Catastrophic Break Research Articles

Novel Chromium–Silicon Slurry Coatings for Hot Corrosion Environments

Ni-based superalloys are commonly used in gas turbines because of their exceptional high-temperature mechanical properties. To secure a long service life, the materials must also have sufficient corrosion resistance. Therefore, diffusion coatings are widely used to enrich the surface in protective oxide scale-forming elements. For temperatures between 650 and 950 °C, where hot corrosion occurs, Cr-based coatings are advantageous. These are commonly applied via the laborious pack cementation process. Recently, a novel cost-effective Cr/Si slurry coating process has been developed which demonstrated resistance to oxidative high-temperature environments. Here, the protection of the slurry coatings against hot corrosion type I at 900 °C on the Ni-based superalloy Rene 80 is investigated and compared to coatings produced by pack cementation. Prior to the 300-h exposures in air containing 0.1% SO2 at 900 °C, 4 mg/cm2 of Na2SO4 was deposited on the material surfaces. The uncoated Rene 80 exhibited rapid dissolution of the initial oxide scale followed by catastrophic break away oxidation. In comparison, the slurry coatings showed significantly improved hot corrosion resistance compared to the uncoated alloy and a better protection than a Cr pack cementation coating. The Cr pack cemented Rene 80 showed improved hot corrosion resistance, but Cr depletion in the subsurface zone occurred with increasing exposure time, associated with the propagation of Al internal oxidation and increasing sulfidation. In contrast, the slurry coatings formed an external Cr2O3 scale coupled with an agglomeration of SiO2 underneath and a continuous Al2O3 subscale which offered a better diffusion barrier and leading to superior long-term protection against hot corrosion.

Freeze range of a condensing gas propagating in a liquid helium-cooled tube

Understanding air propagation and condensation following a catastrophic vacuum break in particle accelerator beamlines cooled by liquid helium is crucial for maintaining the operational safety of these facilities. Previous experimental investigations on nitrogen gas propagation in both normal liquid helium (He I) and superfluid helium (He II) cooled copper tubes unveiled a nearly exponential deceleration of the gas propagation. A comprehensive theoretical model incorporating gas dynamics, heat transfer, and condensation mechanisms has been developed, which effectively reproduces various key experimental observations. An intriguing phenomenon uncovered in our model simulation is that the gas propagation appears to nearly stop beyond a certain distance from the location where condensation starts. We refer to this distance as the freeze range. In this paper, we present our systematic study of the freeze range at various inlet mass fluxes and tube diameters. We show that the results can be well described by a simple correlation. The underlying physical mechanism that supports this useful correlation is explained. Knowing the freeze range may allow accelerator engineers to develop protocols for controlling frost-layer contamination in the beamline tubes, which is of great practical importance.

Experimental and numerical analysis of the emulsification of oil droplets in water with high frequency focused ultrasound

Focused high frequency ultrasound emulsification provides significant benefits such as enhanced stability, finer droplets, elevated focal pressure, lowered power usage, minimal surfactant usage and improved dispersion. Hence, in this study, the high frequency focused ultrasound emulsification of oil droplets in water was investigated through experiments and numerical modeling. The effect of transducer power (74–400 W), frequency (1.1 and 3.3 MHz), oil viscosity (10.6–512 mPas), interfacial tension (25–250 mN/m) and initial droplet radius (10–750 µm) on the emulsification process was assessed. In addition, the mechanism of droplet break-up was examined. The experiments showed that the acoustic pressure increased from 9.01 MPa to 26.24 MPa as the power was raised from 74 W to 400 W. At 74 W, the Weber number (We) at the surface and focal zone are 0.5 and 939.8, respectively. However, at 400 W, the We at the transducer surface and focal region reached 2.7 and 6451.8, respectively. Thus, bulb-like and weak catastrophic break up dominates the emulsification at 74 W. The catastrophic break up at 400 W is more vigorous because the ultrasound disruptive stress and We are higher. The time for the catastrophic dispersion of a single droplet at We = 939.8 and We = 6451.8 are 1.01 ms and 0.45 ms, respectively. The numerical model gives reasonable prediction of the trend and magnitude of the experimental acoustic pressure data. The surface and focal pressure amplitudes were estimated with errors of ∼ 6.5% and ∼ 10%, respectively. The predicted Reynolds number (Re) between 74 and 400 W were 8442 and 21364, respectively. The acoustic pressure at the focal region were ∼ 26 MPa and ∼ 69 MPa at frequencies of 1.1 MHz and 3.3 MHz, respectively. Moreover, the acoustic velocities were ∼ 16 m/s and ∼ 42 m/s at 1.1 MHz and 3.3 MHz, respectively. Hence, smaller droplets could be attained at higher frequency excitation under intense catastrophic modes. The Ohnesorge number (Oh) increased from 0.062 to 3.12 with the viscosity between 10.6 mPas and 530 mPas. However, the We remained constant at 856.14 for the studied range. Generally, higher critical We is required for the different breakup stages as the viscosity ratio is elevated. Moreover, the We increased from 25.68 to 1284.22 as the droplet radius was elevated from 15 to 750 µm. Larger droplets allow for higher possibility and intensity of breakup due to diminished viscous and interfacial resistance.

