The evolution of the star forming sequence in hierarchical galaxy formation models

It has been argued that the specific star formation rates of star forming galaxies inferred from observational data decline more rapidly below z = 2 than is predicted by hierarchical galaxy formation models. We present a detailed analysis of this problem by comparing predictions from the GALFORM semi-analytic model with an extensive compilation of data on the average star formation rates of star-forming galaxies. We also use this data to infer the form of the stellar mass assembly histories of star forming galaxies. Our analysis reveals that the currently available data favour a scenario where the stellar mass assembly histories of star forming galaxies rise at early times and then fall towards the present day. In contrast, our model predicts stellar mass assembly histories that are almost flat below z = 2 for star forming galaxies, such that the predicted star formation rates can be offset with respect to the observational data by factors of up to 2-3. This disagreement can be explained by the level of coevolution between stellar and halo mass assembly that exists in contemporary galaxy formation models. In turn, this arises because the standard implementations of star formation and supernova feedback used in the models result in the efficiencies of these process remaining approximately constant over the lifetime of a given star forming galaxy. We demonstrate how a modification to the timescale for gas ejected by feedback to be reincorporated into galaxy haloes can help to reconcile the model predictions with the data.Comment: 30 Pages, 16 Figures, MNRAS accepte

Electrostatic considerations affecting the calculated HOMO-LUMO gap in protein molecules.

A detailed study of energy differences between the highest occupied and lowest unoccupied molecular orbitals (HOMO-LUMO gaps) in protein systems and water clusters is presented. Recent work questioning the applicability of Kohn-Sham density-functional theory to proteins and large water clusters (E. Rudberg, J. Phys.: Condens. Mat. 2012, 24, 072202) has demonstrated vanishing HOMO-LUMO gaps for these systems, which is generally attributed to the treatment of exchange in the functional used. The present work shows that the vanishing gap is, in fact, an electrostatic artefact of the method used to prepare the system. Practical solutions for ensuring the gap is maintained when the system size is increased are demonstrated. This work has important implications for the use of large-scale density-functional theory in biomolecular systems, particularly in the simulation of photoemission, optical absorption and electronic transport, all of which depend critically on differences between energies of molecular orbitals.Comment: 13 pages, 4 figure

The Barometer

(Lt. Comdr. B.D. Cole, USN, comments on Lt. N. Clark Williams\u27 article, Decision Analysis: Toward Better Naval Management Decisions, July-August 1974.), (Lt. Comdr. Peter H. Cressy amplifies on his article, Developing an Alternative Approach to Race Relations Education: Identifying Military Middle Management Resistance, July-August 1974), and (Comdr. Warren H. Winchester, USN, comments on Lt. Comdr, Peter H. Cressy\u27s and Dr. Louis R. Desfosses\u27 article Developing an Alternative Approach to Race Relations Education, July-August 1974.

DNMT inhibitors reverse a specific signature of aberrant promoter DNA methylation and associated gene silencing in AML

<b>Background</b>. Myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML) are neoplastic disorders of hematopoietic stem cells. DNA methyltransferase inhibitors (DNMTi), 5-azacytidine (AzaC) and 5-aza-2’-deoxycytidine (Decitabine), benefit some MDS/AML patients. However, the role of DNMTi-induced DNA hypomethylation in regulation of gene expression in AML is unclear.<p></p> <b>Results. </b> We compared the effects of AzaC on DNA methylation and gene expression using whole-genome single-nucleotide bisulfite-sequencing (WGBS) and RNA-sequencing in OCI-AML3 (AML3) cells. For data analysis, we used an approach recently developed for discovery of differential patterns of DNA methylation associated with changes in gene expression, that is tailored to single-nucleotide bisulfite-sequencing data (Washington University Interpolated Methylation Signatures (WIMSi)). By this approach, a subset of genes upregulated by AzaC was found to be characterized by AzaC-induced signature methylation loss flanking the transcription start site. These genes are enriched for genes increased in methylation and decreased in expression in AML3 cells compared to normal hematopoietic stem and progenitor cells. Moreover, these genes are preferentially upregulated by Decitabine in human primary AML blasts, and control cell proliferation, death and development. <p></p> <b>Conclusions.</b> Our WGBS and WIMSi data analysis approach has identified a set of genes whose is methylation and silencing in AML is reversed by DNMTi. These genes are good candidates for direct regulation by DNMTi, and their reactivation by DNMTi may contribute to therapeutic activity. This study also demonstrates the ability of WIMSi to reveal relationships between DNA methylation and gene expression, based on single-nucleotide bisulfite-sequencing and RNA-seq data.<p></p&gt

