The location of innovative activity in Europe

In this paper we use new data to describe how firms from 15 European countries organise their innovative activities. The data matches firm level accounting data with information on the patents that those firms and their subsidiaries have applied for at the European Patents Office. We describe the data in detail

Generalized Stacking Fault Energy Surfaces and Dislocation Properties of Silicon: A First-Principles Theoretical Study

The generalized stacking fault (GSF) energy surfaces have received considerable attention due to their close relation to the mechanical properties of solids. We present a detailed study of the GSF energy surfaces of silicon within the framework of density functional theory. We have calculated the GSF energy surfaces for the shuffle and glide set of the (111) plane, and that of the (100) plane of silicon, paying particular attention to the effects of the relaxation of atomic coordinates. Based on the calculated GSF energy surfaces and the Peierls-Nabarro model, we obtain estimates for the dislocation profiles, core energies, Peierls energies, and the corresponding stresses for various planar dislocations of silicon.Comment: 9 figures (not included; send requests to [email protected]

Post-Agricultural Succession in El PetÉn, Guatemala

We compared post-agricultural succession across the range of farming activities practiced in Guatemala's northern lowlands: agroforestry, swidden, ranching, and input-intensive monocultures. At 10 sites over 13 to 40 months we assessed the following characteristics of trees and shrubs that were>1 cm diameter at breast height: height, basal-area accumulation, recruitment of all individuals and fleshy-fruited individuals, and accumulation of all species and fleshy-fruited species. Succession, as measured by all these response variables except height, was dramatically faster on agroforestry and swidden sites than on pastures or input-intensive monocultures. Overall recruitment was faster for swiddens than for agroforests, but other response variables did not differ significantly between the two treatments. Regression results suggest that initial ground cover by herbs inhibited recruitment of woody colonists. The significant positive coefficient for initial basal area and the significant negative coefficient for distance from forest for accumulation of both fleshy-fruited individuals and species are probably explained by the behavioral responses of seed-dispersing animals. Our results suggest that the conservation strategy of discouraging swidden agriculture in favor of sedentary, input-intensive agriculture to relieve pressure on old-growth forest may be counterproductive over the long term.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75095/1/j.1523-1739.2003.01265.x.pd

Small-Scale Magnetic Fields are Critical to Shaping Solar Gamma-Ray Emission

The Sun is a bright gamma-ray source due to hadronic cosmic-ray interactions with solar gas. While it is known that incoming cosmic rays must generally first be reflected by solar magnetic fields to produce outgoing gamma rays, theoretical models have yet to reproduce the observed spectra. We introduce a simplified model of the solar magnetic fields that captures the main elements relevant to gamma-ray production. These are a flux tube, representing the network elements, and a flux sheet, representing the intergranule sheets. Both the tube and sheet have a horizontal size of order $100~{\rm km}$ and serve as sites where cosmic rays are reflected and gamma rays are produced. Despite having no tuning to match gamma-ray data, our model produces a gamma-ray spectrum that reasonably matches both the hard spectrum seen by Fermi-LAT data at $\text{1--200}~{\rm GeV}$ and the considerably softer spectrum seen by HAWC at near $10^3~{\rm GeV}$. We show that lower-energy ($\lesssim 10~{\rm GeV}$) gamma rays are primarily produced in the network elements and higher-energy ($\gtrsim {\rm few} \times 10~{\rm GeV}$) gamma rays in the intergranule sheets. Notably, the spectrum softening observed by HAWC results from the limited effectiveness of capturing and reflecting $\sim 10^4~{\rm GeV}$ cosmic rays by the finite-sized intergranule sheets. Our study is important for understanding cosmic-ray transport in the solar atmosphere and will lead to insights about small-scale magnetic fields in the quiet photosphere.Comment: 22 pages, 12 figure

A second order minimality condition for the Mumford-Shah functional

A new necessary minimality condition for the Mumford-Shah functional is derived by means of second order variations. It is expressed in terms of a sign condition for a nonlocal quadratic form on $H^1_0(\Gamma)$, $\Gamma$ being a submanifold of the regular part of the discontinuity set of the critical point. Two equivalent formulations are provided: one in terms of the first eigenvalue of a suitable compact operator, the other involving a sort of nonlocal capacity of $\Gamma$. A sufficient condition for minimality is also deduced. Finally, an explicit example is discussed, where a complete characterization of the domains where the second variation is nonnegative can be given.Comment: 30 page

Precision Study of Positronium: Testing Bound State QED Theory

As an unstable light pure leptonic system, positronium is a very specific probe atom to test bound state QED. In contrast to ordinary QED for free leptons, the bound state QED theory is not so well understood and bound state approaches deserve highly accurate tests. We present a brief overview of precision studies of positronium paying special attention to uncertainties of theory as well as comparison of theory and experiment. We also consider in detail advantages and disadvantages of positronium tests compared to other QED experiments.Comment: A talk presented at Workshop on Positronium Physics (ETH Zurich, May 30-31, 2003

A high vacuum photoelectron microscope for the study of biological specimens

8 pagesA photoelectron microscope (photoemission electron microscope) has been designed and built for the study of organic and biological samples. The microscope is an oil-free stainless steel high vacuum instrument pumped by a titanium sublimation pump, an ion pump, and molecular sieve roughing pumps. The electron lenses are of the electrostatic unipotential type. The microscope is equipped with a dewar for sample cooling, an internal cryogenic camera, TV-image intensifier, and vibration isolation support. Applications include studies of biological cell surfaces, photosynthetic membranes and aromatic chemical carcinogens. A representative micrograph of mouse 3T3 cells is included. In some respects, photoelectron micrographs resemble scanning electron micrographs, but the basis for contrast is different in these two techniques

