Termination Mechanism Research Articles

Merging New Organoborane Chemistry with Living Radical Polymerization

In this issue of Cell Reports Physical Science, Pan and co-workers synthesize alkylcatecholboranes that can be oxidized by oxygen to drive the release of carbon-centered radicals for initiating reversible addition-fragmentation chain transfer (RAFT) polymerization. These organoboranes can slowly decompose to radicals that enable RAFT polymerization with exceptional control yielding ultra-high molecular weight (UHMW) polymers.

Multihour Stratospheric Flights with the Heliotrope Solar Hot-Air Balloon

AbstractStandard meteorological balloons can deliver small scientific payloads to the stratosphere for a few tens of minutes, but achieving multihour level flight in this region is more difficult. We have developed a solar-powered hot-air balloon named the heliotrope that can maintain a nearly constant altitude in the upper troposphere–lower stratosphere as long as the sun is above the horizon. It can accommodate scientific payloads ranging from hundreds of grams to several kilograms. The balloon can achieve float altitudes exceeding 24 km and fly for days in the Arctic summer, although sunset provides a convenient flight termination mechanism at lower latitudes. Two people can build an envelope in about 3.5 h, and the materials cost about $30. The low cost and simplicity of the heliotrope enables a class of missions that is generally out of reach of institutions lacking specialized balloon expertise. Here, we discuss the design history, construction techniques, trajectory characteristics, and flight prediction of the heliotrope balloon. We conclude with a discussion of the physics of solar hot-air balloon flight.

A Tale of Good Fortune in the Era of DNA.

Two strains of good fortune in my career were to stumble upon the Watson-Gilbert laboratory at Harvard when I entered graduate school in 1964, and to study gene regulation in bacteriophage λ when I was there. λ was almost entirely a genetic item a few years before, awaiting biochemical incarnation. Throughout my career I was a relentless consumer of the work of previous and current generations of λ geneticists. Empowered by this background, my laboratory made contributions in two areas. The first was regulation of early gene transcription in λ, the study of which began with the discovery of the Rho transcription termination factor, and the regulatory mechanism of transcription antitermination by the λ N protein, subjects of my thesis work. This was developed into a decades-long program during my career at Cornell, studying the mechanism of transcription termination and antitermination. The second area was the classic problem of prophage induction in response to cellular DNA damage, the study of which illuminated basic cellular processes to survive DNA damage.

Stress modulation of the seismic gap between the 2008 Ms 8.0 Wenchuan earthquake and the 2013 Ms 7.0 Lushan earthquake and implications for seismic hazard

SUMMARY Between 2008 and 2013, the Ms 8.0 Wenchuan earthquake and the Ms 7.0 Lushan earthquake occurred successively in the Longmenshan fault zone. Their aftershocks delineated a prominent seismic gap approximately 50 km long, hereafter referred to as the WLSG. The possibility of an event of Ms 7.0 or above occurring in the WLSG is a matter of great concern. In this study, we estimated the change of Coulomb failure stress (ΔCFS) along the WLSG caused by historical earthquakes in the last 300 yr. Our results revealed that 20 major earthquakes cast a stress shadow on the WLSG before 2008 (−148.7 to −7.0 kPa), hindering the rupture of the Wenchuan earthquake and the Lushan earthquake. The Wenchuan earthquake had an important influence on the stress redistribution of the WLSG, resulting in significant stress increase (14.7 to 337.5 kPa). As of 2018, although the negative ΔCFS caused by historical earthquakes (especially the Dayi earthquake) pushed the southern end of the WLSG away from failure, the positive peak ΔCFS of 323.0 kPa greatly encouraged the rupture of the northern WLSG. The small afterslip and weak microseismicity indicate that the WLSG is a stress barrier with high seismic potential, which can explain the mechanism of rupture termination of the Wenchuan earthquake and the Lushan earthquake.

