Improvement of ultrasound speckle image velocimetry using image enhancement techniques

Ultrasound-based techniques have been developed and widely used in noninvasive measurement of blood velocity. Speckle image velocimetry (SIV), which applies a cross-correlation algorithm to consecutive B-mode images of blood flow has often been employed owing to its better spatial resolution compared with conventional Doppler-based measurement techniques. The SIV technique utilizes speckles backscattered from red blood cell (RBC) aggregates as flow tracers. Hence, the intensity and size of such speckles are highly dependent on hemodynamic conditions. The grayscale intensity of speckle images varies along the radial direction of blood vessels because of the shear rate dependence of RBC aggregation. This inhomogeneous distribution of echo speckles decreases the signal-to-noise ratio (SNR) of a cross-correlation analysis and produces spurious results. In the present study, image-enhancement techniques such as contrast-limited adaptive histogram equalization (CLAHE), min/max technique, and subtraction of background image (SB) method were applied to speckle images to achieve a more accurate SIV measurement. A mechanical sector ultrasound scanner was used to obtain ultrasound speckle images from rat blood under steady and pulsatile flows. The effects of the image-enhancement techniques on SIV analysis were evaluated by comparing image intensities, velocities, and cross-correlation maps. The velocity profiles and wall shear rate (WSR) obtained from RBC suspension images were compared with the analytical solution for validation. In addition, the image-enhancement techniques were applied to in vivo measurement of blood flow in human vein. The experimental results of both in vitro and in vivo SIV measurements show that the intensity gradient in heterogeneous speckles has substantial influence on the cross-correlation analysis. The image-enhancement techniques used in this study can minimize errors encountered in ultrasound SIV measurement in which RBCs are used as flow tracers instead of exogenous contrast agents.     

ECM and SAGE based joint estimation of timing and frequency offset for DMIMO–OFDM system

Distributed multiple-input multiple-output (DMIMO) technology is a key enabler of coverage extension and enhancement of link reliability in wireless networks through distributed spatial diversity. DMIMO employs classic relay channels in between the source and the destination to opportunistically form a virtual antenna array (VAA) for emulating cooperative diversity. Use of multiple antennas at the relays further increases capacity and reliability of the relay–destination channel through multiplexing and diversity of MIMO antennas respectively. In such network, the signal received at the destination is characterized by multiple timing offsets (MTO) due to different propagation delay and multiple carrier frequency offsets (MCFO) due to independent oscillators of the relays. Hence, synchronization becomes a crucial issue in DMIMO in order to realize the distributed coherence. In this paper, we address joint estimation of MCFO and MTO in DMIMO orthogonal frequency division multiplexing (OFDM) with MIMO configuration at the relays for estimate-and-forward (EF) relaying protocol. Two iterative algorithms, based on expectation conditional maximization (ECM) and space alternating generalized expectation–maximization (SAGE) are proposed for joint estimation in presence of inter carrier interference (ICI). The robustness of both the estimators to ICI is evaluated by mathematical analysis and supported by extensive simulations. The performance of the proposed estimators is assessed in terms of mean square error (MSE) and bit error rate (BER). The theoretical Cramer–Rao lower bound (CRLB) of estimator error variance is also derived.     

Electronic transmission and dwell time on a double barrier system with an accelerating quantum well

Resonant tunneling quantum structures consist of asymmetric wells and barriers have been investigated to find their optimized geometrical parameters and potential profile by the numerical calculations. The results show that the widths and the depths of the asymmetric wells have a significant effect on the transmission coefficient and the dwell time. The properties exhibited in this work may establish guidance to the device applications.     

Waiting times of entangled electrons in normal–superconducting junctions

We consider a normal–superconducting junction in order to investigate the effect of new physical ingredients on waiting times. First, we study the interplay between Andreev and specular scattering at the interface on the distribution of waiting times of electrons or holes separately. In that case the distribution is not altered dramatically compared to the case of a single quantum channel with a quantum point contact since the interface acts as an Andreev mirror for holes. We then consider a fully entangled state originating from splitting of Cooper pairs at the interface and demonstrate a significant enhancement of the probability to detect two consecutive electrons in a short time interval. Finally, we discuss the electronic waiting time distribution in the more realistic situation of partial entanglement.     

On the photon-drag effect of photocurrent of surface states of topological insulators

The photocurrent of surface states of topological insulator due to photon-drag effect is computed, being based on pure Dirac model of surface states. The scattering by disorder is taken into account to provide a relaxation mechanism for the photocurrent. The Keldysh–Schwinger formalism has been employed for the systematic calculation of photocurrent. The helicity dependent photocurrent of sizable magnitude transverse to the in-plane photon momentum is found, which is consistent with experimental data. Other helicity independent photocurrents with various polarization states are also calculated.     

