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Multilayers composed of many thin films of PbTe and Pb1-xSnxTe on BaF2 substrates were grown epitaxially by hot-wall-vapor deposition. In order to investigate the fraction of the total misfit (2.5x10-3 at x=O, 12) accommodated by misfit strain we have performed strain measurements on these superlattices by two different X-ray diffractometer techniques. We also report on substrate induced strain due to different thermal expansion coefficients of films and substrate. For film thicknesses smaller than 300 nm there is clear evidence for almost complete accommodation of lattice mismatch by misfit strain. Below room temperature the substrate induces a tensile strain which is comparable to that of the misfit strain.
The effect of transportation and lairage on the faecal shedding and post-slaughter contamination of carcasses with Escherichia coli O157 and O26 in young calves (4–7-day-old) was assessed in a cohort study at a regional calf-processing plant in the North Island of New Zealand, following 60 calves as cohorts from six dairy farms to slaughter. Multiple samples from each animal at pre-slaughter (recto-anal mucosal swab) and carcass at post-slaughter (sponge swab) were collected and screened using real-time PCR and culture isolation methods for the presence of E. coli O157 and O26 (Shiga toxin-producing E. coli (STEC) and non-STEC). Genotype analysis of E. coli O157 and O26 isolates provided little evidence of faecal–oral transmission of infection between calves during transportation and lairage. Increased cross-contamination of hides and carcasses with E. coli O157 and O26 between co-transported calves was confirmed at pre-hide removal and post-evisceration stages but not at pre-boning (at the end of dressing prior to chilling), indicating that good hygiene practices and application of an approved intervention effectively controlled carcass contamination. This study was the first of its kind to assess the impact of transportation and lairage on the faecal carriage and post-harvest contamination of carcasses with E. coli O157 and O26 in very young calves.
The primate malaria Plasmodium knowlesi has a long-standing history as an experimental malaria model. Studies using this model parasite in combination with its various natural and experimental non-human primate hosts have led to important advances in vaccine development and in our understanding of malaria invasion, immunology and parasite–host interactions. The adaptation to long-term in vitro continuous blood stage culture in rhesus monkey, Macaca fascicularis and human red blood cells, as well as the development of various transfection methodologies has resulted in a highly versatile experimental malaria model, further increasing the potential of what was already a very powerful model. The growing evidence that P. knowlesi is an important human zoonosis in South-East Asia has added relevance to former and future studies of this parasite species.
Measuring cortisol in hair is a promising method to assess long-term alterations of the biological stress response system, and hair cortisol concentrations (HCC) may be altered in psychiatric disorders and in subjects suffering from chronic stress. However, the pattern of associations between HCC, chronic stress and mental health require clarification. Our exploratory study: (1) assessed the association between HCC and perceived stress, symptoms of depression and neuroticism, and the trait extraversion (as a control variable); and (2) made use of the twin design to estimate the genetic and environmental covariance between the variables of interest. Hair samples from 109 (74 female) subjects (age range 12–21 years, mean 15.1) including 8 monozygotic (MZ) and 21 dizygotic (DZ) twin pairs were analyzed. Perceived stress was measured with the Perceived Stress Scale and/or the Daily Life and Stressors Scale, neuroticism, and extraversion with the NEO-Five Factor Inventory or the Junior Eysenck Personality Questionnaire, and depressive symptoms with the Somatic and Psychological Health Report. We found a modest positive association between HCC and the three risk factors — perceived stress, symptoms of depression, and neuroticism (r = 0.22–0.33) — but no correlation with extraversion (-0.06). A median split revealed that the associations between HCC and risk factors were stronger (0.47–0.60) in those subjects with HCC >11.36 pg/mg. Furthermore, our results suggest that the genetic effects underlying HCC are largely shared with those that influence perceived stress, depressive symptoms, and neuroticism. These results of our proof of principle study warrant replication in a bigger sample but raise the interesting question of the direction of causation between these variables.
The variability of CD-24 7599 (V=11.48 mag) was discovered by JCC during observing run XCOV7 of the Whole Earth Telescope (WET, Nather et al. 1990) network in February, 1992. The star was observed as an additional target and 117 hours of high-quality temporal spectroscopic observations were obtained.
Our analysis of these data revealed the presence of 7 independent pulsation modes between 27.0 and 38.1 cycles per day (313 – 441 μHz) with semiamplitudes of 2.1 – 10.2 milli-modulation amplitudes (mma). We showed that peaks at linear combination frequencies detected in the power spectra were not due to eigenmodes excited to visible amplitude by resonant mode coupling.
The influence of threading dislocations (TDs) on the dry thermal oxidation of c-plane gallium nitride (GaN) is investigated for oxidation temperatures above 800°C. The transformation of GaN to gallium oxide (Ga2O3) is preferably found at TDs and grain boundaries, showing enhanced vertical oxidation, compared to defect free surface sites. Therefore, the increase in surface roughness commonly obtained upon oxidation is explained by an inhomogeneous chemical reactivity associated with those crystal defects. Additionally, annealing in an N2 atmosphere showed that also decomposition is favored at such chemically reactive spots. Comparison between decomposition and oxidation suggests that at temperatures above 950°C, the Ga2O3 formation is supported by the decomposition of GaN and subsequent oxidation of the metallic gallium.
