Andrei G. Fedorov

Computational bioheat modeling offers a powerful approach for characterizing brain temperature when direct measurements are limited. We developed a multiscale biophysical model with conservation of mass, momentum, and energy across all spatial scales to predict human brain temperature and compared the temperature maps with a previously developed model without global momentum conservation and in vivo magnetic resonance (MR) thermometry. Subject-specific brain anatomy obtained from MR images was incorporated into bioheat equations, integrating physiological parameters such as metabolic heat and cerebral blood flow. A novel approach using "transitional" microvasculature was introduced to bridge macro- and micro-scale domains, enabling momentum conservation and accurate prediction of cerebral hemodynamics. Across 30 healthy subjects, voxel-wise mean absolute differences of 0.18-0.36 °C between modeled and experimentally measured temperatures were observed. ROI-based analysis showed significant correlations between model predictions and MR measurements of brain temperature when system-wide momentum is properly conserved, but no correlation was observed for model predictions without momentum conservation. A simulated scenario of middle cerebral artery occlusion highlighted the importance of momentum conservation to mimic realistic physiological changes. The agreement of model predicted temperatures with MR measurements support future clinical applications where brain temperature may serve as a biomarker for neurological disorders.

Abstract Background: Cyclin-dependent kinase inhibitors, CDK4/6i, have been one of the most significant practice-changing advances in the treatment of estrogen receptor positive (ER+) breast cancer in the recent decade. Despite their clinical success, CDK4/6i resistance remains a major clinical challenge. Importantly, therapeutic response does not correlate with expression levels of CDK4, CDK6, or other canonical cell cycle proteins, suggesting that resistance arises from complex adaptive mechanisms. Methods: To address this challenge, we generated drug-tolerant persister cell populations (DTPs) from LCC2, LCC9 and T47D breast cancer cell lines to both palbociclib and abemaciclib. Transcriptomic profiling of these DTPs revealed significant alterations in the expression of metabolic enzymes, suggesting that metabolic reprogramming plays a central role in the survival and maintenance of CDK4/6i-tolerant cells. To further identify and quantify changes in metabolites and metabolic pathways, we analyzed these DTP populations using a dynamic sampling platform (DSP) integrating a sample introduction mechanism, a microfabricated processing device, and electrospray ionization mass spectrometry (ESI-MS) analysis. The device, manufactured via advanced microfabrication techniques, enables integration of real-time multiple processing and metabolic profiling. Full untargeted metabolomics data were evaluated using pathway level gene set enrichment analysis (GSEA). Results: Across resistant cell states, multiple metabolic pathways exhibited coordinated shifts associated with DTP-like adaptation. Palbociclib resistant LCC2-DTPs exhibit a distinct metabolic remodeling trajectory characterized by consistently elevated ubiquinone biosynthesis, an adaptation absent in abemaciclib-resistant LCC2-DTPs and other DTP sublines. This drug-specific metabolic signature suggests that palbociclib engages mitochondrial pathways in a unique manner, potentially influencing therapeutic resistance. On the other hand, pathways involving electron transport chain and fatty acid oxidation were upregulated in abemaciclib DTPs, suggesting differential metabolic regulation in response to each CDK4/6i. Conclusions: These findings highlight divergent metabolic consequences for palbociclib and abemaciclib in endocrine-resistant ER+ breast cancer and underscore the utility of microfluidic ESI-MS workflows for resolving drug-specific adaptive states relevant to therapeutic resistance and tumor progression. Citation Format: Gianna A. Slusher, Yuan Gu, Sunil S. Badve, Andrei G. Fedorov, Yesim Gökmen-Polar. Distinct metabolic adaptations to resistance to CDK4/6 inhibitors in ER+ breast cancer identified using microfluidic mass spectrometry platform [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 1895.

In vacuum nanoelectrospray, a stream of electrically charged nanoliter droplets moving at high speed through a rarefied space at sub-atmospheric pressure. A supersonic gas microjet in crossflow can effectively redirect the nanodroplets to control their destination. The fundamental theory predicts the droplet fate to enable applications such as high-resolution inkjet printing, trust vectoring for precise satellite control, and biochemical imaging using desorption electrospray ionization.

