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Search Results: 1 - 10 of 4643 matches for " Dennis Gro?mann "
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Catalytic Behaviour of Mesoporous Cobalt-Aluminum Oxides for CO Oxidation
Ankur Bordoloi,Miguel Sanchez,Heshmat Noei,Stefan Kaluza,Dennis Gromann,Yuemin Wang,Wolfgang Grünert,Martin Muhler
Journal of Catalysts , 2014, DOI: 10.1155/2014/807545
Abstract: Ordered mesoporous materials are promising catalyst supports due to their uniform pore size distribution, high specific surface area and pore volume, tunable pore sizes, and long-range ordering of the pore packing. The evaporation-induced self-assembly (EISA) process was applied to synthesize mesoporous mixed oxides, which consist of cobalt ions highly dispersed in an alumina matrix. The characterization of the mesoporous mixed cobalt-aluminum oxides with cobalt loadings in the range from 5 to 15?wt% and calcination temperatures of 673, 973, and 1073?K indicates that Co2+ is homogeneously distributed in the mesoporous alumina matrix. As a function of the Co loading, different phases are present comprising poorly crystalline alumina and mixed cobalt aluminum oxides of the spinel type. The mixed cobalt-aluminum oxides were applied as catalysts in CO oxidation and turned out to be highly active. 1. Introduction Supported metal oxide catalysts have attracted much attention in recent years due to their widespread applicability in industrially and academically important reactions. The extent and nature of the interaction, dispersion, and reducibility of the metal oxides depend on the synthesis method, loading, calcination temperature, and time. Cobalt supported on alumina is a typical catalyst, which is specially important for Fischer-Tropsch synthesis. Conventionally, the preparation of cobalt catalysts is performed by incipient wetness impregnation using suitable cobalt precursors on commercial alumina at low pH. Weak interaction is normally observed between the positively charged alumina carrier and the cobalt cations resulting in relatively large crystallite sizes [1–4]. Continuous efforts have been made in the last few decades by several groups [5–7] to synthesize porous alumina with high surface area by high-temperature dehydration of bulk powders [8], modified sol-gel synthesis in the presence of organic moieties [9, 10], different surfactants [3], block copolymers [11–14], or evaporation-induced self-assembly (EISA) with colloidal precursors and amine structural agents [15, 16]. These materials represent an active support, which may participate positively or negatively in the formation of the final catalysts. Moreover, the methods of hard templating [17] (carbon template) and microwave irradiation [18] in the presence of surfactants have been applied to synthesize alumina materials with crystalline, ordered, and uniform mesopores. However, this process is very time consuming and hardly scalable for industrial applications. Ordered mesoporous materials
Integriertes Informationsmanagement für Hochschulen – das kiz als Serviceprovider (Festvortrag)
Gromann, Hans Peter
GMS Medizin-Bibliothek-Information , 2007,
Abstract:
Agents of Change - Frauenaktivistinnen in Aceh [Agents of Change - Women Activists in Aceh]
Kristina Gromann
ASEAS : ?sterreichische Zeitschrift für Südostasienwissenschaften , 2008,
Abstract: Aceh befindet sich seit der Dezentralisierungspolitik Indonesiens Ende der 1990er Jahre, der Tsunamikatastrophe 2004 und der Unterzeichnung des Memorandum of Understanding (MoU) 2005in einer politischen, kulturellen und gesellschaftlichen Transformation. Die Situation der Frauen in Aceh ist gepr gt durch Repressionen aufgrund der Einführung der Scharia, durch Einflussnahmevon internationalen Hilfsorganisationen nach dem Tsunami und durch die Neuordnung der Region Acehs seit den Autonomieverhandlungen. Der Transformationsprozess bringt gro e Herausforderungen für die Frauen in Aceh mit sich und beinhaltet zugleich die Chance zur Mitgestaltung. So entwerfen Frauenaktivistinnen innerhalb des Spannungsfeldes islamische Religiosit t, traditionell-kulturelleStrukturen und westliche Wertevorstellungen, Positionen und Strategien, um ihren Wunsch nach Geschlechtergerechtigkeit durchzusetzen. Mein Artikel beleuchtet die Frage, welche Rolle Frauenaktivistinnen innerhalb des Transformationsprozesses einnehmen und welche Chancen, M glichkeiten und Hindernisse es gibt, um Einfluss auf politische und gesellschaftliche Prozesse zunehmen. ----- Aceh, Indonesia’s westernmost province is in a process of political, social and cultural transformation, which is caused by three main factors. First, the process of decentralisation, launched by the government of Indonesia starting from the end of the 1990s and as a consequence of the implementation of sharia bylaws since 2001, second, the tsunami calamity 2004 and third, the