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At least 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Transformer designs for very high isolation with high coupling

Various examples are provided related to transformer designs that offer very high isolation while maintaining high coupling between the windings. In one example, an isolation transformer includes a first excitation coil wound around a first core and a second excitation coil wound about a second core. The second core is electrically separated from the first core by a high resistivity magnetic material or a non-conductive material. The first and second cores can include corresponding core segments arranged in a trident geometry or a quindent geometry. The core segments can align when the first excitation coil is inserted into a void of the second excitation coil. The isolation transformer designs are mechanically separable which can result in safe, energized, plug operations.

Beddingfield, Richard Byron↗
DOE OSTI2023

Utah FORGE 1-2409: Zonal Isolation Solution for Geothermal Wells - Workshop Presentation

This is a presentation on the Zonal Isolation Solution for Geothermal Wells project by PetroQuip Energy Services, presented by VP of operations Robert Coon. The project's objective was to design and develop a multi-stage system for zonally isolating fluids inside and outside of geothermal well casings. This presentation was featured in the Utah FORGE R&D Annual Workshop on September 7, 2023. The workshop provided a valuable opportunity to explore the progress made in each of the 17 Research and Development projects funded under Solicitation 2020-1 which aim to enhance our understanding of the crucial factors influencing the development of Enhanced Geothermal Systems (EGS) reservoirs and resources.

15 GEOTHERMAL ENERGY↗
DOE OSTI2022

A mathematical assessment of the isolation random forest method for anomaly detection in big data

We present the mathematical analysis of the Isolation Random Forest Method (IRF Method) for anomaly detection, proposed by Liu F.T., Ting K.M. and Zhou Z. H. in their seminal work as a heuristic method for anomaly detection in Big Data. We prove that the IRF space can be endowed with a probability induced by the Isolation Tree algorithm (iTree). In this setting, the convergence of the IRF method is proved, using the Law of Large Numbers. Here, a couple of counterexamples are presented to show that the method is inconclusive and no certificate of quality can be given, when using it as a means to detect anomalies. Hence, an alternative version of the method is proposed whose mathematical foundation is fully justified. Furthermore, a criterion for choosing the number of sampled trees needed to guarantee confidence intervals of the numerical results is presented. Finally, numerical experiments are presented to compare the performance of the classic method with the proposed one.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2023

Fault isolation and fault-tolerant control for nonlinear stochastic distribution control systems with multiplicative faults

Here, in this paper, a fault isolation, diagnosis and fault tolerant control algorithm is proposed for nonlinear multiple multiplicative faults stochastic distribution control systems employing Takagi–Sugeno fuzzy system. To obtain the detailed fault information, a fault detection algorithm is introduced to discover the fault occurrence time. Then a fault isolation observer is built to produce the residual, and the error system is separated to subsystems affected only by disturbance and multiplicative faults. Moreover, a fault estimation scheme is presented to obtain the fault magnitude information. When faults occur, the system output probability density function will deviate from the desired distribution. So the model predictive control fault tolerant control scheme is needed to minimize the impact of faults as much as possible to make sure that the post fault output probability density function track the desired probability density function. The validity of the designed algorithm is demonstrated through a simulation example, where the fault tolerant control algorithm ensures that the system output probability density function still track the given output probability density function despite the complex case of multiple multiplicative faults occurring simultaneously.

42 ENGINEERING↗
DOE OSTI2025

Isolated vesicles in submarine pumice: insights from the 2019 Volcano F eruption, Kingdom of Tonga

