Characteristic Cell Size Research Articles

Research on the initiation and wavefront evolution of diverging cylindrical detonations of acetylene and oxygen mixtures

The present study focuses on fundamental research about the transition from a planar detonation to a cylindrical detonation and the propagation of the diverging cylindrical detonation. We aim to figure out the mechanism of the transition and propagation of the diverging cylindrical detonation by analyzing the cellular pattern and critical initial pressure. The findings highlight that the successful detonation in a cylindrical chamber via transition through a straight channel is predominantly influenced by diffraction at the corners and the successive continuous reflections between the front and rear walls. Depending on the initial pressure, the initiation modes exhibit characteristics of subcritical, critical, and supercritical three-stage processes. Sustained propagation of cylindrical detonations necessitates increasing the number of cells to match the growth rate in the front region. Experimental investigations reveal two distinct modes of cell number increase: mild and violent. In the case of the former, cell number increase predominantly occurs on a scale of two to three times the characteristic cell size of the Chapman-Jouguet detonation. In contrast, a decaying Mach stem undergoes twisting and evolves into local kinks, leading to the development of new triple-wave points. The latter mode typically occurs near the limit, where cell increase primarily arises from randomly occurring local explosions, and operates on a scale of ten times the characteristic cell size or the chamber diameter. In addition, a numerical study of two-dimensional fundamental problems abstracted from the experiment is conducted to help interpret experimental results and reveal more about the physics of the problem.

Modelling cellular structure of detonation waves in hydrogen-air mixtures

The paper presents the results of two-dimensional simulations of the cellular structure of a detonation wave in a stoichiometric mixture of hydrogen with air. The dependence on cellular structure on chemical kinetics mechanism proved to be essential in terms of characteristic cell size. Comparison of simulation results with experimental data made it possible distinguishing the kinetic mechanism, which could describe the cellular structure for the conditions under investigations more adequately than other tested mechanisms. The dependence of cellular structure on mixture temperature and channel width was also investigated and comparative results are presented. It was shown in numerical experiments, that the dependence of cell size on temperature could be not monotonous due to manifestation of different effects under different mixture conditions. The cells can grow and then split giving birth to a fine structure.

Formation and Evolution of Cellular Structures in Wedge-Induced Oblique Detonations

Numerical simulation of an oblique detonation induced by a wedge is performed to investigate the formation and evolution of the oblique cellular detonation structure and the quantitative comparison of the cellular structure of a normal and an oblique detonation. The compressible reactive Euler equations are solved using the seventh-order WENO scheme on an adaptive mesh based on the open source program Adaptive Mesh Refinement in Object-oriented C++ (AMROC). The numerical results show that there are two sets of transverse waves, the left-running transverse waves (LRTW) and the right-running transverse waves (RRTW), which form the oblique cellular detonation structure. Although both sets of transverse waves are convected downstream, they propagate at almost the same relative velocity in the opposite direction. The LRTWs start in the transition zone because of the detonation instability. However, the RRTWs form due to the interaction between the deformed detonation front and the reflected shock wave from the wedge. For the same degree of overdrive, numerical simulations reveal that the characteristic cell size of an oblique detonation is almost the same as that of a normal detonation.

First study of lithium boron composite as plasma facing material

Lithium-Boron Composite Material (LBCM) is presented as a plasma-facing material with a lot of promise from the perspective of liquid metal first wall. LBCM consists of ∼ 20 w.% boron and ∼ 80 w.% lithium, arranged in the form of a Li5B4 matrix filled with metal lithium, similar to capillary porous systems (CPS) already used as plasma-facing elements. The characteristic matrix cell size is approximately 5 µm. LBCM was subjected to electron flux and helium plasma in a linear PR-2 device. LBCM maintained physical integrity up to T > 900 °C. Boron didn’t evaporate from LBCM under electron irradiation, but was sputtered during helium bombardment. CPS-like properties, wherein Li from the whole of the LBCM sample was transported to the area of the highest thermal load were observed.

