Regional Development in China: Interregional Transportation Infrastructure and Regional Comparative Advantage

Significant economic disparities among China's Eastern, Central, and Western regions pose unequivocal challenges to social equality and political stability in the country. A major impediment to economic development, especially in the poor, remote Western region, is the shortage of transportation infrastructure. The Chinese government has committed to substantial investment for improving the accessibility of this vast, land-locked region as a mechanism for promoting its development. The paper examines the impacts of the intended transportation infrastructure buildup on the Western region's comparative advantage and its interregional trade. The World Trade Model is extended to represent this investment and applied to determine interregional trade in China based on region-specific technologies, factor endowments and prices, and consumption patterns as well as the capacities and costs of carrying goods among regions using the interregional transportation infrastructure in place in the base year of 1997 and that planned for 2010 and 2020. The model is implemented for 3 regions, 27 sectors, and 7 factors. The results indicate that the planned infrastructure buildup will be cost-effective, will increase benefits especially for the Western region, and that it can conserve energy overall at given levels of demand but substitute oil for coal. Based on these and other model results, some recommendations are offered about strategies for regional development in China.

Influential Publications in Ecological Economics: A Citation Analysis

We assessed the degree of influence of selected papers and books in ecological economics using citation analysis. We looked at both the internal influence of publications on the field of ecological economics and the external influence of those same publications on the broader academic community. We used four lists of papers and books for the analysis: (1) 92 papers nominated by the Ecological Economics (EE) Editorial Board; (2) 71 papers that were published in EE and that received 15 or more citations in all journals included in the Institute for Scientific Information (ISI) Citation Index; (3) 57 papers that had been cited in EE 15 or more times; and (4) 77 monographs and edited books that had been cited in EE 15 or more times. For each publication we counted the total number of ISI citations as well as the total number of citations in EE. We calculated the average number of citations/yr to each paper since its publication in both the ISI database and in EE, along with the percentage of the total ISI citations that were in EE. Ranking the degree of influence of the publications can be done in several ways, including using the number of ISI citations, the number of EE citations or both. We discuss both the internal and external influence of publications and show how these influences might be considered jointly. We display and analyze the results in several ways. By plotting the ISI citations against the EE citations we can identify those papers that are mainly influential in EE with some broader influence, those that are mainly influential in the broader literature but have also had influence on EE, and other patterns of influence. There are both overlaps and interesting lacunae among the four lists that give us a better picture of the real influence of publications in ecological economics versus perceptions of those publications' importance. By plotting the number of citations vs. date of publication, we can identify those publications that are projected to be most influential. Plots of the time series of citations over the 1990-2003 period show a generally increasing trend (contrary to what one would expect for an "average" paper) for the top papers. We suggest that this pattern of increasing citations (and thus influence) over time is one hallmark of a "foundational" paper.

Hard superconducting gap in PbTe nanowires

Semiconductor nanowires coupled to a superconductor provide a powerful testbed for quantum device physics such as Majorana zero modes and gate-tunable hybrid qubits. The performance of these quantum devices heavily relies on the quality of the induced superconducting gap. A hard gap, evident as vanishing subgap conductance in tunneling spectroscopy, is both necessary and desired. Previously, a hard gap has been achieved and extensively studied in III-V semiconductor nanowires (InAs and InSb). In this study, we present the observation of a hard superconducting gap in PbTe nanowires coupled to a superconductor Pb. The gap size ($\Delta$) is $\sim$ 1 meV (maximally 1.3 meV in one device). Additionally, subgap Andreev bound states can also be created and controlled through gate tuning. Tuning a device into the open regime can reveal Andreev enhancement of the subgap conductance, suggesting a remarkable transparent superconductor-semiconductor interface, with a transparency of $\sim$ 0.96. These results pave the way for diverse superconducting quantum devices based on PbTe nanowires

Selection of Anti-Sulfadimidine Specific ScFvs from a Hybridoma Cell by Eukaryotic Ribosome Display

