C. Mark Johnson

Measurements were first made in 2016 of legacy 39 Ar gas from the decades-old Barnwell underground nuclear explosion site within the Nevada National Security Site. This has raised the question of the ubiquity of the radionuclide 39 Ar following underground nuclear explosions in general locations. This work presents a high-level evaluation of the scientific case for using 39 Ar as a long-term indicator of underground nuclear explosions. Assessment is made based on a broad set of assumptions to reasonably estimate the persistence of 39 Ar in the subsurface environment following an explosion to establish potential detectability years to decades after the originating event.

Detecting radionuclide gas seepage from clandestine underground nuclear tests is central to nonproliferation explosion monitoring research. Yet, early-time (<6 day) gas transport driven by the explosive pressure wave remains poorly constrained due to scarcity of field data. We simulate multi-phase gas transport in the vadose zone using pre-shot data from a recent chemical explosion in P-Tunnel at the Nevada National Security Site, USA. Despite using a simplified 2D-radial model, predictions of tracer arrival matched observations within one order-of-magnitude. Our results show how transient blast forcing rapidly mobilizes gases from the cavity into surrounding rock - critical for optimizing sensor placement and test planning. This unique integration of field data and modeling represents a significant improvement in our ability to predict gas migration from underground explosions. More broadly, it offers insights into the coupled dynamics of pressure waves and contaminant transport in the vadose zone, with implications for monitoring and hazard assessment.

Introduction: Deep sternal wound infection is a serious complication after sternotomy for cardiac surgery. Management can necessitate sternectomy with chest wall reconstruction using a pedicled omental flap, which requires an iatrogenic defect in the diaphragm. This defect can ultimately develop into a larger diaphragmatic hernia and necessitate repair. Case Presentation: Our patient was a 70-year-old female with partial sternectomy with omental flap reconstruction after coronary artery bypass surgery who presented with dyspnea, chest pain, and poor food tolerance. Imaging confirmed a large, diaphragmatic hernia at the site of omental flap and was ultimately repaired primarily using a robotic-assisted approach. Discussion: This case highlights a serious complication related to omental flap reconstruction after sternectomy. Repair of the hernia defect can either be accomplished primarily or with mesh. We pursued primary repair given that there was inadequate adjacent tissue to secure mesh and to preserve the omental flap vascular pedicle. Conclusion: Deep sternal wound infections after cardiac surgery can be managed with sternectomy and a pedicled omental flap. The iatrogenic diaphragm defect created can result in herniation of abdominal contents into the chest. Our case report is the first to describe a robotic approach for repairing an intentionally created diaphragmatic defect.

Abstract Efficient co-utilization of hexose and pentose sugars from lignocellulose is essential for microbial production of bio-based chemicals, yet engineered non-native catabolic pathways can be suboptimal and evolutionarily unstable in complex resource environments. We used a Pseudomonas putida strain, previously engineered to catabolize xylose and arabinose to examine how resource abundance, temporal availability, and sub-culturing criteria shape evolutionary outcomes. Using an automated adaptive laboratory evolution (ALE) platform, we evolved the strain under static conditions with single selection pressures and dynamic regimes that imposed selection pressures on multiple sugars. These environments drove divergence between catabolic specialists and generalists. While selection regimes with weak or absent selection for xylose frequently resulted in loss of xylose catabolism, evolution under carbon-limited, mixed-sugar environments promoted stable retention and coordinated optimization of multiple catabolic pathways, increasing total sugar consumption in mixed-sugar conditions. Genomic, proteomic, and biochemical analyses showed that evolutionary stability was determined by pathway-specific fitness costs, leading to either pathway loss or cost-reducing refinement, depending on selection strength. An isolated generalist clone also exhibited improved indigoidine production from mixed sugars when compared to the parental strain. Together, these findings link resource dynamics to fitness landscapes that determine catabolic specialization, generalization, evolutionary trade-offs, and applicability to bioconversion.