Structural characterization and X-ray analysis by Williamson–Hall method for Erbium doped Aluminum Nitride nanoparticles,synthesized using inert gas condensation technique

We have synthesized AlN nanoparticles (NPs) doped in-situ with Er (AlN:Er) using inert gas condensation technique. Using x-ray diffraction (XRD) peak broadening analysis with the Williamson–Hall (W–H) Uniform Deformation Model (UDM) the crystallite size of the NPs and the strain in NPs were found to be 80±38 nm and 3.07×10⁻³±0.9×10⁻³ respectively. In comparison, using the Debye–Scherrer's (DS) formula, we have inferred that the crystallite size of the NPs was 23±6 nm and the average strain was 4.3×10⁻³±0.4×10⁻³. The scanning electron microscopy images show that the NPs are spherical and have an average diameter of ∼300 nm. The crystallite size is smaller than the size of the NPs revealing their polycrystalline behavior. In addition, the NPs strain, stress and energy density were also calculated using W–H analysis combined with the Uniform Deformation Stress Model (UDSM) and the Uniform Deformation Energy Density Model (UDEDM). Suggested by the spherical geometry and polycrystalline nature of the AlN NPs, the strain computed from UDM, UDSM and UDEDM were in agreement confirming an isotropic mechanical nature of the particle. Luminescence measurements revealed the temperature dependence of the optical emission of the Er³⁺ ions, confirming the use of AlN:Er NPs for nano-scale temperature sensing.     

Reprint of : Spin polarization induced by an electric field in the presence of weak localization effects

We evaluate the spin polarization (Edelstein or inverse spin galvanic effect) and the spin Hall current induced by an applied electric field by including the weak localization corrections for a two-dimensional electron gas. We show that the weak localization effects yield logarithmic corrections to both the spin polarization conductivity relating the spin polarization and the electric field and to the spin Hall angle relating the spin and charge currents. The renormalization of both the spin polarization conductivity and the spin Hall angle combine to produce a zero correction to the total spin Hall conductivity as required by an exact identity. Suggestions for the experimental observation of the effect are given.     

A review of commonly used analytical and empirical formulae for predicting sound diffracted by a thin screen

This paper reviews some useful analytical and empirical formulae that are used for the calculation of sound diffracted by a barrier. A brief historic overview of the study of spherical waves diffracted by a rigid half plane is presented also. The physical principles of sound diffraction by a thin plane are explained. The mathematical expressions are cast in a convenient form for ease of numerical implementation. Accurate analytical solutions are expressed in terms of standard mathematical functions that can be computed readily. Among the approximate solutions quoted, quite a few empirical formulations are adequate for most engineering purposes. The information presented in this paper should also be helpful for those who are interested in the study of sound diffracted by a barrier in a room or in a long industrial space.     

Physiochemical and cytotoxicity study of TPGS stabilized nanoemulsion designed by ultrasonication method

The main aim of the present work was to prepare TPGS stabilized D-α-Tocopherol, lemon oil, tween-80, and water nanoemulsion by low cost and highly effective sonication method. The prepared nanoemulsion showed good stability for 60 days at variable temperature conditions i.e. 4, 25 and 37 °C. The tolerance of the prepared nanoemulsion to salt (50 mM–500 mM) and pH (pH 2–pH 7.4) was also studied. The morphology and droplet size of pure and quinine loaded nanoemulsion was characterized with transmission electron microscopy. The prepared formulation was transparent and the obtained average particle size ranged between 25 nm and 35 nm. The nanoemulsion was found to be non toxic. The cell viability study of pure nanoemulsion carried out on Hep G2 cells revealed that the cell viability was 100%. The formulation further exhibited high quinine loading and release capacity with cumulative release up to 76 ± 2% and 65 ± 2% at pH 7.4 and pH 5.5 respectively. The interaction between quinine and vitamins (riboflavin, thiamine and biotin) was also carried out (aqueous medium). The study revealed that riboflavin had strong interaction with quinine and vitamins vis-à-vis thiamine and biotin.     

Sizable band gap in organometallic topological insulator

Based on first principle calculation when Ceperley–Alder and Perdew–Burke–Ernzerh type exchange-correlation energy functional were adopted to LSDA and GGA calculation, electronic properties of organometallic honeycomb lattice as a two-dimensional topological insulator was calculated. In the presence of spin–orbit interaction bulk band gap of organometallic lattice with heavy metals such as Au, Hg, Pt and Tl atoms were investigated. Our results show that the organometallic topological insulator which is made of Mercury atom shows the wide bulk band gap of about ∼120 meV. Moreover, by fitting the conduction and valence bands to the band-structure which are produced by Density Functional Theory, spin–orbit interaction parameters were extracted. Based on calculated parameters, gapless edge states within bulk insulating gap are indeed found for finite width strip of two-dimensional organometallic topological insulators.