Small Characteristic Size Research Articles

Optimized design of macro‐microreactor for scale‐up of liquid–liquid chemical processes

AbstractThe scale‐up of microreactor‐based flow chemical process represents a grand challenge in chemical engineering. The small characteristic size (<1000 μm) of a typical microreactor leads to not only microscale effect (process intensification) but also low throughput. Here, we report macro‐microreactor to achieve scale‐up of liquid–liquid chemical operation with process intensification. By incorporating the designed internals based on computational fluid dynamics, the characteristic size of the macro‐microreactor is expanded into 3000–4000 μm. The optimized design of macro‐microreactor with helical‐shaped internal exhibits both similar or even stronger microscale effect and high throughput in contrast to the typical microreactor. For the liquid–liquid chemical process, seven times higher mass transfer coefficient and about half reduction of the pressure drop are realized. These macro‐microreactors would find further applications in industrial chemical manufacturing.

Energy-saving thermochromic smart shield based on double network hydrogel with intelligent light management and robust mechanical property

Smart-Windows, which automatically regulate the intensity of sunlight entering the building, have attracted tremendous interest in reducing energy consumption by controlling the solar transmittance. Herein, a microgel-based double-network hydrogel (A-DN hydrogel) was prepared as flexible self-adaptable Smart-Shield to regulate sunlight. A novel thermochromic material, P(NIPAm-co-AA) microgels, was synthesized and used to construct a tough double-network hydrogel with polyacrylamide (PAAm). A-DN hydrogel, with a high solar transmittance of 87.2% at 25 °C but gradually decreased to 0% with increasing temperature to 40 °C, can intelligently select the appropriate solar transmittance according to the ambient temperature. In addition, due to the special double network structure of A-DN hydrogel and small characteristic size of microgel, A-DN hydrogel has no volume change after phase transformation and has excellent mechanical properties and high response speed. Energy Plus simulation software was used to construct the application form of simulated Smart-Shield in buildings. Simulations suggested that A-DN shield can cut off 21.04% energy consumption compared with the normal glass, and its energy saving efficiency is higher than that of commercial low-E glass (10.89%). In general, this strategy will provide new avenues for the preparation of intelligent materials with excellent mechanical properties and temperature response.

A theoretical framework for joining multiple locally resonant bandgaps of metamaterials towards a super-wide bandgap

In this paper, we establish a theoretical framework for joining multiple locally resonant bandgaps of composites that consist of a continuous matrix and discrete particles towards a super-wide bandgap through the damping effect of the inclusions or interphases. The binary locally resonant material is taken as an example. The analytical expressions of its first bandgap, effective mass and transmission characteristics are obtained by virtue of the equivalent discrete models. The theoretical framework and the optimized results are validated by numerical examples and experiments. Then, the theoretical framework is further used to design composite metamaterials that have the merits of small characteristic size, light weight, high static stiffness, and low-frequency bandgaps simultaneously which are characterized by a dimensionless comprehensive performance index. The results demonstrate that the generalized bandwidth can be increased by four folds, and the comprehensive performance index can be doubled through optimization. The methods developed in this work are applicable to other kinds of locally resonant metamaterials, and can be used to guide the design of high-performance metamaterials.

First Observations of G‐Band Radar Doppler Spectra

AbstractThe first Doppler spectra ever acquired by an atmospheric radar at 200 GHz (G‐band) are presented. The observations were taken during a light precipitation event in May (rain rates <2 mm hr−1) at Chilbolton Observatory, UK, with coincident Ka‐band and W‐band Doppler radar measurements. The collected rain spectra agree with Mie theory predictions: at G‐band they show significant reductions in the spectral power return—as compared to theoretical Rayleigh scattering—corresponding to high Doppler velocities (i.e., large raindrops) with the presence of multiple peaks and “Mie notches” in correspondence to the maxima and minima of the raindrop backscattering cross sections. The first two G‐band Mie troughs correspond to smaller velocities/sizes than the first W‐band Mie notch. These features offered by G‐band radars pave the way toward applying, in rain, Mie notch vertical wind retrievals and multifrequency drop size distribution microphysical retrievals to smaller rain rates and smaller characteristic sizes than ever before.

