Electric-Field-Induced Resonant Spin Polarization in a Two-Dimensional Electron Gas

Electric response of spin polarization in two-dimensional electron gas with structural inversion asymmetry subjected to a magnetic field was studied by means of the linear and non-linear theory and numerical simulation with the disorder effect. It was found by Kubo linear reponse theory that an electric resonant response of spin polarization occurs when the Fermi surface is located near the crossing of two Landau levels, which is induced from the competition between the spin-orbit coupling and Zeeman splitting. The scaling behavior was investigated with a simplified two-level model by non-linear method, and the resonant peak value is reciprocally proportional to the electric field at low temperatures and to temperature for finite electric fields. Finally numerical simulation illustrated that impurity potential opens an enegy gap near the resonant point and suppresses the effect gradually with the increasing strength of disorder. This resonant effect may provide an efficient way to control spin polarization by an external electric field.Comment: 6 pages, 5 figure

In Situ Biostimulation of Uranium Reducing Microorganisms at the Old Rifle UMTRA Site

Bioremediation is a promising strategy for cleaning up heavy metal and radionuclide contamination. Nutrient or electron donor amendment is an increasingly accepted practice used to stimulate the growth of microorganisms capable of immobilizing dissolved uranium in situ, but there is scant understanding of the systematic effects of nutrient addition on indigenous microbial populations or the progress of the bioremediation. Successful implementation of metal and radionuclide bioremediation in heterogeneous environments requires an understanding of the complex microbial and geochemical interactions that influence the redox speciation and mobility of toxic metals. The major challenge in microbial ecology and biogeochemistry is to connect observed biogeochemical processes to the microbial populations responsible for carrying them out. This thesis thus investigated the effects of electron donor addition to indigenous microbial populations actively involved in uranium bioremediation. Stable Isotope Probing (SIP) technique for environmental application was developed and established. A microcosm study was designed in parallel to a field biostimulation test at the Old Rifle, UMTRA site. In the microcosm study that simulated Rifle in situ biostimulation of uranium reducing organisms, the microbial community dynamics were analyzed quantitatively and qualitatively using Phospholipid Fatty-acid Analysis (PLFA) and Denaturing Gradient Gel Electrophoresis (DGGE) analysis combined with SIP, which was modified to accommodate low biomass environmental samples. The microcosms consisted of sediment and groundwater from the Rifle, Colorado UMTRA site and activated carbon bead microbial traps (Biosep beads). 13C labeled acetate amended and non-amended microcosms were compared. Lipid analyses showed a significant biomass increase with acetate amendment, specifically monounsaturated PLFA. The data also demonstrated a community shift in acetate-amended microcosms, mirroring the observation of DGGE analysis. The bacterial community in non-amended microcosms showed notable differences from those amended with acetate. β-proteobacterial sequences dominated the non-amended community. Furthermore, 13C DNA analysis indicated that acetate treatment encouraged the growth of Gram-negative microorganisms such as Pseudomonas, Geobacter, and sulfate reducing bacteria (SRB). PLFA extracted from beads and sediment also showed uptake of the 13C-acetate, mainly in 14:0, 16:1ω7c, 16:1 ω5c, 16:0, cy17:0 and 18:1 ω7c, supporting the DNA results. Geobacter and SRB sequences were not detected until day 20, while Pseudomonas sequences were prevalent by day 5 and continued to be one of the dominant sequences retrieved. The dominance of Geobacter was much more pronounced in bead samples than in sediments. GC-IRMS analysis also demonstrated the 13C enrichment in fatty acids of i15:0, i17:0, 17:0 and 18:0 extracted from beads samples, which might be indicators of Geobacter, SRB or Gram+.The SIP technique enabled an evaluation of the taxonomic and metabolic diversity of key groups of microbes actively involved in biostimulation. The microbial monitoring in microcosms can elucidate the bacterial populations responsible