TY - THES A1 - Schmitt, Peter T1 - MR imaging of tumors: Approaches for functional and fast morphological characterization T1 - MR-Bildgebung von Tumoren: Ansätze zur funktionellen und schnellen morphologischen Charakterisierung N2 - The subject of this work was to develop, implement, optimize and apply methods for quantitative MR imaging of tumors. In the context of functional and physiological characterization, this implied transferring techniques established in tumor model research to human subjects and assessing their feasibility for use in patients. In the context of the morphologic assessment and parameter imaging of tumors, novel concepts and techniques were developed, which facilitated the simultaneous quantification of multiple MR parameters, the generation of “synthetic” MR images with various contrasts, and the fast single-shot acquisition of purely T2-weighted images. N2 - Gegenstand dieser Arbeit war die Entwicklung, Implementierung, Optimierung und Anwendung von Methoden für die quantitative MR-Bildgebung an Tumoren. In Bezug auf eine funktionelle und physiologische Charakterisierung wurden in der Forschung an Tumormodellen etablierte Verfahren für den Einsatz am Menschen adaptiert und ihre Anwendbarkeit zur Untersuchung von Tumoren wurde an Patienten erforscht. Im Bereich der morphologischen Untersuchung und Parameterbildgebung an Tumoren wurden neue Konzepte und Verfahren entwickelt, welche die simultane Quantifizierung mehrerer MR-Parameter, die Generierung "synthetischer" MR-Bilder mit unterschiedlichen Kontrasten, sowie die schnelle "Single-Shot"-Akquisition rein T2-gewichteter Bilder ermöglichen. KW - Kernspintomografie KW - Tumor KW - MR imaging KW - Tumors KW - Relaxometry KW - IR-TrueFISP KW - synthetic MRI KW - TOSSI Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-135967 ER - TY - JOUR A1 - Weibel, Stephanie A1 - Basse-Luesebrink, Thomas Christian A1 - Hess, Michael A1 - Hofmann, Elisabeth A1 - Seubert, Carolin A1 - Langbein-Laugwitz, Johanna A1 - Gentschev, Ivaylo A1 - Sturm, Volker Jörg Friedrich A1 - Ye, Yuxiang A1 - Kampf, Thomas A1 - Jakob, Peter Michael A1 - Szalay, Aladar A. T1 - Imaging of Intratumoral Inflammation during Oncolytic Virotherapy of Tumors by \(^{19}\)F-Magnetic Resonance Imaging (MRI) JF - PLoS ONE N2 - Background Oncolytic virotherapy of tumors is an up-coming, promising therapeutic modality of cancer therapy. Unfortunately, non-invasive techniques to evaluate the inflammatory host response to treatment are rare. Here, we evaluate \(^{19}\)F magnetic resonance imaging (MRI) which enables the non-invasive visualization of inflammatory processes in pathological conditions by the use of perfluorocarbon nanoemulsions (PFC) for monitoring of oncolytic virotherapy. Methodology/Principal Findings The Vaccinia virus strain GLV-1h68 was used as an oncolytic agent for the treatment of different tumor models. Systemic application of PFC emulsions followed by \(^1H\)/\(^{19}\)F MRI of mock-infected and GLV-1h68-infected tumor-bearing mice revealed a significant accumulation of the \(^{19}\)F signal in the tumor rim of virus-treated mice. Histological examination of tumors confirmed a similar spatial distribution of the \(^{19}\)F signal hot spots and \(CD68^+\)-macrophages. Thereby, the \(CD68^+\)-macrophages encapsulate the GFP-positive viral infection foci. In multiple tumor models, we specifically visualized early inflammatory cell recruitment in Vaccinia virus colonized tumors. Furthermore, we documented that the \(^{19}\)F signal correlated with the extent of viral spreading within tumors. Conclusions/Significance These results suggest \(^{19}\)F MRI as a non-invasive methodology to document the tumor-associated host immune response as well as the extent of intratumoral viral replication. Thus, \(^{19}\)F MRI represents a new platform to non-invasively investigate the role of the host immune response for therapeutic outcome of oncolytic virotherapy and individual patient response. KW - inflammation KW - fluorescence microscopy KW - oncolytic viruses KW - fluorescence imaging KW - macrophages KW - magnetic resonance imaging KW - histology KW - in vivo imaging Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-130311 VL - 8 IS - 3 ER - TY - JOUR A1 - Nordbeck, Peter A1 - Bönhof, Leoni A1 - Hiller, Karl-Heinz A1 - Voll, Sabine A1 - Arias-Loza, Paula A1 - Seidlmaier, Lea A1 - Williams, Tatjana A1 - Ye, Yu-Xiang A1 - Gensler, Daniel A1 - Pelzer, Theo A1 - Ertl, Georg A1 - Jakob, Peter M. A1 - Bauer, Wolfgang R. A1 - Ritter, Oliver T1 - Impact of Thoracic