ALBERT

Beschreibung: [1]  Neutron monitors have recorded the flux of high energy Galactic cosmic rays for more than half a century. During the recent prolonged, deep minimum in solar activity many sources indicate that modulated Galactic cosmic rays have attained new space-age highs. However reported neutron monitor rates are ambiguous; some record new highs while others do not. This work examines the record of 15 long-running neutron monitors to evaluate cosmic ray fluxes during the recent extraordinary solar minimum in a long-term context. We show that ground-level neutron rates did reach a historic high during the recent solar minimum, and we present a new analysis of the cosmic ray energy spectrum in the year 2009 versus year 1987. To do this we define a reference as the average of eight high-latitude neutron monitors, four in the northern hemisphere (Apatity, Inuvik, Oulu, Thule) and four in the southern hemisphere (Kerguelen, McMurdo, Sanae, Terre Adelie). Most stations display changes in sensitivity, which we characterize by a simple linear trend. After correcting for the change in sensitivity, a consistent picture emerges. With our correction all stations considered display new highs at the recent solar minimum, approximately 3% above the previous record high. These increases are shown to be consistent with spacecraft observations.

Beschreibung: [1]  We present the occurrence frequency of downgoing auroral electron beams in magnetic local time and invariant latitude, and the dependence on solar cycle, as indicated by F10.7, on whether the ionospheric footpoint of the satellite is illuminated or dark, and on the energy flux carried by the electrons. As previously reported, we find that the occurrence of electron beams peaks in the pre-midnight local time sector and that solar illumination at the footpoint (solar zenith angle) reduces both the occurrence and energy of the electron beams. The effect of solar maximum conditions (indicated by F10.7) is almost as large as the effect of the solar zenith angle. The characteristic energy of the electron beams is dependent on the energy flux carried, in addition to both solar zenith angle and F10.7. The beam energy (and therefore the parallel potential drop) is ~1.6 times higher for during solar minimum than during solar maximum for both dark and illuminated footpoints. The beam energy during dark solar minimum conditions is a factor of ~3 more than during sunlit minimum conditions. The ‘area’ covered by intense aurora is also reduced during solar maximum, for both sunlit and dark conditions. There is no evidence that the statistical results are due to the fact that acceleration via parallel electric fields moves to lower latitudes during solar maximum.

Beschreibung: [1]  In this paper we describe and quantify the energy transfer, flow and distribution. Our high-resolution data-set covers 13 years of OMNI, SuperMAG and Kyoto data. We employ what we consider to be the best estimates for energy sinks, and relate these to SuperMAG indices for better coverage and spatial resolution. For the energy input we have used the method of dimensional analysis [ Vasyliunas et al ., 1982] that is presented in unit power and makes it appropriate for energy analysis. A cross-correlation analysis parameterizes the magnetospheric response on the solar wind parameters during a wide range of conditions, ranging from substorms and storms up to a decade. The determined functional form is then evaluated and scaled using superposed epoch analysis of geomagnetic storms, revealing that the effective area of interaction can not be considered static. Instead we present a dynamic area which depends to the first order on the cube of the IMF B z component. Also, we find that for longer time periods this area must be increased compared to the area used for geomagnetic storms. We argue that some of the terms in the energy coupling function are contributory to describing magnetosheath conditions, and discuss how our coupling function can be related to Maxwell stress components. Also, we quantify the relative importance of the different energy sinks during substorms, geomagnetic storms and long time series, and present the coupling efficiency of the solar wind. Our energy coupling functions is compared with the ɛ parameter [ Akasofu and Perreault , 1978] and performs better for almost any event.

Beschreibung: [1]  Plasma sheet flow bursts have been suggested to correspond to different types of auroral activity, such as poleward boundary intensifications (PBIs), ensuing auroral streamers, and substorms. The flow-aurora association leads to the important question of identifying the magnetotail source region for the flow bursts and how this region depends on magnetic activity. The present study uses the ARTEMIS spacecraft coordinated with conjugate ground-based auroral imager observations to identify flow bursts beyond 45 R E downtail and corresponding auroral forms. We find that quiet-time flows are directed dominantly earthward with a one-to-one correspondence with PBIs. Flow bursts during the substorm recovery phase, and during steady magnetospheric convection (SMC) periods are also directed earthward, and these flows are associated with a series of PBIs/streamers lasting for tens of minutes with similar durations to that of the series of earthward flows. Pre-substorm onset flows are also earthward and associated with PBIs/streamers. The earthward flows during those magnetic conditions suggest that the flow bursts, which lead to PBIs and streamers, originate from further downtail of ARTEMIS, possibly from the distant tail neutral line (DNL) or tailward-retreated near-Earth neutral line (NENL) rather than from the nominal NENL location in the mid-tail. We find that tailward flows are limited primarily to the substorm expansion phase. They continue throughout the period of auroral poleward expansion, indicating that the expansion-phase flows originate from the NENL and that NENL activity is closely related to the auroral expansion of the substorm expansion phase.

Beschreibung: [1]  The solar eclipse on 15 January 2010 traversed Asia and completed its travel on the Shandong Peninsula in China at sunset. Two vertical-incidence ionosondes at Wuhan and Beijing and the oblique-incidence ionosonde network in North China were implemented to record the ionospheric response to the solar eclipse. Following the initial electron density decrease caused by the eclipse, the ionosphere was characterized by a strong pre-midnight enhancement, and a subsequent ionospheric decay, and a ~10 hour later post-midnight enhancement. Neither geomagnetic disturbance occurred during the eclipse day, nor did obvious nighttime peak appear for the ten-day mean of the F2-layer critical frequency ( fo F2). The electron density profilogram of the Beijing ionosonde indicates that the two enhancements were the result of the plasma flux downward from the top ionosphere, possibly due to the steep decrease of the ionospheric electron density and plasma temperature during the solar eclipse. The two-dimensional differential fo F2 maps present the regional variations of the nighttime electron density peaks and decay. Both the pre- and post-midnight enhancements initially appeared in a belt almost in parallel with the eclipse track and then drifted southward. The different magnitudes of greatest eclipse in the umbra and outside tend to account for the different occurrence times of the plasma flux. The ionospheric decay following the pre-midnight enhancement is also considered as a consequence of the eclipse shade.

Beschreibung: [1]  We study a statistics of ∂  B z /∂  x in a thin stretching current sheet (substorm growth phases) observed by Cluster between 8 and 18 R E downtail. After 2005 spacecraft separation allowed to measure directly this derivative of B z along the tail axis. The near-tail events (within 14 R E ) exhibited a straight decrease of an initially large positive ∂  B z /∂  x to ∼ 1–2 nT/ R E . In the more stretched middle tail, usually the small | ∂  B z /∂  x | 〈 0.5 − 1 nT/ R E had no clear trend and fluctuated around zero with time scales 5–15 min. In general, negative ∂  B z /∂  x were ubiquitous. At some onsets larger negative ∂  B z /∂  x  〈 − 1 nT/ R E were associated with transient dipolarizations, propagating Earthward. There was no clear association of local plasma sheet activity onset with any value of ∂  B z /∂  x . We discuss relation of observations and recent modeling results.

Beschreibung: [1]  ELF/VLF radio waves are difficult to generate with conventional antennas. Ionospheric HF heating facilities generate ELF/VLF waves via modulated heating of the lower ionosphere. HF heating of the ionosphere changes the lower ionospheric conductivity, which in the presence of natural currents such as the auroral electrojet, creates an antenna in the sky when heating is modulated at ELF/VLF frequencies. We present a summary of nearly 100 days of ELF/VLF wave generation experiments at the 3.6 MW HAARP facility near Gakona, Alaska, and provide a baseline reference of ELF/VLF generation capabilities with HF heating. Between February 2007 and August 2008, HAARP was operated on close to 100 days for ELF/VLF wave generation experiments, at a variety of ELF/VLF frequencies, seasons and times of day. We present comprehensive statistics of generated ELF/VLF magnetic fields observed at a nearby site, in the 500-3500 Hz band. Transmissions with a specific HF beam configuration (3.25 MHz, vertical beam, amplitude modulation) are isolated so the data comparison is self-consistent, across nearly 5 million individual measurements of either a tone or a piece of a frequency-time ramp. There is a minimum in the average generation close to local midnight. It is found that generation during local nighttime is on average weaker, but more highly variable, with a small number of very strong generation periods. Signal amplitudes from day to day may vary by as much as 20-30 dB. Generation strengthens by ~5 dB during the first ~30 minutes of transmission, which may be a signature of slow electron density changes from sustained HF heating. Theoretical calculations are made to relate the amplitude observed to the power injected into the waveguide and reaching250 km. The median power generated by HAARP and injected into the waveguide is ~0.05-0.1 W in this base-line configuration (vertical beam, 3.25 MHz, amplitude modulation), but may have generated hundreds of Watts for brief durations. Several efficiency improvements have improved the ELF/VLF wave generation efficiency further.

Beschreibung: [1]  An inversion technique for estimating the properties of the magnetospheric plasma from the harmonic frequencies of the toroidal standing Alfvén waves has been used to derive the global equatorial mass density covering radial distances from 4 to 9 Earth radii ( R E ), within the local time sector spanning from 0300 to 1900 hours. This broad range of L shell extending to the outer magnetosphere allows us to examine the local time and radial dependence of the quiet-time equatorial mass density during solar minimum and thereby construct a global distribution of the equatorial mass density. The toroidal Alfvén waves were detected with magnetometers on the Active Magnetospheric Particle Tracer Explorers (AMPTE)/Charge Composition Explorer (CCE) during the nearly 5 year interval from August 1984 to January 1989 and on the Geostationary Operational Environmental Satellites (GOES) (10, 11 and 12) for 2 years from 2007 to 2008, both of which were operating during solar minimum years. The derived equatorial mass density, ρ eq , at geosynchronous orbit (GEO) monotonically increases with increasing magnetic local time (MLT) from the nightside towards the dusk sector. At other radial distances, ρ eq has the same MLT variation as that of GEO, while the magnitude logarithmically decreases with increasing L value. An investigation of the Dst and Kp dependence shows that the median value of ρ eq varies little in the daytime sector during moderately disturbed times, which agrees with previous studies. ρ eq calculated from the F 10.7 dependent empirical model shows good agreement with that of CCE but overestimates that of GOES probably due to the extreme solar cycle minimum in years 2007–2008.

Beschreibung: [1]  In this paper we compare observations of the high latitude cusp from DMSP data to simulations conducted using the Lyon-Fedder-Mobarry (LFM) global magnetosphere simulation. The LFM simulation is run for the 31 Aug 2005 to 02 Sep 2005 moderate storm, from which the solar wind data exhibits a wide range of conditions that enable a statistical representation of the cusp to be obtained. The location of the cusp is identified using traditional magnetic depression and plasma density enhancement at high altitude. A new diagnostic using the parallel ion number flux is also tested for cusp identification. The correlation of the cusp latitude and various solar wind IMF coupling functions is explored using the three different cusp identification methods. The analysis shows 1) the three methods give approximately the same location and size of the simulated cusp at high altitude; 2) the variations of the simulated cusp are remarkably consistent with the observed statistical variations of the low-altitude cusp. In agreement with observations a higher correlation is obtained using other solar wind coupling functions such as the Kan-Lee electric field. The MLT position of the simulated cusp is found to depend upon the IMF By component, with a lower linear correlation. The width of the simulated cusp in both latitude and MLT is also examined. The size of the cusp is found to increase with the solar wind dynamic pressure with saturation seen when the dynamic pressure is greater than 3 nPa.

Beschreibung: [1]  Daily profiles of phase measurements as observed on fixed VLF-paths generally show a transient phase advance, followed by a phase delay, for about 90 minutes after sunrise hours. This is indicative of a reflecting ionospheric C-region developing along the terminator line at an altitude below the normal D-region. The suggested occurrence of a C-region is consistent with rocket measurements made in the 1960's, showing a maximum of the electron density between 64 and 68 km, and by radio sounding in the 1980's. In order to correctly describe the properties of the phase effect associated with the presence of a C-region, it is important to understand the subionospheric propagation characteristics of the VLF-paths. In this paper, we analyze the variations presented by the temporal properties of the VLF narrow-band phase effect, and determined a parameter associated with the appearance of the C-region at sunrise hours observed by receivers from the South America VLF Network (SAVNET). Periodic patterns emerge from the parameter curves. Two distinct temporal behavior regimes can be identified: one exhibiting slow variations between March and October, and another one exhibiting faster variations between October and March. Solar illumination conditions and the geometrical configuration of the VLF paths relative to the sunrise terminator partly explain the slow variation regime. During periods of faster variations, we have observed good association with atmospheric temperature variability found in the measurements of the TIMED-SABER satellite instrument, which we assume to be related to the Winter Anomaly atmospheric phenomenon. However, when comparing the parameter time series with temperature curves, no direct one-to-one correspondence was found for transient events.

Beschreibung: [1]  On 21 January 2005, one of the fastest interplanetary coronal mass ejections (ICME) of solar cycle 23, containing exceptionally dense plasma directly behind the sheath, hit the magnetosphere. We show from charge-state analysis that this material was a piece of the erupting solar filament, and further, based on comparisons to the simulation of a fast CME, that the unusual location of the filament material was a consequence of three processes. As the ICME decelerated, the momentum of the dense filament material caused it to push through the flux rope towards the nose. Diverging non-radial flows in front of the filament moved magnetic flux to the sides of the ICME. At the same time reconnection between the leading edge of the ICME and the sheath magnetic fields worked to peel away the outer layers of the flux rope creating a remnant flux rope and a trailing region of newly opened magnetic field lines. These processes combined to move the filament material into direct contact with the ICME sheath region. Within one hour after impact and under northward IMF conditions, a cold dense plasma sheet formed within the magnetosphere from the filament material. Dense plasma sheet material continued to move through the magnetosphere for more than 6 hours as the filament passed by the Earth. Densities were high enough to produce strong diamagnetic stretching of the magnetotail despite the northward IMF conditions and low levels of magnetic activity. The disruptions from the filament collision are linked to an array of unusual features throughout the magnetosphere, ionosphere and atmosphere. These results raise questions about whether rare collisions with solar filaments may, under the right conditions, be a factor in producing even more extreme events.

Beschreibung: [1]  We present observations from the Falkland Islands SuperDARN radar of the propagation of HF radio waves via the Weddell Sea ionospheric Anomaly (WSA), a region of enhanced austral summer nighttime ionospheric electron densities covering the southern Pacific and South Americas region. This anomaly is thought to be produced by uplift of the ionosphere by prevailing equatorwards thermospheric winds. Of particular interest are perturbations of the WSA-supported propagation, which suggest that during periods of geomagnetic disturbance the ionospheric layer can be lowered by several 10s of km and subsequently recover over a period of 1 to 2 hours. Perturbations can appear singly or as a train of 2 to 3 events. We discuss possible causes of the perturbations, and conclude that they are associated with equatorward-propagating large-scale atmospheric waves produced by magnetospheric energy deposition in the auroral or sub-auroral ionosphere. Changes in high/mid-latitude electrodynamics during geomagnetic storms may also account for the perturbations, but further modeling is required to fully understand their cause.

