Positive Gradient Research Articles

Plasma potential shaping using end-electrodes in the Large Plasma Device

We perform experiments in the Large Plasma Device at the University of California, Los Angeles, studying how different end-electrode biasing schemes modify the radial potential profile in the machine. We impose biasing profiles of different polarities and gradient signs on a set of five concentric electrodes placed 12 m downstream from the plasma source. We find that imposing concave-down profiles (negative potential radial gradient) on the electrodes creates radial potential profiles halfway up the plasma column that are comparable to those imposed on the electrodes and a few electron temperature in height, regardless of the biasing polarity. On the other hand, imposing concave-up profiles (positive potential radial gradient) leads to non-monotonic radial potential profiles. This observation can be explained by the current drawn through the electrodes and the parallel plasma resistivity, highlighting their important role in controlling the rotation of plasma. Concave-down plasma potential profiles, obtained by drawing electrons on the axis, are predicted to drive azimuthal drift velocities that can approach significant fractions of the ion sound speed in the central region of the plasma column.

Numerical simulation and mechanistic model study of gas pocket distribution characteristics in a centrifugal impeller

The formation and extension of the gas pocket in the impeller can lead to the rapid deterioration or even failure of the centrifugal pump's two-phase pressurization. It is difficult to directly measure the characteristic parameters of the gas pocket in the high-speed rotating impeller, such as the void fraction, by experimental methods. In this paper, the two-phase performance of the centrifugal pump is studied by numerical simulation and validated by the experiment. The positive pressure gradient at the end of the blade pressure surface is the main reason why the centrifugal pump can boost at high inlet gas volume fraction (IGVF). As the IGVF increases, both the length and thickness of the gas pocket gradually increase. The head coefficient of the pump has an approximately quadratic relationship with the void fraction in the impeller. The mechanism model of the gas pocket flow is established by the force analysis of the gas pocket and its downstream single bubble in the impeller channel. The model can effectively predict the extension position of the gas pocket and the void fraction in the centrifugal impeller and is validated by numerical simulation.

Investigation of surfactant-laden bubble migration dynamics in self-rewetting fluids using lattice Boltzmann method

Self-rewetting fluids (SRFs), such as aqueous solutions of long-chain alcohols, show anomalous nonlinear (quadratic) variations of surface tension with temperature involving a positive gradient in certain ranges, leading to different thermocapillary convection compared to normal fluids (NFs). They have recently been used for enhancing thermal transport, especially in microfluidics and microgravity applications. Moreover, surface-active materials or surfactants can significantly alter interfacial dynamics by their adsorption on fluid interfaces. The coupled effects of temperature- and surfactant-induced Marangoni stresses, which arise due to surface tension gradients, on migration bubbles in SRFs remain unexplored. We use a robust lattice Boltzmann method based on central moments to simulate the two-fluid motions, capture interfaces, and compute the transport of energy and surfactant concentration fields, and systematically study the surfactant-laden bubble dynamics in SRFs. When compared to motion of bubbles in NFs, in which they continuously migrate without a stationary behavior, our results show that they exhibit dramatically different characteristics in SRFs in many different ways. Not only is the bubble motion directed toward the minimum temperature location in SRFs, but, more importantly, the bubble attains an equilibrium position. In the absence of surfactants, such an equilibrium position arises at the minimum reference temperature occurring at the center of the domain. The addition of surfactants moves the equilibrium location further upstream, which is controlled by the magnitude of the Gibbs elasticity parameter that determines the magnitude of the surface tension variation with surfactant concentration. The parabolic dependence of surface tension in SRF is parameterized by a quadratic sensitivity coefficient, which modulates this behavior. The lower this quantity, the greater is the role of surfactants modifying the equilibrium position of the bubble in SRF. Furthermore, the streamwise gradient in the surfactant concentration field influences the transient characteristics in approaching the terminal state of the bubble. These findings provide new means to potentially manipulate the bubble dynamics, and especially to tune its equilibrium states, in microchannels and other applications by exploiting the interplay between surfactants and SRFs.

