Development of High-Speed Laser Diagnostics for the Investigation of Scalar Heterogeneities.

The development of advanced engine concepts are, to a large extent, hindered by the lack of suitable multidimensional optical diagnostics that can measure heterogeneities in engines. The combustion process is a complex function of species concentration, temperature, pressure, and flow fields. Fine-tuning the combustion process for efficient combustion with low emissions therefore requires detailed knowledge of these parameters as they vary with space and time. Novel optical diagnostic techniques which probe relevant quantities can either be used to address a specific problem, as with misfires and partial burns in a spark ignition direct-injection (SIDI) stratified charge (SC) gasoline engines; to develop models, such as boundary layer temperature field measurements; or serve both purposes. For these two examples, there are currently no diagnostics which meet the needs of engine developers and modelers, which motivated the current work. Investigations of misfires and partial burns can benefit from novel and improved fuel concentration and combustion progress diagnostics. A high-speed, planar, quantitative fuel concentration diagnostic technique based on laser-induced fluorescence (LIF) of biacetyl was utilized in unison with a spark plug absorption probe to aid in the understanding of both approaches. The LIF diagnostic was improved by using a dual laser approach which increased the signal to noise ratio. Also, its ability to track flame fronts and observe outgassing from engine crevices was demonstrated. The suitability of xxii the spark plug absorption probe for use in an SIDI SG engine was demonstrated. Next, a simplified combustion progress diagnostic using LIF of hydroxyl radicals was demonstrated, which avoids the cost and complexity associated with conventional approaches. Lastly, a novel, high speed, high resolution LIF diagnostic called two color toluene thermometry was developed to quantitatively measure boundary layer temperature fields. Calibration measurements were performed in a heated jet. The diagnostics were then adapted from a two camera design to a single camera design for simplicity and used to evaluate temperature gradients in an engine boundary layer. The results provided insight into the structure of the boundary layer during different parts of the engine cycle and for different engine operation conditions.Ph.D.Mechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/91418/1/mcundy_1.pd

Detection and Measurement of Density Fluctuations Induced by a Magnetohydrodynamic Force in a Supersonic Boundary Layer

This project is producing experimental data which can define the influence of electro-magnetic fields on density fluctuations (turbulence) in a supersonic boundary layer. By investigating the behavior of density fluctuations in the boundary layer under certain conditions, this Air Force funded project will aid in the development of advanced supersonic vehicles. Experiments have been performed with nitrogen gas and air. First, gas is emitted into a M=3 wind tunnel and ionized using an RF power supply. A DC voltage is then applied to draw a transverse current in the flow. A 1.5 T magnetic field is crossed with the DC field, which results in the Lorentz force acting on the free electrons and the positive ions in the flow. The direction of the force can be upstream or downstream, depending on the experimental configuration. Inherent turbulence is modified in both conditions. An accelerating force has shown to reduce density fluctuations by 5-10%, while a decelerating force has shown to increase density fluctuations by approximately the same amount. Currently, experiments are being performed to determine the flow regime in order to supplement these results. A Laser Differential Interferometer (LDI), which I have constructed, is used to measure the density fluctuations. This device, in which a laser beam passing through the boundary layer (probe beam) is combined with a second laser beam passing through the free stream (reference beam), creates a time dependant interference signal which is a function of the average density difference between the two paths. The resulting experimental data is processed using Fourier Transform techniques.This research has been supported by the AFOSR under grant F49620-02-1-0164, Phase II SBIR grant F33615-01-C-3112 of Air Vehicles Directorate of AFRL, and by the National Science Foundation (NSF) Division of Plasma Physics