No reliable method can distinguish between subaerial and submarine pumice, but recent work shows that highly vesicular (total porosity, φ > 65%) submarine pumice from the 2012 Havre and 2021 Fukutoku Oka-no-Ba eruptions contains abundant isolated porosity (connectivity, C < 0.6). This differs from textural measurements of subaerial pumice with similarly high vesicularities, where high connectivities (C > 0.8) are often measured. To investigate the implications of this under-studied texture for bubble nucleation, growth, and coalescence dynamics at submarine eruptions, we analyze the textural characteristics of rafted pumice clasts from the 2019 submarine eruption of Volcano F, located along the Tonga-Kermadec Arc. We examined clasts collected while floating near the vent (50–200 km) and distally on the shores of Fiji (900 km). Using helium pycnometry and X-ray tomography (XRT), we quantified porosity and connectivity in 45 pumice lapilli, classifying them by vesicle macrotexture and edge morphology. Microvesicular clasts, the majority of which have breadcrust and cauliflower textures, exhibit the lowest connectivities (C = 0.61 ± 0.2), while macrovesicular clasts have high connectivities with C ~ 1. We propose that isolated porosity abundance varies according to clast location in the eruption column post-fragmentation. Microvesicular clasts erupted on the edges of the column and experienced high levels of seawater ingestion and subsequent quenching of the entire clast. Macrovesicular clasts, in contrast, erupted in the center of the eruption column and were thus thermally insulated, allowing magmatic bubbles in the molten pumice to nucleate, grow, and coalesce for longer. Our results and interpretation imply that low connectivity, microvesicular clasts preserve pre and syn-eruptive bubble processes at the 2019 Volcano F eruption.

Permeability↗
DOE OSTI2020

Detecting anomalous packets in network transfers: investigations using PCA, autoencoder and isolation forest in TCP

Large-scale scientific workflows rely heavily on high-performance file transfers. These transfers require strict quality parameters such as guaranteed bandwidth, no packet loss or data duplication. To have successful file transfers, methods such as predetermined thresholds and statistical analysis need to be done to determine abnormal patterns. Network administrators routinely monitor and analyze network data for diagnosing and alleviating these, making decisions based on their experience. However, as networks grow and become complex, monitoring large data files and quickly processing them, makes it improbable to identify errors and rectify these. Abnormal file transfers have been classified by simply setting alert thresholds, via tools such as PerfSonar and TCP statistics (Tstat). This paper investigates the feasibility of unsupervised feature extraction methods for identifying network anomaly patterns with three unsupervised classification methods—principal component analysis, autoencoder and isolation forest. Here, we collect file transfer statistics from two experiment sets—synthetic iPerf generated traffic and 1000 Genome workflow runs, with synthetically introduced anomalies. Our results show that while PCA and a simple autoencoder finds it difficult to detect clusters, the tree-variant isolation forest is able to identify anomalous packets by breaking down TCP traces into tree classes early.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2025

Detecting isolated resonance curves using fixed frequency voltage control tests

Isolated resonance curves, or isolas, are resonance branches of the harmonically forced system that exist separately from the main nonlinear forced response curve, leading to excessive vibrations. Traditional stepped or swept sine simulations and tests rely on continuation along the frequency parameter, typically resulting in a jump phenomenon along the primary resonance branch, prior to the disconnected isola. The main objective of this research is to propose an approach to identify isolated resonance curves by performing continuation along the input amplitude that initializes the response from a low-amplitude solution in the linear regime. Furthermore, this is achieved with the open-loop fixed frequency voltage control method that continues along the shaker voltage parameter and measures the so-called S-curves, which are theoretically a continuous solution branch that connect to the isola. The methodology is demonstrated on a fixture-wing-pylon assembly with a vibro-impact nonlinearity localized in a pylon subcomponent attachment. Multi-harmonic balance simulations are deployed to compute both the nonlinear forced response curves and S-curves to demonstrate the isola detection strategy on a reduced-order finite element model of the nonlinear system. Swept sine and fixed frequency voltage control tests are then conducted on the physical structure to demonstrate the isola detection experimentally, revealing the existence of the large amplitude vibrations that are undetected in the forces levels and frequencies measured with traditional frequency sweeping.

