5,568 research outputs found
AGN Feedback models: Correlations with star formation and observational implications of time evolution
We examine the correlation between the star formation rate (SFR) and black
hole accretion rate (BHAR) across a suite of different AGN feedback models,
using the time evolution of a merger simulation. By considering three different
stages of evolution, and a distinction between the nuclear and outer regions of
star formation, we consider 63 different cases. Despite many of the feedback
models fitting the M-\sigma\ relationship well, there are often distinct
differences in the SFR-BHAR correlations, with close to linear trends only
being present after the merger. Some of the models also show evolution in the
SFR-BHAR parameter space that is at times directly across the long-term
averaged SFR-BHAR correlation. This suggests that the observational SFR-BHAR
correlation found for ensembles of galaxies is an approximate statistical
trend, as suggested by Hickox et al. Decomposing the SFR into nuclear and outer
components also highlights notable differences between models and there is only
modest agreement with observational studies examining this in Seyfert galaxies.
For the fraction of the black hole mass growth from the merger event relative
to the final black hole mass, we find as much as a factor of three variation
among models. This also translates into a similar variation in the
post-starburst black hole mass growth. Overall, we find that while qualitative
features are often similar amongst models, precise quantitative analysis shows
there can be quite distinct differences.Comment: Accepted to MNRAS. Comments welcom
Studies in Asymmetric Synthesis: Supramolecular Catalysis, C-H Activation, and D-Cycloserine Synthesis
Rh-catalyzed asymmetric hydrogenation has emerged as a powerful tool for the manufacturing of chiral pharmaceuticals. While the mechanism is well understood, catalyst design a priori is not yet possible. Supramolecular catalysis, the use of non-covalent forces to affect a catalytic process, can afford the catalyst diversity required to uncover efficient catalysts and further our understanding. Using a modular design and self-assembly, a large scale supramolecular catalyst screening in a catalyst scaffold optimization study of rhodium-catalyzed asymmetric hydrogenation was carried out. Analyzing the data yields some new insights into the roles of each module making up the supramolecular catalyst. Perhaps most surprisingly, the presence of a chiral recognition element positioned remote to the site of catalysis can significantly impact the catalytic activity and enantioselectivity.
1,1-Disubstituted alkenes are a challenging class of substrates for the asymmetric hydroboration reaction. Differentiation of the prochiral faces has been met with few successes from either stoichiometric or catalytic approaches. Takacs et al. revealed amide and ester groups direct the gamma-selective Rh-catalyzed hydroboration of 1,1-disubstituted-beta,gamma-unsaturated alkenes. In the work described herein, analogous oxime-directing groups were used in an attempt to diversify the substrate scope. Unlike the amide- or ester-directed examples, we find oxime-directed hydroboration proceeds through an unusual C-H activation/metallation that proves crucial to turnover of borylated products. Whereas it was previously presumed that certain reduced byproducts were derived from adventitious H2 reduction, deuterium-labeling experiments suggest competing pathways from a common intermediate leading to both borylated and reduced products
Low Dirac Eigenmodes and the Topological and Chiral Structure of the QCD Vacuum
Several lattice calculations which probe the chiral and topological structure
of QCD are discussed. The results focus attention on the low-lying eigenmodes
of the Dirac operator in typical gauge field configurations.Comment: Talk presented at the DPF2000 Conferenc
Mankind, Humans, Congressman: It’s All Inclusive, Right Guys?