Seismogenic and tremorgenic slow slip near the stability transition of frictional sliding

Slow-slip events and tremors occur below the seismogenic zone of major plate boundaries. While the physics of aseismic slow-slip events is relatively well understood, the mechanics of seismogenic slow slip remains elusive because the conditions leading to slow or fast ruptures are thought to be mutually exclusive. Here, we explore fault dynamics in the parametric space of frictional conditions to show that seismogenic slow-slip events are the natural behavior of homogeneous faults, as long as the velocity dependence approaches velocity neutral with a small characteristic nucleation size. Tremors can originate from rapid bursts of slow earthquakes that are triggered as the slow-slip rupture spreads over small-scale asperities. The near velocity-neutral conditions explain the underlying mechanics of collocated slow and fast slip of seismogenic slow-slip events commonly found below the seismogenic zone. The presence of material heterogeneity may explain the spatio-temporal clustering and migration features of tremor activity.

FEATURES OF ECOLOGICAL GEOMORPHOMETRY AS A PROSPECTIVE FIELD OF STUDY, ITS MAIN CONCEPTS AND METHODS

Abstract. The main concepts and methods of ecological geomorphometry as a research field aimed at studying relationships between terrain morphometric characteristics and ecological factors and processes are reviewed in the paper. The progress in this research field has been conditioned by the propagation of high-resolution digital elevation models in free access and of methods of their digital analysis, namely: the calculation of derivative quantitative characteristics (attributes and indices) of terrain and the statistical models of analyzing the relationships between the latter and the ecological properties and factors (those relevant for a certain ecological subject). A peculiar feature of ecological approach to regarding terrain (its morphology) is subjectcentrism (that is, regarding it from a point of view of a certain subject). The subject of ecological relationships can be living entities (populations, species, communities) as well as a human, social entities, economy and its branches. Three main concepts of ecological geomorphometry are put forward: terrain attributes (relatively simple quantitative characteristics of terrain form that characterize its geometry and some elementary physical processes); topographic indices (quantitative surrogates for some complex physical or biophysical processes of ecological significance); morphotops (spatial units that are distinguished by terrain morphology, using criteria of ecological homogeneity relevant from a viewpoint of a certain ecological subject). Morphotops can be distinguished with different level of detail (and, as a result, with different characteristic dimensions), relative to the study aim, to the geographic features of the area, and to the available data and the methods of their analysis. While morphotops are distinguished with strictly defined quantitative morphometric parameters (terrain attributes, topographic indices), this enables using formalized methods with their advantages of reproducibility and possibility of automatizing. In our studies aimed at morphotop mapping for a small area in the hilly terrain of Davydiv range near Lviv and for a larger area in the central part of Ukrainian Carpathians, morphotops delineation was based on topographic indices that characterize insolation level (solar radiation incidence on terrain elements of different aspect and slope values), lateral redistribution of water on slopes and redistribution of solid matter by washout on slopes. Morphotops were distinguished with cluster analysis method, which allows to distinguish natural groupings of data in the attribute space. Presetting different number of clusters to be distinguished, morphotopes can be distinguished with different levels of detail, larger number of clusters corresponding to more homogenous morphotops with smaller characteristic sizes. Key words: ecological geomorphology, ecological geomorphometry, morphotops, terrain attributes, topographic indices.

Investigation of the characteristics and mechanism of subnanosecond switching of a new type of plasmas switches. II switching devices based on a combination of ‘open’ and capillary discharges—eptrons

The results of investigation of a new type of switch (eptron), which expands the opportunities of voltage waveform tailoring for low temperature plasma applications, are presented. This switch consists of the device with counter-propagating electron beams (kivotron), which acts as a plasma cathode, and capillary integrated with the kivotron into a single device. The main advantage of a discharge in a capillary is various mechanisms of charge neutralization at different plasma densities. At a low density (1010–1011) cm−3, free transport of electrons to the walls of the capillary occurs, due to which a large delay in the development of the discharge is realized. At a high plasma density, due to Debye screening, a rapid charges multiplication occurs and fast switching is realized. Under optimal conditions corresponding to the maximum value of the Townsend multiplication coefficient, a switching time less than ∼1 ns is achieved. The comparative characteristics of the kivotron and eptron due to different mechanisms of subnanosecond switching are considered. The kivotron has a much lower inductance, which allows it to receive currents of tens of kiloamperes. Eptron operates more efficiently with a small characteristic size of the capillary, preferably a few tens of millimetres square. As a result, plasma recombination in the capillary in the eptron in the interpulse interval is much faster than in the kivotron, which allows operating at pulse repetition frequency above 100 kHz and the operating voltage of tens of kilovolts. The subnanosecond switching time in the eptron is realized at currents up to ∼1 kA. Nevertheless, eptron provides new opportunities of voltage waveform tailoring, specifically for pulses generating with a subnanosecond leading edge. Particularly, it is demonstrated that lasing characteristics of BaII and HgII lasers on self-terminating transitions are significantly improved in comparison with conventional power supply.

