Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “units”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Land carbon sequestration within the conterminous United States: Regional‐ and state‐level analyses

Abstract A quantitative understanding of the rate at which land ecosystems are sequestering or losing carbon at national‐, regional‐, and state‐level scales is needed to develop policies to mitigate climate change. In this study, a new improved historical land use and land cover change data set is developed and combined with a process‐based ecosystem model to estimate carbon sources and sinks in land ecosystems of the conterminous United States for the contemporary period of 2001–2005 and over the last three centuries. We estimate that land ecosystems in the conterminous United States sequestered 323 Tg C yr −1 at the beginning of the 21st century with forests accounting for 97% of this sink. This land carbon sink varied substantially across the conterminous United States, with the largest sinks occurring in the Southeast. Land sinks are large enough to completely compensate fossil fuel emissions in Maine and Mississippi, but nationally, carbon sinks compensate for only 20% of U.S. fossil fuel emissions. We find that regions that are currently large carbon sinks (e.g., Southeast) tend to have been large carbon sources over the longer historical period. Both the land use history and fate of harvested products can be important in determining a region's overall impact on the atmospheric carbon budget. While there are numerous options for reducing fossil fuels (e.g., increase efficiency and displacement by renewable resources), new land management opportunities for sequestering carbon need to be explored. Opportunities include reforestation and managing forest age structure. These opportunities will vary from state to state and over time across the United States.

Lu, Xiaoliang↗
DOE OSTI2019

Defect‐Tailoring Mediated Electron–Hole Separation in Single‐Unit‐Cell Bi 3 O 4 Br Nanosheets for Boosting Photocatalytic Hydrogen Evolution and Nitrogen Fixation

Abstract Solar photocatalysis is a potential solution to satisfying energy demand and its resulting environmental impact. However, the low electron–hole separation efficiency in semiconductors has slowed the development of this technology. The effect of defects on electron–hole separation is not always clear. A model atomically thin structure of single‐unit‐cell Bi 3 O 4 Br nanosheets with surface defects is proposed to boost photocatalytic efficiency by simultaneously promoting bulk‐ and surface‐charge separation. Defect‐rich single‐unit‐cell Bi 3 O 4 Br displays 4.9 and 30.9 times enhanced photocatalytic hydrogen evolution and nitrogen fixation activity, respectively, than bulk Bi 3 O 4 Br. After the preparation of single‐unit‐cell structure, the bismuth defects are controlled to tune the oxygen defects. Benefiting from the unique single‐unit‐cell architecture and defects, the local atomic arrangement and electronic structure are tuned so as to greatly increase the charge separation efficiency and subsequently boost photocatalytic activity. This strategy provides an accessible pathway for next‐generation photocatalysts.

Di, Jun↗
DOE OSTI2020

Electron‐Deficient and Quinoid Central Unit Engineering for Unfused Ring‐Based A 1 –D–A 2 –D–A 1 ‐Type Acceptor Enables High Performance Nonfullerene Polymer Solar Cells with High V oc and PCE Simultaneously

Abstract Here, a pair of A 1 –D–A 2 –D–A 1 unfused ring core‐based nonfullerene small molecule acceptors (NF‐SMAs), BO2FIDT‐4Cl and BT2FIDT‐4Cl is synthesized, which possess the same terminals (A 1 ) and indacenodithiophene unit (D), coupling with different fluorinated electron‐deficient central unit (difluorobenzoxadiazole or difluorobenzothiadiazole) (A 2 ). BT2FIDT‐4Cl exhibits a slightly smaller optical bandgap of 1.56 eV, upshifted highest occupied molecular orbital energy levels, much higher electron mobility, and slightly enhanced molecular packing order in neat thin films than that of BO2FIDT‐4Cl . The polymer solar cells (PSCs) based on BT2FIDT‐4Cl:PM7 yield the best power conversion efficiency (PCE) of 12.5% with a V oc of 0.97 V, which is higher than that of BO2FIDT‐4Cl ‐based devices (PCE of 10.4%). The results demonstrate that the subtle modification of A 2 unit would result in lower trap‐assisted recombination, more favorable morphology features, and more balanced electron and hole mobility in the PM7:BT2FIDT‐4Cl blend films. It is worth mentioning that the PCE of 12.5% is the highest value in nonfused ring NF‐SMA‐based binary PSCs with high V oc over 0.90 V. These results suggest that appropriate modulation of the quinoid electron‐deficient central unit is an effective approach to construct highly efficient unfused ring NF‐SMAs to boost PCE and V oc simultaneously.

