| 1. |
- Abbasiasl, Taher, et al.
(författare)
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Effect of intensified cavitation using poly (vinyl alcohol) microbubbles on spray atomization characteristics in microscale
- 2020
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Ingår i: AIP Advances. - : American Institute of Physics (AIP). - 2158-3226. ; 10:2
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Tidskriftsartikel (refereegranskat)abstract
- In this study, cavitating flows inside a transparent cylindrical nozzle with an inner diameter of 0.9 mm were visualized, and the effect of cavitation on atomization characteristics of emerging sprays was investigated. Different patterns of cavitating flows inside the nozzle were visualized using a high-speed camera. In-house codes were developed to process the captured images to study the droplet size distribution and droplet velocity in different flow regimes. The results show that cavitating flows at the microscale have significant effects on atomization characteristics of the spray. Two working fluids, namely, water and poly(vinyl alcohol) microbubble (PVA MB) suspension, were employed. Accordingly, the injection pressures were detected as 690 kPa, 1035 kPa, and 1725 kPa for cavitation inception, supercavitation, and hydraulic flip flow regimes in the case of water, respectively. The corresponding pressures for the aforementioned patterns for PVA MB suspension were 590 kPa, 760 kPa, and 1070 kPa, respectively. At the microscale, as a result of a higher volume fraction of cavitation bubbles inside the nozzle, there is no large difference between the cavitation numbers corresponding to cavitating and hydraulic flip flows. Although the percentage of droplets with diameters smaller than 200 μm was roughly the same for both cases of water and PVA MB suspension, the Sauter mean diameter was considerably lower in the case of PVA MBs. Moreover, higher droplet velocities were achieved in the case of PVA MBs at lower injection pressures.
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| 2. |
- Amiri, A., et al.
(författare)
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A replacement model to simulate the nonlinear dynamics of electro-responsive liquid crystal coatings
- 2023
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 13:3
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Tidskriftsartikel (refereegranskat)abstract
- An electric circuit replacement model is proposed to simulate the key nonlinear dynamics of electro-responsive liquid crystal polymer networks (LCNs). LCNs are known for having great potential to be integrated into smart functional surfaces due to their ability to generate various surface patterns. However, due to their complex molecular dynamics, low-order dynamic models that can accurately describe and predict their dynamic behavior are still lacking. In light of this research gap, we develop a lumped-parameter replacement model based on the observed dynamics in the experimental data and the physics of LCN dielectric properties. The unique assembly of lumped parameters in its simplest form describes the transformation of a high-frequency input voltage to a relatively slow increase in the local height of the LCN coating in between the electrodes, serving as an excitation mechanism to induce height change. The nonlinear dynamics of this height increase, as a function of both excitation frequency and voltage, is described by the proposed model. Furthermore, the comparison of the simulation results with the experimental data from LCN shows that key LCN response characteristics are captured well by the model. This model makes it possible to accurately predict and control the response of the electro-responsive LCN surfaces to obtain a predefined desired deformation pattern, which is a vital requirement for integrating them in haptic and smart surface devices.
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| 3. |
- Buermans, J., et al.
(författare)
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Triple Langmuir probe calibration in TOMAS ECRH plasma
- 2023
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 13:5
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Tidskriftsartikel (refereegranskat)abstract
- In the TOMAS device, a triple Langmuir probe is used to measure the electron temperature and density. The accuracy of this measurement depends on correct determination of the effective collecting area of the probe, which depends on complex plasma transport processes. The probe can be calibrated by electron cyclotron resonance heating experiments using the cut-off density of the ordinary wave (O-wave). This threshold only depends on the frequency of the injected wave, and the occurrence of this phenomenon is clearly visible in the temperature evolution. The value of density is consequently known at this point and can be used to calibrate the density measurements of the triple Langmuir probe.
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| 4. |
- Capriata, Corrado Carlo Maria, et al.
