4,250 research outputs found

    Theory of double-resonant Raman spectra in graphene: intensity and line shape of defect-induced and two-phonon bands

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    We calculate the double resonant (DR) Raman spectrum of graphene, and determine the lines associated to both phonon-defect processes, and two-phonons ones. Phonon and electronic dispersions reproduce calculations based on density functional theory corrected with GW. Electron-light, -phonon, and -defect scattering matrix elements and the electronic linewidth are explicitly calculated. Defect-induced processes are simulated by considering different kind of idealized defects. For an excitation energy of Ï”L=2.4\epsilon_L=2.4 eV, the agreement with measurements is very good and calculations reproduce: the relative intensities among phonon-defect or among two-phonon lines; the measured small widths of the D, Dâ€ČD', 2D and 2Dâ€Č2D' lines; the line shapes; the presence of small intensity lines in the 1800, 2000 cm−1^{-1} range. We determine how the spectra depend on the excitation energy, on the light polarization, on the electronic linewidth, on the kind of defects and on their concentration. According to the present findings, the intensity ratio between the 2Dâ€Č2D' and 2D lines can be used to determine experimentally the electronic linewidth. The intensity ratio between the DD and Dâ€ČD' lines depends on the kind of model defect, suggesting that this ratio could possibly be used to identify the kind of defects present in actual samples. Charged impurities outside the graphene plane provide an almost undetectable contribution to the Raman signal

    Behaviour of adipose-derived canine mesenchymal stem cells after superparamagnetic iron oxide nanoparticles labelling for magnetic resonance imaging

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    Background: Therapy with mesenchymal stem cells (MSCs) has been reported to provide beneficial effects in the treatment of neurological and orthopaedic disorders in dogs. The exact mechanism of action is poorly understood. Magnetic resonance imaging (MRI) gives the opportunity to observe MSCs after clinical administration. To visualise MSCs with the help of MRI, labelling with an MRI contrast agent is necessary. However, it must be clarified whether there is any negative influence on cell function and viability after labelling prior to clinical administration. Results: For the purpose of the study, seven samples with canine adipose-derived stem cells were incubated with superparamagnetic iron oxide nanoparticles (SPIO: 319.2 ”g/mL Fe) for 24 h. The internalisation of the iron particles occurred via endocytosis. SPIO particles were localized as free clusters in the cytoplasm or within lysosomes depending on the time of investigation. The efficiency of the labelling was investigated using Prussian blue staining and MACS assay. After 3 weeks the percentage of SPIO labelled canine stem cells decreased. Phalloidin staining showed no negative effect on the cytoskeleton. Labelled cells underwent osteogenic and adipogenic differentiation. Chondrogenic differentiation occurred to a lesser extent compared with a control sample. MTT-Test and wound healing assay showed no influence of labelling on the proliferation. The duration of SPIO labelling was assessed using a 1 Tesla clinical MRI scanner and T2 weighted turbo spin echo and T2 weighted gradient echo MRI sequences 1, 2 and 3 weeks after labelling. The hypointensity caused by SPIO lasted for 3 weeks in both sequences. Conclusions: An Endorem labelling concentration of 319.2 ”g/mL Fe (448 ”g/mL SPIO) had no adverse effects on the viability of canine ASCs. Therefore, this contrast agent could be used as a model for iron oxide labelling agents. However, the tracking ability in vivo has to be evaluated in further studies

    Valid model-free spatial prediction

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    Predicting the response at an unobserved location is a fundamental problem in spatial statistics. Given the difficulty in modeling spatial dependence, especially in non-stationary cases, model-based prediction intervals are at risk of misspecification bias that can negatively affect their validity. Here we present a new approach for model-free spatial prediction based on the {\em conformal prediction} machinery. Our key observation is that spatial data can be treated as exactly or approximately exchangeable in a wide range of settings. For example, when the spatial locations are deterministic, we prove that the response values are, in a certain sense, locally approximately exchangeable for a broad class of spatial processes, and we develop a local spatial conformal prediction algorithm that yields valid prediction intervals without model assumptions. Numerical examples with both real and simulated data confirm that the proposed conformal prediction intervals are valid and generally more efficient than existing model-based procedures across a range of non-stationary and non-Gaussian settings.Comment: 30 pages, 9 figures, 3 tables. Comments welcome at https://www.researchers.one/article/2020-06-1

