ALBERT

Description: Direct coagulation casting of alumina suspension via controlled release of high valence counter ions (DCC–HVCI) using calcium citrate as coagulating agent was reported. Hydrolysis of glycerol diacetate shifts the pH of suspension to weakly acidic region which helps to decompose calcium citrate and release calcium ions. The effect of concentration of glycerol diacetate and calcium citrate on the pH and viscosity of alumina suspension was investigated at 25°C and 60°C, respectively. The pH of suspensions with glycerol diacetate and calcium citrate decreases to 8.6 and 7.5 treated at 25°C and 60°C, respectively. It is indicated that high viscosity is achieved by adding 2 vol% glycerol diacetate and 0.5 wt% calcium citrate which is enough to coagulate the suspension. Green body with compressive strength of 1.0 MPa is obtained by treating the alumina suspension with 2 vol% glycerol diacetate and 0.5 wt% calcium citrate at 60°C for 1 h. The alumina ceramics sintered at 1550°C have homogeneous microstructure with relative density above 99.0%.

Description: A series of lead-free perovskite solid solutions of (1 −  x ) Na 0.5 Bi 0.5 TiO 3 (NBT)— x BaSnO 3 (BSN), for 0.0 ≤  x  ≤ 0.15 have been synthesized using a high-temperature solid-state reaction route. The phase transition behaviors are studied using dielectric and Raman spectroscopic techniques. The ferroelectric to relaxor phase transition temperature ( T FR ) and the temperature corresponding to maximum dielectric permittivity ( T m ) are estimated from the temperature-dependent dielectric data. Dielectric studies show diffuse phase transition around ~335°C in pure NBT and this transition temperature decreases with increase in x . The disappearance of x -dependence of A 1 mode frequency at ~134 cm −1 for x  ≥ 0.1 is consistent with rhombohedral-orthorhombic transition. In situ temperature dependence Raman spectroscopic studies show disappearance and discontinuous changes in the phonon mode frequencies across rhombohedral ( x  〈 0.1)/orthorhombic ( x  ≥ 0.1) to tetragonal transition.

Description: Two mole percentage Er -doped ( K 0.5 Na 0.5 ) 1 −  x Li x NbO 3 ceramics have been prepared and their dielectric, ferroelectric, and photoluminescence (PL) properties have been investigated. Under an excitation of 980 nm, the ceramics exhibit intense up-conversion luminescent emission at 548 nm (green), weak emission at 660 nm (red) as well as strong down-conversion luminescent emission in near-infrared (NIR) (1.40–1.65 μm) and mid-infrared (2.60–2.85 μm) regions. Probably due to the induced structure distortion and reduced local symmetry, the PL intensities of the green, red as well as mid-infrared emissions are enhanced by the doping of Li + . Our results show that the Li-doping is effective in establishing a dynamic circulatory energy process to further enhance the PL intensity of the mid-infrared emission at the expense of the NIR emission. At the optimum doping level of Li + (~6 mol%), the full bandwidth at half maximum of the mid-infrared emission reaches a very large value of ~250 nm. The ceramics also exhibit good ferroelectric properties, and thus they should have great potential for multifunctional optoelectronic applications.

Description: We report a power conversion efficiency of ~0.01% in multistacking of BiFeO 3 /BiCrO 3 bilayer thin films used as active layers in a photovoltaic (PV) device. The films were epitaxially deposited by pulse laser deposition onto (100) oriented CaRuO 3 -coated LaAlO 3 substrates and were subsequently illuminated with 1 sun (AM 1.5). The fill factor is determined to be 0.31%, a remarkable value for ferroelectric- and multiferroic-based PV devices. Our results demonstrate that photocurrent density and photovoltage can be tuned by varying the thickness and number of respective bilayers in the improvement of PV properties of multiferroic heterostructures. The maximum photocurrent is generated at an optimal multilayer thickness of 60 nm, with its origin being mainly ascribed to the contribution of ferroelectric polarization.

Description: Temperature dependences of thermal and elastic properties, such as the Grüneisen parameters, thermal expansion, bulk modulus, and heat capacity of Ti 2 AlC and Cr 2 AlC , are studied by combining first-principles method and lattice dynamic calculation based on the quasi-harmonic model. Experimental thermal expansion coefficient is also measured for comparison. Thermal expansion coefficients of Ti 2 AlC and Cr 2 AlC show different trends: Ti 2 AlC exhibits anisotropic thermal expansion while Cr 2 AlC shows generally isotropic character. The mechanism is explored by investigating the isotropy or anisotropy of Grüneisen parameters (phonon anharmonicity and thermal pressure) and elastic stiffness (response to thermal pressure) of Ti 2 AlC and Cr 2 AlC . In addition, the calculated bulk modulus of Cr 2 AlC is higher at ambient temperature but decreases faster than the value of Ti 2 AlC as temperature increasing.

Description: The effects of process parameters on thermal barrier coating (TBC) formation and microstructural properties have been studied. Further understanding of the evolution of properties such as porosity and hardness is an important aspect in the design of efficient TBCs. Plasma-sprayed yttria-stabilized zirconia was coated onto mild steel substrates. The torch was held perpendicular to the substrate to form cone-shaped deposits. Standoff distance (SOD) (80, 90, and 120 mm) and time (15, 30, and 60 s) were altered to investigate the microstructural property relationships of the coatings. Shape characteristics of the coatings were measured via a coordinate measuring machine, and surface roughness measurements were acquired using a 3D optical profiler. The deposition efficiency and coating roughness were affected by SOD and the evolving contour of the underlying surface. Hardness and porosity profiles were mapped to display the effect of process parameters. Dynamic parameters such as particle trajectory, evolving impact angle and dwell time affected changes in porosity, hardness, and density for each coating profile.

Description: Wear resistance of ceramics can be improved by suppressing fracture, which can be accomplished either by decreasing the grain size or by reducing the size of the deformation zone. We have combined these two strategies with the goal of understanding the atomistic mechanisms underlying the plasticity-controlled friction and wear in nanocrystalline (nc) silicon carbide ( SiC ). We have performed molecular dynamics simulations of nanoscale wear on nc- SiC with 5 nm grain diameter with a nanoscale cutting tool. We find that grain-boundary (GB) sliding is the primary deformation mechanism during wear and that it is accommodated by heterogeneous nucleation of partial dislocations, formation of voids at the triple junctions, and grain pull-out. We estimate the stresses required for heterogeneous nucleation of partial dislocations at triple junctions and shear strength of GBs. Pile up in nc- SiC consists of grains that were pulled out during deformation. We compare the wear response of nc- SiC to single-crystal (sc) SiC and show that scratch hardness of nc- SiC is lower than that of sc- SiC . Our results demonstrate that the higher scratch hardness in sc- SiC originates from nucleation and motion of dislocations, whereas nc- SiC is more pliable due to additional mechanism of deformation via GB sliding.

Description: A composite geopolymeric material was synthesized from Bayer red mud combined with granulated blast-furnace slag. Thermal pretreatment was applied to improve the solubility of red mud in alkaline solution to promote geopolymerization. The dissolution efficiencies of alumina and silica reached a maximum when red mud was calcined at 800°C, resulting in the highest compressive strength of binders. It was demonstrated that a higher solubility of calcined red mud led to a higher strength of the composite binders. The characteristic microstructures of hydration products were studied to illustrate the geopolymerization process by XRD, FTIR and SEM. The results showed that aluminosilicates were dissolved in the alkaline solution to form nanostructural particulates during the early dissolution process, and then accumulated to form highly dense geopolymeric matrices through solidification reaction. The coexistence of geopolymer and C–(A)–S–H is suggested to contribute to the good performance of the composite binders.

Description: The crystals Gd 2 SiO 5 and Yb -doped Gd 2 SiO 5 were grown by Czochralski method successfully. Dielectric properties of the two crystals were investigated in the temperature range from 100 to 1100 K and the frequency range from 20 Hz to 10 MHz. Our results revealed that these crystals show intrinsic dielectric behavior in the temperature below room temperature, whereas in above room temperature, a relaxor-like dielectric anomaly and a metal–insulator transition were observed. It was found that the relaxor-like anomaly contains two dielectric relaxations. Impedance analysis showed that the low- and high-temperature relaxations are dipolar- and Maxwell–Wagner-type relaxation, respectively. The transition was found to be strongly related to oxygen vacancies, which leads to positive temperature coefficient of resistance and an abnormal dielectric behavior contrary to the conventional thermally activated behavior at temperatures near the transition temperature.

Description: [1]  We analyze the vertical component of vorticity and the horizontal divergence of the high-latitude neutral wind field in the lower thermosphere during the southern summer time for different interplanetary magnetic field (IMF) conditions with the aid of the National Center for Atmospheric Research (NCAR) Thermosphere Ionosphere Electrodynamics General Circulation Model (TIE-GCM), with the following results. (1) The mean neutral wind pattern in the high-latitude lower thermosphere is dominated by rotational flow, imparted primarily through the ion drag force, rather than by horizontally divergent flow. Poleward of -60° magnetic latitude the magnitude of relative vertical vorticity often exceeds the magnitude of planetary vertical vorticity. (2) The vertical vorticity depends on the IMF. (3) The difference vertical vorticity, obtained by subtracting values with zero IMF from those with non-zero IMF, is much larger than the difference horizontal divergence for all IMF conditions. (4) The effects of IMF penetrate down to 106 km altitude. To determine the processes that are mainly responsible for causing strong rotational flow in the high-latitude lower thermospheric wind fields, a term analysis of the vorticity equation is also performed, with the following results. (1) The magnitude of forcing terms on vertical vorticity is significant poleward of -60° magnetic latitude. (2) The primary forcing term that determines variations of the vertical vorticity is ion drag. This forcing is closely related to the flow of field-aligned current between the ionosphere and magnetosphere. Significant contributions to variations of the vorticity, however, can be made by the horizontal advection term. (3) The effects of the IMF on the ion drag forcing are seen down to around 106 km altitude. (4) The continual forcing of magnetic-zonal-mean B y -dependent vertical vorticity by ion drag can lead to strong polar vortices.

Description: Sol–gel-derived TiO 2 films were prepared by dip-coating from Ti (OC 3 H 7 i ) 4 –CH 3 COCH 2 COCH 3 –HNO 3 – H 2 O – C 2 H 5 OH solutions, and the effect of the H 2 O content in solutions on the crystallization of TiO 2 films during the heat treatment at 800°C was discussed. The crystalline phase, crystallite size, grain size, and refractive index of the TiO 2 films depended on the H 2 O / Ti (OC 3 H 7 i ) 4 mole ratios ( x ) in the coating solutions. Highly dense and crystalline rutile films were obtained at x  = 0.5–10, where the crystallites and grains became larger with increasing x . The further increase in x from 10 to 50 reduced the crystallite size and refractive index of the films, where anatase phase appeared at x  = 30–50.

Description: Dy 3+ -doped Li 8 Bi 2 ( MoO 4 ) 7 (LBM: Dy 3+ ) white-emitting phosphors have been prepared by sol-gel method at about 400~550°C low temperature. The electronic structure of Li 8 Bi 2 ( MoO 4 ) 7 is also calculated using density functional theory. The calculation results show that Li 8 Bi 2 ( MoO 4 ) 7 has a direct band gap with 2.63 eV, the top of the valence band and the bottom of the conduction band are dominated by O 2 p and Mo 4 d , respectively. The effect from Bi 3+ ions is so weak that it could be neglected, which is also be proved by the experimental results. The crystal structure and luminescent properties of the obtained phosphors are characterized by powder X-ray diffraction and photoluminescence spectrum, respectively. Photoluminescence results showed that the obtained phosphors can be excited efficiently by near-UV 387 nm and generated white light emission. The yellow/blue ratio and Commission International de I'Eclairage color coordinates could be tuned by adjusting the concentration of Dy 3+ . Results demonstrated that Li 8 Bi 2 ( MoO 4 ) 7 : Dy 3+ was a potential white light-emitting phosphor candidate for NUV-based w-LEDs.

Description: In this paper, the phase compositions and the dielectric properties of 3 ZnO –2 B 2 O 3 glass-ceramic prepared by solid-state method were investigated. The X-ray diffraction patterns show that all sintered samples consist of Zn 3 B 2 O 6 and α- Zn (BO 2 ) 2 . The dielectric properties changed significantly with the sintering temperature. After sintering at 650°C for 30 min, the glass-ceramic exhibits optimum dielectric properties: a dielectric constant of 7.5 and a dielectric loss of 0.6 × 10 −3 at 10 MHz. The chemical compatibility with Ag electrode under the co-fired process illustrates a potential application in low temperature co-fired ceramic field for the glass-ceramic.

Description: A novel technique was utilized to fabricate fine-scaled piezoelectric ceramic/polymer 2-2 composites for high-frequency ultrasonic transducers. Lead zirconate titanate (PZT) was used as raw material. Tape-casted acetylene black tapes were used to define kerfs after sintering. A one-directional supporter was utilized to avoid distortion of PZT elements. PZT elements with 20 ± 2 μm width exhibited good consistency in longitudinal direction. A resonant method was utilized to evaluate the piezoelectric and dielectric properties of the composites. A 72-μm-thick composite with an aspect ratio of ~3.6 exhibited a k t of 0.61 with satisfied piezoelectric and dielectric properties. A prototype high-frequency ultrasonic transducer was fabricated and evaluated by an underwater pulse-echo test. The center frequency was found to be 23.75 MHz, with −6 dB bandwidth of 5.5 MHz.

