This work addresses the challenges in design of heat integrated low-temperature separation processes. A novel, systematic and robust methodology is developed, which contributes to the design practice of heat-integrated separation sequence and the refrigeration system in the context of low-temperature separation processes. Moreover, the methodology exploits the interactions between the separation and refrigeration systems systematically in an integrated design context. The synthesis and optimisation of heat-integrated separation processes is complex due to the large number of design options. In this thesis, task representation is applied to the separation system to accommodate both simple and complex distillation columns. The stream conditioning processes are simulated and their associated costs are included in the overall cost of the process. Important design variables in separation systems, such as the separation sequence, type and operating conditions of the separation units (e.g. the operating pressure, feed quality and condenser type) are optimised. Various refrigeration provision strategies, such as expansion of a process stream, pure and mixed multistage refrigeration systems and cascades of multistage refrigeration cycles, are considered in the present work. A novel approach based on refrigeration system database is proposed, which overcomes the complexities and challenges of synthesis and optimisation of refrigeration systems in the context of low-temperature separation processes. The methodology optimises the key design variables in the refrigeration system, including the refrigerant composition, the number of compression stages, the refrigeration and rejection temperature levels, cascading strategy and the partition temperature in multistage cascaded refrigeration systems. The present approach has selected a matrix based approach for assessing the heat integration potentials of separation and refrigeration systems in the screening procedure. Non-isothermal streams are not considered isothermal and stream splitting and heat exchangers in series are taken into account. Moreover, heat integration of reboiler and condenser of a distillation column through an open loop heat pump system can be considered in this work. This work combines an enhanced simulated annealing algorithm with MILP optimisation method and develops a framework for simultaneously optimising different degrees of freedom in the heat integrated separation and refrigeration processes. Case studies extend the approach to the design of heat integrated separation sequences in above ambient temperature processes. The robustness of the developed framework is further demonstrated when it is utilised to design the LNG and ethylene plant fractionation trains.

A magnetic force microscope (MFM) is a special type of scanning force microscope which measures the stray field above a ferromagnetic sample with the help of a ferromagnetic cantilever. The aim of this project was to design and build a MFM head and interface it with a commercial scanning probe electronics controller with the help of an appropriate force sensor. The MFM head and the force sensor were to be designed to work at low temperatures (down to 4 K) and in high vacuum. During this work, a magnetic force microscope (MFM) head was designed. Its design is symmetrical and modular. Two dimensional views were prepared to ensure proper geometry and alignment for the various modules. Based on these views, individual parts in the various modules were manufactured and combined for the final assembly of the head. This MFM head has many essential and advanced features which were incorporated during the design process. Our MFM head has an outside diameter of 5 cm and thus has a low thermal mass. The head operates inside a 100 cm long vacuum can which is kept in a cold bath inside a superinsulated dewar. Other features of this MFM head include thermal compensation of the important parts, flexibility to use commercial MFM cantilevers and a large scan range compared to the previous designs. Some of the anticipated system specifications are: 1) room temperature scanning range of 175?? 175 ??m, 2) low temperature scanning range between 35-50 ??m, 3) smallest detectable magnetic force in the range of one pN and 4) smallest detectable magnetic force gradient in the range of 10-3 to 10 -5 N/m. This MFM head was interfaced to a commercial scanning probe electronics apparatus by designing a fiber-optic interferometer as the sensor for the detection of the cantilever deflection. The fiber-optic sensor also has features of its own such as stability, compactness and low susceptibility to noise because of all-fiber construction. With this MFM head, we hope to image many magnetic samples which were previously impossible to image at Texas A&M.

The aim of this project is to find the optimum growth conditions for growing amorphous Zn1-x-yAlxSny (x=0.02 and 0.2) films with various dopents and high transmittance in visible range. By varying substrate temperatures, working pressures, RF powers and growth modes, amorphous Zn1-x-yAlxSny films with high transmittance were successfully grown at low and room temperatures. Grazing-incident small-angle X-ray diffraction data indicates that low temperature, high working pressure, low RF power and the short deposition period are the key for growing amorphous films in which adatoms on the surface of substrate do not have enough energy for migration and constructing a better crystal structure. As a result of this inadequate energy of adatoms, clusters of grains can be observed on the surface of films by the atomic force microscope. Amorphous Zn1-x-yAlxSny films possess crystalline short range order that opens up the optical and electronic bandgap. In terms of transmittance, a blue shift in the critical transmittance and a higher transmittance in IR range are observed. The high level doping of Al and Sn in ZnO films introduces crystal disordering in films and results in amorphous films even they were grown at room temperature. X-ray absorption near edge spectrum (XANES) discovers that the doped Sn behaves as tetra-valence ions for those Zn1-x-yAlxSny films with high oxygen deficiency. All amorphous films grown in this project exhibits a very low conductivity.

We intend to study the magneto-transport properties of two dimensional electron-hole systems in the condition of ultra-low temperature and high magnetic field by SdH measurement and QHE measurement. In these samples, the SdH oscillations show a 2DEG behavior. We observed that the sample shows negative persistent photoconductivity effect at low temperature and high field under illumination. We want to compare with results before 4 years, so we change more sets of measurement. And we want to know if these samples still show the same effect after 4 years.

