Regions Of Low Activity Research Articles

Interfacial local activation strategy tailoring selective zinc deposition pattern for stable zinc anodes

"Tip effect" triggered by uneven zinc deposition accelerates the growth of Zn dendrites. The unfavorable interfacial activity gradient aggravates zinc deposition at the tips, which is the root cause of zinc dendrites. This study reports an interfacial local activation strategy to reconfigure the interfacial activity gradient of zinc anode to promote more stable operation of zinc batteries. A locally activated zinc anode (Zn-ILA) is proposed as the proof-of-concept zinc anode by constructing high-active microchannels to induce preferential zinc deposition, while the remaining low-active region is accompanied by zinc epitaxial growth, thus achieving bottom-up zinc deposition at the anode interface. A fabrication method based on nanosecond pulsed laser is used to modify the zinc anode by creating high-active microchannels through thermal impingement. Additionally, low-active regions covered by dense ZnO nanoparticles are also formed due to the plasma effect. The laser-induced cross-scale oxide layers help improve the corrosion resistance at the full zinc anode interface. The proposed interfacial local activation strategy enables ordered selective deposition at the Zn-ILA interface owing to the activity gradient, as well as stabilizes the long-term operation of symmetric and full cells. The effectiveness of Zn-ILA is also validated in large-area pouch batteries, showing great potential for large-scale energy storage systems.

Migration and Separation of Polymers in Nonuniform Active Baths.

Polymerlike structures are ubiquitous in nature and synthetic materials. Their configurational and migration properties are often affected by crowded environments leading to nonthermal fluctuations. Here, we study an ideal Rouse chain in contact with a nonhomogeneous active bath, characterized by the presence of active self-propelled agents which exert time-correlated forces on the chain. By means of a coarse-graining procedure, we derive an effective evolution for the center of mass of the chain and show its tendency to migrate toward and preferentially localize in regions of high and low bath activity depending on the model parameters. In particular, we demonstrate that an active bath with nonuniform activity can be used to separate efficiently polymeric species with different lengths and/or connectivity.

Mean-field solution of the neural dynamics in a Greenberg-Hastings model with excitatory and inhibitory units.

We present a mean-field solution of the dynamics of a Greenberg-Hastings neural network with both excitatory and inhibitory units. We analyze the dynamical phase transitions that appear in the stationary state as the model parameters are varied. Analytical solutions are compared with numerical simulations of the microscopic model defined on a fully connected network. We found that the stationary state of this system exhibits a first-order dynamical phase transition (with the associated hysteresis) when the fraction of inhibitory units f is smaller than some critical value f_{t}≲1/2, even for a finite system. Moreover, any solution for f<1/2 can be mapped to a solution for purely excitatory systems (f=0). In finite systems, when the system is dominated by inhibition (f>f_{t}), the first-order transition is replaced by a pseudocritical one, namely a continuous crossover between regions of low and high activity that resembles the finite size behavior of a continuous phase transition order parameter. However, in the thermodynamic limit (i.e., infinite-system-size limit), we found that f_{t}→1/2 and the activity for the inhibition dominated case (f≥f_{t}) becomes negligible for any value of the parameters, while the first-order transition between low- and high-activity phases for f<f_{t} remains.

A UK MW catalogue derived from coda envelopes

Summary The United Kingdom (UK) experiences low-to-moderate levels of seismicity; only 12 onshore earthquakes with local magnitude (ML) ≥ 4.0 have been recorded in the past 20 years. It is therefore difficult to estimate moment magnitude (MW) using conventional moment tensor inversion for the majority of UK seismicity, resulting in limited reliable estimates of MW. To address this, we calibrated coda envelopes at 16 broadband seismic stations distributed across the UK, to produce a MW catalogue for 100 events with MW≥2.13 that occurred since 2006. This was achieved using the open-source Coda Calibration Tool, which requires independent source parameter estimates for calibration. For 13 UK events between 2006 and 2022, we used spectral modelling to estimate apparent stress (0.32 to 1.74 MPa), and moment tensor inversion to estimate MW (3.35 to 4.52). These independent source parameters formed a subset of the inputs into the final calibration, which used seismic data from 33 events with coda-derived values of 2.57$\le $Mw$\le $4.49. The resultant coda calibration parameters were applied to 67 further events (MW≥2.13). The coda envelopes exhibit slow seismic coda decay across the UK, with significant energy up to 20 Hz, consistent with other regions of low tectonic activity. This MW catalogue, and the application of the calibration to future UK seismic events, will be useful for both assessing seismic hazard and event characterisation.

