Clustering of microswimmers: Interplay of shape and hydrodynamics

The spatiotemporal dynamics in systems of active self-propelled particles is controlled by the propulsion mechanism in combination with various direct interactions, such as steric repulsion, hydrodynamics, and chemical fields. Yet, these direct interactions are typically anisotropic, and come in different 'flavors', such as spherical and elongated particle shapes for steric repulsion, pusher and puller flow fields for hydrodynamics, etc. The combination of the various aspects is expected to lead to new emergent behavior. However, it is a priori not evident whether shape and hydrodynamics act synergistically or antagonistically to generate motility-induced clustering (MIC) and phase separation (MIPS). We employ a model of prolate spheroidal microswimmers - called squirmers - in quasi-two-dimensional confinement to address this issue by mesoscale hydrodynamic simulations. For comparison, non-hydrodynamic active Brownian particles (ABPs) are considered to elucidate the contribution of hydrodynamic interactions on MIC and MIPS. For spherical particles, the comparison between ABP and hydrodynamic-squirmer ensembles reveals a suppression of MIPS due to hydrodynamic interactions. The fundamental difference between ABPs and squirmers is attributed to an increased reorientation of squirmers by hydrodynamic torques during their collisions. In contrast, for elongated squirmers, hydrodynamics interactions enhance MIPS. Thus, hydrodynamic interactions show opposing effects on MIPS for spherical and elongated microswimmers

Renewable energy sources to secure the base load in electricity supply. Summary

The share of renewable energies in Germany\u27s electricity supply has been increasing at an impressive rate in recent years: it already amounts to over 20 %, about half of which comes from fluctuating sources - mainly wind power and photovoltaics. In the long term (by 2050), the goal is to achieve almost full supply with renewable energies. This makes it clear that the system of electricity supply will be subject to an upheaval of historic proportions in the coming decades. The TAB report addresses the question of how the base load in the electricity supply can continue to be secured under these conditions. This question can only be addressed in a system perspective that encompasses all levels: from generation to transport and distribution to the consumption of electricity. Therefore, the question expands to how a secure supply can be organised as a whole. It is becoming apparent that the electricity system must be able to react much more flexibly than before to different feed-in and demand situations. Options for increasing flexibility exist in many areas: > Increasing the efficiency of the grids > Increasing the flexibility of the conventional power plant fleet and its mode of operation > Greater orientation of electricity production from renewable energies to demand > load management, and not least the construction of additional storage facilities. In all of these fields of action, the TAB report identifies options for action in which the public sector and the energy policy actors in the executive and legislative branches can contribute to the success of the upcoming transformation of the electricity supply by shaping the framework conditions

Facile Synthesis and Characterization of Pure Tochilinite‐like Materials from Nanoparticulate FeS

Abstract In this work, three different tochilinite‐like materials have been obtained by sophisticated synthetic methods that allow to control the distribution of iron ions. The purity of the samples was confirmed by powder X‐ray diffraction. From elemental analysis and Mössbauer spectroscopy data, detailed compositions could be determined: T1) Fe 0.76 S*0.86 [Fe 2+ 0.01 Fe 3+ 0.56 Mg 2+ 0.43 (OH) 2.01 ]; T2) Fe 0.89 S*0.85 [Fe 2+ 0.55 Fe 3+ 0.11 Al 3+ 0.33 (OH) 1.84 (O) 0.16 ]; T3) Fe 0.71 S*0.79 [Fe 2+ 0.25 Fe 3+ 0.73 Mg 2+ 0.01 Al 3+ 0.01 (OH) 1.98 (O) 0.02 ]. These compositions fit to typical compositions of tochilinite in regard of the amount of iron vacancies and the volume ratio of the hydroxide layers to the sulfide layers. Besides hydroxide ions, oxide ions are also present in the hydroxide layers as a result of surface oxidation after the synthesis due to the high reactivity of the particles. TEM and SEM investigations show that the obtained powders consist mainly of thin sheets accompanied by nanotubes with BET surface areas ranging between 20 m 2 /g and 40 m 2 /g. The thermal stability was investigated by TGA and DSC analysis and it depends significantly on the composition.imag

