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This article is concerned with the complex role of assessment in the character development of graduate students in seminary education. It presents the current curricular approach of Denver Seminary to mentored, contextual formation and the variety of assessment strategies that support the growth of individual students and a culture of integrated learning in the institution. Rather than directing assessment strategies on individual character qualities, we argue for the efficacy of assessing the enabling conditions for character growth expressed in the andragogic elements of adult learning skills. Within this model, learning proves to be expansive enough for the contemporary seminary student who has a sense that it is up to them to prepare for and create the work they dream of within a changing culture.

Forty-four years of Wilcox Solar Observatory, 14 years of Michelson Doppler Imager on the Solar and Heliospheric Observatory, and 11 years of Helioseismic and Magnetic Imager on the Solar Dynamics Observatory magnetic field data have been studied to determine the east–west inclination—the toroidal component—of the magnetic field. Maps of the zonal averaged inclination show that each toroidal field cycle begins at around the same time at high latitudes in the northern and southern hemispheres, and ends at the equator. Observation of these maps also shows that each instance of a dominant toroidal field direction starts at high latitudes near sunspot maximum and is still visible near the equator well past the minimum of its cycle, indicating that the toroidal field cycle spans approximately two sunspot cycles. The length of the extended activity cycle is measured to be approximately 16.8 yr.

In the last several decades many researches are focused towards renewable energy sources. Among the variety of renewable energy sources the thermoelectric energy, which is generated by thermoelectric materials. Thermoelectric is one of the most promising sources of renewable energies. It’s based on the conversion of waste energy to a useful one. This work will focus on the enhancement of advanced thermoelectric materials CoSb3 with a 0.2 fraction of Se and several different fractions of Pd (x = 0.2, 0.3, 0.4, 0.5) which prepared by hot pressing and characterized by X-ray. The samples were characterized by the measurement of the electrical and thermal conductivities as well as the Seebeck coefficient between room temperature and 900 K. The sample had n-type conductivity. The dimensionless thermoelectric figure of merit ZT increases with increasing temperature and reaches a maximum value of 1.096 at 873 K for Co3.5Sb11.8Pd0.5Se0.2 composite.

Fossat et al. (2017) recently reported detecting rotational splitting of g modes indirectly via the interaction with p modes observed directly by the GOLF instrument on SOHO. They concluded that the core of the Sun is rotating 3:8 ? 0:1 times faster than the surrounding radiative envelope. This is startling, partly because such rapid rotation almost contradicts direct inferences from the p-mode rotational splitting inferred from the same data. Moreover, the inferred amplitudes of the g modes appear to exceed the upper bound reported by Appourchaux et al. (2010). It is also suspect because the theory of the procedure implies that the principal modes claimed to have been measured should be undetectable. We point out that there are other interpretations: one leads to a core rotation about twice faster than the surrounding envelope; another, to a core rotating more slowly than the envelope. Here we also report on an independent assessment of the Fossat et al. analysis by applying their procedure to different representations of the GOLF data, expanding on Schunker et al. (2018). We also analyze seismic data obtained from LOI and MDI (both also on SOHO), from HMI (on SDO) and from the ground-based BiSON and GONG, and found the evidence reported by Fossat et al. not to be robust. We also illustrate that merely fitting model spectra to observations, which Fossat et al. do to support their g-mode detections and as Fossat & Schmider (2018) do for extracting additional g-mode splittings, is not necessarily reliable. We are therefore led to doubt the claim., To be published in Astrophysical Journal, 20 pages, 11 figures of which 4 have two graphs

NASA's Solar Dynamics Observatory (SDO) was launched 11 February 2010 with 3 instruments on board, including the Helioseismic and Magnetic Imager (HMI). Since beginning normal operations on 1 May 2010, HMI has observed the Sun's entire visible disk almost continuously. HMI collects sequences of polarized filtergrams taken at a fixed cadence with two 4096 x 4096 cameras from which are computed arcsecond-resolution maps of photospheric observables: the line-of-sight (LoS) velocity and magnetic field, continuum intensity, line width, line depth, and the Stokes polarization parameters, I Q U V, at 6 wavelengths. Two processing pipelines implemented at the SDO Joint Science Operations Center (JSOC) at Stanford University compute observables from calibrated Level-1 filtergrams. One generates LoS quantities every 45s, and the other, primarily for the vector magnetic field, computes averages on a 720s cadence. Corrections are made for static and temporally changing CCD characteristics, bad pixels, image alignment and distortion, polarization irregularities, filter-element uncertainty and non-uniformity, as well as Sun-spacecraft velocity. This report explains issues affecting the resulting physical quantities, describes the impact of regular updates to the instrument calibration, and shows how the computations are optimized for actual HMI observations. During the 5 years of the SDO prime mission, regular calibration sequences have been used to regularly improve and update the instrument calibration and to monitor instrument changes. The instrument more than satisfies the original specifications for data quality and continuity. The procedures described here still have significant room for improvement. The most significant remaining systematic errors are associated with the spacecraft orbital velocity., Accepted for publication in Solar Physics

