Effect Of Local Concentration Research Articles

Migration of particles suspended in yield stress fluids: Insights from numerical simulation of pipe flow of 3D printable concrete

In this work, we present a numerical model to analyse particle migration and its impact on local rheological properties when a high-yield stress suspension like 3D printable concrete is transported through a narrow circular pipe. The particle migration is studied through the lens of suspension rheology, where the effect of local particle concentration on rheological properties is accounted for using Krieger–Dougherty-type models. 3D printable mixtures with different aggregate-to-binder (a/b) ratios and flows at various discharge rates are evaluated. It is observed that, depending on the discharge rate and a/b ratio, the flow behaviour could deviate from that expected in a Poiseuille flow of Bingham fluid owing to shear-induced particle migration. Interestingly, as a consequence of particle migration, the formation of a local unsheared region close to the pipe wall is observed, apart from the plug zone at the pipe centre in the partially unsheared pipe flow of Bingham fluids. Often, for concrete pipe flow simulation, the particle size is not small enough to warrant local treatment since the finite size of the particle is not fully reflected in the flow domain. In this work, the developed numerical model is also extended to account for the finite particle size to study the transition between the sheared and unsheared regions and assess the effect of considering finite size in our simulation. Finally, the model’s capability to predict global pressure loss in pipe flow is assessed through comparisons with experimental results.

TGF-β1 mediates tumor immunosuppression aggravating at the late stage post-high-light-dose photodynamic therapy.

Photodynamic therapy (PDT) is an emerging clinical treatment that is expected to become an important adjuvant strategy for the immunotherapeutic cancer treatment. Recently, numerous works have reported combination strategies. However, clinical data showed that the anti-tumor immune response of PDT was not lasting though existing. The immune activation effect will eventually turn to immunosuppressive effect and get aggravated at the late stage post-PDT. So far, the mechanism is still unclear, which limits the design of specific correction strategies and further development of PDT. Several lines of evidence suggest a role for TGF-β1 in the immunosuppression associated with PDT. Herein, this study systematically illustrated the dynamic changes of immune states post-PDT within the tumor microenvironment. The results clearly demonstrated that high-light-dose PDT, as a therapeutic dose, induced early immune activation followed by late immunosuppression, which was mediated by the activated TGF-β1 upregulation. Then, the mechanism of PDT-induced TGF-β1 accumulation and immunosuppression was elucidated, including the ROS/TGF-β1/MMP-9 positive feedback loop and CD44-mediated local amplification, which was further confirmed by spatial transcriptomics, as well as by the extensive immune inhibitory effect of local high concentration of TGF-β1. Finally, a TGF-β blockade treatment strategy was presented as a promising combinational strategy to reverse high-light-dose PDT-associated immunosuppression. The results of this study provide new insights for the biology mechanism and smart improvement approaches to enhance tumor photodynamic immunotherapy.

Market concentration, trade exposure, and firm productivity in developing countries: Evidence from Mexico

To show how local market concentration affects firm productivity, we exploit a rare database for developing-country standards consisting of five rounds of the Mexican Manufacturing Census and geographically disaggregated data on sectoral exports. Our estimates show that a decline by 10 points in the Herfindahl-Hirschman index, a measure of market concentration, explains an increase by 1 percent in the total factor productivity (TFP) of revenue. We also find that greater exposure to trade offsets and, in most cases, reverses the negative effects of local concentration on productivity. Our heterogeneity analysis also shows that informal firms exhibit a higher probability of exiting the market if competitive pressure and exposure to international markets increase and that firms in the southern region of the country would benefit the most from higher competition and exposure to international markets.

