Search

Atomic layer etching (ALE) provides Ångström-level control over material removal and holds potential for addressing the challenges in nanomanufacturing faced by conventional etching techniques. Recent research has led to the development of two main classes of

Aims.We present a low-resolution spectroscopic survey of the Orion nebula. The data are released for public use. We show the possible applications of this dataset analyzing some of the main properties of the nebula.

Detailed neutral hydrogen observations have been obtained of the large barred spiral galaxy NGC 3992 and its three small companion galaxies, UGC 6923, UGC 6940, and UGC 6969. For the main galaxy, the H idistribution is regular with a low level radial extension outside the stellar disc. However, at exactly the region of the bar, there is a pronounced central H ihole in the gas distribution. Likely gas has been transported inwards by the bar and because of the emptyness of the hole no large accretion events can have happened in recent galactic times. The gas kinematics is very regular and it is demonstrated that the influence of the bar potential on the velocity field is negligible. A precise and extended rotation curve has been derived showing some distinct features which can be explained by the non-exponential radial light distribution of NGC 3992. The decomposition of the rotation curve gives a slight preference for a sub maximal disc, though a range of disc contributions, up to a maximum disc situation fits nearly equally well. For such a maximum disc contribution, which might be expected in order to generate and maintain the bar, the required mass-to-light ratio is large but not exceptional.

In this data paper we present the results of an extensive 21 cm-line synthesis imaging survey of 43 spiral galaxies in the nearby Ursa Major cluster using the Westerbork Synthesis Radio Telescope. Detailed kinematic information in the form of position-velocity diagrams and rotation curves is presented in an atlas together with HI channel maps, 21 cm continuum maps, global HI profiles, radial HI surface density profiles, integrated HI column density maps, and HI velocity fields. The relation between the corrected global HI linewidth and the rotational velocities $V_{\max}$and Vflatas derived from the rotation curves is investigated. Inclination angles obtained from the optical axis ratios are compared to those derived from the inclined HI disks and the HI velocity fields. The galaxies were not selected on the basis of their HI content but solely on the basis of their cluster membership and inclination which should be suitable for a kinematic analysis. The observed galaxies provide a well-defined, volume limited and equidistant sample, useful to investigate in detail the statistical properties of the Tully-Fisher relation and the dark matter halos around them.

Electron beam-induced deposition (EBID) enables the direct-write patterning of metallic structures with sub-10 nm lateral resolution without the use of resist films or etching/lift-off steps but generally leads to material of poor quality and suffers from a low throughput. These shortcomings were mitigated in recent work by combining EBID with atomic layer deposition (ALD). This direct-write ALDtechnique comprises the patterning of a thin seed layer by EBID followed by selective thickening of the pattern by ALD. In this work, the throughput of direct-write ALD was drastically improved based on new insights into how the ALD growth initiates on EBID material, and in addition, the conditions for selective ALD growth were identified. The required electron dose was reduced by 2 orders of magnitude to ∼11 pC/μm2by exposing the EBID seed layers to O2in the ALD reactor just before the ALD building step. This improvement of the technique allows for nanopatterning with a throughput comparable to electron beam lithography (EBL).

The Rap-pathway has been implicated in various cellular processes but its exact physiological function remains poorly defined. Here we show that the Caenorhabditis elegans homologue of the mammalian guanine nucleotide exchange factors PDZ-GEFs, PXF-1, specifically activates Rap1 and Rap2. Green fluorescent protein (GFP) reporter constructs demonstrate that sites of pxf-1 expression include the hypodermis and gut. Particularly striking is the oscillating expression of pxf-1 in the pharynx during the four larval molts. Deletion of the catalytic domain from pxf-1 leads to hypodermal defects, resulting in lethality. The cuticle secreted by pxf-1 mutants is disorganized and can often not be shed during molting. At later stages, hypodermal degeneration is seen and animals that reach adulthood frequently die with a burst vulva phenotype. Importantly, disruption of rap-1 leads to a similar, but less severe phenotype, which is enhanced by the simultaneous removal of rap-2. In addition, the lethal phenotype of pxf-1 can be rescued by expression of an activated version of rap-1. Together these results demonstrate that the pxf-1/rap pathway in C. elegans is required for maintenance of epithelial integrity, in which it probably functions in polarized secretion.

