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At least 1,441 records · Page 80

The 3-D world modeling with updating capability based on combinatorial geometry

A 3-D world modeling technique using range data is discribed. Range data quantify the distances from the sensor focal plane to the object surface, i.e., the 3-D coordinates of discrete points on the object surface are known. The approach proposed herein for 3-D world modeling is based on the Combinatorial Geometry (CG) method which is widely used in Monte Carlo particle transport calculations. First, each measured point on the object surface is surrounded by a small sphere with a radius determined by the range to that point. Then, the 3-D shapes of the visible surfaces are obtained by taking the (Boolean) union of all the spheres. The result is an unambiguous representation of the object's boundary surfaces. The pre-learned partial knowledge of the environment can be also represented using the CG Method with a relatively small amount of data. Using the CG type of representation, distances in desired directions to boundary surfaces of various objects are efficiently calculated. This feature is particularly useful for continuously verifying the world model against the data provided by a range finder, and for integrating range data from successive locations of the robot during motion. The efficiency of the proposed approach is illustrated by simulations of a spherical robot in a 3-D room in the presence of moving obstacles and inadequate prelearned partial knowledge of the environment.

Goldstein, M.↗

En Route Descent Advisor Multi-Sector Planning Using Active and Provisional Controller Plans

As decision support tools are developed to support controllers in complex air traffic control environments, new approaches to maintaining situation awareness and managing traffic planning must be developed to handle the ever-increasing amounts of alerting and advisory data. Within high-density metering and other environments where flight path changes are the rule, not the exception, and where interactions between these changes are required, current trial planning approaches are limited by potential increases in workload. The Enroute Descent Advisor (EDA) is a set of decision support tool capabilities for managing high-density en route traffic subject to metering restrictions. The EDA system s novel approach builds aircraft plans from combinations of user intent data and builds controller plans from combinations of aircraft plans to effectively maintain situation awareness during traffic planning. By maintaining both active (current) and provisional (proposed) controller plans, EDA supports controllers in coordinated traffic planning both within and between sectors. Ultimately, EDA s multi-sector planning approach will facilitate a transition from current sector-oriented operations to a new trajectory-oriented paradigm, enabling new levels of efficiency and collaboration in air traffic control.

Vivona, Robert↗

An experimental study of opposed flow diffusion flame extinction over a thin fuel in microgravity

The flame spread and flame extinction characteristics of a thin fuel burning in a low-speed forced convective environment in microgravity were examined. The flame spread rate was observed to decrease both with decreasing ambient oxygen concentration as well as decreasing free stream velocity. A new mode of flame extinction was observed, caused by either of two means: keeping the free stream velocity constant and decreasing the oxygen concentration, or keeping the oxygen concentration constant and decreasing the free stream velocity. This extinction is called quenching extinction. By combining this data together with a previous microgravity quiescent flame study and normal-gravity blowoff extinction data, a flammability map was constructed with molar percentage oxygen and characteristic relative velocity as coordinates. The Damkohler number is not sufficient to predict flame spread and extinction in the near quench limit region.

Ferkul, Paul V.↗

Stable Metal–Organic Electrocatalysts for Anion-Exchange Membrane Water Electrolyzers by Defect Engineering

Developing efficient and durable catalysts for the alkaline oxygen evolution reaction (OER) is vital to achieving practical anion-exchange membrane water electrolyzers (AEMWE) for green hydrogen production. In this work, we break the activity-stability trade-off of electrocatalysis by defect engineering of Ni-based metal-organic electrocatalysts (Ni-benzene dicarboxylate; Ni-BDC) through coordinating ferrocenecarboxylates (Fc) to the metal sites. Experimental results collectively reveal that the defect MOF (Ni-BDC:Fc_5:1) exhibits a high OER turnover frequency of 0.75 O 2 s -1 at 300 mV overpotential. Operando Raman spectroscopy and isotope-labelling electrochemical mass spectrometry measurements indicate the structure of Ni-BDC:Fc_5:1 is also more stable in service than that of pure Ni-BDC. The high activity and stability could be attributed to the moderate defects (i.e., unsaturated Ni sites) in the structure that not only increase the intrinsic activity and stability of the local active environment by inhibiting lattice oxygen exchange, but also electrochemically activates the bulk of the catalysts by creating a porous network that facilitates internal H 2 O/OH - conduction with enhanced electronic conduction. Accordingly, an AEMWE employing Ni-BDC:Fc_5:1 as the OER catalyst delivers an industrial-level current density of 1 A cm -2 at 1.73 V cell and can be steadily operated for more than 120 hours.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Advanced Reactor Cyber Analysis and Development Environment (ARCADE) for System-Level Design Analysis

