Computed tomography from X-rays: old 2-D results, new 3-D problems

We consider old results on 2-D computerized tomography methods and their relevance to new fully 3-D problems. We examine the 2-D filtered back-projection method (FBP) from several perspectives to better understand how it works. Based on that understanding, we question whether stable, reliable reconstruction algorithms can be found for wide-detector cone-beam 3-D machines with their resulting large-slant beams. We use a numerical method of "point response function fitting" to compute convolution kernels H(u, v) (for use with back-projection) for a model slant-beam problem. These kernels exhibit disturbing growing and spreading oscillations which would greatly amplify errors in the projection data

Randomly Branched Polymers and Conformal Invariance

We argue that the field theory that descibes randomly branched polymers is not generally conformally invariant in two dimensions at its critical point. In particular, we show (i) that the most natural formulation of conformal invariance for randomly branched polymers leads to inconsistencies; (ii) that the free field theory obtained by setting the potential equal to zero in the branched polymer field theory is not even classically conformally invariant; and (iii) that numerical enumerations of the exponent $\theta (\alpha )$, defined by $T_N(\alpha )\sim \lambda^NN^{-\theta (\alpha ) +1}$, where $T_N(\alpha )$ is number of distinct configuratations of a branched polymer rooted near the apex of a cone with apex angel $\alpha$, indicate that $\theta (\alpha )$ is not linear in $1/\alpha$ contrary to what conformal invariance leads one to expect.Comment: 1 graph not included, SPhT /92/145, The Tex Macros have been changed. In the present version only jnl.tex is needed. It can be obtained directly from the bulletin boar

Cheap Food Policy: Fact or Rhetoric

The term “cheap food policy” has frequently been used as a descriptor for U.S. commodity programs by those who contend these payments to farmers ultimately result in lower food costs for consumers. More recently, farm policy has been criticized for contributing to the obesity problem in the U.S. by making large quantities of fattening foods widely available and relatively inexpensive. This paper econometrically evaluates the impact of direct government payments to farmers from 1960-1999 on the proportion of disposable income consumers spend on food. The model finds the payments do not significantly affect the affordability of food.Agricultural policy, obesity, food policy, technology

[Review of] Adam Fairclough. To Redeem the Soul of America: The Southern Christian Leadership Conference and Martin Luther King, Jr.

Following David J. Garrow\u27s 1986 Pulitzer Prize-winning biography, Bearing the Cross, Adam Fairclough makes extensive use of information gleaned from FBI wiretaps as well as other sources in an effort to peruse the soul of the Southern Christian Leadership Conference (SCLC) and its president, Martin Luther King, Jr. Fairclough\u27s subtitle is no accident, for he focuses at least as much on the SCLC as he does on King. Significantly, this emphasis causes him to add a chapter about the SCLC after King\u27s death, a postscript not available in other books about King

[Review of] Jo Ann Robinson. The Montgomery Bus Boycott and the Women Who Started It: The Memoirs of Jo Ann Gibson Robinson

Jo Ann Robinson, a major organizer of the Montgomery bus boycott, offers a new and convincing account of the origins of the protest that triggered the entire civil rights movement and launched the career of Martin Luther King, Jr. In an absorbing, first-hand narrative, the dignified and unassuming Robinson focuses on the role of the Women\u27s Political Council (WPC) and details the WPC\u27s plans to engineer a boycott months before the heralded arrest of Rosa Parks

Cheap Food Policy: Fact or Rhetoric?

The term "cheap food policy" has frequently been used as a descriptor for U.S. commodity programs by those who contend these payments to farmers ultimately result in lower food costs for consumers. More recently, farm policy has been criticized for contributing to the obesity problem in the U.S. by making large quantities of fattening foods widely available and relatively inexpensive. This paper econometrically evaluates the impact of direct government payments to farmers from 1960-1999 on the proportion of disposable income consumers spend on food. The model finds the payments do not significantly affect the affordability of food.Agricultural and Food Policy,

An International Comparison of the Effects of Government Agricultural Support on Food Budget Shares

This study evaluates econometrically the effect of government support to agriculture on a measure of the affordability of food in 10 Organization for Economic Cooperation and Development (OECD) countries. The panel model we construct specifically utilizes two values calculated by the OECD: Producer Support Estimates as a percentage of gross farm receipts and the Consumer Nominal Protection Coefficient. These two variables represent transfers from taxpayers to agricultural producers through government programs and transfers from consumers to government through protectionist measures, respectively. By using dummy variables, we find implications for groups of countries on the basis of their relative levels of support and protection.agricultural policy, obesity, Agribusiness, Agricultural and Food Policy, Food Consumption/Nutrition/Food Safety, I18, Q18,

Incentives Matter: Assessing Biofuel Policies in the South

As a result of the increase in the real cost of fossil fuel-based energy in recent years, federal and state governments have taken a more active role in energy policy by creating incentives to develop alternative sources of energy, including biofuels. However, policymakers often become focused on the specific type of energy and not the energy services consumers ultimately value. The lack of recognition of energy as a commodity results in policies that ignore the characteristics of the associated markets: easy entry and exit, no barriers to entry, and sensitivity to changes in supply and demand. Consequently, energy industries may fail to arise because entrepreneurs must be able to account for all costs and earn—at a minimum—a competitive return on the investment. This article evaluates the options available to policymakers related to biofuels, which are of particular concern to the South, and includes an assessment of the knowledge base on which policy decisions are made.alternative energy, biofuels, energy policy, Resource /Energy Economics and Policy, Q41, Q42, Q48,