Measuring performance of transportation carriers

Thesis (M. Eng. in Logistics)--Massachusetts Institute of Technology, Engineering Systems Division, 2009.Includes bibliographical references (leaves 56-57).ChemiCo, a specialty chemical manufacturer for the auto and architectural market is seeking new business opportunities in the Chinese architectural market. Although ChemiCo entered the Chinese automotive market in 2006 with its newly built plant in China, it is still trying to understand the dynamics created by the fierce competition from many small local players in the Chinese market. The objective of this research is to help ChemiCo understand the complex Chinese transportation market specifically and provide guidance in carrier selection. The proposed approach will offer ChemiCo an objective means to procure transportation services for the architectural market and deliver products to customers across China from its existing facilities (plants and warehouses). We employ qualitative research methods to analyze the current Chinese transportation market. Based on this assessment, we evaluate various transportation options available to ChemiCo, keeping in mind their current and future level of supply complexities. We also investigate ChemiCo's existing carriers in the Chinese trucking market. An Analytical Hierarchy Process (AHP) is used to evaluate the key measurements of carrier performances for various customer segments and make recommendations. The thesis proposes a comprehensive set of performance measurement criteria to select transportation carriers and presents a carrier selection process for ChemiCo. This process is designed to meet ChemiCo's specific decision goals and allows it to assess and compare the performance of various carriers in a dynamic fashion.by Weixia Cheng.M.Eng.in Logistic

Diameter Estimation of Cylindrical Metal Bar Using Wideband Dual-Polarized Ground-Penetrating Radar

Ground-penetrating radar (GPR) has been an effective technology for locating metal bars in civil engineering structures. However, the accurate sizing of subsurface metal bars of small diameters remains a challenging problem for the existing reflection pattern-based method due to the limited resolution of GPR. To address the issue, we propose a reflection power-based method by exploring the relationship between the bar diameter and the maximum power of the bar reflected signal obtained by a wideband dual-polarized GPR, which circumvents the resolution limit of the existing pattern-based method. In the proposed method, the theoretical relationship between the bar diameter and the power ratio of the bar reflected signals acquired by perpendicular and parallel polarized antennas is established via the inherent scattering width of the metal bar and the wideband spectrum of the bar reflected signal. Based on the theoretical relationship, the bar diameter can be estimated using the obtained power ratio in a GPR survey. Simulations and experiments have been conducted with different GPR frequency spectra, subsurface mediums, and metal bars of various diameters and depths to demonstrate the efficacy of the method. Experimental results show that the method achieves high sizing accuracy with errors of less than 10% in different scenarios. With its simple operation and high accuracy, the method can be implemented in real-time in situ examination of subsurface metal bars.Comment: 14 pages, 15 figures, will be published at IEEE Transactions on Instrumentation and Measuremen

Highly sensitive transient absorption imaging of graphene and graphene oxide in living cells and circulating blood

We report a transient absorption (TA) imaging method for fast visualization and quantitative layer analysis of graphene and GO. Forward and backward imaging of graphene on various substrates under ambient condition was imaged with a speed of 2 μs per pixel. The TA intensity linearly increased with the layer number of graphene. Real-time TA imaging of GO in vitro with capability of quantitative analysis of intracellular concentration and ex vivo in circulating blood were demonstrated. These results suggest that TA microscopy is a valid tool for the study of graphene based materials

Comparison of Nasopharyngeal MR, 18 F-FDG PET/CT, and 18 F-FDG PET/MR for Local Detection of Natural Killer/T-Cell Lymphoma, Nasal Type.

Objectives The present study aims to compare the diagnostic efficacy of MR, 18F-FDG PET/CT, and 18F-FDG PET/MR for the local detection of early-stage extranodal natural killer/T-cell lymphoma, nasal type (ENKTL). Patients and Methods Thirty-six patients with histologically proven early-stage ENKTL were enrolled from a phase 2 study (Cohort A). Eight nasopharyngeal anatomical regions from each patient were imaged using 18F-FDG PET/CT and MR. A further nine patients were prospectively enrolled from a multicenter, phase 3 study; these patients underwent 18F-FDG PET/CT and PET/MR after a single 18F-FDG injection (Cohort B). Region-based sensitivity and specificity were calculated. The standardized uptake values (SUV) obtained from PET/CT and PET/MR were compared, and the relationship between the SUV and apparent diffusion coefficients (ADC) of PET/MR were analyzed. Results In Cohort A, of the 288 anatomic regions, 86 demonstrated lymphoma involvement. All lesions were detected by 18F-FDG PET/CT, while only 70 were detected by MR. 18F-FDG PET/CT exhibited a higher sensitivity than MR (100% vs. 81.4%, χ2 = 17.641, P < 0.001) for local detection of malignancies. The specificity of 18F-FDG PET/CT and MR were 98.5 and 97.5%, respectively (χ2 = 0.510, P = 0.475). The accuracy of 18F-FDG PET/CT was 99.0% and the accuracy of MR was 92.7% (χ2 = 14.087, P < 0.001). In Cohort B, 72 anatomical regions were analyzed. PET/CT and PET/MR have a sensitivity of 100% and a specificity of 92.5%. The two methods were consistent (κ = 0.833, P < 0.001). There was a significant correlation between PET/MR SUVmax and PET/CT SUVmax (r = 0.711, P < 0.001), and SUVmean (r = 0.685, P < 0.001). No correlation was observed between the SUV and the ADC. Conclusion In early-stage ENKTL, nasopharyngeal MR showed a lower sensitivity and a similar specificity when compared with 18F-FDG PET/CT. PET/MR showed similar performance compared with PET/CT

