Cyclic Closure Research Articles

The Variscan belts of North-West Africa: An African legacy to the Wilson Cycle concept

The concept of cyclic closure and opening of oceans along the same crustal scar was introduced by J.T. Wilson (1966) based on the example of the Atlantic Ocean and its continental borders. At that time, the only Variscan orogen cited south of Europe along the Atlantic coast of Africa was the Mauritanides of Mauritania. Here we report on the recent achievements in the Mauritanides from Mauritania to Morocco, and on the Moroccan Meseta orogen, which also records the Variscan orogeny. The Southern and Central Mauritanides are a poly-orogenic, Pan-African and Variscan orogen characterized by a thin-skinned tectonic style that mirrors the structure of the southern Appalachians, but with a different tectonic history. The Northern Mauritanides crops out in the Moroccan Oulad Dlim massif, northwest of the Reguibat Rise. This part of the belt compares with the southern part, but additionally exhibits in the west a Silurian-Devonian sector that shows possible affinities with Gondwana-derived Appalachian terranes. The Western Meseta is only affected by Variscan events, which were mild in the westernmost Meseta Coastal Block, while the Eastern Meseta was also affected by Eo-Variscan events. The along-strike change from the Mauritanides to the Meseta orogen is interpreted as a transition from a head-on collision south of the South Meseta transform fault (SMF, precursor of the South Atlas Fault, SAF) to a dextral, transpressional collision north of the SMF. South of the SAF, the Anti-Atlas and the Dhlou-Zemmour expose the foreland foldbelts of the Meseta and northernmost Mauritanides. The Coastal Block was likely displaced from the south-westernmost Anti-Atlas during the Early Carboniferous.The Wilson Cycle concept mostly applied in that the Atlantic Ocean opened where the prior Rheic Ocean had closed. Possible exceptions are the Sehoul Block north of Western Meseta and the Silurian-Devonian Sector of the Oulad Dlim massif, which may have separated from NW-Africa and re-amalgamated to it during the Variscan orogeny. Likewise, a NW-African fragment from the Anti-Atlas may have stranded in offshore Massachusetts in eastern North America. An early Ediacaran-Cambrian Wilson cycle nested in the classic cycle introduced by Wilson (1966) occurred along the margin of NW-Africa, where Cadomian terranes rifted off Africa, and some were transferred to Europe and some accreted back to NW-Africa. This early cycle likely controlled the localization of the subsequent Rheic rift, and that of the Atlantic rift along the Mauritanides after the Variscan collision.

Mechanisms for Employee Mobility Between Organizations: A Network Analysis of Faculty Turnover in Communication, 2013 to 2022

Organizations compete for scarce resources such as talent. The mobility of employees between organizations means that the inflow side acquires resources at the expense of the outflow side. This study understands employee turnover from one place to another as a mobility network where directed edges indicate migration flows between organizations. Using observational data on the turnover of tenure-line communication faculty in 129 U.S. universities from 2013 to 2022, this paper investigates the formation mechanisms of the interorganizational mobility network. The results show that the creation of migration flows is driven by transitive closure, but not by cyclic closure. Community cohesion is not a driving force of network formation. While low-prestige universities are more likely to be sources of faculty mobility than high-prestige universities, migration flows are commonly observed between organizations with similar levels of prestige. Additionally, the probability of faculty mobility between universities first decreases and then increases with their geographic distance.

Active shape oscillations of giant vesicles with cyclic closure and opening of membrane necks.

Reaction-diffusion systems encapsulated within giant unilamellar vesicles (GUVs) can lead to shape oscillations of these vesicles as recently observed for the bacterial Min protein system. This system contains two Min proteins, MinD and MinE, which periodically attach to and detach from the GUV membranes, with the detachment being driven by ATP hydrolysis. Here, we address these shape oscillations within the theoretical framework of curvature elasticity and show that they can be understood in terms of a spontaneous curvature that changes periodically with time. We focus on the simplest case provided by a attachment-detachment kinetics that is laterally uniform along the membrane. During each oscillation cycle, the vesicle shape is transformed from a symmetric dumbbell with two subcompartments of equal size to an asymmetric dumbbell with two subcompartments of different size, followed by the reverse, symmetry-restoring transformation. This sequence of shapes is first analyzed within the spontaneous curvature model which is then extended to the area-difference-elasticity model by decomposing the spontaneous curvature into a local and nonlocal component. For both symmetric and asymmetric dumbbells, the two subcompartments are connected by a narrow membrane neck with a circular waistline. The radius of this waistline undergoes periodic oscillations, the time dependence of which can be reasonably well fitted by a single Fourier mode with an average time period of 56 s.