The Augmented Lagrange Multiplier Method for Exact Recovery of Corrupted Low-Rank Matrices

This paper proposes scalable and fast algorithms for solving the Robust PCA problem, namely recovering a low-rank matrix with an unknown fraction of its entries being arbitrarily corrupted. This problem arises in many applications, such as image processing, web data ranking, and bioinformatic data analysis. It was recently shown that under surprisingly broad conditions, the Robust PCA problem can be exactly solved via convex optimization that minimizes a combination of the nuclear norm and the $\ell^1$-norm . In this paper, we apply the method of augmented Lagrange multipliers (ALM) to solve this convex program. As the objective function is non-smooth, we show how to extend the classical analysis of ALM to such new objective functions and prove the optimality of the proposed algorithms and characterize their convergence rate. Empirically, the proposed new algorithms can be more than five times faster than the previous state-of-the-art algorithms for Robust PCA, such as the accelerated proximal gradient (APG) algorithm. Moreover, the new algorithms achieve higher precision, yet being less storage/memory demanding. We also show that the ALM technique can be used to solve the (related but somewhat simpler) matrix completion problem and obtain rather promising results too. We further prove the necessary and sufficient condition for the inexact ALM to converge globally. Matlab code of all algorithms discussed are available at http://perception.csl.illinois.edu/matrix-rank/home.htmlComment: Please cite "Zhouchen Lin, Risheng Liu, and Zhixun Su, Linearized Alternating Direction Method with Adaptive Penalty for Low Rank Representation, NIPS 2011." (available at arXiv:1109.0367) instead for a more general method called Linearized Alternating Direction Method This manuscript first appeared as University of Illinois at Urbana-Champaign technical report #UILU-ENG-09-2215 in October 2009 Zhouchen Lin, Risheng Liu, and Zhixun Su, Linearized Alternating Direction Method with Adaptive Penalty for Low Rank Representation, NIPS 2011. (available at http://arxiv.org/abs/1109.0367

Regenerative Energieträger zur Sicherung der Grundlast in der Stromversorgung. Endbericht zum Monitoring

