7,954 research outputs found
Group classification of the Sachs equations for a radiating axisymmetric, non-rotating, vacuum space-time
We carry out a Lie group analysis of the Sachs equations for a time-dependent
axisymmetric non-rotating space-time in which the Ricci tensor vanishes. These
equations, which are the first two members of the set of Newman-Penrose
equations, define the characteristic initial-value problem for the space-time.
We find a particular form for the initial data such that these equations admit
a Lie symmetry, and so defines a geometrically special class of such
spacetimes. These should additionally be of particular physical interest
because of this special geometric feature.Comment: 18 Pages. Submitted to Classical and Quantum Gravit
Imaging Pulsed Laser Deposition oxide growth by in-situ Atomic Force Microscopy
To visualize the topography of thin oxide films during growth, thereby
enabling to study its growth behavior quasi real-time, we have designed and
integrated an atomic force microscope (AFM) in a pulsed laser deposition (PLD)
vacuum setup. The AFM scanner and PLD target are integrated in a single support
frame, combined with a fast sample transfer method, such that in-situ
microscopy can be utilized after subsequent deposition pulses. The in-situ
microscope can be operated from room temperature (RT) up to 700C and at
(process) pressures ranging from the vacuum base pressure of 10 mbar up
to 1 mbar, typical PLD conditions for the growth of oxide films. The
performance of this instrument is demonstrated by resolving unit cell height
surface steps and surface topography under typical oxide PLD growth conditions.Comment: 8 pages, 8 figure
Determining the energetics of vicinal perovskite oxide surfaces
The energetics of vicinal SrTiO(001) and DyScO(110), prototypical
perovskite vicinal surfaces, has been studied using topographic atomic force
microscopy imaging. The kink formation and strain relaxation energies are
extracted from a statistical analysis of the step meandering. Both perovskite
surfaces have very similar kink formation energies and exhibit a similar
triangular step undulation. Our experiments suggest that the energetics of
perovskite oxide surfaces is mainly governed by the local oxygen coordination.Comment: 16 pages, 4 figure
The RESET Mindset Model applied on decreasing antibiotic usage in dairy cattle in the Netherlands
This article analyses sanctuary initiatives intended to change the situation of ‘irregularised residents’. Through fieldwork, three main activities are identified: assistance for welfare services, alternatives to inaccessible services, and inventing new ways of organising togetherness in the city. The role of activists in the initiatives links to discussions within Critical Human Rights literature, which emphasise the anti-institutionalist origins of rights. Yet, a complex interplay also plays out through co-current resistance against the state’s migration policing and collaboration with city-level state agencies. Understanding this complex process is important to improving knowledge of both the politics of sanctuary and human rights
Colophospermum mopane Wood Utilisation in the Northeast of the Limpopo Province, South Africa
The use of Colophospermum mopane wood was quantified from six villages in the northeast of the Limpopo Province, South Africa. One hundred and eighty individuals were interviewed from the selected villages. Three villages were located in the depleted woodlands and the remaining three at abundant woodlands. Traditional governance structures within the selected villages and relevant conservation department officials were also interviewed. Colophospermum mopane is an essential source of fuelwood and provide poles used for construction of traditional structures. Each family uses 6.8 ± 0.1 kg of Colophospermum mopane fuelwood for cooking day-1 in the woodland depleted villages, while 8.2 ± 0.2 kg is used at the woodland abundant villages. Colophospermum mopane is preferred for construction of traditional structures because its wood is durable and is able to resists the effects of termites and wood borers
Functional consequences of sphingomyelinase-induced changes in erythrocyte membrane structure.
