Electropolymerized molecularly imprinted polymer films of a bis-terthiophene dendron: folic acid quartz crystal microbalance sensing

A folic acid sensor was prepared via an electropolymerized molecularly imprinted polymer (E-MIP) film of a bis-terthiophene dendron on a quartz crystal microbalance (QCM). The cyclic voltammetry (CV) electrodeposition of the imprinted polymer film was monitored by electrochemical QCM or E-QCM, enabling in situ monitoring and characterization of E-MIP film formation and the viscoelastic behavior of the film. A key component of the E-MIP process is the use of a bifunctional monomer design to precomplex with the template and function as a cross-linker. The complex was electropolymerized and cross-linked by CV to form a polythiophene matrix. Stable cavities were formed that specifically fit the size and shape of the folic acid template. The same substrate surface was used for folic acid sensing. The predicted geometry of the 1:2 folic acid/terthiophene complex was obtained through semiempirical AM1 quantum calculations. The analytical performance, expressed through the figures of merit, of the sensor in aqueous solutions of the analyte was investigated. A relatively good linearity, R(2) = 0.985, was obtained within the concentration range 0-100 μM folic acid. The detection limit was found to be equal to 15.4 μM (6.8 μg). The relative cross selectivity of the folic acid imprinted polymer against the three molecules follows this trend: pteroic acid (= 50%) > caffeine (= 41%) > theophylline (= 6%). The potential and limitations of the E-MIP method were also discussed.     

Byzantine quorum systems

Summary. Quorum systems are well-known tools for ensuring the consistency and availability of replicated data despite the benign failure of data repositories. In this paper we consider the arbitrary (Byzantine) failure of data repositories and present the first study of quorum system requirements and constructions that ensure data availability and consistency despite these failures. We also consider the load associated with our quorum systems, i.e., the minimal access probability of the busiest server. For services subject to arbitrary failures, we demonstrate quorum systems over servers with a load of , thus meeting the lower bound on load for benignly fault-tolerant quorum systems. We explore several variations of our quorum systems and extend our constructions to cope with arbitrary client failures. Received: October 1996 / Accepted June 1998     

Dietary acculturation of arab immigrants in the greater toronto area

Purpose: We explored the eating habits of Arab immigrants to determine whether they have maintained their traditional diet or have consumed a more Westernized diet since immigrating to Canada. Methods: Arab immigrants who had been in Canada for at least eight years and were currently living in the Greater Toronto Area were recruited. A sample of 24 Arab immigrants completed a mailed, self-administered questionnaire, and six participated in a focus group. The focus group discussion was transcribed verbatim and results were recorded. Latent content analysis was used to analyze, code, and categorize emerging themes. Results: Arab immigrants consumed a mixture of both Arabic and Western food and perceived their current diet to be healthier than it was before they immigrated to Canada. Factors that influenced their food choices included increased nutrition health awareness, differences in food preferences and preparation methods, and preservation of dietary practices in the new environment. Conclusions: Our findings will help dietitians who work with Arab immigrants to become more aware of factors that motivate this group's food choices, and to create nutrition programs that are more culturally sensitive.     

A unifying framework of rating users and data items in peer-to-peer and social networks

We propose a unifying family of quadratic cost functions to be used in Peer-to-Peer ratings. We show that our approach is general since it captures many of the existing algorithms in the fields of visual layout, collaborative filtering and Peer-to-Peer rating, among them Koren spectral layout algorithm, Katz method, Spatial ranking, Personalized PageRank and Information Centrality. Besides of the theoretical interest in finding common basis of algorithms that where not linked before, we allow a single efficient implementation for computing those various rating methods. We introduce a distributed solver based on the Gaussian Belief Propagation algorithm which is able to efficiently and distributively compute a solution to any single cost function drawn from our family of quadratic cost functions. By implementing our algorithm once, and choosing the computed cost function dynamically on the run we allow a high flexibility in the selection of the rating method deployed in the Peer-to-Peer network. Using simulations over real social network topologies obtained from various sources, including the MSN Messenger social network, we demonstrate the applicability of our approach. We report simulation results using networks of millions of nodes.

3K3A-Activated Protein C Prevents Microglia Activation,Inhibits NLRP3 Inflammasome and Limits Ocular Inflammation

3K3A-Activated Protein C (APC) is a recombinant variant of the physiological anticoagulant APC with pleiotropic cytoprotective properties albeit without the bleeding risks. The anti-inflammatory activities of 3K3A-APC were demonstrated in multiple preclinical injury models, including various neurological disorders. We determined the ability of 3K3A-APC to inhibit ocular inflammation in a murine model of lipopolysaccharide (LPS)-induced uveitis. Leukocyte recruitment, microglia activation, NLRP3 inflammasome and IL-1β levels were assessed using flow cytometry, retinal cryosection histology, retinal flatmount immunohistochemistry and vascular imaging, with and without 3K3A-APC treatment. LPS triggered robust inflammatory cell recruitment in the posterior chamber. The 3K3A-APC treatment significantly decreased leukocyte numbers and inhibited leukocyte extravasation from blood vessels into the retinal parenchyma to a level similar to controls. Resident microglia, which underwent an inflammatory transition following LPS injection, remained quiescent in eyes treated with 3K3A-APC. An inflammation-associated increase in retinal thickness, observed in LPS-injected eyes, was diminished by 3K3A-APC treatment, suggesting its clinical relevancy. Finally, 3K3A-APC treatment inhibited inflammasome activation, determined by lower levels of NLRP3 and its downstream effector IL-1β. Our results highlight the anti-inflammatory properties of 3K3A-APC in ocular inflammation and suggest its potential use as a novel treatment for retinal diseases associated with inflammation.     