This paper takes a look at research surrounding the use of gendered language and how it impacts occupations and careers from ages as young as grade school, and all the way into adulthood. The use of gender-fair language creates a more gender inclusive attitude towards traditionally male occupations. The masculine generic language used in our culture perpetuates gender stereotypes among children as young as six and continues on into adulthood. Changing the language to include both women and men allows for both to self-identify beyond the stereotypical occupations and see themselves as successful. This can be seen in how children view occupations as gendered, in whether or not women apply for job advertisements that use masculine generic language, and even in the job itself when the job relies on students evaluating a teacher’s performance. Self-identification is important in regards to success, and language plays a role in this. Even gender-fair language is not fully inclusive as it reinforces the binary and causes erasure in marginalized groups such as the trans community or someone who identifies as nonbinary. Language is a powerful tool to uphold current power structures and make privileged bodies hyper visible
Toward an Improved Analytical Description of Lagrangian Bias
We carry out a detailed numerical investigation of the spatial correlation
function of the initial positions of cosmological dark matter halos. In this
Lagrangian coordinate system, which is especially useful for analytic studies
of cosmological feedback, we are able to construct cross-correlation functions
of objects with varying masses and formation redshifts and compare them with a
variety of analytical approaches. For the case in which both formation
redshifts are equal, we find good agreement between our numerical results and
the bivariate model of Scannapieco & Barkana (2002; SB02) at all masses,
redshifts, and separations, while the model of Porciani et al. (1998) does well
for all parameters except for objects with different masses at small
separations. We find that the standard mapping between Lagrangian and Eulerian
bias performs well for rare objects at all separations, but fails if the
objects are highly-nonlinear (low-sigma) peaks. In the Lagrangian case in which
the formation redshifts differ, the SB02 model does well for all separations
and combinations of masses, apart from a discrepancy at small separations in
situations in which the smaller object is formed earlier and the difference
between redshifts or masses is large. As this same limitation arises in the
standard approach to the single-point progenitor distribution developed by
Lacey & Cole (1993), we conclude that a more complete understanding of the
progenitor distribution is the most important outstanding issue in the analytic
modeling of Lagrangian bias.Comment: 22 pages, 8 figures, ApJ, in pres
Fitting Correlated Hadron Mass Spectrum Data
We discuss fitting hadronic Green functions versus time to extract mass
values in quenched lattice QCD. These data are themselves strongly correlated
in . With only a limited number of data samples, the method of minimising
correlated is unreliable. We explore several methods of modelling the
correlations among the data set by a few parameters which then give a stable
and sensible fit even if the data sample is small. In particular these models
give a reliable estimate of the goodness of fit.Comment: 14 pages, Latex text, followed by 3 postscript figures in
self-unpacking file. Also available at
ftp://suna.amtp.liv.ac.uk/pub/cmi/corfit
b-quark decay in the collinear approximation
The semileptonic decay of a b-quark, b--> c l nu, is considered in the
relativistic limit where the decay products are approximately collinear.
Analytic results for the double differential lepton energy distributions are
given for finite charm-quark mass. Their use for the fast simulation of
isolated lepton backgrounds from heavy quark decays is discussed.Comment: 7 pages, 1 figure, submitted to Phys.Rev.
Orthopedic management of the extremities in patients with Morquio A syndrome.
BackgroundMusculoskeletal involvement in Morquio A syndrome (mucopolysaccharidosis IVA; MPS IVA) contributes significantly to morbidity and mortality. While the spinal manifestations of the disorder have received considerable attention in the literature, there have been few reported studies to date to guide the management of the orthopedic problems associated with the lower and upper extremities.PurposeThe objective was to develop recommendations for the management of the extremities in patients with Morquio A syndrome.MethodsA group of specialists in orthopedics, pediatrics and genetics with experience in the management of Morquio A patients convened to review and discuss current clinical practices and to develop preliminary recommendations. Evidence from the literature was retrieved. Recommendations were further refined until consensus was reached.Results and conclusionsThis present article provides a detailed review and discussion of the lower and upper extremity deformities in Morquio A syndrome and presents recommendations for the assessment and treatment of these complications. Key issues, including the importance of early diagnosis and the implications of medical therapy, are also addressed. The recommendations herein represent an attempt to develop a uniform and practical approach to managing patients with Morquio A syndrome and improving their outcomes
AGN feedback models: correlations with star formation and observational implications of time evolution
We examine the correlation between the star formation rate (SFR) and black hole accretion rate (BHAR) across a suite of different active galactic nuclei (AGN) feedback models, using the time evolution of a merger simulation. By considering three different stages of evolution, and a distinction between the nuclear and outer regions of star formation, we consider 63 different cases. Despite many of the feedback models fitting the M-σ relationship well, there are often distinct differences in the SFR-BHAR correlations, with close to linear trends only being present after the merger. Some of the models also show evolution in the SFR-BHAR parameter space that is at times directly across the long-term averaged SFR-BHAR correlation. This suggests that the observational SFR-BHAR correlation found for ensembles of galaxies is an approximate statistical trend, as suggested by Hickox etal. Decomposing the SFR into nuclear and outer components also highlights notable differences between models and there is only modest agreement with observational studies examining this in Seyfert galaxies. For the fraction of the black hole mass growth from the merger event relative to the final black hole mass, we find as much as a factor of 3 variation among models. This also translates into a similar variation in the post-starburst black hole mass growth. Overall, we find that while qualitative features are often similar amongst models, precise quantitative analysis shows there can be quite distinct difference
SbcCD regulation and localization in Escherichia coli
The SbcCD complex and its homologues play important roles in DNA repair and in the maintenance of genome stability. In Escherichia coli, the in vitro functions of SbcCD have been well characterized, but its exact cellular role remains elusive. This work investigates the regulation of the sbcDC operon and the cellular localization of the SbcC and SbcD proteins. Transcription of the sbcDC operon is shown to be dependent on starvation and RpoS protein. Overexpressed SbcC protein forms foci that colocalize with the replication factory, while overexpressed SbcD protein is distributed through the cytoplasm
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