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1,118 results on '"Graf, Thomas"'

7. Uncertainties and robustness with regard to the safety of a repository for high-level radioactive waste: introduction of a research initiative

Author

Kurgyis, Kata, Achtziger-Zupančič, Peter, Bjorge, Merle, Boxberg, Marc S., Broggi, Matteo, Buchwald, Jörg, Ernst, Oliver G., Flügge, Judith, Ganopolski, Andrey, Graf, Thomas, Kortenbruck, Philipp, Kowalski, Julia, Kreye, Phillip, Kukla, Peter, Mayr, Sibylle, Miro, Shorash, Nagel, Thomas, Nowak, Wolfgang, Oladyshkin, Sergey, Renz, Alexander, Rienäcker-Burschil, Julia, Röhlig, Klaus-Jürgen, Sträter, Oliver, Thiedau, Jan, Wagner, Florian, Wellmann, Florian, Wengler, Marc, Wolf, Jens, and Rühaak, Wolfram

Published
2024
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17. Human induced-T-to-natural killer cells have potent anti-tumour activities

Author

Jiang, Zhiwu, Qin, Le, Tang, Yuou, Liao, Rui, Shi, Jingxuan, He, Bingjia, Li, Shanglin, Zheng, Diwei, Cui, Yuanbin, Wu, Qiting, Long, Youguo, Yao, Yao, Wei, Zhihui, Hong, Qilan, Wu, Yi, Mai, Yuanbang, Gou, Shixue, Li, Xiaoping, Weinkove, Robert, Norton, Sam, Luo, Wei, Feng, Weineng, Zhou, Hongsheng, Liu, Qifa, Chen, Jiekai, Lai, Liangxue, Chen, Xinwen, Pei, Duanqing, Graf, Thomas, Liu, Xingguo, Li, Yangqiu, Liu, Pentao, Zhang, Zhenfeng, and Li, Peng

Published
2022
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19. High-power thin-disk lasers emitting beams with axially-symmetric polarizations

Author

Abdou Ahmed Marwan, Beirow Frieder, Loescher André, Dietrich Tom, Bashir Danish, Didychenko Denys, Savchenko Anton, Pruss Christof, Fetisova Marina, Li Fangfang, Karvinen Petri, Kuittinen Markku, and Graf Thomas

Subjects
azimuthal polarization, grating waveguide structures, nanograting-based polarization converters, radial polarization, thin-disk lasers, Physics, QC1-999
Abstract

We present the intracavity generation of beams with radial polarization at an average output power of 750 W and an optical efficiency of 43% from a continuous wave thin-disk laser. Circular grating waveguide output couplers (GWOC) were used to select the radial polarization. The sensitivity of the polarizing function of the GWOC with regards to the fabrication tolerances is also analysed in details with a particular emphasis on the effect of the duty cycle and the geometrical profile of the gratings. Furthermore, we present the conversion of femtosecond laser pulses from linear to azimuthal polarization using a nanograting-based polarization converter. Azimuthally polarized beams with an average power of up to 850 W, a pulse duration of 400 fs and a pulse repetition rate of 1 MHz were generated in this way with a conversion efficiency of >90%.

Published
2021
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31. Laser micromachining of bionic transport structures on cemented tungsten carbide for passive directional transport of lubricants.

Author

Holder, Daniel, Kessenbrock, Nils, Cirakoglu, Kathrin, Hagenlocher, Christian, and Graf, Thomas

Abstract

Several 10 ℓ/min of cooling lubricants are used to cool and lubricate the cutting edges during conventional mechanical milling of lightweight metals. Different concepts of minimum quantity lubrication (between 5 mℓ/h and 50 mℓ/h) have been developed in the past since the recycling and disposal of the cooling lubricants is energy-intensive and costly. One promising approach for minimum quantity lubrication during milling processes with closed cutting edges is the passive directional transport of the lubricant along the chip guiding surfaces to the milling area. Laser micromachining with ultrashort laser pulses was used for the fabrication of bionic transport structures on tools made from cemented tungsten carbide. An analytical model for the prediction of the dimensions of the transport structures was derived and experimentally verified. The microscopic surface structures that form on the surface of the transport structures were investigated and their wetting behavior for different lubricants and deionized water was characterized by contact angle measurements. A low contact angle <6° was achieved with laser wavelength-sized ripples on the surface. Finally, passive directional transport of lubricants on tools made from cemented tungsten carbide could be demonstrated with bionic transport structures over a distance of up to 60 mm. [ABSTRACT FROM AUTHOR]

Published
2024
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32. First thin-disk oscillator with ceramic Yb:LuScO3 in comparison to the operation with ceramic Yb:Lu2O3.

Author

Esser, Stefan, Jing, Wei, Xu, Xiaodong, Graf, Thomas, and Abdou Ahmed, Marwan

Subjects
YTTERBIUM, CERAMICS, FLUORESCENCE spectroscopy, SURFACE temperature
Abstract

We report on the characterization and first laser operation of ceramic Yb:LuScO3 in a thin-disk oscillator. The optical performance achieved with a ceramic Yb:LuScO3 disk is compared to the one obtained with an existing ceramic Yb:Lu2O3 disk for reference. The characterization covers the measurement of the fluorescence spectra, the fluorescence lifetimes, and nomarsky imaging. The investigation on the laser operation covers the measurement of resonator losses, output powers, and thermal behavior during continuous-wave operation in a multimode thin-disk oscillator. An average output power of 149 W and a slope efficiency of 51.8% were achieved with the ceramic Yb:LuScO3 disk which reached a maximum surface temperature of about 150 °C. At the same temperature level, a disk made of the already established ceramic Yb:Lu2O3 delivered 957 W of output power with a slope efficiency of 75.7%. [ABSTRACT FROM AUTHOR]

