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The growth of dark matter halos: evidence for significant smooth accretion
Shy Genel,Nicolas Bouché,Thorsten Naab,Amiel Sternberg,Reinhard Genzel
Physics , 2010, DOI: 10.1088/0004-637X/719/1/229
Abstract: We study the growth of dark matter halos in the concordance LCDM cosmology using several N-body simulations of large cosmological volumes. We build merger trees from the Millennium and Millennium-II simulations, covering a range 10^9-10^15 Msun in halo mass and 1-10^5 in merger mass ratio. Our algorithm takes special care of halo fragmentation and ensures that the mass contribution of each merger to halo growth is only counted once. This way the integrated merger rate converges and we can consistently determine the contribution of mergers of different mass ratios to halo growth. We find that all resolved mergers, up to mass ratios of 10^5, contribute only ~60% of the total halo mass growth, while major mergers are subdominant, e.g. mergers with mass ratios smaller than 3:1 (10:1) contribute only ~20% (~30%). This is verified with an analysis of two additional simulation boxes, where we follow all particles individually throughout cosmic time. Our results are also robust against using several halo definitions. Under the assumption that the power-law behaviour of the merger rate at large mass ratios can be extrapolated to arbitrarily large mass ratios, it is found that, independently of halo mass, ~40% of the mass in halos comes from genuinely smooth accretion of dark matter that was never bound in smaller halos. We discuss possible implications of our findings for galaxy formation. One implication, assuming as is standard that the pristine intergalactic medium is heated and photoionized by UV photons, is that all halos accrete >40% of their baryons in smooth "cold" T>~10^4K gas, rather than as warm, enriched or clumpy gas or as stars.
Mutants of GABA Transaminase (POP2) Suppress the Severe Phenotype of succinic semialdehyde dehydrogenase (ssadh) Mutants in Arabidopsis
Frank Ludewig, Anke Hüser, Hillel Fromm, Linda Beauclair, Nicolas Bouché
PLOS ONE , 2008, DOI: 10.1371/journal.pone.0003383
Abstract: Background The γ-aminubutyrate (GABA) shunt bypasses two steps of the tricarboxylic acid cycle, and is present in both prokaryotes and eukaryotes. In plants, the pathway is composed of the calcium/calmodulin-regulated cytosolic enzyme glutamate decarboxylase (GAD), the mitochondrial enzymes GABA transaminase (GABA-T; POP2) and succinic semialdehyde dehydrogenase (SSADH). We have previously shown that compromising the function of the GABA-shunt, by disrupting the SSADH gene of Arabidopsis, causes enhanced accumulation of reactive oxygen intermediates (ROIs) and cell death in response to light and heat stress. However, to date, genetic investigations of the relationships between enzymes of the GABA shunt have not been reported. Principal Findings To elucidate the role of succinic semialdehyde (SSA), γ-hydroxybutyrate (GHB) and GABA in the accumulation of ROIs, we combined two genetic approaches to suppress the severe phenotype of ssadh mutants. Analysis of double pop2 ssadh mutants revealed that pop2 is epistatic to ssadh. Moreover, we isolated EMS-generated mutants suppressing the phenotype of ssadh revealing two new pop2 alleles. By measuring thermoluminescence at high temperature, the peroxide contents of ssadh and pop2 mutants were evaluated, showing that only ssadh plants accumulate peroxides. In addition, pop2 ssadh seedlings are more sensitive to exogenous SSA or GHB relative to wild type, because GHB and/or SSA accumulate in these plants. Significance We conclude that the lack of supply of succinate and NADH to the TCA cycle is not responsible for the oxidative stress and growth retardations of ssadh mutants. Rather, we suggest that the accumulation of SSA, GHB, or both, produced downstream of the GABA-T transamination step, is toxic to the plants, resulting in high ROI levels and impaired development.
