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Off-site construction (OSC) is an innovative and sustainable construction method. One of its critical success factors is the proper management of its supply chain (SC). Recently, significant research attention has been focused on the modelling of OSC-SC to improve its performance and sustainability. However, the literature still lacks a comprehensive review of the modelling studies on off-site construction -supply chain management (OSC-SCM). Therefore, this research contributes by providing a comprehensive and up-to-date mapping and clustering of 309 journal articles on the modelling of OSC-SC to identify its trends and gaps, and hence, highlight future research opportunities. To achieve these objectives, a mixed review method, consisting of scientometric and systematic reviews, is used. The scientometric review identifies the most prolific journals, researchers, co-occurrence network of keywords, and their citation bursts. On the other hand, the systematic review classifies the articles based on OSC type and supply chain (SC) stage. At each SC stage, the articles are further classified based on problem settings and solution methods. The results show that production problems have received the most attention (i.e., by 28% of the included articles), followed by on-site construction (19%), design (13%), and logistics (7%) problems. However, researchers are more inclined to address problems at multiple SC stages (33%) due to the interrelationship between these stages. Besides, the systematic analysis shows that OSC-SC problems have been solved frequently by a variety of solution methods such as optimization (25%), simulation (13%) and building information modelling (BIM) (9.5%). However, researchers tend more to integrate multiple solution methods (35%) to address the complexities of OSC-SC problems. Finally, the included studies are classified based on the three sustainability dimensions. The results show that economic, environmental, and social sustainability dimensions have been considered in previous studies by 72%, 24%, and 4%, respectively. Therefore, the study identifies research gaps at each SC stage of each OSC type to incentivize future studies to consider more environmental and social sustainability factors in OSC-SC models. Since modular integrated construction (MiC) has the highest prefabrication level, this study provides future research directions for sustainable supply chain management (SCM) in MiC. The present research is an important reference guide that helps researchers and practitioners to understand different problem settings and their solution methods in OSC-SCM.

Collaborative Decision Support Systems (CDSSs) have been increasingly used to organize collaborative transport networks to develop sustainable freight transport. CDSSs involve two main components: a collaborative planning algorithm for matching transport orders to trucking capacities and an interactive front-end (e.g., websites and Email systems) for dispatching freight matches and communication among collaborators. The literature has mostly focused on developing and testing advanced algorithms using historical data. However, these studies test only one component and ignore the front-end that greatly affects the CDSS performance in daily practice. Overall, the literature lacks studies that evaluate and improve the CDSSs based on the feedback of end-users with a pilot test. Though poor data availability and quality are well-known issues in the logistics industry, no previous studies have discussed how to deal with the data issues in the real applications of CDSSs. To bridge these gaps, this study reports our experiences with testing an early version of a CDSS for automated freight matching in Denmark. The test results revealed some issues related to the ease of the CDSS usage and validity of the identified matches. A methodology is proposed to analyze the test results and to inspire ideas for improvement. The analyses showed that low data quality (e.g., missing values) is a significant barrier to developing effective front-end and valid matching. Due to the low data quality, automated matching can be more effective if carriers set their matching preferences through access to the CDSS. Besides, the front-end Email system should be developed in a way that reduces the number of emails, enables snap judgment, and visualizes the match details. Finally, some improvement suggestions are proposed and evaluated.

This study provides explicit mathematical formulations for the bistatic scattering coefficient from a randomly rough surface with a complex relative permittivity based on the following analytic models: small perturbation model (SPM), physical optics model (PO), and Kirchhoff approximation model (KA). Then it addresses the two shortcomings associated with each of the three models: i) limited applicability domain, and ii) null predicted values for the cross polarized bistatic scattering coefficients within plane of incidence. The plane of incidence contains both backscattering direction and forward (specular reflection) direction which are of interest to the spectrum community.

