| 1. |
- Tholén, Erik, et al.
(författare)
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Note : The intermodulation lockin analyzer
- 2011
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 82:2, s. 026109-
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Tidskriftsartikel (refereegranskat)abstract
- Nonlinear systems can be probed by driving them with two or more pure tones while measuring the intermodulation products of the drive tones in the response. We describe a digital lockin analyzer which is designed explicitly for this purpose. The analyzer is implemented on a field-programmable gate array, providing speed in analysis, real-time feedback, and stability in operation. The use of the analyzer is demonstrated for intermodulation atomic force microscopy. A generalization of the intermodulation spectral technique to arbitrary drive waveforms is discussed.
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| 2. |
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| 3. |
- Bergqvist, Jonas, et al.
(författare)
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LED array scanner for inline characterization of thin film photovoltaic modules
- 2016
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Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier. - 0927-0248 .- 1879-3398. ; 157:17, s. 1057-1064
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Tidskriftsartikel (refereegranskat)abstract
- Thin film solar cells, and in particular printed organic solar cells, offer a potential route to a low cost power generation from sunlight. However, manufacturing these solar cells rapidly generates large areas that have to be characterized, preferably in-line for a direct feed back in the production process. Here we introduce the LEDimage, a LED array illumination induced photocurrent method suitable for high speed inline characterization and defect detection of organic solar cell modules. The LEDimage enables simultaneous illumination of all connected subcells without additional bias light. Each LED in the array is amplitude modulated at an individual frequency and the photocurrent response is Fourier transformed to generate a photocurrent map. Furthermore, the LEDimage can be used as a hand scanner for fast device characterization. We expect that LEDimage can be an effective research and industry tool for characterization of large area thin film solar cells.
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| 4. |
- Bäckevik, Andreas, et al.
(författare)
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Social Identity in Software Development
- 2019
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Ingår i: 2019 IEEE/ACM 12th International Workshop on Cooperative and Human Aspects of Software Engineering (CHASE). - : IEEE/ACM. - 2574-1780 .- 2574-1837. - 9781728122403
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Konferensbidrag (refereegranskat)abstract
- An agile approach has become very popular over the last decade, which requires good communication and teamwork within teams as well as with outside stakeholders. Therefore, social interaction is central for a software development team to be successful. Such social interactions form social identities and social structures in both teams and organizations. This study investigates possible effects that the social identity of individuals may have on the effectiveness of software development through seven in-dept interviews. The qualitative data from interviews were analyzed and summarized using summative content analysis, and the seven individuals also answered a questionnaire on social identity taken from social psychology research. The qualitative result shows that aspects of social identity affect software developers' behavior, and that we need to build cross-functional stable teams over time also from a pure social identity perspective in addition to the product related aspects to avoid a decreased effectiveness. However, we did not see clear connections to our operationalization of effectiveness in this study, and the quantitative analysis was also inconclusive, but we see value in our suggested method when investigating social identity in software development.
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| 5. |
- Forchheimer, Daniel, et al.
(författare)
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Model-based extraction of material properties in multifrequency atomic force microscopy
- 2012
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 85:19, s. 195449-
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Tidskriftsartikel (refereegranskat)abstract
- We present a method to reconstruct the nonlinear tip-surface force and extract material properties from a multifrequency atomic force microscopy (AFM) measurement with a high-quality-factor cantilever resonance. In a measurement time of similar to 2 ms, we are able to accurately reconstruct the tip-surface force-displacement curve, allowing simultaneous high-resolution imaging of both topography and material properties at typical AFM scan rates. We verify the method using numerical simulations, apply it to experimental data, and use it to image mechanical properties of a polymer blend. We further discuss the limitations of the method and identify suitable operating conditions for AFM experiments.
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| 6. |
- Forchheimer, Daniel, et al.
(författare)
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Simultaneous imaging of surface and magnetic forces
- 2013
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 103:1, s. 013114-
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate quantitative force imaging of long-range magnetic forces simultaneously with near-surface van-der-Waals and contact-mechanics forces using intermodulation atomic force microscopy. Magnetic forces at the 200 pN level are separated from near-surface forces at the 30 nN level. Imaging of these forces is performed in both the contact and non-contact regimes of near-surface interactions.
