Cation distribution in manganese cobaltite spinels Co3−xMnxO4 (0 ≤ x ≤ 1) determined by thermal analysis

Thermogravimetric analysis was used in order to study the reduction in air of submicronic powders of Co3−x Mn x O4 spinels, with 0 ≤ x ≤ 1. For x = 0 (i.e. Co3O4), cation reduction occurred in a single step. It involved the CoIII ions at the octahedral sites, which were reduced to Co2+ on producing CoO. For 0 < x ≤ 1, the reduction occurred in two stages at increasing temperature with increasing amounts of manganese. The first step corresponded to the reduction of octahedral CoIII ions and the second was attributed to the reduction of octahedral Mn4+ ions to Mn3+. From the individual weight losses and the electrical neutrality of the lattice, the CoIII and Mn4+ ion concentrations were calculated. The distribution of cobalt and manganese ions present on each crystallographic site of the spinel was determined. In contrast to most previous studies that took into account either CoIII and Mn3+ or Co2+, CoIII and Mn4+ only, our thermal analysis study showed that Co2+/CoIII and Mn3+/Mn4+ pairs occupy the octahedral sites. These results were used to explain the resistivity measurements carried out on dense ceramics prepared from our powders sintered at low temperature (700–750 °C) in a Spark Plasma Sintering apparatus

HE II Two Phase Flow in an Inclinable 22 m Long Line

In the line of previous work done at CEA Grenoble, large size experiments were performed with the support of CERN for the validation of the LHC two phase superfluid helium cooling scheme. In order to be as close as possible to the real configuration, a straight, inclinable 22 m long line of 40 mm I.D. was built. Very accurate measurements of temperatures and pressures obtained after in situ re-calibration and verified by independent sensors allowed us to validate our two-phase flow model. Although we focus on pressure losses and heat exchange results in relation to power injected, additional measurements such as quality, void fraction, and total mass flow rate enable a complete description of the two-phase flow. Experiments were carried out to cover the whole range of the future LHC He II two-phase flow heat exchanger pipe: slope between 0 and 2.8 %, temperature between 1.8 and 2 K, total mass flow rate up to 7.5 g/s. Results confirm the validity of choice for the LHC cooling scheme

Latest Developments on HeII Co-Current Two-Phase Flow Studies

Large scale experiments were performed at CEA Grenoble with the support of CERN to simulate and understand the HeII cooling circuit of the LHC. This paper describes the latest results obtained in HeII co-current two-phase flow configuration. First we summarize thermal and hydraulic behaviour of flows obtained in a 40 mm I.D., 86 m long tube inclined at 1.4% which resembles closely the LHC heat exchanger tube. For low vapour velocities, the flow pattern is found to be stratified. A model based on this observation has been developed which fits very well the measured pressure losses. However the wetted surface predicted by the model underestimates the measured one, notably for high vapour velocities. In that case, liquid droplets entrainment takes place. Droplets landing on the tube wall increase the wetted surface. Thus we infer that for higher vapour velocities, the stratified two-phase flow model should not be applied anymore. In order to validate the range of availability of the model, and begin to draw a flow pattern map, a 20 mm I.D. horizontal test sector was built and experiments were performed. First results are presented here, including the observation of the stratified-annular flow transition

Hydraulic Behaviour of He II in Stratified Counter-Current Two-Phase Flow

Future large devices using superconducting magnets or RF cavities (e.g. LHC or TESLA) need He II two-phase flow for cooling. The research carried out into counter-current superfluid two-phase flow was the continuation of work on co-current flow and benefited from all the knowledge acquired both experimentally and theoretically. Experiments were conducted on two different pipe diameters (40 and 65 m m I.D. tube) for slopes ranging between 0 and 2%, and for temperatures ranging between 1.8 and 2 K. This paper introduces the theoretical model, describes the tests, and provides a critical review of the results obtained in He II counter current two-phase flow

Probing quantum and classical turbulence analogy through global bifurcations in a von K\'arm\'an liquid Helium experiment

We report measurements of the dissipation in the Superfluid Helium high REynold number von Karman flow (SHREK) experiment for different forcing conditions, through a regime of global hysteretic bifurcation. Our macroscopical measurements indicate no noticeable difference between the classical fluid and the superfluid regimes, thereby providing evidence of the same dissipative anomaly and response to asymmetry in fluid and superfluid regime. %In the latter case, A detailed study of the variations of the hysteretic cycle with Reynolds number supports the idea that (i) the stability of the bifurcated states of classical turbulence in this closed flow is partly governed by the dissipative scales and (ii) the normal and the superfluid component at these temperatures (1.6K) are locked down to the dissipative length scale.Comment: 5 pages, 5 figure

