Georgios Paschos - Academia.edu (original) (raw)

Papers by Georgios Paschos

Arteriosclerosis Thrombosis and Vascular Biology, Apr 1, 2012

2013 11th International Symposium and Workshops on Modeling and Optimization in Mobile Ad Hoc and Wireless Networks, 2013

ABSTRACT Opportunistic routing in wireless networks has been proposed as a method to combat the v... more ABSTRACT Opportunistic routing in wireless networks has been proposed as a method to combat the volatility of wireless links, by leveraging their broadcast nature and choosing the next hop for each transmitted packet post-facto, using the actual reception outcomes at the respective neighbors, rather than based on a priori information. Much of the research on the topic has focused on protocol design issues, e.g. coordination mechanisms among the next-hop candidates; however, the fundamental performance bounds of the scheme are not yet known. In this paper we study the theoretical throughput region of opportunistic routing, for a generic network model with an arbitrary matrix of packet erasure probabilities between any two nodes, which cannot be mapped onto any classical model due to the existence of undirected broadcast from each node. We introduce a generic technique involving a transformation into a virtual network consisting of nodes corresponding to packet states in the original network, and define two different throughput-optimal scheduling policies in the virtual network, one based on a backpressure-like approach, and another that uses a dynamic programming algorithm which finds the minimum time to clear the system from any initial queued backlog. These policies can support both a unidirectional (half-duplex) flow between a given source and destination, and a bidirectional (full-duplex) connection with inter-session network coding in intermediate nodes.

Circulation, Jan 20, 2015

-Genome-wide association studies (GWAS) have established ADAMTS7 as a locus for coronary artery d... more -Genome-wide association studies (GWAS) have established ADAMTS7 as a locus for coronary artery disease (CAD) in humans. Yet, these studies fail to provide directionality for the association between ADAMTS7 and CAD. Previous reports have implicated ADAMTS7 in the regulation of vascular smooth muscle cell (VSMC) migration, but a role and direction of impact for this gene in atherogenesis has not been shown in relevant model systems. -We bred an Adamts7 whole body knockout (KO) mouse onto both the Ldlr and Apoe KO hyperlipidemic mouse models. Adamts7(-/-)/Ldlr(-/-) and Adamts7(-/-)/Apoe(-/-) mice displayed significant reductions in lesion formation in aortas and aortic roots as compared to controls. Adamts7 KO mice also showed reduced neointimal formation after femoral wire injury. Adamts7 expression was induced in response to injury and hyperlipidemia but was absent at later timepoints, and primary Adamts7 KO VSMCs showed reduced migration in the setting of TNFα stimulation. ADAMTS7 localized to cells positive for SMC markers in human CAD lesions, and sub-cellular localization studies in cultured VSMCs placed ADAMTS7 at the cytoplasm and cell membrane, where it co-localized with markers of podosomes. -These data represent the first in vivo experimental validation of the association of Adamts7 with atherogenesis, likely through modulation of vascular cell migration and matrix in atherosclerotic lesions. These results demonstrate that Adamts7 is proatherogenic, lending directionality to the original genetic association and supporting the concept that pharmacological inhibition of ADAMTS7 should be atheroprotective in humans, making it an attractive target for novel therapeutic interventions.

Journal of Biological Chemistry, 2009

isomers generated by free radical-catalyzed peroxidation of polyunsaturated fatty acids (PUFAs). ... more isomers generated by free radical-catalyzed peroxidation of polyunsaturated fatty acids (PUFAs). Urinary F 2 -iPs, PGF 2α isomers derived from arachidonic acid (AA), are used as indices of lipid peroxidation in vivo. We now report the characterization of two major F 3 -iPs, 5-epi-8,12-iso-iPF 3α -VI and 8,12-iso-iPF 3α -VI, derived from the ω-3 fatty acid, eicosapentaenoic acid (EPA). Although the potential therapeutic benefits of EPA receive much attention, a shift towards a diet rich in ω-3 PUFAs may also predispose to enhanced lipid peroxidation. Urinary 5-epi-8,12-iso-iPF 3α -VI and 8,12-iso-iPF 3α -VI are highly correlated and unaltered by cyclooxygenase inhibition in humans. Fish oil dose-dependently elevates urinary F 3 -iPs in mice and a shift in dietary ω-3/ω-6 PUFAs is reflected by an increasing slope [m] of the line relating urinary 8, 12-iso-iPF 3α -VI and 8,12-iso-iPF 2α -VI. Administration of bacterial lipopolysaccharide evokes a reversible increase in both urinary 8,12-iso-iPF 3α -VI and 8,12-iso-iPF 2α -VI in humans on an ad lib diet. However, while excretion of the iPs is highly correlated (R 2 median = 0.8), [m] varies by ~ an order of magnitude, reflecting marked inter-individual variability in the relative peroxidation of ω-3 versus ω-6 substrates. Clustered analysis of F 2 -and F 3 -iPs refines assessment of the oxidant stress response to an inflammatory stimulus in vivo by integrating variability in dietary intake of ω-3 / ω-6 PUFAs.

