Minding the Gap: Bias, Soft Structures, and the Double Life of Social Norms

We argue that work on norms provides a way to move beyond debates between proponents of individualist and structuralist approaches to bias, oppression, and injustice. We briefly map out the geography of that debate before presenting Charlotte Witt’s view, showing how her position, and the normative ascriptivism at its heart, seamlessly connects individuals to the social reality they inhabit. We then describe recent empirical work on the psychology of norms and locate the notions of informal institutions and soft structures with respect to it. Finally, we argue that the empirical resources enrich Witt’s ascriptivism, and that the resulting picture shows theorists need not, indeed should not, choose between either the individualist or structuralist camp

Chemistry of aminoacylation of 5'-AMO and the origin of protein synthesis

Much of our recent work has been a study of aminoacyl AMP derivatives. Elucidation of the character of aminoacyl AMP derivatives has made it obvious that AMP has characteristics which should allow it to preferentially catalyze the synthesis of L-amino acid peptides. The essential features which lead to this conclusion are that all l-amino acids (but not all D amino acids) when esterified to 5'-AMP preferentially (65 percent) distribute to the 3' position of the 5'-AMP; that esterification is predominantly at the 2' position; that 2', 3' diaminoacyl esters are readily formed; and that a peptide bond can be formed between adjacent 2',3' aminoacyl esters

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

Formation time distribution of dark matter haloes: theories versus N-body simulations

This paper uses numerical simulations to test the formation time distribution of dark matter haloes predicted by the analytic excursion set approaches. The formation time distribution is closely linked to the conditional mass function and this test is therefore an indirect probe of this distribution. The excursion set models tested are the extended Press-Schechter (EPS) model, the ellipsoidal collapse (EC) model, and the non-spherical collapse boundary (NCB) model. Three sets of simulations (6 realizations) have been used to investigate the halo formation time distribution for halo masses ranging from dwarf-galaxy like haloes ($M=10^{-3} M_*$, where $M_*$ is the characteristic non-linear mass scale) to massive haloes of $M=8.7 M_*$. None of the models can match the simulation results at both high and low redshift. In particular, dark matter haloes formed generally earlier in our simulations than predicted by the EPS model. This discrepancy might help explain why semi-analytic models of galaxy formation, based on EPS merger trees, under-predict the number of high redshift galaxies compared with recent observations.Comment: 7 pages, 5 figures, accepted for publication in MNRA

Identification of the YfgF MASE1 domain as a modulator of bacterial responses to aspartate

Complex 3'-5'-cyclic diguanylic acid (c-di-GMP) responsive regulatory networks that are modulated by the action of multiple diguanylate cyclases (DGC; GGDEF domain proteins) and phosphodiesterases (PDE; EAL domain proteins) have evolved in many bacteria. YfgF proteins possess a membrane-anchoring domain (MASE1), a catalytically inactive GGDEF domain and a catalytically active EAL domain. Here, sustained expression of the Salmonella enterica spp. Enterica ser. Enteritidis YfgF protein is shown to mediate inhibition of the formation of the aspartate chemotactic ring on motility agar under aerobic conditions. This phenomenon was c-di-GMP-independent because it occurred in a Salmonella strain that lacked the ability to synthesize c-di-GMP and also when PDE activity was abolished by site-directed mutagenesis of the EAL domain. YfgF-mediated inhibition of aspartate chemotactic ring formation was impaired in the altered redox environment generated by exogenous p-benzoquinone. This ability of YfgF to inhibit the response to aspartate required a motif, (213)Lys-Lys-Glu(215), in the predicted cytoplasmic loop between trans-membrane regions 5 and 6 of the MASE1 domain. Thus, for the first time the function of a MASE1 domain as a redox-responsive regulator of bacterial responses to aspartate has been shown

Measuring the Cosmic Equation of State with Counts of Galaxies

The classical dN/dz test allows the determination of fundamental cosmological parameters from the evolution of the cosmic volume element. This test is applied by measuring the redshift distribution of a tracer whose evolution in number density is known. In the past, ordinary galaxies have been used as such a tracer; however, in the absence of a complete theory of galaxy formation, that method is fraught with difficulties. In this paper, we propose studying instead the evolution of the apparent abundance of dark matter halos as a function of their circular velocity, observable via the linewidths or rotation speeds of visible galaxies. Upcoming redshift surveys will allow the linewidth distribution of galaxies to be determined at both z~1 and the present day. In the course of studying this test, we have devised a rapid, improved semi-analytic method for calculating the circular velocity distribution of dark halos based upon the analytic mass function of Sheth et al. (1999) and the formation time distribution of Lacey & Cole (1993). We find that if selection effects are well-controlled and minimal external constraints are applied, the planned DEEP Redshift Survey should allow the measurement of the cosmic equation-of-state parameter w to 10% (as little as 3% if Omega_m has been well-determined from other observations). This type of test has the potential also to provide a constraint on any evolution of w such as that predicted by ``tracker'' models.Comment: 4 pages plus 3 embedded figures; version approved by Ap. J. Letters. A greatly improved error analysis has been added, along with a figure showing complementarity to other cosmological test

Dark-Halo Cusp: Asymptotic Convergence

We propose a model for how the buildup of dark halos by merging satellites produces a characteristic inner cusp, of a density profile \rho \prop r^-a with a -> a_as > 1, as seen in cosmological N-body simulations of hierarchical clustering scenarios. Dekel, Devor & Hetzroni (2003) argue that a flat core of a<1 exerts tidal compression which prevents local deposit of satellite material; the satellite sinks intact into the halo center thus causing a rapid steepening to a>1. Using merger N-body simulations, we learn that this cusp is stable under a sequence of mergers, and derive a practical tidal mass-transfer recipe in regions where the local slope of the halo profile is a>1. According to this recipe, the ratio of mean densities of halo and initial satellite within the tidal radius equals a given function psi(a), which is significantly smaller than unity (compared to being 1 according to crude resonance criteria) and is a decreasing function of a. This decrease makes the tidal mass transfer relatively more efficient at larger a, which means steepening when a is small and flattening when a is large, thus causing converges to a stable solution. Given this mass-transfer recipe, linear perturbation analysis, supported by toy simulations, shows that a sequence of cosmological mergers with homologous satellites slowly leads to a fixed-point cusp with an asymptotic slope a_as>1. The slope depends only weakly on the fluctuation power spectrum, in agreement with cosmological simulations. During a long interim period the profile has an NFW-like shape, with a cusp of 1<a<a_as. Thus, a cusp is enforced if enough compact satellite remnants make it intact into the inner halo. In order to maintain a flat core, satellites must be disrupted outside the core, possibly as a result of a modest puffing up due to baryonic feedback.Comment: 37 pages, Latex, aastex.cls, revised, ApJ, 588, in pres

The mass function

We present the mass functions for different mass estimators for a range of cosmological models. We pay particular attention to how universal the mass function is, and how it depends on the cosmology, halo identification and mass estimator chosen. We investigate quantitatively how well we can relate observed masses to theoretical mass functions.Comment: 14 pages, 12 figures, to appear in ApJ