Modelling of hydrogen-assisted damage at the deforming single crystal crack-tip

A coupled framework of dislocation density-based crystal plasticity model and slip-rate based hydrogen transport model is developed to simulate hydrogen-assisted damage at the deforming crack-tip. Chemical potential-based boundary conditions and mobile dislocation-assisted hydrogen transport account for the evolving hydrogen concentration. A novel fracture indicator parameter is proposed to quantify the damage that considers the combined effect of local hydrogen concentration, accumulated plastic slip and stress triaxiality. Experimentally-informed critical value for hydrogen concentration is considered to model the crack initiation. Depending on the crystal orientation, the damage is shown to be associated either with an individual hydrogen embrittlement mechanism (hydrogen-enhanced localized plasticity, and hydrogen-enhanced decohesion) or their synergistic effect at the crack tip.

Investigation on the Propagation Mechanisms of a Hydraulic Fracture in Glutenite Reservoirs Using DEM

The geometry heterogeneity induced by embedded gravel can cause severe stress heterogeneity and strength heterogeneity in glutenite reservoirs, and subsequently affect the initiation and propagation of hydraulic fractures. Since the discrete element method (DEM) can accurately describe the inter-particle interactions, the macromechanical behavior of glutenite specimen can be preciously represented by DEM. Therefore, the initiation and propagation mechanisms of hydraulic fractures were investigated using a coupling seepage-DEM approach, the terminal fracture morphologies of hydraulic fractures were determined, and the effects of stress differences, permeability, and gravel strength were studied. The results show that the initiation and propagation of hydraulic fractures are significantly influenced by embedded gravel. In addition, the stress heterogeneity and strength heterogeneity induced by the gravel embedded near the wellbore increase local initiation points, causing a complicated fracture network nearby. Moreover, due to the effect of local stress heterogeneity, gravel strength, and energy concentration near the fracture tip, four interactions of attraction, deflection, penetration, and termination between propagating fractures and encountering gravel were observed.

Local concentration effect on nano-electrocatalytic CO2 reduction

Electrocatalytic CO2 reduction reaction (CO2RR) powered by renewable electricity offers an efficient way of capturing CO2 from the environment to mitigate the climate challenge and produce carbon-neutral hydrocarbon fuels. As the electrocatalysts downsize to the nanoscale, the effect of local concentration around catalysts turns to be significant for the performance of CO2 reduction. Herein, we review nanoscale local concentration effect on electrocatalytic CO2RR by summing up some recent related catalyst design strategies and their underlying mechanisms, providing a perspective for future catalyst design taking such an effect into account.

Adjusting Local CO Confinement in Porous-Shell Ag@Cu Catalysts for Enhancing C-C Coupling toward CO2 Eletroreduction.

Tuning the local confinement of reaction intermediates is of pivotal significance to promote C-C coupling for enhancing the selectivity for multicarbon (C2+) products toward CO2 electroreduction. Herein, we have gained insights into the confinement effect of local CO concentration for enhanced C-C coupling over core-shell Ag@Cu catalysts by tuning the pore diameters within porous Cu shells. During CO2 electroreduction, the core-shell Ag@Cu catalysts with an average pore diameter of 4.9 nm within the Cu shells (Ag@Cu-p4.9) exhibited the highest Faradaic efficiency of 73.7% for C2+ products at 300 mA cm-2 among the three Ag@Cu catalysts. Finite-element-method simulations revealed that the pores with a diameter of 4.9 nm in Cu conspicuously enhanced the local CO concentration. On the basis of in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy measurements, Ag@Cu-p4.9 exhibited the highest surface coverage of adsorbed CO intermediates with a linear adsorption configuration due to the confinement effect, thus facilitating C-C coupling.

Janus Cross-links in Supramolecular Networks.

