ALBERT

Description: High-fidelity Monte Carlo simulation of atmospheric turbulence phase screens is important for performance testing of astronomical adaptive optics systems. With a sparse spectrum model and an optimal sampling method, it is possible to generate an atmospheric turbulence phase screen with high fidelity. However, the phase screen generation speed is limited by the algorithm structure of this technique. A non-uniform fast Fourier transform technique is proposed in this paper to accelerate phase screen generation speed. This method is able to generate huge atmospheric turbulence phase screens with high fidelity and an acceptable time-cost enabling practical adaptive optics simulations of forthcoming Extremely Large Telescopes.

Description: As the pupil size of ground-based telescopes increases, adaptive optics systems become more and more important for almost all astronomical observations. To test the performance of adaptive optics systems through simulation and with test bench experiments, we need to model the atmospheric turbulence with high fidelity. To fulfil this goal, a new method based on optimal sampling with a sparse spectrum model is discussed. This method can effectively simulate the atmospheric phase screen of any power spectrum with a controllable error budget.

Description: The transpolar drift is strongly enriched in 228Ra accumulated on the wide Arctic shelves with subsequent rapid offshore transport. We present new data of Polarstern expeditions to the central Arctic and to the Kara and Laptev seas. Because 226Ra activities in Pacific waters are 30% higher than in Atlantic waters, we correct 226Ra for the Pacific admixture when normalizing 228Ra with 226Ra. The use of 228Ra decay as age marker critically depends on the constancy in space and time of the source activity, a condition that has not yet adequately been tested. While 228Ra decays during transit over the central basin, ingrowth of 228Th could provide an alternative age marker. The high 228Th/228Ra activity ratio (AR = 0.8–1.0) in the central basins is incompatible with a mixing model based on horizontal eddy diffusion. An advective model predicts that 228Th grows to an equilibrium AR, the value of which depends on the scavenging regime. The low AR over the Lomonosov Ridge (AR = 0.5) can be due to either rapid transport (minimum age without scavenging 1.1 year) or enhanced scavenging. Suspended particulate matter load (derived from beam transmission and particulate 234Th) and total 234Th depletion data show that scavenging, although extremely low in the central Arctic, is enhanced over the Lomonosov Ridge, making an age of 3 years more likely. The combined data of 228Ra decay and 228Th ingrowth confirm the existence of a recirculating gyre in the surface water of the eastern Eurasian Basin with a river water residence time of at least 3 years.

Description: Aims Nighttime sap flow of trees may indicate transpiration and/or recharge of stem water storage at night. This paper deals with the water use of Acacia mangium at night in the hilly lands of subtropical South China. Our primary goal was to reveal and understand the nature of nighttime sap flow and its functional significance. Methods Granier’s thermal dissipation method was used to determine the nighttime sap flux of A. mangium . Gas exchange system was used to estimate nighttime leaf transpiration and stomatal conductance of studied trees. Important Findings Nighttime sap flow was substantial and showed seasonal variation similar to the patterns of daytime sap flow in A. mangium . Mean nighttime sap flow was higher in the less precipitation year of 2004 (1122.4 mm) than in the more precipitation year of 2005 (1342.5 mm) since more daytime transpiration and low soil water availability in the relatively dry 2004 can be the cause of more nighttime sap flow. Although vapor pressure deficit and air temperature were significantly correlated with nighttime sap flow, they could only explain a small fraction of the variance in nighttime sap flow. The total accumulated water loss ( E L ) by transpiration of canopy leaves was only ~2.6–8.5% of the total nighttime sap flow ( E t ) during the nights of July 17–18 and 18–19, 2006. Therefore, it is likely that the nighttime sap flow was mainly used for refilling water in the trunk. The stem diameter at breast height, basal area and sapwood area explained much more variance of nighttime water recharge than environmental factors and other tree form features, such as tree height, stem length below the branch, and canopy size. The contribution of nighttime water recharge to the total transpiration ranged from 14.7 to 30.3% depending on different DBH class and was considerably higher in the dry season compared to the wet season.

