Competition and Human Capital Accumulation: A Theory of Interregional Specialization and Trade

We consider a model with several regions whose technological ability and factor endowments are identical and in which transport costs between regions are non-negligible. Nonetheless, certain goods are sometimes produced by multiple firms all of which are located in the same region. These goods are then exported from the regions in which their production is agglomerated. Regional agglomeration of production and trade stem from two forces. First, competition between firms for the services of trained workers is necessary for the workers to recoup the cost of acquiring industry-specific human capital. Second, the technology of production is more efficient when plants are larger than a minimum efficient scale and local demand is insufficient to support several firms of that scale. We also study the policy implications of our model.

Quotas and the Stability of Implicit Collusion

This paper shows that the imposition of an import quota by one country can lead to increased competitiveness; protection can reduce the price in the country that imposes the quota, the foreign country, or both. This emerges from a model in which the firms are assumed to sustain collusion by the threat of reversion to more competitive pricing. We consider both prices and quantities as the strategic variables and study competition both in the domestic and the foreign market taken individually, and in the two markets taken together.

A Supergame-Theoretic Model of Business Cycles and Price Wars During Booms

This paper studies implicitly colluding oligopolists facing fluctuating demand. The credible threat of future punishments provides the discipline that facilitates collusion. However, we find that the temptation to unilaterally deflate from the collusive outcome is often greater when demand is high. To moderate this temptation,the optimizing oligopoly reduces its profitability at such times,resulting in lower prices. If the oligopolists' output is an input to other sectors, their output may increase too. This explains the co-movements of outputs which characterize business cycles. The behavior of the railroads in the 1880's, the automobile industry in the 1950's and the cyclical behavior of cement prices and price-cost margins support our theory. (J.E.L. Classification numbers:020, 130, 610).

The Relative Rigidity of Monopoly Pricing

This paper seeks to explain why monopolies keep their nominal prices constant for longer periods than do tight oligopolies. We provide two possible explanations. The first is based on the presence of a small fixed cost of changing prices. The second, on small costs of discovering the optimal price. The incentive to change price for duopolists producing differentiated products exceeds that of a single monopolistic firm which produced the same tange of products as the duopoly.

A semi-microscopic calculation of the potential in heavy ion collisions

A Dissertation Submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg for the degree of Master of Science. Johannesburg March 197

Implantation of 3D-Printed Patient-Specific Aneurysm Models into Cadaveric Specimens: A New Training Paradigm to Allow for Improvements in Cerebrovascular Surgery and Research.

AimTo evaluate the feasibility of implanting 3D-printed brain aneurysm model in human cadavers and to assess their utility in neurosurgical research, complex case management/planning, and operative training.MethodsTwo 3D-printed aneurysm models, basilar apex and middle cerebral artery, were generated and implanted in four cadaveric specimens. The aneurysms were implanted at the same anatomical region as the modeled patient. Pterional and orbitozygomatic approaches were done on each specimen. The aneurysm implant, manipulation capabilities, and surgical clipping were evaluated.ResultsThe 3D aneurysm models were successfully implanted to the cadaveric specimens' arterial circulation in all cases. The features of the neck in terms of flexibility and its relationship with other arterial branches allowed for the practice of surgical maneuvering characteristic to aneurysm clipping. Furthermore, the relationship of the aneurysm dome with the surrounding structures allowed for better understanding of the aneurysmal local mass effect. Noticeably, all of these observations were done in a realistic environment provided by our customized embalming model for neurosurgical simulation.Conclusion3D aneurysms models implanted in cadaveric specimens may represent an untapped training method for replicating clip technique; for practicing certain approaches to aneurysms specific to a particular patient; and for improving neurosurgical research

Dimensions of Disadvantage: Normative and Empirical Analysis of the Effect of Public Insurance on Low-Income Children and Families

