BeiDou-3 orbit and clock quality of the IGS Multi-GNSS Pilot Project

Within the Multi-GNSS Pilot Project (MGEX) of the International GNSS Service (IGS), precise orbit and clock products for the BeiDou-3 global navigation satellite system (BDS-3) are routinely generated by a total of five analysis centers. The processing standards and specific properties of the individual products are reviewed and the BDS-3 orbit and clock product performance is assessed through direct inter-comparison, satellite laser ranging (SLR) residuals, clock stability analysis, and precise point positioning solutions. The orbit consistency evaluated by the signal-in-space range error is on the level of 4-8 cm for the medium Earth orbit satellites whereas SLR residuals have RMS values between 3 and 9 cm. The clock analysis reveals sytematic effects related to the elevation of the Sun above the orbital plane for all ACs pointing to deficiencies in solar radiation pressure modeling. Nevertheless, precise point positioning with the BDS-3 MGEX orbit and clock products results in 3D RMS values between 7 and 8 mm.Comment: 13 pages, 5 figure

Introducing Agile Methods in Undergraduate Curricula, a Systematic Mapping Study

Agile approaches to Software Engineering are widely used nowadays in industry and have also reached academic environments, with universities all around the world including agile related content in their programs. There are no formal studies about the current situation of Agile Software Development in Argentinian Universities. A systematic mapping study was conducted to understand the state of agile in undergraduate curricula. Results show that Agile Software Development is part of the Information Technology and Computer Science Programs and that Scrum is the most popular agile method in that context. There is little information regarding the teaching strategy used but a learningby- doing approach is used in many cases.VIII Workshop Innovación en Educación en Informática.Red de Universidades con Carreras en Informátic

Synthesis, Characterization, and Properties of Graphene-Based Hybrids with Cobalt Oxides for Electrochemical Energy Storage and Electrocatalytic Glucose Sensing

A library of graphene-based hybrid materials was synthesized as novel hybrid electrochemical electrodes for electrochemical energy conversion and storage devices and electrocatalytical sensing namely enzymeless glucose sensing. The materials used were supercapacitive graphene-family nanomaterials (multilayer graphene-MLG; graphene oxide-GO, chemically reduced GO-rGO and electrochemical reduced GOErGO) and pseudocapacitive nanostructured transition metal oxides including cobalt oxide polymorphs (CoO and Co3O4) and cobalt nanoparticles (CoNP). These were combined through physisorption, electrodeposition, and hydrothermal syntheses approaches. This project was carried out to enhance electrochemical performance and to develop electrocatalytic platforms by tailoring structural properties and desired interfaces. Particularly, electrodeposition and hydrothermal synthesis facilitate chemically-bridged (covalently- and electrostatically- anchored) interfaces and molecular anchoring of the constituents with tunable properties, allowing faster ion transport and increased accessible surface area for ion adsorption. The surface morphology, structure, crystallinity, and lattice vibrations of the hybrid materials were assessed using electron microscopy (scanning and transmission) combined with energy dispersive spectroscopy and selected-area electron diffraction, X-ray diffraction, and micro-Raman Spectroscopy. The electrochemical properties of these electrodes were evaluated in terms of supercapacitor cathodes and enzymeless glucose sensing platforms in various operating modes. They include cyclic voltammetry (CV), ac electrochemical impedance spectroscopy, charging-discharging, and scanning electrochemical microscopy (SECM). These hybrid samples showed heterogeneous transport behavior determining diffusion coefficient (4⨯10-8 – 6⨯10-6 m2/s) following an increasing order of CoO/MLG \u3c Co3O4/MLG \u3c Co3O4/rGOHT \u3c CoO/ErGO \u3c CoNP/MLG and delivering the maximum specific capacitance 450 F/g for CoO/ErGO and Co3O4/ rGOHT. In agreement with CV properties, these electrodes showed the highest values of low-frequency capacitance and lowest charge-discharge response (0.38 s – 4 s), which were determined from impedance spectroscopy. Additionally, through circuit simulation of experimental impedance data, RC circuit elements were derived. SECM served to investigate electrode/electrolyte interfaces occurring at the solid/liquid interface operating in feedback probe approach and imaging modes while monitoring and mapping the redox probe (re)activity behavior. As expected, the hybrids showed an improved electroactivity as compared to the cobalt oxides by themselves, highlighting the importance of the graphene support. These improvements are facilitated through molecular/chemical bridges obtained by electrodeposition as compared with the physical deposition