(författare)
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Grain structure influence on synchronized two-dimensional spin-Hall nano-oscillators
- 2023
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 13:5
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Tidskriftsartikel (refereegranskat)abstract
- Nanoconstriction spin-Hall nano-oscillators (NC-SHNOs) are excellent devices for a wide variety of applications, from RF communication to bio-inspired computing. NC-SHNOs are easy to fabricate in large arrays, are CMOS compatible, and feature a narrow linewidth and high output power. However, in order to take full advantage of the device capabilities, a systematic analysis of the array behavior with respect to the number and dimensions of oscillators, the temperature of operation, and the influence of layer quality is needed. Here, we focus on micromagnetic simulations of 2 x 2 and 4 x 4 NC-SHNO arrays with single oscillators separated by up to 300 nm. We observe a synchronization scheme that allows for column-wise selection of the oscillation frequency for a larger pitch. However, for smaller pitches, a coherent oscillation volume was observed, and this volume included both the constrictions and extended beyond that region. A local variation in the exchange coupling in the active oscillator region was investigated by placing physical grains in the free magnetic layer, and it was shown to influence both the stable current range and the resulting frequency and output power. De-coupling the oscillators along rows or columns could provide higher power due to more favorable phase shifts between oscillators. Our investigation helps in achieving a deeper understanding of the intrinsic working principles of NC-SHNO arrays and how they reach fully synchronized states, and this will help to expand non-conventional computing capabilities.
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| 5. |
- Diesen, Elias, et al.
(författare)
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Accuracy of XAS theory for unraveling structural changes of adsorbates : CO on Ni(100)
- 2020
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 10:11
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Tidskriftsartikel (refereegranskat)abstract
- Studying surface reactions using ultrafast optical pump and x-ray probe experiments relies on accurate calculations of x-ray spectra of adsorbates for the correct identification of the spectral signatures and their dynamical evolution. We show that experimental x-ray absorption can be well reproduced for different binding sites in a static prototype system CO/Ni(100) at a standard density functional theory generalized-gradient-approximation level of theory using a plane-wave basis and pseudopotentials. This validates its utility in analyzing ultrafast x-ray probe experiments. The accuracy of computed relative core level binding energies is about 0.2 eV, representing a lower limit for which spectral features can be resolved with this method. We also show that the commonly used Z + 1 approximation gives very good core binding energy shifts overall. However, we find a discrepancy for CO adsorbed in the hollow site, which we assign to the significantly stronger hybridization in hollow bonding than in on-top.
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| 6. |
- Dmitriev, Yurij A., et al.
(författare)
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H/D isotope effect observed in the isotropic Fermi contact interaction of formyl radical : Experimental and theoretical analysis of the inter- and intra-molecular dynamics
- 2020
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Ingår i: AIP Advances. - : American Institute of Physics (AIP). - 2158-3226. ; 10:12
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Tidskriftsartikel (refereegranskat)abstract
- An unexpected deficit of the computed hyper fine coupling constant in normal formyl HCO radicals, compared to that expected based on the proton to deuteron gyromagnetic ratio of the DCO species, was observed in experimental electron paramagnetic resonance studies of HCO and DCO radicals in a CO solid matrix at cryogenic conditions. Still, the matrix was found to have only a small effect on the anisotropic parts of the magnetic parameter tensors. The underlying isotope effect between the lighter proton and the heavier deuteron on the motional dynamics was verified and elucidated by quantum chemical calculations. The experimental results obtained within a temperature range of 1.4 K–4.2 K require special attention due to the tunneling motions of the molecule and its constituent particles. The effect from vibrational, rotational, and librational motion observed in the molecular states of formyl as a probe, averaged over the dynamics of the low temperature CO matrix isolation, reveals a clear proton isotope effect under both classical and quantum conditions.
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| 7. |
- Ferro, Marc D., et al.
