First in the Class? Age and the Education Production Function

We estimate the effects of having more mature peers using data from an experiment where children of the same age were randomly assigned to different kindergarten classrooms. Exploiting this experimental variation in conjunction with variation in expected kindergarten entry age to account for negative selection of older school entrants, we find that exposure to more mature kindergarten classmates raises test scores up to eight years after kindergarten, and may reduce the incidence of grade retention and increase the probability of taking a college-entry exam. These findings are consistent with broader peer effects literature documenting positive spillovers from having higher-scoring peers and suggest that – contrary to much academic and popular discussion of school entry age – being old relative to one’s peers is not beneficial.

Toward Improving Understanding of the Structure and Biophysics of Glycosaminoglycans

Glycosaminoglycans (GAGs) are the linear carbohydrate components of proteoglycans (PGs) that mediate PG bioactivities, including signal transduction, tissue morphogenesis, and matrix assembly. To understand GAG function, it is important to understand GAG structure and biophysics at atomic resolution. This is a challenge for existing experimental and computational methods because GAGs are heterogeneous, conformationally complex, and polydisperse, containing up to 200 monosaccharides. Molecular dynamics (MD) simulations come close to overcoming this challenge but are only feasible for short GAG polymers. To address this problem, we developed an algorithm that applies conformations from unbiased all-atom explicit-solvent MD simulations of short GAG polymers to rapidly construct 3-D atomic-resolution models of GAGs of arbitrary length. MD simulations of GAG 10-mers (i.e., polymers containing 10 monosaccharides) and 20-mers were run and conformations of all monosaccharide rings and glycosidic linkages were analyzed and compared to existing experimental data. These analyses demonstrated that (1) MD-generated GAG conformations are in agreement with existing experimental data; (2) MD-generated GAG 10-mer ring and linkage conformations match those in corresponding GAG 20-mers, suggesting that these conformations are representative of those in longer GAG biopolymers; and (3) rings and linkages in GAG 10- and 20-mers behave randomly and independently in MD simulation. Together, these findings indicate that MD-generated GAG 20-mer ring and linkage conformations can be used to construct thermodynamically-correct models of GAG polymers. Indeed, our findings demonstrate that our algorithm constructs GAG 10- and 20-mer conformational ensembles that accurately represent the backbone flexibility seen in MD simulations. Furthermore, within a day, our algorithm constructs conformational ensembles of GAG 200-mers that we would reasonably expect from MD simulation, demonstrating the efficiency of the algorithm and reduction in its time and computational cost compared to simulation. While there are other programs that can quickly construct atomic-resolution models of GAGs, those programs use conformations from short GAG subunits in solid state. Our findings suggest that GAG 20-mers are more flexible than short GAG subunits, meaning our program constructs ensembles that more accurately represent GAG polymer backbone flexibility and provide valuable insights toward improving the understanding of the structure and biophysics of GAGs

Contesting the neoliberal global agenda: lessons from activists

With the ongoing failure of governments to protect their citizens from impacts of the neoliberal global agenda, civil society groups worldwide have moved into the breach. Social workers, as allies of these groups, are uniquely positioned to help maximise their effectiveness in confronting the threats of corporate globalisation to democracy, economic justice, the environment and protection of the commons. How do activist groups know when they’re making a difference? This chapter builds on a four-year collaboration with nine diverse activist groups to see what we could learn together about effective practice in social/environmental justice work. We report on what activists told us about what ‘success’ means in their work, and what facilitates those successes. Reflecting on the implications of these findings in relation to social work skills and capacities, we suggest how social work educators might enhance our capabilities to contribute to the critical work of challenging and replacing the global neoliberal project

