Local Reorganization Research Articles

Thermomechanical Response of a Representative Porin for Biomimetics.

The thermomechanical response of Omp2a, a representative porin used for the fabrication of smart biomimetic nanomembranes, has been characterized using microcantilever technology and compared with standard proteins. For this purpose, thermally induced transitions involving the conversion of stable trimers to bigger aggregates, local reorganizations based on the strengthening or weakening of intermolecular interactions, and protein denaturation have been detected by the microcantilever resonance frequency and deflection as a function of the temperature. Measurements have been carried out on arrays of 8-microcantilevers functionalized with proteins (Omp2a, lysozyme and bovine serum albumin). To interpret the measured nanofeatures, the response of proteins to temperature has been also examined using other characterization techniques, including real time wide angle X-ray diffraction. Results not only demonstrate the complex behavior of porins, which exhibit multiple local thermal transitions before undergoing denaturation at temperatures higher than 105 °C, but also suggest a posttreatment to control the orientation of immobilized Omp2a molecules in functionalized biomimetic nanomembranes and, thus, increase their efficacy in ion transport.

Functional brain network analysis reveals time-on-task related performance decline.

Because of the undesired consequences, particularly seen in deteriorated performance in real-word workspace, continuous efforts have been made to understand time-on-task (TOT) related mental fatigue. However, our understanding of the underlying neural mechanism of TOT is still rudimentary. In this study, EEG signals were recorded from 26 subjects undergoing a 20-min mentally-demanding psychomotor vigilance test. Instead of a mere two-point comparison (i.e., fatigue vs. vigilant), behaviour and EEG data were divided into 4 quartiles for better revealing the progression of TOT effect. We then employed advanced graph theoretical approach to quantify TOT effect in terms of global and local reorganisation of EEG functional connectivity within the lower alpha (8-10 Hz) band. Interestingly, we found a development trend towards disintegrated network topology with the TOT effect, as seen in significantly increased characteristic path length and reduced small-worldness. Moreover, we found TOT-related reduced local property of interconnectivity in left frontal and central areas with an increased local property in right parietal areas. These findings augment our understanding of how the brain reorganises following the accumulation of prolonged task and demonstrate the feasibility of using network metrics as neural biomarkers for mental fatigue assessment.

Economies of Scale in Local Government Services: A Meta Analysis

In this paper, a meta-regression analysis is presented by 38 empirical studies on the size of scale in various local government services. Our results show that income classification was the most important factor in determining size of scale and all selected local government services recorded decreasing size of scale in the recent decades, with water services exhibiting the largest decreasing size of scale. The existence of scale effects has important ramifications for local government structural reform, given the globally indifferent results of local government reorganization.

Motile bacteria in a critical fluid mixture.

We studied the swimming of Escherichia coli bacteria in the vicinity of the critical point in a solution of the nonionic surfactant C_{12}E_{5} in buffer solution. In phase-contrast microscopy, each swimming cell produces a transient trail behind itself lasting several seconds. Comparing quantitative image analysis with simulations show that these trails are due to local phase reorganization triggered by differential adsorption. This contrasts with similar trails seen in bacteria swimming in liquid crystals, which are due to shear effects. We show how our trails are controlled, and use them to probe the structure and dynamics of critical fluctuations in the fluid medium.

Distinct Electron Conductance Regimes in Bacterial Decaheme Cytochromes

AbstractShewanella oneidensis MR‐1 gains energy by extracellular electron transfer to solid surfaces. They employ c‐type cytochromes in two Mtr transmembrane complexes, forming a multiheme wire for electron transport across the cellular outer membrane. We investigated electron‐ and hole‐transfer mechanisms in the external terminal of the two complexes, MtrC and MtrF. Comparison of computed redox potentials with previous voltammetry experiments in distinct environments (isolated and electrode‐bound conditions of PFV or in vivo) suggests that these systems function in different regimes depending on the environment. Analysis of redox potential shifts in different regimes indicates strong coupling between the hemes via an interplay between direct Coulomb and indirect interactions through local structural reorganization. The latter results in the screening of Coulomb interactions and explains poor correlation of the strength of the heme‐to‐heme interactions with the distance between the hemes.

Distinct Electron Conductance Regimes in Bacterial Decaheme Cytochromes.

