bluuebunny/crossref_metadata_2025 huggingface dataset:
Robust distributed observer for uncertain systems
Authors: Tatafi Saeid Eslahi , Ataei Mohammad , Ekramian Mohsen
Published: July 2024

This paper proposes a robust distributed observer for uncertain systems where some unknown, unstructured, and bounded uncertainties exist in system matrices. In distributed observer, each node includes an observer which directly estimates a part of the system states by its limited measurements and further, the estimation of other states indirectly obtains via exchanging information with neighbouring nodes. It is shown that whole states convergence achieves if the LTI system is observable as well as the network graph is strongly connected. Also, in the proposed distributed observer, by applying a new term in dynamic equation, the robust performance is achieved in dealing with uncertainties in system matrices. The observer gains synthesis is then formulated in terms of linear matrix inequalities. Finally, the simulation results are presented to illustrate the effectiveness of the proposed distributed observer to handle system uncertainties.
Investigating the nature of the 2.4 h-period eclipsing cataclysmic variable W2 in 47 Tuc
Authors: Amato R. , La Palombara N. , Imbrogno M. , Israel G. L. , Esposito P. , de Martino D. , Webb N. A. , Iaria R.
Published: July 2024

Context. W2 (CXOGlb J002415.8–720436) is a cataclysmic variable (CV) in the Galactic globular cluster 47 Tucanae. Its modulation was discovered within the CATS@BAR project. The source shows all the properties of magnetic CVs, but whether it is a polar or an intermediate polar is still a matter of debate.

Aims. This paper investigates the spectral and temporal properties of the source, using all archival X-ray data from Chandra and eROSITA Early Data Release, to establish whether the source falls within the category of polars or intermediate polars.

Methods. We fitted Chandra archival spectra with three different models: a power law, a bremsstrahlung and an optically thin thermal plasma. We also explored the temporal properties of the source with searches for pulsations with a power spectral density analysis and a Rayleigh test (Zn2).

Results. W2 displays a mean luminosity of ∼1032 erg s−1 over a 20-year span, despite lower values in a few epochs. The source is not detected in the latest observation, taken with Chandra in 2022, and we infer an X-ray luminosity ≤7 × 1031 erg s−1. The source spectral shape does not change over time and can be equally well fitted with each of the three models, with a best-fit photon index of 1.6 for the power law and best-fit temperatures of 10 keV for both the bremsstrahlung and the thermal plasma models. We confirm the previously detected period of 8649 s, ascribed to the binary orbital period, and found a cycle-to-cycle variability associated with this periodicity. No other significant pulsation is detected.

Conclusions. Considering the source orbital period, luminosity, spectral characteristics, long-term evolution and strong cycle-to-cycle variability, we suggest that W2 is a magnetic CV of the polar type.
Searching for the stellar cycles of low-mass stars using TESS data
Authors: Ramsay Gavin , Hakala Pasi , Gerry Doyle J.
Published: July 2024

We carried out a search for stellar activity cycles in late low-mass M dwarfs (M0–M6) located in the TESS northern and southern continuous viewing zones using data from sectors 1–61 (Cycle 1 to partway through Cycle 5). We utilised TESS-SPOC data, which initially had a cadence of 30 min and was then reduced to 10 min in Cycle 3. In addition, we required for each star to be observed in at least six sectors in each north and south Cycle: 1950 low-mass stars ultimately met these criteria. Strong evidence was seen in 245 stars for a very stable photometric variation that we assumed to be a signature of the stars’ rotation period. We conducted a similar study for solar-like stars and found that 194 out of 1432 stars had a very stable modulation. We then searched for evidence of a variation in the rotational amplitude. We found 26 low-mass stars that showed evidence of variability in their photometric amplitude and only one solar-like star. Some display a monotonic trend over 3–4 years, whilst others reveal shorter term variations. We determined the predicted cycle durations of these stars using a relationship found in the literature and an estimate of the stars’ Rossby number. Finally, we found a marginally statistically significant correlation between the range in the rotational amplitude modulation and the rotation period.
TESS observations of non-Be fast rotators
Authors: Nazé Yaël , Britavskiy Nikolay , Labadie-Bartz Jonathan
Published: July 2024

Context. The variability of fast-rotating Oe/Be stars has been reported in detail in recent years. However, much less is known about the behaviour of fast-rotating OB stars without known decretion disks, and hence it is difficult to identify the commonalities and differences in the photometric variability of these two populations, especially with regards to their pulsational properties and their link with the presence of circumstellar material.

Aims. Via an in-depth literature search, we identified a set of fast-rotating (vsin(i) > 200 km s−1) early B-type stars not known to have disks. TESS and Kepler light curves were built for 58 stars that appear isolated (no bright neighbour within 1′ and no known companion) to avoid contamination of the light curves. Frequency spectra were calculated and then analysed to determine the noise level and the presence of significant signals above the noise.