On polyhedral structures of lean methane/hydrogen Bunsen flames: Combined experimental and numerical analysis

In premixed flame propagation of lean hydrogen or hydrogen-enriched blends, both hydrodynamic and thermo-diffusive instabilities are governing the flame front shape and affect its propagation velocity. As a result, different types of cellular patterns can occur along the flame front in a laminar scenario. In this context, an interesting phenomenon is the formation of polyhedral flames which can be observed in a Bunsen burner. It is the objective of this work to systematically characterize the polyhedral structures of premixed methane/hydrogen Bunsen flames in a combined experimental and numerical study. A series of lean flames with hydrogen content varying between 20 and 85% at two equivalence ratios is investigated. The experiments encompass chemiluminescence imaging together with Planar Laser-induced Fluorescence (PLIF) measurements of the OH radical. Characteristic cell sizes are quantified from the experiments and related to the characteristic length scales obtained from a linear stability analysis. In the experiments, it is observed that the cell sizes at the base of the polyhedral Bunsen flames decrease almost linearly with hydrogen addition and only a weak dependence on the equivalence ratio is noted. These trends are well reflected in the numerical results and the length scale comparison further shows that the wavelength with the maximum growth rate predicted by the linear stability analysis is comparable to the cell size obtained from the experiment. The correlation between the experimental findings and the linear stability analysis is discussed from multiple perspectives considering the governing time and length scales, furthermore drawing relations to previous studies on cellular flames.

Cell size homeostasis under the circadian regulation of cell division in cyanobacteria

Bacterial cells maintain their characteristic cell size over many generations. Several rod-shaped bacteria, such as Escherichia coli and the cyanobacteria Synechococcus elongatus, divide after adding a constant length to their length at birth. Through this division control known as the adder mechanism, perturbation in cell length due to physiological fluctuation decays over generations at a rate of 2−1 per cell division. However, previous experiments have shown that the circadian clock in cyanobacteria reduces cell division frequency at a specific time of day under constant light. This circadian gating should modulate the division control by the adder mechanism, but its significance remains unknown. Here we address how the circadian gating affects cell length, doubling time, and cell length stability in cyanobacteria by using mathematical models. We show that a cell subject to circadian gating grows for a long time, and gives birth to elongated daughter cells. These elongated daughter cells grow faster than the previous generation, as elongation speed is proportional to cell length and divide in a short time before the next gating. Hence, the distributions of doubling time and cell length become bimodal, as observed in experimental data. Interestingly, the average doubling time over the population of cells is independent of gating because the extension of doubling time by gating is compensated by its reduction in the subsequent generation. On the other hand, average cell length is increased by gating, suggesting that the circadian clock controls cell length. We then show that the decay rate of perturbation in cell length depends on the ratio of delay in division by the gating τG to the average doubling time τ0 as 2τG/τ0−1. We estimated τG≈2.5, τ0≈13.6 hours, and τG/τ0≈0.18 from experimental data, indicating that a long doubling time in cyanobacteria maintains the decay rate similar to that of the adder mechanism. Thus, our analysis suggests that the acquisition of the circadian clock during evolution did not impose a constraint on cell size homeostasis in cyanobacteria.

Research on Blast Resistance of the Cylinder with Aluminium Foam under Internal Explosive Load

Aluminium foam has an excellent performance in terms of impact resistance and energy absorption. The experimental and numerical investigations on the blast resistance of the cylinder with aluminium foam under internal explosive load are carried out in this thesis and the factors influencing the blast resistance are analyzed. First, experiments were carried out under internal explosive load with different relative densities and explosion loads, and the defections of inner and outer layers were obtained. Second, based on the voronoi technique, a 2D finite element model of sandwich cylinders with a core of aluminium foam was constructed, the effectiveness of the model was then confirmed by conflicting results from simulations and experiments. Finally, the finite element model was used to analyze the effects of characteristic cell size and explosive load, which were reflected in the energy absorption and deflection of the outer layer. The test results show that the simulation results agree well with the experimental results. The characteristic cell size has little influence on energy absorption. In the case of homogeneous cores, the energy absorption per unit of mass decreases linearly with increasing relative density and the deflections of outer layers increase slightly.