(författare)
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NeuroRoots, a bio-inspired, seamless brain machine interface for long-term recording in delicate brain regions
- 2024
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 14:8
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Tidskriftsartikel (refereegranskat)abstract
- Scalable electronic brain implants with long-term stability and low biological perturbation are crucial technologies for high-quality brain-machine interfaces that can seamlessly access delicate and hard-to-reach regions of the brain. Here, we created "NeuroRoots," a biomimetic multi-channel implant with similar dimensions (7 mu m wide and 1.5 mu m thick), mechanical compliance, and spatial distribution as axons in the brain. Unlike planar shank implants, these devices consist of a number of individual electrode "roots," each tendril independent from the other. A simple microscale delivery approach based on commercially available apparatus minimally perturbs existing neural architectures during surgery. NeuroRoots enables high density single unit recording from the cerebellum in vitro and in vivo. NeuroRoots also reliably recorded action potentials in various brain regions for at least 7 weeks during behavioral experiments in freely-moving rats, without adjustment of electrode position. This minimally invasive axon-like implant design is an important step toward improving the integration and stability of brain-machine interfacing.
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| 8. |
- Gandhi, Hemi H., et al.
(författare)
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Chalcogen-hyperdoped germanium for short-wavelength infrared photodetection
- 2020
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Ingår i: AIP Advances. - : AMER INST PHYSICS. - 2158-3226. ; 10:7
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Tidskriftsartikel (refereegranskat)abstract
- Obtaining short-wavelength-infrared (SWIR; 1.4 mu m-3.0 mu m) room-temperature photodetection in a low-cost, group IV semiconductor is desirable for numerous applications. We demonstrate a non-equilibrium method for hyperdoping germanium with selenium or tellurium for dopant-mediated SWIR photodetection. By ion-implanting Se or Te into Ge wafers and restoring crystallinity with pulsed laser melting induced rapid solidification, we obtain single crystalline materials with peak Se and Te concentrations of 10(20) cm(-3) (10(4) times the solubility limits). These hyperdoped materials exhibit sub-bandgap absorption of light up to wavelengths of at least 3.0 mu m, with their sub-bandgap optical absorption coefficients comparable to those of commercial SWIR photodetection materials. Although previous studies of Ge-based photodetectors have reported a sub-bandgap optoelectronic response only at low temperature, we report room-temperature sub-bandgap SWIR photodetection at wavelengths as long as 3.0 mu m from rudimentary hyperdoped Ge:Se and Ge:Te photodetectors.
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| 9. |
- Gevari, Moein Talebian, et al.
(författare)
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Deagglomeration of nanoparticle clusters in a "cavitation on chip" device
- 2020
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 10:11
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Tidskriftsartikel (refereegranskat)abstract
- Due to the potential of significant energy release in cavitating flows, early cavitation inception and intensification of cavitating flows are of great importance. To use this potential, we investigated the deagglomeration of nanoparticle clusters with the implementation of hydrodynamic cavitation in a microfluidic device. For this purpose, a microfluidic device with a micro-orifice geometry was designed and fabricated using standard microfabrication processes. The system was tested with distilled water in the assembled experimental setup. The flow patterns were characterized using the cavitation number and inlet pressure. Titania nanoparticles were utilized to prepare nanoparticle suspensions. The suspensions were heated to allow agglomeration of nanoparticles. The system was operated with the new working fluid (nanoparticle clusters) at different inlet pressures. After characterizing flow patterns, the flow patterns were compared with those of pure water. The deagglomeration effects of hydrodynamic cavitation on nanoparticle clusters showed the possibility to apply this method for the stabilization of nanoparticles, which paves way to the implementation of nanoparticle suspensions to thermal fluid systems for increased energy efficiency as well as to drug delivery. Our results also indicate that the presence of nanoparticles in the working fluid enhanced cavitation intensity due to the increase in the number of heterogeneous nucleation sites.
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| 10. |
- Giani, L., et al.
