bluuebunny/crossref_metadata_2025 huggingface dataset:
A novel compact multifunctional coaxial to waveguide power combining transitions for X‐band applications
Authors: Kumar Manoj , Basavarajappa Gowrish
Published: December 2024

This paper presents the design of novel compact multifunctional coaxial to waveguide power combining transition (PCT) for X‐band applications. For the proof of the proposed concept, 2‐way PCT operating over the entire X‐band (8.2–12.4 GHz) and 4‐way PCT operation from 9.5 to 10.8 GHz are designed, developed, and characterised. Two‐way PCT achieves a measured return loss better than 14 dB over the operating band, and the measured amplitude imbalance and phase imbalance are within 0.25 dB and 4°, respectively. Four‐way PCT achieves a measured return loss better than 15 dB over the operating band, and the measured amplitude imbalance and phase imbalance are within 1 dB and 10°, respectively. Furthermore, a 6‐way PCT is also designed, fabricated, and measured to demonstrate the scalability of the proposed concept. The 6‐way PCT achieves the measured return loss better than 15 dB from 9.9 to 10.475 GHz, and measured amplitude and phase imbalances are within 0.6 dB and 10°, respectively. The designed power combining transition is proposed to be used in X‐band applications like antenna array applications and power combining applications.
Dual‐layer model predictive control‐based scheduling of integrated electricity‐hydrogen‐heat microgrid
Authors: Han Pengfei , Xu Xiaoyuan , Yan Zheng , Tan Zhenfei
Published: December 2024

As a newly widely used energy source, hydrogen has not yet been integrated with other energies efficiently, leading to low energy efficiency and high operating costs. This paper develops a novel cooperation model to coordinate electricity, hydrogen, and district heating systems and reduce operating costs. First, the mathematical model of electricity, hydrogen, and district heating systems coupled by electrolysers is established, and the bidirectional heat exchange (BHE) between hydrogen production and district heating networks (DHNs) is proposed. Then, a dual‐layer model predictive control (DLMPC) method is proposed for the integrated electricity, hydrogen, and heating microgrid (IEHHM) scheduling. The upper layer aims to deal with the hourly power variation and determine the IEHHM operation schedules, and the lower layer revises the power of electrolysers and combined heat and power (CHP) plants to follow the real‐time power variation of renewable energy generations (REGs). Simulation results show that: (1) BHE improves the thermal dynamics of electrolysers and DHNs, enhancing operational flexibility; (2) The DLMPC method enables timely adjustments to the dispatch schedule, reducing operating costs by responding to multi‐time‐scale power variations from REGs.
Image processing‐based noise‐resilient insulator defect detection using YOLOv8x
Authors: Hasan Shagor , Rahman Md. Abdur , Islam Md. Rashidul , Tusher Animesh Sarkar
Published: December 2024

Accurate and efficient insulator defect detection is critical for power grid reliability, but it can be affected by the presence of noises in captured images and can be difficult to employ for real‐time operation due to the slow processing of the detection scheme. This paper proposes a novel framework based on the YOLOv8x object detection scheme, addressing the challenge of detecting small defects in complex aerial images and providing a noise mitigation scheme. A Gaussian blur and Laplacian sharpening‐based hybrid scheme is proposed to mitigate the impacts of noises in insulator images. Experimental results indicate that the proposed framework can achieve a mean average precision (mAP) of 98.4% on noise‐free images, surpassing benchmark models, such as YOLOv5x and YOLOv7 by 2.1% and 3.9%, respectively. Also, while the performance of a conventional system can decrease to a mAP of 93.3% in the worst case, the implementation of the proposed mitigation scheme ensures a mAP of 96.7% for that case. With an inference speed of 56.9 ms per image, this approach offers a promising solution for real‐time power line inspection, contributing to enhanced power grid maintenance and safety.
A novel approach for encryption and decryption of digital imaging and communications using mathematical modelling in internet of medical things
Authors: Thalapathiraj S. , Arunnehru J. , Bharathi V. C. , Dhanasekar R. , Vijayaraja L. , Kannadasan R. , Faheem Muhammad , Khan Arfat Ahmad
Published: December 2024

This research introduces an innovative algorithm for the encryption and decryption of greyscale digital imaging and communications in medicine images utilizing Laplace transforms. The proposed method presents a ground breaking approach to image encryption, effectively concealing visual information and ensuring a robust, secure, and reliable encryption process. By leveraging the inherent strengths of Laplace transform, the algorithm guarantees the complete retrieval of the original image without any loss, provided the correct decryption key is used. To thoroughly evaluate the performance of the algorithm, multiple tests were conducted, including extensive statistical analyses and assessments of encryption quality. Key performance metrics were carefully measured, including correlation coefficients and entropy values, which ranged from 7.89 to 7.99. Additionally, the algorithm's effectiveness was demonstrated through peak signal‐to‐noise ratio values, which spanned from 7.597 to 9.915, indicating the degree of similarity between the original and encrypted images. Furthermore, the number of pixels change rate values, ranging from 99.519241 to 99.609375, highlighted the algorithm's ability to produce significantly different encrypted images from the original. The unified average changing intensity values, falling between 35.72345678 and 35.78233456, further underscored the algorithm's proficiency in altering pixel intensities uniformly. Overall, this research offers a significant advancement in the field of image encryption, combining theoretical robustness with practical efficiency.
Characterisation of a 90° inflow radial turbine additively manufactured from Ti-6AL-4V
Authors: Cogho Max E. , Jacobs Gysbert G.
Published: December 2024

