Federal Influences and Intergovernmental Relations: Constraints, Conflicts, and Benefits

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Stress relaxation after low and high-rate deformation of polyurethanes

Polymers possess a wide range of mechanical behaviours depending upon the temperature and loading rate. An often-overlooked aspect is relaxation, important because it acts over a wide range of time periods and begins as soon as the polymer is loaded. In the research presented here, the relaxation behaviour of two polyurethanes (PUs) following deformation was investigated at low-rate, 10-3 s-1, and dynamic, 103 s- 1, loading rates, with the former exploring temperatures from 20 °C to - 60 °C. These are compared to a predictive Prony series model calibrated using mastercurves produced by applying time-temperature superposition to data obtained using a dynamic mechanical analysis machine. For relaxation after dynamic loading, a recently proposed analysis was used to account for the movement of the bars during the relaxation. The model was able to predict the stress-time response after low-rate deformation to strains of 2 %, at all temperatures. As the strains increased, irrecoverable deformation was observed and the model became less accurate. In the dynamic experiments, the model accurately predicted the early stages of relaxation for both PUs but deviated later on. A modification to the model was suggested to account for these observations. Further characterisation of the mechanical response under large strain compressive loading is also reported

The Labor Market Returns to Sub-Baccalaureate College: A Review

This paper reviews recent evidence on the labor market returns to credit accumulation, certificates, and associate degrees from community colleges. Evidence is collated from estimates of earnings gaps across college students using large-scale, statewide administrative datasets from eight states. Six of these states were partners of the Center for Analysis of Postsecondary Education and Employment (CAPSEE), a research center funded by the Institute of Education Sciences of the U.S. Department of Education. CAPSEE researchers conducted extensive analyses of education and earnings in these states. Findings from these studies affirm a “CAPSEE consensus” with three main results and two key features. For associate degrees, this review affirms that completing an associate degree yields strongly positive, persistent, and consistent earnings gains: studies show that completing an associate degree yields on average approximately $4,640–$7,160 per annum in extra earnings compared to entering college but not completing an award. For certificates, the evidence shows positive but modest returns and that these returns may fade out within a few years post-college. For non-completers, there is evidence that earning more credits is associated with higher earnings. Generally, the results establish two main features. First, increments of college lead to higher earnings, but with returns that are heterogeneous by field of study. Second, the evidence is strongly suggestive that returns to college are robust to macroeconomic trends

Model Specifications for Estimating Labor Market Returns to Associate Degrees: How Robust Are Fixed Effects Estimates?

Recently, studies have adopted fixed effects modeling to identify the returns to college. This method has the advantage over ordinary least squares estimates in that unobservable, individual-level characteristics that may bias the estimated returns are differenced out. But the method requires extensive longitudinal data and involves complex specifications, raising the possibility that results are sensitive either to sample restrictions or to alternative specifications. Also, the extra requirements might not be justified if results from fixed effects models are broadly similar to those from conventional ordinary least squares models. In this paper the authors review results from fixed effects models of the earnings gains from completing an associate degree relative to non-completion for community college students. The authors examine both sampling restrictions and specification issues. Results are sensitive to assumptions about missing earnings data and to how time trend specifications are modeled. However, the authors find no substantively meaningful differences between estimates using fixed effects models and ordinary least squares methods. A main benefit of fixed effects models—controlling for unobservable student characteristics—should be weighed against the difficulty in interpreting coefficients and more intensive data requirements. On the other hand, a distinct advantage of fixed effects models is that they allow for analysis of earning profiles over the period from before to after college. Given the large fluctuations in earnings over this period, this advantage may be significant in yielding evidence on the full returns to college

The Impact of Occupational Licensing on Labor Market Outcomes of College-Educated Workers

More than one third of college-educated workers have a license that provides the right to practice a particular occupation. In contrast to certificates, these licenses—serving either as a productivity signal or acting as a restrictive practice—are associated with significantly higher earnings. Thus, it is possible that some part of the returns to college are in fact returns to licensing. In this paper, the authors identify the effects of licenses on a set of labor market outcomes for the college-educated workforce using newly available national Current Population Survey data merged with U.S. Department of Labor. The results show significant discrepancies between individual self-reported licensing rates and state-mandated licensing requirements across occupations. Findings indicate significant advantages from licensing in terms of earnings and labor market participation (hours worked). Moreover, controlling for licensing does not significantly reduce the measured returns to college. Licenses convey economic benefits even in occupations where they are not required. In contrast to prior studies, the current study also finds that licenses reduce wage dispersion across the college-educated workforce

Stackable Credentials: Awards for the Future?

