Frequency Research Articles

Electron beam monitoring of a modified conventional medical accelerator with a portable current transformer system traceable to primary electrical standards.

Ultra-high dose rate radiotherapy (UHDR) delivers therapeutic doses at rates >40Gy/s in a fraction of a second, aiming to enhance the therapeutic ratio through the FLASH effect. The substantial increase in UHDR beam current poses serious challenges for conventional active dosimeters. Integrating current transformers (ICT) offer a nondestructive solution for accurate monitoring, enabling the type of fast transient readout that will be crucial for UHDR treatment verification. The aim of this study is to build and characterize a clinically deployable ICT system and to develop an accurate calibration methodology for absolute charge determination that is traceable to primary electrical standards. The ICT was constructed from a Super MuMetal® toroid, and its secondary winding was made from 50 Ω coaxial cable. A 3D-printed case with an internal conductive coating shields the toroid assembly from interference. The ICT readout involves a custom differential amplifier and a commercial flash analog-to-digital converter. The system was calibrated using a bespoke sub-µs current pulser in the range of (2 to 16) mA, which itself is traceable to electrical standards via an in-house built electrometer with a calibrated feedback capacitor. The performance of the ICT was evaluated as a milliampere-scale beam monitor against concurrent absorbed dose graphite calorimetry irradiation measurements acquired on a specially tuned medical accelerator for UHDR delivery. The ICT responses for nominal test pulses, generated by a function generator and a current pulser, exhibited accurate reproduction of rise and fall times within the 1ns sampling frequency. A systematic droop effect of 0.6(1)%/µs was observed but is accounted for through the calibration chain. The calibration of the current pulser exhibited a repeatability typically better than 0.05%, with a slowly-varying leakage that can be subtracted using a linear regression of the leakage current. The ICT charge calibration demonstrated a repeatability in the range of (0.5 to<0.05)% for charge per pulse values in the range of (0.5 to 50)nC, respectively. The ICT response showed a strong linear relationship (adj-R2=0.99997) to charge per pulse. The in-beam comparison with a graphite calorimeter demonstrated the effectiveness of the ICT as an online beam monitor, independent of pulse repetition frequency in the range of (25 to 200)Hz, reducing the mean excess (i.e., independent of accelerator output) calorimeter variation to 0.3% (0.1% standard error on the mean). This work demonstrates the feasibility of accurately calibrating the ICT in terms of absolute charge and applying it as a clinically deployable monitoring system of mA-scale electron beams delivered by a medical accelerator.

ERG responses to high-frequency flickers require FAT3 signaling in mouse retinal bipolar cells.

Vision is initiated by the reception of light by photoreceptors and subsequent processing via downstream retinal neurons. Proper circuit organization depends on the multifunctional tissue polarity protein FAT3, which is required for amacrine cell connectivity and retinal lamination. Here, we investigated the retinal function of Fat3 mutant mice and found decreases in both electroretinography and perceptual responses to high-frequency flashes. These defects did not correlate with abnormal amacrine cell wiring, pointing instead to a role in bipolar cell subtypes that also express FAT3. The role of FAT3 in the response to high temporal frequency flashes depends upon its ability to transduce an intracellular signal. Mechanistically, FAT3 binds to the synaptic protein PTPσ intracellularly and is required to localize GRIK1 to OFF-cone bipolar cell synapses with cone photoreceptors. These findings expand the repertoire of FAT3's functions and reveal its importance in bipolar cells for high-frequency light response.

Psychophysically measuring the efficiency of rods.

Recent studies suggest that the efficiency of cones to detect photons can be evaluated by measuring the equivalent input noise (EIN; derived from contrast thresholds measured in the presence and absence of visual noise) under specific conditions in which the contrast threshold is limited by the variability in the number of photons detected by photoreceptors (i.e., photon noise). These conditions can be identified based on the known properties of photon noise: spatially and temporally white and inversely proportional to the luminance intensity. The present study aims to adapt this psychophysical paradigm to evaluate the efficiency of rods to detect photons. A motion direction discrimination task was used to evaluate the EIN over a wide range of luminance intensities for various spatial and temporal frequencies when the display was blue or red (to which rods have little sensitivity). The target was either a Gabor patch presented at 20 degrees of eccentricity (first experiment) or a rotating sine-wave annulus with a radius of 10 degrees of eccentricity (second experiment). In both experiments, the EIN was found to be inversely proportional to luminance intensity over a limited range of luminance intensities for both display colors. At these luminance intensities, the EIN was roughly independent of the spatial and temporal frequencies, matching the properties of photon noise. Furthermore, under these conditions, contrast thresholds were lower (i.e., better) when the display was blue rather than red, which suggests that vision was mediated by rods when the display was blue. We conclude that the efficiency of rods to detect photons can be evaluated by measuring contrast thresholds in the presence and absence of visual noise over a limited range of luminance intensities with a blue display.

