bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustic and Optical Flame Transfer Function Measurements in a High-Pressure Lean-Burn Aero-Engine Combustor Fueled With Jet A
Authors: Salazar Victor , Venkatesan Krisna , Han Fei , Wonfor Samuel , Passarelli Mitchell , Zheng Andy , Steinberg Adam
Published: September 2023

This paper reports flame transfer function (FTF) measurements obtained in a high-pressure lean-burn aero-engine combustor using acoustic and optical methods. A liquid fueled lean premixed pre-vaporized combustor was operated at various combustor fuel air ratios (FAR) relevant for supersonic transport. A high-pressure siren was employed to modulate the combustor inlet air flow at frequencies ranging from 30Hz up to 1050Hz. Acoustic FTFs were obtained via multi-microphone method using signals from multiple dynamic pressure sensors. Optical FTFs were obtained simultaneously with acoustic measurements by imaging OH*, CH* and C2* chemiluminescence from the combustor., Specifically, line-of-sight chemiluminescence signal for each species was collected with a fiber optic probe and imaged onto photomultiplier tubes with 10nm bandpass filters centered at 310nm, 430nm and 515nm, respectively. Complementary 2D high speed OH* chemiluminescence images were also acquired using a high-speed camera to gain insight into the flame dynamics and support the interpretation of the FTF findings. A comparison of FTFs using the acoustic and optical methods show good agreement in phases and magnitude trends. The measured FTFs show significant variations with varying fuel-air ratios at various frequency ranges confirming a strong dependency of FTFs with flame shapes.
Numerical Investigation of Steam Injection in a Premixed Swirl-Stabilized Methane-Air Flame Using the Flamelet-Generated-Manifold Method
Authors: Köhler Marius , Hiestermann Marian , Müller Hagen
Published: September 2023

A promising concept to further improve the efficiency of aircraft gas turbines while reducing pollutant emissions is the injection of water steam in the combustor. This approach, known as Water-Enhanced Turbofan (WET) concept, involves that water is recovered from the exhaust, compressed in a liquid state and finally fed to the combustion chamber after passing through a steam generator. In the present work, we investigate the suitability of the flamelet-generated-manifold method to model turbulent combustion under WET conditions, i.e., with high steam loads. As a test case, we use a premixed swirl-stabilized methane-air flame for which experimental reference data are available for dry conditions. The numerical results are in good agreement with both a finite-rate reference simulation as well as with experimental data for velocity and OH*-chemiluminescence. We also observe a significant impact of the steam content in the unburnt gas on the flame shape. In particular, increasing the water-gas-ratio leads to an elongation of the flame. At the same time, the reaction zone becomes wider, leading to reduced heat release maxima. As a consequence, a more homogeneous temperature distribution is observed, which leads to a reduction of NOx formation.
Numerical Investigation on Heat Transfer and Flow Characteristics of Combined Pin-Fin With Rib in a Rectangular Channel
Authors: Yan Shuangjie , Liu Jianjun , An Baitao , Li Chen
Published: September 2023

In this paper, numerical simulation has been conducted to investigate the heat transfer and flow characteristics for cooling schemes which combine pin-fins and ribs. A pin-fin internal cooling channel with an aspect ratio 4:1 was used as baseline, where the pin-fin height-to-diameter ratio was H/D = 2.5, and both streamwise and spanwise spacing were S/D = 2. The combined cooling schemes use partitioned strip ribs to replace part of pin-fins in the rectangular channel. The number of partitioned strip rib is 2, 3, 4 and 4 in Case A, Case B, Case C and Case D, respectively. Simulations were performed at five Reynolds numbers between 7300 and 36000. The results show that the combined cooling schemes bring higher heat transfer, but also produce higher pressure loss. The addition of ribs effectively extends the endwall heat transfer area. The higher blockage ratio of channel sharply increases the pressure loss while enhances heat transfer. Comparing to the baseline pin-fin channel, the overall thermal performance of Case A, Case B, Case C and Case D increases 6.2%, 12.2%, 21.9% and 39.2% respectively, at the Reynolds number of 22,000. The combined cooling scheme could be used in situations where higher cooling load is required and the pressure drop is not of much concern.
Retracted: “Unsteady Flow Phenomena in a 1.5-Stage Test Turbine With an Axial Rim Seal” [ASME Turbo Expo 2023: Turbomachinery Technical Conference and Exposition, Volume 7B, Boston, Massachusetts, June 26–30, 2023, Conference Sponsors: International Gas Turbine Institute, ISBN: 978-0-7918-8701-1, Copyright © 2023 by ASME. Paper No. GT2023-103434, V07BT14A017; 13 pages; doi: https://doi.org/10.1115/GT2023-103434]
Authors: Pehle Lukas , Stotz Stephan , Wirsum Manfred
Published: September 2023

The paper was retracted by ASME, August 2, 2024.
LES/Thickened Flame Model of Reheat Hydrogen Combustion With Water/Steam Injection
Authors: Kruljevic Boris , Cabello López Andrés , Langella Ivan , Ciani Andrea , Duesing Michael
Published: September 2023