Despite the negative consequences on society and environment, urban freight transport is critical for the prosperity of cities. Decision makers have considered the horizontal collaboration between carriers as a solution to reduce the total transportation cost and the related negative impacts. In literature, the collaborative freight delivery is modelled as a Multi-Depot Vehicle Routing Problem (MDVRP) that can be solved by being decomposed into two sub-problems, i.e. assignment problem and a set of vehicle routing problems. The assignment problem allocates customers to the nearest depots while vehicle routing problem determines the optimal routes to serve customers assigned to each depot. However, most of existing approaches did not consider the interrelation between these two sub-problems, which in turn impairs the solution quality of the overall problem. This paper presents an improved two-level mathematical modelling approach to evaluate and optimize the implementation of the collaborative freight distribution in urban areas. Unlike existing studies, the proposed approach considers the interrelation among the two-sub problems. A real-life case is used to illustrate the savings obtained from the collaborative distribution. In addition, the significance of the proposed approach is demonstrated by a comparison against a similar approach found in literature.

In the recent years, Horizontal Collaboration(HC) has gained an increasing attention in literature as anefficient practice for sustainable freight transportation.However, successful applications of HC in freighttransportation, are rarely reported. This paper contributes toliterature by a Decision-Making Trial and EvaluationLaboratory (DEMATEL)-based approach to develop a betterunderstanding of the main barriers to the implementation ofcollaborative freight transportation in practice. A set of barriersis identified by an extensive literature review, and is groupedinto six categories, i.e. “Design of the collaboration process”,“Information sharing and collection”, “ Partners’ behaviors andtheir relationships”, “Decision making algorithm”, “Web-basedinformation system”, and “Market structure and regulatinglaws”. Then, the DEMATEL method is used to develop causalityand prominence relations among these categories. Finally, thecontributions of barrier categories to the success of thecollaboration process and interrelationships among them aredetermined. The results of this work can provide guidelines todecision makers to address those critical barriers for makingcollaborative logistics practices a success.

Cities across Europe face significant challenges in relation to urban freight transport. The economic development in recent years have boosted activities in the city centres demanding increased freight transport. At the same time, urbanization has increased congestion issues and initiatives to minimize traffic in city centres have made city centres less accessible for freight transport vehicles.A number of studies have explored how to optimize freight transport and minimize the negative externalities through collaborative logistics, a concept which has received a lot of attention in recent years. Collaborative logistics can be either a vertical collaboration between actors of the same supply chain, or a horizontal collaboration between direct competitors, for example competing logistics companies, aiming to decrease the costs of transportation and increase fleet utilization by sharing assets, information, knowledge etc.The idea is built around an example if two competing logistics companies each have half a truckload of goods on the same route, then it makes sense for the companies to share the transport, place the goods on one full vehicle and share the saved costs. In turn, this will also generate environmental benefits, i.e. minimize driving and thus emissions of greenhouse gas, particles and noise.This study provides an overview of the concept of collaborative logistics, and employs mathematical modelling to quantify the benefits which can be gained from collaborative logistics in urban freight delivery and interview-based methods to identify the challenges of implementing collaborative logistics in this setting in practice.The study shows that horizontal collaborative logistics, i.e. collaboration between competing logistics companies, is found the most suitable approach to optimize logistics within given case of Aalborg. Within horizontal logistics two approaches are found, capacity sharing and order sharing. The study shows, that order sharing is the most beneficial approach. Using real-life data from two competing logistics companies, the analysis reveals that collaborative delivery and order sharing can reduce the total travelled distance of each company by an average of 24.75% compared to the non-collaborative distribution. Importantly, the analysis also reveals that even if the participating competitors only choose to share a subset of their orders, a significant reduction in travelled distance and emission is still achievable.The analysis of the barriers shows that accessibility limitations in the city, partner selection issues, loss of a competitive advantage, issues in profit and cost sharing, different delivery structures and uncertainty regarding the branding of the delivery were the main barriers. The analysis also revealed that there is a support for collaboration among relevant stakeholders, however, the stakeholders have a low awareness of potential benefits of collaboration.By simulating and proving the potential benefits of collaborative logistics based on real data, and simultaneously identifying the barriers, one of which being limited knowledge about potential benefits of collaboration, this report constitutes an important step towards implementation of collaborative in cities such as Aalborg.

This paper is the third of a series which aims to evaluate the effects of canopy structure on the polarimetric radar response of mangrove forests. It complements the experimental and theoretical study of closed canopies presented in the previous papers by analysing two different mangrove stands of equal biomass but which greatly differ in their structure. For the three considered frequencies (C-, L- and P-band), experimental observations show that the back-scattering from the open declining stand is higher than that of the closed forest. The corresponding enhancement factor increases with wavelength and shows maximum values for the HH polarization. The identification of the scattering mechanisms occurring between the incident radar wave and the forest components was performed with the assistance of a polarimetric scattering model based on a radiative transfer approach. For the co-polarizations, results of the simulation study confirm that the backscatter enhancement is mainly due to an increase of either ...

