4,588 research outputs found
Two-State Migration of DNA in a structured Microchannel
DNA migration in topologically structured microchannels with periodic
cavities is investigated experimentally and with Brownian dynamics simulations
of a simple bead-spring model. The results are in very good agreement with one
another. In particular, the experimentally observed migration order of Lambda-
and T2-DNA molecules is reproduced by the simulations. The simulation data
indicate that the mobility may depend on the chain length in a nonmonotonic way
at high electric fields. This is found to be the signature of a nonequilibrium
phase transition between two different migration states, a slow one and a fast
one, which can also be observed experimentally under appropriate conditions.Comment: Revised edition corresponding to the comments by the referees,
submitted to Physical Review
Efficiently Clustering Very Large Attributed Graphs
Attributed graphs model real networks by enriching their nodes with
attributes accounting for properties. Several techniques have been proposed for
partitioning these graphs into clusters that are homogeneous with respect to
both semantic attributes and to the structure of the graph. However, time and
space complexities of state of the art algorithms limit their scalability to
medium-sized graphs. We propose SToC (for Semantic-Topological Clustering), a
fast and scalable algorithm for partitioning large attributed graphs. The
approach is robust, being compatible both with categorical and with
quantitative attributes, and it is tailorable, allowing the user to weight the
semantic and topological components. Further, the approach does not require the
user to guess in advance the number of clusters. SToC relies on well known
approximation techniques such as bottom-k sketches, traditional graph-theoretic
concepts, and a new perspective on the composition of heterogeneous distance
measures. Experimental results demonstrate its ability to efficiently compute
high-quality partitions of large scale attributed graphs.Comment: This work has been published in ASONAM 2017. This version includes an
appendix with validation of our attribute model and distance function,
omitted in the converence version for lack of space. Please refer to the
published versio
Distinct order of Gd 4f and Fe 3d moments coexisting in GdFe4Al8
Single crystals of flux-grown tetragonal GdFe4Al8 were characterized by
thermodynamic, transport, and x-ray resonant magnetic scattering measurements.
In addition to antiferromagnetic order at TN ~ 155 K, two low-temperature
transitions at T1 ~ 21 K and T2 ~ 27 K were identified. The Fe moments order at
TN with an incommensurate propagation vector (tau,tau,0) with tau varying
between 0.06 and 0.14 as a function of temperature, and maintain this order
over the entire T<TN range. The Gd 4f moments order below T2 with a
ferromagnetic component mainly out of plane. Below T1, the ferromagnetic
components are confined to the crystallographic plane. Remarkably, at low
temperatures the Fe moments maintain the same modulation as at high
temperatures, but the Gd 4f moments apparently do not follow this modulation.
The magnetic phase diagrams for fields applied in [110] and [001] direction are
presented and possible magnetic structures are discussed.Comment: v2: 14 pages, 12 figures; PRB in prin
Rate of convergence in the Smoluchowski-Kramers approximation for mean-field stochastic differential equations
In this paper we study a second-order mean-field stochastic differential
systems describing the movement of a particle under the influence of a
time-dependent force, a friction, a mean-field interaction and a space and
time-dependent stochastic noise. Using techniques from Malliavin calculus, we
establish explicit rates of convergence in the zero-mass limit
(Smoluchowski-Kramers approximation) in the -distances and in the total
variation distance for the position process, the velocity process and a
re-scaled velocity process to their corresponding limiting processes
Physical Layer Security: Detection of Active Eavesdropping Attacks by Support Vector Machines
This paper presents a framework for converting wireless signals into
structured datasets, which can be fed into machine learning algorithms for the
detection of active eavesdropping attacks at the physical layer. More
specifically, a wireless communication system, which consists of K legal users,
one access point (AP) and one active eavesdropper, is considered. To cope with
the eavesdropper who breaks into the system during the uplink phase, we first
build structured datasets based on several different features. We then apply
support vector machine (SVM) classifiers and one-class SVM classifiers to those
structured datasets for detecting the presence of eavesdropper. Regarding the
data, we first process received signals at the AP and then define three
different features (i.e., MEAN, RATIO and SUM) based on the post-processing
signals. Noticeably, our three defined features are formulated such that they
have relevant statistical properties. Enabling the AP to simulate the entire
process of transmission, we form the so-called artificial training data (ATD)
that is used for training SVM (or one-class SVM) models. While SVM is preferred
in the case of having perfect channel state information (CSI) of all channels,
one-class SVM is preferred in the case of having only the CSI of legal users.
We also evaluate the accuracy of the trained models in relation to the choice
of kernel functions, the choice of features, and the change of eavesdropper's
power. Numerical results show that the accuracy is relatively sensitive to
adjusting parameters. Under some settings, SVM classifiers (or even one-class
SVM) can bring about the accuracy of over 90%.Comment: All versions on this site are withdrawn because of their serious
mistakes. Moreover, the contributions of the co-authors were not considered
carefully. Two co-authors have little contributions, which cannot constitute
any main contribution. It was a mistake when the first author forgot to
update the actual authors, and he hurried to upload the incomplete and flaw
file
Riesz transform characterization of Hardy spaces associated with Schr\"odinger operators with compactly supported potentials
Let L=-\Delta+V be a Schr\"odinger operator on R^d, d\geq 3. We assume that V
is a nonnegative, compactly supported potential that belongs to L^p(R^d), for
some p>d/2. Let K_t be the semigroup generated by -L. We say that an
L^1(R^d)-function f belongs to the Hardy space H_L^1 associated with L if
sup_{t>0} |K_t f| belongs to L^1(R^d). We prove that f\in H_L^1 if and only if
R_j f \in L^1(R^d) for j=1,...,d, where R_j= \frac{d}{dx_j} L^{-1/2} are the
Riesz transforms associated with L.Comment: 6 page
- …