Der Anteil erneuerbarer Energien an der Stromversorgung Deutschlands steigt in den letzten Jahren mit beeindruckender Geschwindigkeit: er beträgt bereits über 20 %, davon etwa die Hälfte aus fluktuierenden Quellen – vor allem Windkraft und Photovoltaik. Langfristig (bis 2050) wird die Zielsetzung einer nahezu Vollversorgung mit erneuerbaren Energien verfolgt. Damit wird deutlich, dass das System der Stromversorgung in den nächsten Jahrzehnten einem Umbruch historischen Ausmaßes unterliegen wird. Der TAB-Bericht geht der Frage nach, wie unter diesen Bedingungen die Grundlast in der Stromversorgung weiterhin gesichert werden kann. Diese Frage kann nur in einer Systemperspektive angegangen werden, die alle Ebenen umfasst: von der Erzeugung über den Transport und die Verteilung bis hin zum Verbrauch von Elektrizität. Daher erweitert sich die Fragestellung dahingehend, wie eine gesicherte Versorgung insgesamt organisiert werden kann. Es zeigt sich, dass das Stromsystem wesentlich flexibler als bisher auf unterschiedliche Einspeise- und Nachfragesituationen reagieren können muss. Optionen zur Steigerung der Flexibilität existieren in vielen Bereichen: > Erhöhung der Leistungsfähigkeit der Netze > Flexibilisierung des konventionellen Kraftwerksparks und dessen Betriebsweise > stärkere Orientierung der Stromproduktion aus erneuerbaren Energien an der Nachfrage > Lastmanagement, sowie nicht zuletzt Errichtung von zusätzlichen Speichern In allen diesen Handlungsfeldern werden im TAB-Bericht Handlungsoptionen identifiziert, wie die öffentliche Hand bzw. die energiepolitischen Akteure in Exekutive und Legislative durch Gestaltung von Rahmenbedingungen dazu beitragen können, dass der anstehende Umbau der Stromversorgung gelingen kann. INHALT ZUSAMMENFASSUNG 5 I. EINLEITUNG 19 II. ELEKTRIZITÄTSVERSORGUNG IN DEUTSCHLAND 23 1. Ausbauziele und Szenarien für RES-E 25 2. Grundlast und gesicherte Versorgung 29 III. STROMNETZE 39 1. Erweiterung der Netzkapazität 39 1.1 Optimierung des Netzbetriebs 39 1.2 Massnahmen zur Netzverstärkung 40 1.3 Netzausbau 42 2. Netzausbaubedarf und Kosten 44 2.1 Deutschland 45 2.2 Europäische Perspektive 54 2.3 Transeuropäisches Supergrid 56 IV. SPEICHER UND WEITERE FLEXIBILISIERUNGSOPTIONEN 63 1. Speicher 64 1.1 Speicherbedarf 66 1.2 Speicherkosten 68 1.3 Speichertechnologien 70 2. Weitere Flexibilisierungsoptionen 83 2.1 Biogas 83 2.2 Wärme als Stromsenke – Verbindung zum Wärmesektor 86 2.3 Lastmanagement 88 2.4 Ausbau des Stromaustausches mit Norwegen 92 2.5 Regenerative Kombi-/Hybridkraftwerke 94 3. Speicher und weitere Flexibilisierungsoptionen: Zwischenfazit 97 V. SZENARIENANALYSE 99 1. Vorgehensweise 99 2. Bestimmung der Einspeiseprofile im Referenzjahr 100 3. Szenariodarstellung 101 4. Situation des Stromversorgungsystems ohne Flexibilisierungsoptionen 103 5. Begrenzungen und Flexibilisierungsoptionen 106 5.1 Systemdienstleistungen 107 5.2 Bestehende Flexibilisierungsoptionen 108 5.3 Geplanter Ausbau der bestehenden Flexibiliersungsoptionen bis 2020 109 6. Parametrisierung der Flexibilisierungsoptionen 111 6.1 Beschreibung des Modellierungsansatzes 112 6.2 Ergebnisse zur Glättung der Residuallast 113 6.3 Ergebnisse zur Glättung der RES-E-Einspeisung 115 6.4 Netzengpässe als weitere Begrenzung 118 7. Kernergebnisse der Analyse 118 VI. INTERNATIONALE ERFAHRUNGEN 121 1. Dänemark 122 2. Iberische Halbinsel 124 3. Vergleich mit Deutschland 125 VII. HANDLUNGSFELDER UND HANDLUNGSOPTIONEN 129 1. Netzengpässe und Netzausbau 129 2. Konventionelle Kraftwerke 131 3. Flexibilisierungsoptionen 133 4. Regelmarkt 137 5. Strommarktdesign 138 6. Europäische Kooperation 138 VIII. LITERATUR 139 1. In Auftrag gegebene Gutachten 139 2. Weitere Literatur 139 IX. ANHANG 153 1. Tabellenverzeichnis 153 2. Abbildungsverzeichnis 15

The Ages of Pre-main-sequence Stars

The position of pre-main-sequence or protostars in the Hertzsprung--Russell diagram is often used to determine their mass and age by comparison with pre-main-sequence evolution tracks. On the assumption that the stellar models are accurate, we demonstrate that, if the metallicity is known, the mass obtained is a good estimate. However, the age determination can be very misleading because it is significantly (generally different by a factor of two to five) dependent on the accretion rate and, for ages less than about one million years, the initial state of the star. We present a number of accreting protostellar tracks that can be used to determine age if the initial conditions can be determined and the underlying accretion rate has been constant in the past. Because of the balance established between the Kelvin-Helmholtz, contraction timescale and the accretion timescale a pre-main-sequence star remembers its accretion history. Knowledge of the current accretion rate, together with an H--R-diagram position gives information about the rate of accretion in the past but does not necessarily improve any age estimate. We do not claim that ages obtained by comparison with these particular accreting tracks are likely to be any more reliable than those from comparisons with non-accreting tracks. Instead we stress the unreliability of any such comparisons and use the disparities between various tracks to estimate the likely errors in age and mass estimates. We also show how a set of coeval accreting objects do not appear coeval when compared with non-accreting tracks. Instead accreting pre-main-sequence stars of around a solar mass are likely to appear older than those of either smaller or larger mass.Comment: Accepted by MNRA