Does it take three to dance the Tango? Organizational design, triadic structures and boundary spanning across subunits

In this paper, we investigate the processes of boundary spanning across subunits within organizational networks. We hypothesize that patterns of advice across organizational subunits are explained by different triadic mechanisms depending on the organizational design of the intra-organizational network. In organizational networks characterized by limited hierarchical differentiation among members and horizontal coordination, we found triadic cyclic closure to be positively associated to boundary spanning across subunits; but when the network reflects an organizational structure with formal hierarchical differentiation among members, then we found triadic transitive closure to be associated to boundary spanning across subunits. We test these predictions in two empirical studies consisting of two organizational networks that differ from each other in organizational design. We adopt a Bayesian approach for exponential random graph models specifically designed for the statistical analysis of interpersonal relationships within and across subgroups or subunits. We suggest that the effects of informal, triadic network configurations on boundary spanning are contingent on formal organizational design.

Synthesis, Characterization and Biological Activates Studies of some New Derivatives From 2-aminoo-5-mercapto-1, 3, 4-thiadiazole

In this work, thiadiazole derivatives were prepared by taking advantage of active sites in (2-amino-5-mercapto-1, 3, 4-thiadiazole) as a starting material base. The main heterocyclic compounds (1, 3, 4-thiadiazole, oxazole) etc, 2-amino-5-mercapto-1,3,4-thiadiazole compound (1) was prepared by cyclic closure of thiosemicarbazide compound with anhydrous sodium carbonate and carbon disulfide. Oxidation of (1) via hydrogen peroxide, to have (2) which was treated with chloro acetyl chloride to get (3). Preparation of thiazole ring (4) was from reacting of (3) with thiourea. Synthesis of diazonium salts (5) from compound (4) using sodium nitrite and HCl. Compound (5) reacted with different ester compounds to prepare a new azo compounds (6–8).Compound (3) reacts with viruses secondary amine to prepare compound (9–11). Full characterization of the synthesized compounds was done by using spectroscopic analysis such as FT-IR, 1H-NMR and C.H.N.S. technique.

Synthesis, Characterization and Biological Activates Studies of some New Derivatives From 2-aminoo-5-mercapto-1, 3, 4-thiadiazole

In this work, thiadiazole derivatives were prepared by taking advantage of active sites in (2-amino-5-mercapto-1, 3, 4-thiadiazole) as a starting material base. The main heterocyclic compounds (1, 3, 4-thiadiazole, oxazole) etc, 2-amino-5-mercapto-1,3,4-thiadiazole compound (1) was prepared by cyclic closure of thiosemicarbazide compound with anhydrous sodium carbonate and carbon disulfide. Oxidation of (1) via hydrogen peroxide, to have (2) which was treated with chloro acetyl chloride to get (3). Preparation of thiazole ring (4) was from reacting of (3) with thiourea. Synthesis of diazonium salts (5) from compound (4) using sodium nitrite and HCl. Compound (5) reacted with different ester compounds to prepare a new azo compounds (6–8).Compound (3) reacts with viruses secondary amine to prepare compound (9–11). Full characterization of the synthesized compounds was done by using spectroscopic analysis such as FT-IR, 1H-NMR and C.H.N.S. technique.