A novel thermal wave model is developed for studying heat transfer in nonuniform soils. The model, which is based on the wave-like characteristics of periodic heat flow, discretizes the soil into sublayers. The total thermal reflection and transmission coefficients at the interfaces of those sublayers are formulated and then employed to construct the soil temperature and heat flux profiles from their values at the air-soil interface. Numerical simulations showed that the thermal wave model could predict the predictions of two exact analytic models for the temperature profiles and their derivatives.

Polarimetric AIRSAR data acquired over a variety of mangrove forests are analyzed with the assistance of a three-layer radiative transfer model. The necessary input parameters to the model come from detailed ground measurements performed in 12 mangrove stands that are representative of the different successional stages of the mangrove forest dynamics. On the whole, P-band provides the most pronounced polarimetric signatures. Among the polarimetric parameters, the polarization ratio is found to be useful for analyzing scattering mechanisms and for discriminating between various forest stages. Comparison between AIRSAR data and simulations shows that the model is able to describe the overall radar signature of mangrove forests at P-, L- and C-band. However, this study also points out the limitation of such models.

A microwave polarimetric scattering model for a forest canopy is developed based on the iterative solution of the vector radiative transfer equations up to the second order. The forest canopy constituents (branches, leaves, stems, and trunks) are embedded in a multi-layered medium over a rough interface. The branches, stems, and trunks are modeled as finite randomly oriented cylinders. Deciduous leaves are modeled as randomly oriented discs and coniferous leaves are modeled as randomly oriented needles. The vector radiative transfer equations contain non-diagonal extinction matrices that account for the difference in propagation constants and the attenuation rates between the vertical and horizontal polarizations. For a plane wave exciting the canopy, the average Mueller matrix is formulated, and then used to determine the linearly polarized backscattering coefficients including both the copolarized and cross-polarized power returns. Comparisons of the model with measurements from Les Landes Forest of France showed good agreements over a wide frequency band and gave a quantitative understanding of the relation between the backscattering coefficients and the age of the trees in the forest and forest biomass.

Existing terahertz THz systems for detecting concealed explosives are not capable of identifying explosive type which leads to higher false alarm rates. Moreover, some of those systems are imaging systems that invade personal privacy, and require more processing and computational resources. Other systems have no polarization preference which makes them incapable of capturing the geometric features of an explosive. In this study a non-imaging polarized THz passive system for detecting and identifying concealed explosives overcoming the forgoing shortcomings is developed. The system employs a polarized passive THz sensor in acquiring emitted data from a scene that may have concealed explosives. The acquired data are decomposed into their natural resonance frequencies, and the number of those frequencies is used as criteria in detecting the explosive presence. If the presence of an explosive is confirmed, a set of physically based retrieval algorithms is used in extracting the explosive dielectric constant/refractive index value from natural resonance frequencies and amplitudes of associated signals. Comparing the refractive index value against a database of refractive indexes of known explosives identifies the explosive type. As an application, a system having a dual polarized radiometer operating within the frequency band of 0.62- 0.82 THz is presented and used in detecting and identifying person borne C-4 explosive concealed under a cotton garment. The system showed higher efficiencies in detecting and identifying the explosive.

A reformulated integral equation is solved inside an elliptic disk particle for an electromagnetic field formulation bridging the quasi-static and the physical optics approximations. The scattering amplitude tensor elements associated with such a field formulation are derived and then used to formulate the extinction cross sections. It is shown that the extinction cross sections have a frequency dependence and an incidence angle dependence similar to those associated with the physical optics approximation, and they have a particle shape dependence similar to that associated with the quasi-static approximation. Furthermore, at the high-frequency limits, it is shown that those cross sections could reach the value known in the literature by the extinction paradox, namely, twice the particle geometric shadow area.

