Problem of Time in Quantum Gravity

The Problem of Time occurs because the `time' of GR and of ordinary Quantum Theory are mutually incompatible notions. This is problematic in trying to replace these two branches of physics with a single framework in situations in which the conditions of both apply, e.g. in black holes or in the very early universe. Emphasis in this Review is on the Problem of Time being multi-faceted and on the nature of each of the eight principal facets. Namely, the Frozen Formalism Problem, Configurational Relationalism Problem (formerly Sandwich Problem), Foliation Dependence Problem, Constraint Closure Problem (formerly Functional Evolution Problem), Multiple Choice Problem, Global Problem of Time, Problem of Beables (alias Problem of Observables) and Spacetime Reconstruction/Replacement Problem. Strategizing in this Review is not just centred about the Frozen Formalism Problem facet, but rather about each of the eight facets. Particular emphasis is placed upon A) relationalism as an underpinning of the facets and as a selector of particular strategies (especially a modification of Barbour relationalism, though also with some consideration of Rovelli relationalism). B) Classifying approaches by the full ordering in which they embrace constrain, quantize, find time/history and find observables, rather than only by partial orderings such as "Dirac-quantize". C) Foliation (in)dependence and Spacetime Reconstruction for a wide range of physical theories, strategizing centred about the Problem of Beables, the Patching Approach to the Global Problem of Time, and the role of the question-types considered in physics. D) The Halliwell- and Gambini-Porto-Pullin-type combined Strategies in the context of semiclassical quantum cosmology.Comment: Invited Review: 26 pages including 2 Figures. This v2 has a number of minor improvements and correction

Characteristic Evolution and Matching

I review the development of numerical evolution codes for general relativity based upon the characteristic initial value problem. Progress in characteristic evolution is traced from the early stage of 1D feasibility studies to 2D axisymmetric codes that accurately simulate the oscillations and gravitational collapse of relativistic stars and to current 3D codes that provide pieces of a binary black hole spacetime. Cauchy codes have now been successful at simulating all aspects of the binary black hole problem inside an artificially constructed outer boundary. A prime application of characteristic evolution is to extend such simulations to null infinity where the waveform from the binary inspiral and merger can be unambiguously computed. This has now been accomplished by Cauchy-characteristic extraction, where data for the characteristic evolution is supplied by Cauchy data on an extraction worldtube inside the artificial outer boundary. The ultimate application of characteristic evolution is to eliminate the role of this outer boundary by constructing a global solution via Cauchy-characteristic matching. Progress in this direction is discussed.Comment: New version to appear in Living Reviews 2012. arXiv admin note: updated version of arXiv:gr-qc/050809

Measurement of neutron spectra in liquid hydrogen final report

Neutron spectrum measurement in liquid hydrogen and wate

The Gallium Anomaly

In order to test the end-to-end operations of gallium solar neutrino experiments, intense electron-capture sources were fabricated to measure the responses of the radiochemical SAGE and GALLEX/GNO detectors to known fluxes of low-energy neutrinos. Such tests were viewed at the time as a cross-check, given the many tests of $^{71}$Ge recovery and counting that had been routinely performed, with excellent results. However, the four $^{51}$Cr and $^{37}$Ar source experiments yielded rates below expectations, a result commonly known as the Ga anomaly. As the intensity of the electron-capture sources can be measured to high precision, the neutrino lines they produce are fixed by known atomic and nuclear rates, and the neutrino absorption cross section on $^{71}$Ga is tightly constrained by the lifetime of $^{71}$Ge, no simple explanation for the anomaly has been found. To check these calibration experiments, a dedicated experiment BEST was performed, utilizing a neutrino source of unprecedented intensity and a detector optimized to increase statistics while providing some information on counting rate as a function of distance from the source. The results BEST obtained are consistent with the earlier solar neutrino calibration experiments, and when combined with those measurements, yield a Ga anomaly with a significance of approximately $4\sigma$, under conservative assumptions. But BEST found no evidence of distance dependence and thus no explicit indication of new physics. In this review we describe the extensive campaigns carried out by SAGE, GALLEX/GNO, and BEST to demonstrate the reliability and precision of their experimental procedures, including $^{71}$Ge recovery, counting, and analysis. We also describe efforts to define uncertainties in the neutrino capture cross section. With the results from BEST, an anomaly remains.Comment: Invited submission to Progress in Particle and Nuclear Physic

