Unidirectional Interactions Research Articles

Two-Photon Polymerization 3D-Printing of Micro-scale Neuronal Cell Culture Devices.

Neuronal cultures have been a reference experimental model for several decades. However, 3D cell arrangement, spatial constraints on neurite outgrowth, and realistic synaptic connectivity are missing. The latter limits the study of structure and function in the context of compartmentalization and diminishes the significance of cultures in neuroscience. Approximating ex vivo the structured anatomical arrangement of synaptic connectivity is not trivial, despite being key for the emergence of rhythms, synaptic plasticity, and ultimately, brain pathophysiology. Here, two-photon polymerization (2PP) is employed as a 3D printing technique, enabling the rapid fabrication of polymeric cell culture devices using polydimethyl-siloxane (PDMS) at the micrometer scale. Compared to conventional replica molding techniques based on microphotolitography, 2PP micro-scale printing enables rapid and affordable turnaround of prototypes. This protocol illustrates the design and fabrication of PDMS-based microfluidic devices aimed at culturing modular neuronal networks. As a proof-of-principle, a two-chamber device is presented to physically constrain connectivity. Specifically, an asymmetric axonal outgrowth during ex vivo development is favored and allowed to be directed from one chamber to the other. In order to probe the functional consequences of unidirectional synaptic interactions, commercial microelectrode arrays are chosen to monitor the bioelectrical activity of interconnected neuronal modules. Here, methods to 1) fabricate molds with micrometer precision and 2) perform in vitro multisite extracellular recordings in rat cortical neuronal cultures are illustrated. By decreasing costs and future widespread accessibility of 2PP 3D-printing, this method will become more and more relevant across research labs worldwide. Especially in neurotechnology and high-throughput neural data recording, the ease and rapidity of prototyping simplified in vitro models will improve experimental control and theoretical understanding of in vivo large-scale neural systems.

Tale of two emergent games: Opinion dynamics in dynamical directed networks.

Unidirectional social interactions are ubiquitous in real social networks whereas undirected interactions are intensively studied. We establish a voter model in a dynamical directed network. We analytically obtain the degree distribution of the evolving network at any given time. Furthermore, we find that the average degree is captured by an emergent game. However, we find that the fate of opinions is captured by another emergent game. Beyond expectation, the two emergent games are typically different due to the unidirectionality of the evolving networks. The Nash equilibrium analysis of the two games facilitates us to give the criterion under which the minority opinion with few disciples initially takes over the population eventually for in-group bias. Our work fosters the understanding of opinion dynamics ranging from methodology to research content.

Porous Crystalline Organic Cages Made by Design

AbstractShape‐persistent organic cages are an intriguing class of molecular porous materials. Through hierarchical molecular design, size and shape of the intrinsic molecular voids are controlled by dynamic covalent chemistry, while pore structure and topology are governed by noncovalent alignment in the solid state. However, the predictable and reliable crystallization of organic cages is still challenging since long‐range superstructures are solely based on weak and rather unidirectional supramolecular interactions. In this tutorial review, we provide a general classification of porous solid‐state materials and discuss specific design principles regarding the dynamic covalent reactions, the small‐molecule building blocks and solid‐state engineering. Furthermore, we introduce the most important analytical techniques for porous materials with a special focus on organic cages.

Local sign stability and its implications for spectra of sparse random graphs and stability of ecosystems

Abstract We study the spectral properties of sparse random graphs with different topologies and type of interactions, and their implications on the stability of complex systems, with particular attention to ecosystems. Specifically, we focus on the behaviour of the leading eigenvalue in different type of random matrices (including interaction matrices and Jacobian-like matrices), relevant for the assessment of different types of dynamical stability. By comparing numerical results on Erdós-Rényi and Husimi graphs with sign-antisymmetric interactions or mixed sign patterns, we propose a sufficient criterion, called strong local sign stability, for stability not to be affected by system size, as traditionally implied by the complexity-stability trade-off in conventional models of random matrices. The criterion requires sign-antisymmetric or unidirectional interactions and a local structure of the graph such that the number of cycles of finite length do not increase with the system size. Note that the last requirement is stronger than the classical local tree-like condition, which we associate to the less stringent definition of local sign stability, also defined in the paper.
In addition, for strong local sign stable graphs which show stability to linear perturbations irrespectively of system size, we observe that the leading eigenvalue can undergo a transition from being real to acquiring a nonnull imaginary part, which implies a dynamical transition from nonoscillatory to oscillatory linear response to perturbations. Lastly, we ascertain the discontinuous nature of this transition.

