Study on the general applicability of the collector efficiency model to solar process heat collectors

[eng] According to several studies, the installed capacity of solar thermal collectors to provide heat for industrial processes is going to increase significantly during the next decades. The great variety of designs and large range of operating temperatures of solar process collectors make their performance assessment challenging. Although the quasi-dynamic testing procedure has been designed for most types of collectors, it shows limitations or vagueness when dealing with medium-scaled collectors. This thesis analyzes some limitations, focusing mainly on the optical efficiency assessment. A powerful ray-tracing algorithm has been developed for the optical analyses in this thesis. The algorithm was used to carry out a sensitivity analysis of a Fresnel collector to achieve a better understanding of the most influential parameters in ray-tracing simulations. Two observations were made: First, spectral simulations are not relevant for solar thermal applications unless mirror scattering shows a very high dependency on the wavelength. Second, defining the incidence angle dependency of optical materials is crucial to produce accurate results. In the case of biaxial concentrating collectors, the incidence angle modifier factorization model is commonly applied. This model inherently introduces errors by factorizing the underlying non-factorizable functions. The error was characterized for four different collector geometries by comparing factorization with ray-tracing simulations. Results have been presented as a function of geographical latitude. Factorization in the θi-θT -space performed best in nearly all cases. Four different collector geometries were submitted to ray-tracing simulations in order to analyze the thermal dependency of the factorization error. It is shown that the relative error generally increases with higher operating temperatures, but within the economically viable temperature range it stays fairly constant. With higher temperatures the collector gradually stops operating beginning with moments when sun angles are least favorable for factorization.[cat] Segons diversos estudis, la capacitat instal·lada de captadors solars tèrmics pel subministrament de calor en processos industrials s’incrementarà significativament en els propers anys. La gran diversitat de dissenys i temperatures de treball d’aquest tipus de captador fa difícil l’avaluació dels seus rendiments. Encara que el mètode experimental quasi dinàmic s’ha desenvolupat per la major part de models de captador, segueix tenint limitacions o imprecisions a l’hora d’avaluar captadors específics per calor de procés. Aquesta tesi analitza algunes d’aquestes limitacions, centrant-se principalment en l’avaluació de l’eficiència òptica. Per l’anàlisi òptica, en aquesta tesi s’ha desenvolupat un algoritme avançat de ray-tracing. L’algoritme ha servit per realitzar una anàlisi de sensibilitat d’un captador Fresnel, que ha permès conèixer quins son els paràmetres que tenen una major influència en la qualitat dels resultats obtinguts en les simulacions de ray-tracing. S’ha arribat a dues conclusions: En primer lloc, simulacions espectrals no son rellevants per aplicacions solars tèrmiques, a no ser que la dispersió del mirall depengui significativament de la longitud d’ona. En segon llos és imprescindible especificar al dependència de l’angle d’incidència dels materials òptics per generar resultats acurats. En el cas de captadors concentradors biaxials, s’aplica el model de factorització del modificador d’angle d’incidència. Aquesta factorització te sempre associat un cert error, ja que l’IAM no és en general factoritzable. S’ha caracteritzat l’error per quatre geometries de captadors diferents, comparant el models de factorització amb les simulacions ray-tracing. Els resultats s’han presentat en funció de la latitud geogràfica. La factorització a l’espai θi-θT es la que ofereix més bons resultats en gairebé tots els casos analitzats. Quatre geometries diferents de captador foren analitzades per determinar la dependència amb la temperatura de l’error de factorització. S’ha demostrat que a mesura que s’incrementa la temperatura de treball, s’incrementa l’error relatiu del la factorització, malgrat això, dins del rang de temperatures econòmicament viables, l’error es manté constant. Això és degut a que a mesura s’incrementa la temperatura, es redueixen les hores de treball, i per tant també les hores on el captador treballa sota els angles més desfavorables per la factorització[spa] Según varios estudios, la capacidad instalada de captadores solares térmicos para proveer calor en procesos industriales se va a incrementar significativamente a lo largo de las próximas décadas. La gran variedad de diseños y temperaturas de este tipo de captadores hace complicada la evaluación de sus rendimientos. Aunque el métdodo experimental quasi-dinámico ha sido diseñado para la mayoría de modelos de captadores, sigue teniendo limitaciones o imprecisiones a la hora de evaluar captadores de mediana escala. Esta tesis analiza algunas de dichas limitaciones, centrándose principalmente en la evaluación de la eficiencia óptica. Para el análisis óptico en esta tesis se ha desarrollado un algoritmo avanzado de raytracing. El algoritmo ha servido para realizar un análisis de sensibilidad de un captador Fresnel, para conseguir con ello un mayor conocimiento de los parámetros más influyentes en las simulaciones ray-tracing. Se ha llegado a dos conclusiones: En primer lugar, simulaciones espectrales no son relevantes para aplicaciones solares térmicas, a no ser que la dispersión del espejo dependa significativamente de la longitud de onda. En segundo lugar, es imprescindible especificar la dependencia del ángulo de incidencia de los materiales ópticos para generar resultados precisos. En el caso de captadores concentradores biaxiales, se aplica el modelo de factorización del ‘incidence angle modifier’. Por defecto, este modelo introduce errores factorizando funciones que no son factorizables. Se ha caracterizado el error para cuatro geometrías de captadores diferentes comparando el modelo de factorización con las simulaciones ray-tracing. Los resultados han sido presentados como función de la latitud geográfica. La factorización en el espacio θi-θT ha demostrado los mejores resultados para casi todos los casos. Cuatro geometrías diferentes fueron sometidas a simulaciones de ray-tracing para analizar la dependencia térmica del mismo error de factorización. Se ha demostrado que a medida que aumenta la temperatura del proceso, aumenta también el error relativo de factorización, sin embargo, dentro del rango económicamente viable de temperaturas, el error se mantiene constante. Esto se debe a que a medida se incrementa la temperatura, el captador deja de operar primero en los momentos de ángulos más desfavorables para la factorización

