bluuebunny/crossref_metadata_2025 huggingface dataset:
Microengineering of Collagen Hydrogels Integrated into Microfluidic Devices for Perfusion Culture of Mammalian Cells
Authors: Kato Misaki , Fukushi Mayu , Yamada Masumi , Utoh Rie , Seki Minoru
Published: January 2021

Collagen-based hydrogels are widely used for three-dimensional (3D) culture of mammalian cells because of their high cell-activating characteristis. However, techniques for preparing of cell-embedding collagen hydrogels with micrometer-size precision in perfusable, microfluidic devices have not been fully developed. In this study, we propose a facile strategy enabling microfabrication of collagen hydrogels in microfluidic devices. We used phosphate particle-embedding polydimethylsiloxane (PP-PDMS) as a gelation agent, which neutralizes the acidic collagen soltuion. The collagen solution near the surface of the PP-PDMS is selectively gelled. We fabricated micropatterns and tubular structures made of collagen hydrogel, both of which were used for perfusion culture of mammalian cells encapsulated in the hydrogel matrix. The presented approach would be applicable to various types of cell culture experiments.
Generation of Gene-Engineered Human Hepatoma Cells with Heat-Inducible Liver Functions
Authors: Kitano Hiroyuki , Soto Manuel Souvervielle , Sonoda Yuto , Kawabe Yoshinori , Ito Akira , Kamihira Masamichi
Published: January 2021

Hepatoma cells derived from liver carcinoma are a candidate cell source for bioartificial liver (BAL) systems due to their high proliferative capacity, although liver function of hepatoma cells is considerably low compared with primary hepatocytes. In our previous study, genetically engineered mouse hepatoma cells with inducible high liver function were established by transducing liver-enriched transcription factor (LETF) genes. In this study, we aimed to develop new gene-engineered human hepatoma cells, in which high liver functions are inducible by heat treatment. For this purpose, we constructed a gene expression system for eight LETF genes under control of tetracycline-dependent transactivator (tTA), and the system was introduced into the genome of HepG2-HSP cells, in which a tTA expression system induced by a heat-shock protein promoter with transcriptional amplification was introduced into HepG2 cells. Thus, the heat-inducible tTA promotes LETF genes to induce liver function. Upon the heat treatment of the cells (HepG2-HSP/8F) at 43°C for 30 min, liver functions such as albumin secretion and cytochrome P450 were significantly enhanced. The cells with heat-inducible liver function can be used as a new cell source for various hepatic studies including construction of BAL systems.
Practical Reuse of Activated Carbon in the Exhaust Facility of Semiconductor Production Factory with Supercritical Carbon Dioxide Regeneration
Authors: Ito Yasuyuki , Ushiki Ikuo , Sato Yoshiyuki , Inomata Hiroshi
Published: January 2021

An possible reason why the activated carbon used in the exhaust facility of real semiconductor production factory could not be regenerated by scCO2 regeneration was estimated to be attributable to its high boiling point adsorbates which showed a peak in TGA (Thermogravimetric analysis) curve at 400-900°C. This study was conducted to experimentally verify the above insight by using TGA analysis and scCO2 regeneration for the real samples with different loads from the factory. The experimental results showed that high boiling point ratio defined by TGA analysis was less than 4.0% in case of the heating treatment temperature of 200 °C in the exhasut facility of real semiconductor production factory. This result suggested regeneration rate of the activated carbon was higher than 80%. Our scCO2 regeneration process can achieve high efficiency as a practical application.
Evaluation of Sealing Properties to LED Light Emitting Substrate of Organic-inorganic Hybrid Materials Composed of Polysilsesquioxane with Thiol Group
Authors: Hamasuna Akito , Takao Yoshinari , Ota Akihiro , Ohzuno Yoshihiro , Takei Takayuki , Yoshida Masahiro
Published: January 2021

Novel organic-inorganic hybrid materials were developed as LED sealants. Polysilsesquioxane with an -SH group (PSQ-SH) and acrylic monomer were selected as the inorganic and organic components, respectively. Trimethylolpropane trimethacrylate (TRIM), which is a trifunctional monomer, was selected as an acrylic monomer, and curing of the material was performed by the thiol-ene reaction. The LED was sealed using the prepared PSQ-SH/TRIM hybrid material (PTH), and a light emission test was performed. However, cracks occurred in the hybrid material during lighting. Therefore, ditrimethylol propane tetraacrylate (DTMPTA), which is a tetrafunctional monomer, was selected for the first time to prepare a PSQ-SH/DTMPA hybrid material (PDH) in order to enhance the strength and heat resistance of the material. The characteristics of the novel PDH were evaluated and compared with those of PTH. Specifically, the heat resistance was evaluated by confirming the onset temperature of weight reduction using thermogravimetry-differential thermal analyzer (TG-DTA) analysis, and the mechanical strength was also evaluated by bonding the glass substrates with a hybrid material and measuring the sealing strength. In conclusion, it was possible to suppress crack generation during lighting by using PDH instead of PTH in the light emission test.
Analysis of Fiber Drawing in Wet Spinning for Surface Roughness
Authors: Fukui Yuta , Teramua Tatsuya , Yoshimi Tomoyuki
Published: January 2021