An experimental 90° inflow radial turbine was developed. Selective laser melting was used to manufacture three turbine rotors and three inlet guide vane assemblies. The turbines were manufactured from titanium alloy Ti-6Al-4V. The turbine was tested and characterised, at off- design conditions, with compressed air as the working fluid. The turbines performed worse than was predicted by the ideal design. This is attributed to the off-design test conditions.
Spark plasma sintered Co-Cr-Nb ternary alloys for biomedical application
Authors: Abe John Olorunfemi , Phasani Martha , Popoola Patricia Abimbola , Dada Modupeola , Popoola Olawale Muhammed
Published: December 2024

The development of Co-Cr-Nb ternary alloys as prospective metallic biomaterials for clinical implants via spark plasma sintering was studied in this work. Optimized spark plasma sintering parameters were employed to fabricate the Co-Cr-Nb ternary alloys. The effects of Nb content on the nanomechanical, tribological, and electrochemical properties of the sintered alloys were considered. The results showed the presence of HCP (ε-Co) and FCC (γ- Co) cobalt phases in the microstructures of the ternary alloys, indicating that the addition of Nb stabilizes the mixture through alloying, resulting in a metastable coexistence of HCP and FCC phases. The densification of the ternary alloys depreciated slightly with increasing Nb concentration, likely due to inadequate powder mixing and increased contact regions. It was noted that the nanomechanical properties (hardness and elastic modulus) of the sintered ternary alloys ameliorated as the amount of Nb in the alloys increased. Besides, the ternary alloys showed enhanced wear resistance and superior corrosion characteristics over pure Co-Cr binary alloy as Nb content increased from 5 to 7 wt. %, respectively.
Enhancing indoor place classification for mobile robots using RGB-D data and deep learning architectures
Authors: van Eden Beatrice , Botha Natasha
Published: December 2024

Place classification is crucial for a robot's ability to make high- level decisions. When a robot can identify its operating environment, it can provide more appropriate services. This capability is similar to how humans use their understanding of their surroundings to make informed decisions about appropriate actions. Depth data offers valuable spatial information that can enhance place classification on a robot. However, it is more common for mobile robot applications to rely on RGB data rather than RGB-D data for classifying indoor places. This study demonstrates that incorporating depth information improves the classification of indoor places using a mobile robot. Data were collected from a mobile robot, and indoor scenes were classified based on RGB and RGB-D inputs. A comparison was made between the performance of VGG16, Inception v3, and ResNet50 architectures using RGB data alone. Subsequently, depth information was fused with these RGB models. Experiments showed that classification accuracy improved when tested on the mobile robot by including depth data. In the experiment, the robot created a map of the indoor environment and identified four different rooms on the map using the trained models. This demonstrates the enhanced classification capabilities achieved by incorporating depth information.
Powder bed fusion of pure copper using an electron beam – achieving high conductivity by real-time process monitoring and control
Authors: Ortmann Robert , Hankel Jonas , Grimm Tobias , Röttger Arne , Sehrt Jan T.
Published: December 2024

Powder bed fusion of metals using an electron beam (PBF-EB/M) has reached market maturity. While most parts manufactured with PBF-EB/M are titanium-based, the rising interest in highly conductive pure copper is attracting attention from both industry and research across all additive manufacturing methods. Due to its scalable beam power and processing in a high-temperature vacuum atmosphere, PBF-EB/M is considered one of the most promising additive manufacturing technologies. This study presents a real-time process monitoring and control approach to manufacture pure copper from a feedstock with 99.95 % purity via PBF-EB/M. Manufactured samples achieve high electrical conductivities of over 102 % IACS (International Annealed Copper Standard).
In-situ production of Ti6Al4V single tracks from a blend of CP-Ti and spheroidized Al-V master alloy powders
Authors: Ramosena Lekhetho , Dzogbewu Thywill , du Preez Willie
Published: December 2024

In-situ alloying in additive manufacturing is a technique that has been employed to produce high-quality (defect free), cost-effective Ti6Al4V parts. In a previous study, in-situ alloying of a powder blend consisting of spherical, commercially pure titanium and irregularly shaped aluminum- vanadium master alloy powders was investigated. Although the produced parts were 99.9 % dense, they exhibited porosity that could be attributed to an improper fit between the spherical and irregularly shaped powders in the powder blend. To improve the quality of the alloy, the master alloy powders were spheroidized and then blended with the titanium powder to a ratio of 90 % Ti and 10 % aluminum-vanadium to form a completely spherical powder blend. Therefore, the purpose of this study was to employ this powder blend as feedstock in the laser powder bed fusion process to produce single tracks from a range of laser powers and scan velocities at a fixed layer thickness. From the conducted analysis, it was found that single tracks with the desired geometrical characteristics were produced at laser powers of 80 and 150 W at corresponding scan velocities of 0.2 and 0.6 m/s using a layer thickness of 60 um. The identification of these machine parameters signposts the possibility to produce high-quality Ti6Al4V parts from this powder blend.
An approach to process parameter optimisation for beta titanium alloys
Authors: Rudolph Sabrina Mary-Ann , Dicks James Anthony , Becker Thorsten Hermann
Published: December 2024