Inverse Problem of Identifying a Small Defect Based on an Asymptotic Method

We consider the inverse problem of reconstructing a cavity of small characteristic size in an orthotropic layer based on information about the field of layer surface displacements measured within the framework of frequency sensing. Resolving equations in the inverse problem are based on the system of boundary integral equations formulated only along the cavity boundary. In the case of antiplane oscillations, based on an asymptotic approach, we derive formulas for characterizing a small defect. Results of computational experiments are presented.

An Asymptotic Approach to the Calculation of Wave Fields in a Layer with a Defect with a Small Characteristic Size

Problems about vibrations of an orthotropic layer with a cylindrical cavity with an arbitrary transverse cross section under the action of a load applied on its surface are considered. In the case of cavities with a small relative size, an asymptotic approach to the calculation of fields is proposed. An estimate of the applicability area of the asymptotic approach in comparison with the method of boundary integral equations, as well as a comparison with the solution obtained based on the Born approximation are presented.

Blood flow through the circulatory system element affected by double stenotic lesions

Destruction of the elements of the blood circulatory system may in many cases cause many dangerous diseases. Despite many medical diagnostic tools being used in medical laboratories, mathematical modeling at present can be successfully used for predicting, setting the diagnosis, forming coherent picture of the disease, and determining further treatment. One of the most dangerous pathologies of cardio-vascular system is stenosis. This disease is a consequence, and cause of many dangerous conditions. Due to small characteristic size of the element of the circulatory system (1-3 mm) and moderate values of Reynolds number (0.1-300), non-Newtonian properties of blood appear at the flow in the affected cells of the circulatory system. The rheological constitutive relation FENE - P is used for the flow modeling which predicts rheological properties of the blood such as anomalous viscosity and effects of elasticity. This paper examined the effect of the rigidity of the walls of blood vessels and investigated the effect of double - stenotic lesions on blood flow. An element of the circulatory system with a double - stenotic lesions with 50 % narrowing was chosen as the model case. As a result of the simulation, streamlines were obtained, which are the distribution of the principal stresses difference (PSD) in the most significant places of the affected elements of the circulatory system.

The Size Effect on Forming Quality of Ti–6Al–4V Solid Struts Fabricated via Laser Powder Bed Fusion

Laser powder bed fusion (LPBF) is useful for manufacturing complex structures; however, factors affecting the forming quality have not been clearly researched. This study aimed to clarify the influence of geometric characteristic size on the forming quality of solid struts. Ti–6Al–4V struts with a square section on the side length (0.4 to 1.4 mm) were fabricated with different scan speeds. Micro-computed tomography was used to detect the struts’ profile error and defect distribution. Scanning electron microscopy and light microscopy were used to characterize the samples’ microstructure. Nanoindentation tests were conducted to evaluate the mechanical properties. The experimental results illustrated that geometric characteristic size influenced the struts’ physical characteristics by affecting the cooling condition. This size effect became obvious when the geometric characteristic size and the scan speed were both relatively small. The solid struts with smaller geometric characteristic size had more obvious size error. When the geometric characteristic size was smaller than 1 mm, the nanohardness and elastic modulus increased with the increase in scan speed, and decreased with the decline of the geometric characteristic size. Therefore, a relatively high scan speed should be selected for LPBF—the manufacturing of a porous structure, whose struts have small geometric characteristic size.

