Decay Function Research Articles

Bayesian estimation of multivariate panel probits with higher‐order network interdependence and an application to firms' global market participation in Guangdong

SummaryThis paper proposes a Bayesian estimation framework for panel data sets with binary dependent variables where a large number of cross‐sectional units are observed over a short period of time and cross‐sectional units are interdependent in more than a single network domain. The latter provides for a substantial degree of flexibility towards modeling the decay function in network neighborliness (e.g., by disentangling the importance of rings of neighbors) or towards allowing for several channels of interdependence whose relative importance is unknown ex ante. Besides the flexible parameterization of cross‐sectional dependence, the approach allows for simultaneity of the equations. These features should make the approach interesting for applications in a host of contexts involving structural and reduced‐form models of multivariate choice problems at micro‐, meso‐, and macro‐economic levels. The paper outlines the estimation approach, illustrates its suitability by simulation examples, and provides an application to study exporting and foreign ownership among potentially interdependent firms in the specialized and transport machinery sector in the province of Guangdong.

Locating offenders: Introducing the reverse spatial patterning approach

ObjectivesCurrent strategies for locating where offenders live either focus exclusively on individual suspects or generalize to entire neighborhoods. However, better estimates of where offenders are located may improve models of the ecological distribution of crime, and forecasts of the locations of future crime incidents. MethodsWe propose a novel reverse spatial patterning (RSP) strategy that estimates where offenders may live based on the spatial locations of crime events. We rely on a distance decay function – based on the consistent finding that offenders do not travel far to commit crime – and Hipp's (2016) general theory of spatial crime patterns, to work backwards from the locations of actual crime events to make predictions about where offenders may live in subsequent years. We then use these estimates in models predicting crime locations. We create two versions of the RSP: one which assumes everyone is equally likely to offend, and another that creates an estimate assuming disproportionate offending across persons. ResultsWe test the effectiveness of our proposed strategy for these two measures using offense and arrest data from St. Petersburg, FL, and assess how well they predict the location of offenders (proxied by arrestees) and future crime events. We find consistent evidence that our RSP strategy provides better predictions of the locations of where offenders are located and also future crime incidents across a variety of crime types compared to existing strategies. ConclusionThe RSP approach is useful for creating estimates of where offenders live, which allow for better predictions of the locations of future crime incidents. These better forecasts will allow for more efficient allocation of police resources and targeted crime suppression efforts.

Soil carbon stock assessment using depth and spatial models on afforested arable lands

The change from grasslands and natural shrubs to afforested arable land has a major impact on soil organic carbon (SOC) stocks. Grasslands are known to be SOC sinks as seen in the Chernozems of North America, Eurasia and South Africa. However, determining the SOC stocks of soils can be financially costly as each location must be sampled in depth increments. This study aimed to estimate the SOC stocks for the Mvoti catchment (30° 48′ E and 29° 18′ S) in Kwa-Zulu Natal, South Africa by developing depth functions on a limited number of soil samples and expanding these functions to known land-uses and soil types. The results showed that splines captured the short-term vertical distribution of SOC better than exponential decay functions, which has major implications on arable lands. Long-term forest plantations showed a positive correlation with SOC stocks (32.7 kg m−2), while annual crop cultivation (27.0 kg m−2) showed a negative correlation when compared to natural grasslands (28.8 kg m−2). The Cubist algorithm predicted the total SOC stock of the catchment area at between 12 248 and 17 624 Mg depending on the depth function used. Soils with yellow-brown subsoils tend to have higher SOC stocks and the lowest degree of uncertainty.