Cybersecurity is a persistent concern to the safety and security of Nuclear Power Plants (NPPs), but has lacked data-driven, evidence-based research. Rigorous cybersecurity analysis is critical for the licensing of advanced reactors using a performance-based approach. One tool that enables cybersecurity analysis is modeling and simulation. The nuclear industry makes extensive use of modeling and simulation throughout the decision process but lacks a method to incorporate cybersecurity analysis with existing models. To meet this need, the Advanced Reactor Cyber Analysis and Development Environment (ARCADE) was developed. ARCADE is a suite of publicly available tools that can be used to develop emulations of industrial control system devices and networks and integrate those emulations with physics simulators. This integration of cyber emulations and physics models enables rigorous cyber-physical analysis of cyber-attacks on NPP systems. This report provides an overview of key considerations for using ARCADE with existing physics models and demonstrates ARCADE’s capabilities for cybersecurity analysis. Using a model of the Small Modular Advanced High Temperature Reactor (SmAHTR), ARCADE was able to determine the sensitivity of the primary heat exchangers (PHX) to coordinated cyber-attacks. The analysis determined that while the PHX’s failures cause disruption to the reactor, they did not cause any safety limits to be exceeded because of the plant design, including passive safety features. Further development of ARCADE will enable rigorous, repeatable, and automated cyber-physical analysis of advanced reactor control systems. These efforts will also help reduce regulatory uncertainty by presenting similar types of cybersecurity analyses in a common format, driving standard approaches and reporting.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗

The Effect of Microgravity on the Growth of Lead Tin Telluride

The main objective of this research was to present a model for the prediction of the effect of the microgravity environment on the growth of Lead Tin Telluride. The attitude change and its relation to the experimental objectives: The main objective for the AADSF experiment on USMP 3 involving LTT growth was to estimate the effect of ampoule orientation on the axial and radial segregation of tin telluride. As the furnace was not situated on a gimbal there was no possibility to reorient the ampoule during the flight. Instead the only way to change the growth orientation was to change the attitude of the orbiter. This was accomplished by vernier rocket firings. In what follows it must be noted that the orbiter body coordinates are such that the positive z axis points outward from the 'belly', the positive 'x' axis points outwards from the nose and the positive 'y' axis points outwards from the starboard side. The furnace which was in the pay load had its axis aligned with the orbiter's 'z' axis with the hot end closest to the shuttle body. There were basically three orientations that were desired. These corresponded to the ampoule being seen as a heated from above (thermally stable-solutally unstable) configuration, the heated from below (where the instabilities were reversed from the first orientation) configuration and an 'in between' case where the ampoule axis was misaligned with respect to the orbiters 'g(sub z)' axis.

