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At least 541 records · Page 30

Adequacy of modeling turbulence and related effects on helicopter response

'Blade-fixed' atmospheric turbulence encountered by a helicopter substantially differs from body-fixed (i.e., fuselage) turbulence, because the rotational velocity moves the blade station fore and aft through the turbulence. The present closed-form solution of a frequency-time spectrum for the dominant vertical turbulence velocity at arbitrary blade station defines in what way and in what degree the rotational velocity affects rotor-disk turbulence frequency and temporal characteristics. Blade-flapping response to blade- and body-fixed turbulence is also presented over a range of turbulence-scale length and advance ratio.

George, V. V.↗

All the light we cannot see: Climate manipulations leave short and long‐term imprints in spectral reflectance of trees

Abstract Anthropogenic climate change, particularly changes in temperature and precipitation, affects plants in multiple ways. Because plants respond dynamically to stress and acclimate to changes in growing conditions, diagnosing quantitative plant‐environment relationships is a major challenge. One approach to this problem is to quantify leaf responses using spectral reflectance, which provides rapid, inexpensive, and nondestructive measurements that capture a wealth of information about genotype as well as phenotypic responses to the environment. However, it is unclear how warming and drought affect spectra. To address this gap, we used an open‐air field experiment that manipulates temperature and rainfall in 36 plots at two sites in the boreal‐temperate ecotone of northern Minnesota, USA. We collected leaf spectral reflectance (400–2400 nm) at the peak of the growing season for three consecutive years on juveniles (two to six years old) of five tree species planted within the experiment. We hypothesized that these mid‐season measurements of spectral reflectance capture a snapshot of the leaf phenotype encompassing a suite of physiological, structural, and biochemical responses to both long‐ and short‐time scale environmental conditions. We show that the imprint of environmental conditions experienced by plants hours to weeks before spectral measurements is linked to regions in the spectrum associated with stress, namely the water absorption regions of the near‐infrared and short‐wave infrared. In contrast, the environmental conditions plants experience during leaf development leave lasting imprints on the spectral profiles of leaves, attributable to leaf structure and chemistry (e.g., pigment content and associated ratios). Our analyses show that after accounting for baseline species spectral differences, spectral responses to the environment do not differ among the species. This suggests that building a general framework for understanding forest responses to climate change through spectral metrics may be possible, likely having broader implications if the common responses among species detected here represent a widespread phenomenon. Consequently, these results demonstrate that examining the entire spectrum of leaf reflectance for environmental imprints in contrast to single features (e.g., indices and traits) improves inferences about plant‐environment relationships, which is particularly important in times of unprecedented climate change.

Stefanski, Artur [Department of Forest Resources U↗

Expanded Accident Scenarios and Frequency Characteristics for a Fast Spectrum Molten Salt Reactor in an Integrated Energy System

Integration of advanced nuclear reactors to industrial processes in an integrated energy system (IES) has many potential advantages. The coupling of nuclear power to varied industrial processes introduces additional accident scenarios unique to the specific systems included in the IES. Similarly, noise in one system of the IES could potentially create negative effects in the other systems. Because of the limited amount of comparable nuclear IES operating experience, there is added value in scoping the inherent behavior of these systems in response to these transients. Here, this paper investigates the safety-related behavior of an open-source IES dynamic model of a fast spectrum molten salt reactor (MSR) powering a regenerative Rankine cycle for electricity production and a hybrid sulfur (HyS) cycle for hydrogen production. The simulations include a loss of cooling water to the Rankine cycle, a loss of sulfur in the HyS cycle, and the frequency characteristics of the entire IES across six orders of magnitude of frequency. The results show safe behavior in response to the two accident scenarios, wherein a disruption in heat transfer leads to increased salt temperatures and a decrease in reactor power. The frequency analysis shows that at higher frequencies, temperature changes propagating through an IES are increasingly damped to the point of negligibility.

Dunkle, Nicholas [Univ. of Tennessee, Knoxville, T↗

Dual-pilot tone calibration technique

Pilot-based calibration techniques are used to reduce the effects of multipath fading in mobile satellite receivers. One of the more recent of these techniques, namely the tone calibration technique (TCT), suggests transmitting double sideband modulation with the pilot tone located at the center of its spectrum where the amplitude and phase characteristics of the channel are most stable. To 'make room' for the pilot in the presence of the Doppler shift, the equivalent low-pass data sidebands must be shaped so as to have zero response in the neighborhood of dc. Other techniques such as transparent tone-in-band (TTIB) similarly 'notch out' a hole in the center of the data spectrum for location of the pilot. An alternate possibility which is at the same time much more bandwidth efficient than TCT is a dual-pilot tone calibration technique (DPTCT) that symmetrically locates a pair of pilots outside the data spectrum near the band edges of the channel. The operation and performance of DPTCT are analyzed, and its effectiveness is compared to that of the single tone TCT technique.

