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Artificial neural network-based wall-modeled large-eddy simulations of turbulent channel and separated boundary layer flows
No full textWall-models in a large-eddy simulation (LES) are essential to alleviate the large near-wall resolution requirements for high-Reynolds-number turbulent flow simulations. Among the existing wall-models for a LES, an equilibrium wall-stress model has the highest computational efficiency. Because this model has limitations, such as a lack of non-equilibrium effects and the assumption of a particular law of the wall in the mean velocity, we propose artificial neural network-based wall-stress models (AWMs). The input variables for the AWMs are extracted from the decomposition of the skin-friction coefficient proposed by Fukagata et al. [1], and the AWMs are shown to be able to predict the wall-shear stress in complex flows accurately. The performance of the AWMs is tested for two types of flows, a fully developed turbulent channel flow and a separated turbulent boundary layer flow. A direct comparison of the turbulence statistics with those obtained by previous wall-models (i.e., a log-law-based wall-stress model and a non-equilibrium wall-stress model) shows that better predictions are achieved using the AWMs for both flows, even with untrained Reynolds numbers. When using a coarse grid along the wall-normal direction in wall-modeled LESs (WMLESs) with the AWMs, an upward shift of the mean velocity profile (positive log-layer mismatch, LLM) compared to direct numerical simulation data is found, consistent with previous studies. However, this LLM problem can be overcome by imposing a filtered wall-normal velocity at the wall that is dynamically determined based on the continuity equation and the Taylor series expansion within wall-adjacent cells
Stretchable skin hydration sensor based on hygroscopic and ion conductive polymer composites
No full textTransepidermal water loss (TEWL) is water emission from the skin induced by the diffusion of water molecules. Because TEWL is sensitive to damage on the outermost skin layer, it has been utilized as an indicator of skin barrier function. Here, we demonstrate a stretchable hydration sensor to monitor TEWL based on a porous thermoplastic polyurethane (TPU) film coated with ion conductive polyvinyl alcohol (PVA)/lithium chloride (LiCl) composite layers. The stretchable hydration sensor with the large surface area and the hygroscopic PVA/ LiCl layer coated on the porous structure exhibits a remarkable relative current change (Delta I/I0 (%) similar to 107) under a wide humidity range (10-95 % relative humidity (RH)). Moreover, the highly deformable characteristics of the device up to 50 % strain makes it an appropriate tool for detecting water emission from a curved skin surface. For a proof-of-concept demonstration of monitoring skin barrier function, the hydration sensor can precisely perceive the change in TEWL in response to various external treatments (heat, damage, oil treatment, and applying cosmetics). Finally, the stretchable hydration sensor array enables non-contact finger motion perception through water loss detection, making it suitable for use in touchless human-machine interfaces
Delegation of Information Acquisition, Information Asymmetry, and Outside Option
No full textWe study how a principal with an outside option optimally delegates information acquisition to an agent in a parsimonious environment in which the principal can observe neither the agent's effort nor signal realizations. When the principal chooses an outside option, the true state is not revealed and thus not contractible. We precisely characterize an optimal contract for the principal, illustrating how to construct an optimal contract
Multiferroicity of 2H-BaMnO3 Single Crystal
No full textGeometric ferroelectrics are called as improper ferroelectrics where geometric structural constraints, rather than typical cation-anion pairing, induce proper ferroelectric polarization. Among the geometric structural distortions, trimerization of MnO5 bipyramids is observed in RMnO3 (R = Ho, Er, Yb, Lu, Y), which share same symmetric group with 2H-BaMnO3. And the distortion induces intriguing multiferroicity such as topological vortex-antivortex, angle dependent conducting domain walls, enhanced magnetoelectric coupling at domain walls, etc. In hexagonal RMnO3, it has been unavailable to study thermodynamic behavior of trimerization and polarization because of high ferroelectric transition temperature (1120-1435??C). But, it was reported that polycrystalline 2H-BaMnO3 exhibits antiferromagnetic order at 59 K [1], and ferroelectric transition at 130 K [2]. Here, we present ferroelectric and magnetic properties of single crystalline 2H-BaMnO3.