Zhang, Chao↗
DOE OSTI2013

Cone Beam Computed Tomography Image Guidance System for a Dedicated Intracranial Radiosurgery Treatment Unit

Purpose: Image guidance has improved the precision of fractionated radiation treatment delivery on linear accelerators. Precise radiation delivery is particularly critical when high doses are delivered to complex shapes with steep dose gradients near critical structures, as is the case for intracranial radiosurgery. To reduce potential geometric uncertainties, a cone beam computed tomography (CT) image guidance system was developed in-house to generate high-resolution images of the head at the time of treatment, using a dedicated radiosurgery unit. The performance and initial clinical use of this imaging system are described. Methods and Materials: A kilovoltage cone beam CT system was integrated with a Leksell Gamma Knife Perfexion radiosurgery unit. The X-ray tube and flat-panel detector are mounted on a translational arm, which is parked above the treatment unit when not in use. Upon descent, a rotational axis provides 210 Degree-Sign of rotation for cone beam CT scans. Mechanical integrity of the system was evaluated over a 6-month period. Subsequent clinical commissioning included end-to-end testing of targeting performance and subjective image quality performance in phantoms. The system has been used to image 2 patients, 1 of whom received single-fraction radiosurgery and 1 who received 3 fractions, using a relocatable head frame. Results: Images of phantoms demonstrated soft tissue contrast visibility and submillimeter spatial resolution. A contrast difference of 35 HU was easily detected at a calibration dose of 1.2 cGy (center of head phantom). The shape of the mechanical flex vs scan angle was highly reproducible and exhibited <0.2 mm peak-to-peak variation. With a 0.5-mm voxel pitch, the maximum targeting error was 0.4 mm. Images of 2 patients were analyzed offline and submillimeter agreement was confirmed with conventional frame. Conclusions: A cone beam CT image guidance system was successfully adapted to a radiosurgery unit. The system is capable of producing high-resolution images of bone and soft tissue. The system is in clinical use and provides excellent image guidance without invasive frames.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2015

Synthesis, characterizations and catalytic studies of a new two-dimensional metal−organic framework based on Co–carboxylate secondary building units

A metal–organic framework [Co{sub 3}(BDC){sub 3}(DMF){sub 2}(H{sub 2}O){sub 2}] was synthesized and structurally characterized. X-ray single crystal analysis revealed that the framework contains a 2D polymeric chain through coordination of 1,4-benzenedicarboxylic acid linker ligand to cobalt centers. The polymer crystallize in monoclinic P2{sub 1}/n space group with a=13.989(3) Å, b=9.6728(17) Å, c=16.707(3) Å, and Z=2. The polymer features a framework based on the perfect octahedral Co–O6 secondary building units. The catalytic activities of [Co{sub 3}(BDC){sub 3}(DMF){sub 2}(H{sub 2}O){sub 2}]{sub n} for olefins oxidation was conducted. The heterogeneous catalyst could be facilely separated from the reaction mixture, and reused three times without significant degradation in catalytic activity. Furthermore, no contribution from homogeneous catalysis of active species leaching into reaction solution was detected. - Graphical abstract: A metal–organic framework of [Co{sub 3}(BDC){sub 3}(DMF){sub 2}(H{sub 2}O){sub 2}] was synthesized by hydrothermal method. This 2D-periodic framework is constructed from the infinite Co–O–C secondary building units and crystallizes in the monoclinic P2{sub 1}/n space group based on Co(II)–carboxylate units. The catalytic oxidation of various olefins was effectively carried out with [Co{sub 3}(BDC){sub 3}(DMF){sub 2}(H{sub 2}O){sub 2}]{sub n} catalyst by TBHP as oxidant. - Highlights: • A metal–organic framework of [Co{sub 3}(BDC){sub 3}(DMF){sub 2}(H{sub 2}O){sub 2}] is prepared by hydrothermal method. • The [Co{sub 3}(BDC){sub 3}(DMF){sub 2}(H{sub 2}O){sub 2}]{sub n} is constructed from Co–carboxylate secondary building units. • This coordination polymer displayed high catalytic activity for olefin oxidation reactions. • The catalytic reaction is heterogeneous and catalyst can be simply separated. • The heterogeneous catalyst can be reused several times without significant loss of catalytic activity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Topologically and geometrically flexible structural units in seven new organically templated uranyl selenates and selenite–selenates

