29,657 research outputs found
Effect of surface asperity on elastohydrodynamic lubrication
The important aspects of elastohydrodynamic lubrication, with a single, one-dimensional asperity, have been found by solving numerically the coupled transient Reynolds equation and the elasticity equation. Even though the assumption of a single asperity is highly ideal, this study sheds some light on the effect of surface roughness on elastohydrodynamic lubrication. The results show that the film pressure tends to increase more than the steady state pressure, and in particular, the increase in pressure reaches a maximum as the asperity approaches the inlet of the contact region. The asperity height and the pressure increase above the steady state pressure are closely related to each other; the higher the asperity height, the larger the pressure increase. In the pure rolling case, it has been found that a local pressure peak is not developed. However, in the cases of sliding and rolling, a small, local pressure peak is developed on the pressure profile when the asperity moves into the contact region. In general, the overall film thickness profile increases with increasing asperity height, but is not significantly affected by the asperity width. Moreover, the slope of the overall film thickness profile for the transient cases is much greater than the steady state profile, which is approximately constant across the contact width. The increase in the center film thickness also depends upon the width and height of the asperity
Electronic Interface Reconstruction at Polar-Nonpolar Mott Insulator Heterojunctions
We report on a theoretical study of the electronic interface reconstruction
(EIR) induced by polarity discontinuity at a heterojunction between a polar and
a nonpolar Mott insulators, and of the two-dimensional strongly-correlated
electron systems (2DSCESs) which accompany the reconstruction. We derive an
expression for the minimum number of polar layers required to drive the EIR,
and discuss key parameters of the heterojunction system which control 2DSCES
properties. The role of strong correlations in enhancing confinement at the
interface is emphasized.Comment: 7 pages, 6 figures, some typos correcte
Complete Tidal Evolution of Pluto-Charon
Both Pluto and its satellite Charon have rotation rates synchronous with
their orbital mean motion. This is the theoretical end point of tidal evolution
where transfer of angular momentum has ceased. Here we follow Pluto's tidal
evolution from an initial state having the current total angular momentum of
the system but with Charon in an eccentric orbit with semimajor axis (where is the radius of Pluto), consistent with its impact origin.
Two tidal models are used, where the tidal dissipation function
1/frequency and constant, where details of the evolution are strongly
model dependent. The inclusion of the gravitational harmonic coefficient
of both bodies in the analysis allows smooth, self consistent
evolution to the dual synchronous state, whereas its omission frustrates
successful evolution in some cases. The zonal harmonic can also be
included, but does not cause a significant effect on the overall evolution. The
ratio of dissipation in Charon to that in Pluto controls the behavior of the
orbital eccentricity, where a judicious choice leads to a nearly constant
eccentricity until the final approach to dual synchronous rotation. The tidal
models are complete in the sense that every nuance of tidal evolution is
realized while conserving total angular momentum - including temporary capture
into spin-orbit resonances as Charon's spin decreases and damped librations
about the same.Comment: 36 pages, including 18 figures; accepted for publication in Icaru
Reconfigurable Security: Edge Computing-based Framework for IoT
In various scenarios, achieving security between IoT devices is challenging
since the devices may have different dedicated communication standards,
resource constraints as well as various applications. In this article, we first
provide requirements and existing solutions for IoT security. We then introduce
a new reconfigurable security framework based on edge computing, which utilizes
a near-user edge device, i.e., security agent, to simplify key management and
offload the computational costs of security algorithms at IoT devices. This
framework is designed to overcome the challenges including high computation
costs, low flexibility in key management, and low compatibility in deploying
new security algorithms in IoT, especially when adopting advanced cryptographic
primitives. We also provide the design principles of the reconfigurable
security framework, the exemplary security protocols for anonymous
authentication and secure data access control, and the performance analysis in
terms of feasibility and usability. The reconfigurable security framework paves
a new way to strength IoT security by edge computing.Comment: under submission to possible journal publication
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TFT Small Signal Model and Analysis
We present an accurate small signal model for thin film transistors (TFTs) taking into account non-idealities such as contact resistance, parasitic capacitance, and threshold voltage shift. The model gives high accuracy in s-parameters, and the predicted cutoff frequency yields 1% discrepancy compared with measurement results. In contrast, the conventional CMOS small signal model adapted for TFTs yields 12.5% error. The TFT’s cutoff frequency is also evaluated under bias stress to examine the effect of device instability on small signal behavior.This is the author accepted manuscript. The final version is available from IEEE via http://dx.doi.org/10.1109/LED.2016.257592
Spectral dimensions of hierarchical scale-free networks with shortcuts
The spectral dimension has been widely used to understand transport
properties on regular and fractal lattices. Nevertheless, it has been little
studied for complex networks such as scale-free and small world networks. Here
we study the spectral dimension and the return-to-origin probability of random
walks on hierarchical scale-free networks, which can be either fractals or
non-fractals depending on the weight of shortcuts. Applying the renormalization
group (RG) approach to the Gaussian model, we obtain the spectral dimension
exactly. While the spectral dimension varies between and for the
fractal case, it remains at , independent of the variation of network
structure for the non-fractal case. The crossover behavior between the two
cases is studied through the RG flow analysis. The analytic results are
confirmed by simulation results and their implications for the architecture of
complex systems are discussed.Comment: 10 pages, 3 figure
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