Individual and cumulative effects of socioeconomic factors on hypertension in low- and middle-income countries: a cross-sectional study of 1,071,070 individuals from 26 nationally representative surve

Abstract Background/Introduction Addressing current gaps in hypertension care in low- and middle-income countries (LMICs) requires better understanding of socioeconomic disparities. Variation of the effects of socioeconomic status on hypertension across geographic regions and the shape of the relationship with individual markers of socioeconomic status remains unclear. Purpose This cross-sectional study aims to determine the effect of individual and cumulative effect of socioeconomic disadvantages (poor household wealth, low or no education, and rurality) on hypertension burden across geographic regions. Methods We pooled nationally representative individual level population-based data from Demographic and Health Surveys (DHS) in 26 LMICs. We included surveys conducted after 2002, with at least 50% response rate, and those with information on BP measurement and hypertension status. We included adults aged 15 years and above with hypertension (systolic BP ≥140 mm Hg, diastolic BP ≥90 mm Hg) or those who reported using BP-lowering medication. We excluded individuals with missing information on age, sex, education, hypertension information, rurality, and socioeconomic status. We examined the relationship of hypertension prevalence by education, household wealth, and rurality using regression analyses. Binary categories of household wealth, education, and rurality were summed to create composite socioeconomic disadvantages score (range: 0–3) as a measure of multiple disadvantages. Results We included 1,071,070 participants in the analysis, and majority (81%) belonged to Southeast Asia region. Positive gradients were found by household wealth, educational attainment and rurality. The odds of developing hypertension increased by per quintile increase in household wealth in Southeast Asia (aOR for poorest vs richest, 1·51; 95% CI: 1·47-1·55, P-trend <0.001) contrarily to decreasing prevalence by increasing wealth in Central Asia (aOR 0·67; 95% CI: 0·57-0·79, P-trend <0.001) and Europe (aOR 0·69; 95% CI:0·63-0·76, P-trend <0.001) (P-interaction <0·001). Having multiple socioeconomic disadvantages was associated with lower odds of hypertension in Southeast Asia (aOR for none vs three disadvantages, 0·75; 95% CI, 0·74-0·77) and Africa (aOR 0·47; 95% CI: 0·45-0·50), and higher odds in Europe (aOR 1·41; 95% CI: 1·31-1·51), and Central America (aOR 1·37; 95% CI: 1·20-1·57) (P-interaction <0·001). Household wealth and socio-economic disadvantages can be attributed to 19·4% and 36·9% of hypertension burden respectively. Conclusion This is one of the few studies examining the effect of individual as well as cumulative effect of socioeconomic status markers in hypertension. The shape of the socioeconomic gradient in hypertension varies across regions depending on demographic and epidemiological profile. This calls for context-specific interventions focusing on the most-at-risk population, redressing socioeconomic disparities in hypertension burden.Association between Hypertension and SES

A matter of measurement? Segregation and all-cause mortality in Sweden’s three metropolitan regions

Abstract Background Residential segregation can be operationalized and measured in many ways, along distinct dimensions. There are multiple mechanisms through which segregation and health mutually affect each other. Consequently, contextual health effects of segregation may vary depending on how segregation is measured. Methods We used longitudinal Swedish register data to compare associations between local measures of residential segregation (migrant density, migrant isolation, and the mutual information index) and all-cause mortality among the adult migrant and native-born populations in Sweden’s three largest metropolitan regions between 2004-2016. Results Among migrants, modest positive mortality gradients were observed across measures of migrant density and isolation, where a higher level of segregation was associated with higher risks of all-cause mortality (Q5 RR ranged from 1.08-1.20 across cities and measures). However, these effects were largely attenuated by individual-level socioeconomic factors, and reversed when further controlling for neighborhood economic deprivation (Q5 RR ranged from 0.74-0.87). Among the native-born, a positive gradient for mortality was found (Q5 RR ranged from 1.31-1.45), although this was reduced when accounting for neighborhood deprivation (Q5 RR ranged from 1.01 -1.11). For both migrants and the native-born, the mutual information index showed no clear association with mortality, although a mortality advantage is observed for migrants in the most segregated areas after individual and neighborhood level adjustments (Q5 RR ranged from 0.73-0.86). Conclusions Our findings show that the manner in which residential segregation is conceptualized and operationalized alters associations with health. However, individual and other contextual level confounders are important determinants which influences the patterns. Much of the negative health effects of residential segregation can be perceived through the lack of economic opportunities. Key messages • Associations between segregation and all-cause mortality depends on how segregation is conceptualized and measured. • The mortality disadvantage observed in local areas with high migrant density may be attributed to the lack of economic opportunities in the neighborhood.