Magnitude of formative flows in stream potholes

Although it is generally recognized that geomorphic work is tied to bedrock channel reshaping, the importance of low vs. high flow stages that cause the most geomorphic impact remains unclear. The objective of the research is to study the concept of “formative flow” in bedrock channels and determine, through morphological studies, if those flows have any impact on sculpted features such as potholes and how this relationship relates to various inputs such as flow stages (magnitude and frequency), shear stress, and sediment size. Here, we studied the distribution of the main pothole typologies and tried to understand why potholes are found along bedrock river channels. Specifically, we examined stream potholes from three locations along the Spanish Central System: Alberche, Tietar, and Manzanares rivers. We conducted the research by taking precise geometric measurements, classifying potholes, analyzing flow magnitude and frequency, and using a two-dimensional (2D) hydrodynamic model to assess key variables in Manzanares river. This research demonstrated that bankfull depths completely cover all pothole typologies in all the analyzed sites but are not sufficient to achieve its formative flow depth (FFD). Using a detailed 2D hydrodynamic model in Manzanares river, we discovered that dimensions of cylindrical potholes are closely related to bankfull discharge and that this depth is connected to FFD. Other potholes, such as erosive-compound and erosive-lateral, are historical remnants, and their shapes are not related to any particular FFD and are likely associated with rare events and catastrophic breaks. A collection of laterals that exhibit FFD near bankfull flows appear to represent a part of the recent evolution of a knickpoint. To summarize, it can be inferred from the findings that the utility of morphological analysis in conjunction with the 2D hydrodynamic model is to examine the fraction of erosional/active features to determine the degree of senescence and/or change in natural conditions in a river reach.

Experimental Investigation on Ice Accretion Upon Ice Particle Impacting onto Heated Surface

An experimental study was conducted to examine the dynamic ice accretion process upon the impingement of microsized, airborne ice particles/crystals onto a heated test surface pertinent to aeroengine icing phenomena. The experimental study was conducted in a specially designed ice crystal icing test facility to generate and inject microsized ice particles into a frozen-cold airflow. The microsized ice particles were forced to impinge onto a heated test plate with controllable surface temperatures. Upon impingement of the ice particles onto the heated test surface, the dynamic ice accretion process was found to take place over the heated surface in three distinct stages: 1) an ice-melting stage at the beginning, followed by 2) an ice/water mixture formation stage, and then 3) a water refreezing stage, causing the formation of a solid ice layer accreted on the heated test surface eventually. After impinging onto the test plate, while small ice particles with spheric shapes were found to be more ready to bounce off from the test surface, large, nonspheric-shaped ice particles experienced a catastrophic fragmentation process and break up into smaller pieces with noticeable impingement residues remaining on the test surface. The formation of a liquid water film layer on the test surface due to the melting of the impinged ice particles was found to be very beneficial to make more impinged ice particles stay sticking on the test surface, resulting in a rapid growth of the water/ice layer accreted on the heated test surface. A comprehensive theoretical analysis was also performed to examine the unsteady heat transfer characteristics during the dynamic ice accretion process. The theoretic predictions of the collection efficiency of the impinged ice particles on the heated test surface and the temperature variations of the water layer at the initial ice-melting stage were found to agree well with the experimental measurement results.