Comparison of Evapotranspiration Calculated and Estimated By Different High-Resolution Gridded Analyses For Northeast Brazil

Objective: to present the results of a climatological analysis of evapotranspiration (ET) in the Brazilian Northeast (NEB) between 1961 and 2020, highlighting its seasonality, the identification of homogeneous groups by cluster analysis, and positive trends over the decades. In addition, the text compares the accuracy of two datasets (MODGroETa and ERA5-Land), emphasizing the superiority of ERA5-Land for ET estimates, especially after bias correction. The central purpose is to highlight the relevance of continuously monitoring and evaluating ET data for different regions and time scales. Method: For this study, meteorological data from the National Institute of Meteorology (INMET) and high-resolution gridded analyses (0.1° x 0.1°) adjusted by elevation were used. These data underwent rigorous quality control and altitude correction. It used atmospheric reanalysis data with high spatial resolution (9 km) and hourly temporal frequency, based on observations from satellites, surface stations and snow data. The remote sensing model derived from MOD16 was used to estimate evapotranspiration (ET) based on the Penman-Monteith equation. It is available with a spatial resolution of 0.1° and a decadal time scale. Multivariate statistical technique applied to identify homogeneous areas in Northeast Brazil with similar ET characteristics, based on the monthly distribution of data. Results and Discussion: The climatology of ET (1961-2020) in the NEB showed strong seasonality. Between January and April, the highest values (&gt;4 mm/day) are concentrated in the semi-arid region, decreasing in the west of Piauí and Maranhão (&lt;3.5 mm/day). From May to July, ET decreases in the east, while from September to December, the interior registers maximums (&gt;5.5 mm/day). Cluster analysis identified six homogeneous regions, independent of rainfall patterns, with higher ET from September to November and lower values between April and June, showing significant seasonal variations in the NEB. Research implications: The research contributes to water management, agricultural zoning and environmental conservation in the Brazilian Northeast (NEB). It identifies trends in evapotranspiration (ET) associated with climate change, provides subsidies for improving climate models and public policies, and fosters future research into adaptation and mitigation of impacts on ecosystems and communities. Originality/Value: The study is original in identifying regional patterns of evapotranspiration in the NEB, combining cluster analysis and multiple data sources. Its value lies in its practical application for water management, agricultural zoning, environmental conservation and public policies, strengthening climate adaptation strategies and mitigating impacts on vulnerable ecosystems and communities.

Лазерно-ультразвуковое когнитивное преобразование энергии и информации в электроприводе

Energy-efficiency in contemporary electromachine technology depend on characteristics electrodrives, that requires optimization his exist and new structural elements. A model of optoelectronic electrodrive with laser-ultrasound cognitive transformation of energy and information is investigated. Model includes following basic elements: electromotor, driving a working mechanism; measuring-information complex, controlling and operating electromotor; amplifier on basis multi-modes solid laser with ultrasound quality modulator (UQML); transformer of laser pulses into voltage either current or magnetic field of electromotor. Researches dynamics of generating depend on pumping power and ultrasound intensity executioned on the rubin laser. Transition characteristic of electrodrive is defines by inertia of electromechanic elements, considerably exceed inertia of optoelectronic equipments. Inertia of electrodrive smooth out pulses of frequency-impulse energy (FIE). When estimation transition characteristic of electrodrive, take into account his inertia, FIE of laser radiation was accepted quasyconstant in time interval constant energy of pumping source and estimates alteration of rotation frequency and current force of electromotor were conducting on basic laws Kirchgof and Newton in approximation constant current by medium Matlab, Simulink. In the absence of ultrasound UQML radiates a chaotic optical impulse. By ultrasound control UQML passes into establish regime of frequency-impulse radiation. Repetition frequency of regular pulses is determination by pumping level when ultrasound power is constant, but did not depend on ultrasound frequency. Examined questions: self-regulation frequency-pulse generation, cognitive transformation of UQML; dynamics of electrodrive (ED) with UQML; equivalent powers sources of frequency-pulse and constant current; inertness ED with UQML; structure scheme of automatic ED with UQML. Self-regulation of UQML attach to increase energy-efficiency, possibility automatical of electrodrive.