Early coronary artery atherosclerosis in humans is associated with attenuated coronary retention of klotho

Abstract Background Vascular aging is a key feature of cardiovascular disease. α-klotho (klotho) is a protein inversely associated with aging and may contribute to vascular repair. Lower levels of systemic klotho have been identified in humans with features of early and advanced coronary atherosclerosis. It remains unknown if circulating klotho is present within human coronary circulation and whether cardiovascular klotho retention correlates with atherosclerosis. Purpose The current study aimed to assess the presence of klotho within coronary circulation compared to systemic circulation and hypothesized that net coronary klotho retention is attenuated in patients with early age-related features of coronary artery disease (CAD). Methods A total of 42 patients that underwent clinically indicated coronary angiogram for chest pain that had no obstructive CAD underwent intravascular ultrasound (IVUS) assessment were retrospectively examined. Virtual histology assessed coronary plaque characteristics. Blood samples simultaneously collected from the proximal aorta and coronary sinus were used for klotho detection using enzyme-linked immunosorbent assay. The net gradient of klotho across cardiovascular circulation was calculated by multiplying the arteriovenous klotho gradient by basal coronary blood flow. A net positive gradient indicated less cardiovascular klotho retention; a net negative gradient indicated greater cardiovascular klotho retention. Results Overall, participants were age 54±10 years old and 76% were female. There were overall higher levels of klotho within the coronary sinus (median 0.49 ng/mL [0.15; 1.69]) compared to systemic circulation (median 0.30 ng/mL [0.16; 1.14]). Participant groups were determined by those with positive (n = 20) or negative (n = 22) cardiovascular retention of klotho. Both groups were similar in age (56 ±2 vs. 51 ±2 years old, p = 0.080), gender (72% vs. 80% female, p = 0.580), and had similar occurrences of traditional cardiovascular comorbidities. Those with less cardiovascular klotho retention in the coronary vascular bed had significantly greater degree of non-obstructive coronary artery plaque (Gensini score 3.5 vs. 0, p < 0.001) and had higher percent plaque burden (46% [35; 53] vs. 34% [28; 46], p = 0.044) than those with greater cardiovascular klotho retention. Conclusions Patients with early coronary atherosclerosis may be characterized by attenuated retention of klotho within coronary circulation. Moreover, humans appear to have higher circulating klotho in coronary circulation than in systemic circulation. The current study may support a role for mechanism or potential therapeutic target for klotho in coronary atherosclerosis in humans.

Reliability analysis for running safety of vehicle on slab track via an improved second-order fourth-moment approach

The reliability assessment for running safety of vehicle on slab track under temperature action and seismic excitation is challenging due to the extensive computational efforts. This study proposes an improved second-order fourth-moment (ISOFM) approach for the reliability analysis for running safety of vehicle on slab track under temperature action and seismic excitation. The dimensionless limit state function (LSF) for running safety of vehicle on slab track is formulated considering four failure modes. The proposed ISOFM approach is verified by the Monte Carlo simulation (MCS) method. The proposed ISOFM approach greatly reduces the number of computations of nonlinear LSF. The merit of the proposed ISOFM approach lies in significantly enhancing the computation efficiency and precision of reliability considering nonlinear LSF with multi-failure modes. Additionally, the influences of temperature action and seismic excitation on the reliability for running safety of vehicle on slab track are discussed. The reliability for vehicle running safety decreases more significantly with the increment in overall temperature compared to the positive temperature gradient (PTG). The reliability for running safety of vehicle on slab track decreases nonlinearly with the increase of the earthquake intensity.

Influence of atmospheric state on variability of long-term residual ambient sound level measurements in a subalpine valley.