Colloidal transport by light induced gradients of active pressure

Active fluids, like all other fluids, exert mechanical pressure on confining walls. Unlike equilibrium, this pressure is generally not a function of the fluid state in the bulk and displays some peculiar properties. For example, when activity is not uniform, fluid regions with different activity may exert different pressures on the container walls but they can coexist side by side in mechanical equilibrium. Here we show that by spatially modulating bacterial motility with light, we can generate active pressure gradients capable of transporting passive probe particles in controlled directions. Although bacteria swim faster in the brighter side, we find that bacteria in the dark side apply a stronger pressure resulting in a net drift motion that points away from the low activity region. Using a combination of experiments and numerical simulations, we show that this drift originates mainly from an interaction pressure term that builds up due to the compression exerted by a layer of polarized cells surrounding the slow region. In addition to providing new insights into the generalization of pressure for interacting systems with non-uniform activity, our results demonstrate the possibility of exploiting active pressure for the controlled transport of microscopic objects.

Force-free and autonomous active Brownian ratchets (a)

Autonomous active Brownian ratchets rectify active Brownian particle motion solely by means of a spatially modulated but stationary activity, without external forces. We argue that such ratcheting requires at least a two-dimensional geometry. The underlying principle is similar to the ratcheting induced by steric obstacles in microswimmer baths: suitably polarized swimmers get channeled, while the others get trapped in low-activity regions until they lose direction. The maximum current is generally reached in the limit of large propulsion speeds, in which the rectification efficiency vanishes. Maximum efficiency is attained at intermediate activities and numerically found to be on the order of a few percent, for ratchets with simple wedge-shaped low-activity regions.

Mapping glycine uptake and its metabolic conversion to glutathione in mouse mammary tumors using functional mass spectrometry imaging.

Although glutathione plays a key role in cancer cell viability and therapy response there is no clear trend in relating the level of this antioxidant to clinical stage, histological grade, or therapy response in patient tumors. The likely reason is that static levels of glutathione are not a good indicator of how a tissue deals with oxidative stress. A better indicator is the functional capacity of the tissue to maintain glutathione levels in response to this stress. However, there are few methods to assess glutathione metabolic function in tissue. We have developed a novel functional mass spectrometry imaging (fMSI) method that can map the variations in the conversion of glycine to glutathione metabolic activity across tumor tissue sections by tracking the fate of three glycine isotopologues administered in a timed sequence to tumor-bearing anesthetized mice. This fMSI method generates multiple time point kinetic data for substrate uptake and glutathione production from each spatial location in the tissue. As expected, the fMSI data shows glutathione metabolic activity varies across the murine 4T1 mammary tumor. Although glutathione levels are highest at the tumor periphery there are regions of high content but low metabolic activity. The timed infusion method also detects variations in delivery of the glycine isotopologues thereby providing a measure of tissue perfusion, including evidence of intermittent perfusion, that contributes to the observed differences in metabolic activity. We believe this new approach will be an asset to linking molecular content to tissue function.

Active colloidal molecules in activity gradients.

We consider a rigid assembly of two active Brownian particles, forming an active colloidal dimer, in a gradient of activity. We show analytically that depending on the relative orientation of the two particles the active dimer accumulates in regions of either high or low activity, corresponding to, respectively, chemotaxis and antichemotaxis. Certain active dimers show both chemotactic and antichemotactic behavior, depending on the strength of the activity. Our coarse-grained Fokker-Planck approach yields an effective potential, which we use to construct a nonequilibrium phase diagram that classifies the dimers according to their tactic behavior. Moreover, we show that for certain dimers a higher persistence of the motion is achieved similar to the effect of a steering wheel in macroscopic devices. This work could be useful for designing autonomous active colloidal structures which adjust their motion depending on the local activity gradients.

