Biomedical subjects

R Hänninen

Publications and source records attributed to R Hänninen.

10 recordsLinked to original sources

PubMed2006

Anomalous translational velocity of vortex ring with finite-amplitude Kelvin waves.

We consider finite-amplitude Kelvin waves on an inviscid vortex assuming that the vortex core has infinitesimal thickness. By numerically solving the governing Biot-Savart equation of motion, we study how the frequency of the Kelvin waves and the velocity of the perturbed ring depend on the Kelvin wave amplitude. In particular, we show that, if the amplitude of the Kelvin waves is sufficiently large, the perturbed vortex ring moves backwards.

Journal Article↗

PubMed2006

Twisted vortex state.

We study a twisted vortex bundle where quantized vortices form helices circling around the axis of the bundle in a "force-free" configuration. Such a state is created by injecting vortices into a rotating vortex-free superfluid. Using continuum theory we determine the structure and the relaxation of the twisted state. This is confirmed by numerical calculations. We also present experimental evidence of the twisted vortex state in superfluid 3He-B.

Journal Article↗

PubMed2006

Vortex multiplication in applied flow: A precursor to superfluid turbulence.

A surface-mediated process is identified in 3He-B which generates vortices at a roughly constant rate. It precedes a faster form of turbulence where intervortex interactions dominate. This precursor becomes observable when vortex loops are introduced in low-velocity rotating flow at sufficiently low mutual friction dissipation at temperatures below 0.5Tc. Our measurements indicate that the formation of new loops is associated with a single vortex interacting in the applied flow with the sample boundary. Numerical calculations show that the single-vortex instability arises when a helical Kelvin wave expands from a reconnection kink at the wall and then intersects again with the wall.

Journal Article↗

PubMed2004

Experiences in methods to involve key players in planning protective actions in the case of a nuclear accident.

A widely used method in the planning of protective actions is to establish a stakeholder network to generate a comprehensive set of generic protective actions. The aim is to increase competence and build links for communication and coordination. The approach of this work was to systematically evaluate protective action strategies in the case of a nuclear accident. This was done in a way that the concerns and issues of all key players could be transparently and equally included in the decision taken. An approach called Facilitated Decision Analysis Workshop has been developed and tested. The work builds on case studies in which it was assumed that a hypothetical accident had led to a release of considerable amounts of radionuclides and, therefore, various types of countermeasures had to be considered. Six workshops were organised in the Nordic countries where the key players were represented, i.e. authorities, expert organisations, industry and agricultural producers.

Decision Support Systems, Management↗

PubMed2003

Structure of the surface vortex sheet between two rotating 3He superfluids.

We study a two-phase sample of superfluid 3He where vorticity exists in one phase (3He-A) but cannot penetrate across the interfacial boundary to a second coherent phase (3He-B). We calculate the bending of the vorticity into a surface vortex sheet on the interface and solve the internal structure of this new type of vortex sheet. The compression of the vorticity from three to two dimensions enforces a structure which is made up of 1 / 2-quantum units, independently of the structure of the source vorticity in the bulk. These results are consistent with our NMR measurements.

Journal Article↗

PubMed2002

Whose arm is it anyway? An fMRI case study of supernumerary phantom limb.

Under normal circumstances, information from a number of sources is combined to compute a unitary percept of the body. However, after pathology these influences may be perceived simultaneously, resulting in multiple dissociated conscious representations. In a recent paper, we described subject E.P., a right-handed female stroke patient with a right frontomesial lesion who sporadically experiences a supernumerary 'ghost' left arm that occupies the previous position of the real left arm after a delay of 60-90 s. We used a delayed response paradigm with functional MRI to examine the haemodynamic correlates of E.P.'s illusion. Comparison of periods of time during scanning when the ghost arm was present against when it was not revealed a single cluster (9 voxels, t = 5.11, P < 0.012 corrected for multiple comparisons) located on the right medial wall in the supplementary motor area ('SMA proper'). Our results suggest that areas traditionally classified as part of the motor system can influence the conscious perception of the body. We propose that, as a consequence of her injury, E.P. is aware of the position of the phantom limb in this 'action space' while also continuing to be aware of the true position of her real limb on the basis of afferent somatosensory information.

Adult↗

PubMed1998

Three hands: fragmentation of human bodily awareness.

We describe patient E.P. who occasionally perceives a 'ghost' hand which copies the previous positions of the left hand with a 0.5-1 min time lag, but follows the movement patterns of the right hand. The symptoms started after an operation of a ruptured aneurysm, followed by an infarction of the right frontal lobe; E.P. also has a previously lesioned corpus callosum. Neuromagnetic recordings revealed that activity of the left secondary somatosensory cortex was strongly suppressed during the ghost arm percept, thereby providing an objective correlate for E.P.'s sensations. We conclude that simultaneous mental contents about body scheme may be based on neural information extracted at considerably different times, resulting in fragmentation of bodily awareness.

Adult↗

PubMed1988

Simultaneous and successive cognitive processes in brain damaged adults: hemispheric and anterior-posterior effects.

The relationship between simultaneous and successive processing and their assumed underlying neuro-anatomical structures was examined. According to the model of Das, Kirby, and Jarman (1975, 1979) simultaneous processing, occurs mainly in the posterior parts of the brain (parieto-occipital areas) and successive processing in anterior regions of the brain (fronto-temporal areas). The theory of lateralized hemispheric specialization suggests differences in processing due to right-left hemispheric differences. A battery of measures was factor-analyzed and simultaneous and successive factors identified in 106 brain-damaged adults and a control group. The brain damaged group was divided into four subgroups, left and right anterior and left and right posterior groups. The two-way ANOVA revealed no interactions (laterality x anterior/posterior), but instead two main effects for laterality on simultaneous verbal (p<.01) and successive (p<.05) processing and one weak (p<. 10) main effect for anterior/posterior divisions of simultaneous nonverbal processing. It was concluded that the results partially supported both assumed neuropsychological models of processing.

Journal Article↗

PubMed1985

Phoneme errors in Broca's aphasia: three Finnish cases.

The phonemic errors of three Finnish Broca's aphasics were analyzed according to various phonological features, frequency of segments, syllable, word, and stress positions, as well as for the phonotactic structure of the uncanonical products. It was found, e.g., that the distance between the syntagmatic error and its source could not be satisfactorily counted by phonemes, since the syllable had to be taken into account also in pathological Finnish. As regards the paradigmatic dimension of the errors, the number of incorrect features is even here in reverse relation to the frequency of the erroneous phonemes. Moreover, it was found that pure quantity errors and vowel harmony deviations are infrequent in the speech of Finnish Broca's aphasics.

Adult↗

PubMed1985

A new rapid method for quantification of nitrogen in human serum employing the 14N(p,p' gamma)14N reaction: application to human pregnancy.

The total nitrogen concentrations in dried serum from 54 pregnant women and 17 newborn babies were determined by a new application of the 14N(p,p' gamma)14N reaction resonance at 3.9 MeV. The samples were bombarded in a He atmosphere by 4.1 MeV protons from a tandem Van de Graaff accelerator. The mean dry-weight nitrogen concentration in serum sampled during early pregnancy (6-12 weeks; 13.9 g per 100 g +/- 5.4%) was significantly higher than that in serum sampled during late pregnancy (38-42 weeks: 13.0 g per 100 g +/- 3.9%, p less than 0.001) and than that in serum taken from the umbilical cord (13.3 g per 100 g +/- 4.6%, p less than 0.01). The nitrogen levels measured using this rapid nuclear technique, applied for the first time to human serum analysis, agree well with parallel Kjeldahl analyses.

Female↗