Inflammation enhances the secretion of sphingomyelinases (SMases). SMases catalyze the hydrolysis of sphingomyelin into phosphocholine and ceramide. In erythrocytes, ceramide formation leads to exposure of the removal signal phosphatidylserine (PS), creating a potential link between SMase activity and anemia of inflammation. Therefore, we studied the effects of SMase on various pathophysiologically relevant parameters of erythrocyte homeostasis. Time-lapse confocal microscopy revealed a SMase-induced transition from the discoid to a spherical shape, followed by PS exposure, and finally loss of cytoplasmic content. Also, SMase treatment resulted in ceramide-associated alterations in membrane-cytoskeleton interactions and membrane organization, including microdomain formation. Furthermore, we observed increases in membrane fragility, vesiculation and invagination, and large protein clusters. These changes were associated with enhanced erythrocyte retention in a spleen-mimicking model. Erythrocyte storage under blood bank conditions and during physiological aging increased the sensitivity to SMase. A low SMase activity already induced morphological and structural changes, demonstrating the potential of SMase to disturb erythrocyte homeostasis. Our analyses provide a comprehensive picture in which ceramide-induced changes in membrane microdomain organization disrupt the membrane-cytoskeleton interaction and membrane integrity, leading to vesiculation, reduced deformability, and finally loss of erythrocyte content. Understanding these processes is highly relevant for understanding anemia during chronic inflammation, especially in critically ill patients receiving blood transfusions
Fostering Research Integrity through Institutional Policies: The Case of a Selected Institution of Higher Education1
Truth, trust and integrity are essential to research at higher education institutions. These institutions have accordingly adopted several policies tofoster research integrity. This article explores the likelihood that relevant policies at a selected institution of higher education foster research integrity. The qualitative, single exploratory case study commences with a review of scholarly literature and results in a conceptual model used for a directed content analysis of relevant institutional policies. The findings indicate that these policies do complement each other in fostering research integrity. Further research will be necessary to establish whether policies indeed contribute to responsible researcher conduct
Wall-Fluid and Liquid-Gas Interfaces of Model Colloid-Polymer Mixtures by Simulation and Theory
We perform a study of the interfacial properties of a model suspension of
hard sphere colloids with diameter and non-adsorbing ideal polymer
coils with diameter . For the mixture in contact with a planar hard
wall, we obtain from simulations the wall-fluid interfacial free energy,
, for size ratios and 1, using
thermodynamic integration, and study the (excess) adsorption of colloids,
, and of polymers, , at the hard wall. The interfacial
tension of the free liquid-gas interface, , is obtained following
three different routes in simulations: i) from studying the system size
dependence of the interfacial width according to the predictions of capillary
wave theory, ii) from the probability distribution of the colloid density at
coexistence in the grand canonical ensemble, and iii) for statepoints where the
colloidal liquid wets the wall completely, from Young's equation relating
to the difference of wall-liquid and wall-gas interfacial
tensions, . In addition, we calculate , and using density functional theory and a scaled particle
theory based on free volume theory. Good agreement is found between the
simulation results and those from density functional theory, while the results
from scaled particle theory quantitatively deviate but reproduce some essential
features. Simulation results for obtained from the three
different routes are all in good agreement. Density functional theory predicts
with good accuracy for high polymer reservoir packing fractions,
but yields deviations from the simulation results close to the critical point.Comment: 23 pages, 10 figures, REVTEX. Fig 5a changed. Final versio
Stabilized high-power laser system for the gravitational wave detector advanced LIGO
An ultra-stable, high-power cw Nd:YAG laser system, developed for the ground-based gravitational wave detector Advanced LIGO (Laser Interferometer Gravitational-Wave Observatory), was comprehensively characterized. Laser power, frequency, beam pointing and beam quality were simultaneously stabilized using different active and passive schemes. The output beam, the performance of the stabilization, and the cross-coupling between different stabilization feedback control loops were characterized and found to fulfill most design requirements. The employed stabilization schemes and the achieved performance are of relevance to many high-precision optical experiments
Rosenfeld functional for non-additive hard spheres
The fundamental measure density functional theory for hard spheres is
generalized to binary mixtures of arbitrary positive and moderate negative
non-additivity between unlike components. In bulk the theory predicts
fluid-fluid phase separation into phases with different chemical compositions.
The location of the accompanying critical point agrees well with previous
results from simulations over a broad range of non-additivities and both for
symmetric and highly asymmetric size ratios. Results for partial pair
correlation functions show good agreement with simulation data.Comment: 8 pages with 4 figure
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