Scholarly Works, Aerospace and Ocean Engineering

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Single-Satellite-Based Geolocation of Broadcast GNSS Spoofers from Low Earth Orbit
Clements, Zachary L.; Ellis, Patrick B.; Goodridge, Iain; Murrian, Matthew J.; Psiaki, Mark L.; Humphreys, Todd E. (Institute of Navigation, 2026)
This paper presents an analysis and experimental demonstration of single-satellite single-pass geolocation of a terrestrial broadcast global navigation satellite system (GNSS) spoofer from low Earth orbit (LEO). The proliferation of LEObased GNSS receivers offers the prospect of unprecedented spectrum awareness, enabling persistent GNSS interference detection and geolocation. Accurate LEO-based single-receiver emitter geolocation is possible when a range-rate time history can be extracted for the emitter. This paper presents a technique crafted specifically for indiscriminate broadcast-type GNSS spoofing signals. Furthermore, it explores how unmodeled oscillator instability and worst-case spoofer-introduced signal variations degrade the geolocation estimate. The proposed geolocation technique is validated by a controlled experiment, in partnership with Spire Global, in which a LEO-based receiver captures broadcast GNSS spoofing signals transmitted from a known ground station on a non-GNSS frequency band.
Spherical Grid-Based IMU/Lidar Localization and Uncertainty Evaluation Using Signal Quantization
Hassani, Ali; Joerger, Mathieu (Institute of Navigation, 2025)
This paper describes the design, analysis, and experimental evaluation of a spherical grid-based localization algorithm that leverages quantization theory to bound navigation uncertainty. This algorithm integrates data from light detection and ranging (lidar) and inertial measuring units in an iterative extended Kalman filter to estimate the position and orientation of a moving vehicle. An analytical bound is derived from the vehicle’s state estimation error, which accounts for both random measurement noise and the loss of localization information caused by gridding. The performance of the proposed approach is analyzed and compared with that of a brute-force spherical grid-based method and a landmark-based method in an indoor environment, whereas an outdoor experiment verifies the practicality of the method in a realistic driving scenario.
Pilots and Other Predictable Elements of the Starlink Ku-Band Downlink
Qin, Wenkai; Psiaki, Mark L.; Bowman, John R.; Humphreys, Todd E. (2026)
We identify and characterize dedicated pilot symbols and other predictable elements embedded within the Starlink Ku-band downlink waveform. Exploitation of these predictable elements enables precise opportunistic positioning, navigation, and timing using compact, low-gain receivers by maximizing the signal processing gain available for signal acquisition and time-of-arrival (TOA) estimation. We develop an acquisition and demodulation framework to decode Starlink frames and disclose the explicit sequences of the edge pilots—bands of 4QAM symbols located at both edges of each Starlink channel that apparently repeat identically across all frames, beams, channels, and satellites. We further reveal that the great majority of QPSK-modulated symbols do not carry high-entropy user data but instead follow a regular tessellated structure superimposed on a constant reference template. We demonstrate that exploiting frame-level predictable elements yields a processing gain of approximately 48 dB, thereby enabling low-cost, compact receivers to extract precise TOA measurements even from low-SNR Starlink side beams.
Network-Based GNSS Jamming Prediction Enabling Wideband Interference Observation
Jada, Sandeep; Psiaki, Mark L.; Joerger, Mathieu (Institute of Navigation, 2023)
In this paper, we develop and evaluate autonomous, self-calibrating, receiver-independent C/N0-based jamming detection algorithms capable of processing data from large receiver networks. The algorithm uses optimal detectors that target a predefined false alert rate. Using this algorithm, we processed 8 months of data from hundreds of receivers and identified patterns in jamming detection consistent with intentional interference, providing an opportunity to validate the C/N0 detector. We design a portable experimental RF data collection setup and develop an optimal power-based jamming monitor to independently detect jamming. With this setup, we detected a genuine jamming event while driving on I-25 in Colorado, USA, and validated the C/N0-based detector through time-frequency analysis of wideband RF data from the event.