Description: [1]  The National Center for Atmospheric Research (NCAR) Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM) is utilized to better understand the role that vertically propagating tides play in determining zonal-mean winds, compositionand electron densities in the ionosphere-thermosphere (IT) system. A robust sensitivity assessment of the TIE-GCM shows that TIE-GCM solutions greatly depend on the specified background and tidal lower boundary conditions. We also establish the veracity of the TIE-GCM solutions in the 100-150 km region close to the 97 km boundary, as well as the F-region ionosphere above. To isolate the mean effects of tidal dissipation, differences between zonal- and local time-averaged fields from TIE-GCM simulations with and without lower boundary tidal forcing as specified by the observationally-based Climatological Tidal Model of the Thermosphere (CTMT) are investigated. Dissipation of the DW1, DE3, and SW2 tidal components explains most of ∼ 10-30 m s − 1 seasonal and latitudinal variability in zonal wind fields within the dynamo region, with SW2 playing a greater role than ascribed in previous studies. Dissipation of DW1 and SW2 at low latitudes causes up to a 9% decrease (30% increase) in [O] ([O 2 ]) number density near the F 2 -layer peak, leading to at least a 9% decrease in peak electron density (N m F 2 ) throughout the year. F 2 -layer peak height (h m F 2 ) differences of -4 to 2 km at low latitudes are explained by variations in the field-aligned plasma motion driven by mean meridional wind differences induced by tidal dissipation. The [O], [O 2 ] and N m F 2 effects are mainly driven by DW1 and SW2, which differs from previous interpretations of tidal-driven composition changes by DW1 “tidal mixing" exclusively. We suggest here that the tides may produce a net transport of constituents in the thermosphere similar to the way that, e.g., gravity wavescan drive net transport of sodium in the mesosphere.

Description: [1]  Keograms are constructed from azimuthal profiles of energetic hydrogen atoms (25-55 keV) from Saturn's magnetosphere. The keograms exhibit linear structures or “tracks” that reveal prograde rotational motion of features or “blobs” in the ENA images. From polynomial fits, the first derivatives of these tracks are used to estimate the rotational speeds of the blobs. The total blob speed consists of plasma convective drift plus gradient drift, so the convective speed can be approximated by subtracting the gradient drift of the protons from which the ENA derive. This subtraction gives plasma convection speeds that are ~28°/hr at ~5 R S and decrease to a constant ~21°/hr between 10 R S to 20 R S , which are consistently below corotation (~33.3°/hr) and in substantial agreement with estimates of plasma convection made in situ. The speeds also show a local time dependence, decreasing as much as 4-6°/hr as the blobs move from midnight through noon to midnight.

Description: [1]  We examined the brightness of 630.0-nm airglow, I 630 , associated with polar cap patches observed during a magnetic storm that occurred on 22 January 2012. Brightness was measured using an all sky imager (ASI) located at Longyearbyen, Svalbard. The observed I 630 was compared with the F-region electron density observed by the EISCAT Svalbard Radar (ESR). The I 630 was positively correlated with the F2-layer peak electron density, NmF2, and inversely correlated with the altitude of the F2-layer peak electron density, hmF2, as expected from the known relationship between these parameters. To estimate the altitude of the peak emission of the airglow, we performed model calculations of the volume emission rate, V 630 , under quiet and disturbed conditions, using MSIS-modelled neutral gas profiles and the electron density profile obtained from the ESR data. In order to validate the V 630 calculation, I 630 was calculated by integrating the V 630 along altitude, and then compared with the ASI-observed I 630 . During the observation periods the measured brightness frequently exceeded the calculated I 630 ; we infer that, in most cases, low energy particle precipitation is responsible for the extra brightness. However, when there was less particle precipitation, the observed values were in good agreement with the calculated values. Under the magnetically disturbed conditions during our observations, the model calculation showed that the altitude of V 630 peak increases, the thickness of the emission layer increases, and patch brightness increases.

Description: [1]  Although distant-tail plasmoids are perceived to extend across most of the magnetotail (~40 R E ), recent studies in the near-Earth region (X 〉 -30 R E ) have revealed that near-Earth reconnection (where plasmoids originate) is likely localized and takes place preferentially on the dusk side. This discrepancy in plasmoid azimuthal extent suggests that a plasmoid may grow as it moves from near Earth to the distant tail. Comprehensive multi-point, mid-tail plasmoid observations can be used to test this hypothesis. Between October 2010 and July 2011 the ARTEMIS spacecraft (P1 and P2) at the Earth-Moon Lagrange points (mid-tail, X ~ -45 to -65R E ) provided simultaneous two-point observations across the magnetotail for 4 days every lunar month, with a large range of spacecraft separations (0.1 to 25R E ). We find that plasmoids near lunar orbit, like other near-Earth reconnection-related phenomena, occur preferentially on the dusk side of the magnetotail. Two-point ARTEMIS observations reveal that the typical plasmoid azimuthal size in our dataset is about 5 to 10 R E , much smaller than expected from previous distant-tail observations. Plasmoids with an azimuthal size greater than 9 R E also exist, but only at geomagnetic activity levels higher (AE peak  〉 400nT) than typically found in our dataset (median AE peak  ~ 230 nT for our plasmoid dataset, median AE ~ 100 nT during the entire period of ARTEMIS magnetotail observations). We conclude that plasmoids during small to moderate substorms (AE peak  〈 400nT) do not grow beyond ~10 R E until they have moved tailward of ~ -45 to -65 R E . Plasmoids during large substorms (AE peak  〉 400nT), however, either grow beyond ~10 R E before they reach lunar distance or initially extend across a large portion of the magnetotail.

Description: [1]  The so-called large scale wave structure (LSWS) at the base of F-layer is the earliest manifestation of seed perturbation for the Rayleigh-Taylor (R-T) instability. It has been found to play a deterministic role in the development of equatorial plasma bubbles (EPBs). Except for a few case studies, a comprehensive investigation has not been conducted to determine the characteristics of LSWS. One reason is that it is not straightforward with existing sensors to detect LSWS, particularly, in the spatial domain. In this scenario, a comprehensive study was carried out, for the first time, on the spatial and temporal characteristics of LSWS. Observations were made over the African and Southeast Asian sectors during the year 2011. The observations confirm the findings from case studies, that these wave structures can occur a few degrees west of E-region sunset terminator, and can grow significantly in amplitude at longitudes east of sunset terminator. With the use of additional stations that are located on either side of dip equator, the phase fronts of these spatial structures are shown to be aligned with geomagnetic field ( ) lines over a wide latitudinal belt of 5-6 o (~500 – 600 km) centered on dip equator. The zonal wavelengths of these structures are found to vary from 100 to 700 km which is consistent with the earlier reports. A new statistical finding is that EPBs were consistently observed when the amplitudes of LSWS were grown to sufficient strengths. These results provide better insights on the underlying physical processes involved in excitation of LSWS in terms of important roles being played by the E-region electrical loading and the polarization electric fields that are induced via spatially varying dynamo current due to neutral wind perturbations associated with Atmospheric Gravity Waves (AGWs).

Description: [1]  Controlled experiments with dedicated ground-based ELF/VLF (0.3-30 kHz) transmitters are invaluable in investigating nonlinear whistler mode wave-particle interactions in the Earth's magnetosphere. The most productive such experiment operated between 1973 and 1988 near L  = 4 at Siple Station, Antarctica. A major effort has been undertaken to digitize and preserve a significant portion of the historical data set from the original magnetic tapes, and we describe here the data set and the processing techniques used to remove artifacts introduced during recording and playback. We analyze a commonly transmitted diagnostic format from 1986 and present statistics on the occurrence and properties of amplified ELF/VLF waves received by a ground-based receiver at the geomagnetic conjugate location to Siple at Lake Mistissini, Quebec. For the interval examined, only 11% of Siple transmissions are successfully received in the conjugate hemisphere with quiet geomagnetic conditions being significantly more conducive to successful reception. The total growth for the events examined is estimated to be 5-40 dB, and nonlinear growth rates are in the range of 20-350 dB/s. The observations show that as the nonlinear growth rate increases, the duration of nonlinear growth decreases. Significant linear correlation is found between the noise floor and the saturation level, with higher noise floors resulting from increases in natural magnetospheric emissions. Finally, we find a lack of correlation between the nonlinear growth rate and the noise, threshold, and saturation levels.

Description: [1]  We apply a semi-analytic magnetohydrodynamic approach to describe effects in the nightside magnetosheath related to accelerated magnetosheath flows caused by the draping of interplanetary magnetic field (IMF). Assuming a northward IMF direction, we show the development of slow mode fronts in the far tail (tailward of ∼ -60 R E ). We find that accelerated flows north and south of the equator start to converge towards lower latitudes. The ensuing plasma compression gives rise to slow mode waves in the equatorial region which, further down the tail, evolve into slow mode shocks. These fronts propagating along the magnetic field lines are characterized by sharp increases of plasma density, pressure and temperature and a decrease in the magnetic field strength. The magnetic pressure exhibits an anti-correlation with the plasma pressure, but the total pressure is fairly constant across the fronts. The field–aligned plasma velocity component anti-correlates with the plasma density, while the perpendicular velocity component does not have sharp variations at the fronts. For northward IMF, these fronts appear near the equatorial region and then propagate to higher latitudes. This effect is not very sensitive to the particular shape of the magnetopause. Lowering the upstream Alfvén Mach number increases the strength of the slow mode waves, which also develop closer to Earth. We predict that this effect can be observed by space probes skimming the far tail.

Description: [1]  We present the results of numerical studies of the interaction of solar wind ions with the dayside magnetospheric boundary for a southward IMF and two solar wind speeds (250 and 500 km/s) using the results of global MHD simulations in conjunction with LSK calculations. Results of these studies show that a dawn-dusk asymmetry is found in the precipitation of low to middle energy ions over the high-latitude dayside magnetosphere. This asymmetry is consistent with statistical studies of DMSP data showing that ion precipitation from the mantle is predominantly seen over the morning and pre-noon sector. Analysis of energy-latitude spectra and study of individual particle trajectories from the simulations revealed that low energy ions can enter the magnetopause at high-latitudes in regions where the parallel electric field associated with the magnetopause current is positive and strong enough for the ions to gain energies of the order the parallel potential drop across the magnetopause. Because the parallel electric field in the northern hemisphere is positive in the pre-noon sector and negative in the afternoon-evening sector, solar wind ions reaching the magnetopause in these regions are accelerated toward the ionosphere on the dawn side and outward on the dusk side, creating the asymmetry in precipitation. The same dawn-dusk asymmetry is found in the southern hemisphere because both parallel electric field and magnetic field reverse direction.

Description: [1]  In type III solar radio bursts and planetary foreshocks, Langmuir waves are produced by electron beams and converted partially to radio waves by linear and nonlinear processes. Lower amplitude second harmonic electric fields are observed simultaneously during the most intense Langmuir wave events in type III source regions. The electric fields at the harmonic frequencies can arise from various mechanisms, such as radio wave emission, either by coalescence or antenna mechanisms, nonlinear currents, harmonics of Langmuir waves, electron trapping in Langmuir wave potentials, and Langmuir wave rectification at the sheath surrounding the spacecraft, or can result from instrumental harmonics. In this paper the relative powers and electric field vectors of Langmuir waves and the harmonic fields are compared for multiple events. The structure of the harmonic field is shown to be determined by the Langmuir waveform, but the harmonic field direction is typically closely aligned with the solar wind flow. The magnitude, structure, and orientation of the harmonic fields is used to determine which processes are responsible. It is shown that the dominant process generating the observed harmonic fields is Langmuir wave rectification at the sheath surrounding the spacecraft.

Description: [1]  Solar wind turbulence at large inertial scales is well known for decades and believed to consist of Alfvén cascade. At scales of the order of proton inertial length, Alfvén cascade excites kinetic Alfvén wave, fast wave or whistler wave that carries wave energy to smaller scales. Despite supporting the kinetic Alfvén wave cascade to elucidate the steeper spectra at the kinetic scales we here present another model, the localization of longitudinally propagating dispersive Alfvén wave (DAW) with finite frequency correction to illustrate the same. Inclusion of this finite frequency in Alfvén wave makes them dispersive. In this approach the dynamical equation of the wave in the presence of ponderomotive nonlinearity of the pump is obtained and then solved numerically to study the evolution of the turbulence. The ponderomotive force accounts for the coupling between the DAW and ion acoustic wave (IAW). Taking the adiabatic case, we have first studied the localization of DAW. To have the physical insight of the dynamical system the equation is also studied semi-analytically.