The Helioseismic and Magnetic Imager (HMI) instrument is a major component of NASA's Solar Dynamics Observatory (SDO) spacecraft. Since beginning normal science operations on 1 May 2010, HMI has operated with remarkable continuity, e.g. during the more than five years of the SDO prime mission that ended 30 September 2015, HMI collected 98.4% of all possible 45-second velocity maps; minimizing gaps in these full-disk Dopplergrams is crucial for helioseismology. HMI velocity, intensity, and magnetic-field measurements are used in numerous investigations, so understanding the quality of the data is important. We describe the calibration measurements used to track HMI performance and detail trends in important instrument parameters during the mission. Regular calibration sequences provide information used to improve and update the HMI data calibration. The set-point temperature of the instrument front window and optical bench is adjusted regularly to maintain instrument focus, and changes in the temperature-control scheme have been made to improve stability in the observable quantities. The exposure time has been changed to compensate for a 15% decrease in instrument throughput. Measurements of the performance of the shutter and tuning mechanisms show that they are aging as expected and continue to perform according to specification. Parameters of the tunable-optical-filter elements are regularly adjusted to account for drifts in the central wavelength. Frequent measurements of changing CCD-camera characteristics, such as gain and flat field, are used to calibrate the observations. Infrequent expected events, such as eclipses, transits, and spacecraft off-points, interrupt regular instrument operations and provide the opportunity to perform additional calibration. Onboard instrument anomalies are rare and seem to occur quite uniformly in time. The instrument continues to perform very well., Comment: 50 pages, 18 figures, 20 tables

Objectives: To investigate factors that predict speed of recovery and long-term CD4 cell count in HIV-1 seroconverters initiating combination antiretroviral therapy (cART), and to quantify the influence of very early treatment initiation. We make use of all pre-treatment CD4 counts, because analyses using only a single observation at initiation may be subject to biases. Methods: We used data from the CASCADE (Concerted Action on SeroConversion to AIDS and Death in Europe) multinational cohort collaboration of HIV-1 seroconverters. We analysed pre- and post-treatment data of patients with seroconversion dates estimated January 2003–March 2014 (n = 7600 for primary analysis) using a statistical model in which the characteristics of recovery in CD4 counts are determined by multiple predictive factors. Secondary analyses were performed incorporating uncertainty in the exact timing of seroconversion to allow more precise estimation of the benefit of very early treatment initiation. Results: ‘True’ CD4 count at cART initiation was the strongest predictor of CD4 count beyond 3 years on cART. Allowing for lack of complete certainty in the date of seroconversion, CD4 recovery was more rapid for patients in whom treatment was initiated within 4 months. For a given CD4 count, higher viral load (VL) at initiation was strongly associated with higher post-treatment CD4 recovery. For other patient and drug characteristics, associations with recovery were statistically significant but small in magnitude. Conclusions: CD4 count at cART initiation is the most important factor in predicting post-treatment recovery, but VL provides substantial additional information. If cART is initiated in the first 4 months following seroconversion, recovery of CD4 counts appears to be more rapid. © 2017 The Authors. HIV Medicine published by John Wiley & Sons Ltd on behalf of British HIV Association

We analyze the effect of a sunspot in its quiet surroundings applying a helioseismic technique on almost three years of Helioseismic and Magnetic Imager (HMI) observations obtained during solar cycle 24 to further study the sunspot structure below the solar surface. The attenuation of acoustic waves with frequencies lower than 4.2 mHz depends more strongly on the wave direction at a distance of $6^o-7^o$ from the sunspot center. The amplification of higher frequency waves is highest 6$^o$ away from the active region and it is largely independent of the wave's direction. We observe a mean clockwise flow around active regions, which angular speed decreases exponentially with distance and has a coefficient close to $-0.7$ degree$^{-1}$. The observed horizontal flow in the direction of the nearby active region agrees with a large-scale circulation around the sunspot in the shape of cylindrical shell. The center of the shell seems to be centered around 7$^o$ from the sunspot center, where we observe an inflow close to the surface down to $\sim$2 Mm, followed by an outflow at deeper layers until at least 7 Mm., Comment: Accepted ApJ