Beschreibung: Homogenous liquid precursor for ZrC – SiC was prepared by blending of Zr ( OC 4 H 9 ) 4 and Poly[(methylsilylene)acetylene]. This precursor could be cured at 250°C and converted into binary ZrC – SiC composite ceramics upon heat treatment at 1700°C. The pyrolysis mechanism and optimal molar ratio of the precursor were investigated by XRD. The morphology and elements analyses were conducted by SEM and corresponding energy-dispersive spectrometer. The evolution of carbon during ceramization was studied by Raman spectroscopy. The results showed that the precursor samples heat treated at 900°C consisted of t- ZrO 2 (main phase) and m- ZrO 2 (minor phase). The higher temperature induced phase transformation and t- ZrO 2 converted into m- ZrO 2 . Further heating led to the formation of ZrC and SiC due to the carbothermal reduction, and the ceramic sample changed from compact to porous due to the generation of carbon oxides. With the increasing molar ratios of C / Zr , the residual oxides in 1700°C ceramic samples converted into ZrC and almost pure ZrC – SiC composite ceramics could be obtained in ZS-3 sample. The Zr , Si , and C elements were well distributed in the obtained ceramics powders and particles with a distribution of 100 ~ 300 nm consisted of well-crystallized ZrC and SiC phases.

Beschreibung: [1]  Inner magnetosphere magnetic field and plasma flow data are examined during 228 steady magnetospheric convection events. We find that the B Z component of the magnetic field around geostationary orbit is weaker than during average conditions and the plasma flow speeds are higher than average in the dusk sector just beyond geostationary orbit. The SMC periods include more enhanced Earthward and tailward flow intervals than during average conditions. The steady convection period magnetic field is not steady: The near-geostationary nightside field grows increasingly taillike throughout the steady convection period. In the midtail, Earthward flows are enhanced in a wide region around the midnight sector, which leads to enhanced magnetic flux transport toward the Earth during the steady convection periods. Compared to well-known characteristics during magnetospheric substorms, the inner tail evolution resembles that during the substorm growth phase, while the midtail flow characteristics duringsteady convection periods are similar to those found during substorm recovery phases.

Beschreibung: [1]  A global total electron content (TEC) model response to geomagnetic activity described by the K p -index is built by using the Center for Orbit Determination of Europe (CODE) TEC data for full 13 years, January 1999 - December 2011. The model describes the most probable spatial distribution and temporal variability of the geomagnetically forced TEC anomalies assuming that these anomalies at a given modip latitude depend mainly on the K p -index, local time (LT) and longitude. The geomagnetic anomalies are expressed by the relative deviation of TEC from its 15-day median and are denoted as rTEC. The rTEC response to the geomagnetic activity is presented by a sum of two responses with different time delay constants and different sign of the cross-correlation function. It has been found that the mean dependence of rTEC on K p -index can be expressed by a cubic function. The LT dependence of rTEC is described by Fourier time series which includes the contribution of four diurnal components with periods 24, 12, 8 and 6 hours. The rTEC dependence on longitude is presented by Fourier series which includes the contribution of zonal waves with zonal wavenumbers up to 6. In order to demonstrate how the model is able to reproduce the rTEC response to geomagnetic activity three geomagnetic storms at different seasons and solar activity conditions are presented. The model residuals clearly reveal two types of the model deviation from the data: some underestimation of the largest TEC response to the geomagnetic activity and randomly distributed errors which are the data noise or anomalies generated by other sources. The presented TEC model fits to the CODE TEC input data with small negative bias of -0.204, root mean squares error RMSE  = 4.592 and standard deviation error STDE  = 4.588. The model offers TEC maps which depend on geographic coordinates (5 o x5 o in latitude and longitude), and universal time (UT) at given geomagnetic activity and day of the year. It could be used for both science and possible service (nowcasting and short-term prediction); for the latter a detailed validation of the model at different geophysical conditions has to be performed in order to clarify the model predicting quality.

Beschreibung: [1]  Magnetic reconnection (MR), a fundamental process in space plasmas that changes magnetic topology and converts magnetic energy into kinetic and thermal energies, is an ultimate driver of space weather. There exist two models of MR in the literatures, anti-parallel and component, associated with intensive studies of their generation and applications. In this paper we report an MR event observed by Cluster constellation in the geo-magnetotail where both types of MR were detected. By reconstructing the three-dimensional (3D) MR configuration we find that a pair of A-B nulls existed in both types of MR cases with two fan surfaces intersecting each other to form a separator line connecting the nulls. A weak or sizable magnetic field exists along the separator in the anti-parallel or component case, respectively. In the latter case, field strength is finite away from the two nulls and vanishes close to the nulls. Therefore, at least in the two cases observed, both anti-parallel and component MR geometries are local presentation of the separator MR configuration. This result supports the expectation that 3D nulls often occur as a crucial element of MR at least in the magnetotail and separator MR may play an important role in dynamics and reconfiguration of magnetic field in 3D MR processes.

Beschreibung: Ce -doped BaTiO 3 -based ceramics were prepared and studied to satisfy ultra-broad temperature stability (from −55°C to 300°C, capacitance variation rate based on C 20°C is within ±15%). The sample with 0.6 mol% CeO 2 succeeds to achieve this performance with a remarkably high ceiling temperature of 300°C. Meanwhile, the sample has good dielectric and electrical properties at room temperature (ε r  = 1667, tanδ = 1.478%, ρ V  = 5.9 × 10 12  Ω·cm). Ce ion can substitute for Ti ion as Ce 4+ or Ba ion as Ce 3+ . The substitution decreases the spontaneous polarization of BaTiO 3 , and then weakens the ferroelectricity of BaTiO 3 . As a result, the temperature stability of samples is improved obviously. Besides, CeO 2 addition promotes the formation of exaggerated grains, which are consisting of Ba 6 Ti 17 O 40 .

Beschreibung: This study aims to optimize quantitative X-ray diffraction (XRD) mineralogical analysis of the minority phases in clinker. The proposed method consists of applying Rietveld quantitative refinement to the XRD patterns for both clinker and the insoluble residue remaining after it is attacked with methanol and salicylic acid (Takashima method). The method was tested with industrial clinker and the same material after modifying its mineralogy by refiring at 1500°C followed by slow cooling. The findings showed that the C 4 AF / C 3 A ratios for quickly and gradually cooled clinker were much higher when the clinker diffractograms were refined with the Rietveld procedure than when the proposed method was used. The proportion of C 3 A found with the proposed method was ≈2.8-fold higher than when Rietveld only was applied to the diffractograms for clinkers. Taken together, the refinement data for the two materials (clinker and Takashima residua) revealed that Rietveld quantitative XRD applied to clinker underestimates the low C 3 A content. These findings are supported by postsulfate attack durability studies conducted on cements prepared with the two clinkers.

Beschreibung: The effect of increasing poling fields on the properties of (1− x )BZT– x BCT compositions across the morphotropic phase boundary (MPB) is studied using large signal polarization and strain, small signal permittivity and piezoelectric coefficient, and XRD measurements. Successive poling causes charge carrier migration inducing an internal bias field, which becomes large with respect to the coercive field resulting in biased ferroelectric and ferroelastic switching. Improvements in piezoelectric coefficient of 9% are significantly smaller in the tetragonal 60BCT composition compared with the improvement of approximately 50% in the rhombohedral 40BCT and MPB 50BCT compositions. While the properties continue to change with increased poling fields, the remnant ferroelastic domain texture parallel to the field direction, as observed from XRD, stays approximately constant. The improvement in overall domain alignment leading to largely enhanced intrinsic piezoelectricity originates from the alignment of 180° domains and possibly non-180° domains in grains with orientations inclined to the electric field. As a result, poling is most effective in BZT–BCT materials that have low coercive fields, show low distortions and possess more polarization orientations, such as compositions in the rhombohedral phase field or near the MPB.

Beschreibung: The defect chemistry-modulated dielectric properties of dense yttria-doped zirconia ceramics prepared by conventional sintering (at 1350°C–1500°C) and electric field-assisted flash sintering (55 V/cm at 900°C) were studied by impedance spectroscopy. While the bulk dielectric properties from both sets of samples showed only small and insignificant changes in conductivity and permittivity, respectively, a huge increase of these properties was measured for the grain boundaries in the flash sintered specimens. A close analysis of these results suggests that flash sintering reduced grain-boundary thickness (by about 30%), while increasing the concentration of oxygen vacancies near these interfaces (by about 49%). The underlying mechanism proposed is electric field-assisted generation and accommodation of defects in the space-charge layers adjacent to the grain surface. The changes in measured permittivity are attributed to the boundary thickness effect on capacitance, while conductivity involved variations in its defect density-dependent intrinsic value, accounting for changes also observed in grain-boundary relaxation frequencies. Therefore, in terms of modifications to the specific dielectric properties of these materials, the overall consequence of flash sintering was to considerably lower the semi-blocking character of the grain boundaries.

Beschreibung: This article presents a detailed study on the nanoscaled interface between microelongated gold particles (GP) and biphase leucite/feldspar glass-ceramic matrix. The glass-ceramic composite with a nonuniform GP distribution was processed through hot-pressing under vacuum using a commercial dental ceramic furnace for glass-ceramic dental crown manufacturing. Heat treatments at 900°C, 1100°C, and 1300°C were conducted, and microstructural features along the interface were used to verify the chemical reactions between GP and glass-ceramic matrix. It was observed that the amorphous glass-ceramic matrix had nanoscaled biphase structures, and the distributed nanoscaled amorphous leucite phase was attracted to GP during hot-pressing, and was more reactive with GP than the feldspar phase. The thickness of the interfacial phase formed through chemical reactions between GP and glass-ceramic matrix is around 30 nm. The chemically bonded interface has contributed significantly toward the substantial improvements in both strength and toughness of the GP-reinforced glass-ceramic matrix composite. Characterization techniques, including X-ray diffraction and field-emission scanning electron Microscopy, incorporating X-ray microanalysis using energy dispersive spectrometry, have been employed in this study.

Beschreibung: [1]  The development of equatorial plasma irregularity plumes can be well recorded by steerable backscatter radars operated at and off the magnetic equator due to the fact that the vertically extended plume structures are tracers of magnetically north-south aligned larger scale structures. From observations during March 2012, using two low latitude steerable backscatter radars in Southeast Asia, the Equatorial Atmosphere Radar (EAR) (0.2ºS, 100.3ºE; dip lat 10.4ºS) and the Sanya VHF radar (18.4ºN, 109.6ºE; dip lat 12.8ºN), the characteristics of backscatter plumes over the two sites separated in longitude by ~1000 km were simultaneously investigated. The beam steering measurements reveal frequent occurrences of multiple plumes over both radar sites, of which two cases are analyzed here. The observations on 30 March 2012 show plume structures initiated within the radar scanned area, followed by others drifting from the west of the radar beam over both stations. A tracing analysis on the onset locations of plasma plumes reveals spatially well-separated backscatter plumes, with a maximum east-west wavelength of about 1000 km, periodically generated in longitudes between 85ºE and 110ºE. The post-sunset backscatter plumes seen by the Sanya VHF radar are found to be due to the passage of sunset plumes initiated around the longitude of EAR. Most interestingly, the EAR measurements on the night of 21 March 2012 show multiple plume structures that developed successively in the radar scanned area with east-west separation of ~50 km, with however, no sunset plasma plume over Sanya. Co-located ionogram measurements show that spread F irregularities occurred mainly in the bottomside F-region at Sanya, whereas satellite traces in ionograms that are indications of large-scale wave structures, were observed on that night at both stations. Possible causes for the longitudinal difference in the characteristics of radar backscatter plumes are discussed.

Beschreibung: Recent investigations have revealed the great potential of Raman spectroscopy for the characterization of clinker minerals and commercial Portland cements. The usefulness of this technique for the identification of anhydrous, hydrated, and carbonated phases in cement-based materials has been demonstrated. In the present work, the application of micro-Raman spectroscopy for the characterization of the main clinker phases of calcium aluminate cements and calcium sulfoaluminate cement is explored. The main stable hydrated phases as well as several important carbonated phases are investigated. Raman measurements on the following phases are reported: (i) pure, unhydrated phases: CA, C 12 A 7 , CA 2 , C 2 AS, cubic- C 3 A , C 4 AF, and C 4 A 3 ; (ii) hydrated phases: ettringite, monosulfoaluminate, and hydrogarnet ( C 3 AH 6 ); (iii) carboaluminate phases: hemicarboaluminate and monocarboaluminate. The present results, which are discussed in terms of the internal vibrational modes of the aluminate, carbonate, and sulfate molecular groups as well as stretching O–H vibrations, show the ability of Raman spectroscopy to identify the main hydrated and unhydrated phases in the aluminate and sulfoaluminate cements. The Raman spectra obtained in this work provide an extended database to the existing data published in the literature.

Beschreibung: Acmite ( NaFeSi 2 O 6 ) films were formed on steel coupons via solvothermal reaction of silica, sodium hydroxide, and 1, 4-butanediol in an autoclave under autogenous pressure. Systematic variation in processing variables led to homogenous coatings comprised of pinacoidal acmite grains with an average grain size of ~33 μm. The coatings were produced on the steel coupons from reactant conditions of 0.635 m SiO 2 , 2.546 m NaOH , and 3.087 m 1,4-butanediol for 72 h at 240°C.

Beschreibung: [1]  The solar wind impacting the Earth varies over a wide range of time scales, driving a corresponding range of geomagnetic activity. Past work has strongly indicated the rate of merging on the frontside magnetosphere is the most important predictor for magnetospheric activity, especially over a few hours. However the magnetosphere exhibits variations on other time scales, including UT, seasonal, and solar cycle variations. Much of this geomagnetic variation cannot be reasonably attributed to changes in the solar wind driving – that is, it is not created by the original Russell-McPherron effect or any generalization thereof. In this paper we examine the solar cycle, seasonal, and diurnal effects based upon the frequency of substorm onsets, using a data set of 53,000 substorm onsets. These were identified through the SuperMAG collaboration and span three decades with continuous coverage. Solar cycle variations include a profound minima in 2009 (448 substorms) and peak in 2003 (3727). The magnitude of this variation (a factor of 8.3) is not explained through variations in estimators of the frontside merging rate (such as d Φ MP / dt ), even when the more detailed probability distribution functions are examined. Instead, v , or better, n 1/2 v 2 seems to be implicated in the dramatic difference between active and quiet years, even beyond the role of velocity in modulating merging. Moreover, we find that although most substorms are preceded by flux loading (78.5% are above the mean and 83.8% above median solar wind driving) a high solar wind v is almost as important (68.3% above mean, 74.8% above median). This and other evidence suggests either v or n 1/2 v 2 (but probably not p ) plays a strong secondary role in substorm onset. As for the seasonal and diurnal effects, the elliptical nature of the Earth's orbit, which is closest to the Sun in January, leads to a larger solar wind driving (measured by Bs , vBs , or d Φ MP / dt ) in November, as is confirmed by 22 years of solar wind observations. However substorms peak in October and March, and have a UT dependence best explained by whether a conducting path established by solar illumination exists in at least one hemisphere in the region where substorm onsets typically occur.

