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Coming dissertations at Uppsala university

  • Characterisation of natural dissolved organic matter with liquid chromatography and high resolution mass spectrometry Author: Claudia Patriarca Link: Publication date: 2020-06-11 10:32

    Dissolved organic matter (DOM) is one of the most heterogeneous and complex mixture on Earth. DOM plays a crucial role in biogeochemical processes on the global scale and it is essential to sustain and regulate the biological processes in aquatic ecosystems. DOM originates from a multitude of biological, physical and chemical transformations, leading to its phenomenal chemical diversity. In order to understand and predict its effect on the global carbon cycle, an intimate characterization at molecular level is necessary. The investigation of the extraordinary complexity of the DOM mixture represents a compelling challenge for analytical chemistry. The focus of this thesis was the development of methods for the characterization of DOM in natural waters. High resolution mass spectrometry (HRMS), was combined with high pressure liquid chromatography (HPLC) and electrospray ionization (ESI), to investigate the chemical diversity of DOM. The first study demonstrated that cutting-edge techniques (such as the Fourier-transform ion cyclotron resonance mass spectrometer - FTICR-MS), are not indispensable to disclose essential information on the DOM molecular composition, in fact the Orbitrap mass analyser is a suitable alternative for the analysis of complex natural mixtures. In the second study, the potential benefits offered by the online coupling of HPLC and HRMS instruments were explored, revealing significant advantages in terms of analysis time, achievable information and versatility of the method. The advantages of online separation were further confirmed in the third study, focused on the characterization of autochthonous labile DOM. Chromatographically resolved profiles emerged from the bulk-DOM, allowing the monitoring of labile autochthonous components in presence of heterotrophic bacteria. Despite the advantages achieved by the application of online separation, a strong limiting factor in DOM characterization is the ESI source, suitable only for the analysis of the DOM fraction susceptible to ionization. In the last study, the extent of the DOM material prone to ionization was estimated, revealing the occurrence of an extensive portion of the material resistant to routinely employed ESI approach. The full characterization of DOM is still an open challenge and the combination of multiple techniques is fundamental to unravel is extreme intricacy.

  • Studies of sympathetic nerve activity in cutaneous nerves in healthy subjects using intraneural microneurography : The relationship between nerve activity and effector organ response Author: Pirkko Hynninen Link: Publication date: 2020-06-10 10:01

    The aim of the research presented in this thesis is to gain new knowledge of the characteristic features of sympathetic nerve activity of cutaneous nerves in healthy adult humans using intraneural microneurography. One further goal is to study the relationship between nerve activity and effector organ response.

    The study has three main aims: I) to study temperature regulating mechanisms in human subjects, rhythm generating mechanism of nerve activity and the relationship between nerve activity and effector organs, including sweat glands and blood vessels, II) to study regional similarities and differences in sympathetic nerve activity recorded from different cutaneous nerves, III) to study effector organ response, without central nervous system influences, through intraneural stimulation after proximal nerve blocking.

    The most important results are as follows: 1) By exposing a human subject to warm and cold environments, it is possible to obtain selective activation of either the sudomotor or vasoconstrictor neural system. 2) Bursts of both sudomotor and vasoconstrictor activity occur at certain intervals and several types of rhythmic activity can be observed. 3) Sudomotor bursts have a shorter duration compared to vasoconstrictor bursts. 4) The rhythm generating mechanisms may help to restrict the firing rates of individual nerve fibres to low ranges, which provides high gain in the neuroeffector transfer function. 5) Simultaneous double nerve recordings provide evidence that in the distal glabrous skin area the thermoregulatory functions are mainly executed via vasoconstrictor nerve fibres. Instead, sudomotor fibres are brought into action only at relatively high temperatures. In the hairy skin of forearm and hand reflex thermoregulation is to large extent executed via sudomotor nerve fibres. 6) Intraneural electrical stimulation of sympathetic postganglionic axons in human skin nerves after proximal nerve blocking shows differences between sudomotor and vasoconstrictor effector organ responses.

    These results improve our knowledge of the function of the sympathetic nervous system in healthy human subjects.

  • Inertial motion capture for ambulatory analysis of human movement and balance Author: Fredrik Olsson Link: Publication date: 2020-06-04 10:58

    Inertial sensors (accelerometers and gyroscopes) are ubiquitous in today’s society, where they can be found in many of our everyday mobile devices. These sensors are capable of recording the movement of the device, and by extension, the movement of humans carrying or interacting with the device. Human motion capture is frequently used for medical purposes to assess individual balance performance and movement disorders. Accurate and objective assessment is important in the design of individualized interventions and rehabilitation strategies.

    The increasing availability of inertial sensors, combined with their mobility and low cost, has made inertial motion capture highly relevant as a more accessible alternative to the laboratory based gold standard. However, mobile solutions need to be adopted for plug-and-play use with the end user in mind. Methods that automatically calibrate the sensors, and methods that detect and record relevant motions are required.

    This thesis contributes to the development of human inertial motion capture as a plug-and-play technology. A method for accelerometer calibration, which allows for compensation of systematic sensor errors, is proposed. The method fuses accelerometer and gyroscope data to allow dynamic rotation of the sensor during the calibration procedure. Other proposed methods handles sensor-to-segment calibration in a biomechanical model. The position of a joint center and the direction of a hinge joint’s rotation axis, are identified in each sensor’s intrinsic coordinate system. This is done by fitting recorded motions to the kinematic constraints of the underlying biomechanical model. The methods are evaluated on real sensor data collected from mechanical joint systems that mimics human limbs.

    The state of the current knowledge regarding objective human balance assessment isstudied in the form of a systematic review, that includes methods for modeling and identifying neuromuscular control of human balance. A similar modeling framework is then applied to identify feedback controllers in physical and artificial (simulated) systems. Finally, inertial sensors are applied in tremor quantification in Parkinson’s disease (PD) and essential tremor (ET). The method uses only the inertial sensors in a standard smart phone, and is applied on data from human subjects with PD or ET.