• Nano-electrosprayed droplets thrust ambient gas, producing a narrow gas jet. • Nano-electrosprayed droplets impinge on counter electrode, forming thin liquid film. • Gas jets produced by nano-electrospray impinge on thin liquid film surface. • Evaporation of thin liquid film is significantly enhanced by nES-driven gas jet. • Heat fluxes in excess of 1 kW/cm 2 achievable by nES-driven evaporation cooling. Evaporation cooling is enhanced by forming a thin liquid film with low resistance for heat conduction and using an impinging gas jet for effective removal of the vapor from the interface. Our previous experiments show that when nanoelectrospray (nES) is directed onto a nearby surface, ultra-thin liquid films can be formed with thicknesses less than 260 nm. Our previous experiments and simulations also show that the stream of high-velocity liquid droplets emanating from the nES capillary entrain the surrounding ambient air, forming a narrow gas jet with speeds of tens of meters per second resulting in a means for vapor advection from the evaporating interface. With promising results from the previous work, the current work considers the problem of hotspot thermal management using the nES-generated evaporating films of methanol and water as coolants. A comprehensive model, which considers the charged droplet transport, liquid/gas momentum exchange, fluid film evaporation, vapor transport, and heat transfer by evaporation, convection, and conductive spreading is used to evaluate the theoretical performance of nES evaporative cooling. The key demonstrated result is that hotspots on the order of tens of µm in diameter with heat fluxes of over 1000 W/cm 2 (or larger hotspots of a few hundred µm in diameter with heat fluxes of a few hundred W/cm 2 ) can be effectively cooled while keeping the surface temperatures below the boiling point of the working fluid at atmospheric pressure. The effects of the key nES parameters (emitter positioning, applied potential, droplet size, liquid mass flowrate) and thermophysical properties of the coolants (mass density, maximum stable electric charge density, saturated vapor density, latent heat of vaporization, thermal conductivity) are analyzed, resulting in fundamental guidelines for heat and mass transfer enhancement in thin film evaporative cooling with application to microelectronics thermal management.

The design of hypersonic vehicles is primarily driven by thermal considerations. Additionally, due to the lack of turbomachinery in these vehicles, the provision of electrical energy to vehicle systems is done almost exclusively by batteries. This paper outlines the analysis of photovoltaic cells embedded in the skin of a hypersonic vehicle to reduce the heat transfer from the hot external aerodynamic surface and the internal vehicle structure and to produce electrical energy from a portion of the thermal radiation. By treating each of the surfaces involved in the radiative exchange as coplanar surfaces in local thermodynamic equilibrium, the equations governing the transfer of thermal energy through the skin structure are derived. Two nominal refractory metals and a nominal ceramic matrix composite material are analyzed at a range of temperatures to determine the relative effectiveness of a thermophotovoltaic (TPV) skin in heat flux reduction and electrical energy generation compared to a simple skin structure. A TPV skin is shown to reduce the heat flux to the vehicle interior by more than an order of magnitude and simultaneously convert more than 10% of the external heat load into electrical energy at high temperatures.

Motivation: Brain temperature is a potential marker for prognosis and stratification after stroke and in chronic cerebrovascular disease. Biophysical models have been developed to predict personalized brain temperature; however, the relationship between local temperature, cerebral metabolism, and blood flow remains unexplored. Goal(s): To quantify local brain temperature changes in a systematic manner across varying degrees of stenosis and occlusion. Approach: A computational bioheat model using MR imaging data will be used to evaluate local brain temperature changes across varying degrees of stenosis and occlusion and to determine the relationships between brain temperature, cerebral blood flow, and metabolism. Impact: Brain temperature is a promising marker for prognostication of chronic and acute ischemia. We hypothesize local temperature increases will be positively correlated with degree of stenosis and occlusion, accounting for collateral flow and metabolism.

