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  • 1.
    Carlson, Johan E.
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Hägglund, Fredrik
    Martinsson, Jesper
    Saremi, Amin
    Luleå University of Technology.
    Calibration of simulation models for ultrasonic transducers based on implicit calibration2009Ingår i: 2008 IEEE Ultrasonics Symposium: IUS ; Beijing, China, 2 - 5 November 2008, Piscataway, NJ: IEEE Communications Society, 2009, s. 1528-1531Konferensbidrag (Refereegranskat)
    Abstract [en]

    There are numerous software packages available for modeling of the sound pressure fields emitted by ultrasound transducers and transducer arrays. Accurate modeling of a real-world transducer requires knowledge of several parameters that are generally not known. This paper presents an estimation principle that can be used to calibrate such models, based on measurements of the sound field. The model separates the problem into estimation of the transducer's electro-mechanical impulse response and its spatial impulse response. The latter being what the software packages generally model. We demonstrate the principle with measurements of the sound field from a non-focused 5 MHz transducer. The results show that the modeled sound field agrees well with measurements.

  • 2.
    Carlson, Johan
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Martinsson, Jesper
    Nordenvaad, Magnus Lundberg
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Measurement of methane content in upgraded biogas using pulse-echo ultrasound2008Ingår i: Proceedings of the International Congress on Ultrasonics: Vienna, April 9-13, 2007, Paper ID 1366, Session R03: Acoustic sensors, 2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper we present an ultrasonic pulseecho technique for estimating the methane (CH4) content in binary mixtures of CH4 and carbon dioxide (CO2). The method is based on parametric estimation of phase velocity and frequency dependent attenuation in combination with Partial Least-Squares Regression (PLSR). The technique is verified using experiments on mixtures with a volume fraction of CO2 in the range of 0 % -10 %. The experiments show that the CH4 content can be accurately estimated with high repeatability.

  • 3.
    Gustafsson, Silje
    et al.
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Omvårdnad.
    Martinsson, Jesper
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Välivaara, Britt-Marie
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Omvårdnad.
    Vikman, Irene
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Hälsa och rehabilitering.
    Sävenstedt, Stefan
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Omvårdnad.
    Influence of self-care advice on patient satisfaction and healthcare utilization2016Ingår i: Journal of Advanced Nursing, ISSN 0309-2402, E-ISSN 1365-2648, Vol. 72, nr 8, s. 1789-1799Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    AimThe aim of this study is to explore the influence of nurse-led self-care advice on healthcare utilization and patients' satisfaction with telephone nursing.BackgroundMany consultations in high-cost settings are for conditions that are manageable through self-care and callers with greater satisfaction with the nurse interaction are nearly four times more likely to engage in self-care.DesignCross-sectional study.MethodsQuestionnaires were sent out to 500 randomly selected callers to the Swedish Healthcare Direct in Northern Sweden during March 2014. Callers were asked about their satisfaction with the consultation, their intended actions prior to consultation, the recommendation given by the nurse and the action undertaken after the call.ResultsYoung callers and persons recommended watchful waiting or recurrence if no improvements were significantly less satisfied with their care. When calling on their own behalf, both men and women rated the severity of their symptoms equally and were advised to self-care to the same extent. Self-care advice had a constricting influence on self-reported healthcare utilization, with 66·1% of cases resulting in a lower level of care than first intended. Feeling reassured after the call was the aspect of nursing care that influenced satisfaction the most.ConclusionReceiving self-care advice rather than referral to a general practitioner influences patient satisfaction negatively. Feeling reassured after consultation is strongly related to satisfaction, which in turn has been found to increase the likelihood of engaging in self-care behaviour.

  • 4.
    Gustafsson, Silje
    et al.
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Omvårdnad.
    Sävenstedt, Stefan
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Omvårdnad.
    Martinsson, Jesper
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Välivaara, Britt-Marie
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Omvårdnad.
    Need for reassurance in self-care of minor illnesses2018Ingår i: Journal of Clinical Nursing, ISSN 0962-1067, E-ISSN 1365-2702, Vol. 27, nr 5-6, s. 1183-1191Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    AIMS AND OBJECTIVES:

    This study describes people's need for reassurance in self-care of minor illnesses.

    BACKGROUND:

    Self-care and active surveillance are advocated as important strategies to manage minor illnesses. Reassurance influences patient satisfaction and confidence in the practicing of self-care.

    DESIGN:

    This study is a descriptive and interpretive qualitative study.

    METHODS:

    Twelve persons with experience in self-care and receiving self-care advice were recruited, and data were collected using semi-structured interviews between September and December 2014. Data were analyzed using qualitative content analyses.

