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Sökning: WFRF:(Nordebo Sven)

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41.
  • Sjösten, Per, et al. (författare)
  • Considerations on Large Applications of Active Noise Control, Part I : Theory
  • 2003
  • Ingår i: Acta Acoustica united with Acustica. - : S. Hirzel Verlag. - 1610-1928 .- 1861-9959. ; 89:5, s. 822-833
  • Tidskriftsartikel (refereegranskat)abstract
    • The application of active noise or vibration control to a real situation is usually a great challenge. The step from computer simulations, or even lab studies, to the actual implementation is often much larger than first expected. This is especially true for multiple-error, multiple-output control, in which careful planning and a very great deal of preparatory work is crucial to the success of the project. The present paper is the first in a series of two, that treat the process of preparing and evaluating an active noise control system. Part I gives a general discussion on proposed methods from a theoretical standpoint. Part II describes the application of these methods in practical measurements in an aircraft application. The emphasis is on multiple-error, multiple-output control but the general guidelines haves proven to be useful even in small applications. The discussion covers some acoustical aspects as well as the signal processing view. A method, based on simulated annealing using the metropolis sampler is suggested for searching the suboptimal positions for the control sources and sensors, including a thorough discussion on the preparation of input data for the optimisation process. Finally, a version of the complex lms algorithm, normalised individually for each actuator, is discussed.
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42.
  • Zang, Zhuquan, et al. (författare)
  • Complex Domain Digital Filter Design with Max-Min Type Amplitude Constraints and Group Delay Specifications
  • 2001
  • Konferensbidrag (refereegranskat)abstract
    • This paper considers the design of a digital filter with prescribed magnitude and group delay specifications. Our aim is to devise suitable methods/algorithms which are useful for the design of a set of filters for multiuser communication systems. To do this, we formulate our filter design problem as a constrained L2 space minimization problem in which the performance requirement on the group delay and magnitude in the passband are treated as constraints while minimizing the L2 norm of the error function between the designed and the desired filters. Methods for solving the proposed nonlinear and nonconvex optimization problem are outlined. Numerical results are presented to illustrate the usefulness of the proposed method.
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43.
  • Zang, Zhuquan, et al. (författare)
  • Design of Digital Filters with Amplitude and Group Delay Specifications
  • 2001
  • Konferensbidrag (refereegranskat)abstract
    • This paper considers the design of a digital filter with prescribed magnitude and group delay specifications. First, we outline the derivation of the phase and group delay functions of an Nth order digital Laguerre filter and show that the group delay function of the filter can be written as a ratio of quadratic functions in the filter coefficients. Then, we formulate our filter design problem as a constrained L2 space minimization problem in which the performance requirement on the group delay and magnitude in the passband are treated as constraints while minimizing the L2 norm of the error function between the designed and the desired filters. Methods for solving the proposed nonlinear optimization problem axe outlined. Numerical results are presented to illustrate the usefulness of the proposed method. As a special case, corresponding results for general FIR filters axe also derived
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44.
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45.
  • Aksimsek, Sinan, et al. (författare)
  • TEM wave scattering by a step discontinuity on the outer wall of a coaxial waveguide
  • 2013
  • Ingår i: IEEE transactions on microwave theory and techniques. - : IEEE Press. - 0018-9480 .- 1557-9670. ; 61:8, s. 2783-2791
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, the propagation of TEM waves along a coaxial waveguide with a step discontinuity on its outer wall is investigated rigorously by applying the direct Fourier transform and reducing the problem into the solution of a modified Wiener–Hopf equation. The solution for the field terms are determined in terms of an infinite number of unknown coefficients, which satisfy an infinite set of linear algebraic equations. These equations are solved numerically and the effect of area ratio is presented graphically at the end of the analysis. The same problem is also analyzed by applying the mode-matching technique and the results of the two approaches are compared. It is observed numerically that the Wiener–Hopf technique provides a better convergence than the mode-matching technique.
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46.
  • Bayford, Richard H., et al. (författare)
  • Locating Functionalized Gold Nanoparticles Using Electrical Impedance Tomography
  • 2022
  • Ingår i: IEEE Transactions on Biomedical Engineering. - : IEEE. - 0018-9294 .- 1558-2531. ; 69:1, s. 494-502
  • Tidskriftsartikel (refereegranskat)abstract
    • Objective: An imaging device to locate functionalised nanoparticles, whereby therapeutic agents are transported from the site of administration specifically to diseased tissues, remains a challenge for pharmaceutical research. Here, we show a new method based on electrical impedance tomography (EIT) to provide images of the location of gold nanoparticles (GNPs) and the excitation of GNPs with radio frequencies (RF) to change impedance permitting an estimation of their location in cell models Methods: We have created an imaging system using quantum cluster GNPs as contrast agent, activated with RF fields to heat the functionalized GNPs, which causes a change in impedance in the surrounding region. This change is then identified with EIT. Results: Images of impedance changes of around 80 ± 4% are obtained for a sample of citrate stabilized GNPs in a solution of phosphate-buffered saline. A second quantification was carried out using colorectal cancer cells incubated with culture media, and the internalization of GNPs into the colorectal cancer cells was undertaken to compare them with the EIT images. When the cells were incubated with functionalised GNPs, the change was more apparent, approximately 40 ± 2%. This change was reflected in the EIT image as the cell area was more clearly identifiable from the rest of the area. Significance: EIT can be used as a new method to locate functionalized GNPs in human cells and help in the development of GNP-based drugs in humans to improve their efficacy in the future.