A novel auxetic acoustic metamaterial plate with tunable bandgap

Two-dimensional phononic metamaterials, consisting of plates with resonant cylinders, can significantly attenuate waves by opening a subwavelength bandgap, though their characteristic unit cell size is small. To realize the real-time adjustment of the bandgap, external excitations including mechanical load, temperature field, electric field and magnetic field could be introduced, of which applying mechanical load is the most practical way. In this work, an acoustic metamaterial plate based on the negative Poisson's ratio structure (NP-AMP) is proposed and feasible to achieve lower frequency, wider bandgap, and tunable bandgap compared with traditional ones (T-AMP). A counterpart based on the positive Poisson's ratio structure (PP-AMP) is also introduced for comparison. Studies have indicated that the newly designed structure has a lower frequency bandgap and wider bandwidth. With the increase of compression strain, the initial bandgap of PP-AMP gradually moves to a higher-frequency range. In contrast to PP-AMP, the NP-AMP exhibits lower frequency, which is beneficial for the further research of low-frequency bandgap. Moreover, the bandgap variation range can be enlarged by the enhancement of the auxetic behavior. Finally, the variation range of the NP-AMP initial bandgap frequency increased by 62%. The findings in this work will broaden the design of low-frequency broadband acoustic devices used in a dynamic environment, while providing new ideas and methodologies for real-time adjustment of bandgaps.

Cellular flame structures and thermal characteristics of axi-symmetric ceiling fires: An experimental study and scaling analysis

The present study provides an experimental characterization of cellular flame structures and thermal characteristics of axi-symmetric ceiling fires. Experiments were carried out employing circular gaseous burners of various diameters at the ceiling facing downward using methane and propane as fuel. For this configuration, a hot buoyant diffusion flame burning beneath the cold fuel gas issuing from the ceiling above was naturally resulted in. A cellular flame structure, due to the inherent “Rayleigh-Taylor’’ instability of this buoyant flow configuration, was formed beneath the ceiling. The flame length (radius), temperature and heat flux distribution along the ceiling as well as characteristic inner cell size evolution of this special cellular flame were quantified experimentally for such ceiling fire of various conditions. Scaling analysis was performed to analyze the obtained parameters of the cellular flame structure and thermal characteristics of the ceiling fire. Results showed that the overall length (radius) of the cellular flame has a 2/5 power dependence on heat release rate and is independent of burner sizes and fuel types. Temperature profile and heat flux distribution for various conditions can be universally expressed as a function of L/Rf, the distance from the burner center normalized by the flame length. The characteristic cell size of the cellular flame was related to temperature, which can be well represented by a 2.33 power function based on the “Rayleigh-Taylor’’ instability scaling analysis. The cell size spatial evolution inside the cellular flame was self-similar corresponding to the dependence of temperature on relative position, and a non-dimensional function was obtained. This study provides fundamental data and a scaling analysis into the basic physics of the cellular flame behavior and thermal characteristics of ceiling fires.

Impact of Media Heat Treatment on Cell Morphology and Stability of L. acidophilus, L. johnsonii and L. delbrueckii subsp. delbrueckii during Fermentation and Processing