Intermetallic titanium aluminides solidifying via the disordered β-phase are of great interest for several high-temperature applications in automotive and aircraft industries. In this paper the thermocyclic oxidation behavior of three β-solidifying γ-TiAl-based alloys at 800°C and 900°C in air, with and without fluorine treatment, is reported for the first time. The behavior of the well-known TNM alloy (Ti-43.5Al-4Nb-1Mo-0.1B, in at.%) is compared with that of two Nb-free model alloys which contain different amounts of Mo (Ti-44Al-3Mo and Ti-44Al-7Mo, in at.%). During thermocyclic high-temperature exposure in air a mixed oxide scale develops on all three untreated alloys. Small additions of fluorine in the subsurface region of the alloys change the oxidation mechanism from mixed oxide scale formation to alumina at both temperatures. The oxidation resistance of the fluorine treated samples was significantly improved compared to the untreated samples.
Ensuring microstructural stability under technical relevant conditions is a determining criterion for the development of innovative high-temperature materials. In this work, the influ-ence of C and Si on the microstructural stability during creep exposure was investigated for a β-solidifying γ-TiAl based alloy with a nominal composition of Ti-43.5Al-4Nb-1Mo-0.1B (in at.%), named TNM. With a two-step heat treatment a microstructure consisting of fine lamellar α2/γ-colonies, surrounded by βo-phase and areas of discontinuous precipitation, starting from the boundaries of the lamellar colonies, was adjusted. Creep tests were carried out to examine the potential of C and Si to prevent microstructural instability during creep and hence improving the creep properties. At 815 °C the discontinuous precipitation process of the TNM alloy continues during ensuing creep testing leading to a reduced creep resistance. In comparison, the minimum creep rate of the TNM-0.3C-0.3Si alloy was significantly decreased caused by the lower βo-phase content and average lamellar spacing within the α2/γ-colonies, the precipitation of p-Ti3AlC carbides and the retarded kinetics of discontinuous precipitation.
Anthocyanins (ACN) can exert beneficial health effects not only through their antioxidative potential but also through modulation of inflammatory parameters that play a major role in CVD. A randomised cross-over study was carried out to investigate the effects of ACN-rich beverage ingestion on oxidation- and inflammation-related parameters in thirty healthy female volunteers. The participants consumed 330 ml of beverages (placebo, juice and smoothie with 8·9 (sd 0·3), 983·7 (sd 37) and 840·9 (sd 10) mg/l ACN, respectively) over 14 d. Before and after each intervention, blood and 24 h urine samples were collected. Plasma superoxide dismutase (SOD) and catalase activities increased significantly after ACN-rich beverage ingestion (P< 0·001), whereas after placebo juice ingestion no increase could be observed. Plasma glutathione peroxidase and erythrocyte SOD activities were not affected. An increase in Trolox equivalent antioxidant capacity could also be observed after juice (P< 0·001) and smoothie (P< 0·01) ingestion. The plasma and urinary concentrations of malondialdehyde decreased after ACN-rich beverage ingestion (P< 0·001), whereas those of 8-OH-2-deoxyguanosine as well as inflammation-related parameters (IL-2, -6, -8 and -10, C-reactive peptide, soluble cluster of differentiation 40 ligand, TNF-α, monocyte chemoattractant protein-1 and soluble cell adhesion molecules) were not affected. Thus, ingestion of ACN-rich beverages improves antioxidant enzyme activities and plasma antioxidant capacity, thus protecting the body against oxidative stress, a hallmark of ongoing atherosclerosis.
Grain boundaries (GBs) in polycrystalline silicon (poly-Si) thin film solar cells are frequently found to be detrimental for device performance. Biaxiallytextured silicon with grains that are well-aligned in-plane and out-of-plane can possess fewer GB defects. In this work, we use TCAD Sentaurus device simulator and known experimental work to investigate and quantify the potential performance gains of biaxially-textured silicon. Simulation shows there can be performance gain from well-aligned grains when GB defects dominate carrier recombination or when grains are small. On the other hand, when intra-grain defects dominate recombination and grains are large, well-aligned grains do not lead to much performance gain. Another important result from our simulation is when intra-grain and GB defects are few, Jsc is almost independent of grain size while Voc drops with decreasing grain size.
Thin-film absorber layers for photovoltaics have attracted much attention for their potential for low cost per unit power generation, due both to reduced material consumption and to higher tolerance for defects such as grain boundaries. Cu2ZnGeSe4 (CZGSe) comprises one such material system which has a near-optimal direct band gap of 1.6 eV for absorption of the solar spectrum, and is made primarily from earth-abundant elements.