Anisotropic deformation and fracture mechanisms of physical vapor deposited TiN/ZrN multilayers

This work focuses on the anisotropic deformation and fracture mechanisms of a typical physical vapor deposited TiN/ZrN multilayer, employing novel nanoindentation and micropillar compression techniques. The results highlight a stronger nanoindentation response of the multilayer when loaded perpendicular (90°) to the layer orientation, and the deformation was mainly controlled by the plasticity of ZrN layers. In comparison, at parallel (0°) orientation, the kink banding and the induced cracking may weaken the constraint beneath the indenter, thus leading to degraded hardness. By considering the anisotropic deformation mechanisms, nanoindentation finite element modeling was further performed to give reliable predictions on the strength at the inclined orientation. The modeling results suggest a dominant deformation mechanism that occurred mainly in the ZrN layers, with minor contribution from the stiff TiN layers. As a result, a minimized hardness was predicted at 45° loading direction with respect to layer orientation. Finally, the micropillar compressions show a brittle nature of both 90° and 0° oriented micropillars, and a higher fracture strain was obtained at 90°, due to the observed crack termination mechanism at this orientation.

A modified particle swarm optimization using adaptive strategy

In expert systems, complex optimization problems are usually nonlinear, nonconvex, multimodal and discontinuous. As an efficient and simple optimization algorithm, particle swarm optimization(PSO) has been widely applied to solve various real optimization problems in expert systems. However, avoiding premature convergence and balancing the global exploration and local exploitation capabilities of the PSO remains an open issue. To overcome these drawbacks and strengthen the ability of PSO in solving complex optimization problems, a modified PSO using adaptive strategy called MPSO is proposed. In MPSO, in order to well balance the global exploration and local exploitation capabilities of the PSO, a chaos-based non-linear inertia weight is proposed. Meanwhile, to avoid the premature convergence, stochastic and mainstream learning strategies are adopted. Finally, an adaptive position updating strategy and terminal replacement mechanism are employed to enhance PSO’s ability to solve complex optimization problems in expert systems. 30 complex CEC2017 benchmark functions are utilized to verify the promising performance of MPSO, experimental results and statistical analysis indicate that MPSO has competitive performance compared with 16 state-of-the-art algorithms. The source code of MPSO is provided at https://github.com/lhustl/MPSO .

Effect of O2 adsorption on the termination of Li–O2 batteries discharge

Lithium-oxygen (Li–O2) batteries can exhibit high theoretical energy density and be surely suitable for potential energy storage. However, they suffer from early discharge termination and consequently low practical capacity, which has been regarded as the blockage of the diffusion of oxygen and the electron transfer on cathode surface. Herein, based on experimental results and theoretical simulation, it is confirmed that the discharge termination is largely caused by the surface adsorption of oxygen and the corresponding reaction intermediates. A TiO2-coated binder-free carbon paper has been prepared and used as cathode for Li–O2 battery. During the first discharge, the discharge plateau at ca. 2.55 V has not been observed due to the weak adsorption of oxygen on TiO2 surface, indicative of an early discharge termination of Li–O2 battery. It is further identified that the formed vacancies on TiO2 surface during lithiation/delithiation prevents the early discharge termination. Therefore, the interaction between oxygen and electrode surface plays a key role in discharge termination mechanism of Li–O2 batteries.

Modern views on the predictors of recurrent miscarriage in early gestation (review of literature)

The article presents modern views on the predictors of early miscarriage. The main links of the etiopathogenetic mechanisms of pregnancy termination in the first trimester of gestation are analyzed. The main attention is paid to endocrine, infectious, immunological, genetic factors of miscarriage. The mechanisms of pregnancy termination related to changes in the endometrium due to impaired secretory transformation are discussed in detail. The role of immunosuppression as the main link of preservation of pregnancy is highlighted.Material and methods. A literature review of 30 professional sources was carried out.Conclusions. The necessity of further study of this problem due to the socio-economic condition of the population of Ukraine and the change in the contingent of pregnant women, in particular: an increase in the proportion of women over 35 years, an increase in somatic and endocrine pathology in the population, as well as an increase in the number of pregnancies due to assisted reproductive technologies.