International audience; This paper investigates the performance of a new attic ventilation concept using low-cost thermoelectric (TE) modules. Incident solar radiation heats up roof tiles thus creating a temperature difference between tiles and attic. By making use of this temperature difference, laboratory made low-cost thermoelectric modules, assimilated as roof tiles, could produce an electric current to drive a fan for attic ventilation. First, a low-cost TE module consisting of 7 couples of N and P type Bi-Sb-Te materials was fabricated on a 2x2 cm(2) aluminium substrate. Electrical performance was measured in the laboratory for various temperature differences of roof tiles obtained from field measurement. Then a TE tile of 0.1656 m(2) surface area was designed based on the laboratory made TE module. In total 414 modules were used. Two TE tiles were considered sufficient to generate a 5 V electrical current to drive two small DC fans. Heat gain reduction due to the induced TE attic ventilation was estimated using the TRNSYS program for a regular house in Thailand. It was found that the TE tiles could induce an air ventilation rate of about 100-250 m(3)/h. The average daily percentage of total rate of heat gain reduction through the ceiling during 9 - 17 h was about 14-18%. The proposed concept, using low-cost TE modules, offers a new interesting alternative as it uses the heat accumulated in roof tiles to generate electricity for ventilation.

In order to quantify the influence of magnetic fields on acoustic mode parameters and flows in and around active regions, we analyse the differences in the parameters in magnetically quiet regions nearby an active region (which we call `nearby regions'), compared with those of quiet regions at the same disc locations for which there are no neighboring active regions. We also compare the mode parameters in active regions with those in comparably located quiet regions. Our analysis is based on ring diagram analysis of all active regions observed by HMI during almost five years. We find that the frequency at which the mode amplitude changes from attenuation to amplification in the quiet nearby regions is around 4.2 mHz, in contrast to the active regions, for which it is about 5.1 mHz. This amplitude enhancement (the `acoustic halo effect') is as large as that observed in the active regions, and has a very weak dependence on the wave propagation direction. The mode energy difference in nearby regions also changes from a deficit to an excess at around 4.2 mHz, but averages to zero over all modes. The frequency difference in nearby regions increases with increasing frequency until a point at which the frequency shifts turn over sharply as in active regions. However, this turnover occurs around 4.9 mHz, significantly below the acoustic cutoff frequency. Inverting the horizontal flow parameters in the direction of the neighboring active regions, we find flows that are consistent with a model of the thermal energy flow being blocked directly below the active region., Comment: accepted in ApJ

We compare line-of-sight magnetograms from the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) and the Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory (SOHO). The line-of-sight magnetic signal inferred from the calibrated MDI data is greater than that derived from the HMI data by a factor of 1.40. This factor varies somewhat with center-to-limb distance. An upper bound to the random noise for the 1′′ resolution HMI 720-second magnetograms is 6.3 Mx cm−2, and 10.2 Mx cm−2 for the 45-second magnetograms. Virtually no p-mode leakage is seen in the HMI magnetograms, but it is significant in the MDI magnetograms. 12-hour and 24-hour periodicities are detected in strong fields in the HMI magnetograms. The newly calibrated MDI full-disk magnetograms have been corrected for the zero-point offset and underestimation of the flux density. The noise is 26.4 Mx cm−2 for the MDI one-minute full-disk magnetograms and 16.2 Mx cm−2 for the five-minute full-disk magnetograms observed with four-arcsecond resolution. The variation of the noise over the Sun’s disk found in MDI magnetograms is likely due to the different optical distortions in the left- and right-circular analyzers, which allows the granulation and p-mode to leak in as noise. Saturation sometimes seen in sunspot umbrae in MDI magnetograms is caused by the low intensity and the limitation of the onboard computation. The noise in the HMI and MDI line-of-sight magnetic-field synoptic charts appears to be fairly uniform over the entire map. The noise is 2.3 Mx cm−2 for HMI charts and 5.0 Mx cm−2 for MDI charts. No evident periodicity is found in the HMI synoptic charts.

The Helioseismic and Magnetic Imager (HMI) instrument onboard the Solar Dynamics Observatory produces line-of-sight (LOS) observables (Doppler velocity, magnetic-field strength, Fe i line width, line depth, and continuum intensity) as well as vector magnetic-field maps at the solar surface. The accuracy of LOS observables is dependent on the algorithm used to translate a sequence of HMI filtergrams into the corresponding observables. Using one hour of high-cadence imaging spectropolarimetric observations of a sunspot in the Fe i line at 6173 A through the Interferometric Bidimensional Spectrometer installed at the Dunn Solar Telescope, and the Milne–Eddington inversion of the corresponding Stokes vectors, we test the accuracy of the observables algorithm currently implemented in the HMI data-analysis pipeline: the MDI-like algorithm. In an attempt to improve the accuracy of HMI observables, we also compare this algorithm to others that may be implemented in the future: a least-squares fit with a Gaussian profile, a least-squares fit with a Voigt profile, and the use of second Fourier coefficients in the MDI-like algorithm.