Synthesis, Characterization of New1, 3, 4-thiadiazole Derivatives with Studying their Biological Activity

In this work, thiadiazole derivatives were prepared by taking advantage of active sites in (2-amino-5-mercapto-1,3,4-thiadiazole) as base. The main hetrocyclic compounds (1,3,4-thiadiazole, oxazole) etc. 2-amino-5-mercapto-1,3,4-thiadiazole compound [1] was prepared by cyclic closure of thiosemicarbazide compound with anhydrous sodium carbonate and carbon disulfide. Oxidation of [1] via hydrogen peroxide, to have [2] which was treat with chloro acetyl chloride to get [3]. Preparation of oxazole ring [4] obtained from reacting of [3] with urea. Schiff bases [5 – 7] prepared by reacting [3] with different benzyl aldehyde. And Preparation of derivative [8 – 11], from reaction [3] with of hydrazine derivatives. Full characterization of the synthesized compounds was done by using of spectroscopic analysis such as FT-IR, 1H-NMR and C.H.N.S,

Permutations of context-free, ET0L and indexed languages

For a language $L$, we consider its cyclic closure, and more generally the language $C^{k}(L)$, which consists of all words obtained by partitioning words from $L$ into $k$ factors and permuting them. We prove that the classes of ET0L and EDT0L languages are closed under the operators $C^k$. This both sharpens and generalises Brandstädt's result that if $L$ is context-free then $C^{k}(L)$ is context-sensitive and not context-free in general for $k \geq 3$. We also show that the cyclic closure of an indexed language is indexed.

From calls to communities: a model for time-varying social networks

Social interactions vary in time and appear to be driven by intrinsic mechanisms, which in turn shape the emerging structure of the social network. Large-scale empirical observations of social interaction structure have become possible only recently, and modelling their dynamics is an actual challenge. Here we propose a temporal network model which builds on the framework of activity-driven time-varying networks with memory. The model also integrates key mechanisms that drive the formation of social ties - social reinforcement, focal closure and cyclic closure, which have been shown to give rise to community structure and the global connectedness of the network. We compare the proposed model with a real-world time-varying network of mobile phone communication and show that they share several characteristics from heterogeneous degrees and weights to rich community structure. Further, the strong and weak ties that emerge from the model follow similar weight-topology correlations as real-world social networks, including the role of weak ties.

ROS-GC interlocked Ca(2+)-sensor S100B protein signaling in cone photoreceptors: review.

Photoreceptor rod outer segment membrane guanylate cyclase (ROS-GC) is central to visual transduction; it generates cyclic GMP, the second messenger of the photon signal. Photoexcited rhodopsin initiates a biochemical cascade that leads to a drop in the intracellular level of cyclic GMP and closure of cyclic nucleotide gated ion channels. Recovery of the photoresponse requires resynthesis of cyclic GMP, typically by a pair of ROS-GCs, 1 and 2. In rods, ROS-GCs exist as complexes with guanylate cyclase activating proteins (GCAPs), which are Ca2+-sensing elements. There is a light-induced fall in intracellular Ca2+. As Ca2+ dissociates from GCAPs in the 20–200 nM range, ROS-GC activity rises to quicken the photoresponse recovery. GCAPs then progressively turn down ROS-GC activity as Ca2+ and cyclic GMP levels return to baseline. To date, GCAPs mediate the only known mechanism of ROS-GC regulation in the photoreceptors. However, in mammalian cone outer segments, cone synapses and ON bipolar cells, another Ca2+ sensor protein, S100B, complexes with ROS-GC1 and senses the Ca2+ signal with a K1/2 of 400 nM. Unlike GCAPs, S100B stimulates ROS-GC activity when Ca2+ is bound. Thus, the ROS-GC system in cones functions as a Ca2+ bimodal switch; with rising intracellular Ca2+, its activity is first turned down by GCAPs and then turned up by S100B. This presentation provides a historical perspective on the role of S100B in the photoreceptors, offers a pictorial model for the “bimodal” operation of the ROS-GC switch and projects future tasks that are needed to understand its operation. Some accounts of this review have been adopted from the original publications of these authors.