Abstract Focused electron beams enable nanoscale material modification via localized etching or deposition. In liquid‐phase electron‐beam‐mediated processing, radiolysis‐driven redox reactions present an opportunity to control both etching and deposition simultaneously. Here, this duality using a water‐ammonia solvent as a tunable redox mediator on copper surfaces is demonstrated. At lower ammonia concentrations, the oxidation process dominates, etching copper to sub‐50‐nm depths. The copper ions and ion‐complexes released during this initial oxidation step are reduced by solvated electrons resulting in metal deposition into the etched sites, over longer e‐beam exposures, producing characteristic peak‐in‐valley nanostructures. Conversely, at higher ammonia concentrations copper‐ammine ion complexation and radiolytic oxidizing species scavenging by ammonia occur at higher rates, creating a reducing environment conducive to rapid beam‐guided copper deposition. Reaction‐transport simulations and experiments are performed to show the effects of ammonia‐mediated radiolysis chemistry, describing the direct influence of solvent concentration on redox balance and the outcome of e‐beam guided processing. By uniting both etching and deposition within a single framework, this work provides a versatile route for controlled surface nanostructuring.

Nanoelectrospray (NanoES) generates an aerosol of highly charged nano-to-micrometer size droplets from a conducting liquid dispersed from a tapered order-of-m diameter capillary under the influence of an electric field.These droplets accelerate in the applied electric field, disperse due to the electrostatic inter-droplet interactions and charge-induced instabilities and fission, and engage in complex hydrodynamic interactions with the surrounding gas.The main forces acting on the droplets are the viscous drag and inertia.Depending on the hydrodynamic environment (i.e., stagnant or flowing gas), drag could either promote or impede droplet motions and/or result in the change of droplet trajectories.Reciprocally, the motion of droplets could induce motion of a surrounding gas via interfacial momentum transfer.The induced gas jetting has a complex structure with high kinetic energy, tightly confined (within 10s of micrometers) core and active suction of the surrounding gas from behind of the capillary emitter producing NanoES.We used the Schlieren flow visualization, ion current measurements, mass spectrometry, and multiphysics simulations to uncover the complex behavior and derive the governing laws for multiphase femto-to-nanoliter charged droplet-gas interactions.This fundamental understanding of gasassisted NanoES enables the development of new important applications.Of particular interest is the use of NanoES for delivery of energized precursor molecules to achieve the new modes of atom-by-atom fabrication of topologically complex nanostructures from a variety of materials using the Focused Electron Beam Induced Processing (FEBIP).Energized micro/nano-jets of electro-kinetically energized precursors in liquid phase provide unique capabilities for localized delivery of precursor molecules to the substrate, thus establishing locally controlled deposition/etching site for FEBIP.Understanding of fascinating and interacting chemistry and physics on the most fundamental level will be discussed as a route to develop new FEBIP modes and applications to emerging 2D electronic and quantum devices.

Motivation: Prior research has demonstrated the benefits of thrombectomy after acute ischemic stroke (AIS). Despite improvements in surgical techniques, failed reperfusion after thrombectomy is problematic. Goal(s): Our goal was to evaluate brain temperature-based identification of infarcted and salvageable tissue for improved stratification after AIS. Approach: A patient-specific computational model using imaging data was used to predict local brain temperatures after AIS to identify infarcted and salvageable tissue and compared to existing clinical methods (RAPID). Results: Temperature-based stratification identified infarct regions not observed with RAPID and predicted lower mismatch ratios more consistent with final clinical outcomes. Impact: We demonstrate the potential for model-predicted brain temperatures to quantify infarcted and salvageable tissue after acute ischemic stroke for patient selection for thrombectomy. Local brain temperature may complement existing metrics, particularly for patients without sufficient salvageable tissue.

Prior research has demonstrated the benefits of endovascular thrombectomy after acute ischemic stroke. Despite improvements in surgical techniques, patient selection for thrombectomy remains challenging. In this case study, we explored the utility of brain temperature to accurately predict infarct core and salvageable tissue to stratify patients for thrombectomy. We observed infarct volume estimated from temperature maps was more similar than CT perfusion to the true infarct volume identified using apparent diffusion coefficient images from diffusion weighted imaging. Temperature-based ischemia-to-infarct ratio showed better patient stratification than conventional methods, suggesting the complementary use of brain temperature in patient selection after ischemic stroke.

The advancement of liquid phase electron/ion beam induced deposition has enabled an effective direct-write approach for functional nanostructure synthesis with the possibility of three-dimensional control of morphology. For formation of a metallic solid phase, the process employs ambient temperature, beam-guided, electrochemical reduction of precursor cations, resulting in rapid formation of structures, but with challenges for retention of resolution achievable via slower electron beam approaches. The possibility of spatial control of redox pathways via the use of water-ammonia solvents has opened avenues for improved nanostructure resolution without sacrificing the growth rate. In particular, ammonia enables "electrochemical lensing" in which a tightly confined and highly reducing environment is created locally to enable high resolution, rapid beam-directed nanostructure growth. We demonstrate this unique approach to high resolution synthesis through a combination of analysis and experiment.