Screening competition and cross-feeding interactions during utilization of human milk oligosaccharides by gut microbes.

Background: The infant gut microbiome is a complex community that influences short- and long-term health. Its assembly and composition are governed by variables such as the feeding type. Breast milk provides infants an important supply of human milk oligosaccharides (HMO), a broad family of carbohydrates comprising neutral, fucosylated, and sialylated molecules. There is a positive association between HMOs and the overrepresentation of Bifidobacterium species in the infant gut, which is sustained by multiple molecular determinants present in the genomes of these species. Infant-gut-associated Bifidobacterium species usually share a similar niche and display similar HMO inclinations, suggesting they compete for these resources. There is also strong evidence of cross-feeding interactions between HMO-derived molecules and bifidobacteria. Methods: In this study, we screened for unidirectional and bidirectional interactions between Bifidobacterium and other species using individual HMO. Bifidobacterium bifidum and Bacteroides thetaiotaomicron increased the growth of several other species when their supernatants were used, probably mediated by the partial degradation of HMO. In contrast, Bifidobacterium longum subsp. infantis. supernatants did not exhibit positive growth. Results: Bifidobacterium species compete for lacto-N-tetraose, which is associated with reduced bidirectional growth. The outcome of these interactions was HMO-dependent, in which the two species could compete for one substrate but cross-feed on another. 2'-fucosyllactose and lacto-N-neotetraose are associated with several positive interactions that generally originate from the partial degradation of these HMOs. Conclusion: This study presents evidence for complex interactions during HMO utilization, which can be cooperative or competitive, depending on the nature of the HMO. This information could be useful for understanding how breast milk supports the growth of some Bifidobacterium species, shaping the ecology of this important microbial community.

The architecture of binding cooperativity between densely bound transcription factors.

The binding of transcription factors (TFs) along genomes is restricted to a subset of sites containing their preferred motifs. TF-binding specificity is often attributed to the co-binding of interacting TFs; however, apart from specific examples, this model remains untested. Here, we define dependencies among budding yeast TFs that localize to overlapping promoters by profiling the genome-wide consequences of co-depleting multiple TFs. We describe unidirectional interactions, revealing Msn2 as a central factor allowing TF binding at its target promoters. By contrast, no case of mutual cooperation was observed. Particularly, Msn2 retained binding at its preferred promoters upon co-depletion of fourteen similarly bound TFs. Overall, the consequences of TF co-depletions were moderate, limited to a subset of promoters, and failed to explain the role of regions outside the DNA-binding domain in directing TF-binding preferences. Our results call for re-evaluating the role of cooperative interactions in directing TF-binding preferences.

Customer-to-customer interactions in the sport fan context: typology, framework (C2CIF) and directions for future research

PurposeSocial factors, such as fellow spectators in a stadium or other fans sharing their experiences on online platforms, play a dominant role in spectator sport consumption. This conceptual article sets out to achieve three objectives: classify customer-to-customer (C2C) interactions in the sport fan context, develop a framework that links the classification of interactions to relevant outcomes and identify areas for related future research.Design/methodology/approachThe authors integrate conceptual and empirical contributions on C2C interactions in the service, marketing and sport management literature.FindingsThe article proposes classifying C2C interactions into synchronous multi- and uni-directional interactions as well as asynchronous multi- and uni-directional interactions. The C2C interaction framework (C2CIF) proposes that such C2C interactions have hedonic, social, symbolic and utilitarian value outcomes. It further suggests that physiological, psychological and social processes underlie the co-creation or co-destruction of value and identifies contingencies at both the fan and the brand level.Originality/valueBased on the C2CIF, we identify relevant topics for future research, in particular relating to technology-supported and virtual interactions among fans, fan-to-fan interactions across different countries and cultural backgrounds and fan-to-fan interactions as a way to reduce societal concerns.

