Pb1−xSnxSe-on-Si LWIR sensor arrays and thermal imaging with JFET/CMOS read-out

Long wavelength infrared (LWIR) sensor arrays were fabricated in Pb_1−xSn_xSe layers grown epitaxially on Si-substrates by MBE. A CaF2 intermediate buffer layer ≈30dgA thick was employed for compatibility reasons. The photovoltaic sensors are based on the blocking Pb-contact technique on p-type material. They were fabricated using simple wet-etching process steps only. Cut-off wave-lengths were about 10.5 μm, quantum efficiencies >60%, and resistance-aera products above 3 Ω-cm² at 90K. A demonstrational LWIR thermal imaging camera was assembled with a 256 element line array with 50 μm pitch. Low-noise signal processing was achieved with sensors with differential resistances in the 10 kOhm range by using JFET/CMOS technology. For each channel, an integrator, correlated multiple sampling and sample/hold amplifier was used before multiplexing to a common output.     

<Emphasis Type="Italic">Sphagnum</Emphasis> Species Modulate their Phenolic Profiles and Mycorrhizal Colonization of Surrounding <Emphasis Type="Italic">Andromeda polifolia</Emphasis> along Peatland Microhabitats

Sphagnum mosses mediate long-term carbon accumulation in peatlands. Given their functional role as keystone species, it is important to consider their responses to ecological gradients and environmental changes through the production of phenolics. We compared the extent to which Sphagnum phenolic production was dependent on species, microhabitats and season, and how surrounding dwarf shrubs responded to Sphagnum phenolics. We evaluated the phenolic profiles of aqueous extracts of Sphagnum fallax and Sphagnum magellanicum over a 6-month period in two microhabitats (wet lawns versus dry hummocks) in a French peatland. Phenolic profiles of water-soluble extracts were measured by UHPLC-QTOF-MS. Andromeda polifolia mycorrhizal colonization was quantified by assessing the intensity of global root cortex colonization. Phenolic profiles of both Sphagnum mosses were species-, season- and microhabitat- dependant. Sphagnum-derived acids were the phenolics mostly recovered; relative quantities were 2.5-fold higher in S. fallax than in S. magellanicum. Microtopography and vascular plant cover strongly influenced phenolic profiles, especially for minor metabolites present in low abundance. Higher mycorrhizal colonization of A. polifolia was found in lawns as compared to hummocks. Mycorrhizal abundance, in contrast to environmental parameters, was correlated with production of minor phenolics in S. fallax. Our results highlight the close interaction between mycorrhizae such as those colonizing A. polifolia and the release of Sphagnum phenolic metabolites and suggest that Sphagnum-derived acids and minor phenolics play different roles in this interaction. This work provides new insight into the ecological role of Sphagnum phenolics by proposing a strong association with mycorrhizal colonization of shrubs.     

Integrated low-noise low-power fast charge-sensitive preamplifierfor avalanche photodiodes in JFET-CMOS technology

To take advantage of the compactness of avalanche photodiode (APD) arrays, low-noise power-efficient fast charge-sensitive preamplifier chips with differential current drivers have been developed. A 16-channel and a single-channel version are available. The chips were adapted for low-capacitance 4×8 APD arrays produced by Hamamatsu, Japan. A mixed junction field-effect transistor (JFET)-CMOS production process yielded high-quality integrated JFETs for the input stage of the amplifier's folded cascade. Thus, the 1/f-noise corner is kept at 4 kHz. The JFET has a transconductance of 11 mS at a drain current of 3 mA. The serial noise of the input transistor was found to be 0.8 nV/√(Hz). The signal rise time of the driver outputs is 20 ns. The rms noise of the preamplifier was found to be 480 e^- with a 25 e^- /pF noise slope for a shaping time of 50 ns. The serial input noise of the preamplifier is about 1.4 nV/√(Hz) from 200 kHz up to 40 MHz, and the 1/f-noise corner is at 70 kHz. The power consumption is 30 mW per preamplifier, including the differential driver. The linearity is better than 1.3% over 48 dB dynamic range. For the 16-channel chip, the channel-to-channel gain variation is less than 3.5%. Performance similar to photomultiplier tubes can be achieved with APDs in combination with this integrated preamplifier chip     