A vision-based system for intelligent monitoring: human behaviour analysis and privacy by context

Due to progress and demographic change, society is facing a crucial challenge related to increased life expectancy and a higher number of people in situations of dependency. As a consequence, there exists a significant demand for support systems for personal autonomy. This article outlines the vision@home project, whose goal is to extend independent living at home for elderly and impaired people, providing care and safety services by means of vision-based monitoring. Different kinds of ambient-assisted living services are supported, from the detection of home accidents, to telecare services. In this contribution, the specification of the system is presented, and novel contributions are made regarding human behaviour analysis and privacy protection. By means of a multi-view setup of cameras, people's behaviour is recognised based on human action recognition. For this purpose, a weighted feature fusion scheme is proposed to learn from multiple views. In order to protect the right to privacy of the inhabitants when a remote connection occurs, a privacy-by-context method is proposed. The experimental results of the behaviour recognition method show an outstanding performance, as well as support for multi-view scenarios and real-time execution, which are required in order to provide the proposed services

Effects of Zn Substitution in the Magnetic and Morphological Properties of Fe-Oxide-Based Core-Shell Nanoparticles Produced in a Single Chemical Synthesis

Magnetic, compositional, and morphological properties of Zn-Fe-oxide core-shell bimagnetic nanoparticles were studied for three samples with 0.00, 0.06, and 0.10 Zn/Fe ratios, as obtained from particle-induced X-ray emission analysis. The bimagnetic nanoparticles were produced in a one-step synthesis by the thermal decomposition of the respective acetylacetonates. The nanoparticles present an average particle size between 25 and 30 nm as inferred from transmission electron microscopy (TEM). High-resolution TEM images clearly show core-shell morphology for the particles in all samples. The core is composed by an antiferromagnetic (AFM) phase with a Wüstite (Fe 1-y O) structure, whereas the shell is composed by a Zn x Fe 3-x O 4 ferrimagnetic (FiM) spinel phase. Despite the low solubility of Zn in the Wüstite, electron energy-loss spectroscopy analysis indicates that Zn is distributed almost homogeneously in the whole nanoparticle. This result gives information on the formation mechanisms of the particle, indicating that the Wüstite is formed first, and the superficial oxidation results in the FiM ferrite phase with similar Zn concentration than the core. Magnetization and in-field Mössbauer spectroscopy of the Zn-richest nanoparticles indicate that the AFM phase is strongly coupled to the FiM structure of the ferrite shell, resulting in a bias field (H EB ) appearing below TN FeO , with H EB values that depend on the core-shell relative proportion. Magnetic characterization also indicates a strong magnetic frustration for the samples with higher Zn concentration, even at low temperatures.Fil: Lohr, Javier Hernán. Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. - Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física. Laboratorio de Resonancias Magnéticas; ArgentinaFil: de Almeida, Adriele Aparecida. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física. Laboratorio de Resonancias Magnéticas; ArgentinaFil: Moreno, Mario Sergio Jesus. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; ArgentinaFil: Troiani, Horacio Esteban. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física. Laboratorio de Resonancias Magnéticas; ArgentinaFil: Goya, Gerardo Fabian. Universidad de Zaragoza; EspañaFil: Torres Molina, Teobaldo Enrique. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física. Laboratorio de Resonancias Magnéticas; Argentina. Universidad de Zaragoza; EspañaFil: Fernandez Pacheco, Rodrigo. Universidad de Zaragoza; EspañaFil: Winkler, Elin Lilian. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; ArgentinaFil: Vasquez Mansilla, Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; ArgentinaFil: Cohen, Renato. Universidade de Sao Paulo; BrasilFil: Nagamine, Luiz C. C. M.. Universidade de Sao Paulo; BrasilFil: Rodriguez, Luis Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; ArgentinaFil: Fregenal, Daniel Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; ArgentinaFil: Zysler, Roberto Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; ArgentinaFil: Lima, Enio Junior. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; Argentin