Manufacturers of starter cultures and probiotics aim to provide preparations with the highest possible amount of living cells and assurance of long-term storage stability. Thereby the industrial economy and thus an efficient outcome of the processes is of utmost importance. Earlier research has shown that the sterilization procedure of the microbial culture medium tremendously impacts growth performance of heating product-sensitive Lactobacillus strains. Thus, three different strains, i.e., L. acidophilus NCFM, L. johnsonii La-2801 and L. delbrueckii subsp. delbrueckii La-0704, were investigated for the influence of media heat pretreatment on cell morphology and stability during fermentation and further freeze drying and storage. The data indicate a relationship between the heating time of the culture medium, which is associated with an increase in browning reactions, and the cultural characteristics of the three strains. The resulting characteristic cell sizes of the cultures could be a major reason for the different stability properties during processing and storage that were observed. Besides the obvious relevance of the results for the production of starter cultures and probiotics, the pleomorphic phenomenon described here could also be a subject for other biotechnological processes, where heat-mediated media conversions, and thereby related cellular effects, could be a topic. Future studies have to show if further functional properties are influenced by the cell morphology and which cellular mechanisms lead to the observed pleomorphism.

Blood cell morphometry and leukocyte-thrombocyte profile of indigenous chicken Sikhar of Mizoram

The study revealed age-wise variation in size and number of blood cells of indigenous chicken. The size of erythrocyte was recorded highest at 4 months of age, while TLC declined gradually with age. Size and number of lymphocytes decreased in adults while the reverse was true for heterophils. TTC remained stable till 8 months and declined at 10 months while length and width of thrombocytes increased till 6 months and declined gradually till 10 months. Sikhar chicken appeared to possess characteristic blood cell size and number with the stage of life and different physiological state. Blood cells showed adaptive characteristics to altitude and management.

Mechanical conditions for stable symmetric cell constriction.

Cell constriction is a decisive step for division in many cells. However, its physical pathway remains poorly understood, calling for a quantitative analysis of the forces required in different cytokinetic scenarios. Using a model cell composed by a flexible membrane (actin cortex and cell membrane) that encloses the cytoplasm, we study the mechanical conditions necessary for stable symmetric constriction under radial equatorial forces using analytical and numerical methods. We deduce that stable symmetric constriction requires positive effective spontaneous curvature, while spontaneous constriction requires a spontaneous curvature higher than the characteristic inverse cell size. Surface tension reduction (for example by actin cortex growth and membrane trafficking) increases the stability and spontaneity of cellular constriction. A reduction of external pressure also increases stability and spontaneity. Cells with prolate lobes (elongated cells) require lower stabilization forces than oblate-shaped cells (discocytes). We also show that the stability and spontaneity of symmetric constriction increase as constriction progresses. Our quantitative results settle the physical requirements for stable cytokinesis, defining a quantitative framework to analyze the mechanical role of the different constriction machinery and cytokinetic pathways found in real cells, so contributing to a deeper quantitative understanding of the physical mechanism of the cell division process.

О численной оценке эффективных характеристик периодических ячеистых структур с использованием балочных и оболочечных конечных элементов с помощью CAE Fidesys

Развитие аддитивных технологий (3D-печати) сделало возможным изготовление деталей и изделий регулярной пористой и ячеистой структуры (с целью облегчения конструкции). При этом характерный размер ячейки намного меньше масштаба целого изделия. Численные прочностные и смежные с ними расчёты подобных конструкций требуют предварительной оценки эффективных характеристик такой ячеистой структуры. В данной статье представлена методика численной оценки эффективных упругих характеристик регулярных ячеистых структур, основанная на численном решении краевых задач теории упругости на ячейке периодичности. К ячейке последовательно прикладываются различные периодические граничные условия в виде связей, наложенных на перемещения противоположных граней ячейки. Для каждого вида граничных условий решается краевая задача теории упругости, полученное в результате решения которой поле напряжений осредняется по объёму. Эффективные свойства ячеистого материала оцениваются в виде обобщённого закона Гука.В работе рассматриваются композиционные материалы на основе жёсткого решётчатого каркаса, заполненного более мягким материалом. Расчёты проводятся методом конечных элементов с помощью отечественной CAE-системы «Фидесис». При этом в ряде расчётов для моделирования решётчатого каркаса используются конечные элементы балочного типа. В некоторых расчётах, помимо каркаса и матрицы, учитывается наличие тонкого слоя связующего между ними. Этот слой моделируется при помощи конечных элементов оболочечного типа.Приводятся графики сравнения результатов расчётов композиционных материалов с решётчатым каркасом с моделированием каркаса балочными элементами и результатов аналогичных расчётов, в которых каркас моделируется трёхмерными конечными элементами. Также приводятся графики сравнения результатов расчётов, в которых слой связующего моделируется оболочечными элементами, с результатами аналогичных расчётов, в которых связующее моделируется трёхмерными элементами. Графики показывают, что при достаточно тонких элементах каркаса (либо при достаточно тонком слое связующего) результаты получаются довольно близкими, что подтверждает применимость балочных и оболочечных элементов для численного решения таких задач.

