Pulsed Wave Mode Research Articles

CW/PW dual-beam YAG laser welding of steel/aluminum alloy sheets

Abstract The lap welding of JSC270CC steel and A6111-T4 aluminum alloys were carried out by a dual-beam YAG laser with the continuous wave (CW) and pulse wave (PW) modes. The microstructure of the welded joints were examined with SEM, EPMA while the properties were checked with microhardness tester and tensile testing machine. It was shown that the dual-beam laser welding can effectively reduce or avoid the formation of the blowholes in the welded joints. The PW laser beam penetrated the welding pool, leading to the root-shape structures with enhanced bonding strength at the weld interface. A 10 μm intermetallic compound (IMC) layer was generated at the interface. The shearing strength of lap joint was measured to be 128 MPa.

连续脉冲双激光束焊接钢铝合金

Abstract The lap welding of JSC270CC steel and A6111-T4 aluminum alloys were carried out by a dual-beam YAG laser with the continuous wave (CW) and pulse wave (PW) modes. The microstructure of the welded joints were examined with SEM, EPMA while the properties were checked with microhardness tester and tensile testing machine. It was shown that the dual-beam laser welding can effectively reduce or avoid the formation of the blowholes in the welded joints. The PW laser beam penetrated the welding pool, leading to the root-shape structures with enhanced bonding strength at the weld interface. A 10 μm intermetallic compound (IMC) layer was generated at the interface. The shearing strength of lap joint was measured to be 128 MPa.

Transcranial near infrared laser treatment (NILT) increases cortical adenosine-5′-triphosphate (ATP) content following embolic strokes in rabbits

Transcranial near infrared laser therapy (NILT) improves behavioral outcome following embolic strokes in embolized rabbits and clinical rating scores in acute ischemic stroke (AIS) patients; however, the cellular mechanism(s) involved in NILT neuroprotection have not been elucidated. It has been proposed that mitochondrial energy production may underlie a response to NILT, but this has not been demonstrated using an in vivo embolic stroke model. Thus, we evaluated the effect of NILT on cortical ATP content using the rabbit small clot embolic stroke model (RSCEM), the model originally used to demonstrate NILT efficacy and initiate the NEST-1 clinical trial. Five minutes following embolization, rabbits were exposed to 2 min of NILT using an 808 nm laser source, which was driven to output either continuous wave (CW), or pulsed wave modes (PW). Three hours after embolization, the cerebral cortex was excised and processed for the measurement of ATP content using a standard luciferin-luciferase assay. NILT-treated rabbits were directly compared to sham-treated embolized rabbits and naïve control rabbits. Embolization decreased cortical ATP content in ischemic cortex by 45% compared to naive rabbits, a decrease that was attenuated by CW NILT which resulted in a 41% increase in cortical ATP content compared to the sham embolized group ( p > 0.05). The absolute increase in ATP content was 22.5% compared to naive rabbits. Following PW NILT, which delivered 5 (PW1) and 35 (PW2) times more energy than CW, we measured a 157% (PW1 p = 0.0032) and 221% (PW2 p = 0.0001) increase in cortical ATP content, respectively, compared to the sham embolized group. That represented a 41% and 77% increase in ATP content compared to naive control rabbits. This is the first demonstration that embolization can decrease ATP content in rabbit cortex and that NILT significantly increases cortical ATP content in embolized rabbits, an effect that is correlated with cortical fluence and the mode of NILT delivery. The data provide new insight into the molecular mechanisms associated with clinical improvement following NILT.

Continuous heart murmur in a 26-year-old woman

In this report, we describe a continuous murmur heard in a young woman at the beginning of her lactation period, which illustrates a typical example of 'Mammary Souffle', described one century ago. Colour Doppler and pulsed-wave mode echocardiogram allowed to precise, for the first time, the arterial nature of increased systolic and diastolic blood flow in tortuous branches of internal mammary artery, most probably responsible of the murmur, after ruling out any other origin of continuous murmur.

