Improving thermoelectric performance of TiNiSn by mixing MnNiSb in the half-Heusler structure.

The thermoelectric properties of the n-type semiconductor TiNiSn were optimized by partial substitution with metallic MnNiSb in the half Heusler structure. Herein, we study the transport properties and intrinsic phase separation in the Ti1-xMnxNiSn1-xSbx system. The alloys were prepared by arc-melting and annealed at temperatures obtained from differential thermal analysis and differential scanning calorimetry results. The phases were characterized using powder X-ray diffraction patterns, energy-dispersive X-ray spectroscopy, and differential scanning calorimetry. After annealing, the majority phase was TiNiSn with some Ni-rich sites, and the minority phases were primarily Ti6Sn5, Sn and MnSn2. The Ni-rich sites were caused by Frenkel defects; this led to metal-like behavior in the semiconductor specimens at low temperature. For x ≤ 0.05 the samples showed an activated conduction, whereas for x > 0.05 they showed metallic character. The figure of merit for x = 0.05 was increased by 61% (zT = 0.45) in comparison with the pure TiNiSn.

Long-term stability of phase-separated half-Heusler compounds.

Half-Heusler (HH) compounds have shown high figure of merit up to 1.5. Here, we address the long-term stability of n- and p-type HH materials. For this purpose, we investigated HH materials based on the Ti0.3Zr0.35Hf0.35NiSn-system after 500 cycles (1700 h) from 373 to 873 K. Both compounds exhibit a maximum Seebeck coefficient of |α|≈ 210 µV K(-1) and a phase separation into two HH phases. The dendritic microstructure is temperature resistant and upon cycling the changes in the microstructure are so marginal that the low thermal conductivity values (κ < 4 W m(-1) K(-1)) could be maintained. Our results emphasize that phase-separated HH compounds are suitable low cost materials and can lead to enhanced thermoelectric efficiencies beyond the set benchmark for industrial applications.

Probing bulk electronic structure with hard X-ray angle-resolved photoemission.

Traditional ultraviolet/soft X-ray angle-resolved photoemission spectroscopy (ARPES) may in some cases be too strongly influenced by surface effects to be a useful probe of bulk electronic structure. Going to hard X-ray photon energies and thus larger electron inelastic mean-free paths should provide a more accurate picture of bulk electronic structure. We present experimental data for hard X-ray ARPES (HARPES) at energies of 3.2 and 6.0 keV. The systems discussed are W, as a model transition-metal system to illustrate basic principles, and GaAs, as a technologically-relevant material to illustrate the potential broad applicability of this new technique. We have investigated the effects of photon wave vector on wave vector conservation, and assessed methods for the removal of phonon-associated smearing of features and photoelectron diffraction effects. The experimental results are compared to free-electron final-state model calculations and to more precise one-step photoemission theory including matrix element effects.

Fabrication of layered nanostructures by successive electron beam induced deposition with two precursors: protective capping of metallic iron structures.

We report on the stepwise generation of layered nanostructures via electron beam induced deposition (EBID) using organometallic precursor molecules in ultra-high vacuum (UHV). In a first step a metallic iron line structure was produced using iron pentacarbonyl; in a second step this nanostructure was then locally capped with a 2-3 nm thin titanium oxide-containing film fabricated from titanium tetraisopropoxide. The chemical composition of the deposited layers was analyzed by spatially resolved Auger electron spectroscopy. With spatially resolved x-ray absorption spectroscopy at the Fe L3 edge, it was demonstrated that the thin capping layer prevents the iron structure from oxidation upon exposure to air.

Band gap and electronic structure of an epitaxial, semiconducting Cr0.80Al0.20 thin film.

Cr(1-x)Al(x) exhibits semiconducting behavior for x = 0.15-0.26. This Letter uses hard x-ray photoemission spectroscopy and density functional theory to further understand the semiconducting behavior. Photoemission measurements of an epitaxial Cr(0.80)Al(0.20) thin film show several features in the valence band region, including a gap at the Fermi energy (E(F)) for which the valence band edge is 95 ± 14 meV below E(F). Theory agrees well with the valence band measurements, and shows an incomplete gap at E(F) due to the hole band at M shifting almost below E(F).

Synthesis and characterization of single-phase epitaxial Cr2N thin films by reactive magnetron sputtering.

Cr2N is commonly found as a minority phase or inclusion in stainless steel, CrN-based hard coatings, etc. However, studies on phase-pure material for characterization of fundamental properties are limited. Here, Cr2N thin films were deposited by reactive magnetron sputtering onto (0001) sapphire substrates. X-ray diffraction and pole figure texture analysis show Cr2N (0001) epitaxial growth. Scanning electron microscopy imaging shows a smooth surface, while transmission electron microscopy and X-ray reflectivity show a uniform and dense film with a density of 6.6 g cm-3, which is comparable to theoretical bulk values. Annealing the films in air at 400 °C for 96 h shows little signs of oxidation. Nano-indentation shows an elastic-plastic behavior with H = 18.9 GPa and E r = 265 GPa. The moderate thermal conductivity is 12 W m-1 K-1, and the electrical resistivity is 70 µΩ cm. This combination of properties means that Cr2N may be of interest in applications such as protective coatings, diffusion barriers, capping layers and contact materials.

