Asymmetric Cycles Research Articles

Actin-dependent membrane polarization reveals the mechanical nature of the neuroblast polarity cycle

SUMMARYThe Par complex directs fate-determinant segregation from the apical membrane of asymmetrically dividing Drosophila neuroblasts. While the physical interactions that recruit the Par complex have been extensively studied, little is known about how the membrane itself behaves during polarization. We examined the membrane dynamics of neuroblasts and surrounding cells using a combination of super-resolution and time-lapse imaging, revealing cellular-scale movements of diverse membrane features during asymmetric division cycles. Membrane domains that are distributed across the neuroblast membrane in interphase become polarized in early mitosis, where they mediate formation of cortical patches of the Par protein atypical protein kinase C (aPKC). Membrane and protein polarity cycles are precisely synchronized and are generated by extensive actin-dependent forces that deform the surrounding tissue. In addition to suggesting a role for the membrane in asymmetric division, our results reveal the mechanical nature of the neuroblast polarity cycle.

The Protein Quality Control Network in Caulobacter crescentus.

The asymmetric life cycle of Caulobacter crescentus has provided a model in which to study how protein quality control (PQC) networks interface with cell cycle and developmental processes, and how the functions of these systems change during exposure to stress. As in most bacteria, the PQC network of Caulobacter contains highly conserved ATP-dependent chaperones and proteases as well as more specialized holdases. During growth in optimal conditions, these systems support a regulated circuit of protein synthesis and degradation that drives cell differentiation and cell cycle progression. When stress conditions threaten the proteome, most components of the Caulobacter proteostasis network are upregulated and switch to survival functions that prevent, revert, and remove protein damage, while simultaneously pausing the cell cycle in order to regain protein homeostasis. The specialized physiology of Caulobacter influences how it copes with proteotoxic stress, such as in the global management of damaged proteins during recovery as well as in cell type-specific stress responses. Our mini-review highlights the discoveries that have been made in how Caulobacter utilizes its PQC network for regulating its life cycle under optimal and proteotoxic stress conditions, and discusses open research questions in this model.

Three-Phase Three-Level Isolated DC-DC Soft Switching Converter For Solar Applications

Three-level isolated DC-DC converter is an attractive topology in high input voltage applications, which can provide the voltage stress of the power devices to only a half of the dc voltage and also reduce the size of dc filter requirement. But major limitations in the existing three level ZVS converter topologies are brought out with an increased inductance in the primary side and it required to provide complete ZVS of all primary devices down to light loads. By employing an external inductance in the primary of the transformer, total leakage inductance of the transformer increases which is required for realization of soft switching of the converter switches but there are some disadvantages of connecting external inductance in the primary of the transformer. To overcome all these drawbacks, the three-phase three-level isolated DC-DC soft switching converter has been proposed in order to reduce voltage and current stresses. This converter topology requires less number of control switches and operates with an asymmetrical duty cycle control. The proposed three level DC-DC converters provide two- level voltage waveform before dc output filter, which significantly reduce the size of dc output filter. The proposed work has been implemented using MATLAB/SIMULINK and the performance of the proposed converter is verified through simulation results.

Ratcheting Response of SS316 Steel Samples with Different Notch Shapes under Various Loading Spectra

Ratcheting response of notched 316 stainless steel samples was examined under various low-high-high (LHH) and high-low-low (HLL) loading steps and sequences. Plate samples were tested under uniaxial asymmetric stress cycles contained circular or elliptical notches in center. Local ratcheting strain increased over loading steps of steel samples tested with LHH loading sequence, while it dropped in magnitude for samples tested with HLL loading histories. Local ratcheting strains were further evaluated through use of the Ahmadzadeh–Varvani (A–V) and Chaboche (CH) hardening models coupled with Neuber’s rule to predict ratcheting at the vicinity of notch root in steel samples. Finite element (FE) method was employed to numerically assess local ratcheting around the notch root through the use of ABAQUS software. Horizontal X-ellipse, circular and vertical Y-ellipse notch shapes lead to the highest, intermediate and lowest local ratcheting results for steel samples as predicted by means of the A–V and CH frameworks as well as those simulated results through FE method. Simulated ratcheting results through FE analysis positioned on or above the measured values for various loading steps and sequences. Predicted ratcheting results through the CH model positioned slightly above measured data over the first loading step and were turned to higher magnitudes over steps 2 and 3 in LHH samples with different notch shapes. This model underestimated ratcheting over loading steps 2-3 for HLL loading sequences. The predicted results by the A–V model consistently agreed with experimental data over the first step in notched samples tested under LHH and HLL sequences. Last two steps however resulted in lower ratcheting results through this model.