    Development and validation of an oligonucleotide microarray to characterise ectomycorrhizal fungal communities

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    Background: In forest ecosystems, communities of ectomycorrhizal fungi (ECM) are influenced by several biotic and abiotic factors. To understand their underlying dynamics, ECM communities have been surveyed with ribosomal DNA-based sequencing methods. However, most identification methods are both time-consuming and limited by the number of samples that can be treated in a realistic time frame. As a result of ongoing implementation, the array technique has gained throughput capacity in terms of the number of samples and the capacity for parallel identification of several species. Thus far, although phylochips (microarrays that are used to detect species) have been mostly developed to trace bacterial communities or groups of specific fungi, no phylochip has been developed to carry oligonucleotides for several ectomycorrhizal species that belong to different genera. Results: We have constructed a custom ribosomal DNA phylochip to identify ECM fungi. Specific oligonucleotide probes were targeted to the nuclear internal transcribed spacer (ITS) regions from 95 fungal species belonging to 21 ECM fungal genera. The phylochip was first validated using PCR amplicons of reference species. Ninety-nine percent of the tested oligonucleotides generated positive hybridisation signals with their corresponding amplicons. Cross-hybridisation was mainly restricted at the genus level, particularly for Cortinarius and Lactarius species. The phylochip was subsequently tested with environmental samples that were composed of ECM fungal DNA from spruce and beech plantation fungal communities. The results were in concordance with the ITS sequencing of morphotypes and the ITS clone library sequencing results that were obtained using the same PCR products. Conclusion: For the first time, we developed a custom phylochip that is specific for several ectomycorrhizal fungi. To overcome cross-hybridisation problems, specific filter and evaluation strategies that used spot signal intensity were applied. Evaluation of the phylochip by hybridising environmental samples confirmed the possible application of this technology for detecting and monitoring ectomycorrhizal fungi at specific sites in a routine and reproducible manner

    Untersuchung der vestibulospinalen Funktionen bei Parkinsonpatienten

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    In der Parkinsonerkrankung stehen mit zunehmender Krankheitsdauer Gangstörungen und StĂŒrze im Vordergrund,welche einen erheblichen Anteil an EinschrĂ€nkungen der Patienten im alltĂ€glichen Leben ergeben. An der physiologischen Kontrolle des Gehens und Stehens sind zahlreiche Hirnstammkerne beteiligt. In dieser Studie wurde untersucht, inwieweit eine Dysfunktion vestibulĂ€rer Hirnstammkerne ursĂ€chlich fĂŒr die Gang- und Haltungsstörung ist,und ob diese Dysfunktion therapeutisch beeinflussbar ist. Methodisch wĂ€hlten wir hierfĂŒr die etablierten neurophysiologischen Paradigmen des cVEMPs und die Soleus H-Reflexmodulation durch vertikale Körperkippung. Die Amplitude des cVEMPs zeigt deutlich reduzierte AusprĂ€gung bei Parkinsonpatienten im Vergleich zu den Probanden. Die dopaminerge Medikation vergrĂ¶ĂŸerte die Amplitude, aber normalisierte sie nicht. Die Neurostimulation hatte keinen Effekt. Die Soleus H-Reflexmodulation zeigte sich im vorbeschrieben Maße bei Normalprobanden wie auch bei unbehandelten Parkinsonpatienten. Levodopa Medikation und Neurostimulation erbrachten keine VerĂ€nderung. Diese verringerte Erregbarkeit des medialen Vestibulospinalentraktes in der Parkinsonerkrankung, die nur durch Levodopa moduliert wird bildet eine wichtige neurophysiologische Grundlage fĂŒr die Balance und damit der im langen Krankheitsverlauf immer wichtiger werdenden posturalen Kontrolle. Die unterschiedliche Auslenkbarkeit der Therapieoptionen auf den vestibulospinalen Hirnstammschaltkreis weißen auf eine direkte dopaminerge Beeinflussung hin, möglicherweise auf Hirnstammniveau durch das mesolimbokortikales Systems und die Formatio reticularis. Eine Modulation der inhibitorischen Basalganglieneingangs ist wenig wahrscheinlich,diese mĂŒsste gleichsinnig unter Neurostimulation und Medikation vorliegen. Diese Ergebnisse stehen gut im Einklang mit den Beobachtungen aus klinischen Langzeitstudien,welche nur der medikamentöser Therapie eine Verbesserung auf die posturale Kontrolle zuschreiben