Rey-Osterrieth complex figure recall scores and motor skill learning in older adults: A non-linear mixed effect model-based analysis

Age-related declines in motor learning are well documented. Visuospatial memory has been proposed as a key factor explaining age-related declines in sensorimotor adaptation, but most studies have not used standardized visuospatial memory tests nor controlled for age-related visuospatial memory declines. The present study explores the relationship between visuospatial memory and motor learning in older adults while also controlling for age and utilizing a standardized visuospatial memory test. Forty-nine nondemented older adults repetitively practiced a functional upper-extremity motor task and were re-assessed one week later. Training data were modeled with mixed-effect exponential decay functions, with parameters representing amount of performance change, rate of improvement, and final performance. Age and visuospatial memory were included as possible covariates for the parameter measuring rate of improvement (τ). After controlling for age, higher visuospatial memory scores were associated with faster rates of skill acquisition and better short-term retention one week later. These associations with visuospatial memory were dependent, however, on the level of initial skill. These findings suggest that the extent of re-learning motor skills in geriatric physical rehabilitation may depend on intact visuospatial memory.

A location-or-routing problem with partial and decaying coverage

This paper studies a generalized location-or-routing problem by considering partial coverage of the users according to a distance-decaying coverage function. In this problem, there is a set of candidate locations where to open facilities, and a set of locations with given number of users that must be covered by the open facilities. Users may travel directly to an open facility if they are within the coverage range of it, or they may be transported to facilities by capacitated vehicles. A distance-decaying function for the facility coverage is considered and the vehicles are allowed to partially cover the users located at the same location. Two mixed integer programming models are presented that minimize the number of uncovered users subject to a restricted budget, and an adaptive large neighborhood search metaheuristic is developed as the solution methodology. Through several computational experiments, the efficiency of the proposed formulations and the solution algorithm are evaluated, and the ALNS algorithm is shown to perform well in terms of solution quality and computing time. Computational results indicate that considering the partial coverage of users reduces the number of uncovered ones as the vehicle capacity decreases, and this reduction is more significant under a distance-decaying facility coverage function. It is also observed that considering distance-decaying coverage increases both the number of uncovered users and the spent budget, especially with a continuous function such as an exponential decay function.

Use of a nonlinear model to estimate milk losses due to subclinical mastitis in Holstein-Zebu cows.

The objective of this observational study was to estimate milk loss from subclinical mastitis (SCM) using a nonlinear one-phase exponential decay function fitted to the relationship between the sum of the California mastitis test scores of productive quarters (x1, 0 to 16) and daily milk production per cow (y, kg/day). The function was y = (a - b)e-c1*x1 + b, where a is the predicted y when x is zero, b is the y when x1 tends to infinity, and c1 is a rate constant. The fitted function was y = (10.02 - 5.76)e-0.06137*x1 + 5.76, with an adjusted coefficient of determination (R2adj) of 0.0692, a standard deviation of the residual (Sy.x) equal to 13.49, and an Akaike's information criterion corrected (AICC) of 3902.8. To this function, we added the multiplicative factors test day (x2, 1 to 12), the number of productive quarters (x3, 2, 3 or 4), months of age of cow (x4, 25 to 209), and days in milk (x5, 2 to 196), to adjust the decay function for their effects. The fitted model was y = [(9.65 - 3.95)e-0.03415*x1 + 3.95] (x2-0.1081) (x30.1049) (x40.1589) (x5-0.1972) with R2 of 0.3166, Sy.x = 11.38, and AICC = 3821.9. We used the adjusted decay function parameters to compute a conversion factor (CF, 0 to 1) each x1 integer value from 0 to 16 to project its actual y to that of an SCM-free udder (x = 0). Then, the CF for a x1 of 0 equals to 9.65/9.65 = 1, and for a x1 of 8 equals 8.28, so its CF would be 8.29/9.65 = 0.8588. A cow with a 5.5kg/day milk production at an x1 score of 8 would have an SCM-free production of 5.5/0.8588 = 6.4kg/day, and its daily milk loss would be 6.4-5.5 = 0.9kg/day. The difference, multiplied by MX$ 5.50 (US$ 0.275), would result in an economic loss of 4.95 Mexican pesos per day. This procedure makes possible the timely on-site estimation of economic losses due to subclinical mastitis.