Revisiting the Canadian Lynx Time Series Analysis Through TARMA Models

The class of threshold autoregressive models has been proven to be a powerful and appropriate tool to describe many dynamical phenomena in different fields. In this work, we deploy the threshold autoregressive moving-average framework to revisit the analysis of the benchmark Canadian lynx time series. This data set has attracted great attention among non-linear time series analysts due to its asymmetric cycle that makes the investigation very challenging. We compare some of the best threshold autoregressive models (TAR) proposed in literature with a selection of thresholdautoregressive moving-average models (TARMA). The models are compared under different prospectives: (i) goodness-of-fit through information criteria, (ii) their ability to reproduce characteristic cycles, (iv) their capability to capture multimodality and (iii) forecasting performance. We found TARMAmodels that perform better than TAR models with respect to all these aspects.

Validity of Okun’s Law in a spatially dependent and cyclical asymmetric context

The current article analyzes the validity of Okun?s Law and sizable distortions that can occur in the estimation when spatial dependence and cyclical asymmetric impacts are not considered, which is a concern commonly ignored by the existing literature. Primarily spatial panel regressions (SDM, SAR, and SEM) and nonparametric regressions along with specification tests are adopted in terms of the methodology (such as panel unit root tests, panel cointegration, Moran?s I and Geary?s C tests of global spatial dependence, spatial LM, and Hausman tests). Additionally, spatial heterogeneity and cross-regional variation in Okun?s Law are investigated by adopting geographically weighted regression, LISA (local indicators for spatial association), and local Geary?s C analysis. A panel of 26 Turkish NUTS-2 regions from 2004 to 2018 was analyzed. The results clearly revealed that failing to incorporate spatial proximity and asymmetric cycle impacts leads to the biased estimation of Okun?s coefficient, such that during the downswing years of the national economy, Okun?s Law holds robustly: unemployment increases quickly in response to a decline in output. In contrast, during upswing years, the size of Okun?s coefficient is relatively much lower. Moreover, spatial dependence and heterogeneity are sizably evident. Okun?s coefficient is demonstrated to vary significantly across regions that have different industrial and labor market characteristics. As a policy implication, it has been understood that the reduction of unemployment is more difficult than initially understood, as economic growth itself does not provide a solution during upswing periods. The necessary special and region-specific policies are discussed throughout the text.

Closed-Form Asymmetrical Duty-Cycle Control to Extend the Soft-Switching Range of Three-Phase Dual-Active-Bridge Converters

The three-phase dual-active-bridge (DAB) converter is a promising topology for high-power dc–dc conversion in dc grids and industrial applications. However, the conventional single-phase-shift modulation shows a limited soft-switching range and large reactive currents under light-load operation especially with large voltage variations. This article proposes an asymmetrical duty-cycle control method for the three-phase DAB to extend the soft-switching range and reduce reactive currents by realizing three-phase triangular- and trapezoidal-current-mode operation. Closed-form solutions of the proposed modulation schemes are derived that enable a simple online calculation of the control parameters. The proposed modulation schemes can substantially reduce losses of both power semiconductor devices and the medium-frequency transformer. Thus, the three-phase DAB converter can realize high efficiency over a wide operation range, especially under light-load conditions. Considering the practical implementation, a compensation method is presented to correct the distorted current waveforms caused by the dead time and ensure the desired soft-switching operation. Besides, the power loss imbalance between top and bottom switches induced by the asymmetrical duty cycle is addressed by an active thermal balancing strategy. The effectiveness of the proposed method is validated by simulation results and experiments on a downscaled converter prototype.

