Sonochemical production of a non-crystalline phase of palladium

A non-crystalline phase of palladium was produced by cavitation technique starting from a solution of palladium acetylacetonate and toluene. The microscopic structure of the sample, a very fine powder, was investigated by X-ray diffraction and it showed the characteristic features of a disordered system. Further details about the phase of the sample were gained by studying the crystallization process induced by thermal treatments.     

Effect of oxide tunneling on the measurement of MOS interfacestates

In principle, capacitance-voltage (C-V) and charge pumping techniques should supply the same information on the energy distribution of interface states. On the other hand, we have found from measurements taken on the same samples that the C-V method systematically gives a lower state density in the midgap region, with a steeper energy dependence. We show that the agreement is greatly improved by introducing in both extraction techniques the effects of carrier tunneling in slow oxide traps     

Effect of damping on the propensity of squeal instability: an experimental investigation

Friction induced vibrations in automotive brakes is recognized as a major problem in industry. Squeal is a difficult subject because of its unpredictability caused by a not completely understood sensitivity to variation of the system parameters. In the literature several analytical and numerical studies deal with the relationship between damping and system propensity to have instability. These studies highlight the existence of a nonintuitive effect of damping distribution on modal coupling that gives rise to the unstable vibrations. The complexity of commercial brakes and the difficulties to identify the values of modal damping in brake assemblies lead to the necessity to rely on experimental analysis using simplified test rigs. This paper presents an experimental investigation of the relationship between the distribution of modal damping and the propensity to develop squeal in a beam-on-disk setup, which reliably reproduces squeal events with easy control and measurement of the damping of the disk and the beam, respectively. The experiments highlight the key role played by the modal damping distribution on squeal: A nonuniform repartition of the modal damping causes an increase of the squeal propensity.     

An energy-independent nonlocal potential model. II. The asymmetry term

We analyze the single-particle bound-state properties and the elastic scattering of protons and neutrons in various groups of isotopes, ranging from C up to Sn, by means of an energy-independent nonlocal optical model. The potential is obtained as an extension of the one used in the analysis of N = Z nuclei, the new term being a Lane-type potential with the same geometrical parameters as the isoscalar one. The radius of the potential is determined by the fit of single-particle energies and charge distribution in one nuclide of each group and it is given by $\text{R}{}_{\mathrm{N}}\text{= 1.16 (A?1)}{}^{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{F}$. The well depths of the equivalent local potential are fitted to a large set of single-particle energies, measured in stripping and pick-up reactions, and show an energy dependence which is consistent with a unique nonlocal energy-independent potential having isoscalar nonlocality $\text{β ? 1F}$ and isovector nonlocality $\text{β}{}_{\mathrm{T}}\text{? 1.6F}$. In particular, the bound-state data can determine the isovector part of the potential with fair accuracy, provided that proton and neutron, T> and T<, particle and hole states are analyzed: its average value at zero energy shows an increasing behavior from C to Mo. The nucleon point distribution and r.m.s. radii corresponding to this model potential have been calculated in various nuclei.     

Nucleon polarization and the nuclear charge operator

Effects of nucleon polarization on the nuclear charge operator have been evaluated in a constituent quark model. At momentum transfer q ≈ 4 fm^?1 monopole, dipole and quadrupole excitations are of equal importance. In a harmonic oscillator model for ³He all multipolarities give negative contributions, leading to an overall contribution comparable to the relativistic pair effect. The influence of realistic wave functions, coupling constants and off-shell form factors is discussed.     

Nucleon form factors in a simple three-body quark model

We construct a simple 3-body quark model for the non strange nucleon resonances and we give results for the spectrum, the helicity amplitudes and the transition form factors. All the observables, in particular the transition form factors, are evaluated analytically and the results are compared with those of other models. Received: 15 November 1997     

Novel calcium-doped yttrium-iron-garnet thermistor bolometer in a planar and continuous bridge configuration

A new material, calcium-doped-yttrium iron garnet (Ca:YIG), which proves very promising in room-temperature thermistor bolometer applications, has been used to construct a continuous planar bridge structure which works as a thermistor bolometer detector (YIGTB). Experimental results concerning the electrical response of the bridge as a function of the position of the incident laser light beam are in perfect agreement with those predicted by computer simulation. Since the Ca:YIG has a relatively low thermal capacity and is highly adsorbing from the visible to the infra-red, YIGTB has proved highly responsive and faster than other commercial thermistors.     

Author's Reply

For original article by D'Amico, V. Gianini, and A. Baschirotto, see ibid., vol. 41, no. 7, p. 1630-37, Jul. 2006. For comments by P. V. Ananda see ibid. vol. 42, no. 2, February 2007     

One-pot synthesis and characterization of size-controlled bimagnetic FePt-iron oxide heterodimer nanocrystals

A one-pot, two-step colloidal strategy to prepare bimagnetic hybrid nanocrystals (HNCs), comprising size-tuned fcc FePt and inverse spinel cubic iron oxide domains epitaxially arranged in a heterodimer configuration, is described. The HNCs have been synthesized in a unique surfactant environment by temperature-driven sequential reactions, involving the homogeneous nucleation of FePt seeds and the subsequent heterogeneous growth of iron oxide. This self-regulated mechanism offers high versatility in the control of the geometric features of the resulting heterostructures, circumventing the use of more elaborate seeded growth techniques. It has been found that, as a consequence of the exchange coupling between the two materials, the HNCs exhibit tunable single-phase-like magnetic behavior, distinct from that of their individual components. In addition, the potential of the heterodimers as effective contrast agents for magnetic resonance imaging techniques has been examined.