Analyzing Porpoising on High Downforce Race Cars: Causes and Possible Setup Adjustments to Avoid It

The so-called porpoising is a well-known problem similar to bouncing that is affecting the dynamic behavior of basically all the field of 2022 Formula 1 racing cars. It is due to the extreme sensitivity of aerodynamic loads to ride height variations along a lap. Mid-way through the season race engineers are still struggling to cope with this phenomenon and its consequences, with regard to either physiological stress experienced by the drivers or to overall vehicle performance and stability. The paper introduces two kinds of models based on real-world chassis and aerodynamic data, where the above-mentioned downforce sensitivity has been arbitrarily recreated through the application of a decay function to aero maps. The first one is a quasi-static model, usually adopted as a trackside tool for controlling ride heights and aero balance, while the second, a fully dynamic model, recreates the interaction between oscillating aerodynamic loads and suspension dynamics resulting in a visible porpoising phenomenon. Basic setup changes have been tested, including significant static ride height variations. The paper should be seen as a proposal of guidelines in the search of a trade-off between aerodynamic stability and overall performance, without pretention of quantitative accuracy due to the highly confidential topic, which makes numerical validation impossible.

TEMPERATURE-DEPENDENT DEGRADATION OF SOIL ORGANIC MATTER IN FARMLANDS AND PASTURES.

To determine the rates of soil organic matter degradation in farmlands and pastures and their temperature dependency, soil samples collected in Aomori, Japan, were sieved and incubated at different temperatures (10, 20 and 30°C) for 700d, with amounts of respired CO2 being measured during the incubation period. Results were analysed using a three-compartment model (active, intermediate and resistant compartment), and the decomposition rates of the two labile compartments were approximated using an exponential decay function. The Arrhenius equation was applied to the decay function rate constant to obtain rate constants at the examined temperatures. The estimated degradation rate constants of the most active compartment in pasture soil were more sensitive to temperature than the corresponding value in farmland. The seasonal changes in rate constants were consistent with each soil temperature. At both fields, it is estimated that the degradation of soil organic matter occurred from April to October.

Quantification of the anti-neoplastic polyacetylene falcarinol from carrots in human serum by LC-MS/MS

Falcarinol is a polyacetylene which is found in carrots and known to have anti-neoplastic properties in rodents. Research in the bioactivity of falcarinol in humans require methods for quantification of falcarinol in human serum. Here we report the development of an LC-MS/MS method and its use to measure serum falcarinol concentrations in humans following intake of a carrot product. Falcarinol was measured by LC-MS/MS using the m/z 268 to m/z 182 mass transition. Six calibrator levels (0.2–20 ng/mL) and 3 control levels (0.4, 2 and 8 ng/mL) were prepared by addition of falcarinol to human serum pools. Linearity of the developed method was good with a mean R2 of 0.9942. Within-day, between-day and total coefficients of variation were 6.9–13.1%, 4.1–5.0% and 8.1–14.0%, respectively. The limits of detection and quantitation were 0.1 and 0.2 ng/mL, respectively, matrix effects 84.2%, recovery 101.4–105.4% and carry-over −0.24–0.07%. Serum falcarinol concentrations were measured in 18 healthy volunteers prior to and at 9 time-points following intake of a carrot product. Falcarinol concentrations peaked at the 1-hour time-point after intake in 15 out of 18 volunteers and declined according to a single exponential decay function with an aggregate t½ of 1.5 h.In conclusion, an LC-MS/MS method for quantification of falcarinol in human serum with acceptable performance was developed and used to measure falcarinol concentrations following intake of a carrot product.

Optically end-pumped scheme in rubidium vapor: Theory and experiment

The optimal detuning of the pump light at the rubidium D2 line is calculated and experimentally validated. A three-level optically end-pumped model in a hot rubidium vapor cell is demonstrated, which takes into account the hyperfine structure of the ground state, various collisional processes, and the nonlinear absorption of the pump light along the cell length. By developing a constrained optimization model, we calculate the optimal detuning of the pump light that maximizes the average excited state atom concentration in the cell. Experimentally, a 1529 nm probe light at higher levels, which is attenuated to the weak-probe limit, is introduced to accurately characterize the excited state atom concentration. Coupling with the experimental results, the variation of the pump light optimal detuning with the temperature and the pump light intensity at the unsaturated pumping is analyzed. At the optimal detuning point, the theoretical decay function of the pump light percentage along the vapor cell length almost coincides regardless of the temperature and the pump light intensity changes. Moreover, the theoretical fitted pump light decay function at optimal detuning is predicted. The fitted pump light percentage exiting the vapor cell is 4.75%. A fast implementation method to achieve the maximal average excited state atom concentration in the experiment is demonstrated.

