Erika Renáta Kovács

Investigation into the mechanism of stimulation by low-concentration stressors in barley seedlings

Beneficial effects of low-concentration chemical stressors have been investigated previously in different model systems. The symptoms of stimulation are known from earlier studies, but information about the mechanism is at an initial stage. In the present work, the mechanism of stimulation of low-concentration Cd (5 x 10(-8)M) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU, 10(-7)M) was investigated in barley seedlings. In treated plants, the amount of cytokinins increased in roots and, after being transported to the leaves, they caused stimulation there. To identify the signal transduction pathway(s) involved in the primary stimulation of cytokinin synthesis (and/or activation) in roots, specific phosphatidylinositol-4,5-bisphosphate-inositol-1,4,5-triphosphate/diacylglycerol (PIP(2)-IP(3)/DAG) and mitogen activated protein kinase (MAPK) signaling pathway inhibitors were added to the nutrient solution, and all proved to be effective, eliminating the stimulation by the stressors. Measurements of superoxide dismutase (SOD, EC 1.15.1.1) activity and the amount of malonyldialdehyde (MDA) showed that the increased amount of Cd did not cause oxidative stress in the roots, and no oxidative stress was found in the leaves, where Cd did not even accumulate. DCMU slightly increased the activity of SOD after 1 week in roots, but did not cause lipid peroxidation. In leaves, there was no oxidative stress upon treatment with DCMU. Thus, oxidative stress cannot be responsible for the stimulation with low-concentration stressors, as they changed the activity of SOD differently, while being equally stimulative for the plants.

On the mechanism of rejuvenation of ageing detached bean leaves by low-concentration stressors.

The effect of low concentrations of some stress-inducing compounds of different toxicity and chemical nature, such as Cd and Pb salts or DCMU, was investigated on the senescence of chloroplasts in detached primary leaves of bean (Phaseolus vulgaris L.). After 1 week of senescence followed by root development from the petiole, these agents stimulated chlorophyll accumulation and photosynthetic activity ((14)CO(2) fixation) as compared to the control, thus inducing rejuvenation. Low-concentration stressors increased the level of active cytokinins in roots and leaves during the treatment, as monitored by the Amaranthus betacyanin bioassay and high-pressure liquid chromatography. The lithium ion, an inhibitor of the PIP(2)-IP(3)/DAG signal transduction pathway, abolished the stimulating effect of stressors, both in roots (retarding cytokinin synthesis) and consequently also in leaves (reducing cytokinin-dependent chlorophyll accumulation). This suggests the involvement of the PIP(2)-IP(3)/DAG signal transduction pathway in generation of these consecutive organ-specific responses.

A Network Coding Algorithm for Multi-Layered Video Streaming

Multi-layered video streaming considers different quality requirements of the receivers. Network coding has been shown to be a useful tool to increase throughput of multi-layered service compared to simple multicasting. Kim et al. gave a simple effective algorithm using network coding. We generalize their approach and give an algorithm that solves the problem for two layers optimally for certain natural objective functions and prove NP-hardness of the problem for some other objectives, as well as for more than two layers. We also give some new heuristics for three layers.

Deterministic network coding algorithms and applications for wireless networks

We give new deterministic and randomized algorithms for the wireless model of Avestimehr, Diggavi, Tse for Gaussian relay networks by reducing it to the more general deterministic network coding problem introduced by Harvey, Karger and Murota. We also give a sufficient condition for a subset of coding coefficients which can be fixed arbitrarily to nonzero values, and the remaining coefficients can be determined in order to have a feasible network code. Finally we present applications to networks with nodes of different transmission properties.

Randomized and deterministic algorithms for network coding problems in wireless networks

Network coding is a method for information transmission in a network, based on the idea of enabling internal nodes to forward a function of the incoming messages, typically a linear combination. In this paper we discuss generalizations of the network coding problem with additional constraints on the coding functions called network code completion problem, NCCP. We give both randomized and deterministic algorithms for maximum throughput-achieving network code construction for the NCCP in the multicast case. We also introduce the related problem of fixable pairs, investigating when a certain subset of coding coefficients in the linear combination functions can be fixed to arbitrary non-zero values such that the network code can always be completed to achieve maximum throughput. We give a sufficient condition for a set of coding coefficients to be fixable. For both problems we present applications in different wireless and heterogeneous network models. We give randomized algorithms for both the unicast and multicast network code completion problem over a fixed finite field.The related problem of fixable pairs is introduced.A sufficient condition is given for a set of pairs to be fixable.Applications for both problems in wireless and heterogeneous networks for capacity characterization.

Receiver heterogeneity helps: Network coding for wireless multi-layer multicast

Heterogeneity amongst devices and desired services are commonly seen as a source of additional challenges for setting up an efficient multi-layer multicast service. In particular, devices requiring only the base layer can become a key bottleneck to the performance for other devices. This paper studies the case of a wireless multi-layer multicast setting and shows that the judicious use of network coding allows devices with different computational capabilities to trade-off processing complexity for an improved quality of service. As a consequence, individual devices can determine their required effort, while bringing significant advantages to the system as a whole. Network coding is used as a key element to reduce signaling in order to deliver the multicast service. More importantly, our proposed approach focuses on creating some structure in the transmitted stream by allowing inter-layer coding, in order to create more opportunities for recovering the base layer promptly. We propose a design and analyze its delay distribution and mean performance under various system conditions and present a first implementation to verify our analysis and demonstrate the applicability of our approach.

Worst case bin packing for OTN electrical layer networks dimensioning

The OTN (Optical Transport Network) standard, defined by ITU-T Recommendation G.709 and G.872, contains a flexible digital hierarchy of ODU (Optical Data Unit) signals. The ODU hierarchy provides sub-wavelength grooming in OTN networks, which is necessary for efficient utilization of the high bit rates of optical channels. When dimensioning the links of a transport network consisting of ODU switches, the packing of lower order ODU signals into higher order ODU signals needs to be taken into account. These networks are expected to be controlled by GMPLS (Generalized MPLS), which puts specific constraints on the dimensioning. We assume that there is no explicit label control and that the GMPLS control plane is using first-fit strategy for making reservations on a link. With these assumptions the link dimensioning problem is defined as deciding how many higher order ODU component links are required on an OTN GMPLS bundled link for first-fit packing of a given set of lower order ODU demands, in any order of arrival. The paper provides strict bounds for ODU hierarchy-specific item and bin sizes. Then, it introduces an extended variant of the dimensioning problem, when lower order ODU connections which are not controlled by GMPLS are also present.

The constructive characterization of ( κ,ℓ )-edge-connected digraphs

We give a constructive characterization for (κ, ℓ)-edge-connected digraphs, proving a conjecture of Frank.

Algorithms for multiplayer multicommodity flow problems

We investigate the multiplayer multicommodity flow problem: several players have different networks and commodities over a common node set. Pairs of players have contracts where one of them agrees to route the flow of the other player (up to a given capacity) between two specified nodes. In return, the second player pays an amount proportional to the flow value. We show that the social optimum can be computed by linear programming, and we propose algorithms based on column generation and Lagrangian relaxation. In contrast, we prove that it is hard to decide if an equilibrium solution exists, although some natural conditions guarantee its existence.