In this study, the effects of water injection are analysed in a simplified geometry of a reheat combustor, which is based on a state of the art sequential reheat combustor from Ansaldo Energia. The inlet temperature of this burner and the chemical properties of hydrogen in terms of flame speed and autoignition imply that combustion occurs in an autoignition-assisted propagation regime. Large eddy simulations with an Artificial Thickened Flame modelling have been employed to analyse the dynamic behaviour of the hydrogen flame in lean premixed combustion mode. Results show that this approach can accurately predict the position of the flame front and the autoignition process as compared to a pre-existing DNS dataset. The flame front behaviour is further investigated, and observed to quickly move upstream and downstream, driven by the effect of pressure waves on the autoignition process. The study conducted here shows how the injection of water droplets can prevent the autoignition upstream and thus effectively help in achieving flame stability. Some light is also shed on the influence of the spray design parameters on the stability of the H2 flame and the NOx emissions.
Development and Testing of a Universal High Lift Power Turbine for the LM2500+ Engine
Authors: Guerrero David , Wadia Aspi , Bertini Francesco , Elorriaga Angel , Lopez Yonatan , Paredes Juan , Airaudo Massimiliano , Duckett Dion , Ruiz Alfredo
Published: September 2023

The LM2500 gas turbine was derived from General Electric TF39 and CF6 aircraft engines and has been a best-selling model for over 40 years. The fourth generation LM2500+G4 introduced in 2005 offers an output greater than 34.6 MW at ISO conditions with a thermal efficiency of more than 39%, supporting a wide range of power generation and mechanical drive Land and Marine applications. A fifth generation LM2500+G5 uprate of this successful product has achieved new levels of output shaft power and efficiency, enabled by a more efficient core and a new Universal Power Turbine (UPT) design.

The new power turbine module is briefly described in this document from the basic 1D parameters up to the design of the airfoils, which have high lift characteristics. In addition to the traditional goal of increasing performance, the design of the UPT also focused on achieving robustness and versatility. The UPT is now the best choice for a wide range of applications, with only minor hardware changes needed to adapt it to support the LM2500+, LM2500+G4 and the uprated LM2500+G5 gas generators for both 50Hz and 60Hz applications.

The compliance testing campaign for the LM2500+G5 UPT was conducted on ten engines, using development instrumentation to validate overall gas turbine performance in terms of power, efficiency, and emissions, as well as UPT module performance. The test objectives focused on different power ranges, combustor burner modes and mapping, compressor bleeds, and UPT speeds. The test exceeded expectations, demonstrating the overall engine and component performance of the UPT and, providing valuable data that will be used to further improve the design and performance of the gas turbine.
Numerical Assessment of a Rich-Quench-Lean Staging Strategy for Clean and Efficient Combustion of Partially Decomposed Ammonia in the Constant Pressure Sequential Combustion System
Authors: Heggset Tarjei , Meyer Ole , Gruber Andrea , Tay-Wo-Chong Luis , Ciani Andrea
Published: September 2023

In a future energy-system prospective, predictably dominated by (often) remote and (always) unsteady, non-dispatchable renewable power generation from solar and wind resources, hydrogen (H2) and ammonia (NH3) have emerged as logistically convenient, chemically-simple and carbon-free chemicals for energy transport and storage. Moreover, the reliability of supply of a specific fuel feedstock will remain unpredictable in the upcoming energy transition period. Therefore, the ability of gas turbines combustion systems to seamlessly switch between very disparate types of fuels must be ensured, aiming at intrinsically fuel-flexible combustion systems, i.e. capable of operating cleanly and efficiently with novel carbon-free energy vectors like H2 and NH3 as well as conventional fossil fuels, e.g. natural gas or fuel oils (back-up feedstock). In this context, a convenient feature of Ansaldo’s Constant Pressure Sequential Combustion (CPSC) system, resulting in a fundamental advantage compared to alternative approaches, is the possibility of controlling the amount of fuel independently fed to the two combustion stages, depending on the fuel reactivity and combustion characteristics. The fuel-staging strategy implemented in the CPSC system, due to the intrinsic characteristics of the auto-ignition stabilized reheat flame, has already been proven able of handling fuels with large hydrogen fractions without significant penalties in efficiency and emissions of pollutants. However, ammonia combustion is governed by widely different thermo-chemical processes compared to hydrogen, requiring a considerably different approach to mitigate crucial issues with extremely low flame reactivity (blowout) and formation of significant amounts of undesired pollutants and greenhouse gases (NOx and N2O). In this work, we present a fuel-flexible operational concept for the CPSC system and, based on unsteady Reynolds-Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES) performed in conjunction with detailed chemical kinetics, we explore for the first time full-load operation of the CPSC architecture in a Rich-Quench-Lean (RQL) strategy applied to combustion of partially-decomposed ammonia. Results from the numerical simulations confirm the main features of ammonia-firing in RQL operation already observed from previous work on different combustion systems and suggests that the CPSC architecture has excellent potential to operate in RQL-mode with low NOx and N2O emissions and good combustion efficiency.
A Bayesian Data Driven Multi-Fidelity Modelling Approach for Experimental Under-Sampled Flow Reconstruction
Authors: Cruz Gonçalo G. , Babin Cedric , Ottavy Xavier , Fontaneto Fabrizio
Published: September 2023