Stabilization of Memristor-Based Chua’s Circuits via Dynamic Event-Triggered Mechanism

This brief is concerned with the event-triggered stabilization for a memristor-based Chua’s circuits. A dynamic-periodic event-triggered approach is proposed, whose distinguishing feature is the introduction of two periodic triggering thresholds. One of the thresholds is an exponential decay function, and the other is an internal dynamic variable. Both thresholds contribute to the reduction of events. By Lyapunov theory, a concise criterion is developed for the stabilization of memristor-based Chua’s circuits. Simulation results are offered to support the theoretical results.

Expansion of non-native plant Flaveria bidentis (L.) Kuntze driven by a range of factors leading to patchy distribution patterns.

Given the growing concern over the ecological impacts of non‐native species, exploring these species' expansion edge and distribution patterns and their driving factors is important for developing suitable management measures. Flaveria bidentis (L.) Kuntze, a non‐native plant that was introduced to China in the 1990s, has spread from southern Hebei Province, where it first took root, to the surrounding regions and has become one of the most notorious invasive weeds in northern China. Based on 15 years (2006–2021) of extensive field investigations, the spatial distribution of sampling and occurrence points were mapped in the recently expanded region of F. bidentis' population. Then, nearest neighbor analysis is used to characterize the spatial pattern differences between samplings and occurrences. An exponential decay function was used to elucidate the driving factors contributing to the presence and absence of F. bidentis. Our results demonstrated an effective random sampling setup, a heterogeneous spatial distribution of F. bidentis, and a multi‐regional independent aggregation distribution pattern (p < .01). There were significant spatial correlations between the aggregation areas of plant occurrence points and the locations of roads and construction sand distribution centers. These findings suggest that human activities involving major roads and construction sand distribution centers were driving factors contributing to this long‐distance dispersal and spatially discontinuous distribution patterns. The presence of these patchy distribution patterns has important implications for ongoing efforts to manage populations of non‐native species.

Development of 3D top coal caving angle model for fully mechanized extra-thick coal seam mining

During high-intensity, fully mechanized mining of extra-thick coal seam, the top coal would cave to a certain 3D form. Based on the data collected during drilling, a 3D model of top coal caving surface space was established to determine the relationship between the location of the stope roof and the caving surface, enabling the mathematical computation of the top caving angle (φ). The drilling method was employed to measure the top caving angle on two extra-thick fully mechanized coal caving faces under the conditions of three geological structures, namely, no geological structure, igneous rock structure, and fault structure. The results show that the value of top caving angle could be accurately estimated on-site with the 9-parameter 3D top coal caving surface model built with the drilling method. This method is a novel on-site measurement that can be easily applied. Our findings reveal that the characteristics of the coal-rock in the two mining faces are different; yet their caving angles follow the rule φigneous rock structure < φno geological structure < φfault structure. Finally, through the data fitting with two indexes (the top coal uniaxial compressive strength and the top caving angle), it is found that the relationship between the two indexes satisfies an exponential decay function.

A new method to replicate high-porosity weak rocks subjected to cyclic freezing-thawing: Sand 3D printing and digital image correlation explorations