CYCLIC TORSION WITH INTERNAL PRESSURE OF PRE-STRETCHED THIN-WALLED CYLINDERS

The article considers the following two tasks. 1) Strength calculations are carried out for a long thin-walled cylinder, the ends of which are not closed during reloading. At the first loading, the thin-walled cylinder is stretched by a longitudinal force leading to longitudinal plastic deformations. When reloaded, the cylinder twists and at the same time uniform pressure acts from the inside. It is noted that, in particular, the shaft of wind generators is subjected to such loading. It is proved that the equation of the yield curve in the plane of the normal and tangential stresses of the stress space is an ellipse, whose semi axes are a function of the mechanical characteristics of the material and the residual stresses after the first loading. 2) We consider cyclic twisting with internal pressure of pre-stretched thin-walled cylinders. The yield surface equation is obtained for a thin-walled cylinder under repeated loading τ + p. which stretched upon first loading. It is proved that the yield surface equations also yield the fatigue surface equations if the yield stress σ_(T.) is replaced by the fatigue stress σ_(0.) Expressions are found for the number of cycles required for fatigue failure under an asymmetric loading cycle under repeated loading. It is proved that in order to increase the number of cycles required for fatigue fracture, during the first loading, when the material is strengthened due to plastic deformation, and with repeated cyclic loading, the same stress components must take place. It is proved that if during repeated loading the end of the loading path is inside the endurance surface, then the number of cycles required for fatigue failure in an asymmetric loading cycle tends to infinity. Keywords: Initial loading, reloading, cyclic loading, strength, fatigue failure, plastic deformation, residual stress, yield surface.

Cycle Deformation Enabled Controllable Mechanical Polarity of Bulk Metallic Glasses

Tuning anisotropy in bulk metallic glasses, ideally isotropic, is of practical interest in optimizing properties and of fundamental interest in understanding the amorphous structure and its instability. By employing the quasi-elastic asymmetric mechanical cycling method, we effectively induce the mechanical polarity of a model bulk metallic glass, without damaging the sample or introducing significant annealing or rejuvenation effects. Moreover, the polarized anelastic limit can be well controlled by regulating the amplitude of mechanical cycling. Through the atomic-level analysis of nonaffine displacement, we find that only plastic atomic rearranged events corresponding to the training direction can be exhausted by asymmetric cycling and the survived anelastic events dominate the directional anelastic limit. The polarized distribution of local yield stress reveals that the mechanical polarity is attributed to the plastic-event-healing induced asymmetry of local potential energy surface, rather than frozen-in anelastic strain. Furthermore, the healing of plastic events associated with the redistribution of local residual stress indicates the origin of polarity induced by asymmetric cycling. Our study is of fundamental importance, which furthers our understanding of the mechanical deformation of metallic glasses and shed some light on the prospects for improved properties through induced anisotropy.

Novel Asymmetric Thiazolyl-Substituted Penta-1,4-Dien-3-Ones and 3,5-Diaryl-2-Pyrazolines

Various diaryl/hetaryl representatives of penta-1,4-dien-3-one series attract the attention of synthetic chemists during several decades owing to the possibility of their consequent chemical modification resulted in obtaining compounds of potential interest to materials science. In addition to their synthetic importance, title diarylideneacetones can be applied directly as medical drugs, such as antioxidants and anti-inflammatory agents. In this communication, we report the synthesis of a series of new asymmetric thiazole cycle containing diarylideneacetones, which further demonstrated high regioselectivity in their reaction with hydrazine. To clarify this feature, quantum-chemical modeling of the cyclization process was conducted.

Emergence of multistability and strongly asymmetric collective modes in two quorum sensing coupled identical ring oscillators.

The simplest ring oscillator is made from three strongly nonlinear elements repressing each other unidirectionally, resulting in the emergence of a limit cycle. A popular implementation of this scheme uses repressor genes in bacteria, creating the synthetic genetic oscillator known as the Repressilator. We consider the main collective modes produced when two identical Repressilators are mean-field-coupled via the quorum-sensing mechanism. In-phase and anti-phase oscillations of the coupled oscillators emerge from two Andronov-Hopf bifurcations of the homogeneous steady state. Using the rate of the repressor's production and the value of coupling strength as the bifurcation parameters, we performed one-parameter continuations of limit cycles and two-parameter continuations of their bifurcations to show how bifurcations of the in-phase and anti-phase oscillations influence the dynamical behaviors for this system. Pitchfork bifurcation of the unstable in-phase cycle leads to the creation of novel inhomogeneous limit cycles with very different amplitudes, in contrast to the well-known asymmetrical limit cycles arising from oscillation death. The Neimark-Sacker bifurcation of the anti-phase cycle determines the border of an island in two-parameter space containing almost all the interesting regimes including the set of resonant limit cycles, the area with stable inhomogeneous cycle, and very large areas with chaotic regimes resulting from torus destruction and period doubling of resonant cycles and inhomogeneous cycles. We discuss the structure of the chaos skeleton to show the role of inhomogeneous cycles in its formation. Many regions of multistability and transitions between regimes are presented. These results provide new insights into the coupling-dependent mechanisms of multistability and collective regime symmetry breaking in populations of identical multidimensional oscillators.