This work showcases a multi-fidelity approach, which couples experimental techniques with numerical models within a Bayesian data-driven framework, thus enabling a direct uncertainty assessment. With such an approach, a substantial reduction of the instrumentation effort can be achieved, making it particularly interesting for high intrusiveness applications. A CFD model is employed to provide an initial belief of the flow, which is then updated based on random undersampled experimental observations in a multi-fidelity Gaussian Process framework. The approach is applied to a small aspect ratio axial compressor for which an experimental database is available. With a 70% random undersampling of a complete measurement test, the results exhibit a correct mean flow reconstruction with clear signatures of the typical flow features. The reconstructed flow error is comparable to the experimental measurement uncertainty. An assessment of the approach’s robustness shows an influence of the location of the measurements on the flow reconstruction that decreases with increased flow measurements.
A Combined Experimental and Turbulence-Resolved Modelling Approach for Aeroengine Turbine Rim Seals
Authors: Vella Simon , Darby Peter , Carnevale Mauro , Scobie James A. , Lock Gary D. , Jarrossay Clément , Salvatori Francesco , Bonneau Damien , Sangan Carl M.
Published: September 2023

Ingress is the penetration of hot mainstream gas into the rotor-stator wheel-space formed between adjacent discs; a rim seal is installed at the periphery of the wheel-space. Purge flow is bled from the compressor and re-introduced in the turbine to reduce, or in the limit prevent, ingress. This study presents a unique, concomitant experimental and turbulence-resolved numerical investigation of ingress in an aeroengine rim seal geometry, with leakage flow.

Experimental modelling is conducted in the University of Bath’s 1-stage turbine test facility. Measurements of gas concentration, pressure and swirl were used to assess the performance of the rim seal. A parallel study using Improved Delayed Detached Eddy Simulations (IDDES) was used to generate time-averaged and time-resolved flow-fields, enabling direct comparison with experimental data. The aeroengine architecture conformed to classical rim seal mechanics whereby the effectiveness level increased with purge flow. The inner wheel-space exhibited Batchelor-type flow; in the outer wheel-space, the effectiveness was nonaxisymmetric and synchronised in accordance with the local radial velocity field.

Utilisation of a DES TKE multiplier demonstrated regions where increased turbulence resolution was required to resolve the appropriate scale of turbulent eddies. IDDES computations were found to accurately capture the radial distributions of pressure, swirl and effectiveness, both in the absence and superposition of leakage flows. The IDDES approach exhibits significantly superior agreement with experiments when compared to previous studies employing an Unsteady Reynolds Averaged Navier-Stokes (URANS) methodology.
Effects of Water-to-Air Mass Ratio on Long-Term Washing Efficiency and Erosion Risk in an Axial Compressor Under Online Washing Conditions
Authors: Agati Giuliano , Gabriele Serena , Rispoli Franco , Venturini Paolo , Borello Domenico
Published: September 2023

One of the main reasons of gas turbines performance losses is the deposition of dirt on the compressor blades. Dirt deposit has to be periodically removed to keep the engine performance as high as possible. This is the reason motivating the presence of online water washing systems (WWS) in most of the compressor gas turbines. Such systems aim at cleaning the compressor blades to recover efficiency; thus, the larger the water flow the better it is assumed the compressor is cleaned (fixing all the other conditions). In the present work we simulate the long-term behaviour of a real axial compressor, from the inlet to the first-stage rotor, subject to online water washing with different water flow rates. The frozen rotor approach is adopted to solve the flow field in the rotor region. Simulations are performed by using the unsteady k-ε realizable model coupled with a Lagrangian tracking of the injected liquid phase. Water droplets erosion is handled by using a semi-empirical model developed by the authors. In each simulation 504000 parcels have been tracked, providing statistically reliable predictions. To simulate long-term evolution of the washing process, a discrete mesh morphing technique coupled with the use of specific scale factors is adopted. Each of the tested configuration is composed of three successive erosive steps up to the blade compressor end-of-life. Six different injection configurations are here assessed in terms of long-time average washing efficiency and erosion risk. Results predicted, show the dependence of the considered washing indices on water mass flow rate and set the stage for the development of a washing optimization tool, which helps the design and management processes. In the present simulations the optimal configurations are WAMF* = 0.250 in the case that a small weight is given to the washing indices, and WAMF* = 0.750 for high weights.
Heat Transfer Coefficient Dependence on Coolant Temperature For Supercritical CO2 Leading-Edge Jet Impingement
Authors: Olson Weston , Fernandez Erik , Vesely Ladislav , Kapat Jayanta
Published: September 2023