Surgery on Cardiac Morphology and Function in Small Animal Models of Heart Disease: A Cardiac MRI Study in Rats JF - PLoS ONE N2 - Background Surgical procedures in small animal models of heart disease might evoke alterations in cardiac morphology and function. The aim of this study was to reveal and quantify such potential artificial early or long term effects in vivo, which might account for a significant bias in basic cardiovascular research, and, therefore, could potentially question the meaning of respective studies. Methods Female Wistar rats (n = 6 per group) were matched for weight and assorted for sham left coronary artery ligation or control. Cardiac morphology and function was then investigated in vivo by cine magnetic resonance imaging at 7 Tesla 1 and 8 weeks after the surgical procedure. The time course of metabolic and inflammatory blood parameters was determined in addition. Results Compared to healthy controls, rats after sham surgery showed a lower body weight both 1 week (267.5±10.6 vs. 317.0±11.3 g, n<0.05) and 8 weeks (317.0±21.1 vs. 358.7±22.4 g, n<0.05) after the intervention. Left and right ventricular morphology and function were not different in absolute measures in both groups 1 week after surgery. However, there was a confined difference in several cardiac parameters normalized to the body weight (bw), such as myocardial mass (2.19±0.30/0.83±0.13 vs. 1.85±0.22/0.70±0.07 mg left/right per g bw, p<0.05), or enddiastolic ventricular volume (1.31±0.36/1.21±0.31 vs. 1.14±0.20/1.07±0.17 µl left/right per g bw, p<0.05). Vice versa, after 8 weeks, cardiac masses, volumes, and output showed a trend for lower values in sham operated rats compared to controls in absolute measures (782.2±57.2/260.2±33.2 vs. 805.9±84.8/310.4±48.5 mg, p<0.05 for left/right ventricular mass), but not normalized to body weight. Matching these findings, blood testing revealed only minor inflammatory but prolonged metabolic changes after surgery not related to cardiac disease. Conclusion Cardio-thoracic surgical procedures in experimental myocardial infarction cause distinct alterations upon the global integrity of the organism, which in the long term also induce circumscribed repercussions on cardiac morphology and function. This impact has to be considered when analyzing data from respective animal studies and transferring these findings to conditions in patients. KW - heart rate KW - body weight KW - surgical and invasive medical procedures KW - magnetic resonance imaging KW - blood KW - vascular surgery KW - myocardial infarction KW - cardiac ventricles Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-130064 VL - 8 IS - 8 ER - TY - JOUR A1 - Oostinga, Jeroen B. A1 - Maier, Luis A1 - Schüffelgen, Peter A1 - Knott, Daniel A1 - Ames, Christopher A1 - Brüne, Christoph A1 - Tkachov, Grigory A1 - Buhmann, Hartmut A1 - Molenkamp, Laurens W. T1 - Josephson Supercurrent through the Topological Surface States of Strained Bulk HgTe JF - Physical Review X N2 - Strained bulk HgTe is a three-dimensional topological insulator, whose surface electrons have a high mobility (~ 30 000 cm\(^2\)=Vs), while its bulk is effectively free of mobile charge carriers. These properties enable a study of transport through its unconventional surface states without being hindered by a parallel bulk conductance. Here, we show transport experiments on HgTe-based Josephson junctions to investigate the appearance of the predicted Majorana states at the interface between a topological insulator and a superconductor. Interestingly, we observe a dissipationless supercurrent flow through the topological surface states of HgTe. The current-voltage characteristics are hysteretic at temperatures below 1 K, with critical supercurrents of several microamperes. Moreover, we observe a magnetic-field-induced Fraunhofer pattern of the critical supercurrent, indicating a dominant \(2\pi\)-periodic Josephson effect in the unconventional surface states. Our results show that strained bulk HgTe is a promising material system to get a better understanding of the Josephson effect in topological surface states, and to search for the manifestation of zero-energy Majorana states in transport experiments. KW - topological insulators KW - mesoscopics KW - superconductivity Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-129834 VL - 3 IS - 021007 ER - TY - JOUR A1 - Scholz, M. A1 - Sauer, C. A1 - Wiessner, M. A1 - Nguyen, N. A1 - Scholl, A. A1 - Reinert, F. T1 - Structure formation in organic thin films observed in real time by energy dispersive near-edge