The VLT SINFONI Mg ii Program for Line Emitters (SIMPLE) II: background quasars probing z $\sim$ 1 galactic winds
Ilane Schroetter,Nicolas Bouché,Céline Péroux,Michael T. Murphy,Thierry Contini,Hayley Finley
Physics , 2015, DOI: 10.1088/0004-637X/804/2/83
Abstract: The physical properties of galactic winds are of paramount importance for our understanding of galaxy formation. Fortunately, they can be constrained using background quasars passing near star-forming galaxies (SFGs). From the 14 quasar$-$galaxy pairs in our VLT/SINFONI Mgii Program for Line Emitters (SIMPLE) sample, we reobserved the 10 brightest galaxies in H$_{\alpha}$ with the VLT/SINFONI with 0.7" seeing and the corresponding quasar with the VLT/UVES spectrograph. Applying geometrical arguments to these ten pairs, we find that four are likely probing galactic outflows, three are likely probing extended gaseous disks, and the remaining three are not classifiable because they are viewed face-on. In this paper we present a detailed comparison between the line-of-sight kinematics and the host galaxy emission kinematics for the pairs suitable for wind studies. We find that the kinematic profile shapes (asymmetries) can be well reproduced by a purely geometrical wind model with a constant wind speed, except for one pair (towards J2357$-$2736) that has the smallest impact parameter b = 6 kpc and requires an accelerated wind flow. Globally, the outflow speeds are $\sim$ 100 km/s and the mass ejection rates (or $\dot M _{\rm out}$) in the gas traced by the low-ionization species are similar to the star formation rate (SFR), meaning that the mass loading factor, $\eta$ = $\dot M _{\rm out}$/SFR, is $\sim$1.0. The outflow speeds are also smaller than the local escape velocity, which implies that the outflows do not escape the galaxy halo and are likely to fall back into the interstellar medium.
Complex-Time Singularity and Locality Estimates for Quantum Lattice Systems
Gabriel Bouch
Physics , 2010,
Abstract: We present and prove a well-known locality bound for the complex-time dynamics of a general class of one-dimensional quantum spin systems. Then we discuss how one might hope to extend this same procedure to higher dimensions using ideas related to the Eden growth process and lattice trees. Finally, we demonstrate with a specific family of lattice trees in the plane why this approach breaks down in dimensions greater than one and prove that there exist interactions for which the complex-time dynamics blows-up in finite imaginary time.
The Expected Perimeter in Eden and Related Growth Processes
Gabriel Bouch
Mathematics , 2010, DOI: 10.1007/s00548-010-0128-y
Abstract: Following Richardson and using results of Kesten on First-passage percolation, we obtain an upper bound on the expected perimeter in an Eden Growth Process. Using results of the author from a problem in Statistical Mechanics, we show that the average perimeter of the lattice animals resulting from a very natural family of "growth histories" does not obey a similar bound.
SHOOT GROWTH1 Maintains Arabidopsis Epigenomes by Regulating IBM1
Vincent Coustham, Daniela Vlad, Aurélie Deremetz, Isabelle Gy, Francisco A. Cubillos, Envel Kerdaffrec, Olivier Loudet, Nicolas Bouché
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0084687
Abstract: Maintaining correct DNA and histone methylation patterns is essential for the development of all eukaryotes. In Arabidopsis, we identified SHOOT GROWTH1 (SG1), a novel protein involved in the control of gene methylation. SG1 contains both a Bromo-Adjacent Homology (BAH) domain found in several chromatin regulators and an RNA-Recognition Motif (RRM). The sg1 mutations are associated with drastic pleiotropic phenotypes. The mutants degenerate after few generations and are similar to mutants of the histone demethylase INCREASE IN BONSAI METHYLATION1 (IBM1). A methylome analysis of sg1 mutants revealed a large number of gene bodies hypermethylated in the cytosine CHG context, associated with an increase in di-methylation of lysine 9 on histone H3 tail (H3K9me2), an epigenetic mark normally found in silenced transposons. The sg1 phenotype is suppressed by mutations in genes encoding the DNA methyltransferase CHROMOMETHYLASE3 (CMT3) or the histone methyltransferase KRYPTONITE (KYP), indicating that SG1 functions antagonistically to CMT3 or KYP. We further show that the IBM1 transcript is not correctly processed in sg1, and that the functional IBM1 transcript complements sg1. Altogether, our results suggest a function for SG1 in the maintenance of genome integrity by regulating IBM1.
