On the control of a linear functional- differential equation with quadratic cost

Linear functional differential equations control with quadratic cos

Monolithically integrated active optical devices

Considerations relevant to the monolithic integration of optical detectors, lasers, and modulators with high speed amplifiers are discussed. Some design considerations for representative subsystems in the GaAs-AlGaAs and GaInAs-InP materials systems are described. Results of a detailed numerical design of an electro-optical birefringent filter for monolithic integration with a laser diode is described, and early experimental results on monolithic integration of broadband MESFET amplifiers with photoconductive detectors are reported

SDiff(2) and uniqueness of the Pleba\'{n}ski equation

The group of area preserving diffeomorphisms showed importance in the problems of self-dual gravity and integrability theory. We discuss how representations of this infinite-dimensional Lie group can arise in mathematical physics from pure local considerations. Then using Lie algebra extensions and cohomology we derive the second Pleba\'{n}ski equation and its geometry. We do not use K\"ahler or other additional structures but obtain the equation solely from the geometry of area preserving transformations group. We conclude that the Pleba\'{n}ski equation is Lie remarkable

Using Action Research to Facilitate School Improvement

This study describes a joint project between a mid-sized urban school district and local university. Specifically, district and university personnel collaborated to provide action research training for building leadership teams. A multi-method approach was used to identify the barriers and facilitators of the use of action research training as a method for teachers to create school improvement. A content analysis of the action research plans that were a summative product of the training is provided. Findings include the importance of both technical research skills and attention to the provision of time as a resource for those involved with school improvement efforts

Ethnic Identity and Acculturation of English as Second Language Learners: Implications for School Counselors

Ethnic identity and acculturation are significant issues of English as Second Language students in the intermediate grades. Research has encompassed acculturation and ethnic identity as two distinct elements that differentiate particular ethnic groups. The present study investigates acculturation and ethnic identity and their correlation across groups. This article presents a measure of ethnic identity to understand the relationships to demographic variables. The results of this research study support significant correlations between total ethnic identity of ESL students and identity achievement

