12,450 research outputs found
Technology needs of advanced Earth observation spacecraft
Remote sensing missions were synthesized which could contribute significantly to the understanding of global environmental parameters. Instruments capable of sensing important land and sea parameters are combined with a large antenna designed to passively quantify surface emitted radiation at several wavelengths. A conceptual design for this large deployable antenna was developed. All subsystems required to make the antenna an autonomous spacecraft were conceptually designed. The entire package, including necessary orbit transfer propulsion, is folded to package within the Space Transportation System (STS) cargo bay. After separation, the antenna, its integral feed mast, radiometer receivers, power system, and other instruments are automatically deployed and transferred to the operational orbit. The design resulted in an antenna with a major antenna dimension of 120 meters, weighing 7650 kilograms, and operating at an altitude of 700 kilometers
Escape path complexity and its context dependency in Pacific blue-eyes (Pseudomugil signifer)
The escape trajectories animals take following a predatory attack appear to
show high degrees of apparent 'randomness' - a property that has been described
as 'protean behaviour'. Here we present a method of quantifying the escape
trajectories of individual animals using a path complexity approach. When fish
(Pseudomugil signifer) were attacked either on their own or in groups, we find
that an individual's path rapidly increases in entropy (our measure of
complexity) following the attack. For individuals on their own, this entropy
remains elevated (indicating a more random path) for a sustained period (10
seconds) after the attack, whilst it falls more quickly for individuals in
groups. The entropy of the path is context dependent. When attacks towards
single fish come from greater distances, a fish's path shows less complexity
compared to attacks that come from short range. This context dependency effect
did not exist, however, when individuals were in groups. Nor did the path
complexity of individuals in groups depend on a fish's local density of
neighbours. We separate out the components of speed and direction changes to
determine which of these components contributes to the overall increase in path
complexity following an attack. We found that both speed and direction measures
contribute similarly to an individual's path's complexity in absolute terms.
Our work highlights the adaptive behavioural tactics that animals use to avoid
predators and also provides a novel method for quantifying the escape
trajectories of animals.Comment: 9 page
Alloying, de-alloying and reentrant alloying in (sub-)monolayer growth of Ag on Pt(111)
An in-situ nanoscopic investigation of the prototypical surface alloying
system Ag/Pt(111) is reported. The morphology and the structure of the
ultrathin Ag-Pt film is studied using Low Energy Electron Microscopy during
growth at about 800 K. An amazingly rich dynamic behaviour is uncovered in
which stress relieve plays a governing role. Initial growth leads to surface
alloying with prolonged and retarded nucleation of ad-islands. Beyond 50%
coverage de-alloying proceeds, joined by partial segregation of Pt towards the
centre of large islands in violent processes. Upon coalescence the irregularly
shaped vacancy clusters are filled by segregating Pt, which then take a compact
shape (black spots). As a result at around 85% coverage the strain of the
initially pseudo-morphological film is almost completely relieved and
Pt-segregation is at its maximum. Further deposition of Ag leads to transient
re-entrant alloying and recovery of the pseudo-morphological layer. The black
spots persist even in/on several layers thick films. Ex-situ atomic force
microscopy data confirm that these are constituted by probably amorphous
Pt(-rich) structures. The (sub-)monolayer films are very much heterogeneous
John Y. Templeton III: Pioneer of modern cardiothoracic surgery.
