Phase stability and transformations in NiTi from density functional theory calculations

We used density functional theory to characterize various crystalline phases of NiTi alloys: (i) high-temperature austenite phase B2; (ii) orthorhombic B19; (iii) the monoclinic martensite phase B19′; and (iv) a body-centered orthorhombic phase (BCO), theoretically predicted to be the ground state. We also investigated possible transition pathways between the various phases and the energetics involved. We found B19 to be metastable with a 1 meV energy barrier separating it from B19′. Interestingly, we predicted a new phase of NiTi, denoted B19′′, that is involved in the transition between B19′ and BCO. B19′′ is monoclinic and can exhibit shape memory; furthermore, its presence reduces the internal stress required to stabilize the experimentally observed B19′ structure, and it consequently plays a key role in NiTi’s properties.     

CMOS harmonic upconverter with power management of $$2{\bf nd}$$ harmonic for wideband short-range communications

The design and simulation of a 2nd harmonic based upconverter is introduced. With the proposed upconverter, it is possible to reach a good noise figure with power and area reduction. The design of the circuit was made with the UMC \(0.18\,\upmu \hbox {m}\) Mixed Mode/RF CMOS technology. However, the design methodology can be extended to a different CMOS process. According to the performance exhibited by the purposed mixer, it may be useful in wideband short-range communication technologies, such as certified wireless USB.     

A novel CMOS exponential transconductor operating in weak inversion

A novel CMOS exponential transconductor which employs only three NMOS transistors operating in weak inversion, is presented. The main advantage of the proposed circuit is its wide range of exponential behaviour, which reaches up to five decades of current range, and above 10 μA to an input voltage range of 800 mV. The physical realisation is achieved in two forms: in the first one, the circuit is implemented with discrete MOS transistor arrays by CD4007 series; in the second one, the circuit is fully integrated in a 0.5 μm CMOS standard process. Simulated and experimental results of the proposed exponential transconductor are also presented.     

An 8-Bit Digitally Controlled Programmable Phase Shifter Circuit for Sinusoidal Signals with 252∘ Phase Control Range

In this paper, the synthesis, design, and implementation of a programmable phase shifter circuit for sinusoidal signals is presented. The proposed circuit, built-up herein with operational amplifiers (OPAMPs), high precision resistors and low voltage switches, consists of a digitally controlled amplitude attenuator in combination with a single-tone orthogonalizer. Experimental results agree with theoretical background: the attained phase range was 252^° in 256 steps with a median step of 0.9^°. The inaccuracy of the circuit was determined to be of 0.03 %. Contrary to other OPAMP approaches for sinusoidal signals reported in the literature and based on a first-order all-pass filter structure, the approximation suggested in this work is based on a different concept. The achieved results demonstrate the functionality of the system for the case of a sinusoidal signal with frequency of 1 kHz. Notwithstanding, the proposed architecture can be extended to operate at higher frequencies by using different building blocks with larger bandwidth. Furthermore, it can be extended as well to work out with other periodic input waveforms, like triangular shapes or square waves, with the use of an appropriate orthogonalizer.     

Reconstructing the 3D shape and bone mineral density distribution of the proximal femur from dual-energy X-ray absorptiometry

The accurate diagnosis of osteoporosis has gained increasing importance due to the aging of our society. Areal bone mineral density (BMD) measured by dual-energy X-ray absorptiometry (DXA) is an established criterion in the diagnosis of osteoporosis. This measure, however, is limited by its two-dimensionality. This work presents a method to reconstruct both the 3D bone shape and 3D BMD distribution of the proximal femur from a single DXA image used in clinical routine. A statistical model of the combined shape and BMD distribution is presented, together with a method for its construction from a set of quantitative computed tomography (QCT) scans. A reconstruction is acquired in an intensity based 3D-2D registration process whereby an instance of the model is found that maximizes the similarity between its projection and the DXA image. Reconstruction experiments were performed on the DXA images of 30 subjects, with a model constructed from a database of QCT scans of 85 subjects. The accuracy was evaluated by comparing the reconstructions with the same subject QCT scans. The method presented here can potentially improve the diagnosis of osteoporosis and fracture risk assessment from the low radiation dose and low cost DXA devices currently used in clinical routine.     