In this work a conjugate heat transfer analysis was performed on leading-edge jet impingement heat transfer with sCO2 as the working medium. The internal heat transfer coefficient distribution, as well as external metal temperature profiles, were evaluated for three different coolant temperatures. These coolant temperatures were 360K (pseudo-critical), 500K, and 650K. The heat transfer coefficient distribution was maximum when the coolant temperature was that of the pseudo-critical temperature (360K). A simulation with air as the working medium, with the highest coolant temperature (650K), was also included in the study. The air working medium case had the highest external metal temperature and the heat transfer coefficient was a whole order of magnitude less than that of the sCO2 working medium at the same coolant temperature. The results of the study conclude that convective effectiveness of jet impingement heat transfer is much more effective for sCO2, due to its thermal properties, than it is for air and impingement effectiveness is maximum for a coolant at the pseudo-critical temperature. The nondimensional parameters used to represent heat transfer effectiveness were also evaluated at the three coolant temperatures. The heat transfer coefficient can be characterized by the inertial heat capacitance scaled by the Stanton number.
Prospects for Low-Resolution NDIR Sensors to Discern Ignition Properties of Fuels
Authors: Sutar Ashish , Dalmiya Anandvinod , Sheyyab Manaf , Anahideh Hadis , Mayhew Eric K. , Brezinsky Kenneth , Lynch Patrick T.
Published: September 2023

The cetane number is an important fuel property to consider for compression ignition engines as it is a measure of a fuel’s ignition delay. Derived cetane number (DCN) already varies significantly within jet fuels. With the expected increasing prevalence of alternative jet fuels, additional variability is expected. DCN is usually assigned to fuels using ASTM methods that use large equipment like the Ignition Quality Tester (IQT), which consumes a lot of fuel and is cumbersome to operate. Over the last decade, there have been advances in the development of chemometric models, which use machine learning to correlate infrared spectra of fuels to fuel properties like DCN, density, and C/H ratio, amongst many others. These techniques have certain advantages over the ASTM methods, and previous studies performed on samples of diesel fuels have shown high accuracies in DCN prediction. However, this accuracy is generally a result of high resolution, making the equipment expensive, relatively large for handheld sensors, and power-hungry. On the other hand, nondispersive infrared (NDIR) sensors, despite having a low resolution, are attractive because they can be compact, inexpensive, and power efficient. These characteristics are important for handheld or onboard fuel sensors. However, one would anticipate a trade-off between these advantages and accuracy. This study investigates this trade-off and the feasibility of low-resolution NDIR sensors to discern fuel properties such as DCN by using Machine Learning models trained on real FTIR data, and DCNs obtained from IQT. DCN predictions were made for blends of ATJ/F-24, CN fuels, and neat Jet A1, A2, and JP 5, with an error limit of 10%. It was found that there seems to be sufficient variability in the near infrared range to discern DCN with a feasible number of channels, but the channels have to be narrow (e.g. FWHMs as narrow as 60nm). For the data set in the study, the performance of linear models was better than the non-linear model. Finally, NIR region beyond 1050 nm was found to be more important in DCN prediction, primarily the regions consisting of the first and second C-H overtones and the C-H combination band.
Theoretical Method for Characterizing Textile Failure Mechanics in Mechanical Recycling With Carded Drums
Authors: Teixeira França Alves Paulo Henrique , Clarke-Sather Abigail , Carlson Sam , Martini Angela
Published: September 2023

Due to the increasing speed of production, sale, and discard of home and apparel products, recycling of textiles is important for supporting the UN’s Sustainable Development Goal of Responsible Consumption and Production. In 2020, textile production was estimated to be responsible for 35% of primary microplastics released into the environment, 20% of global clean water pollution, and 10% of global greenhouse gas emissions. In 2018 the US generated around 17 million tons of textile waste and only 14.7% was recycled. Drum-operated textile shredding, a commonly utilized mechanical textile recycling technique, is not yet fully characterized. Even though there are many shredding machines that perform this process, the parameters that influence high-quality fiber output have not been researched; discovering ways to improve reusable fiber output is still a challenge. This research investigates the theory behind carded (toothed) drum textile shredding including how to improve the process outcome in order to obtain more reusable fiber and fewer textile pieces and dust. The mechanics of the textiles and fibers under tensile and shear stresses from the drums and drum teeth respectively were described to relate the textile material failure behavior to shredding process fiber outputs. Focusing on the interactions of the feeding drums and shredding drum, the drum-textile and tooth-yarn failure mechanics were characterized. By decreasing the teeth size and increasing the relative speed between drums, it is expected to increase the shear failure ratio, thus improving the shredding system. With this, it is expected that manufacturing new and better materials from recycled fibers becomes a possibility.
Defect Segmentation From X-Ray Computed Tomography of Laser Powder Bed Fusion Parts: A Comparative Study Among Machine Learning, Deep Learning, and Statistical Image Thresholding Methods
Authors: Ouidadi Hasnaa , Xu Boyang , Guo Shenghan
Published: September 2023