    RESULTS:

    Having previous experience and the ability to actively manage symptoms using self-care interventions was described as reassuring. Participants became stressed and concerned when the symptoms persisted and interventions lacked the desired effect, which often resulted in a decision to consult. Participants wanted to feel that the nurse was an actual person, who was sympathetic, present and understanding, when they received self-care advice. The nurse's assessment and reasoning of the symptoms facilitated care-seekers' assessments of risk, and clear and concrete advice on how to manage the symptoms exerted a calming effect. Patients needed to trust that the nurse understood their situation to embrace the advice, and being invited to return created a feeling that the nurse had listened and taken them seriously.

    CONCLUSION:

    Reassurance has the potential to allay doubts and fears to build confidence, which influences self-care and consultation behavior. Personal presence in the encounter, receiving an assessment and an explanation of the symptoms and precise advice are reassuring. This article is protected by copyright. All rights reserved.

  • 5.
    Gustafsson, Silje
    et al.
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Omvårdnad.
    Vikman, Irene
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Hälsa och rehabilitering.
    Sävenstedt, Stefan
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Omvårdnad.
    Martinsson, Jesper
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Perceptions of needs related to the practice of self-care for minor illness2015Ingår i: Journal of Clinical Nursing, ISSN 0962-1067, E-ISSN 1365-2702, Vol. 24, nr 21-22, s. 3255-3265Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Aims and objectivesThe aim of this study was to describe people's perceptions of needs to feel confident in self-care for minor illnesses as well as their perceptions about supporting and obstructing factors in the practice of self-care.BackgroundMinor illness constitutes a large part of primary care, and patients' attendance to doctors' appointments for minor illness has been seen to increase future attendance for the same condition. Almost half of the consultations with telenurses result in the provision of self-care advice.DesignA cross-sectional survey.MethodPrimary data were collected using a questionnaire, and the study participants (n = 315) were randomly selected from the national Swedish address register.ResultsHaving knowledge and receiving health care advice and reliable information were perceived to be needs in order for participants to feel confident in self-care. Having family or friends to consult with was perceived to be a positive factor influencing confidence in self-care, especially for persons under the age of 35. Health care services were perceived to support self-care practice by offering easy access to care, giving information about self-care, and offering increased follow-up after consultations. Lack of knowledge, along with difficulties being away from work, were obstructing factors in the practice of self-care.ConclusionsYoung age was the factor influencing people's perceptions of needs and supporting factors the most. Young age and low knowledge scores about minor illnesses were the two factors that had the most influence on perceived obstructing factors.Relevance to clinical practiceNurses play a major role in the promotion of self-care and in the dissemination of self-care advice. If health care services fail to meet the needs of care-seekers with minor illnesses, patients might turn to out-of-hours clinics and emergency departments for help.

  • 6. Hägglund, Fredrik
    et al.
    Martinsson, Jesper
    Carlson, Johan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Flaw detection in layered media based on parametric modeling of overlapping ultrasonic echoes2006Ingår i: Proceedings: 2006 IEEE Ultrasonics Symposium : Vancouver, Canada, 3 - 6 October 2006, Piscataway, NJ: IEEE Communications Society, 2006, s. 136-139Konferensbidrag (Refereegranskat)
    Abstract [en]

    In materials consisting of several thin layers, multiple reflections within the structure give rise to received ultrasonic signals composed of overlapping echoes. In this paper we present a parametric model that can be used to decompose such signals into the individual reflections. We derive a Maximum Likelihood Estimator for the the model parameters, which are then used in a Generalized Likelihood Ratio Test (GLRT) to detect flaws in multi-layered structures. We show with simulations how the presence of a thin bonding layer in a three-layer structure can be detected. The probability of detection is shown to be ≈ 96%, for a signal-to-noise ratio (SNR) of 15 dB and a probability of false alarm of 5%.

  • 7. Hägglund, Fredrik
    et al.
    Martinsson, Jesper
    Carlson, Johan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Carlander, Carl
    D-Flow Technology AB.
    Model-based characterization of thin layers using pulse-echo ultrasound2008Ingår i: Proceedings of the International Congress on Ultrasonics: Vienna, April 9-13, 2007, Paper ID 1562, Session R17, 2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    Measurements performed on a thin multilayered structure will imply a received signal waveform consisting of reverberant overlapping echoes. In this paper the multi-layered structure is modeled by a physical model and the Maximum Likelihood Estimator (MLE) is derived for the model parameters. A general recursive expression for the model is given. The model is evaluated using measurements on a thin three-layered structure, where two glass layers are bonded together. We show that measured signal waveforms can be reconstructed using the estimated parameters, and that physical properties can be extracted from the estimated model parameters. Simulations also show that physical parameters can be estimated for thicknesses of the bonding layer down to 50 μm for a wavelength of 200 μm of the ultrasonic pulse.