Russian revolution of 1917 as interpreted by Ivan Ilyin and the eurasianists: two vectors of russian conservative journalism in the 1920s and 1930s

The article provides a comparative analysis of two interpretations of the Russian Revolution presented in the journalistic works of Ivan Ilyin and the Eurasianists. Both Ilyin and the Eurasianists saw the spiritual origins and prerequisites of the revolution in the mindset of the Russian pre-revolutionary society, primarily the Russian intelligentsia. Sharing a common attitude towards the value primacy of national identity, Ilyin and the Eurasianists radically differed in their assessments of the essence and prospects of Russian Bolshevism. This discrepancy is explained by the inconsistency of fundamental historical presumptions. Eurasianists considered the Soviet State a continuation of the centuries-old history of Russia-Eurasia. In turn, Ilyin saw in the Russian Revolution a catastrophic break in historical continuity.

Experimental and numerical investigations of a catastrophic tailings dam break in Daye, Hubei, China

Experimental and numerical investigations of a catastrophic tailings dam break in Daye, Hubei, China

A Proof-of-Concept Study for Hydraulic Model-Based Leakage Detection in Water Pipelines Using Pressure Monitoring Data

It is estimated that about 20% of treated drinking water is lost through distribution pipeline leakages in the United States. Pipeline leakage detection is a top priority for water utilities across the globe as leaks increase operational energy consumption and could also develop into potentially catastrophic water main breaks, if left unaddressed. Leakage detection is a laborious task often limited by the financial and human resources that utilities can afford. Many conventional leak detection techniques also only offer a snapshot indication of leakage presence. Furthermore, the reliability of many leakage detection techniques on plastic pipelines that are increasingly preferred for drinking water applications is questionable. As part of a smart water utility framework, this paper proposes and validates a hydraulic model-based technique for detecting and assessing the severity of leakages in buried water pipelines through monitoring of pressure from across the water distribution system (WDS). The envisioned smart water utility framework entails the capabilities to collect water consumption data from a limited number of WDS nodes and pressure data from a limited number of pressure monitoring stations placed across the WDS. A popular benchmark WDS is initially modified by inducing leakages through addition of orifice nodes. The leakage severity is controlled using emitter coefficients of the orifice nodes. WDS pressure data for various sets of demands is subsequently gathered from locations where pressure monitoring stations are to be placed in that modified distribution network. An evolutionary optimization algorithm is subsequently used to predict the emitter coefficients so as to determine the leakage severities based on the hydraulic dependency of the monitored pressure data on various sets of nodal demands. Artificial neural networks (ANNs) are employed to mimic the popular hydraulic solver EPANET 2.2 for high computational efficiency. The goals of this study are to: (1) validate the proof of concept of the proposed modeling approach for detecting and assessing the severity of leakages and (2) evaluate the sensitivity of the prediction accuracy to number of pressure monitoring stations and number of demand nodes at which consumption data is gathered and used. This study offers new value to prioritize pipes for rehabilitation by predicting leakages through a hydraulic model-based approach.

Superposed Natural Hazards and Pandemics: Breaking Dams, Floods, and COVID-19

Within the engineering domain, safety issues are often related to engineering design and typically exclude factors such as epidemics, famine, and disease. This article provides a perspective on the reciprocal relationship and interaction between a natural hazard and a simultaneous pandemic outbreak and discusses how a catastrophic dam break, combined with the ongoing COVID-19 pandemic, poses a risk to human life. The paper uses grey- and peer-reviewed literature to support the discussion and reviews fundamentals of dam safety management, potential loss of life due to a dam break, and the recent evolution in dam risk analysis to account for the COVID-19 outbreak. Conventional risk reduction recommendations, such as quick evacuation and sheltering in communal centers, are revisited in the presence of a pandemic when social distancing is recommended. This perspective manuscript aims to provide insight into the multi-hazard risk problem resulting from a concurring natural hazard and global pandemic.

