11,108 research outputs found
Remote Sensing of Arctic Landscape Dynamics
Thesis (Ph.D.) University of Alaska Fairbanks, 2013Amplified warming in the Arctic has likely increased the rate of landscape change and
disturbances in northern high latitude regions. Remote sensing provides a valuable tool
for assessing the spatial and temporal patterns associated with arctic landscape dynamics
over annual, decadal, and centennial time scales. In this dissertation, I focused on remote
sensing studies associated with four primary components of arctic landscape change and
disturbance: (1) permafrost coastline erosion, (2) thermokarst lake dynamics, (3) tundra
fires, and (4) using repeat airborne LiDAR for the measurement of vertical deformation
in an arctic coastal lowland landscape. By combining observations from several high
resolution satellite images for a 9 km segment of the Beaufort Sea Coast between 2008
and 2012, I demonstrated that the report of heightened erosion at the beginning of the
2000s was equaled or exceeded in every year except 2010 and that the mean annual
erosion rate was tightly coupled to the number of open water days and the number of
storms. By combining historical aerial photographs from the 1950s and 1980s with
recent high-resolution satellite imagery from the mid-2000s, I assessed the expansion and
drainage of thermokarst lakes on the northern Seward Peninsula. I found that more than
half of the lakes in the study area were expanding as a result of permafrost degradation
along their margins but that the rate of expansion was fairly consistent (0.35 and 0.39
m/yr) between the 1950s and 1980s and 1980s and mid-2000s, respectively. However, it
appeared that in a number of instances that expansion of lakes led to the lateral drainage
and that over the 55-year study period the total lake area decreased by 24%. While these studies highlight the utility of quantifying disturbance during the remotely sensed image
archive period (~1950s to present) they are inherently limited temporally. Thus, I also
demonstrated techniques in which field studies and remote sensing data could be
combined to extend the identification of landscape disturbance events that occurred prior
to the remote sensing archive. I identified two large regions indicative of past
disturbance caused by tundra fires on the North Slope of Alaska, which doubled the
delineated area of tundra fire disturbance on the North Slope over the last 100 to 130
years. I conclude the dissertation by demonstrating the utility of repeat airborne light
detection and ranging (LiDAR) data for arctic landscape change studies, in particular
vertical surface deformation, and provide momentum for going forward with this
emerging technology for remote sensing of arctic landscape dynamics. The
quantification of arctic landscape dynamics during and prior to the remote sensing
archive is important for ongoing monitoring and modeling efforts of the positive and
negative feedbacks associated with amplified Arctic climate change
The Local Labor Market Impacts of US Megafires
As we learn to sustainably coexist with wildfire, there is an urgent need to improve our understanding of its multidimensional impacts on society. To this end, we undertake a nationwide study to estimate how megafires (wildfires \u3e 100,000 acres in size) affect US labor market outcomes in communities located within the flame zone. Both year-of-fire and over-time dynamic impacts are studied between 2010â2017. We find that counties located within a megafire flame zone experience significantly lower per capita wage earnings across multiple sources of earnings data for up to two years after megafire event occurrence. We find preliminary evidence that impacts are nonlinear over megafire size. These results highlight a new dimension of megafire impacts and expand the scope of the potential costs of megafires that should be considered in benefit-cost analyses of wildfire control and suppression decisions, especially along sustainability dimensions
Global Optical Control of a Quantum Spin Chain
Quantum processors which combine the long decoherence times of spin qubits
together with fast optical manipulation of excitons have recently been the
subject of several proposals. I show here that arbitrary single- and entangling
two-qubit gates can be performed in a chain of perpetually coupled spin qubits
solely by using laser pulses to excite higher lying states. It is also
demonstrated that universal quantum computing is possible even if these pulses