Simon, Marvin K.↗

Neutron Response of the EJ-254 Boron-Loaded Plastic Scintillator

Organic scintillators doped with capture agents provide a detectable signal for neutrons over a broad energy range. This work characterizes the fast and slow neutron response of EJ-254, an organic plastic scintillator with 5 loading by weight. For fast neutrons, the primary mechanism for light generation in organic scintillators is n-p elastic scattering. To study the fast neutron response, the proton light yield of EJ-254 was measured at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory. Using a broad-spectrum neutron source and a double time-of-flight technique, the EJ-254 proton light yield was obtained over the energy range of approximately 270 keV to 4.5 MeV and determined to be in agreement with other plastic scintillators comprised of the same polymer base. To isolate the slow neutron response, an AmBe source with polyethylene moderator was made incident on the EJ-254 scintillator surrounded by an array of EJ-309 observation detectors. Events in the EJ-254 target coincident with the signature 477.6 keV γ ray (resulting from de-excitation of the residual 7Li nucleus following boron neutron capture) were identified. Pulse shape discrimination was used to evaluate the temporal differences in the response of EJ-254 scintillation signals arising from γ-ray and fast/slow neutron interactions. Clear separation between γ-ray and fast neutrons signals was not achieved and the neutron capture feature was observed to overlap both the γ-ray and fast neutron bands. Taking into account the electron light nonproportionality, the neutron capture light yield in EJ-254 was determined to be 89.4±1.1 keVee.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

Eta Carinae: Linelist for the Emission Spectrum of the Weigelt Blobs in the 1700-10400Angstrom Wavelength Region

Aims. We present line identifications in the 1700 to 10400A region for the Weigelt Blobs B and D, located 0.1 to 0.3" NNW of Eta Carinae. The aim of this work is to characterize the behavior of these luminous, dense gas condensations in response to the broad maximum and short minimum states of Eta Carinae during its 5.54-year spectroscopic period. Methods. The observations were carried out during March 1998, the minimum spectrum, and in February 1999, early maximum spectrum, with the Hubble Space Telescope/Space Telescope Imaging Spectrograph (HST/STIS) from 1640 to 10400A using the 52"x0.1" aperture centered on Eta Carinae at position angle -28 degrees. Extractions of the reduced spectrum centered on Weigelt B and D, 0.28: in length along the slit, were used to identify the narrow, nebular emission lines, measure their wavelengths and estimate their fluxes. Results. A linelist of 1500 lines is presented for the maximum and minimum states of combined Weigelt blobs B and D. The spectra are dominated by emission lines from the iron-group elements, but include lines from lighter elements. They include parity permitted and forbidden lines. A number of lines are fluorescent lines pumped by H Ly alpha. Other lines show anomalous excitation.

Zethson, T.↗

Computational Evaluation of Thermal Response of Open-Cell Foam With Circular Pore (Computional Evaluation of Thermal Response of Open-Cell Foam with Circular Pore)

The evaluation of effective material properties in heterogeneous materials (e.g., composites or multicomponent structures) critically relevant to a wide spectrum of applications, including nuclear power, electronic packaging, flame retardants, hypersonics, and gas turbine power. The work described in this paper is centered around the numerical assessment of the thermal behavior of porous materials obtained from finite element thermal modeling and simulation. Here, two-dimensional, steady state analyses were performed on unit cells with centered, circular pores using a second order accurate Galerkin finite element method (FEM). The effective thermal conductivities of the porous systems were examined, encompassing a range of porosities from 4.9% to 60.1%. The geometries of the models were generated based on ordered circular pores for each modeled porosity level. The system response quantity (SRQ) under investigation was the dimensionless effective thermal conductivity across the unit cell. The dimensionless effective thermal conductivity was compared across all simulated cases, producing a trend between porosity and effective thermal conductivity. In the presented investigation, the method of manufactured solutions (MMS) was used to perform code verification, and the grid convergence index (GCI) was employed to estimate discretization uncertainty as solution verification. Code verification concluded an approximately second order accurate Galerkin FEM solver. It was found that the introduction of porosity to the unit cell material structure reduces effective thermal conductivity, as anticipated. Numerical results obtained in this study are compared to an analytical solution and to a sample of empirical data.

