Mesoscopic Structures Research Articles

Efficient Tuning of Optical Properties and Morphology of Mesoscopic CdS via a Facile Route

A facile and simple synthetic route has been employed to synthesize rod-shaped optically efficient cadmium sulfide (CdS) mesoscopic structures using high concentrations of cetyl trimethyl ammonium bromide (CTAB) as the stabilizing agent. The mesoscopic structures were characterized using x-ray diffaractometer (XRD), scanning electron microscopy, UV–visible, photoluminescence (PL), and Fourier transform and infrared (FTIR) spectroscopy. It was found that, if the concentration of CTAB is significantly higher than its critical micelle concentration, the nucleation of CdS mesoscopic structures resulted in rod-like structures. The size of the mesoscopic structures initially increased and then decreased with band gaps 2.5–2.7 eV. XRD analysis showed that the samples had a pure cubic phase confirming the particle size. The values of Urbach energy for the absorption tail states were determined and found to be in agreement with the single crystal. PL spectra showed sharp green emission peaks in the 530-nm to 560-nm wavelength range. FTIR spectra showed the adsorption mode of CTAB onto the CdS mesoscopic structures. A possible mechanism of formation of rod-shaped CdS mesoscopic structures is also elucidated.

29pYR-6 メゾスコピック構造のダイナミクス

29pYR-6 メゾスコピック構造のダイナミクス

The role of community structure on the nature of explosive synchronization.

In this paper, we analyze explosive synchronization in networks with a community structure. The results of our study indicate that the mesoscopic structure of the networks could affect the synchronization of coupled oscillators. With the variation of three parameters, the degree probability distribution exponent, the community size probability distribution exponent, and the mixing parameter, we could have a fast or slow phase transition. Besides, in some cases, we could have communities which are synchronized inside but not with other communities and vice versa. We also show that there is a limit in these mesoscopic structures which suppresses the transition from the second-order phase transition and results in explosive synchronization. This could be considered as a tuning parameter changing the transition of the system from the second order to the first order.

On the Connectivity of Microscopic and Mesoscopic Community Structures

On the Connectivity of Microscopic and Mesoscopic Community Structures

Superplastic nanoscale pore shaping by ion irradiation

Exposed to ionizing radiation, nanomaterials often undergo unusual transformations compared to their bulk form. However, atomic-level mechanisms of such transformations are largely unknown. This work visualizes and quantifies nanopore shrinkage in nanoporous alumina subjected to low-energy ion beams in a helium ion microscope. Mass transport in porous alumina is thus simultaneously induced and imaged with nanoscale precision, thereby relating nanoscale interactions to mesoscopic deformations. The interplay between chemical bonds, disorders, and ionization-induced transformations is analyzed. It is found that irradiation-induced diffusion is responsible for mass transport and that the ionization affects mobility of diffusive entities. The extraordinary room temperature superplasticity of the normally brittle alumina is discovered. These findings enable the effective manipulation of chemical bonds and structural order by nanoscale ion-matter interactions to produce mesoscopic structures with nanometer precision, such as ultra-high density arrays of sub-10-nm pores with or without the accompanying controlled plastic deformations.

Diffusion MRI monitoring of specific structures in the irradiated rat brain.

The analysis of biological and mesoscopic structures properties by diffusion MRI (dMRI) in brain after radiation therapy remains challenging. In our study, we described the consequences associated with an unwanted dose to healthy tissue, assessing radiation-induced brain alterations of living rats with dMRI compared to histopathology and behavioral assays. The right primary motor cortex M1 of the rat brain was targeted by stereotactic radiosurgery with a mean radiation dose of 41 Gy. Multidirectional single b-value dMRI data of the whole brain were acquired with a 7T small-animal scanner before irradiation until 110 days post-irradiation. Diffusion tensor imaging metrics, such as fractional anisotropy (FA), mean diffusivity (MD), axial (AD), and radial diffusivity (RD) were compared to brain alterations detected by immunohistochemistry and motor performances measured by a behavioral test. Between days 90 and 110, radiation necrosis was observed into the white matter spreading into M1 . Results showed a reduction of FA in the corpus callosum and in the striatum, which was driven by an increase in RD from 90 to 110 days post-irradiation, whereas only RD increased in M1 . Values of RD and AD increased in the irradiated hippocampus, while FA remained constant. Moreover, an increased MD, AD and RD was observed in the hippocampus that was probably related to inflammation as well as reactive astrogliosis after 110 days post-irradiation. Finally, rats did not exhibit locomotor deficits. dMRI metrics can assess brain damage; the sensitivity of dMRI metrics depends on the brain region.