The drawing process behavior was investigated with focus on fiber stretching speed (spinning acceleration) to improve luster quality of fibers. Wet spinning method has a limitation of low luster at high spinning speed. It was determined that (1) luster quality could be evaluated by arithmetic average (RΔa) of fibers, which indicated the roughness, and (2) the roughness of the fiber was related to the spinning acceleration through the analysis of RΔa. Spinning acceleration was measured by chasing markers that were used to tie fibers. Regardless of the length of spinning bath, fibers were mainly stretched during the first stretching stage. Therefore, a multistep drawing method was used. In the case where the drawing ratio was 220% by one-step, RΔa was 10.1°; however by multi-step drawing (1st and 2nd drawing ratios were 148.3%), RΔa decreased to 8.3°. The multi-step drawing method enabled the reduction in fiber roughness by preventing a sudden change in fiber stress. In addition, high temperatures improved the fiber roughness. At high temperatures, roughness decreased despite the high acceleration because the fiber was easier to stretch than at low temperatures.
Effect of Alkyl Chain Length on Adsorption and Release of Hydrophobic Drug to/from Hydrophobically-modified Gelatin Hydrogel
Authors: Fukuhara Yoshiki , Ohzuno Yshihiro , Takei Takayuki , Yoshida Masahiro
Published: January 2021

Hydrogels have become popular as drug carriers. Controlled release of the drugs from hydrogels can reduce dosage, inducing prevention of side effects. However, the hydrophilicity of hydrogels interferes with controlled release of hydrophobic drugs such as anticancer agents or antibiotics. In this study, we developed hydrophobically-modified gelatin (HMG) hydrogel, which was cross-linked only by hydrophobic interaction. HMG does not require toxic chemical cross-linkers to form hydrogel. In addition, the HMG hydrogel has hydrophobic chambers in its structure which hydrophobic drugs can adsorb to and desorb from. In order to control the amount of hydrophobic drugs adsorbed into the hydrogel, hydrophobic alkyl chains with different lengths (C4-C12) were incorporated into gelatin molecules. Uranine was used as a model for hydrophobic drugs. The adsorption test exhibited that the amount of uranine adsorbed in HMG hydrogels could be controlled by varying hydrophobic alkyl chain length and that the drug could be released in a controlled manner. These results show that HMG hydrogels are promising carriers of hydrophobic drugs.
Preliminary Investigation of an Installed Pilot-Scale Biological Nutrient Removal Technology (BNRT) for Sewage Treatment
Authors: Damalerio Regina , Orbecido Aileen , Promentilla Michael Angelo , Eusebio Ramon Christian , Patacsil Liza , Beltran Arnel
Published: January 2021

Water utilities, commercial and industrial establishments are required to upgrade or install new treatment systems to comply with the revised effluent standards issued by the Department of Environment and Natural Resources – Environment Management Bureau (DENR – EMB) which now includes removal and monitoring of nutrients (nitrogen and phosphorus components). One solution is to utilize a biological nutrient removal technology (BNRT) system capable of removing nutrients from sewage. The on-going study aims to investigate the performance of the pilot-scale system in the removal of nutrients from sewage. The designed pilot-scale anaerobic-anoxic-oxic (A2O) process with a total hydraulic retention time of 8.37 hrs. was operated in an existing sewage treatment plant (STP). System modification was adapted to ensure continuous operation. Dissolved oxygen (DO) and temperature of each compartment were evaluated after 45 days of system modification. The DO of the anaerobic and oxic compartment remained within the required range, while the internal recycling flowrate and/or aeration must be adjusted to achieve a DO concentration of 0.20 – 0.50 mg/L in the anoxic compartment. The research is financially supported by the Philippine Council for Industry, Energy and Emerging Technology Research and Development of the Department of Science and Technology (PCIEERD Project No. 04176).
Microfabrication of Anode Functional Layer in SOFC by 3D Printer
Authors: Takahashi Kazuya , Fujita Hiroaki , Ishikawa Yuya , Nakagaki Takao
Published: January 2021

This work aims to increase the interface between anode and electrolyte in solid oxide fuel cells by controlling the 3D microstructure with a commercial ink-jet 3D printer. Anode and electrolyte inks suitable for use in a 3D printer were prepared by altering the viscosity and the droplet size. A porous anode structure that ensures a flow path for gases was achieved by addition of acrylic particles into the anode ink. A dense electrolyte structure that prevents leakage was created. The anode and electrolyte layers were produced as long, flat strips which were aligned in parallel to form sheets; these sheets were stacked orthogonally to complete the 3D microstructure called the ‘anode functional layer’. The anode functional layer was roughly 100 micrometers on a side with a thickness of 4 micrometers. The anode functional layer was inserted between the anode and electrolyte. The assembled solid oxide fuel cell showed high performance when tested at 600 °C with dry methane as the fuel source.
A review on differential scanning calorimetry as a tool for thermal assessment of nanostructured coatings
Authors: Slobozeanu Anca Elena , Bejan Simona Elena , Tudor Ioan Albert , Mocioiu Ana-Maria , Motoc Adrian Mihail , Romero-Sanchez Maria Dolores , Botan Mihai , Catalin Cristea George , Madalina Cursaru Laura , Piticescu Radu Robert , Predescu Cristian
Published: January 2021