Description: The 0.45 Bi ( Mg 0.5 Ti 0.5 ) O 3 –(0.55 −  x ) PbTiO 3 – x ( Bi 0.5 Na 0.5 ) TiO 3 (BMT–PT– x BNT) ternary solid solution ceramics were prepared via a conventional solid-state reaction method; the evolution of dielectric relaxor behavior and the electrostrain features were investigated. The XRD and dielectric measurements showed that all studied compositions own a single pseudocubic perovskite structure and undergo a diffuse-to-relaxor phase transition owing to the evolution of the domain from a frozen state to a dynamic state. The formation of the above dielectric relaxor behavior was further confirmed by a couple of measurements such as polarization loops, polarization current density curves, as well as bipolar strain loops. A large strain value of ~0.41% at a driving field of 7 kV/mm (normalized strain d 33 * of ~590 pm/V) was obtained at room temperature for the composition with x  = 0.32, which is located near the boundary between ergodic and nonergodic relaxor. Moreover, this electric field-induced large strain was found to own a frequency-insensitive characteristic.

Description: [1]  The recent survey by Andrews et al. (2012) of the separate northern and southern ~10.7 hour periodic magnetic signals in Saturn's magnetosphere limits very much their governing current systems. The existence of signals with pure or close to pure northern or southern periods in respective polar caps taken with the relatively narrow bandwidth of the signals indicates that the actual periodicities are imposed independently from northern and southern polar regions, i.e. the open field line regions. Field-aligned currents must flow on the boundaries of these regions to exclude signals from the other hemisphere. Equatorward of the polar cap, on closed magnetic shells, there are distinct north and south “cam” source currents, the distinction being made clear by a difference in polarization. We outline the consequences for the governing current systems and the implications for sustaining the energy and power dissipation in the system.

Description: Data from the MESSENGER Neutron Spectrometer (NS) have been used to identify energetic neutrons (0.5–8 MeV energy) associated with solar events that occurred on 4 June 2011. Multiple lines of evidence, including measurements from the NS and the MESSENGER Gamma-Ray Spectrometer, indicate that the detected neutrons have a solar origin. This evidence includes a lack of time-coincident charged particles that could otherwise create local neutrons from nearby spacecraft material as well as enhanced count rates from multiple neutron inelastic scatter gamma-ray lines that are consistent with a large fluence of external neutrons interacting with local spacecraft material. The shape of the energy spectrum of the detected neutrons shows a relative enhancement of neutrons in the energy range 0.8–3 MeV compared with cosmic-ray-generated neutrons from the spacecraft or Mercury. The spectral shape of the measured neutron fluence spectrum is consistent with a previously modeled fluence spectrum of neutrons that originate at the Sun and are propagated through the MESSENGER spacecraft to the NS. These measurements provide a compelling detection of solar neutrons in the energy range 0.5–8 MeV and suggest that a large number of low-energy threshold ion evaporation reactions were taking place on the Sun during the neutron event.

Description: [1]  The plasma pressure and current configuration of the near-Earth plasma sheet that creates and sustains the quiet evening auroral arc during the growth phase of magnetospheric substorms is investigated. We propose that the quiet evening arc (QEA) connects to the thin near-Earth current sheet, which forms during the development of the growth phase enhancement of convection. The current sheet's large polarization electric fields are shielded from the ionosphere by an Inverted-V parallel potential drop, thereby producing the electron precipitation responsible for the arc's luminosity. The QEA is located in the plasma sheet region of maximal radial pressure gradient, and, in the east-west direction, follows the vanishing of the approximately dawn-dusk-directed gradient or fold in the plasma pressure. In the evening sector, the boundary between the Region1 and Region 2 current systems occurs where the pressure maximizes (approximately radial gradient of the pressure vanishes) and where the approximately radial gradient of the magnetic flux tube volume also vanishes in an inflection region. The proposed intricate balance of plasma sheet pressure and currents may well be very sensitive to disruption by the arrival of equatorward traveling auroral streamers and their associated earthward traveling dipolarization fronts.

Description: [1]  A radar meteor echo is the radar scattering signature from the free-electrons in a plasma trail generated by entry of extraterrestrial particles into the atmosphere. Three categories of scattering mechanisms exist: specular, non-specular trails, and head-echoes. Generally, there are two types of radars utilized to detect meteors. Traditional VHF meteor radars (often called all-sky radars) primarily detect the specular reflection of meteor trails traveling perpendicular to the line of sight of the scattering trail, while High Power and Large Aperture (HPLA) radars efficiently detect meteor head-echoes and, in some cases, non-specular trails. The fact that head-echo measurements can be performed only with HPLA radars limits these studies in several ways. HPLA radars are very sensitive instruments constraining the studies to the lower masses, and these observations cannot be performed continuously because they take place at national observatories with limited allocated observing time. These drawbacks can be addressed by developing head echo observing techniques with modified all-sky meteor radars. In addition, the fact that the simultaneous detection of all different scattering mechanisms can be made with the same instrument, rather than requiring assorted different classes of radars, can help clarify observed differences between the different methodologies. In this study, we demonstrate that such concurrent observations are now possible, enabled by the enhanced design of the Southern Argentina Agile Meteor Radar (SAAMER) deployed at the Estacion Astronomica Rio Grande (EARG) in Tierra del Fuego, Argentina. The results presented here are derived from observations performed over a period of 12 days in August 2011, and include meteoroid dynamical parameter distributions, radiants and estimated masses. Overall the SAAMER's head echo detections appear to be produced by larger particles than those which have been studied thus far using this technique.

Description: [1]  We report on a detailed global climatology of medium-scale (150-600 km) thermospheric gravity wave (GW) activity using mass density observations onboard the CHAMP satellite from 2001 to 2010. Our study focuses mainly on daytime (09-18 h in local time) and mid-/low-latitude upper thermosphere between 300 km and 400 km altitudes. Mid-latitude GW activity is strongest in the winter hemisphere. GW activity during June solstice adjacent to the Andes and Antarctic Peninsula is stronger than in any other season or location. GW activity in the low-latitude summer hemisphere is stronger above continents than above oceans: especially during December solstice and equinoxes. In terms of relative density variation, GW activity is stronger during solar minimum than solar maximum. These results agree well with the characteristics of stratospheric GWs, implying that the CHAMP GWs are mainly caused by GWs from tropospheric/stratospheric processes. Using mesosphere-lower-thermosphere wind observations at a Korean Antarctic station, we investigated at which altitudes the upper thermospheric GW climatology becomes visible. While the correlation is insignificant at z  = 82 − 88 km, it becomes significant for most cases at z  = 90 − 98 km, suggesting that the upper thermospheric GW climatology may start to emerge at z  ≥ 90 km.

Description: AgNbO 3 is a weak ferroelectric with antiferroelectricity due to Ag displacements at room temperature. A dielectric anomaly at 250 K, which has not been observed previously, reveals a transition between the weak ferroelectric phase (M1 phase) at the higher temperature and a new ferroelectric phase (M0 phase) at the lower temperature in AgNbO 3 . This transition was further verified by the pyroelectric current and differential scanning calorimetry measurements. The spontaneous polarization value is found to be much larger in the M0 phase than that of the M1 phase. A well-defined saturating ferroelectric hysteresis loop can also be observed at 77 K, showing a remnant polarization value of 2.4 μC/cm 2 and a coercive field of 25 kV/cm. All the above results indicate that the larger polarization of the M0 phase mainly comes from the alignment of the antiferroelectric displacements of the Ag atoms.

Description: No abstract is available for this article.

Description: The technique to remotely sense the plasma mass density in magnetosphere using field line resonance (FLR) frequencies detected by ground-based magnetometers has become more and more popular in the last few years. In this paper we examine the error that would be committed at low and middle latitudes ( L  〈 4) in estimating the equatorial plasma mass density if dipole field lines are assumed instead of the more realistic representation given by IGRF field lines. It is found that the use of the centered dipole model may result in an error in the inferred density appreciably larger than what is usually assumed. In particular it has a significant longitudinal dependence being, for example, greater than +30% in the atlantic sector and about −30% at the opposite longitude sector for field lines extending to a geocentric distance of 2 Earth radii. This may result in an erroneous interpretation of the longitudinal variation in plasmaspheric density when comparing results from ground-based arrays located at different longitudes. We also propose simple modifications of the standard technique, such as the use of an effective dipole moment or the eccentric dipole model, which allow to keep using the dipole field geometry but with a significant error reduction.

Description: The first mid-latitude conjugate thermospheric wind observations in the American sector showed various degrees of conjugacy between Palmer (64S, 64 W, MLAT 50S) and Millstone Hill (42.82 N, 71.5 W, MLAT 53 N) under three different geomagnetic conditions (recovery after a substorm, moderately active, and quiet). The agreement with the National Center for Atmospheric Research's (NCAR) Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) simulations also varies with the geomagnetic activity level. During substorm recovery, the observations at Palmer (PA) and Millstone Hill (MH) both showed strong westward zonal winds, which the standard TIEGCM greatly underestimated. Inadequate ion convection pattern-size and lack of effect from Sub Auroral Polarization Streams (SAPS) may be the cause of the large discrepancy. The TIEGCM with a SAPS model produced stronger westward zonal winds near PA, but did not change the zonal wind near MH. The empirical SAPS model needs further refinements. In general, there is better conjugacy with moderate geomagnetic activity levels. The TIEGCM also agrees better with the observations. Under geomagnetically quiet conditions, the meridional winds appear to be less conjugate. The agreement between the observations and model is reasonable. Optical conjugate observations are severely limited by the seasons and weather conditions in the two hemispheres. Yet, they are necessary to understanding the thermospheric dynamics in the sub-auroral region and its relationship with geomagnetic activity levels. The comparisons with TIEGCM are necessary for future model improvements.

Description: The parameterizations of monoenergetic particle impact ionization in Fang et al. [2010] (Fang2010) and Fang et al. [2013] (Fang2013) are applied to the complex energy spectra measured by DMSP F16 satellite to calculate the ionization rates from electron and ion precipitations for a northern hemisphere pass from 0030 UT to 0106 UT on August 6, 2011. Clear enhancement of electron flux is found in the polar cap. The mean electron energy in the polar cap is mostly above 100 eV, while the mean energy in the auroral zone is typically above 1 keV. At the same time, F16 captures a strong Poynting flux enhancement in the polar cap, which is comparable to those in the auroral zone. The particle impact ionization rates using Fang2010 and Fang2013 parameterizations show clear enhancement at F-region altitudes mainly due to the low-energy precipitating electrons, peaking probably in the cusp but also showing enhanced levels throughout most of the polar cap region. The general circulation models (GCMs), NCAR Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM) and Global Ionosphere Thermosphere Model (GITM) using their default empirical formulations of particle impact ionization, do not capture the observed features shown in the total particle ionization rate applying the Fang2010 and Fang2013 parameterizations to DMSP measurements. The difference between GCM simulations and Fang2010&Fang2013 applied to DMSP data is due to the difference of both the inputs to the models and the parameterization of the ionization rates.

Description: A common view is that spectral maxima in observed spectral resonance structures (SRS) of ionospheric Alfvén resonator (IAR) at frequencies f 〈 5 Hz are the signature of resonance frequencies of the IAR. We have studied not only spectra but also waveforms of magnetic fluctuations at IAR frequencies registered at Moshiri station (Japan) and have found that there exist two kinds of signals. The dominant type of signal is a pair of pulses which is caused by an initial exciting impulse, and accompanied by a single reflection from the top boundary of the IAR. In the absence of reflection from the lower ionosphere, such signals are not resonant and hence are not caused by IAR excitation. The minority of cases are trains of three or more pulses separated by a nearly constant time interval reflected from both IAR boundaries. We have found that different kinds of signals in time domain may correspond to similar comb-shaped Fourier spectra. So different kinds of signals in time domain practically cannot be distinguished on the basis of their Fourier spectra. We have calculated waveforms and SRS structures of the magnetic field oscillations generated by a model lightning discharge and IAR resonant frequencies. Calculated IAR resonance frequencies can be in disagreement with those of spectral maxima of pulse trains. Then, an analysis of signal waveforms in time domain is highly required to estimate IAR resonance frequencies.

Description: The oxidation kinetics of ZrB 2 -30 vol% SiC were analyzed statistically with the goal of understanding the underlying mechanisms for observed variability. A box furnace was used to oxidize specimens for times between 30 s and 100 h at temperatures of 1300°C–1550°C in air. The specimens were characterized to determine weight change, scale thickness, and scale composition to quantify the oxidation behavior. Weight gain measurements of different specimens after 100 min of exposure showed differences of up to 2 mg/cm 2 for the same testing conditions where the average weight gain was 2.54 mg/cm 2 . Variation of 30%–80% was observed in the average thickness of each layer of the oxide within a single specimen. Viscous glass flow was ruled out as a potential mechanism. Glass bubble formation was proposed as the main cause for oxidation kinetics variability.

Description: Phase equilibria in the La 1− x Ca x FeO 3−δ (LCF) system were assessed at temperatures below 1350°C in both simulated air and argon atmospheres using a combination of differential scanning calorimetry, thermogravimetric analysis, scanning electron microscopy, and high-temperature X-ray diffraction. The solubility limit of Ca in the perovskite structure was determined to be 38% A-site substitution. A high-temperature orthorhombic to rhombohedral transition was identified and the dependence on oxygen partial pressure and effect on thermal expansion were characterized. A partial, pseudobinary LaFeO 3 –CaFeO 2.5 phase diagram is presented that is based on these analyses combined with data available in the open literature.