Narayanan, R.↗

Evolution of silicate coordination in architected amorphous and crystalline magnesium silicates during carbon mineralization

Advancing durable solutions for carbon storage and removal at the gigaton scale to produce solid carbonates via carbon mineralization requires harnessing earth abundant magnesium silicate resources. Calibrated insights linking the structural and morphological features of earth abundant amorphous and crystalline magnesium silicate phases to their reactivity are essential for scalable deployment but remain underdeveloped. To resolve the influence of silica coordination and mass transfer on carbon mineralization behavior, magnesium silicates bearing amorphous and crystalline phases (AC Mg-silicate) are synthesized. The structural and morphological transitions starting from colloidal precursors to their final synthesized form on heating are delineated using operando ultra small/small/wide angle X-ray scattering (USAXS/SAXS/WAXS) measurements. The evolution of the silicate phases on carbon mineralization of AC Mg-silicate is contrasted with that of highly crystalline Mg-silicate (HC Mg-silicate) when reacted at 200 °C and a CO 2 partial pressure of 20 atm in water and 1 M NaHCO 3 solution in stirred and unstirred environments. These experimental conditions are analogous to those of the water–gas-shift reaction for sustainable recovery of H 2 with inherent carbon mineralization. Enhancement in the extent of carbon mineralization by 13.3–19.5% noted in the presence of NaHCO 3 compared to water in AC and HC Mg-silicate with and without stirring, is attributed to the buffering effect which aids simultaneous silicate dissolution and carbon mineralization. Enhanced extents of carbon mineralization in the presence of NaHCO 3 correspond to the formation of MgSiO 3 and SiO 2 phases from the starting Mg 2 SiO 4 precursors in AC and HC Mg-silicate. Unlocking these silicate transformations during carbon mineralization by harnessing architected Mg-silicate precursors reveals the feasibility of integrating these chemical pathways with sustainable H 2 conversion pathways with inherent carbon mineralization.

Gao, Xun [Cornell Univ., Ithaca, NY (United States↗

Dynamics of iodine geminate recombination in supercritical xenon solvent: Caging effect

Understanding the dynamics of chemical reactions in solutions is vital, as their rates and kinetics are significantly affected by the solvent environment. Supercritical solvents offer extensive applications in chemical reactions by enabling the manipulation of the solution environment. Here, in this study, we investigate the geminate recombination of iodine in a supercritical xenon solvent by using ReaxFF-based molecular dynamics simulations. Our findings reveal that the highest iodine recombination rate occurs near supercritical conditions, while lower-pressure conditions lead to reduced collision rates and unstable recombination, and higher-pressure conditions hinder iodine diffusion, resulting in a lower recombination rate. Our analysis shows that the xenon local density at the time of recombination is at least 2.5 times higher than the global density, confirming the presence of xenon clusters surrounding the Iodine atoms. This observation is further supported by coordination number analysis, which confirms an elevated xenon local density during recombination. In addition, the correlation between the total energy of xenon atoms within a cluster and recombined iodine atoms underscores the kinetic energy transfer process, validating the occurrence of geminate recombination. The excess kinetic energy from the recombining iodine atoms is transferred to the surrounding xenon atoms. Our examination of geminate recombination demonstrates that iodine atoms confined within xenon clusters—whether through manual insertion of atoms or the fast dissociation of an iodine molecule within xenon clusters—are more likely to recombine as primary geminate recombination. However, extending the iodine molecule dissociation time allows iodine atoms to diffuse out of the cluster, and the recombination to shift toward secondary geminate recombination.

Cage effect↗

Validation of Space Weather Models at Community Coordinated Modeling Center

The Community Coordinated Modeling Center (CCMC) is a multi-agency partnership to support the research and developmental work necessary to substantially increase space weather modeling capabilities and to facilitate advanced models deployment in forecasting operations. Space weather models and coupled model chains hosted at the CCMC range from the solar corona to the Earth's upper atmosphere. CCMC has developed a number of real-time modeling systems, as well as a large number of modeling and data products tailored to address the space weather needs of NASA's robotic missions. The CCMC conducts unbiased model testing and validation and evaluates model readiness for operational environment. CCMC has been leading recent comprehensive modeling challenges under GEM, CEDAR and SHINE programs. The presentation will focus on experience in carrying out comprehensive and systematic validation of large sets of. space weather models