Three-dimensional (3D) printing is an emerging technology capable of producing exact replica specimens in rock mechanics. In this work, the sand 3D printing was explored to model the influence of cyclic freezing and thawing (F-T) for high-porosity weak rocks, which is one of the serious threats to rock stability in a cold region. The evolution of pore structure in the printed specimen during the F-T cycles was interpreted by the nuclear magnetic resonance (NMR) relaxation analysis. A series of Brazilian splitting tests combined with the digital image correlation (DIC) were conducted on these specimens experiencing different F-T cycles. The structural and mechanical degradation of the prepared specimens is reproduced, with a 44.30% increase in porosity and a 39.39% reduction in tensile strength at the end of 10 F-T cycles. Printed specimens deform in a less brittle manner in response to the F-T treatment. The accelerating rate of strain dispersion change was proposed to identify the precursor characteristics during the loading process. The F-T treatment induces the occurrence of precursor earlier than the peak stress, with the precursor stress ratios for the F-T untreated and treated specimens in the ranges of 99.62%–99.75%, and 97.15%–97.93%, respectively. Finally, the mechanical property degradation of fractured rock specimens after the F-T cycles is revealed, and a strong correlation between the mechanical property and the number of F-T cycles that display an exponential decay function is found. The sand 3D-printed specimens are shown to exhibit the changes in the pore structure, mechanical properties, failure pattern, strain distribution, and deformation evolution which resemble high-porosity weak rocks subjected to cyclic F-T.

An analytical analysis for the mechanical performance of fully-grouted rockbolts based on the exponential softening model

This paper presented a novel bond-slip model to better reveal the mechanical behavior of the bolt-grout interface for fully-grouted rockbolts under tensile loads by considering the non-linear response in the softening stage. The exponential decay function is adopted for describing the non-linear response in the softening stage. Based on the improved bond-slip model, the corresponding analytical solutions for the interfacial shear stress and the axial force of the bolt under different loading stages are solved. Then, the validity of this proposed model was verified by comparing with the experimental results. The results show that compared with the linear softening model, the proposed model is more suitable for predicting the mechanical performance of fully-grouted rockbolts. Finally, a series of parametric studies are conducted to explore the effect of model parameters on the mechanical properties of fully-grouted rockbolts. The results indicate that compared with the anchor length, the bolt diameter and the bond strength of the bolt-grout interface have a significance influence on the ultimate load of bolt, especially for the elastic and softening stage. Moreover, it can be found that using the linear softening model maybe overestimates the supporting performance of grouted bolt, resulting in an unsafe design for bolt.

A Hybrid Approach to Trust Node Assessment and Management for VANETs Cooperative Data Communication: Historical Interaction Perspective

Vehicular ad hoc networks (VANETs) provide self-organized wireless multihop transmission, where nodes cooperate with each other to support data communication. However, malicious nodes may intercept or discard data packets, which might interfere with the transmission process and cause privacy leakage. We consider historical interaction data of nodes as an important factor of trust. Thus, this paper focuses on the trust node management of VANETs, which aims to quantify node credibility as an assessment method and avoid assigning malicious nodes. First, the integrated trust of each node is proposed, which consists of the direct trust and the recommended trust. The former is dynamically computed by historical interaction records and Bayesian inference considering penalty factors. The latter defines trust by third-party nodes and their reputation. Second, the process of trust calculation and data communication calls for timeliness. Therefore, we introduce a time sliding window and time decay function to ensure that the latest interaction information has a higher weight. We can sensitively identify malicious nodes and make quick responses. Finally, the experimental results demonstrate that our proposed method outperforms bassline methods, especially with respect to the packet delivery ratio and security.

On the Cellular Uptake and Exocytosis of Carbon Dots─Significant Cell Type Dependence and Effects of Cell Division.

Understanding the cellular uptake and exocytosis processes of nanoparticles (NPs) is essential for developing the nanomedicines and assessing the health risk of nanomaterials. Considerable efforts have been made to reveal how physicochemical properties of NPs influence these processes. However, little attention has been paid to how cell type impacts these processes, especially exocytosis. Herein, the uptake and exocytosis of the carbon dots (CDs) obtained from the carbonization of citric acid with polyethylenimine (PEI) oligomers (CDs-PEI) in five human cell lines (HeLa, A549, BEAS-2B, A431, and MDA-MB-468) are analyzed to understand how cell type influences the fate of CDs in cells. The cell division is taken into account by the correction of cell number for accurate quantification of the uptake and exocytosis of CDs-PEI. The results indicate that the cell type significantly affects the cellular uptake, trafficking, and exocytosis of CDs-PEI. Among the cell types investigated, MDA-MB-468 cells have the greatest capacity for both uptake and exocytosis, and HeLa cells have the least capacity. The kinetics of the exocytosis largely follows a single exponential decay function, with the remaining CDs-PEI in cells reaching plateaus within 24 h. The kinetic parameters are cell-dependent but insensitive to the initial intracellular CDs-PEI content. Generally, the Golgi apparatus pathways are more important in exocytosis than the lysosomal pathway, and the locations of CDs-PEI in the beginning of exocytosis are not correlated with their exocytosis pathways. The findings on the cell type-dependent cellular uptake and exocytosis reported here may be valuable to the future design of high-performance and safe CDs and related nanomaterials in general.