Charge transfer effects on the chemical reactivity of Pd(x)Cu(1-x) nanoalloys.

This work reports on the synthesis and characterization of PdxCu1-x (x = 0.7, 0.5 and 0.3) nanoalloys obtained via an eco-friendly chemical reduction method based on ascorbic acid and trisodium citrate. The average size of the quasi-spherical nanoparticles (NPs) obtained by this method was about 4 nm, as observed by TEM. The colloids containing different NPs were then supported on carbon in order to produce powder samples (PdxCu1-x/C) whose electronic and structural properties were probed by different techniques. XRD analysis indicated the formation of crystalline PdCu alloys with a nanoscaled crystallite size. Core-level XPS results provided a fingerprint of a charge transfer process between Pd and Cu and its dependency on the nanoalloy composition. Additionally, it was verified that alloying was able to change the NP's reactivity towards oxidation and reduction. Indeed, the higher the amount of Pd in the nanoalloy, less oxidized are both the Pd and the Cu atoms in the as-prepared samples. Also, in situ XANES experiments during thermal treatment under a reducing atmosphere showed that the temperature required for a complete reduction of the nanoalloys depends on their composition. These results envisage the control at the atomic level of novel catalytic properties of such nanoalloys.

Aerobic requirements of overground versus treadmill running.

There is general agreement that the oxygen demand of level running is similar for both the treadmill (TM) and overground situations at speeds under 260 m X min-1. However, controversy exists with regard to inclined running. The prevailing view, represented by the ACSM prediction formulas, is that overground hill running is theoretically more costly than inclined treadmill running. This study was designed to investigate the problem from an empirical standpoint. Seven male subjects performed overground and TM running at two grades (0 and 5.7%) over a range of speeds between 136-286 m X min-1. For the outdoor trials, subjects covered a distance of 950 m at a constant pace, and expired gas was collected over the last 150 m. Matching trials were then performed on the treadmill at the same speed and % grade. Regression lines were calculated for speed vs oxygen consumption (VO2). For TM and overground level running, these were: VO2 (ml.kg-1.min-1)= 0.222 X speed (m.min-1) - 1.33 and VO2 (ml.kg-1.min-1) = 0.202 X speed (m.min-1) + 3.21 respectively. The regression lines from TM and overground inclined running were: VO2 (ml.kg-1.min-1) = 0.237 X speed (m.min-1) + 7.53. and VO2 (ml.kg-1.min-1) = 0.233 X speed (m.min-1) + 7.78 respectively. A 2 X 3 X 2 ANOVA revealed that the differences between mean values for VO2 for level TM running vs level overground running and grade TM running vs grade overground running were not statistically significant (0.10 less than P less than 0.25).(ABSTRACT TRUNCATED AT 250 WORDS)

Walking efficiency before and after total hip replacement as determined by oxygen consumption.

Seventy-seven patients receiving either unilateral or bilateral total hip replacement were studied before and for as long as four years after operation. Their walking velocity and efficiency (the latter determined by measuring oxygen consumption) improved after operation. Total hip replacement allowed relatively equal postoperative efficiency and velocity for patients with unilateral and bilateral disease. While no consistent relationships were found between the components of the Iowa hip-rating scale, significant correlations were found between the composite Iowa hip-rating score and oxygen consumption. Data indicate that measurement of self-selected velocity in patients with hip disease is a satisfactory indicator of walking efficiency.

Direct observation of half-metallicity in the Heusler compound Co2MnSi.

Ferromagnetic thin films of Heusler compounds are highly relevant for spintronic applications owing to their predicted half-metallicity, that is, 100% spin polarization at the Fermi energy. However, experimental evidence for this property is scarce. Here we investigate epitaxial thin films of the compound Co2MnSi in situ by ultraviolet-photoemission spectroscopy, taking advantage of a novel multi-channel spin filter. By this surface sensitive method, an exceptionally large spin polarization of (93(-11)(+7)) % at room temperature is observed directly. As a more bulk sensitive method, additional ex situ spin-integrated high energy X-ray photoemission spectroscopy experiments are performed. All experimental results are compared with advanced band structure and photoemission calculations which include surface effects. Excellent agreement is obtained with calculations, which show a highly spin polarized bulk-like surface resonance ingrained in a half metallic bulk band structure.

Multi-temperature synchrotron PXRD and physical properties study of half-Heusler TiCoSb.