Role of predator-prey reversal in rock-paper-scissors models

In this letter we consider a single parameter generalization of the standard three species Rock-Paper-Scissors (RPS) model allowing for predator-prey reversal. This model, which shall be referred to as κRPS model, incorporates bidirectional predator-prey interactions between all the species in addition to the unidirectional predator-prey interactions of the standard RPS model. We study the dynamics of a May-Leonard formulation of the κRPS model using lattice-based spatial stochastic simulations with random initial conditions. We find that if the simulation lattices are sufficiently large for the coexistence of all three species to be maintained, the model asymptotically leads to the formation of spiral patterns whose evolution is qualitatively similar to that of the standard RPS model, albeit with larger characteristic length and time scales. We show that if the likelihood of predator-prey reversal is sufficiently large there are two distinct scaling regimes: one transient curvature dominated regime in which the characteristic length of the population network grows with time and another where it becomes a constant. We also estimate the dependence of the asymptotic value of the characteristic length of the population network on the likelihood of predator-prey reversal and show that if the simulation lattices are not sufficiently large then predator-prey reversal could potentially have a negative impact on coexistence. Finally, we interpret these results by considering the much simpler dynamics of circular domains.

Resonance fluorescence of two asymmetrically pumped and coupled two-level systems

We study a driven-dissipative duo of two-level systems in an open quantum systems approach, modelling a pair of atoms or (more generally) meta-atoms. Allowing for complex-valued couplings in the setup, which are of both a coherent and incoherent character, gives rise to a diverse coupling landscape. We consider several points on this landscape, for example where the coupling between the two coupled two-level systems is dominated by coherent, incoherent, unsymmetrical and even unidirectional interactions. Traversing the coupling terrain leads to remarkable features in the populations of the pair, correlations and optical spectra. Most notably, the famous Mollow triplet spectrum for a single atom may be superseded for a pair by a Mollow quintuplet (or even by a spectral singlet) and the setup allows for population trapping to arise, all depending upon the precise nature of the coupling between the two-level systems.

Hypothalamic interaction with reward-related regions during subjective evaluation of foods

The reward system implemented in the midbrain, ventral striatum, orbitofrontal cortex, and ventromedial prefrontal cortex evaluates and compares various types of rewards given to the organisms. It has been suggested that autonomic factors influence reward-related processing via the hypothalamus, but how the hypothalamus modulates the reward system remains elusive. In this functional magnetic resonance imaging study, the hypothalamus was parcellated into individual hypothalamic nuclei performing different autonomic functions using boundary mapping parcellation analyses. The effective interaction during subjective evaluation of foods in a reward task was then investigated between the human hypothalamic nuclei and the reward-related regions. We found significant brain activity decrease in the paraventricular nucleus (PVH) and lateral nucleus in the hypothalamus in food evaluation compared with monetary evaluation. A psychophysiological interaction analysis revealed dual interactions between the PVH and (1) midbrain region and (2) ventromedial prefrontal cortex, with the former correlated with the stronger tendency of participants toward food-seeking. A dynamic causal modeling analysis further revealed unidirectional interactions from the PVH to the midbrain and ventromedial prefrontal cortex. These results suggest that the PVH in the human hypothalamus interacts with the reward-related regions in the cerebral cortex via multiple pathways (i.e., the midbrain pathway and ventromedial prefrontal pathway) to evaluate rewards for subsequent decision-making.

Synthetic mutualism in engineered E. coli mutant strains as functional basis for microbial production consortia.