Low Density Lipoprotein Metabolism by Human Macrophages Activated with Low Density Lipoprotein Immune Complexes: A Possible Mechanism of Foam Cell Formation

Human monocytes are known to be multifunctional cells that combine a variety of functions, including phagocytosis, antigen processing and presentation to immune cells, secretion of a large number of bioactive products with significant roles in the immune and inflammatory reactions, and the ability to kill tumor cells and other abnormal cells by a variety of mechanisms, including antibody-dependent cell-mediated cytotoxicity (1-5). Tissue macrophages are believed to derive from circulating monocytes, although the two types of cells differ by a variety of morphological and functional criteria (6-10). The role of macrophages is not always well understood, since it combines potentially useful properties related to its ability to ingest and process foreign and altered materials with the capacity to secrete large amounts of mediators having the potential to cause inflammatory changes and tissue damage in general (11-14). In atherosclerosis, substantial evidence has been gathered suggesting that the foam cells seen in early atherosclerotic plaques are derived from monocytes/macrophages (15-18). The formation and subendothelial accumulation of foam cells are believed to represent a critical event in the onset of atheromatous plaque formation (19). Some interesting correlations can be drawn between the involvement of macrophages in the pathogenesis of atherosclerosis and increasing evidence suggesting that immunologic mechanisms may influence the development or evolution of this pathologic process. In the early 1970s, it was postulated that immune mechanisms involving circulating immune complexes could contribute to the pathogenesis of atherosclerosis (20). The evidence supporting this role of immune complexes was both experimental (animals undergoing serum sickness and given a lipid-rich diet developed accelerated atherosclerosis [21]) and clinical (patients with IgA myelomas with anti-lipoprotein activity had massive hyperlipemia and accelerated atherosclerosis [22]). More recently, it was also shown that immune complexes (IC)1 involving low density lipoprotein (LDL) induce profound changes on cholesterol metabolism at the cellular level (23). Further support for the involvement of IC in the pathogenesis of atherosclerosis has been recently obtained by Szondy et al. (24), who demonstrated increased levels of IC and anti-LDL antibodies in patients with clinical manifestations of coronary heart disease. The possibility that IC interactions with macrophages may lead to their activation and, therefore, play a pathogenic role in the development of atherosclerosis is extremely challenging. Until recently, the mechanism proposed to explain how monocyte-derived macrophages could be transformed into foam cells has focused upon the interaction between macrophages and modified LDL or lipoproteins of abnormal composition, such as β-very low density lipoproteins (VLDL). Modified LDL can be taken up in a nonregulated fashion via the scavenger receptor, resulting in the intracellular accumulation of cholesteryl esters (CE) and in the formation of a foam cell. In contrast, it has been observed that cultured macrophages exposed to native LDL (NLDL) do not accumulate CE due to the stringent regulation of LDL receptors. However, it has been recently shown that in certain conditions, macrophages exposed to native LDL may accumulate CE. In our laboratory, we have shown that human macrophages stimulated with microbial or microbial-related products have an increased uptake of N-LDL and accumulated CE (25). Tabas et al. (26) observed increased uptake of N-LDL and concomitant CE accumulation in J774 cells, a mouse macrophage-like tumor cell line. They postulated that this was due to the enhanced metabolic activity of this tumor cell line (26). Klimov, et al. (27) had shown excessive CE accumulation in mouse peritoneal macrophages exposed to LDL immune complexes compared with control cells. A common denominator for all these observations is the known ability of microbial products and immune complexes to activate macrophages. Therefore, we decided to examine the effect of macrophage activation on N-LDL metabolism. More specifically, we wanted to investigate the effect of LDL-anti-LDL IC on N-LDL and cholesterol metabolism in human macrophages, and determine whether this type of IC can induce the transformation of human macrophages into foam cells contributing to the development of atherosclerosis

Spectroscopy of a Cooper-Pair box in the Autler-Townes configuration

A theoretical spectroscopic analysis of a microwave driven superconducting charge qubit (Cooper-pair box coupled) to an RLC oscillator model is performed. By treating the oscillator as a probe through the backreaction effect of the qubit on the oscillator circuit, we extract frequency splitting features analogous to the Autler-Townes effect from quantum optics, thereby extending the analogies between superconducting and quantum optical phenomenology. These features are found in a frequency band that avoids the need for high frequency measurement systems and therefore may be of use in qubit characterization and coupling schemes. In addition we find this frequency band can be adjusted to suit an experimental frequency regime by changing the oscillator frequency.Comment: 13 pages, 7 figures. v2: Revised version after referee comments. Accepted for publication by Physical Review

The correction-to-scaling exponent in dilute systems

The leading correction-to-scaling exponent $\omega$ for the three-dimensional dilute Ising model is calculated in the framework of the field theoretic renormalization group approach. Both in the minimal subtraction scheme as well as in the massive field theory (resummed four loop expansion) excellent agreement with recent Monte Carlo calculations [Ballesteros H G, et al Phys. Rev. B 58, 2740 (1998)] is achieved. The expression of $\omega$ as series in a $\sqrt{\epsilon}$-expansion up to ${\cal O}(\epsilon^2)$ does not allow a reliable estimate for $d=3$.Comment: 4 pages, latex, 1 eps-figure include