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► EIS spectra for Ti6Al4V1Zr alloy were fitted with one time constant electric equivalent circuit. ► For covered alloy the equivalent circuit contains two time constants. ► ...Resistances of films increased in time revealing the improvement of the alloy protection capacity. ► Surface roughness significantly increased by apatite formation, being favourably to cell adhesion.
A new titanium base Ti–6Al–4V–1Zr alloy covered with hydroxyapatite or bovine serum albumin/hydroxyapatite was characterized in this paper in order to be used as implant material. Following techniques were used: linear polarization, electrochemical impedance spectroscopy, scanning electronic microscopy, Fourier transform infrared spectroscopy and atomic force microscopy. For HA or BSA/HA covered alloy, the electric equivalent circuit contains two time constants (for the passive film and for coatings). The resistance of the protective films increased in time and BSA/HA coating was slightly rougher than HA coating, this situation being favourably to the cell adhesion.
NRLMSIS® 2.0 is an empirical atmospheric model that extends from the ground to the exobase and describes the average observed behavior of temperature, eight species densities, and mass density via a ...parametric analytic formulation. The model inputs are location, day of year, time of day, solar activity, and geomagnetic activity. NRLMSIS 2.0 is a major, reformulated upgrade of the previous version, NRLMSISE‐00. The model now couples thermospheric species densities to the entire column, via an effective mass profile that transitions each species from the fully mixed region below ~70 km altitude to the diffusively separated region above ~200 km. Other changes include the extension of atomic oxygen down to 50 km and the use of geopotential height as the internal vertical coordinate. We assimilated extensive new lower and middle atmosphere temperature, O, and H data, along with global average thermospheric mass density derived from satellite orbits, and we validated the model against independent samples of these data. In the mesosphere and below, residual biases and standard deviations are considerably lower than NRLMSISE‐00. The new model is warmer in the upper troposphere and cooler in the stratosphere and mesosphere. In the thermosphere, N2 and O densities are lower in NRLMSIS 2.0; otherwise, the NRLMSISE‐00 thermosphere is largely retained. Future advances in thermospheric specification will likely require new in situ mass spectrometer measurements, new techniques for species density measurement between 100 and 200 km, and the reconciliation of systematic biases among thermospheric temperature and composition data sets, including biases attributable to long‐term changes.
Key Points
A major, reformulated upgrade to NRLMSISE‐00 is presented using extensive new data sets from the ground to ~100 km altitude
Vertical structure of the atmosphere is now self‐consistently coupled; O density now extends down to 50 km
New model is warmer in upper troposphere, cooler in stratosphere and mesosphere; thermospheric N2 and O densities are lower
The new NRLMSISE‐00 empirical atmospheric model extends from the ground to the exobase and is a major upgrade of the MSISE‐90 model in the thermosphere. The new model and the associated NRLMSIS ...database now include the following data: (1) total mass density from satellite accelerometers and from orbit determination (including the Jacchia and Barlier data sets), (2) temperature from incoherent scatter radar covering 1981–1997, and (3) molecular oxygen number density, O2, from solar ultraviolet occultation aboard the Solar Maximum Mission. A new component, “anomalous oxygen,” allows for appreciable O+ and hot atomic oxygen contributions to the total mass density at high altitudes and applies primarily to drag estimation above 500 km. Extensive tables compare our entire database to the NRLMSISE‐00, MSISE‐90, and Jacchia‐70 models for different altitude bands and levels of geomagnetic activity. We also explore scientific issues related to the new data sets in the NRLMSIS database. Especially noteworthy is the solar activity dependence of the Jacchia data, with which we study a large O+ contribution to the total mass density under the combination of summer, low solar activity, high latitude, and high altitude. Under these conditions, except at very low solar activity, the Jacchia data and the Jacchia‐70 model indeed show a significantly higher total mass density than does MSISE‐90. However, under the corresponding winter conditions, the MSIS‐class models represent a noticeable improvement relative to Jacchia‐70 over a wide range of F10.7. Considering the two regimes together, NRLMSISE‐00 achieves an improvement over both MSISE‐90 and Jacchia‐70 by incorporating advantages of each.
