Dual-source Model Research Articles

1.79-Approximation Algorithms for Continuous Review Single-Sourcing Lost-Sales and Dual-Sourcing Inventory Models

Stochastic inventory systems with lead times are often challenging to optimize, including single-sourcing lost-sales and dual-sourcing systems. Recent numerical results suggest that capped policies demonstrate superior performance over existing heuristics. However, the superior performance lacks a theoretical foundation. In “1.79-Approximation Algorithms for Continuous Review Single-Sourcing Lost-Sales and Dual-Sourcing Inventory Models,” the author provides a theoretical foundation for this phenomenon in two classical inventory models. First, in a continuous review lost-sales model with lead times and Poisson demand, he proves that a capped base-stock policy has a worst-case performance guarantee of 1.79 by conducting an asymptotic analysis under a large penalty cost and lead time. Second, in a more complex continuous review dual-sourcing model with general lead times and Poisson demand, he proves that a similar capped dual-index policy has a worst-case performance guarantee of 1.79 under large lead time and ordering cost differences. The results provide a deeper understanding of the superior numerical performance of capped policies and present a new approach to proving worst-case performance guarantees of simple policies in hard inventory problems.

Volume Flexibility at Responsive Suppliers in Reshoring Decisions

We investigate how volume flexibility, defined by a sourcing cost premium beyond a base capacity, at a local responsive supplier impacts the decision to reshore supply. The buyer also has access to a remote supplier that is cheaper with no restrictions to volume flexibility. We show that with unit lead time difference between both suppliers, the optimal dual sourcing policy is a modified dual base-stock policy with three base-stock levels. Fast orders follow a modified base-stock policy with two base-stock levels: the inventory position is raised to the higher base-stock level by using the base capacity; no overtime is used if this order increases the inventory position above the lower base-stock level. Else, the base capacity and overtime are used to raise the inventory position up to the low base-stock level. After ordering from the fast supplier, an order to the slow supplier is placed to raise the inventory position to a third base-stock level. Surprisingly, in contrast to single sourcing with limited volume flexibility, a more complex dual sourcing model results in a “simpler policy that replaces demand in each period. The latter allows analytical insights into the sourcing split between the responsive and the remote supplier. Our analysis shows how increased volume flexibility at responsive suppliers promotes the decision to reshore operations and effectively serves as a (cost) benefit. It also shows how investing in base capacity or additional volume flexibility act as strategic substitutes.

Simulation of evapotranspiration and its components for the mobile dune using an improved dual-source model in semi-arid regions

Accurate estimation of evapotranspiration (ET) and its components is essential for a deep understanding of hydrological processes in semi-arid regions. In this study, an improved Shuttleworth-Wallace model (i.e., SWH model) was applied to simulate ET and its components over the growing season in four consecutive years, 2013 to 2016, for mobile dunes in China’s Horqin Sandy Land. The performance of the model was validated using the measurements of eddy covariance (EC) technology and micro-lysimeter; the modeled ET was in good agreement with the measured ET at both half-hourly and daily timescales, and the modeled soil evaporation (E) was consistent with the micro-lysimeter measurements. E accounted for the major fraction of ET in the mobile dune ecosystem, with E/ET being 0.62, 0.84, 0.82, and 0.61, for the 2013 to 2016 growing seasons, respectively. During the vigorous growing stage, the monthly E/ET was mainly controlled by the leaf area index (LAI) in wet years, while water became the limiting factor for E/ET in dry years. At a half-hourly timescale, E/ET was primarily controlled by canopy stomatal conductance and soil moisture content, but when soil moisture content was lower than the wilting point, E/ET depended solely on the soil moisture content. When soil moisture content was between the wilting point and the field capacity, E/ET was mainly controlled by soil moisture content in the early and late growing stages, but by canopy stomatal conductance in the vigorous growing stage. When soil moisture content exceeded the field capacity, E/ET was primarily controlled by canopy stomatal conductance.