Ultrasonic and electromagnetic evaluation of corrosion-induced damage in reinforced concrete structures

Corrosion in steel bars has been a major cause of the degradation of reinforced concrete (RC) structures. At the early stage of corrosion, rust grows from the reinforcing bar and builds up tensile stress within the concrete, leading to cracking of the concrete cover and reduced cross-sectional areas of the bars. To extend the service life of RC structures, non-destructive testing methods are required to assess early corrosion damage, such as internal cracks or reduced cross-sectional areas of reinforcing bars, so that timely repair can be carried out. Among various non-destructive evaluation tools that are commonly applied to RC structures, ultrasonic methods are sensitive to voids and cracks, while electromagnetic methods can be used to assess reinforcing bars. However, there still exist significant challenges to quantitatively evaluate corrosion-induced damage in concrete at an early stage, due to its heterogeneous properties. To overcome this limitation, this thesis aims to explore both ultrasonic and electromagnetic methods for detecting and characterising corrosion-induced cracks, as well as the cross-sectional loss of reinforcing bars. For the inspection and characterisation of corrosion-induced cracks in RC structures, two ultrasonic methods based on diffuse coda waves and Rayleigh waves are investigated. In the diffuse coda wave-based method, the scattering cross-section of the crack is reconstructed with the Locadiff imaging technique. Based on the assumption that both crack tips have the same scattering cross-section, the size of the crack can be estimated when the location of the reinforcing bar is known. Excellent accuracy has been demonstrated by performing numerical simulations on cracks with different lengths, orientations, and shapes. The validation experiment on corroded concrete samples with different crack sizes shows very good agreement with X-ray CT imaging results. It should be noted that the diffuse coda wave-based method is limited to assessing a single crack and requires the pristine condition of the specimen as a baseline. Hence, this thesis also explores a reference-free method to detect multiple internal cracks in concrete based on ultrasonic Rayleigh waves. In this method, the energy spectrum of the Rayleigh wave is analysed using continuous wavelet transform and correlated to the size of the internal crack. This method is not sensitive to the surface roughness of concrete structures and does not need accurate identification of the Rayleigh wave components. The performance of the method has been examined using corroded RC specimens with different cover depths and aggregate sizes. As a comparison, electrochemical tests have also been carried out to map the corrosion potential and corrosion current density, showing very good agreement with the corrosion damage map generated from the proposed Rayleigh wave-based method. In order to determine the cross-sectional loss of reinforcing bars caused by corrosion, an electromagnetic method based on ground-penetrating radar (GPR) array is explored. The diameter of the reinforcing bar is reconstructed using a multiple-input-multiple-output (MIMO) GPR array. This method employs a linear array of ultra-wideband (UWB) antennas to acquire the full-matrix MIMO data of the reinforcing bar embedded in concrete. The diffraction stacking algorithm is applied to the obtained MIMO data to reconstruct the reinforcing bar. The 3 decibels (dB) drop technique is used to measure the chord length that passes through the peak intensity point of reconstruction images of reinforcing bars. Following that, the diameter of reinforcing bars can be determined based on their cover depth and chord length. Numerical studies and experiments have been carried out on reinforcing bars with different diameters and cover depths, showing excellent sizing accuracy. Subsequently, this thesis extends the application of the MIMO GPR array method to monitor the corrosion of reinforcing bars. The reconstructed image of reinforcing bars from MIMO GPR array would be affected by the corrosion, which introduces rust and cracks to RC structures. Therefore, by monitoring the area enclosed by the contour line, it is possible to indicate the development of corrosion from a healthy state. Experimental corrosion monitoring has been carried out to show the feasibility of the proposed GPR array monitoring method. In addition, ultrasonic measurements have been conducted during the corrosion monitoring test. The analysis of coda wave interferometry and spectrum of transmitted Rayleigh wave serves to verify the results obtained from the GPR array imaging method, exhibiting good agreement.Doctor of Philosoph