Thermosets composed of cross-linked polymers demonstrate enhanced thermal, solvent, chemical, and dimensional stability as compared to their non-cross-linked counterparts. However, these often-desirable material properties typically come at the expense of reprocessability, recyclability, and healability. One solution to this challenge comes from the construction of polymers that are reversibly cross-linked. We relied on lessons from Nature to present supramolecular polymer networks comprised of cooperative Janus-faced hydrogen bonded cross-links. A triazine-based guanine-cytosine base (GCB) with two complementary faces capable of self-assembly through three hydrogen bonding sites was incorporated into poly(butyl acrylate) to create a reprocessable and recyclable network. Rheological experiments and dynamic mechanical analysis (DMA) were employed to investigate the flow behavior of copolymers with randomly distributed GCB units of varying incorporation. Our studies revealed that the cooperativity of multiple hydrogen bonding faces yields excellent network integrity evidenced by a rubbery plateau that spanned the widest temperature range yet reported for any supramolecular network. To verify that each Janus-faced motif engages in multiple cross-links, we studied the effects of local concentration of the incorporated GCB units within the polymer chain. Mechanical strength improved by colocalizing the GCB within a block copolymer morphology. This enhanced performance revealed that the number of effective cross-links in the network increased with the local concentration of hydrogen bonding units. Overall, this study demonstrates that cooperative noncovalent interactions introduced through Janus-faced hydrogen bonding moieties confers excellent network stability and predictable viscoelastic flow behavior in supramolecular networks.

Processive Enzymes Kept on a Leash: How Cellulase Activity in Multienzyme Complexes Directs Nanoscale Deconstruction of Cellulose.

Biological deconstruction of polymer materials gains efficiency from the spatiotemporally coordinated action of enzymes with synergetic function in polymer chain depolymerization. To perpetuate enzyme synergy on a solid substrate undergoing deconstruction, the overall attack must alternate between focusing the individual enzymes locally and dissipating them again to other surface sites. Natural cellulases working as multienzyme complexes assembled on a scaffold protein (the cellulosome) maximize the effect of local concentration yet restrain the dispersion of individual enzymes. Here, with evidence from real-time atomic force microscopy to track nanoscale deconstruction of single cellulose fibers, we show that the cellulosome forces the fiber degradation into the transversal direction, to produce smaller fragments from multiple local attacks (“cuts”). Noncomplexed enzymes, as in fungal cellulases or obtained by dissociating the cellulosome, release the confining force so that fiber degradation proceeds laterally, observed as directed ablation of surface fibrils and leading to whole fiber “thinning”. Processive cellulases that are enabled to freely disperse evoke the lateral degradation and determine its efficiency. Our results suggest that among natural cellulases, the dispersed enzymes are more generally and globally effective in depolymerization, while the cellulosome represents a specialized, fiber-fragmenting machinery.

Simulation Investigation on Environment-Induced Pitting Corrosion on the Metal Surface

The prediction of corrosion damage is one of effective research methods in the safety inspection of aging aircraft structures. A mathematical model for quantifying corrosion damage is used in this paper to predict the onset of corrosion on structural surfaces exposed to aggressive environments. Based on the finite difference technique, the evolution process of local pitting corrosion on the surface of aluminum alloy in the medium is simulated, which can consider the sudden onset and the randomness of pitting corrosion. The effect of local ion concentration and oxide film damage on subsequent pitting nucleation was analyzed. Based on the efficient calculation program, the effectiveness of the mathematical model is verified by the comparison between the corrosion damage morphology and the experimental data in the literature. The results show a more widespread distribution of subsequent pits because of stronger aggressive ions are released during the life cycle of active pits and the higher diffusion coefficient of the aggressive ions. The three dimensional morphology is generated by image processing method based on the gray value of the two dimensional image of pits.

Does multimarket contact affect prices in the retail fuel industry? First empirical evidence

Abstract Although multimarket competition is a fairly common characteristic in the retail fuel industry, its effect on the corresponding prices remains unexplored. By using a large dataset of service stations in Spain, a first set of empirical results for this industry is provided. It is consistently found that multimarket contact among chain stations increases prices, which adds support to the classical mutual forbearance hypothesis. However, it is further revealed that such an effect is critically dependent on the degree of concentration of each local market. Since the impact becomes more relevant in markets where concentration is lower, it also seems advisable to closely monitor these cases. Findings also suggest that, in those models where multimarket contact information is ignored, the specific effect of local concentration on prices could be significantly underestimated.