Highly efficient supported AlCl3‐based cationic catalysts to produce polyα‐olefin oil base stocks

AbstractThe main aim of this research is to decrease the amount of AlCl3 content that is very corrosive and hazardous in the catalytic system, required for the α‐olefin oligomerization without substantial change of final oil features. This was successfully achieved by supporting AlCl3 on different carriers. More precisely, a series of supported bimetallic catalysts was synthesized by immobilization of AlCl3 and TiCl4 onto Al2O3, SiO2, and mixed supports, that is, Al2O3/FeCl3 and SiO2/FeCl3. It was found that silica and alumina‐based catalysts had higher catalytic activities compared to support free AlCl3; however, this enhancement for silica‐based supports was more significant. According to gel permeation chromatography (GPC) results, the use of single supports, that is, Al2O3 and SiO2, increased oligomer's molecular weight, while the application of mixed supports resulted in the decrease of molecular weight of the oligomers. Viscosity characteristics of the synthesized oligomers have also been studied at two different temperatures of 40 and 100°C (KV40 and KV100). The viscosity index (VI) values, derived from KV40 and KV100, of the prepared oligomers were in the range of 126–145. The molecular weight and termination mechanisms of the oligomers were studied by 1H‐NMR spectroscopy. The obtained results disclosed that the employed reaction conditions led to the production of oligomer chains with various structures including vinylidene (Vd), and di and three‐substituted vinylene (2Vn, 3Vn) structures.

Multiple Dynamical Mechanisms of Phase-2 Early Afterdepolarizations in a Human Ventricular Myocyte Model: Involvement of Spontaneous SR Ca 2+ Release.

Early afterdepolarization (EAD) is known to cause lethal ventricular arrhythmias in long QT syndrome (LQTS). In this study, dynamical mechanisms of EAD formation in human ventricular myocytes (HVMs) were investigated using the mathematical model developed by ten Tusscher and Panfilov (Am J Physiol Heart Circ Physiol 291, 2006). We explored how the rapid (IKr) and slow (IKs) components of delayed-rectifier K+ channel currents, L-type Ca2+ channel current (ICaL), Na+/Ca2+ exchanger current (INCX), and intracellular Ca2+ handling via the sarcoplasmic reticulum (SR) contribute to initiation, termination and modulation of phase-2 EADs during pacing in relation to bifurcation phenomena in non-paced model cells. Parameter-dependent dynamical behaviors of the non-paced model cell were determined by calculating stabilities of equilibrium points (EPs) and limit cycles, and bifurcation points to construct bifurcation diagrams. Action potentials (APs) and EADs during pacing were reproduced by numerical simulations for constructing phase diagrams of the paced model cell dynamics. Results are summarized as follows: (1) A modified version of the ten Tusscher-Panfilov model with accelerated ICaL inactivation could reproduce bradycardia-related EADs in LQTS type 2 and β-adrenergic stimulation-induced EADs in LQTS type 1. (2) Two types of EADs with different initiation mechanisms, ICaL reactivation–dependent and spontaneous SR Ca2+ release–mediated EADs, were detected. (3) Termination of EADs (AP repolarization) during pacing depended on the slow activation of IKs. (4) Spontaneous SR Ca2+ releases occurred at higher Ca2+ uptake rates, attributable to the instability of steady-state intracellular Ca2+ concentrations. Dynamical mechanisms of EAD formation and termination in the paced model cell are closely related to stability changes (bifurcations) in dynamical behaviors of the non-paced model cell, but they are model-dependent. Nevertheless, the modified ten Tusscher-Panfilov model would be useful for systematically investigating possible dynamical mechanisms of EAD-related arrhythmias in LQTS.

Hallmarks of postoperative liver regeneration: An updated insight on the regulatory mechanisms.