Nanostructured coatings and films play an important role in modern surface engineering due to their ability to improve and optimize materials behavior under different external constraints such as high/low temperatures, stress/strain, corrosive/oxidizing atmosphere, electromagnetic fields/fluxes etc., used practically in all industrial fields. Surface modification may be done using any type of materials: polymers, metals, ceramics, composites or hybrids on any type of substrate by different physical, chemical or combined technologies. Thermal characterization methods are one of the most accessible tools to study, model and predict the process parameters required to preserve the nanostructures during thermal treatment of different coatings, develop novel multi-material coating systems, study the complex correlations between material properties vs. synthesis and processing parameters in real environments. Differential Scanning Calorimetry (DSC) is often used as a standard method to put in evidence different thermal events such as phase transitions, decomposition, oxidation/reduction, nucleation and growth at the substrate/coating interfaces or in coating materials. The present paper aims to review some examples on how DSC may be used to assess the thermal behavior of coatings using standardization tools and developing novel application fields.
A cellular automaton model for a pedestrian flow problem
Authors: Felcman Jiří , Kubera Petr
Published: January 2021

The evacuation phenomena in the two dimensional pedestrian flow model are simulated. The intended direction of the escape of pedestrians in panic situations is governed by the Eikonal equation of the pedestrian flow model. A new two-dimensional Cellular Automaton (CA) model is proposed for the simulation of the pedestrian flow. The solution of the Eikonal equation is used to define the probability matrix whose elements express the probability of a pedestrian moving in finite set of directions. The novelty of this paper lies in the construction of the density dependent probability matrix. The relevant evacuation scenarios are numerically solved. Predictions of the evacuation behavior of pedestrians, for various room geometries with multiple exits, are demonstrated. The mathematical model is numerically justified by comparison of CA approach with the Finite Volume Method for the space discretization and Discontinuous Galerkin Method for the implicit time discretization of pedestrian flow model.
The chemical composition of oyster nut (Telfairia pedata) seeds and oil
Authors: Bondioli Paolo , Folegatti Liliana , Morini Gabriella
Published: January 2021

In this paper, the chemical composition of Telfairia pedata seeds and oil is discussed. This crop belongs to the family of Cucurbitaceae. Unroasted seeds and oil obtained from roasted seeds were collected during a study trip in Tanzania. Oil from unroasted seeds was extracted in the lab using hexane. The seeds contain approximately 60 (% m/m) of oil and 30 (% m/m) of protein, being the remaining amount represented by crude fiber, carbohydrates and mineral constituents. The protein fraction contains glutamic acid, arginine, aspartic acid and leucine as the most representative amino acids. The fatty acid composition is a common one, being palmitic, linoleic, stearic and oleic acids, the most important fatty acids detected. No difference was found in fatty acid composition between oils extracted from roasted and unroasted seeds. On the contrary, the oil obtained from roasted seeds shows a higher concentration in sterols and tocopherols while the distribution between the different constituents remains the same.
Comparison of clinical outcomes with and without volar lunate facet fragments in dorsal displaced distal radius fractures
Authors: Obata Hiroyuki , Naito Kiyohito , Sugiyama Yoichi , Nagura Nana , Goto Kenji , Kaneko Ayaka , Kawakita So , Kaneko Kazuo
Published: January 2021

Introduction: Although many clinical studies about distal radius fracture (DRF) accompanied by volar lunate facet fragments (VLFF) have recently been reported, none focus on the direction of displacement of distal fragments. Many previous cases with difficulty in treating DRF with VLFF were volar-displaced fractures. Thus, the postoperative risk for re-displacement is different between volar- and dorsal-displaced fractures with VLFF. The aim of this study is to compare the outcome of dorsal-displaced fractures treated using proximal volar locking plates (PVLP) between those with VLFF and those without, in order to reconsider the indications of distal volar locking plates (DVLP) and investigate the possibility of treating dorsal-displaced DRF with VLFF using PVLP.Methods: The subjects were 122 patients with dorsal-displaced DRFs treated using PVLP (42 males and 80 females, mean age: 59.2 years old). The patients were divided into 13 patients with VLFF group and 109 patients without VLFF group, and the clinical outcomes at 12 months after surgery were compared.Results: No significant difference was noted on any evaluation between the groups. In addition, no postoperative re-displacement of VLFF was observed and bone union was confirmed. Furthermore, no osteoarthritic change was noted in all patients.Conclusions: We confirmed that surgical treatment for dorsal-displaced DRF using PVLP is possible even in cases of DRF with VLFF. In addition, DVLP is an implant with a high complication risk; therefore, it may be necessary to reconsider the use of DVLP for dorsal-displaced DRF with VLFF treatable by PVLP.
The Interplanetary and Magnetospheric causes of Geomagnetically Induced Currents (GICs) > 10 A in the Mäntsälä Finland Pipeline: 1999 through 2019
Authors: Tsurutani Bruce T. , Hajra Rajkumar
Published: January 2021

The interplanetary and magnetospheric phenomena time-coincident with intense geomagnetically induced current (GIC) > 10 A and > 30 A events during 21 years (1999 through 2019) at the Mäntsälä, Finland (57.9° magnetic latitude) gas pipeline have been studied. Although forward shocks and substorms are predominant causes of intense GICs, some newly discovered geoeffective interplanetary features are: solar wind plasma parcel (PP) impingements, possible interplanetary magnetic field (IMF) northward (Bn) and southward (Bs) turnings, and reverse shocks. The PPs are possibly the loop and filament portions of coronal mass ejections (CMEs).