Single crystals of seven novel uranyl oxysalts of selenium with protonated methylamine molecules, [C{sub 2}H{sub 8}N]{sub 2}[(UO{sub 2})(SeO{sub 4}){sub 2}(H{sub 2}O)] (I), [C{sub 2}H{sub 8}N]{sub 2}[(UO{sub 2}){sub 2}(SeO{sub 4}){sub 3}(H{sub 2}O)] (II), [C{sub 4}H{sub 15}N{sub 3}][H{sub 3}O]{sub 0.5}[(UO{sub 2}){sub 2}(SeO{sub 4}){sub 2.93}(SeO{sub 3}){sub 0.07}(H{sub 2}O)](NO{sub 3}){sub 0.5} (III), [C{sub 2}H{sub 8}N]{sub 3}[H{sub 5}O{sub 2}][(UO{sub 2}){sub 2}(SeO{sub 4}){sub 3}(H{sub 2}O){sub 2}]{sub 2}(H{sub 2}O){sub 5} (IV), [C{sub 2}H{sub 8}N]{sub 2}[H{sub 3}O][(UO{sub 2}){sub 3}(SeO{sub 4}){sub 4}(HSeO{sub 3})(H{sub 2}O)](H{sub 2}SeO{sub 3}){sub 0.2} (V), [C{sub 4}H{sub 12}N]{sub 3}[H{sub 3}O][(UO{sub 2}){sub 3}(SeO{sub 4}){sub 5}(H{sub 2}O)] (VI), and [C{sub 2}H{sub 8}N]{sub 3}(C{sub 2}H{sub 7}N)[(UO{sub 2}){sub 3}(SeO{sub 4}){sub 4}(HSeO{sub 3})(H{sub 2}O)] (VII) have been prepared by isothermal evaporation from aqueous solutions. Their crystal structures have been solved by direct methods and their uranyl selenate and selenite–selenate units investigated using black-and-white graphs from the viewpoints of topology of interpolyhedral linkages and isomeric variations. The crystal structure of IV is based upon complex layers with unique topology, which has not been observed previously in uranyl selenates. Investigations of the statistics and local distribution of the U–O{sub br}–Se bond angles demonstrates that shorter angles associate with undulations, whereas larger angles correspond to planar areas of the uranyl selenite layers. - Graphical abstract: Crystal structures of the seven novel Se-contaning uranyl oxysalts that contain protonated organic molecules as interlayer species have been investigated from the viewpoints of topology of interpolyhedral linkages, isomeric variations and flexibility of structural units. - Highlights: • Single crystals of seven novel uranyl oxysalts were prepared by evaporation method. • The graph theory was used for investigation of topologies of structural units. • The method of orientation matrices was applied to distinguish geometrical isomers. • The flexibility of structural complexes specifies the undulation of layered structural units.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

A comparative study of the status of GSHP applications in the United States and China

Ground source heat pump (GSHP) or geothermal heat pump technology was first developed and commercially introduced in the late 1970s, and GSHP units representing approximately 3.9 million tons of cooling had been installed in the United States by 2012. Applications of GSHP technology also have grown rapidly in China since it was introduced into China in the 1990s through collaboration between the Chinese and US governments. It is estimated that by 2013, about 400 million m2 (4.3 billion ft2) of building floor space in China was heated and/or cooled by GSHP systems. Moreover, governments in both China and the United States have programs that in some way support and/or promote the use of GSHP technology. After decades of practice, both countries have accumulated abundant experience in applying GSHP technology, but both also are confronted with various challenges to rapidly deploying this technology. Under the sponsorship of the US–China Clean Energy Research Center for Building Energy Efficiency, researchers reviewed and compared the current status of GSHP applications in the United States and China, including related policies, standards, technologies, equipment, costs, market development, and barriers. Finally, based on this comparative study, future collaborations between the two countries are recommended to improve the application of the GSHP technology and fully realize its energy saving potential.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2013

Element partitioning in combustion- and gasification-based waste-to-energy units

Highlights: ► Element partitioning of waste-to-energy units by means of a substance flow analysis. ► A comparison between moving grate combustors and high temperature gasifiers. ► Classification of key elements according to their behavior during WtE processes. ► Slags and metals from waste gasifiers are completely and immediately recyclable. ► Potential reduction of amounts of solid residue to be sent to landfill disposal. - Abstract: A critical comparison between combustion- and gasification-based waste-to-energy systems needs a deep knowledge of the mass flows of materials and elements inside and throughout the units. The study collected and processed data from several moving grate conventional incinerators and high-temperature shaft gasifiers with direct melting, which are in operation worldwide. A material and substance flow analysis was then developed to systematically assess the flows and stocks of materials and elements within each waste-to-energy unit, by connecting the sources, pathways, and intermediate and final sinks of each species. The patterns of key elements, such as carbon, chloride and heavy metals, in the different solid and gaseous output streams of the two compared processes have been then defined. The combination of partitioning coefficients with the mass balances on atomic species and results of mineralogical characterization from recent literatures was used to estimate a composition of bottom ashes and slags from the two types of waste-to-energy technologies. The results also allow to quantify some of the performance parameters of the units and, in particular, the potential reduction of the amount of solid residues to be sent to final disposal.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2018