Measuring and modeling evapotranspiration of a Populus euphratica forest in northwestern China

Vegetation is sparsely distributed in the arid regions of northwestern China, and accurately measuring and partitioning of evapotranspiration is of importance for ecosystems in such areas. In this study, we measured and analyzed diurnal and phenological variations in evapotranspiration using the eddy–covariance method based on the Penman–Monteith, Priestley–Taylor, Shuttleworth–Wallace models, a newly proposed improved dual source model and a clumped model in a forest reserve in the Ejin oasis of Populus euphratica in 2015 and 2016 growing seasons. A sensitivity analysis was performed for the models with higher accuracies and we examined the biotic and abiotic controls on evapotranspiration. The results show that the total amounts of evapotranspiration during the two growing seasons in 2015 and 2016 were 622 and 612 mm, respectively. Phenological variations in evapotranspiration produced single-peak curves, while diurnal variations reflected the influence of high temperatures on some afternoons. The Priestley–Taylor and the improved dual source models gave the most accurate evapotranspiration values at the daily scale and appeared to be most suitable for the estimation of evapotranspiration for the species in arid regions. In addition, both models were the most sensitive to net radiation (Rn).

Evaluation of the dual source model to simulate transpiration and evaporation of tomato plants cultivated in a solar greenhouse

Evaluation of the dual source model to simulate transpiration and evaporation of tomato plants cultivated in a solar greenhouse

基于改进的双源模型模拟荒漠河岸胡杨林蒸散发

基于改进的双源模型模拟荒漠河岸胡杨林蒸散发

Modeling scattered radiation from multi-leaf collimators (MLCs) to improve calculation accuracy of in-air output ratio

This study aims to model an extra-focal source for the scattered radiation from multi-leaf collimators (MLCs), namely an MLC scatter source, and to correct in-air output ratio (Sc) calculated using the conventional dual source model (DSM) to achieve better accuracy of point dose calculation. To develop the MLC scatter source, a 6 MV photon beam from a Varian Clinac® iX linear accelerator with millennium 120 MLCs was used. It was assumed that the position for the MLC scatter source was located at the center of the MLC, consisting of line-based and area-based sources to consider the characteristics of the scattered radiation from the MLCs empirically. Based on the measured Sc values for MLC-defined fields, optimal parameters for the line-based and area-based sources were calculated using optimization process. For evaluation of proposed method, measurements were taken for various MLC-defined square and irregular fields. The Sc values calculated using the proposed MLC scatter source and conventional DSM were compared with the measured data. For MLC-defined square fields, the measured Sc values showed better agreement with those calculated using the MLC scatter source (the mean difference was − 0.03%) compared with those calculated using the DSM (the mean difference was 0.18%). For MLC-defined irregular fields, the maximum dose differences between measurements and calculations using the MLC scatter source and DSM were 0.54% and 1.45%, respectively. The developed MLC scatter source could improve the accuracy of Sc calculation for both square and irregular fields defined by MLCs.

A Bayesian Analysis of SDSS J0914+0853, a Low-mass Dual AGN Candidate

Abstract We present the first results from Bayesian AnalYsis of Multiple AGN in X-rays (BAYMAX), a tool that uses a Bayesian framework to quantitatively evaluate whether a given Chandra observation is more likely a single or dual point source. Although the most robust method of determining the presence of dual active galactic nuclei (AGNs) is to use X-ray observations, only sources that are widely separated relative to the instrument's point-spread function are easy to identify. It becomes increasingly difficult to distinguish dual AGNs from single AGNs when the separation is on the order of Chandra's angular resolution (<1″). Using likelihood models for single and dual point sources, BAYMAX quantitatively evaluates the likelihood of an AGN for a given source. Specifically, we present results from BAYMAX analyzing the lowest-mass dual AGN candidate to date, SDSS J0914+0853, where archival Chandra data shows a possible secondary AGN ∼ 0.″3 from the primary. Analyzing a new 50 ks Chandra observation, results from BAYMAX shows that SDSS J0914+0853 is most likely a single AGN with a Bayes factor of 13.5 in favor of a single point source model. Further, posterior distributions from the dual point source model are consistent with emission from a single AGN. We find a very low probability of SDSS J0914+0853 being a dual AGN system with a flux ratio f > 0.3 and separation r > 0.″3. Overall, BAYMAX will be an important tool for correctly classifying candidate dual AGNs in the literature, as well as studying the dual AGN population where past spatial resolution limits have prevented systematic analyses.

