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At least 1,027 records · Page 57Linked to original sources
PubMed2002

Effects of susceptor, coating and conventional browning applications on color and crust formation during microwave baking.

The effects of different browning treatments on the crust color and crust hardness of microwave baked breads were investigated. Microwave oven was operated at 20%, 30% and 40% powers for 3.5-5.5 minutes. As a control, breads were baked in a conventional oven at 200 degrees C for 12 minutes. After microwave baking, breads were browned or conventional browning times increased, crust hardness and weight loss of breads increased. When susceptors were used, desired browning and hardness were obtained on the bottom surfaces of the breads. However, they did not affect top surface color significantly. The optimum microwave baking conditions for safety susceptor and standard susceptor were found as 5.0 minutes at 20% power and 4.5 minutes at 20% power, respectively. Breads coated with a solution composed of 10.5% sodium bicarbonate, 31.6% glucose, 5.3% glycine and 52.6% water (by weight) did not have the desired crust color and hardness. Conventional browning at 200 degrees C for 8 minutes was an alternative to achieve browning on top and bottom surfaces and crust formation on the bottom surface.

Journal Article↗
PubMed2000

Resonant enhancement of dielectronic recombination by a microwave field

We have observed dielectronic recombination of Ba+ and e(-) from a continuum of finite bandwidth in the presence of microwave fields of frequencies 8.08 and 12.05 GHz and amplitudes of up to 2 V/cm. There are sharp resonant enhancements when the microwave frequency matches the Deltan = 1, 2, and 3 resonances of the intermediate autoionizing Rydberg states, and we attribute the enhancements to resonant microwave Stark l mixing. The microwave field provides a simple and powerful way to enhance the recombination rate for incident electrons of a specific energy.

Journal Article↗
PubMed2004

Enhancement of Josephson phase diffusion by microwaves.

We report an experimental and theoretical study of the phase diffusion in small Josephson junctions under microwave irradiation. A peculiar enhancement of the phase diffusion by microwaves is observed. The enhancement manifests itself by a pronounced current peak in the current-voltage characteristics. The voltage position V(top) of the peak increases with the power P of microwave radiation as V(top) proportional to sqrt[P], while its current amplitude weakly decreases with P. As the microwave frequency increases, the peak feature evolves into Shapiro steps with a finite slope. Our theoretical analysis, taking into account the enhancement of incoherent superconducting current by multiphoton absorption, is in good agreement with experimental data.

Journal Article↗
PubMed2005

Resonances in ferromagnetic gratings detected by microwave photoconductivity.

We investigate the impact of microwave excited spin excitations on the dc charge transport in a ferromagnetic (FM) grating. We observe both resonant and nonresonant microwave photoresistance, which are caused, respectively, by spin and charge dissipations of the microwave power into the FM. A macroscopic model based on Maxwell and Landau-Lifschitz equations reveals the mixing of spin and charge dissipations, which shows that the ferromagnetic anti-resonance is shifted when the conductivity is anisotropic. We find that the microwave photoconductivity provides a powerful new tool to study the interplay between photonic, spintronic, and charge effects in FM microstructures.

Journal Article↗
PubMed2006

Power dependence of the frequency bias caused by spurious components in the microwave spectrum in atomic fountains.

The presence of spurious spectral components in the microwave excitation may induce frequency shifts in an atomic fountain frequency standard. We discuss how such shifts behave as a function of power variations of the excitation carrier and in the spur-to-carrier ratio. The discussion here is limited to the case of single-sideband spurs, which are generally much more troublesome due to their ability to cause frequency shifts. We find an extremely rich and unintuitive behavior of these frequency shifts. We also discuss how pulsed operation, typical of today's fountain frequency standards, relates to frequency shifts caused by spurs in the microwave spectrum. The conclusion of these investigations is that it is, at best, difficult to use elevated power microwaves in fountain frequency standards to test for the presence of spurs in the microwave spectrum.

Journal Article↗
PubMed2002

The microwave drill.

We present a drilling method that is based on the phenomenon of local hot spot generation by near-field microwave radiation. The microwave drill is implemented by a coaxial near-field radiator fed by a conventional microwave source. The near-field radiator induces the microwave energy into a small volume in the drilled material under its surface, and a hot spot evolves in a rapid thermal-runaway process. The center electrode of the coaxial radiator itself is then inserted into the softened material to form the hole. The method is applicable for drilling a variety of nonconductive materials. It does not require fast rotating parts, and its operation makes no dust or noise.