Redundant and Specific Roles of the ARGONAUTE Proteins AGO1 and ZLL in Development and Small RNA-Directed Gene Silencing
Allison C. Mallory equal contributor ,Annika Hinze equal contributor,Matthew R. Tucker,Nicolas Bouché,Virginie Gasciolli,Taline Elmayan,Dominique Lauressergues,Vincent Jauvion,Hervé Vaucheret,Thomas Laux
PLOS Genetics , 2009, DOI: 10.1371/journal.pgen.1000646
Abstract: The Arabidopsis ARGONAUTE1 (AGO1) and ZWILLE/PINHEAD/AGO10 (ZLL) proteins act in the miRNA and siRNA pathways and are essential for multiple processes in development. Here, we analyze what determines common and specific function of both proteins. Analysis of ago1 mutants with partially compromised AGO1 activity revealed that loss of ZLL function re-establishes both siRNA and miRNA pathways for a subset of AGO1 target genes. Loss of ZLL function in ago1 mutants led to increased AGO1 protein levels, whereas AGO1 mRNA levels were unchanged, implicating ZLL as a negative regulator of AGO1 at the protein level. Since ZLL, unlike AGO1, is not subjected to small RNA-mediated repression itself, this cross regulation has the potential to adjust RNA silencing activity independent of feedback dynamics. Although AGO1 is expressed in a broader pattern than ZLL, expression of AGO1 from the ZLL promoter restored transgene PTGS and most developmental defects of ago1, whereas ZLL rescued only a few AGO1 functions when expressed from the AGO1 promoter, suggesting that the specific functions of AGO1 and ZLL are mainly determined by their protein sequence. Protein domain swapping experiments revealed that the PAZ domain, which in AGO1 is involved in binding small RNAs, is interchangeable between both proteins, suggesting that this common small RNA-binding domain contributes to redundant functions. By contrast, the conserved MID and PIWI domains, which are involved in 5′-end small RNA selectivity and mRNA cleavage, and the non-conserved N-terminal domain, to which no function has been assigned, provide specificity to AGO1 and ZLL protein function.
Star-Forming Galaxies at z~2: An Emerging Picture of Galaxy Dynamics and Assembly
Kristen L. Shapiro,Reinhard Genzel,Nicolas Bouché,Peter Buschkamp,Giovanni Cresci,Ric Davies,Frank Eisenhauer,Natascha F?rster Schreiber,Shy Genel,Erin Hicks,Dieter Lutz,Linda Tacconi
Physics , 2009,
Abstract: In these proceedings, we summarize recent results from our "SINS" VLT/SINFONI integral-field survey, focusing on the 52 detected UV/optically-selected star-forming galaxies at z~2. Our H-alpha emission-line imaging and kinematic data of these systems illustrates that a substantial fraction (> 1/3) of these galaxies are large, rotating disks and that these disks are clumpy, thick, and forming stars rapidly. We compare these systems to local disk scaling relations and find that the backbones of these relations are already in place at z~2. Detailed analysis of the large disks in our sample provides strong evidence that this population cannot result from a merger-dominated formation history and instead must be assembled by the smooth but rapid inflow of gas along filaments. These systems will then secularly evolve from clump-dominated disks to bulge-dominated disks on short timescales, a phenomenon that is observed in our SINS observations and is consistent with predictions from numerical simulations. These results provide new and exciting insights into the formation of bulge-dominated galaxies in the local Universe.
