114 research outputs found
A broadband FFT spectrometer for radio and millimeter astronomy
The core architecture, tests in the lab and first results of a Fast Fourier
Transform (FFT) spectrometer are described. It is based on a commercially
available fast digital sampler (AC240) with an on-board Field Programmable Gate
Array (FPGA). The spectrometer works continuously and has a remarkable total
bandwidth of 1 GHz, resolved into 16384 channels. The data is sampled with 8
bits, yielding a dynamic range of 48 dB. An Allan time of more than 2000 s and
an SFDR of 37 dB were measured. First light observations with the KOSMA
telescope show a perfect spectrum without internal or external spurious
signals.Comment: Astronomy and Astrophysics, in pres
Thromboembolieprophylaxe: Risikoadaptierte Thromboseprophylaxe
Einführung : Neurochirurgische Patienten tragen ein hohes Risiko für tiefe Beinvenenthrombosen (TBVT) und Lungenembolien (LE): Die Inzidenz klinisch manifester TBVT ohne medikamentöse Prophylaxe beträgt 4,3 %, die subklinischer TBVT 19−50 % [8]. Lungenembolien treten bei 1,5–5 % mit einer Mortalität von 9−50 % auf [9]. Das höchste Risiko besteht bei Patienten mit hirneigenen Tumoren, v. a. in den ersten 2 Monaten. Die Inzidenz von TBVT beträgt hier bis zu 45 % [9]. In einer retrospektiven Analyse von 9489 Gliompatienten fand sich bei 7,5 % eine symptomatische Lungenembolie [23]. Bei Patienten mit ischämischem Schlaganfall stellt die Lungenembolie mit einer Inzidenz von bis zu 25 % eine der häufigsten Todesursachen dar [12].
Dieser hohen Inzidenz von thromboembolischen Ereignissen bei Neurointensivpatienten stehen die fatalen Konsequenzen einer intrakraniellen oder intraspinalen Blutungskomplikation gegenüber. Daher wird die medikamentöse Thromboembolieprophylaxe bei Neurointensivpatienten häufig kontrovers diskutiert, zum Teil sogar gänzlich abgelehnt: Nach einer Umfrage unter 58 Neurochirurgen in Großbritannien setzen 29 % der Befragten eine medikamentöse Prophylaxe postoperativ überhaupt nicht ein [7].
Die wissenschaftliche Evidenz reicht in der Frage der Thromboembolieprophylaxe von neurochirurgischen Patienten nicht aus, um individuell zu einer Entscheidung zu gelangen. Hier sind dann oft Fingerspitzengefühl und Erfahrung gefragt. Dieses Buchkapitel stellt konkrete und praktikable Empfehlungen für den Klinikalltag vor. Sie sollten als diskutable Vorschläge betrachtet werden und beruhen nicht nur auf wissenschaftlichen Daten, sondern auch auf persönlicher Erfahrung.
Bei allen Patienten sollte trotz allgemeingültiger Richtlinien eine Risikoabwägung unter Berücksichtigung der Grunderkrankung, Begleiterkrankungen, Zeitpunkt der Operation und Individualfaktoren erfolgen: Das Einblutungsrisiko, insbesondere intrakraniell und intraspinal mit möglichen fatalen Konsequenzen, sollte gegenüber dem Thromboembolierisiko abgewogen werden
Fatal subarachnoid hemorrhage following ischemia in vertebrobasilar dolichoectasia.
Vertebrobasilar dolichoectasia (VBD) is a chronic disorder with various cerebrovascular and compressive manifestations, involving subarachnoid hemorrhage (SAH). Occurrence of SAH shortly after worsening of clinical VBD symptoms has occasionally been reported. The goal of the study was to examine this association, in particular its pathophysiology, clinical precursor signs, time course, and outcome.To this end, in a retrospective multicenter study, we analyzed 20 patients with VBD and SAH in regard to preceding clinical symptoms, presence of vertebrobasilar thrombosis and ischemia, outcome and neuropathological correlates.Median age of the 7 female and 13 male patients was 70 years (interquartile range [IQR] 18.3 years). Fourteen patients (70%) presented with new or acutely worsening posterior fossa signs at a median of 3 days prior to SAH (IQR 2, range 0.5-14). A thrombus within the VBD was detected in 12 patients (60%). Thrombus formation was associated with clinical deterioration (χ = 4.38, P = 0.04) and ponto-cerebellar ischemia (χ = 8.09, P = 0.005). During follow-up after SAH, 13 patients (65%) died, after a median survival time of 24 hours (IQR 66.2, range 2-264 hours), with a significant association between proven ponto-cerebellar ischemia and case fatality (χ = 6.24, P = 0.01).The data establish an association between clinical deterioration in patients with VBD, vertebrobasilar ischemia, and subsequent SAH. Antithrombotic treatment after deterioration appears controversial and SAH outcome is frequently fatal. Our data also indicate a short window of 3 days that may allow for evaluating interventional treatment, preferably within randomized trials
Dirichlet sigma models and mean curvature flow
The mean curvature flow describes the parabolic deformation of embedded
branes in Riemannian geometry driven by their extrinsic mean curvature vector,
which is typically associated to surface tension forces. It is the gradient
flow of the area functional, and, as such, it is naturally identified with the
boundary renormalization group equation of Dirichlet sigma models away from
conformality, to lowest order in perturbation theory. D-branes appear as fixed
points of this flow having conformally invariant boundary conditions. Simple
running solutions include the paper-clip and the hair-pin (or grim-reaper)
models on the plane, as well as scaling solutions associated to rational (p, q)
closed curves and the decay of two intersecting lines. Stability analysis is
performed in several cases while searching for transitions among different
brane configurations. The combination of Ricci with the mean curvature flow is
examined in detail together with several explicit examples of deforming curves
on curved backgrounds. Some general aspects of the mean curvature flow in
higher dimensional ambient spaces are also discussed and obtain consistent
truncations to lower dimensional systems. Selected physical applications are