John Young Templeton III was born in 1917 in Portsmouth, Virginia, and graduated from Jefferson Medical College in 1941. He completed his residency training under Dr. John H. Gibbon, Jr., and was the first resident who worked on Gibbon\u27s heart-lung machine. After his training, he remained at Jefferson as an American Cancer Society fellow and Damon Runyon fellow and went on to become the fourth Samuel D. Gross Professor and Chair of the Department of Surgery in 1967. Dr. Templeton was the recipient of numerous grants and published over 80 papers in the field of cardiothoracic surgery. As a teacher and mentor, he was a beloved figure who placed great faith in his residents. He participated in over 60 professional societies, serving as president to many such as the Philadelphia Academy of Surgery and the Pennsylvania Association of Thoracic Surgery. He was also recognized through his many awards, in particular the John Y. Templeton III lectureship established in 1980 at Jefferson of whom Denton Cooley was the first lecturer. Dr. Templeton retired from practice in 1987. He is forever remembered as an important model of a modern surgeon evident in numerous academic achievements, the admiration and affection of his trainees, and the lives of patients that he had touched
Building from Scratch: New Cities, Privatized Urbanism and the Spatial Restructuring of Johannesburg after Apartheid
By the start of the twentyâfirst century, the once dominant historical downtown core of Johannesburg had lost its privileged status as the center of business and commercial activities, the metropolitan landscape having been restructured into an assemblage of sprawling, rival edge cities. Real estate developers have recently unveiled ambitious plans to build two completely new cities from scratch: Waterfall City and Lanseria Airport City (formerly called Cradle City) are masterâplanned, holistically designed âsatellite citiesâ built on vacant land. While incorporating features found in earlier cityâbuilding efforts, these two new selfâcontained, privatelyâmanaged cities operate outside the administrative reach of public authority and thus exemplify the global trend toward privatized urbanism. Waterfall City, located on land that has been owned by the same extended family for nearly 100 years, is spearheaded by a single corporate entity. Lanseria Airport City/Cradle City is a planned âaerotropolisâ surrounding the existing Lanseria airport at the northwest corner of the Johannesburg metropole. These two new private cities differ from earlier largeâscale urban projects because everything from basic infrastructure (including utilities, sewerage, and the installation and maintenance of roadways), landscaping, security services, the regulation of common spaces, and selling and branding the city are firmly in the hands of private profitâmaking corporate entities and outside the mandate of public authorities.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/113120/1/ijur12180.pd
Visualization of steps and surface reconstructions in Helium Ion Microscopy with atomic precision
Helium Ion Microscopy is known for its surface sensitivity and high lateral
resolution. Here, we present results of a Helium Ion Microscopy based
investigation of a surface confined alloy of Ag on Pt(111). Based on a change
of the work function of 25\,meV across the atomically flat terraces we can
distinguish Pt rich from Pt poor areas and visualize the single atomic layer
high steps between the terraces. Furthermore, dechanneling contrast has been
utilized to measure the periodicity of the hcp/fcc pattern formed in the 2--3
layers thick Ag/Pt alloy film. A periodicity of 6.65\,nm along the
surface direction has been measured. In terms of
crystallography a hcp domain is obtained through a lateral displacement of a
part of the outermost layer by of a nearest neighbour spacing
along . This periodicity is measured with atomic
precision: coincidence between the Ag and the Pt lattices is observed for 23 Ag
atoms on 24 Pt atoms. The findings are perfectly in line with results obtained
with Low Energy Electron Microscopy and Phase Contrast Atomic Force Microscopy.Comment: 15 pages, 7 figure
Cosmological Density Perturbations with a Scale-Dependent Newton's G
We explore possible cosmological consequences of a running Newton's constant
, as suggested by the non-trivial ultraviolet fixed point
scenario in the quantum field-theoretic treatment of Einstein gravity with a
cosmological constant term. In particular we focus here on what possible
effects the scale-dependent coupling might have on large scale cosmological
density perturbations. Starting from a set of manifestly covariant effective
field equations derived earlier, we systematically develop the linear theory of
density perturbations for a non-relativistic, pressure-less fluid. The result
is a modified equation for the matter density contrast, which can be solved and
thus provides an estimate for the growth index parameter in the
presence of a running . We complete our analysis by comparing the fully
relativistic treatment with the corresponding results for the non-relativistic
(Newtonian) case, the latter also with a weakly scale dependent .Comment: 54 pages, 4 figure
Innate immune receptor NOD2 mediates LGR5+ intestinal stem cell protection against ROS cytotoxicity via mitophagy stimulation
International audienceThe nucleotide-binding oligomerization domain-containing protein 2 (NOD2) agonist muramyl dipeptide (MDP), a peptidoglycan motif common to all bacteria, supports leucine-rich repeat-containing G protein-coupled receptor 5 (LGR5)+ intestinal stem cell (ISC) survival through NOD2 activation upon an otherwise lethal oxidative stress-mediated signal. However, the underlying protective mechanisms remain unknown. Here, using irradiation as stressor and primarily murine-derived intestinal organoids as a model system, we show that MDP induced a significant reduction of total and mitochondrial reactive oxygen species (ROS) within ISCs, which was associated with mitophagy induction. ATG16L1 knockout (KO) and NOD2 KO organoids did not benefit from the MDP-induced cytoprotection. We confirmed the MDP-dependent induction of ISC mitophagy upon stress in vivo. These findings elucidate the NOD2-mediated mechanism of cytoprotection involving the clearance of the lethal excess of ROS molecules through mitophagy, triggered by the coordinated activation of NOD2 and ATG16L1 by a nuclear factor ÎșB (NF-ÎșB)-independent pathway
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