Mental Models or Probabilistic Reasoning or Both

The present paper presents an overview of contemporary reasoning research to examine the evidence for and implications of the Dual Strategy Model of Reasoning. The Dual Strategy Model of Reasoning proposes that there are two types of reasoning strategy applied in deductive reasoning - counterexample and statistical. The paper considers Mental Models Theory and The Probability Heuristics Model as candidate specifications for these respective strategies and hypotheses are proposed on this basis. The Dual Strategy Model is further considered in the context of Dual Process theory, the Dual Source Model and Meta-reasoning and implications of the synergy between these proposals are considered. We finally consider the Dual Strategy Model in the context of individual differences, and normative considerations before proposing novel hypotheses and further avenues of research which we argue require exploration in this context.

Mapping regional turbulent heat fluxes via variational assimilation of land surface temperature data from polar orbiting satellites

Estimation of turbulent heat fluxes by assimilating sequences of land surface temperature (LST) measurements into variational data assimilation (VDA) frameworks has been the subject of several studies. The VDA approaches estimate turbulent heat fluxes by minimizing the difference between LST observations and estimations from the heat diffusion equation. The VDA methods have been tested only with high temporal resolution LST observations (e.g., from geostationary satellites) when applied at regional scales. Geostationary satellites can capture the diurnal cycle of LST, but they have a relatively low spatial resolution and mainly focus on low latitudes. To overcome these shortcomings, this study assimilates high spatial resolution LST data from polar orbiting satellites (e.g., Moderate Resolution Imaging Spectroradiometer, MODIS) into the combined-source (CS) and dual-source (DS) VDA schemes. An expression is developed to obtain an a priori evaporative fraction (EF) estimate from leaf area index (LAI) or apparent thermal inertia (ATI). The a priori EF estimate is used as an initial guess in the VDA approach. The results indicate that the VDA method is able to find the optimal value of EF by assimilating the low-temporal resolution MODIS LST data. The predicted turbulent heat fluxes from VDA are compared with the measurements from the large-aperture scintillometer at three sites (Arou, Daman, and Sidaoqiao) in the Heihe River Basin (located in northwest China). The findings indicate that the CS and DS VDA models perform well in various hydrological and vegetative conditions. The three-site-average root mean square errors (RMSEs) of sensible and latent heat fluxes estimates from the CS scheme are 37.44 W m−2 and 94.30 W m−2, respectively. The DS model reduces the abovementioned RMSEs by 19.82% and 21.37%, respectively. Overall, the results show that using the a priori EF estimate from the proposed expression in the VDA approach eliminates the need for the high resolution LST data from geostationary satellites, and allows the VDA method to estimate turbulent heat fluxes by assimilating LST data from polar orbiting satellites. Finally, several numerical tests are conducted to assess the effect of LST temporal sampling on the turbulent heat fluxes estimates. The results show that the LST measurement at 1400 Local Time (LT) has the most amount of information for partitioning the available energy into sensible and latent heat fluxes.

Evaluation of the SPARSE Dual-Source Model for Predicting Water Stress and Evapotranspiration from Thermal Infrared Data over Multiple Crops and Climates

