Multiphysics simulation of fluid interface shapes in microfluidic systems driven by electrowetting on dielectrics. - In: Journal of applied physics, ISSN 1089-7550, Bd. 132 (2022), 22, S. 224702-1-224702-17
We present a highly efficient simulation method for the calculation of three-dimensional quasi-static interface shapes under the influence of electric fields. The method is especially useful for the simulation of microfluidic systems driven by electrowetting on dielectrics because it accounts automatically and inherently for the highly non-trivial interface shape in the vicinity of the triple-phase contact. In particular, the voltage independence of the local contact angle predicted based on analytical considerations is correctly reproduced in all our simulations. For the calculation of the shape of the interface, the geometry is triangulated and the mesh nodes are shifted until the system energy becomes minimal. The same mesh is also used to calculate the electric field using the boundary-element method. Therefore, only the surface of the geometry needs to be meshed, and no volume meshes are involved. The method can be used for the simulation of closed systems with a constant volume (e.g., droplet-based microfluidics) while preserving the volume very precisely as well as open systems (e.g., the liquid-air interface within micro-cavities or capillaries). Additional effects, such as the influence of gravitational forces, can easily be taken into account. In contrast to other efficient simulations, such as the volume-of-fluid, level-set, or phase-field methods, ideally, sharp interfaces are obtained. We calculate interface shapes for exemplary systems and compare with analytical as well as experimental results.
https://doi.org/10.1063/5.0110149
On the theory of the spin I = 1/2 double quantum NMR: effects of spins spatial displacements between RF pulses. - In: The journal of chemical physics, ISSN 1089-7690, Bd. 157 (2022), 22, S. 224108-1-224108-7
Spatial displacements of spins between radio frequency pulses in a Double-Quantum (DQ) nuclear magnetic resonance pulse sequence generate additional terms in the effective DQ Hamiltonian. We derive a simple expression that allows the estimation and control of these contributions to the initial rise of the DQ build up function by variation of experimental parameters in systems performing anomalous diffusion. The application of polymers is discussed.
https://doi.org/10.1063/5.0124510
Photonic reservoir computing with non-linear memory cells: interplay between topology, delay and delayed input. - In: Emerging Topics in Artificial Intelligence (ETAI) 2022, (2022), 1220408, S. 1220408-1-1220408-7
Photonic reservoir computing is an emerging topic due to the possibility to realize very fast devices with minimal training effort. We will discuss the reservoir computing performance of memory cells with a focus on the impact of delay lines and the interplay between coupling topology and performance for various benchmark tasks. We will further show that additional delayed input can be beneficial for reservoir computing setups in general, as it provides an easy tuning parameter, which can improve the performance of a reservoir on a range of tasks.
https://doi.org/10.1117/12.2633339
Optimizing the cavity-arm ratio of V-shaped semiconductor disk lasers. - In: Physical review applied, ISSN 2331-7019, Bd. 18 (2022), 6, S. 064070
Passively mode-locked semiconductor disk lasers have received tremendous attention from both science and industry. Their relatively inexpensive production combined with excellent pulse performance and great emission-wavelength flexibility make them suitable laser candidates for applications ranging from frequency-comb tomography to spectroscopy. However, due to the interaction of the active medium dynamics and the device geometry, emission instabilities occur at high pump powers and thereby limit their performance potential. Hence, understanding those instabilities becomes critical for an optimal laser design. Using a delay-differential equation model, we are able to detect, understand, and classify three distinct instabilities that limit the maximum achievable pump power for the fundamental mode-locking state and link them to characteristic positive-net-gain windows. We furthermore derive a simple analytic approximation in order to quantitatively describe the stability boundary. Our results enable us to predict the optimal laser-cavity configuration with respect to positive-net-gain instabilities and therefore may be of great relevance for the future development of passively mode-locking semiconductor disk lasers.
https://doi.org/10.1103/PhysRevApplied.18.064070
Master memory function for delay-based reservoir computers with single-variable dynamics. - In: IEEE transactions on neural networks and learning systems, ISSN 2162-2388, Bd. 0 (2022), 0, S. 1-14
We show that many delay-based reservoir computers considered in the literature can be characterized by a universal master memory function (MMF). Once computed for two independent parameters, this function provides linear memory capacity for any delay-based single-variable reservoir with small inputs. Moreover, we propose an analytical description of the MMF that enables its efficient and fast computation. Our approach can be applied not only to single-variable delay-based reservoirs governed by known dynamical rules, such as the Mackey-Glass or Stuart-Landau-like systems, but also to reservoirs whose dynamical model is not available.
https://doi.org/10.1109/TNNLS.2022.3220532
Activated carbon prepared from waste tire pyrolysis carbon black via CO2/KOH activation used as supercapacitor electrode. - In: Science China, ISSN 1869-1900, Bd. 65 (2022), 10, S. 2337-2347
As the quantity of waste tires increases, more pyrolysis carbon black (CBp), a type of low value-added carbon black, is being produced. However, the application of CBp has been limited. Therefore, it is necessary to identify and expand applications of CBp. This work focuses on the preparation of activated carbon (AC) from CBp using the physicochemical activation of carbon dioxide (CO2) and potassium hydroxide (KOH). Thereafter, AC is applied to the electrode of the electrical double-layer capacitor (EDLC). The AC prepared by CO2/KOH activation exhibited a hierarchical pore structure. The specific surface area increased from 415 to 733 m^2 g^-1, and in combination with low ash content of 1.51%, ensured abundant ion diffusion channels and active sites to store charge. The EDLC comprising the AC (AC-2) electrode prepared by excitation of CO2 (300 sccm) and KOH had a reasonable gravimetric specific capacitance of 192 F g^-1 at 0.5 A g^-1, and exhibited a good rate capability of 73% at 50 A g^-1 in a three-electrode system. Moreover, the EDLC device comprising the AC-2 electrode delivered excellent cycling stability (capacitance retention of 106% after 10000 cycles at 2 A g^-1 in a two-electrode system). Furthermore, a symmetric supercapacitor based on an AC electrode that exhibits a supreme energy density of 4.7 Wh kg^-1 and a maximum power density of 6362.6 W kg^-1 is demonstrated.