Context . The Mercury electron analyzer (MEA) obtained new electron observations during the first three Mercury flybys by BepiColombo on October 1, 2021 (MFB1), June 23 , 2022 (MFB2), and June 19, 2023 (MFB3). BepiColombo entered the dusk side magnetotail from the flank magnetosheath in the northern hemisphere, crossed the Mercury solar orbital equator around midnight in the magnetotail, traveled from midnight to dawn in the southern hemisphere near the closest approach, and exited from the post-dawn magnetosphere into the dayside magnetosheath. Aims . We aim to identify the magnetospheric boundaries and describe the structure and dynamics of the electron populations observed in the various regions explored along the flyby trajectories. Methods . We derive 4s time resolution electron densities and temperatures from MEA observations. We compare and contrast our new BepiColombo electron observations with those obtained from the Mariner 10 scanning electron spectrometer (SES) 49 yr ago. Results . A comparison to the averaged magnetospheric boundary crossings of MESSENGER indicates that the magnetosphere of Mercury was compressed during MFB1, close to its average state during MFB2, and highly compressed during MFB3. Our new MEA observations reveal the presence of a wake effect very close behind Mercury when BepiColombo entered the shadow region, a significant dusk-dawn asymmetry in electron fluxes in the nightside magnetosphere, and strongly fluctuating electrons with energies above 100s eV in the dawnside magnetosphere. Magnetospheric electron densities and temperatures are in the range of 10–30 cm −3 and above a few 100s eV in the pre-midnight-sector, and in the range of 1–100 cm −3 and well below 100 eV in the post-midnight sector, respectively. Conclusions . The MEA electron observations of different solar wind properties encountered during the first three Mercury flybys reveal the highly dynamic response and variability of the solar wind-magnetosphere interactions at Mercury. A good match is found between the electron plasma parameters derived by MEA in the various regions of the Hermean environment and similar ones derived in a few cases from other instruments on board BepiColombo.

The advancement of liquid phase electron beam induced deposition has enabled an effective direct-write approach for functional nanostructure synthesis with the possibility of three-dimensional control of morphology. For formation of a metallic solid phase, the process employs ambient temperature, beam-guided, electrochemical reduction of precursor cations resulting in rapid formation of structures, but with challenges for retention of resolution achievable via slower electron beam approaches. The possibility of spatial control of redox pathways via the use of water-ammonia solvents has opened new avenues for improved nanostructure resolution without sacrificing the growth rate. We find that ammonia concentration locally modulates reaction kinetics, altering the balance between reducing and oxidizing species, leading to distinct deposition outcomes. The key effect is an 'electrochemical lensing', achieved at an optimum ammonia concentration, in which a tightly confined and highly reducing environment is created locally to enable high resolution, rapid beam-directed nanostructure growth. We demonstrate this unique approach to high resolution synthesis through a combination of analysis and experiment.

In recent years, cell-based therapies have transformed medical treatment. These therapies present a multitude of challenges associated with identifying the mechanism of action, developing accurate safety and potency assays, and achieving low-cost product manufacturing at scale. The complexity of the problem can be attributed to the intricate composition of the therapeutic products: living cells with complex biochemical compositions. Identifying and measuring critical quality attributes (CQAs) that impact therapy success is crucial for both the therapy development and its manufacturing. Unfortunately, current analytical methods and tools for identifying and measuring CQAs are limited in both scope and speed. This Perspective explores the potential for microfluidic-enabled mass spectrometry (MS) systems to comprehensively characterize CQAs for cell-based therapies, focusing on secretome, intracellular metabolome, and surfaceome biomarkers. Powerful microfluidic sampling and processing platforms have been recently presented for the secretome and intracellular metabolome, which could be implemented with MS for fast, locally sampled screening of the cell culture. However, surfaceome analysis remains limited by the lack of rapid isolation and enrichment methods. Developing innovative microfluidic approaches for surface marker analysis and integrating them with secretome and metabolome measurements using a common analytical platform hold the promise of enhancing our understanding of CQAs across all "omes," potentially revolutionizing cell-based therapy development and manufacturing for improved efficacy and patient accessibility.