Periodic array of quantum rings strongly coupled to circularly polarized light as a topological insulator

We demonstrate theoretically that a strong high-frequency circularly polarized electromagnetic field can turn a two-dimensional periodic array of interconnected quantum rings into a topological insulator. The elaborated approach is applicable to calculate and analyze the electron energy spectrum of the array, the energy spectrum of the edge states and the corresponding electronic densities. As a result, the present theory paves the way to optical control of the topological phases in ring-based mesoscopic structures.

Quality management of high-efficiency planar heterojunction organic-inorganic hybrid perovskite solar cells

The energy extracted from solar radiation is the most abundant and accessible source of renewable energy, which will become progressively more important as time goes on. Solar cells are regarded as one of the most promising candidates for generating renewable clean energy. Recently, a new class of semiconducting material called organic-inorganic halide perovskite has received great attention of academia, and the record power conversion efficiency (PCE) of perovskite solar cell (PSC) rapidly increased from 3.8% in 2009 to 22.7% in late 2017 through intensive research due to some advantages as follows. 1) Excellent optoelectronic property. Perovskite materials exhibit excellent properties, including long diffusion length, high carrier mobility, and high absorption coefficient. 2) Low cost. The ingredients of perovskite materials are cheap, and PSCs can be manufactured by a solution process. 3) Tunable bandgap. Perovskite materials have highly tunable bandgap (1.2-2.2 eV), contributing to the further improvement in PCE of single junction PSCs by realizing the ideal bandgap (1.3-1.4 eV) as demonstrated by the Shockley-Queisser detailed balanced calculation. The basic architectures of PSCs are divided mainly into mesoscopic and planar heterojunction structures. Compared with the former configuration, the later configuration combined with low-temperature processable interlayers provides a method of fabricating flexible PSCs and tandem PSCs. Furthermore, the nonuse of the mesoscopic structure simplifies the structure of PSCs and reduces the cost and time of fabrication. The key requirement to achieve an efficient and reproducible planar heterojunction PSCs is that the perovskite layer should be uniform, continuous, and pinhole free to minimize shunting pathways. So, significant research effort is being devoted to the quality management of perovskite films with the goal of achieving the controllable preparation, including the optimization of their morphology (uniformity, coverage, roughness) and microstructure (grain size/distribution, texture), and the elimination of defects (voids, pinholes, grain boundaries), which influence the PSC performance directly. Especially for the one-step solution coating method, the film quality of perovskite on different planar substrates under varied deposition conditions exhibits a large difference, due to the complex crystallization process and the heightened sensitivity to environmental conditions. In this paper, the characteristics of perovskite materials, the nucleation-growth mechanism of films in the one-step solution method, and the evolution of cell structures are described briefly. The latest quality control methods of high-quality perovskite films prepared by solution method are then discussed emphatically. Finally, to provide references for the future research, the development and existing problems of PSCs are addressed and prospected.

Ut vis sic tensio

The mechanical properties of rubber-like materials have been offering an outstanding challenge to the solid mechanics community for a long time. The behaviour of such materials is quite difficult to predict because rubber self-organizes into mesoscopic physical structures that play a prominent role in determining their complex, history-dependent and strongly nonlinear response. In this framework one of the main problems is to find a functional form of the elastic strain-energy that best describes the experimental data in a mathematical feasible way. The aim of this paper is to give a survey of recent advances aimed at solving such a problem.

Melamine as a single source for fabrication of mesoscopic 3D composites of N-doped carbon nanotubes on graphene.