A Multiobjective Comparative Analysis of Reconstruction Algorithms in the Context of Low-Statistics 90Y-PET Imaging

The popularity of yttrium-90 ( <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">90</sup> Y) PET is growing. However, due to the very low branching ratio of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">90</sup> Y ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.2\times 10^{-5}$ </tex-math></inline-formula> ), images reconstructed are characterized by a high noise level and positive bias in low-activity regions. To overcome this problem, some algorithms use penalized reconstructions, and others allow for negative values in the image. Recently, a post-processing method has also been proposed that removes the induced negative values while maintaining bias reduction. The work presented in this article aims to evaluate and compare these methods to guide the reader in the choice of the best-suited reconstruction algorithm and associated parameters. First, several algorithms were tested using experimental phantom data. Pareto fronts and Pareto sets from the multiobjective optimization formalism were used for the comparison. Next, a dosimetric study (using phantom and patient data) was conducted to assess the final impact of these algorithms. The lowest biases were reached by unconstrained algorithms. When compared to penalized algorithms, the latter allowed for noise reduction at a fixed level of bias, with the best results obtained using a penalty based on relative differences. A good compromise between noise and bias could be reached by combining penalty, early stopping of iterative algorithms, unconstrained algorithms, and post-processing.

CHINGIZ EARTHQUAKE on January 20, 2015, KR=12.2, mb=5.6, I_0^P=5–6 NEAR the SEMIPALATINSK POLYGON (Eastern Kazakhstan)

The work presents the results of data analysis of the earthquake on January 20, 2015, mb=5.6 occurred at the low-active region of Eastern Kazakhstan near the border of the former Semipalatinsk Test Site. The work briefly describes the seismicity of the Semipalatinsk Test Site related to aseismic regions according to the acting map of general seismic zoning. The earthquake was recorded by permanent seismic stations of the Institute of Geophysical Research of the Ministry of Energy of the Republic of Kazakhstan and by two strong-motion accelerometers. The earthquake was felt at distances up to 300 km from the epicentre, its maximum intensity was noted at Medeu settlement where the shaking intensity was 56 by the MSK-64 scale. The earthquake focal mechanism is shown, the parameters of seismic effects and response spectra are calculated.

SUMOylation Potentiates ZIC Protein Activity to Influence Murine Neural Crest Cell Specification.

The mechanisms of neural crest cell induction and specification are highly conserved among vertebrate model organisms, but how similar these mechanisms are in mammalian neural crest cell formation remains open to question. The zinc finger of the cerebellum 1 (ZIC1) transcription factor is considered a core component of the vertebrate gene regulatory network that specifies neural crest fate at the neural plate border. In mouse embryos, however, Zic1 mutation does not cause neural crest defects. Instead, we and others have shown that murine Zic2 and Zic5 mutate to give a neural crest phenotype. Here, we extend this knowledge by demonstrating that murine Zic3 is also required for, and co-operates with, Zic2 and Zic5 during mammalian neural crest specification. At the murine neural plate border (a region of high canonical WNT activity) ZIC2, ZIC3, and ZIC5 function as transcription factors to jointly activate the Foxd3 specifier gene. This function is promoted by SUMOylation of the ZIC proteins at a conserved lysine immediately N-terminal of the ZIC zinc finger domain. In contrast, in the lateral regions of the neurectoderm (a region of low canonical WNT activity) basal ZIC proteins act as co-repressors of WNT/TCF-mediated transcription. Our work provides a mechanism by which mammalian neural crest specification is restricted to the neural plate border. Furthermore, given that WNT signaling and SUMOylation are also features of non-mammalian neural crest specification, it suggests that mammalian neural crest induction shares broad conservation, but altered molecular detail, with chicken, zebrafish, and Xenopus neural crest induction.

Applications of optimal nonlinear control to a whole-brain network of FitzHugh-Nagumo oscillators.