New Perspective on Galaxy Outflows From the First Detection of Both Intrinsic and Traverse Metal-Line Absorption
Glenn G. Kacprzak,Crystal L. Martin,Nicolas Bouché,Christopher W. Churchill,Jeff Cooke,Audrey LeReun,Ilane Schroetter,Stephanie H. Ho,Elizabeth Klimek
Physics , 2014, DOI: 10.1088/2041-8205/792/1/L12
Abstract: We present the first observation of a galaxy (z=0.2) that exhibits metal-line absorption back-illuminated by the galaxy ("down-the-barrel") and transversely by a background quasar at a projected distance of 58 kpc. Both absorption systems, traced by MgII, are blueshifted relative to the galaxy systemic velocity. The quasar sight-line, which resides almost directly along the projected minor axis of the galaxy, probes MgI and MgII absorption obtained from Keck/LRIS and Lya, SiII and SiIII absorption obtained from HST/COS. For the first time, we combine two independent models used to quantify the outflow properties for down-the-barrel and transverse absorption. We find that the modeled down-the-barrel deprojected outflow velocities range between $V_{dtb}=45-255$ km/s. The transverse bi-conical outflow model, assuming constant-velocity flows perpendicular to the disk, requires wind velocities $V_{outflow}=40-80$ km/s to reproduce the transverse MgII absorption kinematics, which is consistent with the range of $V_{dtb}$. The galaxy has a metallicity, derived from H$\alpha$ and NII, of $[{\rm O/H}]=-0.21\pm0.08$, whereas the transverse absorption has $[{\rm X/H}]=-1.12\pm0.02$. The galaxy star-formation rate is constrained between $4.6-15$ M$_{\odot}$/yr while the estimated outflow rate ranges between $1.6-4.2$ M$_{\odot}$/yr and yields a wind loading factor ranging between $0.1-0.9$. The galaxy and gas metallicities, the galaxy-quasar sight-line geometry, and the down-the-barrel and transverse modeled outflow velocities collectively suggest that the transverse gas originates from ongoing outflowing material from the galaxy. The $\sim$1 dex decrease in metallicity from the base of the outflow to the outer halo suggests metal dilution of the gas by the time it reached 58 kpc.
Recently published papers: Sepsis, glucose control and patient–doctor relationships
Christopher Bouch, Gareth Williams
Critical Care , 2008, DOI: 10.1186/cc6769
Abstract: Severe sepsis and septic shock are significant health problems accounting for one in four deaths around the world per year. Target management for this unique group of critically ill patients has been based on the Surviving Sepsis Campaign guidelines of 2004; however, over the short period of time since their publication, a number of issues have changed in the management of this condition. January 2008 reveals the publication in Critical Care Medicine of the updated international guidelines on the management of severe sepsis and septic shock [1]. This publication is essential reading for all who are involved in recognising and managing patients with sepsis.The updated publication follows the format of the previous 2004 guidelines. All recommendations are agreed by an international group of experts who represent 11 organisations and used a structured system to rate the quality of evidence and grade the strength of recommendations in clinical practice.There is no space to review all the new recommendations in this paper here – but most aspects remain as per the 2004 guidelines. Changes from the 2004 guidelines include the removal of the adrenocorticotrophic hormone stimulation test prior to starting steroid therapy, affirming the use of steroid therapy only when hypotension responds poorly to fluid/vasopressor support, and clarification with regard to the use of recombinant human activated protein C. In summary, Dellinger and colleagues' paper is one not to miss and should be read by all medical practitioners [1].In keeping with the sepsis theme, a paper published recently in Chest set out to determine whether gender was linked to survival from severe sepsis [2]. Previous studies looking at the influence of gender on survival have shown that males have a higher incidence of sepsis, but whether this translates into a mortality difference is not known. Some studies have suggested that females have a survival advantage thanks to their sex-hormone profiles, but this has ne
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