Koordinatentransformationen zur Behandlung von Mehrphasensystemen

Übersicht In der elektrischen Energietechnik wird die Lösung von Netzproblemen durch Anwendung von Koordinatentransformationen erleichtert. Dabei werden Symmetrieeigenschaften elektrischer Betriebsmittel ausgenutzt.Die möglichen Transformationen werden hergeleitet. Man stellt fest, daß die bekannten o (Clarke)-, odq (Park)- und o12 (symmetrische)-Komponenten noch um die neu vorgestellten oGH-Komponenten zu ergänzen sind, um ein vollständiges System von Transformationen zu erhalten. Die oGH-Komponenten präzisieren den in der Literatur eingeführten Begriff Raumzeiger.Die richtige Wahl des Komponentensystems ist entscheidend für die Nutzung der möglichen Rechenvorteile. Kriterien für die geeignete Auswahl werden angegeben.

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Contents The solution of network problems in power engineering is often simplified by the use of coordinate transformations. These transformations take advantage of the symmetrical properties of electrical equipment.All possible transformations are deduced in this paper. It is found that the well-known o-(Clarke)-, odq-(Park)- and o12-(symmetrical)-coordinates have to be supplemented by certain oGH-coordinates to form a complete set of transformations. These oGH-coordinates generalize the concept of the complex vector as known in the literature.The proper choice of the coordinate system is essential for the efficient use of these transformations. Criteria for the proper choice are given.

     

The collection efficiency of a particle-loaded single filter fiber

The collection efficiency η(M) of single fibers, both isolated and within a parallel array, was determined as a function of accumulated particle mass for Stokes numbers St=0.3–3 and interception parameters In=0.04–0.32. This regime is dominated by inertia, interception and particle bounce. Measurements were made with an optical in-situ particle counting technique. Monodisperse polystyrene aerosols (1.3, 2.6, 3.6 and 5.2 μm) were deposited onto steel wires of 8 and 30 μm, respectively. Particle accumulation reached values on the order of M=0.5–1 μg/mm fiber, corresponding to 10⁴–10⁶ particles per mm, depending on size.η(M) was found to increase for all operating conditions between about 2 and nearly 50 fold, most strongly however for those conditions were the bare fiber is ineffective as a particle collector, i.e. for very low or very high values of St number, corresponding to low collision or low adhesion probabilities, respectively. The absolute efficiency increased to values approaching or exceeding unity, i.e. the effective fiber collision cross-section exceeded the diameter of the bare fiber. For fibers within an array of parallel fibers (equivalent packing density ∼0.004), the initial efficiency η₀ was higher than for an isolated fiber by almost an order of magnitude. However the increase with loading was substantially smaller, typically by an order of magnitude.The efficiency increase can be described by a power law of the type where b and c are empirical fit coefficients. Within an array, the exponent c is on the order of 0.7±0.05, but lower than reported in earlier work on fiber arrays which suggest a value near unity. For isolated fibers, c→1 as interception becomes dominant (at very low flow velocities) while at high impact velocities and significant particle bounce c≈0.5. The coefficient c correlates with fiber Reynolds number, but not with other parameters. The coefficient b is inversely proportional to η₀ (consistent with earlier work, however with significantly lower values than previously published) and a function of (St/R)².The experimental section of the paper is preceded by a literature review on single-fiber efficiency data and models for the inertia-interception regime, including both information on bare fibers and dust loaded fibers. An improved, general fit function with physically meaningful limits for St→0 and St→∞ is proposed for the efficiency of bare fibers.     

Doxorubicin Impairs Smooth Muscle Cell Contraction: Novel Insights in Vascular Toxicity

Clinical and animal studies have demonstrated that chemotherapeutic doxorubicin (DOX) increases arterial stiffness, a predictor of cardiovascular risk. Despite consensus about DOX-impaired endothelium-dependent vasodilation as a contributing mechanism, some studies have reported conflicting results on vascular smooth muscle cell (VSMC) function after DOX treatment. The present study aimed to investigate the effects of DOX on VSMC function. To this end, mice received a single injection of 4 mg DOX/kg, or mouse aortic segments were treated ex vivo with 1 μM DOX, followed by vascular reactivity evaluation 16 h later. Phenylephrine (PE)-induced VSMC contraction was decreased after DOX treatment. DOX did not affect the transient PE contraction dependent on Ca²⁺ release from the sarcoplasmic reticulum (0 mM Ca²⁺), but it reduced the subsequent tonic phase characterised by Ca²⁺ influx. These findings were supported by similar angiotensin II and attenuated endothelin-1 contractions. The involvement of voltage-gated Ca²⁺ channels in DOX-decreased contraction was excluded by using levcromakalim and diltiazem in PE-induced contraction and corroborated by similar K⁺ and serotonin contractions. Despite the evaluation of multiple blockers of transient receptor potential channels, the exact mechanism for DOX-decreased VSMC contraction remains elusive. Surprisingly, DOX reduced ex vivo but not in vivo arterial stiffness, highlighting the importance of appropriate timing for evaluating arterial stiffness in DOX-treated patients.     