Internal defects, e.g., lack of fusion and porosity, are major quality concerns in Laser Powder Bed Fusion (L-PBF). In post-process part inspection, X-ray Computed Tomography (XCT) is used to scan the part to reveal the defective regions inside. 2-dimensional XCT images are obtained showing the part’s cross-section at different heights (layers). Segmenting the defects from raw XCT images is necessary to locate the defected regions, evaluate the part’s quality, and enable root cause analysis. This study proposes two methods for defect segmentation, one is based on deep learning (DL) and the other based on classic machine learning (ML), and compares them with statistical image thresholding approaches (i.e., K-means, Bernsen’s, Otsu’s Thresholding). A discussion about the method-level difference among these methods is provided, revealing the merits of the proposed DL and ML methods in fast defect segmentation and transfer learning across printing conditions. A Case study is done by applying the DL, ML, and statistical image thresholding methods on real XCT images of L-PBF specimens. The defect segmentation accuracy and efficiency of the proposed DL and ML methods are evaluated. A guideline is developed for automatic defect segmentation from XCT images of L-PBF-ed parts by combining statistical image thresholding and DL/ML methods.
Artificial Intelligence-Based Design of Process Parameters in Laser Powder Bed Fusion of Ti-6Al-4V for Desired Solidification Structure
Authors: Vaghefi Ehsan , Mirkoohi Elham
Published: September 2023

Metallic additive manufacturing (AM) technologies can be utilized to manufacture components with tailored and desired microstructure and properties. However, this is just a promise. Fast and accurate computational methodologies are required to optimize the process parameters to achieve the desired microstructure and eliminate the trial-and-error process optimization methodologies. In this paper, a surrogate machine learning model is implemented to design the additive manufacturing (AM) process parameters, including scan speed, laser power, and scanning strategies, to achieve desired microstructure during AM of Ti-6Al-4V. Temperature gradient and solidification rate are the factors that control the target solidification structure, i.e., columnar to equiaxed transition (CET) of grains, to achieve desired mechanical properties. A multi-track finite element model is established and validated to simulate the temperature field during AM process using different scan strategies within a layer. As a result of this process simulation, a dataset containing temperature gradient (G), maximum temperature (Tmax), and solidification rate (R) is extracted from a collection of temperature distribution graphs by using an automated signal processing technique. Next, various machine learning methods (e.g., Boosting methods, multilayer perceptron, support vector regression, and random forest) are evaluated to design process parameters through a cross-validation procedure. The surrogate model is then validated against experimentally obtained microstructures during the solidification path.
Effect of Ultrasonic Vibration on Physical and Tensile Properties of Fused Deposition Modeled Polylactic Acid Specimens
Authors: Quader Raihan , Grewell David , Narayanan Lokesh Karthik
Published: September 2023

Though the use of fused deposition modeling (FDM) of polymers is ever increasing, their utilization in applications requiring high-strength and high-quality surface finish is limited. The process-inherent voids in-between deposited layers and the coarse outer surface resulting from freeform deposition are the critical deterrents. Applying ultrasonic vibration post-fabrication could minimize these issues. In this study, we FDM printed ASTM D638 Type IV specimens from PLA using LulzBot Taz Pro-S printer. Ultrasonic vibration was applied on both sides of the specimens in two different modes. Surface roughness and thickness were measured before and after ultrasonic application. Tensile strength was measured post-ultrasonic application and compared with the control specimens. For internal detail observation, X-ray computed tomography (X-ray CT) was used. In all cases, surface roughness was reduced significantly on the specimens’ top surfaces post-ultrasonics. The thicknesses were not significantly changed. The mean maximum tensile strength increased for all sets of specimens’ post-ultrasonics. X-ray CT images showed that post-ultrasonic specimens had fewer voids compared to the control specimens. Ultrasonic-generated heat and downforce might have facilitated combined squeeze flow and intermolecular diffusion between the successive layers of deposited plastics to increase interfacial healing.
Demonstration of Rapid Polymer Printing Using a Machining-Integrated Hybrid Fused Filament Fabrication Process
Authors: Nigam Aman , Tai Bruce L.
Published: September 2023

The surface finish and dimensional accuracy in extrusion-based additive manufacturing processes are typically poor. Despite the use of a small nozzle size and layer thickness, postprocessing is often required to reach desired finish and tolerance on top of the already-long printing time. Hybrid manufacturing combines additive and subtractive methods to produce near-net-shape parts with improved quality. However, more research needs to be done to examine the hybrid process on polymers and its potential to reduce the total manufacturing time through rapid printing followed by detailed contour machining. To demonstrate this concept, a custom-built 3-axis machine with separate heads for printing and machining was developed. This study alters the parameters of nozzle diameter (0.4 and 0.8 mm) and the printing speed (3600 and 9000 mm/min) to print two generic parts with drastically different times and quality and then conduct an in-situ finishing process to produce the final parts. The finished and as-printed parts are then compared based on surface finish, dimensional accuracy, and manufacturing time. The results show that the hybrid process can greatly improve the form errors in rapid printing. The study also discusses a feature-size case study that can help implement the results and develop general strategies for hybrid manufacturing.
Low-Cost Nanoscale Metal Printing Beyond the Diffraction Limit via Off-Focus Light Projection
Authors: Choi Jungho , Saha Sourabh K.
Published: September 2023