peace process starting with the signing of the Memorandum of Understanding (MoU) 2005 between representatives of the Government of Indonesia and the Acehnese freedom movement GAM (Gerakan Aceh Merdeka). Today’s situation of women in Aceh is infl uenced by repressions due to a conservative interpretation of Islam, by the impact of international aid organisations, which entered Aceh after the tsunami andby the political, social and cultural reconstruction of Aceh since the beginning of the peace process. The transformation process causes huge challenges for women and at the same time provides a wide range of opportunities for participation and modelling the new province Aceh. In this vibrant atmosphere, where tensions between Islamic religiosity, traditional-cultural structures and Western values are immense, women activists design positions and strategies to aim their desire of gender justice, equity and women’s rights. The present impact of the multiple efforts of women activists to take influence in the political and socio-cultural area can be described as
Finite rank perturbations and solutions to the operator Riccati equation
Julian P. Gromann
Mathematics , 2014,
Abstract: We consider an off-diagonal self-adjoint finite rank perturbation of a self-adjoint operator in a complex separable Hilbert space $\mathfrak{H}_0 \oplus \mathfrak{H}_1$, where $\mathfrak{H}_1$ is finite dimensional. We describe the singular spectrum of the perturbed operator and establish a connection with solutions to the operator Riccati equation. In particular, we prove existence results for solutions in the case where the whole Hilbert space is finite dimensional.
Eastern European Transformation and Youth Attitudes toward Violence
Eva Maria Gro,Berit Hau?mann
International Journal of Conflict and Violence , 2011,
Abstract: This cross-national examination of the motives behind adolescent approval of violence in major cities in Germany and four Eastern European transformation societies (Czech Republic, Poland, Russia, Slovenia) draws on Institutional Anomie Theory (IAT), which leads us to expect higher instrumental motivation for violence among adolescents in the transforming societies. Differences in institutional structure and cultural orientations between Germany and the Eastern European societies are assessed using data from ILO and ESS. Analysis of the different motives for violence is based on data collected by the Criminological Research Institute of Lower Saxony (KFN) in Kraków, Volgograd, Ljubljana, Plzen, and Hamburg. Comparability and cross-cultural interpretability of the violence attitude measure is assessed by applying confirmatory factor analyses in multi-group comparisons. A lack of sufficient data meant that specific assumed linkages as implied by IAT could not be established, but the results for a specific instrumental/utilitarian motive for violence and for institutional structure and cultural orientations point to the utility of applying insights from IAT to understanding the dynamics of violence within the Eastern European context of transformation. We find empirical indications that specific features of the family mediate the “Eastern effect” on the instrumental/utilitarian motive. Further research is needed to discover whether economic dominance affects motives for youth violence indirectly via the socialization provided by non-economic institutions rather than directly via cultural orientations.
Iodine monoxide in the Western Pacific marine boundary layer
K. Gromann,U. Frie?,E. Peters,F. Wittrock
Atmospheric Chemistry and Physics Discussions , 2012, DOI: 10.5194/acpd-12-27475-2012
Abstract: A latitudinal cross-section and vertical profiles of iodine monoxide (IO) are reported from the marine boundary layer of the Western Pacific. The measurements were taken using Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) during the TransBrom cruise of the German research vessel Sonne, which led from Tomakomai, Japan (42° N, 141° E) through the Western Pacific to Townsville, Australia (19° S, 146° E) in October 2009. In the marine boundary layer within the tropics (between 20° N and 5° S), IO mixing ratios ranged between 1 and 2.2 ppt, whereas in the subtropics and at mid-latitudes typical IO mixing ratios were around 1 ppt in the daytime. The profile retrieval reveals that the bulk of the IO was located in the lower part of the marine boundary layer. Photochemical simulations indicate that the organic iodine precursors observed during the cruise (CH3I, CH2I2, CH2ClI, CH2BrI) are not sufficient to explain the measured IO mixing ratios. Reasonable agreement between measured and modelled IO can only be achieved, if an additional sea-air flux of inorganic iodine (e.g. I2) is assumed in the model. Our observations add further evidence to previous studies that reactive iodine is an important oxidant in the marine boundary layer.