Methods. Red noise is detected in all targets, without obvious correlations between noise and stellar parameters. Long-term changes are much less frequent than in Be stars, with only 12% of our targets having the variability below 0.5 d−1 dominating their frequency spectrum. In contrast, strong frequency groups are detected in about a third of targets, as in Be stars. These groups generally occur in pairs with harmonic frequencies, as is usually seen in Be stars, but with the first group more often displaying larger amplitudes. Finally, the most frequent variability is due to isolated frequencies in the 0.5–6. d−1 range (which is found in two-thirds of cases and dominates the spectra in 42% of the sample). Higher-frequency signals (up to 40 d−1) are sometimes also detected but rarely (only 12% of stars) appear as the strongest ones of the frequency spectra. Overall, fast-rotating B-type stars, with or without disks, display similar photometric properties, except as regards their longer-term behaviour.
Gas-phase metallicity for the Seyfert galaxy NGC 7130
Authors: Amiri A. , Knapen J. H. , Comerón S. , Marconi A. , Lehmer B. D.
Published: July 2024

Metallicity measurements in galaxies can provide valuable clues about galaxy evolution. One of the mechanisms postulated for metallicity redistribution in galaxies is gas flows induced by active galactic nuclei (AGNs), but the details of this process remain elusive. We report the discovery of a positive radial gradient in the gas-phase metallicity of the narrow-line region of the Seyfert 2 galaxy NGC 7130, which is not found when considering the star-forming (SF) components in the galaxy disc. To determine gas-phase metallicities for each kinematic component, we used both AGN and SF strong-line abundance relations, as well as Baldwin–Phillips–Terlevich diagnostic diagrams. These relations involve sensitive strong emission lines, namely [O III]λ5007, [N II]λ6584, Hα, Hβ, [S II]λ6716, and [S II]λ6731, observed with the adaptive-optics-assisted mode of the Multi Unit Spectroscopic Explorer at the Very Large Telescope. The presence of a positive radial metallicity gradient in only the ionised AGN component suggests that metals may be transported from central areas of a galaxy to its purlieus by AGN activity.
Investigation of mechanical properties and thermal properties on sugarcane fiber composite material reinforced with polyethylene terephthalate matrix material for sustainable applications
Authors: Saikishore G.J. , Giridhar Saikiran K. , Chakri V. , K Anshuman , Naga Malleswara Rao D.S. , Saravanan G. , Subbu L.S.P.
Published: July 2024

In this modern age composite materials are become the primary material for engineering production because composite materials have several specific properties such as high strength-to-weight ratio, low cost, ease of fabrication, tensile strength, compressive strength, Impact strength, high resistance to thermal which does not realize in pure material or non-composite material. Fabricating composite materials involves producing something useful from waste materials. The experimental investigation involves the fabrication of sugarcane fiber-reinforced PET composites through a controlled manufacturing process. Because of its vast application, every Mechanical Engineer should have the knowledge about the fabricate and test the composite material. In this research, two waste materials are used - bagasse and waste plastic to fabricate a composite. The main purpose of the composite material is for heat insulation that is applicable for industrial roofing. The main purpose of the composite material is for heat insulation that is applicable for industrial roofing applications and manufacturing for sustainable components. The mechanical results after compression and shear tests are 4.57 and 0.37 MPa respectively. The maximum thermal test after an exposed surface temperature test is 54 °C
Enhancing Cucumber Production Sustainability by Incorporated Pest Management: A Comparative Evaluation of Cost and Profitability
Authors: Shankar Raman Ravi , Srilekha Gopu , Kumar B Santosh , Singh Navdeep , Kumar Chandra Pradeep , Sabah Abed AL-Zahra Jabbar Ahmed
Published: July 2024

This research investigates the efficacy of integrated Pest management (IPM) techniques in cucumber cultivation, focusing at the utilization of natural control strategies to reduce pest-associated losses and improve crop productivity. No matter the growing emphasis on biological strategies, their adoption remains limited because of several challenges, including market pressures, regulatory hurdles, and pest resistance. But, through promoting awareness, expertise, and collaboration among organic and IPM communities, barriers to adoption may be overcome. The study underscores the importance of monetary useful resource for natural control and advocates for its integration into sustainable crop protection practices. Through a comparative evaluation of IPM and non-IPM farming processes, the studies highlight the fee implications and profitability of implementing biological control measures in cucumber production. Findings reveal that even as IPM farmers incur higher initial expenses, they reap advanced internet returns and benefit-cost ratios in comparison to non-IPM counterparts, demonstrating the monetary viability and sustainability of IPM strategies in cucumber farming.
Sustainable Removal of Crystal Violet Dye Using Synthesized Albizia Procera-Iron Activated Carbon Nanoparticles (AP-Fe-Ac Nps): Kinetics, Isotherms and Thermodynamics
Authors: Sreekar Kapavarapu , Sri Mahi Saroj Prathap Beeram , Sri Thikkada Yagna , Vyshnavi Kethineedi , Satya Kedarnath Pichika , V Meena
Published: July 2024

