abstract / Chemistry / Doctoral / Doctor of Philosophy

Transient emission of a particle in inductively coupled plasma-atomic emission spectrometry (ICP-AES) depends on the fundamental processes of aerosol desolvation, particle vaporization and atomization, ionization, excitation and diffusion of the analyte. Ideally, the rate of the above processes can be determined from the evolution of the transient emission as the ion plume moves along the central channel of the ICP. However, the dimension of the ion plume is significantly smaller than the central channel. The signal-to-background and signal-to-noise ratios suffer when the entire channel is imaged. Deconvolution of the temporal profile is required to determine the emission intensity of the ion plume versus observation height. Small aperture can be used to locate the vertical emission position accurately, but the evolution of the plume emission is lost. In this study, a double-slit method has been developed to pin-point two vertical positions of an ion plume. An ion plume travelling along the ICP central channel produces two peaks in the temporal emission profile. The temporal evolution of emission intensity can be correlated to delineate the degree of particle vaporization at the two positions. The relative widths and separation of the two peaks in a double-peak can be used to determine the analyte diffusion rate and particle velocity in the ICP, respectively. An unicellular green algae, chlorella vulgaris, was used as the test particles. The average Mg content of the algae is equivalent to MgO particles of diameter of 265nm. The strong ionic emission at wavelength of 279.55nm was monitored using a ¼ -m monochromator equipped with a PMT detector. Method of curve fitting was used to filter out the noise with minimum distortion of the peak shape for accurate determination of peak height and peak width. The merits of curve fitting versus methods of smoothing such as moving average and Savitzky-Golay filtering will be discussed. All transient emissions from the algal cells were detected with sufficient signal-to-noise ratio using a single-slit setup with slit height of 1mm at observation height of 18 mm above the load coil and ICP forward power of 1400 W. However, using the double-slit setup, less than half of the expected double-peaks were observed. One of the peaks in the double-peak can be below the detection limit and the double-peak is lost. An innovative development of this study is that the relative sensitivity corresponding to the 2 slits can be varied to enhance the intensity of the weaker emission peak. The peak with insufficient signal-to-noise ratio for detection can be enhanced to a level above the limit of detection. The number of observed double-peaks in increased and the observed particles are more representative of the population. Two types of double-peaks are categorized according to the relative intensity of the first peak to the second peak. A computer model was used to estimate the intensity ratio of the two emission peaks at different observation position of the ICP. The experimental and theoretical ratios agree generally. The theoretical ratio also shows the bias in the population sampled by the double-slit setup. / published_or_final_version / Chemistry / Master / Master of Philosophy

This research focuses on electrothermal vaporization (ETV) as a sample introduction source for inductively coupled plasma mass spectrometry (ICPMS). ETV creates a dry plasma that causes problems when used at the high applied powers (e.g., 1.2 kW) typically employed for nebulizer-based sample introduction for certain ICPMS instruments. A secondary discharge forms in the sampling region of the spectrometer, but this effect was removed by reducing the applied power (e.g., 0.7 kW). A novel, steady state, dry aerosol introduction system was developed to permit optimization of the ICPMS settings. The device used solid NbF₅, SnBr₄ and a W filament plated with Pb to generate dry aerosols which produced ²⁸Si⁺, ⁷⁹Br⁺, ¹²⁰Sn⁺, ¹⁸⁴W⁺, and ²⁰⁸Pb⁺ that were used to optimize the ICPMS. When compared to an ICPMS optimized using a nebulizer, the dry optimized plasma produced an average enhancement of 4.5(±0.4) for 26 elements when using ETV sample introduction. The ETV produces a short (0.5-2 s) transient pulse once every 2-3 min, resulting in a sample throughput of 20-30 samples/h. To increase this throughput, a low power, low background multiplexed ETV device using carbon braids as vaporizers was developed. Oxygen ashing was demonstrated with recoveries of 96±17% for a suite of elements. Refractory elements (e.g., V and U) showed precision of greater than 25% while medium to high volatility elements were in the 10-20% range. The lifetime of the braids was limited to ca. 30 vaporizations when heated to 2,800°C. A device for coupling an ETV in parallel with a nebulizer was also designed and characterized. The device was designed to minimize the impact of the ETV's presence on nebulizer-based ICPMS performance. The ETV could be easily switched on line to provide complimentary information that may be unavailable with nebulizer sample introduction because of isobaric interference problems. For example, in a 1% HCl matrix, the detection limits for ⁵¹V⁺ (⁵¹ClO⁺ interference), ⁷⁵As⁺ (⁷⁵ArO⁺ interference) and ⁷⁸Se⁺ were found to be 0.008 ppb, 0.088 ppb, 0.063 ppb, respectively. By contrast, the nebulizer detection limits in 1% HCl for ⁵¹V⁺, ⁷⁵As and ⁷⁸Se were found to be 0.593 ppb 1.488 ppb and 1.158 ppb, respectively. / text