Evaluation of Feruloylated and p -Coumaroylated Arabinosyl Units in Grass Arabinoxylans by Acidolysis in Dioxane/Methanol

We report that the arabinosyl side chains of grass arabinoxylans are partially acylated by p-coumarate (pCA) and ferulate (FA). These aromatic side chains can cross-couple wall polymers resulting in modulation of cell wall physical properties. The determination of p-coumaroylated and feruloylated arabinose units has been the target of analytical efforts with trifluoroacetic acid hydrolysis the standard method to release feruloylated and p-coumaroylated arabinose units from arabinoxylans. Herein, we report on a more robust method to measure these acylated units. Acidolysis of extractive-free grass samples in a dioxane/methanol/aqueous 2 M HCl mixture provided the methyl 5-O-p-coumaroyl- and 5-O-feruloyl-l-arabinofuranoside anomers (pCA-MeAra and FA-MeAra). These conjugates were readily analyzed by liquid chromatography combined with both UV and MS detection. The method revealed the variability of the relative acylation of arabinose units by pCA or FA in grass cell walls. Finally, this methodology will permit delineation of hydroxycinnamate acylation patterns in arabinoxylans.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

The Summertime Precipitation Bias in E3SM Atmosphere Model Version 1 over the Central United States

This study analyzes the summertime precipitation bias over the Central United States and its relationship to the simulated large-scale environment and the convection scheme in the Energy Exascale Earth System Model Atmosphere Model version 1. This relationship is mainly examined in a set of short-term hindcasts initialized with realistic large-scale conditions for the summer of 2011. Besides the uniform 1° model resolution, we adopt Regionally Refined Meshes to increase the model resolution to 0.25°over the contiguous United States. Additional five-year Atmospheric Model Intercomparison Project simulations are conducted to confirm that the results from the hindcasts are consistent with the climate runs. We find that the summertime dry precipitation bias over the Great Plains and the wet bias over the Rockies cannot be reduced simultaneously by changing resolution or tuning parameters. As for the diurnal cycle, Energy Exascale Earth System Model Atmosphere Model version 1 captures the general diurnal variation of the large-scale moisture transport and the large-scale upward motion over the Central United States. However, the diurnal cycle of precipitation over the Great Plains is out of phase with the diurnal variation of the large-scale environment because the convective precipitation dominates the total precipitation and its diurnal cycle, and it does not directly respond to the local moisture convergence and the large-scale upward motion. These results reemphasize the importance of improving the coupling of the convection to the large-scale environment in reducing the summer precipitation bias over the Central United States in climate models with the resolution of ~0.25°.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

National‐Scale Assessment of Total Gaseous Mercury Isotopes Across the United States

Abstract With the 2011 promulgation of the Mercury and Air Toxics Standards by the U.S. Environmental Protection Agency, and the successful negotiation by the United Nations Environment Program of the Minamata Convention, emissions of mercury (Hg) have declined in the United States. While the declines in atmospheric Hg concentrations in North America are encouraging, linking the declines to changing domestic and global source portfolios remains challenging. To address these research gaps, the U.S. Geological Survey initiated the first national‐scale effort to establish a baseline of total gaseous mercury stable isotope values at 31 sites distributed across the United States. Results indicated that unique Hg sources, such as Hg evasion from an elemental Hg contaminated site or free tropospheric intrusions in high altitude sites, were distinguishable from background atmospheric values. Minor gradients were observed across the nation, with regions of heavy industrial activity demonstrating lower δ 202 Hg, but no consistent changes in other isotopes such as Δ 199 Hg and Δ 200 Hg were observed. Furthermore, δ 202 Hg was impacted by foliar uptake and senescence but trends varied between forested regions in the northeastern and midwestern United States. These data demonstrate regional emission sources and other environmental variables can impact total gaseous Hg (TGM) isotope values, highlighting the need to characterize atmospheric Hg isotopes over larger geographical areas to evaluate changes related to national and international Hg regulations.

