A GHz Spintronic-Based RF Oscillator

A nano-sized oscillator for RF applications is presented which is based on two spintronic effects, the tunneling magnetoresistance (TMR) and the spin momentum transfer torque. The oscillation frequency is several GHz and can be tuned by both a DC bias current and an external DC magnetic field. High compactness, high tunability and full compatibility with standard CMOS process make this spin torque nano-oscillator (STNO) a promising candidate for future RF transceivers. The main issues to be addressed are spectral purity and output power. First measurements on a hybrid built connecting the STNO to a dedicated wideband amplifier show that today's performance in terms of power is close to but not yet compatible with telecommunication standard requirements. Using time domain analysis we show that frequency fluctuations are an issue for spectral purity. Frequency synthesis concepts based on STNOs are also discussed.     

Predictive (un)distortion model and 3-D reconstruction by biplane snakes

This paper is concerned with the three-dimensional (3-D) reconstruction of coronary vessel centerlines and with how distortion of X-ray angiographic images affects it. Angiographies suffer from pincushion and other geometrical distortions, caused by the peripheral concavity of the image intensifier (II) and the nonlinearity of electronic acquisition devices. In routine clinical practice, where a field-of-view (FOV) of 17-23 cm is commonly used for the acquisition of coronary vessels, this distortion introduces a positional error of up to 7 pixels for an image matrix size of 512 x 512 and an FOV of 17 cm. This error increases with the size of the FOV. Geometrical distortions have a significant effect on the validity of the 3-D reconstruction of vessels from these images. We show how this effect can be reduced by integrating a predictive model of (un)distortion into the biplane snakes formulation for 3-D reconstruction. First, we prove that the distortion can be accurately modeled using a polynomial for each view. Also, we show that the estimated polynomial is independent of focal length, but not of changes in anatomical angles, as the II is influenced by the earth's magnetic field. Thus, we decompose the polynomial into two components: the steady and the orientation-dependent component. We determine the optimal polynomial degree for each component, which is empirically determined to be five for the steady component and three for the orientation-dependent component. This fact simplifies the prediction of the orientation-dependent polynomial, since the number of polynomial coefficients to be predicted is lower. The integration of this model into the biplane snakes formulation enables us to avoid image unwarping, which deteriorates image quality and therefore complicates vessel centerline feature extraction. Moreover, we improve the biplane snake behavior when dealing with wavy vessels, by means of using generalized gradient vector flow. Our experiments show that the proposed methods in this paper decrease up to 88% the reconstruction error obtained when geometrical distortion effects are ignored. Tests on imaged phantoms and real cardiac images are presented as well.     

Toughness and Fracture Properties in Nacre‐Mimetic Clay/Polymer Nanocomposites

Nacre inspires researchers by combining stiffness with toughness by its unique microstructure of aligned aragonite platelets. This brick‐and‐mortar structure of reinforcing platelets separated with thin organic matrix has been replicated in numerous mimics that can be divided into two categories: microcomposites with aligned metal oxide microplatelets in polymer matrix, and nanocomposites with self‐assembled nanoplatelets—usually clay or graphene oxide—and polymer. While microcomposites have shown exceptional fracture toughness, current fabrication methods have limited nacre‐mimetic nanocomposites to thin films where fracture properties remained unexplored. Yet, fracture resistance is the defining property of nacre, therefore centrally important in any mimic. Furthermore, to make use of these properties in applications, bulk materials are required. Here, up to centimeter‐thick nacre‐mimetic clay/polymer nanocomposites are produced by the lamination of self‐assembled films. The aligned clay nanoplatelets are separated by poly(vinyl alcohol) matrix, with 10⁶–10⁷ nanoplatelets on top of each other in the bulk plates. Fracture testing shows crack deflection and a fracture toughness of 3.4 MPa m^1/2, not far from nacre. Flexural tests show high stiffness (25 GPa) and strength (220 MPa) that, despite the hydrophilic constituents, are not substantially affected by exposure to humidity.     

SIRIO-OTS 12 GHz orbital diversity experiment at Fucino

When rain occurs at a site, orbital diversity (OD) may be an alternative diversity scheme for future satellite communications above 10 GHz. The SIRIO-OTS OD attenuation measurements at 12 GHz with an aperture angle of 27.8° at Fucino show that the statistical gain obtainable is 20-25% of the OTS attenuation in decibels (if OTS is assumed as the satellite of the normal mode and SIRIO as OD resource, or spare link), or 30-40% of the SIRIO attenuation (if SIRIO is assumed as the satellite of normal mode, and OTS as OD resource). At 12 GHz these percentages represent a gain of a few decibels but at higher frequencies, such as 20/30 GHz, the gain may be multiplied by 2.5 to 5, giving noticeable power reductions. The instantaneous gain is also analyzed. The fundamental aspects of balancing an unbalanced diversity configuration are shown by applying the theory to the unbalanced SIRIO-OTS OD. Fade durations of the joint link show the same characteristics as the single-path ones: few long fades and many short fades. More important, the intervals of time in which the resource is used are long; this fact is favorable to the diversity configuration since switchover inefficiency is lowered