High-Integrity Modeling of Nonstationary Noise Processes for GNSS/INS Integration
Gallon, Elisa; Joerger, Mathieu; Pervan, Boris (Institute of Navigation, 2025)
This paper describes a power spectral density (PSD) bounding method for deriving high-integrity models of stationary and nonstationary time-correlated measurement error processes. The method is intended for safety-critical commercial aircraft navigation where robust sensor models are required to predict error bounds on position and orientation estimates. These bounds are used both in navigation system design for integrity performance analyses and in operation to determine whether a pilot should proceed with an operation. In prior work, we used PSD upper-bounding to obtain high-integrity models of time-correlated global navigation satellite system (GNSS) measurement errors. However, the method was limited to stationary processes. In this paper, we derive an approach to expand the concept of PSD bounding to nonstationary error modeling for Kalman filter-based estimation using GNSSs and inertial navigation systems in aircraft navigation applications.
GPS Spoofing Resilience via NMA/Watermarks Authentication and IMU Prediction
Esswein, Michael C.; Psiaki, Mark L. (2026)
A tightly coupled GPS/IMU estimation algorithm is developed assuming that all received measurements must first be authenticated by CHIps MEssage Robust Authentication (CHIMERA). CHIMERA is designed to authenticate incoming GPS signals through two methods referred to as the fast and slow channels. This paper analyzes the accuracy of estimation algorithms for both of these channels when using an Inertial Measurement Unit (IMU) to compensate for authentication delay, and it considers the effects of different quality IMUs. This paper also introduces a concept of authentication staggering as a possible approach to improve location and attitude accuracy. The estimation algorithm is modified to account for authentication staggering and different possible estimation architectures are developed for this purpose. The results indicate that the fast channel produces typical GPS navigation accuracy for different quality IMUs while the slow channel has moderately degraded navigation accuracy even with a navigation-grade IMU and highly degraded accuracy with tactical- and MEMS-grade IMUs. Staggering the authentication times of the GPS satellites can be used to improve navigation accuracy for the slow channel.
Confinement in fibrous environments positions and orients mitotic spindles
Sarkar, Apurba; Jana, Aniket; Agashe, Atharva; Wang, Ji; Kapania, Rakesh; Gov, Nir S.; DeLuca, Jennifer G.; Paul, Raja; Nain, Amrinder (Oxford University Press, 2025-07)
Accurate positioning of the mitotic spindle within the rounded cell body is critical to physiological maintenance. Mitotic cells encounter confinement from neighboring cells or the extracellular matrix (ECM), which can cause rotation of mitotic spindles and tilting of the metaphase plate (MP). To understand the effect of confinement on mitosis by fibers (ECM confinement), we use flexible ECM-mimicking nanofibers that allow natural rounding of the cell body while confining it to differing levels. Rounded mitotic bodies are anchored in place by actin retraction fibers (RFs) originating from adhesions on fibers. We discover that the extent of confinement influences RF organization in 3D, forming triangular and band-like patterns on the cell cortex under low and high confinement, respectively. Our mechanistic analysis reveals that the patterning of RFs on the cell cortex is the primary driver of the MP rotation. A stochastic Monte Carlo simulation of the centrosome, chromosome, membrane interactions, and 3D arrangement of RFs recovers MP tilting trends observed experimentally. Under high ECM confinement, the fibers can mechanically pinch the cortex, causing the MP to have localized deformations at contact sites with fibers. Interestingly, high ECM confinement leads to low and high MP tilts, which we mechanistically show to depend upon the extent of cortical deformation, RF patterning, and MP position. We identify that cortical deformation and RFs work in tandem to limit MP tilt, while asymmetric positioning of MP leads to high tilts. Overall, we provide fundamental insights into how mitosis may proceed in ECM-confining microenvironments in vivo.