Nanoscale patterning of metallic structures is desired in various fields such as electronics, biosciences, and plasmonics. However, their practical applicability is often constrained by the high cost of the fabrication techniques. Here, we have developed the off-focus light projection (OF-LP) technique to print sub-micron metal features through localized reduction of metal ions into metal nanoparticles. The OF-LP technique implements printing of sub-micron features with low-intensity light and is therefore significantly more affordable than multi-photon printing techniques that require expensive femtosecond lasers. On-focus projection of light is limited by the optical diffraction limit and it is therefore not capable of generating fine nanoscale structures. Here, we present a modified light projection technique by leveraging the projection of images on planes away from the focal plane to achieve sub-diffraction printing. We demonstrate printing of silver nanowires finer than 380 nm, which is the diffraction limit of the optical system. Therefore, this new projection strategy transforms light projection into a low-cost and high-resolution technique for fabrication of metallic nanostructures.
A Force Sensor-Less Method for Identifying the Young’s Modulus of Soft Tissue
Authors: Wang Zhen , Xu Tian , Lei Yong
Published: September 2023

In the minimally invasive surgical navigation system, force boundary conditions and Young’s modulus of human soft tissue have great influence on the accuracy of the biomechanical modeling. However during the operation, the patient-specific Young’s modulus can not be directly obtained in vivo. Some researchers have proposed the noninvasive methods based on images to calculate elastic modulus, but the relevant force information is needed for actual Young’s modulus acquisition. In this paper, a novel method for estimating force boundary condition is proposed to assist identifying the actual Young’s modulus. An elastic material with known Young’s modulus was used as the medium to estimate the force boundary condition by the deformed displacement field. Then the actual Young’s modulus was identified by the iterative method with the deformed displacement field and the estimated force boundary condition. Finally, numerical experiments were conducted to verify the feasibility of this method as well as prove its potential application in the future.
Investigation of tetrakis(ethylmethylamido)hafnium adsorption mechanism in initial growth of atomic layer deposited-HfO2 thin films on H-/OH-terminated Si (100) surfaces
Authors: Park Jihye , Jeong Minji , Cho Young Joon , Kim Kyung Joong , Tai Truong Ba , Shin Hyeyoung , Lim Jong Chul , Chang Hyo Sik
Published: September 2023

The continuous scaling down of dynamic random access memory devices has necessitated a comprehensive understanding of the initial growth mechanism in atomic layer deposition. In this study, HfO2 was deposited using tetrakis(ethylmethylamido)hafnium (TEMAHf)-H2O on H-/OH-terminated Si (100) surfaces. By analyzing the Hf-O peak in the FTIR spectra and medium-energy ion scattering measurements, it was determined that a monolayer was formed on the H-Si surface at a rate (10 cycles) lower than that for the OH-Si surface (4 cycles). The ligand variations during each cycle, as determined by FTIR measurements, enabled the suggestion of the initial precursor adsorption mechanism. An analysis of the infrared spectra and secondary ion mass spectrometry depth profiles revealed surface-dependent differences in interfacial bonding. This explained the variation in the rate of formation of 1 Ml. Additionally, theoretical investigations using density functional theory calculations identified the reaction pathway with the lowest energy barrier, thereby validating the experimentally proposed mechanism. This study to elucidate the Si surface and the TEMAHf-H2O reaction mechanism provided insights into the analysis of the initial precursor adsorption mechanism for other types of precursors.
Refining and extending measures for fricative spectra, with special attention to the high-frequency range
Authors: Shadle Christine H. , Chen Wei-Rong , Koenig Laura L. , Preston Jonathan L.
Published: September 2023

Fricatives have noise sources that are filtered by the vocal tract and that typically possess energy over a much broader range of frequencies than observed for vowels and sonorant consonants. This paper introduces and refines fricative measurements that were designed to reflect underlying articulatory and aerodynamic conditions These show differences in the pattern of high-frequency energy for sibilants vs non-sibilants, voiced vs voiceless fricatives, and non-sibilants differing in place of articulation. The results confirm the utility of a spectral peak measure (FM) and low–mid frequency amplitude difference (AmpD) for sibilants. Using a higher-frequency range for defining FM for female voices for alveolars is justified; a still higher range was considered and rejected. High-frequency maximum amplitude (Fh) and amplitude difference between low- and higher-frequency regions (AmpRange) capture /f-θ/ differences in English and the dynamic amplitude range over the entire spectrum. For this dataset, with spectral information up to 15 kHz, a new measure, HighLevelD, was more effective than previously used LevelD and Slope in showing changes over time within the frication. Finally, isolated words and connected speech differ. This work contributes improved measures of fricative spectra and demonstrates the necessity of including high-frequency energy in those measures.
An unhealthy climate
Authors: Appenzeller Tim
Published: September 2023

This special issue of
Science
was supported by the Pulitzer Center and the Vapnek Family Foundation.
Expecting extremes
Authors: Wadman Meredith
Published: September 2023

Intense heat is a particular hazard in pregnancy. New studies are probing why
Lurking in the deep freeze?
Authors: Cohen Jon
Published: September 2023

Climate change may release dangerous pathogens frozen for centuries in Arctic permafrost
Environmental transmission of influenza A virus in mallards
Authors: Pepin Kim M. , Leach Clinton B. , Barrett Nicole L. , Ellis Jeremy W. , VanDalen Kaci K. , Webb Colleen T. , Shriner Susan A.
Published: September 2023

Influenza A viruses present a major challenge for animal and human health. They circulate widely in wild waterfowl and frequently spillover into poultry, emphasizing the need for risk-based surveillance in wild birds and an understanding of the relative importance of different transmission mechanisms. We addressed this objective with a replicated (
N
= 6) experimental infection study in which we serially exposed eight cohorts of four naïve contact mallards to an experimentally infected mallard and a shared water pool. Viral concentration in the water was a better predictor of transmission than several direct measures of viral shedding in the focal duck. Our data provide quantification of transmission probability and its variation throughout the infectious period of an infected duck. Our findings highlight the need to consider environmental surveillance in risk-based surveillance planning and provide realistic parameters for identifying optimal control strategies using epidemiological inference.