Performance and advances in liver surgery makes remarkable progress of the understanding of liver regeneration. Liver regeneration after liver resection has been widely researched, and the underlying mechanism mostly concerns proliferation of hepatocytes and the influence by inflammation through activation of Kupffer cells and the other parenchymal cells, the second regenerative pathway by hepatic progenitor cells (HPCs), inducing angiogenesis, remodeling of a extracellular matrix (ECM), and termination mechanisms. New clinical surgeries and the updated multiomics analysis are exploiting the remarkable progress, especially in immune regulation and metabolic process of two emerging hallmarks. This review briefly represents a systemic outline of eight hallmarks, including hepatocyte proliferation, contribution of hepatic progenitor cells, inducing angiogenesis, reprogramming of the extracellular matrix, apoptosis and termination of proliferation, inflammation, immune and metabolic regulation, which are set as organizing characteristics of postoperative liver regeneration and future directions of refining treatment targets.

Photopolymerization of Acrylated Epoxidized Soybean Oil: A Photocalorimetry-Based Kinetic Study.

Photocure kinetics of acrylated epoxidized soybean oil (AESO) was studied via photocalorimetry without adding any diluent/comonomer, in the presence of two different photoinitiators, namely, 2,2-dimethoxy phenylacetophenone and 1-hydroxycyclohexyl phenyl ketone. The effect of varying photoinitiator concentration, light intensity, and temperature on the extent of crosslinking was calculated from the ratio of experimentally measured reaction enthalpy to the theoretical enthalpy of reaction (ΔHtheoretical). Photocuring of AESO was observed to be a second-order reaction exhibiting autocatalytic behavior. Nevertheless, due to the occurrence of vitrification, incomplete crosslinking (α ≠ 1) was observed in most curing conditions. Rate constants and activation energies were determined using both nonlinear model-fitting and model-free isoconversional methods. Activation energy, as determined from the model-free isoconversional method, was observed to increase as the reaction proceeded, indicating the shift in cure mechanism from kinetic-controlled to diffusion-controlled. Finally, the reaction termination mechanism was observed to be a combination of second-order and primary radical termination mechanisms.

Autonomous ascent guidance with multiple terminal constraints for all-solid launch vehicles

Removing the thrust termination mechanism of solid rocket motors is an inevitable trend but reduces the ability of terminal multi-constraints. This paper presents an improved analytic algorithm for rapid and automated ascent guidance of responsive small solid launch vehicles shutting off by fuel exhaustion. The proposed new analytical solution is solved for the two-point boundary value problem with coast arc and constraints of the given burn arc. A velocity increment control method is derived from the minimum steering angle constraints to dissipate the extra energy and an improved pointing algorithm is constructed to restrain the coupling vectors caused by the process of velocity increment control. Then, the solution of the improved pointing algorithm provides the direction of the velocity increment control and the effect of the additional coupling vectors on terminal constraints is suppressed by this direction. Finally, the application of the developed theoretical algorithm in this paper is conducted by using the last stage of all-solid launch vehicles. The proposed guidance method is verified by Monte Carlo simulations and the testing results demonstrate the adaptability, strong robustness and excellent performance for different orbital-insertion missions.

Termination of Contractual Obligations in the Civil Code of Ukraine

A contract is a means for self-organization and self-regulation of civil and legal relations between parties in the Civil Code of Ukraine. A distinguishing feature of a contractual obligation is the dependence of the beginning of a legal fact in its structure on the lawful will of a party (act) to a legal transaction or objective circumstance of reality (events). The objective of the paper is to study the mechanism of termination of obligations by determining the legal framework for its functioning. The specificity of legal facts of normative-compensating nature was determined by the use of normative and protective functions in the legislation. Civil property and its legal regulation of relations are aimed at achieving the legal result determined by their participants at the stage of the exercise of rights. The study reveals that the compensating effect of the legal termination mechanism is expressed at the stage of legal termination, which involves compensating the inability to correct a defect of a legal fact that hinders the achievement of a goal of legal regulation when exercising the right to the start of an anticipated legal effect according to a legal model of legal subjects accepted by the participants of the civil relations. The author dwells upon one of the forms of termination of contractual obligations, more specifically, on the beginning of cancellation and on the deferred status of a legal transaction.