Utahns are Becoming More Likely to Say Human-Caused Climate Change is Happening

Scientists who study the earth’s climate overwhelmingly agree that human activities are causing rapid change1 . Most Americans also agree that global warming is happening (74%) and caused by humans (61%)2 . However, the same research finds that about one in eight (12%) of Americans do not think global warming is happening. This indicates that despite scientific consensus, some Americans remain skeptical about whether climate change is real and if humans are the cause

The ACS LCID project. IX. Imprints of the early Universe in the radial variation of the star formation history of dwarf galaxies

Based on Hubble Space Telescope observations from the Local Cosmology from Isolated Dwarfs project, we present the star formation histories, as a function of galactocentric radius, of four isolated Local Group dwarf galaxies: two dSph galaxies, Cetus and Tucana, and two transition galaxies (dTrs), LGS-3 and Phoenix. The oldest stellar populations of the dSphs and dTrs are, within the uncertainties, coeval ($\sim 13 Gyr$) at all galactocentric radii. We find that there are no significative differences between the four galaxies in the fundamental properties (such as the normalized star formation rate or age-metallicity relation) of their outer regions (radii greater than four exponential scale lengths); at large radii, these galaxies consist exclusively of old ($\geq 10.5 Gyr$) metal-poor stars. The duration of star formation in the inner regions vary from galaxy to galaxy, and the extended central star formation in the dTrs produces the dichotomy between dSph and dTr galaxy types. The dTr galaxies show prominent radial stellar population gradients: the centers of these galaxies host young ($\leq 1 Gyr$) populations while the age of the last formation event increases smoothly with increasing radius. This contrasts with the two dSph galaxies. Tucana shows a similar, but milder, gradient, but no gradient in age is detected Cetus. For the three galaxies with significant stellar population gradients, the exponential scale length decreases with time. These results are in agreement with outside-in scenarios of dwarf galaxy evolution, in which a quenching of the star formation toward the center occurs as the galaxy runs out of gas in the outskirts.Comment: Accepted to be published in Ap

Lake-size dependency of wind shear and convection as controls on gas exchange

High-frequency physical observations from 40 temperate lakes were used to examine the relative contributions of wind shear (u*) and convection (w*) to turbulence in the surface mixed layer. Seasonal patterns of u* and w* were dissimilar; u* was often highest in the spring, while w * increased throughout the summer to a maximum in early fall. Convection was a larger mixed-layer turbulence source than wind shear (u */w*-1 for lakes* and w* differ in temporal pattern and magnitude across lakes, both convection and wind shear should be considered in future formulations of lake-air gas exchange, especially for small lakes. © 2012 by the American Geophysical Union.Jordan S. Read, David P. Hamilton, Ankur R. Desai, Kevin C. Rose, Sally MacIntyre, John D. Lenters, Robyn L. Smyth, Paul C. Hanson, Jonathan J. Cole, Peter A. Staehr, James A. Rusak, Donald C. Pierson, Justin D. Brookes, Alo Laas, and Chin H. W

Translational energy dependence of reaction mechanism: Xe++CH4→XeH++CH3

This is the publisher's version, also available electronically from http://scitation.aip.org/content/aip/journal/jcp/74/9/10.1063/1.441715.The dynamics of the exoergic ion–molecule reaction Xe+(CH4,CH3)XeH+ were studied by chemical accelerator techniques over the relative translational energy range 0.2 to 8 eV. Results of the kinematicmeasurements are reported as scattering intensity contour maps in Cartesian velocity space. Center‐of‐mass angular and energy distributions, derived from these maps, provide information on the reaction mechanism and on the partitioning of available energy between internal and translational modes in the products. The results suggest that reaction proceeds via the formation of a long‐lived complex at low collision energies (below 0.5 eV) and by a direct mechanism approaching spectator stripping at higher energies

Toward ab initio optical spectroscopy of the Fenna-Matthews-Olson complex

We present progress toward a first-principles parametrization of the Hamiltonian of the Fenna–Matthews–Olson pigment–protein complex, a molecule that has become key to understanding the role of quantum dynamics in photosynthetic exciton energy transfer. To this end, we have performed fully quantum mechanical calculations on each of the seven bacteriochlorophyll pigments that make up the complex, including a significant proportion of their protein environment (more than 2000 atoms), using linear-scaling density functional theory exploiting a recent development for the computation of excited states. Local pigment transition energies and interpigment coupling between optical transitions have been calculated and are in good agreement with the literature consensus. Comparisons between simulated and experimental optical spectra point toward future work that may help to elucidate important design principles in these nanoscale devices