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| 7. |
- Hutter, Carsten, et al.
(författare)
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Josephson junction transmission lines as tunable artificial crystals
- 2011
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 83:1, s. 014511-
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Tidskriftsartikel (refereegranskat)abstract
- We investigate one-dimensional Josephson junction arrays with generalized unit cells, beyond a single junction or SQUID, as a circuit approach to engineer band gaps. Within a specific frequency range, of the order of the single junction plasma frequency, the dispersion relation becomes gapped and the impedance becomes purely imaginary. We derive the parameter dependence of this gap and suggest designs to lower it to microwave frequencies. The gap can be tuned in a wide frequency range by applying external flux, and persists in the presence of small imperfections. These arrays, which can be thought of as tunable artificial crystals, may find use in applications ranging filters to the protection of quantum bits.
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| 8. |
- Hutter, Carsten, et al.
(författare)
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Reconstructing nonlinearities with intermodulation spectroscopy
- 2010
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 104:5, s. 050801-
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Tidskriftsartikel (refereegranskat)abstract
- We describe a method of analysis which allows for reconstructing the nonlinear disturbance of a high Q harmonic oscillator. When the oscillator is driven with two or more frequencies, the nonlinearity causes intermodulation of the drives, resulting in a complicated spectral response. Analysis of this spectrum allows one to approximate the nonlinearity. The method, which is generally applicable to measurements based on resonant detection, increases the information content of the measurement without requiring large detection bandwidth, and optimally uses the enhanced sensitivity near resonance to extract information and minimize error due to detector noise.
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| 9. |
- Kolsrud, Oscar, et al.
(författare)
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Effects of atrial natriuretic peptide on renal function during cardiopulmonary bypass: a randomized pig model.
- 2020
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Ingår i: European journal of cardio-thoracic surgery : official journal of the European Association for Cardio-thoracic Surgery. - : Oxford University Press (OUP). - 1873-734X. ; 57:4, s. 652-659
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Tidskriftsartikel (refereegranskat)abstract
- Acute kidney injury is a well-known complication after cardiac surgery and cardiopulmonary bypass (CPB). In this experimental animal study, we evaluated the effects of atrial natriuretic peptide (ANP) on renal function, perfusion, oxygenation and tubular injury during CPB.Twenty pigs were blindly randomized to continuous infusion of either ANP (50ng/kg/min) or placebo before, during and after CPB. Renal blood flow as well as cortical and medullary perfusion was measured. Blood was repeatedly sampled from the renal vein. Glomerular filtration rate was measured by infusion clearance of 51Cr-EDTA.Glomerular filtration rate was higher (P<0.001), whereas renal blood flow or renal oxygen delivery was not affected by ANP during CPB. Renal oxygen consumption did not differ between groups during CPB, whereas renal oxygen extraction was higher in the ANP group (P=0.03). Urine flow and sodium excretion were higher in the ANP group during CPB. Blood flow in the renal medulla, but not in the cortex, dropped during CPB, an effect that was not seen in the animals that received ANP.ANP improved renal function during CPB. Despite impaired renal oxygenation, ANP did not cause tubular injury, suggesting a renoprotective effect of ANP during CPB. Also, CPB induced a selectively reduced blood flow in the renal medulla, an effect that was counteracted by ANP.
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| 10. |
- Platz, Daniel, et al.
(författare)
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Effect of material stiffness on intermodulation response in dynamic atomic force microscopy
- 2010
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Ingår i: ASME 2010 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. - New York : Amer Soc Mechanical Engineers. ; , s. 499-506
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Konferensbidrag (refereegranskat)abstract
- We perform simulations and experiments on an oscillating atomic force microscope cantilever approaching a surface, where the intermodulation response of the cantilever driven with two pure harmonic tones is investigated. In the simulations, the tip and surface interact with a conservative nonlinear force, and the parameter space of approach distance and surface stiffness is explored. Approach experiments are carried out on three surfaces with widely varying stiffness. Qualitative similarities between simulations and experiment can be seen, but quantitative comparison is difficult due to the overly idealized tip-surface force model used in the simulation.
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| 11. |
- Platz, Daniel, et al.