Beschreibung: [1]  The primary sources of energetic electron precipitation (EEP) which affect altitudes 〈100 km (〉30 keV) are expected to be from the radiation belts, and during substorms. EEP from the radiation belts should be restricted to locations between L  = 1.5-8, while substorm produced EEP is expected to range from L  = 4-9.5 during quiet geomagnetic conditions. Therefore, one would not expect any significant D-region impact due to electron precipitation at geomagnetic latitudes beyond about L  = 10. In this study we report on large unexpectedly high latitude D-region ionization enhancements, detected by an incoherent scatter radar at L  ≈ 16, which appear to be caused by electron precipitation from substorms. We go on to reexamine the latitudinal limits of substorm produced EEP using data from multiple low-Earth orbiting spacecraft, and demonstrate that the precipitation stretches many hundreds of kilometers polewards of the previously suggested limits. We find that a typical substorm will produce significant EEP over the IGRF L -shell range L  = 4.6 ± 0.2-14.5 ± 1.2, peaking at L  = 6-7. However, there is significant variability from event to event; in contrast to the median case, the strongest 25% of substorms have significant EEP in the range spaning L  = 4.1 ± 0.1-20.7 ± 2.2, while the weakest 25% of substorms have significant EEP in the range spaning L  = 5.5 ± 0.1-10.1 ± 0.7. We also examine the occurrence probability of very large substorms, focusing on those events which appear to be able to disable geostationary satellites when they are located near midnight MLT. On average these large substorms occur approximately 1-6 times per year, a significant rate given the potential impact on satellites.

Beschreibung: [1]  This paper presents new observations of the behaviour of simulated dust particles in space plasma based on a 3D particle in cell code. Multistep Monte Carlo collision is employed to simulate the dust charging process which is validated for the cases of charging of isolated dust particle and ensemble dust particles, where results indicate good agreement between simulation and theories. The code is then used to investigate plasma properties near a charged surface in a vicinity of a cloud of dust particles. The simulation reveals that a cloud of dust particle close to a spacecraft surface affects plasma densities around the spacecraft as well the spacecraft's surface potential. It is suggested that dust cloud causes the surface to charge to higher negative potential. The simulation also suggests that the combination of surface potential and dust cloud potential produces a region of trapped low energy electrons.

Beschreibung: [1]  We here document with magnetic field observations a passage of the MESSENGER spacecraft through Mercury's magnetosphere under conditions of a quasi-parallel bow shock, i.e., when the direction of the upstream interplanetary magnetic field (IMF) was within 45° of the bow shock normal. The spacecraft's fast transition of the magnetosheath and the steady solar wind conditions during the period analyzed allow both spatial and temporal properties of the shock crossing to be investigated. The observations show that the shock reformation process can be nearly periodic under stable solar wind conditions. Throughout the 25-min-long observation period, the pulsation duration deviated by at most ~10% from the average 10 s period measured. This quasi-periodicity allows us to study all aspects of the shock reconfiguration, including ultra-low-frequency waves in the upstream region and large-amplitude magnetic structures observed in the vicinity of the magnetosheath − solar wind transition region and inside the magnetosheath. We also show that bow shock reformation can be a substantial source of wave activity in the magnetosphere, on this occasion having given rise to oscillations in the magnetic field with peak-to-peak amplitudes of 40–50 nT over large parts of the dayside magnetosphere. The clean and cyclic behavior observed throughout the magnetosphere, the magnetosheath, and the upstream region indicates that the subsolar region was primarily influenced by a cyclic reformation of the shock front, rather than by a spatial and temporal patchwork of short large-amplitude magnetic structures (SLAMS), as is generally the case at the terrestrial bow shock under quasi-parallel conditions.

Beschreibung: [1]  The entry of solar wind into the magnetosphere is strongly influenced by kinetic-scale boundary layers where the rapid variation in the magnetic field and/or velocity can drive transport. In current layers with strong Alfvénic velocity shear, the generation of vortices from the Kelvin-Helmholtz instability can drive magnetic reconnection even in broader current sheets by locally compressing these layers as the vortices develop. Previous two-dimensional (2D) fully kinetic simulations of this vortex-induced reconnection process have demonstrated the copious formation of magnetic islands in regions of strongly compressed current between the vortices. Here we describe the first three-dimensional (3D) fully kinetic simulations of this process and demonstrate that the compressed current sheets give rise to magnetic flux ropes over a range of oblique angles and along the entire extent of the compressed current layer around the periphery of the vortex. These flux ropes propagate with the shear flow and eventually merge with the vortex. Over longer time scales, this basic scenario is repeated as the vortices drive new compressed current sheets. In the final stage, the vortices undergo a merging process that drives new compressed current sheets and flux ropes. Based on these simulations, a simple model is proposed that predicts the size of these flux ropes relative to their parent vortex. Both the relative sizes as well as the structure of the profiles across the vortex are in reasonable agreement with THEMIS observations at the Earth's low-latitude magnetopause.

Beschreibung: A 50:50 vol% MgO – Y 2 O 3 nanocomposite with ~150 nm grain size was prepared in an attempt to make 3–5 μm infrared-transmitting windows with increased durability and thermal shock resistance. Flexure strength of the composite at 21°C is 679 MPa for 0.88 cm 2 under load. Hardness is consistent with that of the constituents with similar grain size. For 3-mm-thick material at 4.85 μm, the total scatter loss is 1.5%, forward scatter is 0.2%, and absorptance is 1.8%. Optical scatter below 2 μm is 100%. Variable intensity OH absorption (~6% absorptance) is observed near 3 μm. The refractive index is ~0.4% below the volume-fraction-weighted average of those of the constituents. Thermal expansion is equal to the volume-fraction-weighted average of expansion of the constituents. Specific heat capacity is equal to the mass-fraction-weighted average of heat capacities of the constituents. Thermal conductivity lies between those of the constituents up to 1200 K. Elastic constants lie between those of the constituents. The Hasselman mild thermal shock resistance parameter for the composite is twice as great as that of common 3–5 μm window materials, but half as great as that of c -plane sapphire.

Beschreibung: [1]  We survey the properties of electron pitch angle distributions in the magnetotail plasma sheet at a distance between 15 and 19 R E from the Earth, using data from the Cluster PEACE instrument. We limit our survey to those pitch angle distributions measured when the IMF had been steadily northward or steadily southward for the previous three hours. We find that, at sub-keV energies the plasma sheet electron pitch angle distribution has an anisotropy such that there is a higher differential energyflux of electrons in the (anti-) field-aligned directions. Fitting the measured pitch angle distributions with both a single and two component kappa distribution reveals that this anisotropy is the result of the presence of a second, cold, component of electrons that is observed more often than not, and occurs during both the northward and southward IMF intervals. We present evidence that suggests the cold electron component has an ionospheric, rather than magnetosheath, source and is linked tothe large scale field aligned current systems that couple the magnetosphere and ionosphere.

Beschreibung: [1]  Driver functions for the Earth's magnetosphere-ionosphere system are derived from physical principles. Two processes act simultaneously: a reconnection-coupled MHD generator G and a viscous interaction. G accounts for the dayside reconnection rate, the length of the reconnection X-line, and current-saturation limits for the solar-wind generator. Two viscous drivers are derived: Bohm viscosity B and the freestream-turbulence effect F. A problematic proxy effect is uncovered wherein the viscous driver functions also describe the strength of reconnection. Two magnetospheric-driver functions written in terms of upstream-solar-wind parameters are constructed: G+B and G+F. The driver functions are tested against 7 geomagnetic indices. The reaction of the geomagnetic indices to G+B and G+F is nonlinear: nonlinear versions of the driver functions are supplied. Applying the driver functions at multiple timesteps yields correlation coefficients of ~85% with the AE and Kp indices; it is argued that multiple timestepping removes high-frequency uncorrelated signal from the drivers. Autocorrelation-function analysis shows strong 1-d and 1-yr periodicities in the AE index that are not in the solar-wind driver functions; correspondingly, highpass and lowpass filtering finds uncorrelated signal at 1-d and 1-yr timescales. Residuals (unpredicted variance) between the geomagnetic indices and the driver functions are analyzed: the residuals are anti-correlated with the solar-wind velocity, the solar F 10.7 radio flux, and the solar-wind current-saturation parameter. Removing diurnal, semiannual, and annual trends from the indices improves their correlation with the solar-wind driver functions. Simplified versions of the driver functions are constructed: the simplified drivers perform approximately as well as the full drivers.

Beschreibung: [1]  Plasma properties of Saturn's pre-midnight tail region are surveyed using Cassini/CAPS ion observations from 2010. Only low-latitude (|lat| 〈 6°) intervals in which the CAPS viewing was roughly symmetric inward and outward around the corotation direction are used. Our numerical moments algorithm returns nonzero ion density for 70% (999) of the intervals selected. Of these, 642 had detectable water-group ion densities, and the remainder were dominantly, if not entirely, light ions. The derived plasma parameters are similar to those found in an earlier study for the post-midnight tail region, except that we find little evidence for the systematic outflows identified in that study, and we do find numerous significant inflow events. One such inflow is identified as a dipolarization event, the first reported plasma properties of such a structure at Saturn. A second, long-lasting event may be evidence for the existence at times of a quasi-steady reconnection region in the pre-midnight tail. The large majority of the plasma flows are found to be within 20° of the corotation direction, though with flow speeds significantly lower than full corotation. While the inflow events represent plausible evidence for internally-driven mass loss in the pre-midnight region, the absence of significant outflow events suggests that in the region surveyed here, tail reconnection has not yet proceeded to involve lobe field lines, so the disconnected plasma continues its general motion in the corotation direction.

Beschreibung: [1]  Following the first-time ionospheric imaging of a seismic fault, here we perform a case-study on retrieval of parameters of the extended seismic source ruptured during the great M9.0 Tohoku-oki earthquake. Using 1Hz ionospheric GPS data from the Japanese network of GPS receivers (GEONET) and several GPS satellites, we analyze spatio-temporal characteristics of co-seismic ionospheric perturbations and we obtain information on the dimensions and location of the sea surface uplift (seismic source). We further assess the criterion for the successful determination of seismic parameters from the ionosphere: the detection is possible when the line-of-sights from satellites to receivers cross the ionosphere above the seismic fault region. Besides, we demonstrate that the multi-segment structure of the seismic fault of the Tohoku-oki earthquake can be seen in high-rate ionospheric GPS-data. Overall, our results show that, under certain conditions, ionospheric GPS-derived TEC measurements could complement the currently working systems, or independent ionospherically-based system might be developed in the future.

Beschreibung: [1]  The non-dipolar portions of the Earth's main magnetic field constitute substantial differences between the two hemispheres. Beside the magnetic flux densities and patterns being different in the Northern Hemisphere (NH) and Southern Hemisphere (SH), also the offset between the invariant magnetic and the geographic poles is larger in the SH than in the NH. We investigated the effects of this magnetic field asymmetry on the high-latitude thermosphere and ionosphere using global numerical simulations, and compared our results with recent observations. While the effects on the high-latitude plasma convection are small, the consequences for the neutral wind circulation are substantial. The cross-polar neutral wind and ion drift velocities are generally larger in the NH than the SH, and the hemispheric difference shows a semidiurnal variation. The neutral wind vorticity is likewise larger in the NH than in the SH, with the difference probably becoming larger for higher solar activity. In contrast, the spatial variance of the neutral wind is considerably larger in the SH polar region, with the hemispheric difference showing a strong semidiurnal variation. Its phase is similar to the phase of the semidiurnal variation of the hemispheric magnitude differences. Hemispheric differences in ion drift and neutral wind magnitude are most likely caused partly by the larger magnetic flux densities in the near-polar regions of the SH, and partly by the larger offset between the invariant and geographic pole in the SH, while differences in spatial variance are probably just caused by the latter. We conclude that the asymmetry of the magnetic field, both in strength and in orientation, establishes substantial hemispheric differences in the neutral wind and plasma drift in the high-latitude upper atmosphere, which can help to explain observed hemispheric differences with EDI/Cluster and CHAMP.

Beschreibung: [1]  We have identified 8 events with double-belt structure in the outer radiation belt from 110 CME-driven magnetic storms and 223 CIR-driven storms during 1994 to 2003 based on the SAMPEX data sets. Among them, 3 cases are related to CME-driven magnetic storms and 5 cases are related CIR-driven storms. All double-belt structure events in the outer radiation belt are found during the recovery phase of a magnetic storm for both CME- and CIR-related events—they usually start to form within 3–4 days after the onset of the magnetic storm. The pre-conditions needed to form a double-belt structure, for all the CME-related events, are found to be high solar wind dynamic pressure ( P dy ) and southward IMF Bz; Nevertheless, for the CIR-related events, they are found to be associated with high speed stream with southward interplanetary magnetic field, which is enhanced by a suitably orientated B y component.It is further found that the flux distributions of the double-belt structure can be fitted well with a simply exponential decay function of L ∗ . Based on the RBC index, the proportion of the total number of 1.5-6.0 MeV electrons inside the position of maximum fluxes to that outside the maximum fluxes keeps rising during the double-belt period, which implies that the acceleration mainly occurs at regions inside the location of maximum fluxes. We suggest that the plasmapause and the strong wave-particle interactions with VLF and ULF waves near it, play an important role in the development of the double-belt structures.

Beschreibung: [1]  The solar minimum period during 2008–2009 was characterized by lower thermospheric density than the previous solar minimum, and lower than any previously measured. Recent work [ Solomon et al ., 2010; 2011] used the NCAR Thermosphere-Ionosphere-Electrodynamics General Circulation Model to show that the primary cause of density changes from 1996 to 2008 was a small reduction in solar extreme-ultraviolet irradiance (EUV), causing a decrease in thermospheric temperature and hence a contracted thermosphere. There are similar effects in the ionosphere, with most measurements showing an F -region ionosphere that is unusually low in density, and in peak altitude. This paper addresses the question of whether model simulations previously conducted, and their solar, geomagnetic, and anthropogenic inputs, produce ionospheric changes commensurate with observations. We conducted a 15-year model run and obtained good agreement with observations of the global mean thermospheric density at 400 km throughout the solar cycle, with a reduction of ~30% from the 1996 solar minimum to 2008–2009. We then compared ionosonde measurements of the mid-day peak density of the ionospheric F -region ( N m F 2 ) to the model simulations at various locations. Reasonable agreement was obtained between measurements and the model, supporting the validity of the neutral density comparisons. The global average N m F 2 was estimated to have declined between the two solar minima by ~15%. In these simulations, a 10% reduction of solar EUV plays the largest role in causing the ionospheric change, with a minor contribution from lower geomagnetic activity, and a very small additional effect from anthropogenic increase in CO 2 .