Experimental study on the effects of compressor rotational speed on surge characteristics: Spatial and temporal frequencies

Experimental study on the effects of compressor rotational speed on surge characteristics: Spatial and temporal frequencies

Improved Longevity and Reliability for Hundreds of Amps, Repetition Frequency Avalanche GaAs PCSS by High Thermal Conductivity Graphene Heat Sink

Improved Longevity and Reliability for Hundreds of Amps, Repetition Frequency Avalanche GaAs PCSS by High Thermal Conductivity Graphene Heat Sink

Analyzing the impact of surgical technique on intraoperative adverse events in laparoscopic Roux-en-Y gastric bypass surgery by video-based assessment.

Despite high-level evidence that variations of surgical technique in laparoscopic Roux-en-Y gastric bypass (LRYGB) are correlated with postoperative outcomes and might be linked to intraoperative adverse events (iAEs), there are a paucity of studies analyzing iAEs in depth. The impact of surgical technique on the temporal occurrence of iAEs regarding phases and steps of LRYGB has not been studied so far. The objective of this study was to analyze the impact of variance in surgical technique on temporal occurrence, frequency, and type of iAEs in a multicentric dataset of LRYGB videos. MultiBypass140, a video dataset containing 70 LRYGB surgeries each from Strasbourg University Hospital (StrasBypass70) and Bern University Hospital (BernBypass70) was annotated with surgical phases, iAE type, and grade. The cumulative severity of iAEs per procedure was measured using the SEVERE score and correlated with procedure duration. Surgical technique significantly differed between StrasBypass70 and BernBypass70 (omentum division: 94% vs. 36%, p < 0.01; closure of mesenteric defects: 100% vs. 21%, p < 0.01). In MultiBypass140, a total of 797 iAEs were analyzed. The most iAE-prone phases were gastric pouch creation, gastrojejunal, and jejunojejunal anastomosis creation containing 77% (616/797) of all iAEs. StrasBypass70 showed significantly more iAEs in the omentum division (23 vs. 5, p < 0.01), Petersen space closure (13 vs. 1, p < 0.01), and mesenteric defect closure phases (34 vs. 1, p < 0.01) compared to BernBypass70. In both centers, SEVERE score was correlated with procedure duration. In BernBypass70, insufficient closure of anastomosis was significantly more frequent in patients with postoperative complications (0.2 ± 0.6 vs. 0.0 ± 0.1, p < 0.01). Variations of the LRYGB technique between centers influence the temporal occurrence and frequency of iAEs. The frequency and severity of iAEs are correlated with procedure duration.

Flexible dispersion engineering in metasurface-based leaky-wave antennas: leveraging spatio-temporally modulated impedance surfaces

This study aims to investigate dispersion engineering mechanisms within unilateral and bilateral metasurface-based leaky-wave antennas, presenting methodologies focused on space-time modulation of impedance boundary conditions. Utilizing the generalized framework based on the Floquet-wave expansion method, the research precisely investigates the effect of periodic space-time modulation on the dispersion characteristics of the leaky-wave antenna. The beam scanning mechanism has been investigated in the momentum and frequency domains. It is shown that by choosing the appropriate spatial-temporal variations in the boundary condition, the radiation beam may be steered in the desired direction and frequency. Through a comprehensive analysis encompassing parameters such as modulation depth, average surface impedance, and space-time modulation frequencies, the paper seeks to elucidate the intricate dynamics governing dispersion phenomena. Furthermore, the inquiry delves into the "rabbit’s ears" phenomenon observed in bilateral space-time modulated leaky-wave antennas. Distinguishing this phenomenon from the conventional pure-space modulated impedance boundary conditions, the research aims to uncover its underlying mechanisms and provide insights into the antenna performance. In addressing this phenomenon, the study also proposes adjusting the temporal pumping frequency as a potential strategy to mitigate the adverse effects associated with the rabbit’s ears phenomenon.