Formulation and characterisation of enzyme-based biomaterials for μFluidic experiments

The fundamental principle of biological compartmentalisation of cellular life provides the basis for space-time resolved reaction processes. Based on this, intensive work is currently done on the use of interconnected, continuously flowing reaction chambers in order to improve the reaction control and efficiency of chemical syntheses, especially with the inclusion of biocatalysts (so called flow biocatalysis). Therefore, the Institute for Biological Interfaces IBG-1 aims at the formulation of enzyme-based biomaterials and the associated testing of novel gene-encoded coupling systems. The resulting enzyme fusions will be used as modular building blocks for the assembly of catalytically active materials, with different formulations (hydrogels or thin films) and characterized in terms of their immobilization and biocatalytic activity in miniaturized flow reactors. During the process of formulating an optimised biomaterial, we developed and established the self-assembling all-enzyme hydogels (AEHs). These protein materials consist of the two homotetrameric enzymes, (R)-selective alcohol dehydrogenase (ADH) and the cofactor regenerating glucose 1-dehydrogenase (GDH), that are genetically fused with either the SpyCatcher (SC) or the SpyTag (ST). The AEHs were characterised via dynamic light scattering (DLS) and scanning electron microscopy (SEM) in terms of physical properties. Moreover, the gels showed excellent stereoselectivity, stable conversion rates and high space-time yields (STY) for more than seven days in continuous flow experiments

Changing nucleotide specificity of the DEAD-box helicase Hera abrogates communication between the Q-motif and the P-loop

