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At least 829 records · Page 46Linked to original sources
PubMed1996

Using neural networks to solve the multicast routing problem in packet radio networks.

The primary function of a packet radio network is the efficient transfer of information between source and destination nodes using minimal bandwidth and end-to-end delay. Many researchers have investigated the problem of minimizing the end-to-end delay from a single source to a single destination for a variety of networks; however, very little work is reported about routing mechanisms for the common case where a particular information packet is intended to be sent to more than one destination in the network. This is known as multicasting. A simplified version of the problem is to ignore the packet delay at each node, then the problem becomes one of finding solutions which require the least number of transmissions. Determination of an optimal solution is NP-complete meaning that suboptimal solutions are frequently tolerated. The problem becomes more rigorous if packet delays are included in the network topology. This paper describes a practical technique for the computation of optimum or near optimum solutions to the multicasting problem with and without packet delay. The method is based on the Hopfield neural network and experiment has shown this method to yield near optimal solutions while requiring a minimum of CPU time.

Algorithms↗
PubMed1988

Long-term occlusion of the porcine cystic duct by means of endoluminal radio-frequency electrocoagulation.

Recurrent cholelithiasis must be expected after gallstone removal without cholecystectomy. Chemical gallbladder ablation may offer prevention but requires preliminary cystic duct occlusion. Radio-frequency (RF) electrocoagulation of the cystic duct was performed in 15 pigs to induce occlusion by a controlled thermal epithelial injury. A flexible coagulation catheter was placed into the cystic duct lumen under fluoroscopic control by means of either subhepatic cholecystostomy or direct, percutaneous transhepatic gallbladder puncture. Complete cystic duct occlusion was proved in 14 animals. Follow-up ranged from 1 to 17 weeks (mean, 11 weeks). Histologically, the RF technique induced an intense chronic inflammatory and fibroblastic reaction, which eventually obliterated the coagulated cystic duct segments. There was no epithelial regeneration or recanalization of the fibrotic cystic duct segments. The adjacent structures, particularly the cystic artery, were intact in all specimens.

Animals↗
PubMed1989

Endoluminal radio-frequency electrocautery for permanent ureteral occlusion in swine.

An animal experiment was undertaken to assess the feasibility of using radio-frequency current-mediated thermal injury of the ureter to produce ureteral occlusion by means of an endoluminal approach. Through open pyelotomies, balloon angioplasty catheters coated with gold bipolar electrodes were introduced into the ureters. Doses (at 650 kHz) were delivered for specific energy totals in 13 of 15 ureters in eight pigs. Two ureters served as controls (balloon inflation without current application). In six experimental animals not killed immediately after the procedure, postoperative ureteral manometric studies and nephrostography were performed and nephrostomy drainage was maintained until death (1-8 weeks). Treatment with 200-400 J produced safe, reliable occlusion by 4 weeks. At histopathologic study at 4 and 8 weeks, necrotic muscularis propria had been replaced by fibrous tissue. Cardiac rhythm was not affected during treatment.

Angioplasty, Balloon↗
PubMed1989

Percutaneous transrenal endoureteral radio-frequency electrocautery for occlusion: case report.

In a patient with advanced cervical carcinoma who had a large vesicovaginal fistula, the authors applied radio-frequency (RF) current endoluminally to the ureter via a percutaneous nephrostomy tract to occlude the ureter. Perineal drainage was initially reduced and then stopped entirely. The procedure was relatively easy to perform and was successful in achieving occlusion until the patient's death 2 1/2 months later.

Adult↗
PubMed1995

Radio-frequency survey at the bore of a 1.5-T MR imager.

A survey at the bore of a 1.5-T magnetic resonance (MR) imager assessed radio-frequency (RF) exposure. With variable pulse sequences and loading conditions, the RF power density at relevant occupational positions was below measurable limits (less than the threshold limit value for occupational workers of 1 mW/cm2). Exposure to RF fields is below safe limits for personnel who routinely work within an MR imaging suite.

Humans↗
PubMed1999

Thermoacoustic CT with radio waves: a medical imaging paradigm.

The authors evaluated images obtained with a prototypic thermoacoustic computed tomographic (CT) scanner constructed for use at 434 MHz, a promising radio frequency for detecting breast cancer. In one excised porcine kidney, acoustic energy emanating from the kidney was detected with transducers. The resultant electric signals were used to create a three-dimensional data set. Two-dimensional images reconstructed in multiple planes were compared with state-of-the-art T1- and T2-weighted magnetic resonance images. The renal outline, parenchyma, and collecting system were clearly delineated on the thermoacoustic CT images.

Acoustics↗
PubMed1986

Improved technique for monitoring electrocardiograms during exposure to radio-frequency radiation.