In nature, microorganisms often reside in symbiotic co-existence providing nutrition, stability, and protection for each partner by applying "division of labor." This principle may also be used for the overproduction of targeted compounds in bioprocesses. It requires the engineering of a synthetic co-culture with distributed tasks for each partner. Thereby, the competition on precursors, redox cofactors, and energy-which occurs in a single host-is prevented. Current applications often focus on unidirectional interactions, that is, the product of partner A is used for the completion of biosynthesis by partner B. Here, we present a synthetically engineered Escherichia coli co-culture of two engineered mutant strains marked by the essential interaction of the partners which is achieved by implemented auxotrophies. The tryptophan auxotrophic strain E. coli ANT-3, only requiring small amounts of the aromatic amino acid, provides the auxotrophic anthranilate for the tryptophan producer E. coli TRP-3. The latter produces a surplus of tryptophan which is used to showcase the suitability of the co-culture to access related products in future applications. Co-culture characterization revealed that the microbial consortium is remarkably functionally stable for a broad range of inoculation ratios. The range of robust and functional interaction may even be extended by proper glucose feeding which was shown in a two-compartment bioreactor setting with filtrate exchange. This system even enables the use of the co-culture in a parallel two-level temperature setting which opens the door to access temperature sensitive products via heterologous production in E. coli in a continuous manner.

Between the Global and Regional: Asia in the Tamil Buddhist Imagination

At the turn of the nineteenth century, Madras became home to a movement that anticipated Ambedkar’s turn to Buddhism by nearly half a century. Founded in 1898, the Sakya Buddhist Society was led by Iyothee Thass (1845–1914) and became the first Dalit Buddhist revival of its kind in late colonial India. In this article, I explore the global dimensions of Sakya Buddhism through an intertextual reading of its journal, Oru Paica Tamilan, and the work of Asian Buddhists like Henry Olcott and Anagarika Dharmapala who were associated with the movement. I argue that Sakya Buddhism’s historical imaginaire of Dalits as indigenous Buddhists intersected with the political concerns that drove Asian Buddhist revivalist movements in important ways. I also show that the movement created a distinctly Tamil tradition of Buddhism for Dalits and attempted to reorient them towards the broader Buddhist world even as they had a notionally marginal presence within this landscape. In doing so, I propose the category of ‘pararegional’ as a way of thinking about seemingly uneven or unidirectional interactions between different spatial scales such as ‘global’ and ‘regional'.

RETRACTED: New interaction solutions to the (2 + 1)-dimensional Hirota–Satsuma–Ito equation

This study aims to determine novel analytical lump solutions to the (2+1)-dimensional Hirota–Satsuma–Ito equation through conducting symbolic computations using the Hirota direct method. This nonlinear model describes the propagation of unidirectional shallow-water waves and interactions of two long waves with different dispersion forms. Some informative descriptions of physical behavior related to the solutions obtained in this article have also been included through several 3D figures and 2D contour plots. The acquired results in this research may be beneficial for better understanding the interaction phenomena of localized nonlinear waves in different research fields of nonlinear science. It is notable that the use of computer algebra in the calculations required by the article is inevitable. Accordingly, in this work, we have used the symbolic package Mathematica. Our results will be meaningful for the investigation of the future development of lump solitons in many physical systems.

Evolution of cooperation with asymmetric social interactions

How cooperation emerges in human societies is both an evolutionary enigma and a practical problem with tangible implications for societal health. Population structure has long been recognized as a catalyst for cooperation because local interactions facilitate reciprocity. Analysis of population structure typically assumes bidirectional social interactions. But human social interactions are often unidirectional-where one individual has the opportunity to contribute altruistically to another, but not conversely-as the result of organizational hierarchies, social stratification, popularity effects, and endogenous mechanisms of network growth. Here we expand the theory of cooperation in structured populations to account for both uni- and bidirectional social interactions. Even though unidirectional interactions remove the opportunity for reciprocity, we find that cooperation can nonetheless be favored in directed social networks and that cooperation is provably maximized for networks with an intermediate proportion of unidirectional interactions, as observed in many empirical settings. We also identify two simple structural motifs that allow efficient modification of interaction directions to promote cooperation by orders of magnitude. We discuss how our results relate to the concepts of generalized and indirect reciprocity.

Inferring directionality of coupled dynamical systems using Gaussian process priors: Application on neurovascular systems.