We apply the framework of optimal nonlinear control to steer the dynamics of a whole-brain network of FitzHugh-Nagumo oscillators. Its nodes correspond to the cortical areas of an atlas-based segmentation of the human cerebral cortex, and the internode coupling strengths are derived from diffusion tensor imaging data of the connectome of the human brain. Nodes are coupled using an additive scheme without delays and are driven by background inputs with fixed mean and additive Gaussian noise. Optimal control inputs to nodes are determined by minimizing a cost functional that penalizes the deviations from a desired network dynamic, the control energy, and spatially nonsparse control inputs. Using the strength of the background input and the overall coupling strength as order parameters, the network's state-space decomposes into regions of low- and high-activity fixed points separated by a high-amplitude limit cycle, all of which qualitatively correspond to the states of an isolated network node. Along the borders, however, additional limit cycles, asynchronous states, and multistability can be observed. Optimal control is applied to several state-switching and network synchronization tasks, and the results are compared to controllability measures from linear control theory for the same connectome. We find that intuitions from the latter about the roles of nodes in steering the network dynamics, which are solely based on connectome features, do not generally carry over to nonlinear systems, as had been previously implied. Instead, the role of nodes under optimal nonlinear control critically depends on the specified task and the system's location in state space. Our results shed new light on the controllability of brain network states and may serve as an inspiration for the design of new paradigms for noninvasive brain stimulation.

Chemotaxis of Cargo-Carrying Self-Propelled Particles.

Active particles with their characteristic feature of self-propulsion are regarded as the simplest models for motility in living systems. The accumulation of active particles in low activity regions has led to the general belief that chemotaxis requires additional features and at least a minimal ability to process information and to control motion. We show that self-propelled particles display chemotaxis and move into regions of higher activity if the particles perform work on passive objects, or cargo, to which they are bound. The origin of this cooperative chemotaxis is the exploration of the activity gradient by the active particle when bound to a load, resulting in an average excess force on the load in the direction of higher activity. Using a new theoretical model, we capture the most relevant features of these active-passive dimers, and in particular we predict the crossover between antichemotactic and chemotactic behavior. Moreover, we show that merely connecting active particles to chains is sufficient to obtain the crossover from antichemotaxis to chemotaxis with increasing chain length. Such an active complex is capable of moving up a gradient of activity such as provided by a gradient of fuel and to accumulate where the fuel concentration is at its maximum. The observed transition is of significance to protoforms of life, enabling them to locate a source of nutrients even in the absence of any supporting sensomotoric apparatus.

Early age hydration, rheology and pumping characteristics of CSA cement-based 3D printable concrete

Calcium sulfoaluminate (CSA) cement is one of the promising low-CO2 alternate binder systems that could replace Portland cement in a variety of applications. In the current study, the feasibility of using CSA cement as a binder for 3D printable concrete was investigated. Very short open time due to the rapid hydration and high plastic viscosity are identified as critical issues in using CSA cement. In this study, the effectiveness of two retarders, (borax and gluconate) on the early age hydration of the CSA cement mixture was investigated using a combination of isothermal calorimetry, ultrasonic pulse velocity measurements, and 1-day compressive strength and compared with a reference Portland cement (PC) mixture. Gluconate, although effective in increasing the open time, significantly affects the early age compressive strength development. Borax, on the other hand, provides a region of low thermal activity to ensure the sufficiently long open time, and thereafter the hydration resumes to reach a compressive strength similar to that of the non-retarded CSA mixture. Although the CSA and PC mixtures showed similar rheological properties for the lubricating layer, the pumping pressure required was higher for the CSA mixture as compared to the PC mixture due to the high plastic viscosity of the bulk material. However, it was observed that partial substitution of CSA with limestone powder could decrease the plastic viscosity of the bulk material and result in reduced pumping pressure. Finally, the buildability of the different mixtures was also evaluated based on the critical failure height. The CSA-limestone mixtures showed increased buildability as compared to the PC mixture, which can be explained based on the trend observed in the growth of P-wave velocity at early ages.