Topology of SU(N) gauge theories at T=0 and T=Tc

We calculate the topological charge density of SU(N) lattice gauge fields for values of N up to N=8. Our T=0 topological susceptibility appears to approach a finite non-zero limit at N=infinity that is consistent with earlier extrapolations from smaller values of N. Near the deconfining temperature Tc we are able to investigate separately the confined and deconfined phases, since the transition is quite strongly first order. We find that the topological susceptibility of the confined phase is always very similar to that at T=0. By contrast, in the deconfined phase at larger N there are no topological fluctuations except for rare, isolated and small instantons. This shows that as N->infinity the large-T suppression of large instantons and the large-N suppression of small instantons overlap, even at T=Tc, so as to suppress all topological fluctuations in the deconfined phase. In the confined phase by contrast, the size distribution is much the same at all T, becoming more peaked as N grows, suggesting that D(rho) is proportional to a delta function at N=infinity, centered on rho close to 1/Tc.Comment: 31 page

The deconfinement transition in SU(N) gauge theories

We investigate the properties of the deconfinement transition in SU(4) and SU(6) gauge theories. We find that it is a `normal' first order transition in both cases, from which we conclude that the transition is first order in the N->infinity limit. Comparing our preliminary estimates of the continuum values of Tc/sqrt(K) with existing values for SU(2) and SU(3) demonstrates a weak dependence on N for all values of N.Comment: 18 page

Last-mile delivery increases vaccine uptake in Sierra Leone

Less than 30% of Africans received a dose of the COVID-19 vaccine even 18 months after vaccine development. Motivated by the observation that residents of remote, rural areas of Sierra Leone faced severe access difficulties, we conducted an intervention with last-mile delivery of doses and health professionals to the most inaccessible areas, along with community mobilization. A cluster randomized controlled trial in 150 communities shows that this intervention with mobile vaccination teams increases the vaccination rate by about 26 percentage points within just 48-72 hours. Moreover, auxiliary populations visited our community vaccination points, more than doubling the number of shots administered. The additional people vaccinated per intervention site translates to an implementation cost of US$ 33 per person vaccinated. Transportation to reach remote villages accounts for a large share of total intervention costs, so bundling multiple maternal and child health interventions on the same trip would lower costs per person treated even further. Current scholarship on vaccine delivery maintains a large focus on individual behavioral issues like hesitancy, but this research demonstrates that prioritizing mobile services to overcome access difficulties faced by remote populations in developing countries can generate larger returns in terms of uptake of health services

Glueballs and k-strings in SU(N) gauge theories : calculations with improved operators

We test a variety of blocking and smearing algorithms for constructing glueball and string wave-functionals, and find some with much improved overlaps onto the lightest states. We use these algorithms to obtain improved results on the tensions of k-strings in SU(4), SU(6), and SU(8) gauge theories. We emphasise the major systematic errors that still need to be controlled in calculations of heavier k-strings, and perform calculations in SU(4) on an anisotropic lattice in a bid to minimise one of these. All these results point to the k-string tensions lying part-way between the `MQCD' and `Casimir Scaling' conjectures, with the power in 1/N of the leading correction lying in [1,2]. We also obtain some evidence for the presence of quasi-stable strings in calculations that do not use sources, and observe some near-degeneracies between (excited) strings in different representations. We also calculate the lightest glueball masses for N=2, ...,8, and extrapolate to N=infinity, obtaining results compatible with earlier work. We show that the N=infinity factorisation of the Euclidean correlators that are used in such mass calculations does not make the masses any less calculable at large N.Comment: 49 pages, 15 figure

Topology and chiral symmetry breaking in SU(N) gauge theories

We study the low-lying eigenmodes of the lattice overlap Dirac operator for SU(N) gauge theories with N=2,3,4 and 5 colours. We define a fermionic topological charge from the zero-modes of this operator and show that, as N grows, any disagreement with the topological charge obtained by cooling the fields, becomes rapidly less likely. By examining the fields where there is a disagreement, we are able to show that the Dirac operator does not resolve instantons below a critical size of about rho = 2.5 a, but resolves the larger, more physical instantons. We investigate the local chirality of the near-zero modes and how it changes as we go to larger N. We observe that the local chirality of these modes, which is prominent for SU(2) and SU(3), becomes rapidly weaker for larger N and is consistent with disappearing entirely in the limit of N -> infinity. We find that this is not due to the observed disappearance of small instantons at larger N.Comment: 41 pages, 12 figures, RevTe

