On collaborative content distribution using multi-message gossip

We study epidemic schemes in the context of collaborative data delivery. In this context, multiple chunks of data reside at different nodes, and the challenge is to simultaneously deliver all chunks to all nodes.     

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 In such a system, some correct servers can be out-of-date after a write and can therefore, return values other than the most up-to-date value in response to a client's read request, thus complicating the task of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     

Probabilistic quorums for dynamic systems

A quorum system is a set of sets such that every two sets in the quorum system intersect. Quorum systems are well known building blocks for maintaining information in a distributed system while providing high availability and good load balance. Probabilistic Quorum Systems (PQS) are variants of quorum systems that relax the strict intersection requirement. They are particularly attractive for large scale systems due to their simplicity and highly efficient availability—load balance tradeoff. We introduce scalable techniques that maintain a PQS in a highly decentralized and highly dynamic setting. We address two challenges. First we show how PQS can be realized efficiently even when each process maintains knowledge of only a constant number of other members. Second, we provide algorithms that adaptively evolve the quorums to adjust to the changes in the system caused by processes leaving and joining the system over time.     

Architected Polymer Foams via Direct Bubble Writing

Polymer foams are cellular solids composed of solid and gas phases, whose mechanical, thermal, and acoustic properties are determined by the composition, volume fraction, and connectivity of both phases. A new high‐throughput additive manufacturing method, referred to as direct bubble writing, for creating polymer foams with locally programmed bubble size, volume fraction, and connectivity is reported. Direct bubble writing relies on rapid generation and patterning of liquid shell–gas core droplets produced using a core–shell nozzle. The printed polymer foams are able to retain their overall shape, since the outer shell of these bubble droplets consist of a low‐viscosity monomer that is rapidly polymerized during the printing process. The transition between open‐ and closed‐cell foams is independently controlled by the gas used, while the foam can be tailored on‐the‐fly by adjusting the gas pressure used to produce the bubble droplets. As exemplars, homogeneous and graded polymer foams in several motifs, including 3D lattices, shells, and out‐of‐plane pillars are fabricated. Conductive composite foams with controlled stiffness for use as soft pressure sensors are also produced.     

Deep-Learning-Enabled Fast Optical Identification and Characterization of 2D Materials

Advanced microscopy and/or spectroscopy tools play indispensable roles in nanoscience and nanotechnology research, as they provide rich information about material processes and properties. However, the interpretation of imaging data heavily relies on the “intuition” of experienced researchers. As a result, many of the deep graphical features obtained through these tools are often unused because of difficulties in processing the data and finding the correlations. Such challenges can be well addressed by deep learning. In this work, the optical characterization of 2D materials is used as a case study, and a neural-network-based algorithm is demonstrated for the material and thickness identification of 2D materials with high prediction accuracy and real-time processing capability. Further analysis shows that the trained network can extract deep graphical features such as contrast, color, edges, shapes, flake sizes, and their distributions, based on which an ensemble approach is developed to predict the most relevant physical properties of 2D materials. Finally, a transfer learning technique is applied to adapt the pretrained network to other optical identification applications. This artificial-intelligence-based material characterization approach is a powerful tool that would speed up the preparation, initial characterization of 2D materials and other nanomaterials, and potentially accelerate new material discoveries.     

Secure execution of Java applets using a remote playground

Mobile code presents a number of threats to machines that execute it. We introduce an approach for protecting machines and the resources they hold from mobile code and describe a system based on our approach for protecting host machines from Java 1.1 applets. In our approach, each Java applet downloaded to the protected domain is rerouted to a dedicated machine (or set of machines), the playground, at which it is executed. Prior to execution, the applet is transformed to use the downloading user's Web browser as a graphics terminal for its input and output, and so the user has the illusion that the applet is running on his own machine. In reality, however, mobile code runs only in the sanitized environment of the playground, where user files cannot be mounted and from which only limited network connections are accepted by machines in the protected domain. Our playground thus provides a second level of defense against mobile code that circumvents language-based defenses. This paper presents the design and implementation of a playground for Java 1.1 applets and discusses extensions of it for other forms of mobile code, including Java 1.2     

Concise version vectors in WinFS

Conflicts naturally arise in optimistically replicated systems. The common way to detect update conflicts is via version vectors, whose storage and communication overhead are number of replicas × number of objects. These costs may be prohibitive for large systems. This paper presents predecessor vectors with exceptions (PVEs), a novel optimistic replication technique developed for Microsoft’s WinFS system. The paper contains a systematic study of PVE’s performance gains over traditional schemes. The results demonstrate a dramatic reduction of storage and communication overhead in normal scenarios, during which communication disruptions are infrequent. Moreover, they identify a cross-over threshold in communication failure-rate, beyond which PVEs loses efficiency compared with traditional schemes.     

Phosphate solubility tests—interference of some accessory minerals

Solubilities of apatites isolated from random samples of Israeli phosphates were determined in citric acid, formic acid and neutral ammonium citrate. Minerals normally associated with the apatites in rock phosphates were then added and the solubility tests repeated. Calcite markedly reduced the apparent solubility in the three solvents but gypsum interfered only in the case of neutral ammonium citrate. The accepted solubility tests therefore favour phosphates containing inert accessory minerals such as quartz and do not reflect the solubility of apatite when it is associated with calcite. A method based on determining the solubility of apatite instead of rock phosphate is suggested.     

TRIBAL AFFILIATIONS IN THE PUBLIC SPHERE

Photography in the Middle East has soared in the last decade as a practice of daily documentation and a dynamic form of visual communication in an organic and vernacular sense. This paper explores tribal dynamics and symbolic affiliations in today’s United Arab Emirates (UAE) through the use of imagery, specifically photography. The central question here is how content produced responds to geography and heritage and influences the identities shared. In exploring the answer, the study aims to untangle the complex psychologies of belonging in relation to physical and social boundaries within the defined attributes of identity and pride. Tribal affiliations are constituted upon an articulated framework of references, geographical and sociocultural boundaries, as convened via adornments as well as rituals and gender roles. People’s surroundings as well as their intimate and private spaces offer an incomparable — and indeed underestimated — insight into their values, cultures and ideologies. Identity, be it in the individual or plural sense, is endlessly reflected in everyday practices. This research visualizes and explores all the above, while deconstructing the dynamics using visual media tools in multimedia communication.     

Analysis of polyethylene surface sulfonation

Attachment of ? SO₃H groups onto the surface of polymers by treatment with fuming sulfuric acid is a well-known procedure. In the present study we compare the number of ? SO₃H groups per unit area measured by a number of methods including weight gain, thickness, FT-IR transmittance spectra, FT-IR surface spectra with ATR method, sodium exchange, and p^H measurement of water in contact with the polymer surface. It can be shown that, under the chosen conditions, i.e., room temperature and 32% SO₃ in H₂SO₄, oxidation of PE is the main reaction, while sulfonation accounts for less than 20% of the weight gained during reaction. Differences in the reactivity of high density and low density polyethylenes are discussed. Deprotonation in water compared with H⁺ /Na⁺ exchange indicates a poor penetration of sodium ions into deeper layers of the polymer. © 1994 John Wiley & Sons, Inc.