Electron spin resonance spectroscopy in drug delivery

The finding of non-viral carriers for the delivery and release of pharmaceutical and biological compounds to ill organs and tissues is one of the most widely investigated topic in medicinal and biological chemistry in the last decades. Prior to being used as drug vehicles in the living organisms, all of the new carriers are required to be fully characterized from a physico-chemical point of view, with respect to stability, charge, size, mobility, etc. To this aim, several molecular and bulky techniques have been employed for characterization. This review considers the results obtained with a molecularly oriented spectroscopic method, i.e. electron spin resonance (ESR). The application of this technique in its various forms derived from continuous-wave (cw-ESR) and pulsed-wave (pw-ESR) modes are reviewed. In particular, carriers such as liposomes (intended for gene therapy, boron neutron capture therapy, oxymetry, and others), micelles, hydrogels, nanoparticles, dendrimers, cyclodextrins and cucurbit[n]urils are considered.

Histological Evaluation of Artifacts in Tongue Tissue Produced by the CO2Laser and the Electrotome

The purpose of this study was to investigate the clinical usefulness of laser surgery in pathologic diagnosis following excisional biopsy of human oral mucosa by CO(2) laser and electrotome. When performing pathologic diagnosis and microscopic analysis of specimens excised by the CO(2) laser, there have been concerns about thermal denaturation of the excisional margin that may prevent diagnosis. Thirty tongue tissue samples from humans that were surgically resected using a CO(2) laser (continuous wave mode for 10 cases and pulse wave mode for 10 cases) and an electrotome (10 cases) were formalin-fixed and paraffin-embedded. These preserved specimens were then cut into thick sections and subjected to hematoxylin and eosin staining followed by microscopic assessment. Despite the differences between the CO(2) laser and electrotome methods, similar thermal denaturation, such as carbonization, vacuolar degeneration, and elongation of nuclei, were observed at the excisional margins for both methods. Use of the CO(2) laser, particularly in pulse wave mode, reduced the amount of thermal denaturation significantly (p < 0.01) compared to the electrotome. These results indicate that the CO(2) laser is better than the electrotome as a means of making excisions for performing pathologic diagnosis.

Effect of laser welding parameters on fusion zone morphological, mechanical and microstructural characteristics of AISI 304 stainless steel

AbstractNowadays, the Nd:YAG laser has been a promising key tool for joining thin components. In this research, mechanical and microstructural properties of laser welded thin austenitic stainless steel sheets were investigated with experimental investigations, as a function of laser welding parameters. Butt welded joints were made using a Nd:YAG laser in the pulsed wave mode. The appropriate laser welding parameters were found in order to obtain quality and strong weld seam. The pulsed laser seam welding process is controlled by a variety of parameters. We focus on the effects of the several processing parameters on mechanical and microstructural characteristics of joint and weld quality. The aim of this research was to evaluate the influence of these processing parameters on joint strength and microstructure. And also we examined the weldability of stainless steels in butt joint configuration by a pulsed Nd:YAG laser beam.

The effect of high intensity focused ultrasound on luciferase activity on two tumor cell lines in vitro, under the control of a CMV promoter

In this study, we compared the effect of high intensity focused ultrasound (HIFU) and thermal stress on the luciferase activity, controlled by a cytomegaly virus (CMV) promoter in an in vitro model using two tumor cell lines (M21, SCCVII). HIFU was applied in a pulsed-wave mode with increasing voltage at constant pulse duration, or thermal stress was delivered over a range of temperatures (36–52 °C) for 5 min. The resulting luciferase activity was measured in live cells using a cooled CCD camera. Luciferase activity was measured at set time intervals over a total of 48 h post-stress. Compared to baseline, the luciferase activity of the M21 tumor cell line when exposed to HIFU was approximately 54.2 ± 67.5% ( p < 0.01) higher at a temperature of 42 °C, and approximately 52.9±128.5% ( p < 0.01) higher at 44 °C. In the SCCVII tumor cell line, the luciferase activity after HIFU application was 55.4 ± 66.6% ( p < 0.01) higher compared to baseline at a temperature of 42 °C. The M21 and SCCVII tumor cell line when exposed to thermal stress alone did not increase the luciferase activity. M21 and SCCVII tumor cells exposed to HIFU showed a maximum decrease in cell viability to 45.3 ± 7.5% and 10.3 ± 7.5%, respectively, and when exposed to thermal stress to 85.3 ± 3.5% and 20.4 ± 6.5%, respectively, compared to the untreated control. In M21 and SCCVII cells exposed to HIFU, free radicals could be detected using the dichlorofluorescein dye. Our findings demonstrate that HIFU can enhance the luciferase activity controlled by a CMV promoter. However it also has a higher damaging effect on the cells.

