The upgraded cold neutron triple axis spectrometer FLEXX enhanced capabilities by new instrumental options

The upgrade of the cold neutron triple axis spectrometer FLEXX, a work-horse instrument for inelastic neutron scattering matching the sample environment capabilities at Helmholtz-Zentrum Berlin, has been successfully accomplished. Experiments confirmed an order of magnitude gain in flux now allowing for intensity demanding options to be fully exploited at FLEXX. In this article, we describe the layout and design of two newly available FLEXX instrument options in detail. The new Heusler analyzer gives an increase of the detected polarized neutron flux due to its superior focusing properties, significantly improving the feasibility of future polarized and neutron resonance spin echo experiments. The MultiFLEXX option provides simultaneous access to large regions in wavevector and energy space for inelastic excitations thus adding mapping capabilities to the spectrometer

Geology, geochemistry and earthquake history of Lō`ihi Seamount, Hawai`i

Author Posting. © The Authors, 2005. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Chemie der Erde - Geochemistry 66 (2006): 81-108, doi:10.1016/j.chemer.2005.09.002.A half century of investigations are summarized here on the youngest Hawaiian volcano, Lō`ihi Seamount. It was discovered in 1952 following an earthquake swarm. Surveying in 1954 determined it has an elongate shape, which is the meaning of its Hawaiian name. Lō`ihi was mostly forgotten until two earthquake swarms in the 1970’s led to a dredging expedition in 1978, which recovered young lavas. This led to numerous expeditions to investigate the geology, geophysics, and geochemistry of this active volcano. Geophysical monitoring, including a realtime submarine observatory that continuously monitored Lō`ihi’s seismic activity for three months, captured some of the volcano’s earthquake swarms. The 1996 swarm, the largest recorded in Hawai`i, was preceded by at least one eruption and accompanied by the formation of a ~300-m deep pit crater, renewing interest in this submarine volcano. Seismic and petrologic data indicate that magma was stored in a ~8-9 km deep reservoir prior to the 1996 eruption. Studies on Lō`ihi have altered conceptual models for the growth of Hawaiian and other oceanic island volcanoes and led to a refined understanding of mantle plumes. Petrologic and geochemical studies of Lō`ihi lavas showed that the volcano taps a relatively primitive part of the Hawaiian plume, producing a wide range of magma compositions. These compositions have become progressively more silica-saturated with time reflecting higher degrees of partial melting as the volcano drifts towards the center of the hotspot. Seismic and bathymetric data have highlighted the importance of landsliding in the early formation of an ocean island volcano. Lō`ihi’s internal structure and eruptive behavior, however, cannot be fully understood without installing monitoring equipment directly on the volcano. The presence of hydrothermal activity at Lō`ihi was initially proposed based on nontronite deposits on dredged samples that indicated elevated temperatures (31oC), and on the detection of water temperature, methane and 3He anomalies, and clumps of benthic micro-organisms in the water column over the volcano in 1982. Submersible observations in 1987 confirmed a low temperature system (15-30oC) prior to the 1996 formation of Pele’s Pit. The sulfide mineral assemblage (wurtzite, pyrrhotite, and chalcopyrite) deposited after the pit crater collapsed are consistent with hydrothermal fluids >250oC. Vent temperatures have decreased to ~60oC during the 2004 dive season indicating the current phase of hydrothermal activity may be waning.This work was supported by a NSF grant to M. Garcia (OCE 97-29894)

Geochemistry of lavas from the Caroline hotspot, Micronesia: Evidence for primitive and recycled components in the mantle sources of lavas with moderately elevated 3He/4He

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The role of lithospheric gabbros on the composition of Galapagos lavas.

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The upgraded cold neutron three axis spectrometer FLEXX at BER II at HZB

The cold neutron three axis spectrometer FLEXX is a work horse instrument for inelastic neutron scattering matching the sample environment capabilities for high magnetic fields up to 17.5 T and low temperatures down to 30 mK at the BER II neutron source at HZB. During the upgrade of the BER II neutron source and its instruments the primary spectrometer of FLEX [1] was completely rebuilt leading to a substantial increase in the flux reaching the sample [2]. The major benefit from the exchange of the entire neutron guide system serving instruments in Neutron Guide Hall I is that it has allowed optimisations of individual instrument positions. As a consequence FLEXX was relocated to a guide end position in an area of the guide hall with intrinsically low background Fig. 1 . The neutron guide system of FLEXX now hosts m 3 guides including a converging elliptical section to focus neutrons onto a virtual source [3, 4]. The neutrons are subsequently imaged onto a new double focussing monochromator, ensuring a substantial increase in neutrons reaching the sample [5]. In addition, a new velocity selector is used to remove higher order scattering which eliminates the need for filters. A polarising S bender may be translated into the beam before the elliptical guide section where the beam is collimated allowing the gains from focussing neutrons onto the sample to be realised for polarised measurements also Fig. 2 . A Heulser analyser is now optionally available replacing the PG analyser when FLEXX is used for longitudinal polarisation analysis or operated with its neutron resonance spin echo option further enhancing polarised neutron capabilities at FLEX

Secure multiparty linear programming using fixed-point arithmetic

Collaborative optimization problems can often be modeled as a linear program whose objective function and constraints combine data from several parties. However, important applications of this model (e.g., supply chain planning) involve private data that the parties cannot reveal to each other. Traditional linear programming methods cannot be used in this case. The problem can be solved using cryptographic protocols that compute with private data and preserve data privacy. We present a practical solution using multiparty computation based on secret sharing. The linear programming protocols use a variant of the simplex algorithm and secure computation with fixed-point rational numbers, optimized for this type of application. We present the main protocols as well as performance measurements for an implementation of our solution