From a study of > 30 A GIC events, it is found that supersubstorm (SSS: SML < −2500 nT) and intense substorm (−2500 nT < SML  < −2000 nT) auroral electrojet intensifications are the most frequent (76%) cause of all of these GIC events. These events occur most often (76%) in superstorm (SYM-H ≤ −250 nT) main phases, but they can occur in other storm phases and lesser intensity storms as well. After substorms, PPs were the most frequent causes of Mäntsälä GIC > 30 A events. Forward shocks were the third most frequent cause of the > 30 A events. Shock-related GICs were observed to occur at all local times.

The two “Halloween” superstorms of 29–30 and 30–31 October 2003 produced by far the greatest number of GICs in the interval of study (9 > 30 A GICs and 168 > 10 A GICs). In the first Halloween superstorm, a shock-triggered SSS (SML < −3548 nT) caused 33, 57, 51 and 52 A GICs. The 57 A GIC was the most intense event of the superstorm and of this study. It is possible that this SSS is a new form of substorm. Equally intense magnetic storms were also studied but their related GICs were far less numerous and less intense.
Multinational energy utilities in the energy transition: A configurational study of the drivers of FDI in renewables
Authors: Patala Samuli , Juntunen Jouni K. , Lundan Sarianna , Ritvala Tiina
Published: January 2021

The global energy system has a long way to go to meet international climate goals, and significant investment in renewable energy is required to accelerate the energy transition (IRENA, 2016, 2019). We examine how firm- and country-specific conditions in the electric utility sector impact foreign direct investment (FDI) in renewables. Using a unique dataset of 289 greenfield investments by 17 multinational energy utilities, we employ a fuzzy set qualitative comparative analysis (fsQCA) that yields five causal configurations leading to FDI in renewables and four configurations leading to investment in non-renewables. Our results indicate that private MNEs are at the forefront of investment in renewables, and while state-owned MNEs (SOMNEs) do invest in them, they tend to follow strategies that are less risky compared to private MNEs and more responsive to host-country incentives. Our analysis suggests that for private MNEs, international experience is strongly associated with investment in renewables, while for SOMNEs it is associated with investment in non-renewables. Further, we also identify instances where MNEs contribute simultaneously to a ‘race to the top’ and a ‘race to the bottom’ by investing in both renewables and non-renewables in different markets, thereby reducing the pace of the energy transition.
Efficient photovoltaics-integrated hydrogen fuel cell-based hybrid system: Energy management and optimal configuration
Authors: Mubaarak Saif , Zhang Delong , Wang Longze , Mohan Menghwar , Kumar Panjwani Manoj , Li Cai , Zhang Yan , Li Meicheng
Published: January 2021

Due to their intermittent nature, the use of renewable energy sources has faced the challenges of power insecurity and low efficiency. Recently, fuel cells (FCs) have become a potential choice for backup-power generation in remote microgrids due to their reduced maintenance needs and long lifecycle. However, the efficiency of hydrogen FCs as backup power needs to be improved. The efficiency is related to system sizing and operational techniques. Thus, this paper proposes an efficient energy management strategy and optimal configuration models based on a hybrid system including photovoltaics (PVs) and hydrogen FCs to achieve a high operational efficiency and optimize the system configuration. The system model is built, and an energy management strategy is proposed first. This strategy determines when the PV and FC supply power to a load under various conditions. Proper sizing of the sub-components in the PV/FC hybrid system also plays an essential role in ensuring continuous power flow. To ensure power quality, the hybrid system configuration is estimated using a systematic method without affecting the power quality to minimize residual power losses. In addition, various essential simulations are performed to verify the proposed model. The results indicate that the total efficiency of the system can reach 47.9%.
Quantitative study of nanofabricated surfaces could help limit food-borne virus spread
Authors: Johnson-Groh Mara
Published: January 2021

How viruses stick to nanofabricated surfaces can allow researchers to optimize materials to repel those viruses.
Discrete self-adjointness and quantum dynamics. Travel times
Authors: Martínez-Pérez Armando , Torres-Vega Gabino
Published: January 2021

We use a discrete derivative to introduce a time operator for non-relativistic quantum systems with point spectrum. The symmetry requirement on the time operator leads to well-defined time values related to the dynamics of discrete quantum systems. As an illustration, we find travel times between hits with the walls for the quantum particle in a box model. These times suggest a classical analog of time eigenstates. We also briefly consider the Woods–Saxon potential and propose classical analogs for it.
Chaos in the peroxidase–oxidase oscillator
Authors: Olsen Lars F. , Lunding Anita
Published: January 2021

