Welcome to the repository for University of Maryland research.

The Digital Repository at the University of Maryland (DRUM) collects, preserves, and provides public access to the scholarly output of the university. Faculty and researchers can upload research products for rapid dissemination, global visibility and impact, and long-term preservation.

  • Faculty may use DRUM to fulfill the Equitable Access to Scholarly Articles Authored by University Faculty policy, and in many cases may use it to fulfill open access requirements from grant funding agencies.
  • Departments can use DRUM to publish or distribute their working papers, technical reports, or other research material.
  • DRUM also includes all UMD theses and dissertations from 2003 forward.

To learn more about DRUM, and how you can make your research openly accessible to the public, visit our DRUM policies website.

 

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Recent Submissions

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Molecular Theory of Detonation Initiation: Insight from First Principles Modeling of the Decomposition Mechanisms of Organic Nitro Energetic Materials
(MDPI, 2016-02-19) Tsyshevsky, Roman V.; Sharia, Onise; Kuklja, Maija M.
This review presents a concept, which assumes that thermal decomposition processes play a major role in defining the sensitivity of organic energetic materials to detonation initiation. As a science and engineering community we are still far away from having a comprehensive molecular detonation initiation theory in a widely agreed upon form. However, recent advances in experimental and theoretical methods allow for a constructive and rigorous approach to design and test the theory or at least some of its fundamental building blocks. In this review, we analyzed a set of select experimental and theoretical articles, which were augmented by our own first principles modeling and simulations, to reveal new trends in energetic materials and to refine known existing correlations between their structures, properties, and functions. Our consideration is intentionally limited to the processes of thermally stimulated chemical reactions at the earliest stage of decomposition of molecules and materials containing defects.
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Crystal Dislocations
(MDPI, 2016-01-06) Armstrong, Ronald W.
Crystal dislocations were invisible until the mid-20th century although their presence had been inferred; the atomic and molecular scale dimensions had prevented earlier discovery. Now they are normally known to be just about everywhere, for example, in the softest molecularly-bonded crystals as well as within the hardest covalently-bonded diamonds. The advent of advanced techniques of atomic-scale probing has facilitated modern observations of dislocations in every crystal structure-type, particularly by X-ray diffraction topography and transmission electron microscopy. The present Special Issue provides a flavor of their ubiquitous presences, their characterizations and, especially, their influence on mechanical and electrical properties.
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A 30+ Year AVHRR LAI and FAPAR Climate Data Record: Algorithm Description and Validation
(MDPI, 2016-03-22) Claverie, Martin; Matthews, Jessica L.; Vermote, Eric F.; Justice, Christopher O.
In- land surface models, which are used to evaluate the role of vegetation in the context of global climate change and variability, LAI and FAPAR play a key role, specifically with respect to the carbon and water cycles. The AVHRR-based LAI/FAPAR dataset offers daily temporal resolution, an improvement over previous products. This climate data record is based on a carefully calibrated and corrected land surface reflectance dataset to provide a high-quality, consistent time-series suitable for climate studies. It spans from mid-1981 to the present. Further, this operational dataset is available in near real-time allowing use for monitoring purposes. The algorithm relies on artificial neural networks calibrated using the MODIS LAI/FAPAR dataset. Evaluation based on cross-comparison with MODIS products and in situ data show the dataset is consistent and reliable with overall uncertainties of 1.03 and 0.15 for LAI and FAPAR, respectively. However, a clear saturation effect is observed in the broadleaf forest biomes with high LAI (>4.5) and FAPAR (>0.8) values.
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Photochemistry of the α-Al2O3-PETN Interface
(MDPI, 2016-02-29) Tsyshevsky, Roman V.; Zverev, Anton; Mitrofanov, Anatoly; Rashkeev, Sergey N.; Kuklja, Maija M.
Optical absorption measurements are combined with electronic structure calculations to explore photochemistry of an α-Al2O3-PETN interface formed by a nitroester (pentaerythritol tetranitrate, PETN, C5H8N4O12) and a wide band gap aluminum oxide (α-Al2O3) substrate. The first principles modeling is used to deconstruct and interpret the α-Al2O3-PETN absorption spectrum that has distinct peaks attributed to surface F0-centers and surface—PETN transitions. We predict the low energy α-Al2O3 F0-center—PETN transition, producing the excited triplet state, and α-Al2O3 F0-center—PETN charge transfer, generating the PETN anion radical. This implies that irradiation by commonly used lasers can easily initiate photodecomposition of both excited and charged PETN at the interface. The feasible mechanism of the photodecomposition is proposed.
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Landsat ETM+ and SRTM Data Provide Near Real-Time Monitoring of Chimpanzee (Pan troglodytes) Habitats in Africa
(MDPI, 2016-05-20) Jantz, Samuel M.; Pintea, Lilian; Nackoney, Janet; Hansen, Matthew C.
All four chimpanzee sub-species populations are declining due to multiple factors including human-caused habitat loss. Effective conservation efforts are therefore needed to ensure their long-term survival. Habitat suitability models serve as useful tools for conservation planning by depicting relative environmental suitability in geographic space over time. Previous studies mapping chimpanzee habitat suitability have been limited to small regions or coarse spatial and temporal resolutions. Here, we used Random Forests regression to downscale a coarse resolution habitat suitability calibration dataset to estimate habitat suitability over the entire chimpanzee range at 30-m resolution. Our model predicted habitat suitability well with an r2 of 0.82 (±0.002) based on 50-fold cross validation where 75% of the data was used for model calibration and 25% for model testing; however, there was considerable variation in the predictive capability among the four sub-species modeled individually. We tested the influence of several variables derived from Landsat Enhanced Thematic Mapper Plus (ETM+) that included metrics of forest canopy and structure for four three-year time periods between 2000 and 2012. Elevation, Landsat ETM+ band 5 and Landsat derived canopy cover were the strongest predictors; highly suitable areas were associated with dense tree canopy cover for all but the Nigeria-Cameroon and Central Chimpanzee sub-species. Because the models were sensitive to such temporally based predictors, our results are the first to highlight the value of integrating continuously updated variables derived from satellite remote sensing into temporally dynamic habitat suitability models to support near real-time monitoring of habitat status and decision support systems.