Shewanella oneidensis MR-1 gains energy by extracellular electron transfer to solid surfaces. They employ c-type cytochromes in two Mtr transmembrane complexes, forming a multiheme wire for electron transport across the cellular outer membrane. We investigated electron- and hole-transfer mechanisms in the external terminal of the two complexes, MtrC and MtrF. Comparison of computed redox potentials with previous voltammetry experiments in distinct environments (isolated and electrode-bound conditions of PFV or in vivo) suggests that these systems function in different regimes depending on the environment. Analysis of redox potential shifts in different regimes indicates strong coupling between the hemes via an interplay between direct Coulomb and indirect interactions through local structural reorganization. The latter results in the screening of Coulomb interactions and explains poor correlation of the strength of the heme-to-heme interactions with the distance between the hemes.

Peculiar Li-storage mechanism at graphene edges in turbostratic carbon black and their application in high energy Li-ion capacitor

We report experimental evidence for the specific Li-storage at turbostratic graphene edges of a well-known and cheap Super P® carbon black (Csp) material, which is usually used as a conductive additive in composite electrodes. Indeed, operando XRD and HR-TEM consistently demonstrate Li insertion occurs with zero expansion of graphene layer up to a composition of Li0.4C6 (150 mA h/g) that is reached at 0.01 V vs. Li+/Li. 7Li NMR substantiates these results and suggests that the weak electronic transfer from the carbon host to the intercalant could help local reorganization of the layer order as suggested by the unexpected reversible changes of the (002) Bragg peak intensity during the charge-discharge process. Our observations also indicate this insertion mechanism is kinetically favored resulting in remarkable cycling stability over 1000 cycles and power capability allowing to sustain 110 mA h/g at 8 A/g (21 C) in half cell. The capability of Csp as an efficient anode is ultimately demonstrated in a lithium hybrid capacitor against a positive electrode of activated carbon. The full cell delivers a maximum energy of 120 Wh/kg (4.3–2 V) and remarkable capacity retention over 1800 cycles.

Re-emergence of modular brain networks in stroke recovery

Studies of stroke have identified local reorganization in perilesional tissue. However, because the brain is highly networked, strokes also broadly alter the brain's global network organization. Here, we assess brain network structure longitudinally in adult stroke patients using resting state fMRI. The topology and boundaries of cortical regions remain grossly unchanged across recovery. In contrast, the modularity of brain systems i.e. the degree of integration within and segregation between networks, was significantly reduced sub-acutely (n = 107), but partially recovered by 3 months (n = 85), and 1 year (n = 67). Importantly, network recovery correlated with recovery from language, spatial memory, and attention deficits, but not motor or visual deficits. Finally, in-depth single subject analyses were conducted using tools for visualization of changes in brain networks over time. This exploration indicated that changes in modularity during successful recovery reflect specific alterations in the relationships between different networks. For example, in a patient with left temporo-parietal stroke and severe aphasia, sub-acute loss of modularity reflected loss of association between frontal and temporo-parietal regions bi-hemispherically across multiple modules. These long-distance connections then returned over time, paralleling aphasia recovery. This work establishes the potential importance of normalization of large-scale modular brain systems in stroke recovery.

Small-worldness of brain networks after brachial plexus injury: A resting-state functional magnetic resonance imaging study.

Research on brain function after brachial plexus injury focuses on local cortical functional reorganization, and few studies have focused on brain networks after brachial plexus injury. Changes in brain networks may help understanding of brain plasticity at the global level. We hypothesized that topology of the global cerebral resting-state functional network changes after unilateral brachial plexus injury. Thus, in this cross-sectional study, we recruited eight male patients with unilateral brachial plexus injury (right handedness, mean age of 27.9 ± 5.4 years old) and eight male healthy controls (right handedness, mean age of 28.6 ± 3.2). After acquiring and preprocessing resting-state magnetic resonance imaging data, the cerebrum was divided into 90 regions and Pearson's correlation coefficient calculated between regions. These correlation matrices were then converted into a binary matrix with affixed sparsity values of 0.1-0.46. Under sparsity conditions, both groups satisfied this small-world property. The clustering coefficient was markedly lower, while average shortest path remarkably higher in patients compared with healthy controls. These findings confirm that cerebral functional networks in patients still show small-world characteristics, which are highly effective in information transmission in the brain, as well as normal controls. Alternatively, varied small-worldness suggests that capacity of information transmission and integration in different brain regions in brachial plexus injury patients is damaged.

