A trace bound for positive definite connected integer symmetric matrices

Abstract. Let A be a connected integer symmetric matrix, i.e., A = (aij) ∈ Mn(Z) for some n, A = AT, and the underlying graph (vertices corresponding to rows, with vertex i joined to vertex j if aij 6 = 0) is connected. We show that if all the eigenvalues of A are strictly positive, then tr(A) ≥ 2n − 1. There are two striking corollaries. First, the analogue of the Schur-Siegel-Smyth trace problem is solved for characteristic polynomials of connected inte-ger symmetric matrices. Second, we find new examples of totally real, separa-ble, irreducible, monic integer polynomials that are not minimal polynomials of integer symmetric matrices

Fast digitization and discrimination of prompt neutron and photon signals using a novel silicon carbide detector

Current requirements of some Homeland Security active interrogation projects for the detection of Special Nuclear Material (SNM) necessitate the development of faster inspection and acquisition capabilities. In order to do so, fast detectors which can operate during and shortly after intense interrogation radiation flashes are being developed. Novel silicon carbide (SiC) semiconductor Schottky diodes have been utilized as robust neutron and photon detectors in both pulsed photon and pulsed neutron fields and are being integrated into active inspection environments to allow exploitation of both prompt and delayed emissions. These detectors have demonstrated the capability of detecting both photon and neutron events during intense photon flashes typical of an active inspection environment. Beyond the inherent insensitivity of SiC to gamma radiation, fast digitization and processing has demonstrated that pulse shape discrimination (PSD) in combination with amplitude discrimination can further suppress unwanted gamma signals and extract fast neutron signatures. Usable neutron signals have been extracted from mixed radiation fields where the background has exceeded the signals of interest by >1000:1

Evaluation of the attachment strength of individuals of Asterina gibbosa (Asteroidea, Echinodermata) during the perimetamorphic period

SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Wissenschaftliche Zeitschrift der Universität Rostock / Gesellschaftswissenschaftliche Reihe

Double bond position and stereochemistry in unsaturated lipids can have profound impact on biological properties and activities but the assignment of these features by mass spectrometry is frequently challenging. Conventional techniques for lipid identification rely on collision-induced dissociation (CID) and are most often unable to differentiate between lipid isomers, particularly those involving double bond position and geometry (i.e., cis and trans). In this study, CID performed on proton-bound complexes of fatty acid methyl esters and iodoaniline (and related reagents) reveals unusual fragmentation patterns. CID products are shown to result from proton transfer and are associated with specific structures of the unsaturated lipids. Notably, CID of these complexes can not only distinguish cis- and trans-fatty acid methyl esters, but also differentiate conjugated double bond arrangements from non-conjugated analogs. Herein, the mechanisms underpinning this unique CID behavior are investigated by stable isotope labeling and are proposed to involve both carbene and free radical intermediates

Extremely fast prey capture in pipefish is powered by elastic recoil

The exceptionally high speed at which syngnathid fishes are able to rotate their snout towards prey and capture it by suction is potentially caused by a catapult mechanism in which the energy previously stored in deformed elastic elements is suddenly released. According to this hypothesis, tension is built up in tendons of the post-cranial muscles before prey capture is initiated. Next, an abrupt elastic recoil generates high-speed dorsal rotation of the head and snout, rapidly bringing the mouth close to the prey, thus enabling the pipefish to be close enough to engulf the prey by suction. However, no experimental evidence exists for such a mechanism of mechanical power amplification during feeding in these fishes. To test this hypothesis, inverse dynamical modelling based upon kinematic data from high-speed videos of prey capture in bay pipefish Syngnathus leptorhynchus, as well as electromyography of the muscle responsible for head rotation (the epaxial muscle) was performed. The remarkably high instantaneous muscle-mass-specific power requirement calculated for the initial phase of head rotation (up to 5795 W  kg−1), as well as the early onset times of epaxial muscle activity (often observed more than 300 ms before the first externally discernible prey capture motion), support the elastic power enhancement hypothesis