Development and application of a portable volatile organic compound analyser

The subject of this PhD is the development and testing of a portable membrane inlet mass spectrometer (MIMS), for the in-situ measurement of volatile organic compounds (VOCs) in air. There are several types of VOC monitor available, but few are able to monitor in-situ with near real-time measurements at concentrations around or lower than ppm levels. This PhD focuses on the development of the MS-200 and demonstrates its performance in laboratory and field conditions to analysis a range of VOCs. The first chapters of this thesis describe the design considerations that led to the development of the MS-200. It also discusses the working principles of the instrument and the laboratory based performance tests that compare the performance of the MS-200 with the industry standard VOC monitor. As the MS-200 has sensitivity and detection limits down to ppb levels, it overcame the limitations of many other instruments, and enabled its use for many new applications. For example, aromatic and chlorinated hydrocarbons report detection limits of between 600ppt to 20ppb, other VOCs investigated, reported detection limits between 20 to 300ppb, low molecular weight alcohols report detection limits of 0.4 to 6ppm. However, some applications require even lower detection limits, so an alternative inlet system was developed to increase the sensitivity but at the expense of the near real-time measurement capability. Typically the alternative inlet system reduces detection limits by two orders of magnitudes compared with the standard MS-200. Subsequent sections of this thesis describe and discuss a range of real world applications for the MS-200. Most of these investigations were successful, although a number would need some further work before the MS-200 would be capable to perform such applications routinely in a commercial environment. The applications discussed include: Investigations into arson where the instrument can be used to detect remnants of accelerants used without needing to return samples to the lab, giving the potential to save both time and money; Monitoring personal exposure to benzene when refuelling a petrol car, where the MS-200 demonstrated the advantage of portable real-time monitoring. It was found that during refuelling the operator could be exposed to benzene concentrations of a few hundred ppb to 4ppm for a duration of about 3 minutes; Measuring VOC markers in human breath as a diagnostic tool for cancer and other illnesses; The use of the MS-200 as an "artificial nose" in the food quality and flavour analysis. The thesis discusses the advantages and limitations of this technology as well as providing a series of recommendations for its future development

Schroedinger Invariance from Lifshitz Isometries in Holography and Field Theory

We study non-relativistic field theory coupled to a torsional Newton-Cartan geometry both directly as well as holographically. The latter involves gravity on asymptotically locally Lifshitz space-times. We define an energy-momentum tensor and a mass current and study the relation between conserved currents and conformal Killing vectors for flat Newton-Cartan backgrounds. It is shown that flat NC space-time realizes two copies of the Lifshitz algebra that together form a Schroedinger algebra (without the central element). We show why the Schroedinger scalar model has both copies as symmetries and the Lifshitz scalar model only one. Finally we discuss the holographic dual of this phenomenon by showing that the bulk Lifshitz space-time realizes the same two copies of the Lifshitz algebra.Comment: 5 pages, modified abstract, clarifications added, typos fixed, refs update

Crystalline and Electronic Structures of Molecular Solid C50_{50}Cl10% _{10}: First-Principles Calculation

A molecular solid C$_{50}$Cl$_{10}$ with possible crystalline structures, including the hexagonal-close-packed (hcp) phase, the face-centered cubic (fcc) phase, and a hexagonal monolayer, is predicted in terms of first-principles calculation within the density functional theory. The stable structures are determined from the total-energy calculations, where the hcp phase is uncovered more stable than the fcc phase and the hexagonal monolayer in energy per molecule. The energy bands and density of states for hcp and fcc C$_{50}$Cl$_{10}$ are presented. The results show that C$_{50}$Cl% $_{10}$ molecules can form either a hcp or fcc indirect-gap band insulator or an insulating hexagonal monolayer.Comment: 5 pages, 6 figure

High-temperature signatures of quantum criticality in heavy fermion systems

We propose a new criterion for distinguishing the Hertz-Millis (HM) and the local quantum critical (LQC) mechanism in heavy fermion systems with a magnetic quantum phase transition (QPT). The criterion is based on our finding that the spin screening of Kondo ions can be completely suppressed by the RKKY coupling to the surrounding magnetic ions even without magnetic ordering and that, consequently, the signature of this suppression can be observed in spectroscopic measurements above the magnetic ordering temperature. We apply the criterion to high-resolution photoemission (UPS) measurements on CeCu$_{6-x}$Au$_{x}$ and conclude that the QPT in this system is dominated by the LQC scenario.Comment: Inveted paper, International Conference on Magnetism, ICM 2009, Karlsruhe. Published version, added discussions of the relevance of Fermi-surface fluctuations and of a structural transition near the QC

Particle acceleration due to shocks in the interplanetary field: High time resolution data and simulation results

Data were examined from two experiments aboard the Explorer 50 (IMP 8) spacecraft. The Johns Hopkins University/Applied Lab Charged Particle Measurement Experiment (CPME) provides 10.12 second resolution ion and electron count rates as well as 5.5 minute or longer averages of the same, with data sampled in the ecliptic plane. The high time resolution of the data allows for an explicit, point by point, merging of the magnetic field and particle data and thus a close examination of the pre- and post-shock conditions and particle fluxes associated with large angle oblique shocks in the interplanetary field. A computer simulation has been developed wherein sample particle trajectories, taken from observed fluxes, are allowed to interact with a planar shock either forward or backward in time. One event, the 1974 Day 312 shock, is examined in detail