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Search Results: 1 - 10 of 6136 matches for " Matthias Kemmler "
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Improving the performance of superconducting microwave resonators in magnetic fields
Daniel Bothner,Tobias Gaber,Matthias Kemmler,Dieter Koelle,Reinhold Kleiner
Physics , 2011, DOI: 10.1063/1.3560480
Abstract: The operation of superconducting coplanar waveguide cavities, as used for circuit quantum electrodynamics and kinetic inductance detectors, in perpendicular magnetic fields normally leads to a reduction of the device performance due to energy dissipating Abrikosov vortices. We experimentally investigate the vortex induced energy losses in such Nb resonators with different spatial distributions of micropatterned pinning sites (antidots) by transmission spectroscopy measurements at 4.2 K. In comparison to resonators without antidots we find a significant reduction of vortex induced losses and thus increased quality factors over a broad range of frequencies and applied powers in moderate fields.
Magnetic hysteresis effects in superconducting coplanar microwave resonators
Daniel Bothner,Tobias Gaber,Matthias Kemmler,Dieter Koelle,Reinhold Kleiner,Stefan Wünsch,Michael Siegel
Physics , 2012, DOI: 10.1103/PhysRevB.86.014517
Abstract: We performed transmission spectroscopy experiments on coplanar half wavelength niobium resonators at a temperature T=4.2 K. We observe not only a strong dependence of the quality factor Q and the resonance frequency f_res on an externally applied magnetic field but also on the magnetic history of our resonators, i.e. on the spatial distribution of trapped Abrikosov vortices in the device. We find these results to be valid for a broad range of frequencies and angles between the resonator plane and the magnetic field direction as well as for resonators with and without antidots near the edges of the center conductor and the ground planes. In a detailed analysis we show, that characteristic features of the experimental data can only be reproduced in calculations, if a highly inhomogeneous rf-current density and a flux density gradient with maxima at the edges of the superconductor is assumed. We furthermore demonstrate, that the hysteretic behaviour of the resonator properties can be used to considerably reduce the vortex induced losses and to fine-tune the resonance frequency by the proper way of cycling to a desired magnetic field.
Optimizing the spin sensitivity of grain boundary junction nanoSQUIDs -- towards detection of small spin systems with single-spin resolution
Roman W?lbing,Tobias Schwarz,Benedikt Müller,Joachim Nagel,Matthias Kemmler,Reinhold Kleiner,Dieter Koelle
Physics , 2013,
Abstract: We present an optimization study of the spin sensitivity of nanoSQUIDs based on resistively shunted grain boundary Josephson junctions. In addition the dc SQUIDs contain a narrow constriction onto which a small magnetic particle can be placed (with its magnetic moment in the plane of the SQUID loop and perpendicular to the grain boundary) for efficient coupling of its stray magnetic field to the SQUID loop. The separation of the location of optimum coupling from the junctions allows for an independent optimization of the coupling factor $\phi_\mu$ and junction properties. We present different methods for calculating $\phi_\mu$ (for a magnetic nanoparticle placed 10\,nm above the constriction) as a function of device geometry and show that those yield consistent results. Furthermore, by numerical simulations we obtain a general expression for the dependence of the SQUID inductance on geometrical parameters of our devices, which allows to estimate their impact on the spectral density of flux noise $S_\Phi$ of the SQUIDs in the thermal white noise regime. Our analysis of the dependence of $S_\Phi$ and $\phi_\mu$ on the geometric parameters of the SQUID layout yields a spin sensitivity $S_\mu^{1/2}=S_\Phi^{1/2}/\phi_\mu$ of a few $\mu_{\rm{B}}/\rm{Hz^{1/2}}$ ($\mu_B$ is the Bohr magneton) for optimized parameters, respecting technological constraints. However, by comparison with experimentally realized devices we find significantly larger values for the measured white flux noise, as compared to our theoretical predictions. Still, a spin sensitivity on the order of $10\,\mu_{\rm B}/\rm{Hz^{1/2}}$ for optimized devices seems to be realistic.
Optimizing the spin sensitivity of grain boundary junction nanoSQUIDs -- towards detection of small spin systems with single-spin resolution
Roman W?lbing,Tobias Schwarz,Benedikt Müller,Joachim Nagel,Matthias Kemmler,Reinhold Kleiner,Dieter Koelle
Physics , 2014, DOI: 10.1088/0953-2048/27/12/125007
Abstract: We present an optimization study of the spin sensitivity of nanoSQUIDs based on resistively shunted grain boundary Josephson junctions. In addition the dc SQUIDs contain a narrow constriction onto which a small magnetic particle can be placed (with its magnetic moment in the plane of the SQUID loop and perpendicular to the grain boundary) for efficient coupling of its stray magnetic field to the SQUID loop. The separation of the location of optimum coupling from the junctions allows for an independent optimization of the coupling factor $\phi_\mu$ and junction properties. We present different methods for calculating $\phi_\mu$ (for a magnetic nanoparticle placed 10\,nm above the constriction) as a function of device geometry and show that those yield consistent results. Furthermore, by numerical simulations we obtain a general expression for the dependence of the SQUID inductance on geometrical parameters of our devices, which allows to estimate their impact on the spectral density of flux noise $S_\Phi$ of the SQUIDs in the thermal white noise regime. Our analysis of the dependence of $S_\Phi$ and $\phi_\mu$ on the geometric parameters of the SQUID layout yields a spin sensitivity $S_\mu^{1/2}=S_\Phi^{1/2}/\phi_\mu$ of a few $\mu_{\rm{B}}/\rm{Hz^{1/2}}$ ($\mu_B$ is the Bohr magneton) for optimized parameters, respecting technological constraints. However, by comparison with experimentally realized devices we find significantly larger values for the measured white flux noise, as compared to our theoretical predictions. Still, a spin sensitivity on the order of $10\,\mu_{\rm B}/\rm{Hz^{1/2}}$ for optimized devices seems to be realistic.