Mechanical cues guide the formation and patterning of 3D spheroids in fibrous environments
Sharma, Sharan; Agashe, Atharva; Hill, Jennifer C.; Ganguly, Keya; Sharma, Puja; Richards, Tara D.; Huang, Weijian; Kaczorowski, David J.; Sanchez, Pablo G.; Kapania, Rakesh; Phillippi, Julie A.; Nain, Amrinder (Oxford University Press, 2025-09)
Multicellular spheroids have shown great promise in 3D biology. Many techniques exist to form spheroids, but how cells take mechanical advantage of native fibrous extracellular matrix (ECM) to form spheroids remains unknown. Here, we identify the role of fiber diameter, architecture, and cell contractility on spheroids’ spontaneous formation and growth in ECM-mimicking fiber networks. We show that matrix deformability revealed through force measurements on aligned fiber networks promotes spheroid formation independent of fiber diameter. At the same time, larger-diameter crosshatched networks of low deformability abrogate spheroid formation. Thus, designing fiber networks of varying diameters and architectures allows spatial patterning of spheroids and monolayers simultaneously. Forces quantified during spheroid formation revealed the contractile role of Rho-associated protein kinase in spheroid formation and maintenance. Interestingly, we observed spheroid–spheroid and multiple spheroid mergers initiated by cell exchanges to form cellular bridges connecting the two spheroids. Unexpectedly, we found large pericyte spheroids contract rhythmically. Transcriptomic analysis revealed striking changes in cell–cell, cell–matrix, and mechanosensing gene expression profiles concordant with spheroid assembly on fiber networks. Overall, we ascertained that contractility and network deformability work together to spontaneously form and pattern 3D spheroids, potentially connecting in vivo matrix biology with developmental, disease, and regenerative biology.
Flow Control of a Rim-Driven Propeller Using Vortex Generators for Enhanced Open-Water Performance
Bang, Ju Seong; Yoon, Seok Pyo; Brizzolara, Stefano; Kinnas, Spyros A.; Ahn, Hyung Taek (MDPI, 2026-01-28)
Rim-driven propellers (RDPs) have attracted renewed attention as an efficient propulsion concept for integrated electric propulsion systems, yet their structural configuration inherently limits duct geometry modification, and viscous losses associated with boundary layer separation near the duct trailing edge remain a key performance constraint. In this study, a vortex generator-based flow control strategy is proposed as a practical means of improving RDP performance without altering the duct geometry. Reynolds-averaged Navier–Stokes (RANS) simulations were conducted to examine the effects of vortex generators installed on the outer surface of the duct, with numerical reliability ensured through a grid convergence index (GCI) analysis. A steady-state multiple reference frame (MRF) approach was employed, and the resulting flow characteristics were analyzed using velocity profiles, line integral convolution (LIC) visualization, pressure field analysis, and distribution of the flow field in the wake. The results show that the vortex generators effectively delay boundary layer separation near the duct trailing edge by re-energizing the near-wall flow, thereby enhancing flow attachment and pressure recovery. Consequently, consistent improvements in thrust coefficient and propulsive efficiency are achieved over the entire range of advance ratios, while the increase in torque coefficient remains negligible. These findings demonstrate that vortex generator-based flow control offers a practical and effective approach for enhancing the open-water performance of rim-driven propellers under structural constraints.
Analytical interaction potential for Lennard-Jones rods
Wang, Junwen; Seidel, Gary D.; Cheng, Shengfeng (American Physical Society, 2025-01-03)
An analytical form has been derived using Ostrogradsky's integration method for the interaction between two thin rods of finite lengths in arbitrary relative configurations in a three-dimensional space, each treated as a line of point particles interacting through the Lennard-Jones 12-6 potential. Simplified analytical forms for coplanar, parallel, and collinear rods are also derived. Exact expressions for the force and torque between the rods are obtained. Similar results for a point particle interacting with a thin rod are provided. These interaction potentials can be widely used for analytical descriptions and computational modeling of systems involving rodlike objects such as liquid crystals, colloids, polymers, elongated viruses and bacteria, and filamentous materials including carbon nanotubes, nanowires, biological filaments, and their bundles.