This study examined the influence of process parameters on porosity and mechanical properties in Laser Powder Bed Fusion (LPBF) of Beta 21S (Ti–15Mo–3Nb–3Al–0.2Si) and Ti5553 (Ti-5Al-5V-5Mo-3Cr) titanium alloys, with Ti64 (Ti-6Al-4V) as the reference material. Using the volumetric energy density – a function of laser power, scan speed, hatch spacing, and layer thickness – to inform the design space, a means to achieve optimal process parameters which minimise porosity content was explored. By employing a constrained design space and response surface methodology, windows of process parameters were identified. Regression models developed for predicting porosity achieved R-squared values of 0.822 for Ti64, 0.859 for Beta 21S, and 0.788 for Ti5553, indicating strong data fit. The model for Ti64 was validated against five literature sources, with four predictions falling within confidence bands and showing an error range of 0.07 to 0.48%. For Beta 21S and Ti5553, the combined error range for validation samples was 0.24 to 0.45%. Optimal volumetric energy density parameters were suggested to maximise relative density. Vickers hardness was assessed and compared favourably to existing literature. Significant variation was found amongst hardness data, suggesting that LPBF parameters influence mechanical performance. Further investigation is recommended to understand the effects of thermal history on the observed hardness behaviour.
X-ray computed tomography-based porosity segmentation in additive manufacturing: Comparison of traditional and AI approaches
Authors: Ledwaba Tebogo , Steenkamp Christine , Moore Karabo , Kouprianoff Dean , du Plessis Anton
Published: December 2024

Additive manufacturing is increasing in popularity and several manufacturing industries are adapting to the technology. This is due to the benefits of the process such as allowing for complex designs using a variety of materials. However, the occurrence of defects such as porosity in the manufacturing process remains a major concern and an active area of research. In this study, we show how the detection and analysis of porosity using X-ray computed tomography images is performed using different state of the art methods. The methods are demonstrated and compared for Ti6Al4V cantilever samples with lack of fusion and gas porosity at varying levels and include global thresholding methods, as well as artificial intelligence approaches. The advantages and disadvantages of each approach are discussed.
Quantum convolutional neural networks for malaria cell classification: A comparative study with classical CNNs
Authors: Mpofu Kelvin , Mthunzi-Kufa Patience
Published: December 2024

This work outlines a quantum convolutional neural network (QCNN) model designed to accurately detect and classify biomedical images. In this work, a classical CNN and QCNN algorithm were developed and compared in diagnosing malaria infected cells from noninfected cells. The QCNN performance metrics in this work were compared with the performance of the classical CNN algorithm. QCNN algorithms can potentially overcome some limitations of their classical counterpart algorithm, i.e. CNN. The theoretical computational complexity of a single convolutional layer in a CNN is O (N × k2), where N is the number of input data points, and k is the size of the convolutional kernel, whereas the theoretical computational complexities as low as O(log(N)) for certain operations, leveraging quantum parallelism to process high-dimensional data more effectively. In this work the authors compared the performance of the CNN and QCNN for a small malaria dataset. The preliminary results of this work show that CNN outperforms QCNN in terms of accuracy, the CNN had a peak accuracy of 75% whereas the QCNN had an accuracy of 54%. The finding of this work can have an impact on quantum computing and quantum machine learning techniques in medical imaging. In this work we find that QCNNs in their current state of development do not outperform CNNs.
Fabrication of bulk metallic glass lattice structures using laser powder bed fusion
Authors: Wegner Jan , Bruckhaus Lars , Schoenrath Hanna , Kleszczynski Stefan
Published: December 2024

Bulk metallic glasses (BMGs) exhibit exceptional mechanical properties, including high strength, hardness, and large elastic limits, making them promising candidates for highly-stressed structural parts. However, their application has been limited by the need for rapid quenching to maintain the amorphous structure and the consequent limitation of the size of fully amorphous parts due to thermal diffusion constraints in casting. Recent advances in additive manufacturing, specifically laser powder bed fusion (PBF-LB/M), have overcome these limitations by enabling high cooling rates and decoupling part size from cooling rate. This study explores the fabrication of cubic body-centered lattice structures from Zr59.3Cu28.8Al10.4Nb1.4 using PBF-LB/M, focusing on the effect of processing conditions on the amorphicity and mechanical properties of the lattices. Through compression tests, the lattices' mechanical strength and failure mechanisms are evaluated. The results provide foundational insights for optimizing PBF processing of BMG-based lattice structures, potentially marrying desired plasticity with part-size geometries despite the inherent brittleness of PBF-LB/M manufactured BMGs.
Oxidation behaviour of Ti6Al4V and titanium based-matrix composites (TiC/Ti6Al4V and TiB/Ti6Al4V)
Authors: Kgomo Hosia , Masina Bathusile , Mathoho Ipfi , Lekoadi Paul , Pesha Thabo , Mulaudzi Vusimusi
Published: December 2024

