New Paths from Splay to Dynamic Optimality

Consider the task of performing a sequence of searches in a binary search tree. After each search, an algorithm is allowed to arbitrarily restructure the tree, at a cost proportional to the amount of restructuring performed. The cost of an execution is the sum of the time spent searching and the time spent optimizing those searches with restructuring operations. This notion was introduced by Sleator and Tarjan in (JACM, 1985), along with an algorithm and a conjecture. The algorithm, Splay, is an elegant procedure for performing adjustments while moving searched items to the top of the tree. The conjecture, called "dynamic optimality," is that the cost of splaying is always within a constant factor of the optimal algorithm for performing searches. The conjecture stands to this day. In this work, we attempt to lay the foundations for a proof of the dynamic optimality conjecture.Comment: An earlier version of this work appeared in the Proceedings of the Thirtieth Annual ACM-SIAM Symposium on Discrete Algorithms. arXiv admin note: text overlap with arXiv:1907.0630

Applying the Dark Target Aerosol Algorithm with Advanced Himawari Imager Observations During the KORUS-AQ Field Campaign

For nearly 2 decades we have been quantitatively observing the Earth's aerosol system from space at one or two times of the day by applying the Dark Target family of algorithms to polar-orbiting satellite sensors, particularly MODIS and VIIRS. With the launch of the Advanced Himawari Imager (AHI) and the Advanced Baseline Imagers (ABIs) into geosynchronous orbits, we have the new ability to expand temporal coverage of the traditional aerosol optical depth (AOD) to resolve the diurnal signature of aerosol loading during daylight hours. The KoreanUnited States Air Quality (KORUS-AQ) campaign taking place in and around the Korean peninsula during MayJune 2016 initiated a special processing of full-disk AHI observations that allowed us to make a preliminary adoption of Dark Target aerosol algorithms to the wavelengths and resolutions of AHI. Here,we describe the adaptation and show retrieval results from AHI for this 2-month period. The AHI-retrieved AOD is collocated in time and space with existing AErosol RObotic NETwork stations across Asia and with collocated Terra and Aqua MODIS retrievals. The new AHI AOD product matches AERONET, and the standard MODIS product does as well, and the agreement between AHI and MODIS retrieved AOD is excellent, as can be expected by maintaining consistency in algorithm architecture and most algorithm assumptions. Furthermore, we show that the new product approximates the AERONET-observed diurnal signature. Examining the diurnal patterns of the new AHI AOD product we find specific areas over land where the diurnal signal is spatially cohesive. For example, in Bangladesh the AOD in-creases by 0.50 from morning to evening, and in northeast China the AOD decreases by 0.25. However, over open ocean the observed diurnal cycle is driven by two artifacts, one associated with solar zenith angles greater than 70t hat may be caused by a radiative transfer model that does not properly represent the spherical Earth and the other artifact associated with the fringes of the 40 degree glint angle mask. This opportunity during KORUS-AQ provides encouragement to move towards an operational Dark Target algorithm for AHI. Future work will need to re-examine masking including snow mask, reevaluate assumed aerosol models for geosynchronous geometry, address the artifacts over the ocean, and investigate size parameter retrieval from the over-ocean algorithm

Remote Sensing of Spectral Aerosol Properties: A Classroom Experience

Bridging the gap between current research and the classroom is a major challenge to today s instructor, especially in the sciences where progress happens quickly. NASA Goddard Space Flight Center and the University of Maryland teamed up in designing a graduate class project intended to provide a hands-on introduction to the physical basis for the retrieval of aerosol properties from state-of-the-art MODIS observations. Students learned to recognize spectral signatures of atmospheric aerosols and to perform spectral inversions. They became acquainted with the operational MODIS aerosol retrieval algorithm over oceans, and methods for its evaluation, including comparisons with groundbased AERONET sun-photometer data

Atmospheric Chemistry Over Southern Africa

During the southern African dry season, regional haze from mixed industrial pollution, biomass burning aerosol and gases from domestic and grassland fires, and biogenic sources from plants and soils is worsened by a semi-permanent atmosphere gyre over the subcontinent. These factors were a driver of several major international field campaigns in the 1990s and early 2000s, and attracted many scientists to the region. Some researchers were interested in understanding fundamental processes governing chemistry of the atmosphere and interaction with climate change. Others found favorable conditions for evaluating satellite-derived measurements of atmospheric properties and a changing land surface. With that background in mind a workshop on atmospheric chemistry was held in South Africa. Sponsored by the International Commission for Atmospheric Chemistry and Global Pollution (ICACGP; http://www.icacgp.org/), the workshop received generous support from the South African power utility, Eskom, and the Climatology Research Group of the University of the Witwatersrand, Johannesburg, South Africa. The purpose of the workshop was to review some earlier findings as well as more recent findings on southern African climate vulnerability, chemical changes due to urbanization, land-use modification, and how these factors interact. Originally proposed by John Burrows, president of ICACGP, the workshop was the first ICACGP regional workshop to study the interaction of air pollution with global chemical and climate change. Organized locally by the University of the Witwatersrand, the workshop attracted more than 60 delegates from South Africa, Mozambique, Botswana, Zimbabwe, France, Germany, Canada, and the United States. More than 30 presentations were given, exploring both retrospective and prospective aspects of the science. In several talks, attention was focused on southern African chemistry, atmospheric pollution monitoring, and climate processes as they were studied in the field campaigns such as Transport and Atmospheric Chemistry Near the Equator-Atlantic (TRACE-A), Southern African Fire-Atmosphere Research Initiative (SAFARI-92), and Southern African Regional Science Initiative (SAFARI 2000). Since those large international efforts, satellites have matured enough to enable quantifiable measurements of regional land surface, atmosphere, and ocean. In addition, global and chemical transport models have also been advanced to incorporate various data. Thus, the timing of the workshop was right for a full-fledged re-assessment of the chemistry, physics, and socio-economical impacts caused by pollution in the region, including a characterization of sources, deposition, and feedbacks with climate change