CZGSe metallic precursor films were sputtered from Cu, Zn, and Ge onto Mo-coated soda lime glass substrates. These were then selenized in a two-zone close-space sublimation furnace using elemental Se as the source, with temperatures in the range of 400 to 500 C, and at a variety of background pressures. Films approximately 1-1.5 µm thick were obtained with the expected stannite crystal structure.
Next, Cu2ZnSnSe4 (CZTSe), which has a direct band gap of 1.0 eV, was prepared in a similar manner and combined with CZGSe as either compositionally homogeneous or layered absorbers. The compositional uniformity of selenide absorbers made by selenizing compositionally homogeneous Cu-Zn-Ge-Sn precursor layers was determined and the band gap as a function of composition was investigated in order to demonstrate that the band gap is tuneable for a range of compositions. For layered Cu-Zn-Ge/Cu-Zn-Sn precursor films, the composition profile was measured before and after selenization to assess the stability of the layered structure, and its applicability for forming a band-gap-graded device for improved current collection.
To establish the structural origins of the perpendicular magnetic anisotropy in Co-Pt alloys, a variety of magnetic and structural characterization techniques have been utilized. We have determined that the development of out-of-plane magnetization in these alloys, strongly depends on growth temperature and in contrast to CO/Pt Multilayers, the highest anisotropics and coercivities are observed in polycrystalline alloys with negligible preferred crystallographic orientation. Lattice strain Measurements, surface roughness determination and crystal growth studies indicate that contributions from magnetostrictive and magnetostatic contributions to the perpendicular anisotropy in these alloys are not significant. H RTEM and synchrotron-based x-ray diffraction experiments, on the other hand, confirm the existence of ordered CoPt3 at elevated temperatures. We suggest that the strong temperature dependence of the perpendicular anisotropy is correlated to the onset of spontaneous chemical ordering during the growth which results in anisotropie pair ordering. A tentative model explaining this strong temperature dependence is described.
Integrated plastic circuits (IPCs) will become an integral component of future low cost electronics. For low cost processes IPCs have to be made of all-polymer Transistors. We present our recent results on fabrication of Organic Field-Effect Transistors (OFETs) and integrated inverters. Top-gate transistors were fabricated using polymer semiconductors and insulators. The source-drain structures were defined by standard lithography of Au on a flexible plastic film, and on top of these electrodes, poly(3-alkylthiophene) (P3AT) as semiconductor, and poly(4-hydroxystyrene) (PHS) as insulator were homogeneously deposited by spin-coating. The gate electrodes consist of metal contacts. With this simple set-up, the transistors exhibit excellent electric performance with a high source-drain current at source - drain and gate voltages below 30V. The characteristics show very good saturation behaviour for low biases and are comparable to results published for precursor pentacene. With this setup we obtain a mobility of 0.2cm2/Vs for P3AT. Furthermore, we discuss organic integrated inverters exhibiting logic capability. All devices show shelf-lives of several months without encapsulation.
Mechanical loss (internal friction) and creep experiments were carried out on specimens of a Ti-46.5at.%Al-4at.%(Cr,Nb,Ta,B) alloy with differently spaced fully lamellar microstructures. The creep tests were performed in a temperature range of 970 K to 1070 K at 175 MPa. For the mechanical loss measurements a low frequency subresonance torsion apparatus was applied, operating in the frequency range of 0.01 Hz to 10 Hz. The mechanical spectra show two phenomena: (i) A loss peak of Debye-type at 900 K (0.01 Hz) which is controlled by an activation enthalpy of 3.0 eV. The loss peak is related to thermally activated (reversible) motion of dislocation segments which are pinned at the lamellae interface and within gamma lamellae. (ii) A viscoelastic high temperature background above 1000 K with an activation enthalpy of 3.8 eV. This value agrees well with the activation enthalpy of 3.6 eV from creep experiments. Both high temperature background as well as creep are assigned to diffusion controlled climb of dislocations.
Metal multilayers are a unique way to manufacture reliable conductive members for MEMS devices. These members are particularly suited for electrostatic switches. Unlike elemental Al, which experiences curvature problems during processing, the residual stress in these beams can be controlled and calibrated during stress measurements to have repeatable shapes and stresses upon release. In this study, curvature experiments were performed to determine the optimal deposition parameters (pressure, thickness) to produce metal multilayer beams with zero average stress and zero bending moment, which can be obtained by alternating tensile and compressive layers within. Resistivity measurements were made to determine the effect of interfaces on resistivity.
Well-annealed thin films are typically observed to exhibit mean grain diameters that are approximately equal to the film thickness. The standard explanation of this “sheet thickness effect” is that it results from a balance of grain boundary curvature in two different directions which, in turn, results from pinning at grain boundary grooves. TEM experiments have been performed to assess this model, and it is found that the predicted curvature about axes in the film plane is absent. Alternate explanations of the sheet thickness effect are considered.