Bilayer surrogate brain response under various blast loading conditions
Norris, Carly; Arnold, B.; Wilkes, Jessica M.; Squibb, Carson; Nelson, Allison J.; Schwenker, Hannah; Mesisca, Jenna K.; Vossenberg, A.; Vandevord, Pamela J. (Springer, 2024-08-01)
Variations in the experimental constraints applied within blast simulations can result in dramatically different measured biomechanical responses. Ultimately, this limits the comparison of data between research groups and leads to further inquisitions about the "correct" biomechanics experienced in blast environments. A novel bilayer surrogate brain was exposed to blast waves generated from advanced blast simulators (ABSs) where detonation source, boundary conditions, and ABS geometry were varied. The surrogate was comprised of Sylgard 527 (1:1) as a gray matter simulant and Sylgard 527 (1:1.2) as a white matter simulant. The intracranial pressure response of this surrogate brain was measured in the frontal region under primary blast loading while suspended in a polyurethane spherical shell with 5 mm thickness and filled with water to represent the cerebrospinal fluid. Outcomes of this work discuss considerations for future experimental designs and aim to address sources of variability confounding interpretation of biomechanical responses.
Atmospheric Tides in the Middle and Upper Atmosphere of Mars at Northern High Latitudes: A Comparison of MAVEN-EUVM and MRO-MCS Observations With Model Results
Kumar, Aishwarya; England, Scott L.; Liu, Guiping; Thiemann, Edward M. B. (American Geophysical Union, 2024-04-01)
Much of the variability in the Martian thermosphere can be attributed to vertically propagating atmospheric tides that are known to achieve significant amplitudes in this region. Concurrent observations from different altitudes have been used previously to discern the vertical propagation characteristics of tides but have primarily focused on low latitudes. The spectrum of tides and their vertical evolution are thereby less constrained at high latitudes. Few studies that have focused on high latitudes identified wavenumber-3 structures which were interpreted to originate mainly from the non-migrating tides SE1 and DE2. This paper presents the first analysis of MAVEN-EUVM solar occultation observations to deduce atmospheric tides in the Martian thermosphere. These are compared to tides observed by MRO-MCS in the middle atmosphere for six cases at high northern latitudes. To identify vertical propagation, wave signatures in the middle and upper atmosphere are compared and are found to be dominated by a mix of zonal wavenumbers-2 and -3 in fixed local time. MCS observations show eastward propagating tides dominate, specifically highlighting SE1 near 76 km. Additionally, these observations indicate the presence of stationary planetary waves and terdiurnal tides. Mars Climate Database also indicates the presence of SE1, DE2, DE1, S0, TW1, and T0 tides. A change in the dominant wavenumber component with local time is seen, which is attributed to the presence of all three diurnal, semidiurnal and terdiurnal components at these latitudes. The significant decrease in the diurnal tide amplitude indicates the effect of zonal mean wind on vertical propagation. Atmospheric tides are a kind of wave in the Martian atmosphere that can cause large oscillations in temperature, density, and pressure. Concurrent observations from different altitudes can determine how tides vary as they propagate into the upper atmosphere. Several previous studies have observed wave signatures from a range of heights but focused mainly on equatorial regions. Previous observations from near polar regions revealed strong tidal signatures, producing wave patterns with three peaks in the upper and middle atmosphere, attributed to a mix of waves with one and half a Mars day frequency. Here, using observations from two instruments that simultaneously measure the middle and upper atmosphere of Mars, dominant wave signatures at high latitudes are identified and how they change between these regions are examined. This study presents the first observations of atmospheric tides from new data derived from the extinction of solar radiation in the Martian upper atmosphere. Additionally, the observations are compared to a model, providing insight into how well the model captures the observations. A key finding is that the strongest wave component seen may vary with local time due to the presence of three different waves with one, half, and third of a Mars day frequency. This study presents the first analysis of tides from solar occultation observations at Mars The dominant wavenumber can change with local time due to the presence of tides with multiple periods at high latitudes Diurnal tides in the model diminish with altitude, suggesting the influence of mean winds on vertical propagation