The transient heat transfer in a thermoelectric leg is modelled. The Thomson effect is into account, whereas it is often neglected in other studies. Thanks to the expressions of the temperature and the heat flux expressed in the Laplace domain, a semi-analytical technique, the so-called quadrupole method is performed. No mesh is required. The whole matrix formulation is given for different initial conditions. It will allow, for instance, to evaluate easily the efficiency or the coefficient of performance of the thermoelement or use it as inverse method, for instance, to perform estimations.

The Atmospheric Imaging Assembly (AIA) provides multiple simultaneous high-resolution full-disk images of the corona and transition region up to 0.5 R ⊙ above the solar limb with 1.5-arcsec spatial resolution and 12-second temporal resolution. The AIA consists of four telescopes that employ normal-incidence, multilayer-coated optics to provide narrow-band imaging of seven extreme ultraviolet (EUV) band passes centered on specific lines: Fe xviii (94 A), Fe viii, xxi (131 A), Fe ix (171 A), Fe xii, xxiv (193 A), Fe xiv (211 A), He ii (304 A), and Fe xvi (335 A). One telescope observes C iv (near 1600 A) and the nearby continuum (1700 A) and has a filter that observes in the visible to enable coalignment with images from other telescopes. The temperature diagnostics of the EUV emissions cover the range from 6×104 K to 2×107 K. The AIA was launched as a part of NASA’s Solar Dynamics Observatory (SDO) mission on 11 February 2010. AIA will advance our understanding of the mechanisms of solar variability and of how the Sun’s energy is stored and released into the heliosphere and geospace.

The use of electronegative species as primary ions considerably enhances the emission of positive secondary ions in SIMS. Considering furthermore that negative primary ions can be required due to instrumental configurations (e.g. the Cameca NanoSIMS 50 requires an opposite polarity of the primary and secondary ions), O− ion bombardment is employed in SIMS analysis. These O− ions are typically created in a duoplasmatron source, which suffers however from its low brightness and which is thus not suited for high resolution imaging applications. The development of new (electro)negative ion sources is thus necessary to optimize the analysis of electropositive elements in terms of lateral resolution and sensitivity. In this paper, we present the performance of a duoplasmatron ion source generating F−, Cl−, Br− and I− ion beams. In particular, we experimentally determine on a dedicated test bench the brightness of the source in the F−, Cl−, Br− and I− modes as a function of the gas pressure, the magnetic field strength and the arc current in the source. The obtained results are compared to the performances of the duoplasmatron in the standard O− mode. In this context, a five times higher brightness was found for F− (200 A/cm2 sr) compared to the standard O− (42 A/cm2 sr).

Mg2Si:Gax and Mg2Si0.6Ge0.4:Gax (x = 0.4% and 0.8%) solid solutions have been synthesized by direct melting in tantalum crucibles and hot pressing. The effect of Ga doping on the thermoelectric properties has also been investigated by measurements of thermopower, electrical resistivity, Hall coefficient and thermal conductivity in temperature range from 300 to 850 K. All samples exhibit a p-type conductivity evidenced by positive sign of both thermopower and Hall coefficient in the investigated temperatures. The maximum value of the dimensionless figure of merit ZT was reached for the Mg2Si0.6Ge0.4:Ga(0.8%) compound at 625 K (ZT ∼ 0.36). The p-type character of thermoelectric behaviours of Ga-doped Mg2Si and Mg2Si0.6Ge0.4 compounds well corroborates with the results of electronic structure calculations performed by the Korringa–Kohn–Rostoker method and the coherent potential approximation (KKR-CPA), since Ga diluted in Mg2Si and Mg2Si0.6Ge0.4 (on Si/Ge site) behaves as hole donor due to the Fermi level shifted to the valence band edge. The onset of large peak of DOS from Ga impurity at the valence band edge, well corroborates with high Seebeck coefficient measured in Ga-doped samples.

Solar activity, such as flares, produce bursts of high-energy radiation that temporarily enhance the D-region of the ionosphere and attenuate low-frequency radio waves. To track these Sudden Ionospheric Disturbances (SIDs), which disrupt communication signals and perturb satellite orbits, Scherrer et al. (2008) developed an international, ground-based network of around 500 SID monitors that measure the signal strength of low-frequency radio waves. However, these monitors suffer from a host of noise contamination issues that preclude their use for rigorous scientific analysis. As such, we attempt to create an algorithm to automatically identify noisy, contaminated SID data sets from clean ones. To do so, we develop a set of features to characterize times series measurements from SID monitors and use these features, along with a binary classifer called a support vector machine, to automatically assess the quality of the SID data. We compute the True Skill Score, a metric that measures the performance of our classifier, and find that it is ~0.75+/-0.06. We find features characterizing the difference between the daytime and nighttime signal strength of low-frequency radio waves most effectively discern noisy data sets from clean ones., Comment: 4 pages, 1 figure, Published in the Research Notes of the AAS

