337 research outputs found
Magic Islands and Barriers to Attachment: A Si/Si(111)7x7 Growth Model
Surface reconstructions can drastically modify growth kinetics during initial
stages of epitaxial growth as well as during the process of surface
equilibration after termination of growth. We investigate the effect of
activation barriers hindering attachment of material to existing islands on the
density and size distribution of islands in a model of homoepitaxial growth on
Si(111)7x7 reconstructed surface. An unusual distribution of island sizes
peaked around "magic" sizes and a steep dependence of the island density on the
growth rate are observed. "Magic" islands (of a different shape as compared to
those obtained during growth) are observed also during surface equilibration.Comment: 4 pages including 5 figures, REVTeX, submitted to Physical Review
Dynamic Education Webs – Expert Questionings, Scenarios, and Recommendations
Contemporary lifetime learning concepts require permeability between higher and further education. Today, human resources development is a critical success factor in a global environment. Shorter innovation cycles and the challenges of the service economy imply the alignment of further education concepts to the employees’ working situation. Standardized contents are no longer sufficient to meet the needs of both learners and companies. Public and private education providers have to collaborate to meet the customers’ learning needs. The providers can establish dynamic business webs – so-called dynamic education webs – in this collaborative process. These partnerships are temporary in nature and are based on incentives instead of contracts. We will focus on this new phenomenon and present research results with high practical relevance. The core questions arise: What promotes dynamic education webs? Who are the key players? What are critical success factors? These questions are answered based on literature and expert questionings of important market players. The recommendations derived can help the management to participate successfully in dynamic education webs. A glance at trends and market potentials as stated by the experts concludes the paper
Input Diffusion and the Evolution of Production Networks
The adoption and diffusion of inputs in the production network is at the heart of technological progress. What determines which inputs are initially considered and eventually adopted by innovators? We examine the evolution of input linkages from a network perspective, starting from a stylized model of network formation. Producers direct their search for new inputs along vertical linkages, screening the network neighborhood of existing suppliers to identify potentially useful inputs. A subset of these is then adopted, following a tradeoff between the benefits from input variety and the costs of customizing new inputs. Guided by this framework, we document a novel stylized fact at both the sector and the firm level: producers are more likely to adopt inputs that are already used – directly or indirectly – by their current suppliers. In particular, using disaggregated input-output data, we show that initial network proximity of a sector in 1967 significantly increases the likelihood of adoption throughout the subsequent four decades. A one-standard deviation decrease in network distance is associated with an increase in the adoption probability by one third to one half. Similarly, U.S. firms are significantly more likely to develop new input linkages among their suppliers' network neighborhood. Our results imply that the existing production network plays a crucial role in the diffusion of inputs and the evolution of technology
Input Diffusion and the Evolution of Production Networks
The adoption and diffusion of inputs in the production network is at the heart of technological progress. What determines which inputs are initially considered and eventually adopted by innovators? We examine the evolution of input linkages from a network perspective, starting from a stylized model of network formation. Producers direct their search for new inputs along vertical linkages, screening the network neighborhood of existing suppliers to identify potentially useful inputs. A subset of these is then adopted, following a tradeoff between the benefits from input variety and the costs of customizing new inputs. Guided by this framework, we document a novel stylized fact at both the sector and the firm level: producers are more likely to adopt inputs that are already used – directly or indirectly – by their current suppliers. In particular, using disaggregated input-output data, we show that initial network proximity of a sector in 1967 significantly increases the likelihood of adoption throughout the subsequent four decades. A one-standard deviation decrease in network distance is associated with an increase in the adoption probability by one third to one half. Similarly, U.S. firms are significantly more likely to develop new input linkages among their suppliers' network neighborhood. Our results imply that the existing production network plays a crucial role in the diffusion of inputs and the evolution of technology