Semidiurnal Non-Migrating Tides in the Middle Thermosphere From Far Ultraviolet Observations
Krier, Christopher S.; England, Scott L. (American Geophysical Union, 2024-04-01)
Much of the longitude/local time dependence of the thermosphere is controlled by non-migrating tides. Observations of semidiurnal (12-hr) tides between 120 and 200 km altitude, that is, the middle thermosphere, are rare owing to the lack of systematic measurements in this region. Since late 2018, the Global-scale Observations of the Limb and Disk (GOLD) Mission has provided unique measurements of thermospheric disk temperature and the column density ratio of atomic oxygen to molecular nitrogen ratio (sigma O/N2) from geostationary orbit. In this paper, we present an approach to deduce the strongest semidiurnal non-migrating tides in the middle thermosphere by adapting the method of Krier et al. (2021, ) that deduces diurnal non-migrating tides in simultaneous observations of temperature and sigma O/N2 made by GOLD. Testing of this approach suggests that the principal sources of uncertainties in the derived semidiurnal non-migrating tides are the limitation on the longitudes sampled, such that uncertainties are higher for tides with longer horizontal wavelength, and contamination of the local time sums by stationary planetary waves, which causes amplitudes to be overestimated. Our approach is applied to GOLD data during solstice conditions in 2019-2021. Comparison to models yield disagreements which are likely due to uncertainties intrinsic to the method and/or misrepresentation of tidal dynamics in the models. These results are the first observations of semidiurnal non-migrating tides in the middle thermosphere from a geostationary observational platform. A class of atmospheric waves called non-migrating tides governs a significant portion of the planetary-scale dynamics of the upper atmosphere. Their impacts have consequences on the variability of the embedded plasma layer, the ionosphere, upon which many space-based technologies are based such as radio and the Global Positioning System (GPS). There are limited observations of these waves in the middle thermosphere, between about 120 and 200 km altitude. Model-observation comparison of tides in this region are needed to assess the performance of physics-based and empirical models. A previous work presented an approach to deduce diurnal non-migrating tides from observations of temperature and composition collected by the NASA Global-scale Observations of the Limb and Disk instrument on a telecommunications satellite in a high Earth orbit fixed over the mouth of the Amazon River. This paper adapts the approach for semidiurnal non-migrating tides. Uncertainties inherent to this approach applied to semidiurnal tides are discussed. We reveal the first observations of these waves in the upper atmosphere from a geostationary platform and interpret results using models. Method to infer semidiurnal non-migrating tides in simultaneous measurements of thermospheric temperature and composition Sources of uncertainty are identified by testing the approach on idealistic data sampled in geostationary orbit observational geometry Major discrepancies are found between SE2, S0, and SW1 derived from Global-scale Observations of the Limb and Disk observations and those simulated by models
Retrieval of Ar, N2, O, and CO in the Martian Thermosphere Using Dayglow Limb Observations by EMM EMUS
Evans, J. S.; Deighan, J.; Jain, S.; Veibell, V.; Correira, J.; Al Matroushi, H.; Al Mazmi, H.; Chaffin, M.; Curry, S.; El-Kork, N.; England, Scott L.; Eparvier, F.; Fillingim, M.; Holsclaw, G.; Khalil, M.; Lillis, R.; Lootah, F.; Mahmoud, S.; Plummer, T.; Soto, E.; Tennyson, J.; Thiemann, E.; Yurchenko, S. N. (American Geophysical Union, 2024-04-01)
The Emirates Ultraviolet Spectrometer (EMUS) onboard the Emirates Mars Mission (EMM) Hope probe images Mars at wavelengths extending from approximately 100 to 170 nm. EMUS observations began in February 2021 and cover over a full Mars year. We report the first limb scan observations at Mars of ultraviolet emissions Ar I 106.6 nm, N I 120 nm, and carbon monoxide (CO) Fourth Positive Group (A - X) band system excited by electron impact on CO. We use EMUS limb scan observations to retrieve number density profiles of argon, molecular nitrogen, atomic oxygen, and CO in the upper atmosphere of Mars from 130 to 160 km. CO is a sensitive tracer of the thermal profile and winds in Mars' middle atmosphere and the chemistry that balances CO2 in the atmosphere of Mars. EMUS insertion orbit special observations demonstrate that far ultraviolet limb measurements of the Martian thermosphere can be spectroscopically analyzed with a robust retrieval algorithm to further quantify variations of CO composition in the Martian upper atmosphere.