Cell Size Control in Plants.

The genetic control of the characteristic cell sizes of different species and tissues is a long-standing enigma. Plants are convenient for studying this question in a multicellular context, as their cells do not move and are easily tracked and measured from organ initiation in the meristems to subsequent morphogenesis and differentiation. In this article, we discuss cell size control in plants compared with other organisms. As seen from yeast cells to mammalian cells, size homeostasis is maintained cell autonomously in the shoot meristem. In developing organs, vacuolization contributes to cell size heterogeneity and may resolve conflicts between growth control at the cellular and organ levels. Molecular mechanisms for cell size control have implications for how cell size responds to changes in ploidy, which are particularly important in plant development and evolution. We also discuss comparatively the functional consequences of cell size and their potential repercussions at higher scales, including genome evolution.

A Visual Framework for Classifying Determinants of Cell Size

SummaryCells control their size by coordinating cell cycle progression with volume growth. Size control is typically studied at specific cell cycle transitions that are delayed or accelerated depending on size. This focus is well suited for revealing mechanisms acting at these transitions, but neglects the dynamics in other cell cycle phases, and is therefore inherently limited for studying how the characteristic cell size is determined. We address this limitation through a formalism that intuitively visualizes the characteristic size emerging from integrated cell cycle dynamics of individual cells. Applying this formalism to budding yeast, we describe the contributions of the un-budded (G1) and budded (S-G2-M) phase to size adjustments following environmental or genetic perturbations. We show that although the budded phase can be perturbed with little consequences for G1 dynamics, perturbations in G1 propagate to the budded phase. Our study provides an integrated view on cell size determinants in budding yeast.

Numerical Study on NOx Reduction in Pulse Detonation Combustion by Using Steam Injection Decoupled From Detonation Development

Recently, the focus has been laid on the characteristics of pollutant emissions from pulse detonation combustion (PDC). Initial studies indicate possibly high nitrogen oxides (NOx) emissions, so the assessment of potential primary reduction methods is advisable. The present work considers the following reduction methods: lean combustion, nitrogen and steam dilution, as well as flue gas recirculation. Since such changes in the combustion mixture reduce its reactivity and thus detonability, they can impair a reliable operation in technical systems. In order to explore the potential and limitations of each of these reduction methods, they are compared for mixtures featuring an identical characteristic detonation cell size at given initial conditions. Furthermore, building upon the use of steam dilution, a modified method to add steam to the combustible mixture is investigated. In order to avoid the strong reduction of mixture detonability by steam addition and ensure a robust detonation formation, steam is injected into the already developed detonation front. It was found that, for sufficiently even steam distribution, NOx reduction comparable to a premixed dilution could be achieved. This approach enables the realization of NOx reduction in PDC also for such conditions, for which premix dilution is not feasible. Therefore, combining the premix dilution with postshock injection offers a promising strategy to substantially reduce NOx emissions from PDC, while at the same time ensuring its reliable operation.