Context. In the solar wind (SW), the particle distribution functions are generally not Gaussian. They present nonthermal features that are related to underlying acceleration and heating processes. These processes are critical in the overall dynamics of this expanding astrophysical fluid. Aims. The Proton Alpha Sensor (PAS) on board Solar Orbiter commonly observes skewed proton distributions, with a more populated high-energy side in the magnetic field direction than the Gaussian distribution. Our objectives are: (1) to identify a theoretical statistical function that adequately models the observed distributions and (2) to use its statistical interpretation to constrain the acceleration and heating processes. Methods. We analyzed the 3D velocity distribution functions (VDFs) measured by PAS and compared them to model statistical functions. Results. We show that the normal inverse Gaussian (NIG), a type of hyperbolic statistical distribution, provides excellent fits of skewed and leptokurtic proton distributions. NIG can model both the core distribution and the beam, if present. We propose an interpretation that is inspired by the mathematical formulation of the NIG. It assumes that the acceleration or heating mechanism can be modeled as a drifting diffusion process in velocity space, controlled (or subordinated) by the time of interaction of the particles with “accelerating structures”. The probability function of the interaction time is an inverse Gaussian (IG), obtained by considering a random drift across structures of a given size. The control of the diffusion by interaction times that follow an IG probability function formally defines the NIG distribution. Following this model, we show that skewness and kurtosis can be used to estimate the kinetic and thermal energy gains provided by the interaction with structures. For example, in the case studies presented here, the analyzed populations would have gained kinetic energy representing approximately two to four times their thermal energy, with an increase in velocity – due to acceleration – of from one-tenth to one-third of the observed flow velocity. We also show that the model constrains the initial temperature of the populations. Conclusions. Overall, the NIG model offers excellent fits of the observed proton distributions. Combining the skewness and the kurtosis, it also leads to constraints in the part of acceleration and heating due to the interactions with structures in the formation of the proton populations. We suggest that these effects add to the classical thermal evolution of the bulk velocity and temperature resulting from SW expansion.

Embodiments of the present disclosure provide for methods and systems for making structures using an electrospray system while under vacuum. In particular, embodiments of the present disclosure provide for methods and systems for ultra-fast growth of high aspect ratio nano/meso/micro-structures with three dimensional topological complexity and control of phase and composition of the structure formed.

To advance our understanding of thermal dynamics in the human brain, a thermal modeling framework was previously developed to facilitate temperature predictions in the absence of clinical thermometry. Here, predicted brain temperatures using our fully conserved model were compared with MR thermometry in 21 healthy human subjects. Bland-Altman plots demonstrated agreement between predictions and MR-measurements for average temperature values, but some differences were observed at the lowest and highest temperatures. Regional variations were similar between predicted and measured temperatures. We anticipate our modeling framework will form the necessary baseline for predicting injury-induced brain temperature changes in patients.

Context. Magnetic reconnection is a fundamental process in astrophysical plasmas that enables the dissipation of magnetic energy at kinetic scales. Detecting this process in situ is therefore key to furthering our understanding of energy conversion in space plasmas. However, reconnection jets typically scale from seconds to minutes in situ, and as such, finding them in the decades of data provided by solar wind missions since the beginning of the space era is an onerous task. Aims. In this work, we present a new approach for automatically identifying reconnection exhausts in situ in the solar wind. We apply the algorithm to Solar Orbiter data obtained while the spacecraft was positioned at between 0.6 and 0.8 AU and perform a statistical study on the jets we detect. Methods. The method for automatic detection is inspired by the visual identification process and strongly relies on the Walén relation. It is enhanced through the use of Bayesian inference and physical considerations to detect reconnection jets with a consistent approach. Results. Applying the detection algorithm to one month of Solar Orbiter data near 0.7 AU, we find an occurrence rate of seven jets per day, which is significantly higher than in previous studies performed at 1 AU. We show that they tend to cluster in the solar wind and are less likely to occur in the tenuous solar wind (< 10 cm −3 near 0.7 AU). We discuss why the source and the degree of Alfvénicity of the solar wind might have an impact on magnetic reconnection occurrence. Conclusions. By providing a tool to quickly identify potential magnetic reconnection exhausts in situ, we pave the way for broader statistical studies on magnetic reconnection in diverse plasma environments.