Arteriosclerosis, Thrombosis, and Vascular Biology, 2007

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IEEE Communications Magazine, 2016

ABSTRACT The backpressure routing policy is known to be a throughput optimal policy that supports... more ABSTRACT The backpressure routing policy is known to be a throughput optimal policy that supports any feasible traffic demand in data networks, but may have poor delay performance when packets traverse loops in the network. In this paper, we study loop-free backpressure routing policies that forward packets along directed acyclic graphs (DAGs) to avoid the looping problem. These policies use link reversal algorithms to improve the DAGs in order to support any achievable traffic demand. For a network with a single commodity, we show that a DAG that supports a given traffic demand can be found after a finite number of iterations of the link-reversal process. We use this to develop a joint link-reversal and backpressure routing policy, called the loop free backpressure (LFBP) algorithm. This algorithm forwards packets on the DAG, while the DAG is dynamically updated based on the growth of the queue backlogs. We show by simulations that such a DAG-based policy improves the delay over the classical backpressure routing policy. We also propose a multicommodity version of the LFBP algorithm, and via simulation we show that its delay performance is better than that of backpressure.

Ieee Journal on Selected Areas in Communications, Feb 1, 2015

ABSTRACT We study a one-hop broadcast channel with two receivers. The receivers have side informa... more ABSTRACT We study a one-hop broadcast channel with two receivers. The receivers have side information obtained by overhearing wireless channels. The relay takes control decisions by coding transmissions based on its knowledge of side information in the receivers. We consider two control mechanisms. In the ACK system, the relay has definite knowledge of side information announced via overhearing reports. In the NACK system, the relay has statistical knowledge of side information and receives feedback after every decoding failure. Our contribution is as follows. We provide the minimal evacuation times for the two systems and obtain analytical expressions of the throughput region for the ACK and the code-constrained region for the NACK system. When the transmission rates are the same pmb(r1=r2)pmb{(r_{1}=r_{2})} pmb(r1=r2) or when the receiver with the highest transmission rate has perfect side information pmb(pf=1)pmb{(p_{f}=1)} pmb(pf=1), we show that the two regions are equal. We then provide simple joint xor coding and scheduling policies that achieve those regions and, thus, are throughput optimal. Subsequently, we evaluate the report overhead performance for both mechanisms and reflect on the involved tradeoff with throughput. Ultimately, we demonstrate by simulations that the proposed throughput optimal policies can be appropriately enhanced to have good delay properties, particularly for protocols that utilize sequenced packet delivery.

2014 Ieee 19th International Workshop on Computer Aided Modeling and Design of Communication Links and Networks, Dec 1, 2014

Eurasip Journal on Wireless Communications and Networking, Jun 1, 2006

A new medium access control (MAC) protocol is proposed for quality-of-service (QoS) support in wi... more A new medium access control (MAC) protocol is proposed for quality-of-service (QoS) support in wireless local area networks (WLAN). The protocol is an alternative to the recent enhancement 802.11e. A new priority policy provides the system with better performance by simulating time division multiple access (TDMA) functionality. Collisions are reduced and starvation of lowpriority classes is prevented by a distributed admission control algorithm. The model performance is found analytically extending previous work on this matter. The results show that a better organization of resources is achieved through this scheme. Throughput analysis is verified with OPNET simulations.

2009 2nd Ifip Wireless Days, Dec 15, 2009

Much research has been devoted to optimizing the power saving mechanism in wireless mobile device... more Much research has been devoted to optimizing the power saving mechanism in wireless mobile devices. Recent advances in wireless radio technology facilitate the implementation of various possible sleep policies. One basic question that arises is: which policy performs best under a certain condition? Furthermore, what are the optimal parameters for a given policy? To answer these questions, we formulate an optimization problem, which entails cost minimization for a given parameterized policy and selection of the best policy among a class. We propose a cost function which captures the inherent tradeoff of delay and energy saving. This takes into account the cost of response time due to the extra sleep, the energy saving during the sleep, and the cost for periodic waking up (for listening). As an application, we consider IEEE 802.16e's power saving mechanism. We study various practical policies and check their performance. We show that the constant duration policy is optimal for Poisson inactivity periods, but not for hyper-exponentially distributed inactivity periods. In the policy where vacations are i.i.d. exponential random variables, we derive analytically the optimal control as a function of the expected inactivity period. This result holds for general inactivity periods. Our framework allows us to compare the performance of several optimal and suboptimal practical policies with that of the IEEE 802.16e standard.