Thermoelectric generators (TEGs) are outstanding devices for automotive waste heat recovery. Their packaging, lack of moving parts, and direct heat to electrical conversion are the main benefits. Usually, TEGs are modeled with a constant hot-source temperature. However, energy in exhaust gases is limited, thus leading to a temperature decrease as heat is recovered. Therefore thermoelectric properties change along the TEG, affecting performance. A thermoelectric generator composed of Mg2Si/Zn4Sb3 for high temperatures followed by Bi2Te3 for low temperatures has been modeled using engineering equation solver (EES) software. The model uses the finite-difference method with a strip-fins convective heat transfer coefficient. It has been validated on a commercial module with well-known properties. The thermoelectric connection and the number of thermoelements have been addressed as well as the optimum proportion of high-temperature material for a given thermoelectric heat exchanger. TEG output power has been estimated for a typical commercial vehicle at 90°C coolant temperature.

Dynamic secondary ion mass spectrometry (D–SIMS) is an extremely powerful analysis technique for studying surfaces and thin films. The development of ion sources using electronegative elements is necessary to optimize the analysis of the electropositive elements. In this paper, we present SIMS analyses carried out with an F− primary ion beam. We discuss the performance of the duoplasmatron ion source operated with different gas mixtures in order to extract F− primary ions. The brightness of the F− ion beam was calculated and found to be superior to that obtained with an O− ion beam. Finally, we compare the useful yields of positive secondary ions obtained with F− bombardment to those determined for O− primary ions. Copyright © 2010 John Wiley & Sons, Ltd.

We present electronic structure calculations of ordered Mg2Si as well as disordered Mg2Si1−xSbx and Mg2−δSi1−xSbx systems, carried out by the Korringa–Kohn–Rostoker method with the coherent potential approximation (KKR-CPA). The computed densities of states (DOS) clearly show that a vacancy on the Mg site behaves as a double hole donor. Such electronic structure behavior together with n-type doping by antimony leads to electron–hole compensation. Consequently, the semiconductor–metal crossover expected in Mg2Si1−xSbx due to the Fermi level shift into conduction states is not observed when important vacancy defects appear on the Mg site. Conversely, the Fermi level remains inside the energy gap if the antimony concentration is twice the vacancy concentration. The possible origin of vacancy formation in Mg2Si1−xSbx is discussed based on the formation energy calculations as well as DOS features. Our KKR-CPA results well support recent electron transport properties measurements.

Mg2Si1−xGex compounds were prepared from pure elements by melting in tantalum crucibles. The reaction was conducted under an inert gas in a special laboratory setup. Samples for thermoelectric measurements were formed by hot pressing. Structure and phase composition of the obtained materials were investigated by x-ray diffraction (XRD). Morphology and chemical composition were examined by scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS), respectively. Thermoelectric properties, i.e., the Seebeck coefficient, the electrical conductivity, and the thermal conductivity, were measured in the temperature range of 500 K to 900 K. The effect of Bi and Ag doping on the thermoelectric performance of Mg-Si-Ge ternary compounds was investigated. The electronic structures of binary compounds were calculated using the Korringa–Kohn–Rostoker (KKR) method. The effects of disorder, including Ge substitution and Bi or Ag doping, were accounted for in the KKR method with coherent potential approximation calculations. The thermoelectric properties of doped Mg2Si1−xGex are discussed with reference to computed density of states as well as the complex energy band structure.

Hot-pressed samples of the semi-conducting compound CoSb3-doped Pd and Te were prepared and characterized by X-ray and microprobe analysis. Thermoelectric characterization was done through measurements of the electrical and thermal conductivities as well as the Seebeck coefficient between room temperature and 900 K. All samples had n-type conductivity. The dimensionless thermoelectric figure of merit ZT increases with increasing temperature and reaches a maximum value of 1 at 873 K.