The formation of parietal endoderm (PE) is one of the first differentiation processes during mouse development and can be studied in vitro using F9 embryonal carcinoma (EC) cells. Treatment of F9 EC cells with retinoic acid (RA) induces differentiation toward primitive endoderm (PrE), while differentiation toward PE is induced by subsequent addition of parathyroid hormone (PTH) or PTH-related peptide (PTHrP). The signal transduction mechanisms involved in this two-step process are largely unclear. We show that the RA-induced differentiation toward PrE is accompanied by a sustained increase in Ras activity and that ectopic expression of oncogenic Ha-Ras is sufficient to induce PrE differentiation. Ras activity subsequently decreases upon PTH-induced differentiation toward PE. This is a necessary event, since expression of oncogenic Ha-Ras in PrE-like cells prevents PTH-induced PE differentiation. Expression of active PKA in PrE-like F9 cells mimics PTH-induced PE differentiation and is again prevented by oncogenic Ha-Ras. The effect of oncogenic Ras on both differentiation steps is abolished by the MEK inhibitor PD98059 and can be mimicked by constitutively active forms of Raf and MEK. In conclusion, our data suggest that activation of the Ras/Erk is sufficient to induce differentiation to PrE and to prevent subsequent differentiation toward PE. Activation of PKA down-regulates Ras activity, resulting in disappearance of this blockade and transmission of signal(s) triggering PE differentiation.

On the {100} and {111} surfaces of C70 crystals the phase transition of the f.c.c. structure towards the trigonal structure has been studied in situ with the help of optical reflection microscopy. Extensive ex situ studies of domain patterns on both types of surface have been performed using both optical and atomic force microscopy. A detailed interpretation of the domain patterns is given. An additional phase transition was observed in situ at 303 K.

A theory is presented for the explanation of equilibrium forms of modulated crystals. In this theory crystallographic concepts are generalized to a superspace description of these crystals. The aim is to be able to deal with the case of incommensurately modulated crystals and consequently to explain the occurrence of satellite faces. The case of a modulated one-dimensional crystal is treated.

In this paper the competences of e-beam lithography are described for the production of computer generated holograms (CGHs). Three principles of e-beam systems are compared. Examples are given of optical devices made with e-beam lithography. Phase shifting masks for integrated circuit production are described. Relief phase gratings with 150 nm structures, binary CGHs and blazed structures have been made successfully.

In a previous study, we demonstrated that parathyroid hormone (PTH) inhibits mitogen-activated protein (MAP) kinase activation in osteosarcoma cells via a protein kinase A-dependent pathway. Here, we show that PTH can induce a transient activation of MAP kinase as well. This was observed in both Chinese hamster ovary R15 cells stably expressing high levels of rat PTH/PTH-related peptide receptor and parietal yolk sac carcinoma cells expressing the receptor endogenously. PTH was a strong activator of adenylate cyclase and phospholipase C in Chinese hamster ovary R15 cells. PTH-induced MAP kinase activation did not depend on activation of Gi, phorbol ester-sensitive protein kinase C, elevated intracellular calcium levels, or release of Gbetagamma subunits. It could, however, be mimicked by addition of forskolin or 8-bromo-cAMP to these cells. Prolonged treatment with forskolin caused sustained protein kinase A activity, whereas MAP kinase activity returned to basal levels. Subsequent treatment with PTH or 8-bromo-cAMP did not result in MAP kinase activation, whereas phorbol ester- or insulin-induced MAP kinase activation was unaffected. Finally, expression of a dominant negative form of Ras (RasAsn-17), which completely blocked insulin-induced MAP kinase activation, did not affect activation by PTH or cAMP. In conclusion, PTH regulates MAP kinase activity in a cell type-specific fashion. The activation of MAP kinase by PTH is mediated by cAMP and independent of Ras.

This is the third in a series of papers in which spiral galaxy rotation curves are considered in the context of Milgrom's modified dynamics (MOND). The present sample of 30 objects is drawn from a complete sample of galaxies in the Ursa Major cluster, with photometric data from Tully et al. and 21 cm line data from Verheijen. The galaxies are roughly all at the same distance (15 to 16 Mpc). The radio observations are made with the Westerbork Synthesis Array, which means that the linear resolution of all rotation curves is comparable. The greatest advantage of this sample is the existence of K'-band surface photometry for all galaxies; the near-infrared emission, being relatively free of the effects of dust absorption and less sensitive to recent star formation, is a more precise tracer of the mean radial distribution of the dominant stellar population. The predicted rotation curves are calculated from the K'-band surface photometry and the observed distribution of neutral hydrogen using the simple MOND prescription, in which the one adjustable parameter is the mass of the stellar disk or the implied mass-to-light ratio. The predicted rotation curves generally agree with the observed curves, and the mean M/Lin the near-infrared is about 0.9 with a small dispersion. The fitted M/Lin the B-band correlates with B-Vcolor in the sense predicted by population synthesis models. Including earlier work, about 80 galaxy rotation curves are now well reproduced from the observed distribution of detectable matter using the MOND formula to calculate the gravitational acceleration; this lends considerable observational support to Milgrom's unconventional hypothesis.