Beschreibung: In this work, novel Y 2 Si 2 O 7 / ZrO 2 composites were developed for structural and coating applications by taking advantage of their unique properties, such as good damage tolerance, tunable mechanical properties, and superior wear resistance. The γ- Y 2 Si 2 O 7 / ZrO 2 composites showed improved mechanical properties compared to the γ- Y 2 Si 2 O 7 matrix material, that is, the Young's modulus was enhanced from 155 to 188 GPa (121%) and the flexural strength from 135 to 254 MPa (181%); when the amount of ZrO 2 was increased from 0 to 50 vol%, the γ- Y 2 Si 2 O 7 / ZrO 2 composites also presented relatively high facture toughness (〉1.7 MPa·m 1/2 ), but this exhibited an inverse relationship with the ZrO 2 content. The composition–mechanical property–tribology relationships of the Y 2 Si 2 O 7 / ZrO 2 composites were elucidated. The wear resistance of the composites is not only influenced by the applied load, hardness, strength, toughness, and rigidity but also effectively depends on micromechanical stability properties of the microstructures. The easy growth of subcritical microcracks in Y 2 Si 2 O 7 grains and at grain boundaries significantly contributes to the macroscopic fracture toughness, but promotes the pull-out of individual grains, thus resulting in a lack of correlation between the wear rate and the macroscopic fracture toughness of the composites.

Beschreibung: [1]  We report the statistical features of sporadic sodium layers (SSLs) and the thermospheric enhanced sodium layers (TeSLs) observed by a lidar chain located at Beijing (40.2°N, 116.2°E), Hefei (31.8°N, 117.3°E), Wuhan (30.5°N, 114.4°E), and Haikou (19.5°N, 109.1°E). The average SSL occurrence rate was approximately 46.0, 12.3, 13.8, and 15.0 hr per SSL at Beijing, Hefei, Wuhan, and Haikou, respectively. However, the TeSLs occurred relatively infrequently and were more likely to appear at low and high latitudinal sites. Both the SSLs and TeSLs at four lidar sites showed evident summer enhancements and correlated well with Es ( f o E s  〉  4  MHz ). The co-observations of SSLs at three lidar site pairs, i.e., Hefei – Beijing, Hefei – Wuhan and Hefei – Beijing, indicated that a large-scale SSL extended horizontally for at least a few hundred kilometers and exhibited a tidal-induced modulation. Moreover, the SSLs were better correlated for the Hefei – Wuhan and Hefei – Haikou pairs than the Hefei – Beijing pair, which suggested a difference in the dynamical/chemical process in mesosphere and lower thermosphere (MLT) between the Beijing site and the other sites.

Beschreibung: [1]  A highly sensitive all-sky EMCCD airglow imager has been operative in Longyearbyen, Norway (78.1°N, 15.5°E) since October 2011. The imager obtains the 630.0 nm all-sky images with an exposure time of 4 sec, which is about 10 times shorter than the conventional cooled CCD airglow imagers. This new equipment allows us to image the on-going structuring of polar cap patches in 2D fashion. Here, we report a case in which faint undulations appeared along the trailing edge of patches propagating in the central polar cap. The separation between the fingers in the undulations was about 50–100 km and the e -folding time of their growth was ~5 min. We suggest that the gradient-drift instability (GDI) is one of the possible generation mechanisms of the undulating structures. The reasons for this interpretation are 1) the asymmetry in the preference of structuring between the leading and trailing edges is qualitatively consistent with the GDI mechanism, and 2) the linear growth rate of GDI calculated by using electron density estimates from simultaneous EISCAT Svalbard radar observations is roughly consistent with the observed growth time of the fingers. Such “unstable polar cap patches" could be important sources of seed irregularities, which would eventually be broken down to smaller-scale density perturbations affecting the trans-ionospheric satellite communications in the central polar cap.

Beschreibung: [1]  As the Polar spacecraft apogee precessed through the magnetic equator in 2001, Polar encountered numerous substorm events in the region between geosynchronous orbit and 10 Re geocentric distance; most of them in the plasma sheet boundary layers. Of these, a small number were recorded near the neutral sheet in the evening sector. Polar/TIDE provides a unique perspective on the lowest energy ion plasma, showing that these events exhibited a damped wavelike character, initiated by a burst of radially outward flow transverse to the local magnetic field at ~ 80 km/sec. They then exhibit strongly damped cycles of inward/outward flow with a period of several minutes. After one or two cycles, they culminated in a hot plasma electron and ion injection, quite similar to those observed at geosynchronous orbit. Cold plasmaspheric plasmas comprise the outward flow cycles, while the inward flow cycles contain counter-streaming field-parallel polar wind like flows. The observed wave-like structure, preceding the arrival of an Earthward moving substorm injection front, suggests an outward displacement driven by the inward motion at local times closer to midnight, that is, a “snowplow” effect. The damped in/out flows are consistent with interchange oscillations driven by the arrival at the observed local time by an injection originating at greater radius and local time.

Beschreibung: The as-prepared BiFeO 3 ceramic shows a piezoelectric d 33 coefficient of −14 pC/N, that is, an obvious ferroelectric self-poling phenomenon. The temperature gradient between the two surfaces of BiFeO 3 ceramic was intentionally enlarged when BiFeO 3 was prepared with a rapid liquid sintering method. This temperature gradient and the corresponding thermal strain can introduce defect dipoles through separating bismuth vacancies from oxygen vacancies. A mass of these dipoles introduce a macroscopic internal electric field ( E in ) which downward poles BiFeO 3 ceramic during its cooling down process. As expected, an E in of 〉10 kV/cm is confirmed by the asymmetrical polarization/strain versus electric field curves.

Beschreibung: The effect of Ba content on the stress sensitivity of the antiferroelectric to ferroelectric phase transition in ( Pb 0.94− x La 0.04 Ba x )[( Zr 0.60 Sn 0.40 ) 0.84 Ti 0.16 ] O 3 ceramics is investigated through monitoring electric field-induced polarization and longitudinal strain under compressive prestresses. It is found that incorporation of Ba significantly suppresses the stress sensitivity of the phase transition, as manifested by slight decreases under prestresses up to 100 MPa in the maximum polarization ( P m ) and longitudinal strain ( x m ). The energy storage density is even increased under the mechanical confinement in compositions x  = 0.02 and 0.04. X-ray diffraction, transmission electron microscopy, and dielectric measurements indicate that the suppressed stress sensitivity is associated with the disruption of micrometersized antiferroelectric domains into nanodomains and the transition from antiferroelectric to relaxor behavior.

Beschreibung: Powders and nanoceramics composed of composites of CoFe 2 O 4 , CoFe 2 , and a small amount of FeO were prepared by heating CoFe 2 O 4 powder in reducing atmosphere and by sintering the product of reducing reaction at 350°C via spark plasma sintering technology. In the powders, increase in the molar ratios of CoFe 2 : CoFe 2 O 4 and a great change in magnetic parameters were observed with the change in heating temperature from 300°C to 400°C, and the dominance of dipole interaction over exchange coupling in the interparticle interactions was confirmed by the steps in magnetic hysteresis loops and the negative Henkel plots. However, in the nanoceramics, significant enhancement in exchange coupling was found when the sintering temperature was raised to 500°C and 650°C, which was confirmed by both the positivity of Henkel plot and the single-phase style of the magnetic hysteresis loop.

Beschreibung: Gas adsorption porosity measurement of geopolymers (GPs) is required for quantitative understanding of such mesoporous structures, but the complex nature of the GP system makes analysis difficult. Previous results in the literature are often ambiguous or contradictory. A systematic investigation of metakaolin GP gas adsorption results was conducted to optimize the use of this measurement technique and verify that results match known theory about GP structure. It was found that GP undergoes structural change upon degassing at 100°C or higher. If and only if this change is prevented by degassing at a lower temperature could it be shown that specific surface area and total gas adsorption increases with both increasing curing temperature and decreased Si : Al ratio. This observation is consistent with previous suggestions of increased zeolitic character under these conditions, where previous gas adsorption investigations had not observed this expected relationship. Hydrogen physisorption is proposed as a substitute technique for micropore isotherms in GPs due to the difficulty of removing trace gasses from GPs and the measurement effect of such gasses at high vacuum. A hydrogen physisorption isotherm qualitatively resembled an equivalent nitrogen micropore isotherm.

Beschreibung: In this work, the role of europium doping of glasses formulated in the ternary system ZnO – CdO – TeO 2 is described. The Eu -doped oxide glasses were prepared by the conventional melt-quenching method and by using three different compositions. Structural studies reveal that there exists a good affinity between Cd and some rare earth (RE) ions to form the crystalline phase. The X-ray diffraction (XRD) diagrams display that the structure of these glasses is amorphous and with the increase in CdO content and the compatibility of Eu 3+ , there is a tendency to form nanocrystals of CdTe 2 O 5 . The scanning electron microscopic (SEM) observation of their microstructure confirms the presence of phase separation. Differential thermal analysis (DTA) of these glasses showed small exothermic peaks noted around 450°C for the V2 glass and 480°C for V1 and V3 glasses, which could be attributed to the formation of these crystals. The infrared spectra showed a main absorption band around 800–600 cm −1 corresponding to the Te – O stretching mode in TeO 4 and TeO 3 groups. By optical absorption (OA), the band gap ( E g ) for each glass was determined; these values were 3.27, 3.14, and 3.3 eV for the V1–V3 glasses, respectively. Furthermore, the presence of Eu 3+ was detected in the 370–470 nm short-range wavelengths. The photoluminescence (PL) experiments of the glasses showed light emission due to the following transitions: 5D0 → 7F1, 5D0 → 7F2, 5D0 → 7F3, and 5D0 → 7F4.

Beschreibung: [1]  Accurate knowledge of the global distribution of magnetospheric chorus waves is essential for radiation belt modeling because it provides a direct link to understanding radiation belt losses and acceleration processes. In this paper, we report on newly developed models of the global distribution of chorus amplitudes based on in-situ measurements of IMF and solar wind parameters as well as geomagnetic indices using an artificial neural network technique. We find that solar wind speed and IMF B Z are the most influential parameters that affect the evolution of the magnetospheric chorus. The variations of chorus amplitudes in the outer ( L  ≥ 7) and in the inner (5 ≤  L  〈 7) regions, respectively, are well correlated with the variations of solar wind speed and IMF B Z . In addition, the solar wind parameter-based chorus model generally results in a slightly higher correlation between measured and modeled chorus amplitudes than any other models including geomagnetic indices AE, Kp, and Dst. The developed model shows that the chorus is amplified near the pre-noon sector during the geomagnetically disturbed conditions. With increasing southward IMF B Z the location of peak chorus amplitude moves from the pre-noon sector to the midnight sector, which is due to the enhanced electron injection near midnight. We also present a comparison of diffusive transport simulations for radiation belt electrons interacting with two newly developed chorus models, solar wind parameter-based and geomagnetic index-based chorus models. The comparison between two models shows that the modeling outside the plasmapause can affect the dynamic even inside the plasmasphere because the populations outside the plasmapause can act as seed population to radiation belt particles inside the plasmapause. One weakness of our chorus modeling is that it is trained during the early phase of solar cycle 24 where very few strong storms occurred. Therefore, our model might not be valid in reproducing the chorus activity under extremely disturbed conditions, which should be updated in the future once chorus measurements for such conditions become available.

Beschreibung: [1]  We investigate the storm-scale morphology of the magnetospheric magnetic field as well as underlying distributions of electric currents, equatorial plasma pressure and entropy for four Steady Magnetospheric Convection (SMC) events that occurred during the May 2000 and October 2011 magnetic storms. The analysis is made using the empirical geomagnetic field model TS07D, in which the structure of equatorial currents is not predefined and it is dictated by data. The model also combines the strengths of statistical and event-oriented approaches in mining data for the reconstruction of the magnetic field. The formation of a near-Earth minimum of the equatorial magnetic field in the midnight sector is inferred from data without ad hoc assumptions of a special current system postulated in earlier empirical reconstructions. In addition, a new SMC class is discovered where the minimum equatorial field is substantially larger and located closer to Earth. The magnetic field tailward of the minimumis also much larger, and the corresponding area of accumulated magnetic flux may occupy a very short tail region. The equatorial current and plasma pressure are found to be strongly enhanced far beyond geosynchronous orbit and in a broad local time interval covering the whole nightside region. This picture is consistent with independent recent statistical studies of the SMC pressure distributions, global MHD and kinetic RCM-E simulations. Distributions of the flux tube volume and entropy inferred from data reveal different mechanisms of the magnetotail convection crisis resolution for two classes of SMC events.

Beschreibung: [1]  Drifts in the Parker spiral interplanetary magnetic field are known to be an important component in the propagation of galactic cosmic rays, while they are thought to be negligible for Solar Energetic Particles (SEPs). As a result they have so far been ignored in SEP propagation modelling and data analysis. We examine drift velocities in the Parker spiral within single particle first-order adiabatic theory, in a local coordinate system with an axis parallel to the magnetic field. We show that, in the presence of scattering in interplanetary space, protons at the high end of the SEP energy range experience significant gradient and curvature drift. In the scatter-free case, drift due to magnetic field curvature is present. The magnitude of drift velocity increases by more than an order of magnitude at high heliographic latitudes compared to near the ecliptic; it has a strong dependence on radial distance r from the Sun, reaching a maximum at r ~1 AU at low heliolatitudes and r ~10 AU at high heliolatitudes. Due to the mass over charge dependence of drift velocities, the effect of drift for partially ionised SEP heavy ions is stronger than for protons. Drift is therefore likely to be a considerable source of cross field transport for high energy SEPs.

Beschreibung: [1]  We present a novel method for the automatic retrieval of local plasma density measurements from the Mars advanced radar for sub-surface and ionospheric sounding (MARSIS) active ionospheric sounder (AIS) instrument. The resulting large data set is then used to study the configuration of the Martian ionosphere at altitudes above ~300 km. An empirical calibration routine is used, which relates the local plasma density to the measured intensity of multiple harmonics of the local plasma-frequency oscillation, excited in the plasma surrounding the antenna in response to the transmission of ionospheric sounding pulses. Enhanced accuracy is achieved in higher-density ( n e  〉 150 cm − 3 ) plasmas, when MARSIS AIS is able to directly measure the fundamental frequency of the local plasma oscillation. To demonstrate the usefulness of this data set, the derived plasma densities are binned by altitude and solar zenith angle (SZA) in regions over weak ( nT) and strong ( nT) crustal magnetic fields, and we find clear and consistent evidence for a significant asymmetry between these two regions. We show that within the ~300-1200 km altitude range sampled, the median plasma density is substantially higher on the dayside in regions of relatively stronger crustal fields than under equivalent illuminations in regions of relatively weaker crustal fields. Conversely, on the nightside, median plasma densities are found to be higher in regions of relatively weaker crustal fields. We suggest that the observed asymmetry arises as a result of the modulation of the efficiency of plasma transport processes by the irregular crustal fields, and the generally horizontal draped interplanetary magnetic field (IMF).