In present era, green synthesis methodologies showcases the liabilities in synthetization of nanoparticles and elimination of stains using this synthesized nanoparticles because of their less influencing environmental toxicity. Alblizia procera leaf extract is used in this present studies as it is a promising capping and reducing agents like phenols and other attributed biomolecules, to synthesize FeNp’s-AC in this experiment. The action of ferrous-activated carbon nano-sized particles is calibrated using FTIR, SEM and XRD methods. This experimentation is based on process called Adsorption in the extraction of crystal violet tint are carried out for different parameters which include: dosage, contact time, pH and temperatures were studied and optimized. The Freundlich, Langumir and Temkin Isotherm models for Crystal violet are proved to be the best adjustments for the AP-Fe-ACNp’s experimental data.
Swarm Robotics in a Sustainable Warehouse Automation: Opportunities, Challenges and Solutions
Authors: Ikumapayi Omolayo Michael , Timothy Laseinde Opeyeolu , Elewa Remilekun R. , Samson Ogedengbe Temitayo , Titilayo Akinlabi Esther
Published: July 2024

The Over 90% of the jobs in the logistics industry between 2010 and 2014 came from freight transport and storage services, according to statistics from the Census and Statistics Department. With the advent of Industry 4.0 and its associated emerging technologies (such as cloud computing, Internet of Things, autonomous robots, etc.), a smart robotic warehouse management system is recommended. These innovations transform picking and put-away procedures in warehouses by enabling autonomous mobile robots to transition from man-to-goods to goods-to-man. A group of robots collaborate to solve problems in swarm robotics by putting together practical structures and behaviours that are similar to those found in flocks of birds, schools of fish, or swarms of bees. However, the transition to industrial applications has not yet been completed to a satisfactory level. There is a dearth of knowledge in the literature regarding real-world swarm applications that make use of swarm algorithms. Typically, swarm algorithm components—or what we call basic swarm behaviours —are used. This paper therefore discusses the opportunities available for this technology as well as the challenges that may come with their use. Finally, some possible solutions have been proposed to help tackle the identified challenges in sustainable warehouse automation.
Effect of Heat Treatment Conditions on the Electrochemical Capability and Mechanical Properties of Titanium Grade V Alloy for Biomedical Applications
Authors: Ramalamula Onndwela , Damilare Baruwa Akinsanya , Elizabeth Makhatha Mamookho
Published: July 2024

This research aimed to investigate the sustainability of grade V Titanium alloy (Ti-6Al-4V) in NaCl, as well as its mechanical properties for biomedical applications. Improving titanium alloys is critical for producing alloys with minimal side effects. The impacts of structure, indentation test, corrosion resistance, and wear resistance of six titanium alloys after aging were explored in this work. The heat treatment was carried out in a tube furnace with an inert gas, commencing at ambient temperature and progressing to a high temperature of 955°C. For 10 minutes, air and water were used to cool the sample. The samples were then heated to a continuous temperature tempering at 525°c in three steps for both air(A) and water(W) cooled samples 2, 3, and 4 hours. The microstructure was examined using an optical microscope, the corrosion rate was calculated using a potentiostat, hardness was estimated using the Rockwell B scale, and wear resistance was determined using a universal wear tester. It was observed that the water-quenched samples performed better than the air-cooled samples in terms of characteristics. Above all, the dwelling period during the aging process has a greater influence on the material’s characteristics.
Towards Sustainable Ceramic Forming: Techniques, Materials, and Applications in Evolving Paradigms
Authors: Parmar Umang , Ahmed Shaymaa , Vayas Rahul , Lavanya C. , Manjunatha  , Singh Navdeep , Kumar Harikishor
Published: July 2024

In the sustainability of ceramic forming this paper will provide a comprehensive review of the way that ceramics have changed over time towards sustainability due to Industry 4.0’s current manufacturing technologies which are improving day by day. Particularly this study focuses on reducing the depletion of resources, energy utilization, and natural pollution by examining how conventional strategies for forming ceramics can be replaced by new ones that emphasize sustainability and form a solution. Basically, this paper highlights a few crucial properties in ceramics including its capacity to resist high temperatures, flexibility, and chemical inactivity, and their significance in several areas like biomedical designing, hardware, aviation, the machinery industry, and many more applications. When the drawbacks of traditional ceramic forming methods were analyzed such as high cost and lengthy processing periods, the study clarifies that there is a need for sustainable alternatives. This study also examines new possibilities such as additive manufacturing (3D printing) and hydroforming, which permit for more accuracy in product shape while utilizing a low amount of materials and energy. Going forward, this research also looks into eco-friendly ceramic materials that make the most of secondary sources or are based on biomass-based added substances and binders. Using examples from real circumstances and information from industry, it demonstrates where sustainable ceramics can be utilized in different divisions like design, space travel, electronics, wellbeing care, or renewable energy sources. By doing so, this paper emphasizes how sustainable ceramic making seems to trigger environmental enhancements as well as keep up resource efficiency and shift towards a circular economy.
CFD Analysis of using Deionized Water in Radiator to Enhance the Efficiency for Sustainable Growth
Authors: Vishwakarm Yogesh , Hayder Nibras , Srinivas Tummala , R J Anandhi , Jain Alok , Prakash Dwivedi Shashi , Kiran Ch. Ravi
Published: July 2024