Description: Endogenous metabolism, environmental exposure, and treatment with some chemotherapeutic agents can all give rise to DNA alkylation, which can occur on the phosphate backbone as well as the ring nitrogen or exocyclic nitrogen and oxygen atoms of nucleobases. Previous studies showed that the minor-groove O 2 -alkylated thymidine ( O 2 -alkyldT) lesions are poorly repaired and persist in mammalian tissues. In the present study, we synthesized oligodeoxyribonucleotides harboring seven O 2 -alkyldT lesions, with the alkyl group being a Me, Et, n Pr, i Pr, n Bu, i Bu or s Bu, at a defined site and examined the impact of these lesions on DNA replication in Escherichia coli cells. Our results demonstrated that the replication bypass efficiencies of the O 2 -alkyldT lesions decreased with the chain length of the alkyl group, and these lesions directed promiscuous nucleotide misincorporation in E. coli cells. We also found that deficiency in Pol V, but not Pol II or Pol IV, led to a marked drop in bypass efficiencies for most O 2 -alkyldT lesions. We further showed that both Pol IV and Pol V were essential for the misincorporation of dCMP opposite these minor-groove DNA lesions, whereas only Pol V was indispensable for the T-〉A transversion introduced by these lesions. Depletion of Pol II, however, did not lead to any detectable alterations in mutation frequencies for any of the O 2 -alkyldT lesions. Thus, our study provided important new knowledge about the cytotoxic and mutagenic properties of the O 2 -alkyldT lesions and revealed the roles of the SOS-induced DNA polymerases in bypassing these lesions in E. coli cells.

Description: After decades of debate, a mostly satisfactory resolution of relationships among the 11 recognized holometabolan orders of insects has been reached based on nuclear genes, resolving one of the most substantial branches of the tree-of-life, but the relationships are still not well established with mitochondrial genome data. The main reasons have been the absence of sufficient data in several orders and lack of appropriate phylogenetic methods that avoid the systematic errors from compositional and mutational biases in insect mitochondrial genomes. In this study, we assembled the richest taxon sampling of Holometabola to date (199 species in 11 orders), and analyzed both nucleotide and amino acid data sets using several methods. We find the standard Bayesian inference and maximum-likelihood analyses were strongly affected by systematic biases, but the site-heterogeneous mixture model implemented in PhyloBayes avoided the false grouping of unrelated taxa exhibiting similar base composition and accelerated evolutionary rate. The inclusion of rRNA genes and removal of fast-evolving sites with the observed variability sorting method for identifying sites deviating from the mean rates improved the phylogenetic inferences under a site-heterogeneous model, correctly recovering most deep branches of the Holometabola phylogeny. We suggest that the use of mitochondrial genome data for resolving deep phylogenetic relationships requires an assessment of the potential impact of substitutional saturation and compositional biases through data deletion strategies and by using site-heterogeneous mixture models. Our study suggests a practical approach for how to use densely sampled mitochondrial genome data in phylogenetic analyses.

Description: Gravity wave packets excited by a source of finite duration and size possess a broad frequency and wavenumber spectrum, and thus span a range of temporal and spatial scales. Observing at a single location relatively close to the source, the wave components with higher frequency and larger vertical wavelength dominate at earlier times and at higher altitudes while the lower frequency components, with shorter vertical wavelength, dominate during the latter part of the propagation. Utilizing observations from the Na lidar at Utah State University and the nearby Mesospheric Temperature Mapper (MTM) at Bear Lake Observatory (BLO) [41.9°N, 111.4°W], we investigate a unique case of vertical dispersion for a spectrally broad gravity wave packet in the mesopause region over Logan, Utah (41.7°N, 111.8°W) that occurred on September 2 nd , 2011, to study the waves’ evolution as it propagates upward. The lidar observed temperature perturbation was dominated by close to a 1-hour modulation at 100 km during the early hours, but gradually evolved into a 1.5-hour modulation during the second half of the night. The vertical wavelength also decreased simultaneously, while the vertical group and phase velocities of the packet apparently slowed, as it was approaching a critical level during the second half of the night. A two-dimensional numerical model is used to simulate the observed GW processes, finding that the location of the lidar relative to the source can strongly influence which portion of the spectrum can be observed at a particular location relative to a source.

Description: Record low austral winter rainfall totals over southwest Western Australia (SWWA) in 2010 saw a continuation of the multidecade-long winter drought plaguing the region. During this season, the highest recorded positive Southern Annular Mode (SAM) value was measured, adding weight to an association of a positive SAM with anomalously low SWWA winter rainfall (SWR), and vice-versa. However, such a SAM-SWR teleconnection has been recently questioned. Using observational data in the post-1979 satellite era, it is shown that such a SAM influence does exist. This coherence is confirmed with 1150 years of modelled 20th century SWR anomalies and SAM values from 23 climate models, showing that a nonlinear impact operates: the influence from a negative SAM is greater than that from a positive SAM. This explains why a small positive shift in the SAM can cause a large SWR reduction, as has been observed. A further test shows that models with a greater positive SAM trend systematically produce a greater future SWR reduction. As all climate models project an increase in the SAM these results suggest that as global warming continues unabated, SWWA winter droughts will be more persistent as atmospheric conditions become more unfavourable for drought-breaking rains.