Formation of the CenH3-Deficient Holocentromere in Lepidoptera Avoids Active Chromatin

Despite the essentiality for faithful chromosome segregation, centromere architectures are diverse among eukaryotes1,2 and embody two main configurations: mono- and holocentromeres, referring, respectively, to localized or unrestricted distribution of centromeric activity. Of the two, some holocentromeres offer the curious condition of having arisen independently in multiple insects, most of which have lost the otherwise essential centromere-specifying factor CenH33 (first described as CENP-A in humans).4-7 The loss of CenH3 raises intuitive questions about how holocentromeres are organized and regulated in CenH3-lacking insects. Here, we report the first chromatin-level description of CenH3-deficient holocentromeres by leveraging recently identified centromere components6,7 and genomics approaches to map and characterize the holocentromeres of the silk moth Bombyx mori, a representative lepidopteran insect lacking CenH3. This uncovered a robust correlation between the distribution of centromere sites and regions of low chromatin activity along B.mori chromosomes. Transcriptional perturbation experiments recapitulated the exclusion of B.mori centromeres from active chromatin. Based on reciprocal centromere occupancy patterns observed along differentially expressed orthologous genes of Lepidoptera, we further found that holocentromere formation in a manner that is recessive to chromatin dynamics is evolutionarily conserved. Our results help us discuss the plasticity of centromeres in the context of a role for the chromosome-wide chromatin landscape in conferring centromere identity rather than the presence of CenH3. Given the co-occurrence of CenH3 loss and holocentricity in insects,7 we further propose that the evolutionary establishment of holocentromeres in insects was facilitated through the loss of a CenH3-specified centromere.

Evolution of strange and multi-strange hadron production with relative transverse multiplicity activity in underlying event

In this work, the relative Underlying event (UE) transverse multiplicity activity classifier (R_mathrm{{T}}) is used to study the strange and multi-strange hadron production in proton-proton collisions. Our study with R_mathrm{{T}} would allow to disentangle these particles, which are originating from the soft and hard QCD processes. We have used the PYTHIA 8 Monte-Carlo (MC) with a different implementation of color reconnection and rope hadronization models to demonstrate the proton-proton collisions data at sqrt{s}~= 13 TeV. The relative production of strange and multi-strange hadrons are discussed extensively in low and high transverse activity regions. In this contribution, the relative strange hadron production is enhanced with increasing R_mathrm{{T}}. This enhancement is significant for the strange baryons as compared to mesons. In addition, the particle ratios as a function of R_mathrm{{T}}~confirm the baryon enhancement in new Color Reconnection (newCR), whereas the Rope model confirms the baryon enhancement only with strange quark content. Experimental confirmation of such results will provide more insight into the soft physics in the transverse region, which will be useful to investigate various tunes based on hadronization and color reconnection schemes.

Evidence of strong electron-phonon interaction in a GaN-based quantum cascade emitter

Abstract We present a GaN-based quantum-cascade device whose inter-subband emission shows strong electron-phonon interaction. To generate the luminescence, an external electrical field – which partially screened the internal polarization – had to be applied. In low intensity spectra, a pattern of secondary peaks occurs. Each side-peak is separated from its fundamental inter-subband transition by a characteristic phonon energy, which shifts with applied field at the same rate as the main transition. At high intensity, there exists resonance between the 92 meV LO-phonon and the vertical inter-subband transition. A strong electrical field of >1 MV cm−1 reduced via QCSE the transition energy from 230 meV to 80 meV. Additionally, the low active region doping necessitated large operating voltages. Besides the emission of mid-infrared radiation, the elevated voltage generated lots of phonons. At an electrical field of 1.02 MV cm−1, the frequency-shifted inter-subband luminescence became resonant with the LO-phonon. The effects of this resonance will be discussed.

Local-Mean Preserving Post-Processing Step for Non-Negativity Enforcement in PET Imaging: Application to 90Y-PET

In a low-statistics PET imaging context, the positive bias in regions of low activity is a burning issue. To overcome this problem, algorithms without the built-in non-negativity constraint may be used. They allow negative voxels in the image to reduce, or even to cancel the bias. However, such algorithms increase the variance and are difficult to interpret since the resulting images contain negative activities, which do not hold a physical meaning when dealing with radioactive concentration. In this paper, a post-processing approach is proposed to remove these negative values while preserving the local mean activities. Its original idea is to transfer the value of each voxel with negative activity to its direct neighbors under the constraint of preserving the local means of the image. In that respect, the proposed approach is formalized as a linear programming problem with a specific symmetric structure, which makes it solvable in a very efficient way by a dual-simplex-like iterative algorithm. The relevance of the proposed approach is discussed on simulated and on experimental data. Acquired data from an yttrium-90 phantom show that on images produced by a non-constrained algorithm, a much lower variance in the cold area is obtained after the post-processing step, at the price of a slightly increased bias. More specifically, when compared with the classical OSEM algorithm, images are improved, both in terms of bias and of variance.