Among the broad spectrum of vertically propagating tides, migrating diurnal (DW1) and semidiurnal (SW2) are prominent modes of energetic and dynamical coupling between the mesosphere and lower ...thermosphere and the upper thermosphere and ionosphere. DW1 and SW2 tides are modulated on time scales ranging from days to years. NASA Thermosphere‐Ionosphere‐Mesosphere Energetic and Dynamics (TIMED) is the first observational platform to perform global synoptic observations of these fundamental tides (for nearly two decades) overcoming previous observational limitations. Here we utilize the extensive archive of TIMED Doppler Interferometer wind measurements and exploit the capabilities of tidal theory to estimate short‐term (<1 month), seasonal (intra‐annual), long‐term (>1 year), and climatological variability in DW1 (1,1), SW2 (2,2), and SW2 (2,3) modes and then compare with tidal estimates derived from the Navy Global Environmental Model‐High Altitude version data assimilation system. Overall, the tidal estimates from TIMED Doppler Interferometer and Navy Global Environmental Model‐High Altitude version are similar and exhibit significant short‐term and intra‐annual variability. The short‐term variability can induce ∼64% change in the DW1 amplitude. Statistically, the short‐term variability in DW1 (1,1), SW2 (2,2), and SW2 (2,3) modes is of the order of ∼9, 33, and 20 m/s, respectively. The biennial oscillations in DW1 and SW2 modes suggest a systematic correlation with the equatorial quasi‐biennial oscillation in the stratosphere and are more apparent in DW1 amplitudes. Although there is significant interannual variability in addition to the apparent biennial signal, there is no clear evidence of any solar cycle dependence or long‐term trend in either DW1 or SW2 modes.
Key Points
Short‐term and intra‐annual variability in DW1 and SW2 tidal modes estimated from TIDI and NAVGEM‐HA are in good agreement
The biennial oscillations in DW1 and SW2 modes are systematically correlated with equatorial stratospheric quasi‐biennial oscillation
There is no clear evidence of any solar cycle dependence or long‐term trend in either DW1 or SW2 modes
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•Native passive film (TiO2, Ta2O5, ZrO2) on Ti–15Ta–5Zr alloy surface has a thickness of 8.5nm.•Duplex oxide film formed by inner, compact and by outer porous layer was modelled by ...EIS.•Passive film thickened over time by new depositions from physiological solutions.•After 1500h in acid Ringer solution the brushite was detected by XPS.•In neutral and alkaline Ringer solutions the hydroxyapatite was identified by XPS and SEM.
The native passive film on the new Ti–15Ta–5Zr alloy surface contains the protective TiO2, Ta2O5 and ZrO2 oxides (XPS analysis). The decrease of the corrosion current densities and the increase of the polarisation resistances values signify the thickening of the passive film in time. The duplex oxide film formed by the inner, compact, layer and by the outer, porous layer was modelled; electrical parameters indicated the thickening over time both of the barrier and porous layers. XPS and SEM analyses demonstrated the in time deposition of new layers consisting by brushite in acid Ringer solution and from hydroxyapatite in neutral and alkaline Ringer solutions.
The generation of a large‐scale wave in the upper atmosphere caused by a solar eclipse was first predicted in the 1970s, but the experimental evidence remains sparse and comprises mostly indirect ...observations. This study presents observations of the wind component of a large‐scale thermospheric wave generated by the 21 August 2017 total solar eclipse. In contrast with previous studies, the observations are made on the nightside, after the eclipse ended. A ground‐based interferometer located in northeastern Brazil is used to monitor the Doppler shift of the 630.0‐nm airglow emission, providing direct measurements of the wind and temperature in the thermosphere, where eclipse effects are expected to be the largest. A disturbance is seen in the zonal and meridional wind which is at or above the 90% significance level based on the measured 30‐day variability. These observations are compared with a first principles numerical model calculation from the Thermosphere‐Ionosphere‐Mesosphere‐Electrodynamics General Circulation Model, which predicted the propagation of a large‐scale wave well into the nightside. The modeled disturbance matches well the difference between the wind measurements and the 30‐day median, though the measured perturbation (∼60 m/s) is larger than the prediction (38 m/s) for the meridional wind. No clear evidence for the wave is seen in the temperature data, however.