https://doi.org/10.1007/s11431-021-2032-3
Structure and origin of antiphase domains and related defects in thin GaP epilayers on As-modified Si(100). - In: Crystal growth & design, ISSN 1528-7505, Bd. 22 (2022), 12, S. 7040-7049
We study the origin and formation of antiphase domains (APDs) and related defects in 7 nm thin, lattice-matched GaP buffer layers deposited by metal-organic chemical vapor deposition (MOCVD) on well-defined, nearly single-domain, double-layer stepped, low-miscut Si(100) substrates obtained by specific treatment with arsenic. Using dark-field imaging modes in low-energy electron microscopy (LEEM), the minority reconstruction domains of Si(100):As and the APDs of the deposited GaP epilayer are identified, quantified, and compared. We show that residual (2x1)-reconstructed terraces of the minority domain on the Si substrate cause the formation of APDs and that the fraction of the minority domain of the substrate (≅0.07) entails a comparable fraction of APDs in thin GaP epilayers. The topographies of APDs are revealed by atomic force microscopy (AFM) and by scanning tunneling microscopy (STM). We observe two very different APD-related defects in the GaP epilayer, both pinned to residual monolayer steps of the substrate. GaP growth on minority domain terraces with widths in the range of 40-100 nm gives rise to APDs of comparable lateral dimensions. Minority domain terraces of the substrate with widths <20 nm cause the formation of 7-20 nm wide trenches in the GaP layer with rampart-like mounds along their rims. Using nanoscale Auger electron spectroscopy (AES), we provide evidence that these trenches extend through the GaP layer down to the exposed, uncovered Si substrate. We conclude that nucleation of GaP on small minority domain terraces is largely inhibited as most Ga and P atoms deposited on these terraces diffuse across the domain boundary and side walls of emerging trenches to adjacent majority domain terraces where they form the observed mounds. Nucleation of GaP does take place on minority domain terraces with widths ≥40 nm and leads to the growth of APDs.
https://doi.org/10.1021/acs.cgd.2c00697
High adsorption graphene oxide prepared by graphite anode from spent lithium-ion batteries for methylene blue removal. - In: Batteries, ISSN 2313-0105, Bd. 8 (2022), 11, 249, S. 1-13
Limited by the service life, a large amount of spent lithium-ion batteries (LIBs) have been produced in recent years. Without proper disposal, spent LIBs can cause environmental pollution and waste of resources. In this paper, we focus on the recycling of the graphite anode (GA) in spent LIBs. GAs from spent LIBs were converted to graphene oxide (GO) through a modified Hummers method. Then the prepared GO was applied to absorb methylene blue in dyeing wastewater under different reaction conditions. The experimental results indicate that GO can quickly and effectively adsorb methylene blue, which also exhibits thermal stability. The maximum adsorption capacity and removal rate are about 833.11 mg/g and 99.95%, respectively. The adsorption kinetics and isotherms were investigated; the adsorption process of GO is more consistent with the pseudo-second-order adsorption kinetic model while the isotherm is close to the Langmuir isotherm. This study is of great significance for the economy and environment. The reaction can turn waste into wealth and is a win-win approach for both spent LIBs recycling and dyeing wastewater cleaning.
https://doi.org/10.3390/batteries8110249
Three mechanisms of room temperature dynamic nuclear polarization occur simultaneously in an ionic liquid. - In: Physical chemistry, chemical physics, ISSN 1463-9084, Bd. 24 (2022), 44, S. 27004-27008
Dynamic nuclear polarization is a versatile approach to increasing the sensitivity of NMR measurements and is achieved by any of four different mechanisms which dominate for either liquids or solids, depending on temperature and radical density. In this work, we unequivocally demonstrate for the first time the coexistence, at a comparable magnitude, of several mechanisms, namely the Overhauser effect, solid effect, and cross-effect/thermal mixing in a viscous ionic liquid at ambient temperatures.
https://doi.org/10.1039/D2CP03437A
Clean and hydrogen-adsorbed AlInP(001) surfaces: structures and electronic properties. - In: Physica status solidi, ISSN 1521-3951, Bd. 259 (2022), 11, 2200308, S. 1-6
Total energy and electronic structure calculations based on density functional theory are performed in order to determine the atomic structure and electronic properties of clean and hydrogen-adsorbed Al0.5In0.5P(001) surfaces. It is found that most of the stable surfaces obey the electron-counting rule and are characterized by surface atom dimerization. The dimer-related surface states are predicted to occur in the vicinity of the bulk band edges. For a very narrow range of preparation conditions, ab initio thermodynamics predicts metal atomic wires formed by surface cations. A surface covered with a monolayer of buckled phosphorus dimers, where half of the phosphorus atoms are hydrogen saturated, is found to be stable for metal-organic vapor-phase epitaxy growth conditions. The occurrence of this structure is confirmed by low-energy electron diffraction and X-ray photoelectron spectroscopy data measured on epitaxially grown Al0.52In0.48P(001) epilayers lattice matched to GaAs.
https://doi.org/10.1002/pssb.202200308