Assessment of laser-induced thermal load on silicon nanostructures based on ion desorption yields

Experimental assessment of the thermal load induced by fast laser pulses on micro- and nanostructures through IR imaging is currently too slow and lacks the spatial resolution to be useful. In this paper, we introduce a method based on measuring the laser-induced yields of ions to compare the thermal loads on nanofabricated silicon structures, when exposed to nanosecond laser pulses. The laser fluences at which the ion yields of, for example, sodiated and potassiated peptides ions are equal for two different structures correspond to equivalent thermal loads. Using alkalinated peptides is a convenient choice because the corresponding ion intensities are easily measured up to the melting point of silicon. As an example, we compare the nanosecond laser heating of silicon nanopost arrays with diverse post diameters and periodicities. Assessment of the thermal load through ion yield measurements can also be used to verify model assumptions for heat transport regimes in nanostructures.     

Influence of age and sex on aortic distensibility assessed by MRI in healthy subjects

Magnetic resonance imaging (MRI) is particularly well adapted to the evaluation of aortic distensibility. The calculation of this parameter, based on the change in vessel cross-sectional area per unit change in blood pressure, requires precise delineation of the aortic wall on a series of cine-MR images. Firstly, the study consisted in validating a new automatic method to assess aortic elasticity. Secondly, aortic distensibility was studied for the ascending and descending thoracic aortas in 26 healthy subjects. Two homogeneous groups were available to evaluate the influence of sex and age (with an age limit value of 35 years). The automatic postprocessing method proved to be robust and reliable enough to automatically determine aortic distensibility, even on artefacted images. In the 26 healthy volunteers, a marked decrease in distensibility appears with age, although this decrease is only significant for the ascending aorta (8.97±2.69 10⁻³ mmHg⁻¹ vs. 5.97±2.02 10⁻³ mmHg⁻¹). Women have a higher aortic distensibility than men but only significantly at the level of the descending aorta (7.20±1.61 10⁻³ mmHg⁻¹ vs. 5.05±2.40 10⁻³ mmHg⁻¹). Through our automatic contouring method, the aortic distensibility from routine cine-MRI has been studied on a healthy subject population providing reference values of aortic stiffness. The aortic distensibility calculation shows that age and sex are causes of aortic stiffness variations in healthy subjects.     

Observation of B(+)-->phiphiK(+) and evidence for B(0)-->phiphiK(0) below eta(c) threshold

We report measurements of the decays B(+)-->phiphiK(+) and B(0)-->phiphiK(0) using a sample of 231 x 10(6) BB pairs collected with the BABAR detector at the PEP-II asymmetric-energy B factory at the Stanford Linear Accelerator Center. The branching fractions are measured to be B(B(+)-->phiphiK(+))=(7.5+/-1.0(stat)+/-0.7(syst)) x 10(-6) and B(B(0)-->phiphiK(0))=(4.1(-1.4)(+1.7)(stat)+/-0.4(syst)) x 10(-6) for a phiphi invariant mass below 2.85 GeV/c(2).     

The effects of multichannel compression/expansion amplification on the intelligibility of nonsense syllables in noise

The effects of six-channel compression and expansion amplification on the intelligibility of nonsense syllables embedded in speech spectrum noise were examined for four hearing-impaired subjects. For one condition (linear) the stimulus was given six-channel amplification with frequency shaping to suit the subject's hearing loss. The other condition (nonlinear) was the same except that low level inputs, to any given channel, received expansion amplification and high level inputs received compression. For each condition, each subject received the nonsense syllables at three different input levels, representing low, average, and high intensity speech. The results of this study, like those of most other studies of multichannel compression, are mainly negative. Nonlinear processing (mainly expansion) of low intensity speech resulted in a significant degradation of speech intelligibility for two subjects and in no improvement for the others. One subject showed a significant improvement in intelligibility for the nonlinearly processed average intensity speech and another subject showed significant improvement for the high intensity input (mainly compression). Clearly, nonlinear processing is beneficial for some subjects, under some listening conditions, but further research is needed to identify the relevent characteristics of such subjects. An acoustic analysis of selected items revealed that the failure of expansion to improve intelligibility was primarily due to the very low intensity consonants /e/ and /k/, in final position, being presented at an even lower intensity in the expansion condition than in the linear condition. Expansion may be worth further investigation with different parameters. Several other problems caused by the multichannel processing were also revealed. These included alteration of spectral shapes and band interaction effects. Ways of overcoming these problems, and of capitalizing on the likely advantages of multichannel amplification, are currently being investigated.     

Bragg grating writing through the polyimide coating of high NA optical fibres with femtosecond IR radiation

Bragg gratings are written with ultrafast 800 nm radiation and a phase mask through the polyimide polymer coatings of commercially available high NA fibres that are both unloaded and loaded with high pressure hydrogen gas. For polyimide coated fibres with very high germanium core concentrations, index modulations greater than 1 × 10⁻⁴ are induced. Stable core index modulations 60% of their original value were present after 115 h at 500 °C.