Melanin films on Au(1 1 1): Adsorption and molecular conductance

We have studied the adsorption and electronic properties of thin melanin films on Au(1 1 1) by scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and density functional (DF) calculations. We have found that the minimum melanin unit detected under different adsorption conditions is consistent with the structural model for eumelanin protomolecules based on tetramer macrocycles formed by four monomer units (hydroquinone, indolequinone and its tautomers) with an inner porphyrin ring. DF calculations reveal that the entire π structure of the tetramers is implied in the chemisorption process through its frontier orbitals (HOMO and LUMO), a fact that is reflected in the change of intramolecular bonds. Also van der Waals interactions give an important contribution to the adsorption energy (≈0.02 eV/Ų). Dried thin melanin films (1 monolayer in thickness) exhibit good electronic conductance due to the presence of localized states near the Fermi level while dried thicker films exhibit a semiconductor-like behavior. Illumination of the thicker films with white light results in significant photo-induced tunneling currents when the melanin-covered Au is made negative with respect to the tip.     

Light‐Fueled,Spatiotemporal Modulation of Mechanical Properties and Rapid Self‐Healing of Graphene‐Doped Supramolecular Elastomers

Gaining spatially resolved control over the mechanical properties of materials in a remote, programmable, and fast‐responding way is a great challenge toward the design of adaptive structural and functional materials. Reversible, temperature‐sensitive systems, such as polymers equipped with supramolecular units, are a good model system to gain detailed information and target large‐scale property changes by exploiting reversible crosslinking scenarios. Here, it is demonstrated that coassembled elastomers based on polyglycidols functionalized with complementary cyanuric acid and diaminotriazine hydrogen bonding couples can be remotely modulated in their mechanical properties by spatially confined laser irradiation after hybridization with small amounts of thermally reduced graphene oxide (TRGO). The TRGO provides an excellent photothermal effect, leads to light‐adaptive steady‐state temperatures, and allows local breakage/de‐crosslinking of the hydrogen bonds. This enables fast self‐healing and spatiotemporal modulation of mechanical properties, as demonstrated by digital image correlation. This study opens pathways toward light‐fueled and light‐adaptive graphene‐based nanocomposites employing molecularly controlled thermal switches.     

Stochastic Contrast Measures for SAR Data: A Survey

“Contrast” is an generic denomination for “difference”. Measures of contrast are a powerful tool in image processing and analysis, e.g., in denoising, edge detection, segmentation, classification, parameter estimation, change detection, and feature selection. We present a survey on techniques that aim at measuring the contrast between (i) samples of SAR imagery, and (ii) samples and models, with emphasis on those that employ the statistical properties of the data.      

Automatic construction of multiple-object three-dimensional statistical shape models: application to cardiac modeling

A novel method is introduced for the generation of landmarks for three-dimensional (3-D) shapes and the construction of the corresponding 3-D statistical shape models. Automatic landmarking of a set of manual segmentations from a class of shapes is achieved by 1) construction of an atlas of the class, 2) automatic extraction of the landmarks from the atlas, and 3) subsequent propagation of these landmarks to each example shape via a volumetric nonrigid registration technique using multiresolution B-spline deformations. This approach presents some advantages over previously published methods: it can treat multiple-part structures and requires less restrictive assumptions on the structure's topology. In this paper, we address the problem of building a 3-D statistical shape model of the left and right ventricle of the heart from 3-D magnetic resonance images. The average accuracy in landmark propagation is shown to be below 2.2 mm. This application demonstrates the robustness and accuracy of the method in the presence of large shape variability and multiple objects.