A magnetic force microscope (MFM) is a special type of scanning force microscope which measures the stray field above a ferromagnetic sample with the help of a ferromagnetic cantilever. The aim of this project was to design and build a MFM head and interface it with a commercial scanning probe electronics controller with the help of an appropriate force sensor. The MFM head and the force sensor were to be designed to work at low temperatures (down to 4 K) and in high vacuum. During this work, a magnetic force microscope (MFM) head was designed. Its design is symmetrical and modular. Two dimensional views were prepared to ensure proper geometry and alignment for the various modules. Based on these views, individual parts in the various modules were manufactured and combined for the final assembly of the head. This MFM head has many essential and advanced features which were incorporated during the design process. Our MFM head has an outside diameter of 5 cm and thus has a low thermal mass. The head operates inside a 100 cm long vacuum can which is kept in a cold bath inside a superinsulated dewar. Other features of this MFM head include thermal compensation of the important parts, flexibility to use commercial MFM cantilevers and a large scan range compared to the previous designs. Some of the anticipated system specifications are: 1) room temperature scanning range of 175?? 175 ??m, 2) low temperature scanning range between 35-50 ??m, 3) smallest detectable magnetic force in the range of one pN and 4) smallest detectable magnetic force gradient in the range of 10-3 to 10 -5 N/m. This MFM head was interfaced to a commercial scanning probe electronics apparatus by designing a fiber-optic interferometer as the sensor for the detection of the cantilever deflection. The fiber-optic sensor also has features of its own such as stability, compactness and low susceptibility to noise because of all-fiber construction. With this MFM head, we hope to image many magnetic samples which were previously impossible to image at Texas A&M.

In this research, a novel low temperature atmospheric pressure plasma generator is successfully developed. The developed plasma generator can generate uniform plasma discharge under the operating conditions of 5 SLM helium flow rate and 5 Watts RF power. The temperature of the plasma generator can be maintained lower than 75oC after 30 minutes of continuous operation. The low temperature property of the proposed plasma generator is feasible for the high temperature sensitive sample. Modify the polymer surface by using this plasma generator, for example, the polydimethylsiloxane. It is successfully improve the hydrophilic property, and the surface energy changed obviously. The result of ATR-FTIR detection, the variation of functional groups proved the hydrophilic property, too. Being used the plasma generator to the ion source in novel mass spectrometry. Results show that the measured ion intensity generated using the proposed plasma generator increases steadily with the increases power and increases gas flow. This confirms that this plasma generator is a good ion source in mass spectrometry and for developing a Radio Frequency Direct Analysis in Real Time (RF-DART) mass spectrometry. The blown gas signals of the chewed gum, garlic, and tobacco can be detected quickly already. The signals of the volatile compounds in the solid Chinese herbs samples can be acquired, too. Mass-spectrometer detection results reveal that the developed low-temperature AP plasma generator can directly detect the sample peaks of various samples without using complicate sample preparation processes. More importantly, this proposed analysis method will not cause the memory effect which may influence the signal peaks while analyzing sequence samples during MS operation. Keywords: Low temperature atmospheric pressure plasma; Radio Frequency Direct Analysis in Real Time(RF-DART); Mass spectrometry; Memory effect.

<p> A single electron in a quantum cyclotron provides the most precise measurement of the electron magnetic moment, given in units of the Bohr magneton by <i> g</i>/2 = 1.001 159 652 180 73 (28) [0.28 ppt]. The most precise determination of the fine structure constant comes from combining this measurement with Standard Model theory, yielding &alpha;^-1 = 137.035 999 173 (34) [0.25 ppb], limited by the experimental uncertainty of the electron <i> g</i>-value. The most stringent test of CPT symmetry in leptons comes from comparing the electron and positron magnetic moments, limited by the positron uncertainty at 4.2 ppt. A new high-stability apparatus has been built and commissioned for improved measurements of the electron and positron magnetic moments, a greatly improved test of lepton CPT symmetry, and an improved determination of the fine structure constant. These new measurements require robust positron loading from a retractable radioactive source that is small enough to avoid compromising the high-precision environment of our experiment. The design and implementation of such a scheme is a central focus of this work. Robust positron loading at a rate of 1-2 e⁺/min from a 6.5 &mu;Ci ²²Na source has been demonstrated.</p>

The metallic single electron transistor (SET) has been shown to provide charge sensitivity on the order of 10-6 e/(Hz)1/2, when operated as a charge amplifier. This makes it an ideal candidate for low-noise measurement schemes, such as monitoring nano-mechanical oscillations, or reading out the charge state of a quantum bit. The SET operates by exploiting quantum tunneling across an ‘island’ between two insulating tunnel junctions, and can be modulated by a capacitively coupled gate electrode. A metallic SET has been fabricated and characterized at low frequencies. The device was fabricated on a silicon substrate coated with a bi-layer resist, using electron beam lithography. The Al-AlOx¬-Al tunnel junctions were created using double angle evaporation. Samples were tested near 300 mK in a custom helium-3 cryostat system. Results which characterize the SET parameters and conductance behaviour were obtained, in both the superconducting and normal states. This thesis contains a discussion of the fabrication procedures and dc measurement techniques required to produce and test a single electron transistor. Relevant background theory relating to SET operation and cryogenic laboratory techniques is presented. A brief discussion of proposed future experiments using a dual gate radio frequency SET as a more sensitive amplifier is introduced. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2007-08-01 14:07:55.427

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