Characterisation of corrosion-induced crack in concrete using ultrasonic diffuse coda wave

Corrosion damage in reinforcing steel bars has been a major cause of cracking and spalling of reinforced concrete. To extend the service life of concrete structures, non-destructive testing methods are necessary to assess the corrosion status in order to conduct a timely repair. At the early stage of corrosion, rust grows from the reinforcing bar, subsequently generates cracks towards the surface of the concrete. Ultrasonic methods have been widely used to detect cracks in concrete. However, it is challenging to characterise them due to the heterogeneous material properties of the concrete. In this paper, ultrasonic imaging technique based on diffuse coda wave has been explored to inspect and characterise corrosion-induced cracks. In this method, scattering cross-section of the crack is reconstructed with the Locadiff imaging technique. Based on the assumption that both crack tips have the same scattering cross-section, the size of the crack can be estimated when the location of the reinforcing bar is known. Numerical simulations were carried out to image straight and curved cracks, showing excellent accuracy. Experiments were designed subsequently on concrete samples with accelerated corrosion. The induced cracks were characterised by the proposed ultrasonic method, and compared with X-ray CT results, showing very good agreement.Ministry of National Development (MND)National Research Foundation (NRF)The authors acknowledge funding from National Research Foundation, Singapore, and Ministry of National Development, Singapore, under its Cities of Tomorrow R&D Programme (CoT Award No. COT-V2-2019-1)

Learning to Remove Clutter in Real-World GPR Images Using Hybrid Data

The clutter in the ground-penetrating radar (GPR) radargram disguises or distorts subsurface target responses, which severely affects the accuracy of target detection and identification. Existing clutter removal methods either leave residual clutter or deform target responses when facing complex and irregular clutter in the real-world radargram. To tackle the challenge of clutter removal in real scenarios, a clutter-removal neural network (CR-Net) trained on a large-scale hybrid dataset is presented in this study. The CR-Net integrates residual dense blocks into the U-Net architecture to enhance its capability in clutter suppression and target reflection restoration. The combination of the mean absolute error (MAE) loss and the multi-scale structural similarity (MS-SSIM) loss is used to effectively drive the optimization of the network. To train the proposed CR-Net to remove complex and diverse clutter in real-world radargrams, the first large-scale hybrid dataset named CLT-GPR dataset containing clutter collected by different GPR systems in multiple scenarios is built. The CLT-GPR dataset significantly improves the generalizability of the network to remove clutter in real-world GPR radargrams. Extensive experimental results demonstrate that the CR-Net achieves superior performance over existing methods in removing clutter and restoring target responses in diverse real-world scenarios. Moreover, the CR-Net with its end-to-end design does not require manual parameter tuning, making it highly suitable for automatically producing clutter-free radargrams in GPR applications. The CLT-GPR dataset and the code implemented in the paper can be found at https://haihan-sun.github.io/GPR.html

Decomposition of Leaves and Fine Roots in Three Subtropical Plantations in China Affected by Litter Substrate Quality and Soil Microbial Community

Leaf and root litter decomposition has been a major research focus. However, the possible effects of belowground microbial community structure and diversity on this process are poorly understood. Understanding the biochemical mechanisms controlling aboveground decomposition processes is important to predict the changes of soil carbon and nutrient cycling in response to changes of forest management regimes. Here, we explore the biochemical controls of leaf and fine root decomposition in three subtropical plantations (Ford Erythrophleum (Erythrophleum fordii Oliver), Masson Pine (Pinus massoniana Lamb.)), and a mixed plantation containing both species) using the litterbag method, and soil microbial communities were determined using phospholipid fatty acid profiles. Overall, leaves decomposed more rapidly than fine roots, potentially due to the faster degradation of their cellulose component, but not lignin. In addition, leaf and fine root decomposition rates varied among plantations, being higher in E. fordii and lower in P. massoniana. Substrate quality such as N, Ca, lignin concentration, and C/N ratio were responsible for the decomposition rate changes among plantation types. Moreover, we used redundancy analysis to examine the relationships between litter decomposition and soil microbial community composition and diversity. Results revealed that actinobacteria and arbuscular mycorrhizal fungi community were the key determinants affecting leaf and fine root litter decomposition, respectively. Our work demonstrates that litter decomposition was linked to substrate quality and to the structure of soil microbial communities, and evidences the probable role of E. fordii in increasing soil nutrient availability, especially N, P and Ca. Additional data on phospholipid fatty acid (PLFA) or DNA marker groups within the litterbags over time may provide insights into litter decomposition dynamics, which represents potential objectives for future long-term decomposition studies