This study explores the oxidation behaviour of Ti64 and titanium-based matrix composites, specifically TiC/Ti64 and TiB/Ti64. Through experimental analysis for oxidation tests using the Ultra furnace, the oxidation characteristics were examined to understand the behaviour of these materials under elevated temperatures (400ºC, 500ºC and 600ºC for 6 hours). Scanning Electron Microscopy (SEM) was used to examine the as- built and after-oxidation microstructures. X-ray Diffraction (XRD) was used to identify phases present before and after oxidation. At 400°C, all materials (Ti64, TiC/Ti64 and TiB/Ti64) exhibited minimal oxidation with no increase in mass. As the oxidation temperature increased to 500°C, Ti64 showed visible oxygen diffused zones (ODZS) on the surface under SEM, whereas TiC/Ti64 showed resistance to oxidation as no ODZs were formed on the surface. TiB/Ti64 exhibited intermediate oxidation behaviour and formed an oxide layer, TiO2 observed on XRD. At 600°C oxidation, Ti64 continued to oxidize significantly, while TiC/Ti64 and TiB/Ti64 showed increased oxidation, though to a lesser extent compared to Ti64.
3D printed microfluidic chip design for diagnostic studies
Authors: Sekhwama Masindi , Mpofu Kelvin , Mcoyi Phumulani , Sivarasu Sudesh , Mthunzi-Kufa Patience
Published: December 2024

In this study, additive manufacturing (3D printing) is utilised to fabricate lateral flow microfluidic chips (LFMC). Our chips were designed using Autodesk design software and printed using a Formlabs 3D printer. They are printed using Formlabs V4 resin polymer. In this work, the design process is highlighted in detail and shows an LFMC design that is made for potential applications in diagnostics studies. Our study also tested the performance of one of the chip designs in actual diagnostics experiment on an optical transmittance setup with a peristaltic pump. The LFMC was integrated onto a custom-built transmittance optical biosensor to measure the transmission intensity. A real-time kinetic study was conducted using an HIV-1 oligonucleotide probe. The study involved performing real-time transmittance analysis by pumping the HIV-1 oligonucleotide probe at different flow rates, ranging from 9.
5 μm/min to 13 μm/min with intervals of 0.5 μm/min. During the experiment, transmission intensity or transmitted light was measured in real time as the oligonucleotide HIV probe bound to neutravidin immobilised on the Au metal surface. These measurements were recorded using a USB400 spectrometer, with a broad- band UV light source that emits wavelengths ranging from 400 to 800 nm. The study underscored the significance of microfluidic chips as devices capable of enhancing the performance of biosensors as well as the use of 3D printing in the design and manufacture of these microfluidic chips.
The introduction of modern techniques in 3D printing of sand cores and moulds – a review
Authors: Oguntuyi Samson , Nyembwe Kasongo , Shongwe Mxolisi , Kabasele Jonathan , Mojisola Tajudeen
Published: December 2024

Growing technological innovation has led to faster, easier, and more efficient methods of getting things done. Owing to increasing requests for parts and the need to enhance 3D printing of sand cores and moulds and their conventional counterparts, Artificial intelligence (AI) and Smart systems are expected to address the existing challenges in using these techniques. Conventional metal-casting techniques often necessitate the application of tools in the design of patterns, cores, dies and moulds. Also, specialised skills are needed for pattern-making in wood, plastic or other materials. Metallurgical models dealing with shrinkage rates, machining, draft allowances and solidification in diverse metals, are essential considerations in pattern designing. Furthermore, the possibility of using 3D sand core and mould printing in high-tech applications necessitates minimal error or error-free production of parts. Therefore, this review explores how AI and Smart systems could be introduced into conventional and 3D printing to make the techniques suitable for high-tech applications, such as in the biomedical, aerospace and automotive industries.
Investigation of student biology teachers’ views on field-based plant exploration exercises in a botany course
Authors: Akpınarlı Sena Seçil , Akaydın Galip
Published: December 2024

This study examines the views of student biology teachers regarding field-based plant exploration exercises. It is believed that the incorporation of outdoor education into biology education enhances students’ knowledge of variety of plant species and strengthens their ecological consciousness. Over the course of an 11-week study, pre-service teachers conducted a botanical education outdoors. The research was carried out with 21 student biology teachers enrolled in a biology teaching program at a public university in Ankara. The data, gathered through semi-structured interviews, were analyzed using thematic analysis. The findings indicated that student biology teachers considered these activities valuable for improving memory retention and learning through hands-on experience. However, factors such as difficult landscape settings and unfavorable weather were identified as obstacles to the implementation of such exercises. All pre-service teachers expressed that they would consider implementing outdoor education in their future teaching practices. These findings suggest that field-based plant exploration exercises can contribute to biology education.
Examining the expectations of local people about sports services in local governments on different variables
Authors: Ekin Abdulkadir , Kizilkaya Kemal , Buyrukoğlu Erhan , Şahan Hasan
Published: December 2024