A detailed investigation of novel air-coupled absorbers for use in a diesel engine exhaust-driven ammonia-water absorption system operating in extreme ambient conditions was conducted. Electrically driven vapor-compression systems are under scrutiny due to the environmental impact of synthetic refrigerants and the exacerbation of electric utility loads during peak demand periods. One alternative to vapor-compression systems is the absorption heat pump that uses environmentally benign working fluids and can be driven by a variety of heat sources, including waste heat and solar thermal processes. Direct air coupling of the absorber and condenser instead of indirect hydronic coupling can reduce absorption system size, complexity, and inefficiency, but materials compatibility issues with ammonia-water and the poor heat transfer properties of air present challenges. Heat and mass transfer modeling was used to predict the performance of round-tube corrugated-fin and compact tube-array absorbers designed for a 2.64-kW absorption chiller operated in high ambient temperature (51.7°C) conditions. A single-pressure ammonia-water test facility was constructed and used in conjunction with a temperature- and humidity-controlled air-handling unit to evaluate the absorbers at design and off-design operating conditions. Absorber performance was recorded over a range of air temperatures (35-54.4°C), air flow rates (0.38-0.74 m3 s-1), inlet solution temperatures (92-102°C), concentrated solution flow rates (0.006-0.010 kg s-1), and concentrated solution concentrations (38-46%). At design conditions, round-tube corrugated-fin absorbers of 394 and 551 Fins Per Meter (FPM) demonstrated comparable performance (Q394-FPM,exp = 4.521±0.271 kW; Q551-FPM,exp = 4.680±0.260 kW), and measured heat transfer rates were 0.7-1.9% AAD higher than those predicted through modeling. The measured heat transfer rate in the prototype tube-array absorber was significantly lower than the values predicted at design conditions (Qprot,exp = 2.22±0.24 kW; Qprot,mod = 4.33 kW). Maldistribution of the two-phase flow in the tube array is the probable cause of the disparity between the prototype absorber data and model predictions. Results from this investigation can be used to guide the development of air-coupled heat and mass exchangers for compact absorption heat pumps.

A new method for automatically integrating the results of hydrodynamic models of currents in Texas bays with the National Oceanic and Atmospheric Administration’s (NOAA) in house oil spill trajectory model, the General NOAA Operational Modeling Environment (GNOME), is presented. Oil spill trajectories are predicted by inputting wind and water current forces on an initial spill in a dedicated spill trajectory model. These currents can be field measured, but in most real and meaningful cases, the current field is too spatially complex to measure with any accuracy. Instead, current fields are simulated by hydrodynamic models, whose results must then be coupled with a dedicated spill trajectory model. The newly developed automated approach based on Python scripting eliminates the present labor-intensive practice of manually coupling outputs and inputs of the separate models, which requires expert interpretation and modification of data formats and setup conditions for different models. The integrated system is demonstrated by coupling GNOME independently with TXBLEND – a 2D depth-averaged model which is currently used by the Texas Water Development Board, and SELFE – a newer 3D hydrodynamic model with turbulent wind mixing. A hypothetical spill in Galveston Bay is simulated under different conditions using both models, and a brief qualitative comparison of the results is used to raise questions that may be addressed in future work using the automated coupling system to determine the minimum modeling requirements for an advanced oil spill nowcast/forecast platform in Texas bays. / text

No description available.

Regulators of G protein signaling (RGSs) are negative regulators of G protein coupled receptors (GPCRs). Our lab has demonstrated that yeast Saccharomyces cerevisiae is a useful system to study RGS and G protein signaling. Mammalian RGSs can be expressed in yeast and favored to interact with mammalian GPCRs as well. / Based on the observation that human RGS1 causes yeast cell growth arrest, I therefore used RGS1 expressing yeast cells to screen a mouse T cell cDNA library in order to find potential interacting proteins. From the screen, I identified a mouse sphingomyelin synthase 1 (SMS1) cDNA. By using a series of different apoptotic stimuli, such as hydrogen peroxide, osmotic stress, exogenous ceramide and its precursors, high temperature etc., SMS1 expression was found to suppress cell growth arrest and prevent viability decline, indicating that SMS1 represents an anti-apoptotic protein that functions by decreasing the intracellular level of pro-apoptotic ceramide. / Gene analysis further indicated that the SMS1 gene consists of 16 exons spread over a 256kb portion of mouse chromosome 19. It is alternatively spliced to produce 4 different transcripts (SMS1alpha1, SMS1alpha2, SMS1beta and SMS1gamma) and encode 3 different proteins (SMS1alpha, SMS1beta and SMS1gamma). Notably, I found that SMS1beta protein does not interfere with SMS1alpha anti-apoptotic function, although both of these two proteins contain the protein-protein interaction domain, sterile alpha motif (SAM), at their N-terminus. / I also carried out a study to examine GPCR-RGS interactions using the yeast expression system. Our lab had noticed that there was an extra RGS5 related protein that was detected by western blot analysis in the protein extracts prepared from yeast and HEK293 cells expressing RGS5. The size of the band was approximately 2 times the molecular weight of RGS5, indicating the possibility that RGS5 forms a dimer. To further examine this hypothesis, I, therefore, performed a series of experiments, included yeast 2 hybrid assays, to demonstrate that RGS5 does interact with itself. This is the first report that RGS can form a dimer. The implications for this finding are discussed in detail.