Scanning Electron Microscopy Methodology for Study of the Pathophysiology of Calcification in Bioprosthetic Heart Valves

Scanning electron microscope (SEM) morphologic analysis combined with energy dispersive characteristic X-ray (EDX) microprobe analysis provides insight into the mechanisms associated with disease-related crystal formation in biological materials. SEM and EDX were employed in analyzing specimens which were embedded in standard fashion in glycolmethacrylate (JB-4). The specimen surfaces under electron microscope investigation resulted from microtomy used in the preparation of reference light microscope histological sections; thus histology served as a direct reference for the SEM and EDX analyses. The particular application of these methods was in the study of bioprosthetic heart valve calcification, largely responsible for clinical failure of these heart valve substitutes. To simulate the clinically observed mineralization processes, glutaraldehyde-pretreated porcine heart valve leaflets were implanted subcutaneously in rats and subsequently removed at various time intervals from 1 to 56 days. Also, to address the hypothesis that the calcification process generates crystalline materials analogous to those in bone, EDX data obtained from pure hydroxyapatite were compared with the embedded tissue results. Further, EDX results were compared with data obtained by chemical analysis of the bulk specimens to assess the validity of the electron microscope technique

Global Aerosol Optical Models and Lookup Tables for the New MODIS Aerosol Retrieval over Land

Since 2000, MODIS has been deriving aerosol properties over land from MODIS observed spectral reflectance, by matching the observed reflectance with that simulated for selected aerosol optical models, aerosol loadings, wavelengths and geometrical conditions (that are contained in a lookup table or 'LUT'). Validation exercises have showed that MODIS tends to under-predict aerosol optical depth (tau) in cases of large tau (tau greater than 1.0), signaling errors in the assumed aerosol optical properties. Using the climatology of almucantur retrievals from the hundreds of global AERONET sunphotometer sites, we found that three spherical-derived models (describing fine-sized dominated aerosol), and one spheroid-derived model (describing coarse-sized dominated aerosol, presumably dust) generally described the range of observed global aerosol properties. The fine dominated models were separated mainly by their single scattering albedo (omega(sub 0)), ranging from non-absorbing aerosol (omega(sub 0) approx. 0.95) in developed urban/industrial regions, to neutrally absorbing aerosol (omega(sub 0) approx.90) in forest fire burning and developing industrial regions, to absorbing aerosol (omega(sub 0) approx. 0.85) in regions of savanna/grassland burning. We determined the dominant model type in each region and season, to create a 1 deg. x 1 deg. grid of assumed aerosol type. We used vector radiative transfer code to create a new LUT, simulating the four aerosol models, in four MODIS channels. Independent AERONET observations of spectral tau agree with the new models, indicating that the new models are suitable for use by the MODIS aerosol retrieval

Comparison of C5 and C6 Aqua-MODIS Dark Target Aerosol Validation

We compare C5 and C6 validation to compare the C6 10 km aerosol product against the well validated and trusted aerosol product on global and regional scales. Only the 10 km aerosol product is evaluated in this study, validation of the new C6 3 km aerosol product still needs to be performed. Not all of the time series has processed yet for C5 or C6, and the years processed for the 2 products is not exactly the same (this work is preliminary!). To reduce the impact of outlier observations, MODIS is spatially averaged within 27.5 km of the AERONET site, and AERONET is temporatally averaged within 30 minutes of the MODIS overpass time. Only high quality (QA = 3 over land, QA greater than 0 over ocean) pixels are included in the mean

Developing and Diagnosing Climate Change Indicators of Regional Aerosol Optical Properties

Given the importance of aerosol particles to radiative transfer via aerosol-radiation interactions, a methodology for tracking and diagnosing causes of temporal changes in regional-scale aerosol populations is illustrated. The aerosol optical properties tracked include estimates of total columnar burden (aerosol optical depth, AOD), dominant size mode (ngstrm exponent, AE), and relative magnitude of radiation scattering versus absorption (single scattering albedo, SSA), along with metrics of the structure of the spatial field of these properties. Over well-defined regions of North America, there are generally negative temporal trends in mean and extreme AOD, and SSA. These are consistent with lower aerosol burdens and transition towards a relatively absorbing aerosol, driven primarily by declining sulfur dioxide emissions. Conversely, more remote regions are characterized by increasing mean and extreme AOD that is attributed to increased local wildfire emissions and long-range (transcontinental) transport. Regional and national reductions in anthropogenic emissions of aerosol precursors are leading to declining spatial autocorrelation in the aerosol fields and increased importance of local anthropogenic emissions in dictating aerosol burdens. However, synoptic types associated with high aerosol burdens are intensifying (becoming more warm and humid), and thus changes in synoptic meteorology may be offsetting aerosol burden reductions associated with emissions legislation