Conventional liquid coolant used in automotive radiators is often used as an engine coolant. Heating systems in automotive air chambers are commonly used to cool circulating fluids, usually water or an aqueous combination of antifreeze agents such as ethylene glycol (EG). This study examines the benefits and issues of the usage of deionized water in all radiators. Deionized (DI) water has received attention as a possible alternative to chemical coolants generally used in automobile air conditioners. Automotive engineers are addressing the demanding situations of intense freezing by developing special garage systems to optimize engine overall performance and limit environmental impact. Compared to conventional refrigerants, the usage of deionized water has lesser environmental consequences, consisting of decreased corrosion and mineral production, which extends radiator lifestyles and improves cooling efficiency. Moreover, DI-water poses several challenges, which include the capability to freeze and compatibility with some radiator materials. Ultimately, this study investigates using deionized water as a refrigerant while used in radiators inside the inlet water. Additionally, it explores the impact of deionized water on engine performance, durability, heat transfer overall performance, corrosion resistance, and potential overheating, at the same time as additionally addressing environmental problems.
Hybrid Wind-Solar System with UPQC
Authors: Saxena Abhishek , Gundlapalle Rajesh , Gupta Manish , Poornima Ediga , Singh Harjeet , Albawi Ali , Arunkumar K
Published: July 2024

The hybrid wind-solar system is a combination of renewable energy sources, specifically wind and solar, that is utilized for power generation. While wind power has historically been used for various purposes such as sails, windmills, and wind pumps, it is now predominantly used for electricity generation. This system incorporates solar panels and small wind turbine generators to produce electricity. The advantage of hybrid systems is that they can generate electricity as needed, taking into account the varying peak working hours of solar and wind systems throughout the year. To ensure a stable power system, UPQC (Unified Power Quality Conditioner) is employed. This multipurpose power conditioner serves multiple functions, including preventing harmonic load current from entering the power system, rectifying voltage fluctuations, and compensating for voltage disturbances from different power sources. It is specifically designed to minimize interference with sensitive or critical loads. With its series and shunt compensation capabilities, UPQC effectively manages power flow, reactive power, harmonics, and voltage disturbances. In this paper, the work addresses the issue of electricity quality that arises from the installation of wind turbines in the grid. To get over this issue, the suggested course of action demonstrates how to install a BESS and a unified power quality conditioner (UPQC) at the connection point. Even though wind power fluctuates, the use of battery energy storage technology helps to provide a constant power supply. With the power system block established in MATLAB/SIMULINK, one can simulate the UPQC control method of a grid-connected wind energy generating plant. As a result, the power's quality will increase. When the recommended approach lowers the load's and the induction generator's reactive power requirements, it is successful. Furthermore, the plan for raising the grid's power quality criteria and developing the grid coordination rule are also provided.
Green Energy Storage Solutions: A Research
Authors: Saritha Kambhampati , Sharma Sanjeev , Dutt Amit , Shrivastava Anurag , Kakoli Rao A. , Haider Jawad Ameer , Saikumar A.
Published: July 2024

One of the key elements of decarbonizing global energy networks and integrating renewable energy sources is green energy storage technology. Energy Storage Systems (ESS), which store surplus produced electricity and make it available on demand, are essential for reducing fluctuations. Electromechanical, electromagnetic, thermodynamic, chemical and hybrid approaches have all been used in the development of energy storage technologies. A comprehensive list of current papers in the literature section is compiled to illustrate the range of advancements in this field. This paper reviews green energy storage systems, focusing on their primary uses. Power utilities will benefit from this thorough analysis of energy storage systems; the researchers choose the finest and newest energy storage technology based on its practicality and affordability. These days, several nations use energy storage systems to plan for future energy needs. Variations in solar radiation cause a solar photovoltaic generator to overproduce electricity. The implementation of a hybrid energy storage system would help to increase the reliability of solar-powered power generation. The microgrid is a crucial component of the smart grid network for solar installations. This study looks at the microgrid's energy storage system for photovoltaic systems. The topologies and storage system configurations of the microgrid are analyzed together with power electronic interference, control systems, and optimization of the energy storage system and renewable sources. a general technique for sizing the HESS of PV systems using design space as well as pinch analysis. HESS scales that link generator ratings to storage capacity are developed in the proper sizes by using pinch analysis to load and resources data.
Cocoa Butter: Evolution from Natural Food Ingredient to Pharmaceutical Excipient and Drug Delivery System
Authors: Loke Ying Hui , Phang Hiu Ching , Mohamad Najwa , Kee Phei Er , Chew Yik-Ling , Lee Siew-Keah , Goh Choon Fu , Yeo Chien Ing , Liew Kai Bin
Published: July 2024

