Power Output Settings Research Articles

Effects of beam power and feed rate in the process of cutting fresh wood with a CO2 laser on water contact angle on the cut surface

The paper describes a study on the effects of beam power and feed rate in the process of cutting fresh wood with a CO2 laser on water contact angle on the cut surface. The study involved several broadleaved tree species (oak, birch, alder, plum, and apple tree) and one coniferous species (pine). Samples were cut with a Trumpf TLC1005 laser equipped with a TruFlow 6000 CO2 resonator at a wavelength of 10.6 μm at three power output settings (1 kW, 2 kW, and 3 kW) and one feed rate (0.4 m∙min− 1). Contact angle was measured by pipetting a drop of distilled water on the wood surface and recording the process with a camera. Subsequently, images of the drop were analyzed over one minute at 10 s intervals to determine changes in contact angle for each of the cases examined. It was not possible to measure the contact angle on saw-cut samples as the water was immediately absorbed, while water drops placed on laser-cut samples remained on the surface for over 60 s, with the contact angle decreasing over time for the examined species from an average of 90° to 40°. The higher beam power settings (2 or 3 kW) were found to be preferable for the hardwood species (oak, birch, alder, and apple tree). In turn, in the case of the softwood species (pine), the laser power output did not matter, as both at the low (1 kW) and high (3 kW) settings the drop did not spread over the surface quickly. Finally, the optimum beam power for plum tree wood was found to be 1 kW.

Microwave ablation of the lung: Comparison of 19G with 14G and 16G microwave antennas in ex vivo porcine lung.

Percutaneous image-guided thermal ablation has an increasing role in the treatment of primary and metastatic lung tumors. Although microwave ablation (MWA) has emerged advantageous as a new ablation technology, more research is needed to improve it. This study aims to investigate the ablation zone of three microwave antennas in ex vivo porcine lung. In the ex vivo standard model and porcine lung model, MWA was performed in three power output settings (50 W, 60 W, and 70 W) for 3, 6, 9, and 12 min using three microwave antennas, with outer diameter of 1.03 mm (19G), 1.6 mm (16G), and 2.0 mm (14G). A total of 108 and 216 sessions were performed (3 or 6 sessions per time setting with the 14G, 16G, and 19G microwave antennas). After the MWA was complete, we evaluated the shape and extent of the coagulation zone and measured the maximum long-axis (along the needle axis; length [L]) and maximum short-axis (perpendicular to the needle; diameter [D]) of the ablation zones using a ruler; subsequently, the sphericity index (L/D) was calculated. The sphericity index can be simplified as long-axis/short-axis. In the ex vivo standard model study, the long- and short-axis diameters and sphericity indices were not statistically different between the 14G, 16G, and 19G groups. In the ex vivo porcine lung study, the long- and short-axis diameters did not differ statistically between the 14G, 16G, and 19G groups (P < 0.05 each). The sphericity index for the 19G microwave antenna was higher than the sphericity indices for the 14G and 16G microwave antennas (P < 0.05); however, the index for the 14G microwave antenna was not statistically different than that for the 16G microwave antenna (P > 0.05). The ablation zone of the 19G antenna was the same as those of the 14G and 16G antennas in vitro. Thus, the 19G antenna may reduce the incidence of complications in lung tumor ablation.

Thermal Penetration Depth of Pulsed Lasers in Gingival Tissues: An In Vitro Study.

Background: With laser irradiation emerging as an adjunctive treatment utilized in nonsurgical periodontal therapy, it is important to understand the variance of penetration depth among the different laser wavelengths. Purpose: To evaluate the thermal penetration depth, as a photothermal effect, of carbon dioxide (CO2)-, erbium: doped yttrium-aluminum-garnett (Er:YAG)-, and erbium, chromium: yttrium-scandium-gallium-garnett (Er,Cr:YSGG)-lasers on the bovine gingiva in an in vitro model. Methods: Four mandibles from freshly slaughtered cows were utilized in this study. Buccal and lingual root debridement was provided using three different laser wavelengths, all in pulsed settings. A CO2- (10,600 nm), Er:YAG- (2940 nm), and Er,Cr:YSGG- (2780 nm) were utilized to irradiate pockets of two mandibular posterior teeth in each group. Laser power output settings were set to 2 W. The posterior teeth were irradiated for 30 sec buccal and 30 sec lingual of each tooth for all selected treatment test groups. Instrumentation with curettes was performed as a control group. Gingival flaps, including the entire gingiva, were fixed in 10% formalin and stained via Elastin van Gieson. Sections were examined microscopically to evaluate thermal damage and statistically compared using mixed effect model with Tukey adjustment. Results: The CO2-laser irradiation presented a statistically significant lower mean compared to Er,Cr:YSGG-laser (p < 0.0001). Er,Cr:YSGG-laser had a higher penetration depth compared to Er:YAG-laser (p < 0.0001). There was no statistically significant difference found in penetration depth between CO2- and Er:YAG-laser irradiation. Conclusions: It can be concluded that all tested pulsed lasers had minimal penetration depth into the gingiva. However, the pulsed CO2- and Er:YAG-lasers presented lower thermal effects compared to Er,Cr:YSGG-laser in vitro.