Cascaded full‐bridge resonant inverter configuration for different material vessel induction cooking

This paper presents a cascaded full-bridge resonant inverter configuration for different material vessel induction cooking. The proposed inverter configuration features simultaneous heating of three different material vessels, and independent power control. In this proposed work, three different induction heating loads are simultaneously operated at their respective resonant frequencies. Vessels of iron, steel, and aluminium materials are used. The output powers are independently controlled by an asymmetric duty cycle control. The proposed inverter is designed and hardware prototype has been implemented. Experimental results are validated with simulation results.

Generating asymmetry in a changing environment: cell cycle regulation in dimorphic alphaproteobacteria.

While many bacteria divide by symmetric binary fission, some alphaproteobacteria have strikingly asymmetric cell cycles, producing offspring that differs significantly in their morphology and reproductive state. To establish this asymmetry, these species employ a complex cell cycle regulatory pathway based on two-component signaling cascades. At the center of this network is the essential DNA-binding response regulator CtrA, which acts as a transcription factor controlling numerous genes with cell cycle-relevant functions as well as a regulator of chromosome replication. The DNA-binding activity of CtrA is controlled at the level of both protein phosphorylation and stability, dependent on an intricate network of regulatory proteins, whose function is tightly coordinated in time and space. CtrA is differentially activated in the two (developing) offspring, thereby establishing distinct transcriptional programs that ultimately determine their distinct cell fates. Phase-separated polar microdomains of changing composition sequester proteins involved in the (in-)activation and degradation of CtrA specifically at each pole. In this review, we summarize the current knowledge of the CtrA pathway and discuss how it has evolved to regulate the cell cycle of morphologically distinct alphaproteobacteria.

Asymmetric cycling of vanadium redox flow batteries with a poly(arylene piperidinium)-based anion exchange membrane

The potential application of a 50 μm thick anion exchange membrane prepared based on poly(terphenyl piperidinium-co-trifluoroacetophenone) (PTPT) is investigated for vanadium redox flow batteries (VRFBs). The PTPT exhibits a considerably lower vanadium permeation than Nafion 212. Therefore, the self-discharge duration of the VRFB based on PTPT is much longer than the VRFB based on Nafion 212. Besides, PTPT shows oxidative stability almost as good as Nafion 212 during immersion in an ex-situ immersion test for more than 400 h. Comparing the VRFB performance when symmetric and asymmetric electrolyte volumes are used yields interesting results. The results show that asymmetric cycling is more effective and efficient for the VRFB assembled with PTPT than Nafion 212 as the capacity fade of 0.03% cycle−1, and the highest coulombic efficiency of 98.8% is attained. Furthermore, the color change of the membrane during cycling can be reversed using a straightforward post-treatment method.

Strain ratcheting failure of dented steel submarine pipes under combined internal pressure and asymmetric inelastic cycling

This paper presents the results of an experimental study in which for the first time the progressive inelastic deformation of high strength steel pressurized pipes with plain and gouged dents was analyzed. The effect of some key loading and geometrical parameters such as initial pre-strain (εmon), dent depth ratio (δ/D) and the presence of the gouge was studied. Local dents with a hemispherical shape and gouges with different dimensions were introduced on the surface of the specimens. Specimens with plain or gouged dents were first internally pressurized, axially compressed to an initial pre-strain then subjected to cyclic nonlinear stressing.The mechanical defects were found to drastically degrade the inelastic cyclic response of the pressurized steel pipes. The presence of a dent, even with small amounts of initial pre-strains, made the pressurized pipes vulnerable to ratcheting failure. Furthermore, the ratcheting responses of the gouged dented specimens significantly differed from those for the corresponding specimens with plain dents. In fact, the combination of a dent and gouge was the severest form of the defect and demonstrated the lowest number of cycles before failure. The degradation effects of gouge were strongly dependent upon the gouge geometry, dent depth and initial pre-strain level.

The Cleavage Profile of Protein Substrates by ClpXP Reveals Deliberate Starts and Pauses.