Insight into the reaction mechanism for condensation reaction of trioxane and dimethoxymethane over HZSM-5 zeolite

Polyoxymethylene dimethyl ethers (DMMn) are considered to be a promising green diesel additive due to their similar physical properties to diesel. At present, the studies are mainly focused on the catalysts and reaction conditions of DMMn condensation reaction (i.e., DMMn was obtained by trioxane (TOX) reacting with dimethoxymethane (DMM)), but little research has been carried out on the reaction mechanism. In this work, four possible reaction mechanisms on the DMMn synthesis by TOX reacting with DMM on HZSM-5 molecular sieve were explored by the density functional theory (DFT) using Gaussian 09 package. Our calculations showed that the most likely reaction mechanism is that TOX is first decomposed into formaldehyde (FA), and then DMMn are obtained by FA reacting with DMM. For the reaction of FA with DMM, DMM firstly decomposes into methanol and carbocation, and then one direction is that FA increases the carbocation chain, while the other direction is the reaction mechanism of methanol termination. In the reaction processes, the active H in HZSM-5 molecular sieve plays an important role, but the structure of HZSM-5 molecular sieve remains basically unchanged.

Termination of pre-mRNA splicing requires that the ATPase and RNA unwindase Prp43p acts on the catalytic snRNA U6.

The termination of pre-mRNA splicing functions to discard suboptimal substrates, thereby enhancing fidelity, and to release excised introns in a manner coupled to spliceosome disassembly, thereby allowing recycling. The mechanism of termination, including the RNA target of the DEAH-box ATPase Prp43p, remains ambiguous. We discovered a critical role for nucleotides at the 3' end of the catalytic U6 small nuclear RNA in splicing termination. Although conserved sequence at the 3' end is not required, 2' hydroxyls are, paralleling requirements for Prp43p biochemical activities. Although the 3' end of U6 is not required for recruiting Prp43p to the spliceosome, the 3' end cross-links directly to Prp43p in an RNA-dependent manner. Our data indicate a mechanism of splicing termination in which Prp43p translocates along U6 from the 3' end to disassemble the spliceosome and thereby release suboptimal substrates or excised introns. This mechanism reveals that the spliceosome becomes primed for termination at the same stage it becomes activated for catalysis, implying a requirement for stringent control of spliceosome activity within the cell.

Design and Characterization of Area-Efficient Trench Termination for 4H-SiC Devices

In this paper, the operation mechanism of trench termination is investigated through 2-D numeric simulation on Silvaco. It is found that in trench termination, the electric field is terminated by the accumulated holes at the outer trench sidewall. In order to ensure a high termination breakdown voltage, the trench is refilled with a combination of SiO2 and polyimide (PI). Through various 2-D numerical simulations, the impact of structural parameters on breakdown voltage has been discussed, namely, trench depth (TD), trench width (TW), and sidewall tilt angle. The 3-D simulations are also conducted to investigate the effect of round corner radius on the device breakdown voltage and electric field in the dielectrics. Based on these results, the trench termination is designed and then fabricated along with a p-i-n diode. The measurement results show that a $14~\mu \text{m}$ wide trench is sufficient to terminate a voltage of 1750V (>96% of the ideal planar breakdown). Comparing with conventional field limiting rings junction termination extension (FLR/JTE) technology, this trench termination can significantly reduce the termination length by a factor of 4. As a result, the area efficiency is largely improved from 62% to around 90% for a 2A device conducting at 1000 A/cm2. These results indicate that the SiC device price can be substantially lowered with such an area-efficient trench termination technology. Furthermore, the 168-h high-temperature reverse bias (HTRB) test under 1200 V and 175 °C shows the potential of this trench termination for long-term reliable operation. Finally, unclamped inductive switching (UIS) tests have been conducted on fabricated devices. Compared to commercial SiC junction barrier Schottky diodes with FLR, fabricated p-i-n diodes with trench termination show significant higher avalanche capability.

HtrA-mediated selective degradation of DNA uptake apparatus accelerates termination of pneumococcal transformation.