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47.
  • Bayford, Richard H., et al. (författare)
  • Locating Functionalized Gold Nanoparticles Using Electrical Impedance Tomography
  • 2022
  • Ingår i: IEEE Transactions on Biomedical Engineering. - : IEEE. - 0018-9294 .- 1558-2531. ; 69:1, s. 494-502
  • Tidskriftsartikel (refereegranskat)abstract
    • Objective: An imaging device to locate functionalised nanoparticles, whereby therapeutic agents are transported from the site of administration specifically to diseased tissues, remains a challenge for pharmaceutical research. Here, we show a new method based on electrical impedance tomography (EIT) to provide images of the location of gold nanoparticles (GNPs) and the excitation of GNPs with radio frequencies (RF) to change impedance permitting an estimation of their location in cell models Methods: We have created an imaging system using quantum cluster GNPs as contrast agent, activated with RF fields to heat the functionalized GNPs, which causes a change in impedance in the surrounding region. This change is then identified with EIT. Results: Images of impedance changes of around 80 +/- 4% are obtained for a sample of citrate stabilized GNPs in a solution of phosphate-buffered saline. A second quantification was carried out using colorectal cancer cells incubated with culture media, and the internalization of GNPs into the colorectal cancer cells was undertaken to compare them with the EIT images. When the cells were incubated with functionalised GNPs, the change was more apparent, approximately 40 +/- 2%. This change was reflected in the EIT image as the cell area was more clearly identifiable from the rest of the area. Significance: EIT can be used as a new method to locate functionalized GNPs in human cells and help in the development of GNP-based drugs in humans to improve their efficacy in the future.
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48.
  • Becher, Tobias H., et al. (författare)
  • Prolonged Continuous Monitoring of Regional Lung Function in Infants with Respiratory Failure
  • 2022
  • Ingår i: Annals of the American Thoracic Society. - : American Thoracic Society. - 2329-6933 .- 2325-6621. ; 19:6, s. 991-999
  • Tidskriftsartikel (refereegranskat)abstract
    • Rationale: Electrical impedance tomography (EIT) allows instantaneous and continuous visualization of regional ventilation and changes in end-expiratory lung volume at the bedside. There is particular interest in using EIT for monitoring in critically ill neonates and young children with respiratory failure. Previous studies have focused only on short-term monitoring in small populations. The feasibility and safety of prolonged monitoring with EIT in neonates and young children have not been demonstrated yet.Objectives: To evaluate the feasibility and safety of long-term EIT monitoring in a routine clinical setting and to describe changes in ventilation distribution and homogeneity over time and with positioning in a multicenter cohort of neonates and young children with respiratory failure.Methods: At four European University hospitals, we conducted an observational study (NCT02962505) on 200 patients with postmenstrual ages (PMA) between 25 weeks and 36 months, at risk for or suffering from respiratory failure. Continuous EIT data were obtained using a novel textile 32-electrode interface and recorded at 48 images/s for up to 72 hours. Clinicians were blinded to EIT images during the recording. EIT parameters and the effects of body position on ventilation distribution were analyzed offline. Results: The average duration of FAT measurements was 53 +/- 20 hours. Skin contact impedance was sufficient to allow image reconstruction for valid ventilation analysis during a median of 92% (interquartile range, 77-98%) of examination time. EIT examinations were well tolerated, with minor skin irritations (temporary redness or imprint) occurring in 10% of patients and no moderate or severe adverse events. Higher ventilation amplitude was found in the dorsal and right lung areas when compared with the ventral and left regions, respectively. Prone positioning resulted in an increase in the ventilation-related EIT signal in the dorsal hemithorax, indicating increased ventilation of the dorsal lung areas. Lateral positioning led to a redistribution of ventilation toward the dependent lung in preterm infants and to the nondependent lung in patients with PMA > 37 weeks.Conclusions: EIT allows continuous long-term monitoring of regional lung function in neonates and young children for up to 72 hours with minimal adverse effects. Our study confirmed the presence of posture-dependent changes in ventilation distribution and their dependency on PMA in a large patient cohort.
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49.
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50.
  • Bernland, Anders, et al. (författare)
  • Physical limitations on the scattering of electromagnetic vector spherical waves
  • 2010
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • Understanding the interaction between electromagnetic waves and matter is vital in applications ranging from classical optics to antenna theory. This paper derives physical limitations on the scattering of electromagnetic vector spherical waves. The assumptions made are that the heterogeneous scatterer is passive, and has constitutive relations which are on convolution form in the time domain and anisotropic in the static limit. The resulting bounds limit the reflection coefficient of the modes over a frequency interval, and can thus be interpreted as limitations on the absorption of power from a single mode. They can be used within a wide range of applications, and are particularly useful for electrically small scatterers. The derivation follows a general approach to derive sum rules and physical limitations on passive systems on convolution form. The time domain versions of the vector spherical waves are used to describe the passivity of the scatterer, and a set of integral identities for Herglotz functions are applied to derive sum rules from which the physical limitations follow.
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