Three Dimensional Polarimetric Neutron Tomography of Magnetic Fields

Through the use of Time-of-Flight Three Dimensional Polarimetric Neutron Tomography (ToF 3DPNT) we have for the first time successfully demonstrated a technique capable of measuring and reconstructing three dimensional magnetic field strengths and directions unobtrusively and non-destructively with the potential to probe the interior of bulk samples which is not amenable otherwise. Using a pioneering polarimetric set-up for ToF neutron instrumentation in combination with a newly developed tailored reconstruction algorithm, the magnetic field generated by a current carrying solenoid has been measured and reconstructed, thereby providing the proof-of-principle of a technique able to reveal hitherto unobtainable information on the magnetic fields in the bulk of materials and devices, due to a high degree of penetration into many materials, including metals, and the sensitivity of neutron polarisation to magnetic fields. The technique puts the potential of the ToF time structure of pulsed neutron sources to full use in order to optimise the recorded information quality and reduce measurement time.Comment: 12 pages, 4 figure

Q^2-Dependence of the Proton's G_1 Structure Function Sum Rule

We study the $Q^2$ variation of the first moment of the nucleon's spin-dependent structure function $G_1$. As $Q^2 \rightarrow 0$ the moment is determined by the low energy theorem for Compton scattering. In the deep-inelastic region the moment is calculated using twist expansion to order $1/Q^2$. Based on these limits, we construct a formula which smoothly interpolates between the two regions.Comment: (revised), 8 pages in REVTEX, 1 figure, MIT-CTP-223

Prosody takes over : towards a prosodically guided dialog system

The domain of the speech recognition and dialog system EVAR is train time table inquiry. We observed that in real human-human dialogs when the officer transmits the information, the customer very often interrupts. Many of these interruptions are just repetitions of the time of day given by the officer. The functional role of these interruptions is often determined by prosodic cues only. An important result of experiments where naive persons used the EVAR system is that it is hard to follow the train connection given via speech synthesis. In this case it is even more important than in human-human dialogs that the user has the opportunity to interact during the answer phase. Therefore we extended the dialog module to allow the user to repeat the time of day and we added a prosody module guiding the continuation of the dialog by analyzing the intonation contour of this utterance.Der Diskursbereich des Spracherkennungs- und Dialogsystems EVAR ist Fahrplanauskunft für Züge. Wir beobachteten, dass in realen Mensch-Mensch Dialogen der Kunde sehr oft den Auskunftsbeamten unterbricht, wenn dieser die Information übermittelt. Viele dieser Unterbrechungen sind ausschließlich Wiederholungen der Uhrzeitangabe des Beamten. Die funktionale Rolle dieser Unterbrechungen wird häufig alleine durch prosodische Mittel bestimmt. Ein wichtiges Ergebnis von Dialog Experimenten mit naiven Personen ergab, dass es schwer ist, den Verbindungsauskünften von EVAR via Sprachsynthese zu folgen. In diesem Fall ist es sogar noch wichtiger als in Mensch-Mensch Dialogen, dass der Benutzer die Möglichkeit hat, während der Antwortphase zu interagieren. Deshalb haben wir das Dialogmodul erweitert, um dem Benutzer die Möglichkeit zu geben, die Uhrzeitangaben zu wiederholen, und wir fügten ein Prosodiemodul hinzu, das die Fortführung des Dialogs steuert, indem die Intonation dieser Äußerung analysiert wir

Prosody takes over : a prosodically guided dialog system

In this paper first experiments with naive persons using the speech understanding and dialog system EVAR are discussed. The domain of EVAR is train table inquiry. We observed that in real human-human dialogs when the officer transmits the information the customer very often interrupts. Many of these interruptions are just repetitions of the time of day given by the officer. The functional role of these interruptions is determined by prosodic cues only. An important result of the experiments with EVAR is that it is hard to follow the system giving the train connection via speech synthesis. In this case it is even more important than in human-human dialogs that the user has the opportunity to interact during the answer phase. Therefore we extended the dialog module to allow the user to repeat the time of day and we added a prosody module guiding the continuation of the dialog

Alteration at the ultramafic-hosted Logatchev hydrothermal field: Constraints from trace element and Sr-O isotope data