Integration of two-dimensional graphene and one-dimensional carbon nanotubes (CNTs) to create potentially useful 3D mesoscopic carbon structures with enhanced properties relative to the original materials is very desirable. Here, we report a novel and simple route using chemical vapor deposition (CVD) methods to fabricate bead-like nitrogen-doped CNT/graphene composites (NCNT/G) via a simple pyrolysis of the N-rich melamine in the presence of graphene oxide (GO) as a substrate using a Mn–Ni–Co ternary catalyst. We have characterized these structures by field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectra, isothermal analyses, and X-ray photoelectron spectroscopy. The three dimensional NCNT/G hybrids have unique network structures, moderate graphitization, high specific surface area, good mesoporosity, and N doping, which makes them promising materials for applications in energy storage and conversion.

Theoretical analyses on water cluster structures in polymer electrolyte membrane by using dissipative particle dynamics simulations with fragment molecular orbital based effective parameters.

The mesoscopic structures of polymer electrolyte membrane (PEM) affect the performances of fuel cells. Nafion® with the Teflon® backbone has been the most widely used of all PEMs, but sulfonated poly-ether ether-ketone (SPEEK) having an aromatic backbone has drawn interest as an alternative to Nafion. In the present study, a series of dissipative particle dynamics (DPD) simulations were performed to compare Nafion and SPEEK. These PEM polymers were modeled by connected particles corresponding to the hydrophobic backbone and the hydrophilic moiety of sulfonic acid group. The water particle interacting with Nafion particles was prepared as well. The crucial interaction parameters among DPD particles were evaluated by a series of calculations based on the fragment molecular orbital (FMO) method in a non-empirical way (Okuwaki et al., J. Phys. Chem. B, 2018, 122, 338–347). Through the DPD simulations, the water and hydrophilic particles aggregated, forming cluster networks surrounded by the hydrophobic phase. The structural features of formed water clusters were investigated in detail. Furthermore, the differences in percolation behaviors between Nafion and SPEEK revealed much better connectivity among water clusters by Nafion. The present FMO-DPD simulation results were in good agreement with available experimental data.

Modeling biomembranes and red blood cells by coarse-grained particle methods

In this work, the previously developed coarse-grained (CG) particle models for biomembranes and red blood cells (RBCs) are reviewed, and the advantages of the CG particle methods over the continuum and atomistic simulations for modeling biological phenomena are discussed. CG particle models can largely increase the length scale and time scale of atomistic simulations by eliminating the fast degrees of freedom while preserving the mesoscopic structures and properties of the simulated system. Moreover, CG particle models can be used to capture the microstructural alternations in diseased RBCs and simulate the topological changes of biomembranes and RBCs, which are the major challenges to the typical continuum representations of membranes and RBCs. The power and versatility of CG particle methods are demonstrated through simulating the dynamical processes involving significant topological changes, e.g., lipid self-assembly vesicle fusion and membrane budding.

Characterization of Low-Frequency Excess Noise in CH3NH3PbI3-Based Solar Cells Grown by Solution and Hybrid Chemical Vapor Deposition Techniques.

In this study, detailed investigations of low-frequency noise (LFN) characteristics of hybrid chemical vapor deposition (HCVD)- and solution-grown CH3NH3PbI3 (MAPI) solar cells are reported. It has been shown that LFN is a ubiquitous phenomenon observed in all semiconductor devices. It is the smallest signal that can be measured from the device; hence, systematic characterization of the LFN properties can be utilized as a highly sensitive nondestructive tool for the characterization of material defects in the device. It has been demonstrated that the noise power spectral densities of the devices are critically dependent on the parameters of the fabrication process, including the growth ambient of the perovskite layer and the incorporation of the mesoscopic structures in the devices. Our experimental results indicated that the LFN arises from a thermally activated trapping and detrapping process, resulting in the corresponding fluctuations in the conductance of the device. The results show that the presence of oxygen in the growth ambient of the HCVD process and the inclusion of an mp-TiO2 layer in the device structure are two important factors contributing to the substantial reduction in the density of the localized states in the MAPI devices. Furthermore, the lifetimes of the MAPI perovskite-based solar cells are strongly dependent on the material defect concentration. The degradation process is substantially more rapid for the devices with higher initial defect density compared to the devices prepared under optimized conditions and structure that exhibit substantially lower initial trap density.