(författare)
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Interaction imaging with amplitude-dependence force spectroscopy
- 2013
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 4, s. 1360-
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Tidskriftsartikel (refereegranskat)abstract
- Knowledge of surface forces is the key to understanding a large number of processes in fields ranging from physics to material science and biology. The most common method to study surfaces is dynamic atomic force microscopy (AFM). Dynamic AFM has been enormously successful in imaging surface topography, even to atomic resolution, but the force between the AFM tip and the surface remains unknown during imaging. Here we present a new approach that combines high-accuracy force measurements and high-resolution scanning. The method, called amplitude-dependence force spectroscopy (ADFS), is based on the amplitude dependence of the cantilever's response near resonance and allows for separate determination of both conservative and dissipative tip-surface interactions. We use ADFS to quantitatively study and map the nano-mechanical interaction between the AFM tip and heterogeneous polymer surfaces. ADFS is compatible with commercial atomic force microscopes and we anticipate its widespread use in taking AFM toward quantitative microscopy.
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| 12. |
- Platz, Daniel, et al.
(författare)
-
Intermodulation atomic force microscopy
- 2008
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 92, s. 153106-
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Tidskriftsartikel (refereegranskat)abstract
- A mode of atomic force microscopy ͑AFM͒ is demonstrated where an oscillating AFM cantileverhaving linear response is driven with two frequencies in the vicinity of a resonance. Newfrequencies in the response, known as intermodulation products, are generated when the linearity ofthe cantilever response is perturbed by the nonlinear tip-surface interaction. A rich structure of theintermodulation products is observed as a function of the probe-surface separation, indicating thatit is possible to extract much more detailed information about the tip-surface interaction than ispossible with the standard amplitude and phase imaging methods.
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| 13. |
- Platz, Daniel, et al.
(författare)
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Interpreting motion and force for narrow-band intermodulation atomic force microscopy
- 2013
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Ingår i: Beilstein Journal of Nanotechnology. - : Beilstein Institut. - 2190-4286. ; 4, s. 45-56
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Tidskriftsartikel (refereegranskat)abstract
- Intermodulation atomic force microscopy (ImAFM) is a mode of dynamic atomic force microscopy that probes the nonlinear tip-surface force by measurement of the mixing of multiple modes in a frequency comb. A high-quality factor cantilever resonance and a suitable drive comb will result in tip motion described by a narrow-band frequency comb. We show, by a separation of time scales, that such motion is equivalent to rapid oscillations at the cantilever resonance with a slow amplitude and phase or frequency modulation. With this time-domain perspective, we analyze single oscillation cycles in ImAFM to extract the Fourier components of the tip-surface force that are in-phase with the tip motion (F-I) and quadrature to the motion (F-Q). Traditionally, these force components have been considered as a function of the static-probe height only. Here we show that F-I and F-Q actually depend on both static-probe height and oscillation amplitude. We demonstrate on simulated data how to reconstruct the amplitude dependence of F-I and F-Q from a single ImAFM measurement. Furthermore, we introduce ImAFM approach measurements with which we reconstruct the full amplitude and probe-height dependence of the force components F-I and F-Q, providing deeper insight into the tip-surface interaction. We demonstrate the capabilities of ImAFM approach measurements on a polystyrene polymer surface.
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| 14. |
- Platz, Daniel, et al.
(författare)
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Phase imaging with intermodulation atomic force microscopy
- 2010
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Ingår i: Ultramicroscopy. - : Elsevier BV. - 0304-3991 .- 1879-2723. ; 110:6, s. 573-577
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Tidskriftsartikel (refereegranskat)abstract
- Intermodulation atomic force microscopy (IMAFM) is a dynamic mode of atomic force microscopy (AFM) with two-tone excitation. The oscillating AFM cantilever in close proximity to a surface experiences the nonlinear tip-sample force which mixes the drive tones and generates new frequency components in the cantilever response known as intermodulation products (IMPs). We present a procedure for extracting the phase at each IMP and demonstrate phase images made by recording this phase while scanning. Amplitude and phase images at intermodulation frequencies exhibit enhanced topographic and material contrast.
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| 15. |
- Platz, Daniel, et al.