Description: TiB 2 powders were synthesized by borothermal reduction in nanoscale TiO 2 with boron under vacuum. Reaction processes were investigated, and the effect of by-product B 2 O 3 was evaluated. Results showed that TiO 2 was firstly reduced by boron to form TiBO 3 and Ti 2 O 3 , and then to produce TiB 2 and B 2 O 3 with increasing temperature. The reaction processes of TiB 2 powders synthesis included two-step reduction in TiO 2 by boron and the removal of B 2 O 3 . The presence of B 2 O 3 , which was previously reported as the most important factor in promoting the coarsening of ZrB 2 and HfB 2 powders by borothermal reduction, did not lead to significant coarsening of TiB 2 powders. Due to the minor effect of B 2 O 3 , TiB 2 powders with small particle size and low oxygen content could be prepared by direct heat treatment of TiO 2 and boron at 1550°C under vacuum for 1 h. The particle size and oxygen content of synthesized TiB 2 powders were ~0.9 μm and ~1.7 wt%, respectively.

Description: In this work, a low-firing microwave dielectric ceramic PbMoO 4 with tetragonal structure was prepared via a solid-state reaction method. The sintering temperature ranges from 570°C to 670°C. Ceramic samples with relative densities above 97% were obtained when sintering temperature was around 600°C. The best microwave dielectric properties were obtained in the ceramic sintered at 650°C for 2 h with a permittivity ~26.7, a Q  ×  f value about 42 830 GHz (at 6.2 GHz) and a temperature coefficient value of 6.2 ppm/°C. From the X-ray diffraction, backscattered electron imaging results of the cofired sample with 30 wt% silver and aluminum additive, the PbMoO 4 ceramic was found not to react with Ag and Al at 630°C. The microwave dielectric properties and low sintering temperature of PbMoO 4 ceramic make it a candidate for low-temperature cofired ceramic applications.

Description: Commercial EIA-Y5V base-metal-electrode multilayer ceramic capacitors (BME-MLCCs) made of ( CaO + ZrO 2 )-doped BaTiO 3 are analyzed for the microstructure and investigated for its relation to dielectric properties. The characteristic diffuse scattering (DS) intensities observed in BaTiO 3 ceramics and the featureless “solid-solution” grains in Y5V capacitor chips are originated from multiple Ti sites in the dynamic BaTiO 3 structure. The pseudo-cubic ( PC )-grains retaining the overall cubic ( C -) symmetry metastably at room temperature are embedded with polar nanoregions (PNRs) in the ferroelectric (FE) tetragonal ( T -), and rhombohedral ( R -) phases, as revealed by high-resolution transmission electron microscopy (HRTEM). The presence of PNRs contributes effectively to large relative permittivity ε r  ≈ 13 200 at 25°C. The FE T -domains grow from within PC -grains at the expense of embedded PNRs after prolonged annealing by extending “oxidizing firing” at 950°C in p O 2  = 10 −7  atm. These domains contain less Zr with otherwise homogeneously distributed solutes in PNR-dispersed PC -grains. Although preserving the relaxors characteristics, ε r is reduced to ~11 000 after 12 h, and then to ~9000 after 24 h annealing. The reduction in ε r is attributed to the annealing-induced FE T -domains grown at the expense of PNRs in PC -grains. The Vögel–Fulcher analysis indicates that Y5V ceramics are in the relaxor FE category, containing PNRs derived from polarization frustration.

Description: The progresses of the relative density, average grain size (GS), and maximum pore size entering into the final sintering stage are investigated in 3 mol% yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP) compacts in the range of 87%~99% theoretical density. It is found that during conventional pressureless sintering, the pores in the compact enlarged dramatically, which appears to be the major obstacle for preparing fully dense nanoceramics. Transparent 3Y-TZP nanoceramics with an average GS of 87 nm were prepared by exploiting microstructural refinement on nanoscale. The yields a maximal optical transmittance of 67% and shows no noticeable low-temperature degradation after 100 h aging at 134°C under a hydrothermal pressure of two bars.

Description: Porous β- Si 3 N 4 ceramics are sintered at 1600°C in N 2 and postheat treated at 1500°C under vacuum using Li 2 O and Y 2 O 3 as the sintering additives. The partial sintering and phase transformation are promoted at low temperature by the addition of Li 2 O . The addition of Y 2 O 3 is advantageous for the formation of high aspect ratio β- Si 3 N 4 grains. After postheat treatment, a large amount of intergranular glassy phase is removed, and the Li content in the samples is decreased. By this method, the β- Si 3 N 4 porous ceramic with a porosity of 54.1% and high flexural strength of 110 ± 8.1 MPa can be prepared with a small amount of sintering additives, 0.66 wt% Li 2 O and 0.33 wt% Y 2 O 3 , and it is suitable for high-temperature applications.

Description: To solve the heavy mass problem of the traditional spinel ferrite using as the microwave absorber, the Co x Zn (1− x ) Fe 2 O 4 ( x  =   0.2, 0.4, 0.6, 0.8) ferrite nanofibres were synthesized by electrospinning method. The phase composition, morphology, and electromagnetic properties were analyzed. The results showed that all the as-prepared Co x Zn (1− x ) Fe 2 O 4 ferrites exhibited the homogeneous nanofibrous shape. The saturation magnetization and coercivity were enhanced by tuning the Co 2+ content. The electromagnetic loss analysis indicated that the Co 0.6 Zn 0.4 Fe 2 O 4 ferrite nanofiber performed the strongest microwave attenuation ability. The microwave absorbing coating containing 15 wt% of Co 0.6 Zn 0.4 Fe 2 O 4 ferrite nanofiber showed the reflection loss less than −10 dB in the whole X -band and 80% of the Ku -band frequencies. Meanwhile, the surface density was only 2.4 Kg/m 2 .

Description: The kinetics of the cristobalite transformation are reported for sintered silica glass from 1200°C to 1650°C and plotted as a time–temperature–transformation diagram. The 1200°C–1350°C transformation data were fit to the Johnson–Mehl–Avrami–Kolmogorov expression with an time exponent of 3.0 ± 0.6 and an apparent activation energy of 555 ± 24 kJ/mol for the kinetic constant. The temperature of maximum transformation rate was found to fall between 1500°C and 1600°C. Seeding amorphous silica powder with cristobalite resulted in accelerated transformation kinetics. Silica glass powder containing residual quartz had faster transformation kinetics than fully amorphous powder seeded with cristobalite.

Description: In the inner magnetosphere inside 65 degree invariant latitude, Cluster Ion Spectrometry (CIS) detected hot He + events of about a few tens to several hundred eV without the same types of hot H + signature at the same energy. During the 2001–2006 period when the Cluster orbit was almost constant and approximately north–south symmetric at constant local time near the perigee, we found nearly 20 examples in Cluster spacecraft 4. These hot He + events are morphologically classified into two burst types and two dispersed types: Short intensification of He + (1a) without corresponding H + or O + signatures, or (1b) with H + signature at different pitch angles. Energy-latitude dispersed He + stripes that continues for tens of minutes at hundreds to a few thousand eV range (2a) at different drift shell from energy-latitude dispersed H + stripes, or (2b) with very weak H + signature if the energy is constant. While type-1a is observed during or right after substorm activities, type-2b is found after long quiet periods, i.e., after long drift. The relationship with the geomagnetic activity indicates that the plasmasphere can be energized in a mass dependent way in the evening sector during substorms to form the bursty types (type-1), while the selective He + energization can also take place during quiet periods near the noon. On the other hand, the source of the two dispersed types (type-2) must be remote from the observation point, and the location and the geomagnetic conditions at the time of the He + filtering is an open question.

Description: The solar minimum between solar cycles 23 and 24 was unusually long and deep. The upward region-1 (R1) field-aligned current (FAC) response to this extreme solar minimum was investigated using DMSP observations. The solar cycle responses on the dayside are different than those on the nightside. The field-aligned current density ( J // ) on the dayside, at 12 – 17 MLT, peaks in the declining phase of the solar cycle, in 2003, when the solar wind speed also peaks, whereas J // on the nightside, at 18 – 23 MLT, appears insensitive to the solar cycle. In 1995 – 2010, J // at 15 – 17 MLT reaches the lowest value during the extreme solar minimum in 2009, when the solar wind speed also reaches the lowest value. At 12 – 17 MLT, R1 is located mostly on open field lines or at the boundary layer, where the current is driven mostly by the velocity shear at the magnetopause boundary. However, on the nightside, R1 is located mostly on the closed field lines where J // is not driven directly and immediately by the solar wind. The nightside current width ( Λ ) exhibits a solar cycle effect such that Λ is smaller at the solar minimum and smallest in 2009. However, the dayside Λ exhibits little solar cycle effect. As a result, the FAC intensity (latitudinally integrated J // ) exhibits a solar cycle variation at all local times and the FAC intensity is lower during the extreme solar minimum than that of the previous solar minimum.

Description: We analyze the statistical properties of magnetic field fluctuations measured by the Cassini spacecraft inside Saturn's magnetosphere. We introduce Saturn's magnetosphere as a new laboratory for plasma turbulence, where background magnetic field is strong(1 nT  〈  B 0  ≤ 75nT), fluctuations are weak (〈 δB / B 〉 = 0.07) and the ion plasma β i is smaller than one. We also show that the dissipation of these magnetic field fluctuations has important implications for the magnetosphere. In a case study of the second orbit of Cassini around Saturn we show that at MHD scales, the spectra and the nature of fluctuations are characterized by large scale non-stationary processes. The spectral slope varies between − 0.8 and − 1.7. At higher frequencies we observe a steeper spectrum with nearly constant power-law exponent. A spectral break correlating with ion scales separates the two frequency ranges. We carry out a statistical study of high frequency range fluctuations using the first seven orbits of Cassini. We find that the energy density of raw frequency spectra depends on radial distance from Saturn, thermal and magnetic pressures. However, normalized spectra depend only on ion plasma β i . Closer to Saturn the spectral slope is about − 2.3 and for radial distances r  〉 9 R s the average slope is − 2.6. The fluctuations have probability density functions with increasingly non-Gaussian tails and a power-law increase of flatness with frequency, which indicates intermittency. We estimate the total energy flux contained in the turbulent cascade as 60 − 100GW, which is on the same order of magnitude as needed to heat an adiabatically expanding plasma to the temperatures measured in Saturn's magnetosphere.

Description: Numerous studies of the terrestrial magnetosphere that use global magnetohydrodynamic codes have found that the model's inner boundary can act as a significant source of plasma, even if the radial velocity about the boundary is held at zero. Though inherent in many models, this “de facto outflow” is poorly understood. This work uses the BATS-R-US MHD model to investigate the behavior of this type of outflow as a function of boundary conditions and solar wind drivers. It is found that even for temporally and spatially constant boundary conditions, the mass is accelerated away from the body in a dynamic manner. Fluxes organize into cusp, polar cap, and auroral zone concentrations. Pressure gradient forces appear predominantly responsible for cusp and polar cap outflow while the Lorentz force, resulting from field aligned current systems, is the strongest driver of outflow in other regions. Integrated fluxes probed just outside of the inner boundary vary linearly as a function of cross polar cap potential and solar wind dynamic pressure. The resulting dynamics strongly resemble patterns found in in-situ measurements while net fluences agree within an order of magnitude. Two free parameters, inner boundary mass density and composition, can strongly affect results. Accounting for these unknowns is likely best left to physics-based or empirical specifications of outflow. Despite this, such outflow appears to be an acceptable proxy.

Description: The interaction of the Enceladean plume with its magnetospheric environment provides a unique natural laboratory for studying plasma-neutral-dust interaction processes. The goal of this study is to analyze the magnetic signatures of dust in order to constrain the dust plume. For the first time, the mutual feedback between the charged nanograins and their plasma environment is investigated. Our model of these interactions combines plasma simulations by means of the hybrid code A.I.K.E.F. ( A daptive I on- K inetic E lectron- F luid) with Monte-Carlo simulations of the 3D profiles of the gas and dust plumes. Data from several instruments of Cassini are considered: the applied neutral plume model is in good agreement with INMS data, whereas theoretical predictions of the peak ion density are compared against CAPS and RPWS data, and properties of the dust plume are obtained by comparing our results with Cassini MAG data from various Enceladus flybys including the recent E14– E19 encounters. Our main results are: (1) due to the ion-neutral chemistry, H3O + is the predominant ion species within the plume; (2) the high nanograin densities observed by CAPS require an effective ionization frequency larger than the sum of photoionization and electron impacts to fulfill quasi-neutrality; (3) the nanograin pick-up current makes only a minor contribution to the current systems,i. e. the major contribution of the dust to the current systems arises from electron absorption; (4) the pick-up of charged nanograins is clearly visible in the magnetic field signatures, even including the distant encounter E15; (5) MAG data indicates a southward extension of the charged dust plume of at least four Enceladus radii; (6) the modification of the current system by the nanograins is responsible for the surprising fact that Cassini did not detect a region with a reduced magnetic field strength.

