12,975 research outputs found
Direct observation of microscopic change induced by oxygen vacancy drift in amorphous TiO2 thin films
To clarify the resistive switching and failure mechanisms in Al/amorphous TiO2 /Al devices we investigate the microscopic change in amorphous titanium oxide films and interface layers after the set process according to film deposition temperatures. For low temperature (<150 ??C) samples, the thickness of top interface layer decreased after the set process due to the dissociation of a top interface layer by uniform migration of oxygen vacancies. Meanwhile, for high temperature samples, crystalline TiO phases emerged in the failed state, meaning the formation of conducting paths from the local clustering of oxygen vacancies in nonhomogeneous titanium oxide film.open221
How people make friends in social networking sites - A microscopic perspective
We study the detailed growth of a social networking site with full temporal
information by examining the creation process of each friendship relation that
can collectively lead to the macroscopic properties of the network. We first
study the reciprocal behavior of users, and find that link requests are quickly
responded to and that the distribution of reciprocation intervals decays in an
exponential form. The degrees of inviters/accepters are slightly negatively
correlative with reciprocation time. In addition, the temporal feature of the
online community shows that the distributions of intervals of user behaviors,
such as sending or accepting link requests, follow a power law with a universal
exponent, and peaks emerge for intervals of an integral day. We finally study
the preferential selection and linking phenomena of the social networking site
and find that, for the former, a linear preference holds for preferential
sending and reception, and for the latter, a linear preference also holds for
preferential acceptance, creation, and attachment. Based on the linearly
preferential linking, we put forward an analyzable network model which can
reproduce the degree distribution of the network. The research framework
presented in the paper could provide a potential insight into how the
micro-motives of users lead to the global structure of online social networks.Comment: 10 pages, 12 figures, 2 table
Inelastic scattering in a monolayer graphene sheet; a weak-localization study
Charge carriers in a graphene sheet, a single layer of graphite, exhibit much
distinctive characteristics to those in other two-dimensional electronic
systems because of their chiral nature. In this report, we focus on the
observation of weak localization in a graphene sheet exfoliated from a piece of
natural graphite and nano-patterned into a Hall-bar geometry. Much stronger
chiral-symmetry-breaking elastic intervalley scattering in our graphene sheet
restores the conventional weak localization. The resulting carrier-density and
temperature dependence of the phase coherence length reveal that the
electron-electron interaction including a direct Coulomb interaction is the
main inelastic scattering factor while electron-hole puddles enhance the
inelastic scattering near the Dirac point.Comment: 12 pages, 3 figures, submitted to PR
Design of a Formation of Solar Pumped Lasers for Asteroid Deflection
This paper presents the design of a multi-spacecraft system for the
deflection of asteroids. Each spacecraft is equipped with a fibre laser and a
solar concentrator. The laser induces the sublimation of a portion of the
surface of the asteroid. The jet of gas and debris thrusts the asteroid off its
natural course. The main idea is to have a swarm of spacecraft flying in the
proximity of the asteroid with all the spacecraft beaming to the same location
to achieve the required deflection thrust. The paper presents the design of the
formation orbits and the multi-objective optimization of the swarm in order to
minimize the total mass in space and maximize the deflection of the asteroid.
The paper demonstrates how significant deflections can be obtained with
relatively small sized, easy-to-control spacecraft.Comment: Advances in Space Research, 201
Individual popularity and activity in online social systems
We propose a stochastic model of web user behaviors in online social systems,
and study the influence of attraction kernel on statistical property of user or
item occurrence. Combining the different growth patterns of new entities and
attraction patterns of old ones, different heavy-tailed distributions for
popularity and activity which have been observed in real life, can be obtained.
From a broader perspective, we explore the underlying principle governing the
statistical feature of individual popularity and activity in online social
systems and point out the potential simple mechanism underlying the complex
dynamics of the systems.Comment: 7 pages, 7 figures, 1 table, accepted for publication in Physica
Microscopic origin of bipolar resistive switching of nanoscale titanium oxide thin films
We report a direct observation of the microscopic origin of the bipolar
resistive switching behavior in nanoscale titanium oxide films. Through a
high-resolution transmission electron microscopy, an analytical TEM technique
using energy-filtering transmission electron microscopy and an in situ x-ray
photoelectron spectroscopy, we demonstrated that the oxygen ions piled up at
top interface by an oxidation-reduction reaction between the titanium oxide
layer and the top Al metal electrode. We also found that the drift of oxygen
ions during the on/off switching induced the bipolar resistive switching in the
titanium oxide thin films.Comment: 10 pages, 4 figure
Spin Qubits in Multi-Electron Quantum Dots
We study the effect of mesoscopic fluctuations on the magnitude of errors
that can occur in exchange operations on quantum dot spin-qubits. Mid-size
double quantum dots, with an odd number of electrons in the range of a few tens
in each dot, are investigated through the constant interaction model using
realistic parameters. It is found that the constraint of having short pulses
and small errors implies keeping accurate control, at the few percent level, of
several electrode voltages. In practice, the number of independent parameters
per dot that one should tune depends on the configuration and ranges from one
to four.Comment: RevTex, 6 pages, 5 figures. v3: two figures added, more details
provided. Accepted for publication in PR
Educing coherent eddy structures in air curtain systems
The work reported here comes within a broader research program dealing with ambiance
separation or confining by means of air curtains (plane air jets). The process is studied
experimentally by Particle Image Velocimetry (PIV). In this paper, the emphasis is put on the
flow structure in the impingement region of such jet systems insofar as it is where transfers
occur preferentially. More precisely, a vortex eduction method was implemented under the
Matlab environment enabling both the automatic detection of 2D coherent patterns embedded
in PIV velocity vector maps, and a statistical analysis of the topological and energy features
of these structures. First, the approach is explained in detail. The second part of this paper is
devoted to its application in the case of plane turbulent impinging simple- and twin-jets for
various jet exit velocities. Results about the size, the shape, the spatial distribution and the
energy content of the detected vortices are provided. Although many questions still remain
open, new insights into the fashion these structures might form, organize and evolve are
given providing an original picture of the plane turbulent impinging jet
Generating multi-scaling networks with different types of nodes
A variety of scale-free networks have been created since the pioneer work by
A.-L. Barab\'{a}si and R. Albert. All this networks are homogeneous since they
are composed of the same kind of nodes. In the realistic world, however, one
element (node or vertex) in the network may play different roles and hence has
different functions. In this Letter, we develop a new kind of network to
account for this property. In our model, each type of nodes may exhibit a
scaling law in the degree distribution and the scaling exponents are
adjustable. As a consequence, the whole network lacks of such scaling
characteristics, which indicates that many previous statistical results based
on empirical data that claimed to be scale-free networks may need to be
reexamined. This model poses an alternative way of the network division other
than the module method. Besides, one can expect that this new network will
exhibit some interesting properties concerning the dynamical processes on it.Comment: 4 figure
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