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We investigate theoretically, on the basis of the steady Stokes equations for a viscous incompressible fluid, the flow induced by a stokeslet located on the centre axis of two coaxially positioned rigid disks. The stokeslet is directed along the centre axis. No-slip boundary conditions are assumed to hold at the surfaces of the disks. We perform the calculation of the associated Green's function in large parts analytically, reducing the spatial evaluation of the flow field to one-dimensional integrations amenable to numerical treatment. To this end, we formulate the solution of the hydrodynamic problem for the viscous flow surrounding the two disks as a mixed boundary-value problem, which we then reduce to a system of four dual integral equations. We show the existence of viscous toroidal eddies arising in the fluid domain bounded by the two disks, manifested in the plane containing the centre axis through adjacent counter-rotating eddies. Additionally, we probe the effect of the confining disks on the slow dynamics of a point-like particle by evaluating the hydrodynamic mobility function associated with axial motion. Thereupon, we assess the appropriateness of the commonly employed superposition approximation and discuss its validity and applicability as a function of the geometrical properties of the system. Additionally, we complement our semi-analytical approach by finite-element computer simulations, which reveals a good agreement. Our results may find applications in guiding the design of microparticle-based sensing devices and electrokinetic transport in small-scale capacitors.
Basal melt of ice shelves is not only an important part of Antarctica's ice sheet mass budget, but it is also the origin of platelet ice, one of the most distinctive types of sea ice. In many coastal Antarctic regions, ice crystals form and grow in supercooled plumes of Ice Shelf Water. They usually rise towards the surface, becoming trapped under an ice shelf as marine ice or forming a semi-consolidated layer, known as the sub-ice platelet layer, below an overlying sea ice cover. In the latter, sea ice growth consolidates loose crystals to form incorporated platelet ice. These phenomena have numerous and profound impacts on the physical properties, biological processes and biogeochemical cycles associated with Antarctic fast ice: platelet ice contributes to sea ice mass balance and may indicate the extent of ice-shelf basal melting. It can also host a highly productive and uniquely adapted ecosystem. This paper clarifies the terminology and reviews platelet ice formation, observational methods as well as the geographical and seasonal occurrence of this ice type. The physical properties and ecological implications are presented in a way understandable for physicists and biologists alike, thereby providing the background for much needed interdisciplinary research on this topic.
We measure the Kelvin–Helmholtz instability in between a layer of a diamagnetic fluid flowing in a channel and a layer of ferrofluid resting on top. When the diamagnetic fluid exceeds a critical flow velocity the interface in between both fluids becomes unstable and waves develop. It has been predicted by Sutyrin & Taktarov (J. Appl. Math. Mech., vol. 39, 1975, pp. 520–524) that a homogeneous magnetic field, oriented horizontally, stabilizes the liquid interface. To test this prediction we apply in a closed flow channel a local periodic perturbation of the interface by magnetic or mechanic means. From the measured growth and decay rates of the interface undulations we determine the critical flow velocity for various driving frequencies and applied magnetic fields. In this way we confirm quantitatively the stabilizing effect of the horizontal field. Moreover we measure the dispersion relation of the interfacial waves.
Latin American folkloric-popular music had an impact on the music scenes of both Germanies, where singer-songwriters emerged and became interested in Chilean Nueva Canción, the Argentinian Movimiento del Nuevo Cancionero, and Cuban Nueva Trova in the 1970s. Particularly interesting in this context is the contact of some Latin American countries with the German Democratic Republic (GDR). Based on translation theory and articles on Nueva Canción in Europe, this article examines the Latin American presence at the Political Song Festival in East Berlin and analyses some publications that focus on this annual event. The article focuses on the singer-songwriter Gerhard Schöne, who during the 1980s, took Nicaragua as a political example, as is shown in songs, and who also composed German lyrics to melodies by Violeta Parra, Atahualpa Yupanqui, and Silvio Rodríguez, transferring the songs into a new context.
The commutative differential graded algebra
of polynomial forms on a simplicial set
is a crucial tool in rational homotopy theory. In this note, we construct an integral version
. Our approach uses diagrams of chain complexes indexed by the category of finite sets and injections
differential graded algebras (dga) by strictly commutative objects, called commutative
-dgas. We define a functor
from simplicial sets to commutative
-dgas and show that it is a commutative lift of the usual cochain algebra functor. In particular, it gives rise to a new construction of the
dga of cochains. The functor
shares many properties of
, and can be viewed as a generalization of
that works over arbitrary commutative ground rings. Working over the integers, a theorem by Mandell implies that
determines the homotopy type of
is a nilpotent space of finite type.
