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We present new microTEGs based on doped Bi 2 Te 3 thin films deposited on polyimide membrane able to operate under a temperature difference as high as 280 K. We developed two microTEGs with different designs to obtain the lowest internal resistance possible. The thermoelectrical properties coupled to the low contact resistance lead to an open circuit voltage of 64 mV and a maximum output power of 36 µW under a temperature difference of 206 K. Such high temperature difference cannot be obtain in bulk commercial TEG systems; it is maintained without heat sink but only using a copper ring supporting a thin polyimide membrane. These thermoelectric devices deposited on suspended polyimide membranes open new ways for waste heat applications, in particular by direct mechanical and thermal contact with hot sources. [Display omitted] • We present new microTEGs based on doped Bi 2 Te 3 thin films deposited on polyimide membrane. • An open circuit voltage of 64 mV and a maximum output power of 36 µW under a temperature difference of 206 K is obtained. • The temperature difference up to 206 K is obtained without heat sink but only using a copper ring. [ABSTRACT FROM AUTHOR]

Abstract: Magneto-optical (MO) imaging was used to study and characterize superconducting Bi2212 multifilaments melted in a 5T magnetic field. MO investigations were performed in presence of a transport current, with and without the superposition of an external magnetic field (30mT). Transport current redistributions via the Ag cladding have been observed in MO self-field experiments for the first time in Bi2212 multifilaments. MO in situ investigations under tensile stress reveal a slow progression of the cracks, that do not cross the entire section of the multifilamentary tape. This crack formation is correlated with the transport critical current versus strain curves: the critical current drop under tensile stress is relatively smooth for Bi2212 multifilaments. [Copyright &y& Elsevier]

A superconducting fault current limiter using YBCO single domains requires long elements cut along the ab-planes or along the c-axis. These elements have to be assembled in series in order to produce a limited fault current after the quench to the resistive state under the network voltage. The superconductor total length is much smaller with c-axis elements because their high resistivity after transition contributes to a very high electric field during the current limitation. The critical current density has to be decreased in order to be sure that the Joule effect related to the limiting current does not increase too much the material temperature before its interruption by a current breaker. The inhomogeneously oxygenated YBCO elements limit the current even if the only surface layer is superconducting and produce an electric field up to 5000 V/m. A homogeneous oxygenation without macrocrack is obtained when the thickness along the ab-planes is thin. Several elements have been tested by applying a 20 ms duration fault current in a liquid nitrogen bath at T=77 K and above. [Copyright &y& Elsevier]

Ni-Co-Mn-In freestanding films, with a magneto-structural transformation at room temperature were successfully produced by co-sputtering and post-annealing methods leading to film composition mastering. For a post-annealing temperature of 700 °C, the phase transformation occurs slightly above room temperature, with a twisted martensitic microstructure phase observed at 300K by Field Emission Scanning Electron Microscopy. Magnetization measurements on a polycrystalline film showed a phase transformation from a weakly magnetic martensite to a magnetic austenite phase. Moreover, an inverse magnetocaloric effect with an entropy variation of 4 J/kgK under 5 T was also measured. A simple magneto-actuation experiment based on the magnetic induced austenite transformation was also successfully completed. The possibility to insert such films in microsystems is clearly demonstrated in this work. [ABSTRACT FROM AUTHOR]

Internal waves (IWs) in the ocean span across a wide range of time and spatial scales and are now acknowledged as important sources of turbulence and mixing, with the largest observations having 200 m in amplitude and vertical velocities close to 0.5 m s−1. Their origin is mostly tidal, but an increasing number of non-tidal generation mechanisms have also been observed. For instance, river plumes provide horizontally propagating density fronts, which were observed to generate IWs when transitioning from supercritical to subcritical flow. In this study, satellite imagery and autonomous underwater measurements are combined with numerical modeling to investigate IW generation from an initial subcritical density front originating at the Douro River plume (western Iberian coast). These unprecedented results may have important implications in near-shore dynamics since that suggest that rivers of moderate flow may play an important role in IW generation between fresh riverine and coastal waters. [ABSTRACT FROM AUTHOR]