Tate, Michael T.↗
DOE OSTI2024

How will future climate change impact prescribed fire across the contiguous United States?

As of 2023, the use of prescribed fire to manage ecosystems accounts for more than 50% of area burned annually across the United States. Prescribed fire is carried out when meteorological conditions, including temperature, humidity, and wind speed are appropriate for its safe and effective application. However, changes in these meteorological variables associated with future climate change may impact future opportunities to conduct prescribed fire. In this study, we combine climate projections with information on prescribed burning windows for ecoregions across the contiguous United States (CONUS) to compute the number of days when meteorological conditions allow for the safe and effective application of prescribed fire under present-day (2006–2015) and future climate (2051–2060) conditions. The resulting projections, which cover 57% of all vegetated area across the CONUS, indicate fewer days with conditions suitable for prescribed burning across ecoregions of the eastern United States due to rising maximum daily temperatures, but opportunities increase in the northern and northwestern United States, driven primarily by rising minimum temperatures and declining wind speeds.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

Implications of water constraints on electricity capacity expansion in the United States

The development of new electricity generation capacity is constrained by water resource availability. However, the sufficiency of available water resources is rarely incorporated into the planning of electricity capacity expansion in the United States. Previous studies on the implications of water constraints on US electricity generation are limited in terms of scale and robustness. Here, we extend previous studies by including physical water constraints within a state-level model of the US energy system embedded within a global integrated assessment model (GCAM-USA) that integrates both supply and demand effects under a consistent framework. We show that water constraints have two general effects across the United States: (1) to increase the cost of electricity generation, which results in slightly reduced electrification of end-use sectors, and (2) to incentivize early retirement of water-intensive technologies before the end of their designed lifetimes, while simultaneously boosting investment in less water-dependent technologies. Our results suggest that water availability constraints may cause substantial capital stock turnover and result in non-negligible economic costs for the western United States, whereas fewer impacts may be anticipated in the eastern United States. Our work emphasizes the need to integrate water availability constraints into electricity capacity planning and highlights the state-level challenges to facilitate regional strategic resource planning.

Liu, Lu↗
DOE OSTI2014

Design of voice coil motor dynamic focusing unit for a laser scanner

Laser scanning systems have been used for material processing tasks such as welding, cutting, marking, and drilling. However, applications have been limited by the small range of motion and slow speed of the focusing unit, which carries the focusing optics. To overcome these limitations, a dynamic focusing system with a long travel range and high speed is needed. In this study, a dynamic focusing unit for a laser scanning system with a voice coil motor (VCM) mechanism is proposed to enable fast speed and a wide focusing range. The VCM has finer precision and higher speed than conventional step motors and a longer travel range than earlier lead zirconium titanate actuators. The system has a hollow configuration to provide a laser beam path. This also makes it compact and transmission-free and gives it low inertia. The VCM's magnetics are modeled using a permeance model. Its design parameters are determined by optimization using the Broyden–Fletcher–Goldfarb–Shanno method and a sequential quadratic programming algorithm. After the VCM is designed, the dynamic focusing unit is fabricated and assembled. The permeance model is verified by a magnetic finite element method simulation tool, Maxwell 2D and 3D, and by measurement data from a gauss meter. The performance is verified experimentally. The results show a resolution of 0.2 μm and travel range of 16 mm. These are better than those of conventional focusing systems; therefore, this focusing unit can be applied to laser scanning systems for good machining capability.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Unit-cell thick BaTiO{sub 3} blocks octahedral tilt propagation across oxide heterointerface