x-ray absorption fine-structure spectroscopy JF - New Journal of Physics N2 - We study the structure formation of 1,4,5,8-naphthalenetetracarboxylicacid- dianhydride (NTCDA) multilayer films on Ag(111) surfaces by energy dispersive near-edge x-ray absorption fine-structure spectroscopy (NEXAFS) and photoelectron spectroscopy. The time resolution of seconds of the method allows us to identify several sub-processes, which occur during the post-growth three-dimensional structural ordering, as well as their characteristic time scales. After deposition at low temperature the NTCDA molecules are preferentially flat lying and the films exhibit no long-range order. Upon annealing the molecules flip into an upright orientation followed by an aggregation in a transient phase which exists for several minutes. Finally, threedimensional islands are established with bulk-crystalline structure involving substantial mass transport on the surface and morphological roughening. By applying the Kolmogorov–Johnson–Mehl–Avrami model the activation energies of the temperature-driven sub-processes can be derived from the time evolution of the NEXAFS signal. KW - physics Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-129749 VL - 15 IS - 083052 ER - TY - JOUR A1 - Bentmann, Hendrik A1 - Reinert, Friedrich T1 - Enhancing and reducing the Rashba-splitting at surfaces by adsorbates: Na and Xe on Bi/Cu(111) JF - New Journal of Physics N2 - The surface alloy Bi/Cu(111) shows a paradigmatic free-electron-like surface state with a very large Rashba-type spin–orbit splitting. Using angle-resolved photoemission we investigate how adsorbates of different chemical nature influence the size of the spin splitting in this system. We find that the adsorption of small amounts of monovalent Na atoms leads to an enhancement of the spin splitting while an overlayer of the closed-shell rare gas Xe causes a reduction. The latter result is in contrast to the Au(111) surface for which an increased splitting size after Xe-adsorption was observed. We discuss these experimental findings in terms of the characteristic differences of the surface state wave functions and their spatial deformation in the presence of different types of adsorbates. Our results provide insight into the complex interplay of atomic and interface potential gradients governing the Rashba effect. KW - Rashba-Splitting Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-129722 VL - 15 IS - 115011 ER - TY - JOUR A1 - Thierschmann, H. A1 - Henke, M. A1 - Knorr, J. A1 - Maier, L. A1 - Heyn, C. A1 - Hansen, W. A1 - Buhmann, H. A1 - Molenkamp, L. W. T1 - Diffusion thermopower of a serial double quantum dot JF - New Journal of Physics N2 - We have experimentally studied the diffusion thermopower of a serial double quantum dot, defined electrostatically in a GaAs/AlGaAs heterostructure. We present the thermopower stability diagram for a temperature difference 1T = (20±10)mK across the device and find a maximum thermovoltage signal of several μV in the vicinity of the triple points. Along a constant energy axis in this regime, the data show a characteristic pattern which is in agreement with Mott’s relation and can be well understood within a model of sequential transport. KW - quantum dot Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-129714 VL - 15 IS - 123010 ER - TY - JOUR T1 - Search for WH production with a light Higgs boson decaying to prompt electron-jets in proton–proton collisions at \(\sqrt {s}=7\)  TeV with the ATLAS detector JF - New Journal of Physics N2 - A search is performed for WH production with a light Higgs boson decaying to hidden-sector particles resulting in clusters of collimated electrons, known as electron-jets. The search is performed with \(2.04 fb^{−1}\) of data collected in 2011 with the ATLAS detector at the Large Hadron Collider in proton–proton collisions at \(\sqrt {s}=7 TeV\) . One event satisfying the signal selection criteria is observed, which is consistent with the expected background rate. Limits on the product of the WH production cross section and the branching ratio of a Higgs boson decaying to prompt electron-jets are calculated as a function of a Higgs boson mass in the range from 100 to 140 GeV. KW - Higgs boson Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-131565 VL - 15 IS - 043009 ER - TY - JOUR T1 - Search for excited electrons and muons in \(\sqrt {s}=8\) TeV proton–proton collisions with the ATLAS detector JF - New Journal of Physics N2 - The ATLAS detector at the Large Hadron Collider is used to search for excited