Analysis of dynamic mechanical response in torsion

We investigate the dynamic response of industrial rubbers (styrene-butadiene random copolymers, SBR) in torsion and compare against common small amplitude oscillatory shear measurements by using a torsion rectangular fixture, a modified torsion cylindrical fixture, and a conventional parallel plate fixture, respectively, in two different rheometers (ARES 2kFRTN1 from TA Instruments, USA and MCR 702 from Anton Paar-Physica, Austria). The effects of specimen geometry (length-to-width aspect ratio) on storage modulus and level of clamping are investigated. For cylindrical specimens undergoing torsional deformation, we find that geometry and clamping barely affect the shear moduli, and the measurements essentially coincide with those using parallel plates. In contrast, a clear dependence of the storage modulus on the aspect ratio is detected for specimens having rectangular cross section. The empirical correction used routinely in this test is based on geometrical factors and can account for clamping effects, but works only for aspect ratios above a threshold value of 1.4. By employing a finite element analysis, we perform a parametric study of the effects of the aspect ratio in the cross-sectional stress distribution and the linear viscoelastic torsional response. We propose a new, improved empirical equation for obtaining accurate moduli values in torsion at different aspect ratios, whose general validity is demonstrated in both rheometers. These results should provide a guideline for measurements with different elastomers, for which comparison with dynamic oscillatory tests may not be possible due to wall slip issues

Doxorubicin and congo red effectiveness on prion infectivity in golden Syrian hamster

The effect of doxorubicin and Congo Red on prion protein (PrP) infectivity in experimental scrapie was studied to better understand the effect of these compounds in prion diseases and to establish whether a dose-response correlation exists for Congo Red. This was performed in order to test the effectiveness of compounds that may easily be used in human prion diseases. Brain homogenate containing membrane bound PrPSc monomers was used as inoculum and was previously incubated with doxorubicin 10(-3) M and with increasing concentrations of Congo Red ranging from 10(-7) to 10(-2) M. This study shows for the first time that doxorubicin, and confirms that Congo Red, may interact with pathological PrP monomers modifying their infectious properties. Pre-incubation of infected brain homogenate with Congo Red resulted in prolonged incubation time and survival, independently of Congo Red concentration (p<0.05). Doxorubicin and Congo Red effects do not depend upon interaction with PrP amyloid material

Adiabatic evolution of a coupled-qubit Hamiltonian

We present a general method for studying coupled qubits driven by adiabatically changing external parameters. Extended calculations are provided for a two-bit Hamiltonian whose eigenstates can be used as logical states for a quantum CNOT gate. From a numerical analysis of the stationary Schroedinger equation we find a set of parameters suitable for representing CNOT, while from a time-dependent study the conditions for adiabatic evolution are determined. Specializing to a concrete physical system involving SQUIDs, we determine reasonable parameters for experimental purposes. The dissipation for SQUIDs is discussed by fitting experimental data. The low dissipation obtained supports the idea that adiabatic operations could be performed on a time scale shorter than the decoherence time.Comment: 10 pages, 4 figures, to be pub.in Phys Rev

Development of a navigation algorithm for autonomous underwater vehicles

In this paper, the authors present an underwater navigation system for Autonomous Underwater Vehicles (AUVs) which exploits measurements from an Inertial Measurement Unit (IMU), a Pressure Sensor (PS) for depth and the Global Positioning System (GPS, used during periodic and dedicated resurfacings) and relies on either the Extended Kalman Filter (EKF) or the Unscented Kalman Filter (UKF) for the state estimation. Both (EKF and UKF) navigation algorithms have been validated through experimental navigation data related to some sea tests performed in La Spezia (Italy) with one of Typhoon class vehicles during the NATO CommsNet13 experiment (held in September 2013) and through Ultra-Short BaseLine (USBL) fixes used as a reference (ground truth). Typhoon is an AUV designed by the Department of Industrial Engineering of the Florence University for exploration and surveillance of underwater archaeological sites in the framework of the Italian THESAURUS project and the European ARROWS project. The obtained results have demonstrated the effectiveness of both navigation algorithms and the superiority of the UKF (very suitable for AUV navigation and, up to now, still not used much in this field) without increasing the computational load (affordable for on-line on-board AUV implementation)

Scaling Up Magnetic Nanobead Synthesis with Improved Stability for Biomedical Applications

The growing interest in multifunctional nano-objects based on polymers and magnetic nanoparticles for biomedical applications motivated us to develop a scale-up protocol to increase the yield of polymeric magnetic nanobeads while aiming at keeping the structural features at optimal conditions. The protocol was applied to two different types of magnetic ferrite nanoparticles: the Mn-ferrite selected for their properties as contrast agents in magnetic resonance imaging and iron oxide nanostar shaped nanoparticles chosen for their heat performance in magnetic hyperthermia. At the same time, some experiments on surface functionalization of nanobeads with amino modified polyethyelene glycol (PEG) molecules have provided further insight into the formation mechanism of magnetic nanobeads and the need to cross-link the polymer shell to improve the stability of the beads, making them more suitable for further manipulation and use. The present work summarizes the most important parameters required to be controlled for the upscaling of nanobead synthesis in a bench protocol and proposes an alternative cross-linking strategy based on prefunctionalization of the polymer prior to the nanobead formation as a key parameter to improve the nanobead structural stability in solutions at different pHs and during surface functionalization

Magnetic nanocarriers with tunable pH dependence for controlled loading and release of cationic and anionic payloads.

Superparamagnetic nanocarriers with tunable pH dependence of the surface charge are designed by a simple co-precipitation method. By exploiting electrostatic interactions, cationic or anionic payloads can be adsorbed and desorbed depending on the pH. On three different resulting nanocarrier systems, experiments of loading and release of gold nanoparticles as well as effective siRNA loading and in vitro delivery on human cells are performed

Topology-Induced Critical Current Enhancement in Josephson Networks

We investigate the properties of Josephson junction networks with inhomogeneous architecture. The networks are shaped as "quare comb" planar lattices on which Josephson junctions link superconducting islands arranged in the plane to generate the pertinent topology. Compared to the behavior of reference linear arrays, the temperature dependencies of the Josephson currents of the branches of the network exhibit relevant differences. The observed phenomena evidence new and surprising behavior of superconducting Josephson arrays as well as remarkable similarities with bosonic junction arrays.Comment: improved figures (added magnetic pattern and single junction switching) some changes in the text and in the titl

Beam Test Results of the BTeV Silicon Pixel Detector

The results of the BTeV silicon pixel detector beam test carried out at Fermilab in 1999-2000 are reported. The pixel detector spatial resolution has been studied as a function of track inclination, sensor bias, and readout threshold.Comment: 8 pages of text, 8 figures, Proceedings paper of Pixel 2000: International Workshop on Semiconductor Pixel Detectors for Particles and X-Rays, Genova, June 5-8, 200