Two natural influences on the acoustic environments of mountainous parks and communities are flowing water and shifting weather. A central purpose of the acoustic measurement design used by the United States National Park Service is to provide spectral estimates of residual ambient sound level metrics at a seasonal time scale. Acoustic monitoring sampling methodologies are often designed using a sequence of similar measurements. When source and residual ambient spectra overlap, an estimate of variability in the latter is beneficial to successful monitoring design. The observed and modelled effects of atmospheric state on sound level are analyzed to reveal variability due to these effects at a long-term monitoring site in Denali National Park, Alaska. The analysis of variability incorporates a covariate that is otherwise challenging to estimate in remote settings: vertical temperature gradients in the atmospheric boundary layer. Results reveal inversions (positive gradients) in the atmosphere ≥30% between 19:00 and 09:00. Inversion strengths above 0.06 °C/m are associated with 10-15 dB increases in sound level over hourly time scales. Because inversions tend to occur during otherwise quiescent times of day, they ultimately reduce seasonal variability at the site and corresponding uncertainty in noise metrics for transportation noise arriving from varied directions.

Direct measurements of sediment geoacoustic properties in the New England Mud Patch and shelf breaka).

This paper reports on an original set of direct sound speed measurements collected with the acoustic coring system in the New England Mud Patch (NEMP) and shelf break area to the south. Cores collected within the NEMP show range-dependence of the mud with slower sound speed and lower attenuation on the west side. In the shelf break region, the highest sound speeds are observed between the 200- and 350-m isobaths. The depth-dependence of the mud layer in the NEMP includes a surficial layer with a negative sound speed gradient of 28 s-1. The remainder of the mud column has a weak positive sound speed gradient of 6.2 s-1 over an isovelocity layer. Comparison between in situ and ex situ sound speed measurements provides an assessment of the effects of sediment disturbance from gravity coring operations. Small differences in the upper 2.5 m were attributed to the changes in the geoacoustic properties caused by disturbance from the coring process. Below 2.5 m, the average difference is close to zero, suggesting that these sediments were minimally disturbed. Finally, an in situ measurement of shear speed was obtained near the depth of maximum penetration. The shear speed was well correlated with sound speed from approximately the same depth interval.

Characterizing and predicting the partial slip subjected to variable gradients of velocity and pressure in eccentric micro-scale Taylor–Couette flows

In the context of eccentric micro-scale Taylor–Couette flow, variations in localized flow scales result in a non-uniform fluid–solid interface slip state, distinct from the typically studied uniform slip velocity distribution. This study introduces a boundary condition definition method aimed at characterizing partial slip states, complemented by a coupled iterative analysis system tailored to address this complexity. Key contributions include the development of a method for calculating the limiting shear stress, which considers local velocity gradients and pressures. Validation demonstrates that the locally derived slip state aligns more closely with Knudsen number distributions of local flow scales compared to traditional uniform slip models, and exhibits greater consistency with experimentally measured pressure distributions. Additionally, the study reveals that eccentric Taylor–Couette flow, characterized by significant variations in local flow scales and strong self-induced pressure effects, leads to complex distributions of local pressure, velocity gradients, and differences in local slip velocities. Specifically, the non-uniform distribution of local pressure gradients due to eccentricity results in partial slip occurring predominantly on the rotor in regions with positive pressure gradients, and on the stator in regions with negative pressure gradients. Furthermore, the variation in gap height exerts a greater influence on local slip compared to rotational speed and eccentricity ratio. Under certain conditions influenced by pressure gradients, the slip velocity on the rotor may exceed its tangential speed.

