28,266 research outputs found
An Improved Composite Hypothesis Test for Markov Models with Applications in Network Anomaly Detection
Recent work has proposed the use of a composite hypothesis Hoeffding test for
statistical anomaly detection. Setting an appropriate threshold for the test
given a desired false alarm probability involves approximating the false alarm
probability. To that end, a large deviations asymptotic is typically used
which, however, often results in an inaccurate setting of the threshold,
especially for relatively small sample sizes. This, in turn, results in an
anomaly detection test that does not control well for false alarms. In this
paper, we develop a tighter approximation using the Central Limit Theorem (CLT)
under Markovian assumptions. We apply our result to a network anomaly detection
application and demonstrate its advantages over earlier work.Comment: 6 pages, 6 figures; final version for CDC 201
Data-driven Estimation of Origin-Destination Demand and User Cost Functions for the Optimization of Transportation Networks
In earlier work (Zhang et al., 2016) we used actual traffic data from the
Eastern Massachusetts transportation network in the form of spatial average
speeds and road segment flow capacities in order to estimate Origin-Destination
(OD) flow demand matrices for the network. Based on a Traffic Assignment
Problem (TAP) formulation (termed "forward problem"), in this paper we use a
scheme similar to our earlier work to estimate initial OD demand matrices and
then propose a new inverse problem formulation in order to estimate user cost
functions. This new formulation allows us to efficiently overcome numerical
difficulties that limited our prior work to relatively small subnetworks and,
assuming the travel latency cost functions are available, to adjust the values
of the OD demands accordingly so that the flow observations are as close as
possible to the solutions of the forward problem. We also derive sensitivity
analysis results for the total user latency cost with respect to important
parameters such as road capacities and minimum travel times. Finally, using the
same actual traffic data from the Eastern Massachusetts transportation network,
we quantify the Price of Anarchy (POA) for a much larger network than that in
Zhang et al. (2016).Comment: Preprint submitted to The 20th World Congress of the International
Federation of Automatic Control, July 9-14, 2017, Toulouse, Franc
The price of anarchy in transportation networks by estimating user cost functions from actual traffic data
We have considered a large-scale road network in Eastern Massachusetts. Using real traffic data in the form of spatial average speeds and the flow capacity for each road segment of the network, we converted the speed data to flow data and estimated the origin-destination flow demand matrices for the network. Assuming that the observed traffic data correspond to user (Wardrop) equilibria for different times-of-the-day and days-of-the-week, we formulated appropriate inverse problems to recover the per-road cost (congestion) functions determining user route selection for each month and time-of-day period. In addition, we analyzed the sensitivity of the total user latency cost to important parameters such as road capacities and minimum travel times. Finally, we formulated a system-optimum problem in order to find socially optimal flows for the network. We investigated the network performance, in terms of the total latency, under a user-optimal policy versus a system-optimal policy. The ratio of these two quantities is defined as the Price of Anarchy (POA) and quantifies the efficiency loss of selfish actions compared to socially optimal ones. Our findings contribute to efforts for a smarter and more efficient city
Analysis of DVB-H network coverage with the application of transmit diversity
This paper investigates the effects of the Cyclic Delay Diversity (CDD) transmit diversity scheme on DVB-H networks. Transmit diversity improves reception and Quality of Service (QoS) in areas of poor coverage such as sparsely populated or obscured locations. The technique not only povides robust reception in mobile environments thus improving QoS, but it also reduces network costs in terms of the transmit power, number of
infrastructure elements, antenna height and the frequency reuse factor over indoor and outdoor environments. In this paper, the benefit and effectiveness of CDD transmit diversity is tackled
through simulation results for comparison in several scenarios of coverage in DVB-H networks. The channel model used in the simulations is based on COST207 and a basic radio planning
technique is used to illustrate the main principles developed in this paper. The work reported in this paper was supported by
the European Commission IST project—PLUTO (Physical Layer DVB Transmission Optimization)
Translational cooling and storage of protonated proteins in an ion trap at subkelvin temperatures
Gas-phase multiply charged proteins have been sympathetically cooled to
translational temperatures below 1 K by Coulomb interaction with laser-cooled
barium ions in a linear ion trap. In one case, an ensemble of 53 cytochrome c
molecules (mass ~ 12390 amu, charge +17 e) was cooled by ~ 160 laser-cooled
barium ions to less than 0.75 K. Storage times of more than 20 minutes have
been observed and could easily be extended to more than an hour. The technique
is applicable to a wide variety of complex molecules.Comment: same version as published in Phys. Rev.