Studies were conducted utilizing improved methodology that examined the effects of radio-frequency (RF) radiation on heart rate (HR), deep body temperature (Tco), and electrocardiographic (ECG) waveform parameters in anesthetized rats. One group of animals was exposed to two power levels of continuous-wave RF radiation averaging 1.0 and 7.4 W/kg at a frequency of 600 MHz. A second group of animals, treated identically but not exposed to RF radiation, served as a control. The electrodes used for monitoring the ECG during RF exposure were fabricated from carbon-loaded Teflon wire, a semiconductor material that does not perturb the RF field. Analyses of the ECG were conducted by use of a recently developed computer-assisted procedure that quantitates HR and waveform intervals over 25-40 individual ECG complexes. There were no artifacts or arrhythmias in the ECGs of the animals exposed to RF radiation. There was a significant linear correlation between HR and Tco in the RF-exposed group that was not present in the control group.

Animals↗
PubMed1990

Radio-frequency ablation: effect of voltage and pulse duration on canine myocardium.

The purpose of this investigation was to examine in vivo the relationship of radio-frequency (RF) pulse voltage and duration on the volume of tissue injury. RF 500-kHz pulses of 20-, 40-, and 60-V amplitude (RMS) were applied to the epicardium of 18 dogs for pulsing periods of 5-20 s. Systematic and quantitative tissue analysis was then performed after 30 days. No chronic lesions were evident on microscopic examination for 20-V RF pulse applications up to 15 s. Application of 20-V pulses for 20 s produced small lesions having a volume of 2.4 +/- 0.7 mm3. At 40 V, the volume of tissue injury ranged from 39.1 +/- 10.3 mm3 for 5 s of pulse application to 128.8 +/- 24.8 mm3 for 20 s of pulse application. Over the first 15 s of 40-V pulse application, the volume of tissue injury increased as pulse application time increased. There was no further increase in tissue injury for 40-V pulsing durations greater than 15 s. At 60 V, volumes of tissue injury ranged from 122.7 +/- 33.5 mm3 at 5 s to 313.6 +/- 73.7 mm3 at 20 s. Lesion size increased significantly for pulse durations of up to 10 s. Thereafter, 60-V pulses yielded little increase in tissue injury. In addition, persistent 60-V pulsing for periods greater than 9 s duration resulted in arcing and tissue vaporization in 28% of the applications. Thus RF energy is limited in its ability to create safe and effective tissue injury.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Reduction in metabolic heat production during exposure to radio-frequency radiation in the rat.

The purpose of this study was to assess the ability of the rat to reduce metabolic rate when exposed to deep-penetrating radio-frequency (RF) radiation. Male Sprague-Dawley rats were maintained at an ambient temperature (Ta) of 10 degrees C and exposed to 600-MHz radiation while metabolic rate (MR) was measured by indirect calorimetry. RF radiation exposures were made in a waveguide-type system that permitted the continuous control of specific absorption rate (SAR). SAR's of 2-5 W/kg led to significant reductions in MR when averaged from 30 to 60 min after the initiation of RF radiation exposure. The total decrease in MR during RF radiation exposure accounted for approximately 37% of the total RF heat load. Exposure of another group of rats to the same SAR's at a Ta of 10 degrees C resulted in a significant elevation in colonic temperature. Thus, despite the decrease in MR, heat gain still exceeded heat loss during RF radiation exposure, with a resultant elevation in deep body temperature. In conclusion, in a cold environment the rat exposed to RF radiation decreases its MR. However, the response time and efficiency of the response is not adequate to prevent an increase in body temperature.

Absorption↗
PubMed1989

Radio frequency (13.56 MHz) energy enhances recovery from mild hypothermia.

The rate of warming after hypothermia depends on the method of rewarming. This study compared the effectiveness of radio frequency (RF) energy against hot (41 degrees C) water immersion (HW) and an insulated cocoon (IC) for rewarming hypothermic men. Six men fasted overnight and were rewarmed for 1 h after attaining a 0.5 degree C reduction in rectal temperature (Tre). Tre and esophageal (Tes) temperature were recorded every 5 min with nonmetallic thermal probes. The base-line value for Tre and Tes just before rewarming was subtracted from each 5 min Tre and Tes during rewarming to give delta Tre and delta Tes. The 12 delta Tes values were averaged for each individual and were compared using analysis of variance. The average delta Tes for RF (1.15 +/- 0.22 degrees C/h) was faster (P less than 0.001) than either IC (0.37 +/- 0.16 degrees C/h) or HW (0.18 +/- 0.09 degree C/h). The present study shows the superiority of RF energy for rewarming mildly hypothermic men.

