Towards a more realistic sink particle algorithm for the RAMSES code

We present a new sink particle algorithm developed for the Adaptive Mesh Refinement code RAMSES. Our main addition is the use of a clump finder to identify density peaks and their associated regions (the peak patches). This allows us to unambiguously define a discrete set of dense molecular cores as potential sites for sink particle formation. Furthermore, we develop a new scheme to decide if the gas in which a sink could potentially form, is indeed gravitationally bound and rapidly collapsing. This is achieved using a general integral form of the virial theorem, where we use the curvature in the gravitational potential to correctly account for the background potential. We detail all the necessary steps to follow the evolution of sink particles in turbulent molecular cloud simulations, such as sink production, their trajectory integration, sink merging and finally the gas accretion rate onto an existing sink. We compare our new recipe for sink formation to other popular implementations. Statistical properties such as the sink mass function, the average sink mass and the sink multiplicity function are used to evaluate the impact that our new scheme has on accurately predicting fundamental quantities such as the stellar initial mass function or the stellar multiplicity function.Comment: submitted to MNRAS, 24 pages, 19 figures, 5 table

On the Dynamics of Supermassive Black Holes in Gas-Rich, Star-Forming Galaxies: the Case for Nuclear Star Cluster Coevolution

We introduce a new model for the formation and evolution of supermassive black holes (SMBHs) in the RAMSES code using sink particles, improving over previous work the treatment of gas accretion and dynamical evolution. This new model is tested against a suite of high-resolution simulations of an isolated, gas-rich, cooling halo. We study the effect of various feedback models on the SMBH growth and its dynamics within the galaxy. In runs without any feedback, the SMBH is trapped within a massive bulge and is therefore able to grow quickly, but only if the seed mass is chosen larger than the minimum Jeans mass resolved by the simulation. We demonstrate that, in the absence of supernovae (SN) feedback, the maximum SMBH mass is reached when Active Galactic Nucleus (AGN) heating balances gas cooling in the nuclear region. When our efficient SN feedback is included, it completely prevents bulge formation, so that massive gas clumps can perturb the SMBH orbit, and reduce the accretion rate significantly. To overcome this issue, we propose an observationally motivated model for the joint evolution of the SMBH and a parent nuclear star cluster (NSC), which allows the SMBH to remain in the nuclear region, grow fast and resist external perturbations. In this scenario, however, SN feedback controls the gas supply and the maximum SMBH mass now depends on the balance between AGN heating and gravity. We conclude that SMBH/NSC co-evolution is crucial for the growth of SMBH in high-z galaxies, the progenitors of massive elliptical today.Comment: accepted for publication in MNRA

Towards a more realistic sink particle algorithm for the ramses code

We present a new sink particle algorithm developed for the adaptive mesh refinement code ramses. Our main addition is the use of a clump finder to identify density peaks and their associated regions (the peak patches). This allows us to unambiguously define a discrete set of dense molecular cores as potential sites for sink particle formation. Furthermore, we develop a new scheme to decide if the gas in which a sink could potentially form, is indeed gravitationally bound and rapidly collapsing. This is achieved using a general integral form of the virial theorem, where we use the curvature in the gravitational potential to correctly account for the background potential. We detail all the necessary steps to follow the evolution of sink particles in turbulent molecular cloud simulations, such as sink production, their trajectory integration, sink merging and finally the gas accretion rate on to an existing sink. We compare our new recipe for sink formation to other popular implementations. Statistical properties such as the sink mass function, the average sink mass and the sink multiplicity function are used to evaluate the impact that our new scheme has on accurately predicting fundamental quantities such as the stellar initial mass function or the stellar multiplicity functio

An innovative concept for a lunar base, based on ecological engineering

In the present study a new concept for ecological life support systems based on complete oxygen, water and food recycling for a future moon base was developed. Starting from the hypothesis that the pyrolysis of human feces to biochar would be a suitable waste treatment measure, a conceptual design for a life support system including hydroponic food production and O2-generation, water recycling and CO2-balancing with biochar incineration was proposed. In the system, the biochar can be used as plant substrate or fertilizer in the hydroponic, or can be incinerated to provide CO2 for plant production. Based on literature review and modelling of mass flows in the system, using a mass balancing approach, several benefits of the inclusion of pyrolysis into a life support system were identified. Pyrolysis ensures complete destruction of pathogens, fibers and organic micropollutants contained in feces that could be harmful for hydroponic food production and human health. Pyrolysis further is a treatment process that does not require oxygen (like incineration). The treatment of wastes can therefore be achieved even without consuming the oxygen required by the crew. Moreover, carbon, and nutrients can be stored in a sterile and stable char and reused when there is need. Difficulties in nutrient recycling from biochar and pH balances in the system were identified as threats to the system. Further research needs to confirm the feasibility of fecal biochar as a hydroponic substrate of fertilizer and its impact on pH balances