A multiscale approach for network intrusion detection based on variance–covariance subspace distance and EQL v2

As an important network defense approach, network intrusion detection is mainly used to identify anomaly traffic behavior. However, dominant network intrusion detection approaches are now struggling to identify the complex and variable means of attack, leading to high false alarm rate. Additionally, the feature redundancy and class imbalance problem in the intrusion detection dataset also constrain the performance of detection methods. This paper proposes a multiscale intrusion detection approach based on variance–covariance subspace distance and Equalization Loss v2 (EQL v2). Firstly, the variance–covariance subspace distance is used for feature selection on the preprocessed dataset to determine a set of representative feature subsets that can effectively approximate the original feature space. Secondly, the loss function, EQL v2, is adopted to balance the positive and negative gradients, addressing the class imbalance problem. Finally, a pyramid depthwise separable convolution model is proposed to capture the multiscale information of the traffic, and the convolutional layer in the depthwise convolution is replaced with self-supervised predictive convolutional attention block to compensate for the performance loss caused by the parameter reduction. Extensive experiments demonstrated that the proposed approach exhibits better performance on the three datasets of NSL-KDD, UNSW_NB15, and CIC-IDS-2017, with accuracy rates of 99.19%, 97.81%, and 99.83%, respectively, effectively improve the intrusion detection performance.

Performance investigation of a thermoelectric generator for vehicle exhaust recovery using graded pore density foam metal

Improving the efficiency of thermoelectric generators (TEGs) used to harness residual heat from automobile exhausts is crucial for their widespread adoption. To enhance fluid heat transfer, the Kelvin tetrahedron model is employed for metal foam, and a multiphysical field model of the thermoelectric generator based on metal foam is established. The effects of inserting metal foam with uniform and gradient pore densities into the heat exchanger on the performance of the TEG are investigated. Experimental verification is conducted by constructing a test bench with dimensions identical to those of the model The findings suggest that inserting foam metal significantly enhances the output performance of the TEG, resulting in increases in both output power and efficiency as pore density rises. At Ta = 573 K and ma = 30 g/s, the output power of the TEG with inserted 20 PPI foam metal is enhanced by 140.46 %, while the efficiency experiences a remarkable increase of 197.50 % compared to a smooth pipe. Compared to the performance metrics of uniform foam metal, the positive gradient foam metal exhibits a maximum power increase of 7.89 % and a maximum efficiency increase of 34.46 %, along with an average pressure drop reduction of 27.29 %.

Variable air blast fireball of HMX/Al with tailored gradient structures

Air blast fireball of the composite explosive is an important way to destroy the target and effectively determines the damage effect. Herein, based on the effect of aluminum powder content on the explosion reaction kinetics of HMX-based aluminized explosives, the cylindrical charges with positive gradient structure (PGS) and negative gradient structure (NGS) were designed and prepared to control the structure and size of air blast fireball. The PGS cylinders exhibited lateral shuttle-shaped flame/fireball and the width of the fireball was 3.901 m, which was increased by about 14% compared with homogeneous cylinders. The NGS cylinders led to the vertical shuttle-shaped flame/fireball that the height of the air blast fireball reached 4.049 m, and had longer durations of the fireball. The numerical fitting results show that the lateral shuttle-shaped flame/fireball and vertical shuttle-shaped flame/fireball gradually changed into spherical-like flame/fireball with an increase from 0 to 30 wt% of outer and inner layer HMX content, respectively. The vertical shuttle flame/fireball gradually changed into a spherical-like flame/fireball with the increase of HMX content. This is a feasible way to regulate the shape and size of the air blast fireball through gradient adjusting the distribution of HMX and Al, which could provide an effective strategy to improve the damage effect.

Distinct response of Asian summer monsoon circulation and precipitation to orbital forcing during six Heinrich events

