First principles based atomistic modeling of phase stability in PMN-xPT

We have performed molecular dynamics simulations using a shell model potential developed by fitting first principles results to describe the behavior of the relaxor-ferroelectric (1-x)PbMg1/3Nb2/3O3-xPbTiO3 (PMN-xPT) as function of concentration and temperature, using site occupancies within the random site model. In our simulations, PMN is cubic at all temperatures and behaves as a polar glass. As a small amount of Ti is added, a weak polar state develops, but structural disorder dominates, and the symmetry is rhombohedral. As more Ti is added the ground state is clearly polar and the system is ferroelectric, but with easy rotation of the polarization direction. In the high Ti content region, the solid solution adopts ferroelectric behavior similar to PT, with tetragonal symmetry. The ground state sequence with increasing Ti content is R-MB-O-MC-T. The high temperature phase is cubic at all compositions. Our simulations give the slope of the morphotropic phase boundaries, crucial for high temperature applications. We find that the phase diagram PMN-xPT can be understood within the random site model.Comment: 27 pages, 9 figure

Skeletal Structural Basis of Density Banding in the Reef Coral Montastrea Annularis

Density banding in coral skeletons can provide for reconstruction of the coral\u27s growth en- vironment over long periods. The physical differ- ences between low and high density portions of a skeletal band are not well understood. The skeletal architecture of M. annularis from Southeast Flor- ida, the Florida Keys, St. Croix, the Bahamas, and Mexico was compared in X-ray revealed high den- sity (HD), low density (LD), and stress HD bands. Density changes arose from differences in the size, but not spacing, of exothecal structural elements (horizontal dissepiments and vertical costae). En- dothecal architecture size (e.g., columella, dissepi- ments, septa) was relatively constant between den- sity band types. Results have implications for studies of coral growth, sclerochronology, and iso- topic/trace element composition

Human action perspectives based on individual plant examination results

This paper provides perspectives on human actions gained from reviewing 76 individual plant examination (IPE) submittals. Human actions found to be important in boiling water reactors (BWRs) and in pressurized water reactors (PWRs) are presented and the events most frequently found important are discussed. Since there are numerous factors that can influence the quantification of human error probabilities (HEPs) and introduce significant variability in the resulting HEPs (which in turn can influence which events are found to be important), the variability in HEPs for similar events across IPEs is examined to assess the extent to which variability in results is due to real versus artifactual differences. Finally, similarities and differences in human action observations across BWRs and PWRs are examined

Climate: Past, present, and future

Climatology and meteorology studies in the Yucca Mountain area have resulted in the following key observations and conclusions: • The present-day arid climate of the Yucca Mountain area can be understood in terms of global-scale atmospheric circulation and regional to-local physiographic features. In general terms, the area is under the influence of mid-latitude westerly winds and associated storm systems during the cool part of the year and and is under the influence of moist air advected from the eastern tropical Pacific Ocean and Gulf of California during the summer. Temperature and precipitation data from Nevada regions 3 and 4 (southern Nevada) between 1895 and 1998 suggest a mean annual temperature of 13.4 °C and a mean annual precipitation of 125 mm at 1524 m (5,000 feet) elevation (Thompson et al. 1999 [109470], Figures 13, 14, pp. 27-28). • Climate change over the past several hundred thousand years can be partially understood in terms of changes in these atmospheric circulation patterns, physiographic features, and predictable variations in the earth\u27s orbital characteristics. • Past climate change can be timed using the Earth\u27s orbital parameters: eccentricity and precession. This implies some past climate or aspects of past climate will recur in the future because future eccentricity and precession can be calculated. • Regional and local evidence indicates that the Yucca Mountain site has experienced, over the past several hundred thousand years, many different climate states, ranging from glacial to interglacial periods. Glacial and intermediate climate periods were periods of sustained greater effective moisture (commonly defined as precipitation minus evaporation, thus temperature is important) with greater infiltration and recharge than the present interglacial period. Although Yucca Mountain experienced glacial climates, it did not experience glaciation. • For the purposes of this report, long-term past climate proxy data were simplified into four climate states (interglacial, monsoon, intermediate, glacial), each with a different level of effective moisture. Climate states typical of the past 500,000 years are thought likely to reoccur in the next 500,000 years. These climate states, their duration, and magnitude are based on the assumptions and methods used and discussed herein. • Six glacial stages are predicted to occur over the next 500,000 years. They may range between 8,000 and 38,000 years in duration and encompass about 19% (95,000 years) of the next 500,000 years. These glacials will vary in magnitude, ranging from relatively warm and wet to cold and dry. • Future glacial period upper bound (most conservative) estimates for mean annual temperature and mean annual precipitation in the Yucca Mountain area are 0°C and 513 mm, respectively. Glacial period lower bound estimates for mean annual temperature and mean annual precipitation in the Yucca Mountain area are approximately 9°C and 430 mm, respectively. Other published estimates of past temperature and precipitation for the Yucca Mountain area and western Great Basin during glacial periods range from 5-15° C colder than today and precipitation from 1.4 to 2.6 times modern. • The intermediate and intermediate/monsoon climate states are estimated to encompass over 68% of the next 500,000 years (\u3e340,000 years). Intermediate climate state bounds range from approximately 9 to 10°C and 430 to 200 mm per year. • Monsoon climate states, which tend to occur between interglacial and intermediate climate states, are estimated to occur 3% of the time over the next 500,000 years during the intermediate/monsoon climate state. Monsoon climate state bounds range from about 13 to 17°C and 125 to 400 mm per year. • Interglacial (e.g. modern) climate is the warmest and driest of all climate states. This climate state has been dominant in the Yucca Mountain area, with some variation, for only the last 7 to 8 ka. The interglacial climate state is estimated to occur about 13% (65,000 years) of the time during the next 500,000 years. Mean annual temperature and precipitation are estimated to be about 13°C and 125 mm per year. • Present-day meteorological stations were selected to represent the four past climate state