Pyrolysis of dry toilet substrate as a means of nutrient recycling in agricultural systems : potential risks and benefits

Biochar is increasingly being applied as a soil amendment in agriculture. Biochar is typically produced from plant biomass and contains relatively low amounts of plant nutrients (e.g., N, P, and K), thus providing limited fertilizer value. Human excreta contains plant nutrients that could be recycled to create sustainable agricultural nutrient cycles. This study investigated the potential of biochar derived from a dry toilet substrate as soil amendment. The substrate consisted of urine, faeces, and wood chips, and was pyrolyzed at 500–650 °C for 10 min. The biochar was analyzed for plant available P, water leachable P and K, carbon stability, pH, electrical conductivity, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), dioxins, and germination tests with barley and lettuce were conducted to estimate the biochar fertilizer value and potential bio-toxicity. The biochar contained 25.0 ± 1.0 g N/kg dry mass (DM), 33.1 ± 2.1 g P/kg DM and 20.7 ± 0.2 g K/kg DM. 65% DM P was extractable by formic acid solution, 31.7% DM P and 60.5% DM K were water leachable in a ten-day column water-leaching experiment. The biochar complied with European regulations for PAHs, PCBs, dioxins and heavy metal concentrations, except for Zn and Ni. Germination of salt-resistant barley was not affected by biochar doses < 50% DM, while salt-sensitive lettuce germination was inhibited at doses ≥ 2% DM, indicating that the dry toilet substrate biochar induced salt stress. Based on these results, it is recommended that urine separation should be considered for biochar of excreta, which could reduce salt stress while maintaining concentrations of “fixed” or bioavailable nitrogen

Sparse graphical Gaussian modeling of the isoprenoid gene network in Arabidopsis thaliana

We present a novel graphical Gaussian modeling approach for reverse engineering of genetic regulatory networks with many genes and few observations. When applying our approach to infer a gene network for isoprenoid biosynthesis in Arabidopsis thaliana, we detect modules of closely connected genes and candidate genes for possible cross-talk between the isoprenoid pathways. Genes of downstream pathways also fit well into the network. We evaluate our approach in a simulation study and using the yeast galactose network

Local Water Loop : Vorstudie für einen energie- und wasserautarken Waschmaschinenbetrieb

Während der Bedarf an Süsswasser weltweit stetig steigt, wird dessen Verfügbarkeit immer knapper. Um dem entgegenzuwirken, ist die lokale Behandlung und Wiederverwendung von Grauwasser ein vielversprechender Ansatz. Von besonderem Interesse sind der Einsatz von grünen Wänden, als platzsparende Alternative zu Pflanzenkläranlagen, und Filtersäulen zur biologischen Reinigung des Abwassers. Im vorliegenden Projekt wurden die Grundlagen für einen energie- und wasserautarken Waschmaschinenbetrieb, basierend auf der biologischen Reinigungstechnologie, erarbeitet. Es wurde eine Reihe von Experimenten durchgeführt, um Waschmaschinenabwasser zu charakterisieren, eine geeignete Vorreinigung auszuwählen, ein geeignetes Filtersubstrat für die grüne Wand zu identifizieren, die Keimbelastung zu analysieren und den Energieautarkiegrad zu bestimmen und zu optimieren. Die Analyse des Waschmaschinenabwassers zeigte, dass ein Grossteil der Verschmutzung im Abwasser vom Waschmittel selbst stammt. Daher ist die Verwendung eines ökologischen Waschmittels und dessen korrekte Dosierung essenziell für einen ressourceneffizienten Betrieb. Für die physikalisch-mechanische Vorreinigung wurden ein Sandfilter und ein Feinfilter getestet. Aufgrund der hohen Faserbelastung im Waschmaschinenabwasser zeigte sich der Sandfilter als ungeeignet, da er schnell verstopfte. Stattdessen konnte mit dem Feinfilter eine gute Vorreinigung erzielt werden. Die Faserbelastung im Waschmaschinenabwasser betrug durchschnittlich 25 mg/L vor der Vorreinigung und konnte durch den Feinfilter auf 2 mg/L reduziert werden. Die Analyse der Reinigungsleistung verschiedener Substrate für die grüne Wand, darunter Vulkaponic, Vulkaponic/Pflanzenkohle-Mischung und Perlit, zeigte, dass mit reinem Vulkaponic die besten Ergebnisse erzielt wurden. Die Reinigungseffizienz von Vulkaponic betrug im Durchschnitt 85%, während die Mischung aus Vulkaponic und Pflanzenkohle eine Reinigungsleistung von 78% aufwies. Perlit erreichte eine Reinigungsleistung von 62%. Die Keimbelastung im Kreislaufsystem der Waschmaschine nimmt nach der Reinigung und UV-Behandlung stetig ab, sodass die Wasserqualität den Anforderungen an Badegewässer entspricht. Die Konzentration der aeroben mesophilen Keime sank von 130’000 KBE/mL auf 1’400 KBE/mL nach der UV-Behandlung. Dies bestätigt die Effektivität der angewandten Reinigungs- und Desinfektionsverfahren. Um den Energieautarkiegrad über ein Jahr zu bestimmen, wurden die gemessenen Werte auf ein Jahr extrapoliert. In der jetzigen Ausführung kann somit ein Autarkiegrad von 30% erzielt werden. Durch den Einsatz zusätzlicher Optimierungsmassnahmen wie die Nutzung von zusätzlichen Solarpanels und einer optimierten Steuerung kann dieser Wert auf 66% erhöht werden. Am Zielstandort in Kapstadt, Südafrika könnte damit ein Autarkiegrad von 86% erreicht werden. Die gewonnenen Erkenntnisse aus den Experimenten dienen dazu, den energie- und wasserautarken Waschmaschinenbetrieb in Folgeprojekten weiterzuentwickeln und zu optimieren

