92 research outputs found
Probability Distributions on Partially Ordered Sets and Network Interdiction Games
This article poses the following problem: Does there exist a probability
distribution over subsets of a finite partially ordered set (poset), such that
a set of constraints involving marginal probabilities of the poset's elements
and maximal chains is satisfied? We present a combinatorial algorithm to
positively resolve this question. The algorithm can be implemented in
polynomial time in the special case where maximal chain probabilities are
affine functions of their elements. This existence problem is relevant for the
equilibrium characterization of a generic strategic interdiction game on a
capacitated flow network. The game involves a routing entity that sends its
flow through the network while facing path transportation costs, and an
interdictor who simultaneously interdicts one or more edges while facing edge
interdiction costs. Using our existence result on posets and strict
complementary slackness in linear programming, we show that the Nash equilibria
of this game can be fully described using primal and dual solutions of a
minimum-cost circulation problem. Our analysis provides a new characterization
of the critical components in the interdiction game. It also leads to a
polynomial-time approach for equilibrium computation
Network Inspection for Detecting Strategic Attacks
This article studies a problem of strategic network inspection, in which a
defender (agency) is tasked with detecting the presence of multiple attacks in
the network. An inspection strategy entails monitoring the network components,
possibly in a randomized manner, using a given number of detectors. We
formulate the network inspection problem as a large-scale
bilevel optimization problem, in which the defender seeks to determine an
inspection strategy with minimum number of detectors that ensures a target
expected detection rate under worst-case attacks. We show that optimal
solutions of can be obtained from the equilibria of a
large-scale zero-sum game. Our equilibrium analysis involves both
game-theoretic and combinatorial arguments, and leads to a computationally
tractable approach to solve . Firstly, we construct an
approximate solution by utilizing solutions of minimum set cover (MSC) and
maximum set packing (MSP) problems, and evaluate its detection performance. In
fact, this construction generalizes some of the known results in network
security games. Secondly, we leverage properties of the optimal detection rate
to iteratively refine our MSC/MSP-based solution through a column generation
procedure. Computational results on benchmark water networks demonstrate the
scalability, performance, and operational feasibility of our approach. The
results indicate that utilities can achieve a high level of protection in
large-scale networks by strategically positioning a small number of detectors
Network Inspection Using Heterogeneous Sensors for Detecting Strategic Attacks
We consider a two-player network inspection game, in which a defender positions heterogeneous sensors according to a probability distribution in order to detect multiple attacks caused by a strategic attacker. We assume the defender has access to multiple types of sensors that can potentially differ in their accuracy. The objective of the defender (resp. attacker) is to minimize (resp. maximize) the expected number of undetected attacks. We derive a Nash equilibrium of this zero-sum game under the assumption that each component in the network can be monitored from a unique sensor location. We then leverage our constructed Nash equilibrium to provide approximate solutions to the general case by solving a minimum set cover problem. Our results illustrate the performance and computational advantage of our solution approach, as well as the value of strategically leveraging heterogeneous sensors to protect critical networks against attacks
Strategic Monitoring of Networked Systems with Heterogeneous Security Levels
We consider a strategic network monitoring problem involving the operator of
a networked system and an attacker. The operator aims to randomize the
placement of multiple protected sensors to monitor and protect components that
are vulnerable to attacks. We account for the heterogeneity in the components'
security levels and formulate a large-scale maximin optimization problem. After
analyzing its structure, we propose a three-step approach to approximately
solve the problem. First, we solve a generalized covering set problem and run a
combinatorial algorithm to compute an approximate solution. Then, we compute
approximation bounds by solving a nonlinear set packing problem. To evaluate
our solution approach, we implement two classical solution methods based on
column generation and multiplicative weights updates, and test them on
real-world water distribution and power systems. Our numerical analysis shows
that our solution method outperforms the classical methods on large-scale
networks, as it efficiently generates solutions that achieve a close to optimal
performance and that are simple to implement in practice
Zwitterionic polymer ligands: An ideal surface coating to totally suppress protein-nanoparticle corona formation?
International audienceIn the last few years, zwitterionic polymers have been developed as antifouling surface coatings. However, their ability to completely suppress protein adsorption at the surface of nanoparticles in complex biological media remains undemonstrated. Here we investigate the formation of hard (irreversible) and soft (reversible) protein corona around model nanoparticles (NPs) coated with sulfobetaine (SB), phosphorylcholine (PC) and carboxybetaine (CB) polymer ligands in model albumin solutions and in whole serum. We show for the first time a complete absence of protein corona around SB-coated NPs, while PC-and CB-coated NPs undergo reversible adsorption or partial aggregation. These dramatic differences cannot be described by naïve hard/soft acid/base electrostatic interactions. Single NP tracking in the cytoplasm of live cells corroborate these in vitro observations. Finally, while modification of SB polymers with additional charged groups lead to consequent protein adsorption, addition of small neutral targeting moieties preserves antifouling and enable efficient intracellular targeting
Preoperative chemoradiation with paclitaxel-carboplatin or with fluorouracil-oxaliplatin-folinic acid (FOLFOX) for resectable esophageal and junctional cancer: the PROTECT-1402, randomized phase 2 trial.
BACKGROUND: Often curative treatment for locally advanced resectable esophageal or gastro-esophageal junctional cancer consists of concurrent neoadjuvant radiotherapy and chemotherapy followed by surgery. Currently, one of the most commonly used chemotherapy regimens in this setting is a combination of a fluoropyrimidin and of a platinum analogue. Due to the promising results of the recent CROSS trial, another regimen combining paclitaxel and carboplatin is also widely used by European and American centers. No clinical study has shown the superiority of one treatment over the other. The objective of this Phase II study is to clarify clinical practice by comparing these two chemotherapy treatments. Our aim is to evaluate, in operable esophageal and gastro-esophageal junctional cancer, the complete resection rate and severe postoperative morbidity rate associated with these two neoadjuvant chemotherapeutic regimens (carboplatin-paclitaxel or fluorouracil-oxaliplatin-folinic acid) when each is combined with the radiation regime utilized in the CROSS trial.
METHODS/DESIGN: PROTECT is a prospective, randomized, multicenter, open arms, phase II trial. Eligible patients will have a histologically confirmed adenocarcinoma or squamous cell carcinoma and be treated with neoadjuvant radiochemotherapy followed by surgery for stage IIB or stage III resectable esophageal cancer. A total of 106 patients will be randomized to receive either 3 cycles of FOLFOX combined to concurrent radiotherapy (41.4 Grays) or carboplatin and paclitaxel with the same radiation regimen, using a 1:1 allocation ratio.
DISCUSSION: This ongoing trial offers the unique opportunity to compare two standards of chemotherapy delivered with a common regimen of preoperative radiation, in the setting of operable locally advanced esophageal or gastro-esophageal junctional tumors.
TRIAL REGISTRATION: NCT02359968 (ClinicalTrials.gov) (registration date: 9 FEB 2015), EudraCT: 2014-000649-62 (registration date: 10 FEB 2014)
Spatiotemporal imaging of 2D polariton wave packet dynamics using free electrons
Peer ReviewedPostprint (author's final draft
- …