Pancreatic α and β cells are globally phase-locked

The Ca2+ modulated pulsatile secretion of glucagon and insulin by pancreatic α and β cells plays a key role in glucose homeostasis. However, how α and β cells coordinate via paracrine interaction to produce various Ca2+ oscillation patterns is still elusive. Using a microfluidic device and transgenic mice in which α and β cells were labeled with different colors, we were able to record islet Ca2+ signals at single cell level for long times. Upon glucose stimulation, we observed heterogeneous Ca2+ oscillation patterns intrinsic to each islet. After a transient period, the oscillations of α and β cells were globally phase-locked, i.e., the two types of cells in an islet each oscillate synchronously but with a phase shift between the two. While the activation of α cells displayed a fixed time delay of ~20 s to that of β cells, β cells activated with a tunable delay after the α cells. As a result, the tunable phase shift between α and β cells set the islet oscillation period and pattern. Furthermore, we demonstrated that the phase shift can be modulated by glucagon. A mathematical model of islet Ca2+ oscillation taking into consideration of the paracrine interaction was constructed, which quantitatively agreed with the experimental data. Our study highlights the importance of cell-cell interaction to generate stable but tunable islet oscillation patterns.

Dynamic modeling and transient stability analysis of distributed generators in a microgrid system

Increasing the penetration level of distributed generation units as well as power electronic devices adds more complexity and variability to the dynamic behaviour of the microgrids. For such systems, studying the transient modelling and stability is essential. One of the major disadvantages of most studies on microgrid modelling is their excessive attention to the steady state period and the lack of attention to microgrid performance during the transient period. In most of the research works, the behaviour of different microgrid loads has not been studied. One of the mechanisms of power systems stability studies is the application of state space modelling. This paper presents a mathematical model for connected inverters in microgrid systems with many variations of operating conditions. Nonlineal tools, phase-plane trajectory analysis, and Lyapunov method were employed to evaluate the limits of small signal models. Based on the results of the present study, applying the model allows for the analysis of the system when subjected to a severe transient disturbance such as loss of large load or generation. Studying the transient stability of microgrid systems in the standalone utility grid is useful and necessary for improving the design of the microgrid’s architecture.

Sub-Transient Response of the DSC Controlled Inverter under Fault

The most important element of the new active distribution system concept is the grid connected converter that needs to offer fault ride through capabilities. The new system topologies require new tools for fault state calculation that would consider different control methodologies. In that regard, this paper investigates the initial response of the grid connected inverter under fault that operates using new control methodology based on the integration of the delay signal cancellation. Using modern laboratory setup for testing of renewable energy sources and their integration in the power system the technique is weighed against the classical technique that does not provide the adequate control under unbalanced faults. Furthermore, through a set of specific experiments the paper demonstrates the behavior of the converter under fault, preparing the outline for the fault response modeling of distributed energy resources. Experimental results present the sub-transient period and the transient period of the response, giving the attention to the inrush current (initial peak current) of the converter. It has been shown that the new technique has similar behavior as the classical control for the balanced faults (symmetrical voltage states), while the values of the peak current for different type of unbalanced faults (asymmetrical voltages where classical technique can be proven to be ineffective) has also been demonstrated.

A Novel Memristor Chaotic System with a Hidden Attractor and Multistability and Its Implementation in a Circuit

By introducing an ideal and active flux-controlled memristor and tangent function into an existing chaotic system, an interesting memristor-based self-replication chaotic system is proposed. The most striking feature is that this system has infinite line equilibria and exhibits the extreme multistability phenomenon of coexisting infinitely many attractors. In this paper, bifurcation diagrams and Lyapunov exponential spectrum are used to analyze in detail the influence of various parameter changes on the dynamic behavior of the system; it shows that the newly proposed chaotic system has the phenomenon of alternating chaos and limit cycle. Especially, transition behavior of the transient period with steady chaos can be also found for some initial conditions. Moreover, a hardware circuit is designed by PSpice and fabricated, and its experimental results effectively verify the truth of extreme multistability.