Introducing Agile Methods in Undergraduate Curricula, a Systematic Mapping Study

Agile approaches to Software Engineering are widely used nowadays in industry and have also reached academic environments, with universities all around the world including agile related content in their programs. There are no formal studies about the current situation of Agile Software Development in Argentinian Universities. A systematic mapping study was conducted to understand the state of agile in undergraduate curricula. Results show that Agile Software Development is part of the Information Technology and Computer Science Programs and that Scrum is the most popular agile method in that context. There is little information regarding the teaching strategy used but a learningby- doing approach is used in many cases.VIII Workshop Innovación en Educación en Informática.Red de Universidades con Carreras en Informátic

Introducing Agile Methods in Undergraduate Curricula, a Systematic Mapping Study

Agile approaches to Software Engineering are widely used nowadays in industry and have also reached academic environments, with universities all around the world including agile related content in their programs. There are no formal studies about the current situation of Agile Software Development in Argentinian Universities. A systematic mapping study was conducted to understand the state of agile in undergraduate curricula. Results show that Agile Software Development is part of the Information Technology and Computer Science Programs and that Scrum is the most popular agile method in that context. There is little information regarding the teaching strategy used but a learningby- doing approach is used in many cases.VIII Workshop Innovación en Educación en Informática.Red de Universidades con Carreras en Informátic

Coupling Scanning Electrochemical Microscopy and 3D Modelling to Probe Membrane Permeability of Human Bladder Cancer (T24) Cells

Scanning electrochemical microscopy (SECM) scans a biased ultramicroelectrode (≤ 25 µm) probe over a sample to characterize topography, physical properties and chemical reactivity. In this dissertation, SECM was used to investigate the metal-induced changes in membrane response of single live human bladder cancer cells (T24). SECM imaging was coupled to 3D finite element method (FEM) simulations which were the first of their kind, providing advanced quantification of sample traits under conditions not previously usable. The effects of Cd2+ on T24 cell membrane permeability were examined. Experimental depth-scan imaging was coupled with full 3D FEM simulations, eliminating many limitations of previous 2D-axially symmetric models. Hundreds of probe approach curves (PACs) can now be extracted from depth-images and theoretically fit to quantify membrane permeability at any location across the cell surface (Chapter 2). SECM was utilized to examine the membrane response of T24 cells following exposure to toxic dichromate (Cr(VI)). Two electrochemical mediators were examined, the membrane permeable ferrocenemethanol (FcCH2OH) and impermeable ferrocenecarboxylate (FcCOO‑). Cr(VI) induced permeability change was observed with both mediators and compared (Chapter 3). Chronic Cr(VI) induced cell stress, was then examined. Similar permeability curve shape was observed, with shifts in response time based on concentration of Cr(VI) stressor (Chapter 4). Trace essential metals such as Cr(III) are essential in low concentrations but toxic in high concentration. Membrane-response was investigated by SECM, using both FcCH2OH and FcCOO- redox mediators. Theoretical SECM depth-scans were produced using 3D FEM simulations, and used to quantify cell membrane permeability (Chapter 5). Complex close-proximity cell clusters were experimentally imaged by SECM 3D scanning mode. Tailored 3D model geometries were created, generating complimentary theoretical maps of the experimental cell clusters. The simulations were capable of providing a strong theoretical fit to the experimental results. Limits of cell proximity for SECM characterization were determined based on the probe size (Chapter 6). Nanoscale SECM imaging of single live cells were performed using a laser-pulled 130 nm radius Pt disk electrode. A tailored 3D model was created, from which cell topography was accurately characterized using membrane-impermeable Ru(NH3)63+, and cell membrane permeability was quantified with FcCH2OH (Chapter 7)

Replay detection in voice biometrics: an investigation of adaptive and non-adaptive front-ends