  • 8. Hägglund, Fredrik
    et al.
    Martinsson, Jesper
    Carlson, Johan E.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Model-based classification of thin layers in multi-layered materials using nondestructive ultrasonic testing2008Ingår i: Paper summaries CD-ROM, ASNT fall conference & quality testing show 2008: Charleston, SC, November 10 - 14, 2008, Columbus, Ohio: American Society for Nondestructive Testing , 2008, s. 213-220Konferensbidrag (Refereegranskat)
  • 9. Hägglund, Fredrik
    et al.
    Martinsson, Jesper
    Carlson, Johan E.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Ultrasonic imaging of thin layers within multi-layered structures2008Ingår i: 2008 IEEE International Ultrasonics Symposium: IUS ; Beijing, China, 2 - 5 November 2008, New York: IEEE Communications Society, 2008, s. 828-831Konferensbidrag (Refereegranskat)
    Abstract [en]

    In the area of process control, non-destructive testing (NDT) using ultrasound is valuable due to its noninvasive properties. In process control, imaging of surface profiles is used to locate defects or problematic areas in order to quickly steer the manufacturing process on track again. This paper presents a method for imaging of parallel thin layers within multi-layered structures. Due to the application in process control a parametric model is used, and all subsequent analysis is performed on the model parameters rather than on the signal waveforms, resulting in a necessary data reduction. The parameters in the model are directly connected to physical properties, such as the reflection coefficients, time-of-flights, and attenuation coefficients. Experimental results shows that the estimated model parameters can be used in imaging of thin layer properties within the material structure. Images of embedded layers with a thickness about the wavelength is shown. Result also show that flaws can be detected in such structures. The results are verified by comparing the images to visual inspections of photographs.

  • 10.
    Lemlikchi, Safia
    et al.
    Division milieu ionisés et lasers, Centre de Developpement des Technologies Avancees, Algiers, Algeria.
    Martinsson, Jesper
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Hamrit, Ahmed
    ALGESCO, Blida, Algeria.
    Djelouah, Hakim
    Universite´ des Sciences et de la Technologie Houari Boumediene, Algiers, Algeria.
    Asmani, Mohammed
    Université d’Alger 1, Algiers, Algeria.
    Carlson, Johan E.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Correction to: Ultrasonic Characterization of Thermally Sprayed Coatings2019Ingår i: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 28, nr 3, s. 591-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The first name of author Ahmed Hamrit was misspelled as “Ahmet” in the original article. Please note that the correct spelling of his name is “Ahmed” as shown in this correction. 

  • 11.
    Lemlikchi, Safia
    et al.
    Division milieu ionisés et lasers, Centre de Developpement des Technologies Avancees, Algiers, Algeria.
    Martinsson, Jesper
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Hamrit, Ahmet
    ALGESCO, Blida, Algeria.
    Djelouah, Hakim
    Universite´ des Sciences et de la Technologie Houari Boumediene, Algiers, Algeria.
    Asmani, Mohammed
    Université d’Alger 1, Algiers, Algeria.
    Carlson, Johan E.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Ultrasonic Characterization of Thermally Sprayed Coatings2019Ingår i: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 28, nr 3, s. 391-404Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper describes the simultaneous determination of the ultrasonic parameters in thermally sprayed coatings. The parameters of interest are the longitudinal wave velocity and the ultrasonic attenuation. The test materials are two cobalt-based coatings (FSX 414 and Diamalloy 4060), both deposited onto stainless steel (310SS) substrates. The ultrasonic measurements were carried out in the pulse-echo configuration using several transducers. The ultrasonic signals reflected from the coatings were successfully estimated using the combined model, together with the maximum likelihood estimation and the Levenberg–Marquardt approach. The best estimate was obtained for 20 MHz measurements. Once the model was validated, the ultrasonic parameters of the thermally sprayed coatings were extracted. Model validation is based on the analysis of the residual between measured and estimated signals. Results showed non-dispersive ultrasonic velocities with average values of (3940±50)m/s" role="presentation" style="box-sizing: border-box; display: inline-table; line-height: normal; letter-spacing: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; position: relative;">(3940±50)m/s(3940±50)m/s in Diamalloy 4060 and (4260±20)m/s" role="presentation" style="box-sizing: border-box; display: inline-table; line-height: normal; letter-spacing: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; position: relative;">(4260±20)m/s(4260±20)m/s in FSX 414. High ultrasonic attenuation with a quadratic frequency dependence was observed for both materials. Moreover, it was found that the ultrasonic parameters in thermally sprayed materials are microstructure dependent. For close densities, the harder the coating, the higher the ultrasonic wave velocity and attenuation.