Description: We investigate the temporal evolution and the spatial distribution of electromagnetic ion cyclotron (EMIC) waves during the 8–11 June 2001 geomagnetic storm, one of storms selected for study by the Geospace Environment Modeling (GEM) program. Generation of EMIC waves in the H + , He + and O + bands are simulated using the kinetic ring current-atmosphere interactions model with a self-consistent magnetic field (RAM-SCB) and a ray tracing code (HOTRAY). Simulations show that strong wave gain occurs in the afternoon sector at L  〉 5 and overlaps with a high-density plasmaspheric drainage plume. EMIC wave gain maximizes during the main phase and decreases in the recovery phase. We find that EMIC wave gain is stronger in the He + band than the other two bands in the inner magnetosphere, except the region of low L (〈 3) where the H + band is dominant due to an enhancement in the ring current anisotropy. Little wave gain is obtained for the O + band. Comparison with in-situ EMIC events and EMIC event proxies at five geosynchronous satellites show consistence in the temporal and local time evolution of the wave distribution. Our simulations of the EMIC wave distribution also agree with proton aurora at sub-auroral latitudes observed from the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite.

Description: The substorm growth phase is characterized by the equatorward motion of the growth phase arc close to or even into the region of diffuse aurora characteristic for a dipolar magnetic field. The presented study examines changes of the near-Earth current sheet and of the mapping of magnetotail feature into the auroral ionosphere based on midnight magnetic flux depletion (MMFD) in the near-Earth tail. MMFD is caused by sunward convection to replenish magnetic flux that is eroded on the dayside by magnetic reconnection during periods of southward IMF. The results demonstrate that MMFD causes the formation of a very thin current sheet in the near-Earth tail. It is found that the removal of magnetic flux in the near-Earth tail causes a contraction of the ionospheric footprints of this tail region such that all of the mapped magnetotail structures move equatorward by about 2 to 3 degrees. The thin current layer is mapped into the region where magnetic flux is strongly depleted, and in close proximity with strong and narrow region 1 and 2 sense field-aligned currents. The ionospheric maps show a sharp transition between the dipole and stretched magnetic field and an evolution of thinning and convergent motion of field-aligned currents in the late growth phase. The results are obtained without loading of magnetic flux and energy into the tail lobes, demonstrating that many typical growth phase properties can be attributed to the depletion of near-Earth closed magnetic flux.

Description: The morphology and crystal growth of devitrite crystals nucleated heterogeneously on glass surfaces have been studied. The crystals grow as fans of needles, with each needle having a characteristic [100] growth direction with respect to the centrosymmetric triclinic unit cell. An analysis of crystal growth data reported here and a reappraisal of crystal growth data reported in prior studies suggests a best estimate of 260 kJ/mol for the activation enthalpy for the crystal growth of devitrite along [100], higher than the values previously reported.

Description: Patterns of the high-latitude ionospheric convection and field-aligned current (FAC) are a manifestation of the solar wind-magnetosphere-ionosphere coupling. By observing them we can acquire information on magnetopause reconnection, a process through which solar wind energy enters the magnetosphere. We use over 10 years of magnetic field and convection data from the CHAMP satellite and SuperDARN radars, respectively, to display combined distributions of the FACs and convection for different IMF orientations and amplitudes. During southward IMF, convection follows the established two-cell pattern with associated Region 1 and Region 2 FACs, indicating subsolar reconnection. During northward IMF, superposed on a weak two-cell pattern there is a reversed two-cell pattern with associated Region 0 and Region 1 FACs on the dayside, indicating lobe reconnection. For dominant IMF B x , the sign of B z determines whether lobe or subsolar reconnection signatures will beobserved, but B x will weaken the signatures compared to pure northward or southward IMF. When the IMF rotates from northward to duskward or dawnward, the distinct reversed and forward two-cell patterns start to merge into a distortedtwo-cell pattern. This is in agreement with the IMF B y displacing the reconnection location from the open lobe field lines to closed dawn or dusk field lines, even though IMF B z  〉 0. As the IMF continues to rotate southward, the distorted pattern transforms smoothly to that of the symmetric two-cell pattern. While the IMF direction determines the configuration of the FACs and convection, the IMF amplitude affects their intensity.

Description: Single crystal (1  − x ) Pb ( Mg 1 / 3 Nb 2 / 3 ) O 3 – x PbTiO 3 [ PMN – x PT] ( x  = 0.32) is a relaxor-ferroelectric material known to exhibit ‘giant’ piezoelectric behavior, with achievable strains in excess of 1% for samples of certain particular crystallographic orientations and chemical compositions close to the morphotropic phase boundary. In this study, we investigate the electric field-induced structural phase transitions in single crystal PMN –0.32 PT with time-of-flight neutron diffraction and macroscopic electrical polarization measurements, and show that both the frequency of the applied ac field and the temperature of the sample are critical factors in determining these phase transition fields.

Description: Glass nanocomposites, fabricated using borosilicate glass microspheres and antimony tin oxide (ATO) nanoparticles, were previously reported to have formed segregated networks at the boundaries of the glass particles. This resulted in an electrically conducting composite at low volume fractions (~0.5–0.8 vol%) of ATO nanoparticles. The wide range of electrical response in these borosilicate glass composites containing networks of varying concentration of ATO was examined using impedance spectroscopy. The electrical resistance of these composites varied over a range of around 12 orders of magnitude and exhibited several different types of insulator and conductor behavior. The formation of the ATO network was identified and tracked by scanning electron microscopy images and energy dispersive X-ray spectroscopy (EDS) scans. Detailed impedance spectroscopy analysis using all of the dielectric functions (impedance, permittivity, electric modulus, and admittance) was found to be an excellent method for detecting the development of the network and the effect that processing variables can have on its formation and the overall electrical properties of the nanocomposites.

Description: By combining the concept of defect chemistry and the small-polaron hopping conduction model, the present work takes an intensively considering of the electron conduction mechanism in the nonstoichiometric SnO 2 nanocrystalline film. The temperature-dependent and atmosphere-dependent relationship between the electrical conductivity and the defect reaction is outlined. To investigate the influence of temperature and atmosphere on the electrical properties of the SnO 2 nanocrystalline film, a temperature-programmed system integrated with the high-throughput screening platform of gas-sensing materials (HTSP-GM) is developed as the test tool in this work. With this platform, the temperature-dependent conductivity of SnO 2 nanocrystalline film in different atmosphere (dry air, nitrogen, and formaldehyde) was conducted. A good fit between the theoretical deductions and experimental results is achieved.

Description: We demonstrate a facile synthesis of monodisperse magnetite ( Fe 3 O 4 ) nanoparticles (NPs) via a simple wet chemical route at 180°C using oleylamine ( C 18 H 37 N ), which serves as a solvent, ligand, and surfactant. The particles have a narrow size distribution centered at about 10 nm. To provide better electron conductivity and structural stability, the as-synthesized particles are given a carbon nanocoating by pyrolysis of the residual surfactant on their surface. This pyrolysis forms a uniform thin nanocoating on each particle, and a core/shell Fe 3 O 4 /carbon NP network was thus obtained. The core/shell Fe 3 O 4 /carbon electrode shows better reversible capacity, cycle life, and rate capability than a bare Fe 3 O 4 NP electrode because of its efficient electron transport and stress relaxation provided by the thin carbon layer.

Description: Nickel ferrite (NiFe 2 O 4 ) is a major constituent of the corrosion deposits formed on the exterior of nuclear fuel cladding tubes during operation. NiFe 2 O 4 has attracted much recent interest, mainly due to the impact of these deposits, known as CRUD, on the operation of commercial nuclear reactors. Although advances have been made in modeling CRUD nucleation and growth under a wide range of conditions, the thermophysical properties of NiFe 2 O 4 at high temperatures have only been approximated, thereby limiting the accuracy of such models. In this study, samples of NiFe 2 O 4 were synthesized to provide the thermal diffusivity, specific heat capacity, and thermal expansion data from room temperature to 1300 K. These results were then used to determine thermal conductivity. Numerical fits are provided to facilitate ongoing modeling efforts. The Curie temperature determined through these measurements was in slight disagreement with literature values. Transmission electron microscopy investigation of multiple NiFe 2 O 4 samples revealed that minor nonstoichiometry was likely responsible for variations in the Curie temperature. However, these small changes in composition did not impact the thermal conductivity of NiFe 2 O 4 , and thus are not expected to play a large role in governing reactor performance.

Description: Boron carbide thin films have been synthesized via pulsed laser deposition process using Spark Plasma Sintered (SPSed) and dual-targets, respectively. Two kinds of structural evolutions have been found by investigation of bonding environments in as-deposited thin films via X-ray photoelectron spectroscopy study. With decreasing of B/C ratio, films deposited from SPSed-target show the transformation of B 11 C -CBB → B 11 C -CBC. In contrast, the films deposited from dual-target present the B 11 C -CBB → B 10 C 2 -CBB structural change.

Description: The SrTiO 3 (STO) thin films were directly grown on Si (111) substrates without buffer layer by an electron-cyclotron-resonance ion beam sputter deposition. The growth temperature was varied from 700°C to 850°C, while other parameters were kept unchanged. X-ray structural analysis demonstrates that the growth temperature has a strong influence in tuning degree of (100) orientation. The STO film grown at 800°C is found to be the highest degree of (100) orientation (98%) and a strong (100) fiber texture. For the surface morphology, the development of plate-shaped grains reveals a good correlation with the change in the degree of (100) orientation. Moreover, the leakage current–voltage characteristics of the Au /STO/ Si (111) metal-insulator-semiconductor capacitors are investigated and discussed in considerable detail.

Description: The effect of combined substitution of Sm 3+ and O 2− with Ca 2+ and F − , respectively, on the structural and superconducting properties of SmFeAsO system is investigated. It is observed that the binary doping using CaF 2 causes considerable structural as well as microstructural changes wherein the preferred orientation of (00  l ) planes and enhancement of grain size are quite interesting. Moreover, a maximum T C of 53.8 K and a transport J C of 880 A/cm 2 (12 K) are achieved in the codoped samples. The achievement of preferred orientation, enhanced T C , and the subsequent increase in J C of the modified SmFeAsO system are particularly significant for high current conductor development.

Description: Lead free piezoelectric ceramics of Y 3+ -doped Ba 1− x Ca x Zr 0.07 Ti 0.93 O 3 with x  = 0.05, 0.10, and 0.15 were prepared. Composition and temperature-dependent structural phase evolution and electrical properties of as-prepared ceramics were studied systematically by X-ray diffraction, Raman spectroscopy, impedance analyzer, ferroelectric test system, and unipolar strain measurement. Composition with x  = 0.10 performs a good piezoelectric constant d 33 of 363 pC/N, coercive field E c of 257 V/mm, remanent polarization P r of 14.5 μC/cm 2 , and a Curie temperature T m of 109°C. High-resolution X-ray diffraction was introduced to indicate presence of orthorhombic phase. Converse piezoelectric constant d 33 * of x  = 0.10 composition performed better temperature stability in the range from 50°C to 110°C. That means decreasing orthorhombic–tetragonal phase transition temperature could be an effective way to enlarge its operating temperature range.

Description: TiO 2 -doped Y 2 O 3 -stabilized ZrO 2 compounds with low thermal conductivity have been considered as a promising thermal barrier coating material. In the present research, a series of TiO 2 -doped Y 2 O 3 -stabilized ZrO 2 compounds have been synthesized and investigated. Lattice distortion and disordering caused by TiO 2 doping were observed and their effects on mechanical properties, such as fracture toughness, elastic modulus, and coefficient of thermal expansion (CTE), were also investigated. Lattice distortion enhanced the ferroelastic toughening and the fracture toughness, whereas the variation in elastic modulus and CTE is due to the lattice disordering. The combination of thermal and mechanical properties bodes well for the potential application as thermal barrier coating materials.

Description: The influence of second phase zirconia particles on the electrical properties and fracture behavior of various polycrystalline soft Pb ( Zr 1− x Ti x ) O 3 (PZT) compositions was investigated. PZT composites with yttria-stabilized tetragonal zirconia particles exhibited enhanced crack resistance in comparison to monolithic compositions, regardless of the PZT composition. The addition of zirconia, however, was found to change the PZT composition through the diffusion of zirconium, resulting in variations in the observed piezoelectric and ferroelectric responses. Through the tailoring of the PZT matrix composition, the large electromechanical response and enhanced fracture toughness could be retained. The variation in both small and large signal properties is contrasted to fracture results and crystal structure changes, as determined by X-ray diffraction.