Effects of inert gas jet on the transition from deflagration to detonation in a stoichiometric methane-oxygen mixture

Detonation is an energetic combustion mode augmenting high flow momentum and thermodynamic efficiency, it has been applied in detonation engines, such as pulse detonation engines (PDEs) and rotating detonation engines (RDEs), they have become potential aerospace propulsion equipment. Recently, fluidic jet-in-cross flow (JICF) has been demonstrated experimentally and numerically that can accelerate the deflagration-to-detonation transition (DDT) process. Nonetheless, most of previous studies focused on the jets using combustible mixture or oxygen, which may bring additional risk for turbulence-generated system in detonation engines. In this study, a more safe and controllable inert gas (i.e., Ar) is applied for JICF, experiments are carried out to investigate effects of argon jet as an enhancement method on promoting the DDT in a stoichiometric methane-oxygen mixture. The effects of local argon concentration, turbulence intensity and injection position on the DDT process are systematically examined. Two-dimensional numerical simulations are also performed to elucidate the details of the injection evolution. The experimental results show that turbulence generated by the argon injection can promote flame acceleration and the onset of detonation only in the fast deflagration regime. The enhancing effect is more prominent at higher turbulence intensity by increasing jet injection pressure and shorter injection time. Too long injection duration increases argon local concentration that leads to an adverse effect prohibiting the DDT occurrence. During the initial laminar flame acceleration, referred to as the slow deflagration regime, no enhancement by the argon jet on DDT can be observed. By looking numerically at the flow structure of the argon jet, the vortical features enhance the transport and mixing between reactants and products. The interaction between the reactive travelling wave and the jet structure further induces turbulence and thus accelerates the chemical reaction rate. With the time elapsed, the injected argon entrains largely and dilutes the ambient combustible mixture, and restrains the DDT. Furthermore, a novel dimensionless criterion and a characteristic parameter Turc are proposed, quantitatively analyzing the dominate mechanism in flame propagation and the initial stage of DDT as inert jet is introduced.

The effect of ropivacaine concentration on common peroneal nerve block duration using a fixed dose: A randomised, double-blind trial in healthy volunteers.

The effect of local anaesthetic concentration on peripheral nerve block duration is unclear. Recent clinical trials found nerve blocks of equivalent duration despite changing local anaesthetic concentration but with a fixed local anaesthetic dose. A criticism of these studies is that the local anaesthetic doses used were above the proposed local anaesthetic dose-duration ceiling level, masking any potential effect of different local anaesthetic concentrations on nerve block duration. We investigated the effect of local anaesthetic concentration on nerve block duration using a fixed local anaesthetic dose below the local anaesthetic dose-duration ceiling level. We hypothesised that changing local anaesthetic concentration would affect nerve block duration. Randomised, double-blind trial. Single-centre, academic hospital. Healthy volunteers. Each participant received an ultrasound-guided common peroneal nerve block with a fixed dose of 10 mg of ropivacaine dissolved in either 2.5, 5, 10, 15 or 20 ml of 0.9% saline according to group allocation, yielding local anaesthetic concentrations of 4, 2, 1, 0.67 and 0.5 mg ml. The primary outcome was duration of sensory block defined as altered or no sensitivity to a cold stimulus. The secondary outcome was duration of motor block defined as either paresis or paralysis. Intergroup differences were tested using one-way Analysis of variance . All participants had sensory block, and 56 out of 60 participants had motor block. From the highest to the lowest concentration groups, mean ± SD sensory block durations were 13.1 ± 2.7, 13.4 ± 3.3, 12.6 ± 3.9, 10.4 ± 2.9 and 11.0 ± 2.1 h (P = 0.073), and mean ± SD motor block durations were 8.5 ± 2.0, 7.9 ± 3.0, 6.1 ± 3.1, 5.9 ± 3.5, 4.0 1.9 h (P = 0.002). In contrast to our hypothesis, we found no changes in mean sensory nerve block duration. However, local anaesthetic dilution resulted in reduced motor block duration. ClinicalTrials.gov, NCT03326609.