The Impact of Dealiasing Biases on Bird and Insect Data Products of C-Band Weather Radars and Consequences for Aeroecological Applications

(1) The aliasing of radial velocities from weather radars is a known challenge in meteorology. It may also occur during bird migration if the unambiguous velocity threshold is below the birds’ ground speed. High variability in birds’ radial velocities and high flight speeds lead to multiple aliasing (folding) and challenge meteorological dealiasing approaches. Unfolded radial velocities are essential for calculating flight directions and speed and derived migration traffic rates for aeroecological applications. (2) We study the occurrence of aliasing in measurements of different pulse repetition frequencies (PRF) in C-band weather radars in bird and insect cases and test the efficiency of a dealiasing algorithm widely used in biological weather radar software. We use dual-PRF measurements as a reference to avoid the folding of radial velocities in quantitative and qualitative bird migration outputs. (3) The dealiasing algorithm performed poorly in single-PRF measurements during bird migration, though not in insect and precipitation cases. In contrast, dual-PRF velocities yielded proper flight speeds, flight directions and migration traffic rates. (4) The study unveils severe biases in aeroecological analyses of C-band weather radars from imperfectly dealiased single-PRF radial velocities. Dual-PRF measurements with appropriate dealiasing postprocessing offer a valid alternative to single PRF and should be preferred whenever available.

Characterization of Microbubble Cavitation in Theranostic Ultrasound-mediated Blood-Brain Barrier Opening and Gene Delivery.

The characterization of microbubble activity has proven critical in assessing the safety and efficacy of ultrasound-mediated blood-brain barrier (BBB) opening and drug and gene delivery. In this study, we build upon our previous work on theranostic ultrasound (ThUS)-mediated BBB opening (ThUS-BBBO) and conduct for the first time a comprehensive characterization of the role of microbubble cavitation in ThUS-BBBO, as well as its impact on gene delivery with adeno-associated viruses (AAV). A repurposed imaging phased array was used throughout the study to generate focused transmits and record microbubble activity through high-resolution power cavitation imaging (PCI). The cavitation of microbubbles under ThUS pulses was first characterized in flow phantom using pulse lengths ranging from 1.5 to 20 cycles and under varying microbubble flow rates using a separate single-element transducer a passive cavitation detector (PCD). A comprehensive in vivo study in mice was then conducted to characterize the in vivo microbubble activity under ThUS and correlate the resulting cavitation with AAV-mediated transgene delivery and expression. The transcranial microbubble activity was first detected in two mice using a PCD, to confirm the findings of the flow phantom study. Next, three mouse studies were conducted to evaluate the relationship between cavitation and AAV delivery; one with three different microbubble size distributions using polydisperse and size-isolated microbubbles, one with variable burst length and burst repetition frequency, and one with different AAV serotypes and injection doses. Electronic beam steering was used to induce bilateral BBB opening with 1.5 cycle on the left and 10 cycles on the right hemisphere. Cavitation dose was correlated with BBB opening volume, AAV transgene expression was evaluated with immunofluorescence staining and histological safety was assessed with T2* imaging and Hematoxylin and Eosin staining. Frequency domain analysis in the phantoms revealed a broadband-cavitation dominance at the shorter pulse lengths, while harmonic cavitation components are significantly increased for longer pulses. The PCD was better at detecting higher frequency harmonics, while the signal received by the theranostic array was more broadband dominated. Analysis of signals in the time domain showed that the longer pulses induce higher microbubble collapse compared to short pulses. In the transcranial in vivo experiments, the PCD was able to detect increased harmonic cavitation for 10-cycle pulses. The microbubble study showed that 3-5 μm microbubbles resulted in the largest cavitation doses, BBBO volumes and AAV transgene expression compared to the smaller microbubble sizes. The burst sequence study revealed that the sequences with shorter bursts and faster burst repetition frequencies induce larger BBBO volumes and AAV transduction due to faster microbubble replenishment in the focal volume. Increased erythrocyte extravasation was observed on the hemisphere sonicated with 10-cycle pulses. Transgene expression was also increased with injection dose, without notable side effects during the three-week survival period. Finally, AAV9 was shown to be the serotype with the highest transduction efficiency compared to AAV2 and AAV5 at the same injected dose. This is the first comprehensive study into the microbubble cavitation under theranostic ultrasound. The phantom and in vivo studies show that the mechanism of ThUS-BBBO is mainly transient cavitation dominant, as microbubble collapse increases with pulse length despite the increased harmonic frequency response. Increased cavitation dose resulted in larger BBBO volumes and transgene expression in vivo . While ThUS induced microhemorrhage for most of the studied conditions, it did not have an impact on the survival and behavior of the mice.