electrons and excited muons in the channel \(pp →ℓℓ^\ast→ℓℓ\gamma \), assuming that excited leptons are produced via contact interactions. The analysis is based on \(13 fb^{−1}\) of pp collisions at a centre-of-mass energy of 8 TeV. No evidence for excited leptons is found, and a limit is set at the 95% credibility level on the cross section times branching ratio as a function of the excitedlepton mass \(m_{ℓ^\ast}\) . For \(m_{ℓ^\ast}\) ≽0.8 TeV, the respective upper limits on \(\sigma B(ℓ→ ℓ\gamma)\) are 0.75 and 0.90 fb for the \(e^\ast\) and \(μ^\ast\) searches. Limits on \(\sigma B\) are converted into lower bounds on the compositeness scale \(\Lambda\). In the special case where \(\Lambda = m_{ℓ^\ast}\), excited-electron and excited-muon masses below 2.2 TeV are excluded. KW - excited electrons KW - muons Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-131557 VL - 15 IS - 093011 ER - TY - JOUR T1 - Search for extra dimensions in diphoton events from proton–proton collisions at \(\sqrt {s} = 7\)  TeV in the ATLAS detector at the LHC JF - New Journal of Physics N2 - The large difference between the Planck scale and the electroweak scale, known as the hierarchy problem, is addressed in certain models through the postulate of extra spatial dimensions. A search for evidence of extra spatial dimensions in the diphoton channel has been performed using the full set of proton–proton collisions at \(\sqrt {s} = 7\) TeV recorded in 2011 with the ATLAS detector at the CERN Large Hadron Collider. This dataset corresponds to an integrated luminosity of \(4.9 fb^{−1}\). The diphoton invariant mass spectrum is observed to be in good agreement with the Standard Model expectation. In the context of the model proposed by Arkani–Hamed, Dimopoulos and Dvali, 95% confidence level lower limits of between 2.52 and 3.92 TeV are set on the ultraviolet cutoff scale MS depending on the number of extra dimensions and the theoretical formalism used. In the context of the Randall–Sundrum model, a lower limit of 2.06 (1.00) TeV at 95% confidence level is set on the mass of the lightest graviton for couplings of \(k/\overline {M}_{Pl} = 0.1 (0.01)\). Combining with the ATLAS dilepton searches based on the 2011 data, the 95% confidence level lower limit on the Randall–Sundrum graviton mass is further tightened to 2.23 (1.03) TeV for \(k/\overline {M}_{Pl} = 0.1 (0.01)\). KW - diphoton events KW - proton-proton collision Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-131548 VL - 15 ER - TY - JOUR T1 - Measurement of hard double-parton interactions in W(→ℓν) + 2-jet events at \(\sqrt{s}=7\) TeV with the ATLAS detector JF - New Journal of Physics N2 - The production of W bosons in association with two jets in proton–proton collisions at a centre-of-mass energy of \(\sqrt{s}=7\),TeV has been analysed for the presence of double-parton interactions using data corresponding to an integrated luminosity of \(36 pb^{−1}\), collected with the ATLAS detector at the Large Hadron Collider. The fraction of events arising from double-parton interactions, \(f^D_{DP}\), has been measured through the pT balance between the two jets and amounts to \(f^D_{DP}\) = 0.08 ± 0.01 (stat.) ± 0.02 (sys.) for jets with transverse momentum \(p_T\) > 20 GeV and rapidity |y| < 2.8. This corresponds to a measurement of the effective area parameter for hard double-parton interactions of \(\sigma_{eff} = 15 ± 3 (stat.)^{+5}_{−3} (sys.)\) mb. KW - hard double-patron interactions Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-131531 VL - 15 IS - 033038 ER - TY - JOUR A1 - Arca, Francesco A1 - Tedde, Sandro F. A1 - Sramek, Maria A1 - Rauh, Julia A1 - Lugli, Paolo A1 - Hayden, Oliver T1 - Interface Trap States in Organic Photodiodes JF - Scientific Reports N2 - Organic semiconductors are attractive for optical sensing applications due to the effortless processing on large active area of several \(cm^2\), which is difficult to achieve with solid-state devices. However, compared to silicon photodiodes, sensitivity and dynamic behavior remain a major challenge with organic sensors. Here, we show that charge trapping phenomena deteriorate the bandwidth of organic photodiodes (OPDs) to a few Hz at low-light levels. We demonstrate that, despite the large OPD capacitances of similar to 10 nF \(cm^{-2}\), a frequency response in the kHz regime can be achieved at light levels as low as 20 nW \(cm^{-2}\) by appropriate interface engineering, which corresponds to a 1000-fold increase compared to state-of-the-art OPDs. Such device characteristics indicate