How Robust is Comparative Advantage?

This paper reviews the theoretical development of the concept of comparative advantage, starting with the two-good model of Ricardo and the two-good extension and reinterpretation by Haberler. In both, the presence of comparative advantage provides the scope for countries to gain from trade by specializing, and the pattern of that trade is explained by the pattern of comparative advantage. These strong results of the two-good model can be extended under certain circumstances to multiple goods and countries, but under more general assumptions such strong results no longer are assured. Instead one can derive much weaker results, usually in the form of correlations between comparative advantage and trade, and these weaker results hold in a much wider variety of circumstances. The paper examines those assumptions that permit such generalizations, but then also examines when those assumptions are most likely to fail, and what happens as a result.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73670/1/j.1467-9396.2005.00552.x.pd

Characteristics of Esophageal Cancer Cases in Tanzania.

PurposeAge-standardized incidence rates for esophageal cancer (EC) in East Africa have been reported as disproportionately high compared with the worldwide incidence of nine per 100,000 population. This study aimed to characterize EC cases seen at Muhimbili National Hospital and Ocean Road Cancer Institute in Dar es Salaam, Tanzania.MethodsDemographic, clinical, and treatment variables were abstracted from charts of patients who received care for a diagnosis of EC at one or both institutions between 2011 and 2013. Categorical data were summarized as frequency counts and percentages. Continuous data were presented as medians and ranges. To compare men and women, Pearson's χ2 and two-sample t tests were applied.ResultsSeven hundred thirty-eight unique cases of EC were identified, of whom 68% were men and the median age was 60 years (range, 19 to 95 years). Notably, 93 cases (13%) were ≤ 40 years old at diagnosis. Squamous cell carcinoma was the dominant histology, comprising 90% of cases with documented histopathology. However, 34% of cases with a diagnosis of EC were not pathologically confirmed. The stage was documented as locoregional in 4% of cases, locally advanced in 20% of cases, metastatic in 14% of cases, and unknown in 63% of cases. Of 430 patients who received treatment at Ocean Road Cancer Institute, 76% were treated with radiation, 44% were treated with chemotherapy, 3% underwent a cancer-related surgical procedure, and 10% of cases received no cancer-directed therapy. The median overall survival for all patients was 6.9 months (95% CI, 5.0 to 12.8), regardless of stage at presentation.ConclusionBetween 2011 and 2013, cases of EC represented a large clinical burden at both institutions

Transforming Climates for the Academic Woman of Color: Facilitating Greater Understanding in the Workplace Climate and in Social Structures

This article explores the findings of a workshop designed to determine impediments for academic success of women of color in Science, Technology, Engineering, and Mathematics (STEM), as well as Social and Behavioral Science (SBS), disciplines at Historically Black Colleges and Universities (HBCUs). Funded by a National Science Foundation (NSF) five-year ADVANCE Institutional Transformation (IT) grant, three concurrent cohorts – single women, women with partners, and the partners of the women – explored various factors that hinder academic women’s progression. Utilizing mixed methods, including focus groups, pre- and post-surveys and recorded interviews, it was found that women of color at HBCUs not only lack informal mentoring and support male colleagues find at work, but also face climates at home where spouses, partners, or family find their work demands unfamiliar. Discussions of the impact of marital status and family life on work success were previously lacking. A clear disconnect of perceptions between partnered and single women were addressed in a joint session. All three cohorts repeatedly noted a definite benefit of the workshop was development of community across the university, and across families. After the workshop, many women noted feeling less isolated and realizing their difficulties were similar to other women at the institution

Large Eddy Simulation of acoustic pulse propagation and turbulent flow interaction in expansion mufflers

