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The discovery of superconductors with high critical temperatures (~) has led to a considerable effort to fabricate Josephson junctions operating at temperatures approaching, or even exceeding, 77 K for both scientific investigations and potential applications. Superconductor-normal-superconductor (SNS) devices, with noble or oxide metals as normal interlayers, are perhaps the most widely explored high-~" junction type at present. Although demonstrations of individual high-~ SNS devices exhibiting excellent current-voltage characteristics, high critical current-resistance products, and low noise behavior have been made, reproducible devices suitable for electronic applications are elusive. It is therefore important to ask how well these nominally SAN high-Tc junctions are understood. We review the available data, with emphasis on junction critical currents, and conclude that there is little evidence supporting a conventional proximity effect interpretation in the majority of reported high-, devices. The strongest candidates for SNS behavior are junctions in which N is a superconductor above its transition temperature. We discuss the present experimental and theoretical understanding of SNS junctions with emphasis on the implications for future research and development of these devices.

Abstract:The Sensor Web is a macro-instrument concept that allows for the spatiotemporal understanding of an environment through coordinated efforts between multiple numbers and types of sensing platforms, including both orbital and terrestrial and both fixed and mobile. Each of these platforms, or pods, communicates within their local neighborhood and thus distributes information to the instrument as a whole. Much as intelligence in the brain is a result of the myriad of connections between dendrites, it is anticipated that the Sensor Web will develop a macro-intelligence as a result of its distributed information with the pods reacting and adapting to their environment in a way that is much more than their individual sum. The sharing of data among individual pods will allow for a global perception and purpose of the instrument as a whole. The Sensor Web is to sensors what the Internet is to computers, with different platforms and operating systems communicating via a set of shared, robust protocols. This paper will outline the potential of the Sensor Web concept and describe the Jet Propulsion Laboratory (JPL) Sensor Webs Project (http://sensorwebs.jpl.nasa.gov/). In particular, various fielded Sensor Webs will be discussed.

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Measuring environmental variables at appropriate temporal and spatial scales remains an important challenge in ecological research. New developments in wireless sensors and sensor networks will free ecologists from a wired world and revolutionize our ability to study ecological systems at relevant scales. In addition, sensor networks can analyze and manipulate the data they collect, thereby moving data processing from the end user to the sensor network itself. Such embedded processing will allow sensor networks to perform data analysis procedures, identify outlier data, alter sampling regimes, and ultimately control experimental infrastructure. We illustrate this capability using a wireless sensor network, the Sensor Web, in a study of microclimate variation under shrubs in the Chihuahuan Desert. Using Sensor Web data, we propose simple analytical protocols for assessing data quality “on‐the‐fly” that can be programmed into sensor networks. The ecological community can influence the evolution of environmental sensor networks by working across disciplines to infuse new ideas into sensor network development.

We describe the fabrication and properties of Nb-AlOx-Nb Josephson tunnel junctions having critical current densities as high as 400 kA/cm2, roughly an order of magnitude larger than any previously reported for this materials system. The quality of the junction characteristics, as indicated by the current level at subgap voltages, is considerably lower in high-Jc than in low-Jc junctions. However, over the entire high-Jc range of 20–400 kA/cm2, the quality of our junctions remains the same (i.e., subgap current scales with critical current).

The confluence of the rapidly expanding sensor, computation, and telecommunication industries has allowed for a new instrument concept: the Sensor Web. A Sensor Web consists of intra-communicating, spatially-distributed sensor pods that are deployed to monitor and explore environments. It is capable of automated reasoning for it can perform intelligent autonomous operations in uncertain environments, respond to changing environmental conditions, and carry out automated diagnosis and recovery. Sensor Webs could have as much an impact on the uses of sensors as the Internet did on the uses of computers.Sensor Webs are often confused with "distributed sensors" or "sensor networks". The unique feature of the Sensor Web is that information gathered by one pod is shared and used by other pods. In contrast, sensor networks merely gather data and information gathered by a particular pod on such a network does not influence the behavior of another pod. Thus, sensor networks collect data while Sensor Webs can react and modify their behavior on the basis of the collected data. This paper will outline the potential of the Sensor Web concept and describe the Jet Propulsion Laboratory Sensor Webs Project (http://sensorwebs.jpl.nasa.gov/). In particular, a prototype Sensor Web deployed at the Huntington Botanical Gardens will be discussed.

In 1997, the Sensor Web was conceived at the NASA/Jet Propulsion Laboratory (JPL)to take advantage of the increasingly inexpensive, yet sophisticated, mass consumer-marketchips for the computer and telecommunication industries and use them to create platforms thatshare information among themselves and act in concert as a single instrument. This instrumentwould be embedded into an environment to monitor and even control it. The Sensor Web’spurpose is to extract knowledge from the data it collects and use this information to intelligentlyreact and adapt to its surroundings. It links a remote end-user's cognizance with the observedenvironment. Here, we examine not only current progress in the Sensor Web technology, butalso its recent application to problems in hydrology to illustrate the general concepts involved