Characterization and Analytical Technique↗
DOE OSTI2022

On the broadband vibration isolation performance of nonlocal total-internal-reflection metasurfaces

The concept of a nonlocal elastic metasurface has been recently proposed and experimentally demonstrated in Zhu et al. (2020). When implemented in the form of a total-internal-reflection (TIR) interface, the metasurface can act as an elastic wave barrier that is impenetrable to deep subwavelength waves over an exceptionally wide frequency band. The underlying physical mechanism capable of delivering this broadband subwavelength performance relies on an intentionally nonlocal design that leverages long-range connections between the units forming the fundamental supercell. This paper explores the design and application of a nonlocal TIR metasurface to achieve broadband passive vibration isolation in a structural assembly made of multiple dissimilar elastic waveguides. The specific structural system comprises shell, plate, and beam waveguides, and can be seen as a prototypical structure emulating mechanical assemblies of practical interest for many engineering applications. The study also reports the results of an experimental investigation that confirms the significant vibration isolation capabilities afforded by the embedded nonlocal TIR metasurface. We report these results are particularly remarkable because they show that the performance of the nonlocal metasurface is preserved when applied to a complex structural assembly and under non-ideal incidence conditions of the incoming wave, hence significantly extending the validity of the results presented in Zhu et al. (2020). Results also confirm that, under proper conditions, the original concept of a planar metasurface can be morphed into a curved interface while still preserving full wave control capabilities.

42 ENGINEERING↗
DOE OSTI2024

Mechanism and Kinetics of Ethanol–Acetaldehyde Conversion to 1,3-Butadiene over Isolated Lewis Acid La Sites in Silanol Nests in Dealuminated Beta Zeolite

Biomass-derived ethanol (EtOH) and acetaldehyde (AcH) conversion to 1,3-butadiene (1,3-BD) is an alternative process for 1,3-BD production. The present investigation reports the preparation and characterization of isolated La sites introduced into the silanol nests in DeAlBEA as well as detailed studies of the mechanism and kinetics for the conversion of an EtOH-AcH mixture to 1,3-BD. La sites supported on DeAlBEA are found to be present as (≡SiO) 2 La-OH groups that are H-bonded with adjacent Si-OH groups, possessing high C-C coupling activity and stability, superior to state-of-the-art Y-DeAlBEA. La sites supported on silica (La-SiO 2 ) with a similar chemical structure but no H-bonding interaction with Si-OH groups were prepared for comparison. Lewis acid La sites promote AcH aldol condensation, and the activity of such sites is nearly identical for both La-DeAlBEA and La-SiO 2 . Further, the rate of C 4 product formation increases by a factor of 4.8 upon addition of EtOH to the feed of AcH over La-DeAlBEA, whereas that over La/SiO 2 remains unchanged. Investigation of the mechanism and kinetics of AcH aldol condensation and EtOH-AcH conversion to 1,3-BD revealed two C-C bond forming pathways-AcH aldol condensation by Lewis acid La sites and direct coupling of EtOH-AcH over H-bonded (≡SiO) 2 La-OH···HO-Si≡ sites. This study provides important information about the role of the local environment of isolated Lewis acid sites and their effects on the direct coupling of EtOH and AcH to form 1,3-BD.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Simultaneous Observation of Two Isolated Proton Auroras at Subauroral Latitudes by a Highly Sensitive All-Sky Camera and Van Allen Probes

Isolated proton auroras (IPAs) appearing at subauroral latitudes are generated by energetic protons precipitating from the magnetosphere through interaction with electromagnetic ion cyclotron (EMIC) waves. An IPA thus indicates the spatial scale and temporal variation of wave-particle interactions in the magnetosphere. In this study, a unique event of simultaneous ground and magnetospheric satellite observations of two IPAs were conducted on March 16, 2015, using an all-sky imager at Athabasca, Canada and Van Allen Probes. The Van Allen Probes observed two isolated EMIC waves with frequencies of ~1 and 0.4 Hz at L ≈ 5.0 when the satellite footprint crossed over the two IPAs. This suggests that the IPAs were caused by localized EMIC waves. Proton flux at 5–20 keV increased locally when the EMIC waves appeared. Electron flux at energies below ~500 eV also increased. Temperature anisotropy of the energetic protons was estimated at 1.5–2.5 over a wide L-value range of 3.0–5.2. Electron density gradually decreased from L = 3.5 to 5.4, suggesting that the EMIC wave at L ≈ 5.0 was located in the gradual plasmapause. From these observations, we conclude that the localized IPAs and associated EMIC waves took place because of localized enhancement of energetic proton flux and plasma density structure near the plasmapause. Furthermore, the magnetic field observed by the satellite showed small variation during the wave observation, indicating that the IPAs were accompanied by the weak field-aligned current.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Environmental Thermodynamic Effects on Future Changes of Mesoscale Convective Systems and Isolated Deep Convection Over the US: A Case Study