The Effects of Local Market Concentration and International Competition on Firm Productivity: Evidence from Mexico

Although market concentration is one of the main impediments to productivity growth globally, data constraints have limited its analysis to developed countries or cross-country studies based on definitions of market concentration across nations and industries. This paper takes advantage of a database that is unusual by developing-country standards by means of leveraging the richness of five rounds of the Mexican Manufacturing Census between 1994 and 2014. The data allow estimation of the effects of local industry concentration on productivity. The main results show that a decline by 10 points in the Herfindahl-Hirschman index (on a 0-100 scale), a measure of market concentration, explains an increase by 1 percent in the total factor productivity of revenue. Local industry concentration also has heterogeneous effects on productivity across industries, while its impact on productivity varies by level of exposure to international markets. The results here show that the effect of greater exposure to trade offsets and, in most cases, reverses the negative effects of local concentration on productivity. These results are robust to specifications based on the estimation of firm productivity using the panels of establishment data from the 2009 and 2014 rounds of the economic census, to controlling for a proxy of markups, and to the use of alternate indicators of local industry concentration.

Economics at the FCC 2018–2019: Competition, Broadband Deployment, and Transaction Review

The U.S. Federal Communications Commission is responsible for regulation in the communications marketplace and for management of the nation’s non-federal radio frequency spectrum. During the past year, Commission economists contributed to the analysis of competition in the communications marketplace as presented in the Commission’s first Communications Marketplace Report. In addition, Commission economists examined issues in the broadcast television industry and performed general and limited analyses of the effects of both national broadcast group size and local market concentration on retransmission fees. Commission economists also evaluated the current Form 477 data collection and helped to develop proposals that would improve the current data collection as well as establish a new data collection that would advance the Commission’s universal service goals. Finally, Commission economists evaluated the likely competitive effects that would be associated with the proposed T-Mobile-Sprint transaction.

On the Conversion Efficiency of CO2 Electroreduction on Gold

Benjamin A. Zhang is a PhD student at Harvard University. His research focus is on the control of mass transport and concentration gradients in electrochemical reactions, in particular CO2 reduction, through nano- and mesostructuring of electrodes. Cyrille Costentin is Professor at Universite Paris Diderot. He received his undergraduate education at Ecole Normale Superieure de Cachan and his PhD at Universite Paris Diderot. He is currently a Visiting Scientist in the group of D.G. Nocera at Harvard University. His interests include mechanisms and reactivity in electron transfer chemistry with particular emphasis on proton-coupled electron transfer and catalysis of electrochemical reactions. Daniel G. Nocera is the Patterson Rockwood Professor of Energy at Harvard University. His group studies mechanisms of biological and chemical energy conversion.

Mathematical Modeling Reveals That the Administration of EGF Can Promote the Elimination of Lymph Node Metastases by PD-1/PD-L1 Blockade.

In the advanced stages of cancers like melanoma, some of the malignant cells leave the primary tumor and infiltrate the neighboring lymph nodes (LNs). The interaction between secondary cancer and the immune response in the lymph node represents a complex process that needs to be fully understood in order to develop more effective immunotherapeutic strategies. In this process, antigen-presenting cells (APCs) approach the tumor and initiate the adaptive immune response for the corresponding antigen. They stimulate the naive CD4+ and CD8+ T lymphocytes which subsequently generate a population of helper and effector cells. On one hand, immune cells can eliminate tumor cells using cell-cell contact and by secreting apoptosis inducing cytokines. They are also able to induce their dormancy. On the other hand, the tumor cells are able to escape the immune surveillance using their immunosuppressive abilities. To study the interplay between tumor progression and the immune response, we develop two new models describing the interaction between cancer and immune cells in the lymph node. The first model consists of partial differential equations (PDEs) describing the populations of the different types of cells. The second one is a hybrid discrete-continuous model integrating the mechanical and biochemical mechanisms that define the tumor-immune interplay in the lymph node. We use the continuous model to determine the conditions of the regimes of tumor-immune interaction in the lymph node. While we use the hybrid model to elucidate the mechanisms that contribute to the development of each regime at the cellular and tissue levels. We study the dynamics of tumor growth in the absence of immune cells. Then, we consider the immune response and we quantify the effects of immunosuppression and local EGF concentration on the fate of the tumor. Numerical simulations of the two models show the existence of three possible outcomes of the tumor-immune interactions in the lymph node that coincide with the main phases of the immunoediting process: tumor elimination, equilibrium, and tumor evasion. Both models predict that the administration of EGF can promote the elimination of the secondary tumor by PD-1/PD-L1 blockade.