For decades, cocoa butter has been extensively used in food industries, particularly in the production of chocolate confectioneries. The composition of fats within cocoa butter, such as stearic acid, palmitic acid, and oleic acid, determines its properties. Studies have indicated the existence of at least six polymorphic forms of cocoa butter, each possessing distinct characteristics and melting points. Recently, cocoa butter has garnered attention for its potential as a delivery system for pharmaceutical products. This review thoroughly explores cocoa butter, encompassing its production process, composition, properties, and polymorphism. It delves into its diverse applications across various industries including food, cosmetics, and pharmaceuticals. Additionally, the review investigates cocoa butter alternatives aiming to substitute cocoa butter and their roles in different drug delivery systems. The unique properties of cocoa butter have sparked interest in pharmaceutical
industries, particularly since its introduction as a drug delivery system and excipient. This has prompted researchers and industry stakeholders to explore novel formulations and delivery methods, thereby expanding the range of options available to consumers in the pharmaceutical market.
Polyp size measurement during colonoscopy using a virtual scale: variability and systematic differences
Authors: van Bokhorst Querijn N. E. , Houwen Britt B. S. L. , Hazewinkel Yark , van der Vlugt Manon , Beaumont Hanneke , Grootjans Joep , van Tilburg Arjan , Fockens Paul , Bossuyt Patrick M. M. , Dekker Evelien ,   on behalf of the SCALE EYE study group
Published: July 2024

Background Accurate polyp size measurement is important for polyp risk stratification and decision-making regarding polypectomy and surveillance. Recently, a virtual scale (VS) function has been developed that allows polyp size measurement through projection of an adaptive VS onto colorectal polyps during real-time endoscopy. We aimed to evaluate the VS in terms of variability and systematic differences.

Methods We conducted a video-based study with 120 colorectal polyps, measured by eight dedicated colorectal gastroenterologists (experts) and nine gastroenterology residents following endoscopy training (trainees). Three endoscopic measurement methods were compared: (1) visual, (2) snare and (3) VS measurement. We evaluated the method-specific variance (as measure of variability) in polyp size measurements and systematic differences between these methods.

Results Variance in polyp size measurements was significantly lower for VS measurements compared to visual and snare measurements for both experts (0.52 vs. 1.59 and 1.96, p < 0.001) and trainees (0.59 vs. 2.21 and 2.53, p < 0.001). VS measurement resulted in a higher percentage of polyps assigned to the same size category by all endoscopists compared to visual and snare measurements (experts: 69 % vs. 55 % and 59 %; trainees: 67 % vs. 51 % and 47 %) and reduced the maximum difference between individual endoscopists regarding the percentage of polyps assigned to the ≥ 10 mm size category (experts: 1.7 % vs. 10.0 % and 5.0 %; trainees: 2.5 % vs. 6.7 % and 11.7 %). Systematic differences between methods were < 0.5 mm.

Conclusions Use of the VS leads to lower polyp size measurement variability and more uniform polyp sizing by individual endoscopists compared to visual and snare measurements.
3D printing of bio-inspired porous polymeric solar steam generators for efficient and sustainable desalination
Authors: Hou Yanbei , Gao Ming , Bai Xueyu , Zhao Lihua , Du Hejun , Zhou Kun
Published: July 2024

Freshwater scarcity is a pressing issue worldwide, and solar steam generators (SSGs) have emerged as a promising device for seawater desalination, harnessing renewable solar energy to facilitate sustainable water evaporation. The facile fabrication approach for SSG with complex topologies to achieve high water evaporation efficiency remains a challenge. Herein, a MIL-101 (Fe)-derived C@Fe3O4 ink was employed to multi-jet fusion (MJF) printing of polymeric porous SSGs with specific topologies. The optimized porous structure endows the printed SSGs with capillary force, greatly promoting water transport. The tree-like topology enables high water evaporation rates under various simulated solar radiation conditions. A finite element model was built to fully understand the light-to-thermal energy conversion and water evaporation processes. Moreover, the MJF-printed SSGs exhibit self-cleaning properties and can automatically remove accumulated salt on their surfaces, enabling sustainable desalination. During prolonged testing, the water evaporation rate of the SSGs remained relatively stable and reached as high as 1.55 kg m−2 h−1. Additionally, the desalinated water met the standards for direct drinking water. This study presents a state-of-the-art technology for producing efficient SSGs for desalination and introduces a novel method for MJF printing of functional nanocomposites.
Deposition pressure-controlled phase tailoring and stability of β-W for spintronic applications
Authors: Sriram K. , Pappu Yaswanth Sai , Peddiraju Vivek C. , Mondal Rohiteswar , Devapriya M. S. , Haldar Arabinda , Murapaka Chandrasekhar
Published: July 2024

Understanding the nucleation and growth of tungsten (W) is technologically important in spin-to-charge interconversion for realizing energy-efficient spintronic devices. Here, we have systematically investigated the effect of Ar deposition pressure (PAr) on the nucleation and growth of W. The observed surface topography as a function of PAr reveals a microstructural transition from zone T to zone 1 in the structure zone model. The physical origin for the increasing roughness as a function of PAr correlates with the surface diffusion of adatoms and growth kinetics in the Volmer–Weber growth mechanism. Grazing incidence x-ray diffraction (GIXRD) results show that W exhibits a structural phase transition from a mixed phase of (α+β)-W to a single phase of β-W as a function of PAr. The analysis of the electron diffraction patterns obtained from the films grown on amorphous-SiNx windows also supports these observations. The observed transition is fundamentally correlated with the growth kinetics in zone T and zone I. Thickness-dependent GIXRD results qualitatively prove that the film grown in zone T exhibits compressive strain, whereas that grown in zone I exhibits only tensile strain. The critical thickness for the phase transition is strongly attributed to the strain during nucleation and growth. The increasing resistivity as a function of PAr corroborates the change in structural phases. Thickness-dependent resistivity measurements correlate with the degree of crystallinity via relative intensity observed from the GIXRD results. Our results strongly suggest that W structural phases can be deterministically controlled via PAr for developing low-power spintronic devices.
Correlation of heat transport mechanism and structural properties of GaN high electron mobility transistors
Authors: Mitterhuber Lisa , Kosednar-Legenstein Barbara , Vohra Anurag , Borga Matteo , Posthuma Niels , Kraker Elke
Published: July 2024