Journal Article↗
PubMed2006

Near-field microwave microscope and electron-spin-resonance detection: ruby crystal surface.

Microwave photons can image a surface by using near-field geometry with spatial resolution close to the nanometer-length scale. We detected electron-spin resonance (ESR) on ruby surfaces by using microwave photons at the S-band frequency (3.73 GHz). The spatial locations of the electron-spin centers were pinpointed with localized incident microwave photons generated by using evanescent microwave microscopy (EMM). We show that the EMM probe is capable of resolving 20,000 spin transitions, compared with the approximately 10(10) minimum detectable spins of the conventional continuous-wave ESR spectrometer. This represents roughly a 6-order-of-magnitude enhancement in sensitivity. Our ultimate goal is to achieve the minimum detectable spin transition of a single electron and nanometer-level spatial resolution by using microfabricated atomic force microscopy-EMM probes.

Journal Article↗
PubMed2004

Demonstration of a microwave spectrum analyzer based on time-domain optical processing in fiber.

We demonstrate a novel method for spectral analysis of microwave signals that employs time-domain processing in fiber. We use anomalous dispersion in single-mode fiber to perform a Fresnel transform followed by a matched amount of dispersion-compensating fiber to perform an inverse Fresnel transform of an ultrashort pulse. After the Fresnel-transformed waveform is modulated by the microwave signal, the waveform at the output of the dispersion-compensating fiber represents the ultrashort pulse convolved with the microwave spectrum. An experimental system for spectral analysis of microwave signals in the range 6-21 GHz is demonstrated.

Journal Article↗
PubMed2006

Balanced optical-microwave phase detectors for optoelectronic phase-locked loops.

A balanced optical-microwave phase detector for the extraction of low-jitter, high-power, and drift-free microwave signals from optical pulse trains is presented. The phase detection is based on electro-optic sampling with a differentially biased Sagnac loop. Because the timing information is transferred in the optical domain, the regenerated microwave signal is robust against drifts and photodetector nonlinearities. In a first experimental implementation, 3 fs in-loop relative timing jitter (integrated from 1 Hz to 10 MHz) between a 44 MHz optical pulse train and a 10.225 GHz microwave signal is demonstrated.

Journal Article↗
PubMed2007

Tunable and reconfigurable photonic microwave filter based on stimulated Brillouin scattering.

A high Q-factor photonic microwave filter showing tuning and reshaping capabilities and based on stimulated Brillouin scattering is demonstrated. The filter bandpass can be continuously tuned, changing the microwave oscillator used to generate the pump power, and the filter shape can be modified by modulating the microwave tone. A single bandpass over the microwave spectrum can be obtained by using single-sideband suppressed carrier modulation. Experimental results demonstrate the wide tuning range of the filter, its reshaping capability, and Q factor of 670.

Journal Article↗
PubMed2000

The effects of microwave irradiation on occluded solvents in illicitly produced cocaine hydrochloride

The current clandestine methodology for the manufacture of illicit cocaine hydrochloride utilizes microwave heating in order to dry the finished product. This study addresses the effects this step has on the occluded solvents present in newly prepared cocaine hydrochloride. Nine 1-kilogram-sized batches of cocaine hydrochloride were prepared from cocaine base using a variety of solvents or solvent mixtures commonly utilized in clandestine laboratories, pressed into bricks, and submitted to microwave heating. Residual solvents were qualitatively and quantitatively monitored before, during, and following the microwaving step by static headspace-gas chromatography-mass spectrometry. All solvents used in the conversion process were easily detected in the bricks even after extensive irradiation, confirming that occluded solvents are extremely resistant to removal by microwave heating. Qualitative and quantitative data corresponding to the residual solvents in the prepared cocaine hydrochloride bricks are presented.

Journal Article↗
PubMedDate not supplied

Percutaneous microwave coagulation therapy for primary or recurrent hepatocellular carcinoma: long-term results.