Cells rely on protein degradation by AAA+ proteases. A well-known example is the hexameric ClpX unfoldase, which captures ATP hydrolysis to feed substrates into the oligomeric ClpP peptidase. Recent studies show that an asymmetric ClpX spiral cycles protein translocation upon ATP hydrolysis. However, how this cycle affects peptide products is less explored in part because ClpP cleavage is thought to be solely defined by sequence constraints. Here, we comprehensively characterize peptides from Caulobacter crescentus ClpXP degradation of three different substrates using high-resolution mass spectrometry and find that cleavage of translocated substrates is driven by factors other than sequence. We report that defined locations in a translocated protein are especially sensitive to cleavage spaced on average every 10-13 residues. These sites are not exclusively controlled by sequence and are independent of bulk changes in catalytic peptidase sites, ATP hydrolysis, or the efficiency of initial recognition. These results fit a model in which processive translocation through ClpX starts at a specific location in a polypeptide and pauses during reset of the ClpX hexamer after a cycle of translocation. Our work suggests that defined peptides, which could be used as signaling molecules, can be generated from a given substrate by a nonspecific peptidase.

Vertex Exponent of Asymmetric Two-coloured Cycle

This paper is about an asymmetric two-coloured cycle. Let D be an asymmetric two-coloured cycle on n vertices, where n is odd and n >= 3, we show that the exponent of the k-th vertex of D is exactly (n2-1)/4 + ⌊ k/2 ⌋.

Stratigraphic Analysis of Gercus Formation in Dohuk area, Northern Iraq

A surface section of the Gercus Formation (Middle-Late Eocene) was studied in Berafat area, Dohuk Governorate, Northern Iraq. The Gercus Formation consists of a mixed siliciclastic sediments, evaporates and carbonate sequences in the studied region, predominantly in the upper and middle parts. Nevertheless, it usually consists of upward-fining carbonate-rich sandstone cyclothems, marl, conglomerate and siltstone along with a gypsum lens and thin micrite carbonate beds. The Gercus Formation was deposited in delta and delta front of occasionally depositional environment which is represented by red-brown claystone and reddish-brown mudstone lithofacies. Cross bedded pebbly sandstone, trough cross-bedded sandstone and laminated cross-bedded sandstone lithofacies are deposited in braided delta environment. Marl lithofacies and gypsum lithofacies are deposited in intertidal and supratidal environments. The sea level fluctuation caused the river base level to occasionally rise and fall. In addition, the process changed from erosion to deposition, while the grain size also changed at different environments from gravel to sand and clays. The Gercus succession of northern Iraq was developed during the Middle-Late Eocene in an active margin basin, where the last stage closure of the New-Tethys and its collision with the Eurasian plate took place between the northeastern Arabian plate. It caused major episodes of uplifts and subsidence along with base level variations due to eustatic ups and downs. Within Gercus Formation, several fourth order cycles can be recognized, reflecting generally asymmetrical cycles, as well as the difference between sediment supply and accommodation space.

Forcing Seasonality of Influenza-like Epidemics with Daily Solar Resonance.

SummarySeasonality of acute viral respiratory diseases is a well-known and yet not fully understood phenomenon. Several models have been proposed to explain the regularity of yearly recurring outbreaks and the phase differences observed at different latitudes on the Earth. Such models consider known internal causes, primarily the periodic emergence of new virus variants that evade the host immune response. Yet, this alone is generally unable to explain the regularity of recurrences and the observed phase differences.Here we show that seasonality of viral respiratory diseases, as well as its distribution with latitude on the Earth, can be fully explained by the virucidal properties of UV-B and UV-A solar photons through a daily, minute-scale, resonant forcing mechanism. Such an induced periodicity can last, virtually unperturbed, from tens to hundreds of cycles, and even in the presence of internal dynamics (host's loss of immunity) much slower than seasonal will, on a long period, generate seasonal oscillations.

The Costs and Benefits of Price Leadership - Evidence from Retail Gasoline

This paper studies the costs and benefits of price leadership in a retail gasoline market with asymmetric price cycles. A unique dataset with high frequency price and volume data for almost all Norwegian gas stations coupled with a particular pricing pattern allow me to provide the first concrete evidence on the costs and benefits of leading price jumps. The main result is that the leader’s volume loss ensuing from being alone with a high price until the other firms match the price increase, is small compared to the large margin increases and profit gains resulting from the price jumps. Furthermore, I find that the leader is not worse off than the non-leading firms.