883,028 research outputs found
Influence of roughness on contact interface in fretting under dry and boundary lubricated sliding regimes
This paper presents experimental results of wear process under dry and boundary lubricated metallic (AISI 1034/AISI 52100) contacting bodies with different surfaces morphologies subjected to a wide range of kinematic fretting conditions. Analysis of damage mode observed under such fretting conditions is elucidated in context of surfaces morphologies therefore associated with surface manufacturing processes. Various surface topographies due to specific machining processes (cutting and abrasive modes) have been investigated. Under boundary lubricated (ZDDTP zinc-dialkyl-dithiophosphate) fretting contact paradoxally has a high coefficient of friction at the transition between Partial and Full slip sliding regime. This paper attempts to bridge the gap between the damage mode, sliding conditions and surface roughness to provide an approach to evaluate the surface finishing as a factor in friction and wear damage processes
On Leveraging Partial Paths in Partially-Connected Networks
Mobile wireless network research focuses on scenarios at the extremes of the
network connectivity continuum where the probability of all nodes being
connected is either close to unity, assuming connected paths between all nodes
(mobile ad hoc networks), or it is close to zero, assuming no multi-hop paths
exist at all (delay-tolerant networks). In this paper, we argue that a sizable
fraction of networks lies between these extremes and is characterized by the
existence of partial paths, i.e. multi-hop path segments that allow forwarding
data closer to the destination even when no end-to-end path is available. A
fundamental issue in such networks is dealing with disruptions of end-to-end
paths. Under a stochastic model, we compare the performance of the established
end-to-end retransmission (ignoring partial paths), against a forwarding
mechanism that leverages partial paths to forward data closer to the
destination even during disruption periods. Perhaps surprisingly, the
alternative mechanism is not necessarily superior. However, under a stochastic
monotonicity condition between current v.s. future path length, which we
demonstrate to hold in typical network models, we manage to prove superiority
of the alternative mechanism in stochastic dominance terms. We believe that
this study could serve as a foundation to design more efficient data transfer
protocols for partially-connected networks, which could potentially help
reducing the gap between applications that can be supported over disconnected
networks and those requiring full connectivity.Comment: Extended version of paper appearing at IEEE INFOCOM 2009, April
20-25, Rio de Janeiro, Brazi
From Politics to the Family: How Sex-Role Attitudes Keep on Diverging in Reunified Germany
What is the role of politics in shaping attitudes about appropriate roles for women in the family and the compatibility of work and motherhood? In this paper we argue that the German separation and later reunification produced a natural experiment to address this question. During the divided years, East German institutions encouraged high levels of full-time employment for women, including mothers. The West German system by contrast deterred women in general, and mothers in particular, from full-time employment. After reunification, family-related policies largely converged in the two Germanies. Against this background, we empirically investigate gender-role attitudes in reunified Germany. Our results show that East Germans are significantly more likely to hold egalitarian or nontraditional sex-role attitudes than West Germans. Despite a scenario of partial policy convergence, we also find evidence that the gap between East and West German gender role attitudes more than doubled in the years after reunification. We suggest that one explanation for this divergence could be found in the notion of social identity.political regimes, gender role attitudes
On the Role of Mobility for Multi-message Gossip
We consider information dissemination in a large -user wireless network in
which users wish to share a unique message with all other users. Each of
the users only has knowledge of its own contents and state information;
this corresponds to a one-sided push-only scenario. The goal is to disseminate
all messages efficiently, hopefully achieving an order-optimal spreading rate
over unicast wireless random networks. First, we show that a random-push
strategy -- where a user sends its own or a received packet at random -- is
order-wise suboptimal in a random geometric graph: specifically,
times slower than optimal spreading. It is known that this
gap can be closed if each user has "full" mobility, since this effectively
creates a complete graph. We instead consider velocity-constrained mobility
where at each time slot the user moves locally using a discrete random walk
with velocity that is much lower than full mobility. We propose a simple
two-stage dissemination strategy that alternates between individual message
flooding ("self promotion") and random gossiping. We prove that this scheme
achieves a close to optimal spreading rate (within only a logarithmic gap) as
long as the velocity is at least . The key
insight is that the mixing property introduced by the partial mobility helps
users to spread in space within a relatively short period compared to the
optimal spreading time, which macroscopically mimics message dissemination over
a complete graph.Comment: accepted to IEEE Transactions on Information Theory, 201
Creation of partial band gaps in anisotropic photonic-band-gap structures
The photonic-band-gap (PBG) structure composed of an anisotropic-dielectric sphere in uniform dielectric medium is studied by solving Maxwell’s equations using the plane-wave expansion method. In particular, for a uniaxial material with large principal refractive indices and sufficient anisotropy between them, the photonic band structures possess a full band gap in the whole Brillouin zone for a diamond lattice. Furthermore, in the 1/3 partial Brillouin zone where the Bloch wave vector has a dominant component along the extraordinary axis of uniaxial sphere, the photonic band structures are found to exhibit full band gaps for all the other lattices such as face-centered-cubic, body-centered-cubic, and simple-cubic lattices, although a complete band gap does not open in the whole Brillouin zone. The partial band gaps persist at a very low filling fraction of uniaxial sphere. This phenomenon is attributed to the breakdown of the photonic band degeneracy at high-symmetry points of the Brillouin zone by the anisotropy of material dielectricity. The combination of such an anisotropic PBG structure with the self-arrangement technique of colloidal crystal may provide a possible way to fabricate the three-dimensional photonic crystal in visible and infrared regimes. The application of a strong electric field may bring into alignment the extraordinary axis of uniaxial sphere as this configuration of spheres is most favorable thermodynamically.published_or_final_versio
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