Band structure observed in the current-voltage characteristics of SINININIS-type junctions

Band structure in the conductivity of 4-barrier Nb/Al-AlO_x-Al-AlO_x-Al-AlO_x-Al-AlO_x-Nb (SINININIS) tunnel junctions is observed at low temperatures. This structure is explained in terms of the interference of quasiparticle waves in a periodic barrier.     

Investigating the mechanisms of diamond polishing using Raman spectroscopy

Recent research has shown that a phase transformation of diamond to a different form of carbon is involved when diamonds are polished in the traditional fashion. The question as to how this phase transformation is activated and maintained to produce high wear rates is of great technological interest since it may radically change the way we view the processing of diamond. This paper describes the use of Raman spectroscopy to examine debris produced on the diamond polishing wheel, both during its preparation and during polishing. In addition, polished diamond surfaces were examined for the possible existence of non-diamond surface layers in an attempt to identify material removal mechanisms. Raman spectroscopy proves ideal for these analyses because its relatively high spatial resolution is well suited to the analysis of small wear features and debris particles, and because of the wealth of information it reveals about chemical structure. This level of structural information has been lacking in previous analyses of diamond polishing debris. In addition to the non-diamond carbon found in the wear debris, significant quantities of two iron oxides, magnetite (Fe₃O₄) and haematite (α-Fe₂O₃), were also found. An interesting observation was that a transformation from magnetite to haematite could be induced either by using high power laser excitation or by frictional heating during polishing. It is suggested that some of the Raman peaks previously attributed to lonsdaleite might better be explained by the presence of these oxides.     

Damping and modal structure of patterned magnetic nanoarrays

A number of studies have shown that ferromagnetic resonance linewidths in magnetic thin films contain a significant contribution due to processes, such as inhomogeneous broadening and two-magnon scattering followed by decay to the phonon thermal bath. We present a classical theoretical approach that permits the calculation of such processes for arrays of arbitrarily shaped magnetic nanoparticles and, by comparison with experimental results, demonstrates that the linewidth broadening and damping are dominated by inhomogenities that strongly depend on the equilibrium state of magnetization and can be used to identify the latter.     

Enhancement of the electrochemical capacitance of TiO2 nanotube arrays through controlled phase transformation of anatase to rutile

Here, we report the fabrication of self-organized titania (TiO(2)) nanotube array supercapacitor electrodes through controlled phase transformation of TiO(2), with aerial capacitances as high as 2.6 mF cm(-2), which far exceeds the values so far reported in the literature. The role of phase transformation in the electrochemical charge-discharge behaviour of nanocrystalline TiO(2) nanotubes is investigated and discussed in detail. The ease of synthesis and the exceptional electrochemical properties make these nanotube arrays an alternative candidate for use in energy storage devices.     

Testing heteroscedasticity by wavelets in a nonparametric regression model

In the nonparametric regression models, a homoscedastic structure is usually assumed. However, the homoscedasticity cannot be guaranteed a priori. Hence, testing the heteroscedasticity is needed. In this paper we propose a consistent nonparametric test for heteroscedasticity, based on wavelets. The empirical wavelet coefficients of the conditional variance in a regression model are defined first. Then they are shown to be asymptotically normal, based on which a test statistic for the heteroscedasticity is constructed by using Fan's wavelet thresholding idea. Simulations show that our test is superior to the traditional nonparametric test.     

Testing coeffcients of AR and bilinear time series models by a graphical approach

AR and bilinear time series models are expressed as time series chain graphical models, based on which, it is shown that the coefficients of AR and bilinear models are the conditional correlation coefficients conditioned on the other components of the time series. Then a graphically based procedure is proposed to test the significance of the coeffcients of AR and bilinear time series. Simulations show that our procedure performs well both in sizes and powers.     

Characteristics of CeCoIn5/Al/AlOx/Nb and CeCoIn5/Al/AlOx/Al tunnel junctions

We report characteristics of CeCoIn₅/Al/AlO_x/Nb and CeCoIn₅/Al/AlO_x/Al tunnel junctions fabricated on the (0 0 1) surface of CeCoIn₅ crystal platelets. The main result of this work is the observation of a low Josephson current (as compared with that expected from the Ambegaokar–Baratoff formula), which is consistent with idea that the order parameter in the heavy-fermion superconductor CeCoIn₅ has unconventional pairing symmetry.     

Enhancement of the supercurrent at a finite voltage in a sandwich-type ballistic SINIS junction

A large, reentrant, Josephson current is observed in SINIS (Nb/Al/AlOx/Al/AlOx/Al/Nb) junctions at a finite voltage close to Delta/e (where Delta is the superconducting energy gap in S) and a bias current exceeding the zero-voltage Josephson current. The effect is studied using a multiterminal device configuration. A theoretical interpretation in terms of quantized electron states in the N layer is provided.