A study of terahertz quantum cascade lasers: Experiment versus simulation

The authors present the testing method and electrical and optical characteristics of a 4.1 THz quantum cascade laser with a four-well resonant-phonon design. The mode evolution in pulsed and continuous wave modes as a function of drive current has been investigated. An ensemble Monte Carlo model is used to analyze the carrier transport and output characteristics of the device. The calculated current density, lasing domain, and lasing frequency as a function of electric field are consistent with the measured results.

Enhancement of Sonoluminescence and Bubble Dynamics using Pulsed Ultrasound at 103 kHz

Enhancement of multibubble sonoluminescence was observed for pulsed ultrasound at 103 kHz. High-speed photography was also used to obtain the images of cavitation bubbles at a frame rate of 150,000 fps in continuous wave mode and pulsed wave mode. Most bubbles oscillated spherically and showed frequent coalescence in continuous wave mode at an applied voltage of 28 Vpp. The maximum bubble radius was measured to be 20–30 µm. Only in pulsed wave mode the following complex structure of bubble oscillation was captured. The radii of bubbles that survived during the pulse-off time were in the range from 5 to 10 µm, and these act as bubble nuclei for the successive pulse. These bubble nuclei grow to large bubbles, which oscillate non-spherically and emit many tiny bubbles. The daughter bubbles oscillate spherically and probably contribute to the enhancement of sonoluminescence. Subharmonic components and the increase in broadband noise obtained in the acoustic spectrum result from bubbles oscillating non-spherically and chaotically.

Postictal suppression correlates with therapeutic efficacy for depression in bilateral sine and pulse wave electroconvulsive therapy

Ictal electroencephalography (EEG) parameters in electroconvulsive therapy (ECT) for depression reportedly correlate with therapeutic response and stimulus dosage, particularly in right unilateral (RUL) ECT. The authors examined ictal EEG parameters as predictors of therapeutic effectiveness in bilateral (BL) sine and pulse wave ECT. A total of 30 consecutive depressed inpatients who had not responded to standard pharmacotherapy were treated using BL ECT given in either sine or pulse wave mode. Ictal EEG parameters (e.g. regularity, postictal suppression) were manually rated by three trained psychiatrists. Polyspike phase duration was significantly longer in sine wave ECT than in pulse wave ECT. Postictal suppression emerged as the only significant predictor of therapeutic outcome when baseline Hamilton Rating Scale for Depression and mode of stimulation were controlled for. Postictal suppression appears to offer a useful predictor of clinical outcome of depression in BL ECT. No EEG parameters were found to be differentially predictive between sine and pulse wave ECT.

Minipermanent magnet high-current microwave ion source

A 2.45GHz high-current microwave ion source with permanent magnet was developed at Peking University. The source body is about 10cm in diameter and 10cm in height, and its weight is less than 5kg. It can operate in both pulse and continuous wave (cw) modes. In pulse mode, more than 100mA hydrogen ion current was extracted from a 5mm ion extraction aperture, when the microwave power is 500W and the extraction voltage is 45kV, which corresponds to a beam density of 500mA∕cm2. In cw mode, up to 60mA of hydrogen ion current can be extracted, and the beam density is 300mA∕cm2 at the same conditions. The proton ratio is about 80% and the normalized root-mean-square emittance is less than 0.1πmmmrad in both modes.

