12,496 research outputs found

    Tropical–North Pacific Climate Linkages over the Past Four Centuries

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    Analyses of instrumental data demonstrate robust linkages between decadal-scale North Pacific and tropical Indo-Pacific climatic variability. These linkages encompass common regime shifts, including the noteworthy 1976 transition in Pacific climate. However, information on Pacific decadal variability and the tropical high-latitude climate connection is limited prior to the twentieth century. Herein tree-ring analysis is employed to extend the understanding of North Pacific climatic variability and related tropical linkages over the past four centuries. To this end, a tree-ring reconstruction of the December-May North Pacific index (NPI)-an index of the atmospheric circulation related to the Aleutian low pressure cell-is presented (1600-1983). The NPI reconstruction shows evidence for the three regime shifts seen in the instrumental NPI data, and for seven events in prior centuries. It correlates significantly with both instrumental tropical climate indices and a coral-based reconstruction of an optimal tropical Indo-Pacific climate index, supporting evidence for a tropical-North Pacific link extending as far west as the western Indian Ocean. The coral-based reconstruction (1781-1993) shows the twentieth-century regime shifts evident in the instrumental NPI and instrumental tropical Indo-Pacific climate index, and three previous shifts. Changes in the strength of correlation between the reconstructions over time, and the different identified shifts in both series prior to the twentieth century, suggest a varying tropical influence on North Pacific climate, with greater influence in the twentieth century. One likely mechanism is the low-frequency variability of the El Nino-Southern Oscillation (ENSO) and its varying impact on Indo-Pacific climate.</p

    Quire: Lightweight Provenance for Smart Phone Operating Systems

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    Smartphone apps often run with full privileges to access the network and sensitive local resources, making it difficult for remote systems to have any trust in the provenance of network connections they receive. Even within the phone, different apps with different privileges can communicate with one another, allowing one app to trick another into improperly exercising its privileges (a Confused Deputy attack). In Quire, we engineered two new security mechanisms into Android to address these issues. First, we track the call chain of IPCs, allowing an app the choice of operating with the diminished privileges of its callers or to act explicitly on its own behalf. Second, a lightweight signature scheme allows any app to create a signed statement that can be verified anywhere inside the phone. Both of these mechanisms are reflected in network RPCs, allowing remote systems visibility into the state of the phone when an RPC is made. We demonstrate the usefulness of Quire with two example applications. We built an advertising service, running distinctly from the app which wants to display ads, which can validate clicks passed to it from its host. We also built a payment service, allowing an app to issue a request which the payment service validates with the user. An app cannot not forge a payment request by directly connecting to the remote server, nor can the local payment service tamper with the request

    Extending the Liaison Workflow Model and Engine to Support Different Signature Purposes

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    Currently, many software systems are developed in offices geographically distributed in different locations. Furthermore, it is also common for a software system development project to contract to different software houses. These contracted software development projects, very often, are further sub-contracted to some other software houses. These software development modes can be supported and managed by good distributed workflow systems. Signatures play an important role in these software development modes. Most workflow systems, at best, can only support digital signatures. Digital signatures with public key cryptosystem are limited to authentication, integrity, confidentiality and non-repudiation. The wide variety of signature purposes such as authorization or multiple signatures in group decision making are not supported explicitly by most workflow systems. We have studied different kinds of signature in software development and workflow systems. The paper discusses the problems and solutions of incorporating these signatures in a distributed workflow engine, in particular, the Liaison Workflow Engine, to support the contemporary modes of software developments.published_or_final_versio
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