1,118 research outputs found
Study of the structural, optical and electrical properties of extended defects in GaN
No full textIn questo progetto si vuole studiare l’attività di ricombinazione dei difetti estesi (dislocazioni, bordi di grano, inversion domain) in GaN attraverso metodi di caratterizzazione strutturale (TEM ad alta risoluzione, olografia elettronica) e spettroscopica (DLTS DeepLevelTransientSpectroscopy, Persistent PhotoCurrent, fotoconducibilità). Finalità del progetto di ricerca è da un lato comprendere la relazione tra struttura atomica e attività opto-elettronica delle dislocazioni e dall’altro analizzare l’influsso delle condizioni di crescita, del drogaggio e della struttura del nucleo delle dislocazioni sulle proprietà ottiche ed elettriche
A Comparative Evaluation of a New Unsupervised Sentence Boundary Detection Approach on Documents in English and Portuguese
Get PDFIn this paper, we describe a new unsupervised sentence boundary detection system and present a comparative study evaluating its performance against dierent systems found in the literature that have been used to perform the task of automatic text segmentation into sentences for English and Portuguese documents. The results achieved by this new approach were as good as those of the previous systems, especially considering that the method does not require any additional training resources
Beiträge zum Quartär der nördlichen Rheinlande
Get PDFDie Niederrheinische Bucht und die rahmenden Gebirgsregionen der Nordeifel zählen zu den klassischen Gebieten der Quartärforschung. Durch die Untersuchungen seitens des Lehrstuhls für Eiszeitenforschung der Universität Köln unter K. Brunnacker sind die stratigraphischen, sedimentologischen, bodenkundlichen und geomorphologischen Entwicklungen im großen und ganzen weitgehend bekannt. Im Zusammenhang mit Quartärforschungen des Geographischen Instituts und des Instituts für Bodenkunde der Universität Bonn ergaben sich jedoch weitere Fragen, die bisher nicht oder unbefriedigend gelöst waren. über einige Ergebnisse berichtet der vorliegende Band.
Das Problem der Tertiär/Pleistozängrenze wird in Verbindung mit einem Wandel der Morphogenese in den Beiträgen von H. Strunk und H. Zepp erneut aufgegriffen. Eine Umdatierung der Erftterrassen (H. Zepp) scheint erforderlich zu werden, denn die Talbildung war im Altpleistozän bereits an der oberen Erft größtenteils abgeschlossen. Die im Jungtertiär und Altpleistozän gebildeten Reliefformen betrachtet H. Strunk am Eifelnordrand und zeigt, daß Hauptterrassen-Rheinschotter und Eifelschotterfächer verschiedenes altpleistozänes Alter haben, jedoch jünger als die Fußflächen sind; auch H. Strunk stellt fest, daß seit dem Altpleistozän die Taleintiefung äußerst gering ist. Der Beitrag von K. Heine gibt eine Erklärung für den Widerspruch zwischen den Formen, Sedimenten und glaziotektonischen Verhältnissen der Louisendorfer Sanderfläche aufgrund einer Rekonstruktion der Bewegungen des saalezeitlichen Eisrandes. H. Siebertz untersucht die äolischen Sedimente im gleichen Raum und kann differenzierte Vorstellungen über die paläogeographischen Bedingungen zur Zeit der Bildung der äolischen Deckschichten auf dem Niederrheinischen Höhenzug entwickeln. Die Arbeiten von Urban, Schröder & Leßmann erfassen die holozänen Bildungen des unteren Niederrheingebietes interdisziplinär; die Vegetations- und Bodenentwicklung wird mit dem Siedlungsgang verknüpft; die räumliche Verteilung der Bodentypen richtet sich nach der Dauer der Bodenentwicklung auf spätpleistozänen bis altholozänen, mittelholozänen und jungholozänen Rheinsedimenten.
