A Counterexample to a Conjecture about Positive Scalar Curvature

Conjecture 1 of Stanley Chang: "Positive scalar curvature of totally nonspin manifolds" asserts that a closed smooth manifold M with non-spin universal covering admits a metric of positive scalar curvature if and only if a certain homological condition is satisfied. We present a counterexample to this conjecture, based on the counterexample to the unstable Gromov-Lawson-Rosenberg conjecture given in Schick: "A counterexample to the (unstable) Gromov-Lawson-Rosenberg conjecture".Comment: v1: 4 pages, AMS-LaTeX; v2: small changes in presentation, typos corrected, v3: comment added, to appear in Proc AM

An Alternative Algebraic Framework for the Simplification of Coupled Cluster Type Expectation Values

The Coupled-Cluster (CC) method is one of the most popular and efficient correlation methods in quantum chemistry. Especially the CCSD(T) approximation, which includes single and double excitations by means of the application of the cluster operator to a reference determinant and triple excitations via a perturbative treatment, has become a standard tool in quantum chemical applications. However, the method is restricted to relatively small system sizes due to its unfavourable scaling (N^7, where N is the number of basis functions applied). For the full treatment of triple excitations the scaling advances to N^8 and every further excitation level increases the exponent by two. The goal of this work is to reduce the calculation time for closed shell systems at least by a factor growing with the excitation level for arbitrary truncation levels. This is done by restricting the spatial parts of the spin orbitals and thus treat pairs of spin orbitals on the same footing. The restrictions can be easily constructed for the CCSD model by spin integration. The derivation of the restrictions arising in higher excited case will be done employing the spatial orbital excitation operators E. In the first part of this work an algorithm is derived that is capable of the derivation of the energy and amplitude equations for arbitrary excitation levels. In the second part an implementation of this algorithm is presented

Does physical realism of articulatory modelin improve the perception of synthetic speech?

International audienceThis article presents the first step in a process to evaluate the potential impact of the physical properties of the articulators on speech perception. The underlying hypothesis is that articulatory biomechanics contribute to shape articulatory and formant trajectories. These in turn become patterns available for speech perception. Perceptual tests on synthetic silent center stimuli were run which are inspired from former studies of Strange and colleagues. Stimuli were generated with a unique timing with different models incorporating various degrees of physical realism. Our results show that silent center stimuli generated with a realistic biomechanical model achieve higher identification scores than stimuli from less realistic, kinematic, models, when only fast reaction times of the listeners are considered, in order to make sure that only low-level cognitive processings are involved

Is pitch perception and discrimination of vowels language-dependent and influencd by the vowels spectral properties?

Presented at the 11th International Conference on Auditory Display (ICAD2005)Pitch discrimination and accuracy has been found to depend on different factors. However, little work has been done (1) on the cross-linguistic influence of the listeners' native language and (2) on the influence of the spectral structure on the pitch perception of vowels as well as (3) cross-linguistic differences regarding different levels of muscial education. If differences in pitch discrimination between different language families exist this would be a crucial knowledge in the design and failure-safe application of auditory displays driven by pitch differences in speech control. Therefore the current study examines pitch discrimination of German vowels with a similar vowel height differing in rounding and tenseness for (1) native German listeners and (2) native Catalan listeners. Significant differences in the sensitivity of pitch perception between these two languages were found. Catalan listeners, independent of their musical education, were mostly insensitive to even large pitch differences in the vowels to be judged. The accuracy of pitch judgements for German listeners were significantly different for musically educated listeners in comparison to musically uneducated listeners. Further, both languages show a significant pitch difference for rounded vowels compared to the unrounded vowels. The current study provides evidence that pitch discrimination is language-dependent, at least partially

Les trajectoires formantiques respectant les lois de la physique contribuent-elles à une meilleure perception de la parole ?

International audiencePhysical properties of speech articulators contribute to shape articulatory and formant trajectories. This study aims at evaluating the role of this shaping in speech perception. We conducted perception tests of synthetic stimuli generated with speech production models accounting for different degrees of physical complexity. Our results do not provide any support to the hypothesis that the degree of physical realism in the models influences the perception of naturalness. However for degraded speech (silent center speech), significant differences are observed

Unusual Epstein-Barr esophageal infection in an immunocompetent patient: a case report

<p>Abstract</p> <p>Introduction</p> <p>Epstein-Barr virus esophagitis in an immunocompetent host is a rare entity. It represents either primary infection or reactivation and is usually characterized by acute onset and extensive ulcerative involvement of the upper and middle third of the esophagus.</p> <p>Case presentation</p> <p>A case of Epstein-Barr virus esophagitis in a 27-year-old woman with no immunosuppressive factors, and having gastrointestinal symptoms is reported here. Using real-time polymerase chain reaction, biopsy and blood specimens were tested for candida and herpes viruses. Epstein-Barr virus DNA was detected in tissue samples. The patient was treated with acyclovir with resolution of the symptomatology.</p> <p>Conclusions</p> <p>The prevalence of esophagitis remains undefined in both immunodeficient and immunocompetent individuals and should be taken into consideration in a patient presenting with esophageal symptoms. This case report stresses the role of Epstein-Barr virus infection in the pathogenesis of esophagitis, a rare condition in an immunocompetent host. In this setting, active infection may represent a primary infection or reactivation. Histopathological examination alone may miss the diagnosis, while polymerase chain reaction techniques optimize the diagnostic sensitivity, establish a diagnosis, and lead to an appropriate therapy.</p

Identifying new topoisomerase II poison scaffolds by combining publicly available toxicity data and 2D/3D-based virtual screening

Molecular descriptor (2D) and three dimensional (3D) shape based similarity methods are widely used in ligand based virtual drug design. In the present study pairwise structure comparisons among a set of 4858 DTP compounds tested in the NCI60 tumor cell line anticancer drug screen were computed using chemical hashed fingerprints and 3D molecule shapes to calculate 2D and 3D similarities, respectively. Additionally, pairwise biological activity similarities were calculated by correlating the 60 element vectors of pGI50 values corresponding to the cytotoxicity of the compounds across the NCI60 panel. Subsequently, we compared the power of 2D and 3D structural similarity metrics to predict the toxicity pattern of compounds. We found that while the positive predictive value and sensitivity of 3D and molecular descriptor based approaches to predict biological activity are similar, a subset of molecule pairs yielded contradictory results. By simultaneously requiring similarity of biological activities and 3D shapes, and dissimilarity of molecular descriptor based comparisons, we identify pairs of scaffold hopping candidates displaying characteristic core structural changes such as heteroatom/heterocycle change and ring closure. Attempts to discover scaffold hopping candidates of mitoxantrone recovered known Topoisomerase II (Top2) inhibitors, and also predicted new, previously unknown chemotypes possessing in vitro Top2 inhibitory activity