The Globular Cluster Systems around NGC 3311 and NGC 3309

We present extensive new photometry in (g',i') of the large globular cluster (GC) system around NGC 3311, the central cD galaxy in the Hydra cluster. Our GMOS data cover a 5.5' field of view and reach a limiting magnitude i' = 26, about 0.5 magnitude fainter than the turnover point of the GC luminosity function. We find that NGC 3311 has a huge population of ~16, 000 GCs, closely similar to the prototypical high specific frequency Virgo giant M87. The color-magnitude distribution shows that the metal-poor blue GC sequence and the metal-richer red sequence are both present, with nearly equal numbers of clusters. Bimodal fits to the color distributions confirm that the blue sequence shows the same trend of progressively increasing metallicity with GC mass that has previously been found in many other large galaxies; the correlation we find corresponds to a scaling of GC metallicity with mass of Z ~ M^0.6 . By contrast, the red sequence shows no change of mean metallicity with mass, but it shows an upward extension to much higher than normal luminosity into the UCD-like range, strengthening the potential connections between massive GCs and UCDs. The GC luminosity function, which we measure down to the turnover point at M_I = -8.4, also has a normal form like those in other giant ellipticals. Within the Hydra field, another giant elliptical NGC 3309 is sitting just 100" from the cD NGC 3311. We use our data to solve simultaneously for the spatial structure and total GC populations of both galaxies at once. Their specific frequencies are S_N (NGC 3311) = 12.5 +/- 1.5 and S_N (NGC 3309) = 0.6 +/-0.4. NGC 3311 is completely dominant and entirely comparable with other cD-type systems such as M87 in Virgo.Comment: 15 pages, 15 figures. Accepted to the Astrophysical Journal. Version with higher resolution figures is available at http://www.thewehners.net/astro/papers/wehner_n3311_highres.pd

Is Being in School Better? The Impact of School on Children’s BMI when Starting Age is Endogenous

In this paper, we investigate the impact of attending school on body weight and obesity using a regression-discontinuity design. As is the case with academic outcomes, school exposure is related to unobserved determinants of weight outcomes because some families choose to have their child start school late (or early). If one does not account for this endogeneity, it appears that an additional year of school exposure results in a greater BMI and a higher probability of being overweight or obese. When we compare the weight outcomes of similar age children with one versus two years of school exposure due to regulations on school starting age, the significant positive effects disappear, and most point estimates become negative, but insignificant. However, additional school exposure appears to improve weight outcomes of children for whom the transition to elementary school represents a more dramatic change in environment (those who spent less time in childcare prior to kindergarten)

Is Being in School Better? The Impact of School on Children's BMI When Starting Age is Endogenous

In this paper, we investigate the impact of attending school on body weight and obesity. We use school starting age cutoff dates to compare weight outcomes for similar age children with different years of school exposure. As is the case with academic outcomes, school exposure is related to unobserved determinants of weight outcomes because some families choose to have their child start school late (or early). If one does not account for this endogeneity, it appears that an additional year of school exposure results in a greater BMI and a higher probability of being overweight or obese. When actual exposure is instrumented with expected exposure based on school starting dates and birthday, the significant positive effects disappear, and most point estimates become negative and insignificant. However, for children not eating the school lunch, there is a significant negative effect on the probability of being overweight.

Further Definition of the Mass-Metallicity Relation in Globular Cluster Systems Around Brightest Cluster Galaxies

We combine the globular cluster data for fifteen Brightest Cluster Galaxies and use this material to trace the mass-metallicity relations (MMR) in their globular cluster systems (GCSs). This work extends previous studies which correlate the properties of the MMR with those of the host galaxy. Our combined data sets show a mean trend for the metal-poor (MP) subpopulation which corresponds to a scaling of heavy-element abundance with cluster mass Z ~ M^(0.30+/-0.05). No trend is seen for the metal-rich (MR) subpopulation which has a scaling relation that is consistent with zero. We also find that the scaling exponent is independent of the GCS specific frequency and host galaxy luminosity, except perhaps for dwarf galaxies. We present new photometry in (g',i') obtained with Gemini/GMOS for the globular cluster populations around the southern giant ellipticals NGC 5193 and IC 4329. Both galaxies have rich cluster populations which show up as normal, bimodal sequences in the colour-magnitude diagram. We test the observed MMRs and argue that they are statistically real, and not an artifact caused by the method we used. We also argue against asymmetric contamination causing the observed MMR as our mean results are no different from other contamination-free studies. Finally, we compare our method to the standard bimodal fitting method (KMM or RMIX) and find our results are consistent. Interpretation of these results is consistent with recent models for globular cluster formation in which the MMR is determined by GC self-enrichment during their brief formation period.Comment: 35 pages, 20 figures. Accepted by Astronomical Journal. Complete preprint including high resolution figures available at http://www.physics.mcmaster.ca/~cockcroft/MMRpape

