Obstructions to algebraizing topological vector bundles

Suppose $X$ is a smooth complex algebraic variety. A necessary condition for a complex topological vector bundle on $X$ (viewed as a complex manifold) to be algebraic is that all Chern classes must be algebraic cohomology classes, i.e., lie in the image of the cycle class map. We analyze the question of whether algebraicity of Chern classes is sufficient to guarantee algebraizability of complex topological vector bundles. For affine varieties of dimension $\leq 3$, it is known that algebraicity of Chern classes of a vector bundle guarantees algebraizability of the vector bundle. In contrast, we show in dimension $\geq 4$ that algebraicity of Chern classes is insufficient to guarantee algebraizability of vector bundles. To do this, we construct a new obstruction to algebraizability using Steenrod operations on Chow groups. By means of an explicit example, we observe that our obstruction is non-trivial in general.Comment: 17 pages; To appear in Forum Math Sigm

Algebraic vector bundles and pp-local A^1-homotopy theory

We construct many``low rank" algebraic vector bundles on ``simple" smooth affine varieties of high dimension. In a related direction, we study the existence of polynomial representatives of elements in the classical (unstable) homotopy groups of spheres. Using techniques of A^1-homotopy theory, we are able to produce ``motivic" lifts of elements in classical homotopy groups of spheres; these lifts provide interesting polynomial maps of spheres and algebraic vector bundles.Comment: 20 pages; minor revisions and additions -- Comments welcome

Die Bedeutung der Fascia stylopharyngea bei intraoralen Blockadetechniken

Zusammenfassung: Hintergrund: Mittels transoraler Blockade des Ganglion cervicale superius des Truncus sympathicus kann bei Trigeminusneuralgien durch Ausbreitung eines Opioids bis zum N.mandibularis eine zusätzliche Schmerzreduktion erzielt werden. Das Vorhandensein der Fascia stylopharyngea senkt möglicherweise die Erfolgsrate. Durch genaue anatomische Untersuchung der Faszie wollen wir auf die Effektivität der zusätzlichen Opioidwirkung rückschließen. Material und Methode: 103 Kopfhälften wurden untersucht, die Faszie von lateral her aufgesucht. Dabei unterschieden wir 3 Gruppen: GruppeA repräsentierte vollständig ausgebildete Faszienblätter, Gruppe Bunvollständige Faszien und in GruppeC war die Faszie nicht ausgebildet. Ergebnis: Die Faszie war in 86 vollständig und in 13 Fällen unvollständig ausgebildet. Lediglich in 4 Fällen fehlte sie vollends. Schlussfolgerung: Die Faszie kann die Erfolgsquote der Schmerzreduktion bei Trigeminusneuralgie beeinflusse

Entropy coding for training deep belief networks with imbalanced and unlabeled data

Session 1aSCb - Speech Communication: Speech Processing Potpourri (Poster Session): no. 1aSCb1Training deep belief networks (DBNs) is normally done with large data sets. In this work, the goal is to predict traces of the surface of the tongue in ultrasoundimages of the mouth during speech. Performance on this task can be dramatically enhanced by pre-training a DBN jointly on human-supplied traces and ultrasoundimages, then training a modified version of the network to predict traces from ultrasound only. However, hand-tracing the entire dataset of ultrasoundimages is extremely labor intensive. Moreover, the dataset is highly imbalanced since many images are extremely similar. This work presents a bootstrapping method which takes advantage of this imbalance, iteratively selecting a small subset of images to be hand-traced, then (re)training the DBN, making use of an entropy-based diversity measure for the initial selection. With this approach, a three-fold reduction in human time required to trace an entire dataset with human-level accuracy was achieved.published_or_final_versio

Theoretical analysis of the electronic structure of the stable and metastable c(2x2) phases of Na on Al(001): Comparison with angle-resolved ultra-violet photoemission spectra

Using Kohn-Sham wave functions and their energy levels obtained by density-functional-theory total-energy calculations, the electronic structure of the two c(2x2) phases of Na on Al(001) are analysed; namely, the metastable hollow-site structure formed when adsorption takes place at low temperature, and the stable substitutional structure appearing when the substrate is heated thereafter above ca. 180K or when adsorption takes place at room temperature from the beginning. The experimentally obtained two-dimensional band structures of the surface states or resonances are well reproduced by the calculations. With the help of charge density maps it is found that in both phases, two pronounced bands appear as the result of a characteristic coupling between the valence-state band of a free c(2x2)-Na monolayer and the surface-state/resonance band of the Al surfaces; that is, the clean (001) surface for the metastable phase and the unstable, reconstructed "vacancy" structure for the stable phase. The higher-lying band, being Na-derived, remains metallic for the unstable phase, whereas it lies completely above the Fermi level for the stable phase, leading to the formation of a surface-state/resonance band-structure resembling the bulk band-structure of an ionic crystal.Comment: 11 pages, 11 postscript figures, published in Phys. Rev. B 57, 15251 (1998). Other related publications can be found at http://www.rz-berlin.mpg.de/th/paper.htm