Emergence of Bursts and Communities in Evolving Weighted Networks

Understanding the patterns of human dynamics and social interaction and the way they lead to the formation of an organized and functional society are important issues especially for techno-social development. Addressing these issues of social networks has recently become possible through large scale data analysis of mobile phone call records, which has revealed the existence of modular or community structure with many links between nodes of the same community and relatively few links between nodes of different communities. The weights of links, e.g., the number of calls between two users, and the network topology are found correlated such that intra-community links are stronger compared to the weak inter-community links. This feature is known as Granovetter's “The strength of weak ties” hypothesis. In addition to this inhomogeneous community structure, the temporal patterns of human dynamics turn out to be inhomogeneous or bursty, characterized by the heavy tailed distribution of time interval between two consecutive events, i.e., inter-event time. In this paper, we study how the community structure and the bursty dynamics emerge together in a simple evolving weighted network model. The principal mechanisms behind these patterns are social interaction by cyclic closure, i.e., links to friends of friends and the focal closure, links to individuals sharing similar attributes or interests, and human dynamics by task handling process. These three mechanisms have been implemented as a network model with local attachment, global attachment, and priority-based queuing processes. By comprehensive numerical simulations we show that the interplay of these mechanisms leads to the emergence of heavy tailed inter-event time distribution and the evolution of Granovetter-type community structure. Moreover, the numerical results are found to be in qualitative agreement with empirical analysis results from mobile phone call dataset.

Role of Airway Recruitment and Derecruitment in Lung Injury

The mechanical forces generated during the ventilation of patients with acute lung injury causes significant lung damage and inflammation. Low-volume ventilation protocols are commonly used to prevent stretch-related injury that occurs at high lung volumes. However, the cyclic closure and reopening of pulmonary airways at low lung volumes, i.e., derecruitment and recruitment, also causes significant lung damage and inflammation. In this review, we provide an overview of how biomedical engineering techniques are being used to elucidate the complex physiological and biomechanical mechanisms responsible for cellular injury during recruitment/derecruitment. We focus on the development of multiscale, multiphysics computational models of cell deformation and injury during airway reopening. These models, and the corresponding in vitro experiments, have been used to both elucidate the basic mechanisms responsible for recruitment/derecruitment injury and to develop alternative therapies that make the epithelium more resistant to injury. For example, models and experiments indicate that fluidization of the cytoskeleton is cytoprotective and that changes in cytoskeletal structure and cell mechanics can be used to mitigate the mechanotransduction of oscillatory pressure into inflammatory signaling. The continued application of biomedical engineering techniques to the problem of recruitment/derecruitment injury may therefore lead to novel and more effective therapies.

Cyclic and lift closures for [formula omitted]-avoiding permutations

We prove that the cyclic closure of the permutation class avoiding the pattern k ( k − 1 ) … 21 is finitely based. The minimal length of a minimal permutation is 2 k − 1 and these basis permutations are enumerated by ( 2 k − 1 ) . c k where c k is the k th Catalan number. We also define lift operations and give similar results. Finally, we consider the toric closure of a class and we propose some open problems.

Pathophysiology of Evolution of Small Airways Disease to Overt COPD

ABSTRACTBackground: The slope of phase III (single breath nitrogen test), an index of ventilation inhomogeneity, has been used for early detection of COPD. Tidal airway closure (cyclic opening and closure of the peripheral airways during tidal breathing; ACT) and expiratory flow limitation (attainment of maximal expiratory flow during tidal expiration; EFLT) cause small airways disease (SAD). The relationships of these indices with COPD severity may reflect the progress from SAD to overt COPD. Methods: In this cross-sectional study we have assessed for the first time the phase III slope, ACT and EFLT in 10 smokers with normal spirometry (group O) and 40 COPD patients with GOLD scores from I to IV. Results: In most group O smokers the phase III slope was increased, and further increased with GOLD severity (up to 800%pred in GOLD IV). A close correlation was found of slope with GOLD (r = 0.77). ACT was absent in smokers with normal spirometry and in most patients with mild COPD. EFLT first appeared in GOLD II patients and its prevalence progressively increased in GOLD III and IV patients. Conclusions: Most group O smokers exhibit increased phase III. With overt COPD there is a progressive increase in phase III and reduction of FEV1/FVC ratio from GOLD I to IV. A reduction of FEV1 occurs from GOLD stage II. As the disease progresses from moderate to severe, there is an increasing presence of ACT. Tidal EFL, with dynamic hyperinflation and severe dyspnea is present only in GOLD III and IV.