It was with great sadness that the heat transfer community learned of the passing of Professor Raymond Viskanta on December 27, 2021.Raymond Viskanta was born in Marijampole, Lithuania in 1931. In 1944, his family escaped the advancing Russian-German front, fleeing to Germany. After a tenuous survival in Germany during the remainder of the war, they were moved to displaced persons camps in West Germany starting in 1945. In 1949, the family came to the United States, initially to work as farm laborers in Michigan. Raymond subsequently moved to Chicago in 1950, where he found employment as a factory worker during the day and attended high school classes in the evening.After receiving his high school degree in 1951, he began his higher education by taking night courses at a junior college, then enrolled full time at the University of Illinois-Navy Pier. He later transferred to the main campus where he received his B.S.M.E. degree with high honors from the University of Illinois in 1955. This was followed by a M.S.M.E degree, focusing on heat transfer, from Purdue in 1956. Raymond Viskanta then accepted a position at the Argonne National Laboratory, pursuing and completing his doctoral research in absentia, and receiving his Ph.D. from Purdue in 1960. Professor Viskanta continued at Argonne until 1962 when he joined the faculty at Purdue as Associate Professor. He was promoted to the rank of Professor in 1966 and was named the W.F.M. Goss Distinguished Professor in 1986.Professor Viskanta's research contributions, in the form of over 500 publications in more than 50 journals, as well as over 200 keynote presentations and invited lectures, have been immensely influential. His earliest work developed an initial understanding of radiation in participating media, including the presence of other significant heat transfer modes. Similarly, his many contributions in convection dealt with little-understood phenomena at the time as disparate as double-diffusion transport and jet impingement boiling. Professor Viskanta's research in melting and solidification in pure materials as well as metallic alloys, including solid–liquid phase change in the presence of convection in the liquid phase, was seminal. While developing the formative understanding of these and many other heat transfer phenomena, his research was simultaneously motivated by practical applications involving combustion and fire, materials processing and manufacturing, and conventional as well as emerging energy generation and storage technologies.Professor Viskanta's service contributions to the heat transfer community were extensive. In addition to organizing many heat transfer conferences, he served as technical editor, associate technical editor, advisory board member, or honorary advisory board member of the Applied Mechanics Reviews, Experimental Heat Transfer, International Communications in Heat and Mass Transfer, International Journal of Heat and Fluid Flow, International Journal of Heat and Mass Transfer, ASME Journal of Heat Transfer, Journal of Quantitative Spectroscopy and Radiative Heat Transfer, AIAA Journal of Thermophysics and Heat Transfer, Numerical Heat Transfer, and the Annual Review of Numerical Fluid Mechanics and Heat Transfer. While he received the most prominent international awards specific to heat transfer, Professor Viskanta's professional accomplishments were also recognized by his election to the National Academy of Engineering in 1987, being named a foreign member of the Lithuanian Academy of Sciences in 1990, and becoming a foreign member of the Academy of Engineering Sciences of the Russian Federation in 1995. Among his many other accolades were his receiving an Honorary Doctorate of Engineering Degree from the Technical University of Munich in 1994, and an Honorary Doctorate of Engineering Degree from Purdue in 2007.During his lifelong academic career at Purdue, Professor Viskanta guided the research of 64 doctoral students, 48 master's students, and 39 postdoctoral researchers and visiting scholars. His professional colleagues at Purdue remember him as an intensely focused researcher who efficiently handled his many responsibilities with warmth, grace, humor, and an enormous intellect. As shared by Frank Incropera, “During my 32 years at Purdue, I was very fortunate to have Ray Viskanta as a mentor, colleague, and collaborator. One of the most important things he taught me was that, however well today's research may be going, one should always be thinking ahead. What will be the important problems of tomorrow, and what seeds could be planted to better address those problems? Yes, he contributed enormously to the science of heat transfer, but he was often at the forefront of applications to some of society's most pressing problems. And, there is another important dimension to the life of Ray Viskanta. He was one of the kindest and most decent human beings I have ever known. For 55 years, I was blessed to have had him as a friend.”Professor Viskanta's lifelong love of heat transfer was also matched by the genuine affection he had for his graduate students who knew him as “RV.” He held us to a high technical standard, at the same time providing frequent warm encouragement. We were taught to break down a research problem into smaller, more tractable subproblems. Through his careful and quick review of draft manuscripts, RV taught us to write well. A draft publication left with RV late in the afternoon would be on the student's desk early the next morning with copious notes and redline corrections. RV was anxious to give applicants from around the world the opportunity to pursue graduate study with him. His lab was a global mix of individuals with a remarkable array of backgrounds and nationalities. Those accepted for graduate study with RV were excited by the news and felt honored to work with him. One former student applied only to Purdue for Ph.D. study, to work only with RV. In response, Professor Viskanta sent duplicate personal letters to the applicant's home and university office to make sure the student was notified of acceptance.The extraordinary research that came out of RV's lab was never more important to him than the personal lives and growth of his graduate students. All of us felt Ray and Barbara Viskanta's deep affection, and they often became surrogate parents to us, especially those of us who were far from home. The Viskantas hosted regular dinners at their home for those studying with RV, and they stayed in touch with many of his students long after graduation watching with pride their accomplishments over the years, and even the accomplishments of their students' children. When the young adult son of a former graduate student was honored for his academic performance at a university and his parents could not attend, Ray and Barbara drove several hours to the award ceremony and accompanied the son to a celebratory dinner.Ray Viskanta was a one-of-a-kind professor, mentor, and friend. As his former graduate students and colleagues, we collectively express our deep appreciation and respect for his influence on our professional and personal lives. The international heat transfer community will remember Professor Raymond Viskanta not only as a scientist and engineer of the first class, but also as a gentle man who was deeply and personally connected to scores of heat transfer researchers and educators around the world.With deep admiration and affection, on behalf of all of RV's former graduate students and colleagues,