for uranium reduction and may indicate that SIP using 13C-acetate added to microbial traps can provide important data on ecosystem function in the field. At Rifle, Colorado, a field-scale acetate amendment experiment was performed to stimulate in situ microbial reduction of U (VI) in groundwater. Geochemical measurements indicated reduction of iron, uranium, and sulfate, which were stimulated by acetate injection. The PCR-DGGE analysis of 16S rRNA genes revealed 15 major lineages in the bacterial domain, enriched during biostimulation. A temporal (T1, T2, and T3, T4) and spatial (B-02, M-03, M-08 and M-13) distribution of the bacterial community structure was demonstrated. The background well showed no significant community shift throughout the experiment, and was dominated by β-proteobacteria with no Geobacteraceae detected. The down-gradient monitoring wells, on the other hand, shared similar community structure with background wells before acetate injection, but exhibited significant enrichment of Geobacter and Desulfuromonas sequences during the injection. This enrichment disappeared after the injection of electron donor ceased and was replaced by sequences originating from organisms of Sulfuricurvum, SRB within δ- proteobacteria, and gram positives closely related to either Desulfotomaculum, or Clostridium. Consistent with the reducing activities determined by geochemical analysis, well M-13, furthest away from the injection gallery, appeared to be less similar with other down gradient monitoring wells in community composition. PLFA analysis indicated a similar trend in community shift and displayed an increase in monounsaturated PLFAs (indicative of Gram-negative bacteria), as well as terminally branched saturated LFAs (indicative of anaerobic sulfate reducing bacteria) relative to the background well. The data presented demonstrates the effects of biostimulation and bioreduction by addition of acetate, and lead to the conclusion that Geobacteraceae was initially responsible for enzymatic uranium reduction, but had no role afterwards. The sulfate reducers played an important role in reducing uranium and also maintaining the low concentration of uranium at the Old Rifle site. Nitrate reducers such as Sulfuricurvum bacteria may also had important part in maintaining the stability of reduced uranium by removing the subsurface nitrate. To evaluate the microorganisms responsible for uranium microbial reduction during the field experiment, Biosep beads baited with 13C labeled acetate were deployed into well boreholes and sampled when groundwater chemistry indicated metal and or sulfate reduction. Incorporation of the 13C into cellular DNA and PLFA biomarkers was examined. The 13C labeled DNA fraction demonstrated an enrichment of Geobacteraceae sequences in down gradient monitoring wells. Geobacter sequences dominated in wells approximately 3.7 meters from the injection gallery. Further down gradient, sequences belonging to Desulfuromonas increased. Pseudomonas sequence was also found to be stimulated. PLFA profiling of activated carbon beads suspended in the monitoring wells showed the incorporation of 13C into the bacterial cellular lipids, particularly the 16:1ω7c. A comparison among groundwater, sediment, and biotraps was performed, which indicated that the biotraps captivated the key populations of both groundwater and sediment but are probably more representative of the groundwater. The research presented in this thesis demonstrates the importance of metal reduction and sulfate reduction in stimulated uranium immobilization, also expands our knowledge of quantitatively important iron and sulfate reducing bacteria in uranium contaminated subsurface environment. The direct introduction of 13C labeled substrates into ecosystems, coupled with DNA and PLFA analyses, which combine detailed taxonomic description with a quantitative measure of metabolic diversity allowed detection and definition of the metabolically active subset of the microbial community. This study provides an effective technique and experimental model to identify particular microbial populations involved in a desired process. Future research may explore whether the sediment or groundwater has even greater diversity of uranium reducing populations than those we have identified. More focused study on sulfate reducers are needed to shed light on their involvement in uranium reduction, either biotic or abiotic, or both