Using surface temperature as a signature of the surface energy balance is a way to quantify the spatial distribution of evapotranspiration and water stress. In this work, we used the new dual-source model named Soil Plant Atmosphere and Remote Sensing Evapotranspiration (SPARSE) based on the Two Sources Energy Balance (TSEB) model rationale which solves the surface energy balance equations for the soil and the canopy. SPARSE can be used (i) to retrieve soil and vegetation stress levels from known surface temperature and (ii) to predict transpiration, soil evaporation, and surface temperature for given stress levels. The main innovative feature of SPARSE is that it allows to bound each retrieved individual flux component (evaporation and transpiration) by its corresponding potential level deduced from running the model in prescribed potential conditions, i.e., a maximum limit if the surface water availability is not limiting. The main objective of the paper is to assess the SPARSE model predictions of water stress and evapotranspiration components for its two proposed versions (the “patch” and “layer” resistances network) over 20 in situ data sets encompassing distinct vegetation and climate. Over a large range of leaf area index values and for contrasting vegetation stress levels, SPARSE showed good retrieval performances of evapotranspiration and sensible heat fluxes. For cereals, the layer version provided better latent heat flux estimates than the patch version while both models showed similar performances for sparse crops and forest ecosystems. The bounded layer version of SPARSE provided the best estimates of latent heat flux over different sites and climates. Broad tendencies of observed and retrieved stress intensities were well reproduced with a reasonable difference obtained for most of the points located within a confidence interval of 0.2. The synchronous dynamics of observed and retrieved estimates underlined that the SPARSE retrieved water stress estimates from Thermal Infra-Red data were relevant tools for stress detection.

A horizontal capacity reservation game under asymmetric information

We investigate a common horizontal dual-sourcing model in the semiconductor industry. The supply chain consists of an integrated device manufacturer (IDM) and a pure-play foundry. The IDM can make internal production and source from the foundry, and only the IDM sells the products to the market. Both the IDM and the foundry must invest in production capacity before making production. We consider stochastic one-period demand, which can either be a high type or a low type. We assume that the true demand type is private information to the IDM such that the IDM and the foundry engage in a signalling game. We identify the unique separating equilibrium in this asymmetrical information setting. We find that information asymmetry may mitigate or aggravate the double marginalisation effect, and that it may also affect the capacity allocation between the IDM and the foundry. Furthermore, we conduct a numerical study to investigate the sensitivity of the equilibrium and the information rent.

Numerical simulation for pulsed laser–gas tungsten arc hybrid welding of magnesium alloy

Based on the extended application of COMSOL multiphysics, a novel dual heat source model for pulsed laser–gas tungsten arc (GTA) hybrid welding was established. This model successfully solved the problem of simulation inaccuracy caused by energy superposition effect between laser and arc due to their different physical characteristics. Numerical simulation for pulsed laser–GTA hybrid welding of magnesium alloy process was conducted, and the simulation indicated good agreements with the measured thermal cycle curve and the shape of weld beads. Effects of pulse laser parameters (laser-excited current, pulse duration, and pulse frequency) on the temperature field and weld pool morphology were investigated. The experimental and simulation results suggest that when the laser pulse energy keeps constant, welding efficiency of the hybrid heat source is increased by increasing laser current or decreasing pulse duration due to the increased ratio of the weld bead depth to width. With large laser currents, severe spatters tend to occur. For optimized welding process, the laser current should be controlled in the range of 150–175 A, the pulse duration should be longer than 1 ms, and the pulse frequency should be equal to or slightly greater than 20 Hz.

A Continuous Review Inventory System with Lost Sales and Emergency Orders

We analyze a continuous review lost sales inventory system with two types of orders—regular and emergency. The regular order has a stochastic lead time and is placed with the cheapest acceptable supplier. The emergency order has a deterministic lead time is placed with a local supplier who has a higher price. The emergency order is not always filled since the supplier may not have the ability to provide the order on an emergency basis at all times. This emergency order has a higher cost per item and has a known probability of being filled. The total costs for this system are compared to a system without emergency placement of orders. This paper provides managers with a tool to assess when dual sourcing is cost optimal by comparing the single sourcing and dual sourcing models.