Among various physiological and behavioural traits, speech has gained popularity as an effective mode of biometric authentication. Even though they are gaining popularity, automatic speaker verification systems are vulnerable to malicious attacks, known as spoofing attacks. Among various types of spoofing attacks, replay attack poses the biggest threat due to its simplicity and effectiveness. This thesis investigates the importance of 1) improving front-end feature extraction via novel feature extraction techniques and 2) enhancing spectral components via adaptive front-end frameworks to improve replay attack detection. This thesis initially focuses on AM-FM modelling techniques and their use in replay attack detection. A novel method to extract the sub-band frequency modulation (FM) component using the spectral centroid of a signal is proposed, and its use as a potential acoustic feature is also discussed. Frequency Domain Linear Prediction (FDLP) is explored as a method to obtain the temporal envelope of a speech signal. The temporal envelope carries amplitude modulation (AM) information of speech resonances. Several features are extracted from the temporal envelope and the FDLP residual signal. These features are then evaluated for replay attack detection and shown to have significant capability in discriminating genuine and spoofed signals. Fusion of AM and FM-based features has shown that AM and FM carry complementary information that helps distinguish replayed signals from genuine ones. The importance of frequency band allocation when creating filter banks is studied as well to further advance the understanding of front-ends for replay attack detection. Mechanisms inspired by the human auditory system that makes the human ear an excellent spectrum analyser have been investigated and integrated into front-ends. Spatial differentiation, a mechanism that provides additional sharpening to auditory filters is one of them that is used in this work to improve the selectivity of the sub-band decomposition filters. Two features are extracted using the improved filter bank front-end: spectral envelope centroid magnitude (SECM) and spectral envelope centroid frequency (SECF). These are used to establish the positive effect of spatial differentiation on discriminating spoofed signals. Level-dependent filter tuning, which allows the ear to handle a large dynamic range, is integrated into the filter bank to further improve the front-end. This mechanism converts the filter bank into an adaptive one where the selectivity of the filters is varied based on the input signal energy. Experimental results show that this leads to improved spoofing detection performance. Finally, deep neural network (DNN) mechanisms are integrated into sub-band feature extraction to develop an adaptive front-end that adjusts its characteristics based on the sub-band signals. A DNN-based controller that takes sub-band FM components as input, is developed to adaptively control the selectivity and sensitivity of a parallel filter bank to enhance the artifacts that differentiate a replayed signal from a genuine signal. This work illustrates gradient-based optimization of a DNN-based controller using the feedback from a spoofing detection back-end classifier, thus training it to reduce spoofing detection error. The proposed framework has displayed a superior ability in identifying high-quality replayed signals compared to conventional non-adaptive frameworks. All techniques proposed in this thesis have been evaluated on well-established databases on replay attack detection and compared with state-of-the-art baseline systems

On the potential contribution of BeiDou-3 to the realization of the terrestrial reference frame scale

Since the release of the phase center calibrations for both the receivers and the satellites, the BeiDou Navigation Satellite System (BDS) became a new potential contributor to the realization of the terrestrial reference frame (TRF) scale of future International Terrestrial Reference Frame releases. This study focuses on the evaluation of the potential usage of the BDS-3 Medium Earth Orbit (MEO) constellation to the definition of the TRF scale. To that aim, we used ground calibrated BDS-3 satellite PCOs provided by the China Satellite Navigation Office and multi-GNSS robot calibrations for the ground antennas conducted by Geo++. Two ionosphere-free linear combinations of signals, namely B1I/B3I, and B1C/B2a, have been investigated to find out whether using different frequencies may lead to different TRF scale definitions. Differences between the z-components of the satellite phase offsets as given by manufacturer calibrations and those estimated based on IGS14 scale amount to 6.55 ± 12.56 cm and -0.32 ± 10.99 cm for B1I/B3I and B1C/B2a frequency pairs, respectively. On the one hand, the substantial deviation from the mean reflects the disparities in the quality of calibrations for the individual spacecraft, especially those manufactured by the Shanghai Engineering Center for Microsatellites (SECM). On the other hand, the difference between the two frequency pairs arises to a great extent from the doubtful quality of the SECM PCO calibrations, which certainly do not reflect the frequency dependence of the PCOs. Eventually, the mean scale bias with respect to IGS14 equals +0.546 ± 0.085 ppb, and +0.026 ± 0.085 ppb for B1I/B3I and B1C/B2a solutions, respectively, when using all 24 BDS-3 MEO satellites