    Dr. med. CĂ€sar Hirsch - ein jĂŒdisches Arztschicksal in Stuttgart

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    Allein die Tatsache, dass Dr. CĂ€sar Hirsch von 1923 – 1933 der erste Chefarzt der Hals-Nasen-Ohrenklinik am Marienhospital in Stuttgart war, diese Klinik aufbaute und zu einem weit ĂŒber Stuttgart hinausgehenden, sehr guten Ruf verhalf, wĂ€re Grund genug, sich mit seiner Vita zu beschĂ€ftigen. Als einer seiner Nachfolger im Amt (1976 – 2003) musste ich mich bereits 2 x mit CĂ€sar Hirsch befassen. Das erste Mal fĂŒr die Festschrift zum 100-jĂ€hrigen JubilĂ€um des Marienhospitals 1990. Hierin habe ich die Geschichte der HNO-Klinik und ihrer ChefĂ€rzte beschrieben. Damals konnte ich nur wenige eigene Recherchen zu C.H. anstellen. Als 2001 von Tilman Brusis fĂŒr die Deutsche Hals-Nasen-Ohren-Gesellschaft die Geschichte der Hals-Nasen-Ohren-Kliniken herausgegeben wurde, war ich das zweite Mal mit CĂ€sar Hirsch konfrontiert. 1996 stattete der Sohn von CĂ€sar Hirsch, Peter Hearst, Deutschland und unter anderem dem Marienhospital Stuttgart einen Besuch ab, um nach eventuell noch vorhandenen GegenstĂ€nden (BĂŒcher, Instrumente) seines Vaters zu forschen. Leider kam es damals zu keiner Begegnung mit dem Sohn. Außerdem waren auch keine persönlichen GegenstĂ€nde von C.H. mehr vorhanden wegen der teilweisen Zerstörung des Marienhospitals im Krieg und der vielen Um- und Neubauten in der Folgezeit bis heute. Im Jahre 1999 entdeckte der TĂŒbinger Historiker und Journalist Dr. Hans-Joachim Lang die bis dahin verschollen geglaubte Bibliothek von C.H. in der UniversitĂ€tsbibliothek von TĂŒbingen und erreichte eine RĂŒckgabe an den Sohn, welcher die BĂŒcher der UniversitĂ€tsbibliothek von Los Angeles stiftete. Durch all diese BerĂŒhrungspunkte veranlasst, war dann irgendwann die Idee vorhanden, eine Biografie und WĂŒrdigung von Dr. CĂ€sar Hirsch zu verfassen. Hierbei konnte ich außerdem auf Berichte und ErzĂ€hlungen inzwischen verstorbener Ordensfrauen zurĂŒckgreifen, welche noch mit CĂ€sar Hirsch zusammengearbeitet haben. Sie waren Zeitzeugen der Flucht und der darauf folgenden dramatischen Ereignisse. Aus dem bisher Bekannten ergab sich fĂŒr C.H. einerseits ein durchaus ĂŒbliches "jĂŒdisches Schicksal" unter den Nazis, andererseits hatte der Fall auch ganz persönliche Momente, welche mich veranlassten, eigene intensive Recherchen anzustellen
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