Mesoscale convective systems (MCSs) and isolated deep convection (IDC) significantly influence local weather conditions and the hydrological cycle across the United States. Their future changes under warming is critical to the society. However, the exact impacts of thermodynamic environmental changes on them are difficult to resolve using climate model simulations which integrate both dynamic and thermodynamic factors. This study explores a theoretical modeling approach to isolate environmental thermodynamic effects on their future changes through a case study. For a 50-day period during the 2020 summer, a pair of convection-permitting model simulations indicate contrasting changes in MCSs and IDC between inland and coastal regions under pseudo global warming. Driven by the thermodynamic environments of these simulations, a single-column parcel model indicates a decrease in the frequency of IDC occurrences, along with increases in duration and precipitation amount under warming, attributable to rising most unstable convective available potential energy (MUCAPE), convective inhibition (MUCIN), and precipitable water (PW). A multi-column parcel model reveals contrasting changes in the frequency and mean area of MCSs between inland and coastal regions, underscoring the increase in mean MUCIN over inland regions and increases in mean MUCAPE and PW over coastal regions. The increase in mean MCS area over inland regions is linked to the interplay between accelerated gust fronts and enhanced subsidence strength, which is further traced to the unchanged mean MUCIN but increased mean MUCAPE in large-scale environments. In conclusion, these case study results suggest a major role of thermodynamic environmental changes in controlling characteristics of MCSs and IDC under warming.

Mesoscale convective system↗
DOE OSTI2026

Improbability of Post-Closure Criticality in Compacted Criticality Control Overpacks after Room Closure at Waste Isolation Pilot Plant

As part of its periodic re-certification of the Waste Isolation Pilot Plant (WIPP), an operating repository in bedded salt for the disposal of transuranic (TRU) waste from atomic energy defense activities, the United States Environmental Protection Agency expects a re-evaluation of features, events, and processes, such as post-closure nuclear criticality. Although salt creep beneficially encapsulates the TRU waste in the closed WIPP repository, the spacing between an array of waste packages is disrupted as the salt creep closes disposal rooms and containers lose structural integrity. For most TRU waste, the possibility of post-closure criticality is exceedingly small either because the salt neutronically isolates TRU waste canisters or because closure of a disposal room from salt creep does not sufficiently compact the low mass of fissile material. The criticality evaluation was updated, however, because of the introduction of criticality control overpack (CCO) containers, which may dispose up to 380 fissile gram equivalent plutonium-239 in each container. The criticality potential is evaluated through high-fidelity geomechanical modeling of a disposal room filled with CCO containers during two representative conditions: (1) large salt block fall, and (2) gradual disposal room closure from salt creep. Geomechanical models of roof fall demonstrate three tiers of CCO containers are not greatly disrupted. Geomechanical models of gradual room closure from salt creep (without brine seepage and subsequent gas generation to permit maximum room closure) were used to predict irregular arrays of closely packed CCOs after 1000 years, when room closure has asymptotically approached maximum compaction. Models of spheres or cylinders with 380 fissile gram equivalent of plutonium (as oxide) at the predicted irregular compacted spacing demonstrate that an array of CCO containers is not critical when surrounded by salt and magnesium oxide, provided the mass of hydrogenous material shipped in CCO containers (usually plastics) is controlled or boron carbide (a neutron poison) is mixed with the fissile contents.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2021

A Study of Integrated Signal and Power Transfer for Compact Isolated SiC MOSFET Gate-Drivers

This work discusses a novel set of alternate implementations of isolated gate driver circuits for power electronic transistors. The proposed topologies for the driver have been designed specifically for SiC power MOSFET. Three different solutions are discussed, all of them providing the required gate turn-on and turn-off command signal with galvanic isolation, but also supplying power to the secondary side of the driver by means of magnetic transformers. The resulting solutions, all of them implemented with simple circuitry, enable the integration of the driver into the power cell, allowing for theoretical higher power density values in the final system. The principle of operation of the different solutions is discussed, and then the main relevant implementation details are presented. After that, the operation of the circuits is demonstrated experimentally, by testing a set of prototypes of these drivers. This provides a comprehensive design example that assesses the feasibility of the proposed solutions. Finally, the main results of the performance of the three gate drivers, on an SiC MOSFET-based prototype are presented and compared.