The phase boundary of superconducting niobium thin films with antidot arrays fabricated with microsphere photolithography
Daniel Bothner,Conrad Clauss,Elisabeth Koroknay,Matthias Kemmler,Tobias Gaber,Michael Jetter,Marc Scheffler,Peter Michler,Martin Dressel,Dieter Koelle,Reinhold Kleiner
Physics , 2012, DOI: 10.1088/0953-2048/25/6/065020
Abstract: The experimental investigation of the $I_c(B)$--$T_c(B)$ phase boundary of superconducting niobium films with large area quasihexagonal hole arrays is reported. The hole arrays were patterned with microsphere photolithography. We investigate the perforated niobium films by means of electrical directed current transport measurements close to the transition temperature $T_c$ in perpendicularly applied magnetic fields. We find pronounced modulations of the critcal current with applied magnetic field, which we interpret as a consequence of commensurable states between the Abrikosov vortex lattice and the quasihexagonal pinning array. Furthermore, we observe Little-Parks oscillations in the critical temperature vs magnetic field.
Nb nano superconducting quantum interference devices with high spin sensitivity for operation in magnetic fields up to 0.5\,T
Roman W?lbing,Joachim Nagel,Tobias Schwarz,Oliver Kieler,Thomas Weimann,Johannes Kohlmann,Alexander Zorin,Matthias Kemmler,Reinhold Kleiner,Dieter Koelle
Physics , 2013, DOI: 10.1063/1.4804673
Abstract: We investigate electric transport and noise properties of microstrip-type submicron direct current superconducting quantum interference devices (dc SQUIDs) based on Nb thin films and overdamped Josephson junctions with a HfTi barrier. The SQUIDs were designed for optimal spin sensitivity $S_\mu^{1/2}$ upon operation in intermediate magnetic fields $B$ (tens of mT), applied perpendicular to the substrate plane. Our so far best SQUID can be continuously operated in fields up to $B\approx\pm50\,\rm{mT}$ with rms flux noise $S_{\Phi,\rm w}^{1/2}\leq250\,\rm{n\Phi_0/Hz^{1/2}}$ in the white noise regime and spin sensitivity $S_{\mu}^{1/2}\leq29\,\rm{\mu_B/Hz^{1/2}}$. Furthermore, we demonstrate operation in $B=0.5\,\rm{T}$ with high sensitivity in flux $S_{\Phi,\rm w}^{1/2}\approx680\,\rm{n\Phi_0/Hz^{1/2}}$ and in electron spin $S_{\mu}^{1/2}\approx79\,\rm{\mu_B/Hz^{1/2}}$. We discuss strategies to further improve the nanoSQUID performance.