[1] E. J. Cussen and P. D. Battle, Chem. Mater. 12, 831-838 (2000)
[2] Stanislav Kamba et al, Physical Review B 95, 174103 (2017
Thermal property of Quasi 1D S = 1 chain NiTe2O5
No full textOne-dimensional magnets are very interesting, although it is well-known that there is no long range-order[1]. Because a spin chain, which is defined as a one-dimensional line of spins pointing in particular directions, in one-dimensional magnets has the possibility of complex excitations like spinons which have spin-1/2 in chains with S=1/2. Lately, we have reported a quasi-one-dimensional S=1 chain system NiTe2O5[2]. About the crystallographic structural feature of NiTe2O5, NiO6 octahedra are connected to each other through the edge-sharing and the spin(S=1) of each Ni2+ ion at the center of the octahedra forms a quasi-one-dimensional spin chain. By decreasing temperature, spins of Ni2+ ions are ordered as antiferromagnetic long-range order at 30.5 K. The single crystal neutron diffraction reveals the unconventional critical behavior of the order parameter around the ordering temperature. 125Te nuclear magnetic resonance(NMR) experiments exhibit intriguing persistent spin fluctuation above the ordering temperature[3]. More recently, even magnetoelectric(ME) coupling was reported[4]. Thermal transport has been used to an experimental tool in solid-state physics even when dealing with magnetic systems[5]. Because heat transport via the spin system itself and thermal conductivities are influenced by scattering between phonon and magnetic excitations. By using the thermal transport experiments on NiTe2O5 single crystal, we studied thermodynamic properties associated with these unusual magnetic behaviors in NiTe2O5.
[1] Stephen Blundell, Magnetism in Condensed Matter, Oxford ; New York : Oxford University Press (2001).
[2] Jun Han Lee, Marie Kratochv??lov??, Huibo Cao, Zahra Yamani, JS Kim, Je-Geun Park, GR Stewart, Yoon Seok Oh, Unconventional critical behavior in the quasi-one-dimensional S=1 chain NiTe2O5, Physical Review B 100, 144441 (2019).
[3] Seung-Ho Baek, Jun Han Lee, Yoon Seok Oh, Kwang-Yong Choi, Bernd B??chner, Persistence of Ising-like easy-axis spin correlations in the paramagnetic state of the spin-1 chain compound NiTe2O5, Physical Review B 104, 214431 (2021).
[4] Ajay Tiwari, D. Chandrasekhar Kakarla, G. Macam, C. H. Hsu, F. C. Chuang, H. C. Wu, T. W. Kuo, Arkadeb Pal, H. Chou, D. P. Gulo, H.L. Liu, Y. C. Lai, C. A. Lee, Mitch M. C. Chou, H. D. Yang, Spin-lattice-charge coupling in quasi-one-dimensional spin-chain NiTe2O5, Physical Review Materials 6, 044409 (2022).
[5] A. V. Sologubenko, T. Lorenz, H. R. Ott, A. Freimuth, Thermal conductivity via magnetic excitations in spin-chain materials, J. Low Temp. Phys. 147, 387-403 (2007)
Model-driven experimental design workflow expands understanding of regulatory role of Nac in Escherichia coli
No full textThe establishment of experimental conditions for transcriptional regulator network (TRN) reconstruction in bacteria continues to be impeded by the limited knowledge of activating conditions for transcription factors (TFs). Here, we present a novel genome-scale model-driven workflow for designing experimental conditions, which optimally activate specific TFs. Our model-driven workflow was applied to elucidate transcriptional regulation under nitrogen limitation by Nac and NtrC, in Escherichia coli. We comprehensively predict alternative nitrogen sources, including cytosine and cytidine, which trigger differential activation of Nac using a model-driven workflow. In accordance with the prediction, genome-wide measurements with ChIP-exo and RNA-seq were performed. Integrative data analysis reveals that the Nac and NtrC regulons consist of 97 and 43 genes under alternative nitrogen conditions, respectively. Functional analysis of Nac at the transcriptional level showed that Nac directly down-regulates amino acid biosynthesis and restores expression of tricarboxylic acid (TCA) cycle genes to alleviate nitrogen-limiting stress. We also demonstrate that both TFs coherently modulate ??-ketoglutarate accumulation stress due to nitrogen limitation by co-activating amino acid and diamine degradation pathways. A systems-biology approach provided a detailed and quantitative understanding of both TF???s roles and how nitrogen and carbon metabolic networks respond complementarily to nitrogen-limiting stress
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No full textBaTiO3 ????????? ??? Dy ?????? ???????????? ?????? ?????? ??? ????????? ?????? ??????