Effect of increasing the microwave density in both continuous and pulsed wave mode on the growth of monocrystalline diamond films

AbstractDiamond synthetic single crystals exhibiting a high and reliable quality would find many applications in different areas such as optics, mechanics, or electronic devices. In this study, thick high quality homoepitaxial diamond films were grown on synthetic substrates using Micro‐Wave Plasma Assisted Chemical Vapour Deposition. The effect of increasing the density of the hydrogen methane discharge was investigated since it is believed to allow higher deposition rates by enhancing the production of precursor species. In continuous wave mode, it was actually observed that increasing the microwave density in the plasma from 65 to 125 W/cm3 leaded to an increase of diamond growth rates from 3 to 8.5 µm/h and from 11 to 19 µm/h when 4% and 7% of CH4 was added to the gas phase respectively. However, when such a high microwave power density is injected, overheating of the reactor walls, windows and wave‐guides occurs leading to problematic cooling‐down and higher contamination of the diamond film. In particular higher silicon incorporation was found by photoluminescence spectroscopy that probably originates from an enhanced etching of the quartz windows. Thanks to the use of a pulsed discharge with a peak power of 190 W/cm3 the deposition of diamond at rates close to 22 µm/h became possible while limiting this problem of overheating. The use of such pulsed discharges is thus considered to be a very promising method for the growth of high quality diamond single‐crystals at high deposition rates. (© 2005 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Different effects of microbubble destruction and translation in Doppler measurements

In flow measurements in which microbubbles are involved, the amplitude and phase of the received echo signal are noticeably influenced by the transmitted ultrasound intensity. Previous studies have shown that, when such intensity is progressively increased, the Doppler spectrum is accordingly distorted, i.e., it is asymmetrically broadened toward the negative frequency side. Such deformation has been attributed to radiation force, which pushes the microbubbles into the sound propagation direction, thus yielding additional phase delays in the received echoes. However, the possible contribution of microbubble destruction to this spectral deformation has not been considered yet. In this paper, this issue is investigated by analyzing the experimental spectra produced by two different types of microbubbles suspended in a moving fluid and insonified in pulsed wave (PW) mode at programmable pulse repetition frequency (PRF) and pressure. Conditions are created in which either the radiation force or the destruction mechanism is expected to be dominant. Effects produced by the two phenomena on the Doppler spectrum are shown to be different. When the PRF is low (2 kHz), so that, according to theoretical simulations, the radiation force effect is negligible, a 26 dB noise floor increase is observed for a 13 dB pressure increment. For a higher PRF (16 kHz), the same pressure increase not only affects the noise floor, but also causes the bubbles to deviate from their original streamlines, yielding a Doppler bandwidth increase by a factor of 5. It is concluded that asymmetrical spectral broadening is mainly due to radiation force, and microbubble destruction mainly results in an increased noise floor without affecting the spectral shape.

Porosity reduction in Nd–YAG laser welding of stainless steel and inconel alloy by using a pulsed wave

This study investigates the influence of the Nd–YAG laser power wave mode on the porosity and mechanical properties of SUS 304L and inconel 690 weldments. Initially, a rectangular laser power waveform is specified. The output is then progressively changed from a pulsed wave mode to a continuous wave mode by reducing the value of ΔP (ΔP = Pp−Pb, where Pp is the peak power and Pb is the base power) to zero. Bead-on-plate (BOP) and butt welding are performed at a constant mean output power (1.7 kW). The BOP results demonstrate that the depth/width (D/W) ratio of both materials increases with ΔP and attains a maximum value when full penetration just occurs. The D/W ratio and the travel speed for full penetration are higher for SUS 304L than for inconel 690. In butt-welds of inconel 690 and SUS 304L, the porosity ratio decreases from 7.1% to 0.5% and from 2.1% to 0.5%, respectively, as ΔP increases from 0 to 2780 W. Therefore, the tensile strength and percentage elongation are enhanced significantly in inconel 690. The degree of porosity reduction in inconel 690 exceeds that of SUS 304L. This suggests that the viscosity of the molten inconel 690 metal is higher than that of SUS 304L. Consequently, the effect of porosity reduction due to the increase in molten metal fluidity caused by increasing ΔP is greater for inconel 690 than for SUS 304L.

