Gravity in a Box

We consider a brane-world construction which incorporates a finite region of flat space, ``the box,'' surrounded by a region of anti-de Sitter space. This hybrid construction provides a framework which interpolates between the scenario proposed by Arkani-Hamed, Dimopoulos and Dvali, and that proposed by Randall and Sundrum. Within this composite framework, we investigate the effects of resonant modes on four-dimensional gravity. We also show that, on a probe brane in the anti-de Sitter region, there is enhanced production of on-shell nonresonant modes. We compare our model to some recent attempts to incorporate the Randall-Sundrum scenario into superstring theory.Comment: 15 pages, 1 figur

Greener Acres or Greener Waters? Potential U.S. Impacts of Agricultural Trade Liberalization

This paper examines the elimination of all agricultural policy distortions in all trading countries and agricultural production decisions in the United States, as well as subsequent environmental quality in the presence and absence of nondegradation environmental standards. The results suggest that trade liberalization has the potential to increase domestic production and boost agricultural returns by as much as 8.5 percent. Consumer surplus would likely fall, and the discharge of nutrients, sediment, and pesticides would likely increase. However, environmental policies can limit these adverse environmental impacts and mute the potential decrease in consumer surplus, while leaving increased returns to agricultural production.agriculture, trade reform, environment, nondegradation, Environmental Economics and Policy, International Relations/Trade,

THE BIG PICTURE: PRODUCTION AND ENVIRONMENTAL IMPACTS OF REDUCED US OBESITY

This paper assesses how successfully reducing the incidence of overweight and obesity in the US to meet public health objectives might influence agricultural production. We also examine the consequent agri-environmental effects of the production changes. Our estimates show that a reduction in aggregate consumption by between 2 and 6 percent, associated with public health goals being met, would lead to reduced production of primary agricultural commodities, increased exports, and reduced discharge of agricultural pollutants. In both cases, neither the estimated changes in commodity production nor the subsequent environmental impacts would be uniform across the landscape. Results indicate that in value terms, the largest changes (either positive or negative) in agricultural producer net returns would occur in the Corn Belt and the Lake States; conversely, the largest impacts on consumer surplus would occur in the Northeast and Pacific regions.Health Economics and Policy,

Dynamic delamination buckling in composite laminates under impact loading: Computational simulation

A unique dynamic delamination buckling and delamination propagation analysis capability has been developed and incorporated into a finite element computer program. This capability consists of the following: (1) a modification of the direct time integration solution sequence which provides a new analysis algorithm that can be used to predict delamination buckling in a laminate subjected to dynamic loading, and (2) a new method of modeling the composite laminate using plate bending elements and multipoint constraints. This computer program is used to predict both impact induced buckling in composite laminates with initial delaminations and the strain energy release rate due to extension of the delamination. It is shown that delaminations near the outer surface of a laminate are susceptible to local buckling and buckling-induced delamination propagation when the laminate is subjected to transverse impact loading. The capability now exists to predict the time at which the onset of dynamic delamination buckling occurs, the dynamic buckling mode shape, and the dynamic delamination strain energy release rate

Consequences of Dust in Metal-Rich HII Regions

Dust and associated depletion of heavy elements from the gas phase can modify the thermal properties of HII regions from the dust-free case, with significant consequences for the emergent optical spectrum. We present the results of theoretical calculations illustrating the effects of grains on the spectra of giant, extragalactic HII regions, with emphasis on high metallicity systems (i.e. solar and higher Z). Dust provides a simple explanation for the observational absence of pure Balmer-line spectra that are expected on theoretical grounds for dust-free, chemically enriched nebulae. Grains may also play a role in enhancements of forbidden-line emission observed in HII regions in the enriched nuclei of normal galaxies. In most cases, depletion introduces the strongest perturbations to the optical spectrum. Selective absorption of the ionizing continuum as well as heating by grain photoelectrons are important in some instances, however, and grain heating can be particularly important for enhancing emission in high-ionization lines. Allowing for depletion, the presence of dust is unlikely to introduce large errors in global metallicity indicators, although uncertainties in depletion factors coupled with the sensitivity of infrared cooling to electron density will make accurate calibrations difficult at high Z. The present calculations establish further that previous relative abundance analyses that fail to take into account dust effects in a self-consistent way (grain heating as well as depletion) may overestimate temperature gradients in high-Z nebulae, resulting in errors in relative abundances for different elements.Comment: 21 pages (AASTeX), plus 9 figures (uuencoded, gzipped, tar), to appear in ApJ, December 199