that large active area OPDs are suitable for industrial sensing and even match medical requirements for single X-ray pulse detection in the millisecond range. KW - ultrafast photonics KW - materials for optics KW - electrical and electronic engineering KW - polymers Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-131507 VL - 3 ER - TY - JOUR A1 - Dasenbrook, Elliot C. A1 - Lu, Luan A1 - Donnola, Shannon A1 - Weaver, David E. A1 - Gulani, Viskas A1 - Jakob, Peter M. A1 - Konstan, Michael W. A1 - Flask, Chris A. T1 - Normalized T1 Magnetic Resonance Imaging for Assessment of Regional Lung Function in Adult Cystic Fibrosis Patients - A Cross-Sectional Study JF - PLOS ONE N2 - Background: Cystic fibrosis (CF) patients would benefit from a safe and effective tool to detect early-stage, regional lung disease to allow for early intervention. Magnetic Resonance Imaging (MRI) is a safe, non-invasive procedure capable of providing quantitative assessments of disease without ionizing radiation. We developed a rapid normalized T1 MRI technique to detect regional lung disease in early-stage CF patients. Materials and Methods: Conventional multislice, pulmonary T1 relaxation time maps were obtained for 10 adult CF patients with normal spirometry and 5 healthy non-CF control subjects using a rapid Look-Locker MRI acquisition (5 seconds/imaging slice). Each lung absolute T1 map was separated into six regions of interest (ROI) by manually selecting upper, central, and lower lung regions in the left and right lungs. In order to reduce the effects of subject-to-subject variation, normalized T1 maps were calculated by dividing each pixel in the absolute T1 maps by the mean T1 time in the central lung region. The primary outcome was the differences in mean normalized T1 values in the upper lung regions between CF patients with normal spirometry and healthy volunteers. Results: Normalized T1 (nT1) maps showed visibly reduced subject-to-subject variation in comparison to conventional absolute T1 maps for healthy volunteers. An ROI analysis showed that the variation in the nT1 values in all regions was <= 2% of the mean. The primary outcome, the mean (SD) of the normalized T1 values in the upper right lung regions, was significantly lower in the CF subjects [.914 (.037)] compared to the upper right lung regions of the healthy subjects [.983 (.003)] [difference of .069 (95% confidence interval .032-.105); p=.001). Similar results were seen in the upper left lung region. Conclusion: Rapid normalized T1 MRI relaxometry obtained in 5 seconds/imaging slice may be used to detect regional early-stage lung disease in CF patients. KW - infants KW - disease KW - ventilation KW - infection KW - guidelines KW - diagnosis KW - children Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-128346 SN - 1932-6203 VL - 8 IS - 9 ER - TY - JOUR A1 - König, Markus A1 - Baenninger, Matthias A1 - Garcia, Andrei G. F. A1 - Harjee, Nahid A1 - Pruitt, Beth L. A1 - Ames, C. A1 - Leubner, Philipp A1 - Brüne, Christoph A1 - Buhmann, Hartmut A1 - Molenkamp, Laurens W. A1 - Goldhaber-Gordon, David T1 - Spatially Resolved Study of Backscattering in the Quantum Spin Hall State JF - Physical Review X N2 - The discovery of the quantum spin Hall (QSH) state, and topological insulators in general, has sparked strong experimental efforts. Transport studies of the quantum spin Hall state have confirmed the presence of edge states, showed ballistic edge transport in micron-sized samples, and demonstrated the spin polarization of the helical edge states. While these experiments have confirmed the broad theoretical model, the properties of the QSH edge states have not yet been investigated on a local scale. Using scanning gate microscopy to perturb the QSH edge states on a submicron scale, we identify well-localized scattering sites which likely limit the expected nondissipative transport in the helical edge channels. In the micron-sized regions between the scattering sites, the edge states appear to propagate unperturbed, as expected for an ideal QSH system, and are found to be robust against weak induced potential fluctuations. KW - mesoscopics KW - topological insulators KW - transport KW - charge KW - wells KW - branched flow KW - nanostructures Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-127225 SN - 2160-3308 VL - 3 IS - 2 ER - TY - JOUR A1 - Hopfmann, C. A1 - Albert, F. A1 - Schneider, C. A1 - Höfling, S. A1 - Kamp, M. A1 - Forchel, A. A1 - Kanter, I. A1 - Reizenstein, S. T1 - Nonlinear emission characteristics of quantum dot-micropillar lasers