According to Articles 58 and 59 of the 1982 Constitution, “The State protects young people, keeps them away from bad habits and encourages them to sports” and “Local governments are responsible for meeting the needs of local people". In line with these articles, in our research, it was aimed to examine the expectations of local people about sports services in local governments on different variables. 460 (Female; N= 268, 58.3%, Male; N=192, 41.7%) individuals who voluntarily agreed to participate in our research residing in Siirt province in 2024 constitute the sample group of our research. ’’Scale of People’s Expectations from Municipalities on Sports Services’’ developed by Çoban [5] was used. The research data were analyzed in SPSS, 25 package program. As a result of the normality analysis of the scale, it was seen that the significance values were greater than 0.05 and it was decided to use nonparametric analyses (Man Witney U, Kruskal Wallis H) in the analysis. According to the results of the analyses, no statistically significant difference was found in the variables of gender, educational status, and monthly income (p>0.05), while a statistical difference was found in the variables of marital status and occupation (p<0.05).
Examining the transformational leadership tendencies of serious and casual leisure participant sports management students
Authors: Beder Cengizhan , Üstün Ümit Doğan
Published: December 2024

The present study aimed to investigate the transformational leadership tendencies exhibited by sports management students who engage in both serious and casual leisure activities. The study employed the relational screening model, which is a quantitative research technique. A total of 117 students from the Department of Sports Management at Recep Tayyip Erdoğan University, Faculty of Sports Sciences, participated in the study. The participants were selected using the simple random sampling method and willingly participated in the study. Data in the study were gathered through the utilization of the “Transformational Leadership Scale” and a personal information form created by the researchers. The scale comprises 8 questions that endorse a unidimensional structure. The data was analyzed using descriptive measures such as percentage, frequency, and cross-tabulation, as well as more advanced statistical tests including independent sample t-test, one-way analysis of variance test, and partial correlation analysis. The analysis results indicate that there were no significant differences in the participants’ transformational leadership tendencies based on their gender and type of being serious or casual leisure participant. However, a significant difference was found based on the participants’ class. First-year students exhibited a significantly higher inclination towards transformational leadership compared to second-year students. Furthermore, there was no significant correlation found between the ages of the participants and their tendency towards transformational leadership.
Estimation of the drift velocity of Equatorial Plasma Bubbles using GNSS and digisonde data
Authors: Navas-Portella Víctor , Altadill David , Blanch Estefania , Altadill Mar , Segarra Antoni , de Paula Víctor , Timoté Cristhian Camilo , Juan José Miguel
Published: December 2024

Equatorial Plasma Bubbles (EPBs) play a crucial role in modulating plasma density and electron content within the equatorial ionosphere. In this work, we present an advanced and more robust version of the method developed by Blanch E et al. (2018, J Space Weather Space Clim., 8, 38–32) for detecting EPBs using data from the Global Navigation Satellite System (GNSS). The enhancements introduced in this version significantly improve the EPB detection process, achieving a notable reduction in the false positive rate compared to the previous approach. These refinements include the application of more rigorous statistical techniques to achieve a more accurate fit for the background Total Electron Content (TEC), leading to better characterization of EPBs through improved estimation of disturbance shapes. Applying the capabilities of this new method in a dense network of GNSS sensors, we have developed an interferometric procedure for estimating EPB drift velocities, including both speed and direction. This procedure provides valuable insights into the dynamic behavior of EPBs in the Caribbean region during 2014. Our analysis reveals a predominant eastward propagation pattern of EPBs, closely aligned with modified dip isolines. Furthermore, by integrating the results from the GNSS-based method with quasi co-located digisondes, we applied a conceptual model to estimate EPB velocities along their drift direction. This model has been tested across different geographical sectors and validated through comparisons with results from other independent studies. This cross-verification confirms the reliability of the methods for capturing EPB characteristics. This approach improves the precision of EPB detection and contributes to a deeper understanding of their spatiotemporal dynamics and behavior, providing a valuable framework for characterizing these phenomena in the equatorial ionosphere.
Mythen in der Kinderrheumatologie – Stimmt es eigentlich, dass…?
Authors: Freudenhammer Mirjam , Hufnagel Markus
Published: December 2024

Infektionen und Impfungen spielen in der Kinderrheumatologie in mehrfacher Hinsicht eine wichtige Rolle und sorgen sowohl bei Kinderärzten als auch bei Eltern regelmäßig für Verunsicherung. So wird gemeinhin davon ausgegangen, dass Patienten mit rheumatischen Erkrankungen, insbesondere unter antirheumatischer Medikation, eine erhöhte Anfälligkeit für Infektionen aufweisen. Daher kommt insbesondere Impfungen zur Prävention von Infektionen eine zentrale Rolle zu. Gleichzeitig würden die meisten Kinderrheumatologen aus Erfahrung wohl zustimmen, dass Infektionen oder Impfungen Schübe triggern können. Und dann kommt Infektionen nach der Hygienehypothese sogar möglicherweise eine präventive Funktion zu…? Einige der verbreiteten Annahmen werden im vorliegenden Artikel etwas genauer unter die Lupe genommen und auf ihre Evidenz hin überprüft
Die Eibe von allen Seiten
Authors: Hohmann Mima
Published: December 2024

