Dissipation of a sheet of heated air in a turbulent flow

Summary A study was made of the dissipation of a single sheet of heated air in a turbulent air flow in a 3 in. pipe. Average temperatures, temperature fluctuations, and spatial correlations of the temperature fluctations were measured in the wake of a heated wire.     

Focusing of high power ultrasound beams and limiting values of shock wave parameters

In this work, the influence of nonlinear and diffraction effects on amplification factors of focused ultrasound systems is investigated. The limiting values of acoustic field parameters obtained by focusing of high power ultrasound are studied. The Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation was used for the numerical modeling. Solutions for the nonlinear acoustic field were obtained at output levels corresponding to both pre- and post-shock formation conditions in the focal area of the beam in a weakly dissipative medium. Numerical solutions were compared with experimental data as well as with known analytic predictions.     

Microbubble-enhanced hemorrhage control using high intensity focused ultrasound

Our objective was to investigate whether hemorrhage control can be achieved faster when high-intensity focused ultrasound (HIFU) is applied in the presence of ultrasound contrast agents (UCA) as compared to HIFU only application. Incisions (3 cm long and 0.5 cm deep) were produced in the livers of anesthetized rabbits. UCA Optison (0.18 ml/kg) was injected into the mesenteric vein. A HIFU applicator (5.5 MHz, 6800 W/cm² in situ) was scanned at a rate of 1–2 mm/s in one direction over the incision (with multiple passes if needed), until hemostasis was achieved. Hemostasis times were 59 ± 23 s (n = 21) in the presence of Optison and 70 ± 23 s (n = 29) without Optison. The presence of Optison produced on average 37% reduction in hemostasis times normalized to initial bleeding rates (p < 0.05), as well as 60% faster formation of the coagulum seal over the incision (p < 0.05). Gross and histological observations showed similar appearance of HIFU lesions produced in the presence of Optison and HIFU lesions produced without Optison. Our results suggest potential utility of UCA for increasing efficiency of HIFU-induced hemostasis of solid organ injuries.     

Indication of reactor ν(e) disappearance in the Double Chooz experiment

The Double Chooz experiment presents an indication of reactor electron antineutrino disappearance consistent with neutrino oscillations. An observed-to-predicted ratio of events of 0.944±0.016(stat)±0.040(syst) was obtained in 101 days of running at the Chooz nuclear power plant in France, with two 4.25 GW(th) reactors. The results were obtained from a single 10 m(3) fiducial volume detector located 1050 m from the two reactor cores. The reactor antineutrino flux prediction used the Bugey4 flux measurement after correction for differences in core composition. The deficit can be interpreted as an indication of a nonzero value of the still unmeasured neutrino mixing parameter sin(2)2θ(13). Analyzing both the rate of the prompt positrons and their energy spectrum, we find sin(2)2θ(13)=0.086±0.041(stat)±0.030(syst), or, at 90% C.L., 0.017相似文献   

Cavitation threshold measurements for microsecond length pulses of ultrasound

The acoustic cavitation threshold of an aqueous solution has been measured at megahertz frequencies as a function of pulse width and pulse repetition frequency for various combinations of these quantities. The fluid tested was a 0.1M KOH-H3BO3 buffer solution with pH 10.9, which contained luminol, was saturated with argon, and filtered to 25 mu. The presence of cavitation was detected by a photomultiplier tube that required the emission of visible light that was both larger in magnitude and longer in duration than a preset criterion. It was observed that the cavitation threshold of water under pulse conditions decreases both when the pulse width is fixed and the pulse repetition frequency is increased, and when the pulse repetition frequency is fixed and the pulse width is increased. Acoustic cavitation thresholds measured in aqueous solutions are significantly less than those acoustic pressures associated with instruments that are currently in widespread use in medicine.     