in the presence of polarized optical feedback JF - New Journal of Physics N2 - We report on electrically pumped quantum dot-microlasers in the presence of polarized self-feedback. The high-\(\beta\) microlasers show two orthogonal, linearly polarized emission modes which are coupled via the common gain medium. This coupling is explained in terms of gain competition between the two lasing modes and leads to distinct differences in their input-output characteristics. By applying polarized self-feedback via an external mirror, we are able to control the laser characteristics of the emission modes in terms of the output power, the coherence time and the photon statistics. We find that linearly polarized self-feedback stabilizes the lasing of a given mode, while cross-polarized feedback between the two modes reduces strongly the intensity of the other emission mode showing particular high-intensity fluctuations and even super-thermal values of the photon autocorrelation function \(g^{(2)} (\tau)\) at zero delay. Measurements of \(g^{(2)} (\tau)\) under external feedback also allow us to detect revival peaks associated with the round trip time of the external cavity. Analyzing the damping and shape of the \(g^{(2)} (\tau)\) revival peaks by a phenomenological model provides us insight into the underlying physics such as the effective exciton lifetime and gain characteristics of the quantum dots in the active region of these microlasers. KW - semiconductor lasers KW - coherence KW - system KW - gain Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-123127 SN - 1367-2630 VL - 15 IS - 025030 ER - TY - JOUR A1 - Kim, N. Y. A1 - Kusudo, K. A1 - Löffler, A. A1 - Höfling, S. A1 - Forchel, A. A1 - Yamamoto, Y. T1 - Exciton-polariton condensates near the Dirac point in a triangular lattice JF - New Journal of Physics N2 - Dirac particles, massless relativistic entities, obey linear energy dispersions and hold important implications in particle physics. The recent discovery of Dirac fermions in condensed matter systems including graphene and topological insulators has generated a great deal of interest in exploring the relativistic properties associated with Dirac physics in solid-state materials. In addition, there are stimulating research activities to engineer Dirac particles, elucidating their exotic physical properties in a controllable setting. One of the successful platforms is the ultracold atom-optical lattice system, whose dynamics can be manipulated and probed in a clean environment. A microcavity exciton-polariton-lattice system offers the advantage of forming high-orbital condensation in non-equilibrium conditions, which enables one to explore novel quantum orbital order in two dimensions. In this paper, we experimentally construct the band structures near Dirac points, the vertices of the first hexagonal Brillouin zone with exciton-polariton condensates trapped in a triangular lattice. Due to the finite spectral linewidth, the direct map of band structures at Dirac points is elusive; however, we identify the linear part above Dirac points and its associated velocity value is similar to ~0.9-2 x \(10^8 cm s^{-1}\), consistent with the theoretical estimate \(1 x 10^8 cm s^{-1}\) with a \(2 \mu m\) lattice constant. We envision that the exciton-polariton condensates in lattices would be a promising solid-state platform, where the system order parameter can be accessed in both real and momentum spaces. KW - Bose-Einstein condensation KW - carbon nanotubes KW - graphene KW - electron KW - dynamics KW - fermions KW - trap KW - gas Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-123103 SN - 1367-2630 VL - 15 IS - 035032 ER - TY - JOUR A1 - Kasprzak, J. A1 - Sivalertporn, K. A1 - Albert, F. A1 - Schneider, C. A1 - Höfling, S. A1 - Kamp, M. A1 - Forchel, A. A1 - Muljarov, E. A. A1 - Langbein, W. T1 - Coherence dynamics and quantum-to-classical crossover in an exciton-cavity system in the quantum strong coupling regime JF - New Journal of Physics N2 - Interaction between light and matter generates optical nonlinearities, which are particularly pronounced in the quantum strong coupling regime. When a single bosonic mode couples to a single fermionic mode, a Jaynes-Cummings (JC) ladder is formed, which we realize here using cavity photons and quantum dot excitons. We measure and model the coherent anharmonic response of this strongly coupled exciton-cavity system at resonance. Injecting two photons into the cavity, we demonstrate a \(\sqrt 2\) larger polariton splitting with respect to the vacuum Rabi