36 MATERIALS SCIENCE↗

Predicting Cell Death and Mutation Frequency for a Wide Spectrum of LET by Assuming DNA Break Clustering Inside Repair Domains

Cosmic radiation, which is composed of high charged and energy (HZE) particles, is responsible for cell death and mutation, which may be involved in cancer induction. Mutations are consequences of mis-repaired DNA breaks – especially double-strand breaks (DSBs) – that induce inter- and intra-chromosomal rearrangements (translocations, deletions, inversion). In this study, a computer simulation model is used to investigate the clustering of DSBs in repair domains, previously evidenced by our group in human breast cells [1]. This model is calibrated with experimental data measuring persistent 53BP1 radiation-induced foci (RIF) and is used to explain the high relative biological effectiveness (RBE) of HZE for both cell death and DNA mutation frequencies. We first validate our DSB cluster model using a new track structure model deployed on a simple geometrical configuration for repair domains in the nucleus; then we extend the scope from cell death to mutation induction. This work suggests that mechanism based on DSB repair process can explain several biological effects induced by HZE particles on different type of living cells

Plante, Ianik↗

Carrier Localization and Spontaneous Formation of Two-Dimensional Polarization Domain in Halide Perovskites

Halide perovskites are known for their rich phase diagram and superior performance in diverse optoelectronics applications. The latter property is often attributed to the long electron-hole recombination time, whose underlying physical mechanism has been a long-standing controversy. In this Letter, we investigate the transport and localization properties of electron and hole carriers in a prototypical halide perovskite (CsPbBr 3 ), through ab initio tight-binding nonadiabatic dynamics approach for large-scale (tens of nm size) supercell calculations, to simulate electron and ion dynamics on the same footing. Here, we found distinct structural, lattice polarization, and electron-phonon coupling properties at low (below 100 K) and high temperatures, consistent with experimental observations. In particular, at low temperature we find spontaneous formation of polar grain boundaries in the nonpolar bulk systems, which result in two-dimensional polarization patterns that serve to localize and separate electrons and holes. We reveal phonon-assisted variable-range hopping mostly responsible for low-temperature transport, and their characteristic frequency correlates with temperature-dependent phonon power spectrum and energy oscillation frequency in nonadiabatic dynamics. We answer the critical questions of long electron-hole recombination lifetime at low temperature and offer the correlation among polarization domains, electron-phonon couplings, and photocarrier dynamics.

Carrier generation & recombination↗

Scaling Automatic Vector Data Alignment to Satellite Imagery

Given the tremendous volume of accessible Earth Observation (EO) data, there is a need to develop scalable Geospatial Artificial Intelligence (GeoAI) solutions for time-sensitive applications. Scalability in this context refers to rapidly processing large-scale EO data using high performance computing resources. Accurate mapping of the built environment from remote sensing (RS) imagery has been one of the crucial components in GeoAI workflows for a wide spectrum of humanitarian applications. Derived vector data of built environment is often leveraged for disaster preparedness and response activities. However, factors such as differences in ortho-rectification, atmospheric conditions and human error, results in spatial misalignment between vector data and the timely available RS imagery. Model training for downstream tasks such as object detection, change analysis, etc., is negatively impacted due to such spatial misalignment. Although there has been progress towards automatic alignment of vector data, the lack of scalability remains an open research challenge. This paper proposes to leverage parallel computing to optimize an automatic vector data alignment workflow. It further employs CPU-level multi-core parallelism for improving the performance of the workflow for scalable built environment mapping. We report observations and discuss findings from the preliminary experiments performed on the Summit Supercomputer.

Potnis, Abhishek↗

Meeting the Challenges of Modern Transit through the Integration of Traditional Transit, On-Demand Micro-Transit Services and Vehicle Automation - A Case Study in Chandler, Arizona

Current technology trends of vehicle automation, electrification and on-demand transit are providing new tools to develop effective public mobility services, yet need to be balanced with traditional modes to serve the spectrum of demand effectively and efficiently. Automated vehicle transportation network company (TNC) services, better known as 'Robotaxis' are beginning to proliferate and scale across the US, with Waymo as the lead commercial entity. Chandler, AZ was the first fully automated deployment of Waymo technology. Chandler was also one of the first municipalities in Arizona to roll out micro-transit service to its citizens in 2022. At present the Chandler Flex micro-transit program is beginning to partner with Waymo to augment micro-transit services during peak demands, another first in the nation. However, the mix of services in Chandler relies not only on new technology, but also on traditional modes including fixed route transit and para-transit services. These are blended and balanced such that both old and new modes are applied within the context in which each excel. This presentation will provide background on the Chandler, AZ public mobility services, and the performance metrics that govern their use and selection within the spectrum of development and population density as well as socio-demographics within Chandler. Additionally, the behavioral response of the use of unmanned, automated vehicles employed to augment micro-transit is novel, the first in the nation - and initial feedback from public transit constituents in Chandler will be shared.