Die hier zusammengestellten Aufsätze sollen zur besseren Kenntnis der nördlichen Rheinlande im Quartär beitragen. Die Autoren würden sich freuen, wenn sie als Diskussionsbeiträge Beachtung fänden. Unsere Vorstellungen über die plio/pleistozäne Talentwicklung in der Nordeifel sollten nicht aus der intensiven Mittelrhein-Terrassenforschung abgeleitet werden (Beiträge H. Strunk und H. Zepp). Einzelprofile und regional eng begrenzte Detailstudien sollten nicht sofort zur weiteren Differenzierung der Quartärstratigraphie führen (Beitrag K. Heine). Die Forschungen über die pleistozänen äolischen Bildungen („Nördliche Lößgrenze“ ) sollten nicht nur zur stratigraphischen, sondern auch zur paläogeographischen Diskussion in der Lößforschung anregen (Beitrag H. Siebertz). Schließlich sollten holozäne Rekonstruktionen der großen Talauen (Beitrag Urban, Schröder, Leßmann) zum besseren Verständnis und zur besseren Nutzung unserer natürlichen Umwelt führen
The energy-critical nonlinear Schrodinger equation on a product of spheres
No full textHerr S, Strunk N. The energy-critical nonlinear Schrodinger equation on a product of spheres. Mathematical Research Letters. 2015;22(3):741-761.Let (M, g) be a compact smooth 3-dimensional Riemannian manifold without boundary. It is proved that the energy-critical nonlinear Schrodinger equation is globally well-posed for small initial data in H-1(M), provided that a certain tri-linear estimate for free solutions holds true. This estimate is known to hold true on the sphere and tori in 3d and verified here in the case S x S-2. The necessity of a weak form of this tri-linear estimate is also discussed
Obstetric litigation is asphyxiating our maternity services
No full textCopyright © 2006 The American College of Obstetricians and GynecologistsObstetric care in the United States, as judged by maternal mortality, neonatal mortality, stillbirth rates, or any other metric, has never been better. Despite this, litigation over "bad outcomes" is threatening the specialty, not only now, but into the future. Despite damage to our specialty, the injured party often benefits little, if at all, from the process. Potential solutions include an emphasis on evidence-based medicine, a qualification and review process for medical experts, and a more rational and fair health court system.Hankins, Gary D. V.; MacLennan, Alastair H.; Speer, Michael E.; Strunk, Albert JD; Nelson, Kari
CLONING OF THE 1.4-kb mRNA SPECIES OF HUMAN COMPLEMENT FACTOR H REVEALS A NOVEL MEMBER OF THE SHORT CONSENSUS REPEAT FAMILY RELATED TO THE CARBOXY TERMINAL OF THE CLASSICAL 150-kDa MOLECULE
Get PDFThree factor H mRNA species of 4.3 kb, 1.8 kb,
and 1.4 kb are constitutively expressed in human
liver. Having previously characterized full-length
cDNA clones derived from the 4.3-kb and 1.8-kb
factor mRNA, we report here the isolation and eucaryotic
expression of full-length cDNA clones coding
for the 1.4-kbm RNA species. The 1266-bp cDNA
codes for a polypeptide of 330 amino acids and
contains two polyadenylation signals and a short
poly(A)+tailT. he protein is composed of a leader
peptide followed by five short consensus repeat domains.
It shows a hybrid structure with the last
three domains being almost identical to the carboxy-
terminal of thcel assical 1 BO-kDa factor H molecule
and the two first domains representing unique
short consensus repeat structures. Eucaryotic
expression in COS7 cells revealed two polypeptides
derived from one cDNA clone that area lso found in
human serum. Differences between the cDcNloAn es
within the last three domains indicate two distinct,
possibly allelic sequences that, in addition, differ
from the authentic 150-kDa factor H sequence.
Southern blot results support the notion that the
4.3-kb factor H and the 1.4-kb factor H-related
mRNA are transcribed from two separate but highly
homologous genes.
Factor H, a glycoprotein of 150,00
Der Rechenknecht für Lipper : nach der durch das Gesetz des Norddeutschen Bundes vom 17. Aug. 1868 festgestellten metrischen Maß- und Gewichts-Ordnung
No full textbearb. von H. StrunkIn Fraktu
Investigation of carbon nanotube quantum dots connected to ferromagnetic leads
Get PDFThe implementation of ferromagnetic contacts in complex nanoelectronic devices,
e.g. in spin-valves bears great potential for applications and fundamental
investigations. Spin-valves are structures with two magnetic contacts and
a non-magnetic medium (M) in-between, where a step-like change in magnetoresistance
(MR) is observed when the relative orientation of the strip magnetization
is changed by an external magnetic field. There is already a very
successful use of the electron spin in electronic devices for magnetic field sensing
for example in read-and-write heads of computer hard discs. Another upcoming
application of spin valves are for example non-volatile random-access
memories (MRAMs) for data storage.
However, electronic devices which use the electron spin directly, like in a spintransistor
or as quantum bits requires materials for the non-magnetic
medium exhibiting long coherence times and electrical tunability. Carbon
based materials like graphene or carbon nanotubes are due to their intrinsic
large coherence times in principle ideal candidates for spintronic devices, as
demonstrated in nonlocal spin-accumulation experiments on graphene or in
electrically tunable spin valves on carbon nanotubes.
Especially the observation of a gate dependent magneto-resistance in carbon
nanotube quantum dots contacted with ferromagnetic leads in 2005 by S. Sahoo
promises an electrical control over spin transport. These devices analog
to field-effect transistors might pave the way for multi-functional spintronic
devices. However, the implementation of ferromagnetic contacts in nanoelectronic
devices has been a proven challenging task due to the complex nature
of ferromagnets and interfaces, where oxidation, surface roughness and mesoscopic
details may induce uncontrolled instabilities in transport measurements.
Spintransport experiments on carbon nanotube quantum dots suffer mainly
from irreproducibilities in the magneto resistance and from the low yield of
electrical contacts to the nanotube. Therefore in this thesis carbon nanotube
quantum dots connected to ferromagnetic leads are investigated, focusing on
the fabrication of stable devices with higher contact yields and first experiments
on stable devices. This allows for further investigations of the not well
understood gate dependence of the magneto resistance in such devices. Moreover
with such stable devices, even more complex experiments or applications like detectors
for spin entanglement can become possible
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