Serpentinized peridotite and gabbronorite represent the host rocks to the active, ultramafic-hosted Logatchev hydrothermal field at the Mid-Atlantic Ridge. We use trace element, δ18O and 87Sr/86Sr data from bulk rock samples and mineral separates in order to constrain the controls on the geochemical budget within the Logatchev hydrothermal system. The trace element data of serpentinized peridotite show strong compositional variations indicating a range of processes. Some peridotites experienced geochemical modifications associated with melt-rock interaction processes prior to serpentinization, which resulted in positive correlations of increasing high field strength element (HFSE) concentrations and light rare earth element (LREE) contents. Other serpentinites and lizardite mineral separates are enriched in LREE, lacking a correlation with HFSE due to interaction with high-temperature, black-smoker type fluids. The enrichment of serpentinites and lizardite separates in trace elements, as well as locally developed negative Ce-anomalies, indicate that interaction with low-T ambient seawater is another important process in the Logatchev hydrothermal system. Hence, mixing of high-T hydrothermal fluids during serpentinization and/or re-equilibration of O-isotope signatures during subsequent low-T alteration is required to explain the trace element and δ18O temperature constraints. Highly radiogenic 87Sr/86Sr signatures of serpentinite and lizardite separates provide additional evidence for interaction with seawater-derived fluids. Sparse talc alteration at the Logatchev site are most likely caused by Si-metasomatism of serpentinite associated with the emplacement of shallow gabbro intrusion(s) generating localized hydrothermal circulation. In summary the geochemistry of serpentinites from the Logatchev site document subsurface processes and the evolution of a seafloor ultramafic hydrothermal system

Southern Ocean and Weddell Sea bottom water Pb isotope compositions trace ice sheet dynamics and regional circulation patterns today and during the past 140 ka

Dissolved lead (Pb) is mainly supplied to the oceans by physical and chemical weathering on the continents. The short residence time of Pb in seawater on the order of only a few decades makes its isotopic compositions an excellent tracer for local continental inputs. Lead was found to be incongruently released during early chemical weathering on the continents (Erel et al., 1994), often generating a more radiogenic runoff signal compared to the bulk rock compositions (Gutjahr et al., 2009; Kurzweil et al., 2010; Crocket et al., 2012; Crocket et al., 2013). In addition, the presence of abundant ice-rafted detrital material (IRD) may also release a highly radiogenic signature in high latitude settings (Kurzweil et al., 2010; Crocket et al., 2012). In the (sub-)Antarctic marine environment, authigenic Pb isotope records from core top sediments offer the possibility of assessing spatial seawater Pb isotopic variability of subglacial Antarctic runoff. Furthermore, palaeo-seawater Pb isotope records extracted from authigenic Fe-Mn oxyhydroxides will likely record periods of enhanced iceberg calving, freshwater input, and/or associated circulation changes. Since the leaching method for extracting authigenic Pb from Antarctic proximal bulk sediments has not been studied to date, we firstly evaluated and refined existing reductive leaching methods (Gutjahr et al., 2007; Blaser et al., 2016;) for efficient and reliable chemical extraction of bottom seawater Pb isotope signals from Weddell Sea and Southern Ocean core top sediment samples. We investigated the effects of (i) the MgCl2 pre-treatment, (ii) the effectiveness of chelates as well as (iii) exposure time of sediments to reducing reagents on the Pb isotopic signals. Chelate EDTA shows stronger complexation ability to Pb than DTPA and can significantly prevent Pb from readsorption back onto sediment surfaces during leaching as described in previous studies (Gutjahr et al., 2007). We also found that leaching without extended (>20 min) shaking, hence only agitating sediments for less than a minute on a vortex mixer to help sediment disperse into leaching solution, can extract quantities of Pb as extracted with via leaching for 20 minutes in a shaker. Using this short-term “vortexing” method, reproducible and in most cases accurate isotopic ratios identical or close to seawater signals can be obtained. Therefore we suggest using the vortexing method with EDTA and without MgCl2 pre-treatment to recover authigenic Pb from Antarctic ice shelf-proximal bulk sediments. Employing this new method, we present Pb isotope records from 90 core top sediment samples from the Weddell Sea and the Atlantic sector of Southern Ocean covering ~4000 km of the Weddell Sea Antarctic continental margin. Furthermore, first results are presented from IODP Site 1094 delineating the authigenic Pb isotopic evolution over the past 140 ka tracing Antarctic ice sheet dynamics and Southern Ocean circulation. References: Blaser, P., Lippold, J., Gutjahr, M., Frank, N., Link, J.M., Frank, M., 2016. Extracting foraminiferal seawater Nd isotope signatures from bulk deep sea sediment by chemical leaching. Chemical Geology 439, 189-204. Crocket, K.C., Foster, G.L., Vance, D., Richards, D.A., Tranter, M., 2013. A Pb isotope tracer of ocean-ice sheet interaction: the record from the NE Atlantic during the Last Glacial/Interglacial cycle. Quaternary Science Reviews 82, 133-144. Crocket, K.C., Vance, D., Foster, G.L., Richards, D.A., Tranter, M., 2012. Continental weathering fluxes during the last glacial/interglacial cycle: insights from the marine sedimentary Pb isotope record at Orphan Knoll, NW Atlantic. Quaternary Science Reviews 38, 89-99. Erel, Y., Harlavan, Y., Blum, J.D., 1994. Lead isotope systematics of granitoid weathering. Geochimica et Cosmochimica Acta 58, 5299-5306. Gutjahr, M., Frank, M., Halliday, A.N., Keigwin, L.D., 2009. Retreat of the Laurentide ice sheet tracked by the isotopic composition of Pb in western North Atlantic seawater during termination 1. Earth and Planetary Science Letters 286, 546-555. Gutjahr, M., Frank, M., Stirling, C.H., Klemm, V., Flierdt, T., Halliday, A.N., 2007. Reliable extraction of a deepwater trace metal isotope signal from Fe-Mn oxyhydroxide coatings of marine sediments. Chemical Geology 242, 351-370. Kurzweil, F., Gutjahr, M., Vance, D., Keigwin, L., 2010. Authigenic Pb isotopes from the Laurentian Fan: Changes in chemical weathering and patterns of North American freshwater runoff during the last deglaciation. Earth and Planetary Science Letters 299, 458-465