24 POWER TRANSMISSION AND DISTRIBUTION↗

Aliased noise in radiometric measurements

The magnitude of aliased noise that degrades the accuracy of continuous reconstructions of discrete radiometric measurements was evaluated as a function of the spatial response and sampling intervals of the radiometer, and of the resolution of the reconstructed measurements. A Wiener spectrum, representative of a wide range of scenes, was used to characterize the radiance fluctuations.

Huck, F. O.↗

Effects of volume averaging on the line spectra of vertical velocity from multiple-Doppler radar observations

Calculations of the ratio of the true one-dimensional spectrum of vertical velocity and that measured with multiple-Doppler radar beams are presented. It was assumed that the effects of pulse volume averaging and objective analysis routines is replacement of a point measurement with a volume integral. A u and v estimate was assumed to be feasible when orthogonal radars are not available. Also, the target fluid was configured as having an infinite vertical dimension, zero vertical velocity at the top and bottom, and having homogeneous and isotropic turbulence with a Kolmogorov energy spectrum. The ratio obtained indicated that equal resolutions among radars yields a monotonically decreasing, wavenumber-dependent response function. A gain of 0.95 was demonstrated in an experimental situation with 40 levels. Possible errors introduced when using unequal resolution radars were discussed. Finally, it was found that, for some flows, the extent of attenuation depends on the number of vertical levels resolvable by the radars.

Gal-Chen, T.↗

IR detectors based on n-i-p-i superlattices

The principles of operation of n-i-p-i photodetectors are discussed. Special consideration is given to issues that are relevant to the performance of IR detectors such as noise, dark current, and surface effects. In addition, a novel IR detector that promises to provide information about the spectral distribution of the infrared radiation emitted from an object and, consequently, about its temperature, independent of the distance between detector and object is discussed. This detector makes use of the possibility to modulate the internal electric fields of an n-i-p-i superlattice with an applied voltage. By this technique the spectral responsivity of the detector may be controlled electrically and some information about the shape of the emission spectrum may be obtained.

Ruden, P. Paul↗

A Coupled Mathematical Model of the Intracellular Replication of Dengue Virus and the Host Cell Immune Response to Infection

Dengue virus (DV) is a positive-strand RNA virus of the Flavivirus genus. It is one of the most prevalent mosquito-borne viruses, infecting globally 390 million individuals per year. The clinical spectrum of DV infection ranges from an asymptomatic course to severe complications such as dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS), the latter because of severe plasma leakage. Given that the outcome of infection is likely determined by the kinetics of viral replication and the antiviral host cell immune response (HIR) it is of importance to understand the interaction between these two parameters. In this study, we use mathematical modeling to characterize and understand the complex interplay between intracellular DV replication and the host cells' defense mechanisms. We first measured viral RNA, viral protein, and virus particle production in Huh7 cells, which exhibit a notoriously weak intrinsic antiviral response. Based on these measurements, we developed a detailed intracellular DV replication model. We then measured replication in IFN competent A549 cells and used this data to couple the replication model with a model describing IFN activation and production of IFN stimulated genes (ISGs), as well as their interplay with DV replication. By comparing the cell line specific DV replication, we found that host factors involved in replication complex formation and virus particle production are crucial for replication efficiency. Regarding possible modes of action of the HIR, our model fits suggest that the HIR mainly affects DV RNA translation initiation, cytosolic DV RNA degradation, and naïve cell infection. We further analyzed the potential of direct acting antiviral drugs targeting different processes of the DV lifecycle in silico and found that targeting RNA synthesis and virus assembly and release are the most promising anti-DV drug targets.

59 BASIC BIOLOGICAL SCIENCES↗

Forced Oscillation Source Location of Bulk Power Systems Using Synchrosqueezing Wavelet Transform

Forced oscillation source location (FOSL) plays a significant role in mitigating forced oscillations (FOs), which threaten the power system stability. Here, this paper proposes a data-driven approach for FOSL in power systems using synchrosqueezing wavelet transform (SWT). The proposed approach conducts SWT on the measured system responses to obtain the SWT matrix. Then, the SWT-based dissipating energy flow (DEF) model in time-frequency domain and dissipating energy spectrum (DES) model in frequency domain are derived from the traditional DEF model. Further, the characteristics of SWT-based DEF and DES are revealed by referring to the traditional DEF, and the FOSL criteria of the SWT-based DEF and DES can be hereby obtained. Using the obtained FOSL criteria, the FO source can be located from the measured responses. The performance of the proposed FOSL method is evaluated by simulation data of the WECC 179-bus test system and field-measurement PMU data of the ISO New England. The results confirm the accuracy and efficiency of the proposed method in the FOSL.

