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We investigate sequential processes underlying the initial development of in‐cloud lightning flashes in the form of initial breakdown pulses (IBPs) between 7.4 and 9.0 km altitudes, using a 30–250 MHz VHF interferometer. When resolved, IBPs exhibit typical stepped leader features but are notably extensive (>500 m) and infrequent (∼1 millisecond intervals). Particularly, we observed four distinct phases within an IBP stepping cycle: the emergence of VHF sources forming edge structures at previous streamer zone edges (interpreted as space stem/leader development), the fast propagation of VHF along the edge structure (interpreted as the main leader connecting the space leader), the fast extension of VHF beyond the edge structure (interpreted as fast breakdown), and a decaying corona fan. These measurements illustrate clearly the processes involved in the initial development of in‐cloud lightning flashes, evidence the conducting main leader forming, and provide insights into other processes known to occur simultaneously, such as terrestrial gamma ray flashes. Plain Language Summary The initial development of a lightning flash inside a cloud has long been a mystery. This study utilizes state‐of‐the‐art lightning imaging techniques with a 30–250 MHz VHF interferometer, providing clear images of the processes involved in the initial development of in‐cloud lightning flashes. New radio features suggest distinct development phases, including what we interpret as space stems, space leaders, connection between the main leader and the space leader, fast breakdown, and corona fan development within an initial breakdown pulse stepping cycle. This provides evidence of the conducting main leader in the initial breakdown stage. These observations showcase the intricate streamer discharge phenomena during initial lightning development, and shed light on other processes known to occur simultaneously, including Terrestrial Gamma ray Flashes. Key Points We observed four distinct VHF processes in the development of 300–1,000 m long initial breakdown pulses (IBPs) in in‐cloud lightning flashes These four processes appear to map to the known processes in a conventional stepped leader, including space stem and space leader formation During an initial breakdown step, fast extension over several hundred meters indicates that fast breakdown may be an essential part of in‐cloud flash

To study the mechanism of space stem formation, the high‐speed direct imaging technique and Schlieren photography are used to simultaneously observe the space stems in a 1.35‐m air gap under the lightning impulse voltage. It is found that the average length and diameter of the space stem is approximately 5 and 0.5 mm, which is about 1/3 of the length and 1/10 of the diameter of the local luminous region respectively. Moreover, the space stem exhibits a non‐uniform distributed temperature with a maximum value of several hundred Kelvin for tens of microseconds. Accordingly, a possible mechanism is proposed that the space stem is formed at the primary corona streamer boundary as a result of the propagation of a secondary ionization wave from the HV electrode and survives long enough (to finish the polarization) due to the fast gas heating and production of atomic oxygen. Plain Language Summary It is well known that negative leaders in the air develop in a step‐wise manner, with each step originating from a space stem. However, the mechanism of space stem formation is still unknown, one of the main reasons being the lack of experimental observations. For this reason, this paper carries out laboratory research to observe the optical and thermal properties of space stems. The observations reveal that the local luminous region at the primary corona streamer boundary is not fully heated into the space stem, but only about 1/3 of its length. If based on conventional direct images, the measured length and diameter of space stems would be 2.5 and 10 times larger than the actual values, respectively. The reconstructed temperature field shows that the axial temperature and diameter of the space stem are not uniformly distributed, with higher temperatures and smaller diameters at the end away from the HV electrode. Finally, a new possible mechanism is proposed for the space stem formation, in which the secondary ionization wave from the HV electrode contributes to the initial formation of the space stem, and then the voltage changes help the space stem survive long enough to finish the polarization. Key Points Only a section of the local luminous region at the primary corona streamer boundary is heated to form a space stem, but not all of it The temperature field of a space stem is reconstructed for the first time and presents a non‐uniform distribution A secondary ionization wave may contribute to the space stem formation at the primary corona streamer burst boundary

A physical model based on the mechanism observed in experimental investigations is introduced to describe the formation of negative leader steps. Starting with a small length of a space leader located at the periphery of the negative streamer system of the stepped leader, the model simulates the growth and the subsequent formation of the leader step. Based on the model, the step length, the step forming time, and the propagation speed of stepped leaders as a function of the prospective return stroke peak current are estimated. The results show that the step length and the leader speed increase with increasing prospective return stroke current. The results also show that the speed of the stepped leader increases as it approaches the ground. For prospective return stroke currents in the range of 15 kA–60 kA, the step lengths lie within the range 5 m–100 m, the step forming times lie within the range 10 μs–250 μs, and the leader speed lies within the range 105 m/s −1.5 × 106 m/s. The results obtained are in reasonable agreement with the experimental observations.