The peroxidase–oxidase (PO) reaction involves the oxidation of reduced nicotinamide adenine dinucleotide by molecular oxygen. When both reactants are supplied continuously to a reaction mixture containing the enzyme and a phenolic compound, the reaction will exhibit oscillatory behavior. In fact, the reaction exhibits a zoo of dynamical behaviors ranging from simple periodic oscillations to period-doubled and mixed mode oscillations to quasiperiodicity and chaos. The routes to chaos involve period-doubling, period-adding, and torus bifurcations. The dynamic behaviors in the experimental system can be simulated by detailed semiquantitative models. Previous models of the reaction have omitted the phenolic compound from the reaction scheme. In the current paper, we present new experimental results with the oscillating PO reaction that add to our understanding of its rich dynamics, and we describe a new variant of a previous model, which includes the chemistry of the phenol in the reaction mechanism. This new model can simulate most of the experimental behaviors of the experimental system including the new observations presented here. For example, the model reproduces the two main routes to chaos observed in experiments: (i) a period-doubling scenario, which takes place at low pH, and a period-adding scenario involving mixed mode oscillations (MMOs), which occurs at high pH. Our simulations suggest alternative explanations for the pH-sensitivity of the dynamics. We show that the MMO domains are separated by narrow parameter regions of chaotic behavior or quasiperiodicity. These regions start as tongues of secondary quasiperiodicity and develop into strange attractors through torus breakdown.
Brain rhythm bursts are enhanced by multiplicative noise
Authors: Powanwe Arthur S. , Longtin André
Published: January 2021

Many healthy and pathological brain rhythms, including beta and gamma rhythms and essential tremor, are suspected to be induced by noise. This yields randomly occurring, brief epochs of higher amplitude oscillatory activity known as “bursts,” the statistics of which are important for proper neural function. Here, we consider a more realistic model with both multiplicative and additive noise instead of only additive noise, to understand how state-dependent fluctuations further affect rhythm induction. For illustrative purposes, we calibrate the model at the lower end of the beta band that relates to movement; parameter tuning can extend the relevance of our analysis to the higher frequency gamma band or to lower frequency essential tremors. A stochastic Wilson–Cowan model for reciprocally as well as self-coupled excitatory (E) and inhibitory (I) populations is analyzed in the parameter regime where the noise-free dynamics spiral in to a fixed point. Noisy oscillations known as quasi-cycles are then generated by stochastic synaptic inputs. The corresponding dynamics of E and I local field potentials can be studied using linear stochastic differential equations subject to both additive and multiplicative noises. As the prevalence of bursts is proportional to the slow envelope of the E and I firing activities, we perform an envelope-phase decomposition using the stochastic averaging method. The resulting envelope dynamics are uni-directionally coupled to the phase dynamics as in the case of additive noise alone but both dynamics involve new noise-dependent terms. We derive the stationary probability and compute power spectral densities of envelope fluctuations. We find that multiplicative noise can enhance network synchronization by reducing the magnitude of the negative real part of the complex conjugate eigenvalues. Higher noise can lead to a “virtual limit cycle,” where the deterministically stable eigenvalues around the fixed point acquire a positive real part, making the system act more like a noisy limit cycle rather than a quasi-cycle. Multiplicative noise can thus exacerbate synchronization and possibly contribute to the onset of symptoms in certain motor diseases.
Spatial-frequency encoded imaging of multangular and multispectral images
Authors: Cai Weiwei , Wang Xiaolei , Yu Tao
Published: January 2021

Modern imaging techniques increasingly require signals to be collected from multiple viewpoints and spectral bands to realize multi-dimensional and multi-species detections. For this purpose, multiple cameras are commonly required. Each camera collects signals from one viewpoint or one spectral band, resulting in a considerable experimental cost. Based on frequency modulation, this work proposes an encoded-imaging technique that can record multangular and multispectral images in one acquisition. The signals recorded from different viewpoints and spectral bands are superimposed in the spatial domain, while being separate in the frequency domain. This allows us to extract individual images based on their respective frequency components. In this work, a proof-of-concept experiment was conducted. The high correlation coefficient between the superimposition of the extracted images and a normal superimposed image demonstrates the effectiveness of this technique. In addition, an improved mathematical formulation was proposed to describe the higher spatial-frequency components, which were considered merely to be residual lines in previous studies. The proposed encoded-imaging technique may have potential for multangular and multispectral imaging, which is especially useful for tomographic reconstructions.
Tribological properties of the QAL9-4 and 17-4PH textured friction pair with water lubrication
Authors: He Tao , Li Jinmiao , Deng Haishun , Wang Chuanli , Shi Rui , Chen Guoyu , Li Zhipeng
Published: January 2021