Noncooperatively Optimized Tolerance: Decentralized Strategic Optimization in Complex Systems

We introduce noncooperatively optimized tolerance (NOT), a generalization of highly optimized tolerance (HOT) that involves strategic (game theoretic) interactions between parties in a complex system. We illustrate our model in the forest fire (percolation) framework. As the number of players increases, our model retains features of HOT, such as robustness, high yield combined with high density, and self-dissimilar landscapes, but also develops features of self-organized criticality (SOC) when the number of players is large enough. For example, the forest landscape becomes increasingly homogeneous and protection from adverse events (lightning strikes) becomes less closely correlated with the spatial distribution of these events. While HOT is a special case of our model, the resemblance to SOC is only partial; for example, the distribution of cascades, while becoming increasingly heavy-tailed as the number of players increases, also deviates more significantly from a power law in this regime. Surprisingly, the system retains considerable robustness even as it becomes fractured, due in part to emergent cooperation between neighboring players. At the same time, increasing homogeneity promotes resilience against changes in the lightning distribution, giving rise to intermediate regimes where the system is robust to a particular distribution of adverse events, yet not very fragile to changes

Estimation of elastic and viscous properties of the left ventricle based on annulus plane harmonic behavior

Assessment of left ventricular (LV) function with an emphasis on contractility has been a challenge in cardiac mechanics during the recent decades. The LV function is usually described by the LV pressurevolume (P-V) diagram. The standard P-V diagrams are easy to interpret but difficult to obtain and require invasive instrumentation for measuring the corresponding volume and pressure data. In the present study, we introduce a technique that can estimate the viscoelastic properties of the LV based on harmonic behavior of the ventricular chamber and it can be applied non-invasively as well. The estimation technique is based on modeling the actual long axis displacement of the mitral annulus plane toward the cardiac base as a linear damped oscillator with time-varying coefficients. The time-varying parameters of the model were estimated by a standard Recursive Linear Least Squares (RLLS) technique. LV stiffness at end-systole and end diastole was in the range of 61.86-136.00 dyne/g.cm and 1.25-21.02 dyne/g.cm, respectively. The only input used in this model was the long axis displacement of the annulus plane, which can also be obtained non-invasively using tissue Doppler or MR imaging

Completion Time Dynamics For Masters And Doctoral Studies At Makerere University

This paper examines the dynamics of completion time of masters studies and how such dynamics relate to those of doctoral studies at Makerere University, Uganda. The assessment is based on administrative data of 605 masters degree students at the University in the 2004 and 2005 enrollment cohorts. The total elapsed time from first enrollment to submission of final dissertation copy was adopted as a measure of completion time. A time-to-event approach in a Cox model was applied in the investigations. A median completion time of 3.8 years (range, 1.85.9) suggests a delayed completion of studies. The established associations, modeled by a range of candidate, candidature, and institutional variables including discipline area corroborate the results obtained by the analysis of doctoral completion time at the University. The findings suggest that masters completion dynamics mirror those of doctoral studies at the University

Examination Phase Of The Masters Thesis: A Plausible Cause Of Delayed Completion Of Graduate Studies At Makerere University, Uganda

This paper investigates the influence of the examination stage of student theses on the completion time of graduate studies at Makerere University, Uganda. The assessment is based on the administrative data of 504 Masters degree students in the 2000 to 2008 enrollment cohorts at the School of Education, Makerere University. The total elapsed time from submission of a thesis for evaluation to a viva voce was adopted as a measure of the examination period. Additionally, the period from viva voce to submission of the final thesis was investigated. The analysis included frequency distribution, summary statistics, and a Pearson Chi-square test. A median examination period of 11 months (range, 155), in the results, is a lengthy one when compared to the two-year stipulated duration of Masters studies at the University. Subsequently, the fact that about six in every ten students (59.9%) submits a final thesis beyond a months period after a viva points to further delays in the review process of students reports. No significant variations in the submission period were observed by student characteristics. In sum, the findings underscore the need to strengthen administrative support systems, particularly aspects related to the review process of students reports, to ensure students timely completion of graduate programs