The study of microgravity, a condition in which an object experiences near-zero weight, is a critical area of research with far-reaching implications for various scientific disciplines. Microgravity allows scientists to investigate fundamental physical phenomena influenced by Earth’s gravitational forces, opening up new possibilities in fields such as materials science, fluid dynamics, and biology. However, the complexity and cost of developing and conducting microgravity missions have historically limited the field to well-funded space agencies, universities with dedicated government funding, and large research institutions, creating a significant barrier to entry. This paper presents the MicroGravity Explorer Kit’s (MGX) design, a multifunctional platform for conducting microgravity experiments aboard suborbital rocket flights. The MGX aims to democratize access to microgravity research, making it accessible to high school students, undergraduates, and researchers. To ensure that the tool is versatile across different scenarios, the authors conducted a comprehensive literature review on microgravity experiments, and specific requirements for the MGX were established. The MGX is designed as an open-source platform that supports various experiments, reducing costs and accelerating development. The multipurpose experiment consists of a Jetson Nano computer with multiple sensors, such as inertial sensors, temperature and pressure, and two cameras with up to 4k resolution. The project also presents examples of codes for data acquisition and compression and the ability to process images and run machine learning algorithms to interpret results. The MGX seeks to promote greater participation and innovation in space sciences by simplifying the process and reducing barriers to entry. The design of a platform that can democratize access to space and research related to space sciences has the potential to lead to groundbreaking discoveries and advancements in materials science, fluid dynamics, and biology, with significant practical applications such as more efficient propulsion systems and novel materials with unique properties.

The formation and structure of the following Italian deverbal nouns is an open question in Italian word-formation research: (1a) cammino, (1b) ritegno, (1c) riparto, (2a) sosta, (2b) classifica, (3a) tema, (3b) basta, (3c) perquisa. While instances such as in (1) and (2) have, depending on the theoretical background, been analysed either as root conversion (cf. (1)) and conversion of the infinitival stem (cf. (2)) or as suffixation (cf. (1) and (2)), the spectrum of accounts for the instances in (3) includes, in addition, root conversion with analogical gender assignment (cf. (3a) and (3b)) as well as analogical ackformation (cf. (3c)). In the present contribution it is shown that the current conversion approaches as well as the suffixation approach are insufficient to explain the formation and structure of the nouns in (1) to (3). While the suffixation account is ruled out mainly for semantic and distributional reasons, it is shown thatthe existing conversionaccounts are, in principle, more plausible to account for the nouns in (1) and (2). However, as for the analogy-based conversion approaches, it is shown that only (3c) is a proper analogy-driven formation. In contrast, type (3b) will be shown to be an instance of root conversion remodelled by blocking.Moreover, in order to explain the formation and structure of the noun type instantiated by (3a), an additionaltype of conversion has to be distinguished: (3a) is shown – by the help of data from Old Italian– to be a synchronic remnant of an Old Italian conversion type: conversion of stem 2 of the Italian verbal stem space (terminology from Giraudo, Montermini&Pirrelli 2009), i.e. the stem on which also some Italian inflectional forms, as e.g. some of the present subjunctive forms are constructed.

Despite efforts to address racial disparities in STEM fields, little attention has been paid to the experiences and aspirations of queer and trans Black (QT Black) students in grades K-12. This study explored whether there were any significant differences in the choice of STEM majors between QT Black students and non-QT Black students. We found that Black QT students are less likely to choose STEM majors. Additionally, we found significant differences in science teachers’ perceptions of teaching, comparing between QT Black and non-QT Black students. Finally, we found that several factors predicted science-teacher perception of collective responsibility, perceptions of content professional learning community (PLC), self-efficacy, perception of content teacher expectations, and perceptions of principal support for teachers of QT Black and non-QT Black students. Implications for research and practice are discussed.

This chapter contains sections titled: Introduction Sample Condition HAADF Imaging Conclusions References

Background: Back pain and radicular pain due to disc degeneration are probably the most common problems encountered in neurosurgical practice. The experience and results of stem cell therapy in animal disc degeneration model will help us while doing clinical trials. Objective: To study the effect of bone marrow-derived mesenchymal stem cells in an established mouse disc degeneration model. Methods: An easily reproducible mouse coccygeal (Co) 4-5 disc degenerated model by CT-guided percutaneous needle injury was established. The mesenchymal stem cells (MSCs) were cultured from mouse bone marrow and validated. By an established technique, 24 mice disc degenerative models were generated and divided equally into 3 groups (test, placebo, and control). The test group received MSCs with fibrin glue scaffold and placebo group received only scaffold after 6 weeks of degeneration. The control group did not receive any injection. The effects of MSCs were analyzed 8 weeks post injection. Results: The test group showed a significant change in disc height index (%) in micro CT, whereas in the placebo and control groups, there was no change. The Safranin O staining showed an increase in glycosaminoglycan content and the polarized imaging of picrosirius red staining showed restoration of the collagen fibers in annulus fibrosus, which was statistically significant. Conclusion: Intradiscal MSC injection restored disc height and promoted regeneration in the discs at the end of 8 weeks. MSC's niche depends on the microenvironment of the host tissue. These findings will be helpful for clinical trials.