Relative hyperbolicity and similar properties of one-generator one-relator relative presentations with powered unimodular relator

A group obtained from a nontrivial group by adding one generator and one relator which is a proper power of a word in which the exponent-sum of the additional generator is one contains the free square of the initial group and almost always (with one obvious exception) contains a non-abelian free subgroup. If the initial group is involution-free or the relator is at least third power, then the obtained group is SQ-universal and relatively hyperbolic with respect to the initial group.Comment: 11 pages. A Russian version of this paper is at http://mech.math.msu.su/department/algebra/staff/klyachko/papers.htm V3: revised following referee's comment

A single H/ACA small nucleolar RNA mediates tumor suppression downstream of oncogenic RAS.

Small nucleolar RNAs (snoRNAs) are a diverse group of non-coding RNAs that direct chemical modifications at specific residues on other RNA molecules, primarily on ribosomal RNA (rRNA). SnoRNAs are altered in several cancers; however, their role in cell homeostasis as well as in cellular transformation remains poorly explored. Here, we show that specific subsets of snoRNAs are differentially regulated during the earliest cellular response to oncogenic RASG12V expression. We describe a novel function for one H/ACA snoRNA, SNORA24, which guides two pseudouridine modifications within the small ribosomal subunit, in RAS-induced senescence in vivo. We find that in mouse models, loss of Snora24 cooperates with RASG12V to promote the development of liver cancer that closely resembles human steatohepatitic hepatocellular carcinoma (HCC). From a clinical perspective, we further show that human HCCs with low SNORA24 expression display increased lipid content and are associated with poor patient survival. We next asked whether ribosomes lacking SNORA24-guided pseudouridine modifications on 18S rRNA have alterations in their biophysical properties. Single-molecule Fluorescence Resonance Energy Transfer (FRET) analyses revealed that these ribosomes exhibit perturbations in aminoacyl-transfer RNA (aa-tRNA) selection and altered pre-translocation ribosome complex dynamics. Furthermore, we find that HCC cells lacking SNORA24-guided pseudouridine modifications have increased translational miscoding and stop codon readthrough frequencies. These findings highlight a role for specific snoRNAs in safeguarding against oncogenic insult and demonstrate a functional link between H/ACA snoRNAs regulated by RAS and the biophysical properties of ribosomes in cancer

Core damage frequency (reactor design) perspectives based on IPE results

This paper provides perspectives gained from reviewing 75 Individual Plant Examination (IPE) submittals covering 108 nuclear power plant units. Variability both within and among reactor types is examined to provide perspectives regarding plant-specific design and operational features, and C, modeling assumptions that play a significant role in the estimates of core damage frequencies in the IPEs. Human actions found to be important in boiling water reactors (BWRs) and in pressurized water reactors (PWRs) are presented and the events most frequently found important are discussed

An assessment of high carbon stock and high conservation value approaches to sustainable oil palm cultivation in Gabon

Industrial-scale oil palm cultivation is rapidly expanding in Gabon, where it has the potential to drive economic growth, but also threatens forest, biodiversity and carbon resources. The Gabonese government is promoting an ambitious agricultural expansion strategy, while simultaneously committing to minimize negative environmental impacts of oil palm agriculture. This study estimates the extent and location of suitable land for oil palm cultivation in Gabon, based on an analysis of recent trends in plantation permitting. We use the resulting suitability map to evaluate two proposed approaches to minimizing negative environmental impacts: a High Carbon Stock (HCS) approach, which emphasizes forest protection and climate change mitigation, and a High Conservation Value (HCV) approach, which focuses on safeguarding biodiversity and ecosystems. We quantify the forest area, carbon stock, and biodiversity resources protected under each approach, using newly developed maps of priority species distributions and forest biomass for Gabon. We find 2.7–3.9 Mha of suitable or moderately suitable land that avoid HCS areas, 4.4 million hectares (Mha) that avoid HCV areas, and 1.2–1.7 Mha that avoid both. This suggests that Gabon's oil palm production target could likely be met without compromising important ecosystem services, if appropriate safeguards are put in place. Our analysis improves understanding of suitability for oil palm in Gabon, determines how conservation strategies align with national targets for oil palm production, and informs national land use planning