  • 12.
    Martinsson, Jesper
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Compensating distortion effects in repeated measurements under non-stationary conditions2009Ingår i: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 20, nr 2Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper a compensation technique is presented for applications using repeated measurements under moderate non-stationary measurement conditions. The assumption is that the measurement conditions are stationary during a single repeated measurement but non-stationary over the entire measurement time. The objective with repeated measurements is often to retrieve an estimate of the (noise reduced) signal and its uncertainties. In order to obtain accurate estimates of these two quantities, stationary measurement conditions must be guaranteed under the measurement time. A condition that in many situations is difficult to achieve, e.g., during long measurement times or in a rapidly changing environment. The proposed method compensates for linear dynamic changes during the measurement time, where the dynamical changes, the underlying signal waveform and the noise covariance are considered unknown. The theoretical effect of moderate non-stationary conditions on repeated measurements is analyzed and experimentally validated. Estimation results using the proposed technique are presented for repeated ultrasonic measurements under non-stationary temperature conditions. The results show accurate signal estimation and noise characterization with uncorrelated normally distributed residuals, in contrast to standard synchronization techniques

  • 13.
    Martinsson, Jesper
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Estimating the underlying signal waveform, noise covariance and synchronization jitter from unsynchronized measurements2008Ingår i: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 19, nr 2Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper a new synchronization technique is presented for applications using repeated measurements or experiments with periodically excited signals. The objective with repeated or periodic measurements is often to retrieve an estimate of the (noise reduced) signal and its uncertainties. However, these measurements need to be synchronized to obtain accurate estimates. Existing synchronization techniques are limited to specific signal and noise conditions, such as white Gaussian noise or narrowband signals, to achieve good performance. The proposed method, not limited by these conditions, extracts statistical information regarding the underlying signal and the noise contained in the measurements, to obtain good synchronization (asymptotically optimal). The Cramér-Rao lower bound (CRLB) is derived for the synchronization problem, including bounds for the underlying signal waveform and the covariance of the measurement noise, both considered unknown. The method, which is shown to be the maximum-likelihood estimator (MLE) in both white and colored Gaussian noise, is compared with the CRLB along with standard sub-sample estimation and aligning techniques using Monte Carlo simulations. The results show significant mean square error (MSE) improvements compared to standard synchronization techniques. Synchronization results using the proposed technique are presented for repeated ultrasonic measurements, to validate the method in a real measurement situation, and to experimentally support theoretical results.

  • 14.
    Martinsson, Jesper
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Evaluating the effect on seismicity of a hydraulic fracturing trial using Bayesian data analysis2018Ingår i: Caving 2018 / [ed] Y Potvin and J Jakubec, 2018, s. 451-658Konferensbidrag (Refereegranskat)
    Abstract [en]

    During the summer of 2017, a hydraulic fracturing trial was performed in the crown pillar of one of the orebodies in LKAB’s mine in Malmberget. Mucking in the orebody beneath the crown pillar recommenced in September 2017, after being shut down since April 2015. The mucking was shut down in 2015 because a number of large seismic events had caused significant disturbances in the nearby town, with vibration up to 35 mm/s. A research project was started with the final goal to start up production again with less disturbance to the town. Hydraulic fracturing was determined to be an interesting method for improving caveability of the crown pillar, and a trial was set up. The trial consisted of partially fracturing three boreholes drilled from the ground surface into the crown pillar, which is between 550 and 650 m thick at the trial location. Hydraulic fractures were placed with 2.5 m spacing at the bottom 50 m of each hole. As part of the evaluation of the effectiveness of the trial, the seismicity before and after the hydraulic fracturing trial has been compared using standard Bayesian techniques to infer differences. The analysis show a difference in b-value before and after the trial, which is demonstrated by the parameter 𝛥b having a positive value. The 95% high density interval (HDI) of 𝛥b excludes the value of zero, which gives confidence in the conclusion. The difference in b-value depends on the choice of magnitude of completeness, so it is recommended that the analysis is repeated with a method using all recorded events, i.e. using the full dataset.

