171 research outputs found
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
Bowling for Fascism: Social Capital and the Rise of the Nazi Party
Using newly collected data on association density in 229 towns and cities in interwar Germany, we show that denser social networks were associated with faster entry into the Nazi Party. The effect is large: one standard deviation higher association density is associated with at least 15 percent faster Nazi Party entry. Party membership, in turn, predicts electoral success. Social networks thus aided the rise of the Nazis that destroyed Germany’s first democracy. The effects of social capital depended on the political context: in federal states with more stable governments, higher association density was not correlated with faster Nazi Party entry
How Merchant Towns Shaped Parliaments: From the Norman Conquest of England to the Great Reform Act
This is the final version. Available from the American Economic Association via the DOI in this recordWe study the emergence of urban self-governance in the late medieval period. We focus on England after the Norman Conquest of 1066, building a novel comprehensive dataset of 554 medieval towns. During the Commercial Revolution (twelfth to thirteenth centuries), many merchant towns obtained Farm Grants: the right of self-governed tax collection and law enforcement. Self-governance, in turn, was a stepping stone for parliamentary representation: Farm Grant towns were much more likely to be summoned directly to the medieval English Parliament than otherwise similar towns. We also show that self-governed towns strengthened the role of Parliament and shaped national institutions over the subsequent centuries
Dipolar interaction between two-dimensional magnetic particles
We determine the effective dipolar interaction between single domain
two-dimensional ferromagnetic particles (islands or dots), taking into account
their finite size. The first correction term decays as 1/D^5, where D is the
distance between particles. If the particles are arranged in a regular
two-dimensional array and are magnetized in plane, we show that the correction
term reinforces the antiferromagnetic character of the ground state in a square
lattice, and the ferromagnetic one in a triangular lattice. We also determine
the dipolar spin-wave spectrum and evaluate how the Curie temperature of an
ensemble of magnetic particles scales with the parameters defining the particle
array: height and size of each particle, and interparticle distance. Our
results show that dipolar coupling between particles might induce ferromagnetic
long range order at experimentally relevant temperatures. However, depending on
the size of the particles, such a collective phenomenon may be disguised by
superparamagnetism.Comment: 11 pages, 5 figure
Impurity-induced diffusion bias in epitaxial growth
We introduce two models for the action of impurities in epitaxial growth. In
the first, the interaction between the diffusing adatoms and the impurities is
``barrier''-like and, in the second, it is ``trap''-like. For the barrier
model, we find a symmetry breaking effect that leads to an overall down-hill
current. As expected, such a current produces Edwards-Wilkinson scaling. For
the trap model, no symmetry breaking occurs and the scaling behavior appears to
be of the conserved-KPZ type.Comment: 5 pages(with the 5 figures), latex, revtex3.0, epsf, rotate, multico
Coherent Stranski-Krastanov growth in 1+1 dimensions with anharmonic interactions: An equilibrium study
The formation of coherently strained three-dimensional islands on top of the
wetting layer in Stranski-Krastanov mode of growth is considered in a model in
1+1 dimensions accounting for the anharmonicity and non-convexity of the real
interatomic forces. It is shown that coherent 3D islands can be expected to
form in compressed rather than in expanded overlayers beyond a critical lattice
misfit. In the latter case the classical Stranski-Krastanov growth is expected
to occur because the misfit dislocations can become energetically favored at
smaller island sizes. The thermodynamic reason for coherent 3D islanding is the
incomplete wetting owing to the weaker adhesion of the edge atoms. Monolayer
height islands with a critical size appear as necessary precursors of the 3D
islands. The latter explains the experimentally observed narrow size
distribution of the 3D islands. The 2D-3D transformation takes place by
consecutive rearrangements of mono- to bilayer, bi- to trilayer islands, etc.,
after exceeding the corresponding critical sizes. The rearrangements are
initiated by nucleation events each next one requiring to overcome a lower
energetic barrier. The model is in good qualitative agreement with available
experimental observations.Comment: 12 pages text, 15 figures, Accepted in Phys.Rev.B, Vol.61, No2
The impact of regional and neighbourhood deprivation on physical health in Germany: a multilevel study
Voigtländer S, Berger U, Razum O. The impact of regional and neighbourhood deprivation on physical health in Germany: a multilevel study. BMC Public Health. 2010;10(1): 403.Background There is increasing evidence that individual health is at least partly determined by neighbourhood and regional factors. Mechanisms, however, remain poorly understood, and evidence from Germany is scant. This study explores whether regional as well as neighbourhood deprivation are associated with physical health and to what extent this association can be explained by specific neighbourhood exposures. Methods Using 2004 data from the German Socio-Economic Panel Study (SOEP) merged with regional and neighbourhood characteristics, we fitted multilevel linear regression models with subjective physical health, as measured by the SF-12, as the dependent variable. The models include regional and neighbourhood proxies of deprivation (i.e. regional unemployment quota, average purchasing power of the street section) as well as specific neighbourhood exposures (i.e. perceived air pollution). Individual characteristics including socioeconomic status and health behaviour have been controlled for. Results This study finds a significant association between area deprivation and physical health which is independent of compositional factors and consistent across different spatial scales. Furthermore the association between neighbourhood deprivation and physical health can be partly explained by specific features of the neighbourhood environment. Among these perceived air pollution shows the strongest association with physical health (-2.4 points for very strong and -1.5 points for strong disturbance by air pollution, standard error (SE) = 0.8 and 0.4, respectively). Beta coefficients for perceived air pollution, perceived noise and the perceived distance to recreational resources do not diminish when including individual health behaviour in the models. Conclusions This study highlights the difference regional and in particular neighbourhood deprivation make to the physical health of individuals in Germany. The results support the argument that specific neighbourhood exposures serve as an intermediary step between deprivation and health. As people with a low socioeconomic status were more likely to be exposed to unfavourable neighbourhood characteristics these conditions plausibly contribute towards generating health inequalities
Scanning tunneling microscopy at multiple voltage biases of stable "ring-like" Ag clusters on Si(111)-(77)
Since more than twenty years it is known that deposition of Ag onto
Si(111)-(7\times7) leads under certain conditions to the formation of so-called
"ring-like" clusters, that are particularly stable among small clusters. In
order to resolve their still unknown atomic structure, we performed voltage
dependent scanning tunneling microscopy (STM) measurements providing
interesting information about the electronic properties of clusters which are
linked with their atomic structure. Based on a structural model of Au cluster
on Si(111)-(7\times7) and our STM images, we propose an atomic arrangement for
the two most stable Ag "ring-like" clusters.Comment: 9 pages and 5 figure
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