A novel hybrid pressure-based compressible solver is developed and validated for low Mach number acoustic flow simulation. The solver is applied to the propagation of an acoustic pulse in a simple expansion muffler, a configuration frequently employed in HVAC and automotive exhaust systems. A set of benchmark results for experimental analysis of the simple expansion muffler both with and without flow are obtained to compare attenuation in forced pulsation for various mean-flow velocities. The experimental results are then used for validation of the proposed pressure-based compressible solver. Compressible, Unsteady Reynolds Averaged Navier-Stokes (URANS) simulation of a muffler with a mean through flow is conducted and results are presented to demonstrate inherent limitations associated with this approach. Consequently, a mixed synthetic inflow boundary condition is developed and validated for compressible Large Eddy Simulation (LES) of channel flow. The mixed synthetic boundary is then employed for LES of a simple expansion muffler to analyse the flow-acoustic and acoustic-pulse interactions inside the expansion muffler. The improvement in the prediction of vortex shedding inside the chamber is highlighted in comparison to the URANS method. Further, the effect of forced pulsation on flow-acoustic is observed in regard to the shift in Strouhal number inside the simple expansion muffler

Adaptively refined large eddy simulations of clusters

We present a numerical scheme for modelling unresolved turbulence in cosmological adaptive mesh refinement codes. As a first application, we study the evolution of turbulence in the intra-cluster medium and in the core of a galaxy cluster. Simulations with and without subgrid scale model are compared in detail. Since the flow in the ICM is subsonic, the global turbulent energy contribution at the unresolved length scales is smaller than 1% of the internal energy. We find that the production of turbulence is closely correlated with merger events occurring in the cluster environment, and its dissipation locally affects the cluster energy budget. Because of this additional source of dissipation, the core temperature is larger and the density is smaller in the presence of subgrid scale turbulence than in the standard adiabatic run, resulting in a higher entropy core value.Comment: Submitted to ApJ, 14 pages, 14 figures, 3 table

The yeast Pan2 protein is required for poly(A)-binding protein-stimulated poly(A)-nuclease activity

The removal of the mRNA poly(A) tail in the yeast Saccharomyces cerevisiae is stimulated by the poly(A)binding protein (Pab1p). A large scale purification of the Pab1p-stimulated poly(A) ribonuclease (PAN) identifies a 76-kDa and two 135-Da polypeptides as candidate enzyme subunits. Antibodies against the Pan1p protein, which is the minor 135-kDa protein in the preparation, can immunodeplete Pan1p but not PAN activity. The protein sequence of the major 135-kDa protein, Pan2p, reveals a novel protein that was also found in the previously reported PAN purification (Sachs, A. B., and Deardorff, J. A. (1992) Cell 70, 961-973). Deletion of the non-essential PAN2 gene results in an increase of the average length of mRNA poly(A) tails in vivo, and a loss of Pab1p-stimulated PAN activity in crude extracts. These data confirm that Pan2p and not Pan1p is required for PAN activity, and they suggest that ribonucleases other than the Pab1p-stimulated PAN are capable of shortening poly(A) tails in vivo

Analysis of the shearing instability in nonlinear convection and magnetoconvection

Numerical experiments on two-dimensional convection with or without a vertical magnetic field reveal a bewildering variety of periodic and aperiodic oscillations. Steady rolls can develop a shearing instability, in which rolls turning over in one direction grow at the expense of rolls turning over in the other, resulting in a net shear across the layer. As the temperature difference across the fluid is increased, two-dimensional pulsating waves occur, in which the direction of shear alternates. We analyse the nonlinear dynamics of this behaviour by first constructing appropriate low-order sets of ordinary differential equations, which show the same behaviour, and then analysing the global bifurcations that lead to these oscillations by constructing one-dimensional return maps. We compare the behaviour of the partial differential equations, the models and the maps in systematic two-parameter studies of both the magnetic and the non-magnetic cases, emphasising how the symmetries of periodic solutions change as a result of global bifurcations. Much of the interesting behaviour is associated with a discontinuous change in the leading direction of a fixed point at a global bifurcation; this change occurs when the magnetic field is introduced