Information Monitoring on the Web: A Scalable Solution

This paper presents WebCQ, a continual query system for large-scale Web information monitoring. WebCQ is designed to discover and detect changes to Web pages efficiently, and to notify users of interesting changes with personalized messages. Users' Web page monitoring requests are modeled as continual queries on the Web and referred to as Web page sentinels. The system consists of five main components: a change detection robot that discovers and detects changes, a proxy cache service that reduces the communication traffics to the original information provider on the remote server, a trigger evaluation tool that can filter only the changes that match certain thresholds, a personalized change presentation tool that highlights Web page changes, and a change notification service that displays and delivers interesting changes and fresh information to the right users at the right time. This paper describes the WebCQ system with an emphasis on the general issues in designing and engineering a large-scale information change monitoring system on the Web. There are two main contributions. First, we present the mechanisms that WebCQ provides to support various types of Web page sentinels for finding and displaying interesting changes to Web pages. The large collection of sentinel types allows WebCQ to efficiently locate and monitor a wide range of changes in Web pages. The second contribution is the development of sentinel grouping techniques for efficient and scalable processing of large number of concurrently running triggers and Web page sentinels. We report our initial experimental results showing the effectiveness of the proposed solutions.     

A JFET-CMOS radiation-tolerant charge-sensitive preamplifier

A monolithic charge-sensitive preamplifier based on n-channel junction field-effect transistors (JFETs) and p-channel MOS has been realized for applications with microelectrode detectors in elementary particle physics. Radiation resistance tests carried out with the preamplifier exposed to γ-rays emitted by a ⁶⁰Co source have shown no significant increase of the equivalent noise source up to 150-krd absorbed dose     

An Approach for Asynchronous Awareness Support in Collaborative Non-Linear Storytelling

Workspace awareness support is mandatory for group support systems. It allows users not only to follow actions of others, but to understand and respond to any changes others make to the workspace. In this paper, we present a novel approach for asynchronous awareness support by offering different filters to retrieve relevant awareness information and visualizing the evolution of the shared artifact. We illustrate our approach with a tool for collaborative non-linear storytelling in which users can jointly create a story graph of interconnected audio files. Such a story graph is an example for a non-linear story. We describe the development of a prototype that visualizes how the collaborative story has evolved over time. We evaluate our approach for asynchronous awareness support in an experiment with 40 participants exploring story graphs of different complexity. The evaluation results show that our visualization approach helps group members to assess who has modified the shared story, how it was modified, what exactly has been modified, and when it has been modified.     

Distribution of Fusarium mycotoxins in UK wheat mill fractions

The EU has set maximum limits for the Fusarium mycotoxins, deoxynivalenol (DON) and zearalenone (ZON). The maximum permitted level decreases from unprocessed wheat, through intermediary products, e.g. flour, to finished products such as bakery goods and breakfast cereals. It is, therefore, important to understand the effects of processing on the mycotoxin distribution in mill fractions. Between 2004 and 2007, samples were taken at commercial flour mills at various points in the milling process and analysed for trichothecenes and ZON. Samples with a range of mycotoxin concentrations harvested in 2004 and 2005 were processed in a pilot mill and the mycotoxins in the different mill fractions quantified. In the commercial samples, DON was the predominant mycotoxin with highest levels detected in the bran fraction. Analysis of the pilot mill fractions identified a significant difference between the two years and between mycotoxins. The proportion of DON and nivalenol in the mill fractions varied between years. DON and nivalenol were higher in flour fractions and lower in bran and offal in samples from 2004 compared to samples from 2005. This may be a consequence of high rainfall pre-harvest in 2004 resulting in movement of these mycotoxins within grains before harvest. There was no significant difference in the distribution of ZON within mill fractions between the two years. For DON, higher concentrations in the grain resulted in a greater proportion of DON within the flour fractions. Understanding the factors that impact on the fractionation of mycotoxins during milling will help cereal processors to manufacture products within legislative limits.     

Ellipsometry in the Study of Dynamic Material Properties

Measurements of the time-dependent absolute temperature of surfaces shocked using high explosives (HE) provide valuable constraints on the equations-of-state (EOS) of materials and on the state of ejecta from those surfaces. In support of these dynamic surface temperature measurements, techniques for measuring the dynamic surface emissivity of shocked metals in the near infrared (IR) are being developed. These consist of time-dependent laser ellipsometric measurements, using several approaches. A discussion of these ellipsometric techniques is included here. Ellipsometry permits an accurate determination of the dynamic emissivity at a given wavelength, and may also provide a signature of melt in shocked metals.