Study of a magnetorheological fluid submitted to a uniform magnetic field

In this work, the rheological and hyperfine properties of a magnetorheological fluid (MRF) under the action of a uniform external magnetic field are analysed. Powders of native mineral magnetite of micrometric particle size, after a pulverization process, form the solute of these fluids. The sizes of these samples are selected by sieving in order to obtain sizes of around 20µm and 45µm. The powders are characterized by means of Mössbauer spectroscopy to analyse their stoichiometry giving rise to a non-stoichiometric magnetite Fe2.96O4 in addition to a hematite component. Result of viscosity and shear stress in the low-speed regime were analysed using the Hershel Buckley method. In particular, the case of surface tension it decreases with the application of a uniform magnetic flux density, which is understood in terms of a phase separation due to the formation of mesoscopic structures, thus decreasing the cohesion force and increasing the adhesion force.

Quantitative investigation of anisotropic characteristics of methane-induced strain in coal based on coal particle tracking method with X-ray computer tomography

In order to quantify the anisotropic characteristics of coal swelling deformation during the process of methane adsorption, the inner mesoscopic structures of coal are scanned with computerized tomography (CT) and a coal particle tracking method (CPTM) is proposed to quantitatively calculate the strain of coal particulates in view of the pixel gray level matrix of CT image. The results show that the spatio-temporal distribution of coal mesoscopic deformation is inhomogeneous during the process of methane adsorption. From the spatial distribution, some parts of coal swell and other parts shrink. The mineral phase and porosity or fracture inside them are mainly swelling deformation and little shrinkage deformation. The swelling and shrinkage deformation is varying constantly with different gas pressure in the organic lithotypes of varying macerals and pore or fracture inside them. The expansion deformation tends to first squeeze the original pore or fracture inside them for more expansion space. From the temporal distribution, the magnitudes of adsorption deformation is also not uniform along with the decrease of gas pressure. After the adsorption balance, the change magnitudes of strain tend to decrease. The mesoscopic deformation of coal samples is anisotropic and the macroscopic deformation is swelling. This is verified by the cumulative total strain values of coal, which are obtained from the mesoscopic strain calculation results. This study presents mesoscopic CT and strain calculation results images of coal deformation. These data will provide the basis for the study of physical structure and mechanical properties of coal with adsorbing methane.

Cascading failures in interdependent modular networks with partial random coupling preference

Cascading failures have been widely analyzed in interdependent networks with different coupling preferences from microscopic and macroscopic perspectives in recent years. Plenty of real-world interdependent infrastructures, representing as interdependent networks, exhibit community structure, one of the most important mesoscopic structures, and partial coupling preferences, which can affect cascading failures in interdependent networks. In this paper, we propose the partial random coupling in communities, investigating cascading failures in interdependent modular scale-free networks under inner attacks and hub attacks. We mainly analyze the effects of the discoupling probability and the intermodular connection probability on cascading failures in interdependent networks. We find that increasing either the dicoupling probability or the intermodular connection probability can enhance the network robustness under both hub attacks and inner attacks. We also note that the community structure can prevent cascading failures spreading globally in entire interdependent networks. Finally, we obtain the result that if we want to efficiently improve the robustness of interdependent networks and reduce the protection cost, the intermodular connection probability should be protected preferentially, implying that improving the robustness of a single network is the fundamental method to enhance the robustness of the entire interdependent networks.

Nuclear Magnetic Resonance characterization of traditional homeopathically manufactured copper (Cuprum metallicum) and plant (Gelsemium sempervirens) medicines and controls