Influence of the initial droplet distribution on the prediction of spray dynamics in Eulerian-Lagrangian simulations

Liquid fuel atomisation is largely affected by in and near nozzle phenomena. In this paper we establish a link between the initial droplet distribution at the nozzle exit, used as an input parameter in Lagrangian solvers, and the effect that this selection has on the subsequent predicted spray physics. Three initial PDFs with similar mean but different variance are tested in order to represent different aspects of the injection physics. Results are validated against an extensive range of experimental data from the Engine Combustion Network for the mildly cavitating Gasoline Spray G. Gasoline Direct injectors present high complexity both due to the importance of the near-nozzle phenomena for the fuel-air mixing, as well as due to the spray plume to plume interactions further downstream. Thus, they provide a well suited benchmark case for our study. We conclude that a correctly selected initial mean droplet size in combination to standard evaporation and break up models can provide reasonable predictions for a range of quantities including liquid and vapour penetration. Different droplet distribution models though exhibit differences in their prediction accuracy in terms of droplet dynamics depending on the initial droplet size variation around the mean. We demonstrate that these differences affect the coupling between the Lagrangian and the Eulerian dynamics through a Stokes numbers analysis close to the nozzle. We also analyse the effects that the stripping and catastrophic break up mechanisms have on the evolution of the droplet PDF at different axial locations depending on the selected initial droplet sizes. Overall, our results allow for a better understanding of the influence of the Lagrangian model input parameters on the global spray development on a numerical level, but can also help the optimisation of the design of new injectors by improving the understanding of the link between initial droplet distributions and the physics of the spray further downstream.

Community Preparedness towards Dam Disaster: Disaster Risk Reduction (DRR) Program in Cameron Highlands

Dam disaster occurrences are an unexpected event that occurs suddenly without warning. It has become very alarming, resulting in a catastrophic break followed by a flood wave at high speed with considerable loss of life and catastrophic damages to infrastructure and the environment. Given these circumstances, the community preparedness for disaster risk reduction (DRR) is important to strengthen disaster response strategies. It helps the community to understand the situations to face disaster and interact with present conditions with efficient manners. The research aims to investigate the community awareness and preparedness and the effectiveness of the DRR program toward dam-related disaster. In this research, two dams in Cameron Highland have been selected as sites study: Sultan Abu Bakar (SAB) Hydroelectric Scheme and its vicinity in Lembah Bertam; and Susu Dam and its vicinity in Pos Telanok. The research utilised questionnaire surveys as a data collection method, where Statistical Package Software SPSS Version 25 was used to analyse data. The finding indicates that an integrated community-based program is an effective approach to increase people's preparedness for the disaster. The result can assist local agencies and dam owners in formulating strategies for future DRR programs. Identifying these pertinent factors enables a greater understanding of the community's preparedness for disaster risk reduction (DRR) in both dams of Cameron Highlands.

Long-term gear life prediction based on ordered neurons LSTM neural networks

• A new gear RUL prediction model based on ON-LSTM is proposed. • The physical explanation of ON-LSTM is firstly achieved. • The frequency center index is found to be suitable for the gear health index. • This method has better long-term prediction ability than other traditional methods. • This method can implement RUL prediction in the case of small samples. Gear failure may affect the operation of mechanical equipment, and even cause the catastrophic break of machine and even casualties. Thus, the remaining useful life (RUL) estimation of the gear has important significance. This paper proposes a gear RUL prediction model based on ordered neurons long short-term memory (ON-LSTM) networks. The proposed methodology consists of two parts: firstly, extract the health index by computing frequency-domain features of raw signals; secondly, the ON-LSTM network model is constructed for generating the target output of the RUL prediction. Unlike the traditional LSTM neural network, the developed model integrating tree structures into LSTM to use the sequential information between neurons, so it has enhanced predictive ability. In comparative experiments, the Scores of ON-LSTM, LSTM, GRU, DLSTM and DNN are 0.398, 0.129, 0.07, 0.029 and 0.102, respectively; and ON-LSTM successfully fulfils twenty-three tasks while LSTM just fulfils five tasks in long-term prediction. Moreover, ON-LSTN only requires about 400 iterations for convergence, which is much faster than other RNNs. Experimental results show that ON-LSTM network achieved the best accuracy of short-term and long-term prediction, and it has the best robustness and convergence speed. And it can be effectively applied to the RUL prediction of gears.