Description: A novel method is employed for the formation of rare earth phosphate solid solution compounds with unique mesoscopic structures. Europium- and lanthanum-doped sodium borate glass microspheres and particles, ranging in sizes from 50 to 300 μm, were reacted in 0.25 M K 2 HPO 4 solution to form hollow spheres of nanocrystalline rare earth phosphate compounds by dissolution–precipitation reactions. The initially X-ray amorphous precipitated rare earth phosphate materials were heat-treated at 700°C for 2 h to form nanocrystalline compounds. Differential thermal analysis (DTA) experiments yield an average activation energy for crystallization of 394 ± 26 kJ/mol. X-ray diffraction (XRD) data indicate that samples crystallized to the monazite structure (monoclinic P2 1 /n) with unit cell volumes ranging from 306.5 Å 3 for LaPO 4 to 282.5 Å 3 for EuPO 4 and with crystallite grain sizes of 56 ± 14 nm. Compositions containing both rare earth elements formed solid solutions with the composition La (1− x ) Eu x PO 4 . Raman spectroscopy indicates that the P–O symmetric stretching vibrations (ν 1 ) change systematically from 963 cm −1 for LaPO 4 to 986 cm −1 for EuPO 4 , consistent with a systematic decrease in average P–O bond length. Photoluminescence measurements show maximum emission intensity for the La 0.65 Eu 0.35 PO 4 composition.

Description: A single crystal of α- Ca 2 [ HSiO 4 ](OH) (α- C 2 SH) was repeatedly imaged at room temperature with synchrotron mid-infrared microscopy after heating to 310°C, 340°C, 370°C, and 400°C respectively. The mechanisms of the observed phase transformations are discussed on the basis of a modular concept of the crystal structures. All images show domains of dellaite, Ca 6 [ Si 2 O 7 ][ SiO 4 ](OH) 2 , which are predominantly formed in the core of the crystal. In the crystal rim area α- C 2 SH persists in higher abundance. The mechanism of the phase transformation of α- C 2 SH into dellaite includes the following: (1) Partial formation of killalaite ( Ca 3 [ HSi 2 O 7 ](OH)) as nuclei according to the isochemical reaction 2 Ca 2 [ HSiO 4 ](OH) → Ca 3 [ HSi 2 O 7 ](OH) +  Ca (OH) 2 probably induced by anisotropic thermal expansion, local chemical fluctuations, structural (proton) disorder, and different bond strengths of the OH groups in the α- C 2 SH structure. (2) Further dehydration of killalaite and α- C 2 SH domains results in the formation of dellaite according to Ca 3 [ HSi 2 O 7 ](OH) + Ca(OH) 2  + Ca 2 [ HSiO 4 ](OH) – 2 H 2 O → Ca 6 [ Si 2 O 7 ][ SiO 4 ](OH) 2 . The results suggest that the polymerization of two isolated [ HSiO 4 ] tetrahedra takes place without dehydration according to reaction (1) rather than through condensation with simultaneous H 2 O release: 2[ HSiO 4 ] → [ Si 2 O 7 ] +  H 2 O . We suggest that reaction (1) cannot be completed at ambient pressure. Thus in the regions close to the rim of the crystals we expect the formation of x - C 2 S , which starts along the crystal edges according to Ca 2 [ HSiO 4 ](OH) → Ca 2 SiO 4  +  H 2 O . Based on a modular concept, a structural relationship between α- C 2 SH, killalaite, dellaite, and x - C 2 S has been established. Similarities and differences in the thermal behavior of α- C 2 SH and afwillite have been highlighted.

Description: The oxygen permeability of polycrystalline α-alumina wafers, which served as models for alumina scales on alumina-forming alloys, under steep oxygen potential gradients ( ) was evaluated at 1873 K. Oxygen permeation occurred by the grain-boundary (GB) diffusion of oxygen from the higher-oxygen-partial-pressure ( ) surface to the lower- surface, along with the simultaneous GB diffusion of aluminum in the opposite direction. The fluxes of oxygen and aluminum at the outflow side of the wafer were significantly larger than at the inflow side. Furthermore, Lu and Hf segregation at the GBs selectively reduced the mobility of oxygen and aluminum, respectively. A wafer with a bilayer structure, in which a Lu-doped layer was exposed to a lower and an Hf-doped layer was exposed to a higher , decreased the oxygen permeability. When the sign of was reversed, however, the oxygen permeability of the wafer was comparable to that of a nondoped wafer. Co-doping with both Lu and Hf markedly increased the oxygen permeation, presumably because the Lu-stabilized HfO 2 particles that were segregated at the GBs acted as extremely fast diffusion paths for oxygen through the large number of oxygen vacancies introduced by the solid solution of Lu in the particles.

Description: Scandium fluoride ( ScF 3 ) belongs to one of the rare compounds which exhibit isotropic negative thermal expansion. Here, a facile and environmentally friendly hydrothermal synthesis method has been presented. High-quality single-crystalline ScF 3 cubes, with an average size of 200 nm, can be easily fabricated in a large scale. Sc (NO 3 ) 3 and NH 4 HF 2 were used as precursors. The as-prepared ScF 3 demonstrates cubic symmetry ( Pm -3  m ), which was confirmed by X-ray diffraction and selected-area electron diffraction. Its uniform morphology and size were characterized by high-resolution transmission electron microscopy. Furthermore, thermal analysis was also performed in argon gas atmosphere to investigate its thermal stability.

Description: Results of the spectroscopic characteristics and upconversion luminescence in Er 3+ doped yttria ( Y 2 O 3 ) transparent ceramics prepared by a modified two-step sintering method are presented. The near-infrared (1.5 μm) luminescence properties were evaluated as a function of Er 3+ concentration. Judd–Ofelt intensity parameters, radiative rates, branching ratios, and emission lifetimes were determined and compared with results reported for Er 3+ -doped Y 2 O 3 single crystal and nanocrystals. Following pumping at 1.532 μm, weak blue (~0.41 μm, 2 H 9/2 → 4 I 15/2 ), strong green (~0.56 μm, 2 H 11/2 , 4 S 3/2 → 4 I 15/2 ), and red (~0.67 μm, 4 F 9/2 → 4 I 15/2 ) emission bands were observed as well as weak near-infrared emissions at 0.8 μm ( 4 I 9/2 → 4 I 15/2 ) and 0.85 μm ( 4 S 3/2 → 4 I 13/2 ) at room temperature. The upconversion luminescence properties under ~1.5 μm pumping were further investigated through pump power dependence and decay time studies. Sequential two-photon absorption leads to the 4 I 9/2 upconversion emission, whereas energy-transfer upconversion is responsible for the emission from the higher excited states 2 H 9/2 , 2 H 11/2 , 4 S 3/2 , and 4 F 9/2 . The enhanced red emission with increasing Er 3+ concentration most likely occurred via the cross-relaxation process between ( 4 F 7/2 → 4 F 9/2 ) and ( 4 I 11/2 → 4 F 9/2 ) transitions, which increased the population of the 4 F 9/2 level.

Description: Zirconia phase transformation is usually studied on surface. For in-depth study, three methods were proposed using Raman microspectroscopy quantitative evaluation: direct measurement on sample cross section, confocal Raman spectroscopy (CRS), and progressive pinhole aperture enlargement (PPAE). The aim of this study was to compare transformation profiles obtained with these three methods on the same sample. Three 3Y-TZP samples were aged, respectively, for 25, 72, and 90 h in artificial saliva. Transformation profiles were determined with cross-sectional measurement, CRS and PPAE. A transformation profile simulation model based on PPAE measurements is proposed, using the convolution of the excitation intensity profile and the Beer–Lambert law (optical properties of zirconia). The simulation model was validated with the determination of 3Y-TZP transformation factor, T  = 1.15 μm −1 , identical for the three aging durations. Both cross section and PPAE measured similar in-depth transformation decrease, but with a 10 μm-shift: transformed zirconia layer is more important in cross-sectional protocol (36 μm with PPAE and 46 μm with cross-sectional after 90 h aging). Complementary measurements on a 10 h aged sample, where transformation is initiated by Low-Temperature Degradation, showed that sample preparation and polishing, necessary in the cross-sectional method, were responsible for the higher transformation. PPAE method enables noninvasive in-depth measurements with limited optical and mechanical biases.

Description: New cementitious materials based on calcium hydrosilicate hydrates were recently developed as potential substitutes for ordinary portland cement, but with a reduced CO 2 footprint. The materials are produced by hydrothermal processing of SiO 2 and Ca ( OH ) 2 , giving rise to calcium silicate hydrates, followed by mechanical activation of the latter via cogrinding with various siliceous materials. Thus, the chemical composition in terms of C/S ratio could be adjusted over a broad range (1–3). In this study the synthesis of a previously unknown cementitious material produced via the combination of mechanical activation in a laboratory mill and thermal treatment of a mixture of quartz and hydrothermally synthesized calcium silicate hydrates: α- Ca 2 [ HSiO 4 ]( OH ) (α- C 2 SH ) and Ca 6 [ Si 2 O 7 ]( OH ) 6 (jaffeite) are reported. It forms independently of the type of mill used (eccentric vibrating mill, vibration grinding mill) after thermal treatment of the ground materials at 360°C–420°C. The new material is X-ray amorphous and possesses a CaO / SiO 2 ratio of 2. A characteristic feature in regards to the silicate anionic structure is the increased silicate polymerization (up to 27% Si 2 O 7 dimers) as revealed by the trimethylsilylation method. Infrared (IR) spectra show a very broad absorption band centered at about 935 cm −1 . Another characteristic feature is the presence of ~2.5 wt% H 2 O as shown by thermogravimetry (TG) coupled with IR spectroscopy. As this water is bound mostly as hydroxyl to Ca, we refer to this new cementitious material as calcium-oxide–hydroxide–silicate ( C – CH – S ). Calorimetric measurements point to a very high hydraulic reactivity which is beyond that for typical C 2 S materials. The influence of the type of grinding on the thermal behavior of α- C 2 SH upon its transformation into water-free Ca 2 SiO 4 modifications is discussed.

Description: A series of Ce 3+ , Tb 3+ , Eu 3+ tri-doped Ba 2 Y (BO 3 ) 2 Cl red-emitting phosphor have been synthesized by solid-state method. The Ce 3+ → Tb 3+ → Eu 3+ energy-transfer scheme has been proposed to realize the sensitization of Eu 3+ ion emission by Ce 3+ ions. Following this energy-transfer model, near-UV convertible Eu 3+ -activated red phosphors have been obtained in Ba 2 Y (BO 3 ) 2 Cl : Ce 3+ , Tb 3+ , Eu 3+ phosphors. Energy transfers from Ce 3+ to Tb 3+ , and Tb 3+ to Eu 3+ , as well as corresponding energy-transfer efficiencies are investigated. The combination of narrow-line red emission and near-UV broadband excitation makes Ba 2 Y (BO 3 ) 2 Cl : Ce 3+ , Tb 3+ , Eu 3+ as a novel and efficient red phosphor for NUV LED applications.

Description: Computational simulations of glass extrusion are performed to quantify the effects of material behavior and slip at the die/glass interface on the die swell. Experimental data for three glass types are used to guide the computational study, which considers glass material to be viscous with and without shear thinning and viscoelastic using the Maxwell upper-convected model. The study starts with assuming no-slip at the glass/die interface to see if material behavior alone can explain the die swell results, and then considers slip using the Navier model where interface shear is directly proportional to the relative slip speed at the interface. Consistent with the possibility of slip and intended high viscosity applications, viscosity ranging from 10 7.4 –10 8.8  Pa·s was used. Based on optimization of the various input parameters required to achieve the measured die swell and ram force values, the study concludes that interface slip occurred as only extreme values of the shear thinning parameters provided an alternative.

Description: A bilayer concept was proposed to adjust the electrical properties of NTC thermistors. The conventional NTC material Ni 0.75 Mn 2.25 O 4 was chosen as the sensitive layer, and high conductive LaMnO 3 – Ni 0.75 Mn 2.25 O 4 composite was chosen as the support layer. The bilayer NTC thermistors were successfully fabricated by classical uniaxial pressing method. After cosintering at 1235°C for 4 h, the two layers adhered well to each other without any cracking or delamination. The resistance decreased linearly with the decrease in the thickness of Ni 0.75 Mn 2.25 O 4 layer, and the B values varied between 3868 and 3901 K. After annealing at 150°C in air for 500 h, the resistance shifts at 25°C were less than 1%, which mean that the bilayer NTC thermistors had high stability.

Description: Easy sinterable Ti 3 SiC 2 powder was synthesized from a powder mixture with a molar ratio of 1.0 Ti , 0.3 Al , 1.2 Si , and 2.0 TiC by heating at 1200°C in the flowing Ar. Here, the Al powder acts as a deoxidation agent and provides a liquid phase for the reaction. The powder compacts subjected to pressureless sintering at 1300°C in Ar had a relative density up to 99%. The results of chemical analysis and the measured lattice constant suggest that the Al–Si liquid phase was formed at approximately 1200°C and that liquid-phase sintering was promoted by the 0.1 molar ratio of Al and the 0.2 molar ratio of Si remaining in excess. The three-point bending strength, fracture toughness, and electrical resistivity of the sintered samples were 380 MPa, 4.1 MPa m 1/2 , and 0.34μΩm, respectively.

