1,069 research outputs found
Spatial properties of conjugated network in semicrystalline polymer thin films studied by intensity x-ray cross-correlation functions
We present results of x-ray study of spatial properties of
conjugated networks in polymer thin films. We applied the x-ray
cross-correlation analysis to x-ray scattering data from blends of
poly(3-hexylthiophene) (P3HT) and gold nanoparticles. The Fourier spectra of
the intensity cross-correlation functions for different films contain non-zero
components of orders and measuring the degree of structural order
in the system.Comment: 6 pages, 2 figures, Proceedings ICXOM22 Conference, 2-6 September
2013, Hamburg, German
Perioperative Cardiac Arrests
Perioperative cardiac arrests represent the most serious complication of anesthesia and surgery. It is believed that the incidence and mortality of cardiac arrest has declined, however, a more recent review questioned whether these rates have changed over the last 5 decades. It is difficult to compare the reports from different epochs, because medical practice has advanced, surgical acuity increased, and patients in extremes of age undergo surgery today. In the present article we review the information regarding the incidence of perioperative cardiac arrests and predictors of survival covering the period since the first comprehensive report by Beecher and Todd in 1954. We focus on our publications that report perioperative cardiac arrest at Mayo Clinic for adult noncardiac surgery, during regional anesthesia, and arrests in our pediatric surgical practice
Electron transmission and phase time in semiconductor superlattices
We discuss the time spent by an electron propagating through a finite
periodic system such as a semiconductor superlattice. The relation between
dwell-time and phase-time is outlined. The envelopes of phase-time at maximum
and minimum transmission are derived, and it is shown that the peaks and
valleys of phase-time can be well described by parameters fitted at the
extrema. For a many-period system this covers most of the allowed band.
Comparison is made to direct numerical solutions of the time-dependent
Schr\"odinger equation by Veenstra et al. [cond-mat/0411118] who compared
systems with and without addition of an anti-reflection coating (ARC). With an
ARC, the time delay is consistent with propagation at the Bloch velocity of the
periodic system, which significantly reduces the time delay, in addition to
increasing the transmissivity.Comment: 8 pages, 10 figures, based on a talk at Theory-Canada 3 in Edmonton
AB, June 200
Nuclear Charge Density Distributions from Elastic Electron Scattering Data
The model independent procedure of extracting charge density distributions
from elastic electron scattering data is investigated. The charge density
distributions are expanded on an orthonormal basis and the parameters of the
expansions are fixed by the comparison with the experimental data. Two bases
with different analytical properties (Fourier-Bessel and Hermite) are used.
This allows us to disentangle the uncertainties coming from the choice of the
expansion basis from those intrinsic to the extraction procedure. We design a
set of tests to select the number of the expansion coefficients adequate for a
proper description of the data. The procedure is applied to elastic data
measured on C, Ca and Pb nuclei.Comment: 17 pages, 11 figures available on request to [email protected], to
be published in Nucl.Phy
Long time deviation from exponential decay: non-integral power laws
Quantal systems are predicted to show a change-over from exponential decay to
power law decay at very long times. Although most theoretical studies predict
integer power-law exponents, recent measurements by Rothe et al. of decay
luminescence of organic molecules in solution {Phys. Rev. Lett. 96 (2006)
163601} found non-integer exponents in most cases. We propose a physical
mechanism, within the realm of scattering from potentials with long tails,
which produces a continuous range of power law exponents. In the tractable case
of the repulsive inverse square potential, we demonstrate a simple relation
between the strength of the long range tail and the power law exponent. This
system is amenable to experimental scrutiny
Hour-glass magnetic excitations induced by nanoscopic phase separation in cobalt oxides LaSrCoO
The magnetic excitations in the cuprate superconductors might be essential
for an understanding of high-temperature superconductivity. In these cuprate
superconductors the magnetic excitation spectrum resembles an hour-glass and
certain resonant magnetic excitations within are believed to be connected to
the pairing mechanism which is corroborated by the observation of a universal
linear scaling of superconducting gap and magnetic resonance energy. So far,
charge stripes are widely believed to be involved in the physics of hour-glass
spectra. Here we study an isostructural cobaltate that also exhibits an
hour-glass magnetic spectrum. Instead of the expected charge stripe order we
observe nano phase separation and unravel a microscopically split origin of
hour-glass spectra on the nano scale pointing to a connection between the