No full textDepartment of Materials Science and EngineeringMulti-layered ceramic capacitors (MLCCs) which are composed of dielectric materials are used in electronic devices and electric automobiles and have a role of stably supplying voltage required for semiconductor devices and circuits. Specially nowadays, with an automotive electrification, the demand of MLCC also increases. Therefore, it is essential to ensure high reliability for dielectrics to operate stably at wide working temperature for safety. In response to this need, dielectrics capacitors based on BaTiO3(BT) composition are actively being studied. The BaTiO3 composition shows high permittivity(????????) around 2000 at room temperature, but the low curie temperature around 120oC limits the application on capacitor leading to low reliability. So many researchers are trying to improve this disadvantage by synthesizing BT system doped with Dysprosium(Dy) which has amphoteric behavior. However, the researches about the analysis of properties according to the role of Dy are lack. Here, by introducing 2-step calcination, we doped Dy3+ ion on each site of BT (A-site, B-site, and A&B site) and systematically compared the properties according to the Dy-doped site. As a result, Dy-doped on B site in BT system showed leaky properties, leading to worse reliability and Dy-doped on A&B site exhibited improved dielectric properties and reliability. In addition, in order to confirm that Dy was well doped at the target site through 2-step calcination, dielectric and electrical properties were compared with the conventional solid solution method that was used in previous research. To conclude, there are some differences between them, meaning that it is hard to control doping site with conventional solid solution method and 2-step calcination should be introduced when the dopants has amphoteric behavior.ope
Biomechanical and Neuromuscular Investigation on the Mechanism of Neck Pain During Smartphone Use
No full textDepartment of Biomedical Engineering (Human Factors Engineering)As screen time and dependence on the smartphone have increased, the prevalence of neck discomfort and pain has also increased. Since many people adopt a smartphone posture, concerns about neck pain or injury risks related to excessive smartphone use have been increasing. Prolonged and excessive exposure to smartphone use posture can affect the active and passive tissues of the neck, and the changes in neck tissues can be connected to the development of neck pain.
The biomechanical and neuromuscular response changes in active and passive tissues were observed in extreme cases, such as exposure to the maximum flexion of the spine, and fatiguing protocols with high muscle contractions. Therefore, the relationship between exposure to that extreme posture and its effect on the changes in tissues is well established. However, there is a lack of biomechanical and neuromuscular investigation related to the smartphone use posture that requires sub-maximal flexion and low-level muscle contraction. It was unclear whether the passive tissues were deformed, or whether muscle fatigue developed during prolonged smartphone use. Objectively evaluating the effect of smartphone use on the active and passive tissues of the neck and understanding their relationship with pain development is essential to understand musculoskeletal pain related to smartphone use, and to prevent related neck injuries.
With the aim of concluding which tissues would be changed by prolonged smartphone use and related neck pain, three experiments were conducted in Study 1. The first experiment investigated the viscoelastic changes in passive tissues, but passive tissue laxity was not observed. The second experiment was conducted to investigate the occurrence of neck muscle fatigue. However, it also failed to observe local muscle fatigue. The third experiment aimed to explore the changes in passive tissues by evaluating head stability, but it also did not observe any changes in head stability. In the three experiments, neck pain developed during smartphone use. It implies that prolonged smartphone use might affect the active and passive tissues in the pain development pathway, but no objective evidence about changed tissue properties was found. It is determined that the effect of prolonged smartphone posture on the active and passive tissues should be investigated independently and sensitively with various measurements.
Three independent smartphone-use conditions that depart from each tissue's effects were newly designed to investigate the effect of each tissue on subjective pain development, excluding the other tissues' effects in Study 2. The "normal" condition was the common smartphone-use posture of flexing the head approximately 40 ??. The "posture-only" condition induced only flexed posture without muscle activation. Finally, the "muscle-only" condition activated muscles similar to the "normal" condition, without flexed posture. The biomechanical and neuromuscular changes in each tissue were also investigated in the controlled and independent conditions during 60 minutes of exposure. Pain levels, head kinematics, and electromyography (EMG) were collected over time during smartphone use. In the flexion relaxation phenomenon (FRP), tissue laxity and load-sharing timing were observed. The reflexive responses of muscles and passive tissues were evaluated in the presence of unexpected head perturbations. The local muscle fatigue was confirmed through EMG responses in isometric contraction. The seven responses were investigated three times intermittently: pre-, mid-, and post-exposure.
The results of Study 2 revealed that increasing musculoskeletal symptoms with smartphones were highly related to sustained muscle activation, but local muscle fatigue was not related to pain development. The possible mechanisms between sustained muscle activation and pain development are capillary compression and reduced oxygenation, spine joint compression, and irritating byproducts. In addition, passively stretched passive tissue was not significantly related to pain, but its micro-damage was confirmed through biomechanical and neuromuscular investigation. Repetitive micro-damage to passive tissues without full recovery could lead to chronic neck pain or future injuries, so it should be carefully considered. These newly designed experimental conditions allowed for observing changes in each tissue that were not revealed in previous studies. The findings of this study may help understand the mechanism of neck pain resulting from prolonged smartphone use and its effect on each tissue.clos
Co-application of Colicins with Bdellovibrio bacteriovorus HD100 to Eradicate Multi-drug Resistant Escherichia coli
No full textDepartment of Biological Sciencesclos