2,000 research outputs found
Emergence of intrinsic superconductivity below 1.178 K in the topologically non-trivial semimetal state of CaSn3
Topological materials which are also superconducting are of great current
interest, since they may exhibit a non-trivial topologically-mediated
superconducting phase. Although there have been many reports of pressure-tuned
or chemical-doping-induced superconductivity in a variety of topological
materials, there have been few examples of intrinsic, ambient pressure
superconductivity in a topological system having a stoichiometric composition.
Here, we report that the pure intermetallic CaSn3 not only exhibits topological
fermion properties but also has a superconducting phase at 1.178 K under
ambient pressure. The topological fermion properties, including the nearly zero
quasi-particle mass and the non-trivial Berry phase accumulated in cyclotron
motions, were revealed from the de Haas-van Alphen (dHvA) quantum oscillation
studies of this material. Although CaSn3 was previously reported to be
superconducting at 4.2K, our studies show that the superconductivity at 4.2K is
extrinsic and caused by Sn on the degraded surface, whereas its intrinsic bulk
superconducting transition occurs at 1.178 K. These findings make CaSn3 a
promising candidate for exploring new exotic states arising from the interplay
between non-trivial band topology and superconductivity, e.g. topological
superconductivityComment: 20 pages,4 figure
Large-volume metrology instrument selection and measurability analysis
A wide range of metrology processes are involved in the manufacture of large products. In addition to the traditional tool-setting and product-verification operations, increasingly flexible metrology-enabled automation is also being used. Faced with many possible measurement problems and a very large number of metrology instruments employing diverse technologies, the selection of the appropriate instrument for a given task can be highly complex. Also, as metrology has become a key manufacturing process, it should be considered in the early stages of design, and there is currently very little research to support this. This paper provides an overview of the important selection criteria for typical measurement processes and presents some novel selection strategies. Metrics that can be used to assess measurability are also discussed. A prototype instrument selection and measurability analysis application is also presented, with discussion of how this can be used as the basis for development of a more sophisticated measurement planning tool. © 2010 Authors
Observation of a mesoscopic magnetic modulation in chiral Mn1/3NbS2
We have investigated the structural, magnetic, thermodynamic, and charge
transport properties of Mn1/3NbS2 single crystals through x-ray and neutron
diffraction, magnetization, specific heat, magnetoresistance, and Hall effect
measurements. Mn1/3NbS2 displays a magnetic transition at TC ~ 45 K with highly
anisotropic behavior expected for a hexagonal structured material. Below TC,
neutron diffraction reveals increased scattering near the structural Bragg
peaks having a wider Q-dependence along the c-axis than the nuclear Bragg
peaks. This indicates helimagnetism with a long pitch length of ~250 nm (or a
wavevector q~0.0025 {\AA}-1) along the c-axis. This q is substantially smaller
than that found for the helimagnetic state in isostructural Cr1/3NbS2 (0.015
{\AA}-1). Specific heat capacity measurements confirm a second-order magnetic
phase transition with a substantial magnetic contribution that persists to low
temperature. The large low-temperature specific heat capacity is consistent
with a large density of low-lying magnetic excitations that are likely
associated with topologically interesting magnetic modes. Changes to the
magnetoresistance, the magnetization, and the magnetic neutron diffraction,
which become more apparent below 20 K, imply a modification in the character of
the magnetic ordering corresponding to the magnetic contribution to the
specific heat capacity. These observations signify a more complex magnetic
structure both at zero and finite fields for Mn1/3NbS2 than for the
well-investigated Cr1/3NbS2.Comment: 22 pages, 7 figure
Extreme High-Field Superconductivity in Thin Re Films
We report the high-field superconducting properties of thin, disordered Re
films via magneto-transport and tunneling density of states measurements. Films
with thicknesses in the range of 9 nm to 3 nm had normal state sheet
resistances of 0.2 k to 1 k and corresponding
transition temperatures in the range of 6 K to 3 K. Tunneling spectra were
consistent with those of a moderate coupling BCS superconductor.
Notwithstanding these unremarkable superconducting properties, the films
exhibited an extraordinarily high upper critical field. We estimate their
zero-temperature to be more than twice the Pauli limit. Indeed, in 6
nm samples the estimated reduced critical field 5.6 T/K is
among the highest reported for any elemental superconductor. Although the sheet
resistances of the films were well below the quantum resistance ,
their 's approached the theoretical upper limit of a strongly
disordered superconductor for which .Comment: 12 pages, 10 figure
State-of-the-art in lean design engineering:a literature review on white collar lean
Lean is usually associated with the âoperationsâ of a manufacturing enterprise; however, there is a growing awareness that these principles may be transferred readily to other functions and sectors. The application to knowledge-based activities such as engineering design is of particular relevance to UK plc. Hence, the purpose of this study has been to establish the state-of-the-art, in terms of the adoption of Lean in new product development, by carrying out a systematic review of the literature. The authors' findings confirm the view that Lean can be applied beneficially away from the factory; that an understanding and definition of value is key to success; that a set-based (or Toyota methodology) approach to design is favoured together with the strong leadership of a chief engineer; and that the successful implementation requires organization-wide changes to systems, practices, and behaviour. On this basis it is felt that this review paper provides a useful platform for further research in this topic
Measurements in Film Cooling Flows With Periodic Wakesâ.
ABSTRACT Film cooling flows subject to periodic wakes were studied experimentally. The wakes were generated with a spoked wheel upstream of a flat plate. Cases with a single row of cylindrical film cooling holes inclined at 35 degrees to the surface were considered at blowing ratios of 0.25, 0.50, and 1.0 with a steady freestream and with wake Strouhal numbers of 0.15, 0.30, and 0.60. Temperature measurements were made using an infrared camera, thermocouples, and constant current (cold wire) anemometry. Hot wire anemometry was used for velocity measurements. The local film cooling effectiveness and heat transfer coefficient were determined from the measured temperatures. Phase locked flow temperature fields were determined from cold wire surveys. Wakes decreased the film cooling effectiveness for blowing ratios of 0.25 and 0.50 when compared to steady freestream cases. In contrast, effectiveness increased with Strouhal number for the 1.0 blowing ratio cases, as the wakes helped mitigate the effects of jet liftoff. Heat transfer coefficients increased with wake passing frequency, with nearly the same percentage increase in cases with and without film cooling. The time resolved flow measurements show the interaction of the wakes with the film cooling jets. Near-wall flow measurements are used to infer the instantaneous film cooling effectiveness as it changes during the wake passing cycle
The interaction of lean and building information modeling in construction
Lean construction and Building Information Modeling are quite different initiatives, but both are having profound impacts on the construction industry. A rigorous analysis of the myriad specific interactions between them indicates that a synergy exists which, if properly understood in theoretical terms, can be exploited to improve construction processes beyond the degree to which it might be improved by application of either of these paradigms independently. Using a matrix that juxtaposes BIM functionalities with prescriptive lean construction principles, fifty-six interactions have been identified, all but four of which represent constructive interaction. Although evidence for the majority of these has been found, the matrix is not considered complete, but rather a framework for research to
explore the degree of validity of the interactions. Construction executives, managers, designers and developers of IT systems for construction can also benefit from the framework as an aid to recognizing the potential synergies when planning their lean and BIM adoption strategies
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