Effect of VEGF on Inflammatory Regulation, Neural Survival, and Functional Improvement in Rats following a Complete Spinal Cord Transection.

After complete transection of the thoracic spinal segment, neonatal rats exhibit spontaneous locomotor recovery of hindlimbs, but this recovery is not found in adult rats after similar injury. The potential mechanism related to the difference in recovery of neonatal and adult rats remains unknown. In this study, 342 animals were analyzed. The vascular endothelial growth factor (VEGF) level in spinal segments below injury sites was significantly higher in postnatal day 1 rats (P1) compared with 28-day-old adult rats (P28) following a complete T9 transection. VEGF administration in P28 rats with T9 transection significantly improved the functional recovery; by contrast, treatment with VEGF receptor inhibitors in P1 rats with T9 transection slowed down the spontaneous functional recovery. Results showed more neurons reduced in the lumbar spinal cord and worse local neural network reorganization below injury sites in P28 rats than those in P1 rats. Transynaptic tracing with pseudorabies virus and double immunofluorescence analysis indicated that VEGF treatment in P28 rats alleviated the reduced number of neurons and improved their network reorganization. VEGF inhibition in neonates resulted in high neuronal death rate and deteriorated network reorganization. In in vivo studies, T9 transection induced less increase in the number of microglia in the spinal cord in P1 animals than P28 animals. VEGF treatment reduced the increase in microglial cells in P28 animals. VEGF administration in cultured spinal motoneurons prevented lipopolysaccharide (LPS)-induced neuronal death and facilitated neurite growth. Western blots of the samples of lumbar spinal cord after spinal transection and cultured spinal motoneurons showed a lower level of Erk1/2 phosphorylation after the injury or LPS induction compared with that in the control. The phosphorylation level increased after VEGF treatment. In conclusion, VEGF is a critical mediator involved in functional recovery after spinal transection and can be considered a potential target for clinical therapy.

Tax and Expenditure Limitations and Special District Formation

This paper empirically examines the formation of special districts in the United States. It investigates, in particular, the adoption of tax and expenditure limitations (TELs) on local governments to determine how the have motivated special district formation. The paper extends the research agenda by reporting a longitudinal analysis for TELs and special district formation through the post-Proposition 13 tax revolt in the states. Theory from the literatures on special-purpose governments and, on TELs, guides the research – literatures interested in the impact of fiscal institutions on local government reorganization. Main findings are that adoption of one type of TEL – general limitations – is encouraging formation of special districts with taxing powers. Substantively, adoption of general limitations raises the number of taxing districts by approximately 13 percent. A flexible model for panel data, inclusive of fixed effects and time trends, turns out to be crucial for identifying estimates for the impact of TELs in special district formation.

Cytokinesis in vertebrate cells initiates by contraction of an equatorial actomyosin network composed of randomly oriented filaments.

The actomyosin ring generates force to ingress the cytokinetic cleavage furrow in animal cells, yet its filament organization and the mechanism of contractility is not well understood. We quantified actin filament order in human cells using fluorescence polarization microscopy and found that cleavage furrow ingression initiates by contraction of an equatorial actin network with randomly oriented filaments. The network subsequently gradually reoriented actin filaments along the cell equator. This strictly depended on myosin II activity, suggesting local network reorganization by mechanical forces. Cortical laser microsurgery revealed that during cytokinesis progression, mechanical tension increased substantially along the direction of the cell equator, while the network contracted laterally along the pole-to-pole axis without a detectable increase in tension. Our data suggest that an asymmetric increase in cortical tension promotes filament reorientation along the cytokinetic cleavage furrow, which might have implications for diverse other biological processes involving actomyosin rings.