Variability of Atomic Hydrogen Brightness in the Martian Exosphere: Insights From the Emirates Ultraviolet Spectrometer on Board Emirates Mars Mission
Susarla, R.; Deighan, J.; Chaffin, M. S.; Jain, S.; Lillis, R. J.; Chirakkil, K.; Brain, D.; Thiemann, E.; Eparvier, F.; Lootah, F.; Holsclaw, G.; Gacesa, M.; Fillingim, M. O.; El-Kork, N.; England, Scott L.; Evans, J. S.; AlMazmi, H.; AlMatroushi, H. (American Geophysical Union, 2024-06-01)
The Emirates Mars Ultraviolet Spectrometer (EMUS), aboard the Emirates Mars Mission (EMM), has been conducting observations of ultraviolet emissions within the Martian exosphere. Taking advantage of the distinctive orbit of the EMM around Mars, EMUS utilizes a dedicated strafe observation strategy to scan the illuminated Martian exosphere at tangential altitudes ranging from 130 to over 20,000 km. To distinguish between emissions of Martian origin and those from the interplanetary background, EMUS conducts specialized background observations by looking away from the planet. This approach has allowed us to investigate the radial and seasonal variations in Martian coronal emission features at H Lyman-alpha, beta and gamma wavelengths. Our analysis supports the previous studies indicating that Martian exospheric hydrogen Lyman emission brightness attains its highest levels around the southern summer solstice and reaches its lowest levels when Mars is near aphelion. Additionally, a secondary peak emission at all altitudes is observed after perihelion during Martian Year (MY) 36, which can be attributed to a Class C dust storm. Our study establishes a strong correlation between solar flux and coronal brightness for these emissions, highlighting the impact of solar activity on the visibility of Martian corona. In addition, we have examined interannual variability and found that emission intensities in MY 37 surpassed those in MY 36, primarily due to increased solar activity. These observations help to understand potential seasonal patterns of exospheric hydrogen, which is driven by underlying mechanisms in the lower atmosphere and solar activity, eventually suggesting an impact on water loss in the Martian atmosphere. Atomic hydrogen primarily forms as a product when Martian water undergoes various photochemical reactions. These hydrogen atoms encircle Mars and become illuminated by solar radiation, leading to the creation of Martian hydrogen corona. The Emirates Mars Ultraviolet Spectrometer (EMUS), on the Emirates Mars Mission spacecraft, is currently studying the Martian atmosphere using the ultraviolet light emissions of different atoms and molecules on Mars. In this study, we have analyzed EMUS observations and determined that atomic hydrogen emission intensities increase during the Martian southern summer and decrease as Mars moves farther away from the Sun. Furthermore, we have compared the hydrogen brightness between two consecutive Martian years and have found that the hydrogen brightness is higher in the most recent year primarily due to increased solar radiation. These observations help us understand possible patterns that occur during different seasons on Mars and the mechanisms underlying water loss in the Martian atmosphere. We present the variability in Martian atomic hydrogen brightness from early Martian year (MY) 36 to the first quarter of MY 37 Martian exospheric H Ly-beta and gamma emissions reach their peak brightness during the southern summer of MY 36 Martian corona is much brighter at H Ly-beta wavelength in MY 37 compared to the previous year due to increased solar irradiance
Errors and uncertainties in CFD validation for non-equilibrium turbulent boundary layer flows at high Reynolds numbers