Plain Language Summary
Solar eclipses are natural experiments that allow us to test our models of the upper atmosphere. It has long been theorized that during a solar eclipse, the fast motion of the Moon's shadow across the Earth should cause a wave in the upper atmosphere, similar to the bow wave that develops in front of a boat. In contrast with the boat, which pushes water ahead of it, the cold atmosphere inside the shadow acts like a sinkhole that pulls the air ahead of it. In this paper, we report the first direct observations of the atmosphere moving in response to an eclipse, using data taken during and after the Great American eclipse on 21 August 2017. These observations match well the predictions made by a commonly used upper atmosphere model, in both the timing and size of the response. An interesting aspect of these observations is that they were made in Brazil, after the eclipse had ended, emphasizing the global nature of the eclipse response. This study is important because it provides direct evidence to support previous theoretical eclipse studies, and it furthers our confidence that our first principles models of the upper atmosphere are capturing the relevant physics.
Key Points
Direct detection of the wind perturbation of a large‐scale wave generated by the 21 August 2017 total solar eclipse is presented
Ground‐based observations are made on the nightside, after the eclipse forcing has subsided
The measured wind perturbation agrees well with the TIME‐GCM first principles model, but the temperature measurement is inconclusive
The Horizontal Wind Model (HWM) has been updated in the thermosphere with new observations and formulation changes. These new data are ground‐based 630 nm Fabry‐Perot Interferometer (FPI) ...measurements in the equatorial and polar regions, as well as cross‐track winds from the Gravity Field and Steady State Ocean Circulation Explorer (GOCE) satellite. The GOCE wind observations provide valuable wind data in the twilight regions. The ground‐based FPI measurements fill latitudinal data gaps in the prior observational database. Construction of this reference model also provides the opportunity to compare these new measurements. The resulting update (HWM14) provides an improved time‐dependent, observationally based, global empirical specification of the upper atmospheric general circulation patterns and migrating tides. In basic agreement with existing accepted theoretical knowledge of the thermosphere general circulation, additional calculations indicate that the empirical wind specifications are self‐consistent with climatological ionosphere plasma distribution and electric field patterns.
Key Points
The horizontal wind model has been updated
New data fill observational gaps
Empirical specifications are consistent with ionospheric models
Abstract
The Naval Research Laboratory Sami3 is Also a Model of the Ionosphere (SAMI3) ionosphere/plasmasphere code is used to examine the physics of metallic layers at altitudes from 80 to 160 km. ...Results are presented near the simulated location of the Arecibo observatory (18°N, 66°W). We find that simulations, using winds from the empirical horizontal wind model, produce layers consistent with those observed at Arecibo. Specifically, we find upper semidiurnal and lower diurnal traces similar to those identified in previous observational surveys. While metallic layers are shaped by meridional winds, zonal winds, and electric fields, much of the observed structure is produced if only meridional wind forces are included in the model. Stratification below 110 km, where the ions are very weakly magnetized, is supported mainly by meridional wind shear.