Description: Dense nanocrystalline barium strontium titanate Ba 0.6 Sr 0.4 TiO 3 (BST) ceramics with an average grain size around 40 nm and very small dispersion were obtained by spark plasma sintering at 950°C and 1050°C starting from nonagglomerated nanopowders (~20 nm). The powders were synthesized by a modified “Organosol” process. X-ray diffraction (XRD) and dielectric measurements in the temperature range 173–313 K were used to investigate the evolution of crystal structure and the ferroelectric to paraelectric phase transformation behavior for the sintered BST ceramics with different grain sizes. The Curie temperature T C decreases, whereas the phase transition becomes diffuse for the particle size decreasing from about 190 to 40 nm with matching XRD and permittivity data. Even the ceramics with an average grain size as small as 40 nm show the transition into the ferroelectric state. The dielectric permittivity ε shows relatively good thermal stability over a wide temperature range. The dielectric losses are smaller than 2%–4% in the frequency range of 100 Hz–1 MHz and temperature interval 160–320 K. A decrease in the dielectric permittivity in nanocrystalline ceramics was observed compared to submicrometer-sized ceramics.

Description: Very few studies have been directed at the compositional dependence of the intrinsic photostability of the Ge x Se 1− x binary ChG films especially for the Ge-rich films with the mean coordination number (MCN) larger than 2.67. Here, by measuring the in-situ transmission changes, it shows that the photosensitivity (e.g., photobleaching, PB) of the Ge-rich films (as compared to the GeSe 2 film) is attenuated, in fact almost completely eliminated in the film with the largest MCN. A straightforward technique, in-situ Raman spectroscopy, is used to record the time-resolved intrinsic structural changes during the irradiation of the films. The result indicates a transition from PB towards photostability occurs at the critical composition of GeSe 2 corresponding to the structural phase transition. The stressed rigid structures of the Ge-rich films inhibit any significant photo-structural changes.

Description: Although chemically inert nanosize mineral fillers have been shown to modify early cement hydration kinetics, with the effects dependent upon usage rate, particle size, and dispersibility, the effects of such fillers on the “apparent activation energy” ( E a ) of cement has not been previously examined. Here, cement E a was calculated from isothermal calorimetry performed at different temperatures with two different types of fillers (i.e., titanium dioxide and limestone) using a linear method as well as a modified ASTM C1074 method. The use of both types of nanoparticles increased the rate of cement hydration as well as accelerated the reaction rate, due to heterogeneous nucleation effect, as previously demonstrated. E a increased in the presence of nanosized fillers, demonstrating an increased temperature sensitivity of the filler-cement composites relative to ordinary cement. These results show that chemically inert nanoparticles behave fundamentally differently compared with supplementary cementitious materials such as fly ash and silica fume which instead decrease temperature sensitivity. The increased temperature sensitivity could thus be used to modify and optimize the reaction mechanism and kinetics of cement hydration, especially to increase the rate of cement hydration, to decrease setting time, and to achieve faster strength gain accounting for higher or lower temperatures during curing.

Description: The growing demand of reliable high-performance membrane materials for separation processes requires new simple, straightforward, environmental friendly, sustainable approaches for membrane fabrication. In this study, we present an environmentally friendly gel-casting, one-pot process based on ionotropic-gelation for obtaining alumina membranes. A slurry of alumina particles and the biopolymer alginate, which acts in combination with calcium iodate like a resin, was gelled in a controllable temperature dependent manner. Alumina membranes are obtained by three different shaping routes (extrusion, free-forming, casting). The suitability of extruded capillaries in a polymer-ceramic hybrid state (green body) and after sintering (1150°C for 2 h) for potential application in micro- and ultrafiltration is evaluated by monitoring the chemical and mechanical stability, permeability and separation behavior. Varying the initial alumina particle size from 200 to 900 nm, membranes with a narrow pore size distribution, predictable and tunable average pore diameters from 70 up to 480 nm and a constant open porosity of ~40%, are obtained. The permeability behavior is tested with fluorescence labeled submicron- and nano-particles. Our novel colloidal processing route represents a very versatile tool for designing and manufacturing ceramic membranes with complex shapes for micro- (〉0.1 μm) and ultrafiltration (0.1–0.01 μm).

Description: Amorphous thin films of Ti 1− y Si y (N,O) with y  ≥ 0.38 were prepared by reactive sputter deposition in a nitrogen atmosphere. Thermal annealing of the films in an ammonia flow above 800°C yielded Si (N,O) amorphous thin films dispersed with precipitated TiN nanosized particles. The film color changed with Si content y and the annealing conditions, from carrot orange to cream yellow in the as-deposited films due to their oxynitride nature, and from dark green to canary yellow and from iron blue to horizon blue at respective annealing temperatures of 800°C and 900°C due to metallic nature of the TiN nanosized particles precipitated in the annealing.

Description: A series of phosphors Ca 12(0.97− x ) Al 14 O 32 F 2 : 0.03 Ce 3+ , x Tb 3+ have been prepared by a hightemperature solid-state reaction using boric acid as flux. These oxyfluorides crystallize in cubic structure, space group. Under the near ultraviolet excitation within wavelength range 310–390 nm, Ca 12(0.97− x ) Al 14 O 32 F 2 : 0.03 Ce 3+ , x Tb 3+ phosphors exhibit an intense emission covering a broad band of 370–500 nm derived from the 5 d →4 f transitions of Ce 3+ and a characteristic emission at 544 nm of Tb 3+ . The emission can be tuned from blue to green by altering the relative ratio of Ce 3+ to Tb 3+ in the composition. The energy-transfer mechanism from Ce 3+ to Tb 3+ is investigated based on the site occupancy of the luminescence center in the crystal structure of the Ca 12 Al 14 O 32 F 2 host. More importantly, when a certain amount of boric acid is added as flux in the synthesis, the fluorescence intensity of the phosphors increases about 65%. Because of its broad excitation and efficiently tunable blue to green luminescence, the Ca 12(0.97− x ) Al 14 O 32 F 2 : 0.03 Ce 3+ , x Tb 3+ phosphors may find promising application as a near UV-convertible phosphor for white-light-emitting diodes.

Description: Ti , TiC , Al and AlN powders were mixed to synthesize Ti 2 Al ( C x N y ) ( x  +  y  〈 1) solid solutions, Ti 2 AlC x ( x  〈 1) and Ti 2 AlN -related end-members by hot isostatic pressing at 1400°C/80 MPa for 4 h. For the pure carbides, it is demonstrated that single-phased samples can only be obtained when about 15% of substoichiometry on the carbon site is applied. Such a result likely implies that Ti 2 AlC x can only exist in a narrow range of carbon composition. Ti 2 AlN nitride can be synthesized with y  = 1. Assuming that vacancy content varies linearly from 0 to 0.15 going from Ti 2 AlN to Ti 2 AlC 0.85 in the solid solutions, element concentrations have been calculated to synthesize different solid solutions. Thus, it is demonstrated that single-phased and fully dense Ti 2 Al ( C 0.23 N 0.71 ), Ti 2 Al ( C 0.45 N 0.45 ), and Ti 2 Al ( C 0.66 N 0.22 ) carbonitrides can be synthesized.

Description: The dielectric and electromechanical properties of 0.75 Bi 1/2 Na 1/2 TiO 3 –0.25 SrTiO 3 (25 ST ) as a function of temperature and frequency were studied. It is shown that the 25 ST is a relaxor ferroelectric as evidenced by the temperature-dependent dielectric relaxations with an incipient piezoelectricity featured by the presence of a reversible electric-field-induced phase transformation at room temperature. The transition occurs on a broad electric field strength range depending on field amplitude and frequency. It is also accompanied by a huge strain that is attributed to repetitive poling and depoling originating due to the reversibility of the phase transition. The 25 ST makes an attractive lead-free candidate for stack actuators as it presents a high normalized d 33 * of ~600 pm/V at a low electric field of 4 kV/mm for frequencies ranging from 0.1 up to 100 Hz.

Description: Sodium-doped ZnO (ZnO:Na) nanowires were grown with a high-pressure pulsed-laser deposition process on silicon substrates using sputtered gold particles as catalysts. The introduction of sodium dopants into ZnO nanowires was confirmed by both X-ray diffraction spectrum and X-ray photoelectron spectroscopy. The morphology and microstructural changes in ZnO nanowires due to sodium doping were investigated with scanning electron microscope, high-resolution transmission electron microscope, and Raman spectrum. Detailed photoluminescence studies of ZnO:Na nanowires revealed characteristic sodium acceptor-related peaks, for example, neutral acceptor-bound exciton emission (A 0 X, 3.356 eV), free-to-neutral-acceptor emission (e, A 0 , 3.314 eV), and donor-to-acceptor pair emission (DAP, 3.241 eV). This indicated that sodium doping induces stable acceptor level with a binding energy of 133 meV in ZnO:Na nanowires.

Description: Multiferroic Bi 1− x La x FeO 3 [ BLFO ( x )] ceramics with x  = 0.10–0.50 and Mn-doped BLFO ( x  = 0.30) ceramics with different doping contents (0.1–1.0 mol%) were prepared by solid-state reaction method. They were crystallized in a perovskite phase with rhombohedral symmetry. In the BLFO ( x ) system, a composition ( x )-driven structural transformation ( R 3 c → C 222) was observed at x  = 0.30. The formation of Bi 2 Fe 4 O 9 impure phase was effectively suppressed with increasing the x value, and the rhombohedral distortion in the BLFO ceramics was decreased, leading to some Raman active modes disappeared. A significant red frequency shift (~13 cm −1 ) of the Raman mode of 232 cm −1 in the BLFO ceramics was observed, which strongly perceived a significant destabilization in the octahedral oxygen chains, and in turn affected the local FeO 6 octahedral environment. In the Mn-doped BLFO ( x  = 0.30) ceramics, the intensity of the Raman mode near 628 cm −1 was increased with increasing the Mn-doping content, which was resulted from an enhanced local Jahn–Teller distortions of the ( Mn,Fe ) O 6 octahedra. Electron microscopy images revealed some changes in the ceramic grain sizes and their morphologies in the Mn-doped samples at different contents. Wedge-shaped 71° ferroelectric domains with domain walls lying on the {110} planes were observed in the BLFO ( x  = 0.30) ceramics, whereas in the 1.0 mol% Mn-doped BLFO ( x  = 0.30) samples, 71° ferroelectric domains exhibited a parallel band-shaped morphology with average domain width of 95 nm. Dielectric studies revealed that high dielectric loss of the BLFO ( x  = 0.30) ceramics was drastically reduced from 0.8 to 0.01 (measured @ 10 4  Hz) via 1.0 mol% Mn-doping. The underlying mechanisms can be understood by a charge disproportion between the Mn 4+ and Fe 2+ in the Mn-doped samples, where a reaction of Mn 4+  + Fe 2+ →Mn 3+  + Fe 3+ is taken place, resulting in the reduction in the oxygen vacancies and a suppression of the electron hopping from Fe 3+ to Fe 2+ ions effectively.

Description: There is a growing requirement for high-temperature piezoelectric materials in the petrochemical, automotive, and aerospace industries. Here, the piezoelectric materials of Fe and Mn comodified 0.36 BiScO 3 –0.64 PbTiO 3 (BS-PTFMn) ceramics with high Curie temperature ( T c ), large mechanical quality factor ( Q m ), and reduced strain hysteresis were presented. XRD results revealed that all the BS- PTFMn ceramics have a pure perovskite structure with tetragonal symmetry, and the ratio of c/a is insensitive to the contents of Fe . With the modifications of Fe, the dielectric loss tanδ and strain hysteresis decrease clearly, while the mechanical quality factor improves significantly. The Curie temperature, piezoelectric constant, planar electromechanical coupling factor, dielectric loss, and mechanical quality factor of the BS- PTFMn with 3% Fe content are 492°C, 235 pC/N, 0.38, 0.6%, and 280, respectively. BS-PTFMn ceramics show 50°C higher T c than BS-PT morphotropic phase boundary composition. The figure of merit (product of Q m , and k ij ) of BS-PTFMn ceramics is about five times than that of pure BS-PT ceramics. Furthermore, for the BS- PTFMn ceramics with Fe content of 3 mol%, the high field strain coefficient value calculated from the electric-field-induced strain curves ( S max / E max ) is 320 pm/V, while the strain hysteresis (under 40 kV/cm) is reduced to one fifth that of unmodified BS-PT ceramics. Moreover, the temperature-dependent electromechanical coupling coefficient and dielectric constant are very stable in the temperature range from room temperature (RT) to 450°C. These results indicated that BS- PTFMn ceramics are promising for high-temperature piezoelectric applications.

Description: It has recently been shown that a three-parameter Weibull function with a large threshold strength of ≈2 GPa is needed to accurately describe the failure strength statistics of micromachined polycrystalline silicon samples. Here, we explore how to apply this function to predict strength size effects over a size range of 100. A two-parameter function is unsatisfactory in predicting the size effect. If a three-parameter Weibull fit to only the largest specimen is used, the prediction also does not satisfactorily agree with strength data in smaller specimens. The prediction is greatly improved if the two largest specimens, a factor of 10 different in size, are used for fitting. It is further demonstrated that the threshold strength depends on geometry in notched samples due to their large stress gradients.