(författare)
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Isotope effect on the formation of CN by radiative association reactions
- 2024
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Ingår i: AIP ADVANCES. - 2158-3226. ; 14:3
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Tidskriftsartikel (refereegranskat)abstract
- The formation of CN and its isotopologue (CN)-N-15 through radiative association has been investigated. We considered two processes for the collisions of ground state C(P-3) and N(S-4) atoms (A(2)Pi -> X-2 Sigma(+) and b(4)Pi -> a(4)Sigma(+)), as well as, for the first time, we investigated the radiative association of ground state C(P-3) and excited N(D-2) atoms (B-2 Sigma(+) -> X-2 Sigma(+)). The cross-sections for the three processes have been calculated using semi-classical, quantum mechanical, and Breit-Wigner theories. The rate constants, derived from the combination of semi-classical and Breit-Wigner results, have been fitted to the Kooij formula to be used in astrochemical modeling. The rate constant for the B-2 Sigma(+) -> X-2 Sigma(+) process dominates in the investigated temperature range (10-10 000 K), when its own asymptotic energy is used as a reference level. Moreover, the B-2 Sigma(+) -> X-2 Sigma(+ )process presents the most pronounced isotope effect on the rate constant. We suggest considering these newly investigated radiative association processes for the formation of CN and (CN)-N-15 in the interstellar medium.
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| 11. |
- Gogova, Daniela, et al.
(författare)
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Epitaxial growth of β -Ga 2 O 3 by hot-wall MOCVD
- 2022
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 12:5, s. 055022-055022
-
Tidskriftsartikel (refereegranskat)abstract
- The hot-wall metalorganic chemical vapor deposition (MOCVD) concept, previously shown to enable superior material quality and highperformance devices based on wide bandgap semiconductors, such as Ga(Al)N and SiC, has been applied to the epitaxial growth ofβ-Ga2O3. Epitaxial β-Ga2O3 layers at high growth rates (above 1 μm/h), at low reagent flows, and at reduced growth temperatures(740 ○C) are demonstrated. A high crystalline quality epitaxial material on a c-plane sapphire substrate is attained as corroborated by a combination of x-ray diffraction, high-resolution scanning transmission electron microscopy, and spectroscopic ellipsometry measurements. Thehot-wall MOCVD process is transferred to homoepitaxy, and single-crystalline homoepitaxial β-Ga2O3 layers are demonstrated with a 201 ¯rocking curve width of 118 arc sec, which is comparable to those of the edge-defined film-fed grown (201) ¯ β-Ga2O3 substrates, indicative ofsimilar dislocation densities for epilayers and substrates. Hence, hot-wall MOCVD is proposed as a prospective growth method to be furtherexplored for the fabrication of β-Ga2O3
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| 12. |
- Gogova, Daniela, 1967-, et al.
(författare)
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Epitaxial growth of β-Ga2O3 by hot-wall MOCVD
- 2022
-
Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 12:5
-
Tidskriftsartikel (refereegranskat)abstract
- The hot-wall metalorganic chemical vapor deposition (MOCVD) concept, previously shown to enable superior material quality and high performance devices based on wide bandgap semiconductors, such as Ga(Al)N and SiC, has been applied to the epitaxial growth of beta-Ga2O3. Epitaxial beta-Ga2O3 layers at high growth rates (above 1 mu m/h), at low reagent flows, and at reduced growth temperatures (740 degrees C) are demonstrated. A high crystalline quality epitaxial material on a c-plane sapphire substrate is attained as corroborated by a combination of x-ray diffraction, high-resolution scanning transmission electron microscopy, and spectroscopic ellipsometry measurements. The hot-wall MOCVD process is transferred to homoepitaxy, and single-crystalline homoepitaxial beta-Ga2O3 layers are demonstrated with a 201 rocking curve width of 118 arc sec, which is comparable to those of the edge-defined film-fed grown (201) beta-Ga2O3 substrates, indicative of similar dislocation densities for epilayers and substrates. Hence, hot-wall MOCVD is proposed as a prospective growth method to be further explored for the fabrication of beta-Ga2O3.
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| 13. |
- Indykiewicz, Kornelia, 1986, et al.
(författare)
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Current-induced enhancement of photo-response in graphene THz radiation detectors
- 2022
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226 .- 2158-3226. ; 12:11
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Tidskriftsartikel (refereegranskat)abstract
- Thermoelectric readout in a graphene terahertz (THz) radiation detector requires a p-n junction across the graphene channel. Even without an intentional p-n junction, two latent junctions can exist in the vicinity of the electrodes/antennas through the proximity to the metal. In a symmetrical structure, these junctions are connected back-to-back and therefore counterbalance each other with regard to rectification of the ac signal. Because of the Peltier effect, a small dc current results in additional heating in one and cooling in another p-n junction, thereby breaking the symmetry. The p-n junctions then no longer cancel, resulting in a greatly enhanced rectified signal. This allows simplifying the design and controlling the sensitivity of THz radiation detectors.