BACKGROUND/AIMS: To clarify the indication of percutaneous microwave coagulation therapy for hepatocellular carcinoma. METHODOLOGY: Thirty-three hepatocellular carcinoma patients who underwent percutaneous microwave coagulation therapy were enrolled in this study, including 18 primary and 15 recurrent hepatocellular carcinoma patients. We examined the local recurrence rates and the long-term results after the treatment. RESULTS: The overall survival rates of the primary group at 1, 2, 3, 4 and 5 years were 94.4%, 77.8%, 77.8%, 77.8% and 48.6%, respectively, whereas those of the recurrent group were 100%, 85.7%, 66.7% and 50.0% at 1, 2, 3 and 4 years, respectively. Local recurrence after percutaneous microwave coagulation therapy was found in about 50% of patients in both groups. Seventeen of the 27 patients (63.0%) with a moderately or poorly differentiated hepatocellular carcinoma tumor had local recurrence, while none of the 6 patients with a well-differentiated hepatocellular carcinoma tumor did (P = 0.005). CONCLUSIONS: Irrespective of primary or recurrent hepatocellular carcinoma, the indication of percutaneous microwave coagulation therapy as an alternative to hepatic resection should be limited to cases of a well-differentiated hepatocellular carcinoma tumor smaller than 2 cm in diameter.

Aged↗
PubMed1994

High temperature microwave thermotherapy of the prostate.

Transurethral microwave thermotherapy of the prostate has been touted as a minimally invasive means of treating symptomatic prostatism. High temperatures (>55 degrees C) appear to yield improved results but require general anesthesia. To determine if high temperature thermotherapy of the prostate was feasible in an outpatient, nonanesthetic setting, we subjected men with symptomatic prostatism secondary to benign prostatic hyperplasia to treatment with a newly developed circumferentially cooled transurethral microwave thermotherapy device, the UroWave. Intraprostatic temperatures were measured on-line and treatment was targeted to achieve temperatures ranging from 45 degrees C-65 degrees C. Fifty-five men with benign prostatic hyperplasia underwent transurethral microwave thermotherapy using the UroWave in an outpatient setting without general anesthesia. Baseline mean peak urinary flow rates were 8.0 cc/sec and mean American Urology Association of the prostate displayed three distinct phases: an initial slow heating phase, a plateau phase of variable duration and a rapid secondary heating phase. The final intraprostatic temperature did not correlate with urethral or rectal temperatures or the amount of power applied. At six months, peak flow increased by 50% and symptoms score declined by 52%. Ninety-four percent of patients had a transurethral resection of the prostate-like defect at cystoscopy with a greater proportion at higher temperatures. Side effects were rare and no patients had to be admitted to hospital. Transurethral microwave thermotherapy at high intraprostatic temperatures can be achieved with general anesthesia. Symptom relief was considerable and anatomic changes resembling a transurethral resection of the prostate were noted in the majority of patients. Intraprostatic temperatures are the only means of assessing the thermal damage to the prostate and thus the effectiveness if therapy. Future studies must develop less invasive means of monitoring intraprostatic temperatures and define the role of the bladder neck. Ultimately, randomized controlled trials will define the value of this treatment.

Journal Article↗
PubMed1999

[Clinical observation of one-visit root canal therapy by microwave instrument]

OBJECTIVE:To analysis post-treatmental reaction and long-term effect of one-visit root canal therapy by microwave instrument. METHODS:Applying heat effect and the other ones of microwave,the changes of dentine tissue of extracted teeth were observated by SEM examination.48hs and 1 year post-treatmental effect of 47 patients of periapical periodontitis treated by one-visit root canal therapy were observated and compared with the results of 54 cases treated with common method.RESULTS:In the cases of acute and chronic periapical periodontitis microwave applied in root canal therapy can close the openings of dentine,enhance the effects of sterilization and decrease times of treatment.CONCLUSION:Microwave applied in one-visit root canal therapy is competent.

Journal Article↗
PubMed2005

[Application of microwave dielectric spectrum to analysis of low-carbon alcohols in water].

A novel technique for detecting low-carbon alcohols in water at microwave frequency is presented. The technique is based on the measurement of microwave scattering parameters of aqueous solutions containing alcohols. The method employs transmission-line technique at frequency field. The scattering parameters were obtained by measuring the microwave transmission power. The changes in scattering parameters were measured when a sample vessel filled with aqueous solution containing low-carbon alcohols was inserted in the microwave transmission line. It is shown, from the experimental data, that there are good linear relationships between the scattering parameters and the concentrations of alcohols within a certain range.