On the Performance of Tailored Base-Surge Policies: Theory and Application at Walmart.Com

Problem Definition: Many import items sold at Walmart.com have two suppliers: one is faster and has a random production capacity limit while the other is slower and has infinite capacity. The lead time difference of the two suppliers could be as large as 12 weeks. Walmart.com faces an important and challenging supply chain problem and must make routine inventory replenishment decisions. Academic/Practical Relevance: Dual-sourcing inventory models have been extensively studied in academia and dual-sourcing strategies have been widely implemented in practice. Recently, the so-called Tailored Base-Surge (TBS) policy has begun to receive more attention and demonstrated good performance in existing dual-sourcing models. TBS is intuitive and easy to manage: a constant-order is placed from the slow (regular) supplier every period and a base-stock policy is adapted from the fast (express) supplier. Methodology: This paper develops a new dual-sourcing inventory model incorporating large lead time difference as well as random capacity of the express supplier, and investigates the performance of TBS both theoretically and empirically by using Walmart’s data. Results: We prove that a TBS policy is asymptotically optimal as the regular lead time grows, extending the previous asymptotic optimality of TBS policies in the dual-sourcing system without random capacities. We complement the theory and compare TBS with three well-known heuristics in a “simulated” real-world setting through model calibration by using historical sales data from Walmart.com. Our results demonstrate that TBS outperforms others as for minimizing the long-run average inventory cost. In particular, the inventory cost would be reduced by at least 33% if adapting a TBS policy. Our results also suggest that at an aggregate level, TBS could reduce Weeks of Supply by 2.7 weeks while increasing Met Demand by 3.3% compared with the single-sourcing policy using only the import supplier. Managerial Implications: Our results show that if the proposed dual-sourcing model and algorithm are adapted, Walmart’s inventory system would be significantly improved especially for import items.

Diagnostic efficacy of fractional flow reserve with coronary angiography in dual-source computed tomography scanner

Objective: The management of patients with intermediate coronary lesions is a major clinical issue. Fractional flow reserve (FFR) is considered the gold criterion for the assessment of ischaemic stenosis, but it requires an invasive procedure. Coronary computed tomography angiography (CTA) for fractional flow reserve (FFRCT) is a novel noninvasive alternative for the diagnosis of ischaemic lesions. The aim was to determine the diagnostic efficacy of FFRCT for ischaemic coronary artery stenosis lesions of intermediate severity.Methods: A total of 129 patients underwent 64-row dual-source CTA and invasive coronary angiography (ICA). In all, 156 vessels were identified as intermediate-grade coronary artery stenosis by subsequent ICA, defined as a maximum diameter reduction of 50%–70%. The FFR was also measured during ICA. FFRCT was computed from the three-dimensional dual-source CTA model and coronary flow dynamics data.Results: Per-patient diagnostic sensitivity, specificity, positive predictive values, negative predictive values and accuracy of FFRCT amounted to 89.2%, 81.5%, 66.0%, 94.9% and 83.7%, respectively; and 86.9%, 73.6%, 58.0%, 93.1% and 77.6% on the per-vessel basis, respectively. FFRCT and FFR showed a good positive correlation. Bland–Altman analysis displayed good concordance between FFRCT and FFR. The receiver operating characteristic curve revealed that the area under the curve of FFRCT was 0.918 (95% confidence interval 0.849–0.986) on the per-patient analysis and 0.916 (95% confidence interval 0.863–0.969) on per-vessel analysis, respectively.Conclusions: FFRCT is featured by moderate accuracy in discriminating lesions of intermediate coronary artery stenosis that cause myocardial ischaemia.Impact statementHow to treat intermediate coronary stenosis represents a major clinical issue. FFRCT has recently emerged as a novel noninvasive method evaluating ischemic lesions. In this study, we defined such lesion as 50–70% diameter stenosis. We designed the study to assess the diagnostic efficacy of FFRCT both at per-vessel level and at per-vessel levels for ischemic lesions.