(författare)
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Polynomial force approximations and multifrequency atomic force microscopy
- 2013
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Ingår i: Beilstein Journal of Nanotechnology. - : Beilstein Institut. - 2190-4286. ; 4:1, s. 352-360
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Tidskriftsartikel (refereegranskat)abstract
- We present polynomial force reconstruction from experimental intermodulation atomic force microscopy (ImAFM) data. We study the tip-surface force during a slow surface approach and compare the results with amplitude-dependence force spectroscopy (ADFS). Based on polynomial force reconstruction we generate high-resolution surface-property maps of polymer blend samples. The polynomial method is described as a special example of a more general approximative force reconstruction, where the aim is to determine model parameters that best approximate the measured force spectrum. This approximative approach is not limited to spectral data, and we demonstrate how it can be adapted to a force quadrature picture.
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| 16. |
- Platz, Daniel, et al.
(författare)
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The role of nonlinear dynamics in quantitative atomic force microscopy
- 2012
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 23:26, s. 265705-
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Tidskriftsartikel (refereegranskat)abstract
- Various methods of force measurement with the atomic force microscope are compared for their ability to accurately determine the tip-surface force from analysis of the nonlinear cantilever motion. It is explained how intermodulation, or the frequency mixing of multiple drive tones by the nonlinear tip-surface force, can be used to concentrate the nonlinear motion in a narrow band of frequency near the cantilever's fundamental resonance, where accuracy and sensitivity of force measurement are greatest. Two different methods for reconstructing tip-surface forces from intermodulation spectra are explained. The reconstruction of both conservative and dissipative tip-surface interactions from intermodulation spectra are demonstrated on simulated data.
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| 17. |
- Platz, Daniel, et al.
(författare)
-
Tip-surface interactions in dynamic atomic forcemicroscopy
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In atomic force microscopy (AFM) tip-surface interactions are usuallyconsidered as functions of the tip position only, so-called force curves. However,tip-surface interactions often depend on the tip velocity and the past tip trajectory.Here, we introduce a compact and general description of these interactionsappropriate to dynamic AFM where the measurement of force is restricted toa narrow frequency band. We represent the tip-surface interaction in termsof a force disk in the phase space of position and velocity. Determination ofthe amplitude dependence of tip-surface forces at a fixed static probe heightallows for a comprehensive treatment of conservative and dissipative interactions.We illuminate the fundamental limitations of force reconstruction with narrowband dynamic AFM and we show how the amplitude dependence of the F ouriercomponent of the force at the tip oscillation frequency, gives qualitative insight intothe detailed nature of the tip-surface interaction. With minimal assumptions thisamplitude dependence force spectroscopy allows for a quantitative reconstruction ofthe effective conservative tip-surface force as well as a position-dependent dampingfactor. We demonstrate this reconstruction on simulated intermodulation AFMdata.
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| 18. |
- Sanandaji, Nima, et al.
(författare)
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Inkjet printing as a possible route to study confined crystal structures
- 2012
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Ingår i: European Polymer Journal. - : Elsevier BV. - 0014-3057 .- 1873-1945. ; 49:1, s. 203-208
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Tidskriftsartikel (refereegranskat)abstract
- Inkjet printing is a technique for the precise deposition of liquid droplets in the pL-volume range in well-defined patterns. Previous studies have shown that inkjet printing is attractive in polymer technology since it permits the controlled deposition of functional polymer surfaces. We suggest that the technique might also be useful for studying crystallization, in particular confined crystallization. Inkjet printing is a non-contact deposition method with minimal risk of contamination, which allows the exact deposition of both polymer solutions and polymer melts. This paper demonstrates the possibility of utilizing the technique to create surfaces where polymer chains form isolated small structures. These structures were confined by both the low polymer content in each droplet and the time constraint on crystal formation that arose as the result of the rapid solvent evaporation from the pL-sized droplets. In theory, inkjet printing enables the exact deposition of systems with as few as a single polymer chain in the average droplet. With appropriate instrumentation, the versatile inkjet technology can be utilized to create whole surfaces covered with polymer structures formed by the crystallization of small, dilute and rapidly evaporating droplets. 110 pL droplets of a 10 -6 g L -1 poly(ε-caprolactone) solution in 1-butanol have been deposited and studied by atomic force microscopy. Small structures of ca. 10 nm thickness and ca. 50 nm diameter also seemed to exhibit crystalline features. Some of the small structures had unusual rectangular forms whilst others were interpreted to be early precursors to six-sided single crystals previously observed for poly(ε-caprolactone). The unusual forms observed may have resulted from the entrapment of crystal structures into metastable phases, due to the limited amount of polymer material present and the rapid evaporation of the droplets.