Multiferroic magnetic shape memory alloys with first-order magntostructural transformation exhibit much enhanced magnetocaloric effect which incorporates the latent heat associated with the phase transformation itself, but they suffer from the drawbacks of large hysteresis and transformation interval and consequently too high critical field to actuate the magnetocaloric effect, greatly impeding their applications. Here, by generating a kind of specific stacking-mediated structure of martensite through minor Al substitution to improve the geometric compatibility between martensite and austenite in the Ni 40 Co 10 Mn 40 Sn 9 Al 1 alloy, we greatly reduced the thermal hysteresis and transformation temperature interval while conserving the large magnetization difference between the two phases. Consequently, a low-field-actuated giant magnetocaloric effect with isothermal entropy change of 23 J kg −1  K −1 for a field change from 0 to 2 T, which is among the highest values reported heretofore for all magnetocaloric materials, was successfully achieved. Meanwhile, with minor Al substitution, the present single-phase multiferroic alloy that is intermetallic in nature exhibits superior mechanical properties, including excellent compressive properties over a wide temperature range and a relatively high fracture toughness, which are quite beneficial for practical applications. Incorporating the advantages of low cost, environment friendliness and easy fabrication, this alloy shows great potential for magnetocaloric applications. [ABSTRACT FROM AUTHOR]

The martensitic transformation in Ni 50 Mn 34.5 In 15.5 single crystal was studied by electrical resistivity measurements under controlled and constant uniaxial stress. We observed that the kinetics of the transformation under uniaxial stress, defined as the derivative of the volume fraction of martensite (austenite) with respect to time, present two maxima during heating at a constant rate of 3 K/min. An additional energy is required for the complete transformation to happen and there is a distortion in the hysteretic cycle depending on the rate. The interaction between transformed volume and untransformed volume and inter-variant conversion could be responsible for this distortion adding a local internal stress in the material. The transformation during heating is consequently isothermal. However, a new increase of the austenite restoration rate occurs in an avalanche form when additional superheating leads to an increase in the driving force that does not compensate any more the total strain energy. [ABSTRACT FROM AUTHOR]

Electrical resistivity and magnetization measurements realized on polycrystalline Ni 45.2 Co 4.7 Mn 36.2 In 13.9 film showed that the austenite phase was blocked upon a magnetic field during the martensitic transformation. Besides, the shift of the temperature transition upon a magnetic field towards the lower temperature is responsible for a large magnetoresistance that can be irreproducible in the heating branch of the transformation and that was measured in this work. We studied how the magnetoresistance was changing inside the hysteresis loop depending on whether the temperature lies on the forward or reverse transformation path. The analysis is interpreted in terms of the non equilibrium state consequent to the field cooled process and how martensite is converted into austenite inside the hysteresis loop when the magnetic field is applied. [ABSTRACT FROM AUTHOR]

Abstract: We report here preliminary results on the deposition and structural characterization of thin films of Mg2Si1− x Sn x solid solutions (x =0.4–0.6) with Ag-doping (for p-type material) by plasma co-sputtering, using individual targets of constituent elements. Polycrystalline thin films with nano-size crystallites were deposited on SiO2/Si substrates at room temperature. Chemical composition is controlled by the bias voltage of individual targets, while the microstructure is tailored by the flux and particle energy through the operating conditions namely, gas pressure, microwave power and geometrical configuration. The electrical conductivity strongly depends on layers microstructure. [Copyright &y& Elsevier]

The Grenoble High Magnetic Field Laboratory was built to meet the requirements of scientists for experiments implying the use of very high magnetic fields. Currently, the facility operates for over 5000 h a year and thanks to its most powerful magnets, it allows the production of steady magnetic fields up to 30 T. Scientists have access to the high magnetic field facility provided they have submitted a proposal for experiments in high magnetic fields and have obtained the Program Committee’s approval to carry out their research project. As illustration of the use of our specific instrumentation, we present a study of the behavior of the critical currents of superconducting tapes, performed in collaboration between CNRS Grenoble, France and NIN Xi’an, China. [Copyright &y& Elsevier]