Theory is presented to provide insight into the observation that attenuation through vegetation is proportional to vegetation water content. In this analysis, the canopy is modeled as a sparse layer of randomly oriented particles (leaves, stalks, etc.) over a flat, homogeneous ground plane (soil) and an expression is obtained for the "optical depth". The formulas developed by Ulaby and El Rayes are used to relate this expression to the water content of the canopy. In the low frequency extreme (Rayleigh scatterers), the attenuation varies almost linearly with water content and inversely with wavelength. In contrast, in the high frequency limit, the attenuation is independent of both water content and frequency, in between, geometry dependent "resonances" occur even at the low frequency end of the microwave spectrum (e.g. L-band) making the dependence of attenuation on frequency and water content specific to canopy architecture.

This study accounts for the contribution of multiple scattering to microwave brightness temperature of sea ice and its snow cover. The application of the distorted Born approximation in conjunction with the strong fluctuation theory has led to calculated values for brightness temperatures in agreement with measurements from sea ice and its snow cover at frequencies below 37 GHz. However, at frequencies above 37 GHz, the distorted Born approximation overestimates the brightness temperature. This is due to the fact that the distorted Born approximation accounts only for the singly scattered field. Physical and mathematical arguments showed that inclusion of higher order multiple scattering would lead to more reasonable values for the brightness temperature at higher frequencies where the multiple scattering is expected to be dominant.

A model is developed to relate the attenuation through a vegetation canopy, to the geometric and dielectric parameters of the canopy constituents. The model is designed to operate over a wide frequency band in the microwave region and include both deciduous and coniferous trees. The vegetation canopy is represented by a discrete random layer of cylinders and disks having the same geometric and dielectric properties as the vegetation canopy constituents. The Foldy-Twersky Integral Equation is used to relate the attenuation to the scattering amplitude of the vegetation constituent evaluated in the forward direction. Numerical results are presented to show how the level and frequency dependance of the attenuation depend on type of vegetation constituent and its orientation.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A mathematical evaluation of the potential of active microwave sensors for monitoring underground permafrost is carried out. For this purpose, the Helmholtz Integral is used to relate the scattered field to the field inside the permafrost. A mathematical formation is derived for the scattered field by estimating the inner field through a generalized Rayleigh- Gans approximation. Numerical calculation show that the freezing thawing process is the dominant factor determining the relative level of the backscattered signal.

The classical optical theorem that describes the extinction of electromagnetic radiation by an arbitrary particle is reformulated by use of the diffusion properties of the mutual spectral densities. This reformulation yields three novel coherency tensors: an extinction-loss coherency tensor, a scattering-loss coherency tensor, and an absorption-loss coherency tensor. The first tensor is used to establish the polarimetric optical theorem and to derive the extinction-loss matrix. The second tensor is used to derive the scattering-loss matrix. The third tensor is used to develop the absorption-loss matrix and the absorption cross sections. Furthermore, the derived extinction- and scattering-loss matrices are found to be similar to the extinction coefficient and phase matrices of the vector radiative transfer equations.

The conventional integral equation governing the electric field inside dielectric particles is reformed to bridge and to provide mathematical foundations for analytic techniques widely used to estimate such a field. The solution of the reformed equation inside a dielectric slab explained how inner-field formulations based on the Rayleigh, the Rayleigh-Gans, the quasi-static, and the Shifrin approximations can be supported by the particles. It also confirmed the approach employed to reform the integral equation. The analysis performed uncovered the differences between the depolarization tensor characterizing electrostatic fields inside the particles and the source dyadic resulting from the extraction of the singularity of the integral equation kernel.

The problem of electromagnetic wave interaction with a stratified dielectric medium is solved in the framework of molecular optics, leading to a new derivation for the refraction and reflection laws at stratified media interfaces. In addition, the solution confirms the Lorentz–Lorenz refractive index formula characterizing the transverse propagation modes and the characteristic frequencies associated with the longitudinal mode. The analytic results presented in this study support the existence of another longitudinal mode propagating with the vacuum wave number within the medium, and they provide a new concept for the Ewald–Oseen extinction theorem. Other new results of this study are that (1) the relation between Fresnel horizontal and vertical reflection coefficients and the relation between the corresponding transmission coefficients are revealed and (2) a new concept is presented for the Brewster angle, and (3) the concept is introduced of multiple reflections in formulating the reflection coefficient at the interface between two different dielectric materials.