Plain Language Summary
The ionosphere reflects radio signals below and up to a given frequency. Above that frequency, which is proportional to the square root of the peak density of the ionosphere, signals are transmitted. The peak ionosphere density normally occurs in the ionosphere
region, at roughly 200‐ to 600‐km altitude. Metal atoms and associated ions, which are deposited almost continuously by meteors, tend to form layers at altitudes of 90–200 km, in what is known as the ionosphere
region. These layers, which can have densities in excess of the
region peak density, occur almost entirely as a result of wind and electric field‐driven transport. Also known as “sporadic
layers,” metallic ion layers can reflect radio signals, affecting communication and navigation signals. We show that commonly observed metallic ion layers are formed by tidal winds (versus local waves), we confirm previously identified stratification mechanisms at high (magnetized) and middle (partially magnetized) altitudes. We show that stratification at low (unmagnetized) altitudes is driven mainly by meridional winds.
Key Points
SAMI3 describes metallic layers observed at Arecibo
Observed layers are produced by tidal zonal and meridional winds
Metallic layers below 110 km associated mainly with meridional wind shear
In this work, a multi-elementary Ti–10Zr–5Nb–5Ta alloy, with non-toxic alloying elements, was used to develop an accumulative roll bonding, ARB-type procedure in order to improve its structural and ...mechanical properties. The alloy was obtained by cold crucible semi-levitation melting technique and then was ARB deformed following a special route. After three ARB cycles, the total deformation degree per layer is about 86%; the calculated medium layer thickness is about 13 μm. The ARB processed alloy has a low Young’s modulus of 46 GPa, a value very close to the value of the natural cortical bone (about 20 GPa). Data concerning ultimate tensile strength obtained for ARB processed alloy is rather high, suitable to be used as a material for bone substitute. Hardness of the ARB processed alloy is higher than that of the as-cast alloy, ensuring a better behaviour as a implant material. The tensile curve for the as-cast alloy shows an elastoplastic behaviour with a quite linear elastic behaviour and the tensile curve for the ARB processed alloy is quite similar with a strain-hardening elastoplastic body. Corrosion behaviour of the studied alloy revealed the improvement of the main electrochemical parameters, as a result of the positive influence of ARB processing. Lower corrosion and ion release rates for the ARB processed alloy than for the as-cast alloy, due to the favourable effect of ARB thermo-mechanical processing were obtained.
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► New Ti–10Zr–5Nb–5Ta alloy was processed by an accumulative roll bonding (ARB) method. ► After three ARB cycles, total deformation degree/layer is 86%; medium layer thickness is about 13 μm. ► ARB processed alloy has a low Young’s modulus (46 GPa), very close to the value of the natural cortical bone (30 GPa). ► Ultimate tensile strength for ARB processed alloy is high, suitable for a bone implant. ► Improvement of corrosion resistance as result of ARB processing positive influence was obtained.
Many structural and dynamical features of the ionized and neutral upper atmosphere are strongly organized by the geomagnetic field, and several magnetic coordinate systems have been developed to ...exploit this organization. Quasi‐Dipole coordinates are appropriate for calculations involving horizontally stratified phenomena like height‐integrated currents, electron densities, and thermospheric winds; Modified Apex coordinates are appropriate for calculations involving electric fields and magnetic field‐aligned currents. The calculation of these coordinates requires computationally expensive tracing of magnetic field lines to their apexes. Interpolation on a precomputed grid provides faster coordinate conversions, but requires the overhead of a sufficiently fine grid, as well as finite differencing to obtain coordinate base vectors. In this paper, we develop a compact and robust representation of the transformation from geodetic to Quasi‐Dipole (QD), Apex, and Modified Apex coordinates, by fitting the QD coordinates to spherical harmonics in geodetic longitude and latitude. With this representation, base vectors may be calculated directly from the expansion coefficients. For an expansion truncated at order 6, the fitted coordinates deviate from the actual coordinates by a maximum of 0.4°, and typically by 0.1°. The largest errors occur in the equatorial Atlantic region. Compared to interpolation on a pre‐computed grid, the spherical harmonic representation is much more compact and produces smooth base vectors. An algorithm for efficiently and concurrently computing scalar and vector spherical harmonic functions is provided in the appendix. Computer code for producing the expansion coefficients and evaluating the fitted coordinates and base vectors is included in the auxiliary material.
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