Prosodic asymmetry in phonetic reorganization of Seoul Korean 3-way voiceless stop contrast

In younger generation Seoul Korean speakers, a phonetic reorganization of VOT and f0 in the phrase-initial stop contrast (i.e. aspirated, lenis, fortis) has been well documented. The current study elucidates how this local consonant effect on f0 further interacts with the global tonal patterns of the accentual phrase (AP). We test how the initial 3-way stop contrast is phonetically realized in AP-initial and AP-internal prosodic positions for six younger generation speakers (born 1980-1990). Our results show that the consonant effect on f0 is categorical in AP-initial position, compared to exhibiting a gradient effect in AP-internal position. We confirm an AP-initial VOT merger between aspirated and lenis stops, accompanied by an increased between-consonant f0 difference. In AP-internal position, along with a small but significant f0 difference, we found a near-merger of VOT between lenis and fortis stops, arising from the substantially reduced occurrence of intervocalic lenis voicing. Taken together, our findings provide novel evidence of an intricate interaction between phrase-level prosody and the local phonetic reorganization in the newly emerged phonetic system of Seoul Korean stops. [Work supported by NIH.]

Tax and Expenditure Limitations and Special District Formation

This paper empirically examines the formation of special districts in the United States. It investigates, in particular, the adoption of tax and expenditure limitations (TELs) on local governments to determine how the have motivated special district formation. The paper extends the research agenda by reporting a longitudinal analysis for TELs and special district formation through the post-Proposition 13 tax revolt in the states. Theory from the literatures on special-purpose governments and, on TELs, guides the research – literatures interested in the impact of fiscal institutions on local government reorganization. Main findings are that adoption of one type of TEL – general limitations – is encouraging formation of special districts with taxing powers. Substantively, adoption of general limitations raises the number of taxing districts by approximately 13 percent. A flexible model for panel data, inclusive of fixed effects and time trends, turns out to be crucial for identifying estimates for the impact of TELs in special district formation.

Mesoscale martensitic transformation in single crystals of topological defects

Liquid-crystal blue phases (BPs) are highly ordered at two levels. Molecules exhibit orientational order at nanometer length scales, while chirality leads to ordered arrays of double-twisted cylinders over micrometer scales. Past studies of polycrystalline BPs were challenged by the existence of grain boundaries between randomly oriented crystalline nanodomains. Here, the nucleation of BPs is controlled with precision by relying on chemically nanopatterned surfaces, leading to macroscopic single-crystal BP specimens where the dynamics of mesocrystal formation can be directly observed. Theory and experiments show that transitions between two BPs having a different network structure proceed through local reorganization of the crystalline array, without diffusion of the double-twisted cylinders. In solid crystals, martensitic transformations between crystal structures involve the concerted motion of a few atoms, without diffusion. The transformation between BPs, where crystal features arise in the submicron regime, is found to be martensitic in nature when one considers the collective behavior of the double-twist cylinders. Single-crystal BPs are shown to offer fertile grounds for the study of directed crystal nucleation and the controlled growth of soft matter.

Special District Formation: Evidence from Panel Data

This paper empirically examines the formation of special districts in the United States. It investigates, in particular, the adoption of tax and expenditure limitations (TELs) on local governments to determine how they have motivated special district formation. The paper extends the research agenda by reporting an analysis for TELs and special district formation through the post-Proposition 13 tax revolt in the states. Theory on special-purpose governments and, on TELs, guides the research – literatures interested in the impact of fiscal institutions on local government reorganization. Main findings are that adoption of one type of TEL – general limitations – is encouraging the formation of special districts with taxing powers. Substantively, adoption of general limitations raises the number of taxing districts by approximately 13 percent. A flexible model for panel data, inclusive of fixed effects and time trends, turns out to be crucial for identifying estimates for the role of TELs in special district formation.

Development of structural correlations and synchronization from adaptive rewiring in networks of Kuramoto oscillators.

Synchronization of non-identical oscillators coupled through complex networks is an important example of collective behavior, and it is interesting to ask how the structural organization of network interactions influences this process. Several studies have explored and uncovered optimal topologies for synchronization by making purposeful alterations to a network. On the other hand, the connectivity patterns of many natural systems are often not static, but are rather modulated over time according to their dynamics. However, this co-evolution and the extent to which the dynamics of the individual units can shape the organization of the network itself are less well understood. Here, we study initially randomly connected but locally adaptive networks of Kuramoto oscillators. In particular, the system employs a co-evolutionary rewiring strategy that depends only on the instantaneous, pairwise phase differences of neighboring oscillators, and that conserves the total number of edges, allowing the effects of local reorganization to be isolated. We find that a simple rule—which preserves connections between more out-of-phase oscillators while rewiring connections between more in-phase oscillators—can cause initially disordered networks to organize into more structured topologies that support enhanced synchronization dynamics. We examine how this process unfolds over time, finding a dependence on the intrinsic frequencies of the oscillators, the global coupling, and the network density, in terms of how the adaptive mechanism reorganizes the network and influences the dynamics. Importantly, for large enough coupling and after sufficient adaptation, the resulting networks exhibit interesting characteristics, including degree–frequency and frequency–neighbor frequency correlations. These properties have previously been associated with optimal synchronization or explosive transitions in which the networks were constructed using global information. On the contrary, by considering a time-dependent interplay between structure and dynamics, this work offers a mechanism through which emergent phenomena and organization can arise in complex systems utilizing local rules.