In the Federal Republic of Germany about 3 million people suffer from tinnitus/are hit by tinnitus, numerous of them depend on intensive medical care. The repetitive transcranial magnetic stimulation is considered to be an innovative and promising therapy in tinnitus treatment. Low frequency stimulation is meant to reduce the abnormal neural activity in the auditory cortex. This study focuses on the efficacy of rTMS with tinnitus patients in the course of a multi disciplinary / an interdisciplinary therapy concept.
From November 2008 to June 2009 29 outpatients with chronic tinnitus were treated by low frequency rTMS (1 Hz frequency, 2000 impulses, intensity 110%) for 10 proceedings, stimulating the sinistral auditory cortex with a figure-of-eight-coil. Prior to and afterwards the proceedings questionnaires and assessments of a psychologist took place, afterwards statistical analyses were conducted, the data was explored and systematically discussed.
The severity index of the tinnitus as well as the depression symptoms of the subjects improved significantly. The average reduction rate of the tinnitus score is set at 7 points. With a response criterion at the minimum of 5 points, 57% were declared as responder, 29% as non-responder and 4 patients (14%) described an increase of the tinnitus loudness/annoyance.
The results show that the rTMS works as a helpful treatment tool with tinnitus patients and should be considered as an option in the routine tinnitus treatment.
Patients with untreated obstructive sleep apnea often report depressive symptoms, such as low mood, loss of interest and reduction of drive. In this study we examined the frequency of significant depressive symptoms amongst patients with untreated obstructive sleep apnea over a one year period.
From January to December 2008 we screened 1260 consecutive patients with untreated obstructive sleep apnea (AHI > 9) seen at our Center for Sleep Medicine were screened for depression. Based on self-administered questionnaires, patients with significant depressive symptoms were defined as having either a BDI II score ≥ 14 or WHO-5 ≤ 13. Additionally, severity of depression was rated based on BDI II scores.
Depressive symptoms were reported frequently. Based on BDI-II, 27.9% of patients report significant depressive symptoms. Of these, 46.2% were mild, 35.9% moderate and 17.9% severe. In addition, 52.6% of patients self-reported feeling unwell based on their WHO-5 scores.
Significant depressive symptoms measured by standardised self-rating scales were detected in over a quarter of our patients with untreated sleep apnea. It remains unknown whether treatment of OSA alone abolishes depressive symptoms, or whether depressive mood may reduce the compliance with treatment. Patients may need an interdisciplinary approach to initial treatment.
The Clinic of Psychiatry and Psychotherapy of Nuremberg established rTMS as a standard tool in the treatment of patients with depressive disorder since 2001. The stimulation protocol was modified in October 2008 to match the current standard procedure reported in the literature. The pulse number was heightened form 800 to 2000 per proceeding. This study examines the effects of the modified stimulation protocol and contrasts the results with the former stimulation efficacy.
The authors compared patients suffering from depression, who were treated by rTMS with 800 pulses/day and with 2000 pulses/day. The results of psychological examinations (MADRS, HAMD, BDI, grading, cognitive screening) prior to and afterwards the three-weeks-rTMS-cycle were submitted. Variance analyses were used for statistical reason.
The subsamples were comparable by sex, age, premorbid intellectual level as well as by self- and other-rated depression severity at treatment beginning. Statistical analyses showed a significant reduction of the depression symptoms in both stimulation protocol groups. Solely the HAMD score reduction in the 2000 pulse sample exceeded the decrease in the 800 pulse sample. Analogically the grading of human functions partly differed depending on the sample affiliation. Concerning the screening of cognitive functioning neither group was impaired.
rTMS still seems to be a well-functioning tool in the treatment of depressive disorders in the bounds of daily psychiatric health care. Although the modified stimulation protocol didn’t show many advantages in respect to improving depression symptoms, the results indicate the continual adjustment of the stimulation parameter to meet the current standards.
Psychoanalytical, behavioural and cognitive theories assume a continuous process in the development of self-acceptance as an important psychological variable by parent-child interaction during childhood and adolescence. The objective of the present study was to investigate the relationships between perceived parental rearing behaviour and self-acceptance in psychiatric inpatients. The results of extreme group comparisons pointed to the reciprocal discriminative power of parental rearing factors and self-acceptance scores, supporting the hypothesis of a continuous process in the development of self-acceptance and mood traits. Perceived parental rearing predicted aspects of psychopathology in adulthood. The effects of maternal and paternal behaviour appeared to be gender-specific. Alternative interpretations of these findings are discussed.