It is well known that liquid coupling agents, which are commonly used in conventional ultrasonic testing to couple an ultrasonic transducer to a solid specimen, cause a number of problems including inconsistency in results and slowness of the inspection. This is especially true when the specimen surface is rough, such as those in field concrete structures; here the solution involves time-consuming surface preparation to polish every single point of inspection, making it impractical to inspect field structures with conventional, contact methods. To address this issue, this thesis proposes a new, fully non-contact, air-coupled measurement setup in the mid to high ultrasonic frequencies (50-150 kHz). This advanced setup and measurement technique is evaluated by calculating the signal to noise ratio for different numbers of signal averages. In addition, the effect of the lift-off distance of the transducer over the sample is also investigated. Ultrasonic waves are generated and detected in this frequency range with a sufficiently high signal to noise ratio (SNR), which enables performing a fast scan with a small number of signal averages. Using this setup, phase velocity and attenuation of Rayleigh surface waves in a concrete specimen are first measured. Then, the air coupled ultrasound technique is used to detect dicontinuities such as cracks at a concrete joint and reinforcement bars in a concrete block. Also, the capability of the proposed technique for measuring depths of surface-breaking cracks using air-coupled generated Rayleigh waves is demonstrated. Since this measurement setup directly generates Rayleigh waves, most of the disadvantages in the techniques based on the impact-echo method can be avoided and thus data processing is much simpler than that in the impact-echo based techniques. The results of the measurements show that this setup is highly promising and a big advancement towards the rapid ultrasonic nondestructive testing on large-scale field concrete structures.

Fundamental and applied aspects of ICP-MS have been investigated to gain an increased understanding of the technique and improve on its analytical capabilities. Dissociation temperatures of polyatomic ions were calculated using a double-focusing sector instrument, to obtain more reliable mass spectral data with controlled vapour introduction via a Dreschel bottle to allow accurate calculation of the ingredients in the plasma. The equilibrium temperature for the plasma, operated at 1280 W calculated using CO*, and as the thermometric probes, was c.a. 5800 - 7400 K, while using ArO* and ArC* as the thermometric probes the temperature calculated was c.a 2000 - 7000 K. Calculated dissociation temperatures were used to elucidate the site of formation of these ions. Results confirmed that strongly bound ions such as CO* and C2* were formed in the plasma whereas weakly bound ions such as ArO* and ArC* were formed in the interface region due to gross deviation of the calculated temperatures from those expected for a system in thermal equilibrium. The use of helium gas in a hexapole collision cell Attenuated the signals of ArH* Ar* ArO*, Arc*, ArCl* and Ara* allowing improved determination of ^^K*, *'Ca*, ^^e* ^^Cr*, ''As* and ^°Se*in standard solutions. The use of the hexapole collision cell also resulted in an enhancement of analyte signals due to the thermalisation of the ion beam. The ion kinetic energy of ions sampled from the plasma and those sampled from the skimmer cone were determined using a modified lens stack to assess the significance for memory effects of material deposited on the skimmer cone. The most probable kinetic energy of Be* ions sampled from the skimmer cone was found to be 2A eV, which was considerably lower than the most probable kinetic energy of Be* ions sampled from the plasma, which was found to be 9.5 eV. The low kinetic energy of the ions deposited on the skimmer cone means they will only contribute to the analytical signal under certain instrumental operating conditions. The feasibility of liquid sample introduction into a LP-ICP-MS system designed for gaseous sample introduction was investigated using a particle beam separator. The low signal was attributed to the low gas kinetic temperature of the plasma which was confirmed by the fact that the signal increased rapidly with increasing temperature of the transfer line between the particle beam separator and the LP-ICP torch. This was also supported by the fact that more volatile compounds gave mass spectra whereas less volatile compounds did not. A limit of detection of 30 mg 1'^ for chlorobenzene was achieved. Finally, silicon and phosphorus speciation was performed by HPLC coupled to sectorfield ICP-MS. Silicones ranging in molecular weight from 162 g mol'^ - 16500 g mol"^ were extracted from spiked human plasma and separated by size exclusion chromatography. Limits of detection ranged from 12 ng ml"' Si* for the 162 gmol'^ silicone to 30 ng ml'' Si* for the 16500 g mol' silicone. Organophosphate pesticides were extracted from spiked plasma and separated by reversed phase chromatography. Recoveries were between 55 - 81 %. Limits of detection were 0.9 ng ml'' P* 1.8 ng ml'' P* 1.6 ng ml"' P* and 3.0 ng ml'' P* for dichlorvos, methyl parathion, malathion and quinolphos respectively. Phosphates were extracted from various food products and separated by ion-exchange chromatography. Limits of detection were 1.0 ng ml"' P* 2.3 ng ml"' P*, and 39 ng ml"' P* for P04^", PaOy"^ and PsOio^" respectively.

No description available.