Effect of hydrogen fuel at higher flow rate under dual fuel mode in CRDI diesel engine

The prime intention of this work is to provide a maximum replacement for diesel using hydrogen in a common rail direct injection equipped diesel engine. The experiment was conducted upto 5.2 kW brake power constant speed water-cooled engine. In the combustion chamber, diesel fuel was injected at a crank angle of 23⁰ bTDC, making it an ignitor for the premixed mixture of hydrogen and air. Hydrogen is injected at 6 different proportions ranging from 6 to 36 liter per min (LPM). The air and hydrogen gas were mixed homogeneously using the timed manifold injection technique, which was controlled through the in-house PC based data acquisition (DAQ) program developed on data factory. The electronic control unit helps to induct the hydrogen for a period of 211⁰ CA during the suction stroke. Performance, emission and combustion studies were made with the different levels of hydrogen injection, which proves that the 30 LPM of hydrogen provide the best results. Further, 30.65% improvement was achieved in brake thermal efficiency with 23.48% decreased brake specific energy consumption. This also helped to reduce the harmful emissions like CO, CO2, UHC and smoke by 22.3%, 14%, 32.74% and 43.86%, respectively. However, oxides of nitrogen emission level was increased by 7.3% compared to that of the diesel fuel at its maximum power output setting. The duration of the combustion also reduced due to the higher flame speed character of hydrogen. Thus, the overall results conclude that the addition of hydrogen improved the performance factors and reduced all the emission values of the common rail direct injection diesel engine at an optimum level of 30 LPM.

On the Development of a Light Dosimetry Planning Tool for Photodynamic Therapy in Arbitrary Shaped Cavities: Initial Results.

Previous dosimetric studies during photodynamic therapy (PDT) of superficial lesions within a cavity such as the nasopharynx, demonstrated significant intra- and interpatient variations in fluence rate build-up as a result of tissue surface re-emitted and reflected photons, which depends on the optical properties. This scattering effect affects the response to PDT. Recently, a meta-tetra(hydroxyphenyl)chlorin-mediated PDT study of malignancies in the paranasal sinuses after salvage surgery was initiated. These geometries are complex in shape, with spatially varying optical properties. Therefore, preplanning and in vivo dosimetry is required to ensure an effective fluence delivered to the tumor. For this purpose, two 3D light distribution models were developed: first, a simple empirical model that directly calculates the fluence rate at the cavity surface using a simple linear function that includes the scatter contribution as function of the light source to surface distance. And second, an analytical model based on Lambert's cosine law assuming a global diffuse reflectance constant. The models were evaluated by means of three 3D printed optical phantoms and one porcine tissue phantom. Predictive fluence rate distributions of both models are within±20% accurate and have the potential to determine the optimal source location and light source output power settings.

Hydroxyl Radicals in E-Cigarette Vapor and E-Vapor Oxidative Potentials under Different Vaping Patterns.

