Effects of Ca2+ deregulation on mitochondrial membrane potential and cell viability in nucleated cells following lytic complement attack

We have previously shown [Papadimitriou JC. Ramm LE. Drachenberg CB. Trump BF. Shin ML. (1991) J. Immunol., 147, 212-217] that formation of lytic C5b-9 channels on Ehrlich ascites tumor cells induced rapid depletion of adenine nucleotides associated with prelytic leakage preceding cell death. Extracellular Ca2+ concentration ([Ca2+]e) reduction by chelation markedly delayed the onset of cell death, although the adenine nucleotide leakage was enhanced. In the present study, we examined the temporal relationships between ionized cytosolic Ca2+ ([Ca2+]i), mitochondrial membrane potential (delta psi m) and cell death in individual cells by digital imaging fluorescence microscopy (DIFM), during the earliest phase of C5b-9 attack. The results showed an immediate, > 20-fold rise in [Ca2+]i, rapidly followed by dissipation of delta psi m and subsequent acute cell death. These events were markedly delayed by chelation of Ca2+e, but not by nominally Ca2+ free medium. Differing from previous reports indicating propidium iodide labeling of viable cells bearing C5b-9 channels, with DIFM we observed nuclear fluorescence with that marker only in association with cell death. These findings indicate that Ca2+ influx through lytic C5b-9 channels is responsible for the massive increase in [Ca2+]i, as well as for the rapid loss of delta psi m, followed by acute cell death. When this [Ca2+]i increase is prevented, the cell death is probably related to metabolic depletion.     

Acute renal failure in pregnancy

Between 1982 and 1992, 18 cases of pregnancy-related acute renal failure (PR-ARF) were observed (9% of the total number of ARF). Mean age of the women was 32 years (22-40 years). Uterine hemorrhage and preeclampsia/eclampsia were the major causes of ARF, accounting for 61% of the cases. Patchy renal cortical necrosis was suspected in 2 cases whereas signs of disseminated intravascular coagulation (DIC) or microangiopathic hemolytic anemia were present in 6 (33%) and 9 (50%) cases, respectively. Ten women required hemodialysis; and 6 of them, additional plasma exchange sessions. Five patients (28%) died during the acute phase of the illness, mainly due to brain damage, hepatic failure, and sepsis. Among the survivors, a complete (61.5%) or partial recovery (23.1%) was usually seen, but irreversible renal failure was recorded in 2 cases with postpartum hemolytic uremic syndrome (HUS). Short-lasting oligoanuria (< 3 days) represents a good prognostic index. However, the presence of vascular injury (cortical necrosis, HUS) seems to carry a poor prognosis. In conclusion, PR-ARF is still a critical occurrence, associated with serious prognosis for both women and kidneys. So far, the most effective measures remain the careful prevention and the aggressive management of the obstetric complications.     

The Euclidean travelling salesman problem is NP-complete

The Travelling Salesman Problem is shown to be NP-Complete even if its instances are restricted to be realizable by sets of points on the Euclidean plane.     

Moving resonance in nonlinear response to fully nonstationary stochastic ground motion

A parsimonious stochastic seismic ground-motion model is used to study the effect of ground-motion nonstationarities on the response of simple linear and softening nonlinear systems. This model captures with at most nine parameters the features of the ground motion which are important for computing dynamic response, including the amplitude and frequency-content nonstationarities of the earthquake. Simple approximate expressions for the mean-square response statistics are obtained and are used to demonstrate analytically the importance of modeling the temporal nonstationarity in the frequency content of the ground motion, not only as expected for the nonlinear system, but also for linear systems. For the nonlinear systems, the phenomenon of ‘moving resonance’ is demonstrated whereby the shortening of the system frequencies, due to stiffness softening with increasing amplitudes, tracks the shift of the dominant frequencies of the ground motion, leading to a large resonant build-up in response amplitudes.     

Designing secure communication protocols from trust specifications

In a very large distributed system, entities may trust and mistrust others with respect to communication security in arbitrarily complex ways. We formulate the problem of designing a secure communication protocol, given a network interconnection and a ternary relation which captures trust between the entities. We didentify several important ways of synthesizing secure channels, and study the algorithmic problem of designing a secure communication protocol connecting the entities, given the connectivity of the network and the trust relationship between the nodes. We show that whether secure communication is possible can be decided easily in polynomial time. If we also require that channel synthesis proceed along unambiguous paths (in which case the protocol is defined on a spanning tree of the network), we show that the design problem is NP-complete, and we give a linear-time algorithm for an interesting special case of the problem.Research supported by the ESPRIT Basic Research Action No. 3075 ALCOM, a grant from the Volkswagen Foundation to the Universities of Patras and Bonn, and by the NSF.     

Modular Representation of Agent Interaction Rules through Argumentation

Communication between agents needs to be flexible enough to encompass together a variety of different aspects such as, conformance to society protocols, private tactics of the individual agents, strategies that reflect different classes of agent types (or personal attitudes) and adaptability to the particular external circumstances at the time when the communication takes place. In this paper, we propose an argument-based framework for representing communication theories of agents that can take into account in a uniform way these different aspects. We show how this approach can be used to realize existing types of dialogue strategies and society protocols in a way that facilitates their modular development and extension to make them more flexible in handling different or special circumstances.     

Clustering‐based scheduling: A new class of scheduling algorithms for single‐hop lightwave networks

In wavelength division multiplexing (WDM) star networks, the construction of the transmission schedule is a key issue, which essentially affects the network performance. Up to now, classic scheduling techniques consider the nodes' requests in a sequential service order. However, these approaches are static and do not take into account the individual traffic pattern of each node. Owing to this major drawback, they suffer from low performance, especially when operating under asymmetric traffic. In this paper, a new class of scheduling algorithms for WDM star networks, which is based on the use of clustering techniques, is introduced. According to the proposed Clustering‐Based Scheduling Algorithm (CBSA), the network's nodes are organized into clusters, based on the number of their requests per channel. Then, their transmission priority is defined beginning from the nodes belonging to clusters with higher demands and ending to the nodes of clusters with fewer requests. The main objective of the proposed scheme is to minimize the length of the schedule by rearranging the nodes' service order. Furthermore, the proposed CBSA scheme adopts a prediction mechanism to minimize the computational complexity of the scheduling algorithm. Extensive simulation results are presented, which clearly indicate that the proposed approach leads to a significantly higher throughput‐delay performance when compared with conventional scheduling algorithms. We believe that the proposed clustering‐based approach can be the base of a new generation of high‐performance scheduling algorithms for WDM star networks. Copyright © 2008 John Wiley & Sons, Ltd.