splitting. This is achieved using coherent nonlinear spectroscopy, specifically four-wave mixing, where the coherence between the ground state and the first (second) rung of the JC ladder can be interrogated for positive (negative) delays. With increasing excitation intensity and thus rising average number of injected photons, we observe spectral signatures of the quantum-to-classical crossover of the strong coupling regime. KW - Jaynes-Cummings ladder KW - spectral interferometry KW - photon KW - dot KW - spectroscopy KW - oscillations KW - microcavity KW - resonance KW - light Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-123005 SN - 1367-2630 VL - 15 IS - 045013 ER - TY - JOUR A1 - Okada, Michio A1 - Rotenberg, Eli A1 - Kevan, S. D. A1 - Schäfer, J. A1 - Ujfalussy, Balazs A1 - Stocks, G. Malcolm A1 - Genatempo, B. A1 - Bruno, E. A1 - Plummer, E. W. T1 - Evolution of the electronic structure in \(Mo_{1-x}Re_x\) alloys JF - New Journal of Physics N2 - We report a detailed experimental and theoretical study of the electronic structure of \(Mo_{1-x}Re_x\) random alloys. We have measured electronic band dispersions for clean and hydrogen-covered \(Mo_{1-x}Re_x\) ( 110) with x = 0-0.25 using angle-resolved photoemission spectroscopy. Our results suggest that the bulk and most surface electronic bands shift relative to the Fermi level systematically and approximately rigidly with Re concentration. We distinguish and quantify two contributions to these shifts: a raise of the Fermi energy and an increase of the overall bandwidth. Alloy bands calculated using the first-principles Korringa-Kohn-Rostoker coherent-potential-approximation method accurately predict both of these effects. As derived from the rigid band model, the Fermi energy shift is inversely related to the bulk density of states in this energy region. Using our results, we also characterize an electronic topological transition of the bulk Fermi surface and relate this to bulk transport properties. Finally, we distinguish effects beyond the rigid band approximation: a highly surface-localized state and a composition-dependent impact of the spin-orbit interaction. KW - topological transitions KW - surface state KW - metals KW - total energy KW - W(110) KW - hydrogen KW - mo KW - superconductivity KW - spectra KW - coherent potential approximation Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-122993 SN - 1367-2630 VL - 15 IS - 093010 ER - TY - JOUR A1 - Moffet, R. C. A1 - Rödel, R. C. A1 - Kelly, S. T. A1 - Yu, X. Y. A1 - Carroll, G. T. A1 - Fast, J. A1 - Zaveri, R. A. A1 - Laskin, A. A1 - Gilles, M. K. T1 - Spectro-microscopic measurements of carbonaceous aerosol aging in Central California JF - Atmospheric Chemistry and Physics N2 - Carbonaceous aerosols are responsible for large uncertainties in climate models, degraded visibility, and adverse health effects. The Carbonaceous Aerosols and Radiative Effects Study (CARES) was designed to study carbonaceous aerosols in the natural environment of the Central Valley, California, and learn more about their atmospheric formation and aging. This paper presents results from spectro-microscopic measurements of carbonaceous particles collected during CARES at the time of a pollution accumulation event (27-29 June 2010), when in situ measurements indicated an increase in the organic carbon content of aerosols as the Sacramento urban plume aged. Computer-controlled scanning electron microscopy coupled with an energy dispersive X-ray detector (CCSEM/EDX) and scanning transmission X-ray microscopy coupled with near-edge X-ray absorption spectroscopy (STXM/NEXAFS) were used to probe the chemical composition and morphology of individual particles. It was found that the mass of organic carbon on individual particles increased through condensation of secondary organic aerosol. STXM/NEXAFS indicated that the number fraction of homogenous organic particles lacking inorganic inclusions (greater than similar to 50 nm equivalent circular diameter) increased with plume age, as did the organic mass per particle. Comparison of the CARES spectro-microscopic dataset with a similar dataset obtained in Mexico City during the MILAGRO campaign showed that fresh particles in Mexico City contained three times as much carbon as those sampled during CARES. The number fraction of soot particles at the Mexico City urban site (ranging from 16.6 to 47.3 %) was larger than at the CARES urban site (13.4-15.7%), and the most aged samples from CARES contained fewer carbon-carbon double bonds. Differences between carbonaceous