Dirac's Footsteps and Supersymmetry

One hundred years after its creator's birth, the Dirac equation stands as the cornerstone of XXth Century physics. But it is much more, as it carries the seeds of supersymmetry. Dirac also invented the light-cone, or "front form" dynamics, which plays a crucial role in string theory and in elucidating the finiteness of N=4 Yang-Mills theory. The light-cone structure of eleven-dimensional supergravity (N=8 supergravity in four dimensions) suggests a group-theoretical interpretation of its divergences. We speculate they could be compensated by an infinite number of triplets of massless higher spin fields, each obeying a Dirac-like equation associated with the coset $F_4/SO(9)$. The divergences are proportional to the trace over a non-compact structure containing the compact form of $F_4$. Its nature is still unknown, but it could show the way to $M$-theory.Comment: Invited Talk at Dirac's Centennial Symposium, Tallahasse, Florida, Dec 200

Explorations, Vol. 3, No. 1

Cover: Debouche, a thermo-formed acrylic sculpture, by Deborah de Moulpied, Associate Professor of Art at the University of Maine, (from the collection of Barbara Heldt and Gerald Smith, Oxford, England); photograph by Dale and Nedra Van Volkinburg. Articles include: Biotechnology, by Michael R. Gross The Search for Tom Swift or Some Reflections on One of America\u27s Best-Known Cultural Heroes, by David K. Vaughan ENDO-EXO 1 Sculpture in Motion Communication is Not Just Saying Words; It is Creating True Understanding, by Marisue Pickering Maine Outreach: Teaching Success, by Richard A. Hale and James F. Philp Through Cloud and Fog, Hunting the Elusive pH, by Richard Jagels Ocean Basin with a Past A Cryptic History: Breaking the Code Discerning a Future, by Detmar Schnitker We Stand Corrected in Volume II, Number 2, of EXPLORATIONS Dialogue: Letters [to the Editor] Updates from the Dispatch Cas

The absence of myocardial calcium-independent phospholipase a2γ results in impaired prostaglandin e2 production and decreased survival in mice with acute trypanosoma cruzi infection

Cardiomyopathy is a serious complication of Chagas' disease, caused by the protozoan parasite Trypanosoma cruzi. The parasite often infects cardiac myocytes, causing the release of inflammatory mediators, including eicosanoids. A recent study from our laboratory demonstrated that calcium-independent phospholipase A(2)γ (iPLA(2)γ) accounts for the majority of PLA(2) activity in rabbit ventricular myocytes and is responsible for arachidonic acid (AA) and prostaglandin E(2) (PGE(2)) release. Thus, we hypothesized that cardiac iPLA(2)γ contributes to eicosanoid production in T. cruzi infection. Inhibition of the isoform iPLA(2)γ or iPLA(2)β, with the R or S enantiomer of bromoenol lactone (BEL), respectively, demonstrated that iPLA(2)γ is the predominant isoform in immortalized mouse cardiac myocytes (HL-1 cells). Stimulation of HL-1 cells with thrombin, a serine protease associated with microthrombus formation in Chagas' disease and a known activator of iPLA(2), increased AA and PGE(2) release, accompanied by platelet-activating factor (PAF) production. Similarly, T. cruzi infection resulted in increased AA and PGE(2) release over time that was inhibited by pretreatment with (R)-BEL. Further, T. cruzi-infected iPLA(2)γ-knockout (KO) mice had lower survival rates and increased tissue parasitism compared to wild-type (WT) mice, suggesting that iPLA(2)γ-KO mice were more susceptible to infection than WT mice. A significant increase in iPLA(2) activity was observed in WT mice following infection, whereas iPLA(2)γ-KO mice showed no alteration in cardiac iPLA(2) activity and produced less PGE(2). In summary, these studies demonstrate that T. cruzi infection activates cardiac myocyte iPLA(2)γ, resulting in increased AA and PGE(2) release, mediators that may be essential for host survival during acute infection. Thus, these studies suggest that iPLA(2)γ plays a cardioprotective role during the acute stage of Chagas' disease

Employment Gains from Minimum-Wage Hikes under Perfect Competition: A Simple General-Equilibrium Analysis

Contrary to conventional wisdom, higher minimum wages may lead to greater levels of employment under perfect competition. We demonstrate this possibility in a simple generalequilibrium model with two goods produced by two factors and consumed by two representative households. Within our model, hiking a minimum wage redistributes income between heterogeneous consumers. This redistribution may create an excess demand for the laborintensive good, and hence increase employment to restore equilibrium, despite the fact that every firm becomes less labor intensive

Unemployment and Income-Distribution Effects of Economic Growth: A Minimum-Wage Analysis with Optimal Saving

Theoretically and numerically, we analyze the unemployment and income-distribution effects of economic growth, in a model with optimal saving (investment) and a minimum wage for unskilled labor. Within this three-factor model (including skilled labor), an exogenous rise in the growth rate increases unemployment if capital and unskilled labor are complements (versus substitutes), implying a trade-off between (faster) growth and (lower) unemployment. We also show how the growth rate affects the skill premium and factor shares of national income, providing little support for Piketty’s (2014) controversial thesis that capital’s share is higher when growth is slower

A Minimum-Wage Model of Unemployment and Growth: The Case of a Backward-Bending Demand Curve for Labor

We add a minimum wage and hence involuntary unemployment to a conventional two-sector model of a perfectly competitive economy with optimal saving and endogenous growth. Our resulting model highlights the possible case of a backward-bending demand curve for labor, along which a hike in the minimum wage might increase total employment. This possibility provides theoretical support for some controversial empirical studies, which challenge the textbook prediction of an inverse relationship between employment and the minimum wage. Our model also implies that a minimum-wage hike has negative implications for both the growth rate and lifetime utilit

Design and fabrication of materials with desired deformation behavior

Figure 1: Two examples of real and replicated objects. Thanks to our data-driven process, we are able to measure, simulate, and obtain material combinations of non-linear base materials that match a desired deformation behavior. We can then print those objects with multi-material 3D printers using two materials (blue and black) with varying internal microstructure. This paper introduces a data-driven process for designing and fab-ricating materials with desired deformation behavior. Our process starts with measuring deformation properties of base materials. For each base material we acquire a set of example deformations, and we represent the material as a non-linear stress-strain relationship in a finite-element model. We have validated our material measure-ment process by comparing simulations of arbitrary stacks of base materials with measured deformations of fabricated material stacks. After material measurement, our process continues with designing stacked layers of base materials. We introduce an optimization pro-cess that finds the best combination of stacked layers that meets a user’s criteria specified by example deformations. Our algorithm employs a number of strategies to prune poor solutions from the combinatorial search space. We demonstrate the complete process by designing and fabricating objects with complex heterogeneous materials using modern multi-material 3D printers

Spacings of Quarkonium Levels with the Same Principal Quantum Number

The spacings between bound-state levels of the Schr\"odinger equation with the same principal quantum number $N$ but orbital angular momenta $\ell$ differing by unity are found to be nearly equal for a wide range of power potentials $V = \lambda r^\nu$, with $E_{N \ell} \approx F(\nu, N) - G(\nu,N) \ell$. Semiclassical approximations are in accord with this behavior. The result is applied to estimates of masses for quarkonium levels which have not yet been observed, including the 2P $c \bar c$ states and the 1D $b \bar b$ states.Comment: 20 pages, latex, 3 uuencoded figures submitted separately (process using psfig.sty