This study examines curriculum vitae (CV) data from 447 scientists and engineers at academic research centers in the United States, ranging from post-doctoral researchers to full professors and research directors in order to figure out the pattern of scientific discipline trajectory and the relation of the scientists discipline mobility to productivity. This study shows that natural sciences have highest percentage of scientists who have the same bachelors degree field as their highest degree field and higher degree of mobility across the disciplines is negatively associated with their productivity. On the contrary, for life sciences, higher degree of mobility across the disciplines is positively associated with scientific productivity.

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The quality of GaN template layer plays a very important role in high electron mobility transistors. We proposed a special method in the growth of molecular beam epitaxy to deal with the dilemma between structure and the morphology of GaN. In our study, we used a nitrogen-rich GaN growth condition to deposit the initial varied layer. After that, we changed the N/Ga ratio stepwise to the growth condition of gallium-rich GaN and grew the epitaxy layer right away. In X-ray diffraction analysis, the full width at half-maximum (FWHM) value of rocking curves of GaN(002) was improved relatively to gallium-rich sample from 531.69 arcsecond to 59.43 arcsecond. In atomic force microscopy (AFM) analysis, the root mean square (rms) roughness of sample surface was improved relatively to nitrogen-rich sample from 18.28 nm to 1.62 nm over 5 £gm ¡Ñ 5 £gm area. The Raman scattering shows there is a slightly tilted plane in gradient layer and the gradient layer can also slash the strain force which is caused from Ga-rich GaN epitaxy layer and AlN buffer layer. A series high mobility AlxGa1-xN/GaN heterostructures samples were grown on MOVPE-grown GaN templates substrate by molecular beam epitaxy with different Al concentrations (x = 0.017~0.355). The quality checked by XRD and AFM indicated that the excellent properties agreed with the GaN-template. The highest mobility in this series samples at 8 K is 19593 cm2/Vs with carrier concentration 3.13 ¡Ñ 1012 cm-2 and Al concentration x = 0.017. In our experiments, the carrier density decreases as Al concentration reduces. In the illuminated Hall measurement, there are only few electrons increased following blue LED illumination. It shows that there are only few deep level defects existing near the heterointerface. From temperature-depended Shubnikov-de Haas (SdH) oscillations, the electron effective mass m* in 2DEG are evaluated as 0.213 mo and for x = 0.207 0.227 moand 0.136 respectively. The high mobility AlxGa1-xN/GaN was fabricated to a series of wires by focused ion beam (FIB) equipment, and the width of the active channel is ranged from 900 nm to 50 nm (900 nm, 500 nm, 300 nm, 200 nm, 100 nm, 80 nm and 50 nm) with the channel orientation in [11 0] direction. The largest spin-splitting energy in the series of wires is 2.14 meV. Due to larger spin-splitting energy and quasi-ballistic transportation, the 200 nm wire is the best candidate to be the channel of the quantum-ring interferometer in our case.

A Matrix-assisted Laser Desorption/Ionization (MALDI) – Ion Mobility (IM) – Surface-induced Dissociation (SID) – Time-of-Flight (TOF) instrument with three different collision source configurations was developed in order to improve the SID performance in high throughput peptide sequencing. The first version of the instrument was equipped with an angle resolved SID source in order to maximize the collection efficiency of the SID scattering ions. An orthogonal TOF was also implemented as the second MS stage in this instrument to increase mass resolution. The second version of the instrument was developed towards simplifying the coupled configuration of the IM, SID and TOF components by using a combined SID/TOF source with a confinement ring electrode as the collision target. The fragmentation efficiency of SID in this configuration was increased up to 50% due to the surface normal impact angle used as compared with the results from a previous experiment using 45 degree impact angle. The third version of the instrument was equipped with a dual-source/dual-detector TOF to facilitate high throughput tandem analysis of peptides through simultaneous separation, fragmentation and mass analysis, while retaining precursor ion identity in the same experimental sequence. A series of small organic molecules, model peptides and tryptic peptides from a protein digest were analyzed to demonstrate the utility of these new designs for enhanced SID performance and peptide sequencing capability. Finally, a new mobility drift cell using a periodic focusing mechanism has been designed and fabricated to replace the previous uniform field drift cell. Improvement in ion transmission has been observed in the periodic focusing drift cell instrument without sacrificing the mobility resolution.

OFDM-based WLAN systems are originally used for nearly static environment. But in the trend of user-convenience, if we want to support mobility, the most important issue is the Doppler effect caused by the object velocity. We investigate how the Doppler effect, signal-to-noise ratio (SNR) and imperfect estimation of channel impulse response (CIR) and the maximum Doppler shift fd influence the final bit error rate (BER) under the simulation environment, modified WLAN 802.11a specification. For these effects, we give some simulation results and conclusions. If CIR and df are known with the same number of multipath, we can see some phenomenon. First, the BER is dominated by AWGN noise. Second, under the same channel delay spread, the higher the object velocity is, the more serious the BER is. Third, under the same the object velocity, the more serious the BER is. If CIR is known instead of fd, under the same error percentage of fd and the same number of multipath, the lesser the velocity is the lesser the BER curve changes. If fd is known instead of CIR with the same number of multipath, the longer the channel delay spread is, the more serious the BER is.