Available studies, while limited in number, suggest that e-cigarette vaping induces oxidative stress, with one potential mechanism being the direct formation of reactive oxygen species (ROS) in e-vapor. In the present studies, we measured the formation of hydroxyl radical (•OH), the most destructive ROS, in e-vapor under a range of vaping patterns (i.e., power settings, solvent concentrations, flavorings). Study results show that increased power output and puff volume correspond with the formation of significantly higher amounts of •OH in e-vapor because of elevated coil temperature and oxygen supply. Vegetable glycerin (VG) e-liquids generated higher •OH levels than propylene glycol (PG) e-liquids, as did flavored e-liquids relative to nonflavored e-liquids. E-vapor in combination with ascorbic acid, which is an abundant biological molecule in human epithelial lining fluid, can also induce •OH formation. The dose of radical per puff associated with e-cigarette vaping was 10-1000 times lower than the reported dose generated by cigarette smoking. However, the daily average •OH dose can be comparable to that from cigarette smoking depending on vaping patterns. Overall, e-cigarette users who use VG-based flavored e-cigarettes at higher power output settings may be at increased risk for •OH exposures and related health consequences such as asthma and chronic obstructive pulmonary disease.

Distributed optimal active power dispatch with energy storage units and power flow limits in smart grids

Dynamic optimal active power dispatch with energy storage units and power flow limits is an important problem in smart grids. This problem is usually described as a convex optimization model. In our model, not only the conventional equality and inequality constraints, energy storage units’ constraints and power flow constraints are considered, but also the energy storage units’ operational costs and the power price of the main grid are considered in the total costs. To solve this problem, a fully distributed algorithm based on the alternating direction method of multipliers (ADMM), the projected gradient method and the average consensus is proposed. The proposed algorithm can obtain the optimal output power settings of the energy storage units, distributed generators and the main grid for different demand loads with different initial states. In the proposed algorithm, firstly, the dispatch problem is decomposed into multiple subproblems on the basis of the alternating direction method of multipliers; then the subproblems can be solved according to the projected gradient method and the average consensus algorithm. In order to apply the projected gradient method, every bus is equipped with a bus agent which is responsible for information communication and the output power optimization calculation. Simulation studies demonstrate the effectiveness of the proposed algorithm. .

The In Vivo Effect of Ytterbium-Doped Fiber Laser on Rat Buccal Mucosa as a Simulation of Its Effect on the Urinary Tract: A Preclinical Histopathological Evaluation.

PurposeThe aim of this study was to perform a histological analysis of the effect of a ytterbium-doped fiber (YDF) laser on oral buccal mucosa tissue in vivo to simulate its effect on the mucosa of the lower urinary tract.MethodsA total of 90 8-week-old Sprague-Dawley rats were anesthetized with urethrane (1.2 g/kg intraperitoneally). A prespecified inner buccal mucosal site was irradiated with a YDF master-oscillator power amplifier (MOPA) system for 60 seconds, with output power settings of 0.5, 1, and 2 W, respectively, in 3 treatment groups. Specimens of irradiated tissue were harvested at 2 hours, 24 hours, 2 weeks, and 4 weeks after irradiation. The tissue specimens were stained with hematoxylin and eosin for histological analysis. ResultsIn the group treated with 0.5 W, basal cell elongation and vacuolization were observed at 2 hours and 24 hours after treatment, respectively. No evident injury was observed after 2 or 4 weeks. The group treated with 1 W presented partial basal layer separation, and even complete epidermal ablation, within 2 hours. At 24 hours after laser treatment, new capillaries on an edematous background of fibroblasts and myofibroblasts, as well as profuse infiltration of the neutrophils to the basal layer, were observed. Collagen deposition and reepithelization were observed in specimens taken 2 weeks and 4 weeks after treatment. The group treated with 2 W presented bigger and deeper injuries at 2 hours after irradiation. Meanwhile, subepidermal bullae with full-thickness epidermal necrosis and underlying inflammatory infiltrate were observed 24 hours after treatment. The presence of fibrous connective tissue and collagen deposition were observed 2 weeks and 4 weeks after the treatment.ConclusionsTo our knowledge, this is the first report regarding the effect of a YDF laser on living tissue. Our study demonstrated that the typical histological findings of the tissue reaction to the YDF MOPA apparatus were very similar to those associated with thermal injuries. The extent and degree of tissue damage increased proportionally to the output power.