42 ENGINEERING↗
DOE OSTI2020

The Preservation of Super-Earths and the Emergence of Gas Giants after Their Progenitor Cores Have Entered the Pebble-isolation Phase

The omnipresence of super-Earths suggests that they are able to be retained in natal disks around low-mass stars, whereas exoplanets' mass distributions indicate that some cores have transformed into gas giants through runaway gas accretion at ≳1 au from solar-type stars. In this paper, we show that transition to runaway gas accretion by cores may be self-impeded by an increase of the grain opacity in their envelope after they have acquired sufficient mass (typically ~ 10M ⊕ ) to enter a pebble-isolation phase. The accumulation of approximately millimeter- to meter-sized pebbles in their migration barriers enhances their local fragmentation rates. The freshly produced submillimeter grains pass through the barrier, elevate the effective dust opacity, and reduce the radiative flux in the core's envelope. These effects alone are adequate to suppress the transition to runaway accretion and preserve super-Earths in the stellar proximity (~0.1 au), albeit entropy advection between the envelope and the disk can further reduce the accretion rate. At an intermediate distance (~1 au) from their host stars, the escalation in the dust opacity dominates over entropy advection in stalling the transition to runaway accretion for marginally pebble-isolated cores. Beyond a few astronomical unit, the transformation of more-massive cores to gas giants is reachable before severe depletion of disk gas. This requirement can be satisfied either in extended disks with large scale height via orderly accretion of migrating pebbles or through the mergers of oligarchic protoplanetary embryos, and can account for the correlated occurrence of long-period gas giants and close-in super-Earths.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1966

A Vibration Isolation Mount

This paper describes a vibration isolation mount for low-frequency isolation, and presents some preliminary test results. The mount described can be designed for any allowable stroke length and can provide the system with a low natural frequency. However, it is limited to an atmospheric environment and a specified load.

VIBRATION↗
NASA NTRS2002

Physiological changes, sleep, and morning mood in an isolated environment

BACKGROUND: Previous isolation studies have shown increased 24-h urine volumes and body weight gains in subjects. This project examined those and other physiological variables in relationship to sleep motor activity, subjective sleep quality, mood, and complaints during confinement. METHODS: Six male and two female subjects lived for 7 d in the National Space Development Agency of Japan's isolation chamber, which simulates the interior of the Japanese Experiment Module. Each 24-h period included 6 h of sleep, 3 meals, and 20 min of exercise. Each morning, subjects completed Sleep Sensation and Complaint Index questionnaires. Catecholamine and creatinine excretion, urine volume, and body weight were measured on the 2 d before and 2 d after confinement, and sleep motor activity was measured during confinement. RESULTS: Confinement produced no significant change in body weight, urine volume, or questionnaire results. In contrast, epinephrine, norepinephrine, and sleep motor activity exhibited significant differences during confinement (p < 0.05). Higher nocturnal norepinephrine excretion correlated with higher sleep motor activity. CONCLUSION: The 24-h epinephrine values were slightly higher than normal throughout the experiment, but lower than for subjects working under time-stress. High sympathetic activity (as indicated by norepinephrine) may have interfered with sleep.

NASA Discipline Space Human Factors↗
NASA NTRS2014

Vibration Isolation Design for the Micro-X Rocket Payload

Micro-X is a NASA-funded, sounding rocket-borne X-ray imaging spectrometer that will allow high precision measurements of velocity structure, ionization state and elemental composition of extended astrophysical systems. One of the biggest challenges in payload design is to maintain the temperature of the detectors during launch. There are several vibration damping stages to prevent energy transmission from the rocket skin to the detector stage, which causes heating during launch. Each stage should be more rigid than the outer stages to achieve vibrational isolation. We describe a major design effort to tune the resonance frequencies of these vibration isolation stages to reduce heating problems prior to the projected launch in the summer of 2014.

Transition-edge sensors↗