Dynamical system theory has recently shown promise for uncovering causality and directionality in complex systems, particularly using the method of convergent cross mapping (CCM). In spite of its success in the literature, the presence of process noise raises concern about CCM's ability to uncover coupling direction. Furthermore, CCM's capacity to detect indirect causal links may be challenged in simulated unidrectionally coupled Rossler-Lorenz systems. To overcome these limitations, we propose a method that places a Gaussian process prior on a cross mapping function (named GP-CCM) to impose constraints on local state space neighborhood comparisons. Bayesian posterior likelihood and evidence ratio tests, as well as surrogate data analyses are performed to obtain a robust statistic for dynamical coupling directionality. We demonstrate GP-CCM's performance with respect to CCM in synthetic data simulation as well as in empirical electroencephelography (EEG) and functional near infrared spectroscopy (fNIRS) activity data. Our findings show that GP-CCM provides a statistic that consistently reports indirect causal structures in non-separable unidirectional system interactions; GP-CCM also provides coupling direction estimates in noisy physiological signals, showing that EEG likely causes, i.e., drives, fNIRS dynamics.

Metabolic dissimilarity determines the establishment of cross-feeding interactions in bacteria

The exchange of metabolites among different bacterial genotypes profoundly impacts the structure and function of microbial communities. However, the factors governing the establishment of these cross-feeding interactions remain poorly understood. While shared physiological features may facilitate interactions among more closely related individuals, a lower relatedness should reduce competition and thus increase the potential for synergistic interactions. Here, we investigate how the relationship between a metabolite donor and recipient affects the propensity of strains to engage in unidirectional cross-feeding interactions. For this, we performed pairwise cocultivation experiments between four auxotrophic recipients and 25 species of potential amino acid donors. Auxotrophic recipients grew in the vast majority of pairs tested (63%), suggesting metabolic cross-feeding interactions are readily established. Strikingly, both the phylogenetic distance between donor and recipient and the dissimilarity of their metabolic networks were positively associated with the growth of auxotrophic recipients. Analyzing the co-growth of species from a gut microbial community in silico also revealed that recipient genotypes benefitted more from interacting with metabolically dissimilar partners, thus corroborating the empirical results. Together, our work identifies the metabolic dissimilarity between bacterial genotypes as a key factor determining the establishment of metabolic cross-feeding interactions in microbial communities.

Overcoming the complexity barrier of the dynamic message-passing method in networks with fat-tailed degree distributions.

The dynamic cavity method provides the most efficient way to evaluate probabilities of dynamic trajectories in systems of stochastic units with unidirectional sparse interactions. It is closely related to sum-product algorithms widely used to compute marginal functions from complicated global functions of many variables, with applications in disordered systems, combinatorial optimization, and computer science. However, the complexity of the cavity approach grows exponentially with the in-degrees of the interacting units, which creates a defacto barrier for the successful analysis of systems with fat-tailed in-degree distributions. In this paper, we present a dynamic programming algorithm that overcomes this barrier by reducing the computational complexity in the in-degrees from exponential to quadratic, whenever couplings are chosen randomly from (or can be approximated in terms of) discrete, possibly unit-dependent, sets of equidistant values. As a case study, we analyze the dynamics of a random Boolean network with a fat-tailed degree distribution and fully asymmetric binary ±J couplings, and we use the power of the algorithm to unlock the noise-dependent heterogeneity of stationary node activation patterns in such a system.

Equity market-related economic uncertainty and the “economic contagion phenomenon”

PurposeThis study examines potential causal interactions between a dominant economy and its trading partners, with the view of verifying surmised economic contagion effects traditionally presumed to emanate from dominant economies toward trading partners.Design/methodology/approachThe study used the Toda–Yamamoto Wald test approach to bi-variate causality analysis.FindingsThis study verified the existence of the economic contagion phenomenon; Estimated empirical evidence failed to fully support the presumption that such contagion effects mostly emanates from dominant economies toward trading partners, all things being equal. For instance, although this study found significant economic contagion effects emanating from the US economy toward the Chinese economy, the authors also detected six different uni-directional causal interactions with the direction of causality emanating from trading partners toward the US economy.Originality/valueThe uniqueness of this study stems not from its verification of the economic contagion phenomenon using equity market-related economic uncertainty as the potential contagion. This study fills a gap in the present literature by focusing on the happenings in the equity market as the potential candidate of the economic contagion phenomenon between a dominant economy and its key trading partners.