are applied {\it globally} to a chain; by employing a repeating pattern of four
distinct qubit units the need for individual qubit addressing is removed. Some
current experimental qubit systems would lend themselves to implementing this
idea.Comment: 5 pages, 3 figure
The role of working memory and verbal fluency in autobiographical memory in early Alzheimerâs disease and matched controls
Retrieval of autobiographical memories (AMs) is important for âsense of selfâ. Previous research and theoretical accounts suggest that working memory (WM) and semantic and phonemic fluency abilities facilitate the hierarchical search for, and reliving of past, personal events in the mindâs eye. However, there remains a lack of consensus as to the nature of the relationships between these cognitive functions and the truly episodic aspects of AM. The present study therefore aimed to explore the associations between these variables in a sample with a wide range of cognitive abilities. The study incorporated a between-groups component, and a correlational component with multiple regression. Participants with Alzheimerâs disease (n = 10) and matched healthy controls (n = 10) were assessed on measures of semantic and episodic AM search and retrieval, auditory and spatial WM, and semantic and phonemic fluency. The AD group produced less episodic AM content compared to controls. Semantic fluency predicted episodic AM retrieval independent of age effects but there were no significant relationships between measures of phonemic fluency, WM and episodic AM. The results suggest that the ability to maintain hierarchical search of the semantic knowledge-base is important for truly episodic reliving, and interventions for people with AM impairment might therefore benefit from incorporating structured, individualised external memory-aids to facilitate AM search and retrieval
The Hadamard gate cannot be replaced by a resource state in universal quantum computation
We consider models of quantum computation that involve operations performed
on some fixed resourceful quantum state. Examples that fit this paradigm
include magic state injection and measurement-based approaches. We introduce a
framework that incorporates both of these cases and focus on the role of
coherence (or superposition) in this context, as exemplified through the
Hadamard gate. We prove that given access to incoherent unitaries (those that
are unable to generate superposition from computational basis states, e.g.
CNOT, diagonal gates), classical control, computational basis measurements, and
any resourceful ancillary state (of arbitrary dimension), it is not possible to
implement any coherent unitary (e.g. Hadamard) exactly with non-zero
probability. We also consider the approximate case by providing lower bounds
for the induced trace distance between the above operations and Hadamard
gates. To demonstrate the stability of this result, this is then extended to a
similar no-go result for the case of using Hadamard gates to exactly
implement Hadamard gates.Comment: 31 pages, 3 figures. V3 includes minor edits and a fixed referenc
A review and critique of UK housing stock energy models, modelling approaches and data sources
The UK housing stock is responsible for some 27% of national energy demand and associated carbon dioxide emissions. 80% of this energy demand is due to heating (60%) and domestic hot water (20%), the former reflecting the poor average thermal integrity of the envelope of the homes comprising this stock. To support the formulation of policies and strategies to decarbonise the UK housing stock, a large number of increasingly sophisticated Housing Stock Energy Models (HSEMs) have been developed throughout the past 25 years. After describing the sources of data and the spatio-temporal granularity with which these data are available to represent this stock, as well as the physical and social phenomena that are modelled and the range of strategies employed to do so, this paper evaluates the 29 HSEMs that have been developed and deployed in the UK. In this we consider the models' predictive accuracy, predictive sensitivity to design parameters, versatility, computational efficiency, the reproducibility of predictions and software usability as well as the models' transparency (how open they are) and modularity. We also discuss their comprehensiveness. From this evaluation, we conclude that current HSEMs are lacking in transparency and modularity, they are limited in their scope and employ simplistic models that limit their utility; in particular, relating to the modelling of heat flow and in the modelling of household behaviours relating to investment decisions and energy using practices. There is a need for an open-source and modular dynamic housing stock energy modelling platform that addresses current limitations, can be readily updated as new (e.g. housing survey) calibration data is released and be readily extended by the modelling community at large: improving upon the utilisation of scarce developmental resources. This would represent a considerable step forward in the formulation of housing stock decarbonisation policy that is informed by sound evidence