Die Eibe ist ein besonderer Baum, der in vielen Kulturen verehrt wurde.
Eigentlich giftig, kann er fachgerecht aufbereitet in der Homöopathie eingesetzt
werden. Wer alle giftigen Pflanzenteile sorgfältig entfernt, kann aus den
Eibenscheinfrüchten sogar Likör oder Marmelade zubereiten.
Manifestation of Luttinger liquid effects in a hybrid metal-semiconductor double-quantum dot device
Authors: Parafilo A. V.
Published: December 2024

We theoretically study the transport properties of a hybrid nanodevice comprised of two large metallic islands incorporated in a two-dimensional electron gas. The high-tunability of the conducting channels electrically connecting two islands to each other and to the leads allows us to treat the setup as a realization of a multi-channel two-site charge Kondo (2SCK) model. It is shown that the leading temperature dependence of the conductance in the 2SCK circuit satisfies the conductance scaling of a single-impurity problem in a Luttinger liquid, whose interaction parameter is fully determined by the number of conducting channels in the device. We demonstrate that the finite weak backscattering in all conducting channels features the appearance of the sub-leading temperature dependencies in linear conductance. At the special critical point, we predict an equivalency between the 2SCK nanodevice and a single-site two-channel charge Kondo problem, where one Kondo channel is implemented by a non-interacting electron gas and the second Kondo channel is attributed to the Luttinger liquid.
Comparison of the compressibility coefficient versus temperature, pressure, chemical potential dependencies for water and argon based on the principle of corresponding states
Authors: Bulavin L. A. , Rudnikov Ye. G. , Lebovka N. I.
Published: December 2024

The application of the entropy-driven and density-driven phase transitions for analysis of phase diagram of water and argon is discussed. The reduced coefficient of isothermal compressibility is evaluated as βr = –(dV/dP)T(Pc/Vc) (Pc and Vc are the values in the critical point). The data are presented as dependencies of βr on the reduced temperature T/Tc, pressure P/Pc, and chemical potential μ/μc. Consideration is based on the principle of corresponding states. For water, the regions with anomalous behavior associated with the entropy-driven liquid–hexagonal ice phase transition and minima observed at T = (315.3 ± 0.2) K, P = (8.30 ± 0.04) kPa, and μ = (1122 ± 5) kJ/kg. For water, the baric dependence βr(P/Pc) along the liquid–vapor equilibrium line forms a closed loop with line of the liquid–hexagonal ice equilibrium. The thermodynamic similarity of water and argon is observed at relatively large temperatures T/Tc > 0.56, pressures P/Pc > 0.00358, and chemical potentials μ/μc > 0.505.
A 62 Hz high-Q 4-spiral mechanical resonator fabricated of a silicon wafer
Authors: Klochkov Y. Yu. , Mitrofanov V. P.
Published: December 2024

High purity silicon is considered as the test mass material for future cryogenic gravitational-wave detectors, in particular Einstein Telescope-low frequency and LIGO Voyager [(LIGO) Laser Interferometer Gravitational-Wave Observatory]. To reduce the thermal noise of the test masses, it is necessary to study the sources of corresponding losses. Mechanical resonators with frequencies 300 Hz–6 kHz are successfully used for studying, for example, losses in optical coatings of the test mass. However, the frequency range of the interferometric gravitational-wave detectors starts at 10 Hz, and the investigation of different dissipation mechanisms for the test masses in the low-frequency region is relevant. We developed a design of a four-spiral mechanical resonator for studying dissipation and noise in the low frequency range. The resonator was fabricated of a 3-in. silicon wafer using an anisotropic wet etching technique. It consists of four spiral cantilevers on a common base, linked together with additional coupling beams for increasing the frequency difference between the resonator normal modes corresponding to the fundamental flexural off-plane mode of a single spiral cantilever. The measured Q-factor of the 62 Hz out-of-phase mode of the four-spiral silicon resonator at room temperature is limited mainly by the thermoelastic loss. At 123 K, the measured Q = (1.5 ± 0.3) × 107. The main contribution to the total loss comes from clamping and surface losses.
The importance of hemodynamics in stented vessels: A conceptual model for predicting restenosis using the time-averaged shear stress
Authors: Peruzzo Paolo , Del Ferraro Jacopo , Lanzoni Stefano
Published: December 2024

The role of hemodynamics has often been overlooked in mathematical modeling aimed at replicating the restenosis process in stented arteries. This study seeks to address this gap by proposing a simplified model of tissue growth driven by the distribution of mean shear stress acting on the vessel wall. Using an iterative sequence of three-dimensional Computational Fluid Dynamics simulations applied to idealized coronary and femoral arteries, combined with a semi-empirical parametrization of endothelium growth, we demonstrated that the progression of restenosis can be effectively modeled and differentiated according to the intensity of time-varying flow velocities. Notably, restenosis develops faster in the femoral artery (approximately 17 days) compared to the coronary artery (approximately 25 days). The progress of tissue accretion is well defined by the evolution of time-averaged wall shear stress. After an initial decrease (triggering phase), significant increases in wall shear stress are observed during the main accretion phase until the shear stress eventually recovers a sufficient level to arrest the process (stabilization phase). This process, attributed to varying hemodynamic conditions within the stent, highlights the significant influence of local flow dynamics and emphasizes the necessity of accurately modeling both the anatomical structure and the corresponding hemodynamics of arteries when predicting in-stent restenosis.
From high-dimensional committors to reactive insights
Authors: Strand Nils E. , Nicholson Schuyler B. , Vroylandt Hadrien , Gingrich Todd R.
Published: December 2024

