Non-invasive Evaluation of Aortic Stiffness Dependence with Aortic Blood Pressure and Internal Radius by Shear Wave Elastography and Ultrafast Imaging

Elastic properties of arteries have long been recognized as playing a major role in the cardiovascular system. However, non-invasive in vivo assessment of local arterial stiffness remains challenging and imprecise as current techniques rely on indirect estimates such as wall deformation or pulse wave velocity. Recently, Shear Wave Elastography (SWE) has been proposed to non-invasively assess the intrinsic arterial stiffness. In this study, we applied SWE in the abdominal aortas of rats while increasing blood pressure (BP) to investigate the dependence of shear wave speed with invasive arterial pressure and non-invasive arterial diameter measurements. A 15MHz linear array connected to an ultrafast ultrasonic scanner, set non-invasively, on the abdominal aorta of anesthetized rats (N=5) was used. The SWE acquisition followed by an ultrafast (UF) acquisition was repeated at different moment of the cardiac cycle to assess shear wave speed and arterial diameter variations respectively. Invasive arterial BP catheter placed in the carotid, allowed the accurate measurement of pressure responses to increasing does of phenylephrine infused via a venous catheter. The SWE acquisition coupled to the UF acquisition was repeated for different range of pressure. For normal range of BP, the shear wave speed was found to follow the aortic BP variation during a cardiac cycle. A minimum of (5.06$\pm$0.82) m/s during diastole and a maximum of (5.97$\pm$0.90) m/s during systole was measured. After injection of phenylephrine, a strong increase of shear wave speed (13.85$\pm$5.51) m/s was observed for a peak systolic arterial pressure of (190$\pm$10) mmHg. A non-linear relationship between shear wave speed and arterial BP was found. A complete non-invasive method was proposed to characterize the artery with shear wave speed combined with arterial diameter variations. Finally, the results were validated against two parameters the incremental elastic modulus and the pressure elastic modulus derived from BP and arterial diameter variations

Superdiffusive heat conduction in semiconductor alloys -- II. Truncated L\'evy formalism for experimental analysis

Nearly all experimental observations of quasi-ballistic heat flow are interpreted using Fourier theory with modified thermal conductivity. Detailed Boltzmann transport equation (BTE) analysis, however, reveals that the quasi-ballistic motion of thermal energy in semiconductor alloys is no longer Brownian but instead exhibits L\'evy dynamics with fractal dimension $\alpha < 2$. Here, we present a framework that enables full 3D experimental analysis by retaining all essential physics of the quasi-ballistic BTE dynamics phenomenologically. A stochastic process with just two fitting parameters describes the transition from pure L\'evy superdiffusion as short length and time scales to regular Fourier diffusion. The model provides accurate fits to time domain thermoreflectance raw experimental data over the full modulation frequency range without requiring any `effective' thermal parameters and without any a priori knowledge of microscopic phonon scattering mechanisms. Identified $\alpha$ values for InGaAs and SiGe match ab initio BTE predictions within a few percent. Our results provide experimental evidence of fractal L\'evy heat conduction in semiconductor alloys. The formalism additionally indicates that the transient temperature inside the material differs significantly from Fourier theory and can lead to improved thermal characterization of nanoscale devices and material interfaces

Imaging the effect of acoustically induced cavitation bubbles on the generation of shear-waves by ultrasonic radiation force

In soft solids, the acoustic radiation force on bubbles generates a shear wave. This bubble-based shear wave can be imaged using high frame rate ultrasound imaging. We report here an experiment where cavitation is induced in a tissue mimicking material by an ultrasonic tone-burst excitation, which also pushes the bubbles. The generated shear wave was imaged and the energy backscattered by the bubbles measured. The tone burst excitation was iterated at the same location and the decrease of both the amplitude of the particle velocity induced by the shear wave and the backscattered energy was shown. Data treatment to extract the bubbles' contribution to this two quantities, and a simple theoretical model allowed us to point out their linear dependence.http://deepblue.lib.umich.edu/bitstream/2027.42/84304/1/CAV2009-final129.pd

Bacterial pore-forming toxins: The (w)hole story?

