4,247 research outputs found
The growth, structure and properties of sputtered barium titanate thin films
The design and construction of a sputtering system for the deposition of barium titanate thin films is described. The growth and structure of barium titanate films deposited on a variety of substrates including amorphous carbon fi1ms, potassium bromide single crystals, and polycrystalline gold films has been studied. Films deposited on all substrates at room temperature were amorphous. Polycrystalline titanate films were formed on polycrystalline and amorphous substrates at temperatures above 450°C while films with a pronounced texture could be expitaxially deposited on single crystal potassium bromide above a temperature of only 200°C. Results of dielectric measurements made on the films are reported. Amorphous films were highly insulating (resistivities ~1014 ohm.cm with dielectric constants of between 10 and 20
Space-time thermodynamics and subsystem observables in a kinetically constrained model of glassy systems
In a recent article [M. Merolle et al., Proc. Natl. Acad. Sci. USA 102, 10837
(2005)] it was argued that dynamic heterogeneity in -dimensional glass
formers is a manifestation of an order-disorder phenomenon in the
dimensions of spacetime. By considering a dynamical analogue of the free
energy, evidence was found for phase coexistence between active and inactive
regions of spacetime, and it was suggested that this phenomenon underlies the
glass transition. Here we develop these ideas further by investigating in
detail the one-dimensional Fredrickson-Andersen (FA) model in which the active
and inactive phases originate in the reducibility of the dynamics. We
illustrate the phase coexistence by considering the distributions of mesoscopic
spacetime observables. We show how the analogy with phase coexistence can be
strengthened by breaking microscopic reversibility in the FA model, leading to
a non-equilibrium theory in the directed percolation universality class.Comment: 12 pages, 11 figures, final version with minor change
Glassy behaviour in an exactly solved spin system with a ferromagnetic transition
We show that applying simple dynamical rules to Baxter's eight-vertex model
leads to a system which resembles a glass-forming liquid. There are analogies
with liquid, supercooled liquid, glassy and crystalline states. The disordered
phases exhibit strong dynamical heterogeneity at low temperatures, which may be
described in terms of an emergent mobility field. Their dynamics are
well-described by a simple model with trivial thermodynamics, but an emergent
kinetic constraint. We show that the (second order) thermodynamic transition to
the ordered phase may be interpreted in terms of confinement of the excitations
in the mobility field. We also describe the aging of disordered states towards
the ordered phase, in terms of simple rate equations.Comment: 11 page
An experimental and theoretical study of transient negative ions in Mg, Zn, Cd and Hg
A range of experimental and theoretical techniques have been applied to the study of transient negative ions (resonances) formed in electron scattering from the Group II metals Mg, Zn, Cd, and Hg at incident electron energies below the first ionization potential. A wealth of resonance structures have been observed and from the experimental observations and theoretical information, classifications are proposed for some of these negative ion states
How the U.S. Air Force Space Command Optimizes Long-Term Investment in Space Systems
Interfaces, 33, p.p. 1-14.United States Air Force Space Command spends billions of dollars each year acquiring and
developing launch vehicles and space systems. The space systems in orbit must continually meet defensive and offensive requirements and remain interoperable over time. Space command can launch additional space systems only if it has a launch vehicle of sufficient capacity. Space planners using space and missile optimization analysis (SAMOA) consider a 24-year time horizon when determining which space assets and launch vehicles to fund and procure. A key tool which in SAMOA is an integer linear program called the space command optimizer of utility toolkit (SCOUT) that Space Command uses for long-range planning. SCOUT gives planner insight into the annual funding profiles needed to meet Space Command's acquisition goals. The 1999 portfolio of 74 systems will cost about #310 billion and includes systems that can lift satellites into orbit; yield information on space, surface, and subsurface events, activities, and threats; and destroy terrestrial, airborne, and space targets
Cross-over behaviour in a communication network
We address the problem of message transfer in a communication network. The
network consists of nodes and links, with the nodes lying on a two dimensional
lattice. Each node has connections with its nearest neighbours, whereas some
special nodes, which are designated as hubs, have connections to all the sites
within a certain area of influence. The degree distribution for this network is
bimodal in nature and has finite variance. The distribution of travel times
between two sites situated at a fixed distance on this lattice shows fat
fractal behaviour as a function of hub-density. If extra assortative
connections are now introduced between the hubs so that each hub is connected
to two or three other hubs, the distribution crosses over to power-law
behaviour. Cross-over behaviour is also seen if end-to-end short cuts are
introduced between hubs whose areas of influence overlap, but this is much
milder in nature. In yet another information transmission process, namely, the
spread of infection on the network with assortative connections, we again
observed cross-over behaviour of another type, viz. from one power-law to
another for the threshold values of disease transmission probability. Our
results are relevant for the understanding of the role of network topology in
information spread processes.Comment: 12 figure
Psychological resilience of entrepreneurs: A review and agenda for future research
Given that entrepreneurs face substantial adversity in initiating and developing new ventures, a burgeoning stream of research has sought to understand the concept of entrepreneurs’ psychological resilience. To structure and synthesize what we know about entrepreneurs’ psychological resilience, we systematically review the empirical literature to provide insights on how it has been conceptualized and operationalized, along with its key antecedents and outcomes. Based on our review, we advance a promising agenda for future research, grounded in connecting the psychological resilience of entrepreneurs to other research areas connected to the new venture development process. Overall, we point to the urgent need for theoretical precision to enhance the utility of empirical contributions, suggest promising research designs, expand on the important role of adversity, discuss potential boundary conditions, elaborate on the link between entrepreneurs’ psychological resilience and organizational resilience, and address the potential dark side of resilience
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