DEAD-box proteins disrupt or remodel RNA and protein/RNA complexes at the expense of ATP. The catalytic core is composed of two flexibly connected RecA-like domains. The N-terminal domain contains most of the motifs involved in nucleotide binding and serves as a minimalistic model for helicase/nucleotide interactions. A single conserved glutamine in the so-called Q-motif has been suggested as a conformational sensor for the nucleotide state. To reprogram the Thermus thermophilus RNA helicase Hera for use of oxo-ATP instead of ATP and to investigate the sensor function of the Q-motif, we analyzed helicase activity of Hera Q28E. Crystal structures of the Hera N-terminal domain Q28E mutant (TthDEAD_Q28E) in apo- and ligand-bound forms show that Q28E does change specificity from adenine to 8-oxoadenine. However, significant structural changes accompany the Q28E mutation, which prevent the P-loop from adopting its catalytically active conformation and explain the lack of helicase activity of Hera_Q28E with either ATP or 8-oxo-ATP as energy sources. 8-Oxo-adenosine, 8-oxo-AMP, and 8-oxo-ADP weakly bind to TthDEAD_Q28E but in non-canonical modes. These results indicate that the Q-motif not only senses the nucleotide state of the helicase but could also stabilize a catalytically competent conformation of the P-loop and other helicase signature motif

Intracellular Assembly of Interacting Enzymes Yields Highly‐Active Nanoparticles for Flow Biocatalysis

All-enzyme hydrogel (AEH) particles with a hydrodynamic diameter of up to 120 nm were produced intracellularly with an Escherichia coli-based in vivo system. The inCell-AEH nanoparticles were generated from polycistronic vectors enabling simultaneous expression of two interacting enzymes, the Lactobacillus brevis alcohol dehydrogenase (ADH) and the Bacillus subtilis glucose-1-dehydrogenase (GDH), fused with a SpyCatcher or SpyTag, respectively. Formation of inCell-AEH was analyzed by dynamic light scattering and atomic force microscopy. Using the stereoselective two-step reduction of a prochiral diketone substrate, we show that the inCell-AEH approach can be advantageously used in whole-cell flow biocatalysis, by which flow reactors could be operated for >4 days under constant substrate perfusion. More importantly, the inCell-AEH concept enables the recovery of efficient catalyst materials for stable flow bioreactors in a simple and economical one-step procedure from crude bacterial lysates. We believe that our method will contribute to further optimization of sustainable biocatalytic processes

A small viral potassium ion channel with an inherent inward rectification

Some algal viruses have coding sequences for proteins with structural and functional characteristics of pore modules of complex K+ channels. Here we exploit the structural diversity among these channel orthologs to discover new basic principles of structure/function correlates in K+ channels. The analysis of three similar K+ channels with ≤ 86 amino acids (AA) shows that one channel (Kmpv1) generates an ohmic conductance in HEK293 cells while the other two (KmpvSP1, KmpvPL1) exhibit typical features of canonical Kir channels. Like Kir channels, the rectification of the viral channels is a function of the K+ driving force. Reconstitution of KmpvSP1 and KmpvPL1 in planar lipid bilayers showed rapid channel fluctuations only at voltages negative of the K+ reversal voltage. This rectification was maintained in KCl buffer with 1 mM EDTA, which excludes blocking cations as the source of rectification. This means that rectification of the viral channels must be an inherent property of the channel. The structural basis for rectification was investigated by a chimera between rectifying and non-rectifying channels as well as point mutations making the rectifier similar to the ohmic conducting channel. The results of these experiments exclude the pore with pore helix and selectivity filter as playing a role in rectification. The insensitivity of the rectifier to point mutations suggests that tertiary or quaternary structural interactions between the transmembrane domains are responsible for this type of gating

Extending the Tally-Hiding Ordinos System: Implementations for Borda, Hare-Niemeyer, Condorcet, and Instant-Runoff Voting