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| 19. |
- Sjöstrand, Joachim, et al.
(författare)
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Phase Space Topology of a Switching Current Detector
- 2006
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 73, s. 132511-
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Tidskriftsartikel (refereegranskat)abstract
- We examine in theory and by numerical simulation, the dynamic process of switching from a zero voltage to a finite voltage state in a Josephson junction circuit. The theoretical model describes small capacitance Josephson junctions which are overdamped at high frequencies, and can be applied to detection of the quantum state of a qubit circuit. We show that the speed and fidelity of the readout are strongly influenced by the topology of the phase space attractors. The readout will be close to optimal when choosing the circuit parameters so as to avoid having an unstable limiting cycle which separates the two basins of attraction.
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| 20. |
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| 21. |
- Tholén, Erik, 1979-
(författare)
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Intermodulation in microresonators : for microwave amplification and nanoscale surface analysis
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This work explores the effects of weak nonlinearity on harmonic oscillators.Two particular systems are studied experimentally: A superconductingresonator formed from a coplanar waveguide that oscillates at microwave frequencies,and the cantilever of an atomic force microscope (AFM) vibratingat ultrasonic frequencies. Both of these systems are described in the introduction,followed by a theory chapter giving a general theoretical framework for nonlinear oscillators. Basic properties of nonlinear oscillators, such asbifurcation and intermodulation, are explained using simple models. Experimental methods, including cryogenic and microwave measurement techniques,are described in some detail.The nonlinear superconducting resonator is studied for use as a parametric amplifier. A strong drive tone, called the pump, drives the oscillator nearthe point of bifurcation. A second, much weaker drive signal that is slightlydetuned from the pump, will cause energy to move from the pump to the signal, giving signal amplification. We have measured a signal gain greaterthan 22 dB in a bandwidth of 30 kHz, for a resonator pumped at 7.6 GHz.This type of amplifier is phase-sensitive, meaning that signals in phase withthe pump will be amplified, but signals in quadrature phase of the pump will be deamplified. Phase-sensitivity has important implications on the amplifier’snoise properties. With a parametric amplifier, a signal can be amplified without any additional noise being added by the amplifier, something that is fundamentally impossible for a standard amplifier.The vibrating AFM cantilever becomes a nonlinear oscillator when it is interacting with a surface. When driven with two frequencies, the amplitudeand phase of the cantilever’s response will develop mixing products, or intermodulation products, that are very sensitive to the exact form of the nonlinearity. Very small changes in the surface properties will be detectable when measuring the intermodulation products. Simultaneously measuring many intermodulation products, or acquiring an intermodulation spectrum,allows one to reconstruct the tip-surface interaction. Intermodulation AFM increases the sensitivity of the measurement or the contrast of the acquiredimages, and provides a means of rapidly measuring the nonlinear tip-surface interaction. The method promises to enhance the functionality of the AFM beyond simple topography measurement, towards quantitative analysis of the chemical or material properties of the surface.
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| 22. |
- Tholén, Erik, 1979-, et al.
(författare)
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Nonlinearities and parametric amplification in superconducting coplanar waveguide resonators
- 2007
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 90:25, s. 253509-
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Tidskriftsartikel (refereegranskat)abstract
- Experimental investigations of the nonlinear properties of superconducting niobium coplanarwaveguide resonators are reported. The nonlinearity due to a current dependent kinetic inductanceof the center conductor is strong enough to realize bifurcation of the nonlinear oscillator. Whendriven with two frequencies near the threshold for bifurcation, parametric amplification with a gainof +22.4 dB is observed.
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| 23. |
- Tholén, Erik, 1979-, et al.
(författare)
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Parametric amplification with weak-link nonlinearity in superconducting microresonators
- 2009
-
Ingår i: Nobel Symposium 141: Qubits for Future Quantum Information; Gothenburg; 25 May 2009 through 28 May 2009.