Formaldehyde and nitrogen dioxide over the remote western Pacific Ocean: SCIAMACHY and GOME-2 validation using ship-based MAX-DOAS observations
E. Peters,F. Wittrock,K. Gromann,U. Frie?
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2012, DOI: 10.5194/acp-12-11179-2012
Abstract: In October 2009, shipborne Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements were performed during the TransBrom campaign over the western Pacific Ocean (≈ 40° N to 20° S). Vertical tropospheric trace gas columns and profiles of nitrogen dioxide (NO2) and formaldehyde (HCHO) as well as stratospheric NO2 columns were retrieved in order to validate corresponding measurements from the GOME-2 and SCIAMACHY satellite instruments and to estimate tropospheric background concentrations of these trace gases. All instruments reproduced the same characteristic, latitude-dependent shape of stratospheric NO2. SCIAMACHY and GOME-2 data differ by about 1% from each other while yielding lower vertical columns than MAX-DOAS morning values as a consequence of measurement time and stratospheric NO2 diurnal cycle. Due to this diurnal cycle, an increase of 8.7 ± 0.5 × 1013 molec cm 2 h 1 of stratospheric NO2 was estimated from MAX-DOAS data at low latitudes during the day. Tropospheric NO2 was above the detection limit only in regions of higher anthropogenic impact (ship traffic, transport of pollution from land). A background column of 1.3 × 1014 molec cm 2 (or roughly 50 ppt boundary layer concentration) can be estimated as upper limit for the remote ocean, which is in agreement with GOME-2 monthly mean values. In the marine boundary layer close to the islands of Hokkaido and Honshu, up to 0.8 ppbv were retrieved close to the surface. Background HCHO concentrations over the remote ocean exhibit a diurnal cycle with maximum values (depending strongly on weather conditions) of 4 × 1015 molec cm 2 for the vertical column at noontime. Corresponding peak concentrations of up to 1.1 ppbv were retrieved in elevated altitudes (≈ 400 m) around noon while maximum concentrations in the evening are close to the ground. An agreement between MAX-DOAS and GOME-2 data was found for typical vertical columns of 3 × 1015 molec cm 2 over the remote ocean at the time of overpass.
A geometric approach to self-propelled motion in isotropic and anisotropic environments
Robert Gromann,Fernando Peruani,Markus B?r
Physics , 2015,
Abstract: We propose a geometric perspective to describe the motion of self-propelled particles moving at constant speed in d dimensions. We exploit the fact that the vector that conveys the direction of motion of the particle performs a random walk on a $(d-1)$-dimensional manifold. We show that the particle performs isotropic diffusion in d-dimensions if the manifold corresponds to a hypersphere. In contrast, we find that the self-propelled particle exhibits anisotropic diffusion if this manifold corresponds to a deformed hypersphere (e.g. an ellipsoid). This simple approach provides an unified framework to deal with isotropic as well as anisotropic diffusion of particles moving at constant speed in any dimension.
Long-range order induced by superdiffusion of classical XY spins
Robert Gromann,Fernando Peruani,Markus B?r
Physics , 2015,
Abstract: Motivated by observations of synchronization of motile chemical and biological oscillators, we study an ensemble of random walkers in two dimensions carrying an internal noisy clock which is synchronized among the walkers by local interaction. This system corresponds to an ensemble of moving classical XY spins. We consider two mobility patterns for the walkers: normal diffusive motion and L\'{e}vy flights. In particular, we investigate the crucial influence of the mobility pattern on the nonequilibrium phase transition from incoherence to synchronization focusing on the large system limit. For normally diffusing oscillators, a finite-size scaling analysis reveals a Berezinskii-Kosterlitz-Thouless transition from incoherence to quasi long-range order. In contrast, we show that L\'{e}vy flight motion induces a continuous phase transition to synchronization and long-range order in two dimensions.
Diffusion properties of active particles with directional reversal
Robert Gromann,Fernando Peruani,Markus B?r
Physics , 2015,
Abstract: The diffusion properties of self-propelled particles which move at constant speed and, in addition, reverse their direction of motion repeatedly are investigated. The internal dynamics of particles triggering these reversal processes is modeled by a stochastic clock. The velocity correlation function as well as the mean squared displacement is investigated and, furthermore, a general expression for the diffusion coefficient for self-propelled particles with directional reversal is derived. Our analysis reveals the existence of an optimal, finite rotational noise amplitude which maximizes the diffusion coefficient. We comment on the relevance of these results with regard to microbiological systems and suggest further experiments in this context.
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