Effect of stress on NiO reduction in solid oxide fuel cells: A new application of energy-resolved neutron imaging

Recently, two new phenomena linking stress field and reduction rates in anode supported solid oxide fuel cells SOFCs have been demonstrated, so called accelerated creep during reduction and reduction rate enhancement and nucleation due to stress Frandsen et al., 2014 . These complex phenomena are difficult to study and it is demonstrated here that energy resolved neutron imaging is a feasible technique for combined mechanics chemical composition studies of SOFC components, including commercially produced ones. Cermet anode supports, which prior to the measurements were reduced under varying conditions such as different temperatures, various times and different values of applied stress, have been measured. Thus, samples with different contents and gradients of Ni and NiO phases were investigated. The first Bragg edge transmission neutron measurements applied for the studies of the reduction progress in these samples were performed at two neutron beamline facilities ISIS in the UK, Helmholtz Zentrum Berlin in Germany . The obtained results demonstrate the possibility to image and distinguish NiO and Ni phases within SOFC anode supports by energy resolved neutron imaging and the potential of the neutron imaging method for in situ studies of reduction processe

Prosody takes over : towards a prosodically guided dialog system

The domain of the speech recognition and dialog system EVAR is train time table inquiry. We observed that in real human-human dialogs when the officer transmits the information, the customer very often interrupts. Many of these interruptions are just repetitions of the time of day given by the officer. The functional role of these interruptions is often determined by prosodic cues only. An important result of experiments where naive persons used the EVAR system is that it is hard to follow the train connection given via speech synthesis. In this case it is even more important than in human-human dialogs that the user has the opportunity to interact during the answer phase. Therefore we extended the dialog module to allow the user to repeat the time of day and we added a prosody module guiding the continuation of the dialog by analyzing the intonation contour of this utterance.Der Diskursbereich des Spracherkennungs- und Dialogsystems EVAR ist Fahrplanauskunft für Züge. Wir beobachteten, dass in realen Mensch-Mensch Dialogen der Kunde sehr oft den Auskunftsbeamten unterbricht, wenn dieser die Information übermittelt. Viele dieser Unterbrechungen sind ausschließlich Wiederholungen der Uhrzeitangabe des Beamten. Die funktionale Rolle dieser Unterbrechungen wird häufig alleine durch prosodische Mittel bestimmt. Ein wichtiges Ergebnis von Dialog Experimenten mit naiven Personen ergab, dass es schwer ist, den Verbindungsauskünften von EVAR via Sprachsynthese zu folgen. In diesem Fall ist es sogar noch wichtiger als in Mensch-Mensch Dialogen, dass der Benutzer die Möglichkeit hat, während der Antwortphase zu interagieren. Deshalb haben wir das Dialogmodul erweitert, um dem Benutzer die Möglichkeit zu geben, die Uhrzeitangaben zu wiederholen, und wir fügten ein Prosodiemodul hinzu, das die Fortführung des Dialogs steuert, indem die Intonation dieser Äußerung analysiert wir