SENFIS: a Sensor Node File System for increasing the scalability and reliability of Wireless Sensor Networks applications

In the last years the Wireless Sensor Networks’ (WSN) technology has been increasingly employed in various application domains. The extensive use of WSN posed new challenges in terms of both scalability and reliability. This paper proposes Sensor Node File System (SENFIS), a novel file system for sensor nodes, which addresses both scalability and reliability concerns. SENFIS can be mainly used in two broad scenarios. First, it can transparently be employed as a permanent storage for distributed TinyDB queries, in order to increase the reliability and scalability. Second, it can be directly used by a WSN application for permanent storage of data on the WSN nodes. The experimental section shows that SENFIS implementation makes an efficient use of resources in terms of energy consumption, memory footprint, flash wear levelling, while achieving execution times similarly with existing WSN file systems.     

Heavy Ion Source with Pulsed Magnetic Field

A compact P.I.G. ion source with pulsed field and end extraction is described. The source produces multiply ionized N, C, Ne, A, Kr and Xe. Pulsed currents of C3+, N3+, Ne3+, A3+, Kr3+ , Xe6+ between a few tens of ?A and a few hundreds of ?A have been obtained. Small size and power consumption make it compatible with a Van de Graaff terminal where space and power are at a premium.     

Development of a Cryogenic Detector for Coherent Neutrino Nucleus Scattering

In Coherent Neutrino Nucleus Scattering (CNNS) the neutrinos interact coherently with all nucleons leading to a cross section which is much larger than for all other neutrino interactions. Because of the small momentum transfer as well as the small recoil energy in CNNS, and the relatively low count rate, a low energy threshold and a large target mass (several hundred grams) are required to observe CNNS. Our aim is to build a cryodetector for that purpose. Such a cryodetector, installed in the vicinity of a nuclear power plant, could probe new physics like non-standard neutral current interactions or a neutrino magnetic moment. We describe the results of three detectors, with Ge absorbers of 0.8 and 3.2 g and with a CaWO₄ absorber of 10 g. For Ge (0.8 g) an energy threshold of 0.43 keV and an energy resolution of 0.27 keV at ∼6 keV could be reached. We demonstrate that surface roughness effects deteriorate both threshold and resolution. For the 10 g CaWO₄ absorber we obtained 0.27 keV and 0.35 keV for threshold and energy resolution at ∼6 keV respectively.      

Neutron scattering facility for characterization of CRESST and EURECA detectors at mK temperatures

CRESST (cryogenic rare event search with superconducting thermometers) is an experiment located at the Gran Sasso underground laboratory and aimed at the direct detection of dark matter in the form of WIMPs. The setup has just completed a one year commissioning run in 2007 and is presently starting a physics run with an increased target mass. Scintillating CaWO₄ single crystals, operated at temperatures of a few millikelvin, are used as target to detect the tiny nuclear recoil induced by a WIMP. The powerful background identification and rejection of α, e^- and γ events is realized via the simultaneous measurement of a phonon and a scintillation signal generated in the CaWO₄ crystal. However, neutrons could still be misidentified as a WIMP signature. Therefore, a detailed understanding of the individual recoil behaviour in terms of phonon generation and scintillation light emission due to scattering on Ca, O or W nuclei, respectively, is mandatory. The only setup which allows to perform such measurements at the operating temperature of the CRESST detectors has been installed at the Maier-Leibnitz-Accelerator Laboratory in Garching and is presently being commissioned. The design of this neutron scattering facility is such that it can also be used for other target materials, e.g. ZnWO₄, PbWO₄ and others as foreseen in the framework of the future multi-target tonne-scale experiment EURECA (European underground rare event calorimeter array).     

