A quantum mechanical approach to establishing the magnetic field orientation from a maser Zeeman profile

Recent comparisons of magnetic field directions derived from maser Zeeman splitting with those derived from continuum source rotation measures have prompted new analysis of the propagation of the Zeeman split components, and the inferred field orientation. In order to do this, we first review differing electric field polarization conventions used in past studies. With these clearly and consistently defined, we then show that for a given Zeeman splitting spectrum, the magnetic field direction is fully determined and predictable on theoretical grounds: when a magnetic field is oriented away from the observer, the left-hand circular polarization is observed at higher frequency and the right-hand polarization at lower frequency. This is consistent with classical Lorentzian derivations. The consequent interpretation of recent measurements then raises the possibility of a reversal between the large-scale field (traced by rotation measures) and the small-scale field (traced by maser Zeeman splitting).Comment: 10 pages, 5 Figures, accepted for publication in MNRA

Control of NOx by combustion process modifications

A theoretical and experimental study was carried out to determine lower bounds of NOx emission from staged combustion of a 0.7%N #6 fuel oil. Thermodynamic and chemical kinetic calculations have shown minimum NOx emissions at fuel rich stage equivalence ratios between 1.6 and 1.8 and fuel rich stage temperatures in the range of 1900 to 2100 K (2960 to 3812 0F).In the experimental investigations the use of the MIT Combustion Research Facility permitted the detailed study of aerodynamically complex industrial-type turbulent flames in thermal and chemical environments similar to those in utility boiler furnaces. The primary stage fuel equivalence ratio, the flow and mixing pattern in the flame, the level of air preheat and the mode and quality of fuel atomization, were varied to determine their effect upon the NOx and combustibles emission.Unstaged flame studies were carried out to establish baseline data for comparison with those obtained in fuel rich-lean staged flames in which a fuel rich stage was formed near the burner and the lean stage was established by the admixing of the rest of the combustion air at a distance farther downstream.Results of the computational modeling studies have shown that in the fuel rich zone of the flame the fuel bound nitrogen compounds (FBN) can be converted to molecular nitrogen, N2, which renders the FBN innocuous for forming NOx in the lean stage of the flame.Care has to be taken however to ensure that the mixing of the secondary air with the products from the fuel rich stage does not produce high flame temperatures, in excess of 1800K (27800K) and hence "thermal NOx." The modeling studies have shown also that the FBN conversion to N2 goes through a minimum as the fuel equivalence ratio is varied and that this minimum is lower, and shifts more towards the fuel rich as the fuel rich stage temperature is raised.The experiments guided by the modeling have led to significant reduction in NOx emission; NOx was reduced from a level of 0.51 lb/106 Btu (400 ppm @ 3% 02) in a single stage flame to 0.10 lb/106 Btu (80 ppm @ 3% 02) in staged combustion when the fuel equivalence ratio in the fuel rich stage was maintained in the range of =1.5 to 1.7 (50 to 70% fuel rich), very close to that predicted from the model. The overall excess air was maintained in all experiments at EA=10%, and the combustibles (soot) emission was generally low, always well below the emission standard of 0.1 lb/106 Btu.It is considered that an important factor in the very low NOx emission levels obtained in this study is the favorable mode of secondary air admixing with the fuel rich flame gases which ensure complete combustion without any additional "thermal" NOx formation.It is emphasized that the conditions for these experiments were carefully selected to approach optimum values for the concentration and temperature history of the fuel. The tight controls of combustion aerodynamics and of the heat extraction along the flame available in the MIT Combustion Research Facility were highly favorable for the physical realization and experimental study of these flames.Due to the practical difficulties in controlling mixing and heat extraction in existing utility boiler furnaces, it is not considered realistic to expect the same low NOx and soot emission levels by combustion WINY modifications. It is thought that the results of this study should be used as guidance in design strategy for low NOx emission from the combustion of high nitrogen-bearing fuels rather than as an indication of the absolute levels of NOx which can be achieved by staged combustion techniques in utility boilers.Because of the significance of the flow and mixing pattern in the flame for both the formation of NOx and carbonaceous particulates it is recommended that in the second phase of this study the effect of mixing and heat extraction along both single and multiple staged flames be studied in more detail with a view of application of these controls to the combustion in large utility boilers

Sensitivity of the interlayer magnetoresistance of layered metals to intralayer anisotropies

Many of the most interesting and technologically important electronic materials discovered in the past two decades have two common features: a layered crystal structure and strong interactions between electrons. Two of the most fundamental questions about such layered metals concern the origin of intralayer anisotropies and the coherence of interlayer charge transport. We show that angle dependent magnetoresistance oscillations (AMRO) are sensitive to anisotropies around an intralayer Fermi surface. Hence, AMRO can be a probe of intralayer anisotropies that is complementary to angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM). However, AMRO are not very sensitive to the coherence of the interlayer transport. We illustrate this with comparisons to recent AMRO experiments on an overdoped cuprate.Comment: 7 pages, 3 figure