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Konferensbidrag (refereegranskat)abstract
- Nonlinear kinetic inductance in a high Q superconducting coplanarwaveguide microresonator can cause a bifurcation of the resonance curve. Near thecritical pumping power and frequency for bifurcation, large parametric gain is observedfor signals in the frequency band near resonance. We show experimental results onsignal and intermodulation gain which are well described by a theory of the parametricamplification based on a Kerr nonlinearity. Phase dependent gain, or signal squeezing,is verified with a homodyne detection scheme.
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| 24. |
- Tholén, Maria, et al.
(författare)
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Atrial natriuretic peptide in the prevention of acute renal dysfunction after heart transplantation-a randomized placebo-controlled double-blind trial
- 2023
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Ingår i: Acta Anaesthesiologica Scandinavica. - : Wiley. - 0001-5172 .- 1399-6576. ; 67:6, s. 738-745
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Tidskriftsartikel (refereegranskat)abstract
- Background: Acute kidney injury (AKI) and renal dysfunction after heart transplantation are common and serious complications. Atrial natriuretic peptide (ANP) has been shown to increase glomerular filtration rate (GFR) and exert renoprotective effects when used for the prevention/treatment of AKI in cardiac surgery. We tested the hypothesis that intraoperative and postoperative administration of ANP could prevent a postoperative decrease in renal function early after heart transplantation.Methods: Seventy patients were randomized to receive either ANP (50 ng/kg/min) (n = 33) or placebo (n = 37) starting after induction of anesthesia and continued for 4 days after heart transplantation or until treatment with dialysis was started. The primary end-point of the present study was measured GFR (mGFR) at day 4, assessed by plasma clearance of a renal filtration marker. Also, the incidence of postoperative AKI and dialysis were assessed.Results: Median (IQR) mGFR at day 4 postoperatively was 60.0 (57.0) and 50.1 (36.3) ml/min/1.72 m(2) for the placebo and ANP groups, respectively (p = .705). During ongoing ANP infusion, the need for dialysis was 21.6% and 9.1% for the placebo and ANP groups, respectively (p = .197). The incidences of AKI for the placebo and the ANP groups were 76.5% and 63.6%, respectively (p = .616). The incidences of AKI stage 1 were 32.4% and 21.2% for the placebo and ANP groups, respectively (p = .420) and for AKI stage 2 or 3, 37.8% and 42.4%, respectively (p = .808).Conclusion: The study failed to detect that ANP infusion attenuates renal dysfunction or decreases the incidence of AKI after heart transplantation.
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| 25. |
- Tholén, Maria, et al.
(författare)
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Effects of levosimendan on renal blood flow and glomerular filtration in patients with acute kidney injury after cardiac surgery: a double blind, randomized placebo-controlled study
- 2021
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Ingår i: Critical Care. - : Springer Science and Business Media LLC. - 1364-8535. ; 25:1
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Tidskriftsartikel (refereegranskat)abstract
- Background: Acute kidney injury (AKI) is a common and serious complication after cardiac surgery, and current strategies aimed at treating AKI have proven ineffective. Levosimendan, an inodilatating agent, has been shown to increase renal blood flow and glomerular filtration rate in uncomplicated postoperative patients and in patients with the cardiorenal syndrome. We hypothesized that levosimendan through its specific effects on renal vasculature, a preferential vasodilating effect on preglomerular resistance vessels, could improve renal function in AKI-patients with who did not have clinical indication for inotropic support. Methods: In this single-center, double-blind, randomized controlled study, adult patients with postoperative AKI within 2 days after cardiac surgery, who were hemodynamically stable with a central venous oxygen saturation (ScvO(2)) >= 60% without inotropic support were eligible for inclusion. After randomization, study drug infusions, levosimendan (n = 16) or placebo (n = 13) were given for 5 h. A bolus infusion of levosimendan (12 mu g/kg), were given for 30 min followed by 0.1 mu g/kg/min for 5 h. Renal blood flow and glomerular filtration rate were measured using infusion clearance of para-aminohippuric acid and a filtration marker, respectively. As a safety issue, norepinephrine was administered to maintain mean arterial pressure between 70-80 mmHg. Intra-group differences were tested by Mann-Whitney U-tests, and a linear mixed model was used to test time and group interaction. Results: Twenty-nine patients completed the study. At inclusion, the mean serum creatinine was higher in the patients randomized to levosimendan (148 +/- 29 vs 127 +/- 22 mu mol/L, p = 0.030), and the estimated GFR was lower (46 +/- 12 vs 57 +/- 11 ml/min/1.73 m(2), p = 0.025). Levosimendan induced a significantly (p = 0.011) more pronounced increase in renal blood flow (15%) compared placebo (3%) and a more pronounced decrease in renal vascular resistance (- 18% vs. - 4%, respectively, p = 0.043). There was a trend for a minor increase in glomerular filtration rate with levosimendan (4.5%, p = 0.079), which did differ significantly from the placebo group (p = 0.440). The mean norepinephrine dose was increased by 82% in the levosimedan group and decreased by 29% in the placebo group (p = 0.012). Conclusions: In hemodynamically stable patients with AKI after cardiac surgery, levosimendan increases renal blood flow through renal vasodilatation.