Grain sizes, impurities, and layer thicknesses in the nm-range affect the heat transport and, hence, hinder proper heat dissipation of GaN-based devices. To obtain a clear picture of heat dissipation, the mechanisms of heat transport must be linked to the structural properties of the nitride-based materials in the device. In this paper, a systematic investigation of the typical layers of GaN high-electron mobility transistor stacks was conducted by time-domain thermoreflectance analysis and Raman measurements. The analyzed layers are the AlN nucleation layer, the Al0.3Ga0.7N transition layer, the AlGaN/AlN superlattice, the C-doped GaN back-barrier, and the uid GaN layer. The results were interpreted using the Born–van Karman model, including the suppression function approach to describe the governing heat transport mechanisms. Investigation of this AlN nucleation layer showed that its phonon scattering is dominated by impurity and grain boundary scattering. The Al0.3Ga0.7N transition layer was shown to have a reduced thermal conductivity not only due to alloy scattering but also because of grain boundary scattering. The AlGaN/AlN superlattice showed a thermal conductivity lower than the Al0.3Ga0.7N transition layer, especially at higher temperatures (7.2 ± 0.2 W/mK vs 14.1 ± 0.4 W/mK at 300 °C). Caused by the enhanced AlGaN/AlN interface density, the thermal conductance was found to be 2 GW/m2 K. The AlGaN/AlN superlattice indicated an anisotropic thermal transport with a factor of ∼1.5. The C-doped GaN layers were analyzed in terms of their size-dictated thermal conductivity, resulting in a reduction of ∼66% from 1 μm to 250 nm at 30 °C. Raman spectroscopy revealed that the thicker the GaN layer, the higher the compressive stress in GaN, which additionally results in a higher thermal transport. The investigations of the heat transport depending on the structural properties enabled an accurate determination of the thermal conductivity of the layer stack. These thermal conductivities served as input parameters for 3D simulation to extract the temperature, in terms of the thermal resistance, of such high-electron mobility transistor stacks. This simulation shows the importance of the GaN layer in terms of thermal management. This work uncovers the thermal transport in GaN-based transistor stacks with the aim to improving the thermal design.
Families of non time-symmetric initial data sets and Penrose-like energy inequalities
Authors: Cabrera Pacheco Armando J. , Wolff Markus
Published: July 2024

Motivated by solving the constraint equations in the evolutionary form suggested by Rácz in 2016, we propose a family of asymptotically flat initial data sets which are “asymptotically spherically symmetric” at infinity. Within this family, we obtain Penrose-like energy estimates and establish the existence of solutions for the constraint equations in the spherical symmetric and totally umbilic cases.
Optimization study on airfoil aerodynamic performance with local indentation treatment based on drainage characteristics of dolphin fluke
Authors: Huang Shengxian , Wang Ying
Published: July 2024

Enhancing the aerodynamic performance of airfoils is the key to optimizing the energy harvesting efficiency of rotating machinery such as wind turbines. Motivated by the bowl-shaped outline of the dolphin's fluke during the propulsion process, this paper proposes a local indentation method that generates a concave region on the pressure surface of the airfoil. The NACA 0018 airfoil is selected as the reference airfoil, and two types of treatments are applied near the trailing edge point: rigid deformation and flexible deformation. Based on the grid quantity independence and experimental results validation, the results demonstrate that compared with the original airfoil, the local indentation method can modify the pressure distribution of the indentation section itself and optimize the airfoil's overall aerodynamic performance. The lift coefficient of the whole airfoil increases gradually with the rise in the indentation depth and reaches a stable value eventually. Quantitative results reveal that when the indentation depth D = 0.020c, the lift coefficient of the whole airfoil can increase by up to 26.27%; when the indentation depth D = 0.010c, the airfoil's lift-to-drag ratio reaches the maximum, which is 16.39% higher than that of the original airfoil. When replacing the rigid indentation section with a flexible medium, the fluid flowing over the pressure surface interacts with the flexible medium. The method of local indentation proposed in this paper can provide valuable reference for optimizing the aerodynamic profile of airfoils and improving the energy harvesting efficiency of wind turbines.
Effect of neural firing pattern on NbOx/Al2O3 memristor-based reservoir computing system
Authors: Ju Dongyeol , Ji Hyeonseung , Lee Jungwoo , Kim Sungjun
Published: July 2024