The phase shift of line solitons for the KP-II equation

The KP-II equation was derived by [B. B. Kadomtsev and V. I. Petviashvili,Sov. Phys. Dokl. vol.15 (1970), 539-541] to explain stability of line solitary waves of shallow water. Stability of line solitons has been proved by [T. Mizumachi, Mem. of vol. 238 (2015), no.1125] and [T. Mizumachi, Proc. Roy. Soc. Edinburgh Sect. A. vol.148 (2018), 149--198]. It turns out the local phase shift of modulating line solitons are not uniform in the transverse direction. In this paper, we obtain the $L^\infty$-bound for the local phase shift of modulating line solitons for polynomially localized perturbations

Orbital motion of the young brown dwarf companion TWA 5 B

With more adaptive optics images available, we aim at detecting orbital motion for the first time in the system TWA 5 A+B. We measured separation and position angle between TWA 5 A and B in each high-resolution image available and followed their change in time, because B should orbit around A. The astrometric measurement precision is about one milli arc sec. With ten year difference in epoch, we can clearly detect orbital motion of B around A, a decrease in separation by ~ 0.0054 arc sec per year and a decrease in position angle by ~ 0.26 degrees per year. TWA 5 B is a brown dwarf with ~ 25 Jupiter masses (Neuh\"auser et al. 2000), but having large error bars (4 to 145 Jupiter masses, Neuh\"auser et al. 2009). Given its large projected separation from the primary star, ~ 86 AU, and its young age ~ 10 Myrs), it has probably formed star-like, and would then be a brown dwarf companion. Given the relatively large changes in separation and position angle between TWA 5 A and B, we can conclude that they orbit around each other on an eccentric orbit. Some evidence is found for a curvature in the orbital motion of B around A - most consistent with an elliptic (e=0.45) orbit. Residuals around the best-fit ellipse are detected and show a small-amplitude (~ 18 mas) periodic sinusoid with ~ 5.7 yr period, i.e., fully consistent with the orbit of the inner close pair TWA 5 Aa+b. Measuring these residuals caused by the photocenter wobble - even in unresolved images - can yield the total mass of the inner pair, so can test theoretical pre-main sequence models.Comment: 6 pages, 4 figures, accepted for publication in A&A; corrected typo in amplitude below Fig.

Astrometric and photometric monitoring of GQ Lup and its sub-stellar companion

Neuhaeuser et al. (2005) presented direct imaging evidence for a sub-stellar companion to the young T Tauri star GQ Lup. Common proper motion was highly significant, but no orbital motion was detected. Faint luminosity, low gravity, and a late-M/early-L spectral type indicated that the companion is either a planet or a brown dwarf. We have monitored GQ Lup and its companion in order to detect orbital and parallactic motion and variability in its brightness. We also search for closer and fainter companions. We have taken six more images with the VLT Adaptive Optics instrument NACO from May 2005 to Feb 2007, always with the same calibration binary from Hipparcos for both astrometric and photometric calibration. By adding up all the images taken so far, we search for additional companions. The position of GQ Lup A and its companion compared to a nearby non-moving background object varies as expected for parallactic motion by about one pixel (2 \pi with parallax \pi). We could not find evidence for variability of the GQ Lup companion in the K-band (standard deviation being \pm 0.08 mag), which may be due to large error bars. No additional companions are found with deep imaging. There is now exceedingly high significance for common proper motion of GQ Lup A and its companion. In addition, we see for the first time an indication for orbital motion (about 2 to 3 mas/yr decrease in separation, but no significant change in the position angle), consistent with a near edge-on or highly eccentric orbit. We measured the parallax for GQ Lup A to be \pi = 6.4 \pm 1.9 mas (i.e. 156 \pm 50 pc) and for the GQ Lup companion to be 7.2 \pm 2.1 mas (i.e. 139 \pm 45 pc), both consistent with being in the Lupus I cloud and bound to each other.Comment: A&A in pres

Optical Investigations of HeII Two Phase Flow

The LHC development program relies on cryogenic tests of prototype and model magnets. This vigorous program is pursued in a dedicated test facility based on several vertical cryostats working at superfluid helium temperatures. The performance of the facility is detailed. Goals and test equipment for currently performed studies are reviewed: quench analysis and magnet protection studies, measurement of the field quality, test of ancillary electrical equipment like diodes and busbars. The paper covers the equipment available for tests of prototypes and some special series of LHC magnets to come