magnetic resonance peak and the spin gap originating in islands of the
antiferromagnetic parent insulator. Our findings open new ways to theories of
magnetic excitations and superconductivity in cuprate superconductors.Comment: Nature Communications 5, 5731 (2014
A Mesoarchean Large Igneous Province on the Eastern Kaapvaal Craton (Southern Africa) Confirmed by Metavolcanic Rocks from Kubuta, Eswatini
Mesoarchean magmatism is widespread on the eastern margin of the Kaapvaal Craton, but its origin is still poorly understood, mainly because geochemical data is rare. To shed some light on the source of this Mesoarchean magmatism and to relate different Mesoarchean volcanic sequences to each other, we provide major and trace element data as well as Hf-Nd isotope compositions of amphibolites sampled close to the Kubuta Ranch in south-central Eswatini. These amphibolites, so far, were of unknown correlation to any volcanic sequence in Eswatini or South Africa. Hence, the aim of our study is to characterize the mantle source composition of these volcanic rocks and, furthermore, to constrain their genetic relation to other volcanic sequences in Eswatini and South Africa. Our findings reveal that, based on coherent trace element patterns and similar Nd isotope characteristics, the Kubuta volcanic rocks can be genetically linked to the ca. 3.0 Ga Usushwana Igneous Complex in West-Central Eswatini and the ca. 2.9 Ga Hlagothi Complex located in the KwaZulu-Natal province. In contrast, the coeval ca. 3.0 Ga Nsuze and ca. 2.9 Ga Mozaan Groups (Pongola Supergroup) of south-central Eswatini and northern KwaZulu-Natal province have slightly enriched compositions compared to the newly sampled Kubuta volcanic rocks. Our results suggest that the Nsuze and Mozaan Groups were sourced from a primitive mantle reservoir, whereas the Usushwana, Hlagothi, and Kubuta mafic rocks were derived by melting of a more depleted mantle source comparable to that of modern depleted MORB. Furthermore, our assimilation-fractional crystallization (AFC) calculations and Nd isotope constraints reveal that some samples were contaminated by the crust and that the crustal contaminants possibly represent felsic rocks related to the ca. 3.5 Ga crust-forming event in the Ancient Gneiss Complex. Alternatively, melting of a metasomatized mantle or plume-lithospheric mantle interaction may also produce the trace element and isotopic compositions observed in the samples. From a synthesis of our geochemical observations and age data from the literature, we propose a refined petrogenetic model, for a continental flood basalt setting in a Mesoarchean large igneous province on the eastern Kaapvaal Craton. Our petrogenetic model envisages two magma pulses sourced from a primitive mantle reservoir that led to the formation of the Nsuze (first) and Mozaan (second) lavas. Conductive heating of ambient depleted mantle by the mantle plumes caused partial melting that led to the formation of the Usushwana Igneous Complex associated with the first magmatic event (Nsuze) and the Hlagothi Igneous Complex associated with the second magmatic event (Mozaan). However, due to lacking age data of sufficient resolution, it is not possible to affiliate the Kubuta lavas to either the first or the second magmatic event
Pediatric surgical extracorporeal membrane oxygenation - a case series
Objective. To review demographic and procedural factors and their association with weaning rate and survival from extracorporeal membrane oxygenation (ECMO) in pediatric patients undergoing repair of cardiac malformations.
Methods. The hospital records of children requiring ECMO during cardiac operation due to failure to wean from cardio-pulmonary by pass (CPB) were retrospectively reviewed, and an analysis of variables affecting survival was performed.
Results. Thirty-five pediatric patients between January 1, 2000 and December 31, 2006 required ECMO for cardiopulmonary support during cardiac operations. ECMO survival was 54.3% and was comparable across all age groups. The lowest pH during ECMO treatment was the only predictor of mortality (P = 0.006). No other patient, surgical or anesthetic, factor was associated with either weaning from ECMO or hospital survival.
Conclusions. No clear risk factor could be identified for survival from ECMO in our pediatric patients who underwent cardiac surgery and failed weaning from cardiopulmonary bypass
Electronic and magnetic nano phase separation in cobaltates LaSrCoO
The single-layer perovskite cobaltates have attracted enormous attention due
to the recent observation of hour-glass shaped magnetic excitation spectra
which resemble the ones of the famous high-temperature superconducting
cuprates. Here, we present an overview of our most recent studies of the spin
and charge correlations in floating-zone grown cobaltate single crystals. We
find that frustration and a novel kind of electronic and magnetic nano phase
separation are intimately connected to the appearance of the hour-glass shaped
spin excitation spectra. We also point out the difference between nano phase
separation and conventional phase separation.Comment: * plenary talk SUPERSTRIPES conference 201
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