Methodical developments for hydrodynamic scanning electrochemical microscopy

Within this thesis, the new research field of scanning electrochemical microscopy in combination with forced convection, that was started by the Matysik group in 2017, was extended to various directions. Within the first main project, compared to an electrical high precision stirrer, that was originally used to generate forced convection, two electrochemical flow cells were developed to diversify the methodical approaches for the generation of forced convection. The effects of forced convection originating from a flowing mediator solution on SECM experiments were investigated utilizing chronoamperometric measurements and SECM imaging in hydrodynamic SG/TC mode. Moreover, the velocity profile within the semi-closed cell design was characterized calculating Comsol simulations. Constant convection was successfully established within both flow cells resulting in stable diffusion layers around macroscopic substrate electrodes. Hence, next to the electrical high precision stirrer setup, a second methodical approach was established enabling time-independent and reproducible measurements in the context of the amperometric SG/TC mode. In the majority of cases, complementary to the SG/TC mode, the conventional feedback mode is applied to gain additional information about the surface of interest. For better comparison, these two modes have to be applied with experimental parameters as similar as possible meaning that if the newly established hydrodynamic SG/TC mode is applied, ideally also feedback mode images have to be recorded with forced convection applied to the system. Thus, the effects of forced convection originating from the electrical high precision stirrer on the amperometric feedback mode were examined within the second main project. Within this broadly arranged fundamental study, the crucial SECM parameters being UME dimensions, substrate-to-tip distance and probe scan rate were characterized regarding their interdependence with forced convection. Most importantly, it was found that forced convection has no negative impacts on imaging in feedback mode meaning that the hydrodynamic feedback mode can be applied for complementary imaging. Interestingly, the performance of the SECM measurements was even enhanced with forced convection for a certain combination of experimental parameters. Within the third main project, the applicability of forced convection on biological systems was investigated. Different-sized enzyme spots and a structured enzyme surface were investigated utilizing PSCs and SECM imaging. Analogous to the amperometric SG/TC, stable diffusion layers of H₂O₂ produced during the enzyme reaction of glucose oxidase were established. An enzyme structure not visible without forced convection due to time-dependent changing diffusion layers was successfully resolved with forced convection applied to the system. Consequently, in contrast to rather complex techniques from literature, here, with forced convection, a feasible approach was presented preventing a loss of resolution due to diffusive broadening and enabling time-independent SECM measurements of enzyme activity in the context of the G/C mode. Within a side project, forced convection was applied to generate constant diffusion layers around a macroscopic BDD electrode. Hence, whereas other techniques only deliver information about the whole electrode surface, utilizing hydrodynamic SECM the electrode was characterized locally concerning reactive oxygen species formed during the electrochemical oxygen evolution. Imaging in hydrodynamic SG/TC mode revealed that different reactive oxygen species were generated at different areas of the BDD electrode. Within another side project, resolving contrast between two conducting materials, which is not possible in conventional feedback mode, was established utilizing the hydrogen evolution reaction to generate the mediator species. In a third side project, a new electrochemical flow cell configuration was established to improve measurements in the presence of air bubbles. In summary, the field of forced convection in SECM was successfully expanded concerning new methodical developments, fundamental research and applications of the concept

Contribution of cellular automata to the understanding of corrosion phenomena

We present a stochastic CA modelling approach of corrosion based on spatially separated electrochemical half-reactions, diffusion, acido-basic neutralization in solution and passive properties of the oxide layers. Starting from different initial conditions, a single framework allows one to describe generalised corrosion, localised corrosion, reactive and passive surfaces, including occluded corrosion phenomena as well. Spontaneous spatial separation of anodic and cathodic zones is associated with bare metal and passivated metal on the surface. This separation is also related to local acidification of the solution. This spontaneous change is associated with a much faster corrosion rate. Material morphology is closely related to corrosion kinetics, which can be used for technological applications.Comment: 13 pages, 9 figure