Noncontact Material Testing Using Low-Energy Optical Generation and Detection of Acoustic Pulses

We will discuss preliminary results on the use of a low-energy laser and a sensitive laser interferometer for noncontact material testing of metals and nonmetals. There have been numerous reports [1–12] on the use of lasers to generate acoustic signals, but this is the first use of a relatively low-energy tunable laser source and improved interferometer to measure acoustic waveforms in both metals and nonmetals [13]. The use of a laser interferometer for the noncontact detection of acoustic pulses has also been reported previously [14–20], but we now report the use of a sensitive “non-Michelson” interferometer with increased signal-to-noise capabilities. The combination of these features allows noncontact, low-energy optical generation and optical detection in a variety of materials, in potentially hostile environments, and provides accurate accoustic waveforms which can be used to characterize specimens. These results, therefore, begin to demonstrate the feasibility of a portable (entirely) optical system for the nondestructive evaluation of materials

Gene expression changes of prostanoid synthases in endothelial cells and prostanoid receptors in vascular smooth muscle cells caused by aging and hypertension

The present study was designed to assess whether or not changes in genomic expression of cyclooxygenases (COX-1, COX-2), endothelial nitric oxide synthase (eNOS), and prostanoid synthases in the endothelium and of prostanoid receptors in vascular smooth muscle contribute to the occurrence of endothelium-dependent contractions during aging and hypertension. Gene expression was quantified by real-time PCR using isolated endothelial cells and smooth muscle cells (SMC) from the aorta of Wistar-Kyoto and spontaneously hypertensive rats. Genes for all known prostanoid synthases and receptors were present in endothelial cells and SMC, respectively. Aging caused overexpression of eNOS, COX-1, COX-2, thromboxane synthase, hematopoietic-type prostaglandin D synthase, membrane prostaglandin E synthase-2, and prostaglandin F synthase in endothelial cells and COX-1 and prostaglandin E2 (EP)4 receptors in SMC. Hypertension augmented the expression of COX-1, prostacyclin synthase, thromboxane synthase, and hematopoietic-type prostaglandin D synthase in endothelial cells and prostaglandin D2 (DP), EP3, and EP4 receptors in SMC. The increase in genomic expression of endothelial COX-1 explains why in aging and hypertension the endothelium has greater propensity to release cyclooxygenase-derived vasoconstrictive prostanoids. The expression of prostacyclin synthase was by far the most abundant, explaining why the majority of the COX-1-derived endoperoxides are transformed into prostacyclin, substantiating the role of prostacyclin as an endothelium-derived contracting factor. The expression of thromboxane synthase was increased in the cells of aging or hypertensive rats, explaining why the prostanoid can contribute to endothelium-dependent contractions. It is uncertain whether the gene modifications caused by aging and hypertension directly contribute to endothelium-dependent contractions or rather to vascular aging and the vascular complications of the hypertensive process. Copyright © 2008 the American Physiological Society.link_to_subscribed_fulltex

Mandibular distraction osteogenesis: basic research on animal model

Ultrasonic techniques are being currently used in a wide range of applications. However, there are situations where it is difficult to utilize ultrasound for NDT purposes. They are severely limited in non-contact applications due to attenuation in air. Since the present day technology requires a physical contact or a couplant between the transducer and the specimen surface to minimize diffraction effects, the temperatures sensitive piezoelectric transducers are not suited for hostile operating environments and extreme temperature gradients. Another drawback of piezoelectric transducers is the narrow banded source signals. Generation of very high frequency ultrasound becomes difficult and expensive. Complex contoured specimens are, also, difficult to handle, since traditional ultrasound is sensitive to the normalization of the incident ultrasonic beam. As with all mechanical devices, the rate of scanning of these transducers is very slow

A two-layer model for the laser generation of ultrasound in graphite-epoxy laminates

International audienceIn this contribution, we describe the principle of a 2 layer model of thermoelastic generation of ultrasound. This model allows to bury the thermoelastic source under the first layer when this layer is transparent to the illumination wavelength, resulting in an enhanced efficiency of thermoelastic ultrasound generation. The predictions of the model are confronted to exerimental results collected on our laser-ultrasonics equipment, and the agreement is quite good

Is there a role for Hedgehog genes in Hirschsprung's diseases?

There has been considerable interest lately in imaging techniques that employ thermal waves [1–4]. In thermal-wave imaging, a beam of energy, usually a laser or electron beam, is focused and scanned across the surface of a sample. This beam is generally intensity-modulated at a frequency in the range of 10kHz to 10MHz. As the beam scans across the sample it is absorbed at or near the surface, and periodic surface heating results at the beam modulation frequency. This periodic heating is the source of thermal waves, which propagate from the heated region. The thermal waves are diffusive waves similar to eddy current waves, evanescent waves, and other critically damped phenomena that travel only one to two wavelengths before their intensity becomes negligibly small. Nevertheless, within their range, the thermal waves interact with thermal features in a manner that is mathematically similar to the scattering and reflection processes of conventional propagating waves [5], Thus any features on or beneath the surface of the sample that are within the range of these thermal waves and that have thermal characteristics different from their surroundings will reflect and scatter the waves and thus become visible