The effect of Er:YAG laser irradiation on the bond stability of self-etch adhesives at different dentin depths

The aim of this study was to evaluate the effect of Er:YAG laser irradiation on the micro-shear bond strength of self-etch adhesives to the superficial dentin and the deep dentin before and after thermocycling. Superficial dentin and deep dentin surfaces were prepared by flattening of the occlusal surfaces of extracted human third molars. The deep or superficial dentin specimens were randomized into three groups according to the following surface treatments: group I (control group), group II (Er:YAG laser; 1.2 W), and group III (Er:YAG laser; 0.5 W). Clearfil SE Bond or Clearfil S3 Bond was applied to each group’s dentin surfaces. After construction of the composite blocks on the dentin surface, the micro-shear bond testing of each adhesive was performed at 24 h or after 15,000 thermal cycles. The data were analyzed using a univariate analysis of variance and Tukey’s test (p < 0.05). Laser irradiation in superficial dentin did not significantly affect bond strength after thermocycling (p > 0.05). However, deep-dentin specimens irradiated with laser showed significantly higher bond strengths than did control specimens after thermocycling (p < 0.05). Thermocycling led to significant deterioration in the bond strengths of all deep-dentin groups. The stable bond strength after thermocycling was measured for all of the superficial-dentin groups. No significant difference was found between the 0.5 and 1.2 W output power settings. In conclusion, the effect of laser irradiation on the bond strength of self-etch adhesives may be altered by the dentin depth. Regardless of the applied surface treatment, deep dentin showed significant bond degradation.

Effects of Er,Cr:YSGG Laser Pulse Frequency on Microtensile Bond Strength to Enamel.

Literature regarding the influence of Er,Cr:YSGG laser pulse frequency with different output power levels on adhesion properties of adhesive resin to lased enamel is limited. Therefore, the aim of the present study was to evaluate the effects of laser pulse frequency (20, 35, and 50 Hz) at two different output power settings (3 and 6 W) of Er,Cr:YSGG on the microtensile bond strength (μTBS) of adhesive resin to enamel. Crowns of 35 intact bovine incisors were embedded into self-cure acrylic resin individually, and then flat enamel surfaces were prepared with 600-grit silicon carbide papers under water cooling. Teeth were divided randomly into seven groups. Enamel surfaces were irradiated with Er,Cr:YSGG laser operated at one of six output power-pulse frequency combinations (6 W20 Hz, 6 W-35 Hz, 6 W-50 Hz, 3 W-20 Hz, 3 W-35 Hz, and 3 W-50 Hz) in groups 1-6, respectively. Bur-treated surfaces served as a control in group 7. After surface treatments and bonding procedures, composite build-ups were done in three layers up to a height of 4 mm. Next, all bonded teeth were sectioned into the resin-enamel sticks to be tested in a μTBS testing machine. The μTBS data were analyzed with univariate analysis of variance under a general linear model with the factor 'tooth' added as a random effect to the design. Resin-enamel interfaces were evaluated with scanning electron microscopy (SEM). The μTBS to laser-irradiated enamel in group 1 (6 W-20 Hz) was significantly lower than those of bur-treated enamel (p<0.05). However, group 6 (3 W-50 Hz) showed significantly higher μTBS values than did bur-treated teeth (p<0.05). SEM evaluation revealed enormous morphological alterations of laser-irradiated specimens, such as extensive vertical and horizontal microcracks and gaps, with the exception of group 6. The bonding effectiveness of adhesive resin to laser-irradiated enamel was affected by the pulse frequency of the Er,Cr:YSGG laser. Although the parameters recommended by the manufacturer lowered μTBS, increasing the pulse rate may maintain optimum μTBS.

Design of Modifications for Constructional Elements of Manipulator Arm Aimed at Measuring of Operational Torque

There are often designed such constructional elements in the engineering practice that are specified for sensing of operational loading and for a precise setting of the individual components in the given technical device, for example components of a robot arm. Positioning of the robot arms is regulated by means of power output setting (or torque setting) of the driving parts (motors) predominately. Driving effect is transferred between the individual components by means of the connecting parts designed for transfer of force flow. There is described in this paper such design of modification for constructional element of the robot arm, which enables to perform measuring of torque in the joining parts of the robot arm during a current operation.

Optimization of the generator settings for endobiliary radiofrequency ablation.