Gold-catalyzed Cycloisomerization Reactions within Guanidinium M12L24 Nanospheres: the Effect of Local Concentrations.

Gold‐catalyzed cycloisomerization reactions have been explored using guanidinium functionalized M12L24 nanospheres that strongly encapsulate gold complexes functionalized with a sulfonate group through hydrogen bonds. As the M12L24 nanospheres can bind up to 24 gold complexes, the effect of local catalyst concentration on the reaction outcome can be easily evaluated. Also, the guanidinium groups of the sphere can weakly interact with the carboxylic group of the substrates, facilitating the pre‐organization of the substrate near to the catalytic active site. Both effects can influence the selectivity and rate of the gold‐catalyzed transformation. Challenging acetate‐containing substrates with internal acetylene functional groups can be cyclized efficiently within the M12L24 nanospheres, where the pre‐organization of the substrate plays a crucial role. For 2‐alkynyl benzoic acids the selectivity of the reaction can be controlled by adjusting the local concentration of gold catalyst in the guanidinium functionalized M12L24 nanosphere.

Deformation twinning activity and twin structure development of pure titanium at cryogenic temperature

We compared deformation twinning activity and twin structure development of pure Ti at cryogenic temperature and room temperature by conducting unidirectional rolling at 77 K and 293 K. Twinning activity was significantly higher in rolling at 77 K than in rolling at 293 K. This was because lowering the deformation temperature increased the necessity for twinning operation to compensate for reduced accommodation of strain along the c-axis of the crystal structure, caused by inhibition of <c+a> slips. Twin structure was also entirely different between the two rolling temperatures. Compared to the case of rolling at 293 K, rolling at 77 K generated thin and numerous individual twins in the twinned grains, thereby giving rise to the development of a totally different twin structure. The differences in twin structure were caused by the combined effect of significant local stress concentration at grain boundaries and a reduction in stacking fault energy by rolling at 77 K. The twin structure strongly contributed to severe twinning-induced grain refinement that occurs at cryogenic temperature.

Integrating Proteomics and Targeted Metabolomics to Understand Global Changes in Histone Modifications

The chromatin fiber is the control panel of eukaryotic cells. Chromatin is mostly composed of DNA, which contains the genetic instruction for cell phenotype, and histone proteins, which provide the scaffold for chromatin folding and part of the epigenetic inheritance. Histone writers/erasers "flag" chromatin regions by catalyzing/removing covalent histone post-translational modifications (PTMs). Histone PTMs chemically contribute to chromatin relaxation or compaction and recruit histone readers to modulate DNA readout. The precursors of protein PTMs are mostly small metabolites. For instance, acetyl-CoA is used for acetylation, ATP for phosphorylation, and S-adenosylmethionine for methylation. Interestingly, PTMs such as acetylation can occur at neutral pH also without their respective enzyme when the precursor is sufficiently concentrated. Therefore, it is essential to differentially quantify the contribution of histone writers/erasers versus the effect of local concentration of metabolites to understand the primary regulation of histone PTM abundance. Aberrant phenotypes such as cancer cells have misregulated metabolism and thus the composition and the modulation of chromatin is not only driven by enzymatic tuning. In this review, the latest advances in mass spectrometry (MS) to analyze histone PTMs and the most adopted quantification methods for related metabolites, both necessary to understand PTM relative changes, are discussed.