Modern electronic voting systems (e-voting systems) are designed to achieve a variety of security properties, such as verifiability, accountability, and vote privacy. Some of these systems aim at so-called tally-hiding: they compute the election result, according to some result function, like the winner of the election, without revealing any other information to any party. In particular, if desired, they neither reveal the full tally consisting of all (aggregated or even individual) votes nor parts of it, except for the election result, according to the result function. Tally-hiding systems offer many attractive features, such as strong privacy guarantees both for voters and for candidates, and protection against Italian attacks. The Ordinos system is a recent provably secure framework for accountable tally-hiding e-voting that extends Helios and can be instantiated for various election methods and election result functions. So far, practical instantiations and implementations for only rather simple result functions (e.g., computing the $k$ best candidates) and single/multi-vote elections have been developed for Ordinos. In this paper, we propose and implement several new Ordinos instantiations in order to support Borda voting, the Hare-Niemeyer method for proportional representation, multiple Condorcet methods, and Instant-Runoff Voting. Our instantiations, which are based on suitable secure multi-party computation (MPC) components, offer the first tally-hiding implementations for these voting methods. To evaluate the practicality of our MPC components and the resulting e-voting systems, we provide extensive benchmarks for all our implementations

Lumpy Structures in Self-Gravitating Disks

Following Toomre & Kalnajs (1991), local models of slightly dissipative self-gravitating disks show how inhomogeneous structures can be maintained over several galaxy rotations. Their basic physical ingredients are self-gravity, dissipation and differential rotation. In order to explore the structures resulting from these processes on the kpc scale, local simulation of self-gravitating disks are performed in this paper in 2D as well as in 3D. The third dimension becomes a priori important as soon as matter clumping causes a tight coupling of the 3D equations of motion. The physically simple and general framework of the model permits to make conclusions beyond the here considered scales. A time dependent affine coordinate system is used, allowing to calculate the gravitational forces via a particle-mesh FFT-method, increasing the performance with respect to previous direct force calculations. Persistent patterns, formed by transient structures, whose intensity and morphological characteristic depend on the dissipation rate are obtained and described. Some of our simulations reveal first signs of mass-size and velocity dispersion-size power-law relations, but a clear scale invariant behavior will require more powerful computer techniques.Comment: 28 pages, 32 figures. Accepted for publication in A&A. Full resolution paper available at http://obswww.unige.ch/Preprints/dyn_art.htm

Analysis of routine blood parameters in patients with amyotrophic lateral sclerosis and evaluation of a possible correlation with disease progression—a multicenter study

ObjectiveAmyotrophic lateral sclerosis (ALS) pathogenesis is still unclear, its course is considerably variable, and prognosis is hard to determine. Despite much research, there is still a lack of easily accessible markers predicting prognosis. We investigated routine blood parameters in ALS patients regarding correlations with disease severity, progression rate, and survival. Additionally, we analyzed disease and patients' characteristics relating to baseline blood parameter levels.MethodsWe analyzed creatine kinase (CK), albumin (ALB), creatinine (CREA), total cholesterol (TC), high-density lipoprotein cholesterol (HDL), low-density lipoprotein cholesterol (LDL), and triglycerides (TG) levels around time of diagnosis in 1,084 ALS patients. We carried out linear regression analyses including disease and patients' characteristics with each blood parameter to detect correlations with them. Linear regression models were performed for ALSFRS-R at study entry, its retrospectively defined rate of decay and prospectively collected progression rate. Different survival analysis methods were used to examine associations between blood parameters and survival.ResultsWe found higher CK (p-value 0.001), ALB (p-value <0.001), CREA (p-value <0.001), and HDL levels (p-value 0.044) at time of diagnosis being associated with better functional status according to ALSFRS-R scores at study entry. Additionally, higher CREA levels were associated with lower risk of death (p-value 0.003).ConclusionsOur results indicate potential of CK, ALB, CREA, and HDL as disease severity or progression markers, and may also provide clues to ALS pathogenesis. However, these values are highly dependent on other variables, and further careful, longitudinal analyses will be necessary to prove the relevance of our findings