The Anthropocene is a prospective epoch/series, not a geological event

The Anthropocene defined as an epoch/series within the Geological Time Scale, and with an isochronous inception in the mid-20th century, would both utilize the rich array of stratigraphic signals associated with the Great Acceleration and align with Earth System science analysis from where the term Anthropocene originated. It would be stratigraphically robust and reflect the reality that our planet has far exceeded the range of natural variability for the Holocene Epoch/Series which it would terminate. An alternative, recently advanced, time-transgressive ‘geological event’ definition would decouple the Anthropocene from its stratigraphic characterisation and association with a major planetary perturbation. We find this proposed anthropogenic ‘event’ to be primarily an interdisciplinary concept in which historical, cultural and social processes and their global environmental impacts are all flexibly interpreted within a multi-scalar framework. It is very different from a stratigraphic-methods-based Anthropocene epoch/series designation, but as an anthropogenic phenomenon, if separately defined and differently named, might be usefully complementary to it

Theta dependence of SU(N) gauge theories in the presence of a topological term

We review results concerning the theta dependence of 4D SU(N) gauge theories and QCD, where theta is the coefficient of the CP-violating topological term in the Lagrangian. In particular, we discuss theta dependence in the large-N limit. Most results have been obtained within the lattice formulation of the theory via numerical simulations, which allow to investigate the theta dependence of the ground-state energy and the spectrum around theta=0 by determining the moments of the topological charge distribution, and their correlations with other observables. We discuss the various methods which have been employed to determine the topological susceptibility, and higher-order terms of the theta expansion. We review results at zero and finite temperature. We show that the results support the scenario obtained by general large-N scaling arguments, and in particular the Witten-Veneziano mechanism to explain the U(1)_A problem. We also compare with results obtained by other approaches, especially in the large-N limit, where the issue has been also addressed using, for example, the AdS/CFT correspondence. We discuss issues related to theta dependence in full QCD: the neutron electric dipole moment, the dependence of the topological susceptibility on the quark masses, the U(1)_A symmetry breaking at finite temperature. We also consider the 2D CP(N) model, which is an interesting theoretical laboratory to study issues related to topology. We review analytical results in the large-N limit, and numerical results within its lattice formulation. Finally, we discuss the main features of the two-point correlation function of the topological charge density.Comment: A typo in Eq. (3.9) has been corrected. An additional subsection (5.2) has been inserted to demonstrate the nonrenormalizability of the relevant theta parameter in the presence of massive fermions, which implies that the continuum (a -> 0) limit must be taken keeping theta fixe

The varved succession of Crawford Lake, Milton, Ontario, Canada as a candidate Global boundary Stratotype Section and Point for the Anthropocene series

An annually laminated succession in Crawford Lake, Ontario, Canada is proposed as the Global boundary Stratotype Section and Point (GSSP) for the Anthropocene as a series/epoch with a base dated at 1950 CE. Varve couplets of organic matter capped by calcite precipitated each summer in alkaline surface waters reflect environmental change at global to local scales. Spheroidal carbonaceous particles and nitrogen isotopes record an increase in fossil fuel combustion in the early 1950s, coinciding with fallout from nuclear and thermonuclear testing—239+240Pu and 14C:12C, the latter more than compensating for the effects of old carbon in this dolomitic basin. Rapid industrial expansion in the North American Great Lakes region led to enhanced leaching of terrigenous elements by acid precipitation during the Great Acceleration, and calcite precipitation was reduced, producing thin calcite laminae around the GSSP that is marked by a sharp decline in elm pollen (Dutch Elm disease). The lack of bioturbation in well-oxygenated bottom waters, supported by the absence of fossil pigments from obligately anaerobic purple sulfur bacteria, is attributed to elevated salinities and high alkalinity below the chemocline. This aerobic depositional environment, unusual in a meromictic lake, inhibits the mobilization of 239Pu, the proposed primary stratigraphic guide for the Anthropocene