Identification of a membrane binding peptide in the envelope protein of MHV coronavirus
Coronaviruses (CoVs) are enveloped, positive sense, single strand RNA viruses that cause respiratory, intestinal and neurological diseases in mammals and birds. Following replication, CoVs assemble on intracellular membranes including the endoplasmic reticulum Golgi intermediate compartment (ERGIC) where the envelope protein (E) functions in virus assembly and release. In consequence, E potentially contains membrane-modifying peptides. To search for such peptides, the E coding sequence of Mouse Hepatitis Virus (MHV) was inspected for its amino acid conservation, proximity to the membrane and/or predicted amphipathic helices. Peptides identified in silico were synthesized and tested for membrane-modifying activity in the presence of giant unilamellar vesicles (GUVs) consisting of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), sphingomyelin and cholesterol. To confirm the presence of membrane binding peptides identified in the context of a full-length E protein, the wild type and a number of mutants in the putative membrane binding peptide were expressed in Lenti-X-293T mammalian and insect cells, and the distribution of E antigen within the expressing cell was assessed. Our data identify a role for the post-transmembrane region of MHV E in membrane binding
Modern Erosion Rates and Loss of Coastal Features and Sites, Beaufort Sea Coastline, Alaska
This study presents modern erosion rate measurements based upon vertical aerial photography captured in 1955, 1979, and 2002 for a 100 km segment of the Beaufort Sea coastline. Annual erosion rates from 1955 to 2002 averaged 5.6 m a-1. However, mean erosion rates increased from 5.0 m a-1 in 1955â79 to 6.2 m a-1 in 1979â2002. Furthermore, from the first period to the second, erosion rates increased at 60% (598) of the 992 sites analyzed, decreased at 31% (307), and changed less than ± 30 cm at 9% (87). Historical observations and quantitative studies over the past 175 years allowed us to place our erosion rate measurements into a longer-term context. Several of the coastal features along this stretch of coastline received Western place names during the Dease and Simpson expedition in 1837, and the majority of those features had been lost by the early 1900s as a result of coastline erosion, suggesting that erosion has been active over at least the historical record. Incorporation of historical and modern observations also allowed us to detect the loss of both cultural and historical sites and modern infrastructure. U.S. Geological Survey topographic maps reveal a number of known cultural and historical sites, as well as sites with modern infrastructure constructed as recently as the 1950s, that had disappeared by the early 2000s as a result of coastal erosion. We were also able to identify sites that are currently being threatened by an encroaching coastline. Our modern erosion rate measurements can potentially be used to predict when a historical site or modern infrastructure will be affected if such erosion rates persist.Cette Ă©tude prĂ©sente les mesures de taux dâĂ©rosion contemporains Ă©tablies en fonction de photographies aĂ©riennes verticales prises en 1955, en 1979 et en 2002 sur un segment de 100 km du littoral de la mer de Beaufort. Entre 1955 et 2002, les taux dâĂ©rosion annuels ont atteint 5,6 m a-1 en moyenne. Cependant, les taux dâĂ©rosion moyens se sont accrus pour passer de 5,0 m a-1 pendant les annĂ©es 1955- 1979 Ă 6,2 m a-1 dans les annĂ©es 1979 - 2002. Par ailleurs, de la premiĂšre pĂ©riode Ă la deuxiĂšme pĂ©riode, les taux dâĂ©rosion ont augmentĂ© Ă 60 % (598) des 992 sites analysĂ©s, ont diminuĂ© dans le cas de 31 % (307) des sites, et changĂ© de moins de ± 30 cm Ă 9 % (87) des sites. Les observations historiques et les Ă©tudes quantitatives recueillies au cours des 175 derniĂšres annĂ©es nous ont permis de placer nos