Fault detection for Byzantine quorum systems

In this paper, we explore techniques to detect Byzantine server failures in asynchronous replicated data services. Our goal is to detect arbitrary failures of data servers in a system where each client accesses the replicated data at only a subset (quorum) of servers in each operation. In such a system, some correct servers can be out-of-date after a write and can therefore, return values other than the most up-to-date value in response to a client's read request, thus complicating the task of determining the number of faulty servers in the system at any point in time. We initiate the study of detecting server failures in this context, and propose two statistical approaches for estimating the risk posed by faulty servers based on responses to read requests     

The cost of recovery in message logging protocols

Past research in message logging has focused on studying the relative overhead imposed by pessimistic, optimistic and causal protocols during failure-free executions. In this paper, we give the first experimental evaluation of the performance of these protocols during recovery. Our results suggest that applications face a complex tradeoff when choosing a message logging protocol for fault tolerance. On the one hand, optimistic protocols can provide fast failure-free execution and good performance during recovery, but are complex to implement and can create orphan processes. On the other hand, orphan-free protocols either risk being slow during recovery (e.g. sender-based pessimistic and causal protocols) or incur a substantial overhead during failure-free execution (e.g. receiver-based pessimistic protocols). To address this tradeoff, we propose hybrid logging protocols, which are a new class of orphan-free protocols. We show that hybrid protocols perform within 2% of causal logging during failure-free execution and within 2% of receiver-based logging during recovery     

A Comparison of Short-Term Water Demand Forecasting Models

Water Resources Management - This paper presents a comparison of different short-term water demand forecasting models. The comparison regards six models that differ in terms of: forecasting...     

Evaluating Water Demand Shortfalls in Segment Analysis

In this paper, two procedures for assessing water demand shortfalls following segment isolation are compared. The first (topological) procedure is based on a simple topological network analysis, and identifies the water demand shortfall as the water demand (under normal operational conditions) relative to the directly and/or indirectly isolated segment(s). The second (hydraulic) procedure is based on a pressure-driven hydraulic simulation of the network after segment isolation. Each of the two procedures was applied to two case studies, and the reliability (expressed in terms of maximum D _max and weighted average [`(D)] \overline D water demand shortfall) and economic burden (expressed in terms of number N <sub>val</sub> or cost C <sub>val</sub> of installed valves) of the resulting isolation valve system solution were compared. As a whole, the results show that network analysis and redesign are affected by the choice of the global variables (D <sub>max</sub> or [`(D)] \overline D ) used to characterize the demand shortfalls in network segments. Analysis of the case studies is followed by a discussion of the rationale behind the choice between the two procedures, which needs to balance accurate demand shortfall characterization with limited computation times, particularly in the multi-objective design stage.     

Sol–Gel Processing and Characterization of Pure and Metal-Doped SnO2 Thin Films

A chloride-based inorganic sol–gel route was used for preparing pure and metal (osmium, nickel, palladium, platinum)-doped SnO₂ sol. SnCl₄ was first reacted with propanol, then the resulting compound was hydrolyzed and subsequently mixed with solutions of the metal dopants. The obtained sols were used for depositing thin films by spin coating or for preparing powders by solvent evaporation at 110°C. FTIR spectroscopy and thermal analysis of the powders revealed that chlorine still bound to tin stabilized the sol against gelation by hindering the condensation reactions. Film characterizations showed that platinum and palladium, unlike nickel and osmium, were likely to form nanoparticles in the SnO₂ lattice. This result was discussed with regard to the different ways that platinum and palladium, on one hand, and nickel and osmium, on the other, modified the growth of SnO₂ grains and the film roughness and morphology. Dopants that formed nanoparticles (platinum, palladium) resulted in the roughest film, while dopants that did not form particles (nickel, osmium) resulted in SnO₂ grain size very close to that of pure SnO₂.     

Causality tracking in causal message-logging protocols

Casual message-logging protocols have several attractive properties: they introduce no blocking, send no additional messages over those sent by the application, and never create orphans. Causal message logging, however, does require the casual effects of the deliveries of messages to be tracked. The information concerning causality tracking is piggybacked on application messages, and the amount of such information can become large. In this paper we study the cost of tracking causality in causal message-logging protocols. One can track causality as accurately as possible, but to do so requires piggybacking a considerable amount of additional information. One can reduce the amount of piggybacked information on each message by reducing the accuracy of causality tracking. But then, causal message logging may piggyback the reduced amount of information on more messages. We specify six different methods of tracking causality, each representing a natural choice based on the specification of causal message logging. We describe how these six methods can be implemented and compare them in terms of how large of a piggyback load they impose. This load depends on the application that is using causal message logging. We characterize some applications for which a given method has the smallest piggyback load, and study using simulation the size of the piggyback load for two different models of applications. Received: July 1999 / Accepted: July 2001     

Respiratory effects of pharingeal gas insufflation in patients with chronic obstructive pulmonary disease

In the cranio-facial region the giant-cell reparative granuloma (GCRG) is a typical lesion of the maxillary bones. Because giant-cell reparative granuloma is not strictly a granuloma, clinically and histologically, many authors prefer call it giant-cell lesion (GCL). A review of the literature have along with our experiences is reported. Authors present 17 patients with giant-cell lesion and their results, treated at the Maxillo-Facial Department of Parma. Clinical, radiographic and pathologic features were evaluated and differential diagnosis was considered, showing the real great difficulty in differential diagnosis also and especially for surgical treatment.     

Carbon nanotube films as a platform to transduce molecular recognition events in metalloporphyrins

Porphyrins have been widely used for many years as functional materials for chemical sensors. Their outstanding chemical features are balanced by some restrictions in terms of transduction techniques. In particular, porphyrin layers are barely conductive, with the consequence that the fabrication of porphyrin based chemiresistors is not possible, except in few rare cases. On the other hand, carbon nanotubes (CNTs) have superior electric properties ranging from metallic to semiconductor in character. Although the conductivity of CNTs is very sensitive to adsorbed molecules, it should be considered that the adsorption onto carbon structures is also scarcely selective and cannot be modified unless other molecular recognition systems are coupled with the CNTs. Following this approach, in this paper we investigated the sensing properties of hybrid CNT-porphyrin films to explore the possibility of transducing the adsorption events occurring in a porphyrin layer into resistance changes of the CNT layers. The results obtained indicate that the presence of the porphyrin films increases the sensitivity of the electric resistance of the CNTs to the concentration of volatile compounds. This enhancement is probably due to the catalytic effect of the metalloporphyrin in conveying the charge transfer from the adsorbate molecule to the CNTs substrate. This property of metalloporphyrins may introduce a further differentiation between porphyrin based sensors that could be positively utilized in sensor array configurations.     

Volume leases for consistency in large-scale systems

This article introduces volume leases as a mechanism for providing server-driven cache consistency for large-scale, geographically distributed networks. Volume leases retain the good performance, fault tolerance, and server scalability of the semantically weaker client-driven protocols that are now used on the Web. Volume leases are a variation of object leases, which were originally designed for distributed file systems. However, whereas traditional object leases amortize overheads over long lease periods, volume leases exploit spatial locality to amortize overheads across multiple objects in a volume. This approach allows systems to maintain good write performance even in the presence of failures. Using trace-driven simulation, we compare three volume lease algorithms against four existing cache consistency algorithms and show that our new algorithms provide strong consistency while maintaining scalability and fault-tolerance. For a trace-based workload of Web accesses, we find that volumes can reduce message traffic at servers by 40 percent compared to a standard lease algorithm, and that volumes can considerably reduce the peak load at servers when popular objects are modified