Higher-loop integrability in gauge theory

The dilatation operator measures scaling dimensions of local operator in a conformal field theory. Algebraic methods of constructing the dilatation operator in four-dimensional N=4 gauge theory are reviewed. These led to the discovery of novel integrable spin chain models in the planar limit. Making use of Bethe ansätze a superficial discrepancy in the AdS/CFT correspondence was found, we discuss this issue and give a possible resolution. To cite this article: N. Beisert, C. R. Physique 5 (2004).

Résumé

L'opérateur de dilatation mesure les dimensions d'échelles des opérateurs locaux des théories conformes des champs. Nous passons en revue les méthodes algébriques de construction de l'opérateur de dilatation pour la théorie de jauge N=4 en quatre dimensions. Ceci nous a conduit à découvrir, dans la limite planaire, de nouveaux modèles intégrables de chaînes de spin. En utilisant l'ansätze de Bethe une incompatibilité avec la correspondance AdS/CFT fut découverte, nous discutons ce problème et une résolution possible. Pour citer cet article : N. Beisert, C. R. Physique 5 (2004).     

Effects of feedback from collimating, focusing, and spot-array generating outcoupler gratings in surface-emitting semiconductor lasers

We experimentally demonstrate that a grating outcoupler used for complex beam shaping (spot-array generation) can produce unintentional optical feedback that severely disturbs the integrated in-plane laser that illuminates the coupler. Simulations show that these outcouplers, in contrast to conventional collimating or focusing outcouplers, tend to produce high levels of feedback in spite of the detuning used to suppress feedback. Further, this feedback is focused to high intensity in the laser gain medium. This focused light acts as a seed for the nonlinear self-focusing that causes wave-front distortion and filamentation, which degrades the beam quality.     

Optimal topological test for degeneracies of real Hamiltonians

We consider adiabatic transport of eigenstates of real Hamiltonians around loops in parameter space. It is demonstrated that loops that map to nontrivial loops in the space of eigenbases must encircle degeneracies. Examples from Jahn-Teller theory are presented to illustrate the test. We show furthermore that the proposed test is optimal.     

An online nano‐LC‐ESI‐FTICR‐MS method for comprehensive characterization of endogenous fragments from amyloid β and amyloid precursor protein in human and cat cerebrospinal fluid

Amyloid precursor protein (APP) is the precursor protein to amyloid β (Aβ), the main constituent of senile plaques in Alzheimer's disease (AD). Endogenous Aβ peptides reflect the APP processing, and greater knowledge of different APP degradation pathways is important to understand the mechanism underlying AD pathology. When one analyzes longer Aβ peptides by low‐energy collision‐induced dissociation tandem mass spectrometry (MS/MS), mainly long b‐fragments are observed, limiting the possibility to determine variations such as amino acid variants or post‐translational modifications (PTMs) within the N‐terminal half of the peptide. However, by using electron capture dissociation (ECD), we obtained a more comprehensive sequence coverage for several APP/Aβ peptide species, thus enabling a deeper characterization of possible variants and PTMs. Abnormal APP/Aβ processing has also been described in the lysosomal storage disease Niemann–Pick type C and the major large animal used for studying this disease is cat. By ECD MS/MS, a substitution of Asp7 → Glu in cat Aβ was identified. Further, sialylated core 1 like O‐glycans at Tyr10, recently discovered in human Aβ (a previously unknown glycosylation type), were identified also in cat cerebrospinal fluid (CSF). It is therefore likely that this unusual type of glycosylation is common for (at least) species belonging to the magnorder Boreoeutheria. We here describe a detailed characterization of endogenous APP/Aβ peptide species in CSF by using an online top‐down MS‐based method. Copyright © 2012 John Wiley & Sons, Ltd.