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| 26. |
- Tholén, Maria, et al.
(författare)
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Renal Near-Infrared Spectroscopy for Assessment of Renal Oxygenation in Adults Undergoing Cardiac Surgery: A Method Validation Study
- 2020
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Ingår i: Journal of Cardiothoracic and Vascular Anesthesia. - : Elsevier BV. - 1053-0770. ; 34:12, s. 3300-3305
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Tidskriftsartikel (refereegranskat)abstract
- Objective: To investigate the correlation between invasively measured renal venous oxygen saturation (SrvO2) and tissue oxygenation (rSO2) measured with near-infrared spectroscopy (NIRS) in adult patients undergoing cardiac surgery. Design: Prospective observational study. Setting: Single cardiac surgery center at a university hospital. Participants: Thirteen adult patients with skin- to- kidney distance ≤4 cm undergoing open cardiac surgery with cardiopulmonary bypass (CPB). Interventions: All patients received renal vein catheters for invasive measurement of SrvO2, and NIRS electrodes for assessment of renal rSO2 were placed over the kidney using ultrasound guidance. Measurements were made before CPB, during CPB at 3 different flow rates (2.4, 2.7, and 3.0 L/min/m2), and after CPB. Measurements and Main Results: Repeated- measures correlation analyses and Bland-Altman plots were used to study the correlation and agreement between rSO2 and SrvO2. For all measurement points, renal rSO2 correlated with SrvO2 (rrm = 0.61, p < 0.001), and the mean difference (bias) between rSO2 and SrvO2 was –2.71 ± 7.22 (p = 0.002), with an error of 17.6%. When measurements during CPB and before and after CPB were studied separately, rSO2 and SrvO2 were correlated (rrm = 0.51, p < 0.007 and rrm = 0.73, p < 0.001, respectively). During CPB, renal rSO2 predicted SrvO2 with a bias of –3.41 ± 7.76 (p = 0.009) and an error of 18.8%. Before and after CPB, the mean difference was –1.93 ± 6.60 (p = 0.092), with an error of 16.2%. Conclusions: Renal rSO2 is correlated to and predicts SrvO2 with a small bias and acceptable agreement. Further studies are needed before renal NIRS can be used as a surrogate marker of renal oxygenation in clinical practice. © 2020 Elsevier Inc.
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| 27. |
- Walter, Jochen, et al.
(författare)
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Pulse and hold strategy for switching current measurements
- 2007
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:9, s. 94515-
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Tidskriftsartikel (refereegranskat)abstract
- We investigate by theory and experiment, the Josephson junction switching current detector in an environment with frequency-dependent damping. Analysis of the circuit's phase space shows that a favorable topology for switching can be obtained with overdamped dynamics at high frequencies. A pulse-and-hold method is described, where a fast switch pulse brings the circuit close to an unstable point in the phase space when biased at the hold level. Experiments are performed on Cooper pair transistors and quantronium circuits, which are overdamped at high frequencies with an on-chip RC shunt. For 20 mu s switch pulses the switching process is well described by thermal equilibrium escape, based on a generalization of the Kramers formula to the case of frequency-dependent damping. A capacitor bias method is used to create very rapid, 25 ns switch pulses, where it is observed that the switching process is not governed by thermal equilibrium noise.
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