OBJECTIVE: Obesity, or excessive body fat, is a significant health risk factor. Western diets (WD) contribute to metabolic dysfunction and obesity, while Mediterranean diets (MD) improve metabolic health. This study examined the contrasting effects of WD versus MD on visceral and subcutaneous adipose tissues (VAT, SAT) using a randomized preclinical trial in 38 female cynomolgus macaques assigned to consume either WD (n = 21) or MD (n = 17) for 31 months. METHODS: Body composition, metabolic parameters, and adipose transcriptomics were evaluated. RESULTS: WD significantly induced VAT and SAT accumulation, which was directly associated with insulin resistance, hepatosteatosis, and time spent alone and inversely related to cortisol suppression response to dexamethasone indicating hypothalamic-pituitary glucocorticoid insensitivity. Diet significantly influenced the VAT transcriptome, with MD upregulating pathways linked to RNA processing and protein folding while downregulating those involved in fatty acid oxidation and aerobic respiration. CONCLUSIONS: These findings highlight the protective role of MD against fat accumulation and metabolic dysfunction and provide novel insights into the molecular mechanisms underlying diet-induced obesity. Promoting this dietary pattern may help reduce obesity and chronic disease risk. Further research integrating proteomics and metabolomics is required to better understand diet-induced molecular changes.

In recent years, the demand for high-efficiency voltage regulation over a wide input voltage range is appearing in many applications, such as fuel cells, solar panels, and battery-powered systems. In this context, although resonant converters can achieve high efficiency level, the regulation over a wide input voltage range remains a challenge. Additionally, the newer Gallium Nitride (GaN) devices offer new opportunities for power conversion, owed mainly to their exceptional switching performance. Therefore, this paper presents an isolated topology-morphing Series Resonant Converter (SRC) applied to the solar panel application, with a rated power of 300 W, which operates in three distinct modes to offer high efficiencies above <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{9 2 \%}$</tex> with a large input voltage variation (8-35 Volts) and an impressive peak efficiency of over <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{9 8. 4 \%}$</tex>. Design guidelines and experimental results are showcased in this paper to demonstrate the feasibility of this proposal.

Protein phosphatase 2A (PP2A), an important therapeutic target, comprises a scaffold subunit PR65 composed of 15 HEAT (Huntingtin/elongation/A-subunit/TOR1) repeats, a catalytic subunit, and one of many different regulatory subunits that enable binding to specific substrates. Recently, small molecule activators of PP2A (SMAPs) were identified, although their mechanisms of action have not been fully defined. Here we explore the interaction of PR65 with two SMAPs, ATUX-8385 and the non-functional DBK-776, using single-molecule optical tweezers, ensemble methods, and computational analysis. In the absence of SMAP, PR65 shows multiple unfolding and refolding transitions, and the force-extension profiles are very heterogeneous with evidence of misfolding. Similar heterogeneity has been observed for chemical-induced unfolding of tandem-repeat proteins like PR65, a consequence of the internal symmetry of the repeat architecture. In the presence of ATUX-8385, higher unfolding and refolding forces are observed globally, and there is less misfolding, suggesting that ATUX-8385 acts like a pharmacological chaperone. In contrast, DBK-766-binding induces higher unfolding forces for only a few repeats of PR65, suggestive of a more localised effect; moreover, subsequent stretch-relax cycles show that PR65 is irreversibly locked in the unfolded state. Docking and molecular dynamics simulations provide additional insights how SMAP binding modulates PR65 structure and function.

This paper presents a multicellular converter topology allowing compact switching cells to be connected in series and in parallel, to aid in the adoption of Gallium Nitride (GaN) high-electron-mobility-transistors (HEMTs) for higher power applications. Maximising the potential of GaN based semiconductors for applications with greater blocking voltages than 600 V and current ratings over 50 A. The topology presented intends to operate in medium/high voltage DC/AC applications with a low frequency output, overcoming barriers relating to high commutation inductance and the high dv/dt present in other power converters. This paper will provide a comprehensive theoretical analysis for single-phase operation of the converter, offering a method of selection for the main circuit parameters. A loss analysis, using PLECS, for varying operating scenarios is also included.

This paper introduces a novel approach of using surface mount resistor (SMR) for measuring switching current in power module applications. To overcome the challenge of the SMR parasitic inductance on measurement results, the SMR impedance is characterised first and used to compensate the switching current measurement results. To validate the approach, a SiC-MOSFET half-bridge circuit is built and both Rogowski coil and SMR are used to measure the switching current. The switching current measured by SMR using our proposed approach shows agreement with the results obtained by Rogowski coil. The measurement error without using our proposed approach is quantified, and illustrates that our proposed approach helps to reduce the measurement error. Thus, it provides a compact switching current measurement solution by comparing with state-of-the-art current measurement approaches, which shows that it is promising for future highly integrated wide bandgap power module application.