Affinity P2P: A self-organizing content-based locality-aware collaborative peer-to-peer network

The last years have brought a dramatic increase in the popularity of collaborative Web 2.0 sites. According to recent evaluations, this phenomenon accounts for a large share of Internet traffic and significantly augments the load on the end-servers of Web 2.0 sites. In this paper, we show how collaborative classifications extracted from Web 2.0-like sites can be leveraged in the design of a self-organizing peer-to-peer network in order to distribute data in a scalable manner while preserving a high-content locality. We propose Affinity P2P (AP2P), a novel cluster-based locality-aware self-organizing peer-to-peer network. AP2P self-organizes in order to improve content locality using a novel affinity-based metric for estimating the distance between clusters of nodes sharing similar content. Searches in AP2P are directed to the cluster of interests, where a logarithmic-time parallel flooding algorithm provides high recall, low latency, and low communication overhead. The order of clusters is periodically changed using a greedy cluster placement algorithm, which reorganizes clusters based on affinity in order to increase the locality of related content. The experimental and analytical results demonstrate that the locality-aware cluster-based organization of content offers substantial benefits, achieving an average latency improvement of 45%, and up to 12% increase in search recall.     

Model-based energy-aware data movement optimization in the storage I/O stack

The increasing data demands of applications from various domains and the decreasing relative power cost of CPU computation have gradually exposed data movement cost as the prominent factor of energy consumption in computing systems. The traditional organization of the computer system software into a layered stack, while providing a straightforward modularity, poses a significant challenge for the global optimization of data movement in particular and, thus, the energy efficiency in general. Optimizing the energy efficiency of data movement in large-scale systems is a difficult tasks because it depends on a complex interplay of various factors at different system layers. In this work, we address the challenge of optimizing the data movement of the storage I/O stack in a holistic manner. Our approach consists of a model-based system driver that obtains the current I/O power regime and adapts the CPU frequency level according to this information. On the one hand, for simplifying the understanding of the relation between data movement and energy efficiency, this paper proposes novel energy prediction models for data movement based on series of runtime metrics from several I/O stack layers. We provide an in-depth study of the energy consumption in the data path, including the identification and analysis of power and performance regimes that synthesize the energy consumption patterns in a cross-layer approach. On the other hand, we propose and prototype a kernel driver that exploits data movement awareness for improving the current CPU-centric energy management.     

Characterization of the Response of CaWO4 on Recoiling Nuclei from Surface Alpha Decays

A potentially harmful background for experiments attempting direct dark matter detection like the CRESST (= Cryogenic Rare Event Search with Superconducting Thermometers) experiment is caused by recoiling nuclei from ²¹⁰Po alpha decays on surfaces close to the detector. In order to characterize this kind of background in CRESST, calibration measurements have been performed at the TU München. A for this purpose an optimized version of the CRESST detector has been developed consisting of a 38 g CaWO₄ crystal and a separate cryogenic light detector, both equipped with Ir/Au transition edge sensors (TESs). The simultaneous measurement of the phonon signal and the scintillation light from the CaWO₄ crystal allows to discriminate between electron and nuclear recoils using their different light outputs. The unexpected results of a first measurement with a ²¹⁰Po source can be understood with the help of a Monte Carlo simulation performed for a similar system.      

Application of the Neganov-Luke Effect for Scintillation Light Detection

For the phonon-light technique employed in the CRESST experiment very sensitive light detectors are needed as only a small fraction of the energy of incident particles is detected as light. Following Neganov and Luke, the sensitivity can be improved by drifting the generated charge carriers in a semiconductor absorber by an applied electric field. For an efficient charge collection substrates with low trap densities are required. For this purpose and for electrical decoupling the TES is glued onto the drift device. Results from measurements with Neganov-Luke amplification using glued TES will be presented.      

A Synchronization Pulse for the Princeton-Pennsylvania Accelerator

The basic synchronizing pulse in the P.P.A., tying the injection pulse and the R. F. to the magnetic field, is derived from the total current flowing through one of the Accelerator magnets. This pulse is generated in a biased toroidal coil wound on a supermalloy core, by the magnetic field H(t) created by the magnet current in a coaxial conductor. This method has provided us with a synchronization signal pulse with excellent long term stability and very little time-jitter. Part of the time-jitter may be attributed to the variations of dH/dt at the time of the reversal of the magnetization of the core due to variations of Imin in the magnets. A method has been developed to effectively cancel out the dH/dt effect in the supermalloy core.