The International Heliophysical Year (IHY) aims to advance our understanding of the fundamental processes that govern the Sun, Earth, and heliosphere. The IHY Education and Outreach Program is dedicated to inspiring the next generation of space and Earth scientists as well as spreading the knowledge, beauty, and relevance of our solar system to the people of the world. In our Space Weather Monitor project we deploy a global network of sensors to high schools and universities to provide quantitative diagnostics of solar-induced ionospheric disturbances, thunderstorm intensity, and magnetospheric activity. We bring real scientific instruments and data in a cost-effective way to students throughout the world. Instruments meet the objectives of being sensitive enough to produce research-quality data, yet inexpensive enough for placement in high schools and universities. The instruments and data have been shown to be appropriate to, and usable by, high school age and early university students. Data contributed to the Stanford data center is openly shared and partnerships between groups in different nations develop naturally. Students and teachers have direct access to scientific expertise. The result is a world-wide collaboration of scientists, teachers, and students to investigate the variability of the ionosphere. The research-quality AWESOME (Atmospheric Weather Electromagnetic System of Observation, Modeling, and Education) instruments have been selected as a participating program by the United Nations Basic Space Science Initiative (UNBSSI). The IHY Committee for International Education and Public Outreach has designated the simpler SID (Sudden Ionospheric Disturbance) monitors to be provided to teacher/student teams in each of the 192 countries of the world.

Silicon, germanium and indium phosphide targets are sputtered with a cesium ion beam. The energy of impact is changed from 2 keV to 10 keV and the incidence angle of bombardment is modified from 30° to 60°. Emitted matter is collected on a semi-cylindrical copper foil. Subsequently, spatially resolved thicknesses and elemental compositions of the deposit are determined by means of SIMS depth profiles. These distributions across the deposit allow us to deduce the angular distribution of emitted matter. Our experimental data show that the preferential direction as well as the spreading around this direction can be altered, with more or less efficiency, by the variation of the bombardment parameters. For the indium phosphide, we also study the elemental composition of the deposit in function of the emission angle. It shows an increasing deviation from stoichiometry with increasing emission angle.

Hot-pressed samples of the semi-conducting compound Zn 4 Sb 3 with the stoichiometric composition were prepared and characterized by X-ray and microprobe analysis. Thermoelectric characterization was done through measurements of the electrical and thermal conductivities as well as the Seebeck coefficient between room temperature and 650 K. All samples had p-type conductivity. High thermoelectric figures of merit (ZT) were obtained between 450 and 650 K and a maximum of about 1.3 were obtained at a temperature of 650 K.

The negative secondary ion yields in secondary ion mass spectrometry (SIMS) increase when electropositive elements, especially alkali metals, are used as primary ions. In previous papers by the same authors, useful yield variations of several elements have been studied experimentally with respect to the neutral cesium deposition conditions. Besides, the Cs surface concentrations have been simulated using the TRIDYN code. The determined secondary ion sensitivities have been discussed with respect to the experimental conditions and they have been compared to the electron-tunneling model describing ion emission from metallic and semi-conducting samples. In this paper, the variations of the electron work function of the sample will be studied with respect to the experimental conditions used in the previous papers. The energy distributions of negative secondary ions will be recorded for the different experimental conditions. The electron work function shift, on which is based the electron-tunneling model and which thus gives evidence for the influence of cesium on ion emission, is extracted from these distributions. The variations of the electron work function are discussed with respect to the experimental conditions as well as the simulated cesium surface concentration. Besides, the secondary ion sensitivities are plotted with respect to the electron work function, giving a direct comparison with the electron-tunneling model.

In time-distance helioseismology, the time signals (Doppler shifts) at two points on the solar surface, separated by a fixed angular distance are cross-correlated, and this leads to a wave packet signal. Accurately measuring the travel times of these wave packets is crucial for inferring the sub-surface properties in the Sun. The observed signal is quite noisy, and to improve the signal-to-noise ratio and make the cross-correlation more robust, the temporal oscillation signal is phase-speed filtered at the two points in order to select waves that travel a fixed horizontal distance. Hence a new formula to estimate the travel times is derived, in the presence of a phase speed filter, and it includes both the radial and horizontal component of the oscillation displacement signal. It generalizes the previously used Gabor wavelet that was derived without a phase speed filter and included only the radial component of the displacement. This is important since it will be consistent with the observed cross-correlation that is computed using a phase speed filter, and also it accounts for both the components of the displacement. The new formula depends on the location of the two points on the solar surface that are being cross correlated and accounts for the travel time shifts at different locations on the solar surface., Comment: 27 pages, 8 figures, ApJ in press

A type of saturation is sometimes seen in sunspot umbrae in MDI/SOHO magnetograms. In this paper, we present the underlying cause of such saturation. By using a set of MDI circular polarization filtergrams taken during an MDI line profile campaign observation, we derive the MDI magnetograms using two different approaches: the on-board data processing and the ground data processing, respectively. The algorithms for processing the data are the same, but the former is limited by a 15-bit lookup table. Saturation is clearly seen in the magnetogram from the on-board processing simulation, which is comparable to an observed MDI magnetogram taken one and a half hours before the campaign data. We analyze the saturated pixels and examine the on-board numerical calculation method. We conclude that very low intensity in sunspot umbrae leads to a very low depth of the spectral line that becomes problematic when limited to the 15-bit on-board numerical treatment. This 15-bit on-board treatment of the values is the reason for the saturation seen in sunspot umbrae in the MDI magnetogram. Although it is possible for a different type of saturation to occur when the combination of a strong magnetic field and high velocity moves the spectral line out of the effective sampling range, this saturation is not observed.