Knopp, T.; Eca, L.; Toxopeus, S. L.; Fritsch, D.; Gargiulo, A.; Lowe, K. Todd; Roy, Christopher J.; Deng, G.; Visonneau, M.; Guilmineau, E. (Taylor & Francis, 2024-11-01)
NATO AVT-RTG-349 was dedicated to the validation of computational fluid dynamics (CFD) methods based on the Reynolds-Averaged Navier-Stokes (RANS) equations and statistical turbulence models for non-equilibrium turbulent-boundary-layer flows at high Reynolds numbers. This paper describes and discusses the errors and uncertainties arising in the comparison of RANS simulation results with experimental data from wind-tunnel experiments. These errors and uncertainties are associated with the CFD grid and the discretization, the physical modelling, the measurement accuracy, and the differences in the flow conditions between the experimental facility and the computational set-up. The results show the need for a grid-convergence study using systematically-refined families of CFD grids. The two major sources of errors are the RANS turbulence model and the uncertainty originating from the differences between the computational set-up and the wind-tunnel. Then two possible paths for future research are described: future CFD mesh generation, and future validation experiments at high Reynolds numbers.
Damage sensing in multi-functional nanocomposite polymer bonded energetics with embedded multi-walled carbon nanotube sensing networks
Shirodkar, Nishant; Talluru, Viswajit; Seidel, Gary D. (IOP Publishing, 2024-11-01)
This experimental investigation evaluates the strain and damage sensing abilities of multi-walled carbon nanotube (MWCNT) networks embedded in the binder phase of polymer-bonded energetics (PBEs). PBEs are a special class of particulate composite materials that consist of energetic crystals bound by a polymer matrix, wherein the polymer matrix serves to maintain the composite's shape and form. The structural health monitoring (SHM) approach presented in this work exploits the piezoresistive properties of the distributed MWCNT networks. Major challenges faced during such implementation include the low binder concentrations of PBEs, the presence of conductive/non-conductive particulate phases, the high degree of heterogeneity in the PBE microstructure, and achieving the optimal MWCNT dispersion. In this study, ammonium perchlorate (AP) crystals as the oxidizer, Aluminum grains as the metallic fuel, and Polydimethylsiloxane (PDMS) as the binder are used as the constituents for fabricating PBEs. To study the effect of each constituent on the MWCNT network's SHM abilities, various materials systems are comprehensively studied: MWCNT/PDMS materials are first evaluated to study the binder's electromechanical response, followed by AP/MWCNT/PDMS to assess the impact of AP addition, and finally, AP/AL/MWCNT/PDMS to evaluate the impact of adding conductive aluminum grains. Compression samples (ASTM D695) were fabricated and subjected to monotonic compression. Electrical resistance is recorded in conjunction with the mechanical test via an LCR meter. Gauge factors relating to the change in normalized resistance to applied strain are calculated to quantify the electromechanical response. MWCNT dispersions and mechanical failure modes are analyzed via scanning electron microscopy imaging of the fracture surfaces. Correlations between the electrical behavior in response to the mechanical behavior are presented, and possible mechanisms that influence the electromechanical behavior are discussed. The results presented herein demonstrate the successful ability of MWCNT networks as SHM sensors capable of real-time strain and damage assessment of PBEs.