BESS Assisted Frequency Management for Black Start Process of Microgrid

This paper proposes a method for restoring the nominal frequency and improving the system recovery time using battery energy storage system (BESS) for an islanded microgrid (MG) which is operated by a black start unit (BSU). The frequency stability is controlled by varying the apparent power (MVA) rating of the BESS after simultaneously connecting with the BSU during the post fault scenarios. Simulations are performed on the IEEE Std. 399-1997 test MG using DIgSILENT PowerFactory. Results show that the nominal frequency of the system can be retained by connecting the BESS during the transient period and increasing the MVA rating up to a maximum value. Simulation results also show that with a higher distributed connection of the BESS units over the system, the frequency recovery time can be reduced.

Kegunaan radiografi panoramik pada masa mixed dentition

Objectives: The purpose of this review is to determine the usefulness of panoramic radiography during mixed dentition and also to capture panoramic radiographs during mixed dentition. Review: Mixed dentition is a period of mixed dentition and a period of transition from sequential deciduous teeth followed by the eruption of the replacement tooth, namely the permanent tooth. The mixed dental phase occurs in children aged 6-12 years, beginning with the eruption of the first permanent tooth, usually a central incisor or mandibular first molar. Changes in occlusion occur significantly during this time due to the loss of the deciduous teeth and the eruption of the replacement permanent teeth. Conclusion: The mixed dentition period can be classified into 3 phases, namely. (1) the first transitional period, occurs at 6-8 years of age. In this phase, the eruption of the permanent first molars and the replacement of the deciduous incisors with the permanent incisors occurred. (2) the inter-transitional period, after the first molars and permanent incisors erupt, there is a transient period of about 1-2 years before the second transition phase begins. In this phase, it is called inter-transitional because the maxillary and mandibular arches consist of deciduous and permanent teeth. In the inter-transitional phase it is relatively stable and no changes occur. (3) the second transitional period at age (10-13 years), the date of the mandibular canine at about 10 years of age usually begins the second transitional period.

Auditory processing remains sensitive to environmental experience during adolescence

Development is a time of great opportunity. A heightened period of neural plasticity contributes to dramatic improvements in perceptual, motor, and cognitive skills. However, developmental plasticity poses a risk: greater malleability of neural circuits exposes them to environmental factors that may impede behavioral maturation. While these risks are well-established prior to sexual maturity (i.e., critical periods), the degree of neural vulnerability during adolescence remains uncertain. To address this question, we induced a transient period of hearing loss (HL) spanning adolescence in the gerbil, confirmed by assessment of circulating sex hormones, and asked whether behavioral and neural deficits are diminished. Wireless recordings were obtained from auditory cortex neurons during perceptual task performance, and within-session behavioral and neural sensitivity were compared. We found that a transient period of adolescent HL caused a significant perceptual deficit (i.e., amplitude modulation detection thresholds) that could be attributed to degraded auditory cortex processing, as confirmed with both single neuron and population-level analyses. To determine whether degraded auditory cortex encoding was attributable to an intrinsic change, we obtained auditory cortex brain slices from adolescent HL animals, and recorded synaptic and discharge properties from auditory cortex pyramidal neurons. There was a clear and novel phenotype, distinct from critical period HL: excitatory postsynaptic potential amplitudes were elevated in adolescent HL animals, whereas inhibitory postsynaptic potentials were unchanged. This is in contrast to critical period deprivation, where there are large changes to synaptic inhibition. Taken together, these results show that sensory perturbations suffered during adolescence can cause long-lasting behavioral deficits that originate, in part, with a dysfunctional cortical circuit.Abstract FigureSummary of experimental design and main findings.