IMPORTANCE

Wild birds are the natural reservoir hosts of influenza A viruses. Highly pathogenic strains of influenza A viruses pose risks to wild birds, poultry, and human health. Thus, understanding how these viruses are transmitted between birds is critical. We conducted an experiment where we experimentally infected mallards which are ducks that are commonly exposed to influenza viruses. We exposed several contact ducks to the experimentally infected duck to estimate the probability that a contact duck would become infected from either exposure to the virus shed directly from the infected duck or shared water contaminated with the virus from the infected duck. We found that environmental transmission from contaminated water best predicted the probability of transmission to naïve contact ducks, relatively low levels of virus in the water were sufficient to cause infection, and the probability of a naïve duck becoming infected varied over time.
Distinct dynamics of the nucleolus in response to nutrient availability and during development in the rice blast fungus
Authors: Cho Eunbyeol , Lee Song Hee , Dean Ralph A. , Jeon Junhyun
Published: September 2023

The nucleolus has emerged as a central hub for nuclear functions in eukaryotes. Studies in mammals and the model yeast
Saccharomyces cerevisiae
showed that the nucleolus is pivotal to nuclear functions other than ribosome biogenesis. Importantly, rDNA transcription and ribosome assembly were shown to positively correlate with the size of the nucleolus. However, little is known about the nucleolus of filamentous fungi. Here, we investigated how the size and shape of nucleolus in the plant pathogenic filamentous fungus,
Magnaporthe oryzae,
respond to nutrient conditions and infection-related development by monitoring the nucleolar marker protein, MoNOP1 tagged with red fluorescent protein (MoNOP1-RFP). Our work revealed that in the hyphae of
M. oryzae,
the nucleolar size is decoupled from the nucleolar activity under low nutrient condition. A complete lack of carbon or nitrogen did not cause such decoupling. In conidia, no or faint RFP signals were initially observed, hinting at the absence of functional nucleoli. RFP signals only started to become visible in conidia within 2 hours of germination when the germ tube tip began to differentiate a specialized infection structure, the appressorium. RFP signals diminished thereafter. In contrast, in the appressorium, signals became concentrated after 6 hours as the appressorium matured. We propose that such nucleolar dynamics may reflect the strategy of filamentous fungi under low nutrient availability to forage for food resources as well as the roles of the nucleolus during fungal development.

IMPORTANCE

The nucleolus is a dynamic subnuclear structure that is involved in many fundamental processes of the nucleus. In higher eukaryotic cells, the size and shape of nucleoli correlate with nucleolar activities. For fungi, knowledge of the nucleolus and its functions is primarily gleaned from budding yeast. Whether such correlation is conserved and how nucleolar functions are regulated in filamentous fungi including important human and crop pathogens are largely unknown. Our observations reveal that the dynamics of nucleolus in a model plant pathogenic fungus,
Magnaporthe oryzae,
is distinct from those of animal and yeast nucleoli under low nutrient availability and during pathogenic development. Our data not only provide new insight into the nucleoli in filamentous fungi but also highlight the need for investigating how nucleolar dynamics is regulated in comparison to other eukaryotes.
Biased eviction of variant histone H3 nucleosomes triggers biofilm growth in
Candida albicans
Authors: Brahma Priya , Aggarwal Rashi , Sanyal Kaustuv
Published: September 2023

Candida albicans
is an opportunistic human pathogen that colonizes the gastrointestinal and genitourinary tracts of healthy individuals.
C. albicans
yeast cells can switch to filamentous forms. On biotic and abiotic surfaces, the planktonic free-floating yeast cells often form biofilms, a multi-drug-resistant three-dimensional community of yeast and filamentous cells. While alterations in gene expression patterns during planktonic to biofilm growth transitions in
C. albicans
have been studied, the underlying molecular mechanisms largely remain unexplored. Previously, we identified a histone H3 variant (H3V
CTG
), which acts as a negative regulator of biofilm growth in
C. albicans
. In the current study, we performed genome-wide profiling of H3V
CTG
nucleosomes in
C. albicans
planktonic cells and found them to be enriched at promoter regions. In planktonic cells, H3V
CTG
-enriched regions are mostly devoid of histone H3 post-translational modifications that allow active transcription, thus strengthening the role of H3V
CTG
as a negative regulator of biofilm formation. By combining genome-wide transcriptional alterations, nucleosome positioning (MNase-seq), and DNA accessibility (ATAC-seq) assays, we show a significant reduction in the total number of nucleosomes in biofilm cells as compared to planktonic cells indicating a more open chromatin state during biofilm growth. Finally, we propose that H3V
CTG
-nucleosome eviction at promoters of biofilm-relevant genes in biofilm-grown cells contributes to achieve the open chromatin state by facilitating easy promoter access of master regulators (activators and repressors) for modulation of gene expression observed during growth phase transitions.

