Analysis of the effect of initial conditions on the initial development of a turbulent jet

The effect of the initial condition at the jet exit on the downstream evolution, particularly within the potential core length, were numerically investigated as well as with available experimental data. In order to select the most dependable computational model for the present numerical experiment, a comparative study has been performed with different turbulence models at k-epsilon level, and it was found that the k-epsilon-gammma model yields superior prediction accuracy over other conventional models. The calculated results show that the potential core length and the spreading rate the initial mixing layer are dependent on the initial length scale as well as the turbulent kinetic energy at the jet exit. Such effect of the initial length scale increases with higher initial turbulence level. An empirical parameter has been devised to collapse the calculated data of the potential core length and the spreading rate with various initial conditions onto a single curve

Slow and soft passage through tipping point of the Atlantic Meridional Overturning Circulation in a changing climate

Paleo-proxy records suggest that the Atlantic Meridional Overturning Circulation (AMOC) exhibits a threshold for an abrupt change, a so-called tipping point. A classical bifurcation theory, a basis of the tipping dynamics of AMOC implicitly assumes that the tipping point is fixed. However, when a system is subjected to time-varying forcing (e.g., AMOC exposed to ice meltwater) an actual tipping point can be overshot due to delayed tipping, referred to as the slow passage effect. Here, using an Earth system model of intermediate complexity and a low-order model with freshwater forcing, we show that the tipping point of AMOC is largely delayed by the slow passage effect. It causes a large tipping lag of up to 1300 years, and strongly relaxes the abruptness of tipping as well. We further demonstrate that the tipping modulation can actively occur in past, present, and future climates by quantifying the effect during Dansgaard-Oeschger events, meltwater pulse 1A (MWP-1A), and current Greenland ice sheet melting. The suggested slow passage effect may explain the observed lagged AMOC collapse to MWP-1A of about 1000 years and provides implications tipping risk in the future

Frequent Occurrence of Mitochondrial DNA Mutations in Barrett’s Metaplasia without the Presence of Dysplasia

BACKGROUND: Barrett's esophagus (BE) is one of the most common premalignant lesions and can progress to esophageal adenocarcinoma (EA). The numerous molecular events may play a role in the neoplastic transformation of Barrett's mucosa such as the change of DNA ploidy, p53 mutation and alteration of adhesion molecules. However, the molecular mechanism of the progression of BE to EA remains unclear and most studies of mitochondrial DNA (mtDNA) mutations in BE have performed on BE with the presence of dysplasia. METHODS/FINDINGS: Thus, the current study is to investigate new molecular events (Barrett's esophageal tissue-specific-mtDNA alterations/instabilities) in mitochondrial genome and causative factors for their alterations using the corresponding adjacent normal mucosal tissue (NT) and tissue (BT) from 34 patients having Barrett's metaplasia without the presence of dysplasia. Eighteen patients (53%) exhibited mtDNA mutations which were not found in adjacent NT. mtDNA copy number was about 3 times higher in BT than in adjacent NT. The activity of the mitochondrial respiratory chain enzyme complexes in tissues from Barrett's metaplasia without the presence of dysplasia was impaired. Reactive oxygen species (ROS) level in BT was significantly higher than those in corresponding samples. CONCLUSION/SIGNIFICANCE: High ROS level in BT may contribute to the development of mtDNA mutations, which may play a crucial role in disease progression and tumorigenesis in BE

Argonne National Laboratory Reports

Cross sections for inelastic collisions of slow electrons and the dipole oscillator-strength distribution for the neon atom are given in tabular form. The results are based on experimental data that were checked and adjusted for internal consistency

Fokker–Planck dynamics of the El Niño-Southern Oscillation

© 2020, The Author(s). The asymmetric nature of the El Niño-Southern Oscillation (ENSO) is explored by using a probabilistic model (PROM) for ENSO. Based on a Fokker–Planck Equation (FPE), PROM describes the dynamics of a nonlinear stochastic ENSO recharge oscillator model for eastern equatorial Pacific temperature anomalies and equatorial Pacific basin-averaged thermocline depth changes. Eigen analyses of PROM provide new insights into the stationary and oscillatory solutions of the stochastic dynamical system. The first probabilistic eigenmode represents a stationary mode, which exhibits the asymmetric features of ENSO, in case deterministic nonlinearities or multiplicative noises are included. The second mode is linked to the oscillatory nature of ENSO and represents a cyclic asymmetric probability distribution, which emerges from the key dynamical processes. Other eigenmodes are associated with the temporal evolution of higher order statistical moments of the ENSO system. The model solutions demonstrate that the deterministic nonlinearity plays a stronger role in establishing the observed asymmetry of ENSO as compared to the multiplicative stochastic part.11Nsciescopu

A low-order dynamical model for fire-vegetation-climate interactions

Climate conditions play a key role in determining the occurrence and severity of wildfires. Despite the impacts of wildfires on ecosystems, human livelihoods, and air quality, little is known conceptually about how natural or anthropogenic shifts in climate may influence the fire activity on a regional or global scale. Here, we introduce a new low order dynamical model that describes the nonlinear interactions between climate, vegetation (fire fuel) and fire probabilities. This 1-dimensional model describes the influence of precipitation and temperature on burned area and fuel availability. Estimating key parameters from observations, the model successfully reproduces the spatio-temporal variability of wildfire occurrences, particularly, in semi-arid regions in Africa, South America, and northern Australia. The fidelity of the model translates into a high degree of longer-term predictability of fire conditions in these vulnerable regions. Our new low-order modeling framework may provide guidance to forestry managers to assess fire risks under present and future climate conditions.11Nsciescopu

Development of new buffer layers for Cu(In,Ga)Se 2 solar cells*

Abstract: Recent progress in the field of Cu(In,Ga)Se 2 (CIGS) thin film solar cell technology is briefly reviewed. New wide-bandgap In x (OOH,S) y and ZnS x (OH) y O z buffers for CIGS solar cells have been developed. Advances have been made in the film deposition by the growth process optimization that allows the control of film properties at the micro-and nanolevels. To improve the CIGS cell junction characteristics, we have provided the integration of the developed Cd-free films with a very thin CdS film. Transmittances of the developed buffers were greatly increased compared to the standard CdS. In x (OOH,S) y buffer has been applied to low-bandgap CIGS devices which have shown poor photovoltaic properties. The experimental results obtained suggest that low efficiency can be explained by unfavorable conduction band alignment at the In x (OOH,S) y /CIGS heterojunction. The application of a wide-gap Cu(In,Ga)(Se,S) 2 absorber for device fabrication yields the conversion efficiency of 12.55 %. As a result, the In x (OOH,S) y buffer is promising for wide-bandgap Cu(In,Ga)(Se,S) 2 solar cells, however, its exploration for low-bandgap CIGS devices will not allow a high conversion efficiency. The role played by interdiffusion at the doublebuffer/CIGS heterojunction and its impact on the electronic structure and device performance has also been discussed