To determine the optimal generator settings for endobiliary radiofrequency ablation. Endobiliary radiofrequency ablation was performed in live swine on the ampulla of Vater, the common bile duct and in the hepatic parenchyma. Radiofrequency ablation time, "effect", and power were allowed to vary. The animals were sacrificed two hours after the procedure. Histopathological assessment of the depth of the thermal lesions was performed. Twenty-five radiofrequency bursts were applied in three swine. In the ampulla of Vater (n = 3), necrosis of the duodenal wall was observed starting with an effect set at 8, power output set at 10 W, and a 30 s shot duration, whereas superficial mucosal damage of up to 350 μm in depth was recorded for an effect set at 8, power output set at 6 W and a 30 s shot duration. In the common bile duct (n = 4), a 1070 μm, safe and efficient ablation was obtained for an effect set at 8, a power output of 8 W, and an ablation time of 30 s. Within the hepatic parenchyma (n = 18), the depth of tissue damage varied from 1620 μm (effect = 8, power = 10 W, ablation time = 15 s) to 4480 μm (effect = 8, power = 8 W, ablation time = 90 s). The duration of the catheter application appeared to be the most important parameter influencing the depth of the thermal injury during endobiliary radiofrequency ablation. In healthy swine, the currently recommended settings of the generator may induce severe, supratherapeutic tissue damage in the biliary tree, especially in the high-risk area of the ampulla of Vater.

The relationship between the temperature increase caused by phacoemulsification and the damage to the corneal endothelium

Endothelial cell damage can be found after a phacoemulsification. The reason for this cell damage is not yet known. The temperature rise inside the anterior chamber during the emulsification of the lens is considered as a potential damage mechanism. The aim of this study was to investigate the relationship between the temperature increase and the cell damage. This study was performed with 86 enucleated porcine eyes, which were divided into six groups A-F. Group A served as control group. Phacoemulsification was simulated in the groups B-E with different surgically relevant system settings. The temperature change was measured simultaneously with temperature sensors inside the anterior chamber. Inside the eyes of group F, the instruments were positioned and irrigation and aspiration were activated, but no ultrasound was applied. For all 86 corneas, the endothelial cell damage was quantified with a standardised evaluation protocol using scanning electron microscopy (SEM). A potential correlation was checked between the observed cell damage and the measured temperature rise. The highest temperature increase in group E with an obstructed aspiration line and an output power setting of 50 % was 17.77 °C. The temperature increase in group D with an output power setting of 100 % and unblocked fluid flow was significantly lower (p = 0.006). The highest temperature increase in group D was 8.89 °C. In contrast, the cells in group D were rated with a significantly lower score value than the cells in group E (p < 0.001). No significant correlation between the temperature rise and the cell damage could be obtained in due consideration of all measured data. However, an increase of the output power setting was connected with a non-linear increase of the cell loss. The temperature rise was not the main reason for the endothelial cell damage in the performed experiments. Therefore, there seems to be no causal relationship between the temperature increase inside the anterior chamber during a common phacoemulsification and the endothelial cell damage. Due to the strong dependence between the output power setting and the cell damage, the lowest output power setting should be used during surgery which ensures the emulsification of the nucleus.

A Load-Power Adaptive Dual Pulse Modulated Current Phasor-Controlled ZVS High-Frequency Resonant Inverter for Induction Heating Applications

A new prototype of an efficiency-improved zero voltage soft-switching (ZVS) high-frequency resonant (HF-R) inverter for induction heating (IH) applications is presented in this paper. By adopting the dual pulse modulation mode (DPMM) that incorporates a submode power regulation scheme such as pulse density modulation, pulse frequency modulation, and asymmetrical pulse width modulation into main one of the resonant current phase angle difference ( θ) control, the IH load power can be widely regulated under the condition of ZVS, while significantly improving the efficiency in the low output power setting. The essential performances on the output power regulations and ZVS operations with the DPMM schemes are demonstrated in an experiment based on a 1 kW-60 kHz laboratory prototype of the ZVS HF-R inverter. The validity of each DPMM scheme is originally compared and evaluated from a practical point of view.

Radiofrequency Catheter Ablation of Left-sided Accessory Atrioventricular Pathways at Atrial Insertion Sites