  • 15.
    Martinsson, Jesper
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Statistical tools for ultrasonic analysis of dispersive fluids2006Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    This thesis focuses on the possibility of using ultrasonic measurement techniques for energy gas characterization. The idea is to combine both on-line flow measurements with non-invasive fluid characterization in the same measurement setup using the same sensor(s). The long-term goal of the project is to develop measurement methods based on ultrasonic techniques that can measure; the flow rate, the energy content, detect impurities, and estimate the composition. In this thesis different problems concerning gas characterization and modeling are addressed. The information obtained from ultrasonic measurements are limited to spectral variations in the attenuation and phase velocity. Hence, part of the research is focused on estimating these quantities accurately with low uncertainty. Another area is parametric modeling and identification of the bulk modulus, where a new model structure for gas mixtures with complex dynamic behavior and/or unknown components is presented, capable of handling the combined effect of the absorption mechanisms. Finally, the problem of estimating the composition of a gas mixture is considered. The results show that it is possible to estimate the composition of processed and upgraded biogas, with high accuracy and precision, by combining the developed estimation techniques with multiple linear regression methods. The thesis consists of two parts. The first part includes an introduction to the research area together with a short summary of the contributions. The second part contains a collection of four papers describing the research.

  • 16.
    Martinsson, Jesper
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Ultrasonic measurement principles: modeling, identification, and parameter estimation2008Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    This thesis presents contributions within the fields of ultrasonic modeling and measurement technology, with focus on solutions to difficult modeling and measurement problems. The work is divided into two categories: 1) processing of measurements obtained under non-ideal conditions, such as unsynchronized, distorted, and superimposed signals; 2) estimating acoustic models and parameters from materials, fluids, fluid mixtures, and thin-layered structures. The ultrasonic research field has traditionally been focused on either physical models to describe acoustic properties based on wave propagation experiments, or on statistical/empirical models to describe more complex systems. Physical models have the advantage that the parameters are directly connected to physical properties of the media, enabling an understanding of the underlying dynamics and simplifying the inverse problem. However, their disadvantage is that the derivations are often based on crude approximations and ideal conditions; limitations often leading to correlated residuals, biased parameter estimates, and the necessity of calibration measurements to solve the inverse problem. Conversely, statistical or empirical models often describe the measured data well with uncorrelated residuals, but have the disadvantage that the parameters (or models) are not directly connected to the physical properties of the material or fluid. In this case this connection is often retrieved through calibration. A key ingredient in the work presented in this thesis, is the use of a combination of physical and empirical models. This allows for a description of dynamic elements with both known and unknown structures, and the ability to have both uncorrelated residuals and unbiased parameter estimates related to the physical properties of the media. If sufficient prior knowledge exists of the physical structure and the location of possible non-ideal effects, calibration steps may be avoided or reduced significantly. This combination of hard physical structures with the variability of empirical models inherits advantages and disadvantages from both models. The benefits and limitations of the proposed solutions are analyzed and discussed, and the presented results are supported and validated with real experiments or with combinations of real experiments and simulations

  • 17. Martinsson, Jesper
    et al.
    Carlson, Johan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Parametric estimation of ultrasonic phase velocity and attenuation in dispersive media2006Ingår i: Ultrasonics, ISSN 0041-624X, E-ISSN 1874-9968, Vol. 44, nr Supplement 1, s. e991-e994Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In ultrasonic characterization of liquids, gases, and solids, accurate estimation of frequency dependent attenuation and phase velocity is of great importance. Non-parametric methods, such as Fourier analysis, suffers from noise sensitivity, and the variance of the estimated quantities is limited by the signal-to-noise ratio. In this paper we present a parametric method for estimation of these properties. Pulse echo experiments in ethane, oxygen and mixtures of the two show that the proposed method can estimate phase velocity and attenuation with up to 50 times lower variance than standard non-parametric methods.

  • 18. Martinsson, Jesper
    et al.
    Carlson, Johan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Parametric modeling of wave propagation in gas mixtures: a system identification approach2005Ingår i: 2005 IEEE Ultrasonics Symposium: 18 - 21 September 2005, Rotterdam, the Netherlands, Piscataway, NJ: IEEE Communications Society, 2005, s. 2288-2292Konferensbidrag (Refereegranskat)
    Abstract [en]

    In ultrasonic pulse-echo systems, the observable properties are restricted to frequency dependent attenuation and phase velocity, which in turn are related to the material properties of the investigated media. In this paper we present a parametric model of the bulk modulus, composed of the basic physical building blocks of absorption (relaxation blocks). The parametric model is capable of handling the combined effect of the absorption mechanisms present in a gas or gas mixture and captures the experimental variation in the observation. The performance of the parametric model is demonstrated with pulse-echo experiments in oxygen, ethane and mixtures of the two. Compared to standard Fourier analysis techniques, the parametric model gives higher accuracy when estimating attenuation and phase velocity, and physical parameters such as relaxation strengths and relaxation frequencies can be extracted from it.

