29,760 research outputs found
Effects of longevity and dependency rates on saving and growth: Evidence from a panel of cross countries
While earlier empirical studies found a negative saving effect of old-age dependency rates without considering longevity, recent studies have found that longevity has a positive effect on growth without considering old-age dependency rates. In this paper, we first justify the related yet independent roles of longevity and old-age dependency rates in determining saving and growth by using a growth model that encompasses both neoclassical and endogenous growth models as special cases. Using panel data from a recent World Bank data set, we then find that the longevity effect is positive and the dependency effect is negative in savings and investment regressions. The estimates indicate that the differences in the demographic variables across countries or over time can well explain the differences in aggregate savings rates. We also find that both population age structure and life expectancy are important contributing factors to growth.
Evolutions of SIFs of concrete under sustained loading by considering the effects of stress relaxations
A Universal Gauge for Thermal Conductivity of Silicon Nanowires With Different Cross Sectional Geometries
By using molecular dynamics simulations, we study thermal conductivity of
silicon nanowires (SiNWs) with different cross sectional geometries. It is
found that thermal conductivity decreases monotonically with the increase of
surface-to-volume ratio (SVR). More interestingly, a simple universal linear
dependence of thermal conductivity on SVR is observed for SiNWs with modest
cross sectional area (larger than 20 nm^2), regardless of the cross sectional
geometry. As a result, among different shaped SiNWs with the same cross
sectional area, the one with triangular cross section has the lowest thermal
conductivity. Our study provides not only a universal gauge for thermal
conductivity among different cross sectional geometries, but also a designing
guidance to tune thermal conductivity by geometry.Comment: 22 pages, 6 figure
Facility location with double-peaked preference
We study the problem of locating a single facility on a real line based on
the reports of self-interested agents, when agents have double-peaked
preferences, with the peaks being on opposite sides of their locations. We
observe that double-peaked preferences capture real-life scenarios and thus
complement the well-studied notion of single-peaked preferences. We mainly
focus on the case where peaks are equidistant from the agents' locations and
discuss how our results extend to more general settings. We show that most of
the results for single-peaked preferences do not directly apply to this
setting; this makes the problem essentially more challenging. As our main
contribution, we present a simple truthful-in-expectation mechanism that
achieves an approximation ratio of 1+b/c for both the social and the maximum
cost, where b is the distance of the agent from the peak and c is the minimum
cost of an agent. For the latter case, we provide a 3/2 lower bound on the
approximation ratio of any truthful-in-expectation mechanism. We also study
deterministic mechanisms under some natural conditions, proving lower bounds
and approximation guarantees. We prove that among a large class of reasonable
mechanisms, there is no deterministic mechanism that outperforms our
truthful-in-expectation mechanism
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