Positivity of Chern Classes for Reflexive Sheaves on P^N

It is well known that the Chern classes $c_i$ of a rank $n$ vector bundle on \PP^N, generated by global sections, are non-negative if $i\leq n$ and vanish otherwise. This paper deals with the following question: does the above result hold for the wider class of reflexive sheaves? We show that the Chern numbers $c_i$ with $i\geq 4$ can be arbitrarily negative for reflexive sheaves of any rank; on the contrary for $i\leq 3$ we show positivity of the $c_i$ with weaker hypothesis. We obtain lower bounds for $c_1$, $c_2$ and $c_3$ for every reflexive sheaf \FF which is generated by H^0\FF on some non-empty open subset and completely classify sheaves for which either of them reach the minimum allowed, or some value close to it.Comment: 16 pages, no figure

Theory of Neutron Diffraction from the Vortex Lattice in UPt3

Neutron scattering experiments have recently been performed in the superconducting state of UPt3 to determine the structure of the vortex lattice. The data show anomalous field dependence of the aspect ratio of the unit cell in the B phase. There is apparently also a change in the effective coherence length on the transition from the B to the C phases. Such observations are not consistent with conventional superconductvity. A theory of these results is constructed based on a picture of two-component superconductivity for UPt3. In this way, these unusual observations can be understood. There is a possible discrepancy between theory and experiment in the detailed field dependence of the aspect ratio.Comment: 11 pages; uses REVTEX, APS and PRABIB styles; 2 Postscript figure files include

Nonlinear Micromechanical Casimir Oscillator

The Casimir force between uncharged metallic surfaces originates from quantum mechanical zero point fluctuations of the electromagnetic field. We demonstrate that this quantum electrodynamical effect has a profound influence on the oscillatory behavior of microstructures when surfaces are in close proximity (<= 100 nm). Frequency shifts, hysteretic behavior and bistability caused by the Casimir force are observed in the frequency response of a periodically driven micromachined torsional oscillator.Comment: 4 pages, 4 figures; added and rearranged references; added comments on sensitivit

Targeted Enforcement against Illicit Trade in Tobacco Products

Illicit trade in tobacco is a substantial and growing problem in the U.S., causing loss of tax revenue, damage to public health, and threats to public safety. Decisions about enforcement against ITTP involve tradeoffs among competing objectives. Good policy design can improve the terms of those tradeoffs but cannot eliminate them. We examine questions about the allocation of enforcement resources against ITTP, and its distribution across activities, individuals, and organizations: in particular, whether and how to differentially target ITTP that involves violence or support for terrorism. We consider the problem of developing effective strategies for enforcement, applying both lessons from experience with markets for illicit drugs and theoretical insights about enforcement targeting and dynamic concentration. We show that targeted enforcement and focused deterrence are more efficient than unfocused enforcement, and that – when other policy changes increase the potential rewards to illicit activity – enforcement resources applied earlier (before illicit markets have grown) will have greater impact than enforcement resources applied later (and therefore to larger markets). We discuss additional considerations, ranging from real-world complications left out of the simple models to examination of how insights from behavioral law and economics may modify conclusions based on a theory of deterrence designed for homo economicus

Corelike Nature Of The Pd Mvv Shift In Pd-based Alloys

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)We present arguments based on the formal similarity of the Cini and Koster-Slater models to show that, in alloys, iVV Auger spectra that are significantly distorted from the quasiatomic form may present kinetic-energy shifts that do not correspond to the quasiatomic situation, even when the origin of the terms of the line shape is quasiatomic. By comparing measured shifts of the Pd M5VV and L3M4,5M4,5 true core-level spectrum in Pd-Cu alloys, we verify this conclusion in this case. The corresponding experimental shifts of Ag in Pd-Ag alloys are, however, closely related, as expected from the quasiatomic nature of the Ag MVV spectrum. In alloy studies, therefore, true core-level Auger kinetic-energy shifts should be employed. © 1992 The American Physical Society.4524138991390303/12595-7; FAPESP; São Paulo Research FoundationFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Countervailing Effects: What the FDA Would Have to Know to Evaluate Tobacco Regulations

The Family Smoking Prevention and Tobacco Control Act [P.L. 111-31] gives the US Food and Drug Administration (FDA) the authority to regulate tobacco products, including placing restrictions on product composition, sale, and distribution. A complete accounting of the costs and benefits of any tobacco regulation includes harms from possible illicit trade in tobacco products (ITTP): costs of enforcement, violence, incarceration, etc. Indeed, the law instructs the FDA to take into account the “countervailing effects” of regulation on public health, “such as the creation of a significant demand for contraband or other tobacco products that do not meet the requirements.” While the law’s narrow focus on public health may limit the scope of an inquiry by the FDA compared to a full benefit-cost analysis, aspects of ITTP such as violence and incarceration have substantial health impacts. Illicit markets in drugs such as cocaine, heroin, and methamphetamine, not to mention the grand experiment of alcohol Prohibition in the early 20th century, illustrate the substantial risks of unwanted side effects of drug prohibition. But taxes, product limitations, access restrictions, and narrowly defined product bans constitute “lesser prohibitions,” and are subject to the same kind (if not degree) of risks. All tobacco policy-making should therefore consider ITTP. This article sets forth a research agenda for the FDA to consider in order to estimate the effects of contemplated tobacco-product regulation and ITTP. We argue that, to carry out fully its legislative mandate, the FDA would have to determine the current size and impact of ITTP, analyze how these may be expected to change under new regulations, and look for interdependencies among tobacco-product markets that may complicate single-product regulation. A more challenging element of the research agenda would be to develop a better theoretical groundwork for the prediction of the emergence, size, and side effects of illicit markets