Variable-delay feedback control of unstable steady states in retarded time-delayed systems

We study the stability of unstable steady states in scalar retarded time-delayed systems subjected to a variable-delay feedback control. The important aspect of such a control problem is that time-delayed systems are already infinite-dimensional before the delayed feedback control is turned on. When the frequency of the modulation is large compared to the system's dynamics, the analytic approach consists of relating the stability properties of the resulting variable-delay system with those of an analogous distributed delay system. Otherwise, the stability domains are obtained by a numerical integration of the linearized variable-delay system. The analysis shows that the control domains are significantly larger than those in the usual time-delayed feedback control, and that the complexity of the domain structure depends on the form and the frequency of the delay modulation.Comment: 13 pages, 8 figures, RevTeX, accepted for publication in Physical Review

Topographical anisotropy and wetting of ground stainless steel surfaces

Microscopic and physico-chemical methods were used for a comprehensive surface characterization of different mechanically modified stainless steel surfaces. The surfaces were analyzed using high-resolution confocal microscopy, resulting in detailed information about the topographic properties. In addition, static water contact angle measurements were carried out to characterize the surface heterogeneity of the samples. The effect of morphological anisotropy on water contact angle anisotropy was investigated. The correlation between topography and wetting was studied by means of a model of wetting proposed in the present work, that allows quantifying the air volume of the interface water drop-stainless steel surface

Radiative damping: a case study

We are interested in the motion of a classical charge coupled to the Maxwell self-field and subject to a uniform external magnetic field, B. This is a physically relevant, but difficult dynamical problem, to which contributions range over more than one hundred years. Specifically, we will study the Sommerfeld-Page approximation which assumes an extended charge distribution at small velocities. The memory equation is then linear and many details become available. We discuss how the friction equation arises in the limit of "small" B and contrast this result with the standard Taylor expansion resulting in a second order equation for the velocity of the charge.Comment: 4 figure

Low-Density Granulocytes Are a Novel Immunopathological Feature in Both Multiple Sclerosis and Neuromyelitis Optica Spectrum Disorder

Objective: To investigate whether low-density granulocytes (LDGs) are an immunophenotypic feature of patients with multiple sclerosis (MS) or neuromyelitis optica spectrum disorder (NMOSD). Methods: Blood samples were collected from 20 patients with NMOSD and 17 patients with MS, as well as from 15 patients with Systemic Lupus Erythematosus (SLE) and 23 Healthy Donors (HD). We isolated peripheral blood mononuclear cells (PBMCs) with density gradient separation and stained the cells with antibodies against CD14, CD15, CD16, and CD45, and analyzed the cells by flow cytometry or imaging flow cytometry. We defined LDGs as CD14-CD15(high) and calculated their share in total PBMC leukocytes (CD45+) as well as the share of CD16(hi) LDGs. Clinical data on disease course, medication, and antibody status were obtained. Results: LDGs were significantly more common in MS and NMOSD than in HDs, comparable to SLE samples (median values HD 0.2%, MS 0.9%, NMOSD 2.1%, SLE 4.3%). 0/23 of the HDs, but 17/20 NMOSD and 11/17 MS samples as well as 13/15 SLE samples had at least 0.7 % LDGs. NMOSD patients without continuous immunosuppressive treatment had significantly more LDGs compared to their treated counterparts. LDG nuclear morphology ranged from segmented to rounded, suggesting a heterogeneity within the group. Conclusion: LDGs are a feature of the immunophenotype in some patients with MS and NMOSD

Effects of Surface Coatings on the Joint Formation During Magnetic Pulse Welding in Tube-to-Cylinder Configuration

Magnetic Pulse Welding (MPW) is a joining technique favorable for the generation of strong atomic bonded areas between different metals, e.g. aluminum and steel. Brittle intermetallic phases can be avoided due to the high-speed collision and the absence of external heat. The demand for the use of this technique in industries like automotive and plant engineering rises. However, workpieces used in these fields are often coated, e.g. in order to improve the corrosion resistance. Since the weld quality depends on the material’s behavior at the collision zone, surface layers in that region have to be taken into account as well. This work investigates the influences of different coating types. Aluminum to steel welding is used as an example system. On the inner steel part (C45) coatings like zinc, nickel and chrome are applied, while the aluminum flyer tubes (EN AW-6060) are anodized, chromated and passivated. Welding tests are performed using two different welding systems with varying discharging frequencies and four geometrical part setups. For all combinations, the flyer velocity during the process is measured by Photon Doppler Velocimetry (PDV). By using the uncoated material combination as a reference, the removal of surface layers due to jetting is analyzed. Finally, the weld quality is characterized in peel tests, shear-push tests and by the help of metallographic analysis. It is found that certain coatings improve the joint formation, while others are obstructive for the performance of MPW. Some coatings have no influence on the joining process at all