The dynamics of R&D network in the IT industry

In this paper, we provide an empirical analysis of evolving networks of successful R&D collaborations in the IT industry (consisting of firms that obtained patents in the technological category of computers and communication) in the U.S. between 1985 and 1995. We first show that the R&D network has become more extensive, more clustered, and more unequal in the sense that ‘stars’ have emerged in the network. We then analyze the effect of the existing network structure in the process of new R&D collaboration formation. We control for unobserved similarities among firms based on the community structures within the network that the algorithm developed by Girvan and Newman (2004) identifies and find a significant cyclic closure and preferential-attachment effect.

Influence of cytoskeletal structure and mechanics on epithelial cell injury during cyclic airway reopening

Although patients with acute respiratory distress syndrome require mechanical ventilation, these ventilators often exacerbate the existing lung injury. For example, the cyclic closure and reopening of fluid-filled airways during ventilation can cause epithelial cell (EpC) necrosis and barrier disruption. Although much work has focused on minimizing the injurious mechanical forces generated during ventilation, an alternative approach is to make the EpC less susceptible to injury by altering the cell's intrinsic biomechanical/biostructural properties. In this study, we hypothesized that alterations in cytoskeletal structure and mechanics can be used to reduce the cell's susceptibility to injury during airway reopening. EpC were treated with jasplakinolide to stabilize actin filaments or latrunculin A to depolymerize actin and then exposed to cyclic airway reopening conditions at room temperature using a previously developed in vitro cell culture model. Actin stabilization did not affect cell viability but significantly improved cell adhesion primarily due to the development of more numerous focal adhesions. Surprisingly, actin depolymerization significantly improved both cell viability and cell adhesion but weakened focal adhesions. Optical tweezer based measurements of the EpC's micromechanical properties indicate that although latrunculin-treated cells are softer, they also have increased viscous damping properties. To further investigate the effect of "fluidization" on cell injury, experiments were also conducted at 37 degrees C. Although cells held at 37 degrees C exhibited no changes in cytoskeletal structure, they did exhibit increased viscous damping properties and improved cell viability. We conclude that fluidization of the actin cytoskeleton makes the EpC less susceptible to the injurious mechanical forces generated during cyclic airway reopening.

Model of community emergence in weighted social networks

Over the years network theory has proven to be rapidly expanding methodology to investigate various complex systems and it has turned out to give quite unparalleled insight to their structure, function, and response through data analysis, modeling, and simulation. For social systems in particular the network approach has empirically revealed a modular structure due to interplay between the network topology and link weights between network nodes or individuals. This inspired us to develop a simple network model that could catch some salient features of mesoscopic community and macroscopic topology formation during network evolution. Our model is based on two fundamental mechanisms of network sociology for individuals to find new friends, namely cyclic closure and focal closure, which are mimicked by local search-link-reinforcement and random global attachment mechanisms, respectively. In addition we included to the model a node deletion mechanism by removing all its links simultaneously, which corresponds for an individual to depart from the network. Here we describe in detail the implementation of our model algorithm, which was found to be computationally efficient and produce many empirically observed features of large-scale social networks. Thus this model opens a new perspective for studying such collective social phenomena as spreading, structure formation, and evolutionary processes.

Entendendo os mecanismos determinantes da lesão pulmonar induzida pela ventilação mecânica

Mechanical ventilation is considered a basic element of life support in the intensive care unit and is essential for patients with acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). Experimental studies have demonstrated that mechanical ventilation with high volumes and/or high pressures can exacerbate (VALI) or induce lung injury (VILI) with histological aspect similar to ALI/ARDS. This systematic review included the literature on MedLine and SciElo database published in the last 20 years. In this review, we will highlight the most recent data on the mechanisms of VILI. The main mechanisms of VILI are: volutrauma caused by overinflation and uneven expansion of the lungs due to high ventilation pressures or volumes; aletectrauma induced by shear forces generated during cyclic closure and reopening of terminal airways; and biotrauma where the injury resulted from the release inflammatory mediators due to physical stresses associated with mechanical ventilation. It is fundamental to understand the mechanisms related to volutrauma, atelectrauma, and biotrauma to avoid ventilator-associated lung injury.