>700W continuous-wave output power from single laser diode bar

>700 W continuous-wave output power has been demonstrated from a single 1 cm-wide laser bar (~940 nm) with 77% fill factor. Maximum power conversion efficiency (PCE) of 65% has been achieved. Facet power density of 170 mW/mum and maximum PCE of 69% have been measured for 10% fill-factor bars with 3 mm cavity length     

Hemorrhage control in arteries using high-intensity focused ultrasound: a survival study

High-intensity focused ultrasound (HIFU) has been shown to provide an effective method for hemorrhage control of blood vessels in acute animal studies. The objective of the current study was to investigate the long-term effects of HIFU-induced hemostasis in punctured arteries. The femoral arteries ( approximately 2mm in diameter) of 25 adult anesthetized rabbits were surgically exposed, and either punctured and treated with HIFU (n=15), served as control (no puncture and no HIFU application: n=7), or were punctured and left untreated (n=3). Treated animals were allowed to recover, and examined and/or sacrificed on days 0, 1, 3, 7, 14, 28, and 60 after treatment to obtain ultrasound images and samples of blood and tissue. Hemostasis (arrest of bleeding) was achieved in all 15 of the HIFU-treated arteries. Eleven of the arteries were patent after HIFU treatment, and four arteries were occluded, as determined by Doppler ultrasound. The median HIFU application time to achieve hemostasis was 20s (range 7-55 s) for the patent arteries and 110 s (range 50-134 s) for the occluded arteries. In untreated animals, bleeding had not stopped after 120 s. One of the occluded arteries had reopened by day 14. No immediate or delayed re-bleeding was observed after HIFU treatment. Maximal blood flow velocities were similar in HIFU-treated patent vessels and control vessels. No significant difference in hematocrits was found between HIFU-treated and control groups at different time points after the procedure. Light microscopy observations of the HIFU-treated arteries showed disorganization of adventitia, and coagulation and thinning of the tunica media. The general organization of the adventitia and tunica media recovered to normal appearance within 28 days, with some thinning of the tunica media observed up to day 60. Neointimal hyperplasia was observed on days 14 and 28. The results show that HIFU can produce effective and long-term (up to 60 days) hemostasis of punctured femoral arteries while preserving normal blood flow and vessel wall structure in the majority of vessels.     

Applications of high-intensity focused ultrasound in medicine: Spotlight on neurological applications

High-intensity focused ultrasound (HIFU) has the potential to become a modality of treatment for a wide range of clinical conditions. HIFU enables non-invasive, selective ablation of tissues including tumors and punctured vessels. Another promising area of research within the field of therapeutic ultrasound is the application of HIFU to treat neurological disorders by selectively targeting the brain, spinal cord, or nerves. This paper provides an overview of the current applications of focused ultrasound in medicine with an emphasis on its use in the fields of neurology and neurosurgery.     

Calculation of optical matrix elements in Gallium Arsenide

Results are presented for optical matrix elements calculated numerically for a 2 × 2 lattice of delta-function impurity potentials in Gallium Arsenide. The calculations show clearly the change in the character of the state with increasing binding energy and particularly the increase in importance of the higher minima over the absolute conduction band minimum at г. Comparison with some experimental work is made from which good qualitative agreement is clear.     

Controlled tissue emulsification produced by high intensity focused ultrasound shock waves and millisecond boiling

In high intensity focused ultrasound (HIFU) applications, tissue may be thermally necrosed by heating, emulsified by cavitation, or, as was recently discovered, emulsified using repetitive millisecond boiling caused by shock wave heating. Here, this last approach was further investigated. Experiments were performed in transparent gels and ex vivo bovine heart tissue using 1, 2, and 3 MHz focused transducers and different pulsing schemes in which the pressure, duty factor, and pulse duration were varied. A previously developed derating procedure to determine in situ shock amplitudes and the time-to-boil was refined. Treatments were monitored using B-mode ultrasound. Both inertial cavitation and boiling were observed during exposures, but emulsification occurred only when shocks and boiling were present. Emulsified lesions without thermal denaturation were produced with shock amplitudes sufficient to induce boiling in less than 20 ms, duty factors of less than 0.02, and pulse lengths shorter than 30 ms. Higher duty factors or longer pulses produced varying degrees of thermal denaturation combined with mechanical emulsification. Larger lesions were obtained using lower ultrasound frequencies. The results show that shock wave heating and millisecond boiling is an effective and reliable way to emulsify tissue while monitoring the treatment with ultrasound.