mentioned in the text, including tachyon condensation in open string theory and
the resistive diffusion of force-free fields in magneto-hydrodynamics.Comment: 77 pages, 21 figure
Asymptotic Analysis of Coagulation–Fragmentation Equations of Carbon Nanotube Clusters
The possibility of the existence of single-wall carbon nanotubes (SWNTs) in organic solvents in the form of clusters is discussed. A theory is developed based on abundletmodel for clusters describing the distribution function of clusters by size. The phenomena have a unified explanation in the framework of the bundlet model of a cluster, in accordance with which the free energy of an SWNT involved in a cluster is combined from two components: a volume one, proportional to the number of moleculesnin a cluster, and a surface one, proportional ton1/2. During the latter stage of the fusion process, the dynamics were governed mainly by the displacement of the volume of liquid around the fusion site between the fused clusters. The same order of magnitude for the average cluster-fusion velocity is deduced if the fusion process starts with several fusion sites. Based on a simple kinetic model and starting from the initial state of pure monomers, micellization of rod-like aggregates at high critical micelle concentration occurs in three separated stages. A convenient relation is obtained for <n> at transient stage. At equilibrium, another relation determines dimensionless binding energy α. A relation with surface dilatational viscosity is obtained
The higher-level phylogeny of Archosauria (Tetrapoda:Diapsida)
Crown group Archosauria, which includes birds, dinosaurs, crocodylomorphs, and several extinct Mesozoic groups, is a primary division of the vertebrate tree of life. However, the higher-level phylogenetic relationships within Archosauria are poorly resolved and controversial, despite years of study. The phylogeny of crocodile-line archosaurs (Crurotarsi) is particularly contentious, and has been plagued by problematic taxon and character sampling. Recent discoveries and renewed focus on archosaur anatomy enable the compilation of a new dataset, which assimilates and standardizes character data pertinent to higher-level archosaur phylogeny, and is scored across the largest group of taxa yet analysed. This dataset includes 47 new characters (25% of total) and eight taxa that have yet to be included in an analysis, and total taxonomic sampling is more than twice that of any previous study. This analysis produces a well-resolved phylogeny, which recovers mostly traditional relationships within Avemetatarsalia, places Phytosauria as a basal crurotarsan clade, finds a close relationship between Aetosauria and Crocodylomorpha, and recovers a monophyletic Rauisuchia comprised of two major subclades. Support values are low, suggesting rampant homoplasy and missing data within Archosauria, but the phylogeny is highly congruent with stratigraphy. Comparison with alternative analyses identifies numerous scoring differences, but indicates that character sampling is the main source of incongruence. The phylogeny implies major missing lineages in the Early Triassic and may support a Carnian-Norian extinction event.Marshall Scholarship for study in the United KingdomJurassic FoundationUniversity of BristolPaleontological Societ
Phylogenetic Analysis of Seven WRKY Genes across the Palm Subtribe Attaleinae (Arecaceae) Identifies Syagrus as Sister Group of the Coconut
BACKGROUND:The Cocoseae is one of 13 tribes of Arecaceae subfam. Arecoideae, and contains a number of palms with significant economic importance, including the monotypic and pantropical Cocos nucifera L., the coconut, the origins of which have been one of the "abominable mysteries" of palm systematics for decades. Previous studies with predominantly plastid genes weakly supported American ancestry for the coconut but ambiguous sister relationships. In this paper, we use multiple single copy nuclear loci to address the phylogeny of the Cocoseae subtribe Attaleinae, and resolve the closest extant relative of the coconut. METHODOLOGY/PRINCIPAL FINDINGS:We present the results of combined analysis of DNA sequences of seven WRKY transcription factor loci across 72 samples of Arecaceae tribe Cocoseae subtribe Attaleinae, representing all genera classified within the subtribe, and three outgroup taxa with maximum parsimony, maximum likelihood, and Bayesian approaches, producing highly congruent and well-resolved trees that robustly identify the genus Syagrus as sister to Cocos and resolve novel and well-supported relationships among the other genera of the Attaleinae. We also address incongruence among the gene trees with gene tree reconciliation analysis, and assign estimated ages to the nodes of our tree. CONCLUSIONS/SIGNIFICANCE:This study represents the as yet most extensive phylogenetic analyses of Cocoseae subtribe Attaleinae. We present a well-resolved and supported phylogeny of the subtribe that robustly indicates a sister relationship between Cocos and Syagrus. This is not only of biogeographic interest, but will also open fruitful avenues of inquiry regarding evolution of functional genes useful for crop improvement. Establishment of two major clades of American Attaleinae occurred in the Oligocene (ca. 37 MYBP) in Eastern Brazil. The divergence of Cocos from Syagrus is estimated at 35 MYBP. The biogeographic and morphological congruence that we see for clades resolved in the Attaleinae suggests that WRKY loci are informative markers for investigating the phylogenetic relationships of the palm family
A Holocene environmental record reflecting vegetation, climate, and fire variability at the Páramo of Quimsacocha, southwestern Ecuadorian Andes
Tooth loss and alveolar remodeling in Sinosaurus triassicus (Dinosauria: Theropoda) from the lower jurassic strata of the Lufeng Basin, China
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