24 POWER TRANSMISSION AND DISTRIBUTION↗

Exact dynamic responses of periodic multi-span beams under convected pressure fields

Response of a structure to a convected pressure field generated by far-field jet-noise or turbulent boundary layer is often of interest in engineering. The structure considered in present study is a periodic beam with equally rotational elastic supports. The convected pressure field is characterized by a broad frequency spectrum and a particular convection velocity. In the first order approximation, all the frequency components in the pressure spectrum are convected with the same velocity. In this paper, both finitely and infinitely long periodic beams under convected harmonic pressure are investigated. The exact harmonic responses are obtained by introducing new expressions of mode shapes for these two types of beams into the normal mode approach. Thus, both locations and values of the response peaks in the propagation bands can be precisely predicted and the important coincidence phenomenon can be investigated in exact terms. This work provides a foundation on which the study on vibration control of structure can be conducted.

Zhu, Li-Ping↗

Supporting Hazard Analysis for Wildfire Response Using fmdtools and MIKA

The System Wide Safety (SWS) Safety Demonstrator (SD) Series drives development of an increasingly capable In-Time Aviation Safety Management System (IASMS) focusing on humanitarian applications, starting with wildfire response (SD-1). The goals of this report are to (1) provide an early hazard analysis and mitigation evaluation of wildfire response to support these efforts and (2) provide a demonstration of capabilities of the Fault Model Design Tools (fmdtools) and Manager for Intelligent Knowledge Access (MIKA) tools. fmdtools provides a modeling, simulation, and resiliency analysis framework in which a wildfire response model, the System Modeling and Analysis of Resiliency in Scalable Traffic Management for Emergency Response Operations (SMARt-STEReO), is built. MIKA is an intelligent knowledge manager with several capabilities, including assisting in hazard analysis by extracting and analyzing hazards from historical incident reports. The following topics are covered in the report: Understanding Wildfire Hazard Dynamics. We provide a description and simulated examples of how hazards occur in the SMARt-STEReO model of wildfire response and their effect on its outcome. This provides a common mental model and focuses the analysis presented in the remainder of the report. Wildfire Hazard Identification. MIKA identifies wildfire hazards from three relevant datasets: the ICS-209-PLUS, SAFECOM, and SAFENET. Hazards are manually organized into a taxonomy and MIKA analyzes each hazard’s effects, likelihood, severity, and risk. Evaluating Mitigation Strategies. The SMARt-STEReO wildfire response model built in fmdtools evaluates a subset of identified hazards. Specifically, we simulate the effect of communications faults and equipment faults on operator safety, the effect of changing winds and flammability, and a scenario with multiple ignition points and heavy smoke. Tool Limitations and Usage Considerations. We provide a discussion of appropriate tool use cases as well as limitations and considerations for usage. The tool findings are used to synthesize recommendations for wildfire response operations, which can be captured as part of an IASMS. Key recommendations are as follows: Hazards are identified from a broad spectrum of sources including aircraft subsystems, operational sources, and ground crew operations. Highest risk operational environment hazards identified are Evacuations. The highest risk manned aerial operations hazard categorized is Jumper Operations Mishap. Ground crew hazards that are highest risk are Burns, Cargo Operations Overhead, Dehydration, Entrapment, Falling Objects, Heart Attacks, Heat Exhaustion, Inadequate Training or Certification, Vehicle Breakdown, and Vehicle Collision. Modelled containment failures arise from a mismatch between the difficulty of the firefighting scenario and the capacity (e.g., speed, effectiveness, awareness) of the response. In firefighting scenarios where containment is possible (e.g., because the fire does not spread too quickly), these mismatches can occur because of a change in environmental conditions (e.g., wind, flammability, etc) or because of planning, equipment, or communications faults. Improvements to communications increase the capacity of the firefighting response by reducing the time needed to respond to the fire. While surveillance does not increase this capacity by itself, it increases operator safety by increasing state awareness, enabling firefighters to evade approaching fires. Increasing both has a synergistic effect. In general, these performance and resilience increases generalize over fault scenarios as well as unforeseen changes to circumstances (i.e., wind, aridity, etc.). However, these improvements need to be designed so as not to make the system prone to persistent large-scale communications outages, which can reduce performance.

Hazard analysis↗