We present a high-level architecture for how artificial intelligences might advance and accumulate scientific and technological knowledge, inspired by emerging perspectives on how human intelligences advance and accumulate such knowledge. Agents advance knowledge by exercising a technoscientific method—an interacting combination of scientific and engineering methods. The technoscientific method maximizes a quantity we call “useful learning” via more-creative implausible utility (including the “aha!” moments of discovery), as well as via less-creative plausible utility. Society accumulates the knowledge advanced by agents so that other agents can incorporate and build on to make further advances. The proposed architecture is challenging but potentially complete: its execution might in principle enable artificial intelligences to advance and accumulate an equivalent of the full range of human scientific and technological knowledge.

Abstract This paper deals with the performance of sintered nano-silver bonds used as wide-bandgap power module die attachment technology. The paper specifically explores the fine-scale microstructures of highly porous sintered attachments under power cycling to provide a deeper understanding of the significance of porosity as a reliability-related microstructural parameter. Attachments prepared at 220°C using a pressure of 6 MPa for 1 s (parameters known to generate approximately 50% porosity from previous work) and subsequently subjected to 650,000 power cycles between 50°C and 200°C are assessed. A correlative workflow integrating x-ray computed tomography, focused ion beam (FIB) and electron backscatter diffraction (EBSD) data is applied to merge meso- and nanoscale microstructural features to illuminate the degradation mechanisms. The as-sintered Ag layer has a high volume of heterogeneously distributed pores, and consists of randomly oriented equiaxed grains whose sizes vary depending on the local density of the region sampled. Power cycling promotes grain growth and the loss of twin boundaries, and these changes are more pronounced within more dense regions of the Ag attachment. In contrast, the copper substrate appears to undergo some grain refinement, with deformation twins visible within finer-grained zones during power cycling. Cracks, which appear to start off within the Ag layer, propagate across the Ag-Cu boundary and transgranularly through fine-grained regions within the copper with little tortuosity. These observations are discussed within the context of reliability behaviour. Graphical Abstract

Gallium Nitride (GaN) High Electron Mobility Transistors (HEMT) are an increasingly adopted choice for power conversion in the low voltage range. Their increased efficiency enables novel, high-power density converter design. The performance of these devices has been well explored in the higher power rated devices, but the high voltage, low current GaN HEMTs have been less explored. This paper presents a double pulse test setup, which was constructed to measure switching times and losses for both the turn-on and turn-off events. The setup provides novel data on the dynamic performance of discrete (GS66502B) and monolithically integrated (NV6115) 650V GaN HEMT transistors. Layout and test design guidelines are also provided. The results are compared to examine the potential benefits of using a monolithic solution and provide data for designers, enabling accurate prediction of switching loss.

The spontaneous emergence of function from diverse RNA sequence pools is widely considered an important transition in the origin of life. Here we show that diverse sequence pools are not a prerequisite for the emergence of function. Starting five independent selection experiments each from a single RNA seed sequence - comprising a central homopolymeric poly-A (or poly-U) segment flanked by different conserved primer binding sites - we observe transformation (continuous drift) of the seeds into low diversity sequence pools by mutation, truncation and recombination without ever reaching that of a random pool even after 24 rounds. Upon continuous error prone replication and selection for ATP binding we isolate specific ATP- or GTP-binding aptamers with low micromolar affinities. Our results have implications for early RNA evolution in the light of the high mutation rates associated with both non-enzymatic and enzymatic prebiotic RNA replication.

A high-voltage thyristor converter is realized by many valve sections, whose volume is approximately occupied for only the 10% by thyristors and for the 10% by the relevant gate drivers. The remaining 80% is taken by passive auxiliary circuits, needed to protect thyristors during turn-on and turn-off commutations. This work represents a preliminary validation of an innovative architecture that aims to reduce the auxiliary circuit cost, volume, and weight of the overall valve, through the investigation of active, instead of passive solutions. The work starts from the investigation of the phenomena behind the valve transient behaviors and proceeds with simulations and experimental tests, using a reduced-scale circuit prototype. The match between the obtained results validates the investigated active configurations, confirming that the proposed solution can be used for improving thyristor valves.