Re-evaporation nuclei and evaporation in a Wilson cloud chamber

Experimental techniques are developed for observing droplet evaporation in the submicroscopic size range. An expansion-compression cloud chamber with an atmosphere of tank helium saturated with water vapor is employed. This work was undertaken with the aim of examining submicroscopic droplet behavior and the existence of re-evaporation nuclei, a form of memory effect. The theories of evaporation and nucleation on submicroscopic drop residues were re-examined, and alterations which appear to be consistent with the results of this work were incorporated into the evaporation theory. The observed continually decreasing evaporation rate with diminishing droplet size confirms the existence of re-evaporation nuclei, but these observed terminal evaporation rates appear to be too small to be compatible with existing theory. The results do support the viewpoint that surface effects predominate in controlling the terminal rate of evaporation. When the critical supersaturations required for renucleation on the residues were analyzed with Fletcher\u27s heterogeneous nucleation theory by assuming a value for m, the experimental points agreed well with theory which postulated that the evaporation coefficient varied directly as the area of the drop after the drop reached a certain size. It appears that this work could lead to a verification of Fletcher\u27s heterogeneous nucleation theory, providing that the drop contaminant(s) can be determined and an independent measurement of size can be made. An independent mobility measurement was attempted, but yielded null results. These results are consistent with the existence of an insoluble surface layer on the drop. Such a layer is consistent with sizes determined by using Fletcher\u27s heterogeneous nucleation theory for values of m less than 0.95. Calculations which assumed the drops to be pure water predicted complete evaporation in 0.37 seconds after the beginning of the cloud chamber compression. The experimental results indicate that the drops approach a stable size. Determination of radii with the Kelvin equation for pure water yielded mean radii of 112 Å and 91 Å for respective times of 0.57 and 0.88 seconds after the beginning of the compression. Evaporation theory, assuming the presence of a solute in the drop, predicts a stable size for the drop in 0.38 seconds. Experimental results disagree by showing a finite evaporation rate much later in the compression. The Kelvin equation, amended for solute content, predicts mean drop radii of about 70 Å and 60 Å for the respective times 0.57 and 0.88 seconds. Corresponding radii determination using Fletcher\u27s heterogeneous nucleation theory for an assumed m = 0.95 yielded radii of 80 Å and 218 Å respectively. These latter values are consistent with the null result of the mobility experiment --Abstract, pages ii-iv

DEVELOPMENT OF PROTEIN DISPLAY SYSTEMS AND GENETIC TOOLS FOR SPORE-FORMING BACTERIA

One major area of synthetic biology is to engineer microbial cells and subcellular systems for diverse applications including biosynthesis, biocatalysis, therapeutics, drug delivery, and bioremediation. For most applications, robust cellular systems are preferred for longer activity half-life and resistance to harsh environments. Two projects related to robust cellular systems involving Gram-positive bacteria are presented in this work. One is to develop thermostable genetic reporters for Geobacilli species and the other is to display an enzyme on the Bacillus subtilis spore surface to enhance its robustness and present an alternative to purified enzymes for industrial applications. Bacillus subtilis and Geobacillus thermoglucosidans are gram-positive, spore-forming bacteria. They secrete many proteins used industrially for the production of paper, food, textiles, chemicals, medicine, and cosmetics. Since G. thermoglucosidans is thermostable with an optimal growth temperature of 60ºC, its secreted proteins are also thermostable which proves advantageous for a variety of industrial applications. Additionally, a strain of G. thermoglucosidans has been used for the production of ethanol from biomass. Unfortunately the inner workings of G. thermoglucosidans are still poorly understood and a genetic toolkit is necessary to better discover how to improve them via genetic engineering for industrial use. Important components of this toolkit are genetic reporters which allow for the analysis of gene expression in G. thermoglucosidans. Fluorescent proteins are commonly used reporters for other bacterial species due to their easily observed and readily measured signal, however no thermostable fluorescent proteins have been shown to be functional in Geobacillus. Seven different fluorescent proteins including mCherry, Venus, GFP, sfGFP, GFPmut3, mCherry (Gt), and Venus (Gt) were tested for stability and functionality in Geobacillus thermoglucosidans. Venus (Gt) and mCherry (Gt) were codon optimized for this bacterium with the goal of increasing expression level and thus improving the fluorescence signal. The fluorescence intensity of each fluorescent protein expressed in G. thermoglucosidans was measured after several hours of bacterial growth at 50ºC and 60ºC. Venus, mCherry, Venus (Gt), mCherry (Gt), and sfGFP all had signal when expressed in G. thermoglucosidans at 50ºC and sfGFP had signal at 60ºC. Therefore, fluorescent reporter proteins in three different colors were found to be functional in G. thermoglucosidans. This will further genetic engineering of the species for thermostable protein production, bioremediation, and biofuel production. Bacillus subtilis is Generally Regarded as Safe (GRAS) by the FDA and amenable toward genetic manipulation. Thus it has been engineered for the production of many heterologous proteins. Oftentimes, proteins secreted by bacteria are purified for industrial use. However, protein purification is expensive and time-consuming and long-term storage of purified proteins requires extremely low temperatures (-20ºC). B. subtilis spores have been used to immobilize a variety of proteins for vaccines, biosensors, and bioremediation applications. Spore surface display eliminates the need for purification and provides a way to easily separate proteins from the final product if necessary. A novel and thermostable laccase, a copper-containing oxidase, was isolated and purified from G. thermoglucosidans. It can be used to degrade lignin and a variety of phenolic compounds and thus has applications for the production of paper, textiles, food, and biofuel. This laccase was isolated, characterized, and immobilized on the surface of B. subtilis spores. The purified and spore displayed laccase were tested for heat stability and catalytic function. The purified laccase showed high activity toward 2,6-dimethoxyphenol (2,6-DMP) and moderate activity toward veratryl alcohol and 2,2′-Azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) while the spore displayed laccase showed high activity toward 2,6-DMP. The purified laccase was considerably more heat stable than a commonly used fungal laccase. The spore displayed laccase was also found to be heat stable with a half-life of about 6 hours at 80ºC. The binding affinity of the immobilized laccase for the substrate 2,6-DMP was virtually the same as that of the purified laccase, plus the immobilized laccase showed solid activity. These results show that spore surface display of proteins is a promising, more inexpensive alternative to purifying proteins for industrial use