Adult↗
PubMed2000

Human sleep EEG under the influence of pulsed radio frequency electromagnetic fields. Results from polysomnographies using submaximal high power flux densities.

Former exploratory investigations of sleep alterations due to global system for mobile communications (GSM) signals have shown a hypnotic and REM-suppressive effect under field exposure. This effect was observed in a first study using a power flux density of 0.5 W/m(2), and the same trend occurred in a second study with a power flux density of 0.2 W/m(2). For the present study, we applied a submaximal power flux density of 50 W/m(2). To investigate putative effects of radio frequency electromagnetic fields (EMFs) of cellular GSM phones on human sleep EEG pattern, all-night polysomnographies of 20 healthy male subjects both with and without exposure to a circularly polarized EMF (900 MHz, pulsed with a frequency of 217 Hz, pulse duration 577 microseconds) were recorded. The results showed no significant effect of the field application either on conventional sleep parameters or on sleep EEG power spectra.

Adaptation, Physiological↗
PubMed2005

The effect of radio-frequency glow discharge treatment of polystyrene on the behavior of porcine chondrocytes in vitro.

The aim of this study was to determine the effects of physicochemical surface properties of tissue-culture substrata on chondrocyte behavior. Polystyrene was modified by radio-frequency glow discharge (RFGD) plasma treatment with various monomers. The changes in surface properties of the modified polystyrene were verified by ESCA and water contact angle measurements. Porcine chondrocytes were seeded on these surfaces and cultured for 5 days. After 5 days of culture, the number of chondrocytes was highest on the N2 plasma-treated surface, followed by the CH2/N2 plasma-treated surface, untreated polystyrene and CF4 plasma-treated surface. The number of chondrocytes decreased with increasing water contact angle. The surface chemical properties influenced the morphology and gene expression of cultured chondrocytes. The cells cultured on the CF4 plasma-treated surface retained a round morphology characteristic of chondrocytes after day 1, while most of the cells grown on the N2 plasma-treated surface or the untreated polystyrene showed a flattened morphology. Using RT-PCR, expression of type-I collagen could not be detected in the chondrocytes cultured on the CF4 plasma-treated surface and the CH2/N2 plasma-treated surface. In contrast, the chondrocytes grown on the N2 plasma-treated surface or the untreated polystyrene surface expressed type-I collagen mRNA. This study shows that modification by RFGD treatment could modulate chondrocyte culture and gene expression.

Acetylene↗
PubMed1991

Endothelial cell growth on oxygen-containing films deposited by radio-frequency plasmas: the role of surface carbonyl groups.

Polystyrene substrates were modified by radio-frequency plasma deposition from mixtures of various organic vapors (acetone, methane, methanol, and formic acid) and oxygen. The resulting surfaces exhibited a wide range of surface oxygen concentrations, as measured by electron spectroscopy for chemical analysis (ESCA). The surface hydroxyl, carboxyl, and carbonyl groups were derivatized with trifluoroacetic anhydride, trifluoroethanol, or hydrazine, respectively, and their concentrations subsequently determined by ESCA. The growth of bovine aortic endothelial cells was found to increase with the surface carbonyl concentration but did not appear to correlate with the hydroxyl or carboxyl concentrations.

Acetone↗
PubMed1992

The immobilization of glucose oxidase onto radio-frequency plasma-modified poly(etherurethaneurea).

Glucose oxidase was covalently immobilized onto a radio-frequency plasma-modified poly(etherurethaneurea). Thin (90-100 nm) plasma-polymerized N-vinyl-2-pyrrolidone films were deposited onto poly(etherurethaneurea) films. Active sites for the immobilization were obtained via reduction with aqueous sodium borohydride and activation with 1-cyano-4-dimethylaminopyridinium tetrafluoroborate. Modified poly(etherurethaneurea) films were assayed for binding and activity of the immobilized glucose oxidase layer. The results of a modified radioimmunoassay and an 'immunochemical stain' indicated that washing in 900 ml of continuously stirred 2% sodium dodecyl sulfate, 2% Triton X-100, and 20 mM sodium phosphate, pH 7.0, for 24 h each at 4 degrees C was necessary to remove physically adsorbed glucose oxidase from the solid supports. An amperometric activity determination in 9 ml of well-stirred 20 mM sodium phosphate-0.1 M sodium chloride, pH 7.4, gave a qualitative demonstration of the activity of the immobilized enzyme on 18.75 cm2 of modified poly(etherurethaneurea) film. A colorometric activity determination using the coupled reaction with o-dianisidine and peroxidase indicated that glucose oxidase covalently immobilized on approximately 2.4 cm2 of modified poly(etherurethaneurea) film had an activity approximately equal to that of 13.4 nM glucose oxidase in 50 mM sodium acetate, pH 5.1, with a specific activity of approximately 32.0 U/mg at pH 5.1 and room temperature.