Size Laws and Division Ring Dynamics in Filamentous Escherichia coli cells

Our understanding of bacterial cell size control is based mainly on stress-free growth conditions in the laboratory [1-10]. In the real world, however, bacteria are routinely faced with stresses that produce long filamentous cell morphologies [11-28]. Escherichia coli is observed to filament in response to DNA damage [22-25], antibiotic treatment [11-14, 28], host immune systems [15, 16], temperature [17], starvation [20], and more [18, 19, 21], conditions which are relevant to clinical settings and food preservation[26]. This shape plasticity is considered a survival strategy [27]. Size control in this regime remains largely unexplored. Here we report that E.coli cells use a dynamic size ruler to determine division locations combined with an adder-like mechanism to trigger divisions. As filamentous cells increase in size due to growth, or decrease in size due to divisions, its multiple Fts division rings abruptly reorganize to remain one characteristic cell length away from the cell pole and two such length units away from each other. These rules can be explained by spatiotemporal oscillations of Min proteins. Upon removal of filamentation stress, the cells undergo asequence of division events, randomly at one of the possible division sites, on average after the time required to grow one characteristic cell size. These results indicate that E.coli cells continuously keep track of absolute length to control size, suggest a wider relevance for the adder principle beyond the control of normally sized cells, and provide a new perspective on the function of the Fts and Min systems.

Senescence chips for ultrahigh-throughput isolation and removal of senescent cells.

SummaryCellular senescence plays an important role in organismal aging and age‐related diseases. However, it is challenging to isolate low numbers of senescent cells from small volumes of biofluids for downstream analysis. Furthermore, there is no technology that could selectively remove senescent cells in a high‐throughput manner. In this work, we developed a novel microfluidic chip platform, termed senescence chip, for ultrahigh‐throughput isolation and removal of senescent cells. The core component of our senescence chip is a slanted and tunable 3D micropillar array with a variety of shutters in the vertical direction for rapid cell sieving, taking advantage of the characteristic cell size increase during cellular senescence. The 3D configuration achieves high throughput, high recovery rate, and device robustness with minimum clogging. We demonstrated proof‐of‐principle applications in isolation and enumeration of senescent mesenchymal stem cells (MSCs) from undiluted human whole blood, and senescent cells from mouse bone marrow after total body irradiation, with the single‐cell resolution. After scale‐up to a multilayer and multichannel structure, our senescence chip achieved ultrahigh‐throughput removal of senescent cells from human whole blood with an efficiency of over 70% at a flow rate of 300 ml/hr. Sensitivity and specificity of our senescence chips could be augmented with implementation of multiscale size separation, and identification of background white blood cells using their cell surface markers such as CD45. With the advantages of high throughput, robustness, and simplicity, our senescence chips may find wide applications and contribute to diagnosis and therapeutic targeting of cellular senescence.

Fatigue tests results of blade steels with modified surface

The paper presents the results of metallographic studies and fatigue tests of blade steel 12kH13 and EI961samples with modified nearsurface layer. Fatigue tests and studies of the samples with the modified layer were carried out using the research equipment URI (unique research installation) “Hydroshock rig Erosion-M” of NRU “MPEI”. The surface modification is found to increase the fatigue strength of blade steel up to 50%. Sample surface after modifications features a cell structure with the characteristic cell size ranging from 1÷2 μm to 4÷8 μm; total thickness of the modified layer for steel samples 12kH13 and EI961 was about 40 μm.

Observation of trampoline phenomena in 3D-printed metamaterial plates

Two dimensional phononic metamaterials, consisting of plates with resonant cylinders have been shown to attenuate waves much larger than their characteristic unit cell size by opening subwavelength band gaps. However the bandwidth of the gap correlates strongly with the resonator mass, which limits metamaterials functionality in mass sensitive applications. Trampoline phenomena have theoretically been shown to broaden the width of the first partial band gap by up to a factor 4 of the linear, resonant band gap. In this work, we provide an experimental demonstration of the trampoline phenomena in 3D-printed plates, consisting of pillars and holes, composed of a single material. We observe the opening of significant locally resonant band gaps, ≈ 30% normalized width, without adding any significant mass to the homogeneous plate. We show numerically and experimentally that trampoline plates increase both partial and full band gaps width, while reducing the base-plate’s mass by ≈30% in the studied configurations.