We consider random medium access schemes for devices that support sleep modes, i.e. turning off e... more We consider random medium access schemes for devices that support sleep modes, i.e. turning off electronic compartments for energy saving. Due to hardware limitations, sleep mode transitions cannot occur at the medium access timescale. Each terminal can choose when to turn on/off and its probability to transmit on an arbitrary slot. Thus, we develop a two level model, consisting of

Contemporary mobile devices are battery powered and due to their shrinking size and increasing co... more Contemporary mobile devices are battery powered and due to their shrinking size and increasing complexity operate on a tight energy budget. Thus, energy consumption is becoming one of the major concerns regarding the current and upcoming wireless communication systems. On the other hand, the available bandwidth resources are limited and modern applications are throughput demanding, leading thus to strong competition

2013 IEEE 18th International Workshop on Computer Aided Modeling and Design of Communication Links and Networks (CAMAD), 2013

ABSTRACT We study the problem of Wireless Network Coding with imperfect overhearing, a joint codi... more ABSTRACT We study the problem of Wireless Network Coding with imperfect overhearing, a joint coding/scheduling problem that arises naturally in multihop wireless networks. We map this problem to specific instances of index coding. In this direction, we propose an approach that decouples the problem of scheduling and coding, and ultimately results in comparison of different policies for evacuating packets from the system. Using this framework we propose a heuristic approach that is based on a rank minimization method proposed in the literature. We show by simulations that the proposed heuristic outperforms powerful schemes of the past like Random Linear Network Coding (RLNC) and COPE-like greedy Immediately Decodable Network Codes (IDNC).

We study the problem of broadcasting packets in wireless networks. At each time slot, a network c... more We study the problem of broadcasting packets in wireless networks. At each time slot, a network controller activates non-interfering links and forwards packets to all nodes at a common rate; the maximum rate is referred to as the broadcast capacity of the wireless network. Existing policies achieve the broadcast capacity by balancing traffic over a set of spanning trees, which are difficult to maintain in a large and time-varying wireless network. We propose a new dynamic algorithm that achieves the broadcast capacity when the underlying network topology is a directed acyclic graph (DAG). This algorithm utilizes local queue-length information, does not use any global topological structures such as spanning trees, and uses the idea of in-order packet delivery to all network nodes. Although the in-order packet delivery constraint leads to degraded throughput in cyclic graphs, we show that it is throughput optimal in DAGs and can be exploited to simplify the design and analysis of optimal algorithms. Our simulation results show that the proposed algorithm has superior delay performance as compared to tree-based approaches.

Science translational medicine, Jan 3, 2016

The absence of Bmal1, a core clock gene, results in a loss of circadian rhythms, an acceleration ... more The absence of Bmal1, a core clock gene, results in a loss of circadian rhythms, an acceleration of aging, and a shortened life span in mice. To address the importance of circadian rhythms in the aging process, we generated conditional Bmal1 knockout mice that lacked the BMAL1 protein during adult life and found that wild-type circadian variations in wheel-running activity, heart rate, and blood pressure were abolished. Ocular abnormalities and brain astrogliosis were conserved irrespective of the timing of Bmal1 deletion. However, life span, fertility, body weight, blood glucose levels, and age-dependent arthropathy, which are altered in standard Bmal1 knockout mice, remained unaltered, whereas atherosclerosis and hair growth improved, in the conditional adult-life Bmal1 knockout mice, despite abolition of clock function. Hepatic RNA-Seq revealed that expression of oscillatory genes was dampened in the adult-life Bmal1 knockout mice, whereas overall gene expression was largely unch...

Corr, Oct 4, 2010

This paper focuses on a particular transmission scheme called local network coding, which has bee... more This paper focuses on a particular transmission scheme called local network coding, which has been reported to provide significant performance gains in practical wireless networks. The performance of this scheme strongly depends on the network topology and thus on the locations of the wireless nodes. Also, it has been shown previously that finding the encoding strategy, which achieves maximum performance, requires complex calculations to be undertaken by the wireless node in real-time. Both deterministic and random point pattern are explored and using the Boolean connectivity model we provide upper bounds for the maximum coding number, i.e., the number of packets that can be combined such that the corresponding receivers are able to decode. For the models studied, this upper bound is of order of sqrtN\sqrt{N}sqrtN, where NNN denotes the (mean) number of neighbors. Moreover, achievable coding numbers are provided for grid-like networks. We also calculate the multiplicative constants that determine the gain in case of a small network. Building on the above results, we provide an analytic expression for the upper bound of the efficiency of local network coding. The conveyed message is that it is favorable to reduce computational complexity by relying only on small encoding numbers since the resulting expected throughput loss is negligible.

2014 52nd Annual Allerton Conference on Communication Control and Computing, Sep 5, 2014

2013 Ifip Ieee International Symposium on Integrated Network Management, 2013

ABSTRACT Distributed, large-scale, enterprise applications are commonly supported in multi-tier d... more ABSTRACT Distributed, large-scale, enterprise applications are commonly supported in multi-tier data-center environments. In this paper, we study a scheduling problem for sharing CPU time in a cluster of servers among a number of enterprise customers. Such sharing is typically mandated by service differentiation requirements and QoS guarantees. Our main contribution is the formal definition of a CPU allocation/scheduling problem with respect to QoS quarantees and evaluation of scheduling policies that address the following design criteria: they have provable performance, they do not require a priori knowledge of service statistics and their overhead is adjustable. We provide the necessary mathematical framework for policies that satisfy the above criteria and evaluate proposed algorithms via theoretical analysis and extensive simulations.