Phase pure samples of the half-Heusler material TiCoSb were synthesised and investigated. Multi-temperature synchrotron powder X-ray diffraction (PXRD) data measured between 90 and 1000 K in atmospheric air confirm the phase purity, but they also reveal a decomposition reaction starting at around 750 K. This affects the high temperature properties since TiCoSb is semiconducting, whereas CoSb is metallic. Between 90 K and 300 K the linear thermal expansion coefficient is estimated to be 10.5 × 10(-6) K(-1), while it is 8.49 10(-6) K(-1) between 550 K and 1000 K. A fit of a Debye model to the Atomic Displacement Parameters obtained from Rietveld refinement of the PXRD data gives a Debye temperature of 395(4) K. The heat capacity was measured between 2 K and 300 K and a Debye temperature of 375(5) K was obtained from modelling of the data. Coming from low temperatures the electrical resistivity shows a metallic to semiconducting transition at 113 K. A relatively high Seebeck coefficient of ∼-250 µV K(-1) was found at 400 K, but the substantial thermal conductivity (∼10 W mK(-1) at 400 K) leads to a moderate thermoelectric figure of merit of 0.025 at 400 K.

Evaluation of the E test for the assessment of synergy of antibiotic combinations against multiresistant Pseudomonas aeruginosa isolates from cystic fibrosis patients.

The determination of synergistic effects of antimicrobial drug combinations can lead to improved therapeutic options in the antibiotic treatment of cystic fibrosis patients who are chronically infected with multiresistant Pseudomonas aeruginosa isolates. The aim of this study was to evaluate the performance of the E test versus the standard agar dilution checkerboard susceptibility test in the assessment of synergy and, in addition, to determine the activity of two antimicrobial combinations against 163 multiresistant P. aeruginosa isolates from cystic fibrosis patients. The agreement between the checkerboard method and the E test was excellent (>90%) for nonmucoid as well as mucoid isolates from cystic fibrosis patients. The rate of synergy was higher for the antibiotic combination of ceftazidime and tobramycin (28.8% of the cystic fibrosis strains) than for the combination of meropenem and tobramycin (19.0%). However, the probability of synergy for the second antibiotic combination increased significantly when the synergy of the first antibiotic combination had already been demonstrated (Fischer's exact test, p=0.049). The results show that the E test is a valuable and practical method for routine microbiological diagnostics and can aid in the selection of improved antibiotic options in the treatment of cystic fibrosis patients chronically infected with P. aeruginosa.

Physical fitness, insulin secretion, and glucose tolerance in healthy males and mild type-2 diabetes.

The nature of the relation between physical fitness and glucose homeostasis was evaluated in two studies: (A) a cross-sectional study on 108 middle-aged non-diabetic men; (B) a five-month training program involving nine males with non-insulin-dependent (type 2) diabetes. It was found that the level of physical fitness was positively related to glucose tolerance, and that this relation was largely independent of body weight and basal insulin secretion. Furthermore, the training program for the diabetics resulted in improved glucose tolerance without change in either body weight or glucose-induced insulin secretion. It is concluded that glucose balance is significantly influenced by the physical fitness level, which is likely to be an important element in the pathogenesis of type 2 diabetes as well as in the treatment of that disease.

Comparison of the Micronaut Merlin automated broth microtiter system with the standard agar dilution method for antimicrobial susceptibility testing of mucoid and nonmucoid Pseudomonas aeruginosa isolates from cystic fibrosis patients.

The aim of this study was to compare a commercially available automated broth microdilution system (Merlin; Micronaut, Germany) with the standard agar dilution method for susceptibility testing of pulmonary isolates from cystic fibrosis patients. Accurate susceptibility testing of bacterial isolates from cystic fibrosis patients is known to pose problems. Although commercially available automated test systems could facilitate susceptibility testing of such isolates in routine diagnostics, these systems have not been recommended thus far. However, a pilot study recently indicated that the Merlin system, which is based on an endpoint measurement rather than on growth curves, might be applicable in the susceptibility testing of isolates from cystic fibrosis patients. In the present study, the Merlin system was further evaluated using an extended panel of nonmucoid and mucoid Pseudomonas aeruginosa isolates. The results showed that the MICs obtained with the Merlin system tended to be lower than those obtained with the agar dilution method, a finding that became increasingly apparent when mucoid Pseudomonas aeruginosa strains were tested. The correlation coefficients (r values) of the MIC results for all strains tested were between 0.6 and 0.8 for five of the seven antimicrobial agents, with r values exceeding 0.8 for only meropenem and ciprofloxacin. However, since the overall rate of serious discrepancies was within an acceptable range, the Merlin system appears to be applicable for routine clinical use in susceptibility testing of P. aeruginosa isolates from cystic fibrosis patients.