Critical Nodes In Directed Networks

Critical nodes or "middlemen" have an essential place in both social and economic networks when considering the flow of information and trade. This paper extends the concept of critical nodes to directed networks. We identify strong and weak middlemen. Node contestability is introduced as a form of competition in networks; a duality between uncontested intermediaries and middlemen is established. The brokerage power of middlemen is formally expressed and a general algorithm is constructed to measure the brokerage power of each node from the networks adjacency matrix. Augmentations of the brokerage power measure are discussed to encapsulate relevant centrality measures. We use these concepts to identify and measure middlemen in two empirical socio-economic networks, the elite marriage network of Renaissance Florence and Krackhardt's advice network.Comment: 28 pages, 6 figures, 2 table

Fundamental R&D Spillovers and the Internationalization of a FirmÌs Research Activities

A conceptual framework is proposed for analyzing how differences in national R&D stocks can impact on a firmÌs decision to internationalize its R&D activities. A central finding is that the integration of product markets can generate an added incentive to undertake R&D abroad. A three-stage analysis of a non-cooperative game is proposed, which entails cost-reducing process innovation in an international model of duopoly. Each firmÌs technological efficiency depends not only on its investment in applied R&D, but also on its absorption of domestic and foreign fundamental R&D, as well as the extent to which the latter are substitutes or complements. In a first stage, a firmÌs absorption of foreign fundamental R&D can be impacted by a decision to localize R&D activities abroad. The interrelation between this decision and initial production costs is also explored.Fundamental R&D, spillovers, international location, economic integration

Residual Dispersion in a Combiner Ring

In this paper we present a proof to show that there exists no system of linear or nonlinear optics which can simultaneously close multiple local orbit bumps and dispersion through a single beam transport region. The second combiner ring in the CLIC drive beam recombination system, CR2, is used as an example of where such conditions are necessary. We determine the properties of a lattice which is capable of closing the local orbit bumps and dispersion and show that all resulting solutions are either unphysical or trivial.Comment: Submitted to PRST-AB on 04/18/201

International Human Capital Formation, Brain Drain and Brain Gain: A conceptual Framework

A two-country, two-period model of international migration highlights microeconomic foundations for examining the interrelation between brain drain, brain gain and the location of human capital formation, at home or abroad. Ex ante choices regarding where to study depend on relative qualities of university systems, individuals' abilities, sunk educational investment costs, government grants, and expected employment prospects in both countries. The analysis underscores an inherently widerange of conceivable positive or negative effects on domestic net welfare. These changes depend critically on the foregoing factors, as well as the optimal design of educational grant schemes, given eventual informational imperfections regarding individuals' capabilities.

The periodic standing-wave approximation: nonlinear scalar fields, adapted coordinates, and the eigenspectral method

The periodic standing wave (PSW) method for the binary inspiral of black holes and neutron stars computes exact numerical solutions for periodic standing wave spacetimes and then extracts approximate solutions of the physical problem, with outgoing waves. The method requires solution of a boundary value problem with a mixed (hyperbolic and elliptic) character. We present here a new numerical method for such problems, based on three innovations: (i) a coordinate system adapted to the geometry of the problem, (ii) an expansion in multipole moments of these coordinates and a filtering out of higher moments, and (iii) the replacement of the continuum multipole moments with their analogs for a discrete grid. We illustrate the efficiency and accuracy of this method with nonlinear scalar model problems. Finally, we take advantage of the ability of this method to handle highly nonlinear models to demonstrate that the outgoing approximations extracted from the standing wave solutions are highly accurate even in the presence of strong nonlinearities.Comment: RevTex, 32 pages, 13 figures, 6 table

Role of orientation reference selection in motion sickness

Previous experiments with moving platform posturography have shown that different people have varying abilities to resolve conflicts among vestibular, visual, and proprioceptive sensory signals used to control upright posture. In particular, there is one class of subjects with a vestibular disorder known as benign paroxysmal positional vertigo (BPPV) who often are particularly sensitive to inaccurate visual information. That is, they will use visual sensory information for the control of their posture even when that visual information is inaccurate and is in conflict with accurate proprioceptive and vestibular sensory signals. BPPV has been associated with disorders of both posterior semicircular canal function and possibly otolith function. The present proposal hopes to take advantage of the similarities between the space motion sickness problem and the sensory orientation reference selection problems associated with the BPPV syndrome. These similarities include both etiology related to abnormal vertical canal-otolith function, and motion sickness initiating events provoked by pitch and roll head movements. The objectives of this proposal are to explore and quantify the orientation reference selection abilities of subjects and the relation of this selection to motion sickness in humans

Human Capital and Economic Growth : Dynamic Implications of Insider-outsider Problem for Macroeconomics

This paper considers a dynamic model with human capital accumulation, for which both firm-specific skills and general skills are sources of growth. We analyze how the existence of firm-specific skills changes the effects of productivity shocks on economic growth. It is well known that the insider-outsider problem can cause employment inertia in the macro economy because workers with firm-specific skills (insiders) face the hold up problem. However, most previous studies have been static in nature, so that they have paid little attention to dynamic interactions between firm-specific skills and general skills during the adjustment to the new steady state. This paper considers dynamic models that involve creation of human capital from both firm-specific skills and general skills. We show that the insider-outsider problem that is generated through the creation of firm-specific skills can cause a dramatic decline in the youth labor force during a transition path to the steady state. We also show that the problem may result in a temporary economic downturn even if the shock is positive. In Japan, since the mid-1990s, there has been a dramatic increase in the unemployment rate and a substantial decrease in the working population ratio together with increased irregular employment among young people. By analyzing firm-specific human capital as an engine of economic growth, this paper shows that these trends are consistent with our dynamic model. It also demonstrates that the productivity shocks might explain recent dramatic declines in youth employment and temporary declines in growth rates.firm-specific human capital, labor markets, insider-outsider problem