The implementation of reservoir computing using resistive random-access memory as a physical reservoir has attracted attention due to its low training cost and high energy efficiency during parallel data processing. In this work, a NbOx/Al2O3-based memristor device was fabricated through a sputter and atomic layer deposition process to realize reservoir computing. The proposed device exhibits favorable resistive switching properties (>103 cycle endurance) and demonstrates short-term memory characteristics with current decay. Utilizing the controllability of the resistance state and its variability during cycle repetition, electrical pulses are applied to investigate the synapse-emulating properties of the device. The results showcase the functions of potentiation and depression, the coexistence of short-term and long-term plasticity, excitatory post-synaptic current, and spike-rate dependent plasticity. Building upon the functionalities of an artificial synapse, pulse spikes are categorized into three distinct neural firing patterns (normal, adapt, and boost) to implement 4-bit reservoir computing, enabling a significant distinction between “0” and “1.”
High-quality Ge1−xSnx (x = 0–0.11) realized by UHV-CVD using Ge2H6 and SnCl4: Materials growth, structural/optical properties, and prototype IR photodetectors
Authors: Xie Changjiang , Li Yue , Wu Zhengjie , Wu Songsong , Wang Yixin , Lin Guangyang , Li Cheng , Cong Hui , Xu Chi , Xue Chunlai
Published: July 2024

GeSn materials with Sn contents ranging between 0% and 11% have been successfully grown by using Ge2H6 and SnCl4 in a hot-wall UHV-CVD system at low reaction pressures of 0.2–0.4 Torr. Both fully strained and partially relaxed materials have been produced. It was found that the materials were of high crystallinity as evidenced by few threading dislocations from cross-sectional TEM. Photoluminescence studies have shown that the PL spectra shift to longer wavelengths, and the PL intensity increases exponentially as the Sn contents increase. The photoemission cutoff for a 9.5% Sn sample is beyond 2600 nm, and low temperature PL measurements have confirmed that this sample is already in the direct gap material regime. Prototype photoconductor devices were fabricated with a partially strained 5% Sn sample, showing much smaller dark currents and similar spectral coverage as compared to a fully strained 7.8% Sn device reported in the literature. The reported technical route has provided a new path toward high quality, low cost GeSn epitaxy, and will contribute to the development of group IV optoelectronics.
The role of carbon segregation in the electrical activity of dislocations in carbon doped GaN
Authors: Scales Ze F. , Koller Christian , Lymperakis Liverios , Nelhiebel Michael , Stoeger-Pollach Michael
Published: July 2024

Dislocations have been proposed to affect the performance and reliability of GaN power semiconductors by being conductive pathways for leakage current. However, no direct evidence of a link between their electrical behavior and physical nature in carbon-doped semi-insulating GaN buffer layers has been obtained. Therefore, we investigate the electrical activity of dislocations by conductive atomic force microscopy and electron beam induced current to distinguish electrically active dislocations from non-active ones. We investigated six electrically active dislocations and discovered distinct carbon enrichment in the vicinity of all six dislocations, based on cross-sectional scanning transmission electron microscopy using electron energy loss spectrometry. Electrically non-active dislocations, which are the vast majority, sometimes also showed carbon enrichment, however, in only two out of seven cases. Consequently, carbon segregation seems to be a requirement for electrical activity, but a carbon surplus is not sufficient for electrical activity. We also performed first-principles total-energy calculations for mixed type threading dislocations, which validates carbon accumulation in the dislocation vicinity. The electrical and physical characterization results, complemented by density functional theory simulations, support the previously hypothesized existence of a carbon defect band and add new details.
Characterization of quantum dot-like emitters in programmable arrays of nanowrinkles of 1L-WSe2
Authors: Strasbourg Matthew C. , Yanev Emanuil S. , Darlington Thomas P. , Faagau Kavika , Holtzman Luke N. , Barmak Katayun , Hone James C. , Schuck P. James , Borys Nicholas J.
Published: July 2024

When combined with nanostructured substrates, two-dimensional semiconductors can be engineered with strain to tailor light–matter interactions on the nanoscale. Recently, room-temperature nanoscale exciton localization with controllable wrinkling in 1L-WSe2 was achieved using arrays of gold nanocones. Here, the characterization of quantum dot-like states and single-photon emitters in the 1L-WSe2/nanocone system is reported. The nanocones induce a wide range of strains, and as a result, a diverse ensemble of narrowband, potential single-photon emitters is observed. The distribution of emitter energies reveals that most reside in two spectrally isolated bands, leaving a less populated intermediate band that is spectrally isolated from the ensembles. The spectral isolation is advantageous for high-purity quantum light emitters, and anti-bunched emission from one of these states is confirmed up to 25 K. Although the spatial distribution of strain is expected to influence the orientation of the transition dipoles of the emitters, multimodal emission polarization anisotropy and atomic force microscopy reveal that the macroscopic orientation of the wrinkles is not a good predictor of dipole orientation. Finally, the emission is found to change with thermal cycling from 4 to 290 K and back to 4 K, highlighting the need to control factors such as temperature-induced strain to enhance the robustness of this quantum emitter platform. The initial characterization here shows that controlled nanowrinkles of 1L-WSe2 generate quantum light in addition to uncovering potential challenges that need to be addressed for their adoption into quantum photonic technologies.
Scale analysis of undercut and bulge driven by thermocapillary convection due to surface-active solute on a solidified surface
Authors: Wei P. S. , Pan G. Y. , Weng C. H.
Published: July 2024