Brain temperature, regulated by the balance between blood circulation and metabolic heat generation, is an important parameter related to neural activity, cerebral hemodynamics, and neuroinflammation. A key challenge for integrating brain temperature into clinical practice is the lack of reliable and non-invasive brain thermometry. The recognized importance of brain temperature and thermoregulation in both health and disease, combined with limited availability of experimental methods, has motivated the development of computational thermal models using bioheat equations to predict brain temperature. In this mini-review, we describe progress and the current state-of-the-art in brain thermal modeling in humans and discuss potential avenues for clinical applications.

BepiColombo was launched in October 2018 and is currently en route to Mercury. Although its orbit insertion is planned for December 2025, BepiColombo will acquire new measurements during planetary flybys. During the cruise phase, the two spacecraft are docked together with Mio being protected behind the MOSIF sun shield. Thus, only partial observations of plasma distribution functions can be obtained by the Mercury Plasma Particle Experiment (MPPE) onboard Mio. However, since electrons have small Larmor radii and more isotropic distributions even in the solar wind, the two Mercury Electron Analyzer (MEA) of MPPE will provide us with new and unique measurements in the range of 5 eV to 3 keV when in solar wind mode and 3 eV to ~ 26 keV when in magnetospheric mode. We will present the interesting observations obtained by MEA onboard Mio/BepiColombo during its second Mercury flyby that happened on the 23rd of June, 2022. In particular we will focus on the properties of the low- and high-energy electron populations observed during its crossing of Mercury’s magnetosphere.

Magnetic reconnection is a fundamental process in astrophysical plasma, as it enables the dissipation of energy at kinetic scales. Detecting it in-situ is therefore key to further our understanding of energy conversion in space plasma. However, ion reconnection jets usually scale from seconds to minutes in-situ, and as such they can be quite tedious to find in the months or years of data provided by Wind, ACE, Helios, PSP and Solar Orbiter.In this work, we use a new approach to identify automatically reconnection exhausts in-situ. The method strongly relies on the Walén relation and uses Bayesian inference as well as physical considerations to detect reconnection jets in-situ. Applying the detection algorithm to one month of Solar Orbiter data at 0.7 ~AU, we find an occurrence rate of 6.4~jets/day, which is significantly higher than in previous studies performed at 1~AU.  We repeat the analysis over the Solar Orbiter perihelion at 0.3 AU and show that the occurrence rate of magnetic reconnection tends to increase with radial distance.We show that magnetic reconnection exhausts clearly cluster in the solar wind. We perform a statistical analysis, distinguishing between the exhausts associated with the heliospheric current sheet and turbulent reconnection. We find that the source and the degree of Alfvénicity of the solar wind might have an impact on magnetic reconnection occurrence.