In-Situ Interferometric Metrology with Optical Comb

Optical frequency comb has various characteristics such as short pulse, broad spectra, many spectral lines, and high temporal coherency. In this paper, historical progress of the optical frequency comb is introduced in the metrology field and its temporalcoherence inteferometric applications are discussed for optical metrology. Specially, in-situ length metrology is presented on new measurement applications using the characteristics of the repetition frequency, brad spectra and high accuracy of the optical frequency comb.

Position-definable coherent microwave pulse train generation in an actively mode-locked optoelectronic oscillator.

An approach to generating position-definable coherent microwave pulse trains is proposed and demonstrated based on an actively mode-locked optoelectronic oscillator (OEO). In this scheme, a low-frequency signal with a customized waveform is employed as the mode-locking signal to periodically manipulate the intracavity gain of the OEO. Once the repetition frequency of the mode-locking signal satisfies the active mode-locking condition, microwave pulses are generated at the time positions corresponding to the gain peaks. The temporal distribution of the microwave pulses within one period is determined by the waveform of the mode-locking signal. Therefore, through designing the waveform of the mode-locking signal, coherent microwave pulse trains with user-defined pulse positions can be obtained. In the experiment, a non-uniformly spaced microwave pulse train, a series of microwave pulse clusters, and a binary-encoded microwave pulse sequence with a "Barker code" format are generated by the actively mode-locked OEO, all of which are with an identical carrier frequency of 10 GHz.

Acousto-optically induced single-frequency Nd:YAG ring laser based on double corner cube retroreflectors

Using an acousto-optic modulator (AOM) to enforce the unidirectional operation of a Nd:YAG ring laser based on double corner cube retroreflectors (CCRs) was demonstrated for the first time, to the best of our knowledge. By tilting the AOM with RF applied to deviate from the Bragg angle, a different diffraction loss was introduced between the counterpropagating beams in the ring cavity. A continuous wave single-frequency laser with a maximum output power of 2.99 W was successfully obtained at 1064.5 nm, with a tunable wavelength range from 1064.3 nm to 1064.7 nm. The experimental results indicated the unidirectional operated ring cavity comprising the double CCRs performed significant tolerance to the misalignment of the cavity. By changing the RF to pulsed mode and adjusting the angle of the AOM closer to the Bragg angle, the unidirectional Q-switched operation was achieved with the increase of the diffraction loss of the oscillating light. At the repetition frequency of 110 Hz, a 0.882 mJ single-frequency pulse energy with a pulse width of 70.2 ns was obtained, corresponding to a peak power of 12.6 kW. Sngle-frequency pulses with energy of 0.761 mJ and pulse width of 72.4 ns were also obtained at the repetition frequency of 1 kHz, corresponding to a peak power of 10.5 kW.

Static and dynamic brain functional connectivity patterns in patients with unilateral moderate-to-severe asymptomatic carotid stenosis.

Asymptomatic carotid stenosis (ACS) is an independent risk factor for ischemic stroke and vascular cognitive impairment, affecting cognitive function across multiple domains. This study aimed to explore differences in static and dynamic intrinsic functional connectivity and temporal dynamics between patients with ACS and those without carotid stenosis. We recruited 30 patients with unilateral moderate-to-severe (stenosis ≥ 50%) ACS and 30 demographically-matched healthy controls. All participants underwent neuropsychological testing and 3.0T brain MRI scans. Resting-state functional MRI (rs-fMRI) was used to calculate both static and dynamic functional connectivity. Dynamic independent component analysis (dICA) was employed to extract independent circuits/networks and to detect time-frequency modulation at the circuit level. Further imaging-behavior associations identified static and dynamic functional connectivity patterns that reflect cognitive decline. ACS patients showed altered functional connectivity in multiple brain regions and networks compared to controls. Increased connectivity was observed in the inferior parietal lobule, frontal lobe, and temporal lobe. dICA further revealed changes in the temporal frequency of connectivity in the salience network. Significant differences in the temporal variability of connectivity were found in the fronto-parietal network, dorsal attention network, sensory-motor network, language network, and visual network. The temporal parameters of these brain networks were also related to overall cognition and memory. These results suggest that ACS involves not only changes in the static large-scale brain network connectivity but also dynamic temporal variations, which parallel overall cognition and memory recall.