Background: This study assessed the efficacy and safety of techniques used to ablate left-sided accessory atrioventricular pathways at atrial insertion sites by retrograde aortic approach. Radiofrequency catheter ablation of left-sided accessory pathways by way of retrograde aortic approach can be highly successful. Methods: This study were done in the department of Cardiology, National Institute of Cardiovascular Diseases (NICVD), Dhaka from June 2009 and March 2010, a total 30 patients with recurrent SVT who has left sided accessory atrioventricular pathways found after electrophysiological study, underwent attempted radiofrequency catheter ablation of one or more accessory atrioventricular pathways by retrograde aortic approach. The ablation catheter was inserted into the femoral artery and passed retrogradely across the aortic valve .Once an optimal target site has been identified, radiofrequency energy at a pre-selected temperature of 55 - 60 0 C and power output set at 50 watts was delivered through the ablation catheter. Loss of preexcitation or interruption of the tachycardia within 5 seconds of RF application was considered effective and RF current was continued in this location 30 to 60 seconds. Ablation success was defined at completion of procedure as acutely successful or unsuccessful on the basis of successful elimination of all ablation targets. Results: During EP study it was found that 9 patients had concealed accessory pathways and 21 had manifest pre-excitation. WPW left-lateral pathway was present in 10 (33.3%), concealed left lateral in 08 (26.7%), WPW left posterior in 11 (36.7%), concealed left posterior in 1 (3.3%). Out of 30 accessory pathways, 24 were successfully interrupted with radiofrequency catheter ablation with a primary success rate of 80 %. The ratio of atrial/ ventricular electrogram in successful sites was 0.83 ±0.27 (0.53-1.46). There were no major complications with retrograde aortic approach. Six failed patients were ablated via transseptal method. Conclusion: The retrograde atrial insertion approach to left-sided accessory pathway ablation is very safe and high effective, especially suitable for the failed patients by using retrograde ventricular insertion ablation procedure and by using single-catheter ablation of accessory pathway. DOI: http://dx.doi.org/10.3329/uhj.v9i1.19507 University Heart Journal Vol. 9, No. 1, January 2013; 18-24

A New Current Phasor-Controlled ZVS Twin Half-Bridge High-Frequency Resonant Inverter for Induction Heating

A novel soft-switching high-frequency (HF) resonant (HF-R) inverter for induction heating (IH) applications is presented in this paper. By adopting the current phasor control of changing a phase shift (PS) angle between two half-bridge inverter units, the IH load resonant current can be regulated continuously under the condition of wide-range soft-switching operations. In addition to this, the dual-mode power regulation scheme-based PS angle control and asymmetrical pulsewidth modulation in one inverter unit is proposed for improving the efficiency in low output power settings. The essential performances on the output power regulation and soft-switching operations are demonstrated in an experiment using its 1-kW 60-kHz HF-R inverter prototype, and then, the topological validity is evaluated from a practical point of view.

Influence of Loudness Compression on Hearing with Bone Anchored Hearing Implants

Bone Anchored Hearing Implants (BAHI) are routinely used in patients with conductive or mixed hearing loss, e.g. if conventional air conduction hearing aids cannot be used. New sound processors and new fitting software now allow the adjustment of parameters such as loudness compression ratios or maximum power output separately. Today it is unclear, how the choice of these parameters influences aided speech understanding in BAHI users. In this prospective experimental study, the effect of varying the compression ratio and lowering the maximum power output in a BAHI were investigated. Twelve experienced adult subjects with a mixed hearing loss participated in this study. Four different compression ratios (1.0; 1.3; 1.6; 2.0) were tested along with two different maximum power output settings, resulting in a total of eight different programs. Each participant tested each program during two weeks. A blinded Latin square design was used to minimize bias. For each of the eight programs, speech understanding in quiet and in noise was assessed. For speech in quiet, the Freiburg number test and the Freiburg monosyllabic word test at 50, 65, and 80 dB SPL were used. For speech in noise, the Oldenburg sentence test was administered. Speech understanding in quiet and in noise was improved significantly in the aided condition in any program, when compared to the unaided condition. However, no significant differences were found between any of the eight programs. In contrast, on a subjective level there was a significant preference for medium compression ratios of 1.3 to 1.6 and higher maximum power output.

Treatment of dentinal hypersensitivity by means of Nd:YAP Laser: a preliminary in vitro study.