Kuznetsova, M. M.↗

Probabilistic Mixture Model-Based Spectral Unmixing

Spectral unmixing attempts to decompose a spectral ensemble into the constituent pure spectral signatures (called endmembers) along with the proportion of each endmember. This is essential for techniques like hyperspectral imaging (HSI) used in environment monitoring, geological exploration, etc. Several spectral unmixing approaches have been proposed, many of which are connected to hyperspectral imaging. However, most extant approaches assume highly diverse collections of mixtures and extremely low-loss spectroscopic measurements. Additionally, current non-Bayesian frameworks do not incorporate the uncertainty inherent in unmixing. We propose a probabilistic inference algorithm that explicitly incorporates noise and uncertainty, enabling us to unmix endmembers in collections of mixtures with limited diversity. We use a Bayesian mixture model to jointly extract endmember spectra and mixing parameters while explicitly modeling observation noise and the resulting inference uncertainties. We obtain approximate distributions over endmember coordinates for each set of observed spectra while remaining robust to inference biases from the lack of pure observations and the presence of non-isotropic Gaussian noise. As a direct impact of our methodology, access to reliable uncertainties on the unmixing solutions would enable robust solutions to noise, as well as informed decision-making for HSI applications and other unmixing problems.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

In-Flight Characterization of the Electromagnetic Environment Inside an Airliner

In 1995, the NASA Langley Research Center conducted a series of experimental measurements that characterized the electromagnetic environment (EME) inside a Boeing 757 airliner while in flight, Measurements were made of the electromagnetic energy coupled into a commercially configured aircraft as it was flown in close proximity to ground-based radio frequency (RF) transmitters operating at approximately 26, 173. and 430 MHz. The goal of this experiment was to collect data for the verification of analytical predictions of the internal aircraft response to an external stimulus. This paper describes the experiment, presents the data collected by it, and discusses techniques used to compute both the magnitude of the electric field illuminating the aircraft and its direction of propagation relative to a coordinate system fixed to the aircraft. The latter is determined from Global Positioning System (GPS) and aircraft Inertial Reference Unit (IRU) data. The paper concludes with an examination of the shielding effectiveness of the test aircraft. as determined by comparison of' the measured internal EME and computed external EME.

Moeller, Karl J.↗

Hydrogen Absorbing Materials for Use as Radiation Shielding During Extended Space Flight Missions

Minimizing radiation exposure from the galactic cosmic ray (GCR) environment during extended space missions is particularly crucial to crew health and safety. Here, an ideal candidate for shielding would be pure solid or liquid hydrogen, a material that effectively fragments heavy ions into ones of lower mass and energy that are more easily attenuated. Unfortunately, utilizing pure hydrogen is not presently feasible. It is, however, known that the hydrogen content of other materials (for example, metal hydrides, palladium alloys, and organic compounds) can exceed that of pure solid hydrogen and thus merit consideration as shielding candidates. This presentation will discuss an ongoing effort to develop novel shielding from such materials in concert with a coordinated testing/evaluation and modeling effort.

Grugel, Richard N.↗

Lessons Learned from Shuttle Payload Verification Loads Analysis

When a system experiences a loading environment characterized by rapidly varying forces, such as a rocket launch, a transient analysis is used to analyze the response of the system. The most common transient analysis methodology is the Coupled Loads Analysis (CLA). CLAs are used by the automotive and aerospace industry to analyze cars, trucks, planes, helicopters, spacecraft, etc. The Space Shuttle program also uses the CLA methodology to assess the compatibility of the payload with the Orbiter and the flight environment. The Space Shuttle Verification Loads Analysis (VLA) was a standardized process that started between ten and thirteen months prior to launch, and included several meetings as well as analysis by both the Shuttle Program and the payload developers. Over the course of the Space Shuttle Program, many improvements were made to the process which helped to reduce cycle time and improve manifest flexibility. There were also several issues which were never properly addressed, but a work-around would be developed to keep the process flowing. The lessons learned included automation of some processes and standardization of others, early assessments, improved documentation and better coordination with all stakeholders in the process. Lessons learned also included the limitations in the current process, and what needs to be planned for in the future to avoid the same issues.