Influence of auditory-based cognitive training on auditory resolution, executive function, and working memory skills in individuals with mild cognitive impairment – a pilot randomized controlled study

Background Age-related central auditory processing disorder and mild cognitive impairment (MCI) can be concomitant in older adults, making it difficult to communicate, especially in challenging listening conditions. This preliminary study investigated the efficacy of auditory-based cognitive training on the auditory processing abilities and cognitive functions of older adults with MCI. Methods In this randomized controlled trial twenty-two older adults with mild cognitive impairment (MCI) were randomly assigned to either an experimental (n=11) or a control group (n=11). The experimental group received 15 cognitive training sessions through tasks involving the auditory domain. The outcome measures of this study included auditory resolution (Temporal gap detection, frequency discrimination, and modulation detection) and cognitive measures (Trail making tests and digit recall), which were administered at three-time points (before training, post-training, and follow-up). The linear mixed model computed the effects of training on the outcome measures. Results A significant improvement was observed in the modulation detection threshold between baseline and follow-up and between post-training and follow-up sessions. However, GDT and FD thresholds did not reveal any statistically significant difference. In the trail making test, Part B showed consistent significance across the time points, whereas Part A and the delayed recall task showed no significant difference. Conclusion Auditory-based cognitive training may improve auditory processing and executive function in older adults with mild cognitive impairment (MCI). Trial registration CTRI/2019/01/017073, registered on 14.01.2019

Single-photon single-pixel dual-wavelength imaging via frequency spectral harmonics extraction strategy.

In this paper, a single-photon single-pixel dual-wavelength imaging technology based on frequency spectral harmonics extraction is proposed. Using the independent repetition frequencies of pulsed light as multiplexed signals, the reconstructed image with optimal quality is obtained via extracting the sum of the intensities of the first 7 harmonics. Meanwhile, the post-pulse and fluctuation noise are effectively eliminated by applying preprocessing to the photon counting sequence, reducing the crosstalk of dual-wavelength to 2.29 × 10-4. Moreover, the frequency spectral analysis of the photon counting sequence at sub-photon level of per pixel in a single measurement is realized. With 4.5 × 10-3 photons per pixel in a single measurement, the 256 × 256 image is well reconstructed. Compared to photon counting single-pixel imaging technology, the proposed technique significantly enhances image quality and enables the dual-wavelength imaging with fewer photons. These results can promote the applications of dual-wavelength imaging in extremely low-light scenes.

Effect of ultrasound combined with microbubbles therapy on tumor hypoxic microenvironment.

Tumor tissues exhibit significantly lower oxygen partial pressure compared to normal tissues, leading to hypoxia in the tumor microenvironment and result in resistance to tumor treatments. Strategies to mitigate hypoxia include enhancing blood perfusion and oxygen supply, for example,by decomposing hydrogen peroxide within the tumor. Improving hypoxia in the tumor microenvironment could potentially improve the efficacy of cancer treatments. Previous studies have demonstrated that ultrasound of appropriate intensity when combined with microbubbles, can improve tumor blood perfusion. However, its effects on tumor hypoxia remain unclear. This study aimed to assess the effects of low-frequency non-focused ultrasound combined with microbubbles at different intensities on tumor microenvironment hypoxia and to identify the optimal ultrasound parameters for alleviating tumor hypoxia. Rabbits with VX2 tumors received ultrasound and microbubble treatments at different acoustic pressures and pulse repetition frequencies. The changes in tumor tissue blood perfusion before and after treatment were observed by contrast enhanced ultrasound (CEUS). The changes in tumor tissue hypoxia before and after treatment were observed by measuring oxygen partial pressure directly with in tumor tissue and immunohistochemical staining for hypoxia-inducible factor-1α (HIF-1α). Results indicated that low frequency, non-focused ultrasound at 0.5MPa/20Hz and 0.5MPa/40Hz, when combined with microbubbles, could increase tumor tissue blood perfusion and improve the hypoxia in tumor tissues. This study provides a new method for improving hypoxia in the tumor microenvironment (TME) which could potentially improve the cancer treatments resistance.