particles in Mexico City and California result from different sources, photochemical conditions, gas phase reactants, and secondary organic aerosol precursors. The detailed results provided by these spectro-microscopic measurements will allow for a comprehensive evaluation of aerosol process models used in climate research. KW - photochemical air-pollution KW - Mexico City KW - black carbon KW - mixing state KW - atmospheric aerosols Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-121827 SN - 1680-7324 VL - 13 IS - 20 ER - TY - THES A1 - Bollmann, Stefan T1 - Structural Dynamics of Oligopeptides determined by Fluorescence Quenching of Organic Dyes T1 - Bestimmung struktureller Dynamiken von Oligopeptiden mittels Fluoreszenzlöschung von organischen Fluorophoren N2 - For determination of structures and structural dynamics of proteins organic fluorophores are a standard instrument. Intra- and intermolecular contact of biomolecular structures are determined in time-resolved and stationary fluorescence microscopy experiments by quenching of organic fluorophores due to Photoinduced Electron Transfer (PET) and dimerization interactions. Using PET we show in this work that end-to-end contact dynamics of serine-glycine peptides are slowed down by glycosylation. This slow down is due to a change in reaction enthalpy for end-to-end contact and is partly compensated by entropic effects. In a second step we test how dimerization of MR121 fluorophore pairs reports on end-to-end contact dynamics. We show that in aqueous solutions containing strong denaturants MR121 dimerization reports advantageously on contact dynamics for glycine-serine oligopeptides compared to the previously used MR121/tryptophane PET reporters. Then we analyze dimer interactions and quenching properties of different commercially available fluorophores being standards in Förster Resonance Energy Transfer (FRET) measurements. Distances in biomolecules are determinable using FRET, but for very flexible biomolecules the analysis of masurement data can be distorted if contact of the two FRET fluorophores is likely. We quantify how strong the quenching of fluorophore pairs with two different or two identical fluorophores is. Dimer spectra and association constants are quantified to estimate if fluophores are applicable in various applications, e.g. in FRET measurements with unstructured peptides and proteins. N2 - Zur Charakterisierung von Proteinen werden in der fluoreszenzbasierten Mikroskopie organische Farbstoffe benutzt, um strukturelle Informationen bzw. Informationen über dynamische Prozesse zu gewinnen. In der zeitaufgelösten und stationären Fluoreszenzmikroskopie können hiermit Kontaktprozesse durch photoinduzierten Elektronentransfer und auch Dimerisierung der Fluorophore analysiert werden. In dieser Arbeit wird mittels photoinduziertem Elektronentransfer PET gezeigt, dass Glykosylierung End-zu-End Kontaktkinetiken verändert. Sehr flexible Serin-Glycin Peptide zeigen glykosyliert langsamere Kinetiken durch Veränderung der Reaktionsenthalpie der Kontaktreaktion beider Peptidenden verglichen zu unglykosylierten. Diese enthalpischen Beiträge werden zum Teil von entropischen Beiträgen kompensiert. Außerdem wird gezeigt, dass Glycin-Serin Peptiddynamiken auch mittels Farbstoffpaaren gemessen werden können, die auf Löschwechselwirkungen durch Dimerisierung beruhen. Die Stärke dieser Löschwechselwirkungen hängt vom Farbstoffpaar ab. In Lösungen mit Denaturierungsmitteln können Farbstoffpaare des Fluoreszenzfarbstoffes MR121 vorteilhaft für Messungen von Dynamiken von Glycin-Serin Peptiden genutzt werden. Die Dimerwechselwirkungen können bei sehr flexiblen Biomolekülen und möglichem Kontakt von Fluorophoren die konventionelle Analyse von Förster Resonanz Energie Transfer (FRET) Messungen erschweren. Wir untersuchen an Glycin-Serin Oligopeptiden das Dimerisierungsverhalten kommerziell erhältlicher Fluorophore, die in FRET Messungen verwendet werden. Für gleiche und verschiedene Fluorophore wird die Löschung durch Dimerwechselwirkungen quantifiziert. Dabei werden Dimerspektren und Assoziationskonstanten für Dimerisierungsreaktionen bestimmt. Letztere helfen bei der Abschätzung, ob Fluorophorpaare für verschiedene Anwendungen geeignet sind, zum Beispiel in FRET-Messungen in unstrukturierten Peptiden und Proteinen. KW - Fluorophore KW - Fluoreszenzlöschung KW - h-dimerization KW - Lumineszenzlöschung KW - Fluoreszenzkorrelationsspektroskopie KW - Glykosylierung KW - Dimerisierung Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-92191 ER -