48,800 research outputs found

    Silicon-based microfabricated droplet-microfluidics electrospray emitter for neurochemical sensing

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    Dynamic chemical heterogeneity of the nervous system is essential to numerous physiological processes. The detection of neurochemical concentration transients is therefore a prerequisite for better understanding the functionality of neural circuits and for implementing strategies for treatment of neural disorders. Currently, the analysis of real-time response of neural circuitry to chemical signaling is hindered by a lack of approaches that enable the chemical composition of brain extracellular space to be detected with sufficient time and chemical resolutions, because of the low basal concentration level of many neuromodulators of interest and chemical dispersion problem during chemical delivery. In this dissertation, a silicon-based miniaturized integrated microfluidic device has been developed for time-resolved detection of neurochemicals with improved chemical sensitivity and selectivity. To alleviate chemical dispersion problem and improve time resolution, analytes are first segmented into ultra-small droplets of volume down to picoliters. Diffusion is confined to a single droplet containing the interface and thereby dispersion is minimized. To this end, a detailed study has been implemented for picoliter-scale droplet generation on chip, so as to achieve satisfactory droplet properties in a stable and reliable manner. Next, to tackle the demanding challenge for sensitive detection of limited amount of analytes encapsulated within picoliter-scale compartments, an integrated Nano-Electrospray Ionization (nESI) emitter has been designed on chip for interfacing of analyte segmentation with online detection by mass spectrometry. By optimizing the emitter design, it was validated that the developed silicon nESI system could realize multiplex detection of various neurochemicals, including Dopamine (DA), Acetylcholine (Ach), Norepinephrine (NE), Serotonin (5-HT), Adenosine (Ado) and Gamma-aminobutyric acid (GABA), with limit of detection as sensitive as attomole level. Further study on nESI tip geometry demonstrates ability of spatial and temporal separation of electrosprayed oil and aqueous phases of the segmented flow, which could potentially further improve the performance of detection by alleviating interference from carrier oil phase. The optimized microfabrication and packaging recipe has been developed to enable precise definition of miniaturized geometrical features of each function module aforementioned and monolithic integration of all modules into single chip, including down-scaled silicon microfluidic channels, miniaturized T-junction droplet generator, and on-chip nESI emitter for efficient ionization and delivery of analytes to subsequent online mass spectrometry analysis. Such microfabricated integrated silicon-based platform demonstrates sensitive detection of segmented neurochemical contents, which would be a powerful tool for neuroscience study in future.U of I OnlyAuthor requested U of Illinois access only (OA after 2yrs) in Vireo ETD syste

    Experimental Study of the Heater Performance of a High Current Hollow Cathode

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    Thermionic hollow cathodes are electrodes mainly used in Hall-effect and Ion thrusters and they are crucial parts of those electric propulsion devices. Cathodes are subjected to extreme environments during operation and thousands of cycles of high power ignitions. The most sensitive part of the cathode, apart from electron emitter, is a heater that has a high record of failure and meltdown. Designing a more reliable heater is essential for the future development of high current hollow cathodes. HC60 is a high current hollow cathode currently under development at Sitael. In order to verify heating performance of the new heater solution, the real HC60 heater is installed on the real cathode tube and tested. To ensure representativeness in terms of thermal behavior, a mock-up of the additional cathode elements were used to reproduce the thermal capacitance and conductivity that will be experienced by the HC60 during operation. The purpose of this approach was to estimate the heating performance of the cathode and thermal transient behavior during the ignition phase. Additionally, cathode mock-up was cycled up to ignition temperature multiple times to test the thermo-mechanical robustness of the heater assembly. Comsol software has been used to verify if the cathode mock-up design is thermally representative. Heat Transfer analysis is divided into two cases. Case 1 is considering cathode assembly mockup mounted on support flange while Case 2 is analyzing original titanium interface. Results of the first and second case analysis were used for comparison and validation of thermal behavior of the cathode assembly mockup, particularly considering percentages of heat dissipated by means of heat conduction and radiation. Finally, results of two major tests were compared with thermal model and suggestions about design changes and improvement possibilities are presented

    In situ power-loss estimation of IGBT modules

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    A fault detection and prediction method for insulated-gate bipolar transistors (IGBTs) has been improved over the past decades to reduce system downtime. In situ lifetime estimation of IGBT modules has been challenging due to a number of requirements: the necessity to operate at high voltage in the switching environment and the measurement precision of the gate-threshold voltage or collector-to-emitter voltage. This thesis presents a wear-fatigue estimation framework that consists of collector-to-emitter measurement, power loss calculation, and thermal lifetime prediction model. The measurement circuit enables the estimation of power loss across a variety of IGBT modules with minimum impact on system reliability.LimitedAuthor requested closed access (OA after 2yrs) in Vireo ETD syste

