Search results for "Sound"

Elastic constants in RbI, determined by inelastic neutron scattering

1978

Long-wavelength acoustic phonons have been studied in the whole (100)-plane of RbI at 295 K by means of inelastic neutron scattering. The raw data have been corrected for resolution effects taking into account the curvature of the dispersion surface and variations of the mode eigenvectors. The shifts of the neutron groups due to these resolution effects are discussed in detail. The analysis of the experimental results gives for the zero sound elastic constantsc11=28.15±0.5,c12=3.7±0.5 andc44=2.85±0.1 1010 dyn/cm2. A comparison with first sound elastic constants taken from ultrasonic measurements yields significant differences between the high and low frequency elastic constantsc11 andc″=(c1…

Synchronized photonic modulators driven by surface acoustic waves

2013

Photonic modulators are one of the most important elements of integrated photonics. We have designed, fabricated, and characterized a tunable photonic modulator consisting of two 180 degrees-dephased output waveguide channels, driven by a surface acoustic wave in the GHz frequency range built on (Al,Ga)As. Odd multiples of the fundamental driven frequency are enabled by adjusting the applied acoustic power. A good agreement between theory and experimental results is achieved. The device can be used as a building block for more complex integrated functionalities and can be implemented in several material platforms. (C) 2013 Optical Society of America

Theoretical Studies of the Propagation of Sound in Channels Filled with Helium II

1974

The two-fluid nature of liquid helium II leads to the possibility of several types of wave motion, e.g., first sound, second sound, fourth sound, and the fifth wave mode. First and second sound appear in the bulk liquid. The characters of these wave modes alter materially if helium is bounded by solid walls, e.g., between two plane-parallel plates forming a channel. This paper reports upon the calculation of the properties of wave modes which can exist in such channels.

Phononic crystals: Harnessing the propagation of sound, elastic waves, and phonons

2016

Comptes Rendus Physique - In Press.Proof corrected by the author Available online since jeudi 3 mars 2016

MEASUREMENTS OF THE ATTENUATION OF FOURTH SOUND IN HELIUM II

1978

A two-dimensional liquid-filled ionization chamber array prototype for small-field verification: characterization and first clinical tests.

2012

In this work we present the design, characterization and first clinical tests of an in-house developed two-dimensional liquid-filled ionization chamber prototype for the verification of small radiotherapy fields and treatments containing such small fields as in radiosurgery, which consists of 2 mm × 2 mm pixels arranged on a 16×8 rectangular grid. The ionization medium is isooctane. The characterization of the device included the study of depth, field-size and dose-rate dependences, which are sufficiently moderate for a good operation at therapy radiation levels. However, the detector presents an important anisotropic response, up to ≃ 12% for front versus near-lateral incidence, which can …

Sound attenuation and anharmonic damping in solids with correlated disorder

2010

We study via self-consistent Born approximation a model for sound waves in a disordered environment, in which the local fluctuations of the shear modulus G are spatially correlated with a certain correlation length The theory predicts an enhancement of the density of states over Debye's omega(2) law (boson peak) whose intensity increases for increasing correlation length, and whose frequency position is shifted downwards as lg. Moreover, the predicted disorder-induced sound attenuation coefficient r(k) obeys a universal scaling law F(k) = f (ke) for a given variance of G. Finally, the inclusion of the lowest-order contribution to the anharmonic sound damping into the theory allows us to rec…

Multistage recovery process of seaweed pigments: Investigation of ultrasound assisted extraction and ultra-filtration performances

2017

International audience; The objectives of this study were first to evaluate the performance of seaweed pigments’ recovery through ultrasound assisted extraction (UAE) and ultra-filtration (UF), and second to investigate the membrane fouling mechanism and evidence the threshold flux during filtration. The pigments’ recovery from the extract was performed using 5 kDa and 10 kDa ultra-filtration membranes. Results showed that increasing the extraction temperature in the range of 40–60 °C was proportional to chlorophyll extraction efficiency, while the maximal carotenoid yield was achieved at 50 °C. Ultrasonic power (from 100 W to 300 W) facilitated the extraction of both chlorophylls and carot…

Hypogonadotrophic Pituitary Insufficiency in Transfusional Hemochromatosis Complicating Thalassemia Major: MR Imaging

1999

To identify pituitary iron overload in patients with transfusion-dependent thalassemia major causing secondary hypogonadism, we prospectively evaluated signal intensity abnormalities of the anterior lobe of the pituitary gland of 30 patients comparing spin-echo, gradient-echo imaging and pituitary T2 relaxation times measurement. We found that pituitary iron overload can best be assessed by MR imaging using gradient-echo T2*-weighted technique to establish signal reduction in the anterior lobe of the pituitary gland. This finding is correlated to increasing serum ferritin level — a parameter that reflects the severity of iron overload, and is more evident in patients with secondary hypogon…

From Sample to Section

1998

A sound analysis of microstructures relies on correct sampling and on the right choice of the direction in which thin sections are cut from samples. This chapter discusses the steps of sample collection; choice of sectioning plane, and problems involved in the interpretation of three-dimensional structures from two-dimensional sections.