An assessment of alternative state space models for count time series

This paper compares two alternative models for autocorrelated count time series. The first model can be viewed as a ‘single source of error’ discrete state space model, in which a time-varying parameter is specified as a function of lagged counts, with no additional source of error introduced. The second model is the more conventional ‘dual source of error’ discrete state space model, in which the time-varying parameter is driven by a random autocorrelated process. Using the nomenclature of the literature, the two representations can be viewed as observation-driven and parameter-driven respectively, with the distinction between the two models mimicking that between analogous models for other non-Gaussian data such as financial returns and trade durations. The paper demonstrates that when adopting a conditional Poisson specification, the two models have vastly different dispersion/correlation properties, with the dual source model having properties that are a much closer match to the empirical properties of observed count series than are those of the single source model. Simulation experiments are used to measure the finite sample performance of maximum likelihood (ML) estimators of the parameters of each model, and ML-based predictors, with ML estimation implemented for the dual source model via a deterministic hidden Markov chain approach. Most notably, the numerical results indicate that despite the very different properties of the two models, predictive accuracy is reasonably robust to misspecification of the state space form.

Quantifying the effect on flood regime of land-use pattern changes via hydrological simulation in the upper Huaihe River basin, China

Both landscape and river systems over most regions of the world, within China in particular, have experienced unprecedented changes in the past decades, and their impacts from these changes undoubtedly have altered storm runoff generation characteristics and flood regimes in these areas. To assess the effect on flood regime of land-use pattern changes, the upper Huaihe River basin above the Dapoling station was selected as the case study site. On the basis of the topography, land-use/land cover, hydrological and meteorological data in 1990s and 2000s, quantification of the response to the land-use pattern change of flood characteristics was made by using the semi-distributed Xinanjiang model integrated with a distributed dual-source evapotranspiration model. The results revealed that land-use pattern change had significant impact on runoff depth, runoff coefficient, together with flood peak size, duration and timing. Moreover, land-use pattern change also altered the partitioning of runoff components and rainfall–runoff relationship. The output could provide valuable references for the prediction and mitigation of flood hazards, and also for river ecological health, scientific planning, sustainable development and management of the Huaihe River basin in the future.

Probabilistic conditional reasoning: Disentangling form and content with the dual-source model

The present research examines descriptive models of probabilistic conditional reasoning, that is of reasoning from uncertain conditionals with contents about which reasoners have rich background knowledge. According to our dual-source model, two types of information shape such reasoning: knowledge-based information elicited by the contents of the material and content-independent information derived from the form of inferences. Two experiments implemented manipulations that selectively influenced the model parameters for the knowledge-based information, the relative weight given to form-based versus knowledge-based information, and the parameters for the form-based information, validating the psychological interpretation of these parameters. We apply the model to classical suppression effects dissecting them into effects on background knowledge and effects on form-based processes (Exp. 3) and we use it to reanalyse previous studies manipulating reasoning instructions. In a model-comparison exercise, based on data of seven studies, the dual-source model outperformed three Bayesian competitor models. Overall, our results support the view that people make use of background knowledge in line with current Bayesian models, but they also suggest that the form of the conditional argument, irrespective of its content, plays a substantive, yet smaller, role.

Evidence of biphonation and source-filter interactions in the bugles of male North American wapiti (Cervus canadensis).

With an average male body mass of 320 kg, the wapiti, ITALIC! Cervus canadensis, is the largest extant species of Old World deer (Cervinae). Despite this large body size, male wapiti produce whistle-like sexual calls called bugles characterised by an extremely high fundamental frequency. Investigations of the biometry and physiology of the male wapiti's relatively large larynx have so far failed to account for the production of such a high fundamental frequency. Our examination of spectrograms of male bugles suggested that the complex harmonic structure is best explained by a dual-source model (biphonation), with one source oscillating at a mean of 145 Hz (F0) and the other oscillating independently at an average of 1426 Hz (G0). A combination of anatomical investigations and acoustical modelling indicated that the F0 of male bugles is consistent with the vocal fold dimensions reported in this species, whereas the secondary, much higher source at G0 is more consistent with an aerodynamic whistle produced as air flows rapidly through a narrow supraglottic constriction. We also report a possible interaction between the higher frequency G0 and vocal tract resonances, as G0 transiently locks onto individual formants as the vocal tract is extended. We speculate that male wapiti have evolved such a dual-source phonation to advertise body size at close range (with a relatively low-frequency F0 providing a dense spectrum to highlight size-related information contained in formants) while simultaneously advertising their presence over greater distances using the very high-amplitude G0 whistle component.