An Investigation of Computation Time Based on Domain Size in WRF Model

Estimating WRF model computation time is necessary because of the need for domain expansion for weather prediction. However, the optimum computation time is not simply gained by enlarging the domain and adding processor numbers. Thus, an investigation was carried out to determine the correlation between computation time on domain size, number of grids, and number of processors used to run the WRF model. This study uses a collection of computation time as the data input from running the WRF model with two domain group ratios, 2: 1 and 1: 1, and various processors. Negative Exponential Function (NEF) and Power Function (PF) as exponential decay functions are evaluated to represent the curve formed from the computation time against the number of processors in one domain case. This study also evaluates the speed up and efficiency of the use of processor numbers against the tested domains. NEF represents the decrease in computation time curve in a domain case better than PF since this function has a steeper slope, better initial value, and k constant that keeps the computation time falling below 0. The computation time can be optimally saved by adding approximately eight processors at the same domain ratio with four times larger grid size and the same amount of grid number. Investigations for other domain ratios need to be carried out to determine the characteristics of computation time on the number of processors, grid size, and domain size.

Accessibility measurements for urban parks considering age-grouped walkers’ sectorial travel behavior and built environment

A walking-accessible urban park system is essential to the physical and mental health of urban residents. However, it is difficult to accurately describe the walking behavior of elderly and young visitors using empirical models (i.e., empirical threshold distance and empirical decay function), because of the differences in walking ability and distance decay among visitors of different ages. To address this challenge, this study used survey data to extract the travel behavior of elderly and younger visitors from a survey of 3625 walking respondents using a sectional threshold distance in central Wuhan. A multiple linear regression model was then built to discover how the factors influence the sectional threshold distance for different age groups. The results show that the travel time threshold for elderly visitors was approximately 0.47–1 min shorter than for other visitors, and the difference became more obvious for the 85th percentile of visitors’ segment travel time. The correlation analysis and regression results suggest that the surrounding built environment, such as restaurants, mostly had to a positive impact on sectional threshold distances, while park facilities were negatively correlated with the threshold distance. This consequently led to different accessibility levels for visitors by age, and elderly people presented an accessibility 0.0012 person/ha lower than young visitors. These findings provide a more accurate and refined decision-making basis for urban planners and managers to optimize park layouts.

A layout optimization approach to urban park green spaces based on accessibility evaluation: a case study of the central area in Wuxi city

ABSTRACT Planning urban park green spaces equitably and effectively is a central concern for maintaining a sustainable city and enhancing the quality of life of urban dwellers. In this case study of Wuxi city, facilitated by multisource big data, a new approach for optimizing the urban park green space distribution was explored. The improved two-step floating catchment area method was employed in combination with the network analyst in ArcGIS, the real entrances of urban park green spaces as search centres, multiple radii, and the distance decay function. The districts with low accessibility to urban park green spaces were mapped accurately as the main zones for equity promotion. Then, the key plots for the layout optimization of urban park green spaces at different scales were identified based on the location-allocation model. The results indicated a significant spatial gradient pattern of the accessibility index and a lower degree of spatial fitting between the service capacity of urban park green spaces and user demands in the old town. Additionally, operable location selection strategies prioritizing the urban natural environment and integrating the urban inventory space for urban park green space layout to improve the accessibility level were tentatively proposed. Finally, for the factors influencing accessibility, the park’s size and conditions, transportation network, and the social attribute of urban residents were further discussed. This study could help city managers and planners conduct the layout optimization of urban park green spaces more effectively with the aim of promoting an environmentally equitable and sustainable life.