  • 19.
    Martinsson, Jesper
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Carlson, Johan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system. Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Niemi, Jan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Model-based phase velocity and attenuation estimation in wideband ultrasonic measurement systems2007Ingår i: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, ISSN 0885-3010, E-ISSN 1525-8955, Vol. 54, nr 1, s. 138-146Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A parametric method to estimate frequencydependent phase velocity and attenuation is presented in this paper. The parametric method is compared with standard nonparametric Fourier analysis techniques using numerical simulations as well as real pulse-echo experiments. Approximate standard deviations are derived for bothmethods and validated with numerical simulations. Compared to standard Fourier analysis, the parametric model gives considerably lower variance when estimating attenuation and phase velocity. In contrast to nonparametric techniques, the proposed estimator avoids the phase unwrapping problem because analytical expressions for thecontinuous phase velocity and attenuation can be derived.

  • 20.
    Martinsson, Jesper
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Gustafsson, Silje
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Omvårdnad.
    Modeling the effects of telephone nursing on healthcare utilization2018Ingår i: International Journal of Medical Informatics, ISSN 1386-5056, E-ISSN 1872-8243, Vol. 113, s. 98-105Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Background

    Telephone nursing is the first line of contact for many care-seekers and aims at optimizing the performance of the healthcare system by supporting and guiding patients to the correct level of care and reduce the amount of unscheduled visits. Good statistical models that describe the effects of telephone nursing are important in order to study its impact on healthcare resources and evaluate changes in telephone nursing procedures

    Objective

    To develop a valid model that captures the complex relationships between the nurse's recommendations, the patients’ intended actions and the patients’ health seeking behavior. Using the model to estimate the effects of telephone nursing on patient behavior, healthcare utilization, and infer potential cost savings.

    Methods

    Bayesian ordinal regression modelling of data from randomly selected patients that received telephone nursing. Inference is based on Markov Chain Monte Carlo (MCMC) methods, model selection using the Watanabe-Akaike Information Criteria (WAIC), and model validation using posterior predictive checks on standard discrepancy measures.

    Results and Conclusions

    We present a robust Bayesian ordinal regression model that predicts three-quarters of the patients’ healthcare utilization after telephone nursing and we found no evidence of model deficiencies. A patient's compliance to the nurse's recommendation varies and depends on the recommended level of care, its agreement with and level of the patient's prior intention, and the availability of different care options at the time. The model reveals a risk reducing behavior among patients and the effect of the telephone nursing recommendation is 7 times higher than the effect of the patient's intended action prior to consultation if the recommendation is the highest level of care. But the effect of the nurse's recommendation is lower, or even non-existing, if the recommendation is self-care. Telephone nursing was found to have a constricting effect on healthcare utilization, however, the compliance to nurse's recommendation is closely tied to perceptions of risk, emphasizing the importance to address caller's needs of reassurance

  • 21. Martinsson, Jesper
    et al.
    Hägglund, Fredrik
    Carlson, Johan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Estimating the underlying signal waveform and synchronization jitter from repeated measurements2006Ingår i: Proceedings: 2006 IEEE Ultrasonics Symposium : Vancouver, Canada, 3 - 6 October 2006, Piscataway, NJ: IEEE Communications Society, 2006, s. 440-443Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper we present a synchronization technique, for applications using repeated or periodically excited measurements. The problem with existing techniques is their limitations to specific signal and noise conditions, such as white Gaussian noise or narrowband signals. The proposed method extracts statistical information about the underlying signal and noise in the measurements to obtain good synchronization (asymptotically optimal). The Cramér-Rao lower bound (CRLB) is derived for the synchronization problem, including bounds for the underlying signal waveform and the covariance of the noise. The method, which is the maximum-likelihood estimator for both white and colored Gaussian noise, is compared with standard sub-sample estimation and aligning techniques using Monte Carlo simulations. The results show significant improvements compared to standard synchronization techniques.

  • 22. Martinsson, Jesper
    et al.
    Hägglund, Fredrik
    Carlson, Johan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Separation of dispersive coinciding signals by combining hard and soft modeling2008Ingår i: Proceedings of the International Congress on Ultrasonics: Vienna, April 9-13, 2007, Paper ID 1563, Session R17, 2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    In some ultrasonic measurement situations, an adequate signal separation is difficult to achieve. A typical situation is material characterization of thin media, relative to the emitted signal's time support. In this paper a new method is proposed that enables accurate signal separation of measured coinciding signals in the postprocessing stage. The method is based on a combination of hard physical and soft empirical models, which allows for a description of both known and unknown dynamics making the separation possible. The proposed technique is verified using real measurements on thin dispersive samples and validated with residual analysis.

