitable type of soil structure depending on the desired soil function.

This research proposes a new index to evaluate the stability of the melting process, in three-phase electric arc furnaces (EAFs), based on the acoustic signals generated during the different stages of the casting. The proposed stability index is obtained by characterizing the time and frequency domain of the acoustic signals. During EAF monitoring, acoustic signals were acquired using a microphone coupled to an NI USB-9234 acquisition system. To validate the results, the voltage and current signals were measured with the aid of a Circutor AR6 power analyzer for three-phase electrical networks. The results showed that the acoustic signal energy in the frequency range of 1 to 12 kHz can be used as an indicator of the process stability in the EAF. Finally, the validity of the proposed stability index is evaluated from the process characterization using the harmonic distortion analysis methods and the dynamic U-I characteristics of the arc voltage and current signals. The results obtained demonstrated the effectiveness of the proposal and constitute a starting point for advances in the automatic control of the process in the EAF, from the acoustic signals.

The use of deinking paper sludge (DPS) as a fertilizer instead of sending it to landfill could play a role in reducing greenhouse gases and improving soil properties. The objectives of this study were (1) to evaluate the changes in the physical (permeability and structural stability), chemical (particularly soil pH), and biological (microbial metabolic quotient (qCO2), microbial biomass soil CO2 emissions) of a calcareous agricultural soil following two successive annual amendments with three treatments (0, 30, and 60 Mg DPS ha−1—control, DPS30, and DPS60, respectively); and (2) to determine whether the addition of N-fertilizer to these treatments (controlF, DPS30F, and DPS60F, respectively) causes changes to soil fertility. The DPS application increased soil organic matter (+0.80%: DPS60 vs. control; and +0.35%: controlF vs. DPS60F), available phosphorus (+23.14 mg kg−1: DPS60 vs. control; and +14.34 mg kg−1: DPS60F vs. controlF), potassium (+0.6 g kg−1: controlF vs. DPS30F), and calcium (+0.28 g kg−1: DPS60 vs. control). The 60 Mg DPS ha−1 rate improved permeability and structural stability, regardless of the presence or absence of N-fertilizer. On the other hand, the 60 Mg DPS ha−1 rate without N-fertilizer lead to a decrease in total mineralization rate and qCO2, thereby indicating a reduction in CO2 emissions. The rate of 60 Mg ha−1 DPS could be effectively used to enhance the permeability and stability (soil restoration) and mitigate CO2 emissions, whereas the 30 Mg ha−1 rate could be used as fertilizer to improve the fertility of calcareous soils.

Mapping coastal dune vegetation is critical to understand dune mobility and resilience in the context of climate change, sea level rise, and increased anthropogenic pressure. However, the identification of plant species from remotely sensed data is tedious and limited to broad vegetation communities, while such environments are dominated by fragmented and small-scale landscape patterns. In June 2019, a comprehensive multi-scale survey including unmanned aerial vehicle (UAV), hyperspectral ground, and airborne data was conducted along approximately 20 km of a coastal dune system in southwest France. The objective was to generate an accurate mapping of the main sediment and plant species ground cover types in order to characterize the spatial distribution of coastal dune stability patterns. Field and UAV data were used to assess the quality of airborne data and generate a robust end-member spectral library. Next, a two-step classification approach, based on the normalized difference vegetation index and Random Forest classifier, was developed. Results show high performances with an overall accuracy of 100% and 92.5% for sand and vegetation ground cover types, respectively. Finally, a coastal dune stability index was computed across the entire study site. Different stability patterns were clearly identified along the coast, highlighting for the first time the high potential of this methodology to support coastal dune management.

The purpose of present study was to determine the effect of different levels of balance task difficulty and visual feedback on balance in elderly women. Fourteen healthy elderly women (mean age 57/65 yr) were selected voluntarily. Participants were asked to stand still on a stability platform under each of two conditions (with visual feedback and without visual feedback) in three levels of difficulty (6, 8, 10). Stability index scores (Overall, Anterior- Posterior and Medial- Lateral) were calculated by Biodex Balance System. Duration of each test was 20 seconds and rest times were 20 seconds. Results showed that with increasing task difficulty, score of Medial- Lateral balance (p= 0/02) increased significantly. In addition, There was a significant reduction in the scores of Overall balance (p= 0/001), anterior - posterior balance (p= 0/01) and medial - lateral balance (p= 0/01) in visual feedback condition compared with without feedback condition. Overall, the results of this study showed that increasing task difficulty increases postural sway and availability of visual feedback can improve balance and reduce the postural sway.

Corrosion and scaling in drinking water sources can lead to economic and health damages. These processes produce by-products in distribution systems, reduce chemical water quality, and are the cause of health issues among consumers. The aim of this study was to evaluate the corrosion and scaling potential of water supply sources of Marivan villages, Iran. In total, 106 water samples were collected through grab sampling from 64 wells and 42 springs in Marivan villages. The values of the Langelier saturation index (LSI), Ryznar stability index (RSI), Aggressive index (AI), and Puckorius index (PI) were calculated using parameters such as temperature, calcium hardness, total alkalinity (TA), total dissolved solids (TDS), and pH according to the last edition of the standard methods. Based on the RSI, 3% of the springs and 9% of the wells were in stable condition, 97% of the springs were corrosive and 90% of the wells had scale forming potential. The LSI was positive for 57% of the springs and 78% of the wells. The AI value of 40% of the springs and 64% of the wells was higher than 12 and the PI value was lower than 6 for all the springs and wells. The results of this study indicated that most of the springs were corrosive and a few of them had scale-forming potential. It was also found that the wells had scaling tendency. Thus, routine monitoring of the sources is necessary to control corrosion and scaling and maintain water quality.