Abstract Like the other developing countries, there was an obvious dual structural economy in the process of economic transition in PRC. There were a lot of rural surplus labor forces in the agricultural sector, and massive underemployments in the industrial sector resulted from imbalanced development policies of Chinese Communist Party (CCP) central-planning economic system. Moreover, the formation of dual structure in PRC was partly in response to differences of natural environment. The most important is that it was caused deeply political and social institutions of Chinese characteristics. With economic reform all the more, large urban-rural gap brought about rural labor mobility from rural to rural, or mobility from underdeveloped interior region to developed coastal region. In the process of mobility, social networks play key role, which provided non-native labors some employment opportunities, information and some places to stay. But the kinds of networks were strengthened by discriminations of local residents¡¦ collective exclusiveness, which resulted in rural-urban dual structure divided into two sub-structures further. People of two sub-structures exclude each other for self-benefits on the one hand, and there would be mutual actions and competitions mutually on the other hand. Labor allocation was the most easily influenced by polity, society and economy of a nation. Therefore, in the meanwhile labor mobility emerged in the geographical space or economic structure, and there would be implications of economic transitions. When we explore the differences of economic development through expression of labor mobility that was helpful to probe into institutional changes of China and to explain differences of economic development and structure between regions. Consequently, this paper makes labor mobility to be a kind of indicators to examine economic development, which would be useful for us to find diversities of innate characters of economic development between provinces of China.

Traffic congestion continues to be a growing problem for cities of all sizes in the United States. Transportation agencies in urban areas are facing the difficult challenges of providing an efficient and reliable transportation system for residents and businesses despite ever-diminishing resources. Agencies in these areas need the capability of determining the future benefits of transportation investments so they can communicate this information to the public. This capability is difficult for many agencies, especially some of the smaller ones, who may not have the resources to make these analyses without turning to expensive long-range models. This research uses readily available socio-economic, land use, and traffic congestion data from many of the Texas urban areas to create prediction models to estimate future traffic congestion levels. Many of the transportation agencies that could utilize this tool do not have the resources to deal with large complex databases. Thus, basic information such as income, employment, single family residences, or commercial properties, to name a few, is used to create the predictions models. Results from this research show that traffic congestion prediction models can be created from socio-economic and land use data. These models were created for eighteen individual Texas urban areas and several combinations of areas. Transportation agencies could use the results of this research to estimate future congestion in their respective areas.

Separations coupled to mass spectrometry (MS) are widely used for large-scale protein identification in order to reduce the adverse effects of analyte ion suppression, increase the dynamic range, and as a deconvolution technique for complex datasets typical of cellular protein complements. In this work, matrix assisted laser desorption-ionization is coupled with ion mobility (IM) separation for the analysis of biological molecules. The utility of liquid-phase separations coupled to MS lies in the orthogonality of the two separation dimensions for all analytes. The data presented in this work illustrates that IM-MS relies on the correlation between separation dimensions for different classes (either structural or chemical) of analyte ions to obtain a useful separation. For example, for a series of peptide ions of increasing mass-to-charge (m/z) a plot drift time in the IM drift cell vs. m/z increases in a near-linear fashion, but DNA or lipids having similar m/z values will have very different IM drift time-m/z relationships, thus drift time vs. m/z can be used as a qualitative tool for compound class identification. In addition, IM-MS is applied to the analysis of large peptide datasets in order to determine the peak capacity of the method for bottom-up experiments in proteomics, and it is found that IM separation increases the peak capacity of an MS-only experiment by a factor of 5-10. The population density of the appearance area for peptides is further characterized in terms of the gas-phase structural propensities for tryptic peptide ions. It is found that a small percentage (~3%) of peptide sequences form extended (i.e., helical or β-sheet type) structures in the gas-phase, thus influencing the overall appearance area for peptide ions. Furthermore, the ability of IM-MS to screen for the presence of phosphopeptides is characterized, and it is found that post translationally modified peptides populate the bottom one-half to one-third of the total appearance area for peptide ions. In general, the data presented in this work indicates that IM-MS offers dynamic range and deconvolution capabilities comparable to liquid-phase separation techniques coupled to MS on a time scale (ms) that is fully compatible to current MS, including TOF-MS, technology.

Thesis (Ph. D.)--University of Chicago, Department of Economics, 2001. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Colorado, 2001. / Includes bibliographical references.