Beschreibung: [1]  Global models of the Van Allen radiation belts usually include resonant wave-particle interactions as a diffusion process, but there is a large uncertainty over the diffusion rates. Here we present a new diffusion matrix for whistler mode chorus waves that can be used in such models. Data from seven satellites are used to construct 3,536 power spectra for upper and lower band chorus for 1.5 ≤  L ∗  ≤ 10, MLT, magnetic latitude 0 o  ≤ | λ m | ≤ 60 o and five levels of K p . Five density models are also constructed from the data. Gaussian functions are fitted to the spectra and capture typically 90% of the wave power. The frequency maxima of the power spectra vary with L ∗ and are typically lower than that used previously. Lower band chorus diffusion increases with geomagnetic activity and is largest between 21:00 and 09:00 MLT. Energy diffusion extends to a few MeV at large pitch angles 〉 60 o and at high energies exceeds pitch angle diffusion at the loss cone. Most electron diffusion occurs close to the geomagnetic equator (〈 12 o ). Pitch angle diffusion rates for lower band chorus increase with L ∗ and are significant at L ∗  = 8 even for low levels of geomagnetic activitywhile upper band chorus is restricted to mainly L ∗  〈 6. The combined drift and bounce averaged diffusion rates for upper and lower band chorus extend from a few keV near the loss cone up to several MeV at large pitch angles indicating loss at low energies and net acceleration at high energies.

Beschreibung: [1]  We report that radio science (RS) experiment onboard Mars Express (MEX) have observed three plasma layers in the nighttime ionosphere of Mars at altitudes ~80-100 km, ~120 km and ~160 km, which are reproduced by model calculation due to impact of meteoroid, solar wind proton and electron respectively. The densities of 21 ions (Mg + , Fe + , Si + , MgO + , MgCO 2 + , MgO 2 + , MgN 2 + , FeO + , FeO 2 + , FeN 2 + , FeCO 2 + , SiO + , SiCO 2 + , SiN 2 + , SiO 2 + , CO 2 + , N 2 + , O + , O 2 + , CO + , and NO + ) have been computed between altitude 50 km and 200 km. The model shows that all atmospheric ions (CO 2 + , N 2 + , O + , CO + , O 2 + and NO + ) are produced above 100 km due to solar wind electron and proton impact ionizations. The metallic ions are formed between 50 km and 100 km due to ablation of micrometeoroids. It is found that mass ~3.0 × 10 -4  g of incoming meteoroid is sufficient for meteor ablation and its characteristic flux ~4.0 × 10 -15  cm -2  s -1 could produce the nighttime metallic layer observed by MEX. The calculated electron densities are also compared with the occultation measurements made by Mars 4/5 in the nighttime ionosphere of Mars.

Beschreibung: [1]  Ultra Low Frequency (ULF) waves transfer energy in the Earth's magnetosphere through a variety of mechanisms that impact the Earth's ionosphere, radiation belts, and other plasma populations. Measurements of the electromagnetic portion of the energy transfer rate are an important source of information for assessing the importance of ULF waves relative to other energy transfer mechanisms as well as a diagnostic for studying the behavior of ULF waves. Using THEMIS satellite data, we examine the time averaged electromagnetic energy transfer rate, or Poynting vector, as a function of frequency and region of the magnetosphere; for this study, we focus on the direction and rate of energy transfer relative to the background magnetic field, comparing perpendicular and parallel transfer rates. This study extends earlier studies of the ULF wave Poynting vector that focused on narrower frequency ranges or specific regions of the magnetosphere; here, we consider the 3–50 mHz frequency range, all local time sectors, radial distances from 3 to 13 Re, and magnetic latitudes close to the equatorial plane. We measure time averaged Poynting vectors that range from  10 − 11 to 10 − 5 W / m 2 , with larger Poynting vector magnitudes occurring at largerradial distances and smaller frequencies. In every spatial region and frequency we examined, we found a large degree of scatter in both the Poynting vector magnitude and direction. The Poynting vector tends to be anisotropic at all frequencies,with more energy transferred along rather than across the background magnetic field. This preference for parallel energy transfer near the magnetic equator suggests that Joule dissipation in the ionosphere and the acceleration of auroral electrons are the largest sinks of ULF wave energy in the magnetosphere.

Beschreibung: [1]  Previous statistical studies have found a close relationship between high speed streams and high latitude geomagnetic activity. The speed by itself would increase the geoeffectivity of the solar wind. But it is also believed that pure Alfvénic fluctuations, often found in the trailing part of the streams, play a role in the solar wind driving of geomagnetic activity by amplifying the north-south component of the magnetic field ( B Z ), and thereby the dayside reconnection electric field. By automatically identifying slow and fast solar wind streams and by analysing them for more than one solar cycle, we aimed to study the relation between speed, Alfvénicity and B Z in the solar wind. It was found out that streams whose trailing parts are dominated by pure Alfvénic fluctuations, are the most geoeffective streams, on average. However, it is not the pure Alfvénic fluctuations themselves which cause the streams to be more geoeffective. There is only a variation of about 10 % in B Z due to the Alfvénicity of the fluctuations. Instead the streams are more geoeffective because the pure Alfvénic fluctuations tend to occur during high solar wind speed and strong IMF. There is a substantial variation within the solar cycle of how Alfvénic the solar wind streams are, and years with many extremely Alfvénic streams tends to have more days with moderately large geoeffectivity. The list of solar wind streams is included as extra material to this paper.

Beschreibung: [1]  Data Interpolating Empirical Orthogonal Functions (DINEOFs) are a data-based method for determining a few orthogonal basis functions that optimally reproduce a given data set. This technique is applied to meridional drift measurements performed by the Coupled Ion Neutral Dynamics Investigation (CINDI) onboard the Communication/Navigation Outage Forecasting System (C/NOFS) as well as electron density profiles derived from GPS Radio Occulations (RO) performed by COSMIC. The low densities of the equatorial ionosphere spanning 2009 - 2010 restricted quality drift measurements by CINDI to altitudes near perigee, limiting the local time coverage of measurements. Full local time descriptions may be obtained as perigee moves through all local times though this requires a minimum 67 day season. To increase the data coverage of the ionosphere CINDI data is supplemented with COSMIC GPS RO data. DINEOFs are applied to median meridional drift measurements as well as COSMIC measurements spanning 2009-10 and are used to make a best estimate of the equatorial ionosphere at locations not observed. The scattered distribution of COSMIC profiles as well as the physical relationship between meridional ion drifts and the distribution of density with altitude improve thequality of the reconstructions compared to using CINDI alone. The DINEOF reconstructions demonstrate that the annual anomomly of reduced ionospheric densities in June compared to December measured by COSMIC is coincident with a change in the meridional ion drifts at the geomagnetic equator measured by CINDI.

Beschreibung: The conductivity of nominal CaWO 4 , CaW 0.99 Ta 0.01 O 4–δ , 0.7( CaWO 4 )–0.3( La 0.99 Ca 0.01 NbO 4–δ ), and Ca 0.9 La 0.1 WO 4+δ has been studied by means of a.c. impedance measurements. Proton conductivity was observed for CaW 0.99 Ta 0.01 O 4–δ , which displayed exothermic hydration with enthalpy and entropy of –82 kJ/mol and –120 J/molK, respectively. The proton mobility in CaW 0.99 Ta 0.01 O 4–δ was low, with enthalpy and preexponential factor of mobility of 82 kJ/mol and 0.7 cm 2 K/Vs. The high enthalpy of mobility is interpreted to reflect association between the acceptor dopant and protonic defects, whereas the low preexponential factor of mobility may reflect a lower proton concentration than assumed. Rietveld refinement indicated low solubilities of La on Ca -site and Ta on W-site. Proton conductivity was also observed in undoped CaWO 4 , however, not in Ca 0.9 La 0.1 WO 4+δ . The conductivity of 0.7( CaWO 4 )–0.3( La 0.99 Ca 0.01 NbO 4–δ ) behaved much like that of undoped LaNbO 4 , likely due to a very low acceptor dopant concentration.

Beschreibung: A new lead-free BNT-based piezoelectric ceramics of (1 −  x ) Bi 0.5 Na 0.5 TiO 3 – x Bi ( Al 0.5 Ga 0.5 ) O 3 ( x  = 0, 0.02, 0.03, 0.04, and 0.05) were synthesized using a conventional ceramic fabrication method. Their structures and electrical properties were investigated. All the samples show a typical ferroelectric P ( E ) loops and S ( E ) curves at room temperature. The optimal properties are obtained at the composition of the x  = 0.03. The substitution of Bi ( Al 0.5 Ga 0.5 ) O 3 enhances piezoelectric constant and increases Curie temperature from 58 pC/N and 310°C of pure BNT to 93 pC/N and 325°C of the x  = 0.03. The temperature-dependent P ( E ) loops and S ( E ) curves of 0.97BNT–0.03BAG indicate that phase transition from ferroelectric to antiferroelectric takes place over a very wide temperature region from 80°C to 180°C. The results show that the introduction of BAG improves the electrical properties of BNT.

Beschreibung: [1]  It is well accepted that the propagation of electromagnetic ion cyclotron (EMIC) waves are bidirectional near their source regions and unidirectional when away from these regions. The generally believed source region for EMIC waves is around the magnetic equatorial plane. Here we describe a series of EMIC waves in the Pc1 (0.2-5 Hz) frequency band above the local He + cyclotron frequency observed in situ by all four Cluster spacecraft on 9 April 2005 at mid-magnetic latitudes (MLAT = ~33°-49°) with L = 10.7-11.5 on the dayside (MLT = 10.3-10.4). A Poynting vector spectrum shows that the wave packets consist of multiple groups of packets propagating bidirectionally, rather than unidirectionally, away from the equator, while the local plasma conditions indicate that the spacecraft are entering into a region sufficient for local wave excitation. One possible interpretation is that, while part of the observed waves are inside their source region, the others are either close enough to the source region, or mixed with the wave packets from multiple source regions at different latitudes.

Beschreibung: [1]  Using mesospheric temperature information obtained by Rayleigh lidar observations over Gadanki (13.5°N, 79.2°E) and temperature, chemical constituents and their exothermic chemical reaction heating rates obtained by Sounding of Atmosphere by Broadband Emission Radiometry (SABER) instrument onboard Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite over and near to Gadanki location, it is demonstrated that, the dominant role of chemical heating for the occurrence of a few large mesospheric inversion layer (MIL) events during January-February 2011. The heating rates due to exothermic chemical reactions among atomic oxygen (O), atomic hydrogen (H), molecular oxygen (O 2 ), ozone (O 3 ) and hydroxyl (OH) species are the key factors involved in the MIL formation. As relatively larger (lower) ozone mixing ratios are observed at the top (bottom) of the inversion layers, large heating rate (~ 15 K/day) is found to occur between 80 and 85 km due to the exothermic reaction between atomic hydrogen and ozone H + O 3  → OH + O 2 , which dominates all other important exothermic chemical reactions during these MIL events and the large volume emission rates of energy of O 2 , OH are found to be mostly due to the reaction between H and O 3. It is also demonstrated that dynamics plays a negligible role in the formation of these MILs as conditions for the convective and dynamic instability are found to be not satisfied during these MIL events.

Beschreibung: [1]  Bursty bulk flows (BBFs) play an important role for the mass, energy and magnetic flux transport in the plasma sheet, and the flow pattern in and around a BBF has important consequences for the localized energy conversion between the electromagnetic and plasma mechanical energy forms. The plasma flow signature in and around BBFs is often rather complicated. Return flows and plasma vortices are expected to exist at the flanks of the main flow channel, especially near the inner plasma sheet boundary, but also further down-tail. A dipolarization front (DF) is often observed at the leading edge of a BBF, and a flux pileup region (FPR) behind the DF. Here we present Cluster data of three FPRs associated with vortex flows observed in the mid-tail plasma sheet on August 15, 2001. According to the principles of Fu et al . [2011] and Fu et al . [2012c], two of the FPRs are considered to be in an early stage of evolution (growing FPRs). The third FPR is in a later stage of evolution (decaying FPR). For the first time, the detailed energy conversion properties during various stages of the FPR evolution have been measured. We show that the later stage FPR has a more complex vortex pattern than the two earlier stage FPRs. The two early stage FPR correspond to generators, E  ⋅  J  〈 0, while the later stage FPR only shows weak generator characteristics and is instead dominated by load signatures at the DF, E  ⋅  J  〉 0. Moreover, to our knowledge this is one of the first times BBF related plasma vortices have been observed to propagate over the spacecraft in the mid-tail plasma sheet at geocentric distances of about 18 R E . Our observations are compared to recent simulation results [ Wiltberger et al ., 2000; Birn et al ., 2011] and previous observations [ Fu et al ., 2011, 2012c; Pang et al ., 2012].

Beschreibung: We studied ancient enamels on gilded copper from a collection of archeological horse harness pendants of the Museo Instituto Valencia de Don Juan (Madrid, Spain) to test the benefits of a new, nondestructive analytical methodology based on chemometric analysis (i.e., Principal Component Analysis, PCA) on micro-ATR-FTIR spectral data and chemical quantification using SEM-EDS. The novelty of this approach was threefold: (i) PCA allowed the discrimination of the different harness pendants of known origin and attributed to the 14th and 15th centuries according to the chemical complex composition, nanostructure, glass weathering, and/or coloring mechanisms of each colored enamel, separately (i.e., red, purple, blue, and white), (ii) it is a cheap, easily available and nondestructive methodology that enables us to (iii) draw archeological conclusions about the quality of the manufacturing process, reassess the chronology of these objects and attempt to attribute them to different workshops according to the different traditional recipes identified. In particular, the enamels were made of alkali and/or alkaline earth lead-glass with a wide range of chemical compounds in the form of pigments or opacifiers. Two types of coloring mechanisms were identified, colloidal particles such as copper-ruby for red enamels, and ionic mechanisms such as Fe (II) and Co (II) to achieve a blue pigments; Mn (III) in the purple pigment; and two kind of white enamels were identified, i.e., tin oxide as an opacifier and uranium oxide. In addition, we established the reason for the poor state of conservation of some of the enamels by means of the identification of depolymerization and ion exchanges, well-known harmful effects of glass weathering, and finally a chronology was assigned for some of these pieces according to the enamel composition.

Beschreibung: Novel glass-ceramics with embedded thermoelectric Bi 2 Se 3 crystals were prepared from glass matrices in the Ge 20 Se 100− x Bi x ( x  = 5, 10, 12 mol%) system. Based on DSC results performed at different heating rates, characteristic activation energies ( E c ) and Avrami exponents ( n ) were obtained and analyzed by using Kissinger's relation, Ozawa's method, Augis–Bennett approximation and Matusita–Sakka theory. XRD results showed that pure Bi 2 Se 3 crystalline phase precipitated upon annealing at different temperatures for various time. The crystal size and crystalline fraction in the samples could be tuned by controlling the annealing time.