Biocompatible Materials↗
PubMed1993

Activity of horseradish peroxide adsorbed on radio frequency glow discharge-treated polymers.

Horseradish peroxidase (HRP) has been used as a model enzyme in this study of its physical adsorption and residual enzyme activity on radio frequency glow discharge (RFGD)-treated polymers. The specific enzymatic activity of HRP adsorbed on different surfaces was assumed to be an indication of the extent of its conformational alterations on the surfaces. The surfaces studied were poly (ethylene terephthalate) (PET), polytetrafluoroethylene (PTFE), and tetrachloroethylene and tetrafluoroethylene glow discharge-treated PET, abbreviated as TCE/PET and TFE/PET. All surfaces were characterized by electron spectroscopy for chemical analysis (ESCA) and liquid contact angles in air. HRP adsorbs more strongly onto the two discharge-treated surfaces than onto the untreated polymers, as evidenced by the lower amount of HRP eluted by sodium dodecyl sulfate (SDS) from the treated polymers. For example, seventy percent of the HRP adsorbed on TCE/PET or TFE/PET remains on the surface after overnight elution with a 1% solution of SDS. In contrast, untreated PET and PTFE each retains only c. 20% of the absorbed enzyme. The enzymatic activity of HRP adsorbed on the different surfaces was studied using hydrogen peroxide (H2O2) as the substrate. HRP adsorbed on the higher energy surfaces, PET and TCE/PET, retains significantly more activity than the HRP adsorbed on the lower energy surfaces, PTFE and TFE/PET which appear to destroy rapidly almost all of the activity of HRP after it adsorbs. HRP adsorbed on TCE/PET is relatively more stable over time than HRP adsorbed on PET or free HRP in solution. (For example, only 45% of the specific enzymatic activity of HRP adsorbed on TCE/PET was lost after 3 h of storage in phosphate buffer at 37 degrees C, while 70% of that adsorbed on PET was lost.) In summary, when HRP is adsorbed on TCE/PET, it is very tightly bound, and yet it maintains a significant fraction of its initial specific activity and also retains this activity for 3 h in phosphate buffer at 37 degrees C. Thus, tenacious physical adsorption of proteins such as enzymes on TCE glow discharge-treated surfaces may have potential as a new method of immobilization of such molecules, for uses in biosensors, diagnostics, bioseparations, cell culture and bioreactors.

Adsorption↗
PubMed1982

Auditory hallucinations treated by radio headphones.

A young man with chronic auditory hallucinations was treated according to the principle that increasing external auditory stimulation decreases the likelihood of auditory hallucinations. Listening to a radio through stereo headphones in conditions of low auditory stimulation eliminated the patient's hallucinations.

Acoustic Stimulation↗
PubMed1991

Potential and limitations of angle-independent flow detection algorithms using radio-frequency and detected echo signals.

New techniques to estimate local blood and tissue velocities have been developed by several groups, including our own. The performance of these techniques is ultimately limited by the characteristics of ultrasonic imaging systems that determine the second-order statistics of speckle. These statistical parameters vary widely depending on the dimension of analysis in the image plane (lateral or axial) and on the echo input signal (radio-frequency or detected data). We use experiments and theory to examine these factors and describe their impact on the performance of our correlation-based technique for angle-independent tracking of blood or tissue motion. The results indicate that the second-order statistics determine the performance of our correlation-based algorithm and can be used to predict the performance of other angle-independent flow detection techniques.

Algorithms↗
PubMed1985

Transient sensorineural hearing loss after overuse of portable headphone cassette radios.

Noise-induced sensorineural hearing loss has been associated with industry for many years. One conservative estimate suggests that 10 million Americans may have industry-related, noise-induced hearing loss. Acoustic trauma from any source, whether associated with work or recreations, is detrimental to hearing. The Occupational Safety and Health Administration has set industrial standards for noise levels, with current standards limiting noise exposure to 95 dBA for 2 hours daily. To date, however, there are no recreational standards. Many portable headphone cassette radios produce peak outputs of more than 100 dBA. Temporary threshold shifts could result from listening levels near the maximum output. Permanent sensorineural loss may result with repeated exposure. A pilot study was conducted in which 16 volunteers listened to headphone sets for 3 hours at their usual maximum level. Six volunteers showed transient shifts of 10 dB, and one volunteer showed a transient shift of approximately 30 dB. These shifts returned to normal within 24 hours. As expected, transient shifts frequently occur with recreational use. Therefore, recreational warnings and standards should be established.

Auditory Fatigue↗