Influence of the Wall Thicknesses on the Joint Quality During Magnetic Pulse Welding in Tube-to-Tube Configuration

The implementation of multi-material concepts, for example, in automotive engineering or aerospace technologies, requires adequate joining techniques. The Magnetic Pulse Welding (MPW) process allows for joining both similar and dissimilar materials without additional mechanical elements, chemical binders, or adverse influences of heat on the joining partners. In this process, an electro-conductive at (‘flyer’) part is accelerated by Lorentz forces and impacts the inner (‘parent’) part under high velocity and high pressure, leading to the formation of a metallurgical joint. Besides joining of sheets and tubes to solid cylinders, the connection of two tubes is of particular interest due to the increased lightweight potential. The present paper focuses on the MPW of aluminum (EN AW-6060) to steel (C45) tubes. An experimental study was performed, in which the wall thickness of the parent part was reduced successively. The deformation behavior of both the flyer and parent parts was recorded during the experiments by a two-probe Photon Doppler Velocimeter (PDV). The final shape of the joined specimens was analyzed by a 3D digitizer. An instrumented peel test was used for the determination of the weld quality. It was found that defect-free MPW of aluminum tubes on steel tubes without supporting mandrel is possible

Influence of the Free Compression Stage on Magnetic Pulse Welding of Tubes

In magnetic pulse welding (MPW) of tubular parts, the acceleration of the ‘flyer’ part typically corresponds to a free electromagnetic compression (EMC) process over the distance of the initial standoff between the outer and inner tube. During this process stage, already significant plastic strains occur. In addition, wrinkling is a phenomenon frequently observed during EMC. In this manuscript, influencing factors on the wrinkling effect are identified, taking the initial geometry of the flyer tube and its manufacturing process into account. Moreover, a link between the strains and wrinkles caused by the tube compression and the MPW process is made. An experimental study is performed aiming for the quantification of the plastic deformation during EMC. The effect of this deformation on the stability and adhesion of brittle surface layers is analyzed. Accompanying numerical simulations help to understand the wrinkle formation and its influencing factors. Based on the results, hints for an improved process design of MPW are given

5-Oxoprolin (Pyroglutaminsäure) Azidose unter Paracetamol - Eine Differentialdiagnose der metabolischen Azidose mit erhöhter Anionenlücke

Zusammenfassung. In seltenen Fällen ist eine metabolische Azidose mit stark erweiterter Anionenlücke bei chronischer Paracetamol Therapie auf eine 5-Oxoprolin (Pyroglutaminsäure) Akkumulation zurück zu führen. Begleitende Risikofaktoren, wie Malnutrition, Alkoholabusus, Nieren- oder Lebererkrankungen, Komedikation mit Flucloxacillin, Vigabatrin, Netilmicin oder Sepsis wurden beschrieben. Eine medikamentös induzierte Inhibition der Glutathion Synthetase oder der 5-Oxoprolinase führt zur 5-Oxoprolinerhöhung in Serum und Urin. Andere häufigere Differentialdiagnosen, wie Laktatazidose, Intoxikationen oder Ketoazidose sollten ausgeschlossen werden. Potentiell auslösende Medikamente sollten gestoppt werden, während 5-Oxoprolinkonzentrationen quantifiziert werden können. Bisher unbekannten oder in der Fachinformation des betreffenden Medikamentes ungenügend erwähnte unerwünschte Arzneimittelwirkungen sollten einem regionalen Pharmacovigilance Zentrum zur Signaldetektion gemeldet werden. 5-Oxoprolin Azidose wird demnächst als potentiell unerwünschte Arzneimittelreaktion in den Schweizer Fachinformationen von Paracetamol aufgenommen. </jats:p

Thaumasite form of sulfate attack in limestone cement mortars: A study on long term efficiency of mineral admixtures

Concrete and mortar made from limestone cement may exhibit a lack of durability due to the formation of thaumasite. The addition of minerals that improve the concrete durability is expected to slow down the formation of thaumasite. in this work the effect of natural pozzolana, fly ash, ground granulated blast-furnace slag and metakaolin on the thaumasite formation in limestone cement mortar is examined. A limestone cement, containing 15% w/w limestone, was used. Mortar specimens were prepared by replacing a part of limestone cement with the above minerals. The specimens were immersed in a 1.8% MgSO4 solution and cured at 5 and 25 degrees C. The status of the samples after a storage period of 5 years was reported based on visual inspection, compressive strength, mass measurements, ultrasonic pulse velocity measurements and analytical techniques. It is concluded that the use of specific minerals, as partial replacement of cement, inhibits thaumasite formation in limestone cement mortar. (C) 2008 Elsevier Ltd. All rights reserved