Transition path theory (TPT) offers a powerful formalism for extracting the rate and mechanism of rare dynamical transitions between metastable states. Most applications of TPT either focus on systems with modestly sized state spaces or use collective variables to try to tame the curse of dimensionality. Increasingly, expressive function approximators such as neural networks and tensor networks have shown promise in computing the central object of TPT, the committor function, even in very high-dimensional systems. That progress prompts our consideration of how one could use such a high-dimensional function to extract mechanistic insights. Here, we present and illustrate a straightforward but powerful way to track how individual dynamical coordinates evolve during a reactive event. The strategy, which involves marginalizing the reactive ensemble, naturally captures the evolution of the dynamical coordinate’s distribution, not just its mean reactive behavior.
How to define temperature in active systems?
Authors: Hecht Lukas , Caprini Lorenzo , Löwen Hartmut , Liebchen Benno
Published: December 2024

We are used to measuring temperature with a thermometer, and we know from everyday life that different types of thermometers measure the same temperature. This experience can be based on equilibrium thermodynamics, which explains the equivalence of different possibilities to define temperature. In contrast, for systems out of equilibrium such as active matter, measurements performed with different thermometers can generally lead to different temperature values. In the present work, we systematically compare different possibilities to define temperature for active systems. Based on simulations and theory for inertial active Brownian particles, we find that different temperatures generally lead to different temperature values, as expected. Remarkably, however, we find that different temperatures not only lead to the same values near equilibrium (low Péclet number or high particle mass) but also even far from equilibrium, several different temperatures approximately coincide. In particular, we find that the kinetic temperature, the configurational temperature, and temperatures based on higher moments of the velocity distribution constitute a class of temperatures that all assume very similar values over a wide parameter range. Notably, the effective temperature and temperatures exploiting the virial theorem, the Stokes–Einstein relation, or a harmonic confinement form a second class of temperatures whose values approximately coincide with each other but which strongly differ from those of the first class. Finally, we identify advantages and disadvantages of the different possibilities to define temperature and discuss their relevance for measuring the temperature of active systems.
Characteristics of cylindrical Hall ion source with floating potential magnetic pole discharge
Authors: Nie Junwei , Chen Qingchuan , Yang Fazhan , Li Pingchuan , Zhang Fan , Tang Deli
Published: December 2024

The discharge characteristics of a cylindrical Hall ion source (CHIS) with floating potential magnetic poles and grounded magnetic poles were investigated through experiments and simulations. The results revealed that the ion density distribution and ion energy were mainly affected by the discharge voltage and magnetic pole potential. The current utilization rate is 82%–93%, which is much more efficient than that of the conventional Hall ion source with grounded magnetic poles. As the gas supply increased, the floating potential of the magnetic pole increased. Under the same discharge current condition, the discharge voltage of a Hall ion source with floating magnetic poles is 300 V larger than that of grounded magnetic poles; meanwhile, this type of ion source has a higher mean ion energy and better uniformity of ion beam distribution. Ion acceleration in the CHIS with floating magnetic poles is expected to occur predominantly in the longitudinal direction and toward the CHIS outlet. The non-uniformity of the ion beam current density within a diameter of 40 mm along the radial directions approximately ±11.7% at a discharge voltage of 800 V, which is helpful for material surface cleaning, etching, sputtering, and ion beam-assisted deposition applications.
The globally exponential decay and inviscid limit of analytic solutions to the compressible Oldroyd-B model
Authors: Pan Xinghong , Yang Yuxuan
Published: December 2024

In this paper, we derive the globally exponential decay and inviscid limit of analytic solutions to the compressible Oldroyd-B model. Due to the pure damping effects of the linearized compressible Oldroyd-B model without viscosity, we obtain a globally viscosity-independent a priori estimate. However, the bilinear term possesses one more order of derivative than the linear part, and no effective structure has been found to address this derivative loss problem. Therefore, we can only establish our results in the analytic energy space rather than the Sobolev space.
Numerical analysis on the ducted propeller aerodynamics in sidewall-ground effect
Authors: Li Huadong , Dong Xin , Gao Yuzhe , Liu Yiliang , Bie Dawei , Li Daochun , Xiang Jinwu , Tu Zhan
Published: December 2024