Climatic fingerprint of Heinrich (H) events was characterized by widespread megadroughts over the Asian summer monsoon (ASM) region accompanied by systemic weakening of the ASM. However, recent studies of hydroclimate proxies suggest huge spatial discrepancies in precipitation over the ASM region during some H events, characterized by increased precipitation in the Yangtze River Valley contrasting with the prevalent megadroughts across the whole ASM region. The mechanism responsible for the spatial discrepancies in precipitation and the relationship between local precipitation and the ASM intensity remain elusive. In this study, we investigate the response of the ASM circulation and precipitation to orbital forcing during six H events based on simulations with a coupled atmosphere-ocean general circulation model. The results show that changes in insolation alone can induce spatial discrepancies in precipitation over the ASM region during the H events. During the H1, 3, 4, 5, 6 events, the amplification of the land-sea pressure contrast in response to a positive interhemispheric insolation gradient (30°N-30°S) during boreal summer intensifies moisture transport from the adjacent oceans to the ASM region. The ensuing moisture divergence, combined with anomalous downdrafts, results in decreased precipitation in the South Asian Summer Monsoon (SASM) region, but converse scenario for the East Asian Summer Monsoon (EASM) region. During the H2 event, the increased precipitation across the Yangtze River Valley sharply contrasts the widespread drought over the ASM region, attributing to an anticyclone anomaly over the subtropical Western North Pacific and a cyclone anomaly over Japan and Korea. Moisture budget analysis shows that the dynamic effect, especially the vertical term, rather than the thermodynamic effect, is the dominant control of precipitation changes over the ASM region. Our results also suggest that despite the synchronous variation in the strength of the EASM and SASM in response to orbital forcing, the EASM should not be regarded as an eastward and northward extension of the SASM. Furthermore, our model simulates a weak correlation between the monsoon intensity and precipitation in the SASM region in response to orbital forcing, calling for caution in employing precipitation to reconstruct SASM intensity on orbital time scale.

Overeducation and economic mobility

We assess the hypothesis that declining intergenerational economic mobility in Norway is attributable to a rising signaling value of education accompanied by more overeducation particularly among upper-class offspring. We identify five empirical facts that together point in this direction:• The educational earnings premium has risen, but only through the extensive (employment) margin.• The rising earnings premium is associated with completed degrees only. When educational attainment is measured as time actually invested, the premium has declined.• Both educational attainment and the labor market's skill-requirements (as predicted by the occupational distribution) have increased, but attainment has risen faster than requirements such that the incidence of overeducation has increased.• There is a steep positive social gradient in overeducation: Overeducation is more frequent and has risen faster among offspring in upper-class families.• There is a steep negative social gradient in non-employment: Non-employment is more frequent and has risen faster among offspring in lower-class families.

Aerial dispersal of Venturia inaequalis ascospores with under-canopy sprinkler irrigation for apple scab management

AbstractSprinkler irrigation systems can release ascospores of Venturia inaequalis, the cause of apple scab, from infected leaves on the ground under conditions unsuitable for infection, and thus reducing the primary inoculum. Under-canopy irrigation was carried out for two hours in the middle of the day over overwintered apple leaves heavily infected with scab, either in a wind-protected enclosure or in a wind-exposed orchard. Ascospores were captured with rotating-arm spore traps at heights ranging from 0.3 m to 3.0 m above the ground. Ascospores dispersed above the irrigated layer and were detected at all heights above the sprinklers. Wind played a critical role in spore transport, evident from the set-up where wind interference was minimised by a wind fence, resulting in higher airborne spore numbers across all measured heights compared with the orchard exposed to unrestricted wind conditions. Furthermore, vertical temperature gradients significantly correlated with spore distributions, particularly where negative gradients at heights between 0.3 m and 0.05 m and positive gradients at heights between 1.0 m and 0.3 m led to spore retention within the irrigated zone. The findings highlight that ascospores, dispersed above the irrigated layers, could settle on susceptible tissues. It thus becomes imperative to ensure a rain-free period of at least 24 h post-irrigation and, if a rainfall shortly occurs after irrigation, the application of curative fungicides becomes essential following unexpected rain. Reliable weather forecasts are therefore crucial in determining the effectiveness of under-canopy irrigation to reduce apple scab incidence.

Dynamic Response of Gradient Aluminum Foam Sandwich Tubes under External Explosive Loads.

In this paper, we numerically investigate the dynamic response and explosion resistance of gradient aluminum foam sandwich tubes subjected to external blast loads. Based on 3D-Voronoi technology, we construct density-graded aluminum foam cores to systematically explore the influence of core density distribution, density gradient, and average relative density on the protective performance of these structures. Our primary objective is to identify optimal design parameters that maximize explosion mitigation capabilities while balancing energy absorption and specific energy absorption capacities. The research results show that a positive gradient core configuration exhibits superior anti-explosion performance, significantly outperforming its uniform and negatively graded counterparts, particularly when the gradient value is substantial. For the positive gradient cores, an increase in the gradient value leads to a corresponding enhancement in explosion resistance. Conversely, in negatively graded cores, a higher gradient value diminishes the anti-explosion performance. Furthermore, while augmenting the relative density of the core layer does improve the overall explosion resistance of the sandwich tube, it comes at the cost of reduced energy absorption and specific energy absorption capabilities, highlighting the need for a delicate balance among these competing factors.