To study the lubrication and wear reduction characteristics of the QAL9-4 and 17-4pH textured friction pair during water lubrication, the dynamic pressure bearing and cavitation characteristics were analyzed using a computational fluid dynamics method. Then, based on 13 groups of samples with different depths, diameters, and area ratios, relevant frictional and wear tests were carried out. The results showed that the texture affected the pressure distribution in the textured region and improved the liquid film bearing capacity, which increased gradually as the equivalent Reynolds number increased. Under test conditions, the texture parameters had a significant influence on lubrication and wear reduction performance. The optimum texture diameter, the depth, and the area ratio were 300 µm, 40 µm, and 10%, respectively. The wear tracks on the textured specimens were small in size and shallow in depth compared to those on the non-textured specimens. The wear tracks on the textured specimens were regional, and there were more wear tracks in the area without micro-dimples. In summary, it was feasible to apply surface texture to the QAL9-4 and 17-4PH friction pair to improve the lubrication and wear reduction characteristics with water lubrication.
Multiphase phase-field approach for solid–solid phase transformations via propagating interfacial phase in HMX
Authors: Roy Arunabha M.
Published: January 2021

In this study, a thermodynamically consistent multiphase phase-field theory has been formulated to describe temperature-induced solid–solid phase transformations via an interfacial phase. This theory satisfies all thermodynamic equilibrium and stability conditions. It allows us to formulate the analytical solutions of the interface profile, energy, width, and velocity for each of the propagating solid–melt and solid–solid interfaces. The formation of the intermediate melt during solid–solid phase transformation has been studied hundreds of degrees below melting temperature in the HMX energetic crystal. The effect of the penalizing term in the phase-field model and two nanoscale material parameters on the appearance and degree of disordering of intermediate melt has been analyzed for the non-equilibrium interface. The developed approach is applicable to phase transitions in geological, pharmaceutical, ferroelectric, colloidal, and superhard materials where phase transformations occur via the intermediate phase.
Single-molecule stretching experiments of flexible (wormlike) chain molecules in different ensembles: Theory and a potential application of finite chain length effects to nick-counting in DNA
Authors: Everaers Ralf , Becker Nils B. , Rosa Angelo
Published: January 2021

We propose a formalism for deriving force–elongation and elongation–force relations for flexible chain molecules from analytical expressions for their radial distribution function, which provides insight into the factors controlling the asymptotic behavior and finite chain length corrections. In particular, we apply this formalism to our previously developed interpolation formula for the wormlike chain end-to-end distance distribution. The resulting expression for the asymptotic limit of infinite chain length is of similar quality to the numerical evaluation of Marko and Siggia’s variational theory and considerably more precise than their interpolation formula. A comparison to numerical data suggests that our analytical finite chain length corrections achieve a comparable accuracy. As an application of our results, we discuss the possibility of inferring the time-dependent number of nicks in single-molecule stretching experiments on double-stranded DNA from the accompanying changes in the effective chain length.
Investigation of the performance of mid-Z Hohlraum wall liners for producing x-ray drive
Authors: Owen J. , Pasley J. , Ridgers C. P.
Published: January 2021

M-band transitions (n = 4 → 3) in gold are responsible for a population of x-rays with energy >1.8 keV in indirect drive inertial fusion. These x-rays can preheat the fuel, cause the ablator–fuel interface to become unstable to Rayleigh–Taylor instabilities, and introduce radiation nonuniformity to the x-ray drive. This work investigates the performance of mid-Z lined Hohlraums for producing an efficient drive spectrum absent of M-band x-rays using the two-dimensional Lagrangian radiation hydrodynamics code h2d. The removal of the M-band transitions is observed in the Cu-lined Hohlraum reducing the total x-ray energy above 1.8 keV to 58% that of the un-lined Hohlraum. Total radiation energy in the Cu-lined Hohlraum is 93% that of the energy in the pure Au Hohlraum for a 1 ns pulse. However, the soft x-ray drive energy (below 1.8 keV) for the lined Hohlraum is 98% that of the pure Au Hohlraum.
Improved design for a highly efficient pulsed-valve supersonic source with extended operating frequency range
Authors: Barnea A. Ronny , Narevicius Edvardas , Narevicius Julia , Vinetsky Michael , Even Uzi
Published: January 2021

We present a new design for a pulsed supersonic-beam source, inspired by the Even-Lavie valve, which is about four times more energy efficient than its predecessor and can run at more than double the repetition rate without experiencing resonances. Its characteristics make it a better candidate as a source for cryogenic-related experiments as well as spectroscopy with rapidly pulsed lasers. The new design is also simpler to build and is more robust, making it accessible to a larger portion of the scientific community.
Experimental study of natural convection in a V-shape-section cavity
Authors: Wang Xingyu , Bhowmick Sidhartha , Tian Zhao Feng , Saha Suvash C. , Xu Feng
Published: January 2021

Natural convection in a V-shaped section cavity heated from below and cooled from above is investigated experimentally for the first time in the literature. Temperature measurements using fast-response thermistors and flow visualization using the shadowgraph technology have been performed. The natural convection development in the cavity including the conductional, the transitional, and the fully developed stages is described. It is experimentally proven that the scaling law of the thermal boundary layer thickness is δT ∼ (κt)1/2 and the scaling law of the plume velocity is vp ∼ κRa7/15/l. Furthermore, the occurrence of Hopf bifurcation in the transition to chaos and the flow structure are also identified experimentally. The power spectral density of the temperature time series reveals that the dominant frequency of the oscillations of the unsteady flow depends on the Rayleigh number, which is quantified.
Iron content titanium dioxide nanoparticles as exogenous contrast agent for tissue imaging using swept-source optical coherence tomography
Authors: Barkhade Tejal , Indoliya Abhishek , Poddar Raju , Mahapatra Santosh Kumar , Banerjee Indrani
Published: January 2021

