1,721,002 research outputs found
Anelasticity in 20 keV Proton-Implanted Tantalum
No full textInternal friction measurements have been carried out versus temperature in a tantalum specimen after hydrogen implantation obtained by a proton beam of 20 keV.
The result show a thin layer on the exposed surface of the specimen with a large concentration of hydrogen with respect to the bulk concentration. From the experimental data it is possible to obtain some information about the "range" and the diffusion parameters of the implanted ions. The effect of supertail is also observed
Experimental Remarks on the Range of 20 keV Protons in Vanadium
No full textIn this paper the results of an experimental study of ion implantation in Vanadium are reported. The use of an ultraacoustic tecnique allows to measure the average penetration of the protons, which results significantly greater than expected
Sonoluminescence Emission in Interacting Fields
No full textThe influence of the intensities of both interacting low frequency (LF) and high frequency (HF) fields on resulting sonoluminescence emission as well on the generation of the LF field on sonoluminescence generated by the HF field was studied. It was shown that the generation of the new cavitation nuclei upon collapse driven by the LF field is the main factor in superadditive enhancement of SL emission from a multibubble cavitation zone. Factors connected with the direct interaction of the fields such as interference of the fields or generation of waves with combined frequencies play a role in the case when the intensities of the fields when operating separately are lower than their SL thresholds. The phenomena of strong afteraction (memory effect) of the LF field on cavitation generated by the HF field is explained by the fact that new nuclei generated by the LF field have rather long “life” period in the liquid and disappear due to slow diffusion of air from the bubble
Enhancement of the Conversion and Concentration of Energy in a Multibubble Cavitation Zone
No full textHydrogen-implantation ed effetti di anelasticità in metalli di transizione
No full textQuesta memoria contiene la tesi di laurea in Fisica di Alberto Francescutto (Relatore prof. L. Verdini, Corr: prof. P. Ciuti) pubblicata come Rapporto Tecnico dell’Istituto Nazionale di Acustica “O. M. Corbino”
Enhanced Sonoluminescence Following Pulse-Induced Bubble Formation
No full textAn influence of low-frequency (LF, 27.2 kHz) ultrasound pulses on cavitation thresholds and intensity of sonoluminescence generated by the high – frequency (HF, 730 kHz) ultrasound field has been investigated. It is shown that such a pulse causes decrease of the cavitation thresholds, and increase of a sonoluminescence intensity (in some cases for more than by 2-3 orders of magnitude). The enhanced sonoluminescence emission is observed both in the case of the simultaneous action of the fields and in the сase of preliminary sonification of the liquid sample by the LF field. The increase in the SL intensity, generated by the HF is observed for long time (up to several hours) after switching off the LF source. This is evidence of the long-time afteraction of the LF ultrasound on the magnitude of SL generated by the HF ultrasound
Inverse Ultrasonic Capillary Effect
No full textAn inverse ultrasonic capillary effect is shown to occur when a very small gap exists between the end of a capillary and the ultrasonic emitter surface. Depending on the shape of the capillary there can be either an increase in the capillary rise of the liquid or a decrease to negative values
Cavitazione acustica in soluzioni di acqua e sale
No full textIn questa memoria si è applicata la tecnica della cavitazione ultrasonora impulsata per studiare la dipendenza dell’emissione acustica di sub armonica 1⁄2 e di sono luminescenza dalla concentrazione di NaCl in acqua. Le misure di sono luminescenza sono state condotte a temperatura ambiente con concentrazioni di NaCl fino al valore di saturazione (circa 270 g/l) e in corrispondenza a diversi valori della tensione di trasduttore. Il comportamento dei campioni esaminati mostra che le soglie per i due fenomeni crescono con la concentrazione di sale. L’efficienza dell’emissione di sub armonica decresce, mentre quella di sono luminescenza cresce
Ultrasonic Cavitation Threshold in Very Dilute NaCl-Water Solutions
No full textThe pulsed ultrasonic cavitation technique was employed to measure the dependence of the thresholds for emission of subharmonic and light on the concentration of dilute solutions of NaCl in distilled water. The concentration was varied from 10-9 d/cm3 to saturation, for different values of the inverse duty ratio. Preceeding results indicate an increase of both thresholds with concentration. In the case of very low values of concentration (10-9 to 10-3 g/cm3) the trend is reversed. Possible mechanisms that can explain the presence of the minimum, based on the dynamics of nuclei and bubbles population are indicated
Clarification of the Cavitation Zone by Pulse Modulation of the Ultrasound Field
No full textThe cavitation zone generated by a pulsed ultrasonic field absorbs less acoustic energy than that generated by continuous irradiation, i.e. an acoustic clarification effect is shown to exist in a pulsed ultrasonic field. The pulse modulation of an acoustic field decreases the bubble concentration in the cavitation zone. The acoustic power available for each transient bubble is increased and the energy stored by the bubbles during the expansion phase increases too. The decrease of the bubble density decreases the intensity of their interactions and provides the possibility of preserving their shape down to deeper stages of collapse and so the energy concentration in the implosion is increased. This is confirmed by the increase of sonoluminescence intensity in pulsed ultrasonic fields
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