High temperature oxidation of NiCrAlY coated Alloy 625 manufactured by selective laser melting

The high temperature oxidation of fully SLM-processed NiCrAlY coated Alloy 625 parts was investigated between 800 °C and 1000 °C. For comparison, bulk NiCrAlY and bulk Alloy 625 were also fabricated using SLM. Two thin layers of NiCrAlY powder were lasered at the surface of Alloy 625 to form the bi-materials. Bulk NiCrAlY and bi-materials showed an improved oxidation behavior compared to Alloy 625. The oxidation of the NiCrAlY coating results in regions with a dense and continuous external Al2O3 layer and regions composed of a mixture of external Cr2O3 and internal Al2O3. Large EDS maps at the surface and cross-sections of the bi-material highlighted a heterogeneous distribution of constitutive elements of the NiCrAlY coating, resulting in some regions with an Al activity lower than the one required for the formation of a continuous and dense Al2O3 layer (≤10 atomic percent). Low Al activity and high Al activity regions were related to the topography of the SLMed surface and correspond to hill and valley regions, respectively. In addition, cracks, mainly occurring in high Al activity regions, were observed across NiCrAlY specimens. The fabrication of coated but small components with a brittle coating by SLM is not trivial and needs further investigations.

Reactive VOC Production from Photochemical and Heterogeneous Reactions Occurring at the Air-Ocean Interface.

The ocean surface serves as a source and sink for a diverse set of reactive trace gases in the atmosphere, including volatile organic compounds (VOCs), reactive halogens, and oxidized and reduced nitrogen compounds. The exchange of reactive trace gases between the atmosphere and ocean has been shown to alter atmospheric oxidant concentrations and drive particle nucleation and growth. Uncertainties in cloud radiative forcing and aerosol-cloud interactions are among the largest uncertainties in current global climate models. Climate models are particularly sensitive to cloud cover over the remote ocean due to large changes in albedo between the ocean surface and cloud tops. Oceanic emissions contribute to cloud condensation nuclei concentrations, either through the direct emission of particles during wave breaking or through the formation of secondary aerosol particles following the emission of reactive gas-phase compounds. Despite generally small and diffuse oceanic emission rates for reactive trace gases, it has been shown that oxidant and particle number concentrations are acutely sensitive to air-sea trace gas exchange rates and the chemical composition of emitted species. To date, field measurements of air-sea reactive gas exchange have focused primarily on the emission of gases of biological origin, such as dimethyl sulfide (DMS). While DMS emissions are relatively well constrained, the gas-phase oxidation that connects DMS to sulfate aerosol is less well understood. Recent laboratory measurements suggest that heterogeneous and photochemical reactions occurring at the air-sea interface can also lead to the production and emission of a wide array of reactive VOC. When laboratory-based measurements are used to derive global scale emissions, the calculated sea-to-air fluxes of reactive VOC generated from heterogeneous and photochemical processes are comparable or larger in magnitude to the sea-to-air flux of DMS. It is not yet clear how the mechanisms proposed in these laboratory experiments translate to atmospheric conditions. The proposed abiotic emissions are also a potential source of VOC in regions of low biological activity, which carries important implications for regional and global modeling.This Account reviews recent laboratory and field experiments of biotic and abiotic ocean VOC emissions, with a specific focus on exploring open questions related to proposed abiotic reactive VOC emissions and the impact of including a large, abiotic VOC emission source on atmospheric oxidants and aerosol particles. To date, abiotic emissions are not typically included in global chemical transport models. The proposed abiotic emissions mechanisms discussed here have the potential to drive significant changes to current understanding of chemistry in the marine atmosphere if present at the magnitudes suggested by laboratory studies. In order to validate their proposed significance, a coordinated set of laboratory, field, and modeling studies under ocean-relevant conditions are necessary.