NbS3_{3}: A unique quasi one-dimensional conductor with three charge density wave transitions

Through transport, compositional and structural studies, we review the features of the charge-density wave (CDW) conductor of NbS$_{3}$ (phase II). We highlight three central results: 1) In addition to the previously reported CDW transitions at $T_{P1}$ = 360\,K and $T_{P2}$ = 150\,K, another CDW transition occurs at a much higher temperature $T_{P0}$ = 620-650\,K; evidence for the non-linear conductivity of this CDW is presented. 2) We show that CDW associated with the $T_{P2}$ - transition arises from S vacancies acting as donors. Such a CDW transition has not been observed before. 3) We show exceptional coherence of the $T_{P1}$-CDW at room-temperature. Additionally, we report on the effects of uniaxial strain on the CDW transition temperatures and transport.Comment: 16 pages, 18 figure

Stable Isotope Biogeochemistry of Seabird Guano Fertilization: Results from Growth Chamber Studies with Maize (Zea Mays)

Stable isotope analysis is being utilized with increasing regularity to examine a wide range of issues (diet, habitat use, migration) in ecology, geology, archaeology, and related disciplines. A crucial component to these studies is a thorough understanding of the range and causes of baseline isotopic variation, which is relatively poorly understood for nitrogen (δ(15)N). Animal excrement is known to impact plant δ(15)N values, but the effects of seabird guano have not been systematically studied from an agricultural or horticultural standpoint.This paper presents isotopic (δ(13)C and δ(15)N) and vital data for maize (Zea mays) fertilized with Peruvian seabird guano under controlled conditions. The level of (15)N enrichment in fertilized plants is very large, with δ(15)N values ranging between 25.5 and 44.7‰ depending on the tissue and amount of fertilizer applied; comparatively, control plant δ(15)N values ranged between -0.3 and 5.7‰. Intraplant and temporal variability in δ(15)N values were large, particularly for the guano-fertilized plants, which can be attributed to changes in the availability of guano-derived N over time, and the reliance of stored vs. absorbed N. Plant δ(13)C values were not significantly impacted by guano fertilization. High concentrations of seabird guano inhibited maize germination and maize growth. Moreover, high levels of seabird guano greatly impacted the N metabolism of the plants, resulting in significantly higher tissue N content, particularly in the stalk.The results presented in this study demonstrate the very large impact of seabird guano on maize δ(15)N values. The use of seabird guano as a fertilizer can thus be traced using stable isotope analysis in food chemistry applications (certification of organic inputs). Furthermore, the fertilization of maize with seabird guano creates an isotopic signature very similar to a high-trophic level marine resource, which must be considered when interpreting isotopic data from archaeological material

Optimisation of the laser surface remelting process on strain criteria

This paper shows a process of selection of optimum conditions for laser remelting of nodular cast iron. The optimisation takes into account a specified depth of the hardened layer, for which an appropriate energy input is specified while taking into account the mode of guiding the laser beam. Strain criteria are given for the optimisation of the remelting process, i.e., minimum energy input at a given depth of the hardened layer, minimum distortion of the machine part and a desired variation of residual stresses across the hardened layer. Practical tests of optimisation showed the logic of adhering to the aforementioned criteria, because we can significantly influence the quality of the product at lower costs of manufacturing

An electromagnetic sensor with a metamaterial lens for nondestructive evaluation of composite materials

International audienceThis paper proposes the study and implementation of a sensor with a metamaterial (MM) lens in electromagnetic nondestructive evaluation (eNDE). Thus, the use of a new type of MM, named Conical Swiss Rolls (CSR) has been proposed. These structures can serve as electromagnetic flux concentrators in the radiofrequency range. As a direct application, plates of composite materials with carbon fibers woven as reinforcement and polyphenylene sulphide as matrix with delaminations due to low energy impacts were examined. The evaluation method is based on the appearance of evanescent modes in the space between carbon fibers when the sample is excited with a transversal magnetic along z axis (TMz) polarized electromagnetic field. The MM lens allows the transmission and intensification of evanescent waves. The characteristics of carbon fibers woven structure became visible and delaminations are clearly emphasized. The flaws can be localized with spatial resolution better than λ/2000. © 2015, by the authors; licensee MDPI, Basel, Switzerland

