Anomalous Hall effect in L10-MnAl films with controllable orbital two-channel Kondo effect

The anomalous Hall effect (AHE) in strongly disordered magnetic systems has been buried in persistent confusion despite its long history. We report the AHE in perpendicularly magnetized L10-MnAl epitaxial films with variable orbital two-channel Kondo (2CK) effect arising from the strong coupling of conduction electrons and the structural disorders of two-level systems. The AHE is observed to excellently scale with pAH/f=a0pxx0+bpxx2 at high temperatures where phonon scattering prevails. In contrast, significant deviation occurs at low temperatures where the orbital 2CK effect becomes important, suggesting a negative AHE contribution. The deviation of the scaling agrees with the orbital 2CK effect in the breakdown temperatures and deviation magnitudes

Quantum state engineering with flux-biased Josephson phase qubits by Stark-chirped rapid adiabatic passages

In this paper, the scheme of quantum computing based on Stark chirped rapid adiabatic passage (SCRAP) technique [L. F. Wei et al., Phys. Rev. Lett. 100, 113601 (2008)] is extensively applied to implement the quantum-state manipulations in the flux-biased Josephson phase qubits. The broken-parity symmetries of bound states in flux-biased Josephson junctions are utilized to conveniently generate the desirable Stark-shifts. Then, assisted by various transition pulses universal quantum logic gates as well as arbitrary quantum-state preparations could be implemented. Compared with the usual PI-pulses operations widely used in the experiments, the adiabatic population passage proposed here is insensitive the details of the applied pulses and thus the desirable population transfers could be satisfyingly implemented. The experimental feasibility of the proposal is also discussed.Comment: 9 pages, 4 figure

Velocity estimation error reduction in stenosis areas using a correlation correction method

The advent of ultrafast ultrasound imaging proved beneficial for capturing transient flow patterns which was never readily achievable before. Velocity estimation methods based on 2D block-matching outperform Doppler based methods by offering higher frame rate with the cost of increased uncertainty in presence of out-of-plane motion as a result of turbulent flow. Local median filtering can partially address the estimation error reduction in stenosis areas at the risk of higher inaccuracy, since neighboring values may be also outliers. In this study, a correlation correction method is proposed, where the out-of-plane motion is eliminated by means of multiplying correlation maps from a same area but in two adjacent pairs of RF images. Experimental investigations were performed on a wall-less flow phantom, and proposed method achieved an error reduction of 66% in turbulent flow regions

Linear Dynamic Sparse Modelling for functional MR imaging

The reconstruction quality of a functional MRI sequence is determined by reconstruction algorithms as well as the information obtained from measurements. In this paper, we propose a Linear Dynamic Sparse Modelling method which is composed of measurement design and reconstruction processes to improve the image quality from both aspects. This method models an fMRI sequence as a linear dynamic sparse model which is based on a key assumption that variations of functional MR images are sparse over time in the wavelet domain. The Hierarchical Bayesian Kalman filter which follows the model is employed to implement the reconstruction process. To accomplish the measurement design process, we propose an Informative Measurement Design (IMD) method. The IMD method addresses the measurement design problem of selecting k feasible measurements such that the mutual information between the unknown image and measurements is maximised, where k is a given budget and the mutual information is extracted from the linear dynamic sparse model. The experimental results demonstrated that our proposed method succeeded in boosting the quality of functional MR images

Acoustic microbubble trapping in blood mimicking fluid

Microbubble (MB) volumetric pulsations can be selectively seeded with external ultrasonic fields. The therapeutic use of this phenomenon encompass mechanical thrombolysis and targeted drug deliveries through sonoporating endothelial cells. However, expected outcomes are still plagued by low bubble concentrations and short circulation time after administration. MBs preferentially flow along the centerline of large vessels which deteriorates biological targeting methodology in the case of vascular disease treatment with MBs. Simultaneous MB imaging and trapping against high flow rates has been recently proposed by instantaneously switching optimized ultrasonic beams. Principles were previously validated by circulating MBs with purified water through a flow phantom. But differences between blood and water call for preliminary investigations with blood mimicking fluid (BMF). This study demonstrated the capability of trapping bubbles in BMF with the acoustic trap but with nearly 40% efficiency reduction over the control in water, being present by the suppressed increase of image brightness

Polymer brush lubrication of the silicon nitride-steel contact: a colloidal force microscopy study

A greener lubrication solution for the steel–silicon nitride hybrid contact is proposed. The utilisation of surface-initiated (SI) activators-regenerated-by-electron-transfer (ARGET) atom-transfer radical polymerisation (ATRP) is employed to produce an oleophilic polymer brush which is based on methyl methacrylate. The current study presents the synthesis and characterisation of poly methyl methacrylate brushes. X-ray photoelectron spectroscopy, contact angle, gel permeation chromatography and atomic force microscopy were used to characterise the initiators and brushes. The lubricating effects of the polymer brushes under dry and swollen states were elucidated by lateral force microscopy with a steel colloid with a normal load in the nanoscale range. By testing in water and in poly α-olefin (PAO) this work shows that the frictional response of surface initiated polymers is highly dependent on the interaction between polymer brushes and fluid

Simultaneous trapping and imaging of microbubbles at clinically relevant flow rates

Mechanisms for non-invasive target drug delivery using microbubbles and ultrasound have attracted growing interest. Microbubbles can be loaded with a therapeutic payload and tracked via ultrasound imaging to selectively release their payload at ultrasound-targeted locations. In this study, an ultrasonic trapping method is proposed for simultaneously imaging and controlling the location of microbubbles in flow by using acoustic radiation force. Targeted drug delivery methods are expected to benefit from the use of the ultrasonic trap, since trapping will increase the MB concentration at a desired location in human body. The ultrasonic trap was generated by using an ultrasound research system UARP II and a linear array transducer. The trap was designed asymmetrically to produces a weaker radiation force at the inlet of the trap to further facilitate microbubble entrance. A pulse sequence was generated that can switch between a long duration trapping waveform and short duration imaging waveform. High frame rate plane wave imaging was chosen for monitoring trapped microbubbles at 1 kHz. The working principle of the ultrasonic trap was explained and demonstrated in an ultrasound phantom by injecting SonoVue microbubbles flowing at 80 mL/min flow rate in a 3.5 mm diameter vessel

A miniature HIFU excitation scheme to eliminate switching-induced grating lobes and nullify hard tissue attenuation

Phased array transducers are increasingly prevalent in a therapeutic contex as they facilitate precise control of the beam intensity and focus. To produce enough acoustic energy for ablation, large and costly amplifiers are required. Miniaturised switched circuits provide an alternative that is both more cost effective and more efficient. However, the high Q factor and curved geometry of a therapeutic transducer lends itself to grating lobes that deposit energy in undesirable areas when driven with switched circuitry. In this work, harmonic reduction pulse with modulation (HRPWM) is applied to a simulation of a therapeutic array. An array was simulated along with a skull that varied in attenuation. A number of switching schemes were tested and where possible, their amplitude was adjusted to reduce pressure variation in the acoustic field after propagation through the skull. Of the switched schemes tested, HRPWM performed best; reducing harmonically induced grating lobes by 12 dB and limiting pressure field variance to 0.1 dB which increases intensity at the focal point and makes therapy more efficient