mesures des taux dâĂ©rosion dans un contexte Ă plus long terme. Plusieurs des caractĂ©ristiques cĂŽtiĂšres le long de cette Ă©tendue du littoral ont reçu des noms dâendroits typiques de lâOuest dans le cadre de lâexpĂ©dition de Dease et Simpson en 1837, et la majoritĂ© de ces caractĂ©ristiques avaient disparu vers le dĂ©but des annĂ©es 1900 en raison de lâĂ©rosion cĂŽtiĂšre. Cela laisse donc entendre que lâĂ©rosion sâest Ă tout le moins manifestĂ©e pendant la pĂ©riode visĂ©e par les donnĂ©es historiques. GrĂące Ă lâutilisation dâobservations historiques et dâobservations contemporaines, nous avons pu dĂ©celer la perte de sites culturels et historiques de mĂȘme que dâinfrastructures modernes. Les cartes topographiques de lâU.S. Geological Survey rĂ©vĂšlent un certain nombre de sites culturels et historiques connus, ainsi que des sites dotĂ©s dâinfrastructures modernes datant des annĂ©es 1950, sites et infrastructures qui avaient disparu vers le dĂ©but des annĂ©es 2000 en raison de lâĂ©rosion cĂŽtiĂšre. Nous avons Ă©galement Ă©tĂ© en mesure de cerner des sites qui sont prĂ©sentement menacĂ©s par un littoral qui empiĂšte sur le terrain. Nos mesures des taux dâĂ©rosion contemporains pourraient Ă©ventuellement servir Ă dĂ©terminer Ă quel moment un site historique ou une infrastructure moderne sera touchĂ© advenant que des taux dâĂ©rosion similaires persistent
First cohomology for finite groups of Lie type: simple modules with small dominant weights
Let be an algebraically closed field of characteristic , and let
be a simple, simply connected algebraic group defined over .
Given , set , and let be the corresponding
finite Chevalley group. In this paper we investigate the structure of the first
cohomology group where is the
simple -module of highest weight . Under certain very mild
conditions on and , we are able to completely describe the first
cohomology group when is less than or equal to a fundamental dominant
weight. In particular, in the cases we consider, we show that the first
cohomology group has dimension at most one. Our calculations significantly
extend, and provide new proofs for, earlier results of Cline, Parshall, Scott,
and Jones, who considered the special case when is a minimal nonzero
dominant weight.Comment: 24 pages, 5 figures, 6 tables. Typos corrected and some proofs
streamlined over previous versio
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Evaluation of uncomplicated acute respiratory tract infection management in veterans: A national utilization review.
BackgroundAntibiotics are overprescribed for acute respiratory tract infections (ARIs). Guidelines provide criteria to determine which patients should receive antibiotics. We assessed congruence between documentation of ARI diagnostic and treatment practices with guideline recommendations, treatment appropriateness, and outcomes.MethodsA multicenter quality improvement evaluation was conducted in 28 Veterans Affairs facilities. We included visits for pharyngitis, rhinosinusitis, bronchitis, and upper respiratory tract infections (URI-NOS) that occurred during the 2015-2016 winter season. A manual record review identified complicated cases, which were excluded. Data were extracted for visits meeting criteria, followed by analysis of practice patterns, guideline congruence, and outcomes.ResultsOf 5,740 visits, 4,305 met our inclusion criteria: pharyngitis (n = 558), rhinosinusitis (n = 715), bronchitis (n = 1,155), URI-NOS (n = 1,475), or mixed diagnoses (>1 ARI diagnosis) (n = 402). Antibiotics were prescribed in 68% of visits: pharyngitis (69%), rhinosinusitis (89%), bronchitis (86%), URI-NOS (37%), and mixed diagnosis (86%). Streptococcal diagnostic testing was performed in 33% of pharyngitis visits; group A Streptococcus was identified in 3% of visits. Streptococcal tests were ordered less frequently for patients who received antibiotics (28%) than those who did not receive antibiotics 44%; P < .01). Although 68% of visits for rhinosinusitis had documentation of symptoms, only 32% met diagnostic criteria for antibiotics. Overall, 39% of patients with uncomplicated ARIs received appropriate antibiotic management. The proportion of 30-day return visits for ARI care was similar for appropriate (11%) or inappropriate (10%) antibiotic management (P = .22).ConclusionsAntibiotics were prescribed in most uncomplicated ARI visits, indicating substantial overuse. Practice was frequently discordant with guideline diagnostic and treatment recommendations
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