Summary In vitro penetration of the micropyle of freshly isolatedGasteria verrucosa ovules by pollen tube was monitored on agar medium. 40–60% of the micropyles were penetrated, comparable with in vivo penetration percentages. When germinated on agar,Gasteria pollen tube elongation lasts for up to 8 h while plasma streaming continues for about 20–24 h. The generative cell divides between 7 and 20 h after germination, and after 20 h the pollen tube arrives at one of the synergids. The sperm cells arrive after 22 h. The whole process takes more time in vitro than in vivo. In fast growing pollen tubes, a pulsed telescope-like growth pattern of tube elongation is observed. The formation of pollen tube wall material precedes tube elongation and probably prevents regular enlargement of the pollen tube tip-zone. Rapid stretching of the new pollen tube wall material follows, probably due to gradually increased osmotic pressure and the use of lateral wall material below the tip. The stretching ceases when the supplies of plasma membrane and excretable wall material are exhausted. Multiple pollen tube penetration of the micropyle occurs in vitro as it does in vivo. Most pollen tube growth ceases within the micropyle but, if it continues, the pollen tubes curl. Inside the micropyle the pollen tube shows haustorial growth. At the ultrastructural level, the wall thickening of in vitro pollen tubes is quite similar to that in vivo. Before transfer of pollen tube cytoplasm a small tube penetrates one of the synergids. Sperm nuclei with condensed chromatin are observed in the pollen tube and the synergid. In vivo prometaphase nuclei are found in the most chalazal part of a synergid, against the egg cell nucleus and nucleus of the central cell at a later stage. Using media forLilium ovule culture,Gasteria ovules were kept alive for at least 6 weeks. Swelling of the ovule depends on pollen tube penetration. The conditions for fertilization to occur after in vitro ovular pollination seem to be present.

The crystallization behavior of thin strontium titanate (SrTiO3,STO) films with ∼15 nm thickness was studied by Transmission Electron Microscopy (TEM). Amorphous STO films with [Sr]/([Sr]+[Ti]) ratio ranging from 0.50 to 0.63 were deposited at 350°C by plasma-assisted ALD and subsequently treated by rapid thermal annealing in flowing N2for crystallization. Different temperatures and annealing durations were employed to fully characterize the crystallization process. TEM analysis showed that transrotational crystals were formed and evidenced the influence of the STO composition and of the thermal budget applied on the grain size, crack and void formation. In particular, Sr-rich layers ([Sr]/([Sr]+[Ti] ≥ 0.59) showed a finer crystalline structure which was imputed to a higher nucleation probability at the onset of the crystallization process. Crystallization into the perovskite structure was confirmed for all the film compositions studied. By tuning the STO composition and the thermal budget of the annealing step it was demonstrated that it is possible to control the microstructure of the crystallized film as a further step in optimizing the STO film properties.

Aims.The aim of this work is to investigate the possible presence of extended diffuse synchrotron radio emission associated with the intracluster medium of the complex galaxy cluster A1689.

The electrical and physical properties of CeO2–HfO2nanolaminates on Si(100), by pulsed laser deposition, are investigated. Layers were deposited using pure CeO2and HfO2targets at various substrate temperatures ranging from 220to620°Cat Ar+H2and O2and in situ postdeposition anneal of nanolaminates performed by controlled cooling from deposition temperature to room temperature under high oxygen pressure. After layer growth and anneal, top and bottom Au electrodes were deposited by sputtering. Electrical characterization was done by C-Vand I-Vmeasurements. The highest kvalue of 30 was found for the laminates deposited at 520°Cin Ar+H2ambient. It is found that the properties of CeO2–HfO2nanolaminates deposited at reducing atmosphere are dependent on the layer thickness. Thicker layers showed a higher dielectric constant and higher leakage current densities than thinner layers.