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| 14. |
- Kumar, Rohan, et al.
(författare)
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Toward a renewable future: Attaining 100% renewable electricity generation through sustainable transition
- 2024
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Ingår i: AIP Advances. - 2158-3226. ; 14:8
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Tidskriftsartikel (refereegranskat)abstract
- Despite efforts made over the past two decades, Pakistan continues to face electricity crises. The heavy reliance on fossil fuels, which make up 60% of the country’s energy mix, has raised concerns about energy security and environmental degradation due to greenhouse gas (GHG) emissions. Developing effective electricity generation scenarios has been challenging for policymakers and researchers, despite the steady increase in electricity demand. The LEAP software was used in this study to forecast the country’s power demand, and four supply-side scenarios were constructed and examined for the years 2018 through 2040. These scenarios include a baseline scenario, a renewable energy scenario, a more renewable energy scenario, and a near-zero emission scenario, focusing on electricity generation and carbon emissions. The study’s findings, projecting into 2040, indicate that the renewable energy scenarios are environmentally sustainable, with lower GHG emissions compared to the baseline scenario. According to the findings of this study, it is projected that around 615 TWh (terawatt-hours) of renewable energy and nuclear energy will be necessary by the year 2040. The anticipated contributions include 393 TWh from hydroelectric energy, 57 TWh from wind energy, 41 TWh from solar energy, and 62 TWh from other renewable sources. The surge in renewable energy is forecasted to bring near-zero CO2 emissions by 2040, a pivotal step toward a sustainable energy future. A projected energy generation of 615 TWh is expected, which adequately meets the country’s energy demand. Transition to renewable energy is critical for addressing Pakistan’s increasing electricity demands, emphasizing both energy security and environmental sustainability.
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| 15. |
- Kumar, Rohan, et al.
(författare)
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Transforming the transportation sector : Mitigating greenhouse gas emissions through electric vehicles (EVs) and exploring sustainable pathways
- 2024
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Ingår i: AIP Advances. - : American Institute of Physics (AIP). - 2158-3226. ; 14:3
-
Tidskriftsartikel (refereegranskat)abstract
- Transportation-related emissions in Pakistan have been rapidly increasing in recent years. This study aims to determine how important it is to electrify road transportation in Pakistan to reduce greenhouse gas (GHG) emissions from the transportation sector. Motivated by the need to tackle the growing environmental issues related to conventional fuel-powered automobiles, this research explores the application of electrification techniques in the context of Pakistan’s transportation system. During the 2019 fiscal year, the transportation industry in Pakistan consumed 23 × 106 tonnes of energy from the burning of fossil fuels and produced 52.9 × 106 metric tons of CO2, which made up 31% of the country’s total carbon emissions. In this research, different scenarios, such as business as usual, low carbon, strengthen low carbon, and Pakistan National Electric Vehicle Policy 2040, are evaluated for the transportation sector of the country. Using the LEAP model, this study projects the effects of electrification on Pakistan road transportation over 30 years. When estimating how electrification will affect road transportation in Pakistan over the next 30 years, several factors were taken into account, including policy frameworks, changing consumer behavior, technology advancements, and infrastructure improvements. The analysis covered the emission levels, adoption hurdles, and possible advantages of transitioning to electric vehicles (EVs). The outcomes illustrate that adopting EVs can produce substantial drops in fuel consumption and environmental emissions, providing a sustainable solution to mitigate global warming. This work is directly associated with various Sustainable Development Goals, including SDG3 (good health and well-being), SDG7 (affordable and clean energy), and SDG13 (climate action). The results of this study highlight the considerable potential for GHG reduction associated with the widespread adoption of EVs, offering crucial insights to stakeholders and policymakers.