BACKGROUND:Ribosome display technology has provided an alternative platform technology for the development of novel low-cost antibody based on evaluating antibiotics derived residues in food matrixes. METHODOLOGY/PRINCIPAL FINDINGS:In our current studies, the single chain variable fragments (scFvs) were selected from hybridoma cell lines against sulfadimidine (SM(2)) by using a ribosome library technology. A DNA library of scFv antibody fragments was constructed for ribosome display, and then mRNA-ribosome-antibody (MRA) complexes were produced by a rabbit reticulocyte lysate system. The synthetic sulfadimidine-ovalbumin (SM(2)-OVA) was used as an antigen to pan MRA complexes and putative scFv-encoding genes were recovered by RT-PCR in situ following each panning. After four rounds of ribosome display, the expression vector pCANTAB5E containing the selected specific scFv DNA was constructed and transformed into Escherichia coli HB2151. Three positive clones (SAS14, SAS68 and SAS71) were screened from 100 clones and had higher antibody activity and specificity to SM(2) by indirect ELISA. The three specific soluble scFvs were identified to be the same molecular weight (approximately 30 kDa) by Western-blotting analysis using anti-E tag antibodies, but they had different amino acids sequence by sequence analysis. CONCLUSIONS/SIGNIFICANCE:The selection of anti-SM(2) specific scFv by in vitro ribosome display technology will have an important significance for the development of novel immunodetection strategies for residual veterinary drugs

Ballistic PbTe Nanowire Devices

Disorder is the primary obstacle in current Majorana nanowire experiments. Reducing disorder or achieving ballistic transport is thus of paramount importance. In clean and ballistic nanowire devices, quantized conductance is expected with plateau quality serving as a benchmark for disorder assessment. Here, we introduce ballistic PbTe nanowire devices grown using the selective-area-growth (SAG) technique. Quantized conductance plateaus in units of $2e^2/h$ are observed at zero magnetic field. This observation represents an advancement in diminishing disorder within SAG nanowires, as none of the previously studied SAG nanowires (InSb or InAs) exhibit zero-field ballistic transport. Notably, the plateau values indicate that the ubiquitous valley degeneracy in PbTe is lifted in nanowire devices. This degeneracy lifting addresses an additional concern in the pursuit of Majorana realization. Moreover, these ballistic PbTe nanowires may enable the search for clean signatures of the spin-orbit helical gap in future devices

Concentration protile of etchant measured by microelectrode technique in the process of chemical micromachining

A carbon-disk microelectrode was used to investigate the surface concentration profile of etchant Br-2, which was electrogenerated on the Pt working electrode. The steady state reducing currents of Br-2 at different distances away from the Pt electode was measured. The concentration profile was estimated from the current-distance variation curves as a function of different sampling times. Experimentally determined concentration profiles are in good agreement with those estimated from the microetching results. The microelectrode technique has offered a good method to choose suitable etching solution for chemical micromachining