Owing to their compact structure and robust protective features, unmanned aerial vehicles (UAVs) equipped with ducted propellers are particularly suited for search and detection missions in confined environments. However, in such spaces, proximity effects can lead to pronounced instability in the aerodynamic performance of the UAV, particularly under the influence of multiple wall interactions. This study employs a sliding mesh technique and the Unsteady Reynolds-Averaged Navier-Stokes method to perform computational fluid dynamics simulations, analyzing the ground-sidewall effect's impact on ducted propeller aerodynamic performance across various hovering positions. Research shows that sidewall effects remain largely unaffected by ground effects. However, when the ground height is less than 2r and the sidewall distance is less than r, the ground effect noticeably alters the strength of the sidewall effect. In this region, sidewall suction effects increase sharply as ground height decreases; however, once the ground height falls below 1r, the mean side force diminishes rapidly. Based on the simulation results, this study proposes an empirical formula for side force under coupled sidewall-ground effects, with a mean absolute percentage error of approximately 10% compared to simulation results. Through an analysis of the unstable motion of vortex structures, this study further explains the causes of substantial transient force fluctuations observed near the walls. The findings of this study provide theoretical guidance for the design of flight controllers and the planning of safe flight paths in confined environments.
Nonlinear Bragg resonance of focused wave groups by periodic seabed topography
Authors: Wu Qian , Feng Xingya , Dong You
Published: December 2024

Bragg resonance induced by periodic bottoms has potential applications for coastal protection. Under extreme wave conditions, nonlinearity may play a critical role in the wave-topography interactions. It is important to understand the nonlinear effects in Bragg resonance of periodic bottoms subject to a nonlinear focused wave group, as a representation of an extreme transient event. An efficient fully nonlinear numerical model using the conformal mapping method is developed to simulate wave-topography interaction problems. Validation of this model is performed against theoretical predictions and experimental data in the literature. It is then employed to study Bragg reflection triggered by nonlinear focused wave groups. The nonlinear analysis finds that increased wave group amplitudes slightly weaken the Bragg reflection and shift the value of the corresponding relative wavelength 2S/LP, as a result of the free surface nonlinear effect. The three bottom configurations tested include ripples, rectified cosinoidal bars, and steps. A second order Bragg reflection is observed at 2S/LP=2.0, with reflection coefficients potentially exceeding the fundamental reflection coefficients by up to 20% at greater bar heights. This study provides new insights into the nonlinear Bragg Resonance of free surfaces and periodic seabed topography under extreme wave conditions.
Improving agent performance in fluid environments by perceptual pretraining
Authors: Zhang Jin , Xue Jianyang , Cao Bochao
Published: December 2024

In this paper, we construct a pretraining framework for fluid environment perception, which includes an information compression model and the corresponding pretraining method. We test this framework in a two-cylinder problem through numerical simulation. The results show that after unsupervised pretraining with this framework, the intelligent agent can acquire key features of surrounding fluid environment, thereby adapting more quickly and effectively to subsequent multi-scenario tasks. In our research, these tasks include perceiving the position of the upstream obstacle and actively avoiding shedding vortices in the flow field to achieve drag reduction. Better performance of the pretrained agent is discussed in the sensitivity analysis.
Mapping chaos: Bifurcation patterns and shrimp structures in the Ikeda map
Authors: F. M. Oliveira Diego
Published: December 2024

This study examines the dynamical properties of the Ikeda map, with a focus on bifurcations and chaotic behavior. We investigate how variations in dissipation parameters influence the system, uncovering shrimp-shaped structures that represent intricate transitions between regular and chaotic dynamics. Key findings include the analysis of period-doubling bifurcations and the onset of chaos. We utilize Lyapunov exponents to distinguish between stable and chaotic regions. These insights contribute to a deeper understanding of nonlinear and chaotic dynamics in optical systems.
Dynamic response characteristics of coal/rock during water injection and freezing process under gas atmosphere and its control effect on gas outburst
Authors: Zhou Aitao , Sun Yongxin , Wang Kai , Ma Shujun , Wang Zhaofeng , Ma Xingying , Chen Yanqi
Published: December 2024

The freezing method compensates for the defect of sacrificing coal integrity to reduce gas content, which is the case with traditional methods, achieving the improvement of coal body strength while reducing coal seam gas energy storage, improving the safety of coal and gas outburst accidents in deep coal seams during the process of rock cross-cut coal uncovering. This study conducted water injection and low-temperature freezing experiments on coal/rock samples under the gas atmosphere, analyzing the effects of water and temperature on sample temperature, deformation, and gas adsorption and desorption characteristics. The results indicate that water can displace adsorbed gas in coal/rock samples, and the relationship between the gas displacement and the water content of the sample satisfies an improved exponential function. The center temperature Tm of low water content coal/rock samples decreases with time and gradually tends to stabilize, while the Tm of high water content samples experiences a short-term deceleration or stagnation due to the phase transition heat release of water when it drops to around 0 °C. The cooling rate of samples with low water content and no gas is higher and that of rocks is higher than that of coal samples. Coal/rock samples with high water content experience frost heave during the freezing process, but the overall deformation is still dominated by cold shrinkage, and the amount of deformation is negatively correlated with temperature and water. The gas adsorption capacity of coal decreases linearly with the temperature. At the same time, an increase in water content and a decrease in freezing temperature will significantly reduce the gas desorption capacity of coal samples, effectively reducing the gas expansion energy of coal samples, especially the desorption gas expansion energy. In engineering implementation of this method, the ice phase network can fill the coal pores and cracks and improve the mechanical properties of the coal/rock mass, and the gas pressure in the coal seam and stress concentration near the coal rock interface can be reduced by low temperature and cold shrinkage, thereby achieving safe exposure of the coal seam and preventing accidents from occurring.