The addition of silver to YBa2Cu3O7−δ (Y123) is well known to decrease its decomposition temperature. This study demonstrates the success in welding large Y123 textured samples with Ag doped Y123 junctions. Attempts to weld two melt textured domains of Y123 by a 1 mm thick layer of Ag doped Y123 are reported. The crucial importance of the initial Y211 excess content in the spacer material is pointed out. Microstructural observations, trapped field measurements and transport critical current density measurements prove that for a given Y211 amount a very high joint quality can be obtained. A transport critical current density as high as 10 kA/cm2 is registered through the junction at 77 K and 5 T when the applied field is parallel to the (a,b) planes. [Copyright &y& Elsevier]

Thirty seven filamentary Bi-2223 Ag sheathed tapes have been fabricated by the PIT method using precursors which were prepared by the two-powder process. The different types of the precursors are the following: (a) a mixture of 2212 and CaCuO2 (powder A), (b) a mixture of 2201 and CaCuO2 (powder B). A nearly pure 2223 phase can be obtained after anneals at 818 °C in 8.5% O2 in less than 40 h and 60 h for powder A and powder B, respectively. However, a small amount of impurity phases, especially the 2201 phase, still appears in the oxide core for tape B (fabricated from powder B) using a conventional thermomechanical process. An additional low-temperature annealing procedure at the end of the last thermal cycle was used to convert any residual 2201 in tape B into 2212, thereby improving the grain connectivity and overall Ic of tape B dramatically. But, this additional annealing stage had no distinct effect on the phase evolution and the critical current of the tape A (fabricated from powder A). Using both types of precursor mixtures, we obtain tapes with high phase purity, well-aligned grains, and reproducible critical current densities. The maximum Ic values (77 K, 0 T) of fully processed tapes with 0.20 mm thickness are 52 A and 42 A for powder A and powder B respectively. [Copyright &y& Elsevier]

Superconducting materials offer the unique possibility to limit fault currents by their self-triggering quench to a resistive state above a given threshold current. Their use in power networks would improve the power quality, which is a real need today. YBCO or BSCO bulk materials are good candidates for current limitation. Their behaviours are rather different, in particular the electric field versus current characteristics. BSCO compounds are protected by their homogeneous quench due to the numerous defects (grain boundaries) distributed along the material. An assembling of 60 sintered Bi bars was tested under 1 kV. The current limitation is effective (a 5000 A short-circuit has been limited to 1080 A) but it occurs at 24 times the critical current. The increase of the critical current density of Bi compounds by their texturation reduces the current excursion above the critical value. In YBCO bulk elements, the defects are localized and make YBCO very sensitive to hot spots. Those are unavoidable and the operating conditions should be adapted in order to make them non-destructive. That is the self-protection concept. To fulfil it, we chose to operate near the critical temperature (above 90 K) to reduce the critical current density. The small difference with Tc is very favourable for the quench. A fault current limiter based on 43 YBCO meanders working at 90.5 K in a pressurized liquid nitrogen bath is presented. The meanders are cut in 45 mm in diameter single domain pellets elaborated using the top-seeding technique. Supplied under a maximum voltage of 1 kV, the current was limited at 740 A instead of the theoretical value of 6500 A without quench. [Copyright &y& Elsevier]

Forty three meanders were mounted and put in series to build a resistive FCL prototype. The nominal current and the temperature were respectively fixed at 100 A and 90.5 K. The voltage and the mean electric field respectively reached 1 kV and 106 V/m during 20 ms. The current was limited to 730 A whereas it would have reached 5.1 kA without limitation. The superconducting parameters were adjusted so as to reduce the temperature (self-protection) reached by the samples. Bulk YBCO proved in our experiment their strong ability to limit the current. However, meanders suffered large electromechanical and thermal stresses during the transition. In this article, we analyse the prototype results. [Copyright &y& Elsevier]

Describes current limitation using bulk Yttrium-Barium-Copper-Oxygen (YBCO). Protection of bulk superconductors; Pellet synthesis and meader cutting; Limitation properties; Use of a fault current limiter; Study of meander pattern conductors cut from bulk melt textured YBCO; Observation under steady state operation and during current limitation.

