Proposal and testing for a fiber-optic-based measurement of flow vorticity

A fiber-optic arrangement is devised to measure the velocity difference, ␦v͑l ͒, down to small separation l. With two sets of optical fibers and couplers the new technique becomes capable of measuring one component of the time-and space-resolved vorticity vector ͑r, t͒. The technique is tested in a steady laminar flow, in which the velocity gradient ͑or flow vorticity͒ is known. The experiment verifies the working principle of the technique and demonstrates its applications. It is found that the new technique measures the velocity difference ͑and hence the velocity gradient when l is known͒ with the same high accuracy and high sampling rate as laser Doppler velocimetry does for the local velocity measurement. It is nonintrusive and capable of measuring the velocity gradient with a spatial resolution as low as ϳ50 m. The successful test of the fiber-optic technique in the laminar flow with one optical channel is an important first step for the development of a two-channel fiber-optic vorticity probe, which has wide use in the general area of fluid dynamics, especially in the study of turbulent flows

Measurements of the instantaneous velocity difference and local velocity with a fiber-optic coupler

New optical arrangements with two single-mode input fibers and a fiber-optic coupler are devised to measure the instantaneous velocity difference and local velocity. The fibers and the coupler are polarization-preserving to guarantee a high signal-to-noise ratio. When the two input fibers are used to collect the scattered light with the same momentum transfer vector but from two spatially separated regions in a flow, the obtained signals interfere when combined via the fiber-optic coupler. The resultant light received by a photomultiplier tube contains a cross-beat frequency proportional to the velocity difference between the two measuring points. If the two input fibers are used to collect the scattered light from a common scattering region but with two different momentum transfer vectors, the resultant light then contains a self-beat frequency proportional to the local velocity at the measuring point. The experiment shows that both the cross-beat and self-beat signals are large and the standard laser Doppler signal processor can be used to measure the velocity difference and local velocity in real time. The new technique will have various applications in the general area of fluid dynamics.Comment: Patent number: 67437 for associated information on the hardware, see http://karman.phyast.pitt.edu/horvath

Long-ranged attraction between charged polystyrene spheres at aqueous interfaces

We report an optical and atomic force microscopic study of interactions between charged polystyrene spheres at a water-air interface. Optical observations of bonded particle clusters and formation of circular chainlike structures at the interface demonstrate that the interaction potential is of dipole origin. Atomic force microscope phase images show patchy domains on the colloidal surface, indicating that the surface charge distribution is not uniform as is commonly believed. Such surface heterogeneity introduces inplane dipoles, leading to an attraction at short interparticle distances.Peer reviewedChemistr

Measured long-ranged attractive interaction between charged polystyrene latex spheres at a water-air interface

We report results of a systematic experimental study of interactions between charged polystyrene (PS) latex spheres at a water-air interface. Optical observations of stable bonded particle clusters and formation of circular chainlike structures at the interface demonstrate that the interaction potential is of dipole origin. Atomic force microscopy (AFM) is used to examine the distribution of charge groups on the colloidal surface. AFM phase images show patchy domains of size ~100 nm on the particle surface, indicating that the surface charge distribution of the PS spheres is not uniform, as is commonly believed. Such patchy charges can introduce fluctuating in-plane dipoles, leading to an attraction at short interparticle separations. A theoretical analysis is given to explain the mechanism for attractions between like-charged particles at the interface.Peer reviewedChemistr

The deep-subsurface sulfate reducer Desulfotomaculum kuznetsovii employs two methanol-degrading pathways

Methanol is generally metabolized through a pathway initiated by a cobalamine-containing methanol methyltransferase by anaerobic methylotrophs (such as methanogens and acetogens), or through oxidation to formaldehyde using a methanol dehydrogenase by aerobes. Methanol is an important substrate in deep-subsurface environments, where thermophilic sulfate-reducing bacteria of the genus Desulfotomaculum have key roles. Here, we study the methanol metabolism of Desulfotomaculum kuznetsovii strain 17T, isolated from a 3000-m deep geothermal water reservoir. We use proteomics to analyze cells grown with methanol and sulfate in the presence and absence of cobalt and vitamin B12. The results indicate the presence of two methanol-degrading pathways in D. kuznetsovii, a cobalt-dependent methanol methyltransferase and a cobalt-independent methanol dehydrogenase, which is further confirmed by stable isotope fractionation. This is the first report of a microorganism utilizing two distinct methanol conversion pathways. We hypothesize that this gives D. kuznetsovii a competitive advantage in its natural environment.Research was funded by grants of the Division of Chemical Sciences (CW-TOP 700.55.343) and Earth and Life Sciences (ALW 819.02.014) of The Netherlands Organisation for Scientific Research (NWO), the European Research Council (ERC grant 323009), and the Gravitation grant (024.002.002) of the Netherlands Ministry of Education, Culture and Scienceinfo:eu-repo/semantics/publishedVersio

Ein Ansatz zur methoden- und werkzeuggestützten Anforderungs- und Systemspezifikation auf der Grundlage objektorientierter Modellierungs- und Simulationstechniken

Vorgestellt wird ein Ansatz zur objektorientierten Modellierung, Simulation und Animation von Informationssystemen. Es wird ein Vorgehensmodell dargestellt, mit dem unter Verwendung des beschriebenen Ansatzes Anforderungs- oder Systemspezifikationen von Rechnergestützten Informationssystemen erstellt werden können. Der Ansatz basiert auf einem Metamodell zur Beschreibung Rechnergestützter Informationssysteme und verfügt über eine rechnergestützte Modellierungsumgebung. Anhand eines Projektes zur Entwicklung einer Anforderungsspezifikation für ein rechnergestütztes Pflegedokumentations- und -kommunikationssystems wird der Einsatz der Methode beispielhaft illustriert