A comparison of methods to estimate seismic phase delays: numerical examples for coda wave interferometry

Time-shift estimation between arrivals in two seismic traces before and after a velocity perturbation is a crucial step in many seismic methods. The accuracy of the estimated velocity perturbation location and amplitude depend on this time shift. Windowed cross-correlation and trace stretching are two techniques commonly used to estimate local time shifts in seismic signals. In the work presented here we implement Dynamic Time Warping (DTW) to estimate the warping function – a vector of local time shifts that globally minimizes the misfit between two seismic traces. We compare all three methods using acoustic numerical experiments. We show that DTW is comparable to or better than the other two methods when the velocity perturbation is homogeneous and the signal-to-noise ratio is high. When the signal-to-noise ratio is low, we find that DTW and windowed cross-correlation are more accurate than the stretching method. Finally, we show that the DTW algorithm has good time resolution when identifying small differences in the seismic traces for a model with an isolated velocity perturbation. These results impact current methods that utilize not only time shifts between (multiply) scattered waves, but also amplitude and decoherence measurements

Silicon isotopic abundance toward evolved stars and its application for presolar grains

Galactic chemical evolution (GCE) is important for understanding the composition of the present-day interstellar medium (ISM) and of our solar system. In this paper, we aim to track the GCE by using the 29Si/30Si ratios in evolved stars and tentatively relate this to presolar grain composition. We used the APEX telescope to detect thermal SiO isotopologue emission toward four oxygen-rich M-type stars. Together with the data retrieved from the Herschel science archive and from the literature, we were able to obtain the 29Si/30Si ratios for a total of 15 evolved stars inferred from their optically thin 29SiO and 30SiO emission. These stars cover a range of masses and ages, and because they do not significantly alter 29Si/30Si during their lifetimes, they provide excellent probes of the ISM metallicity (or 29Si/30Si ratio) as a function of time. The 29Si/30Si ratios inferred from the thermal SiO emission tend to be lower toward low-mass oxygen-rich stars (e.g., down to about unity for W Hya), and close to an interstellar or solar value of 1.5 for the higher-mass carbon star IRC+10216 and two red supergiants. There is a tentative correlation between the 29Si/30Si ratios and the mass-loss rates of evolved stars, where we take the mass-loss rate as a proxy for the initial stellar mass or current stellar age. This is consistent with the different abundance ratios found in presolar grains. We found that older objects (up to possibly 10 Gyr old) in our sample trace a previous, lower 29Si/30Si value of about 1. Material with this isotopic ratio is present in two subclasses of presolar grains, providing independent evidence of the lower ratio. Therefore, the 29Si/30Si ratio derived from the SiO emission of evolved stars is a useful diagnostic tool for the study of the GCE and presolar grains.Comment: 7 pages, 4 figure

Large extra dimensions, the galaxy power spectrum and the end of inflation

We consider the production of gravitational KK modes via cosmological photon-photon and electron-positron annihilation in models with large factorisable extra dimensions. We place constraints on this production using recent results from a joint analysis of the power spectra of the 2dF Galaxy Redshift Survey (2dFGS) and the cosmic microwave background (CMB) anisotropies. We obtain a more accurate upper limit for the temperature corresponding to matter-radiation equality and show that, even for the case of 6 extra dimensions and a fundamental scale of 1 TeV, a period of inflation is required that ends at a temperature much lower than that of the QCD phase transition.Comment: 12 pages, 2 figures, hadronic branching+typos corrected,accepted in JHE

Analytical sun synchronous low-thrust manoeuvres

Article describes analytical sun synchronous low-thrust manoeuvres

Mesothelioma mortality in Great Britain from 1968 to 2001.

BACKGROUND: The British mesothelioma register contains all deaths from 1968 to 2001 where mesothelioma was mentioned on the death certificate. AIMS: To present summary statistics of the British mesothelioma epidemic including summaries by occupation and geographical area. METHODS: Standardized mortality ratios (SMRs) were calculated for local authorities, unitary authorities and counties. Temporal trends in SMRs were also examined. Proportional mortality ratios (PMRs) were calculated using the Southampton (based on the 1980 standard occupational classification) coding scheme. Temporal trends in PMRs were also examined. RESULTS: The annual number of mesothelioma deaths has increased from 153 in 1968 to 1848 in 2001. Current deaths in males account for about 85% of the cases. The areas of West Dunbartonshire (SMR 637), Barrow-in-Furness (593), Plymouth (396) and Portsmouth (388) have the highest SMRs over the period 1981-2000. The occupations with the highest PMRs are metal plate workers (PMR 503), vehicle body builders (526), plumbers and gas fitters (413) and carpenters (388). CONCLUSIONS: These data reinforce earlier findings that geographical areas and occupations associated with high exposure to asbestos in the past continue to drive the mesothelioma epidemic in Great Britain. However, the trends over time suggest a change in the balance of risk away from traditional asbestos exposure industries to industries where one could describe the exposure as secondary, such as plumbers and gas fitters, carpenters, and electricians