The Dynamics of R&D Collaboration in the IT Industry

In this paper, we provide an empirical analysis of evolving networks of successful R&D collaborations in the IT industry in the U.S. between 1985 and 1995. We first show that the network has become more extensive, more clustered, and more unequal in the sense that 'stars' have emerged in the network. We then run regressions in which we control for firm similarity, including unobserved similarities inferred from the community structure of the network. The results indicate a significant cyclic closure effect and a preferential attachment effect.

Dabigatran Inhibits Arterial Thrombosis in a Porcine Model of Cyclic Flow Reduction.

The use of vitamin K antagonists in the prevention of arterial thrombosis is hampered by many limitations, such as a narrow therapeutic window, frequent monitoring and drug and food interactions. Dabigatran is a potent, direct thrombin inhibitor that effectively inhibits venous thrombosis in several animal models. It can be given orally as the prodrug, dabigatran etexilate, and is rapidly converted by ubiquitous esterases to the active principle dabigatran during absorption. It has no drug-drug or food interaction potential and therefore does not need monitoring.The objective of this study was to investigate the antithrombotic and anticoagulant effects of dabigatran in an arterial thrombosis model that measures cyclic flow (Folt's model) in injured arteries of pigs.Domestic pigs (15–18g) were anesthetized, ventilated and monitored during the entire procedure (n=4–6 /treatment group). Acute compression damage and stenosis of the right carotid artery resulted in thrombus formation as measured using a Doppler flow probe. Mechanical embolization of the clot restored flow through the vessel until a new thrombus reoccluded the vessel a few min later. Subsequent thrombosis and embolization created a reproducible pattern of flow reduction in the vessel. Dabigatran was given i.v. in doses of 0.1–3 mg/kg either before injury (prevention) or after injury (treatment) was induced. The frequency of recurrent thrombosis was measured in 20 min intervals over the first hour and in 30 min intervals over the 2nd hr post-injury. Antithrombotic effectiveness was measured as the reduction in closure frequency during each interval. Anticoagulant effects were monitored as the aPTT.In placebo-treated animals there were ~10 closures per interval (9.81± 0.92) after injury. When dabigatran was given prior to vessel damage, there was a dose-dependent inhibition of cyclic closure, 94% with 1 mg/kg i.v. in the first 20 min interval. There was still a 66% reduction in cyclic closures in the final 30 min interval 1.5–2 hrs after injury. Baseline aPTT values of 14.7 ± 0.5 s were elevated in a dose-dependent manner to peak levels of 31.7, 42.7 and 71.8 s 5 min after dosing with 0.1, 0.3 and 1.0 mg/kg, respectively.Dosing dabigatran post-vessel injury also resulted in a dose-dependent inhibition of cyclic closure. In placebo-treated animals there were a constant ~15 closures per interval (15.2 ± 0.3). There was a dose-dependent inhibition in the frequency of arterial closure, with an 84% reduction in the first 20 min after an i.v. dose of 3 mg/kg. Interestingly, the reduction in cyclic closure frequency was maintained over the entire 2 hr period after a single bolus dose and between 90–120 min post dosing, cyclic closure was also inhibited by 84% with the 3 mg/kg dose. These antithrombotic effects were associated with a dose-dependent elevation in the aPTT from 14.2 s with placebo, to a 5 min peak level of 29.2, 60.7 and 218.1 s, respectively with 0.1, 1 and 3 mg/kg.These results indicate that dabigatran is effective in the prevention and treatment of arterial thrombosis in this model. A single bolus dose administered just after injury was sufficient to dampen the thrombogenic response of the damaged arterial wall for up to 2 hrs post injury, illustrating the potential benefit from inhibition of clot-bound thrombin. Thus dabigatran may be an effective alternative to current anticoagulant therapy in arterial indications.