Stackable credentials—sequential postsecondary awards that allow individuals to progress on a career path—can enhance the labor market prospects of middle-skill workers. In light of recent labor market changes, these credentials may represent an important buffer against job displacement. However, very little evidence exists as to what constitutes a stackable credential and how many persons have obtained them. The authors distinguish three types of stacking—progression, supplemental, and independent. Using national, survey, and college-system-level datasets, the authors estimate that between 3 and 5 percent of the college-educated population have stackable credentials. However, there are several substantial empirical challenges in identifying stackable credentials related to the ordering of awards and to the degree of skill complementarity across awards. Significantly, the authors find that general vocational awards—earned at any institution and typically not credit-bearing—are often conflated with stackable certificates. The incidence of these awards is far greater than of stackable credentials. A review of the evidence shows that certificates convey modestly positive gains in earnings, but there is no evidence that stacking yields earnings gains. Finally, despite frequent changes in skills needs across the economy, the authors identify barriers to the expansion of stackable credentials

The Grenadian Crisis and the Caribbean Left

SUMMARY Prior to October 1983 ‘popular forces’ had established a hitherto unmatched degree of hegemony throughout the Caribbean region. The self?destruction of the Grenadian revolution opened the way to the restoration of colonial or neo colonial principles under US hegemony. The article examines the importance of democracy in the Caribbean political tradition, and the responsibility of the New Jewel Movement's leadership, and of the Caribbean intelligentsia who supported them, for ignoring this. RESUMEN La crisis de Grenada y la izquierda caribeña Con anterioridad a octubre de 1983, las ‘fuerzas populares’ establecieron un grado de hegemonía hasta entonces inédito en la región caribeña. La autodestrucción de la revolución de Grenada abrió el camino para la restauración de los principios coloniales o neocoloniales bajo la hegemonía estadounidense. El artículo examina la importancia de la democracia en la tradición política del Caribe y la responsabilidad que le cabe a la lideranza del Movimiento New Jewel, así como a la intelectualidad caribeña que la apoyó, por haberlo ignorado. SOMMAIRE La crise de la Grenade et la gauche Antillaise Avant Octobre 1983, les ‘forces populaires’ ont établi une hégémonie à un degré jusqu à present inégalé dans la région des Antilles. L'autodestruction de la révolution grenadine a ouvert la route à la restauration des principes coloniaux et néo?coloniaux sous l'hégémonie américaine. L'article examine l'importance de la Démocratie dans la tradition politique des Caraïbes et la responsabilité de la direction du mouvement du ‘Nouveau Bijou’ et de l'Intelligentsia des Caraïbes qui la supporte et veut ignorer cette première donnée

Influence of surface preparation and polymer backing properties on the quasi-static and impact response of ceramic faced 1d armour systems

Ballistic impact is a highly complex environment, the understanding of which is compounded by the advanced materials used for ceramic-polymer composite armours. In this study, the influence of surface preparation and polymer backing properties on the energy absorptive capabilities and ballistic performance of simplified model armours was approached via a methodical investigation using simplified materials and geometries. Quasi-1D (beam) specimens consisting of polyurethane-backed alumina were loaded under three-point bend quasi-statically and at impact speeds. The specimen geometries allowed for the fracture pathways to be observed. To produce the specimens, two polyurethanes with different glass transition temperatures were cured onto alumina strips, eliminating the requirement for a dedicated adhesive and thus simplifying the interfacial dynamics. Further modifications were made by applying a primer surface treatment, by using unbonded polyurethane and adhered polyurethane, and by replacing the polyurethane with glass-reinforced polycarbonate. The beam specimens were loaded quasi-statically at 0.05 mm s-1 at ambient and sub-ambient temperatures, and at 50-300 m s-1 at ambient temperatures. The quasi-static specimens were found to fail by one of two failure modes with approximately a 3x energy absorption difference; the failure was highly dependent upon the interface and polymer characteristics. Under impact, a significant proportion of the energy absorption was provided by the kinetic energy of the fragments. Although, the polymer backing and interfacial properties were found to influence fracture paths during loading. FEA simulations were used to model the behaviours using characterisation data from a previous study; these were found to predict the experimental response well

Deferiprone and gallium-protoporphyrin have the capacity to potentiate the activity of antibiotics in Staphylococcus aureus small colony variants

Small colony variants (SCVs) of bacteria like Staphylococcus aureus are characterized by a reduced colony size and are linked to increased antibiotic tolerance and resistance. Their altered expression of virulence factors, slow growing properties and their ability to form biofilms make the eradication of SCVs challenging. In the context of biofilm-related infectious diseases involving S. aureus SCVs, a therapy targeting bacterial iron metabolism was evaluated. The combination of the iron-chelator deferiprone (Def) and the heme-analog gallium-protoporphyrin (GaPP), in solution and incorporated in a surgical wound gel, was tested for activity against planktonic and sessile SCVs. To this end, the activity of Def-GaPP was assessed against planktonic S. aureus SCVs, as well as against in vitro and in vivo biofilms in the colony biofilm model, an artificial wound model and a Caenorhabditis elegans infection model. While Def alone failed to show substantial antibacterial activity, GaPP and the combination of Def-GaPP demonstrated concentration- and strain-dependent antibacterial properties. Specifically, the Def-GaPP combination significantly reduced the bacterial load in an artificial wound model and increased the survival of S. aureus SCV infected C. elegans. When Def-GaPP were combined with gentamicin or ciprofloxacin, the triple combinations exceeded the antibiofilm activity of the individual compounds in the colony biofilm model. In targeting bacterial iron metabolism, Def-GaPP showed significant activity against planktonic and sessile SCVs. Moreover, Def-GaPP could potentiate the activity of gentamicin and ciprofloxacin. Delivered in a wound healing gel, Def-GaPP showed promise as a new topical strategy against infections with S. aureus SCVs.Katharina Richter, Nicky Thomas, Guimin Zhang, Clive A. Prestidge, Tom Coenye, Peter-John Wormald and Sarah Vreugd