Ex vivo tissue imaging was performed by swept-source optical coherence tomography (SS-OCT) using titanium dioxide (TiO2) and Fe content TiO2 nanoparticles (NPs). The comparative effects of TiO2 and Fe content TiO2 NPs in terms of contrast enhancement, penetration, scattering, and accumulation in the chicken breast tissue have been monitored at different exposure times. Powder NP samples were synthesized using the sol–gel method, and characterization was carried out via transmission electron microscopy, x-ray photoelectron spectroscopy, and diffuse reflectance spectroscopy techniques. Fe incorporation in the TiO2 matrix reduces its toxic effect on tissue skin and produces a safe exogenous contrast agent, which is analyzed by SS-OCT. The scattering coefficients and contrast to noise ratio of the tissues with and without NPs were determined to study the imaging efficacy. The improvement in the coefficient was observed with an increase in the exposure time of NPs. Nano-TiO2 has shown the ability to penetrate within the tissue layer up to 780 µm while Fe content TiO2 NPs samples showed the lowest rate of penetration up to 210 µm after a 30 min time interval.
MD simulations of charged binary mixtures reveal a generic relation between high- and low-temperature behavior
Authors: Hecht L. , Horstmann R. , Liebchen B. , Vogel M.
Published: January 2021

Experimental studies of the glassy slowdown in molecular liquids indicate that the high-temperature activation energy E∞ of glass-forming liquids is directly related to their glass transition temperature Tg. To further investigate such a possible relation between high- and low-temperature dynamics in glass-forming liquids, we analyze the glassy dynamics of binary mixtures using molecular dynamics simulations. We consider a binary mixture of charged Lennard-Jones particles and vary the partial charges of the particles and, thus, the high-temperature activation energy and the glass transition temperature of the system. Based on previous results, we introduce a phenomenological model describing relaxation times over the whole temperature regime from high temperatures to temperatures well inside the supercooled regime. By investigating the dynamics of both particle species on molecular and diffusive length scales along isochoric and isobaric pathways, we find a quadratic charge dependence of both E∞ and Tg, resulting in an approximately constant ratio of both quantities independent of the underlying observable, the thermodynamic ensemble, and the particle species, and this result is robust against the actual definition of Tg. This generic relation between the activation energy and the glass transition temperature indicates that high-temperature dynamics and the glassy slowdown are related phenomena, and the knowledge of E∞ may allow us to approximately predict Tg.
Role of substrate strain to tune energy bands–Seebeck relationship in semiconductor heterostructures
Authors: Proshchenko Vitaly S. , Settipalli Manoj , Pimachev Artem K. , Neogi Sanghamitra
Published: January 2021

In doped semiconductors and metals, the Seebeck coefficient or thermopower decreases monotonically with increasing carrier concentration in agreement with the Pisarenko relation. Here, we establish a fundamental mechanism to modulate and increase the thermopower of silicon (Si)/germanium (Ge) heterostructures beyond this relation, induced by the substrate strain. We illustrate the complex relationship between the lattice strain and the modulated thermopower by investigating the electronic structure and cross-plane transport properties of substrate strained [001] Si/Ge superlattices (SLs) with two independent theoretical modeling approaches: first-principles density functional theory and the analytical Krönig–Penny model in combination with the semi-classical Boltzmann transport equation. Our analysis shows that the SL bands, formed due to the cubic structural symmetry, combined with the potential perturbation and the intervalley mixing effects, are highly tunable with epitaxial substrate strain. The strain tuned energy band shifts lead to modulated thermopowers, with a peak approximately fivefold Seebeck enhancement in strained [001] Si/Ge SLs in the high-doping regime. As a consequence, the power factor of a 2.8% substrate strained SL shows a ≈1.8-fold improvement over bulk Si at high carrier concentrations, ≈12×1020cm−3. It is expected that the fundamental understanding discussed here, regarding the complex effect of lattice strain to control energy bands of heterostructures, will help to exploit strain engineering strategies on a class of future technology-enabling materials, such as novel Si/Ge heterostructures as well as layered materials, including van der Waals heterostructures.
Effects of an immersed tube in deep and shallow slugging fluidized beds
Authors: Koe Joshua Kok Tong , Lim Eldin Wee Chuan
Published: January 2021