Published
2024
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35. CTCF chromatin residence time controls three-dimensional genome organization, gene expression and DNA methylation in pluripotent cells

Author

Soochit, Widia, Sleutels, Frank, Stik, Gregoire, Bartkuhn, Marek, Basu, Sreya, Hernandez, Silvia C., Merzouk, Sarra, Vidal, Enrique, Boers, Ruben, Boers, Joachim, van der Reijden, Michael, Geverts, Bart, van Cappellen, Wiggert A., van den Hout, Mirjam, Ozgur, Zeliha, van IJcken, Wilfred F. J., Gribnau, Joost, Renkawitz, Rainer, Graf, Thomas, Houtsmuller, Adriaan, Grosveld, Frank, Stadhouders, Ralph, and Galjart, Niels

Published
2021
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42. Measuring the α-particle charge radius with muonic helium-4 ions

Author

Krauth, Julian J., Schuhmann, Karsten, Ahmed, Marwan Abdou, Amaro, Fernando D., Amaro, Pedro, Biraben, François, Chen, Tzu-Ling, Covita, Daniel S., Dax, Andreas J., Diepold, Marc, Fernandes, Luis M. P., Franke, Beatrice, Galtier, Sandrine, Gouvea, Andrea L., Götzfried, Johannes, Graf, Thomas, Hänsch, Theodor W., Hartmann, Jens, Hildebrandt, Malte, Indelicato, Paul, Julien, Lucile, Kirch, Klaus, Knecht, Andreas, Liu, Yi-Wei, Machado, Jorge, Monteiro, Cristina M. B., Mulhauser, Françoise, Naar, Boris, Nebel, Tobias, Nez, François, dos Santos, Joaquim M. F., Santos, José Paulo, Szabo, Csilla I., Taqqu, David, Veloso, João F. C. A., Vogelsang, Jan, Voss, Andreas, Weichelt, Birgit, Pohl, Randolf, Antognini, Aldo, and Kottmann, Franz

Published
2021
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43. Rate of Urinary Tract Infections, Bacteremia, and Meningitis in Preterm and Term Infants.

Author

Graf, Thomas, Malay, Sindhoosha, and Frank, Erin

Subjects
*DIAGNOSIS of fever, *RESEARCH funding, *URINARY tract infections in children, *BACTEREMIA, *MENINGITIS, *SCIENTIFIC observation, *LONGITUDINAL method, *RESEARCH, *CONFIDENCE intervals, *COMPARATIVE studies
Abstract

Background and objectives: There are very limited data on the rate of urinary tract infections (UTI), bacteremia, and meningitis in preterm infants with fever. Many of the studies on the incidence of these infections excluded preterm infants. This study compared the rate of these infections in preterm infants born at 32-36 weeks to term infants born at 37-42 weeks. Methods: A multicenter observational cohort study was conducted to evaluate rates of UTI, bacteremia, and meningitis in term and preterm infants 8-60 days of age with a diagnosis of fever from 2016 through 2022 using encounter data from children's hospitals in the Pediatric Health Information System. Results: There were 19 507 total febrile infants identified, of which 2162 were preterm and 17 345 were term. Preterm infants had a lower rate of UTI than term infants (1.8% confidence interval [CI] [1.3-2.5] vs 3.0% CI [2.7-3.2], P = .001). Preterm and term infants did not have statistically different rates of bacteremia (1.5% CI [1.3-1.7] vs 1.2% CI [0.8-1.8], P = .44) or meningitis (0.16% CI [0.1-0.2] vs 0.05% CI [0-0.2], P = .36). Conclusions: There was no difference in the rate of bacteremia or meningitis between term and preterm infants in a large multicenter cohort of febrile infants. Preterm infants had a lower rate of UTI than term infants. This is the first multicenter study to compare UTI, bacteremia, and meningitis between term and preterm febrile infants. [ABSTRACT FROM AUTHOR]

Published
2024
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44. Self-Shielding of X-ray Emission from Ultrafast Laser Processing Due to Geometrical Changes of the Interaction Zone.

Author

Holland, Julian, Hagenlocher, Christian, Weber, Rudolf, and Graf, Thomas

Subjects
ULTRASHORT laser pulses, HIGH power lasers, ULTRA-short pulsed lasers, X-rays, IONIZING radiation, PULSED lasers
Abstract

Materials processing with ultrashort laser pulses is one of the most important approaches when it comes to machining with very high accuracy. High pulse repetition rates and high average laser power can be used to attain high productivity. By tightly focusing the laser beam, the irradiances on the workpiece can exceed 1013 W/cm2, and thus cause usually unwanted X-ray emission. Pulsed laser processing of micro holes exhibits two typical features: a gradual increase in the irradiated surface within the hole and, with this, a decrease in the local irradiance. This and the shielding by the surrounding material diminishes the amount of ionizing radiation emitted from the process; therefore, both effects lead to a reduction in the potential X-ray exposure of an operator or any nearby person. The present study was performed to quantify this self-shielding of the X-ray emission from laser-drilled micro holes. Percussion drilling in standard air atmosphere was investigated using a laser with a wavelength of 800 nm a pulse duration of 1 ps, a repetition rate of 1 kHz, and with irradiances of up to 1.1·1014 W/cm. The X-ray emission was measured by means of a spectrometer. In addition to the experimental results, we present a model to predict the expected X-ray emission at different angles to the surface. These calculations are based on raytracing simulations to obtain the local irradiance, from which the local X-ray emission inside the holes can be calculated. It was found that the X-ray exposure measured in the surroundings strongly depends on the geometry of the hole and the measuring direction, as predicted by the theoretical model. [ABSTRACT FROM AUTHOR]

Published
2024
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