  • 23. Martinsson, Jesper
    et al.
    Hägglund, Fredrik
    Carlson, Johan E.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Complete post-separation of overlapping ultrasonic signals by combining hard and soft modeling2008Ingår i: Ultrasonics, ISSN 0041-624X, E-ISSN 1874-9968, Vol. 48, nr 5, s. 427-443Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In some ultrasonic measurement situations, an adequate signal separation is difficult to achieve. A typical situation is material characterization of thin media using pulse-echo or through-transmission techniques, when the time-of-flight in the media is shorter than the emitted signal's time support. Separated signals are necessary to obtain accurate estimates of material properties and transit times. In this paper a new method is proposed that enables complete post separation of measured coinciding signals. The method is based on a combination of hard physical and soft empirical models, which allows for a description of both known and unknown properties making a complete separation possible. The validity and limitations of the model and the separation results are thoroughly addressed. The proposed technique is verified using real measurements on thin dispersive samples and validated using residual analysis. The experimental results show a complete separation with uncorrelated and normally distributed residuals. The method enables characterization and/or flow analysis in difficult overlapping situations.

  • 24.
    Martinsson, Jesper
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper. Department of Mining Technology, Luossavaara-Kiirunavaara AB, 98381 Malmberget.
    Jonsson, Adam
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    A New Model for the Distribution of Observable Earthquake Magnitudes and Applications to b-Value Estimation2018Ingår i: IEEE Geoscience and Remote Sensing Letters, ISSN 1545-598X, E-ISSN 1558-0571, Vol. 15, nr 6, s. 833-837Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The b-value in the Gutenberg–Richter (GR) law contains information that is essential for evaluating earthquake hazard and predicting the occurrence of large earthquakes. Estimates of b are often based on seismic events whose magnitude exceed a certain threshold, the so-called magnitude of completeness. Such estimates are sensitive to the choice of threshold and often ignore a substantial portion of available data. We present a general model for the distribution of observable earthquake magnitudes and an estimation procedure that takes all measurements into account. The model is obtained by generalizing previous probabilistic descriptions of sensor network limitations and using a generalization of the GR law. We show that our model is flexible enough to handle spatio-temporal variations in the seismic environment and captures valuable information about sensor network coverage. We also show that the model leads to significantly improved b-value estimates compared with established methods relying on the magnitude of completeness.

  • 25.
    Martinsson, Jesper
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper. Luossavaara-Kiirunavaara AB (LKAB), R&D, Kiruna, Sweden.
    Törnman, Wille
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi. Luossavaara-Kiirunavaara AB (LKAB), R&D, Kiruna, Sweden.
    Modelling the Dynamic Relationship Between Mining Induced Seismic Activity and Production Rates, Depth and Size: A Mine-Wide Hierarchical Model2019Ingår i: Pure and Applied Geophysics, ISSN 0033-4553, E-ISSN 1420-9136Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The dynamic properties of mining induced seismic activity with respect to production rate, depth and size are studied in seven orebodies in the same underground iron ore mine. The objective is to understand the relationship between the measured seismic activity and the: seismic decay time, planned production rate, production size and mining depth. This relationship is the first step to individually customise the production rate for each orebody in the mine, make short-term predictions of future seismicity given planned productions, and to find out in what way the available predictors affect the seismicity. The seismic response with respect to the dependent variables is parametrised and the estimated decay times for each orebody, which are of particular interest here, are compared. An autoregressive model is proposed to capture the dynamic relationship between the induced seismic activity, the current production rate and the past seismic activity. Bayesian estimation of the parameters is considered and parameter constraints are incorporated in the prior distributions. The models for all orebodies are tied together and modelled hierarchically to capture the underlying joint structure of the problem, where the mine-wide parameters are learnt together with the individual orebody parameters from the observed data. Comparisons between the parameters from the hierarchical model and independent models are given. Group-level regressions reveal dependencies on size and mining depth. Model validation with posterior predictive checking using several discrepancy measures could not detect any model deficiencies or flaws. Posterior predictive intervals are evaluated and inference of model parameters are presented.

  • 26.
    Melander, Catharina
    et al.
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Omvårdnad.
    Martinsson, Jesper
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Gustafsson, Silje
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Omvårdnad.
    Measuring Electrodermal Activity to Improve the Identification of Agitation in Individuals with Dementia2017Ingår i: Dementia and geriatric cognitive disorders extra, E-ISSN 1664-5464, Vol. 7, nr 3, s. 430-439Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Background: Understanding and interpreting the complexity of agitation in people with dementia is challenging. Objective: To explore whether a sensor measuring electrodermal activity (EDA) can improve the identification of agitation in individuals with dementia. Methods: Nine individuals with dementia wore a sensor that measured EDA. During the same time, assistant nurses annotated the observed behavior of the person with dementia. A binary logistic regression model was applied to assess the relationship between the sensor and the assistant nurses’ structured observations of agitation. Results: The sensor values correlated with the assistant nurses’ observations both at the time of the observation and 1 and 2 h prior to the observation. Conclusion: A sensor measuring EDA can support early detection of agitation in persons with dementia