    Efficient simulations of ionized ISM emission lines: A detailed comparison between the FIRE high-redshift suite and observations

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    The Atacama Large Millimeter/Submillimeter Array (ALMA) in the sub-millimeter and the James Webb Space Telescope (JWST) in the infrared have achieved robust spectroscopic detections of emission lines from the interstellar medium (ISM) in some of the first galaxies. These unprecedented measurements provide valuable information regarding the ISM properties, stellar populations, galaxy morphologies, and kinematics in these high-redshift galaxies and, in principle, offer powerful tests of state-of-the-art galaxy formation models, as implemented in hydrodynamical simulations. To facilitate direct comparisons between simulations and observations, we develop a fast post-processing pipeline for predicting the line emission from the HII regions around simulated star particles, accounting for spatial variations in the surrounding gas density, metallicity, temperature, and incident radiation spectrum. Our ISM line emission model currently captures Hα\alpha, Hβ\beta, and all of the [OIII] and [OII] lines targeted by ALMA and the JWST at z>6z>6. We illustrate the power of this approach by applying our line emission model to the publicly available FIRE high-zz simulation suite and perform a detailed comparison with current observations. We show that the FIRE mass--metallicity relation is in 1σ1\sigma agreement with ALMA/JWST measurements after accounting for the inhomogeneities in ISM properties. We also quantitatively validate the one-zone model description, which is widely used for interpreting [OIII] and Hβ\beta line luminosity measurements. This model is publicly available and can be implemented on top of a broad range of galaxy formation simulations for comparison with JWST and ALMA measurements.Comment: 15 pages, 13 figure

    Cavity-Catalyzed Hydrogen Transfer Dynamics in an Entangled Molecular Ensemble under Vibrational Strong Coupling

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    Microcavities have been shown to influence the reactivity of molecular ensembles by strong coupling of molecular vibrations to quantized cavity modes. In quantum mechanical treatments of such scenarios, frequently idealized models with single molecules and scaled, effective molecule-cavity interactions or alternatively ensemble models with simplified model Hamiltonians are used. In this work, we go beyond these models by applying an ensemble variant of the Pauli-Fierz Hamiltonian for vibro-polaritonic chemistry and numerically solve the underlying time-dependent Schr\"odinger equation to study the cavity-induced quantum dynamics in an ensemble of thioacetylacetone (TAA) molecules undergoing hydrogen transfer under vibrational strong coupling (VSC) conditions. Beginning with a single molecule coupled to a single cavity mode, we show that the cavity indeed enforces hydrogen transfer from an enol to an enethiol configuration with transfer rates significantly increasing with light-matter interaction strength. This positive effect of the cavity on reaction rates is different from several other systems studied so far, where a retarding effect of the cavity on rates was found. It is argued that the cavity ``catalyzes'' the reaction by transfer of virtual photons to the molecule. The same concept applies to ensembles with up to N=20N=20 TAA molecules coupled to a single cavity mode, where an additional, significant, ensemble-induced collective isomerization rate enhancement is found. The latter is traced back to complex entanglement dynamics of the ensemble, which we quantify by means of von Neumann-entropies. A non-trivial dependence of the dynamics on ensemble size is found, clearly beyond scaled single-molecule models, which we interpret as transition from a multi-mode Rabi to a system-bath-type regime as NN increases.Comment: Manuscript 9 pages, 5 figures (minor changes in v2). Supplementary Information 7 pages, 5 figures (Section III rewritten in v2 after peer-review

    EMPRESS. XI. SDSS and JWST Search for Local and z~4-5 Extremely Metal-Poor Galaxies (EMPGs): Clustering and Chemical Properties of Local EMPGs

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    We search for local extremely metal-poor galaxies (EMPGs), selecting photometric candidates by broadband color excess and machine-learning techniques with the SDSS photometric data. After removing stellar contaminants by shallow spectroscopy with Seimei and Nayuta telescopes, we confirm that three candidates are EMPGs with 0.05--0.1 ZZ_\odot by deep Magellan/MagE spectroscopy for faint {\sc[Oiii]}λ\lambda4363 lines. Using a statistical sample consisting of 105 spectroscopically-confirmed EMPGs taken from our study and the literature, we calculate cross-correlation function (CCF) of the EMPGs and all SDSS galaxies to quantify environments of EMPGs. Comparing another CCF of all SDSS galaxies and comparison SDSS galaxies in the same stellar mass range (107.0108.4M10^{7.0}-10^{8.4} M_\odot), we find no significant (>1σ>1\sigma) difference between these two CCFs. We also compare mass-metallicity relations (MZRs) of the EMPGs and those of galaxies at zz\sim 0--4 with a steady chemical evolution model and find that the EMPG MZR is comparable with the model prediction on average. These clustering and chemical properties of EMPGs are explained by a scenario of stochastic metal-poor gas accretion on metal-rich galaxies showing metal-poor star formation. Extending the broadband color-excess technique to a high-zz EMPG search, we select 17 candidates of zz\sim 4--5 EMPGs with the deep (30\simeq30 mag) near-infrared JWST/NIRCam images obtained by ERO and ERS programs. We find galaxy candidates with negligible {\sc[Oiii]}λλ\lambda\lambda4959,5007 emission weaker than the local EMPGs and known high-zz galaxies, suggesting that some of these candidates may fall in 0--0.01 ZZ_\odot, which potentially break the lowest metallicity limit known to date

