427 research outputs found
Technology requirements for post-1985 communications satellites
The technical and functional requirements for commercial communication satellites are discussed. The need for providing quality service at an acceptable cost is emphasized. Specialized services are postulated in a needs model which forecasts future demands. This needs model is based upon 322 separately identified needs for long distance communication. It is shown that the 1985 demand for satellite communication service for a domestic region such as the United States, and surrounding sea and air lanes, may require on the order of 100,000 MHz of bandwith. This level of demand can be met by means of the presently allocated bandwidths and developing some key technologies. Suggested improvements include: (1) improving antennas so that high speed switching will be possible; (2) development of solid state transponders for 12 GHz and possibly higher frequencies; (3) development of switched or steered beam antennas with 10 db or higher gain for aircraft; and (4) continued development of improved video channel compression techniques and hardware
Technology requirements for communication satellites in the 1980's
The key technology requirements are defined for meeting the forecasted demands for communication satellite services in the 1985 to 1995 time frame. Evaluation is made of needs for services and technical and functional requirements for providing services. The future growth capabilities of the terrestrial telephone network, cable television, and satellite networks are forecasted. The impact of spacecraft technology and booster performance and costs upon communication satellite costs are analyzed. Systems analysis techniques are used to determine functional requirements and the sensitivities of technology improvements for reducing the costs of meeting requirements. Recommended development plans and funding levels are presented, as well as the possible cost saving for communications satellites in the post 1985 era
The Expected Perimeter in Eden and Related Growth Processes
Following Richardson and using results of Kesten on First-passage
percolation, we obtain an upper bound on the expected perimeter in an Eden
Growth Process. Using results of the author from a problem in Statistical
Mechanics, we show that the average perimeter of the lattice animals resulting
from a very natural family of "growth histories" does not obey a similar bound.Comment: 11 page
The pre-shock gas of SN1006 from HST/ACS observations
We derive the pre-shock density and scale length along the line of sight for
the collisionless shock from a deep HST image that resolves the H alpha
filament in SN1006 and updated model calculations. The very deep ACS
high-resolution image of the Balmer line filament in the northwest (NW)
quadrant shows that 0.25 < n_0 < le$ 0.4 cm-3 and that the scale along the line
of sight is about 2 x 10^{18} cm, while bright features within the filament
correspond to ripples with radii of curvature less than 1/10 that size. The
derived densities are within the broad range of earlier density estimates, and
they agree well with the ionization time scale derived from the Chandra X-ray
spectrum of a region just behind the optical filament. This provides a test for
widely used models of the X-ray emission from SNR shocks. The scale and
amplitude of the ripples are consistent with expectations for a shock
propagating though interstellar gas with ~ 20% density fluctuations on parsec
scales as expected from studies of interstellar turbulence. One bulge in the
filament corresponds to a knot of ejecta overtaking the blast wave, however.
The interaction results from the rapid deceleration of the blast wave as it
encounters an interstellar cloud.Comment: 16 pages, 6 figures, to appear in Ap
Choice of steel material for bridge bearings to avoid brittle fracture
Bridge bearings need verification against brittle failure at low temperatures. The design of bearings according to EN 1337 may lead to structural components with thicknesses no longer covered in the relevant technical construction regulations. Due to its specific geometry, the loading and stressing and the fabrication process the prerequisites for using the rules in EN 1993 1 10 lead to conservative restrictions or uneconomical choice of steel material. For an economical bearing design further modifications of the existing rules are necessary. This report adapts the fracture mechanical approach used in EN 1993 1 10 and gives information for a “safe-sided” choice of steel material for bearings. The main modifications refer to the hypothetical design crack scenario and the definition of the “nominal design stress” at the geometric “hot-spot”. An advanced methodology using Finite Elements and a simplified method using linear bending theory are evaluated.JRC.G.5-European laboratory for structural assessmen
Commentary and Worked Examples to EN 1993-1-10 "Material Toughness and Through Thickness Properties" and Other Toughness Oriented Rules in EN 1993
This commentary gives explanations and worked examples to the design rules in Eurocode 3 that are influenced by the strength and toughness properties of the structural steels used. It is a commentary and background document to EN 1993-1-10 "Material toughness and through thickness properties" and its extension in EN 1993-1-12 "Design rules for high-strength steels", where toughness properties are explicitly addressed.