2-(Carboxy­methyl­sulfan­yl)pyridine-3-carboxylic acid monohydrate

The title compound, C8H7NO4S·H2O, was obtained by reaction of 2-mercaptopyridine-3-carboxylic acid with chloro­acetic acid. In the mol­ecular structure, the dihedral angle between the two least-squares planes defined by the pyridine ring and the carb­oxy group is 8.32 (9)°. The carboxy­methyl­sulfanyl group makes a torsion angle of 82.64 (12)° with the pyridine ring. An intra­molecular O—H⋯N hydrogen bond between the acidic function of the carboxy­methyl­sulfanyl group and the pyridine N atom stabilizes the conformation, whereas inter­molecular O—H⋯O hydrogen bonding with the uncoordinated water mol­ecules is responsible for packing of the structure, leading to chains propagating in [001]

Self-organization and phase transition in financial markets with multiple choices

Market confidence is essential for successful investing. By incorporating multi-market into the evolutionary minority game, we investigate the effects of investor beliefs on the evolution of collective behaviors and asset prices. When there exists another investment opportunity, market confidence, including overconfidence and under-confidence, is not always good or bad for investment. The roles of market confidence is closely related to market impact. For low market impact, overconfidence in a particular asset makes an investor become insensitive to losses and a delayed strategy adjustment leads to a decline in wealth, and thereafter, one's runaway from the market. For high market impact, under-confidence in a particular asset makes an investor over-sensitive to losses and one's too frequent strategy adjustment leads to a large fluctuation in asset prices, and thereafter, a decrease in the number of agents. At an intermediate market impact, the phase transition occurs. No matter what the market impact is, an equilibrium between different markets exists, which is reflected in the occurrence of similar price fluctuations in different markets. A theoretical analysis indicates that such an equilibrium results from the coupled effects of strategy updating and shift in investment. The runaway of the agents trading a specific asset will lead to a decline in the asset price volatility and such a decline will be inhibited by the clustering of the strategies. A uniform strategy distribution will lead to a large fluctuation in asset prices and such a fluctuation will be suppressed by the decrease in the number of agents in the market. A functional relationship between the price fluctuations and the numbers of agents is found

How Much Can VR Improve Spatial Experience? - A Case Study with a Commercial Building Project

With the development of Industry 4.0 and the impact of the COVID-19 epidemic, the global construction industry has undergone a rapid digital transformation, pushing the development of building information modeling (BIM), virtual reality (VR), augmented reality (AR) and mixed reality (MR) technologies towards greater maturity. However, from the perspective of building developers and end users, does VR technology have any benefit for complex building projects? What are users' acceptance and evaluation on VR emerging technology? After constructing a VR simulation navigation system for an actual commercial building project, this study investigated and compared the differences between using the VR system and the traditional navigation system in the four dimensions of the technology acceptance model. The results showed that the subjects generally believed that the VR system has significant benefits in terms of usefulness, users’ attitude, and users’ intention, however, there is still room for improvement in the perceived ease of use. Moreover, feedback from developers supported the benefits of the VR technology validated the system effectiveness. Hence, VR and BIM technologies are recommended to be effectively integrated, in order to enhance the integrity of industrial applications and establish a new design communication and collaboration model for the architecture, engineering, construction, and facility management industry

How Much Can VR Improve Spatial Experience? - A Case Study with a Commercial Building Project

With the development of Industry 4.0 and the impact of the COVID-19 epidemic, the global construction industry has undergone a rapid digital transformation, pushing the development of building information modeling (BIM), virtual reality (VR), augmented reality (AR) and mixed reality (MR) technologies towards greater maturity. However, from the perspective of building developers and end users, does VR technology have any benefit for complex building projects? What are users' acceptance and evaluation on VR emerging technology? After constructing a VR simulation navigation system for an actual commercial building project, this study investigated and compared the differences between using the VR system and the traditional navigation system in the four dimensions of the technology acceptance model. The results showed that the subjects generally believed that the VR system has significant benefits in terms of usefulness, users’ attitude, and users’ intention, however, there is still room for improvement in the perceived ease of use. Moreover, feedback from developers supported the benefits of the VR technology validated the system effectiveness. Hence, VR and BIM technologies are recommended to be effectively integrated, in order to enhance the integrity of industrial applications and establish a new design communication and collaboration model for the architecture, engineering, construction, and facility management industry