Temperature gradient estimation of long-span concrete box girders using average conditional exceedance rate function

An accurate assessment of temperature gradients in box girders is crucial for design and maintenance of long-span bridges. Although the current bridge specifications have provided temperature gradient patterns, these existing specifications are insufficient to accurately describe temperature gradients of bridges in service period. In this article, a novel methodology for determining an efficient positive temperature gradient pattern considering condition dependent and whole design service life is proposed. Firstly, statistical analysis and curve fitting are performed by using the long-term temperature data collected through structural health monitoring system, which indicates that temperature gradient patterns can be described as exponential functions. Secondly, the representative values of temperature difference have been estimated using average conditional exceedance rate (ACER) functions, which can use short-term data and consider conditional dependencies to predict long-term extreme values. Finally, the temperature gradient patterns of box girder of bridges in the whole service life have been estimated. Compared with the gradient patterns in current Chinese specification, the proposed temperature gradient pattern demonstrates better applicability in a long-span continuous concrete box-girder bridge. This result is expected to provide a research reference for accurately assessment of temperature gradients in box girders, which is crucial for design and maintenance of long-span bridges.

Energy-based criteria for identification of impact-induced interfacial damage of longitudinally connected slab ballastless track structure

Interfacial damage as a potential threat affects the stability of the longitudinally connected slab ballastless track structure (LCSBTS). In most related research, the interfacial damage of LCSBTS is identified in terms of stiffness degradation, which makes it difficult to explore the role of energy in the development of the interfacial damage. As an alternative, a set of energy-based criteria rooted in a bilinear cohesive zone model was proposed, together with a new damage indicator that evaluates the loss of interfacial fracture energy. The proposed criteria were utilized in the simulation of the interfacial damage of LCSBTS subjected to wheel impact. Results show that, the energy-based damage indicator describes the growth of the interfacial damage at a slower speed than the stiffness-based damage indicator, better coordinating with the variation of the interfacial fracture energy. Under wheel impact, interfacial damages are most likely to occur out of a peanut-shaped region surrounding the impact point where shear stress surpasses tension stress. However, by considering a coupling action of the positive temperature gradient, severe interfacial damages appear around the center of the track slab where tension stress surpasses shear stress and interfacial damages caused by shear stress are located near the longitudinal edges of the track slab.

Numerical study on the combined application of multiple phase change materials and gradient metal foam in thermal energy storage device

Latent heat thermal energy storage (LHTES) offers significant energy-saving benefits, but its application is limited due to the low thermal conductivity of phase change material (PCM). To address this issue, this article studied the combined application of metal foam structures with different porosity gradients and multiple PCMs with different melting points through numerical simulation to accelerate the melting of PCM and enhance system efficiency. The results showed that the application of multiple PCMs improved the heat transfer performance of the system, reducing the complete melting time by 9.18% compared to using a single PCM with uniform metal foam. Based on the multi-PCM storage system with an average porosity of 0.90, this article designed metal foam structures with one-dimensional and two-dimensional porosity gradients and explored their impacts. The results indicated that in the structure with a one-dimensional porosity gradient along the heat flow direction, the positive gradient decreased thermal resistance, further reducing the complete melting time by 6.18%, while the negative gradient increased it by 19.78%. However, the temperature non-uniformity was lowest with the negative gradient and highest with the positive gradient. The optimal two-dimensional porosity gradient multi-PCM storage model not only reduced thermal resistance but also effectively solved the issue of uneven melting, reducing the complete melting time by 17.96% and increasing the energy storage efficiency by 20.16% compared to the single PCM system with uniform porosity. Furthermore, the article conducted a dimensionless analysis of the optimal structure and different gradient structures, establishing formulas for the liquid fraction concerning modified Fourier number, modified Stefan number, and modified Rayleigh number.