Chiral gauge theories and their applications

This thesis is concerned with so called chiral gauge theories, also known as self dual gauge theories. In particular, the aim of this thesis to investigate the role that chiral gauge theories play in duality symmetries in lower dimensions through dimensional reduction. Chapter one serves as an introduction to the notions of duality in field and string theory. The problems of formulating well defined actions for self-dual gauge theories are introduced as well as a brief presentation of the different approaches used to over come these problems. Chapter two introduces dimensional reduction and demonstrates how duality symmetries arise from the dimensional reduction of self-dual theories in a variety of dimensions and on different compact spaces. Examples are presented where the couplings of the resulting theories are calculated explicitly in terms of the geometrical data of the compact space. The duality generators acting on these couplings are also calculated explicitly and related to the geometry/topology of the compact space. Chapter three deals with the idea of duality manifest actions and their relation to the self-dual theories in higher dimensions. Non-linear Born-Infeld type actions are introduced and again dimensional reduction is shown to play a role in the duality of the Born-Infeld action. This leads to a duality manifest version of the Born-Infeld action. Chapter four describes perhaps the main application of this thesis. The effective action of the M-theory five brane wrapped on a torus is identified with the effective action of the IIB D-3 brane dimensionally reduced on a circle (after some appropriate world volume dualizations). The IIB S-duality then arises as a result of the modular symmetry of the torus. The final chapter contains a brief summary and a hint of further directions for research that were outside the scope of this thesis

High-throughput microfluidic assay devices for culturing of soybean and microalgae and microfluidic electrophoretic ion nutrient sensor

In the past decade, there are significant challenges in agriculture because of the rapidly growing global population. Meanwhile, microfluidic devices or lab-on-a-chip devices, which are a set of micro-structure etch or molded into glass, silicon wafer, PDMS, or other materials, have been rapidly developed to achieve features, such as mix, separate, sort, sense, and control biochemical environment. The advantages of microfluidic technologies include high-throughput, low cost, precision control, and highly sensitive. In particular, they have offered promising potential for applications in medical diagnosis, drug discovery, and gene sequencing. However, the potential of microfluidic technologies for application in agriculture is far from being developed. This thesis focuses on the application of microfluidic technologies in agriculture. In this thesis, three different types of microfluidic systems were developed to present three approaches in agriculture investigation. Firstly, this report a high throughput approach to build a steady-state discrete relative humidity gradient using a modified multi-well plate. The customized device was applied to generate a set of humidity conditions to study the plant-pathogen interaction for two types of soybean beans, Williams and Williams 82. Next, a microfluidic microalgal bioreactor is presented to culture and screen microalgae strains growth under a set of CO2 concentration conditions. C. reinhardtii strains CC620 were cultured and screened in the customized bioreactor to validate the workability of the system. Growth rates of the cultured strain cells were analyzed under different CO2 concentrations. In addition, a multi-well-plate-based microalgal bioreactor array was also developed to do long-term culturing and screening. This work showed a promising microfluidic bioreactor for in-line screening based on microalgal culture under different CO2 concentrations. Finally, this report presents a microchip sensor system for ions separation and detection basing electrophoresis. It is a system owning high potential in various ions concentration analysis with high specificity and sensitivity. In addition, a solution sampling system was developed to extract solution from the soil. All those presented technologies not only have advantages including high-throughput, low cost, and highly sensitive but also have good extensibility and robustness. With a simple modification, those technologies can be expanded to different application areas due to experimental purposes. Thus, those presented microfluidic technologies provide new approaches and powerful tools in agriculture investigation. Furthermore, they have great potential to accelerate the development of agriculture