Recommended from our members
Adhesive and degradative properties of human placental cytotrophoblast cells in vitro.
Human fetal development depends on the embryo rapidly gaining access to the maternal circulation. The trophoblast cells that form the fetal portion of the human placenta have solved this problem by transiently exhibiting certain tumor-like properties. Thus, during early pregnancy fetal cytotrophoblast cells invade the uterus and its arterial network. This process peaks during the twelfth week of pregnancy and declines rapidly thereafter, suggesting that the highly specialized, invasive behavior of the cytotrophoblast cells is closely regulated. Since little is known about the actual mechanisms involved, we developed an isolation procedure for cytotrophoblasts from placentas of different gestational ages to study their adhesive and invasive properties in vitro. Cytotrophoblasts isolated from first, second, and third trimester human placentas were plated on the basement membrane-like extracellular matrix produced by the PF HR9 teratocarcinoma cell line. Cells from all trimesters expressed the calcium-dependent cell adhesion molecule cell-CAM 120/80 (E-cadherin) which, in the placenta, is specific for cytotrophoblasts. However, only the first trimester cytotrophoblast cells degraded the matrices on which they were cultured, leaving large gaps in the basement membrane substrates and releasing low molecular mass 3H-labeled matrix components into the medium. No similar degradative activity was observed when second or third trimester cytotrophoblast cells, first trimester human placental fibroblasts, or the human choriocarcinoma cell lines BeWo and JAR were cultured on radiolabeled matrices. To begin to understand the biochemical basis of this degradative behavior, the substrate gel technique was used to analyze the cell-associated and secreted proteinase activities expressed by early, mid, and late gestation cytotrophoblasts. Several gelatin-degrading proteinases were uniquely expressed by early gestation, invasive cytotrophoblasts, and all these activities could be abolished by inhibitors of metalloproteinases. By early second trimester, the time when cytotrophoblast invasion rapidly diminishes in vivo, the proteinase pattern of the cytotrophoblasts was identical to that of term, noninvasive cells. These results are the first evidence suggesting that specialized, temporally regulated metalloproteinases are involved in trophoblast invasion of the uterus. Since the cytotrophoblasts from first trimester and later gestation placentas maintain for several days the temporally regulated degradative behavior displayed in vivo, the short-term cytotrophoblast outgrowth culture system described here should be useful in studying some of the early events in human place
Equilibration of High Molecular-Weight Polymer Melts: A Hierarchical Strategy
A strategy is developed for generating equilibrated high molecular-weight
polymer melts described with microscopic detail by sequentially backmapping
coarse-grained (CG) configurations. The microscopic test model is generic but
retains features like hard excluded volume interactions and realistic melt
densities. The microscopic representation is mapped onto a model of soft
spheres with fluctuating size, where each sphere represents a microscopic
subchain with monomers. By varying a hierarchy of CG
representations at different resolutions is obtained. Within this hierarchy, CG
configurations equilibrated with Monte Carlo at low resolution are sequentially
fine-grained into CG melts described with higher resolution. A Molecular
Dynamics scheme is employed to slowly introduce the microscopic details into
the latter. All backmapping steps involve only local polymer relaxation thus
the computational efficiency of the scheme is independent of molecular weight,
being just proportional to system size. To demonstrate the robustness of the
approach, microscopic configurations containing up to chains with
polymerization degrees are generated and equilibration is confirmed by
monitoring key structural and conformational properties. The extension to much
longer chains or branched polymers is straightforward
- …