Byzantine disk paxos: optimal resilience with byzantine shared memory

We present Byzantine Disk Paxos, an asynchronous shared-memory consensus algorithm that uses a collection of n < 3t disks, t of which may fail by becoming non-responsive or arbitrarily corrupted. We give two constructions of this algorithm; that is, we construct two different t-tolerant (i.e., tolerating up to t disk failures) building blocks, each of which can be used, along with a leader oracle, to solve consensus. One building block is a t-tolerant wait-free shared safe register. The second building block is a t-tolerant regular register that satisfies a weaker termination (liveness) condition than wait freedom: its write operations are wait-free, whereas its read operations are guaranteed to return only in executions with a finite number of writes. We call this termination condition finite writes (FW), and show that wait-free consensus is solvable with FW-terminating registers and a leader oracle. We construct each of these t-tolerant registers from n < 3t base registers, t of which can be non-responsive or Byzantine. All the previous t-tolerant wait-free constructions in this model used at least 4t + 1 fault-prone registers, and we are not familiar with any prior FW-terminating constructions in this model. We further show tight lower bounds on the number of invocation rounds required for optimal resilience reliable register constructions, or more generally, constructions that use less than 4t + 1 fault-prone registers. Our lower bounds show that such constructions are inherently more costly than constructions that use 4t + 1 registers, and that our constructions have optimal round complexity. Furthermore, our wait-free construction is early-stopping, and it achieves the optimal round complexity with any number of actual failures. A preliminary version of this paper, by the same authors and with the same title, appears in Proceedings of the 23rd ACM Symposium on Principles of Distributed Computing (PODC ’04), July 2004, pages 226–235.     

Scalable Secure Storage When Half the System Is Faulty

In this paper, we provide a method to safely store a document in perhaps the most challenging settings, a highly decentralized replicated storage system where up to half of the storage servers may incur arbitrary failures, including alterations to data stored in them. Using an error correcting code (ECC), e.g., a Reed–Solomon code, one can take n pieces of a document, replace each piece with another piece of size larger by a factor of such that it is possible to recover the original set even when up to t of the larger pieces are altered. For t close to n/2 the space blowup factor of this scheme is close to n, and the overhead of an ECC such as the Reed–Solomon code degenerates to that of a trivial replication code. We show a technique to reduce this large space overhead for high values of t. Our scheme blows up each piece by a factor slightly larger than two using an erasure code which makes it possible to recover the original set using n/2−O(n/d) of the pieces, where d≈80 is a fixed constant. Then we attach to each piece O(d log n/log d) additional bits to make it possible to identify a large enough set of unmodified pieces, with negligible error probability, assuming that at least half the pieces are unmodified and with low complexity. For values of t close to n/2 we achieve a large asymptotic space reduction over the best possible space blowup of any ECC in deterministic setting. Our approach makes use of a d-regular expander graph to compute the bits required for the identification of n/2−O(n/d) good pieces.     

Objects shared by Byzantine processes

Work to date on algorithms for message-passing systems has explored a wide variety of types of faults, but corresponding work on shared memory systems has usually assumed that only crash faults are possible. In this work, we explore situations in which processes accessing shared objects can fail arbitrarily (Byzantine faults). Received: December 2000 / Accepted: July 2002 RID="*" ID="*" A preliminary version of the results presented in this paper appeared in Proceedings of the 14th International Symposium on Distributed Computing, Toledo, Spain, October 2000.     

Chasing the Weakest System Model for Implementing Ω and Consensus

Aguilera et al. and Malkhi et al. presented two system models, which are weaker than all previously proposed models where the eventual leader election oracle Ω can be implemented, and thus, consensus can also be solved. The former model assumes unicast steps and at least one correct process with f outgoing eventually timely links, whereas the latter assumes broadcast steps and at least one correct process with f bidirectional but moving eventually timely links. Consequently, those models are incomparable. In this paper, we show that Ω can also be implemented in a system with at least one process with f outgoing moving eventually timely links, assuming either unicast or broadcast steps. It seems to be the weakest system model that allows to solve consensus via Ω-based algorithms known so far. We also provide matching lower bounds for the communication complexity of Ω in this model, which are based on an interesting “stabilization property” of infinite runs. Those results reveal a fairly high price to be paid for this further relaxation of synchrony properties.     

Probabilistic Quorum Systems

We initiate the study of probabilistic quorum systems, a technique for providing consistency of replicated data with high levels of assurance despite the failure of data servers. We show that this technique offers effective load reduction on servers and high availability. We explore probabilistic quorum systems both for services tolerant of benign server failures and for services tolerant of arbitrary (Byzantine) ones. We also prove bounds on the server load that can be achieved with these techniques.