In a previous paper by the same authors, the sensitivity variations of negative secondary ions during Secondary Ion Mass Spectrometry (SIMS) analysis have been studied with respect to conditions of neutral cesium deposition. An experimental determination of the Cs surface concentration was impossible and it has been described by characteristic parameters. In this paper, the TRIDYN model is used to simulate these surface concentrations with respect to the different conditions used in the experimental study. The simulations give implantation profiles as well as sputtering yields of the involved elements with respect to the primary ion fluence. For the different experimental conditions, the implantation profiles at steady state are used to calculate mean Cs surface concentrations that have been averaged over different depths. The sensitivities of negative secondary ions can now be plotted with respect to these concentrations and experimental and simulated results can be compared to the electron-tunneling model describing ion emission from metallic and semi-conducting samples. Nevertheless, approximations included in this simulation model induce some artefacts which are discussed in this paper.

We have studied the phonon spectrum of ${\text{Mg}}_{2}{\text{Si}}_{1\ensuremath{-}x}{\text{Sn}}_{x}$ alloys using both density-functional theory calculations and neutron measurements. In the low tin concentration limit a resonance is obtained in the lower part of the spectrum. At higher concentrations comparison between theory and experiments shows that a simple averaging of the force constants of the perfect crystals ${\text{Mg}}_{2}\text{Si}$ and ${\text{Mg}}_{2}\text{Sn}$ can explain the main features of the density of states. However we suggest that the tin resonance persists up to large tin concentrations and may therefore be important for transport properties.

The self-diffusivities of Ti and Cr were determined in (Ti x W y Cr z )B2 ceramics which are a model system for the development of in-situ reinforced boride ceramics by tailored precipitate formation. Homogeneous solid solutions of composition (Ti0.3W0.5Cr0.2)B2, (Ti0.5W0.3Cr0.2)B2, and (Ti0.4W0.5Cr0.1)B2 were studied in the temperature interval between 1100 and 1500°C, using ion implanted stable 49Ti and 54Cr isotopes and secondary ion mass spectrometry (SIMS). The diffusivities of each element obey an Arrhenius law. The Cr diffusivities of all three compounds can be fitted to a unique Arrhenius line with an activation enthalpy of 3.5 eV and a low pre-exponential factor of 2×10−7 m2/s. The Ti diffusivities are smaller by 1–2 orders of magnitude than the Cr diffusivities, showing, however, higher activation enthalpies of 3.9 eV and approximately the same pre-exponential factors. The consequences of the results for the formation kinetics of precipitates in supersaturated (Ti x W y Cr z )B2 solid solutions are discussed.

To overcome the SIMS matrix effect in the negative secondary ion mode, analyses can be performed on the Cation Mass Spectrometer using neutral cesium deposition with simultaneous primary ion bombardment. This paper discusses the advantages of this technique by applying it on several samples. The useful yields of various elements detected as negative secondary ions are calculated and discussed in terms of work function and electron affinity. The additional Cs deposition allows a significant increase of the useful yields of negative secondary ions and thus of the analysis sensitivity compared to traditional Cs + primary ion bombardment. At maximal cesium surface concentrations, quantitative analyses become possible for elements with high electron affinities. For other elements a significant increase of the analysis sensitivity is achieved.

Diffusion of the stable tracer isotope 96Zr in 12 mol% polycrystalline scandia stabilized zirconia was studied in air in the temperature range from 1200 to 1600 °C. Secondary ion mass spectroscopy (SIMS) was used to record the tracer diffusion profiles. The activation enthalpies for bulk and grain boundary diffusion were determined to be (5.0 ± 0.4) eV and (3.9 ± 0.5) eV, respectively, with the latter being six to seven orders in magnitude faster than the first. Using XRD, it was proved that the diffusion occurs only in the cubic phase.

A numerical simulation and various test-structure configurations were developed which enable the measurement of the in-plane thermal conductivity and emissivity of on-membrane thin films in a versatile and accurate manner. The simulation takes into account the two-dimensional heat transfer in the membrane. Consequently, shorter membrane can be used and strained materials can be measured. The numerical simulation along with the new test-structures is used to understand the convective heat transfer at small scales and to quantify it. The measurement method is tested on various materials ranging from ceramics, metals to polycrystalline silicon.