Volcanic gas quantification under suboptimal conditions

Dissertation (Ph.D.) University of Alaska Fairbanks, 2023Volcanic gas emissions are challenging to quantify. Achieving high confidence in gas composition, column concentrations, and emission rates acquired using remote sensing techniques is thought to require optimal atmospheric conditions. These conditions are often not met, creating a reluctance to preform measurements under non-ideal atmospheric conditions with inherent uncertainty about how useful those measurements may be. In the case of volcanic eruptions, the hazardous nature of the volcanic plume creates an environment where it is often not safe to collect measurements. This dissertation presents three projects which aim to constrain the quantity of two specific volcanic gases, mercury (Hg) and sulfur dioxide (SO₂), released under non-ideal measurement conditions. Specifically, chapter 2 aims to constrain Hg emission during volcanic eruptions, chapter 3 aims to characterize the uncertainty in SO₂ emission rates acquired under specific non-ideal atmospheric conditions, and chapter 4 aims to improve constraints on plume altitude for scanning remote sensing measurements of SO₂ emission rates acquired from a single instrument. Ash is a potential sink of volcanically-sourced atmospheric mercury, and the concentration of particle-bound Hg may provide constraints on Hg emissions during eruptions. In Chapter 2, the Hg concentrations in 227 bulk ash samples from the Mt. Spurr (1992), Redoubt (2009), and Augustine (2006) volcanic eruptions are examined to investigate large-scale spatial, temporal, and volcanic-source trends. No significant difference in Hg concentrations is found in bulk ash by distance from the eruption source or for discrete eruptive events at each volcano, suggesting that in-plume reactions converting gaseous Hg⁰ to adsorbed Hg²⁺ are happening on timescales shorter or longer than considered in this study (minutes to hours) and any additional in-plume controls may be masked by intra-volcanic sample variability. A significant difference is found in Hg concentration in ash among volcanic sources, which indicates that specific volcanoes may emit comparatively high or low quantities of Hg. These findings allow for the calculation of minimum, first-order estimates of volcanic Hg emissions during eruption in combination with total mass estimates of ashfall deposits. Mt. Spurr is found to be a high Hg emitting volcano such that its 1992 particulate Hg emissions likely contributed substantially to the global eruptive volcanic Hg budget for that year. Based on this study, previous approaches that used long-term Hg/SO₂ mass ratios to estimate eruptive total Hg under-account for Hg emitted in explosive events, and global volcanogenic Total Hg estimates need revisiting. A large source of error in SO₂ emission rates derived from mobile differential optical absorption spectroscopy (DOAS) is the uncertainty in atmospheric light paths between the scattered sunlight and the instrument, particularly under non-ideal atmospheric conditions such as the presence of clouds beneath the volcanic plume. In Chapter 3, numerical simulations using the McArtim model are used to examine the radiative transfer associated with zenith-facing mobile DOAS traverses for scenarios where there is a cloud layer between the instrument and the volcanic plume. In total, 217 permutations of atmospheric optical conditions are considered, allowing for the determination of errors associated with atmospheric scattering. Objective criteria are also developed for selecting SO₂ baselines and plume limits for each simulated traverse. This study then applies models to a real-world dataset from the 2021 Cumbre Vieja eruption to explore the effects of ground-level haze on a measured SO₂ column densities for the volcanic plume. All modeling results find large modifications in the shape of the analyzed plume SO₂ column density versus distance curve, even under scenarios with translucent clouds. Despite modification of the plume shape, the presence of a low cloud or haze layer is typically not a large source of error in determination of the total SO₂ quantity measured over the entirety of the traverse, which suggests that fairly accurate SO₂ emission rate measurements can be obtained even under non-ideal atmospheric measurement conditions. The real-world dataset from Cumbre Vieja is found to be best explained by a layer of ground-level laze containing SO₂ and a volcanic plume located between 2 - 4 km altitude. A large source of uncertainty in SO₂ emission rates derived from scanning DOAS instruments is the cross-sectional area of the detection, which is determined from the vertical and horizontal distance of the plume from the instrument. In Chapter 4, a novel method is employed to estimate plume altitude based on modeled wind speed data and validated against available webcam imagery at Cleveland Volcano in the Aleutian Islands, Alaska. This estimated plume altitude is used to calculate SO2 emission rates from single-station campaign scanning DOAS measurements at Cleveland Volcano, Gareloi Volcano, and Korovin Volcano (Alaska) in 2019, where the instrument was deployed for several days at each site. This method is also applied to a long-term dataset of scanning SO2 measurements acquired from a permanent scanning DOAS instrument installed at Cleveland Volcano September 2022 - June 2023. It is found that the method of estimating plume altitude in the long-term dataset produces a lower emission rate and a smaller sample variance than assuming a fixed summit plume altitude. The remaining variance in the data is then interpreted to represent variability in SO₂ emissions during times of relative quiescence at each studied volcano

The filtering equations revisited

The problem of nonlinear filtering has engendered a surprising number of mathematical techniques for its treatment. A notable example is the change-of--probability-measure method originally introduced by Kallianpur and Striebel to derive the filtering equations and the Bayes-like formula that bears their names. More recent work, however, has generally preferred other methods. In this paper, we reconsider the change-of-measure approach to the derivation of the filtering equations and show that many of the technical conditions present in previous work can be relaxed. The filtering equations are established for general Markov signal processes that can be described by a martingale-problem formulation. Two specific applications are treated

The impact of the state of the troposphere on the response to stratospheric heating in a simplified GCM

Previous studies have made use of simplified general circulation models (sGCMs) to investigate the atmospheric response to various forcings. In particular, several studies have investigated the tropospheric response to changes in stratospheric temperature. This is potentially relevant for many climate forcings. Here the impact of changing the tropospheric climatology on the modeled response to perturbations in stratospheric temperature is investigated by the introduction of topography into the model and altering the tropospheric jet structure. The results highlight the need for very long integrations so as to determine accurately the magnitude of response. It is found that introducing topography into the model and thus removing the zonally symmetric nature of the model’s boundary conditions reduces the magnitude of response to stratospheric heating. However, this reduction is of comparable size to the variability in the magnitude of response between different ensemble members of the same 5000-day experiment. Investigations into the impact of varying tropospheric jet structure reveal a trend with lower-latitude/narrower jets having a much larger magnitude response to stratospheric heating than higher-latitude/wider jets. The jet structures that respond more strongly to stratospheric heating also exhibit longer time scale variability in their control run simulations, consistent with the idea that a feedback between the eddies and the mean flow is both responsible for the persistence of the control run variability and important in producing the tropospheric response to stratospheric temperature perturbations

CONVERGENCE OF AMERICAN OPTION VALUES FROM DISCRETE- TO CONTINUOUS-TIME FINANCIAL MODELS 1

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75553/1/j.1467-9965.1994.tb00059.x.pd