Math and Myth: A Quantitative Approach to Comparative Mythology

The article is devoted to the application of a certain mathematical apparatus–the theory of complex networks–to quantitatively describe and compare myths belonging to different cultures. One of the fundamental results of comparative mythology is the finding of structures common for many cultures–monomyths. In our study, we focus on other aspects that are also common to different narratives. The approach we take is based on a new way of getting information about the relationships between the characters in the narrative. These characteristics are uniquely expressed in numerical form, and thus there is the possibility for quantitative comparison of different characters of the same text and texts belonging to different periods and different cultures. The method of analysis we use is based on the study of social connections between the characters of a particular epic narrative and on the quantitative analysis of these connections. To this end, the structure of a narrative is depicted as a network (graph) where the nodes are the characters and the edges are the connections (friendly or hostile) between the characters. This enables one, within a unique approach, to carry out a quantitative analysis and comparison of network structures that correspond to different texts. In particular, our work covers such texts as Homer’s epic poem The Iliad , the Irish sagas Táin Bó Cúailnge and Gaedhel re gallaibh, the five largest Icelandic sagas, and Beowulf, the Anglo-Saxon heroic epic. A quantitative analysis of the networks of connections between the characters of these works suggests that, in addition to the existence of monomyths, there are common universal characteristics in the structure of characters’ social networks. Among the common properties is the small characteristic size of the network (the average length of the shortest path) and significant correlations between the network nodes (high value of the clustering coefficient). Common features of these networks include the social balance corresponding to the location of hostile and friendly relationships and characteristic behaviour under the node removal from the network. Our findings suggest that network analysis can serve as another way of addressing issues related to the classification or study of narratives.

Pore-scale modeling of The Geysers

We initiate pore-scale modeling of The Geysers to characterize the formation’s pore space. For this purpose, we analyze the drainage data obtained from mercury intrusion for different samples where the variation of the capillary pressure with wetting phase saturation shows a non-plateau-like trend. The non-plateau-like trend is inconsistent with cyclic pore models such as the regular lattice model, in which the random assignment of the pore size to a lattice results in a plateau-like variation of the capillary pressure with wetting phase in drainage. Our study reveals that we can capture the pore space of The Geysers using acyclic void models. The connectivity of pores is limited in acyclic models and there is only a single path between two pores when they are connected. To capture the pore space, we determine the number of pore throats required to model the drainage results. We also use the characterized acyclic models to analyze the single-phase flow behavior of The Geysers at pore scale. Our analysis of the single-phase permeability suggests that the fluid flow is controlled primarily by a small fraction of the pores whose characteristic sizes are notably larger than others, although the data are not sufficient to eliminate the possible contribution of other pores with smaller characteristic sizes. This study could have major implications for understanding transport phenomena in The Geysers at pore scale.

Experimental investigation of spray cooling on smooth and micro-structured surfaces

The heat transfer during spray cooling was studied experimentally using deionized water to investigate the spray characteristics and the differences between spray cooling on smooth and enhanced silicon surfaces with micro-structures (characteristic size 25–200μm). The spray cooling experiments show that the heat transfer was not significantly greater for the micro-structured surfaces than for the smooth surface in the flooded region, but was much greater in the thin film and partial dryout regions. The micro-structured surface with larger characteristic sizes had a smaller area enhancement factor and worse heat transfer rates. However, on the micro-structured surface with much smaller characteristic sizes, most droplets were not able to completely enter the bottom of the micro grooves since the groove size was smaller than most of the droplets and the heat transfer surface could not be fully wetted. There is an optimal groove depth corresponding to a given droplet parameter, groove width and stud size that gives the best heat transfer rates. The wall temperature increase and the temperature fluctuations are small in the boiling regime as the power increases for the micro-structured surfaces.

Enhanced ferromagnetism of cluster-assembled BiFeO3 nanostructured films

Cluster-assembled BiFeO3 nanostructured films were prepared using low-energy cluster beam deposition method with our homemade cluster apparatus. It is shown that the nanostructured films are perovskite structure and assembled uniformly and compactly with monodisperse spherical clusters with average diameter of ~22nm. The enhanced ferromagnetism is observed for the as-prepared films, which is attributed to the uncompensated surface spins and the release of the latent magnetization locked within the cycloid induced by the size effect of the clusters with the smaller characteristic size than the long-range cycloid order of 62nm. The present work provides a way on enhancing ferromagnetism of single-phase multiferroics.

