915 research outputs found
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
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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
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