Abstract.: Pore-forming toxins (PFTs) are the most common class of bacterial protein toxins and constitute important bacterial virulence factors. The mode of action of PFT is starting to be better understood. In contrast, little is known about the cellular response to this threat. Recent studies reveal that cells do not just swell and lyse, but are able to sense and react to pore formation, mount a defense, even repair the damaged membrane and thus survive. These responses involve a variety of signal-transduction pathways and sophisticated cellular mechanisms such as the pathway regulating lipid metabolism. In this review we discuss the different classes of bacterial PFTs and their modes of action, and provide examples of how the different bacteria use PFTs. Finally, we address the more recent field dealing with the eukaryotic cell response to PFT-induced damag

Acoustically induced and controlled micro-cavitation bubbles as active source for transcranial adaptive focusing

The skull bone is a strong aberrating medium for ultrasound in the low MHz range. Brain treatment with High Intensity Focused Ultrasound (HIFU) can however be achieved through the skull by multichannel arrays using an adaptive focusing technique. Time-reversal is a robust adaptive technique for correction of aberrations. It achieves moreover a matched filter and then allows the optimal energy concentration for thermal therapy. Nevertheless, this method requires a reference signal sent by a source embedded in brain tissues. Acoustically generated cavitation bubbles are active acoustic sources which can be remotely generated. Therefore, they are suited for this non-invasive time reversal aberration correction. We report here in vitro experiments where micro-cavitation was induced transcranially in agar gel at targeted positions using a coarse aberration correction either obtained from CT-scan based simulations or conventional steering. The bubbles' ultrasonic signature received by the array were then successfully used to optimally focus at the designated locations.http://deepblue.lib.umich.edu/bitstream/2027.42/84308/1/CAV2009-final134.pd

Constrained fitting of B-Spline curves based on the Force Density Method

This paper presents a novelapproach for constrained B-Spline curve approximation based on the Force Density Method (FDM). This approach aims to define a flexible technique tool for curve fitting, which allows approximating a set of points taking into account shape constraints that may be related to the production process, to the material or to other technological re- quirements. After a brief introduction on the property of the FDM and the definition of the network usedfor the formulation of the fitting problem, the paper explains in detail the mathematical approach, the methods and the techniques adopted for the definition of the proposed constrained B- Splinecurve approximation. The results suggest that the adoption of a mechanical model of bar networks allows develop- ing a more flexible tool than the traditional least squared methods (LSM) usually adopted for fitting problems. Numerical examples show that the new approach is effective in fitting prob- lems when the satisfaction of shape constraints, such as those related to production orto technological processes, are required

Reaction Networks For Interstellar Chemical Modelling: Improvements and Challenges

We survey the current situation regarding chemical modelling of the synthesis of molecules in the interstellar medium. The present state of knowledge concerning the rate coefficients and their uncertainties for the major gas-phase processes -- ion-neutral reactions, neutral-neutral reactions, radiative association, and dissociative recombination -- is reviewed. Emphasis is placed on those reactions that have been identified, by sensitivity analyses, as 'crucial' in determining the predicted abundances of the species observed in the interstellar medium. These sensitivity analyses have been carried out for gas-phase models of three representative, molecule-rich, astronomical sources: the cold dense molecular clouds TMC-1 and L134N, and the expanding circumstellar envelope IRC +10216. Our review has led to the proposal of new values and uncertainties for the rate coefficients of many of the key reactions. The impact of these new data on the predicted abundances in TMC-1 and L134N is reported. Interstellar dust particles also influence the observed abundances of molecules in the interstellar medium. Their role is included in gas-grain, as distinct from gas-phase only, models. We review the methods for incorporating both accretion onto, and reactions on, the surfaces of grains in such models, as well as describing some recent experimental efforts to simulate and examine relevant processes in the laboratory. These efforts include experiments on the surface-catalysed recombination of hydrogen atoms, on chemical processing on and in the ices that are known to exist on the surface of interstellar grains, and on desorption processes, which may enable species formed on grains to return to the gas-phase.Comment: Accepted for publication in Space Science Review

A 380 GHz SIS receiver using Nb/AlO(x)/Nb junctions for a radioastronomical balloon-borne experiment: PRONAOS

The superheterodyne detection technique used for the spectrometer instrument of the PRONAOS project will provide a very high spectral resolution (delta nu/nu = 10(exp -6)). The most critical components are those located at the front-end of the receiver: their contribution dominates the total noise of the receiver. Therefore, it is important to perform accurate studies for specific components, such as mixers and multipliers working in the submillimeter wave range. Difficulties in generating enough local oscillator (LO) power at high frequencies make SIS mixers very desirable for operation above 300 GHz. The low LO power requirements and the low noise temperature of these mixers are the primary reason for building an SIS receiver. This paper reports the successful fabrication of small (less than or equal to 1 sq micron) Nb/Al-O(x)/Nb junctions and arrays with excellent I-V characteristics and very good reliability, resulting in a low noise receiver performance measured in the 368/380 GHz frequency range