Abstract In this paper we investigate the problem of influence of parametric perturbations on the Lyapunov spectrum of the discrete linear time-varying system. The main result of the paper is that for any two sequences of positive real numbers and any rate of convergence there exist a discrete linear time-varying system and a perturbation tending to zero with the given rate of convergence such that the spectra of the perturbed and unperturbed systems coincide with the a priori given sequences. Moreover, we show that this phenomenon is possible even when the perturbations are different from zero, rarely, in a certain sense. Finally, as a conclusion from the main result, we obtain that the separation type and the index of exponential stability may vary arbitrarily under the influence of exponentially decreasing perturbations. [ABSTRACT FROM AUTHOR]

High stability of crop yields is a key objective in crop production and breeding, especially under the conditions of a changing climate. Reliable indices are therefore needed for quantifying yield stability. Recently it was shown that some frequently used indices of yield stability, such as the coefficient of variation (CV) may be wrongly interpreted if there is a systematic dependence of the variance σ² from the mean yield μ following Taylor’s power law. Here we propose a method to adjust the standard CV to account for the systematic dependence of σ² from μ. This adjusted CV can be used as a stability index that is expressed in units that are equivalent to the standard CV, as a percentage of the mean, and can therefore be used in agronomic studies that aim to provide guidance for farmers and advisors. Applying this adjusted CV (called aCV) to FAO cereal yield data, we show that the temporal yield stability of both wheat and rye has weakly but significantly decreased over the last five decades and this trend was not picked up with the standard CV in wheat, and was more marked with the aCV than with the standard CV in rye. For the intensifying research on yield stability in agronomy, the suggested method is a novel alternative to estimate yield stability more conclusively, allowing straight-forward interpretation and providing the basis for developing cropping systems with higher yield stability in the future. [ABSTRACT FROM AUTHOR]

Background/Aims: Rebound exercises using a trampoline and BOSU ball provides proprioceptive and vestibular stimulation and improve postural control and balance. Although there is no evidence to support the benefits of using rebound exercises, it is widely used in rehabilitation. The current study aimed to investigate the effect of a rebound exercises on balance in children with spastic diplegia. Methods: Forty children with spastic diplegia from both sexes, age ranged from 6 to 10 years participated in this study. They were allocated randomly into two groups of equal numbers, one was the control group and the other was the study group. The control group received a designed physical therapy programme for 1 hour and balance training for 1 hour. The study group received the same physical therapy programme as the control group in addition to rebound exercises for one hour. The treatment programmes of both groups were conducted 3 days a week for 2 successive months. The assessments of dynamic balance were conducted pre, post treatment and 1 month after the end of the treatment using the Biodex balance system. Results: Baseline and post treatment comparisons showed a statistically significant improvement of balance in the two groups. There was no significant difference between post treatment and post 1 month follow-up in the control group, while a significant difference was recorded in the study group. Conclusions: Rebound exercises conducted with a designed physical therapy programme is beneficial and has a significant effect in improving balance. [ABSTRACT FROM AUTHOR]

Even though extensive research have been done on electromyogram (EMG) based prosthetic hand control, relatively lesser attention have been received for control of individual prosthetic hand fingers. An EMG based recognition of individual finger movements will enable a more dexterous control of prosthetic hands. This paper reports the recognition of index finger movements: flexion-extension and abduction-adduction based on two channel EMG. The focus was on deriving an EMG feature vector through combination of features for higher recognition rate based on a stability index. Feature vector derived through linear discriminant analysis of the average combination of three time and frequency domain features with the highest stability index resulted into a recognition of 98%. The recognition was using Levenberg-Marquardt (L-M) algorithm based back propagation neural network. The experimental result shows that the stability index holds promise in deriving a feature vector for higher recognition rate of finger movements. [ABSTRACT FROM AUTHOR]

We compared the regional synoptic patterns and local meteorological conditions during persistent and non-persistent pollution events in Beijing using US NCEP-Department of Energy reanalysis outputs and observations from meteorological stations. The analysis focused on the impacts of high-frequency (period < 90 days) variations in meteorological conditions on persistent pollution events (those lasting for at least 3 days). Persistent pollution events tended to occur in association with slow-moving weather systems producing stagnant weather conditions, whereas rapidly moving weather systems caused a dramatic change in the local weather conditions so that the pollution event was short-lived. Although Beijing was under the influence of anomalous southerly winds in all four seasons during pollution events, notable differences were identified in the regional patterns of sea-level pressure and local anomalies in relative humidity among persistent pollution events in different seasons. A region of lower pressure was present to the north of Beijing in spring, fall, and winter, whereas regions of lower and higher pressures were observed northwest and southeast of Beijing, respectively, in summer. The relative humidity near Beijing was higher in fall and winter, but lower in spring and summer. These differences may explain the seasonal dependence of the relationship between air pollution and the local meteorological variables. Our analysis showed that the temperature inversion in the lower troposphere played an important part in the occurrence of air pollution under stagnant weather conditions. Some results from this study are based on a limited number of events and thus require validation using more data. [ABSTRACT FROM AUTHOR]