If deprived of exogenous glutamine, naive mouse embryonic stem cells are shown to be capable of generating the amino acid from other sources to enable their proliferation; the stem cells use glutamine and glucose catabolism to maintain a high level of intracellular α-ketoglutarate and promote demethylation of chromatin and ensure sufficient expression of pluripotency-associated genes. Alternative metabolism in stem cells The role of cellular metabolism in regulating stem cell proliferation and differentiation has not been explored in great detail. Craig Thompson and colleagues now show that naive mouse embryonic stem cells can proliferate in the absence of exogenous glutamine, an amino acid normally essential for the growth of mammalian cells, while consuming it avidly when it is present. The cells catabolize glutamine and glucose to maintain high levels of downstream metabolites controlling chromatin modifications and DNA methylation, so as to ensure sufficient expression of pluripotency-associated genes. The role of cellular metabolism in regulating cell proliferation and differentiation remains poorly understood 1 . For example, most mammalian cells cannot proliferate without exogenous glutamine supplementation even though glutamine is a non-essential amino acid 1 , 2 . Here we show that mouse embryonic stem (ES) cells grown under conditions that maintain naive pluripotency 3 are capable of proliferation in the absence of exogenous glutamine. Despite this, ES cells consume high levels of exogenous glutamine when the metabolite is available. In comparison to more differentiated cells, naive ES cells utilize both glucose and glutamine catabolism to maintain a high level of intracellular α-ketoglutarate (αKG). Consequently, naive ES cells exhibit an elevated αKG to succinate ratio that promotes histone/DNA demethylation and maintains pluripotency. Direct manipulation of the intracellular αKG/succinate ratio is sufficient to regulate multiple chromatin modifications, including H3K27me3 and ten-eleven translocation (Tet)-dependent DNA demethylation, which contribute to the regulation of pluripotency-associated gene expression. In vitro , supplementation with cell-permeable αKG directly supports ES-cell self-renewal while cell-permeable succinate promotes differentiation. This work reveals that intracellular αKG/succinate levels can contribute to the maintenance of cellular identity and have a mechanistic role in the transcriptional and epigenetic state of stem cells.

Background Mesenchymal stem cell-derived conditioned medium (MSC-CM) has emerged as a promising cell-free tool for restoring degenerative diseases and treating traumatic injuries. The present study describes the effect of selenium as a reactive oxygen species (ROS) scavenger and its additive effect with basic fibroblast growth factor (bFGF) on in vitro expansion of amniotic fluid (AF)-MSCs and the paracrine actions of AF-MSC-CM as well as the associated cellular and molecular mechanisms. Methods In this study, we obtained CM from human AF-MSCs cultured with selenium. The stemness of selenium-treated AF-MSCs was evaluated by cell growth and differentiation potential. Human fibroblasts were treated with AF-MSC-CM and analyzed for cell signaling changes. For in vivo wound healing assay, ICR mice with a full-thickness skin wound were used. Results Selenium played a critical role in in vitro expansion of AF-MSCs through activation of the AKT-ERK1/2, Smad2, and Stat3 signaling pathways along with inactivation of GSK3β. When administered together with bFGF, it showed remarkable effect in inhibiting ROS accumulation and preserving their multipotency. Proliferation and migration of human dermal fibroblasts and in vivo wound healing were improved in the CMs derived from AF-MSCs exposed to selenium and bFGF, which was caused by the Smad2, AKT-MEK1/2-ERK, and NFκB signaling triggered by the paracrine factors of AF-MSCs, such as TGF-β, VEGF, and IL-6. Our results suggest the following: (a) supplementation of selenium in AF-MSC culture contributes to in vitro expansion and preservation of multipotency, (b) ROS accumulation causes progressive losses in proliferative and differentiation potential, (c) the separate activities of bFGF and selenium in MSCs exert an additive effect when used together, and (d) the additive combination improves the therapeutic effects of AF-MSC-derived CMs on tissue repair and regeneration. Conclusion Antioxidants, such as selenium, should be considered as an essential supplement for eliciting the paracrine effects of MSC-CMs.