ALBERT

Notizen: The ohmic transport of holes in p-type Al-doped 4H–SiC samples is investigated using a Monte Carlo tool based on a full-potential band structure. The temperature and doping dependence of the hole mobility and its anisotropy are calculated and discussed from a physical point of view, where we stress the importance of considering two-band conduction. Acoustic and optical phonon scattering, as well as ionized and neutral impurity scattering, have been considered. The Monte Carlo program also considers incomplete ionization of impurity atoms compatible with an Al ionization energy of 0.2 eV. © 2002 American Institute of Physics.

Notizen: The effect of the proportion of Calluna vulgaris cover on diet composition, intake and performance of sheep grazing hill vegetation communities in northern Spain is examined. A total of 591 non-lactating Gallega ewes grazed for five consecutive grazing seasons (June to September) on replicated plots of hill pastures (1700 m.a.s.l.) composed principally of Festuca, Agrostis, Nardus and Calluna spp. but with different proportions of Calluna vulgaris cover, either 0·3 (C0·3) or 0·7 (C0·7) of the total area. In 1 year, twenty-eight ewes suckling single lambs also grazed the plots. The mean stocking density over the 5 years was 8·7 ewes ha–1. On treatment C0·3, daily liveweight gains (33 g d–1) of non-lactating ewes were significantly (P 〈 0·001) greater than on treatment C0·7 (12 g d–1). Likewise in lactating ewes the difference in mean daily liveweight change was 40 g d–1 (–5 vs. –45 g d–1 for C0·3 and C0·7 treatments respectively; P 〈 0·001). Liveweight gains of lambs were only 80–100 g d–1 from June to August and lambs only maintained live weight during August and September. The effect of lactational status on liveweight changes was not significant. Liveweight gains of non-lactating ewes increased significantly (P 〈 0·001) from the first to the last year of the experiment on both treatments.The composition of the diet was significantly affected by treatment (P 〈 0·001), with a higher proportion of grass species on the C0·3 treatment and a higher digestibility of the diet in the first half of the grazing season (P 〈 0·001). The proportion of C. vulgaris in the diet was significantly (P 〈 0·001) higher on the C0·7 treatment and increased significantly (P 〈 0·001) from July to September on both treatments. There were no significant differences in the composition of the diet selected by lactating and non-lactating ewes.The results demonstrate that on hill vegetation communities, in which the grass components (Festuca rubra, Agrostis capillaris, and Nardus stricta) cover at least 0·3 of the area and on which the preferred grass component (Festuca and Agrostis spp.) is maintained at a sward height of at least 2·5 cm, non-lactating ewes can increase their live weight and body condition, but this increase is influenced by the proportion and quantity of species of grass in the diet, which is affected in turn by the species of grass available and their nutritive quality. However, ewes suckling lambs were not able to maintain their live weight and body condition except when Calluna cover was 0·3 and grass height was more than 3·5 cm.It is concluded that these indigenous vegetation communities can be used in sheep production systems to complement the use of improved pastures at other times of year. In particular, they can be utilized during the non-lactating period (summer) to increase body condition before the beginning of the mating period in autumn.

Notizen: In the present work process methodology was optimized to synthesize oriented barium strontium titanate (BST) (50/50) and (60/40) thin films on strontium titanate (100) and lanthanum aluminate (LAO) (100) substrates by using the chemical solution deposition technique. These films were characterized in terms of their phase formation behavior and structural growth characteristics using x-ray diffraction and atomic force microscopy. A tentative mechanism of the epitaxial growth has been proposed. Films were also characterized in terms of their dielectric properties. The high tunability and low dielectric loss of these films make them attractive for fabricating tunable dielectric devices. Accordingly, we have fabricated eight element coupled microstrip phase shifters and tested them in terms of their degree of phase shift and insertion loss characteristics. An insertion loss of 8.435 dB, phase shift in the order of 320° (2.6–14.5 V/μm) and κ factor (phase shift/dB of loss) of about 38.0°/dB was achieved in BST (60/40) films deposited on LAO (100) substrate which is comparable to the films grown by other film deposition techniques reported in the literature. The microstructure of the sol–gel derived films show surface porosity which may be responsible for the low dielectric strength of these films. Presently, we are studying the sintering mechanism and kinetics of these films in order to improve the density which is believed to further improve the phase shift and lower insertion loss to result in an improved tunability. © 2001 American Institute of Physics.