Dense Bi2223 superconductors have been successfully formed by hot stacking-forging process (HSF). Neutron diffraction measurements were used to investigate the bulk textures of HSF-Bi2223 samples. Angular dependence of transport critical current density, Jc values were measured at various temperatures and different applied magnetic fields. Several textured pieces were hot-stacked. This procedure leads to an increase of both the sample thickness and the nominal engineering critical current (Ic), favourable hints for use of textured-Bi2223 in power generation supplies. [Copyright &y& Elsevier]

Pnictogen and chalcogenide compounds have been seen as high-potential materials for efficient thermoelectric conversion over the past few decades. It is also known that with nanostructuration, the physical properties of these pnictogen-chalcogenide compounds can be further enhanced towards a more efficient heat conversion. Here, we report the reduced thermal conductivity of a large ensemble of Bi2Te3 alloy nanowires (70 nm in diameter) with selenium for n-type and antimony for p-type (Bi2Te3-ySey and Bi2-xSbxTe3 respectively). The nanowire growth was carried out through electrodeposition in nanoporous aluminium oxide templates with high aspect ratios leading to a forest (109 per centimetre square) of nearly identical nanowires. The temperature dependence of thermal conductivity for the nanowire ensembles was acquired through a highly sensitive 3ω measurement technique. The change in the thermal conductivity of nanowires is largely affected by the roughness in addition to the size effect due to enhanced boundary scattering. The major factor that influences the thermal conductivity was found to be the ratio of the rms roughness to the correlation length of the nanowire. With a high Seebeck coefficient and electrical conductivity at room temperature, the overall thermoelectric figure of merit ZT allows the consideration of such forests of nanowires as efficient potential building blocks of future TE devices.

The 3 ω method is a dynamic measurement technique developed for determining the thermal conductivity of thin films or semi-infinite bulk materials. A simplified model is often applied to deduce the thermal conductivity from the slope of the real part of the ac temperature amplitude as a function of the logarithm of frequency, which in-turn brings a limitation on the kind of samples under observation. In this work, we have measured the thermal conductivity of a forest of nanowires embedded in nanoporous alumina membranes using the 3 ω method. An analytical solution of 2D heat conduction is then used to model the multilayer system, considering the anisotropic thermal properties of the different layers, substrate thermal conductivity, and their thicknesses. Data treatment is performed by fitting the experimental results with the 2D model on two different sets of nanowires (silicon and BiSbTe) embedded in the matrix of nanoporous alumina templates, having thermal conductivities that differ by at least one order of magnitude. These experimental results show that this method extends the applicability of the 3 ω technique to more complex systems having anisotropic thermal properties.

Internal solitary waves are hump-shaped, large-amplitude waves that are physically analogous to surface waves except that they propagate within the fluid, along density steps that typically characterize the layered vertical structure of lakes, oceans and the atmosphere. As do surface waves, internal solitary waves may overturn and break, and the process is thought to provide a globally significant source of turbulent mixing and energy dissipation. Although commonly observed in geophysical fluids, the origins of internal solitary waves remain unclear. Here we report a rarely observed natural case of the birth of internal solitary waves from a frontally forced interfacial gravity current intruding into a two-layer and vertically sheared background environment. The results of the analysis carried out suggest that fronts may represent additional and unexpected sources of internal solitary waves in regions of lakes, oceans and atmospheres that are dynamically similar to the situation examined here in the Saguenay Fjord, Canada.

Electrical conductivity is a key parameter to increase the performance of thermoelectric materials. However, the measurement of such performance remains complex for 1D structures, involving tedious processing. In this study, we present a non-destructive, rapid and easy approach for the characterization of electrical conductivity of Bi2Te3 based single nanowires. By controlling the nanowire overgrowth, each nanowire emerges in the form of a micrometric hemisphere constituting a unique contact zone for direct nanoprobing. As nanowires need no preliminary preparation and remain in their template during measurement, we avoid oxidation effects and time-consuming processing. Electrical transport results show a low nanowire resistivity for compact nanowires obtained at low overpotential. Such values are comparable to bulk materials and thin films. This method not only confirmed its reliability, but it could also be adopted for other semiconducting or metallic electrodeposited nanowires.

Two fundamental sign errors were found in a computer code used for studying the oxygen minimum zone (OMZ) and hypoxia in the Estuary and Gulf of St. Lawrence. These errors invalidate the conclusions drawn from the model, and call into question a proposed mechanism for generating OMZ that challenges classical understanding. The study in question is being cited frequently, leading the discipline in the wrong direction.