Objective. The aim of this study is to evaluate the effectiveness of Nd:YAP laser to seal dentinal tubules at different parameters. Material and Methods. 24 caries-free human wisdom impacted molars were used. The crowns were sectioned transversally in order to totally expose the dentin. The smear layer was removed by a 1 min application of EDTA. Each surface was divided into four quadrants, but only three quadrants were irradiated at a different output power setting (irradiation speed: 1 mm/sec; optical fiber diameter: 320 µm; tangential incidence of beam and in noncontact mode). Samples were smeared with a graphite paste prior to laser irradiation. All specimens were sent for SEM analysis. Pulp temperature increases in additional twenty teeth were measured by a thermocouple. Results. Morphological changes in dentin surfaces depend on the value of used energy density. Higher energy densities (2 W–4 W; 200–400 mJ; pulse duration: 100 m sec.; and 10 Hz) induce higher dentin modifications. Our results confirmed that Nd:YAP laser irradiations can lead to total or partial occlusion of dentin tubules without provoking fissures or cracks. Measurements of pulp temperature increases showed that Nd:YAP laser beam can be considered as harmless for pulp vitality for following irradiation conditions: 2 W (200 mJ) to 4 W (400 mJ) with an irradiation speed of 1 mm/sec; fiber diameter: 320 micrometers; 10 Hz; pulse duration: 100 m sec; noncontact mode and in tangential incidence to exposed dentin. The perpendicular incidence of the laser beam on exposed dentin may injure pulp vitality even at low output power of 3 W. Conclusions. Nd:YAP laser beam was able to seal the dentin tubules without damaging dentinal surfaces and without harming pulp vitality. Nd:YAP laser is effective and may be safely used for future in vivo treatments of dentinal hypersensitivity under certain conditions.

A New Resonant Current Phase-Angle-Difference-Controlled Zero Voltage Soft-Switching High-Frequency Inverter and Its Experimental Evaluation

A novel zero voltage soft-switching (ZVS) high-frequency resonant (HF-R) inverter using a reverse-conducting insulated gate bipolar transistor (RC-IGBT) for induction heating (IH) applications is presented in this paper. By utilizing the newly developed fixed-frequency phase angle difference (θ) control of two resonant currents, the IH load power can be continuously regulated in the proposed HF-R inverter over a wide range of output power setting under the conditions of ZVS while maintaining high efficiency. Its operating principle is described with theoretical analysis and simulation results, after which the wide-range power regulation and full-range ZVS operations are clarified by theory and analysis. Furthermore, the essential characteristics on the output power regulations, ZVS operations, and actual conversion efficiency are demonstrated in an experiment with a 1kW-60kHz laboratory prototype of the proposed HF-R inverter. Finally, its feasibility is evaluated from a practical point of view.

Radiofrequency Catheter Ablation of Left-sided Accessory Atrioventricular Pathways at Atrial Insertion Sites.

Background: This study assessed the efficacy and safety of techniques used to ablate left-sided accessory atrioventricular pathways at atrial insertion sites by retrograde aortic approach. Radiofrequency catheter ablation of left-sided accessory pathways by way of retrograde aortic approach can be highly successful. Methods: This study were done in the department of Cardiology, National Institute of Cardiovascular Diseases (NICVD), Dhaka from June 2009 and March 2010, a total 30 patients with recurrent SVT who has left sided accessory atrioventricular pathways found after electrophysiological study, underwent attempted radiofrequency catheter ablation of one or more accessory atrioventricular pathways by retrograde aortic approach. The ablation catheter was inserted into the femoral artery and passed retrogradely across the aortic valve .Once an optimal target site has been identified, radiofrequency energy at a pre-selected temperature of 55 - 60 0 C and power output set at 50 watts was delivered through the ablation catheter. Loss of preexcitation or interruption of the tachycardia within 5 seconds of RF application was considered effective and RF current was continued in this location 30 to 60 seconds. Ablation success was defined at completion of procedure as acutely successful or unsuccessful on the basis of successful elimination of all ablation targets. Results: During EP study it was found that 9 patients had concealed accessory pathways and 21 had manifest pre-excitation. WPW left-lateral pathway was present in 10 (33.3%), concealed left lateral in 08 (26.7%) ,WPW left posterior in 11 (36.7%), concealed left posterior in 1 (3.3%). Out of 30 accessory pathways, 24 were successfully interrupted with radiofrequency catheter ablation with a primary success rate of 80 %. The ratio of atrial/ ventricular electrogram in successful sites was 0.83 ±0.27 (0.53-1.46). There were no major complications with retrograde aortic approach. Six failed patients were ablated via transseptal method. Conclusion: The retrograde atrial insertion approach to left-sided accessory pathway ablation is very safe and high effective, especially suitable for the failed patients by using retrograde ventricular insertion ablation procedure and by using single-catheter ablation of accessory pathway. DOI: http://dx.doi.org/10.3329/uhj.v8i2.16081 University Heart Journal Vol. 8, No. 2, July 2012