This dissertation considers some challenges to delivering effective and equitable health care to disadvantaged children and families in the United States. Chapter one examines whether expanded access to health insurance following the enactment of the Children’s Health Insurance Program (CHIP) in 1997 reduced the prevalence of economic hardships (food insecurity, problems affording housing) and postponed medical care. In difference-in-differences analysis, I find that relative to a comparison group of families that missed the eligibility cutoffs, families that gained eligibility under CHIP did not experience changes in food or housing problems, but were significantly less likely to postpone medical care. These findings suggest that while public insurance for families with children likely improves access to care, it does not significantly reduce other forms of hardship. Chapter two provides an ethical argument for subsidizing health insurance for low income families – a central component of the 2010 Affordable Care Act (ACA). I argue subsidies are a vehicle for promoting equality of opportunity: specifically, subsidies ensure access to specific “basic opportunities” (such as the ability to attend college) when out-of-pocket spending on insurance would have otherwise crowded out those opportunities. Subsidies thus make a modest, but important, contribution to mitigating the negative effect of health spending on social mobility and financial security, even if they fall short of comprehensive income protection. I raise and respond to some potential concerns about inequities created by this system, and conclude with implications for evaluating the subsidies under the ACA. Chapter three investigates whether diffusion of long-acting stimulants, a medication for Attention-Deficit/Hyperactivity Disorder (ADHD), narrowed racial/ethnic disparities among diagnosed children in the Florida Medicaid program. In longitudinal analysis, we found that minorities were substantially less likely than whites to use medications overall, but minority medication users were equally likely to switch to long-acting medications after market introduction. The increase in prescribed days was comparable for white and black medication users, but lower for Hispanics. Geography and provider setting helped explain overall medication utilization disparities, but adherence disparities were not explained by any of the covariates. We recommend targeting interventions to increase medication adherence to high-volume, minorityserving providers

Primary Care Appointment Availability and Preventive Care Utilization: Evidence From an Audit Study

Insurance expansions under the Affordable Care Act raise concerns about primary care access in communities with large numbers of newly insured. We linked individual-level, cross-sectional data on adult preventive care utilization from the 2011-2012 Behavioral Risk Factor Surveillance System to novel county-level measures of primary care appointment availability collected from an experimental audit study conducted in 10 states in 2012-2013 and other county-level health service and demographic measures. In multivariate regressions, we found higher county-level appointment availability for privately-insured adults was associated with significantly lower preventive care utilization among adults likely to have private insurance. Estimates were attenuated after controlling for county-level uninsurance, poverty, and unemployment. By contrast, greater availability of Medicaid appointments was associated with higher, but not statistically significant, preventive care utilization for likely Medicaid enrollees. Our study highlights that the relationship between preventive care utilization and primary care access in small areas likely differs by insurance status

Contrast material–enhanced MRA overestimates severity of carotid stenosis, compared with 3D time-of-flight MRA

AbstractObjectiveNon–contrast-enhanced magnetic resonance angiography (MRA) carotid imaging with the time-of-flight (TOF) technique compares favorably with angiography, ultrasound, and excised plaques. However, gadolinium contrast-enhanced MRA (CE-MRA) has almost universally replaced TOF-MRA, because it reduces imaging time (25 seconds vs 10 minutes) and improves signal-to-noise ratio. In our practice we found alarming discrepancies between CE-MRA and TOF-MRA, which was the impetus for this study.Study designTo compare the two techniques, we measured stenosis, demonstrated on three-dimensional images obtained at TOF and CE-MRA, in 107 carotid arteries in 58 male patients. The measurements were made on a Cemax workstation equipped with enlargement and measurement tools. Measurements to 0.1 mm were made at 90 degrees to the flow channel at the area of maximal stenosis and distal to the bulb where the borders of the internal carotid artery lumen were judged to be parallel (North American Symptomatic Carotid Endarterectomy Trial criteria). Experiments with carotid phantoms were done to test the comtribution of imaging software to image quality.ResultsTwelve arteries were occluded. In the remaining 95 arteries, compared with TOF-MRA, CE-MRA demonstrated a greater degree of stenosis in 42 arteries, a lesser degree of stenosis in 14 arteries, and similar (±5%) stenosis in 39 arteries (P = .02, χ2 analysis). The largest discrepancies were arteries with 0% to 70% stenosis. In those arteries in which CE-MRA identified a greater degree of stenosis than shown with TOF-MRA, mean increase was 21% for 0% to 29% stenosis, 36% for 30% to 49% stenosis, and 38% for of 50% to 69% stenosis. The carotid phantom experiments showed that the imaging parameters of CE-MRA, particularly the plane on which frequency encoding gradients were applied, reduced signal acquisition at the area of stenosis.ConclusionsCollectively these data demonstrate that CE-MRA parameters must be retooled if the method is to be considered reliable for determination of severity of carotid artery stenosis. CE-MRA is an excellent screening technique, but only TOF-MRA should be used to determine degree of carotid artery stenosis