Disordered semantic representation in schizophrenic temporal cortex revealed by neuromagnetic response patterns

BACKGROUND: Loosening of associations and thought disruption are key features of schizophrenic psychopathology. Alterations in neural networks underlying this basic abnormality have not yet been sufficiently identified. Previously, we demonstrated that spatio-temporal clustering of magnetic brain responses to pictorial stimuli map categorical representations in temporal cortex. This result has opened the possibility to quantify associative strength within and across semantic categories in schizophrenic patients. We hypothesized that in contrast to controls, schizophrenic patients exhibit disordered representations of semantic categories. METHODS: The spatio-temporal clusters of brain magnetic activities elicited by object pictures related to super-ordinate (flowers, animals, furniture, clothes) and base-level (e.g. tulip, rose, orchid, sunflower) categories were analysed in the source space for the time epochs 170–210 and 210–450 ms following stimulus onset and were compared between 10 schizophrenic patients and 10 control subjects. RESULTS: Spatio-temporal correlations of responses elicited by base-level concepts and the difference of within vs. across super-ordinate categories were distinctly lower in patients than in controls. Additionally, in contrast to the well-defined categorical representation in control subjects, unsupervised clustering indicated poorly defined representation of semantic categories in patients. Within the patient group, distinctiveness of categorical representation in the temporal cortex was positively related to negative symptoms and tended to be inversely related to positive symptoms. CONCLUSION: Schizophrenic patients show a less organized representation of semantic categories in clusters of magnetic brain responses than healthy adults. This atypical neural network architecture may be a correlate of loosening of associations, promoting positive symptoms

Star cluster formation in a turbulent molecular cloud self-regulated by photoionization feedback

Most stars in the Galaxy are believed to be formed within star clusters from collapsing molecular clouds. However, the complete process of star formation, from the parent cloud to a gas-free star cluster, is still poorly understood. We perform radiation-hydrodynamical simulations of the collapse of a turbulent molecular cloud using the ramses-rt code. Stars are modelled using sink particles, from which we self-consistently follow the propagation of the ionizing radiation. We study how different feedback models affect the gas expulsion from the cloud and how they shape the final properties of the emerging star cluster. We find that the star formation efficiency is lower for stronger feedback models. Feedback also changes the high-mass end of the stellar mass function. Stronger feedback also allows the establishment of a lower density star cluster, which can maintain a virial or sub-virial state. In the absence of feedback, the star formation efficiency is very high, as well as the final stellar density. As a result, high-energy close encounters make the cluster evaporate quickly. Other indicators, such as mass segregation, statistics of multiple systems and escaping stars confirm this picture. Observations of young star clusters are in best agreement with our strong feedback simulation

Star cluster formation in a turbulent molecular cloud self-regulated by photoionization feedback

International audienceMost stars in the Galaxy are believed to be formed within star clusters from collapsing molecular clouds. However, the complete process of star formation, from the parent cloud to a gas-free star cluster, is still poorly understood. We perform radiation-hydrodynamical simulations of the collapse of a turbulent molecular cloud using the RAMSES-RT code. Stars are modelled using sink particles, from which we self-consistently follow the propagation of the ionizing radiation. We study how different feedback models affect the gas expulsion from the cloud and how they shape the final properties of the emerging star cluster. We find that the star formation efficiency is lower for stronger feedback models. Feedback also changes the high-mass end of the stellar mass function. Stronger feedback also allows the establishment of a lower density star cluster, which can maintain a virial or sub-virial state. In the absence of feedback, the star formation efficiency is very high, as well as the final stellar density. As a result, high-energy close encounters make the cluster evaporate quickly. Other indicators, such as mass segregation, statistics of multiple systems and escaping stars confirm this picture. Observations of young star clusters are in best agreement with our strong feedback simulation