Detection and reconstruction of catastrophic breaks of high-frequency financial data with local linear scaling approximation

Catastrophic breaks of high-frequency financial data usually contain important information, and it is crucial for investment decision making to accurately detect and analyze these catastrophic breaks. In this paper, we use a robust algorithm, the local linear scale approximation (LLSA), which enriches nonlinear filtering methods in data mining to detect and reconstruct catastrophic breaks. Guided by this methodology, we detect the catastrophic breaks in the high-frequency financial data of the Shanghai composite index from 2015 to 2018, and ten catastrophic breaks are found. Our results confirm that the LLSA is able to preserve smooth trends and accurately display any catastrophic breaks. In addition, we find that all these breaks are consistent with three types of economic events — the adjustment of monetary policies, the introduction of macroeconomic policies or government guidance, and the revolutionary events of the securities market. Explanations are given for the emergence of these events.

Ring-core integral method to measurement residual stress distribution of Al-7075 alloy processed by cyclic close die forging

Cyclic close die forging (CCDF) is one the severe plastic deformation (SPD) process. In this study, the CCDF has been used to improve the mechanical properties of the Al 7075 alloy. It is observed that performing the CCDF at ambient temperature, cause to catastrophic cracks and breaks. To avoid the breaks, the T6 pick aged samples have been over-aged at 470 °C for 1 h and CCDF has been performed at 200 °C. The mechanical properties of an over-aged Al 7075 alloy processed by CCDF have been examined by tensile test and microhardness. The results have been indicated that performing the CCDF at 200 °C could improve the yield point, ultimate stress and elongation simultaneously. The residual stress distribution after 3, 9 and 15 passes of CCDF has been measured by the ring-core method and integral computational technique. The results indicate that, increasing the CCDF passes at 200 °C decrease the magnitude of the residual stresses in processed Al 7075 alloy. By considering the difference between the principal residual stresses, it is concluded that the diameter of the related Mohr circle is small and consequently trivial shear stress is expected after CCDF process of Al 7075 alloy at 200 °C.

Design, manufacturing and testing of hybrid adhesive joints with metallic pins to join steel with fiberglass reinforced composite

Traditional hybrid adhesive joints have been frequently used to join composite with metals as they provide a greater rigidity, higher failure stress than conventional mechanical bonding and a progressive ductile failure. However, this joining continues to require drilling the adherends and have got more weight than the adhesive bonds. A technical option that could improve the behavior of this bond is to use millimetric metal pins. Those pins are incorporated and distributed in the metallic material and, they are inserted into the composite material (before curing), during the assembly with adhesives. This type of hybrid joining has got more mechanical strength than equivalent adhesive bonding and absorbs more mechanical energy during breakage as a consequence of a non-abrupt failure mode. The mechanical behavior of this joint depends on the technique used to incorporate the pins on the metal substrate. In the present work, a manufacturing method has been developed for two types of double-overlap hybrid adhesive joints: with threaded pins and with wire pins, both are inserted into the metallic adherend. These manufacturing types are simple because they use economical conventional techniques, in contrast to other methods currently used. Joints reinforced with wire pins have shown a better mechanical behaviour since they have provided bond strength after adhesive breakage. Therefore, this system provides to the joint a safety mechanism against catastrophic breaks (due to premature failure of the adhesive) and, so, greater reliability.

Закономерности размещения уникальных и крупных месторождений нефти и газа в земной коре, нефтегазогенерирующие глубинные зоны образования углеводородов и первичные астеносферные землетрясения как единый планетарный процес

The causal relationship between the location of the largest discovered hydrocarbon deposits (about 1000) and the lithosphere thickness in the regions of the Earth crust is shown. Only the significant amount of facts may be considered as the arguments of uniqueness of the existence of deep zones of hydrocarbon generation on planetary rheological in nature, lithospheric-asthenospheric boundary followed by catastrophic break in the lithosphere. In the framework of the proposed model, the next migration process can be both sequential and abrupt. The model is based on the well-known physical formula transformed into a geodynamic expression that describes a natural process of hydraulic fracturing of the lithosphere crystalline rocks when the plume achieves the critical volume. It seems that the process of accumulation of matter in the plume and its evacuation interacts and goes parallel to the earthquake activity.