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| 16. |
- Li, Xiaolong, 1991, et al.
(författare)
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Solid solution softening or hardening induced by minor substitutional additions in a Hf 20 Nb 31 Ta 31 Ti 18 refractory high entropy alloy
- 2023
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Ingår i: AIP Advances. - 2158-3226 .- 2158-3226. ; 13:8
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of minor additions of substitutional elements such as Al, Cu, Mn, and Fe on the room-temperature (RT) and elevated-temperature hardness of a single bcc phase Hf20Nb31Ta31Ti18 refractory high entropy alloy is studied here. Interestingly, 2.5 at. % nominal addition of Fe hardened the base Hf20Nb31Ta31Ti18 alloy in the temperature range from RT to 800 °C, while the same nominal content of addition of Al, Cu, and Mn softened the base alloy from RT to 1000 °C. Regardless of solid solution hardening or solid solution softening, the hardness variation with temperature essentially showed the same three-stage pattern for all studied alloys here: a temperature-dependent decrease in hardness below 300 °C/400 °C, followed by a temperature-independent hardness plateau between 300/400 and 800 °C, and finally a temperature-dependent decrease in hardness at temperatures higher than 800 °C. The mechanism for solid solution hardening or softening in bcc-structured refractory high entropy alloys is discussed, together with their temperature dependence.
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| 17. |
- Lin, Chang, et al.
(författare)
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Particle acceleration and pressure gradient in a solitary wave traveling over a horizontal bed
- 2020
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 10:11
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Tidskriftsartikel (refereegranskat)abstract
- This study presents experimental data on the hydrodynamic features of a nonlinear solitary wave of height H-0 = 2.9 cm propagating over a horizontal bed in otherwise still water depth h(0) = 8.0 cm. High-speed particle image velocimetry is used to quantify the local and convective particle accelerations and pressure gradients under the solitary wave. It is found that the magnitudes of the horizontal and vertical particle local accelerations are invariably larger than their convective counterparts, highlighting the important contribution of local acceleration to the pressure gradient in a solitary wave. The dimensionless pressure gradient in the horizontal direction is favorable, zero, and adverse for time before, at, and after the wave crest passes the section of interest. The dimensionless adverse pressure gradient exhibits a maximum for the dimensionless time T[=t(g/h(0))(1/2), where g is the gravitational acceleration and t is the time with respect to the crest passing the section] = 1.39, at which the dimensionless local acceleration has a negative maximum. Subsequently, flow reversal takes place above the bed surface. The relationship is elucidated between flow reversal at the bed surface and the evolution of the adverse pressure gradient in the near-bed zone, where uniform horizontal/free stream velocity exists.
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| 18. |
- Löfgren, Robin, et al.
(författare)
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The diamond NV-center transition energies in the vicinity of an intrinsic stacking fault
- 2022
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Ingår i: AIP Advances. - : American Institute of Physics (AIP). - 2158-3226. ; 12:3
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Tidskriftsartikel (refereegranskat)abstract
- The negatively charged nitrogen vacancy (NV−) center in a diamond is a nanometer-sized defect with very sensitive properties that can be manipulated, for example, for single-molecule photoluminescence and nuclear magnetic resonance sensing, as a single photon source for quantum cryptography and as a qubit in room temperature quantum computing. To have a minimal perturbation of its properties, it is important to isolate the NV-center from other defects. One type of the extended defects that can be common in diamonds is the intrinsic stacking fault (ISF) associated with dislocations. In this work, we use density functional theory simulations to investigate how the distance between the NV− center and an ISF affects its properties, including the transition energies, spin density, and energy eigenvalues in the Kohn–Sham bandgap. We have found that the NV-center properties are only slightly perturbed when placed in the vicinity of an ISF. Even for an interdistance of only 3.8 Å between the NV-center and the ISF, the decrease in its zero phonon line (ZPL) energy is less than 6.8%. To more significantly perturb the ZPL, the NV-center has to be placed inside the stacking fault glide plane (11.3% decrease). The changes in ZPL are in the majority of cases lower than the bulk value, which can be used to guide experimental observations. We find that the NV-center is only weakly interacting with ISFs, which in addition to a small bulk conversion depth of 5 Å to a diamond surface is important for their technological use.