English Abstract↗
PubMed2000

The effect of microwave heating on the acidity of 0.9% saline in 1 litre and 100 mL polyvinyl chloride packaging.

OBJECTIVE: Microwave warming of intravenous crystalloid solutions is an accepted practice in operating suites and emergency departments. These intravenous solutions are stored in polyvinyl chloride (PVC) and are known to be acidic. Some of this acidity may be from PVC packaging. We asked if microwave heating affected the acidity of 0.9% saline solution in 1 litre and 100 mL PVC bags. METHODS: Seven 1 litre bags were heated in an 800 Watt microwave for 2 minutes each and seven 100 mL bags were heated for 30 seconds each. After overnight cooling to room temperature, pH and temperature were measured and compared with two control groups of 7 unheated bags. RESULTS: There was no significant difference between the pH of heated and unheated solutions of saline. The median pH of the 1 litre bags were 5.01 (control) and 5.02 (heated). The median pH of the 100 mL bags were 4.58 (control) and 4.59 (heated). Post hoc, we found the 100 mL bags were more acidic than the 1 litre bags by a median difference of 0.43 pH units (P = 0.002). CONCLUSIONS: Microwave heating does not change the acidity of 0.9% saline in 1 litre or 100 mL PVC packaging.

Journal Article↗
PubMed2006

[Evaluation of long-term therapeutic effects of ultrasound-guided percutaneous microwave ablation of liver metastases].

OBJECTIVE: To explore therapeutic results of local microwave ablation for hepatic metastasis and the factors influencing the survival after percutaneous microwave ablation therapy. METHODS: From July 1995 to June 2005 128 patients with 282 hepatic metastases nodules with the primary diseases of upper gastrointestinal tumor (n = 26), colorectal tumor (n = 44), breast carcinoma (n = 19), pulmonary carcinoma (n = 15), and malignant tumor in other part of the body (n = 24), underwent percutaneous microwave ablation therapy and were followed up for 29.7 +/- 19.9 months (1 - 103 months). The largest diameter of the metastatic nodules was 3.5 +/- 1.6 cm (0.7 - 8.6 cm). Sixty-four cases had 140 nodules 3.0 cm in diameter. Forty-seven patients had single nodule, 44 patients had 2 nodules, and 93 patients had 3 or more nodules. Fifty-seven patients had tumor of low differentiation, 53 had tumor of middle differentiation, and 18 had highly differentiated tumors. Kaplan-Meier method was used to calculate the cumulative survival rate. Statistical comparison of the effects of potential predictive factors on survival rate was performed using log-rank analysis. Multivariate analysis of the survival rates was performed by using Cox's proportional hazard model. RESULTS: The 1, 2, 3, 4, and 5-year cumulative survival rates of all 128 patients were 90.88%, 73.84%, 51.09%, 36.14%, and 31.89% respectively. Univariate analysis showed that tumor size (P = 0.028), tumor differentiation (P = 0.026) and local recurrence or new metastases (P < 0.001) significantly affected the survival. Multivariate analysis revealed that tumor size (P = 0.035), recurrence or new metastases (P = 0.001) and tumor differentiation (P = 0.038) each had a significant effect on survival. CONCLUSION: There is a significantly higher probability of long-term survival for patients with well-differentiated tumors 3.0 cm or less in diameter and without recurrence or new metastasis after percutaneous microwave ablation.

Adult↗
PubMed1991

Microwave cyclodestruction for glaucoma in a rabbit model.

Microwave thermotherapy was used to treat experimentally induced glaucoma. Microwave-induced cyclodestruction was successful in reducing intraocular pressure in all treated glaucomatous eyes for 4 weeks. Two additional glaucomatous eyes were left untreated to serve as controls, and were noted to have persistently elevated intraocular pressures. Six additional eyes were then subjected to an equivalent treatment (50 degrees C in five 1-minute applications), which resulted in approximately 180 degrees of heat treatment just posterior to the corneoscleral limbus. These specimens were evaluated with light microscopy at baseline, 24 hours, and 7 days after treatment. Our clinical and histopathologic evaluations suggested that microwave thermotherapy (delivered under thermometry control) allowed for chorioretinal/ciliary body destruction that resulted in reductions of intraocular pressure in glaucomatous eyes.

Animals↗