Beschreibung: In the present investigations nano size high alumina cements (HAC) were prepared by very effective co-melt precursor sintering technique from their metal nitrate precursors. The prime cementing phases observed were CA, CA 2 , and C 12 A 7 . The addition of nano structured cements in refractory castables has improved the thermo-chemical-mechanical properties to a significant extent. Each batch of low cement castables (LCC) was prepared from calcined Chinese bauxite, HAC, and superfine additives. The effect of HAC in bauxite castable with the additives similar to Silicon Carbide, reactive alumina, and micro-fine silica on the sinterability and properties of these castables was investigated. Physical properties such as apparent porosity and bulk density, mechanical properties such as hot modulus of rupture (HMOR), cold and hot modulus of rupture (CMOR), and cold crushing strength (CCS) of hydrated and sintered castables were studied. The sintered castables were also characterized for their solid phase compositions and microstructure using X-ray diffraction (XRD) and FE-SEM, respectively. In the castables new phases such as mullite, α-alumina were formed at the expense of bauxite and silica. Solid solution of mullite formed at high temperature acts as a bonding phase and is accounted for high HMOR, CMOR, and CCS values. These excellent properties of such castables may enable their uses in various applications such as refractory lining for fabrication of steel, aluminium, copper, glass, cement, chemicals, and ceramics.

Beschreibung: [1]  We use the measurements by the Vector Electric Field Investigation (VEFI) on board the C/NOFS satellite to study the local time, seasonal, and longitudinal dependent climatology of equatorial F region zonal plasma drifts during 2008-2011. These drifts are essentially westward during the day and eastward at night. Over Jicamarca, the satellite measurements are in good agreement with incoherent scatter radar drifts. Our data show strong longitudinal variations, particularly in the South American sector during the solstices. The equinoctial data exhibit short-lived and largely enhanced westward drifts near sunrise, and wave-4 structures from theearly afternoon to late night equinoctial periods. The nighttime eastward drifts are largest near the western American sector at all seasons. The June solstice post-midnight eastward drifts decrease sharply at longitudes of about 310˚ and have much smaller values in the entire eastern hemisphere. We also briefly discuss the relationship between the longitude dependent vertical and zonal plasma drifts.

Beschreibung: Zn 2 GeO 4 ceramic materials were synthesized by the solid-state method. Zn 2 GeO 4 powders were investigated with X-ray powder diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Oxygen defects in the Zn 2 GeO 4 ceramics were investigated by photoluminescence, Raman, and EDS spectra. Conductivity of Zn 2 GeO 4 was 0.18 S/cm at low temperature of 773 K, and its activation energy was 0.49 eV. The results showed that Zn 2 GeO 4 was a promising low-temperature electrolyte with high conductivity.

Beschreibung: [1]  Long-term variation in the geomagnetic Sq field and the cause of the variation were examined. 　The amplitude of the geomagnetic Y component (Sq(Y)) in equinox was averaged for each year, and adopted as a proxy of the Sq field. Sq(Y) was combined with the ionospheric conductivity estimated by the IRI model to determine the dynamo electric field and neutral wind velocity by using the geomagnetic main field strength. It was found that the solar activity dependence of the Sq field could be almost completely attributed to the conductivity variation, and neutral winds tend to decrease when the solar activity increases Although the long-term variation in the dynamo field differed among observatories, these differences were mostly attributed to the locality of the geomagnetic secular variation, whereas the variations in neutral wind amplitude were nearly the same in all regions. On the other hand, no clear long-term variation in neutral wind was detected other than that by solar activity.

Beschreibung: This article details the influence of zirconium doping on the piezoelectric properties and relaxor characteristics of 94( Bi 1/2 Na 1/2 ) TiO 3 –6 Ba ( Zr x Ti 1− x ) O 3 (BNT–6BZT) bulk ceramics. Neutron diffraction measurements of BNT–6BZT doped with 0%–15% Zr revealed an electric-field-induced transition of the average crystal structure from pseudo-cubic to rhombohedral/tetragonal symmetries across the entire compositional range. The addition of Zr up to 10% stabilizes this transition, resulting in saturated polarization hysteresis loops with a maximum polarization of 40 μC/cm 2 at 5.5 kV/mm, while corresponding strain hysteresis measurements yield a maximum strain of 0.3%. With further Zr addition, the ferroelectric order is progressively destabilized and typical relaxor characteristics such as double peaks in the current density loops are observed. In the strain hysteresis, this destabilization leads to an increase of the maximum strain by 0.05%. These changes to the physical behavior caused by Zr addition are consistent with a reduction of the transition temperature T F-R , above which the field-induced transformation from the relaxor to ferroelectric state becomes reversible.

Beschreibung: Precursor glasses for the ferroelectric barium bismuth titanate ( BaBi 4 Ti 4 O 15 ) (BBiT) have been prepared by the melt-quench technique in the SiO 2 – K 2 O – BaO – Bi 2 O 3 – TiO 2 (SKBBT) glass system with and without Eu 2 O 3 doping. BBiT glass–ceramic (GC) nanocomposites have been derived from these glasses by controlled heat treatment. The structural properties of the GCs have been investigated using X-ray diffraction (XRD), electron microscopy (FE-SEM, TEM), and FT-IR reflectance spectroscopy. FE-SEM images show the formation of randomly oriented hexagonal rod-shaped crystals of 200–400 nm and TEM images show 10–20 nm crystallites. FT-IR spectra exhibit the characteristic bands of BBiT at 480, 585, and 680 cm −1 . The activation energy of crystallization ( E c ) varies from 295 to 307 kJ/mol. The dielectric constants (ε r ) of glass and GC nanocomposites increase with an increase in frequency up to 3.0 MHz and then decrease up to 5.0 MHz. Heat-treated GCs show higher ε r values, in the range 25–55, compared to the precursor glasses (20–37). Dielectric losses (tan δ) for all the samples increase from 0.005 to 1.0 with an increase in frequency from 100 Hz to 5.0 MHz. Excitation spectra were recorded by monitoring emission at 613 nm corresponding to the 5 D 0 → 7 F 2 transition. An intense 466 nm excitation band corresponding to the 7 F 0 → 5 D 2 transition was observed. Emission spectra were then recorded by exciting the glass samples at 466 nm. Longer heat-treatment times led to a 15-fold increase in the intensity of the red emission at 612 nm, attributed to the segregation of Eu 3+ ions into the low phonon energy BBiT crystallites. The hardness (3.8–5.1 GPa) and fracture toughness (1.8–3.5 MPam 0.5 ) values obtained in the GCs are high and suitable for structural applications.

Beschreibung: Carbon doping is known to be very effective for enhancing the high-field properties of magnesium diboride, MgB 2 , but not for the low-field properties. Here, we report that both the high- and the low-field properties can be improved simultaneously without doping by increasing the initial magnesium partial pressure, by simply reducing the size of the magnesium particles. It is shown that in situ processed bulk MgB 2 sintered with fine magnesium powders has superior superconducting properties compared with a bulk sample fabricated using coarse magnesium lumps. The change in the lattice parameters was almost negligible; however, a clear increase in lattice strain can be observed for the sample sintered with fine magnesium powders. The increase in the lattice strain results in an enhancement of the high-field properties. Furthermore, it has also been found that the low-field critical current density is not reduced, but rather slightly increased for the fine magnesium powder sample. This is due to a closer linkage among the grains that drastically improves grain connectivity. These findings demonstrate that the initial growth mechanism of MgB 2 is very crucial for its superior superconducting properties, and it especially indicates the importance of magnesium vapor pressure.

Beschreibung: Revisiting classic phase diagrams and chemical phase relations in the solid state of a very well-studied oxide system, such as the lithium aluminosilicate (LAS) system, can open a new window for the design of new advanced materials with improved properties. Crystal chemistry and phase equilibria are used to demonstrate the ability to design materials with particular desired properties in the alumina-rich corner of the LAS phase diagram. The experimental results demonstrate the alumina and β-eucryptite solid-state compatibility.

Beschreibung: This work reports the crystallization, microstructure, and surface composition of Cu In 0.7 Ga 0.3 Se 2 (CIGS) thin films grown by femtosecond pulsed laser deposition at different annealing temperatures. The structural and optical properties of the CIGS films were characterized by X-ray diffraction, Raman scattering, UV-visible spectroscopy, and Hall effect measurement. The results indicate that binary crystals of CuS e initially formed on the as-deposited film, but then completely turned into a quaternary chalcopyrite structure after annealing at 400°C. Phase transformation significantly affects the surface morphology, Hall properties, and band gap. Transmission electron microscopy further revealed that an interface between the Mo substrate and CIGS crystallites contains an amorphous layer even at the high temperature of 500°C. For the application of photovoltaic devices, we also report on the photoresponse of both as-deposited and annealed films as demonstrated by preliminary tests.

Beschreibung: Reactive sintering of 3 Ti : Sn :2 C and 3Ti:Sn:2C:0.6Fe powder mixtures is studied in the temperature range 510°C–1200°C under argon. It is demonstrated that the recently discovered Ti 3 SnC 2 phase is formed, provided that Fe is added to a 3 Ti : Sn :2 C reactant mixture within the synthesis conditions used. Using dilatometric and X-Ray diffraction analyses, the formation mechanism of Ti 3 SnC 2 is discussed. Results show that at low temperature (about 510°C), tin is consumed to form Fe x Sn y intermetallics. At high temperature (about 1060°C), tin is newly available to form Ti 3 SnC 2 due to the melting of Fe x Sn y . Then, the intermediate phases, TiC and Ti 2 SnC , and/or Ti 5 Sn 3 , TiC , C , and Ti are dissolved in the ( Fe  +  Sn ) liquid phase and Ti 3 SnC 2 very likely precipitate from the melt. The second part of the study deals with the optimization of the Fe content in the initial 3Ti:Sn:2C reactant powder mixture to synthesize samples with larger Ti 3 SnC 2 content by hot isostatic pressing.

Beschreibung: The effects of non-stoichiometry on the microstructure, oxygen vacancies, and piezoelectric properties of ( Na 0.5 K 0.5 ) x NbO 3 (NK x N, where x  =   0.98, 1.00, 1.01, and 1.02) ceramics doped with sintering aid CuTa 2 O 6 (CT) doping were investigated. X-ray diffraction (XRD) patterns indicated that a secondary phase formed in CT-doped NK x N (NK x NCT) ceramics with x  〈   1.00 and that a pure phase was obtained with x  ≥   1.00. The grain size of NK x NCT ceramics increased with increasing x value due to the formation of a liquid phase. The internal bias field, activation energy, and Raman analysis for NK x NCT ceramics showed that the number of induced oxygen vacancies increased with decreasing x value. The high mechanical quality factor ( Q m ) value obtained for NK x NCT ceramics did not correspond to a higher concentration of oxygen vacancies, illustrating that the suitable compensation (excess Na and K ) is more important than the concentration of oxygen vacancies to obtain the ceramics with high Q m values. The NK x NCT ceramics with x  =   1.01 exhibited excellent piezoelectric properties, with k p and Q m values of 39.9% and 2,070, respectively.

Beschreibung: Low-temperature sintering of β-spodumene ceramics with low coefficient of thermal expansion (CTE) was attained using Li 2 O – GeO 2 sintering additive. Single-phase β-spodumene ceramics could be synthesized by heat treatment at 1000°C using highly pure and fine amorphous silica, α-alumina, and lithium carbonate powders mixture via the solid-state reaction route. The mixture was calcined at 950°C, finely pulverized, compacted, and finally sintered with or without the sintering additive at 800°C–1400°C for 2 h. The relative density reached 98% for the sample sintered with 3 mass% Li 2 O – GeO 2 additive at 1000°C. Its Young's modulus was 167 GPa and flexural strength was 115 MPa. Its CTE (from R.T. to 800°C) was 0.7 × 10 −6  K −1 and dielectric constant was 6.8 with loss tangent of 0.9% at 5 MHz. These properties were excellent or comparative compared with those previously reported for the samples sintered at around 1300°C–1400°C via melt-quenching routes. As a result, β-spodumene ceramics with single phase and sufficient properties were obtained at about 300°C lower sintering temperature by adding Li 2 O – GeO 2 sintering additive via the conventional solid-state reaction route. These results suggest that β-spodumene ceramics sintered with Li 2 O – GeO 2 sintering additive has a potential use as LTCC for multichip modules.

Beschreibung: Pyrochlore-structured lanthanide stannate ceramic ( Ln 2 Sn 2 O 7 ) has been synthesized via a new complex precipitation method. A suite of characterization techniques, including FTIR, Raman, X-ray, and electron diffraction as well as nitrogen sorption were employed to investigate the structural evolution of the synthesized and calcined powder. Raman, XRD, and selected area electron diffraction results confirm the presence of the pyrochlore structure after calcination of the powder above 1200°C. TEM imaging shows fine crystallites gradually increased in size from approximately 100 nm to about 500 nm with higher calcination temperatures. Grain growth and powder densification upon increasing the calcination temperature was confirmed by nitrogen sorption results. This aqueous synthetic method provides a simple pathway for the preparation of homogeneous lanthanide stannate ceramics.

Beschreibung: [1]  We analyze data recorded from October 2010 to September 2011, during the ascending phase of the 24 th solar cycle, from an AIS-INGV (Advanced Ionospheric Sounder - Istituto Nazionale di Geofisica e Vulcanologia) ionosonde and a GISTM (GPS Ionospheric Scintillation and TEC Monitor) scintillation receiver, co-located at low-latitude in the Southern American longitudinal sector (Tucumán, 26.9°S, 294.6°E, mag. Lat. 15.5°S, Argentina). The site offers the opportunity to perform spread-F and GPS scintillation statistics of occurrence under the southern crest of the equatorial ionospheric anomaly. Spread-F signatures, classified into four types (strong range spread-F (SSF), range spread-F (RSF), frequency spread-F (FSF) and mixed spread-F (MSF)), the phase and amplitude scintillation index ( σ Φ and S 4 , respectively), the total electron content ( TEC ) and the rate of TEC ( ROT ) parameter, marker of the TEC gradients, that can cause scintillations, are considered. The seasonal behavior results as follows: the occurrence of all four types of spread-F is higher in summer and lower in winter, while the occurrence of scintillations peaks at equinoxes in the post-sunset sector and shows a minimum in winter. The correspondence between SSF and scintillations seems to be systematic, and a possible correlation between S 4 and FSF peaks is envisaged at the terminator. The investigation focused also on two particular periods, from 12 to 16 March 2011, and from 23 to 29 September 2011, both characterized by the simultaneous presence of SSF signatures and scintillation phenomena allowing to discuss the role of Travelling Ionospheric Disturbances as a strong candidate causing ionospheric irregularities.