    Pollution-induced community tolerance in freshwater biofilms – from molecular mechanisms to loss of community functions

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    Exposure to herbicides poses a threat to aquatic biofilms by affecting their community structure, physiology and function. These changes render biofilms to become more tolerant, but on the downside community tolerance has ecologic costs. A concept that addresses induced community tolerance to a pollutant (PICT) was introduced by Blanck and Wängberg (1988). The basic principle of the concept is that microbial communities undergo pollution-induced succession when exposed to a pollutant over a long period of time, which changes communities structurally and functionally and enhancing tolerance to the pollutant exposure. However, the mechanisms of tolerance and the ecologic consequences were hardly studied up to date. This thesis addresses the structural and functional changes in biofilm communities and applies modern molecular methods to unravel molecular tolerance mechanisms. Two different freshwater biofilm communities were cultivated for a period of five weeks, with one of the communities being contaminated with 4 μg L-1 diuron. Subsequently, the communities were characterized for structural and functional differences, especially focusing on their crucial role of photosynthesis. The community structure of the autotrophs was assessed using HPLC-based pigment analysis and their functional alterations were investigated using Imaging-PAM fluorometry to study photosynthesis and community oxygen profiling to determine net primary production. Then, the molecular fingerprints of the communities were measured with meta-transcriptomics (RNA-Seq) and GC-based community metabolomics approaches and analyzed with respect to changes in their molecular functions. The communities were acute exposed to diuron for one hour in a dose-response design, to reveal a potential PICT and uncover related adaptation to diuron exposure. The combination of apical and molecular methods in a dose-response design enabled the linkage of functional effects of diuron exposure and underlying molecular mechanisms based on a sensitivity analysis. Chronic exposure to diuron impaired freshwater biofilms in their biomass accrual. The contaminated communities particularly lost autotrophic biomass, reflected by the decrease in specific chlorophyll a content. This loss was associated with a change in the molecular fingerprint of the communities, which substantiates structural and physiological changes. The decline in autotrophic biomass could be due to a primary loss of sensitive autotrophic organisms caused by the selection of better adapted species in the course of chronic exposure. Related to this hypothesis, an increase in diuron tolerance has been detected in the contaminated communities and molecular mechanisms facilitating tolerance have been found. It was shown that genes of the photosystem, reductive-pentose phosphate cycle and arginine metabolism were differentially expressed among the communities and that an increased amount of potential antioxidant degradation products was found in the contaminated communities. This led to the hypothesis that contaminated communities may have adapted to oxidative stress, making them less sensitive to diuron exposure. Moreover, the photosynthetic light harvesting complex was altered and the photoprotective xanthophyll cycle was increased in the contaminated communities. Despite these adaptation strategies, the loss of autotrophic biomass has been shown to impair primary production. This impairment persisted even under repeated short-term exposure, so that the tolerance mechanisms cannot safeguard primary production as a key function in aquatic systems.:1. The effect of chemicals on organisms and their functions .............................. 1 1.1 Welcome to the anthropocene .......................................................................... 1 1.2 From cellular stress responses to ecosystem resilience ................................... 3 1.2.1 The individual pursuit for homeostasis ....................................................... 3 1.2.2 Stability from diversity ................................................................................. 5 1.3 Community ecotoxicology - a step forward in monitoring the effects of chemical pollution? ................................................................................................................. 6 1.4 Functional ecotoxicological assessment of microbial communities ................... 9 1.5 Molecular tools – the key to a mechanistic understanding of stressor effects from a functional perspective in microbial communities? ...................................... 12 2. Aims and Hypothesis ......................................................................................... 14 2.1 Research question .......................................................................................... 14 2.2 Hypothesis and outline .................................................................................... 15 2.3 Experimental approach & concept .................................................................. 16 2.3.1 Aquatic freshwater biofilms as model community ..................................... 16 2.3.2 Diuron as model herbicide ........................................................................ 17 2.3.3 Experimental design ................................................................................. 18 3. Structural and physiological changes in microbial communities after chronic exposure - PICT and altered functional capacity ................................................. 21 3.1 Introduction ..................................................................................................... 21 3.2 Methods .......................................................................................................... 23 3.2.1 Biofilm cultivation ...................................................................................... 23 3.2.2 Dry weight and autotrophic index ............................................................. 23 3.2.4 Pigment analysis of periphyton ................................................................. 23 3.2.4.1 In-vivo pigment analysis for community characterization ....................... 24 3.2.4.2 In-vivo pigment analysis based on Imaging-PAM fluorometry ............... 24 3.2.4.3 In-vivo pigment fluorescence for tolerance detection ............................. 26 3.2.4.4 Ex-vivo pigment analysis by high-pressure liquid-chromatography ....... 27 3.2.5 Community oxygen metabolism measurements ....................................... 28 3.3 Results and discussion ................................................................................... 