Evaluation of thermal shock resistance of silicon oxycarbide materials for high-temperature receiver applications

Materials used as solar receivers in concentrated solar power technology must withstand severe operational conditions caused by concentrated solar radiation. For this solar technology several ceramic material candidates (silicon carbide, porous and dense silicon oxycarbide) have been subjected to thermal shock resistance test by using Fresnel lens, the equipment available, that concentrates the solar radiation more than 2600 times. Fast heating (37 °C s−1) and cooling rates (28 °C s−1) from 100 to 1200 °C and dwelling time of 10 min are employed. The evolution of materials surface has been evaluated during test by spectroscopic methods and both confocal and electronic microscopies. It has been obtained the surface map of each analyzed sample in order to evaluate the effect of the concentrated solar radiation on the surface and the relationship with their durability. The absorptance values were also determined before and after the ageing test using normal direction between 400 and 1100 nm. Concentrated solar radiation facilitates the decomposition of tested materials producing the formation of gaseous species (mainly CO and CO2) and a dense SiO2 layer which is formed over the material surface. SiC and porous silicon oxycarbide materials fail the thermal shock resistance test. SiC experiences a catastrophic break and in the case of porous silicon oxycarbide, gases generated can evolve easily through the pores producing a severe degradation of the material surface. However, dense silicon oxycarbide resists 100 cycles at 1200 °C due to the formation of a protective SiO2 layer over the material surface and its dense microstructure that slow down the diffusion of the gases preventing bulk material from being degraded. The surface studies confirm the formation of a crystalline SiO2 phase all over the surface. Furthermore, the very similar coefficients of thermal expansion of silicon oxycarbide and silica (≈0.4 × 10−6 °C), protects material against catastrophic failure. Finally, the absorptance values remain fairly constant before and after thermal shock test (94.78 to 95.96–96.09%). The high resistance of dense silicon oxycarbide materials to thermal shock under concentrated solar radiation makes these materials suitable candidates of being used as high temperature solar receivers.

Petrographic shock indicators and noble gas signatures in a H and an L chondrite from Antarctica

Petrographic shock indicators and noble gas signatures are studied in two ordinary chondrites, Grove Mountain (GRV) 13083 (H4) and GRV 13095 (L5), from Antarctica to investigate the degree of shock metamorphism and impact related chronologies on H and L chondrite parent bodies. In the study, we have combined both noble gas signatures and petrographic observations to understand impact effects. Based on the impact features in silicates and metal-troilite assemblages, the shock stages of the samples are classified as S6 and S5 for GRV 13095 (L5) and GRV 13083 (H4) respectively. The nominal K-Ar gas retention age of GRV 13095 (L5, S6) using bulk sample is estimated as 459 ± 13 Ma, supporting the recent major catastrophic break up event at 470 Ma on the L-chondrite parent body. The cosmic ray exposure age based on He, Ne and Ar noble gas measurements is estimated as 14.1 ± 2.5 Ma. The radiogenic gas contents in GRV 13095 (avg. 4He = 61.5 × 10−8 ccSTP/g and avg. 40Ar = 173.5 × 10−8 ccSTP/g) are observed as depleted. The depletion in radiogenic gases is consistent with the severe shock metamorphism in GRV 13095 as indicated by olivine-ringwoodite transformation in it. The estimated nominal K-Ar age of 3.67 ± 0.26 Ga for GRV 13083 shows that it falls in the major impact age distribution between 3.5 and 4.0 Ga among H-chondrites. The cosmic ray exposure age of GRV 13083 is 3.9 ± 0.7 Ma, which is younger than the major peak in the exposure age distribution for H-chondrites. The He gas retention ages in both samples are found to be younger/lower than their respective nominal K-Ar ages, which could be due to partial loss of radiogenic He. Trapped gas loss along with radiogenic gas losses in both samples, are the adverse effects of shock metamorphism.

Genome Stability by DNA Polymerase β in Neural Progenitors Contributes to Neuronal Differentiation in Cortical Development.