Beschreibung: ABSTRACT [1]  Neutrons contribute a significant radiation dose at commercial passenger airplane altitudes. With cosmic ray energies 〉 1  GeV , these effects could in principle be propagated to ground level. Under current conditions, the cosmic ray spectrum incident on the Earth is dominated by particles with energies 〈 1  GeV . Astrophysical shocks from events such as supernovae accelerate high energy cosmic rays (HECRs) well above this range. The Earth is likely episodically exposed to a greatly increased HECR flux from such events. Solar events of smaller energies are much more common and short lived, but still remain a topic of interest due to the ground level enhancements (GLEs) they produce. The air showers produced by cosmic rays (CRs) ionize the atmosphere and produce harmful secondary particles such as muons and neutrons. Although the secondary spectra from current day terrestrial cosmic ray flux are well known, this is not true for spectra produced by many astrophysical events. This work shows the results of Monte Carlo simulations quantifying the neutron flux due to CRs at various primary energies and altitudes. We provide here lookup tables (described later) that can be used to determine neutron fluxes from proton primaries with total energies 1  MeV – 1 PeV . By convolution, one can compute the neutron flux for any arbitrary CR spectrum. This contrasts with all other similar work, which is spectrum dependent. Our results demonstrate the difficulty in deducing the nature of primaries from the spectrum of ground level neutron enhancements.

Beschreibung: [1]  Rayleigh lidar temperature observations over Gadanki show a few mesospheric inversion layer (MIL) events during 20-25 January 2007. The zonal mean removed SABER temperature shows warm anomalies around 50°E and 275°E indicating the presence of planetary wave of zonal wavenumber 2. The MIL amplitudes in SABER temperature averaged for 10°N-15°N and 70°E-90°E show a clear 2-day wave modulation during 20-28 January 2007. Prior to 20 January 2007, a strong 2-day wave (zonal wavenumber 2) is observed in the height region of 80-90 km and it gets largely suppressed during 20-26 January 2007 as the condition for vertical propagation is not favourable, though it prevails at lower heights. The 10-day mean zonal wind over Tiruneveli shows deceleration of eastward winds indicating the westward drag due to wave dissipation. The nightly mean MF radar observed zonal winds show the presence of alternating eastward and westward winds during the period of 20-26 January 2007. The two dimensional spectrum of Rayleigh lidar temperature observations available for the nights of 20, 22 and 24 January 2007 shows the presence of gravity wave activity with periods 18 min, 38 min, 38 min, and vertical wavelengths 6.4 km, 4.0 km, 6.4 km respectively. From the dispersion relation of gravity waves, it is inferred that, these waves are internal gravity waves rather than inertia gravity waves with the horizontal phase speeds of ~40 m/s, ~37 m/s and ~50 m/s respectively. Assuming the gravity waves are eastward propagating waves, they get absorbed only in the eastward local wind fields of the planetary wave thereby causing turbulence and eddy diffusion which can be inferred from the estimation of large drag force due to the breaking of gravity wave leading to the formation of large amplitude inversion events in alternate nights. The present study shows that, the mesospheric temperature inversion is caused mainly due to the gravity wave breaking and the inversion amplitude may get modulated by the interaction between gravity waves and planetary waves. The eddy diffusion associated with gravity wave drag may also cause suppression in the planetary wave activity.

Beschreibung: [1]  To evaluate whether ground magnetic responses traditionally viewed as signatures of substorm onset may be related to post-onset auroral streamers rather than to substorm onset seen in aurora, we have analyzed ground magnetic and all-sky image responses for 14 substorm onsets selected solely on imager coverage. We find evidence supporting this possibility, the response being approximately coincident for mid-latitude positive bay and Pi2 pulsation enhancements and for abrupt auroral zone H decreases at stations near a streamer. These are all signatures of current wedge formation, indicating that substorm current wedge formation may be more of a response to plasma sheet flow channels associated with post-onset streamers than to the process leading to auroral onset, and that the current wedge may develop via a series of distinctly narrower wedge-like structures. We also find evidence that periods of streamers can occur more than once during a substorm expansion phase, and can give magnetic signatures of multiple onsets even if there are no additional auroral onsets. Furthermore, the peak auroral zone H decreases are seen in association with streamers and at times varying from just a few minutes to well over a half hour after substorm auroral onset if there is a prolonged period of streamers. This indicates peak substorm AE and AL values are likely related to features of post-onset streamers and their locations relative to observing stations, and are not a measure of the strength of the substorm auroral onset processes. We discuss possible additional implications on substorm expansion phase development.

Beschreibung: [1]  We statistically examine the occurrence rate of electromagnetic ion cyclotron (EMIC) waves observed by AMPTE/CCE. We use the 8-Hz magnetic field dataset that covers the whole CCE mission period of nearly 4.5 years from Augutst 1984 to Janauary 1989, which is more than three times the period studied by Anderson et al. [1992] (~452 days). The large data volume allows us to evaluate the storm phase dependence of the spatial occurence pattern of EMIC waves. The major results of this study are summarized as follows. (a) The occurrence rate is below 5% on the nightside at all L. On the dayside the rate is 〈5% in the inner magnetosphere (L 〈 6), while it is higher than 5% in the outer magnetosphere (L ≥ 6), up to 25%. The highest rate appears in the afternoon sector. (b) The overall occurrence rate is higher for H-band events than He-band events, except for the opposite feature seen in the inner magnetosphere on the early afternoon-to-post midnight side (L 〈 6, 14 h 〈 MLT 〈 22 h). (c) H-band events occur frequently in the outer magnetosphere (L ≥ 7) in the afternoon sector, regardless of geomagnetic activity. Under quiet conditions, H-band events also occur in the outer magnetosphere on the morning side (4 h ≤ MLT 〈 8 h). (d) He-band events frequently occur in the inner magnetosphere (L 〈 7) on the pre-noon to dusk side (10 h ≤ MLT 〈 19 h) under disturbed conditions (Dst ≤ −50 nT). (e) The storm-time He-band waves are generated more frequently during the main phase than the recovery phase, with the main-phase wave excitation seen toward the afternoon-side outer magnetosphere (L 〉 7). The results indicate two independent major processes that cause EMIC wave excitation in the Earth's magnetosphere: one externally triggers H-band waves on the dayside, and the other internally excites He-band waves on the dusk to afternoon side. We suggest that the former is due to solar wind compression which leads to perpendicular adiabatic ion heating and in turn an increase in temperature anisotropy, and that the latter is caused by injections of new, highly energetic ion population from the plasma sheet, with its velocity distributions becoming pancake-like on the dusk-to-afternoon side. The frequent occurrence seen on the afternoon side, at a wide L range, and during the main/development phase, strongly suggests the significant role of the sunward surge of the plasmasphere and plasma plumes in the injection-associated (i.e., storm-time) EMIC wave generation.

Beschreibung: Ceramics have played a crucial role in the development of fission based nuclear power, in glass & glass composite high level wasteforms, in composite cements to encapsulate intermediate level wastes (ILW) and also for oxide nuclear fuels based on UO 2 and PuO 2 /UO 2 mixed oxides. They are also used as porous filters with the ability to absorb radionuclides (RN) from air and liquids and are playing a key role in the cleanup at Fukushima. Non-oxides also find current fission applications including in graphite moderators and B 4 C control rods. Ceramics will continue to be significant in the near-term expansion of nuclear power via next-step developments of fuels with inert matrices or based on thoria and in wasteforms using alternative composite cements or single or multiphase ceramics that can host Pu & other difficult RN. Longer term advances for Generation IV reactors, which will operate at higher temperatures & with higher fuel burn-up require innovative fuel developments potentially via carbides & nitrides or composite fuel systems. Novel non-thermal (cement-like) and thermal techniques are currently being developed to treat some of the difficult legacy wastes. Non-thermally derived wasteforms developed from geopolymers, composite cements, hydroceramics, and phosphate-bonded ceramics and thermally derived wasteforms made by Hot Isostatic Pressing and fluidized bed steam reforming (FBSR) as well as vitrification techniques based on cold crucible melting (CCM), Joule-heater in-container melting and plasma melting (PM) are described. Future developments in waste treatment will be based on separation technologies for partitioning individual RN along with design & construction of RN-containing ceramic targets for inducing transmutation reactions. Near demonstration actinide-hosting ceramic wasteforms including multiphase Synroc systems are described. Opportunities also exist for ceramics in structural applications in Generation IV reactors such as composite SiC / SiC and C / C for fuel cladding and control rods and MAX phases and ultrahigh-temperature ceramics (UHTCs) may find near core fuel coating and cladding applications. Uses of ceramics in fusion reactor systems will be both functional (ceramic superconductors in magnet systems for plasma control and in Li silicate breeder blankets in tokamaks) and structural including as sapphire diagnostic windows, graphite diverters, and plasma facing C and UHTCs. In all these cases, performance is limited by poorly understood radiation damage and interface controlled processes, which demands a combined modeling/experimental approach.

Beschreibung: [1]  We performed a statistical study of downward moving protons and alpha particles of ~ keV energy (assumed to be of solar wind origin), inside the Martian induced magnetosphere from July 2006 to July 2010. Ion and electron data are from the Analyzer of Space Plasma and Energetic Atoms (ASPERA-3) package onboard Mars Express. We investigated the solar wind ion entry into the ionosphere, excluding intervals of low altitude magnetosheath encounters. The study compares periods of quiet solar wind conditions and periods of solar wind pressure pulses, including interplanetary coronal mass ejections and corotating interaction regions. The solar wind ion precipitation appears localized and/or intermittent, consistent with previous measurements. Precipitation events are less frequent and the precipitating fluxes do not increase during pressure pulse encounters. During pressure pulses the occurrence frequency of observed proton precipitation events is reduced by a factor ~3 and for He 2+ events the occurrence frequency is reduced by a factor ~2. One explanation is that during pressure pulse periods, the mass loading of the solar wind plasma increases due to a deeper penetration of the interplanetary magnetic flux tubes into the ionosphere. The associated decrease of the solar wind speed thus increases the pile-up of the interplanetary magnetic field on the dayside of the planet. The magnetic barrier becomes thicker in terms of solar wind ion gyroradii, causing the observed reduction of H + /He 2+ precipitations.

Beschreibung: [1]  We present THEMIS observations of a " Spontaneous Hot Flow Anomaly" (SHFA) upstream from the pre-noon bow shock at 0431 UT on August 12, 2007. Although the SHFA exhibited the greatly heated and deflected solar wind plasmas used to identify hot flow anomalies (HFAs), it did not result from the standard mechanism invoked for the formation of HFAs, namely the interaction of an interplanetary magnetic field (IMF) discontinuity with the bow shock. We employ THEMIS A, B, C, and D observations to describe the evolution of the event from a proto-SHFA exhibiting regions of depressed magnetic field strength and density but little evidence for plasma heating or flow deflection, to a well-developed SHFA further downstream. These observations show that SHFA can be generated without the presence of an IMF discontinuity and are therefore a new category of HFAs.

Beschreibung: The promotion of zircon ( ZrSiO 4 ) crystallization by ZnO from a zirconium-based frit glaze was studied and the possible mechanism was discussed. X-ray diffraction was used to analyze the relative quantities of zircon and other transitional crystals in the samples. The results show that ZnO can significantly decrease the crystallization temperature of zirconium-based glaze, depress the formation of Ca 2 ZrSi 4 O 12 , and promote the devitrification of transitional crystals t - ZrO 2 and Ca 2 ZnSi 2 O 7 , as well as lead to the formation of more zircon than the ZnO -free glaze. It was also found that zircon not only can form from the interaction between t - ZrO 2 and SiO 2 but also can devitrify directly from the glass phase of zirconium-based glaze.

Beschreibung: Barium-substituted CsAlSi 2 O 6 pollucites, Cs x Ba (1− x )/2 AlSi 2 O 6 , and barium- and iron-substituted pollucites, Cs x Ba (1− x )/2 Al x Fe 1− x Si 2 O 6 and Cs x Ba 1− x Al x Fe 1− x Si 2 O 6 were synthesized with 1 ≥  x ≥ 0.7 using a hydrothermal synthesis procedure. Rietveld analysis of X-ray diffraction data confirmed the substitution of Ba for Cs and Fe for Al , respectively. The crystallographic analysis also describes the effects of three different types of pollucite substitutions on the pollucite unit cell: Ba 2+ for Cs 1+ cation results in little effect on cell dimensions, intermediate concentrations of Ba 2+ and Fe 3+ substitution result in net minor expansion due to Fe 3+ addition, and large Ba and Fe substitutions result in overall framework contraction. Elemental analysis combined with microscopy further supports the phase purity of these new phases. These materials can be used to study the stability of CsAlSi 2 O 6 as a durable ceramic waste form, which could accommodate with time Cs and its decay product, Ba . Furthermore, success in iron substitution for aluminum into the pollucite lattice predicts that redox charge compensation for Cs cation decay is possible.

Beschreibung: Nitrogen-doped mullite fibers were first synthesized through the nitridation of Al 2 O 3 – SiO 2 gel fibers in NH 3 . The results showed that nitrogen take-up began at 800°C, reached the maximum at 900°C, and then decreased with increasing temperature. The ceramic fibers nitridated at 900°C were essentially amorphous, but contained a small amount of nano-sized Al – Si spinel crystals. Mullite was formed after nitridation at 1200°C, accompanied by crystallization of χ- SiAlON and δ- Al 2 O 3 . The incorporation of nitrogen resulted in the formation of a variety of nitrogen-containing crystalline phases. The grain size of the mullite fibers can be adjusted by changing of the nitrogen content.

Beschreibung: The solubility limit of Ca in 99.99% pure α- Al 2 O 3 (alumina) was measured using a wavelength dispersive spectrometer mounted on a scanning electron microscope. Al 2 O 3 samples were equilibrated at a concentration which ensured saturation of the Al 2 O 3 grains with Ca , and were quenched in water from 1600°C. The results were compared with those from samples which were furnace cooled from 1600°C. For the quenched samples, the Ca solubility limit was found to be 51 ± 1 ppm, which is significantly larger than the solubility limit for samples which were furnace cooled (26 ± 1 ppm).

Beschreibung: [1]  The two primary methods responsible for solar wind magnetosphere coupling are magnetic reconnection and the viscous interaction. The viscous interaction is generated due to the antisunward dragging of plasma inside the magnetopause by the plasma flowing in the magnetosheath, creating a return flow deeper inside the magnetosphere and producing a circulation pattern. This viscous circulation pattern is mapped into the ionosphere via magnetic field lines, which results in ionospheric electric field in the non-rotating Earth's frame. We measure this interaction in terms of an electric potential, the viscous potential. In this paper, we use the results obtained from the LFM simulation model during periods of purely northward IMF for different solar wind velocity and ionospheric conductivity, showing a reduction of the viscous potential with increasing magnitude of northward IMF. The viscous potential is found to settle around 5-10 kV for large + B z values. The decrease in viscous potential was found to be associated with a weak or non-existent sunward plasma flow in the nightside plasmasheet. Instead, the return flow to the dayside occurs at high latitudes and is associated with the reconnection topology and dynamics that occur during northward IMF periods. We also show that the magnetosphere remains closed during purely northward IMF, except for two small regions-one on each hemisphere, where the magnetic reconnection occur. We argue that the reduction of the viscous potential is due to a reduction of the velocity shear across the magnetopause and the lack of sunward convection in the equatorial tail.