This study scales the shape of the undercut, a depression region near the triple-phase line parallel to the scanning direction, and the bulge in the central region within the fusion zone, considering thermocapillary convection affected by a surface-active solute in the molten pool for the first time. Undercuts, commonly encountered in welding, additive manufacturing, and re-solidification processes, reduce fatigue and fracture strength while enhancing stress concentration. Utilizing the interfacial Young–Laplace equation and Bernoulli equations in the shear layer driven by thermocapillary force influenced by the surface-active solute-affected critical temperature, and introducing the concept of mass conservation, the scale analysis finds that the undercut depth and bulge height increase as Marangoni and Prandtl numbers increase, and the loss coefficient decreases. Furthermore, the widths of the undercut and bulge exhibit increases with dimensionless beam power, fusion zone width, and the ratio of solid-to-liquid thermal conductivity. The COMSOL Multiphase code is also used for simulation and successful comparison, aligning with experimental data from laser polishing. This analysis aids in understanding and controlling microstructures in various processes beyond laser polishing.
Simulating ultrafast transient absorption spectra from first principles using a time-dependent configuration interaction probe
Authors: Mehmood Arshad , Silfies Myles C. , Durden Andrew S. , Allison Thomas K. , Levine Benjamin G.
Published: July 2024

Transient absorption spectroscopy (TAS) is among the most common ultrafast photochemical experiments, but its interpretation remains challenging. In this work, we present an efficient and robust method for simulating TAS signals from first principles. Excited-state absorption and stimulated emission (SE) signals are computed using time-dependent complete active space configuration interaction (TD-CASCI) simulations, leveraging the robustness of time-domain simulation to minimize electronic structure failure. We demonstrate our approach by simulating the TAS signal of 1′-hydroxy-2′-acetonapthone (HAN) from ab initio multiple spawning nonadiabatic molecular dynamics simulations. Our results are compared to gas-phase TAS data recorded from both jet-cooled (T ∼ 40 K) and hot (∼403 K) molecules via cavity-enhanced TAS (CE-TAS). Decomposition of the computed spectrum allows us to assign a rise in the SE signal to excited-state proton transfer and the ultimate decay of the signal to relaxation through a twisted conical intersection. The total cost of computing the observable signal (∼1700 graphics processing unit hours for ∼4 ns of electron dynamics) was markedly less than that of performing the ab initio multiple spawning calculations used to compute the underlying nonadiabatic dynamics.
Shock responses of nanocrystalline molybdenum via molecular dynamics simulation: Grain size and shock intensity effects
Authors: Lang Zhe , Xu Chao , Hu Mingdong , Li Pengwei , Hu Ruiheng , Shao Meiyan , Zhang Jing , Wang Zhexi , Liu Huaping , Liu Chunmei
Published: July 2024

Molybdenum (Mo) is a strategic metal for the manufacture of aerospace equipment, satellite components, and vehicle armor. Thus, understanding its behaviors under harsh conditions like shock compression is crucial for its practical utilization. Through molecular dynamic simulations, we have explored the mechanical responses and microstructural evolutions of nano-polycrystalline (NPC) Mo under different shock intensities, with grain sizes ranging from 5 to 33 nm. Our study reveals that grain size considerably influences the Hugoniot data and waveform of NPC Mo. NPC Mo with a smaller grain size exhibits higher compressibility and lower Hugoniot shear stress. As the grain size increases, the presence of a double-wave structure becomes more pronounced. Additionally, with the increase in shock intensity, there is a reduction in the shock front width. Significantly, when the shock stress ranges from approximately 60 to 100 GPa, twinning structures are detected in samples with grain sizes ranging from 10 to 33 nm. Moreover, the elevated temperature behind the shock wave further promotes detwinning reactions. When the shock stresses exceed 100 GPa, twinning–detwinning as well as amorphization-recrystallization become the predominant deformation mechanisms, almost unaffected by grain size. As the shock stress exceeds 250 GPa, the atoms in the samples become completely disordered. These findings provide new insights into the mechanical responses as well as the microstructural evolutions of NPC Mo under shock compression.
Mount for spectroscopic analysis of samples under sustained tensile stress
Authors: Drake Shane M. , Farnsworth Alexander J. , Pinto Gabriele , Meyer Gabriel , Patterson James E.
Published: July 2024

Spectroscopic methods offer valuable insights into the molecular and structural changes induced by stress, but existing techniques are often unable to perform real-time measurements during deformation. A novel solid open mount design is presented that enables spectroscopic investigations of materials under sustained tensile stress while maintaining crucial alignment of the optical system. The mount design allows for sample movement in response to applied strain while maintaining the position of the sample plane, ensuring consistent and reliable spectroscopic measurements. The effectiveness of the mount design is demonstrated with vibrational sum-frequency generation measurements of an elastomer, cured hydroxyl-terminated polybutadiene, and a plastic, high-density polyethylene, taken before, during, and after tensile deformation. The application of this mount to other spectroscopic techniques is discussed. The ability to collect spectroscopic data during a stress event would provide valuable insights into the behavior of stressed materials.