The geometry of on-membrane thermoelectric power supplies has been optimized to obtain the highest useful electric power for a given heating power. Assuming the use of materials with moderate thermoelectric performances, an analytical one-dimensional model has been developed to find the optimum thermoelectric film thickness and leg length together with the best heat source configuration. The optimal geometry of these thermoelectric devices is discussed according to the thermal properties and emissivity of the materials as well as based on their working environment, i.e. air or vacuum, and on their operational mode. These investigations have been extended to more realistic micro-device geometries and to more efficient thermoelectric materials, using a numerical model. The performance of on-membrane thermopile is predicted for various materials and geometry combinations.

The Michelson Doppler Imager instrument on board SOHO has operated for most of a solar cycle. Here we present a careful analysis of solar astrometric data obtained with it from above the Earth's turbulent atmosphere. These data yield the most accurate direct constraint on possible solar radius variations on timescales from minutes to years and the first accurate determination of the solar radius obtained in the absence of atmospheric seeing.

The Cation Mass Spectrometer (CMS) has been developed in our laboratory to perform quantitative measurements with an optimal sensitivity and excellent depth and lateral resolution. For positive secondary ions, the MCsx+ mode has been used to circumvent the problems linked to the matrix effect by decoupling the Cs surface concentration from the sputtering conditions, so that an optimal Cs surface concentration is guaranteed and permits one to obtain high sensitivity. Similarly, flooding the sample surface with Cs lowers the work function and permits high useful yields for negative secondary ions. To obtain these performances, a patented neutral Cs deposition column is used for Cs surface concentration control in combination with a surface ionisation Cs+ gun for the sputtering of depth profiles or a Ga+ LMIS for imaging.

The electronic structure of defected MxMo6Se8−δ Chevrel phases (M = Ti, Sn and vacancy) is investigated with the KKR–CPA method. In all cases presented the Se vacancy does appear to behave as a double donor, filling some of the holes below the gap. From the computed densities of states the stability of the defects in these compounds can be understood through the presence of an energy gap near the Fermi level. Then it seems energetically favourable to fill the bonding holes at the valence band edge, which may tentatively explain why x>1 in SnxMo6Se7.5 (), and x

The paper focuses on the electrical performance of skutterudites based solar thermoelectric generators (STG). Basics of STG mathematical modeling are reported. Two STG concepts, namely the flat plate model with identical collector and radiator areas and the STG configuration with concentrators have been considered. Their performance is assessed for different solar intensities. The idea is to understand how such systems would perform if they were on board a spacecraft on journey towards the Sun.

The detection of gravity (g) modes of solar oscillations is important for probing the physical conditions in the Sun's energy-generating core. We have developed a new method of spatial masks optimized to reveal solar g-modes of angular degree l = 1-3 and applied it to Michelson Doppler Imager data in the frequency range of 50-500 μHz. These masks take into account the horizontal component of g-mode velocity eigenfunctions and the variations in the level of noise across the solar disk and adjust for the time-dependent mode projection properties caused by the inclination of the Sun's axis of rotation. They allow us to optimize the signal-to-noise ratio in the oscillation power spectra for potential g-modes of various angular order and degree. The peaks in the resulting spectra are analyzed in terms of their instrumental origin, long-term stability, and correspondence to the theoretically predicted g-mode spectrum. As a consequence of failing to detect any g-mode candidates, new upper limits for the surface amplitude of g-modes are obtained. The lowest upper limits in the range of 5-6 mm s-1 are found for sectorial g-modes (l = m). These limits are an order of magnitude higher than the theoretical prediction of Kumar et al. in 1996.

Self-diffusion studies of Ti and Cr were carried out in a two-phase ceramic compound with nominal composition (Ti 0.3 W 0.5 Cr 0.2 )B 2 , which is a model system for the development of in situ reinforced boride ceramics, via precipitation of a supersaturated host matrix. In the temperature interval 1000 °C⩽ T ⩽1400 °C, the diffusivities were determined with secondary ion mass spectrometry (SIMS) using co-implanted and simultaneously diffusing stable 49 Ti and 54 Cr isotopes. This procedure minimizes systematic errors, reduces experimental time, and enables a direct comparison of the results. The two- phase nature of the material is directly reflected in non-uniform Cr depth profiles, while for Ti, uniform depth profiles indicate nearly the same diffusivities in both phases. The diffusivities of both elements obey an Arrhenius behaviour with activation enthalpies of Δ H Ti =3.1 eV and Δ H Cr =3.3 eV, respectively, and very low pre-exponential factors of about D 0 Ti =1×10 −9 m 2 /s and D 0 Cr =6×10 −8 m 2 /s, which is a hint that no simple vacancy mechanism is operating in the material. The experimental results also suggest that the growth of the precipitates at 1600 °C is controlled by the volume diffusion of Cr and Ti.