Bruno, Erica↗

Subject Matter Expert Evaluation of Multi-Flight Common Route Advisories

Traffic flow management seeks to balance the demand for National Airspace System (NAS) flight resources, such as airspace and airports, with the available supply. When forecasted weather blocks nominal air traffic routes, traffic managers must re-route affected flights for weather avoidance. Depending on the nature and scope of the weather, traffic managers may use pre-coordinated re-routes such as Playbook Routes or Coded Departure Routes, or may design ad hoc local re-routes. The routes of affected flights are modified accordingly. These weather avoidance routes will, of course, be less efficient than the nominal routes due to increased flight time and fuel burn. In current traffic management operations, the transition into a weather avoidance re-routing initiative is typically implemented more aggressively than the transition out of that initiative after the weather has dissipated or moved away. For example, strategic large-scale Playbook re-routes are sometimes left in place (as initially implemented) for many hours before being lifted entirely when the weather dissipates. There is an opportunity to periodically modify the re-routing plan as weather evolves, thereby attenuating its adverse impact on flight time and fuel consumption; this is called delay recovery. Multi-Flight Common Routes (MFCR) is a NASA-developed operational concept and associated decision support tool for delay recovery, designed to assist traffic managers to efficiently update weather avoidance traffic routes after the original re-routes have become stale due to subsequent evolution of the convective weather system. MFCR groups multiple flights to reduce the number of advisories that the traffic manager needs to evaluate, and also merges these flights on a common route segment to provide an orderly flow of re-routed traffic. The advisory is presented to the appropriate traffic manager who evaluates it and has the option to modify it using MFCRs graphical user interface. If the traffic manager finds the advisory to be operationally appropriate, he or she would coordinate with the Area Supervisor(s) of the sectors that currently control the flights in the advisory. When the traffic manager accepts the MFCR advisory via the user interface, the corresponding flight plan amendments would be sent to the displays of the appropriate sector controllers, using the Airborne Re-Routing (ABRR) capability which is scheduled for nationwide operation in 2017. The sector controllers would then offer this time-saving route modification to the pilots of the affected flights via datalink (or voice), and implement the corresponding flight plan amendment if the pilots accept it. MFCR is implemented as an application in the software environment of the Future Air traffic management Concepts Evaluation Tool (FACET). This paper focuses on an initial subject matter expert (SME) evaluation of MFCR. The evaluation covers MFCRs operational concept, algorithm, and user interface.

Human-in-the-loop Evaluation↗

Subject Matter Expert Evaluation of Multi-Flight Common Route Advisories

Traffic flow management seeks to balance the demand for National Airspace System (NAS) flight resources, such as airspace and airports, with the available supply. When forecasted weather blocks nominal air traffic routes, traffic managers must re-route affected flights for weather avoidance. Depending on the nature and scope of the weather, traffic managers may use pre-coordinated re-routes such as Playbook Routes or Coded Departure Routes, or may design ad hoc local re-routes. The routes of affected flights are modified accordingly. These weather avoidance routes will, of course, be less efficient than the nominal routes due to increased flight time and fuel burn. In current traffic management operations, the transition into a weather avoidance re-routing initiative is typically implemented more aggressively than the transition out of that initiative after the weather has dissipated or moved away. For example, strategic large-scale Playbook re-routes are sometimes left in place (as initially implemented) for many hours before being lifted entirely when the weather dissipates. There is an opportunity to periodically modify the re-routing plan as weather evolves, thereby attenuating its adverse impact on flight time and fuel consumption; this is called delay recovery. Multi-Flight Common Routes (MFCR) is a NASA-developed operational concept and associated decision support tool for delay recovery, designed to assist traffic managers to efficiently update weather avoidance traffic routes after the original re-routes have become stale due to subsequent evolution of the convective weather system. MFCR groups multiple flights to reduce the number of advisories that the traffic manager needs to evaluate, and also merges these flights on a common route segment to provide an orderly flow of re-routed traffic. The advisory is presented to the appropriate traffic manager who evaluates it and has the option to modify it using MFCRs graphical user interface. If the traffic manager finds the advisory to be operationally appropriate, he or she would coordinate with the Area Supervisor(s) of the sectors that currently control the flights in the advisory. When the traffic manager accepts the MFCR advisory via the user interface, the corresponding flight plan amendments would be sent to the displays of the appropriate sector controllers, using the Airborne Re-Routing (ABRR) capability which is scheduled for nationwide operation in 2017. The sector controllers would then offer this time-saving route modification to the pilots of the affected flights via datalink (or voice), and implement the corresponding flight plan amendment if the pilots accept it. MFCR is implemented as an application in the software environment of the Future Air traffic management Concepts Evaluation Tool (FACET). This paper focuses on an initial subject matter expert (SME) evaluation of MFCR. The evaluation covers MFCRs operational concept, algorithm, and user interface.