Natural transformation mediates horizontal gene transfer, and thereby promotes exchange of antibiotic resistance and virulence traits among bacteria. Streptococcus pneumoniae, the first known transformable bacterium, rapidly activates and then terminates the transformation state, but it is unclear how the bacterium accomplishes this rapid turn-around at the protein level. This work determined the transcriptomic and proteomic dynamics during the window of pneumococcal transformation. RNA sequencing revealed a nearly uniform temporal pattern of rapid transcriptional activation and subsequent shutdown for the genes encoding transformation proteins. In contrast, mass spectrometry analysis showed that the majority of transformation proteins were substantially preserved beyond the window of transformation. However, ComEA and ComEC, major components of the DNA uptake apparatus for transformation, were completely degraded at the end of transformation. Further mutagenesis screening revealed that the membrane-associated serine protease HtrA mediates selective degradation of ComEA and ComEC, strongly suggesting that breakdown of the DNA uptake apparatus by HtrA is an important mechanism for termination of pneumococcal transformation. Finally, our mutagenesis analysis showed that HtrA inhibits natural transformation of Streptococcus mitis and Streptococcus gordonii. Together, this work has revealed that HtrA regulates the level and duration of natural transformation in multiple streptococcal species.

Alkyl nitrates in the boreal forest: formation via the NO<sub>3</sub>-, OH- and O<sub>3</sub>-induced oxidation of biogenic volatile organic compounds and ambient lifetimes

Abstract. The formation of alkyl nitrates in various oxidation processes taking place throughout the diel cycle can represent an important sink of reactive nitrogen and mechanism for chain termination in atmospheric photo-oxidation cycles. The low-volatility alkyl nitrates (ANs) formed from biogenic volatile organic compounds (BVOCs), especially terpenoids, enhance rates of production and growth of secondary organic aerosol. Measurements of the NO3 reactivity and the mixing ratio of total alkyl nitrates (ΣANs) in the Finnish boreal forest enabled assessment of the relative importance of NO3-, O3- and OH-initiated formation of alkyl nitrates from BVOCs in this environment. The high reactivity of the forest air towards NO3 resulted in reactions of the nitrate radical, with terpenes contributing substantially to formation of ANs not only during the night but also during daytime. Overall, night-time reactions of NO3 accounted for 49 % of the local production rate of ANs, with contributions of 21 %, 18 % and 12 % for NO3, OH and O3 during the day. The lifetimes of the gas-phase ANs formed in this environment were on the order of 2 h due to efficient uptake to aerosol (and dry deposition), resulting in the transfer of reactive nitrogen from anthropogenic sources to the forest ecosystem.

Monarch butterflies use an environmentally sensitive, internal timer to control overwintering dynamics.

The monarch butterfly (Danaus plexippus) complements its iconic migration with diapause, a hormonally controlled developmental programme that contributes to winter survival at overwintering sites. Although timing is a critical adaptive feature of diapause, how environmental cues are integrated with genetically-determined physiological mechanisms to time diapause development, particularly termination, is not well understood. In a design that subjected western North American monarchs to different environmental chamber conditions over time, we modularized constituent components of an environmentally-controlled, internal diapause termination timer. Using comparative transcriptomics, we identified molecular controllers of these specific diapause termination components. Calcium signalling mediated environmental sensitivity of the diapause timer, and we speculate that it is a key integrator of environmental condition (cold temperature) with downstream hormonal control of diapause. Juvenile hormone (JH) signalling changed spontaneously in diapause-inducing conditions, capacitating response to future environmental condition. Although JH is a major target of the internal timer, it is not itself the timer. Epigenetic mechanisms are implicated to be the proximate timing mechanism. Ecdysteroid, JH, and insulin/insulin-like peptide signalling are major targets of the diapause programme used to control response to permissive environmental conditions. Understanding the environmental and physiological mechanisms of diapause termination sheds light on fundamental properties of biological timing, and also helps inform expectations for how monarch populations may respond to future climate change.