Vapour bubbles produced by long-pulsed laser: a race between advection and phase transition
Zhao, Xuning; Ma, Wentao; Chen, Junqin; Xiang, Gaoming; Zhong, Pei; Wang, Kevin (Cambridge University Press, 2024-11-21)
Vapour bubbles produced by long-pulsed laser often have complex non-spherical shapes that reflect some characteristics of the laser beam. The transition between two commonly observed shapes, namely, a rounded pear-like shape and an elongated conical shape, is studied using a new computational model that combines compressible multiphase fluid dynamics with laser radiation and phase transition. Two laboratory experiments are simulated, in which a holmium:YAG or thulium fibre laser is used to generate bubbles of different shapes. In both cases, the predicted bubble nucleation and morphology agree reasonably well with the experimental observation. The full-field results of laser irradiance, temperature, velocity and pressure are analysed to explain bubble dynamics and energy transmission. It is found that due to the lasting energy input, the vapour bubble's dynamics is driven not only by advection, but also by the continued vaporisation at its surface. Vaporisation lasts less than 1 mu s in the case of the pear-shaped bubble, compared with over 50 mu s for the elongated bubble. It is thus hypothesised that the bubble's morphology is determined by competition. When the speed of advection is higher than that of vaporisation, the bubble tends to grow spherically. Otherwise, it elongates along the laser beam direction. To test this hypothesis, the two speeds are defined analytically using a model problem, then estimated for the experiments using simulation results. The results support the hypothesis. They also suggest that when the laser's power is fixed, a higher laser absorption coefficient and a narrower beam facilitate bubble elongation.
Different Behavior of Density Perturbations Between Dayside and Nightside in the Martian Thermosphere and the Ionosphere Associated With Atmospheric Gravity Waves
Nakagawa, Hiromu; England, Scott L.; Kumar, Aishwarya; Benna, Mehdi; Harada, Yuki; Sakai, Shotaro; Terada, Naoki; Seki, Kanako; Yoshida, Nao (American Geophysical Union, 2024-12-01)
To investigate the excitation mechanism of ionospheric perturbations on Mars by the Neutral Gas and Ion Mass Spectrometer (NGIMS) onboard Mars Atmosphere and Volatile EvolutioN (MAVEN), we categorize ionospheric perturbations into three cases: (a) the ion-neutral coupling cases where ion and neutral perturbations are well coupled, (b) the ion-specific cases where ion perturbations move independently from neutrals, and (c) the coronal mass ejection cases associated with solar wind extreme events. A representative number of cases from total profiles are compared with a numerical model to determine the fraction that can be explained by an atmospheric gravity waves (GW). The neutral perturbations on the dayside at 170-190 km altitudes are in excellent agreement with the GW. Whereas, contrary to previous thoughts, neutral perturbations are not necessarily explained by the GW especially on the nightside at 190-210 km. Ion perturbations on the dayside at 170-190 km also show a good agreement with the GW. The agreement becomes extremely low on the nightside at 190-210 km, reaching the limit of strong ion-neutral coupling around 190 km. Further investigation found that the behavior of the ion perturbations explicitly depends on the dayside and nightside. Its dominant driver potentially differs clearly between dayside and nightside. Statistics of relative perturbations demonstrate a clear effect associated with species scale height in neutrals. Whereas, the correlation between ions and neutrals breaks down at high solar zenith angle near southern dusk. We see currently unexplained behavior that cannot be fully interpreted by GW both at night and near southern dusk.
Gradient-Guided Search for Autonomous Contingency Landing Planning
Tekaslan, Huseyin Emre; Atkins, Ella M. (MDPI, 2025-09-13)
The growing reliance on autonomy in uncrewed aircraft systems (UASs) necessitates a real-time solution for assured contingency landing management during in-flight emergencies. This paper presents a novel gradient-guided search algorithm for risk-aware emergency landing trajectory generation with a wing-lift UAS loss-of-thrust use case. This framework integrates a compact four-dimensional discrete search space with aircraft kinematic and ground-risk cost. A multi-objective cost function is employed, combining flight envelope feasibility, optimal descent, and overflown population risk terms. To ensure discrete search convergence, a constrained hypervolume definition is introduced around the destination. A holding pattern identification algorithm is defined to minimize risk during the necessary flight path angle-constrained descent to final approach. Planner effectiveness is validated through randomly generated case studies over a region of Long Island, NY, under steady wind conditions. Benchmark comparisons with a 3D Dubins solver demonstrate the approach’s improved risk mitigation and acceptable real-time computation overhead. Future development will focus on integrating collision avoidance into the discrete search-based landing planner.

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