DNA repair is crucial for genome stability in the developing cortex, as somatic de novo mutations cause neurological disorders. However, how DNA repair contributes to neuronal development is largely unknown. To address this issue, we studied the spatiotemporal roles of DNA polymerase β (Polβ), a key enzyme in DNA base excision repair pathway, in the developing cortex using distinct forebrain-specific conditional knock-out mice, Emx1-Cre/Polβ fl/fl and Nex-Cre/Polβ fl/fl mice. Polβ expression was absent in both neural progenitors and postmitotic neurons in Emx1-Cre/Polβ fl/fl mice, whereas only postmitotic neurons lacked Polβ expression in Nex-Cre/Polβ fl/fl mice. We found that DNA double-strand breaks (DSBs) were frequently detected during replication in cortical progenitors of Emx1-Cre/Polβ fl/fl mice. Increased DSBs remained in postmitotic cells, which resulted in p53-mediated neuronal apoptosis. This neuronal apoptosis caused thinning of the cortical plate, although laminar structure was normal. In addition, accumulated DSBs also affected growth of corticofugal axons but not commissural axons. These phenotypes were not observed in Nex-Cre/Polβ fl/fl mice. Moreover, cultured Polβ-deficient neural progenitors exhibited higher sensitivity to the base-damaging agent methylmethanesulfonate, resulting in enhanced DSB formation. Similar damage was found by vitamin C treatment, which induces TET1-mediated DNA demethylation via 5-hydroxymethylcytosine. Together, genome stability mediated by Polβ-dependent base excision repair is crucial for the competence of neural progenitors, thereby contributing to neuronal differentiation in cortical development.SIGNIFICANCE STATEMENT DNA repair is crucial for development of the nervous system. However, how DNA polymerase β (Polβ)-dependent DNA base excision repair pathway contributes to the process is still unknown. We found that loss of Polβ in cortical progenitors rather than postmitotic neurons led to catastrophic DNA double-strand breaks (DSBs) during replication and p53-mediated neuronal apoptosis, which resulted in thinning of the cortical plate. The DSBs also affected corticofugal axon growth in surviving neurons. Moreover, induction of base damage and DNA demethylation intermediates in the genome increased DSBs in cultured Polβ-deficient neural progenitors. Thus, genome stability by Polβ-dependent base excision repair in neural progenitors is required for the viability and differentiation of daughter neurons in the developing nervous system.

Late Pleistocene outburst floods from Issyk Kul, Kyrgyzstan?

AbstractElevated shorelines and lake sediments surrounding Issyk Kul, the world's second largest mountain lake, record fluctuating lake levels during Quaternary times. Together with bathymetric and geochemical data, these markers document alternating phases of lake closure and external drainage. The uppermost level of lake sediments requires a former damming of the lake's western outlet through the Boam gorge. We test previous hypothesised ice or landslide dam failures by exploring possible links between late Quaternary lake levels and outbursts. We review and recompile the chronology of reported changes in lake site, and offer new ages of abandoned shorelines using 14C in bivalve and gastropod shells, and plant detritus, as well as sand lenses in delta and river sediments using Infrared Stimulated Luminescence. Our dates are consistent with elevated lake levels between ~45 ka and 22 ka. Cosmogenic 10Be and 26Al exposure ages of fan terraces containing erratic boulders (>3 m) downstream of the gorge constrain the timing of floods to 20.5–18.5 ka, postdating a highstand of Issyk Kul. A flow‐competence analysis gives a peak discharge of >104 m3 s–1 for entraining and transporting these boulders. Palaeoflood modelling, however, shows that naturally dammed lakes unconnected to Issyk Kul could have produced such high discharges upon sudden emptying. Hence, although our data are consistent with hypotheses of catastrophic outburst floods, average lake‐level changes of up to 90 mm yr–1 in the past 150 years were highly variable without any outbursts, so that linking lake‐level drops to catastrophic dam breaks remains ambiguous using sedimentary archives alone. This constraint may readily apply to other Quaternary lakes of that size elsewhere. Nonetheless, our reconstructed Pleistocene floods are among the largest reported worldwide, and motivate further research into the palaeoflood hydrology of Central Asia. Copyright © 2017 John Wiley & Sons, Ltd.