A Rheological Investigation of the Crystallization Kinetics of Syndiotactic Polypropylene of Varying Degree of Tacticity

The crystallization behavior of five Syndiotactic Polypropylene (sPP) samples of varying degree of tacticity has been studied by means of rheological techniques and compared to the results of more standard DSC measurements. Small Amplitude Oscillatory Shear (SAOS) measurements have been performed on a controlled stress rotational rheometer equipped with a nitrogen-fed, forced convection oven, which allows for good temperature stability and relatively high heating/cooling rates. Both non-isothermal and isothermal crystallization tests have been carried out. The former proved useful to determine the melting and crystallization temperature of the polymers. The latter were exploited to determine the temperature dependence of the polymer crystallization rate. The results showed the strong influence of the degree of tacticity on the crystallization behaviour of sPP. In particular, it was confirmed that a decrease in the stereo-regularity of the polymer chain considerably shifts the crystallization process to lower temperatures. For the case of the lowest tacticity sample, rheology was crucial in determining the temperature where the maximum (but very small) crystallization rate is attained, a result that could not be achieved by standard calorimetry measurements.

Internal Transport Barrier Broadening through Subdominant Mode Stabilization in Reversed Field Pinch Plasmas

The reversed field pinch (RFP) device RFX-mod features strong internal transport barriers when the plasma accesses states with a single dominant helicity. Such transport barriers enclose a hot helical region with high confinement whose amplitude may vary from a tiny one to an amplitude encompassing an appreciable fraction of the available volume. The transition from narrow to wide thermal structures has been ascribed so far to the transport reduction that occurs when the dominant mode separatrix, which is a preferred location for the onset of stochastic field lines, disappears. In this Letter we show instead that the contribution from the separatrix disappearance, by itself, is marginal and the main role is instead played by the progressive stabilization of secondary modes. The position and the width of the stochastic boundary encompassing the thermal structures have been estimated by applying the concept of a 3D quasiseparatrix layer, developed in solar physics to treat reconnection phenomena without true separatrices and novel to toroidal laboratory plasmas. Considering the favorable scaling of secondary modes with the Lundquist number, these results open promising scenarios for RFP plasmas at temperatures higher than the presently achieved ones, where lower secondary modes and, consequently, larger thermal structures are expected. Furthermore, this first application of the quasiseparatrix layer to a toroidal plasma indicates that such a concept is ubiquitous in magnetic reconnection, independent of the system geometry under investigation.

Toward hyperuniform disordered plasmonic nanostructures for reproducible surface-enhanced Raman spectroscopy

We report on the self-assembling of clusters of gold-nanoparticles (Au-NPs) directed by the phase separation of poly(styrene)-b-poly(methylmethacrylate) (PS-b-PMMA) block-copolymer (BCP) on indium tin oxide coated glass, which induces the onset of vertical lamellar domains. After thermal evaporation of gold on BCP, Au-NPs of 4 nm are selectively included into PS-nanodomains by thermal annealing, and then clustered with large density of hot spots (> 10(4) μm(2)) in a random two-dimensional pattern. The resulting nanostructure exhibits near-hyperuniform long-range correlations. The consequent large degree of homogeneity of this isotropic plasmonic pattern gives rise to a highly reproducible Surface-Enhanced Raman Scattering (SERS) enhancement factor over the centimeter scale (std. dev. ∼ 10% over 0.25 cm(2)). We also discuss the application of a static electric field for modulating the BCP host morphology. The electric field induces an alignment of Au-NP clusters into ordered linear chains, exhibiting a stronger SERS activity, but reduced SERS spatial reproducibility.

Experimental observation of microtearing modes in a toroidal fusion plasma

Experimental evidences of short wavelength electromagnetic modes are found in the reversed-field-pinch configuration device RFX-mod by means of in-vessel magnetic probes. The modes are revealed during the helical states of the plasma. Their amplitude is well correlated to the electron temperature gradient strength in the core. On the basis of linear gyrokinetic calculations we interpret these instabilities as microtearing modes.

Bifurcation to 3D helical magnetic equilibrium in an axisymmetric toroidal device

We report the first direct measurement of the internal magnetic field structure associated with a 3D helical equilibrium generated spontaneously in the core of an axisymmetric toroidal plasma containment device. Magnetohydrodynamic equilibrium bifurcation occurs in a reversed-field pinch when the innermost resonant magnetic perturbation grows to a large amplitude, reaching up to 8% of the mean field strength. Magnetic topology evolution is determined by measuring the Faraday effect, revealing that, as the perturbation grows, toroidal symmetry is broken and a helical equilibrium is established.

Active-feedback control of the magnetic boundary for magnetohydrodynamic stabilization of a fusion plasma

Stable operation with control on magnetohydrodynamic modes has been obtained in the modified reversed field experiment employing a set of 192 feedback controlled saddle coils. Improvements of plasma temperature, confinement (twofold), and pulse length (threefold) and, as a consequence of the magnetic fluctuation reduction, strong mitigation of plasma-wall interaction and mode locking are reported.

[Treatment of ischemic heart disease in the elderly. Comparison of diltiazem, verapamil and gallopamil]

The medical therapy of myocardial ischemia in elderly patients has not been well evaluated. We studied the age-related changes in 127 patients with proved coronary artery disease and stable effort angina the efficacy and the safety of diltiazem 120 mg tid, verapamil 120 mg tid and gallopamil 50 mg tid a medium term parallel, double blind cross-over placebo controlled study. All patients have been clinically and ergometrically evaluated. In middle-age patients diltiazem, verapamil and gallopamil induced a significant increasing of exercise duration and time to onset ST segment depression > or = 1 mm. In the elderly patients both verapamil and diltiazem as increased the exercise duration and ischemic threshold, while the diltiazem did not increased the exercise duration even if the time of onset ST segment depression > or = 1 mm is increased. At peak exercise the ST segment depression have been reduced both in middle-age and elderly patients after active drugs. Weekly angina and DNT consumption have been significantly reduced after diltiazem, verapamil and gallopamil in middle-age and elderly patients. Side effects have not been relevant even if gallopamil as a lower frequency of them in comparison to diltiazem and verapamil. No patients stopped the treatment because major side effects. Our experience suggests that diltiazem, verapamil and gallopamil have a similar efficacy and rare well tolerated. The choice of one instead of another must be suggested on the basis of side effects developing.

[Safety of the dipyramidole echocardiography test in elderly coronary disease patients]

We prospectively studied the feasibility and safety of high-dose dipyridamole echocardiography in 166 patients (77 younger and 89 elderly patients) referred for clinical evaluation of coronary artery disease. The feasibility of dipyridamole echocardiography test was 80.5% in the young and 82% in the elderly (p = n.s.). The incidence of side effects during dipyridamole echocardiography was similar in two groups, except for dyspnea which was observed in 20% in the older and 4% in the younger (p < 0.01). Our data demonstrate that the dypiridamole test combined with echocardiographic monitoring of regional myocardial contractility may be considered a valid non invasive method for evaluating coronary artery disease in the elderly.