Ultrasound-induced Gas Release from Contrast Agent Microbubbles

We investigated gas release from two hard-shelled ultrasound contrast agents by subjecting them to high-mechanical index (MI) ultrasound and simultaneously capturing high-speed photographs. At an insonifying frequency of 1.7 MHz, a larger percentage of contrast bubbles is seen to crack than at 0.5 MHz. Most of the released gas bubbles have equilibrium diameters between 1.25 and 1.75 /spl mu/m. Their disappearance was observed optically. Free gas bubbles have equilibrium diameters smaller than the bubbles from which they have been released. Coalescence may account for the long dissolution times acoustically observed and published in previous studies. After sonic cracking, the cracked bubbles stay acoustically active

Optical observations of acoustical radiation force effects on individual air bubbles

Previous studies dealing with contrast agent microbubbles have demonstrated that ultrasound (US) can significantly influence the movement of microbubbles. In this paper, we investigated the influence of the acoustic radiation force on individual air bubbles using high-speed photography. We emphasize the effects of the US parameters (pulse length, acoustic pressure) on different bubble\ud patterns and their consequences on the translational motion of the bubbles. A stream of uniform air bubbles with diameter ranging from 35 um to 79 um was generated and insonified with a single US pulse emitted at a frequency of 130 kHz. The bubble sizes have been chosen to be above, below, and at resonance. The peak acoustic pressures used in these experiments ranged from 40 kPa to 120 kPa. The axial displacements of the bubbles produced by the action of the US pulse were optically recorded using a high-speed camera at 1 kHz frame rate. The experimental results were compared to a simplified force balance theoretical model, including the action of the primary radiation force and the fluid drag force. Although the model is quite simple and does not take into account phenomena like bubble shape oscillations and added mass, the experimental findings agree with the predictions. The measured axial displacement increases quasilinearly with the burst length and the transmitted acoustic pressure. The axial displacement varies with the size and the density of the air bubbles, reaching a maximum at the resonance size of 48 um. The predicted displacement values differ by 15% from the measured data, except for resonant bubbles for which the displacement was overestimated by about 40%. This study demonstrates that even a single US pulse produces radiation forces that are strong enough to affect the bubble position

Toward a Smart EU Energy Policy: Rationale and 22 Recommendations

We are in desperate need of an EU Energy Policy. The facts are that, yes, there is indeed an EU Energy Policy. It is a policy based on a vision, a vision with three components. The policy is aiming for “markets, competition and efficiency”, it is equally focussing on “a sustainable energy economy”, and thirdly, it wants to “secure the EU’s energy supply”. Three objectives, three separate action lines. Balancing the three objectives in an integrated approach is challenging and difficult. To what extent is the market approach consistent with the other two policy packages? What impact does a climate package with tradable emission rights and non-tradable targets for green energy have on the market designs for gas and electricity? Are the necessary investments in new pipes and wires for securing our energy supplies sufficiently coming under the prevailing regulatory framework? Or, to put it differently; are we smart enough in the way in which we are making implementing steps in order to meet our stated objectives? Our paper ends with a proposed new vision and a set of 22 recommendations to the new European Commission.energy policy; climate change; security of energy supply; EU internal marke

Harmonic chirp imaging method for ultrasound contrast agent

Coded excitation is currently used in medical ultrasound to increase signal-to-noise ratio (SNR) and penetration depth. We propose a chirp excitation method\ud for contrast agents using the second harmonic component of the response. This method is based on a compression filter that selectively compresses and extracts the second harmonic component from the received echo signal. Simulations have shown a clear increase in response for chirp excitation\ud over pulse excitation with the same peak amplitude. This was confirmed by two-dimensional (2-D) optical observations of bubble response with a fast framing camera. To evaluate the harmonic compression method, we applied it to\ud simulated bubble echoes, to measured propagation harmonics, and to B-mode scans of a flow phantom and compared it to regular pulse excitation imaging. An increase of approximately 10 dB in SNR was found for chirp excitation. The\ud compression method was found to perform well in terms of resolution. Axial resolution was in all cases within 10% of the axial resolution from pulse excitation. Range side-lobe levels were 30 dB below the main lobe for the simulated bubble echoes and measured propagation harmonics. However,\ud side-lobes were visible in the B-mode contrast images

Normal crossing properties of complex hypersurfaces via logarithmic residues

We introduce a dual logarithmic residue map for hypersurface singularities and use it to answer a question of Kyoji Saito. Our result extends a theorem of L\^e and Saito by an algebraic characterization of hypersurfaces that are normal crossing in codimension one. For free divisors, we relate the latter condition to other natural conditions involving the Jacobian ideal and the normalization. This leads to an algebraic characterization of normal crossing divisors. As a side result, describe all free divisors with Gorenstein singular locus.Comment: 17 page

Charge transport in nanoscale vertical organic semiconductor pillar devices

We report charge transport measurements in nanoscale vertical pillar structures incorporating ultrathin layers of the organic semiconductor poly(3-hexylthiophene)(P3HT). P3HT layers with thickness down to 5 nm are gently top-contacted using wedging transfer, yielding highly reproducible, robust nanoscale junctions carrying high current densities (up to $10^6$ A/m$^2$). Current-voltage data modeling demonstrates excellent hole injection. This work opens up the pathway towards nanoscale, ultrashort-channel organic transistors for high-frequency and high-current-density operation.Comment: 30 pages, 8 figures, 1 tabl

Air bubble in an ultrasound field:theoretical and optical results

The radial motion of a gas bubble has been widely investigated in various studies using different theoretical models. The aim of this study is to compare, qualitatively and quantitatively, the results obtained by optical recording with those of a theoretical model. Bubble oscillations were optically recorded using an ultrafast digital camera, Brandaris. The radius-time, R(t), curves are directly computed from 128 video frames. The resting diameters of the air bubbles were 26-100 /spl mu/m. The ultrasound field was defined as an 8 cycle pulse at a frequency of 130 kHz generating an acoustic pressure of 10-150 kPa. The time and the frequency response of the bubble radial motion were compared to the Keller model. From the results, it is concluded that the Keller model can be used to accurately predict the fundamental and harmonic behavior of gas bubbles

Toward a Smart EU Energy Policy: Rationale and 22 Recommendation

QM-AI-10-003-EN-C (print)/QM-AI-10-003-EN-N (online)In the spring of 2007, the European Council agreed on a policy vision with three components: the green component (to promote a sustainable energy economy), the market component (to enhance efficiency and competition) and the security of supply component (to secure the EU’s energy supply). With regard to these three components, distinct implementing paths and action lines were developed. The existence of separate implementing paths entails some coordination issues. Coordination is necessary here to guarantee that the three action lines are integrated into a consistent EU Energy Policy. EU Energy policy needs to get smarter and align the incentives deriving from the three components to produce an integrated vision that moves beyond 2020. 22 policy recommendations can then be formulated for the most relevant energy-related issues which the EU is facing nowadays