Constructing applicative functors
Applicative functors define an interface to computation that is more general, and correspondingly weaker, than that of monads. First used in parser libraries, they are now seeing a wide range of applications. This paper sets out to explore the space of non-monadic applicative functors useful in programming. We work with a generalization, lax monoidal functors, and consider several methods of constructing useful functors of this type, just as transformers are used to construct computational monads. For example, coends, familiar to functional programmers as existential types, yield a range of useful applicative functors, including left Kan extensions. Other constructions are final fixed points, a limited sum construction, and a generalization of the semi-direct product of monoids. Implementations in Haskell are included where possible
Growth and magnetism of self-organized arrays of Fe(110) wires formed by deposition on kinetically grooved W(110)
Homoepitaxy of W(110) and Mo(110) is performed in a kinetically-limited
regime to yield a nanotemplate in the form of a uniaxial array of hills and
grooves aligned along the [001] direction. The topography and organization of
the grooves were studied with RHEED and STM. The nanofacets, of type {210}, are
tilted 18° away from (110). The lateral period could be varied from 4 to
12nm by tuning the deposition temperature. Magnetic nanowires were formed in
the grooves by deposition of Fe at 150°C on such templates. Fe/W wires
display an easy axis along [001] and a mean blocking temperature Tb=100KComment: Proceedings of ECOSS 2006 (Paris
Electrical resistance of individual defects at a topological insulator surface
Three-dimensional topological insulators host surface states with linear
dispersion, which manifest as a Dirac cone. Nanoscale transport measurements
provide direct access to the transport properties of the Dirac cone in real
space and allow the detailed investigation of charge carrier scattering. Here,
we use scanning tunnelling potentiometry to analyse the resistance of different
kinds of defects at the surface of a (Bi0.53Sb0.47)2Te3 topological insulator
thin film. The largest localized voltage drop we find to be located at domain
boundaries in the topological insulator film, with a resistivity about four
times higher than that of a step edge. Furthermore, we resolve resistivity
dipoles located around nanoscale voids in the sample surface. The influence of
such defects on the resistance of the topological surface state is analysed by
means of a resistor network model. The effect resulting from the voids is found
to be small compared to the other defects
Structure of self-organized Fe clusters grown on Au(111) analyzed by Grazing Incidence X-Ray Diffraction
We report a detailed investigation of the first stages of the growth of
self-organized Fe clusters on the reconstructed Au(111) surface by grazing
incidence X-ray diffraction. Below one monolayer coverage, the Fe clusters are
in "local epitaxy" whereas the subsequent layers adopt first a strained fcc
lattice and then a partly relaxed bcc(110) phase in a Kurdjumov-Sachs epitaxial
relationship. The structural evolution is discussed in relation with the
magnetic properties of the Fe clusters.Comment: 7 pages, 6 figures, submitted to Physical Review B September 200
Demonstration of astrocytes in cultured amniotic fluid cells of three cases with neural-tube defect
We have investigated the origin of rapidly adhering (RA) cells in three cases of neural tube defects (two anencephali, one encephalocele). We were able to demonstrate the presence of glial fibrillary acidic (GFA) protein in variable percentages (4–80%) of RA cells cultured for 4–6 days by use of indirect immunofluorescence with GFA antiserum. Cells cultured from amniotic fluids of normal pregnancies and fetal fibroblasts were completely GFA protein negative. GFA protein is well established as a highly specific marker for astrocytes. Demonstration of astrocytes may prove to be a criterion of high diagnostic value for neural tube defects. The percentage of astrocytes decreased with increasing culture time, while the percentage of fibronectin positive cells increased both in amniotic fluid cell cultures from neural tube defects and normal pregnancies
Point-by-point inscription of apodized fiber Bragg gratings
We demonstrate apodized fiber Bragg gratings inscribed with a point-by-point
technique. We tailor the grating phase and coupling amplitude through precise
control over the longitudinal and transverse position of each laser-inscribed
modification. This method of apodization is facilitated by the
highly-localized, high-contrast modifications generated by focussed IR
femtosecond laser inscription. Our technique provides a simple method for the
design and implementation of point-by-point fiber Bragg gratings with complex
apodization profiles.Comment: 6 pages, 4 figures, article in revie
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