Plateau's problem in Finsler 3-space

We explore a connection between the Finslerian area functional based on the Busemann-Hausdorff-volume form, and well-investigated Cartan functionals to solve Plateau's problem in Finsler 3-space, and prove higher regularity of solutions. Free and semi-free geometric boundary value problems, as well as the Douglas problem in Finsler space can be dealt with in the same way. We also provide a simple isoperimetric inequality for minimal surfaces in Finsler spaces.Comment: 42 page

On minimal immersions in Finsler spaces

We explore a connection between the Finslerian area functional and well-investigated Cartan functionals to prove new Bernstein theorems, uniqueness and removability results for Finsler-minimal graphs, as well as enclosure theorems and isoperimetric inequalities for minimal immersions in Finsler spaces. In addition, we establish the existence of smooth Finsler-minimal immersions spanning given extreme or graphlike boundary contours.Comment: 26 pages, changed numbering of equation

Representation of statistical sound properties in human auditory cortex

The work carried out in this doctoral thesis investigated the representation of statistical sound properties in human auditory cortex. It addressed four key aspects in auditory neuroscience: the representation of different analysis time windows in auditory cortex; mechanisms for the analysis and segregation of auditory objects; information-theoretic constraints on pitch sequence processing; and the analysis of local and global pitch patterns. The majority of the studies employed a parametric design in which the statistical properties of a single acoustic parameter were altered along a continuum, while keeping other sound properties fixed. The thesis is divided into four parts. Part I (Chapter 1) examines principles of anatomical and functional organisation that constrain the problems addressed. Part II (Chapter 2) introduces approaches to digital stimulus design, principles of functional magnetic resonance imaging (fMRI), and the analysis of fMRI data. Part III (Chapters 3-6) reports five experimental studies. Study 1 controlled the spectrotemporal correlation in complex acoustic spectra and showed that activity in auditory association cortex increases as a function of spectrotemporal correlation. Study 2 demonstrated a functional hierarchy of the representation of auditory object boundaries and object salience. Studies 3 and 4 investigated cortical mechanisms for encoding entropy in pitch sequences and showed that the planum temporale acts as a computational hub, requiring more computational resources for sequences with high entropy than for those with high redundancy. Study 5 provided evidence for a hierarchical organisation of local and global pitch pattern processing in neurologically normal participants. Finally, Part IV (Chapter 7) concludes with a general discussion of the results and future perspectives

Repression and reactivation of the variant surface glycoprotein gene in Trypanosoma brucei

AbstractRapid repression of variant surface glycoprotein (VSG) synthesis is an early event during the in vitro transformation of Trypanosoma brucei from coated bloodstream forms to uncoated procyclic cells. Repression occurs at the transcriptional level and is triggered by the combined action of two signals: a reduction in temperature from 37 to 27°C and the addition of the citric acid cycle intermediates citrate and cis-aconitate. It is shown that synthesis of VSG mRNA can be reactivated up to 8 h after triggering differentiation by releasing either one or both of the signals. After 30 h repression is irreversible. The results suggest that transformation of bloodstream forms to procyclic cells proceeds through a reversible phase to an irreversible committed state. A reversible repression of VSG mRNA synthesis is also observed upon inhibition of protein synthesis in bloodstream forms at 37°C

An information theoretic characterisation of auditory encoding.

The entropy metric derived from information theory provides a means to quantify the amount of information transmitted in acoustic streams like speech or music. By systematically varying the entropy of pitch sequences, we sought brain areas where neural activity and energetic demands increase as a function of entropy. Such a relationship is predicted to occur in an efficient encoding mechanism that uses less computational resource when less information is present in the signal: we specifically tested the hypothesis that such a relationship is present in the planum temporale (PT). In two convergent functional MRI studies, we demonstrated this relationship in PT for encoding, while furthermore showing that a distributed fronto-parietal network for retrieval of acoustic information is independent of entropy. The results establish PT as an efficient neural engine that demands less computational resource to encode redundant signals than those with high information content

Purification and characterization of a tartrate-sensitive acid phosphatase of Trypanosoma brucei

AbstractIn search for invariant surface proteins in Trypanosoma brucei bloodstream forms, acid phosphatase was investigated. Earlier work had shown that part of the cellular phosphatase activity is associated with the flagellar pocket of the parasite. It is demonstrated that T. brucei contains at least two membrane-bound enzymes, one is sensitive to the inhibitor L-(+)-tartrate while the other is resistant. The tartrate-sensitive phosphatase was purified to homogeneity by monoclonal antibody affinity chromatography and shown to be a glycoprotein of low abundance (13,000 molecules/ cell). It has an apparent molecular weight of 70,000 Da. The usefulness of acid phosphatase as a marker for characterizing the membrane lining the flagellar pocket is discussed