Description: Improved performance by texturing has become attractive in the field of lead-free ferroelectrics, but the effect depends heavily on the degree of texture, type of preferred orientation, and whether the material is a rotator or extender ferroelectric. Here, we report on successful texturing of K 0.5 Na 0.5 NbO 3 (KNN) ceramics by alignment of needlelike KNN templates in a matrix of KNN powder using tape casting. Homotemplated grain growth of the needles was confirmed during sintering, resulting in a high degree of texture parallel to the tape casting direction (TCD) and the aligned needles. The texture significantly improved the piezoelectric response parallel to the tape cast direction, corresponding to the direction of the strongest 〈001〉 pc orientation, while the response normal to the tape cast plane was lower than for a nontextured KNN. In situ X-ray diffraction during electric field application revealed that non-180° domain reorientation was enhanced by an order of magnitude in the TCD, compared to the direction normal to the tape cast plane and in the nontextured ceramic. The effect of texture in KNN is discussed with respect to possible rotator ferroelectric properties of KNN.

Description: The stability of the field-induced ferroelectric (FE) state was studied in relaxor lead-free ceramics (1 −  y )[0.81 Bi 1/2 Na 1/2 TiO 3 –0.19 Bi 1/2 K 1/2 TiO 3 ]– y BiZn 1/2 Ti 1/2 O 3 both macroscopically and microscopically. A strong dc electric field results in the formation of a stable FE state with a large piezoelectric coefficient for compositions with a small amount of Bi ( Zn 1/2 Ti 1/2 ) O 3 , which are in the non-ergodic relaxor state at room temperature. Increasing temperature promotes ergodic relaxor behavior, which is accompanied by the rapid destabilization of the induced state, that is, small relaxation times. Based on the obtained data, it is proposed that the depolarization is a two-step process consisting of an initial realignment of the FE domains and their subsequent breakup into polar nanoregions. The ergodic relaxor behavior is also promoted by increasing the Bi ( Zn 1/2 Ti 1/2 ) O 3 content. The related charge disorder results in an enhancement of random electric fields and consequently a stable FE state cannot be induced even at room temperature.

Description: The hydraulic behavior of synthetic merwinite was investigated after activation by two different methods, aiming to enhance its hydraulic activity which is weak in water. Mechanical activation, by means of extensive milling in a bead mill, led to amorphization of merwinite and a decrease in its crystallite size. The combined effect of higher specific surface area and of structural disorder resulted in a notable increase of hydraulic reactivity. The hydraulic reactivity was substantially more pronounced with chemical activation compared to mechanical activation. Crystalline and amorphous C-S-H and brucite were the main hydration products formed in the hydrated, mechanically activated merwinite, whereas portlandite precipitated additionally in the case of chemical activation. Spectroscopic analyses of FTIR and 29 Si MAS NMR verified the C-S-H formation. TEM investigations revealed formation of Mg-low C-S-H gel around the merwinite particles. Both mechanically and chemically activated merwinite systems were capable of developing mechanical strength.

Description: While pressure balance can predict how far the magnetopause will move in response to an upstream pressure change, it cannot determine how fast the transient reponse will be. Using Time History of Events and Macroscale Interactions during Substorms (THEMIS), we present multipoint observations revealing, for the first time, strong (thermal + magnetic) pressure gradients in the magnetosheath due to a foreshock transient, most likely a Hot Flow Anomaly (HFA), which decreased the total pressure upstream of the bow shock. By converting the spacecraft time series into a spatial picture, we quantitatively show that these pressure gradients caused the observed acceleration of the plasma, resulting in fast sunward magnetosheath flows ahead of a localised outward distortion of the magnetopause. The acceleratation of the magnetosheath plasma was fast enough to keep the peak of the magnetopause bulge at approximately the equilibrium position i.e. in pressure balance. Therefore, we show that pressure gradients in the magnetosheath due to transient changes in the total pressure upstream can directly drive anomalous flows and in turn are important in transmitting information from the bow shock to the magnetopause.

Description: We applied Ensemble Empirical Mode Decomposition (EEMD) for the first time to ionosonde data to study trends in the critical frequency of the F 2 peak, f o F 2 , and its height, h m F 2 , from 1959 to 2005. EEMD decomposes a time series into several quasi-cyclical components, called Intrinsic Mode Functions (IMFs), and a residual, which can be interpreted as a long-term trend. In contrast to the more commonly used linear regression-based trend analysis, EEMD makes no assumptions on the functional form of the trend and no separate correction for the influence of solar activity variations is needed. We also adopted a more rigorous significance testing procedure with less restrictive underlying assumptions than the F-test, which is normally used as part of a linear regression-based trend analysis. EEMD analysis shows that trends in h m F 2 and f o F 2 between 1959 and 2005 are mostly highly linear, but the F-test tends to overestimate the significance of trends in h m F 2 and f o F 2 in 30% and 25% of cases, respectively. EEMD-based trends are consistently more negative than linear regression-based trends, by 30-35% for h m F 2 and about 50% for f o F 2 . This may be due to the different treatment of the influence of a long-term decrease in solar activity from 1959 to 2005. We estimate the effect of this decrease in solar activity with two different data-based methods as well as using numerical model simulations. While these estimates vary, all three methods demonstrate a larger relative influence of the Sun on trends in f o F 2 than on trends in h m F 2 .

Description: The source fluence distribution of Terrestrial Gamma-ray flashes (TGFs) has been extensively discussed in recent years, but few have considered how the TGF fluence distribution at the source, as estimated from satellite measurements, depends on the distance from satellite footpoint and assumed production altitude. As the absorption of the TGF photons increases significantly with lower source altitude and larger distance between the source and the observing satellite these might be important factors. We have addressed the issue by using the tropopause pressure distribution as an approximation of the TGF production altitude distribution and WWLLN spheric measurements to determine the distance. The study is made possible by the increased number of RHESSI TGFs found in the second catalog of the RHESSI data. One find is that the TGF/lightning ratio for the tropics probably has an annual variability due to an annual variability in the Dobson-Brewer circulation. The main result is an indication that the altitude distribution and distance should be considered when investigating the source fluence distribution of TGFs, as this leads to a softening of the inferred distribution of source brightness.

Description: Global Positioning System (GPS) has been widely used to sense crustal deformation and ionospheric anomalies, particularly seismic ionospheric disturbances. In March 2011, the earthquakes with magnitude of up to Mw = 9 occurred in Tohoku near the east coast of Honshu, Japan. The GPS Earth Observation Network (GEONET) in Japan with more than 1200 continuously operating stations provides a unique opportunity to study the detailed seismic ionospheric disturbances. In this paper, the pattern and evolution of seismic ionospheric disturbances following the Tohoku earthquakes are investigated by dense GEONET data, including amplitude, propagation pattern, direction, speed and evolution. Maximal co-seismic ionospheric disturbances are found with up to more than 4 TECU and the disturbance period is around 10 ~ 20 minutes. The seismic ionospheric effects following the aftershocks are attenuating with the increase of the time and distance between the ionospheric pierce point and the epicentre of main event, which last more than two hours. Seismic ionospheric disturbance detected by GPS measurement is not only related to the main shock but also the giant aftershocks. Propagation velocities of the TEC disturbance show a decrease when it spreads 400 ~ 600 kilometres away from the epicentre in the north-western direction, where is just near the west coast of Japan. Furthermore, the TEC disturbance also has an obvious directional features. In the first half hour, the TEC disturbance in the southeast direction has the biggest amplitude, while the dominant direction is changed to northwest tens of minutes later. In addition, signals with higher frequencies are existed in seismic TEC variation at the epicentre region, but do not appear in far field.

Description: This study presents a fusion of data-driven and physics-driven methodologies of energetic electron flux forecasting in the outer radiation belt. Data-driven NARMAX model predictions for geosynchronous orbit fluxes have been used as an outer boundary condition to drive the physics-based VERB code, to simulate energetic electron fluxes in the outer radiation belt environment. The coupled system has been tested for three extended time periods totalling several weeks of observations. The time periods involved periods of quiet, moderate and strong geomagnetic activity and captured a range of dynamics typical of the radiation belts. The model has successfully simulated energetic electron fluxes for various magnetospheric conditions. Physical mechanisms that may be responsible for the discrepancies between the model results and observations are discussed.

Description: . We applied the Grad-Shafranov reconstruction (GSR) technique to Martian magnetic flux ropes observed downstream from strong crustal magnetic fields in the southern hemisphere. The GSR technique can provide a two-dimensional axial magnetic field map as well as the axial orientation of flux ropes from single spacecraft data under assumptions that the structure is magneto-hydrostatic and time-independent. The reconstructed structures, including their orientation, allowed us to evaluate possible formationprocesses for the flux ropes. We reconstructed 297 magnetic flux ropes observed by Mars Global Surveyor between April 1999 and November 2006. Based on characteristics of their geometrical axial orientation and transverse magnetic field topology, we found that they can be mainly distinguished according to whether draped interplanetary magnetic fields overlaying the crustal magnetic fields are involved or not. Approximately two-thirds of the flux ropes can be formed by magnetic reconnection between neighboring crustal magnetic fields attached to the surface. The remaining events seem to require magnetic reconnection between crustal and overlaid draped magnetic fields. The latter scenario should allow planetary ions to be transferred from closed magnetic flux tube to flux tubes connected to interplanetary space, allowing atmospheric ions to escape from Mars. We quantitatively evaluate lower limits on potential ion escape rates from Mars owing to magnetic flux ropes.

Description: In this paper, we have presented the influence of precipitating energetic ions caused by electromagnetic ion cyclotron (EMIC) waves on the sub-auroral ionospheric E region during a geomagnetic storm on March 8, 2008 with observations of the Meteorological Operational (METOP-02) of the Polar Orbiting Environmental Satellites (POES), a GPS receiver in Vaasa of Finland and Finnish network of search coil magnetometers. Conjugate observations of the POES METOP-02 satellite and Finnish network of search coil magnetometers have demonstrated that enhancements of the precipitating energetic ion flux within the proton anisotropic zone are attributed to the interaction between ring current (RC) ions and EMIC waves. With enhancements of the intensity of Pc1 waves observed by search coil magnetometers, the total electron content (TEC) observed by the GPS receiver accordingly increased, meaning that the enhancement of the ionospheric electron density is attributed to the precipitation of RC ions caused by EMIC waves. The electron density profiles derived by the IRI-2007 model and with precipitating energetic protons observed by the POES METOP-02 satellite show that the energetic proton precipitation can cause the E layer peak electron density to increase from 1.62 × 10 9  m −3 to 5.05 × 10 11  m −3 by 2.49 orders of magnitude. In comparison with the height-integrated conductivities derived by the IRI-2007 model, the height-integrated Pedersen and Hall conductivities derived with precipitating energetic protons increase by 2.4 and 2.34 orders of magnitude, respectively. Our result suggests that precipitating energetic ions caused by EMIC waves can lead to an obvious enhancement of the electron density and conductivities in the sub-auroral ionospheric E region during geomagnetic storms.

Description: Auroral patches in diffuse auroras are very common features in the post-midnight local time. However, the processes that produce auroral patches are not yet well understood. In this paper we present two examples of auroral fragmentation which is the process by which uniform aurora is broken into several fragments to form auroral patches. These examples were observed at Athabasca, Canada (geomagnetic latitude: 61.7°N), and Tromsø, Norway (67.1°N). Captured in sequences of images, the auroral fragmentation occurs as finger-like structures developing latitudinally with horizontal scale sizes of 40–100 km at ionospheric altitudes. The structures tend to develop in a north–south direction with speeds of 150–420 m/s without any shearing motion, suggesting that pressure-driven instability in the balance between the earthward magnetic-tension force and the tailward pressure gradient force in the magnetosphere is the main driving force of the auroral fragmentation. Therefore, these observations indicate that auroral fragmentation associated with pressure-driven instability is a process that creates auroral patches. The observed slow eastward drift of aurora during the auroral fragmentation suggests that fragmentation occurs in low-energy ambient plasma.

Description: In order to facilitate usage of optical data in space climate studies we have developed an automated algorithm to quantify the complexity of auroral structures as they appear in ground-based all-sky images. The image analysis is based on a computationally determined ”arciness” value, which describes how arc-like the auroral structures in the image are. With this new automatic method we have analysed the type of aurora in about one million images of green aurora (λ = 557.7 nm) captured at five camera stations in Finnish and Swedish Lapland in 1996–2007. We found that highly arc-like structures can be observed in any time sector and their portion of the auroral structures varies much less than the fraction of more complex forms. The diurnal distribution of arciness is in agreement with an earlier study with high arc occurrence rate in the evening hours and steadily decreasing towards the late morning hours. The evolution of less arc-like auroral structures is more dependent on the level of geomagnetic activity and solar cycle than the occurrence of arcs. The median arciness is higher during the years close to the solar minimum than during the rest of the solar cycle. Unlike earlier proposed, the occurrence rate of both arcs and more complex auroral structures increases towards the solar maximum and decreases towards the solar minimum. The cyclic behaviour of auroral structures seen in our data is much more systematic and clear than previously reported visual studies suggest. The continuous arciness index describing the complexity of auroral structures can improve our understanding on auroral morphology beyond the few commonly accepted structure classes, such as arcs, patches and omega bands. Arciness can further be used to study the relationship of auroral structures at different complexity levels and magnetospheric dynamics.