NMR proton relaxation is sensitive to the dynamics of the water molecule H2O, through the interaction of the spin of the proton (1H) with external magnetic and electromagnetic fields. We measured dilution and potentization processes through measurements of 1H spin-lattice T1 and spin-spin T2 relaxation times. In order to interpret the recorded fluctuations in T1- or T2-values, experimental data were linearized by investigating how the area under a fluctuating time=f(dilution) curve (dilution integral or DI) changes with dilution. Two kinds of fitting procedures were considered: chi-square fitting with a goodness-of-fit probability, and least absolute deviations criterion with Pearson's linear correlation coefficient. We showed that fluctuations are not attributable to random noise and/or experimental errors, evidencing a memory effect quantifiable by the slope of the DI=f(dilution) straight line. For all experiments, correlation coefficients were found to lie above 0.9999, against 0.999 for random noise. The discrimination between experimental slopes and slopes associated with random noise data was very good at a five-sigma level of confidence (i.e. probability 3×10-7). Discrimination between experimental slopes at a five-sigma level was possible in most cases, with three exceptions: gelsemium aqua pura v gelsemium dilution (four-sigma); copper aqua pura v gelsemium aqua pura (four-sigma) and copper simple dilution v gelsemium simple dilution (three-sigma). All potentized samples show very good discrimination (at least nine-sigma level) against aqua pura, lactose or simple dilution. It was possible to transform the associated relaxation times into a molecular rotational correlation time τc and an average spin-spin distance d. Our experiments thus point to a considerable slowing down of molecular movements (τc>1300ps or T=224-225K) around water molecules up to a distance of 3.7Å, values. It was also possible to rule out other possible mechanisms of relaxation (diffusive motion, 17O-1H relaxation or coupling with the electronic spin, S=1, of dissolved dioxygen molecules). There is clear evidence that homeopathic solutions cannot be considered as pure water as commonly assumed. Instead, we have evidenced a clear memory effect upon dilution/potentization of a substance (water, lactose, copper, gelsemium) reflected by different rotational correlation times and average H⋯H distances. A possible explanation for such a memory effect may lie in the formation of mesoscopic water structures around nanoparticles and/or nanobubbles mediated by zero-point fluctuations of the vacuum electromagnetic field as suggested by quantum field theories. The existence of an Avogadro's 'wall' for homeopathically-prepared medicines is not supported by our data. Rather it appears that all dilutions have a specific material configuration determined by the potentized substance, also by the chemical nature of the containers, and dissolved gases and the electromagnetic environment. This sensitivity of homeopathically-prepared medicines to electromagnetic fields may be amplified by the highly non-linear processing routinely applied in the preparation of homeopathic medicines. Future work is needed in such directions. The time is now ripe for a demystification of the preparation of homeopathic remedies.

Efficiency enhancement of hybridized solar cells through co-sensitization and fast charge extraction by up-converted polyethylene glycol modified carbon quantum dots

Photovoltaics are promising solutions to energy crisis and environmental pollution problems. The dye-sensitized solar cells with mesoscopic structures have attracted growing interests because of zero emissions, easy fabrication, scalable materials and techniques, etc. However, the state-of-the-art dye-sensitized solar cells have narrow spectral absorption for photoelectric conversion and high electron-hole recombination rate under sunlight illumination. Therefore, it is a persistent object to make wide-spectral absorption and fast charge extraction solar cells for energy harvest in both solar and dark-light conditions. To address this issue, we present here experimental realization of a category of solar cells converting visible and near-infrared light into electricity by co-sensitizing photoanode with N719 dye and polyethylene glycol (PEG) modified carbon quantum dots (PEG-m-CQDs), arising from up-conversion and hole-transporting behaviors of PEG-m-CQDs as well as photofluorescence of green-emitting long persistence phosphors. The optimized solar cell yields maximized photoelectric conversion efficiencies of 9.89% and 25.81% under simulated sunlight (air mass 1.5, 100 mW cm−2) illumination and dark conditions, respectively. This work is far from optimization, but the physical proof-of-concept hybridized solar cell may markedly increase electricity generation time and total power output of photovoltaic platforms.

Large-scale and long-term correlations in collective motions of atoms of liquid argon. Computer simulation

The correlation coefficients of displacements of pairs of neighboring particles located in spheres of a given radius have been studied within the molecular dynamics models of liquid argon including 50000 and 500000 atoms. Atoms separated by distances of about ten diameters from each other are correlated and correlations last nanoseconds. A size effect has been revealed: correlations increase with the size of the model. All these properties indicate that mesoscopic supramolecular structures exist in a liquid.

Superconducting and mesoscopic structures: in honor of A. N. Omelyanchuk's 70th birthday

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