We fabricated SrRuO{sub 3}/BaTiO{sub 3}/GdScO{sub 3} heterostructures in which the BaTiO{sub 3} layer is one unit cell thick by pulsed laser deposition and elucidated how the BaTiO{sub 3} layer influences structural and magneto-transport properties of the SrRuO{sub 3} layer through octahedral connections across the heterointerface. Our X-ray-diffraction-based structural characterizations show that while an epitaxial SrRuO{sub 3} layer grown directly on a GdScO{sub 3} substrate is in the monoclinic phase with RuO{sub 6} octahedral tilts, a one-unit-cell-thick BaTiO{sub 3} layer inserted between SrRuO{sub 3} and GdScO{sub 3} stabilizes the tetragonal SrRuO{sub 3} layer with largely reduced RuO{sub 6} tilts. Our high-angle annular dark-field and annular bright-field scanning transmission electron microscopy observations provide an atomic-level view of the octahedral connections across the heterostructure and reveal that the BaTiO{sub 3} layer only one unit cell thick is thick enough to stabilize the RuO{sub 6}-TiO{sub 6} octahedral connections with negligible in-plane oxygen atomic displacements. This results in no octahedral tilts propagating into the SrRuO{sub 3} layer and leads to the formation of a tetragonal SrRuO{sub 3} layer. The magneto-transport property characterizations also reveal a strong impact of the octahedral connections modified by the inserted BaTiO{sub 3} layer on the spin-orbit interaction of the SrRuO{sub 3} layer. The SrRuO{sub 3} layer on BaTiO{sub 3}/ GdScO{sub 3} has in-plane magnetic anisotropy. This is in contrast to the magnetic anisotropy of the monoclinic SrRuO{sub 3} films on the GdScO{sub 3} substrate, in which the easy axis is ∼45° to the film surface normal. Our results demonstrate that the one-unit-cell-thick layer of BaTiO{sub 3} can control and manipulate the interfacial octahedral connection closely linked to the structure-property relationship of heterostructures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Clamping characteristics study on different types of clamping unit

Plastic products are becoming more and more widely used in aerospace, IT, digital electronics and many other fields. With the development of technology, the requirement of product precision is getting higher and higher. However, type and working performance of clamping unit play a decisive role in product precision. Clamping characteristics of different types of clamping unit are discussed in this article, which use finite element numerical analysis method through the software ABAQUS to study the clamping uniformity, and detect the clamping force repeatability precision. The result shows that compared with toggled three-platen clamping unit, clamping characteristics of internal circulation two-platen clamping unit are better, for instance, its mold cavity deformation and force that bars and mold parting surface suffered are more uniform, and its clamping uniformity and repeatability precision is also better.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

A novel three-unit tRNA splicing endonuclease found in ultrasmall Archaea possesses broad substrate specificity

tRNA splicing endonucleases, essential enzymes found in Archaea and Eukaryotes, are involved in the processing of pre-tRNA molecules. In Archaea, three types of splicing endonuclease [homotetrameric: α 4 , homodimeric: α 2 , and heterotetrameric: (αβ) 2 ] have been identified, each representing different substrate specificity during the tRNA intron cleavage. Here, we discovered a fourth type of archaeal tRNA splicing endonuclease (ε 2 ) in the genome of the acidophilic archaeon Candidatus Micrarchaeum acidiphilum, referred to as ARMAN-2 and its closely related species, ARMAN-1. The enzyme consists of two duplicated catalytic units and one structural unit encoded on a single gene, representing a novel three-unit architecture. Homodimeric formation was confirmed by crosslinking assay, and site-directed mutagenesis determined that the conserved L10-pocket interaction between catalytic and structural unit is necessary for the assembly. A tRNA splicing assay reveal that ε 2 endonuclease cleaves both canonical and noncanonical bulge–helix–bulge motifs, similar to that of (αβ) 2 endonuclease. Unlike other ARMAN and Euryarchaeota, tRNAs found in ARMAN-2 are highly disrupted by introns at various positions, which again resemble the properties of archaeal species with (αβ) 2 endonuclease. Thus, the discovery of ε 2 endonuclease in an archaeon deeply branched within Euryarchaeota represents a new example of the coevolution of tRNA and their processing enzymes.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2011

Case report of a near medical event in stereotactic radiotherapy due to improper units of measure from a treatment planning system

Purpose: The authors hereby notify the Radiation Oncology community of a potentially lethal error due to improper implementation of linear units of measure in a treatment planning system. The authors report an incident in which a patient was nearly mistreated during a stereotactic radiotherapy procedure due to inappropriate reporting of stereotactic coordinates by the radiation therapy treatment planning system in units of centimeter rather than in millimeter. The authors suggest a method to detect such errors during treatment planning so they are caught and corrected prior to the patient positioning for treatment on the treatment machine. Methods: Using pretreatment imaging, the authors found that stereotactic coordinates are reported with improper linear units by a treatment planning system. The authors have implemented a redundant, independent method of stereotactic coordinate calculation. Results: Implementation of a double check of stereotactic coordinates via redundant, independent calculation is simple and accurate. Use of this technique will avoid any future error in stereotactic treatment coordinates due to improper linear units, transcription, or other similar errors. Conclusions: The authors recommend an independent double check of stereotactic treatment coordinates during the treatment planning process in order to avoid potential mistreatment of patients.

61 RADIATION PROTECTION AND DOSIMETRY↗