Beschreibung: [1]  We present an analytical model of the Poynting flux that is generated by the interaction between the plume of Enceladus and Saturn's magnetospheric plasma. Our purpose is to analyze the influence of two key elements of Enceladus’ magnetospheric interaction on the electromagnetic energy radiated away in the moon's Alfvén wings. First, the north-south asymmetry of the obstacle generates a system of hemisphere coupling currents which allows a transport of electromagnetic energy into Saturn's northern hemisphere, even if the field-aligned currents connecting to the plume are completely blocked at the non-conducting icy crust of Enceladus. Second, the presence of electron-absorbing dust grains within the plume was recently found to drastically modify the electromagnetic field configuration within Enceladus’ Alfvén wings (Anti-Hall effect), thereby also altering the energy flux radiated away from the interaction region. By systematically studying the impact of varying strengths of the hemisphere coupling currents and varying electron absorption fractions on the energy flux, we come to the following conclusions: (1) The integrated Poynting flux into Saturn's southern hemisphere always exceeds the integrated flux into the northern hemisphere. In particular, the power transmitted towards the south may become several orders of magnitude larger than the power transmitted towards the north. (2) The search for Enceladus’ auroral footprint has so far mainly focused on Saturn's northern hemisphere. However, based on the Poynting fluxes radiated away by the interaction, detections of the footprint should occur more likely in the giant planet's southern hemisphere, if no other far-field effects play a role. (3) Electron absorption by the dust grains within the plume makes a measurable contribution to the energy flux. Thus, changes in the brightness of the observed footprints cannot exclusively be ascribed to variations in the incident magnetospheric flow conditions or the neutral gas content of the plume, but variations in the properties of the dust component need to be taken into account as well.

Beschreibung: [1]  Suprathermal singly-charged molecular ions, O 2 + (at ~32 Da/e) and the Mass-28 ion group 28 M + (ions at ~28 Da/e, with possible contributions from C 2 H 5 + , HCNH + , N 2 + , and/or CO + ), are present throughout Saturn's ~4-20 Rs (1 Saturn radius, Rs = 60,268 km) near-equatorial magnetosphere from mid-2004 until mid-2012. These ~83-167 keV/e heavy ions measured by Cassini's CHarge-Energy-Mass Spectrometer, CHEMS, have long-term temporal profiles that differ from each other and differ relative to the dominant water group ions, W + (O + , OH + , H 2 O + , and H 3 O + ). O 2 + /W + , initially ~0.05, declined steadily until equinox in mid-2009 by a factor of ~6, and 28 M + /W + , initially ~0.007, declined similarly until early-2007 by a factor of ~2. The O 2 + /W + decline is consistent with Cassini's in-situ ring-ionosphere thermal ion measurements, and with proposed and modeled seasonal photolysis of Saturn's rings for thermal O 2 and O 2 + . The water ice dominated main rings and Enceladus plume depositions thereon are the two most likely O 2 + sources. Enceladus' dynamic plumes, though, have no known long-term dependence. After declining, O 2 + /W + and 28 M + /W + levels remained low until late-2011 when O 2 + /W + increased, but 28 M + /W + did not. The O 2 + /W + increase was steady and became statistically significant by mid-2012, indicating a clear increase after a decline, that is, a possibly delayed O 2 + “seasonal” recovery. Ring insolation is driven by solar UV flux which itself varies with the sun's 11-year activity cycle. The O 2 + /W + and 28 M + /W + declines are consistent with seasonal ring insolation. No O 2 + /W + response to the late-2008 solar-cycle UV minimum and recovery is evident. However, the O 2 + /W + recovery from the post-equinox baseline levels in late-2011 coincided with a strong solar UV enhancement. We suggest a scenario/framework in which the O 2 + observations can be understood.

Beschreibung: [1]  We analyze ion temperature data near 350 km altitude over the years 1966–2012 to seek explanations for three outstanding questions concerning the long-term cooling observed in the upper thermosphere: (1) why is the cooling so much larger than expected, (2) why has the cooling lasted so long, and (3) why is the thermospheric density response to the cooling so small? We speculate that gravity waves may cause this cooling and provide answers to these questions. Recent simulations have shown that gravity waves are expected to cool the upper thermosphere by an amount comparable to that observed over our data timeline. A gravity-wave proxy formed from the non-tidal fluctuations in temperature shows a positive long-term trend throughout its timeline, consistent with the increasing cooling observed. The time scales of the long-term trend and its decadal fluctuations are characteristic of the ocean, not the atmosphere. We suggest that the following scenario may explain these behaviors: (a) the climate regime shift of 1976–1977 launched slow Rossby waves across the oceans which continue to propagate to this day, (b) winds over this increasingly corrugated ocean have launched increasing fluxes of gravity waves into the atmosphere, (c) these increasing fluxes of gravity waves have propagated to the thermosphere to produced increasing amounts of cooling. The strong thermospheric cooling seen would be expected to produce thermospheric density declines much larger than those observed via satellite drag. These temperature and density results would be compatible if the turbopause were lowered 4 km over the time span of observations.

Beschreibung: The possibility of developing large solid oxide fuel cell (SOFC) stacks based upon 25 cm 2 ceramic oxide anode-supported cells is investigated. Planar fuel cells comprising strontium titanate-based anode support impregnated with active catalysts were prepared using a combination of deposition techniques. The fuel cell tests performed in a semisealed rig have shown power densities of 185 mW cm −2 at 850°C using humidified hydrogen as fuel and air as oxidant. The structure and evolution of the catalytically active impregnated materials-10 mol% Gd -doped CeO 2 and nickel- are analysed using electron microscopy at the end of the fuel cell test, revealing that a ceria and nickel layer surrounds the titanate backbone grains while ~50–150 nm spherical-like nickel particles uniformly decorate this top layer.

Beschreibung: Structural and dielectric properties of (1− x ) BaTiO 3 – x Bi ( Mg 1/2 Ti 1/2 ) O 3 ( x  = 0.1–0.5) were investigated to understand the binary system and utilize it for high-voltage, high energy density capacitors. The solubility limit for Bi ( Mg 1/2 Ti 1/2 ) O 3 in a BaTiO 3 perovskite was between x  = 0.4 and x  = 0.5. A phase with pseudocubic symmetry was formed for x  = 0.1–0.4; a secondary phase developed at x  = 0.5. Dielectric measurements showed highly diffusive and dispersive relaxor-like characteristics from 10 to 40 mol% of Bi ( Mg 1/2 Ti 1/2 ) O 3 . These compositions also showed high relative permittivity with low-temperature coefficients of permittivity over a wide range of temperatures −100°C–600°C. Relaxation behavior was quantitatively investigated using the Vogel–Fulcher model, which revealed the activation energy of 0.17–0.22 eV. Prototyped multilayer capacitors of 18 mm × 17 mm × 4 mm dimensions with a capacitance of 12.5 nF at 1 kHz were successfully constructed and demonstrated multiple charge–discharge characteristics up to 10 kV.

Beschreibung: K 3 Gd ( PO 4 ) 2 : RE 3+ (RE = Eu, Tb) are prepared by solid-state reaction and their photoluminescence (PL) properties are investigated under UV and VUV excitation, respectively. The obtained experimental data show that no energy transfer happens among the activator ions Tb 3+ or Eu 3+ under UV excitation. Under 147-nm excitation, the strongest emission intensity of K 3 Gd ( PO 4 ) 2 : RE 3+ (RE = Eu, Tb) is obtained when the activator ions Tb 3+ or Eu 3+ concentration is 0.8 mol, the integrate emission intensity of K 3 Gd 0.2 (PO 4 ) 2 :0.8Tb 3+ is about 204% of commercial phosphor Zn 1.96 SiO 4 :0.04 Mn 2+ with chromaticity coordinates of (0.340, 0.561) and the decay time of about 5.09 ms under 147-nm excitation. We analyze the experimental data and propose a possible energy-transfer mechanism under 147-nm excitation.

Beschreibung: The 0.72 Bi ( Fe 1− x Al x ) O 3 –0.28 BaTiO 3 ( x  = 0, 0.01, 0.03, 0.05, and 0.07, abbreviated as BFA x – BT ) lead-free high-temperature ceramics were prepared by the conventional ceramic processing. Systematic investigation on the microstructures, crystalline structures, dielectric and piezoelectric properties, and high-temperature stability of piezoelectric properties was carried out. The crystalline structures of BFA x –BT ceramics evolve from rhombohedral structure with x 〈  0.01 to the coexistence of rhombohedral structure and pseudocubic phases with x  ≈ 0.01, finally to pseudocubic phases when x 〉  0.03. Remarkably high-temperature stability with near-zero temperature coefficient of piezoelectric properties ( TCk p ), together with improved piezoelectric properties has been achieved for x  = 0.01 BFA x –BT ceramics. The BFA x –BT( x  = 0.01) ceramics simultaneously show the excellent piezoelectric properties of d 33  = 151 pC/N, k p  = 0.31 and super-high-temperature stability of T d  = 420°C, TCk p  = 1 × 10 −4 . It is considered that the observed strong piezoelectricity and remarkably high-temperature stability should be ascribed to the phase coexistence of rhombohedral and pseudocubic phases. The rhombohedral phases have a positive TCk p value and the pseudocubic phases possess a negative TCk p value. Thus, the TCk p value of BFA x –BT ceramics can be tuned by composition of x .

Beschreibung: [1]  We introduce a new model to study Jupiter's magnetosphere and how it interacts with the solar wind. We first derive a set of one-fluid MHD equations to consistently include the ion-neutral collisions in Jupiter's ionosphere, and the mass-loading in the Io torus. The mass-loading and the subsequent radial mass transport in Jupiter's magnetosphere leads to a deviation from full corotation of the magnetospheric plasma. Ion-neutral collisions in Jupiter's ionosphere and subsequent transport of angular momentum out into the magnetosphere acts to spin up the magnetosphere's plasma. Our model explicitly includes mass-loading in the Io plasma torus and an inner boundary region, which represents the effects of Jupiter's ionosphere. We present the results of five model runs where different mass-loading rates and ionospheric conductances are used. For these model runs, we consider an anti-parallel interplanetary magnetic field and a strong solar wind dynamic pressure, resulting in a compressed magnetosphere. The results are compared with analytical models, in situ measurements, and remote-sensing observations. Our azimuthal velocity profiles and the position of the corotation break-down are in quantitative agreement with theoretical predictions by Hill [1979, 2001] and Saur et al . [2004a], and Voyager observations [ McNutt et al ., 1981]. The total current flowing into and out of the ionosphere is 48.7 MA, which is in agreement with estimates from measurements and analytical models. Using the field aligned electric current j ║ to determine the position of the aurorae, we find that our main auroral oval is associated, as expected, with the position of the corotation break-down (between 20.6 R J and 30.1 R J for the different model runs). The discontinuity in the main oval observed by Radioti et al . [2008] is also present in our results, where it is caused by an asymmetry in the pressure distribution, due to the interaction between the rotating plasma and the magnetopause.

Beschreibung: Owing to the widespread presence of electromagnetic interferences, it is necessary to develop new materials with excellent high-temperature electromagnetic wave (EM) absorption properties. In the present work, ZnO is infiltrated into porous ZrSiO 4 substrates to form ZnO / ZrSiO 4 composite ceramics using sol-gel process. The doping of aluminum results in the improvement of electrical conductivity and the significant change in the morphology of ZnO . With the increase in environment temperature during measurement, the permittivity of the composite ceramics increases first and then decreases dramatically, which is attributed to the change in conductive loss. The electrical conductivity increases with increasing measurement temperature. However, the concentration of oxygen vacancies decreases under air atmosphere when the measurement temperature increases continuously, which results in the reduction in conductivity. Therefore, permittivities of the undoped and doped ceramics measured at 673 K are higher than the ones at the other temperatures. The composite ceramics maintain a relatively high EM absorption coefficient, low reflection coefficient (RC), and wide effective absorption bandwidth at environment temperatures up to 773 K. As a result, we conclude that the ZnO / ZrSiO 4 composite ceramics exhibit a promising prospect as a kind of high-temperature EM absorbing material.

Beschreibung: [0001] textured alumina ceramics with a fine grain size were fabricated between 1400°C and 1600°C via templated grain growth (TGG) using fine alumina platelets (~0.6 and ~3 μm diameter) aligned by tape casting in either a 50 nm α- Al 2 O 3 matrix powder, or in a seeded boehmite sol. The 3 μm templates could be readily aligned by tape casting in both matrices (orientation parameters r  = 0.27 and 0.18, respectively), whereas 0.6 μm diameter templates were well aligned in the seeded boehmite sol only ( r  = 0.29). Improved alignment in boehmite sols is attributed to inorganic gelation, resulting in a strongly pseudo-plastic rheology that preserves template alignment against the influence of Brownian motion. The in situ formation of fine α- Al 2 O 3 matrix after transformation in the seeded boehmite system results in a higher driving force for TGG and improves texture development. The combination of 3 μm templates with a seeded boehmite matrix results in extremely high texture qualities (texture fraction f  = 0.97–0.99, r  = 0.17) while maintaining a relatively fine grain size (5–10 μm in diameter and 1.5–3 μm in thickness). Although undoped samples can be fully textured at 1600°C, adding as little as ~0.25 wt% CaO / SiO 2 dopant improves TGG kinetics and yields full texture at 1400°C.

Beschreibung: [1]  In this study we quantify the contribution of individual large-scale waves to ionospheric electrodynamics, and examine the dependence of the ionospheric perturbations on solar activity. We focus on migrating diurnal tide (DW1) plus mean winds, migrating semidiurnal tide (SW2), quasi-stationary planetary wave 1 (QSPW1), and nonmigrating semidiurnal westward wave 1 (SW1) under northern winter conditions, when QSPW1 and SW1 are climatologically strong. From TIME-GCM simulations under solar minimum conditions, it is found that the mean winds and DW1 produce a wave 2 pattern in equatorial vertical E  ×  B drift that is upward in the morning and around dusk. The modeled SW2 also produces a wave 2 pattern in the ionospheric vertical drift that is nearly a half wave cycle out of phase with that due to mean winds and DW1. SW1 can cause large vertical drifts around dawn, while QSPW1 does not have any direct impact on the vertical drift. Wind components of both SW2 and SW1 become large at mid to high latitudes in the E-region, and kernel functions obtained from numerical experiments reveal that they can significantly affect the equatorial ion drift, likely through modulating the E-region wind dynamo. The most evident changes of total ionospheric vertical drift when solar activity is increased are seen around dawn and dusk, reflecting the more dominant role of large F-region Pedersen conductivity and of the F-region dynamo under high solar activity. Therefore, the lower atmosphere driving of the ionospheric variability is more evident under solar minimum conditions, not only because variability is more identifiable in a quieter background, but also because the E-region wind dynamo is more significant. These numerical experiments also demonstrate that the amplitudes, phases and latitudinal and vertical structures of large-scale waves are important in quantifying the ionospheric responses.