It however provides also background to other parts of EN 1993, e.g. to EN 1993-1-1 "Design of steel structures - Basic rules and rules for buildings", where the design rules are related only to strength properties as the yield strength and the tensile strength without explicitly mentioning the role of toughness that is hidden behind the resistance formulae. Finally it gives some comments to chapter 6 of EN 1998-1: "Design of structures for earthquake resistance - Part 1: General rules, seismic actions and rules for buildings".JRC.G.5-European laboratory for structural assessmen
Organization of Patient Management and Fungal Epidemiology in Cystic Fibrosis
The achievement of a better life for cystic fibrosis (CF) patients is mainly caused by a better management and infection control over the last three decades. Herein, we want to summarize the cornerstones for an effective management of CF patients and to give an overview of the knowledge about the fungal epidemiology in this clinical context in Europe. Data from a retrospective analysis encompassing 66,616 samples from 3235 CF patients followed-up in 9 CF centers from different European countries are shown
Gregariousness Does Not Vary with Geography, Developmental Stage, or Group Relatedness in Feeding Redheaded Pine Sawfly Larvae
Aggregations are widespread across the animal kingdom, yet the underlying proximate and ultimate causes are still largely unknown. An ideal system to investigate this simple, social behavior is the pine sawfly genus Neodiprion, which is experimentally tractable and exhibits interspecific variation in larval gregariousness. To assess intraspecific variation in this trait, we characterized aggregative tendency within a single widespread species, the redheaded pine sawfly (N. lecontei). To do so, we developed a quantitative assay in which we measured interindividual distances over a 90-min video. This assay revealed minimal behavioral differences: (1) between early-feeding and late-feeding larval instars, (2) among larvae derived from different latitudes, and (3) between groups composed of kin and those composed of nonkin. Together, these results suggest that, during the larval feeding period, the benefits individuals derive from aggregating outweigh the costs and that this cost-to-benefit ratio does not vary dramatically across space (geography) or ontogeny (developmental stage). In contrast to the feeding larvae, our assay revealed a striking reduction in gregariousness following the final larval molt in N. lecontei. We also found some intriguing interspecific variation: While N. lecontei and N. maurus feeding larvae exhibit significant aggregative tendencies, feeding N. compar larvae do not aggregate at all. These results set the stage for future work investigating the proximate and ultimate mechanisms underlying developmental and interspecific variation in larval gregariousness across Neodiprion
Treosulfan-fludarabine-thiotepa-based conditioning treatment before allogeneic hematopoietic stem cell transplantation for pediatric patients with hematological malignancies
Treosulfan-based conditioning prior to allogeneic transplantation has been shown to have myeloablative, immunosuppressive, and antineoplastic effects associated with reduced non-relapse mortality (NRM) in adults. Therefore, we prospectively evaluated the safety and efficacy of treosulfan-based conditioning in children with hematological malignancies in this phase II trial. Overall, 65 children with acute lymphoblastic leukemia (35.4%), acute myeloid leukemia (44.6%), myelodysplastic syndrome (15.4%), or juvenile myelomonocytic leukemia (4.6%) received treosulfan intravenously at a dose of 10 mg/m2/day (7.7%), 12 g/m2/day (35.4%), or 14 g/m2/day (56.9%) according to their individual body surface area in combination with fludarabine and thiotepa. The incidence of complete donor chimerism at day +28 was 98.4% with no primary and only one secondary graft failure. At 36 months, NRM was only 3.1%, while relapse incidence was 21.7%, and overall survival was 83.0%. The cumulative incidence of acute graft-vs.-host disease was 45.3% for grades I–IV and 26.6% for grades II–IV. At 36 months, 25.8% overall and 19.4% moderate/severe chronic graft-vs.-host disease were reported. These data confirm the safe and effective use of treosulfan-based conditioning in pediatric patients with hematological malignancies. Therefore, treosulfan/fludarabine/thiotepa can be recommended for myeloablative conditioning in children with hematological malignancies
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