IMPORTANCE

Candida albicans
lives as a commensal in most healthy humans but can cause superficial skin infections to life-threatening systemic infections.
C. albicans
also forms biofilms on biotic and abiotic surfaces. Biofilm cells are difficult to treat and highly resistant to antifungals. A specific set of genes is differentially regulated in biofilm cells as compared to free-floating planktonic cells of
C. albicans
. In this study, we addressed how a variant histone H3V
CTG
, a previously identified negative regulator of biofilm formation, modulates gene expression changes. By providing compelling evidence, we show that biased eviction of H3V
CTG
nucleosomes at the promoters of biofilm-relevant genes facilitates the accessibility of both transcription activators and repressors to modulate gene expression. Our study is a comprehensive investigation of genome-wide nucleosome occupancy in both planktonic and biofilm states, which reveals transition to an open chromatin landscape during biofilm mode of growth in
C. albicans
, a medically relevant pathogen.
Improvement of psoriatic skin lesions following pirfenidone use in patients with fibrotic lung disease
Authors: Karampitsakos Theodoros , Sotiropoulou Vasilina , Katsaras Matthaios , Tzouvelekis Argyrios
Published: September 2023

Psoriasis is an immune-mediated inflammatory disorder of the skin, characterised by uncontrolled proliferation and dysfunctional differentiation of keratinocytes. In our case series, pirfenidone was administered for the management of fibrotic lung disease and, serendipitously, we noticed remission of coexisting cutaneous psoriatic lesions few months after treatment initiation. Pirfenidone’s antifibrotic and immunomodulatory properties have been well studied; yet, not fully elucidated. In line with this, pirfenidone may exert pleiotropic therapeutic effects in other immune-mediated diseases such as psoriasis, while, at the same time, spare immunosuppression-related side effects of current antipsoriatic drugs. Pirfenidone-mediated enhanced absorption of ultraviolet A and ultraviolet B by skin keratinocytes might represent a potential mechanism. The possible role of pirfenidone as an antipsoriatic drug requires large-scale and long-term study.
Association between changes in carbohydrate intake and long term weight changes: prospective cohort study
Authors: Wan Yi , Tobias Deirdre K , Dennis Kristine K , Guasch-Ferré Marta , Sun Qi , Rimm Eric B , Hu Frank B , Ludwig David S , Devinsky Orrin , Willett Walter C
Published: September 2023

Objective

To comprehensively examine the associations between changes in carbohydrate intake and weight change at four year intervals.

Design

Prospective cohort study.

Setting

Nurses’ Health Study (1986-2010), Nurses’ Health Study II (1991-2015), and Health Professionals Follow-Up Study (1986-2014).

Participants

136 432 men and women aged 65 years or younger and free of diabetes, cancer, cardiovascular disease, respiratory disease, neurodegenerative disorders, gastric conditions, chronic kidney disease, and systemic lupus erythematosus before baseline.

Main outcome measure

Weight change within a four year period.

Results

The final analyses included 46 722 women in the Nurses’ Health Study, 67 186 women in the Nurses’ Health Study II, and 22 524 men in the Health Professionals Follow-up Study. On average, participants gained 1.5 kg (5th to 95th centile −6.8 to 10.0) every four years, amounting to 8.8 kg on average over 24 years. Among men and women, increases in glycemic index and glycemic load were positively associated with weight gain. For example, a 100 g/day increase in starch or added sugar was associated with 1.5 kg and 0.9 kg greater weight gain over four years, respectively, whereas a 10 g/day increase in fiber was associated with 0.8 kg less weight gain. Increased carbohydrate intake from whole grains (0.4 kg less weight gain per 100 g/day increase), fruit (1.6 kg less weight gain per 100 g/day increase), and non-starchy vegetables (3.0 kg less weight gain per 100 g/day increase) was inversely associated with weight gain, whereas increased intake from refined grains (0.8 kg more weight gain per 100 g/day increase) and starchy vegetables (peas, corn, and potatoes) (2.6 kg more weight gain per 100 g/day increase) was positively associated with weight gain. In substitution analyses, replacing refined grains, starchy vegetables, and sugar sweetened beverages with equal servings of whole grains, fruit, and non-starchy vegetables was associated with less weight gain. The magnitude of these associations was stronger among participants with overweight or obesity compared with those with normal weight (P<0.001 for interaction). Most of these associations were also stronger among women.

Conclusions

The findings of this study highlight the potential importance of carbohydrate quality and source for long term weight management, especially for people with excessive body weight. Limiting added sugar, sugar sweetened beverages, refined grains, and starchy vegetables in favor of whole grains, fruit, and non-starchy vegetables may support efforts to control weight.