Ion-acoustic waves are often observed in the solar wind along the Solar Orbiter’s orbit. These electrostatic waves are generated via ion-ion or current-driven instabilities below the local proton plasma frequency. Due to the Doppler shift, they are typically observed in the frequency range between the local electron and proton plasma frequency in the spacecraft frame. Ion-acoustic waves often accompany large-scale solar wind structures and play a role in the energy dissipation in the propagating solar wind. Time Domain Sampler (TDS) receiver, a part of the Radio and Plasma Waves (RPW) instrument, is sampling wave emissions at frequencies below 200 kHz almost continuously from the beginning of the mission. Almost three years of observations allow us to perform a detailed study of ion-acoustic waves in the solar wind under variable plasma conditions. The emission tends to be observed when proton density and temperature are highly perturbed. A detailed analysis of the proton velocity distribution and wave generation using solar wind data from a Proton and Alpha particle Sensor (PAS) of the Solar Wind Analyzer (SWA) is shown.

Around 17 December 2021, the Solar Orbiter spacecraft was predicted to have had its closest approach to comet C/2021 A1 (Leonard) with a minimum streamline distance < 0.01 AU. This encounter provided an unprecedented opportunity to investigate in situ comet Leonard's interaction with the solar wind and the composition of pick-up ions produced by ionization and dissociation of outgassed neutrals from its coma. It was a long-period comet originating from the Oort Cloud with a nucleus about 1 km in diameter, with ground-based telescope observations after its perihelion pass (at ~0.62 AU on 3 January 2022) indicating that it had subsequently disintegrated. Prior to perihelion, outbursts had been reported as well as variations in brightness, which had resulted in speculation about an impending disintegration. However, the dimming in November 2021, before the Solar Orbiter encounter, was argued to be due to a transition from outgassing dominated by carbon dioxide to water. Comet Leonard was the brightest comet of the year and noted for its spectacular ion tail with complex structures, including knots and streamers. Preliminary analysis of in situ Solar Orbiter observations have revealed tell-tale signatures of a cometary encounter around the time of predicted closest approach, such as evidence for magnetic field line draping. However, the clearest evidence has come from Solar Wind Analyzer-Heavy Ion Sensor (SWA-HIS) observations of singly-charged oxygen ions, which are typically not of solar origin and are usually produced when the solar wind interacts with a comet or other Solar System body. In this presentation we use SWA-HIS and EDP-STEP data to investigate aspects of the solar wind interaction and composition of cometary pick-up ions from this active, long-period comet shortly before its disintegration.

Comet Interceptor is the ESA F1 space mission aiming to explore a comet very likely entering the inner Solar System for the first time, or to encounter an interstellar object originating at another star, scheduled for launch in 2029 together with the ESA L-class Ariel spacecraft. Following the mission adoption in June 2022, the spacecraft and scientific payload development have advanced to the Phase C. In our contribution we present the status of development of the Low-energy electron spectrometer (LEES) that is a part of the Dust-Fields-Plasma multi-instrument suite deployed at the main spacecraft A (DFP-A).The DFP-A/LEES sensor will determine the thermal and suprathermal electron densities, temperatures, and the velocity distribution functions of the local plasma environment of both the solar wind and coma. It will also measure the local properties of negatively charged ions and dust, and detect photoelectrons resulting from neutral-plasma interactions in order to infer the magnetic connectivity between the cometary environment and the spacecraft. The LEES measurements are needed to understand the ionization sources of the cometary neutral gas as well as to infer the plasma boundaries of the induced magnetosphere of the comet. The electron spectrometer is a further miniaturized version of the top-hat analyser inherited from the Stereo, Maven and BepiColombo missions. We present the overall design, simulation of the spacecraft electromagnetic and particle environment influence to the LEES measurements and the intermediate results of testing of the LEES components to survive a potential harsh dust environment during the comet flyby.