Notizen: The room-temperature electrical conductivity of sulfur-incorporated nanocomposite carbon (n-C:S) thin films synthesized by hot-filament chemical vapor deposition was investigated as a function of the sulfur concentration. The films were prepared using a 2% CH4/H2 gas mixture and H2S as the dopant source. The n-C:S films exhibited an increase in conductivity by four orders of magnitude (up to 160 S cm−1) with an increase in sulfur content compared with those grown without sulfur (n-C). The films grown at the highest [H2S] possess the highest carrier concentration (∼5×1019/cm3) and the lowest carrier mobility (0.005 cm2 V−1 s−1). These findings are discussed in terms of the multiple roles of sulfur atoms in the films: (i) induction of structural defects and their corresponding midgap states, (ii) enhancement of the spatial connectivity of the sp2-bonded carbon network, and (iii) electrical activity of only a small fraction of the sulfur atoms. © 2002 American Institute of Physics.

Notizen: Abstract A broad array of biological responses, including cell polarization, movement, immune and inflammatory responses, and prevention of HIV-1 infection, are triggered by the chemokines, a family of structurally related chemoattractant proteins that bind to specific seven-transmembrane receptors linked to G proteins. Here we discuss one of the early signaling pathways activated by chemokines, the JAK/STAT pathway. Through this pathway, and possibly in conjunction with other signaling pathways, the chemokines promote changes in cellular morphology, collectively known as polarization, required for chemotactic responses. The polarized cell expresses the chemokine receptors at the leading cell edge, to which they are conveyed by rafts, a cholesterol-enriched membrane fraction fundamental to the lateral organization of the plasma membrane. Finally, the mechanisms through which the chemokines promote their effect are discussed in the context of the prevention of HIV-1 infection.

Notizen: We have calculated the static polarizabilities of polymers with small linear and medium-size cyclic elementary cells and their constituent molecules. The basis set dependence has been investigated for the average and the longitudinal polarizabilities. The influence on the results of the selected method for the calculation (finite field or coupled perturbed Hartree–Fock) was analyzed. The effect of the electron correlation for this property in these systems has been calculated for the first time in the frames of the crystal orbital approach. The results show that this correction amounts up to 35% of the ab initio Hartree–Fock values. © 2002 American Institute of Physics.

Notizen: Abstract Effects of breed and sward surface height on ewe liveweight and body condition changes and on lamb liveweight gains during grazing in the spring and autumn were studied. The output per hectare in each season was also calculated.A total of 112 Gallega ewes (35·6 kg live weight) and 204 Latxa ewes (47·5 kg live weight) with their lambs were used during the spring (March–June) to study the effect of five target sward heights (3·0, 4·5, 5·5, 6·5 and 8·0 cm) and the interaction with breed. In autumn (October–December) 155 Gallega and 126 Latxa ewes were used to study the effect of three target sward heights (4·0, 5·5 and 7·0 cm) and the interaction with breed. Each study was replicated twice.A quadratic relationship was found between sward height and ewe liveweight and body condition changes and lamb liveweight gain during the spring grazing season, with the maximum individual performance being achieved at around a sward height of 6·0 cm. There were significant breed × sward height treatment interactions for ewe liveweight and body condition changes, and lamb liveweight gains. Higher liveweight gains were achieved by Latxa ewes and lambs in swards taller than 6·5 cm but they also sustained higher liveweight losses in swards shorter than 4·5 cm. Nevertheless, a higher output (liveweight gains of ewes + lambs) per hectare for a given weaning date or age was achieved by the Gallega ewes. In autumn, the relationship between liveweight change and sward height was linear, with a breed–sward height interaction similar to that observed in the spring.Sward surface heights of 4·0–4·5 cm and 4·5–5·0 cm were required to maintain live weight and body condition in spring and autumn respectively. Lamb and ewe liveweight gains per hectare decreased considerably in swards taller than 6·5 cm.

Notizen: : Isothermal and non-isothermal heat resistance studies were carried out on Bacillus pumilus spores. The non-isothermal study revealed a non-linear behavior of the survivor curve, which was revealed as a tail after an isothermal study. Results indicated that the spores obtained by isolating cells from colonies of the tail section were more heat resistant than the original ones (D104°c= 0.15 and 1.9 min for spores from the original population and from the tail, respectively). Application of the Weibull distribution model to analyze the tail produced good results at the 3 temperatures studied. Nevertheless, when the model was applied to curves having both concave downward and concave upward sections a poor result was obtained, with an accuracy factor greater than 1.

Notizen: [Auszug] Here we show that the cell-cycle regulator p21 is involved in immune system function. T lymphocytes from p21−/− mice exhibit significant proliferative advantage over wild-type cells following prolonged stimulation, but not after primary activation. Consistent with this, p21-deficient ...