  • 27.
    Mishra, Madhav
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Martinsson, Jesper
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Rantatalo, Matti
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Goebel, Kai
    NASA Ames Research Center, Intelligent Systems Division, Moffett Field, CA.
    Bayesian hierarchical model-based prognostics for lithium-ion batteries2018Ingår i: Reliability Engineering & System Safety, ISSN 0951-8320, E-ISSN 1879-0836, Vol. 172, s. 25-35Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    To optimise operation and maintenance, knowledge of the ability to perform the required functions is vital. The ability is governed by the usage of the system (operational issues) and availability aspects like reliability of different components. This paper proposes a Bayesian hierarchical model (BHM)-based prognostics approach applied to Li-ion batteries, where the goal is to analyse and predict the discharge behaviour of such batteries with variable load profiles and variable amounts of available discharge data. The BHM approach enables inferences for both individual batteries and groups of batteries. Estimates of the hierarchical model parameters and the individual battery parameters are presented, and dependencies on load cycles are inferred. A BHM approach where the operational and reliability aspects end of life (EoD) and end of life (EoL) is studied where its shown that predictions of EoD can be made accurately with a variable amount of battery data. Without access to measurements, e.g. predicting a new battery, the predictions are based only on the prior distributions describing the similarity within the group of batteries and their dependency on the load cycle. A discharge cycle dependency can also be identified in the result giving the opportunity to predict the battery reliability.

  • 28.
    Mishra, Madhav
    et al.
    Division of Operation and Maintenance Engineering within the framework of the SKF-University of Technology Centre (UTC).
    Martinsson, Jesper
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper. Luossavaara-Kiirunavaara AB.
    Rantatalo, Matti
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Goebel, Kai
    NASA Ames Research Center, Intelligent Systems Division, Moffett Field, CA, USA.
    Hierarchical model-based prognostics for Li-ion batteries2018Ingår i: Advances In ENGINEERINGArtikel i tidskrift (Övrig (populärvetenskap, debatt, mm))
    Abstract [en]

    Recent global trend towards a fossil-fuel-free society has yielded the rapid soar in demand of electrically powered systems. Specifically, the demand for battery powered systems has fueled the desire to have better performing batteries with lithium-ion batteries being the most widely used. Presently, for application in unmanned vehicles, exploratory rovers, submarines among others demand a better comprehension of battery performance metrics. Case and point, battery capacity and state of charge have become increasingly vital when it comes to determining the end of discharge. As of now, several techniques have already been established for determining such parameters. Unfortunately, their prognostic capability for determining remaining battery charge is still not optimal. Therefore, there is a need to develop prognostic and health management technology for critical systems (such as Mars rovers) to successfully predict and manage the lifetime of batteries, monitor their health state in real time, evaluate the performance and predict the remaining useful life.

    To this note, Luleå University of Technology researchers in Sweden: Dr. Madhav Mishra, Dr. Jesper Martinsson, and Dr. Matti Rantatalo in collaboration with Dr. Kai Goebel at NASA in the United States proposed a study whose main objective was to measure the battery discharge and predict the end of discharge considering the operating conditions for lithium ion batteries. To be precise, they purposed on employing a Bayesian Hierarchical Model (BHM)-based end of discharge prognostic for Li-ion batteries. Their work is currently published in the research journal, Reliability Engineering and System Safety.

    The research technique employed entailed the utilization of two batteries with 16 discharge events with a simplified battery circuit model of the battery. Next, the research team examined the detailed discharge voltage profiles during different discharging cycles with variable load profiles. They then proceeded to demonstrate the BHM approach and group-level dependencies by utilizing more than one battery and more than one discharge cycle.

    The authors observed that the BHM approach enabled inferences for both individual batteries and groups of batteries. The researchers then recorded the estimates of the hierarchical model parameters and the individual battery parameters after which their dependencies on load cycles were inferred. In addition, they noted that by using the BHM approach the predictions of end of discharge could be made accurately with a variable amount of battery data. Furthermore, this technique was seen to applicable even for new batteries without prior recorded data where the predictions were based only on the prior distributions describing the similarity within the group of batteries and their dependency on the load cycle.

    In conclusion, the study presented a Bayesian hierarchical model (BHM)-based prognostics approach for Li-ion batteries, where the goal was to analyze and predict the discharge behavior of such batteries with variable load profiles and variable amounts of available discharge data. The results obtained showed that the technique could address cases with or without data. Altogether, the proposed method can capture additional relationships between parameters and use it to improve prognostics. Lastly, the BHM approach has been seen to permit inference at both the individual battery level and group of battery level.

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