Investigation of oscillations above the acoustic cut-off frequency for a sample of Kepler stars. II. Identifying temporal frequency shifts

Abstract Stellar oscillations with frequencies greater than the acoustic cut-off frequency are not trapped within the star’s interior. Geometric interference between these high-frequency waves produces a peak-like structure in the power spectrum of the star, known as the pseudo-modes. In this study, we aim to analyse 51 stars previously identified (from a sample of 91 Kepler stars) to contain statistically significant evidence for pseudo-modes, to determine if the pseudo-mode frequencies vary in time. We obtained these frequency variations and the uncertainty by the resampled periodogram approach, where periodogram realisations were created from successive, overlapping 90-day time segments, and a cross-correlation function was generated between them. The computed shifts were compared against temporal p-mode frequency shifts and a stellar magnetic activity proxy, Sph. We found that for 16 % of the stars pseudo-mode frequency shifts were significantly anti-correlated with p-mode shifts, as is the case for the Sun. However, we also found pseudo-mode and p-mode shifts to be significantly correlated in-phase in 8 % of our sample. The remainder showed no significant correlation. We also searched for trends between the maximum variation of pseudo-mode frequency shifts and stellar parameters. Whilst we found no correlation between the maximum variation and stellar photospheric and chromospheric proxies, we found frequency variations to have a greater amplitude for cooler and slower rotating stars, which is in opposition to p-mode frequency shift variation. Temporal changes to pseudo-mode frequencies may be attributable to variations in stellar magnetic activity, and therefore can contribute to our understanding of stellar activity cycles.

Combining UAS LiDAR, Sonar, and Radar Altimetry for River Hydraulic Characterization

Accurate river hydraulic characterization is fundamental to assess flood risk, parametrize flood forecasting models, and develop river maintenance workflows. River hydraulic roughness and riverbed/floodplain geometry are the main factors controlling inundation extent and water levels. However, gauging stations providing hydrometric observations are declining worldwide, and they provide point measurements only. To describe hydraulic processes, spatially distributed data are required. In situ surveys are costly and time-consuming, and they are sometimes limited by local accessibility conditions. Satellite earth observation (EO) techniques can be used to measure spatially distributed hydrometric variables, reducing the time and cost of traditional surveys. Satellite EO provides high temporal and spatial frequency, but it can only measure large rivers (wider than ca. 50 m) and only provides water surface elevation (WSE), water surface slope (WSS), and surface water width data. UAS hydrometry can provide WSE, WSS, water surface velocity and riverbed geometry at a high spatial resolution, making it suitable for rivers of all sizes. The use of UAS hydrometry can enhance river management, with cost-effective surveys offering large coverage and high-resolution data, which are fundamental in flood risk assessment, especially in areas that difficult to access. In this study, we proposed a combination of UAS hydrometry techniques to fully characterize the hydraulic parameters of a river. The land elevation adjacent to the river channel was measured with LiDAR, the riverbed elevation was measured with a sonar payload, and the WSE was measured with a UAS radar altimetry payload. The survey provided 57 river cross-sections with riverbed elevation, and 8 km of WSE and land elevation and took around 2 days of survey work in the field. Simulated WSE values were compared to radar altimetry observations to fit hydraulic roughness, which cannot be directly observed. The riverbed elevation cross-sections have an average error of 32 cm relative to RTK GNSS ground-truth measurements. This error was a consequence of the dense vegetation on land that prevents the LiDAR signal from reaching the ground and underwater vegetation, which has an impact on the quality of the sonar measurements and could be mitigated by performing surveys during winter, when submerged vegetation is less prevalent. Despite the error of the riverbed elevation cross-sections, the hydraulic model gave good estimates of the WSE, with an RMSE below 3 cm. The estimated roughness is also in good agreement with the values measured at a gauging station, with a Gauckler–Manning–Strickler coefficient of M = 16–17 m1/3/s. Hydraulic modeling results demonstrate that both bathymetry and roughness measurements are necessary to obtain a unique and robust hydraulic characterization of the river.