Silicon nanowires based inorganic/organic hybrid solar cells

As the importance of renewable energy source becomes more apparent, tremendous efforts have been devoted to developing photovoltaics (PV) since solar energy is plentiful and widespread. However, the high production cost of the conventional high-efficiency Silicon (Si) solar cells poses a barrier for solar energy to compete with fossil fuels. This has led to the search of novel solar cells that are low-cost and highly efficient. Recently, there has been significant interest in the study of inorganic/organic hybrid solar cells incorporating Si nanostructures such as Si nanowires (SiNWs) and organic semiconductors, to leverage on the advantages of the former such as high carrier mobility and excellent light trapping capability, and the latter that include low material cost, low temperature and solution based process. The objective of this work is to design, fabricate and characterize SiNWs based inorganic/organic hybrid solar cells. Firstly, various Si surface texturing structures such as SiNWs and SiNWs-on-pyramid have been investigated to form hybrid cells based on bulk crystalline Si, and the choice of organic materials includes conjugated polymer and small molecule. Next, the effects of Si/organic interface treatment on the cell performance have been studied. Finally, hybrid solar cells have been successfully demonstrated on epitaxial Si thin films to bypass the use of costly bulk Si wafer. A simple approach has been demonstrated to fabricate high-efficiency hybrid solar cells based on n-type SiNWs and a p-type conductive polymer, poly(3,4-ethylene-dioxythiophene): polystyrenesulfonate (PEDOT:PSS). PEDOT is directly spin coated on vertical SiNWs arrays fabricated by metal-catalyzed electroless etching (MCEE) to form the core-sheath heterojunction. Compared to planar Si/PEDOT cell, the power conversion efficiency (PCE) of the SiNWs/PEDOT cell increases greatly from 6.2% to 9.0%. Cells with different SiNWs lengths are also studied and it is found that enhanced aggregations of longer SiNWs lead to poor surface coverage by PEDOT which has long polymer chain, and hence degrade the performance of the hybrid cells. In order to further improve the light trapping of the device, the Si/PEDOT hybrid solar cells have been fabricated using synergistic surface texturing of SiNWs-on-pyramids binary structure. The fabrication process involves the formation of the SiNWs/pyramids binary structure by a two-step chemical etching process, followed by spin coating of a PEDOT layer. The cells are found to have a maximum short-circuit current density (Jsc) of 31.9 mA/cm2 and PCE of 9.9%, which are higher than similar cells fabricated using planar Si, pyramid-textured Si and SiNWs. A new hybrid cell has been fabricated by incorporating a small organic molecule, 2,2’,7,7’-Tetrakis-(N,N-di-4-methoxyphenylamino)-9,9’-spirobifluorene (Spiro-OMeTAD), on SiNWs arrays to form a new core-sheath heterojunction. The small molecular size of Spiro-OMeTAD enables it to infiltrate well into the small gaps among the SiNWs arrays, leading to larger heterojunction area and better passivation on the SiNWs surface. A maximum PCE of 10.3% has been obtained from the SiNWs/Spiro cell with a 0.35-µm long SiNWs. The PCE is the highest reported to-date in the field of SiNWs/organic hybrid solar cells. The characteristics of the hybrid cells are investigated as a function of SiNWs length from 0.15 to 5 μm. It is found that enhanced aggregations in longer SiNWs still limit the SiNWs/Spiro cell performance due to increased series resistance and higher carrier recombination in the shorter wavelength region. The effects of Si surface native oxide on the performance of hybrid cells have been studied. The cells were fabricated based on PEDOT and planar Si wafers with (100) and (111) orientations. Compared to cell with hydrogen-terminated Si surface, the cell with oxygen-terminated Si surface reveals a 530-fold increase in PCE from 0.02% to 10.6%. The formation of SiOx-Si bonds poses a net positive surface dipole which leads to a favorable band alignment for charge separation. However, for thicker oxide the cell performance is degraded due to higher series resistance. The PCE of 10.6% demonstrates the highest PCE reported to-date in the field of planar Si/organic hybrid solar cells. The Si/PEDOT hybrid cells have been further fabricated on a 2.2 μm epitaxial Si absorber thin-film. The Jsc and PCE of SiNWs/PEDOT cell increases from 12.5 to 13.6 mA/cm2 and 5.4% to 5.6%, respectively, as compared to planar epitaxial Si/PEDOT cell. A maximum external quantum efficiency (EQE) of 56.6% is obtained for the SiNWs/PEDOT cell. Our results have demonstrated a promising route to realizing low-cost and efficient Si or SiNWs/organic hybrid solar cells using low-cost Si thin films instead of costly bulk Si wafers.Doctor of Philosophy (EEE

Investigation of multilayer thin films using ellipsometry

Spectroscopic Ellipsometry (SE) is a powerful and universal optical technique for the investigation of optical properties of semiconductor thin films. It is an extremely sensitive measurement tool for the characterization of single layer thin film and even multilayer structures. This project focuses on the study of optical properties of amorphous silicon rich nitride (a-SRN) in single bulk layer and in multilayer by SE fitting using software Wvase32. SE itself is not a direct readout type technique. It is actually a model-based technique. Thus, it is important to build correct and suitable model for a particular material in the SE fitting. In this project, several dispersion models are investigated to find the one which is best suitable for the fitting of a-SRN. Those dispersion models include Cauchy urbach model, Lorentz oscillator model, Forouhi & Bloomer’s model, Cauchy absorption model and Tauc-Lorentz model. Furthermore, the optical properties of a-SRN in single bulk layer with different SiH4/NH3 ratio have been studied by SE fitting using Tauc-Lorentz model. It is clearly shown that the bandgap of a-SRN will decrease and optical constants (n & k) will increase with increasing SiH4/NH3 ratio. Finally, the SE fitting of four a-SRN quantum well multilayer samples has been conducted. Two samples consist of 45 alternating layers of a-SRN well and SiO2 barrier. Another two consist of 40 alternating layers of a-SRN well and Si3N4 barrier. The optical properties of these samples have been studied in detail using SE and photoluminescence (PL). It is observed that the SE fitting for multilayer samples are much more challenging than single bulk layer due to their structure complexity. The multilayer samples after annealing have also been studied. A second peak emerges in the PL spectra of the annealed samples, which may be attributed to the formation of Si nanocrystals in the well layers.Bachelor of Engineerin