29 3.3.1 Comparison of the structural community parameters ............................... 29 3.3.2 Photosynthetic activity and primary production of the communities after selection phase ................................................................................................. 33 3.3.3 Acquisition of photosynthetic tolerance .................................................... 34 3.3.4 Primary production at exposure conditions ............................................... 36 3.3.5 Tolerance detection in primary production ................................................ 37 3.4 Summary and Conclusion ........................................................................... 40 4. Community gene expression analysis by meta-transcriptomics ................... 41 4.1 Introduction to meta-transcriptomics ............................................................... 41 4.2. Methods ......................................................................................................... 43 4.2.1 Sampling and RNA extraction................................................................... 43 4.2.2 RNA sequencing analysis ......................................................................... 44 4.2.3 Data assembly and processing................................................................. 45 4.2.4 Prioritization of contigs and annotation ..................................................... 47 4.2.5 Sensitivity analysis of biological processes .............................................. 48 4.3 Results and discussion ................................................................................... 48 4.3.1 Characterization of the meta-transcriptomic fingerprints .......................... 49 4.3.2 Insights into community stress response mechanisms using trend analysis (DRomic’s) ......................................................................................................... 51 4.3.3 Response pattern in the isoform PS genes .............................................. 63 4.5 Summary and conclusion ................................................................................ 65 5. Community metabolome analysis ..................................................................... 66 5.1 Introduction to community metabolomics ........................................................ 66 5.2 Methods .......................................................................................................... 68 5.2.1 Sampling, metabolite extraction and derivatisation................................... 68 5.2.2 GC-TOF-MS analysis ............................................................................... 69 5.2.3 Data processing and statistical analysis ................................................... 69 5.3 Results and discussion ................................................................................... 70 5.3.1 Characterization of the metabolic fingerprints .......................................... 70 5.3.2 Difference in the metabolic fingerprints .................................................... 71 5.3.3 Differential metabolic responses of the communities to short-term exposure of diuron ............................................................................................................ 73 5.4 Summary and conclusion ................................................................................ 78 6. Synthesis ............................................................................................................. 79 6.1 Approaches and challenges for linking molecular data to functional measurements ...................................................................................................... 79 6.2 Methods .......................................................................................................... 83 6.2.1 Summary on the data ............................................................................... 83 6.2.2 Aggregation of molecular data to index values (TELI and MELI) .............. 83 6.2.3 Functional annotation of contigs and metabolites using KEGG ................ 83 6.3 Results and discussion ................................................................................... 85 6.3.1 Results of aggregation techniques ........................................................... 85 6.3.2 Sensitivity analysis of the different molecular approaches and endpoints 86 6.3.3 Mechanistic view of the molecular stress responses based on KEGG functions ............................................................................................................ 89 6.4 Consolidation of the results – holistic interpretation and discussion ............... 93 6.4.1 Adaptation to chronic diuron exposure - from molecular changes to community effects.............................................................................................. 93 6.4.2 Assessment of the ecological costs of Pollution-induced community tolerance based on primary production ............................................................. 94 6.5 Outlook ............................................................................................................ 9

    Manual for seed yam production in hydroponics system

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    Webots Simulator for Lyapunov-based Cooperative Omnidirectional Mobile Robots Evaluation

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    A multi-robot system is a set of robots that share a common objective and collaborate to achieve it. Multi-robot systems can address distributed and complicated real-world issues more effectively in various industries, including logistics, transportation, and industrial manufacturing. The higher system performance because of the collaborative efforts of numerous robots provides a substantial possible benefit of using a multi- robot system rather than a single robot. The Lyapunov control approach is one advanced approach to coordinating multiple robots in warehouse logistics applications. The method has been successfully simulated on point masses. However, to be physically implemented in robotic devices still requires several processes that are not simple. The case study focuses on finding the possibility of a distributed cooperative mobile robot using a LiDAR sensor to recognize the ’friend’ robot and the obstacle. This paper shows that each robot can recognize well between its neighbor or obstacles and maintain its formation of 1 m during the trip with obstacle presence. The simulations were performed in Webots to verify the proposed algorithms. The mathematical analysis and the experiment prove the system’s stability by seeing the robots’ velocity
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