An electromagnetic sensor with a metamaterial lens for nondestructive evaluation of composite materials

This paper proposes the study and implementation of a sensor with a metamaterial (MM) lens in electromagnetic nondestructive evaluation (eNDE). Thus, the use of a new type of MM, named Conical Swiss Rolls (CSR) has been proposed. These structures can serve as electromagnetic flux concentrators in the radiofrequency range. As a direct application, plates of composite materials with carbon fibers woven as reinforcement and polyphenylene sulphide as matrix with delaminations due to low energy impacts were examined. The evaluation method is based on the appearance of evanescent modes in the space between carbon fibers when the sample is excited with a transversal magnetic along z axis (TMz) polarized electromagnetic field. The MM lens allows the transmission and intensification of evanescent waves. The characteristics of carbon fibers woven structure became visible and delaminations are clearly emphasized. The flaws can be localized with spatial resolution better than λ/2000. © 2015, by the authors; licensee MDPI, Basel, Switzerland

Experimental and numerical analysis of laminated carbon fibre-reinforced polymer gears with implicit model for coefficient-of-friction evaluation

Laminated composites have so far received little attention as a potential material for gear drive applications. In the presented study, the thermomechanical performance of a newly developed type of epoxy impregnated, autoclave-cured carbon fibre-reinforced polymer gear—running in pair with a steel pinion—was analysed, using a combination of experimental and numerical approaches. The employed methods enabled the identification of the composite’s mechanical, thermal, and tribological characteristics, as related to the studied gear pair application. A newly proposed, finite-element-analysis-based iterative procedure enabled an implicit evaluation of the analysed material pair’s coefficient of friction (COF), which is a key parameter in determining the gear pair’s thermomechanical characteristics. For the considered material pair, a value of 0.34 was identified for the coefficient in the quasi-steady region. As the coefficient is strongly correlated with frictional heat generation and significantly affects the surface shear stress, it can consequently have a meaningful influence on the composite’s wear rate. The developed COF identification procedure was validated using a reciprocating cylinder-on-flat tribological test method. The composite gear’s service life was additionally tested at various running loads, resulting in pitch contact pressures ranging between 400 and 540 MPa. Lifetime gear test results showed a markedly superior performance compared to the high-temperature thermoplastic polyether ether ketone, which is typically employed in the most demanding polymer gear applications. Several methods are additionally proposed that could further improve the developed composite gears’ performance

Lowering the thermal conductivity of Sr(Ti0.8Nb0.2)O3 by SrO and CaO doping: microstructure and thermoelectric properties

Excess SrO and CaO were added to the Sr(Ti0.8Nb0.2)O3 thermoelectric material, which was structurally compensated by the formation of Ruddlesden–Popper-type planar faults with the compositions SrO and/or (Sr, Ca)O. Both types of doping significantly changed the original isotropic Sr(Ti0.8Nb0.2)O3 microstructure and resulted in the formation of lamellar Ruddlesden–Popper-type phases within the Sr(Ti0.8Nb0.2)O3 grains. Three-dimensional networks of single Ruddlesden–Popper-type faults were also observed in the Sr(Ti0.8Nb0.2)O3 for both types of doping. The combination of both structural features significantly lowered the thermal conductivity in comparison with Sr(Ti0.8Nb0.2)O3 due to the enhanced phonon scattering observed at the planar faults, which proves that introducing such defects is a promising method for lowering the thermal conductivity of the Sr(Ti0.8Nb0.2)O3 thermoelectric material. The highest figure of merit (ZT = 0.08) was achieved with CaO doping, since the significantly reduced thermal conductivity was accompanied by an increased power factor