Late Mio-Pliocene chemical weathering of the Yulong porphyry Cu deposit in the eastern Tibetan Plateau constrained by goethite (U–Th)/He dating: Implication for Asian summer monsoon

Chemical weathering has provided a potentially important feedback between tectonic forcing and climate evolution of the Asian continent, although precise constraints on the timing and history of weathering are only variably documented. Here, we use goethite (U–Th)/He and 4He/3He geochronology to constrain the timing and rates of chemical weathering at the Yulong porphyry Cu deposit on the eastern Tibetan Plateau. Goethite grains have (U–Th)/He ages ranging from 6.73±0.51 to 0.53±0.04 Ma that correlate with independent paleoclimatic proxies inferred from supergene Mn-oxides and loess deposits under variable tectonic regimes and vegetation zones over the southeastern Asia. This correlation indicates that regional climatic conditions, especially monsoonal precipitation, controlled chemical weathering and goethite precipitation in a vast area of southeastern Asia. The goethite ages suggest that the Asian summer monsoon was relatively strong from 7 to 4.6 Ma, but weakened between 4.6 and 4 Ma, and then significantly intensified from 4 to 2 Ma. The precipitation ages of goethites collected along a 100-m-thick weathering profile decrease with depth, and indicate a downward propagation of the weathering front at rates of <6.7, 53.5±10.8, and 4.8±0.6 m/Ma during the intervals of 7–4, 4–2, and 2–0.7 Ma, respectively. The rapid propagation of weathering front during 4–2 Ma was caused by abrupt lowering of the water table, which was possibly related to local surface uplift or reorganization of the river systems in southeastern Tibet during this period.

The sound of avalanches: from a global to a local perspective.

We present an experimental study aiming to understand the local origin of the acoustic bursts recorded globally during a two-dimensional shear experiment of a granular medium. In order to explain the power-law distribution of energy of these events (also called avalanches), the analysis focuses on their acoustic frequencies. Experiments with single grains have also been performed, trying to separate the contributions related to collision between neighbours from shear movements between grains. Preliminary results indicate that both frictional sliding and collision-like mechanisms are involved in the origin of the acoustic bursts. The evolution of the structure of the medium around a large acoustic burst is analysed both with high resolution and high-speed imaging. The energy of the acoustic bursts seems related to single and well-localised events with very large variations in energy. However, these local reorganisation processes may eventually bring the global relaxation of the system, which is also captured by a force drop in the resistance to shear.

Excitation wavelength dependent fluorescence of graphene oxide controlled by strain.

Unlike conventional fluorophores, the fluorescence emission of graphene oxide (GO) sheets can shift hundreds of nanometers as the excitation wavelength increases. The excitation wavelength dependent fluorescence is referred to as a giant red-edge effect and originates in a local reorganization potential slowing down the solvation dynamics of the excited state to the same time scale as the fluorescence lifetime. The present work has discovered that out-of-plane strain in the graphene oxide sheet leads to the intra-layer interaction necessary to slow down the solvation time scale. The oxygen percentage, dopant percentage, disorder, and strain are correlated with the presence and extent of the red-edge effect in oxygen, boron, nitrogen, and fluorine doped graphene oxide. Of these commonly cited possibilities, only out-of-plane strain is directly correlated to the red-edge effect. Furthermore, it is shown that the extent of the red-edge effect, or how far the emission wavelength can shift with increasing excitation wavelength, can be tuned by the electronegativity of the dopant. The present work interprets why the giant red-edge effect is present in some GO sheets but not in other GO sheets.