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| 19. |
- Mühlberger, Korbinian, et al.
(författare)
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High-performance arduino-based interferometric quadrature phase-shift detection system with 1 nm resolution
- 2021
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 11:10, s. 105304-
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Tidskriftsartikel (refereegranskat)abstract
- A quadrature phase-shift detection system for interferometry has been conceptualized and evaluated. The main components, a microcontroller and two photodetectors, make a versatile low-cost detection system for displacement measurements or more generally phase-change measurements. The system is capable of sampling at 5 kHz with a spatial resolution of 1 nm.& nbsp;
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| 20. |
- Mörée, Gustav, et al.
(författare)
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Comparison of Poynting's vector and the power flow used in electrical engineering
- 2022
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Ingår i: AIP Advances. - : American Institute of Physics (AIP). - 2158-3226. ; 12:8
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Tidskriftsartikel (refereegranskat)abstract
- This paper will analyze how the energy flux of Poynting's vector is compared to the power flow in electrical engineering, where the power, instead, is defined by voltages and currents. There are alternatives to Poynting's energy flux vector that agree more with circuit theory methods such that the energy flow is in the current conductor and not in the insulation surrounding it. One such basic formulation would only consist of the total current density and the voltage potential, but it would need an alternative theorem for energy transfer. Another formulation proposed by Slepian would instead still agree with Poynting's energy transfer theorem, but it needs to add the power of alternating magnetic vector potential. The alternatives to Poynting's vector may better illustrate the energy flow in electrical engineering, but two things could be considered in their generality. First, since they are expressed by potentials, they are gauge invariant and depend on the definition of the potentials. Second, Poynting's vector is used to formulate the electromagnetic momentum, and any alternative energy flow vectors would not. These two notes are of minor importance in electrical engineering, and the alternatives could be used as good alternatives for describing power flow. The main purpose of this paper is to bridge the differences between the physical theory of energy flux and the methods in electrical power engineering. This could simplify the use of energy flux and Poynting's vector in engineering problems.
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| 21. |
- Mörée, Gustav, et al.
(författare)
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The force density in electrical machines modeled as tension and pressure gradients of magnetic field lines
- 2023
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Ingår i: AIP Advances. - : American Institute of Physics (AIP). - 2158-3226. ; 13:2
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Tidskriftsartikel (refereegranskat)abstract
- This paper shows how to model the force density in electrical machines based on the field lines of the magnetic flux density. The force density is written as two vector components: the magnetic tension force and the magnetic pressure gradient force. This approach has been applied in physics but never to forces in engineering problems. The magnetic tension force acts to straighten bent field lines, based on the curvature of the flux density. The magnetic pressure gradient force acts from regions of high flux density to regions of low flux density. Both force densities are derived from the Lorentz force using the tnb-frame of Frenet–Serret formulas and shown to be equivalent to the divergence of the Maxwell stress tensor. It is shown how the force density could describe the forces in a synchronous machine, including both the angular torque of the load and the radial forces between the rotor and the stator. It could also be linked to the power flow and thereby to the energy flux of Poynting’s vector. The force densities could be used to improve the understanding of the Maxwell stress tensor, since they are easier to illustrate as vectors compared to the matrix form of the Maxwell stress tensor. It also shows the location of the force density, which could improve the use of enclosing volumes when calculating the force based on the divergence theorem with the Maxwell stress tensor.
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| 22. |
- Nam, Youngwoo, 1983, et al.