Valuable carcasses: postmortem preservation of fatty acid composition in heart tissue

In order to effectively conserve species, we must understand the structure and function of integral mechanisms at all levels of organismal organisation, from intracellular biochemistry to whole animal ecophysiology. The accuracy of biochemical analyses depend on the quality and integrity of the samples analysed. It is believed that tissue samples collected immediately postmortem provide the most reliable depiction of the living animal. Yet, euthanasia of threatened or protected species for the collection of tissue presents a number of ethical complications. Polyunsaturated fatty acids (PUFA) are essential to the cardiovascular system of all animals and the structure of PUFA can be degraded by peroxidation, potentially modifying the fatty acid composition of the tissue over postmortem time. Here, we assessed the composition of PUFA in cardiac tissue of bats (Carollia perspicillata) over the course of 12-h postmortem. We show that PUFA are resistant to naturally occurring postmortem degradation in heart tissue, with no difference in the overall composition of fatty acids across all time classes (0, 3, 6 or 12-h postmortem). Our results suggest that carcasses that would otherwise be discarded may actually be viable for the assessment of fatty acid composition in a number of tissues. We hope to spur further investigations into the viability of carcasses for other biochemical analyses as they may be an untapped resource available to biologists

Optimizing electrode implantation in sacral nerve stimulation—an anatomical cadaver study controlled by a laparoscopic camera

Background and aim: Sacral nerve stimulation is the therapy of choice in patients with neurogenic faecal and urine incontinence, constipation and some pelvic pain syndromes. The aim of this study is to determine the best insertion angles of the electrode under laparoscopic visualization of the sacral nerves. Materials and methods: Five fresh cadaver pelvises were dissected through an anterior approach of the presacral space, exposing the ventral sacral roots. Needles and electrodes were inserted into the S3 foramen. Both right and left sides were used, with the traditional percutaneous procedure. The validation was done by a laparoscopic camera controlling the position of the needle and electrode on the nerve. The angles were assessed with a goniometer and were confirmed in two living patients. Results: The mean angle of insertion in the sagittal plane was 62.9 ± 3° (range, 59-70). In the axial plane, the mean angle for the left side was 91.7 ± 13.5° (range, 80-110) and 83.2 ± 7.7° for the right side (range, 75-95). These angles resulted in the optimal placement of the leads along the S3 sacral root, in all these cases. Conclusions: This study allows direct visualization during the placement of the needle and electrode, thus permitting accurate calculations of the best angle of approach during the surgical procedure in sacral nerve stimulation. These objective findings attempt to standardize this technique, which is often performed with the aid of intra-operative fluoroscopy but still leaving a lot to chance. These insertion angles should help to find more consistent and reproducible results and thus improved outcome in patient

The path to fusion power†

The promise, status and challenges of developing fusion power are outlined. The key physics and engineering principles are described and recent progress quantified. As the successful demonstration of 16 MW of fusion in 1997 in the Joint European Torus showed, fusion works. The central issue is therefore to make it work reliably and economically on the scale of a power station. We argue that to meet this challenge in 30 years we must follow the aggressive programme known as the ‘Fast Track to Fusion’. This programme is described in some detail

Anatomy of the anterior cruciate ligament

The anterior cruciate ligament (ACL) is a band of dense connective tissue which courses from the femur to the tibia. The ACL is a key structure in the knee joint, as it resists anterior tibial translation and rotational loads. When the knee is extended, the ACL has a mean length of 32mm and a width of 7-12mm. There are two components of the ACL, the anteromedial bundle (AMB) and the posterolateral bundle (PLB). They are not isometric with the main change being lengthening of the AMB and shortening of the PLB during flexion. The ACL has a microstructure of collagen bundles of multiple types (mostly type I) and a matrix made of a network of proteins, glycoproteins, elastic systems, and glycosaminoglycans with multiple functional interactions. The complex ultrastructural organization and abundant elastic system of the ACL allow it to withstand multiaxial stresses and varying tensile strains. The ACL is innervated by posterior articular branches of the tibial nerve and is vascularized by branches of the middle genicular arter