Traffic flow management↗

Pressure-Driven Changes in the Electronic Bonding Environment of GeO 2 Glass above Megabar Pressures

Noncrystalline oxides under pressure undergo gradual structural modifications, highlighted by the formation of a dense noncrystalline network topology. The nature of the densified networks and their electronic structures at high pressures may account for the mechanical hardening and the anomalous changes in electromagnetic properties. Despite its importance, direct probing of the electronic structures in amorphous oxides under compression above the Mbar pressure (>100 GPa) is currently lacking. Here, we report the observation of pressure-driven changes in electronic configurations and their delocalization around oxygen in glasses using inelastic X-ray scattering spectroscopy (IXS). In particular, the first O K-edge IXS spectra for compressed GeO 2 glass up to 148 GPa, the highest pressure ever reached in an experimental study of GeO 2 glass, reveal that the glass densification results from a progressive increase of oxygen proximity. While the triply coordinated oxygen [3] O is dominant below ~50 GPa, the IXS spectra resolve multiple edge features that are unique to topologically disordered [4] O upon densification above 55 GPa. Topological compaction in GeO 2 glass above 100 GPa results in pronounced electronic delocalization, revealing the contribution from Ge d-orbitals to oxide densification. Strong correlations between the glass density and the electronic configurations beyond the Mbar conditions highlight the electronic origins of densification of heavy-metal-bearing oxide glasses. Furthermore, current experimental breakthroughs shed light on the direct probing of the electronic density of states in high-Z oxides above 1 Mbar, offering prospects for studies on the pressure-driven changes in magnetism, superconductivity, and electronic transport properties in heavy-metal-bearing oxides under compression.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Real-time Simulation of Coordinated Sub-Transmission Volt-Var Control Tool under High Distributed PV Penetration

With the rapid penetration of intermittent solar photovoltaic (PV) and other distributed energy resources (DER) into the grid, and subsequent changes in power flow patterns in both distribution and sub-transmission, voltage regulation is becoming a major challenge. It is prudent to leverage PV and DER to provide ancillary services to the grid, such as voltage regulation. Recently, a quasi-static, coordinated real-time sub transmission volt-var control algorithm (CReST-VCT) was developed for voltage regulation under high PV penetration by dispatching the reactive power settings of the shunt devices and PV inverters. The algorithm was validated offline, on a quasistatic study. Such quasi-static dispatching algorithms cannot guarantee its performance for highly nonlinear dynamical power systems. In this paper the performance of the algorithm is validated with a real time nonlinear dynamic simulation of a modified IEEE 118 bus system in Opal-RT. The real time simulation is used to emulate the actual system operation, providing a more realistic testing environment for CReST-VCT. The dispatch and control signals are communicated between the power system (Opal solver) and the control center (GAMS solver) in real-time with a MODBUS bridge. The results demonstrate i) system is stable with the new dispatch points ii) significant improvement in system-wide voltage profiles compared to an uncontrolled scenario. Another significant contribution of the work is developing a framework for dispatchable, long duration dynamic simulations that can be leveraged for market/dispatch studies.

CReST-VCT, Opal-RT, Volt/Var Control, renewable in↗