Alternative Exercise Technologies to Fight against Sarcopenia at Old Age: A Series of Studies and Review
Wolfgang Kemmler,Simon von Stengel
Journal of Aging Research , 2012, DOI: 10.1155/2012/109013
Abstract: The most effective physiologic mean to prevent sarcopenia and related muscle malfunction is a physically active lifestyle, or even better, physical exercise. However, due to time constraints, lack of motivation, or physical limitations, a large number of elderly subjects are either unwilling or unable to perform conventional workouts. In this context, two new exercise technologies, whole-body vibration (WBV) and whole-body electromyostimulation (WB-EMS), may exhibit a save, autonomous, and efficient alternative to increase or maintain muscle mass and function. Regarding WB-EMS, the few recent studies indeed demonstrated highly relevant effects of this technology on muscle mass, strength, and power parameters at least in the elderly, with equal or even higher effects compared with conventional resistance exercise. On the contrary, although the majority of studies with elderly subjects confirmed the positive effect of WBV on strength and power parameters, a corresponding relevant effect on muscle mass was not reported. However, well-designed studies with adequate statistical power should focus more intensely on this issue. 1. Introduction The negative change of muscle mass from maturity to senescence and the corresponding loss of functional capacity are of high clinical significance [1, 2]. The most physiologic means to fight this decline of muscle mass and function is a physically active lifestyle or even better, physical exercise [3]. Indeed, a plethora of exercise studies (review in [4–7]) proved favorable changes of muscle mass, power, and strength parameters. However, to realize relevant changes of muscle mass, strength, and power, exercise has to be performed regularly with moderate exercise frequency (≥2 sessions/week) and moderate to high levels of intensity [6, 8]. Due to physical limitations or to lack of motivation, a large number of elderly subjects obviously seem to be either unable or unwilling to perform (intense) corresponding resistance exercise programs. In this context, exercise technologies that increase the impact of low-level exercise on the musculoskeletal system are of high relevance. Recently, two promising new technologies that primarily focus on the aim to increase endogenous loading by external strain were presented. One of both technologies focuses on the increased response of muscular activity when exposed to vibration stimuli (whole body vibration (WBV) training); the other focuses on the stimulation of large muscle groups by electric stimuli (whole-body electromyostimulation (WB-EMS) training). The purpose of this paper is
Female Sprague Dawley Rats Show Impaired Spatial Memory in the 8-Arm Radial Maze under Dim Blue and Red Light
Michael Pirchl,Georg Kemmler,Christian Humpel
International Journal of Zoology , 2010, DOI: 10.1155/2010/507524
Abstract: Light intensity and wavelength strongly influence mood and cognition in humans and rodent animal models. The aim of the present study was to explore if dim white (7.6–17.7?lux) , blue (1.3–2.3?lux), and red light (0.8–1.4?lux) affect spatial memory of male and female Sprague Dawley rats in the 8-arm radial maze. Our data show that spatial memory significantly improved within 5 daily learning sessions (each 5 trials) under dim white light, which was not different between male and female rats. However, dim blue and red light significantly reduced spatial learning of female rats in the 8-arm radial maze in the last training session (session 5). In conclusion, we suggest that female Sprague Dawley rats show reduced learning under blue and red light. 1. Introduction Light strongly influences human behavior, and it has positive effects on mood and cognition. These nonvisual effects of light rely on the wavelength, intensity, and duration of light exposure [1]. However, recent studies indicate that the nonvisual effects of light are acute (within 50 seconds) [2] and even occur at dim light exposure [1]. Interestingly, it has been found in humans that blue light increased alertness and speed of information processing and improved cognitive performance [3]. Furthermore, working memory was affected in a wavelength-dependent manner in humans [4]. In addition, a wavelength-dependent effect of light therapy was observed in patients with seasonal affective disorders [5]. The observed effects of light on human behavior are based on the activation of the nonvisual photoreceptor system and related structures, like the suprachiasmatic nucleus, and the release of hormones and neurotransmitters [6–8]. This nonvisual photoreceptor system was extensively studied in rodents. However, only little is known about the influence of different wavelengths on cognition in rats. The 8-arm radial maze is a prominent tool to study spatial learning and memory of rats under controlled conditions. Numerous recent studies revealed significant differences between male and female rats in spatial memory tasks [9–11], which may rely on anatomical and hormonal dimorphisms. Interestingly a growing body of evidence reveals sexual differences in diverse brain areas [12–14]. The nonvisual photoreceptor system together with the circadian system is closely connected to brain structures associated with learning and memory [15, 16]. Therefore, it is likely that wavelength differentially affects spatial learning in male and female rats. Thus, in the present study we were interested to investigate the
Combined Hemostasis and Adhesion Prevention with the Novel Agent 4DryField® PH—Initial Observations  [PDF]
Matthias Korell
Surgical Science (SS) , 2014, DOI: 10.4236/ss.2014.512081
Abstract: Large size peritoneal trauma from extended surgery for high-grade expansive uterus pathology or endometriosis might result in severe diffuse bleeding and peritoneal adhesion formation with objectionable sequelae. This paper introduces 4DryField® PH polysaccharide powder certified for two indications: 1) given as powder 4DryField® PH provides hemostasis; 2) transformed into gel, 4DryField® PH forms an adhesion prevention barrier. Twenty-one women with expanded uterus pathology and/or deep infiltrating endometriosis had surgery including repair of intestine lesions (n = 8), ureterolysis/repair of bladder, including retrograde ureteric stents (n = 5). Subjective impression of hemostatic effect, drain loss and infection parameters were recorded. Six women had scheduled second look laparoscopy. 4DryField® PH applied as powder showed an immediate significant hemostatic effect in all instances, especially in profound diffuse bleeding. Mean drain loss was 497 ± 339 mL, moderate considering the extent of disease. Dripped with saline solution, 4DryField® PH immediately formed a viscous gel acting as a barrier for adhesion prevention. Second look laparoscopy revealed only one patient with significant adhesions. No adverse events were observed; discharge was at Day 6.2 ± 1.4. In this cohort with extended gynecological laparoscopic surgery 4DryField®
Sublingual Buprenorphine and Methadone Maintenance Treatment: A Three-Year Follow-Up of Quality of Life Assessment
Salvatore M. Giacomuzzi,Markus Ertl,Georg Kemmler,Yyvonne Riemer
The Scientific World Journal , 2005, DOI: 10.1100/tsw.2005.52
Abstract:
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