The MINC proximity function for fractured reservoirs flow modeling with non-uniform block distribution

Reservoir simulation is a powerful technique to predict the amount of produced hydrocarbon. After a solid representation of the natural fracture geometry, an accurate simulation model and a physical reservoir model that account for different flow regimes should be developed. Many models based on dual-continuum approaches presented in the literature rely on the Pseudo-Steady-State (PSS) assumption to model the inter-porosity flow. Due to the low permeability in such reservoirs, the transient period could reach several years. Thus, the PSS assumption becomes unjustified. The numerical solution adopted by the Multiple INteracting Continua (MINC) method was able to simulate the transient effects previously overlooked by dual-continuum approaches. However, its accuracy drops with increasing fracture network complexity. A special treatment of the MINC method, i.e., the MINC Proximity Function (MINC–PF) was introduced to address the latter problem. And yet, the MINC–PF suffers a limitation that arises from the existence of several grid-blocks within a studied cell. In this work, this limitation is discussed and two possible solutions (transmissibility recalculation/adjusting the Proximity Function by accounting for nearby fractures) are put forward. Both proposed methods have demonstrated their applicability and effectiveness once compared to a reference solution.

Seed traits linked to differential survival of plants during the Cretaceous/Paleogene impact winter

In past investigations the pattern of differential survival of plants across the K/Pg boundary has been viewed as incompatible with severe asteroid impact winter scenarios (i.e., an impact winter lasting more than a few months), particularly the enigmatic survival of coryphoid palms and Pandanus (screw pine). Stateof- the-art climate models based on soot, sulfate and nano-sized dust aerosols predict a global impact winter that drastically reduced precipitation and resulted in a transient period of total darkness and permafrost conditions. This suggests that the plants most likely to have been affected by the global mass-extinction event were tropical phanerophytes that produce recalcitrant seeds, which by definition are desiccation-intolerant, survive less than a year, and cannot survive freezing. However, this hypothesis has never been tested. In this study I sampled over 100 plant species from the global fossil record that have a high probability of having produced either recalcitrant seeds/disseminules (n1 = 58) or orthodox seeds (n2 = 59), based on their phylogenetic relationships with extant taxa that either are monomorphic for these traits or specifically exhibit a genetic marker for abscisic acid inhibition associated with seed dormancy and recalcitrance. A one-tailed z-test for the difference between two proportions revealed that plant taxa with a high probability of having produced recalcitrant seeds had significantly lower survivorship than plant taxa with a high probability of having produced orthodox seeds (p < 0.0001). Based on these data, it can be concluded that plants which formed a frost-tolerant seed bank during the latest Maastrichtian were significantly more likely to survive the K/Pg impact winter than plants which did not (including palms). These data clearly indicate that the K/Pg impact winter probably lasted longer than a year and that it selected for seed-based traits that effectively sorted correlated functional traits of mature plants (i.e., leaf physiognomic features). This novel hypothesis stands as an alternative to J.A. Wolfe’s classic hypothesis that a mild K/Pg impact winter selected for fast-growing angiosperms with deciduous leaves and did not affect the plant communities of the Southern Hemisphere. Potential mechanisms for the rare survival of tropical, recalcitrant-seeded plants are discussed.

Washing Machine Dynamic Model to Prevent Tub Collision during Transient State

In horizontal-axis washing machines, the front gasket as well as the damping system are crucial owing to the possible collision of the tub with the housing during the transient period. However, most dynamic models for predicting tub motion focus on the steady state and consider only the suspension system without including the gasket. We conducted an experimental study to analyze the effect of the gasket on the transient motion of the tub. The results obtained indicate the necessity of implementing the gasket in the multibody model of a washing machine to accurately predict the tub behavior during this period. The gasket model is formed by a combination of Voigt elements. Stiffness parameters are determined using a load cell, and damping factors are estimated using a process that integrates Adams/View, Matlab optimization algorithms, and displacement measurements that are taken using accelerometers. A D-optimal design used to predict the effect of the gasket parameters reveals that the tub displacement is most sensitive to the changes in linear stiffness in the transversal direction. Finally, the model of the gasket provides a better approach for predicting the tub movement during resonance that can be used in the design phase to avoid tub collision.