(författare)
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Graphene thermocouple fabricated on a flexible and transparent substrate
- 2024
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Ingår i: AIP Advances. - 2158-3226 .- 2158-3226. ; 14:6
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the realization of reliable, high-quality, micro-sized graphene-based field-effect devices on a flexible and transparent substrate, ethylene vinyl acetate (EVA)/polyethylene terephthalate (PET), using a convenient hot-press lamination transfer and employing parylene-N as a dielectric material for gating. Using this technique, we fabricate a graphene thermocouple on the EVA/PET substrate. Specifically, the graphene is patterned in a U-shape, and its legs are equipped with two independent top gates. Full control of the carrier density and type by electrostatic gating in the two graphene regions allow the formation of a thermocouple layout, exhibiting an enlarged thermovoltage signal when the two regions are doped with opposite types of carriers and leading to a maximum sensitivity with a thermopower of ∼73 µV/K. This agrees well with the working principle of thermocouple, and it proves the good compatibility and functionality of the graphene thermocouple on the EVA/PET substrate. Our findings suggest possible applications for producing scalable and reliable graphene-based electronic devices on flexible and transparent substrates in a simple way.
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| 23. |
- Nguyen, Thi Quynh Hoa, et al.
(författare)
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Numerical study of a broadband metamaterial absorber using a single split circle ring and lumped resistors for X-band applications
- 2020
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 10:3
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Tidskriftsartikel (refereegranskat)abstract
- We report a numerical study on the design of a broadband metamaterial absorber (MMA) with a single layer of metal-dielectric-metal based on an FR-4 substrate for X-band applications. The MMA structure consists of a periodic array of a split circle ring and lumped resistors coupled within split segments. The MMA structure achieves a broadband absorption response in the frequency range of 7.8-12.6 GHz with an absorptivity of above 90% under normal incidence for all polarization angles. The absorptivity remains above 70% in the frequency range of 6.8-11.8 GHz at wide incident angles from 0 degrees to 30 degrees for both transverse electric and transverse magnetic polarizations. The physical mechanism of the absorber is explained by the electric and the surface current distributions that, in turn, are significantly affected by magnetic resonance.
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| 24. |
- Pei, Y., et al.
(författare)
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A specialized partial discretized optimization algorithm for SLL suppression in FSS design
- 2023
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 13:8
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Tidskriftsartikel (refereegranskat)abstract
- Side Lobe Level (SLL) suppression is a challenging but essential part of frequency selective surface (FSS) structural design. The SLL of the radiation pattern is a key parameter demonstrating the directional anti-interference ability and mainly depends on the geometry of the FSS. However, the correlation between SLL and FSS structural parameters is extremely complicated. A minor FSS structure change may result in a drastic diversion in the sidelobes direction or level, making the SLL the most difficult parameter to optimize. In this paper, an efficient optimization method specifically for SLL suppression is proposed. We discretized the edges of split square ring FSS structures by binary representation and generated new patterns based on the genetic algorithm. Optimization results showed that in the most optimal structure, the SLL was -23.41 dB, exhibiting a 5.17 dB reduction. Meanwhile, the center frequency variation was less than 2%. Moreover, the computation time cost was reduced by over 90% compared with that of the fully discretized pattern optimization method, showing that this novel method was truly effective in getting SLL suppressed FSS structures.
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| 25. |
- Rafei, Mouna, et al.
(författare)
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Study on the electronic and structural properties of oxidized copper films
- 2022
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Ingår i: AIP Advances. - : American Institute of Physics (AIP). - 2158-3226. ; 12:10
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Tidskriftsartikel (refereegranskat)abstract
- A detailed study of the oxidation of Cu substrates was carried out under controlled conditions by regulating the pressure, atmosphere composition, process time, and temperature. By tuning the synthesis conditions, the formation of cuprous oxide (Cu2O) or cupric oxide (CuO) could be preferentially promoted. The oxidation temperature was varied from 400 to 1050 °C, and a gradual oxidation of metallic Cu to Cu2O was achieved at mild oxidation conditions (400-600 °C), while the formation of CuO was only observed at higher temperatures (≥900 °C). The surface morphology was also affected changing from a highly granular texture (400 °C) with grain sizes between 0.59 ± 0.15 μm to smooth large crystallites (≥900 °C) with a size within 2.76 ± 0.97 μm. We also show that by controlling the oxidation temperature (400-1050 °C), it is possible to tune the work function and the ionization potential of the resulting Cu2O/CuO film, properties that are important for various optoelectronic applications.
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