Inducing Order from Disordered Copolymers: On Demand Generation of Triblock Morphologies Including Networks

Disordered block copolymers are generally impractical in nanopatterning applications due to their inability to self-assemble into well-defined nanostructures. However, inducing order in low molecular weight disordered systems permits the design of periodic structures with smaller characteristic sizes. Here, we have induced nanoscale phase separation from disordered triblock copolymer melts to form well-ordered lamellae, hexagonally packed cylinders, and a triply periodic gyroid network structure, using a copolymer/homopolymer blending approach, which incorporates constituent homopolymers into selective block domains. This versatile blending approach allows one to precisely target multiple nanostructures from a single disordered material and can be applied to a wide variety of triblock copolymer systems for nanotemplating and nanoscale separation applications requiring nanoscale feature sizes and/or high areal feature densities.

Determination of the position and volume of a cavity in an elastic rod from its two vibration eigenfrequencies

The direct and inverse problems of the longitudinal vibrations of a cylindrical rod with a flaw in the form of a cavity with a small characteristic size are considered. An approach to the determination of the location and volume of a small cavity of an arbitrary shape, which is based on the representation of the cavity by a negative mass, is proposed. The results of numerical experiments and their analysis are presented.

Water Defect and Pore Formation in Atomistic and Coarse-Grained Lipid Membranes: Pushing the Limits of Coarse Graining.

Defects in lipid bilayers are important in a range of biological processes, including interactions between antimicrobial peptides and membranes, transport of polar molecules (including drugs) across membranes, and lipid flip-flop from one monolayer to the other. Passive lipid flip-flop and the translocation of polar molecules across lipid membranes occur on a slow time scale because of high-energy intermediates involving water defects and pores in the membrane. Such defects are an interesting test case for coarse-grained models because of their relatively small characteristic size at the level of water molecules and the complex environment of water and polar head groups in a low-dielectric membrane interior. Here we compare coarse-grained simulations with the MARTINI model with the standard MARTINI water and two recently developed coarse-grained polarizable water models to atomistic simulations. Although in several cases the MARTINI model reproduces the correct free energies, there are structural differences between the atomistic and coarse-grained models. The polarizable water model improves the free energies but only moderately improves the structures. Atomistic test simulations in which water molecules are artificially tethered to each other in groups of four, the resolution of MARTINI, suggest that the limiting factor is not the size of the coarse-grained particles but rather the simple interaction potential and/or the entropy lost in coarse graining the system. By increasing the attractive interaction between the lipids' headgroup and water, we did observe pore formation but at the expense of the correct equilibrium properties of the bilayers.

Particle plasmon resonances in L-shaped gold nanoparticles

We present an extensive experimental and theoretical study of the particle plasmon resonances of L-shaped gold nanoparticles. For the small characteristic size of the particles, we observe more higher-order resonances than previously from related shapes, and show that a short-wavelength resonance arises from the particle arm width and is not the suggested volume plasmon. We interpret the resonances through the local vector electric field in the structure and by fully taking into account the particle symmetry.

The different domains of the point spread function ‐ Small angle vs large angle

Abstract Purpose The Point‐Spread‐Function peaks at 107, and drops off to 10‐2 at 90 degrees, a dynamic range of 109. Important changes in the PSF already occur within the first 1 minute of arc, so spatially the dynamic range is 105. Very different experimental techniques are needed to describe the small angle (aberrometry, double pass) and the large angle (straylight) domains. What optical irregularities achieve such PSF? Methods Literature models for the aberration structure of the human eye media, in particular Thibos et al. JOSA A 2002 were used to derive the PSF. The Thibos et al. model was extrapolated to allow inclusion of the high orders of aberration not normally included in aberrometry, but potentially visible with double pass, so as to encompass as much as possible from the PSF. Results The modeled aberration structures of the eye covers the central part of the PSF up till about 0.3 degrees if extreme high orders were included. For angles >1 degree predicted values were far below the actual values of the PSF. On the other hand, double pass techniques grossly overestimate PSF values at angles of 0.3 degree and above. Using an alternative model for the aberration structure of the eye the PSF could be described up till 1 degree. Small particle scattering was essential to predict the PSF for angles above 1 degree. Conclusion In the assessment of disturbances to the optical media two domains must be discriminated: the aberration domain and the small particle domain, with corresponding parts (small angle vs large angle) to the PSF. Straylight originates from irregularities of small characteristic size (10 micrometer and below), as opposed to disturbances to the central part of the psf (<0.3 degrees), originating from large scale irregularities. Commercial interest