Cumulative mutagenesis of the basic residues in the 201-218 region of insulin-like growth factor (IGF)-binding protein-5 results in progressive loss of both IGF-I binding and inhibition of IGF-I biological action

We have reported previously that mutation of two conserved nonbasic amino acids (G203 and Q209) within the highly basic 201–218 region in the C-terminal domain of IGF-binding protein-5 (IGFBP-5) decreases binding to IGFs. This study reveals that cumulative mutagenesis of the 10 basic residues in this region, to create the C-Term series of mutants, ultimately results in a 15-fold decrease in the affinity for IGF-I and a major loss in heparin binding. We examined the ability of mutants to inhibit IGF-mediated survival of MCF-7 cells and were able to demonstrate that this depended not only upon the affinity for IGF-I, but also the kinetics of this interaction, because IGFBP-5 mutants with similar affinity constants (KD) values, but with different association (Ka) and dissociation (Kd) rate values, had markedly different inhibitory properties. In contrast, the affinity for IGF-I provided no predictive value in terms of the ability of these mutants to enhance IGF action when bound to the substratum. Instead, these C-Term mutants appeared to enhance the actions of IGF-I by a combination of increased dissociation of IGF-IGFBP complexes from the substratum, together with dissociation of IGF-I from IGFBP-5 bound to the substratum. These effects of the IGFBPs were dependent upon binding to IGF-I, because a non-IGF binding mutant (N-Term) was unable to inhibit or enhance the actions of IGF-I. These results emphasize the importance of the kinetics of association/dissociation in determining the enhancing or inhibiting effects of IGFBP-5 and demonstrate the ability to generate an IGFBP-5 mutant with exclusively IGF-enhancing activity

A Mutation in LTBP2 Causes Congenital Glaucoma in Domestic Cats (Felis catus)

The glaucomas are a group of diseases characterized by optic nerve damage that together represent a leading cause of blindness in the human population and in domestic animals. Here we report a mutation in LTBP2 that causes primary congenital glaucoma (PCG) in domestic cats. We identified a spontaneous form of PCG in cats and established a breeding colony segregating for PCG consistent with fully penetrant, autosomal recessive inheritance of the trait. Elevated intraocular pressure, globe enlargement and elongated ciliary processes were consistently observed in all affected cats by 8 weeks of age. Varying degrees of optic nerve damage resulted by 6 months of age. Although subtle lens zonular instability was a common feature in this cohort, pronounced ectopia lentis was identified in less than 10% of cats examined. Thus, glaucoma in this pedigree is attributed to histologically confirmed arrest in the early post-natal development of the aqueous humor outflow pathways in the anterior segment of the eyes of affected animals. Using a candidate gene approach, significant linkage was established on cat chromosome B3 (LOD 18.38, θ = 0.00) using tightly linked short tandem repeat (STR) loci to the candidate gene, LTBP2. A 4 base-pair insertion was identified in exon 8 of LTBP2 in affected individuals that generates a frame shift that completely alters the downstream open reading frame and eliminates functional domains. Thus, we describe the first spontaneous and highly penetrant non-rodent model of PCG identifying a valuable animal model for primary glaucoma that closely resembles the human disease, providing valuable insights into mechanisms underlying the disease and a valuable animal model for testing therapies