2.9 THz quantum cascade lasers operating up to 70K in continuous wave

We report the operation of a quantum cascade laser emitting at a 103μm wavelength (2.9THz). The active region is based on a bound-to-continuum design allowing a low parasitic leakage current, and a high upper-to-lower-state lifetime ratio. The latter is demonstrated by a pronounced decrease of the differential resistance at threshold, which is visible up to high temperatures, and by a weak temperature dependence of the slope efficiency. At 4K, we report a threshold current density of only 105A∕cm2 both in pulsed and continuous-wave operation, and an emitted peak power of 15mW independent of the duty cycle. Maximum operating temperatures of 95K and 70K are observed in pulsed and continuous wave modes, respectively.

Le Doppler Tissulaire myocardique: une nouvelle technique échocardiographique prometteuse

Tissue Doppler Imaging (TDI) is a recent ultrasound technique allowing quantification of regional myocardial function by measurement of myocardial velocities throughout the cardiac cycle. The physical principle of TDI is based on the ability of ultrasound machines to selectively display the low velocity--high amplitude Doppler signals from the myocardial walls. Three TDI modes may be used: the pulsed wave mode, the 2D color mode and the color M-mode. Several studies have already shown that TDI is a more sensitive and specific technique than conventional Doppler echocardiography for detecting moderate myocardial alterations in different settings such as hypertrophic and dilated cardiomyopathies, ischemia and heart transplant disorders. TDI might therefore be used as an accurate technique for screening cardiomyopathies, and could also represent in the next future a useful tool for evaluating the efficacy of early cardiac therapeutic interventions.

Microbubble-augmented Ultrasound Declotting of Thrombosed Arteriovenous Dialysis Grafts in Dogs

Transcutaneous low-frequency ultrasound (LFUS) can effectively lyse clots in the presence of microbubbles. This study was designed to test the commercially available human albumin microspheres injectable suspension octafluoropropane formulation, Optison, to establish efficacy and assess US parameters of intensity and wave modes in a canine model of a thrombosed arteriovenous (dialysis) graft. Arteriovenous grafts in five dogs were cannulated, temporarily ligated, and thrombosed. Different declotting techniques were randomized to treat nine groups. Control groups involved direct saline (4.5 mL) clot injection in 0.5-1.0-mL increments. One group underwent peripheral intravenous microbubble injection (13.5 mL). Six groups underwent direct incremental clot injection of 4.5 mL of microspheres with LFUS for 30 minutes in 3-5-minute increments with use of various intensity settings in continuous-wave and pulsed-wave (PW) modes. At each increment, angiography was used to grade flow, declotting, and overall success. One hundred four procedures showed success in all 24 high-intensity PW modes (1.2-2.0 W/cm(2)); only one of 20 control experiments was successful (P <.0001). Medium-intensity modes yielded intermediate success rates. Lowest-intensity direct-injection groups and intravenous and control groups ranked lower. Results at 30 minutes were better than at 15 minutes (P <.0001). LFUS with direct injection of microbubbles is effective in lysing moderate-sized clots and recanalizing thrombosed arteriovenous grafts. It best succeeds at the higher range of intensity settings tested in PW mode. Further development is justified.

Tissue Doppler Imaging: a promising technique for quantifying regional myocardial function

Tissue Doppler Imaging (TDI) is a recent ultrasound technique that enables the quantification of regional myocardial function by measuring myocardial velocities. Three TDI modes are available: pulsed wave mode, 2D color mode and color M-mode. Each of them allows the specific analysis of radial and longitudinal myocardial motion. Both phase and amplitude of regional myocardial motion may be analyzed by TDI. Therefore, TDI appears to be a precise non-invasive method for assessing myocardial dysfunction: several studies have already shown that TDI is a more sensitive technique than conventional echocardiography for detecting mild myocardial alterations in human heart diseases as well as in animal models.

PHONON EXCITATION IN STIMULATED BRILLOUIN SCATTERING

Stimulated Brillouin Scattering (SBS) is an example of traveling wave parametric interaction involving photons and phonons. When one of the interacting waves is a backward traveling wave, which yields spatial nonlinear distributed regeneration covering the entire medium, the system exhibits a typical backward traveling wave parametric interaction. It may oscillate with a distinct threshold. The generation of backward traveling light becomes known as optical phase conjugation. In this paper, both pulsed and continuous wave modes of phonon excitations for SBS are described.