The effects of an immersed tube on slugging fluidization and particle behaviors in slugging fluidized beds were investigated using computational fluid dynamics. Both shallow and deep slugging fluidized beds with and without an immersed tube were simulated using the two-fluid model. The presence of an immersed tube gave rise to regions of high voidage below the tube and regions of low voidage above the tube. Formation of the high voidage region occurred by particle deflection away from the immersed tube, while that of the low voidage region resulted from particle vortices above the tube. The presence of an immersed tube was observed to facilitate bubble formation and bubble coalescence in both shallow and deep slugging fluidized beds. In shallow beds, an immersed tube regularized pressure fluctuations but increased the amplitude of fluctuations. In deep beds, an immersed tube reduced the frequency of pressure fluctuations by facilitating wall slug formation. Based on random sampling and statistical testing (Z-test) of mean slug lengths, it was concluded that mean slug lengths increased when U was increased from 0.90 m/s to 1.0 m/s in the deep free column (p-value = 0.0422). Based on an F-test of the slug length variance, it was concluded that there was larger variability of slug lengths for U of 1.0 m/s than for U of 0.90 m/s in the deep free column (p-value = 0.0202). However, the results of these statistical tests on mean slug lengths and slug length variance for the deep single tube column showed that U had no significant effect on mean slug length or slug length variance at the 5% significance level. Thus, one of the effects of an immersed tube in a deep slugging fluidized bed was regulation of the size of slugs formed and prevention of any significant increase in mean slug size or slug size variability.
Influence of reservoir properties on the dynamics of a migrating current of carbon dioxide
Authors: De Paoli Marco
Published: January 2021

Storage of carbon dioxide (CO2) in saline aquifers is a promising tool to stabilize the anthropogenic CO2 emissions. At the reservoir conditions, injected CO2 is buoyant with respect to the ambient fluid (brine) and spreads as a current laterally and toward the top cap rock of the aquifer, with the potential risk of a leakage into the upper aquifer layers. However, CO2 is partially soluble in brine and the resulting mixture (CO2 + brine) is denser than both starting fluids. This heavy mixture makes the configuration unstable, producing a convective flow that enhances the dissolution of CO2. Motivated by this geophysical problem, we analyze the influence of the porous medium properties on the evolution of a buoyant current that is weakly soluble with the ambient fluid. A time-dependent large-scale model [C. W. MacMinn et al., “Spreading and convective dissolution of carbon dioxide in vertically confined, horizontal aquifers,” Water Resour. Res. 48, W11516 (2012)] is used to analyze the evolution of the flow. In this work, we include additional physical effects to this model, and we investigate the role of horizontal confinement, anisotropy, and dispersion of the porous layer in the dynamics of the fluid injected. The effect of anisotropy and dispersion is accounted by changing the dissolution rate of CO2 in brine, which is obtained from experiments and Darcy simulations and represents a parameter for the model. Our results reveal that while the confinement has a remarkable effect on the long-term dynamics, i.e., on the lifetime of the current, anisotropic permeability and dispersion of the medium influence mainly the short-term behavior of the flow. Finally, we outline possible implications for the CO2 sequestration process.
Model DFT exchange holes and the exact exchange hole: Similarities and differences
Authors: Wang Yiting , Proynov Emil , Kong Jing
Published: January 2021

Exchange and correlation holes are unique quantum concepts for understanding the nature of electron interactions based on quantum conditional probabilities. Among those, the exact exchange hole is of special interest since it is derived rigorously from first principles without approximations and is often modeled by approximate exchange expressions of density functional theory. In this work, the algorithm for the computation of the spherically averaged exact exchange hole for a given reference point is developed and implemented for molecular orbitals in Gaussian basis functions. The formulas include a novel recursive relation for the spherical average of the Bessel function of the first kind and the asymptotic expressions when the exponential factor of the Bessel function becomes large. This new capability is used to explore the extent to which current popular model exchange holes resemble or differ from the exact exchange hole. Point-wise accuracy of the exchange holes for isolated atoms is important in local hybrid schemes, real-space models of static correlation, and others. We find in this vein that among the models tested here, only the BR89 exchange hole seems more or less suitable for that purpose, while better approximations are still very much on demand. Analyzing the deviations of model exchange holes from the exact exchange hole in molecules such as H2 and Cr2 upon bond stretching reveals new aspects of the left-right static correlation.
Coherence in single photon emission from droplet epitaxy and Stranski–Krastanov quantum dots in the telecom C-band
Authors: Anderson M. , Müller T. , Skiba-Szymanska J. , Krysa A. B. , Huwer J. , Stevenson R. M. , Heffernan J. , Ritchie D. A. , Shields A. J.
Published: January 2021

The ability of two photons to interfere lies at the heart of many photonic quantum networking concepts and requires that the photons are indistinguishable with sufficient coherence times to resolve the interference signals. However, for solid-state quantum light sources, this can be challenging to achieve as they are in constant interaction with noise sources in their environment. Here, we investigate the noise sources that affect InAs/InP quantum dots emitting in the telecom C-band by comparing their behavior on a wetting layer for Stranski–Krastanov grown quantum dots with a nearly wetting layer-free environment achieved with the droplet epitaxy growth mode. We show that the droplet epitaxy growth mode is beneficial for a quiet environment, leading to 96% of exciton transitions having a coherence time longer than the typical detector resolution of 100 ps, even under non-resonant excitation. We also show that the decay profile indicates the presence of slow dephasing processes, which can be compensated for experimentally. We finally conduct Hong–Ou–Mandel interference measurements between subsequently emitted photons and find a corrected two-photon interference visibility of 98.6 ± 1.6% for droplet-epitaxy grown quantum dots. The understanding of the influence of their surroundings on the quantum optical properties of these emitters is important for their optimization and use in future quantum networking applications.