Performance evaluation of three optical particle counters with an efficient “multimodal” calibration method

The sizing accuracies of two widely used yet hitherto unevaluated optical particle counters (OPCs—Grimm Model 1.109 and Palas Model WELAS 2100) as well as one high-resolution, non-commercial OPC were evaluated. The measured data were compared to scattering intensity calculations based on Mie theory. Additionally, the counting efficiency for all three counters was measured, as was the influence of coincidence effects for the OPC with the lowest (manufacturer specified) upper concentration limit.Beside the traditional polystyrene latex calibration, a little-known, very fast and precise “multimodal” calibration method was used, which is based on the simultaneous generation of up to eight sharp multiple-charge modes from polydisperse di-ethyl-hexyl-sebacate (DEHS) particles by electrical mobility classification.     

Structure and density of deposits formed on filter fibers by inertial particle deposition and bounce

The morphology and packing density of particle deposits formed by accumulation on thin steel fibers suspended in an aerosol stream were studied by confocal microscopy. Measurements were made with electrically neutral polystyrene spheres (d_P=1.3, 2.0, 2.6 and 5.2 μm) as a function of flow velocity (v=0.7–5 m/s) and fiber diameters (d_F=8 and 30 μm). Deposition under these conditions was dominated by inertia (Stokes number St=0.3–9), interception (interception parameter R=0.04–0.35) and particle bounce, with a negligible contribution from diffusion.The experiments show a systematic transition of deposit morphologies with a newly introduced particle bounce parameter β～St/R, where St and R are based on the diameter d_F of the bare fiber. Compact, forward facing deposit structures dominate in case of significant particle bounce (i.e. for β>β?, where β* represents the critical conditions for the onset of bounce on the bare fiber). Dendritic structures with pronounced sideways branching are formed at β<β*. R is of relatively little influence as an independent parameter, probably because interception occurs mostly on preexisting deposit structures with dimensions in the order of d_P.The mean porosity ε of the deposit structures was determined on the basis of contour measurements by confocal microscopy, in combination with data on the accumulated particle volume per unit fiber length (known accurately from a previous paper by Kasper, Schollmeier, Meyer, and Hoferer (2009). Once noticeable deposits had formed, ε was found to attain stable values between 0.80 at d_P=1.3 μm and 0.55 at d_p=5.2 μm.     

Polyurethane tri‐block copolymers—Synthesis,mechanical, elastic,and rheological properties

A series of polyurethane tri‐block copolymers were synthesized by reacting a 4,4′‐methylenebis(phenyl isocyanate) (MDI)‐endcapped poly(tetramethylene oxide) (PTMO, M_n = 2,000 g/mol) with a monoamine‐diamide (6T6m) hard segment (HS). The concentration of the HS in the copolymer was varied between 9 and 33 wt % by changing the length of the soft mid‐block segment. The structure of the copolymers was analyzed by nuclear magnetic resonance, the amide crystallinity was investigated by Fourier transform infra‐red and the thermal properties were studied by differential scanning calorimetry. The mechanical and elastic properties of the tri‐block copolymer were subsequently explored by dynamic mechanical analysis, compression set and tensile experiments, and the melt rheological behavior was studied by a parallel plate method. The amide end groups displayed a high crystallinity and the modulus of the tri‐block copolymers was relatively high. The fracture strain increased strongly with the molecular weight and the copolymers demonstrated a ductile fracture behavior for molecular weights above 6000 g/mol. Good compression set values were obtained for the tri‐block copolymers despite their low molecular weight. In the molten state, the tri‐block polymers displayed a gelling effect at low frequencies, which was believed to be a result of a clustering of the end‐segments. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Fragment-Based Drug Discovery for RNA Targets

Rapid development within the fields of both fragment-based drug discovery (FBDD) and medicinal targeting of RNA provides possibilities for combining technologies and methods in novel ways. This review provides an overview of fragment-based screening (FBS) against RNA targets, including a discussion of the most recently used screening and hit validation methods such as NMR spectroscopy, X-ray crystallography, and virtual screening methods. A discussion of fragment library design based on research from small-molecule RNA binders provides an overview on both the currently limited guidelines within RNA-targeting fragment library design, and future possibilities. Finally, future perspectives are provided on screening and hit validation methods not yet used in combination with both fragment screening and RNA targets.