An Efficient Vector Hysteresis Model for Unidirectional Magneto-Elastic Interactions

Utilization of magneto-elastic materials has been recently on the rise especially in applications involving linear actuators, sensors, and energy harvesting. There is no doubt, though, that precise magneto-elastic models capable of correlating the coupled nonlinear and history dependent mechanical and magnetic components are crucial for the design and construction of devices related to the aforementioned applications. In the past, several efforts have been carried out toward the enhancement of accuracy and computational efficiency of relevant magnetostriction models. In this article, a novel approach to the modeling of unidirectional magneto-elastic interactions is presented. This approach capitalizes on the physical fact that an applied mechanical stress along a magnetized rod axial direction results in off-axis domain rotation. The approach employs a superposition of vector magnetic hysteresis models where x- and y-axes inputs are correlated with the applied magnetic field and a mapping of the mechanical stress. The corresponding x- and y-axes outputs represent the magnetic flux density and mechanical strain, simultaneously. To check the validity of the proposed approach, model identification was carried out for a Terfenol rod material. Simulations were performed and compared with experimental measurements involving different field-stress variations. Experimental validation results demonstrate the good qualitative and quantitative agreement of the model output with experimental measurements. Theoretical and computational details of the proposed model, its identification, and comparisons with experimentally measured data are given in this article.

Landscape dynamics and human-environment interactions in the northern foothills of Cho Oyu and Mount Everest (southern Tibet) during the Late Pleistocene and Holocene

Here we present an integrated earth surface process and paleoenvironmental study from the Tingri graben and the archaeological site of Su-re, located on the southern rim of the Tibetan plateau, spanning the past ca. 30 ka. The study area is characterized by cold climate earth surface processes and aridity due to its altitude and location in the rain shadow of the Mount Everest–Cho Oyu massif and is thus sensitive to climatic and anthropogenic perturbations. In this highly dynamic geomorphic environment, paired-cosmogenic nuclide results from boulders on a massive hummocky moraine in the southern Tingri graben reveal complex exposure histories that limit our capability of directly dating the corresponding glacial advance, and shed a note of caution on previously published single-nuclide-based exposure ages along the northern Himalaya. Based on geomorphic considerations, however, the moraine clearly represents the local last glacial maximum, and likely coincided with a ∼344 ± 109 m drepression of discontinuous permafrost zone relative to today during the global last glacial maximum (gLGM). This greatly intensified permafrost and periglacial hillslope processes and led to fluvial aggradation of the valley floors of ≥12 m. We observe formation of a thick (≥50 cm) pedo-complex starting at ca. 6.7 ka before present (BP) and erosional truncation at ca. 3.9 ka BP. Widespread landscape instability and erosion characterize the region subsequent to 3.9 ka and intensifies in the 15th century AD. Several lines of (geo)archaeological evidence, including the presence of pottery sherds, sling-shot projectiles and hammer stones within the sedimentary record, indicate human presence at Su-re since ca. 3.9 ka BP. Our data suggest that in the Su-re-Tingri area climatic conditions were warm and moist enough to allow vegetation expansion and soil formation only from ca. 6.7–3.9 ka, followed by weakening of the Indian summer monsoon (ISM) strength between ca. 4.2 and 3.9 ka, which is a prominent climatic event in the wider Asian monsoon region, and reflected in the investigation area by the 3.9 ka erosional boundary. Merging our Holocene landscape reconstruction with the geoarchaeological evidence, we speculate that the combined effect of Little Ice Age (LIA) cooling and an anthropogenic overuse of the landscape led to climatically induced landscape degradation and ultimately to an anthropogenically triggered ecological collapse in the 15th century. Such a scenario is in-line with regional historical data on declining monastery construction and migration of the ethnic group of the Sherpas.From an earth surface dynamics perspective, we find that transient landscape processes on the southern rim of the Tibetan plateau are strongly linked to millennial scale changes in the ISM intensity and duration. We identify three types of unidirectional non-linear ISM-landscape interactions. Given that the Tibetan plateau is the largest high-altitude landmass on our planet and our limited understanding of several of the key earth surface processes on the plateau, we pinpoint the need for more long-term (Quaternary scale) empirical data particularly on permafrost and periglacial processes and human-environment interactions.