Distribution by Scientific Domains
Distribution within Medical Sciences

Terms modified by RF

  • rf ablation
  • rf application
  • rf catheter ablation
  • rf channel
  • rf characteristic
  • rf coil
  • rf energy
  • rf excitation
  • rf exposure
  • rf field
  • rf inhomogeneity
  • rf lesion
  • rf magnetron sputtering
  • rf mem switch
  • rf performance
  • rf power
  • rf pulse
  • rf signal
  • rf value

  • Selected Abstracts

    A modified high linearity CMOS micromixer for UWB systems

    Shui-Yang Lin
    Abstract A CMOS Micromixer for 3,5 GHz UWB receivers is presented in this article. Modified class-AB input stage is developed to improve the LO/RF, LO/IF isolation and to reduce the mixer's noise figure. A LO buffer and an output buffer are integrated in it for on-wafer testing. Our measurement results show that, with a 50-, output loaded, it can achieve 5-dB power conversion gain, 12.5 dB SSB NF, and 4 dBm IIP3. The mixer-core consumes 2.6 mA of current from 1.8-V power supply, and the on-chip area occupied by this mixer with pads excluded is only about 350 400 ,m2. 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1463,1466, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23395 [source]

    Visual Support for Interactive Post-Interventional Assessment of Radiofrequency Ablation Therapy

    Christian Rieder
    Abstract Percutaneous radiofrequency (RF) ablation is a minimally invasive, image-guided therapy for the treatment of liver tumors. The assessment of the ablation area (coagulation) is performed to verify the treatment success as an essential part of the therapy. Traditionally, pre- and post-interventional CT images are used to visually compare the shape, size, and position of tumor and coagulation. In this work, we present a novel visualization as well as a navigation tool, the so-called tumor map. The tumor map is a pseudo-cylindrical mapping of the tumor surface onto a 2D image. It is used for a combined visualization of all ablation zones of the tumor to allow a reliable therapy assessment. Additionally, the tumor map serves as an interactive tool for intuitive navigation within the 3D volume rendering of the tumor vicinity as well as with familiar 2D viewers. [source]

    Simulation of Accuracy Performance for Wireless Sensor-Based Construction Asset Tracking

    Miros, aw J. Skibniewski
    In particular, identifying the location of distributed mobile entities throughout wireless communications becomes the primary task to realize the remote tracking and monitoring of the construction assets. Even though several alternative solutions have been introduced by utilizing recent technologies, such as radio frequency identification (RFID) and the global positioning system (GPS), they could not provide a solid direction to accurate and scalable tracking frameworks in large-scale construction domains due to limited capability and inflexible networking architectures. This article introduces a new tracking architecture using wireless sensor modules and shows an accuracy performance using a numerical simulation approach based on the time-of-flight method. By combining radio frequency (RF) and ultrasound (US) signals, the simulation results showed an enhanced accuracy performance over the utilization of an RF signal only. The proposed approach can provide potential guidelines for further exploration of hardware/software design and for experimental analysis to implement the framework of tracking construction assets. [source]

    Thermal relaxation and coherence dynamics of spin 3/2.


    Abstract The relaxation dynamics of the spin 3/2 density operator in the presence of fluctuating and static quadrupolar interactions is reviewed. The nuclear magnetic resonance (NMR) line shapes are analyzed for any value of the static quadrupolar interaction, ranging from isotropic systems to systems exhibiting large splitting far exceeding the line widths. Pulse sequences optimized for the elimination of line broadening due to an inhomogeneous static quadrupolar interaction and for the detection of nuclei involved in slow molecular motion and/or in anisotropic, liquid crystalline environment are discussed. In Part II, the dynamics of spin 3/2 in the presence of a (pulsed) radio frequency (RF) field is reviewed. 2003 Wiley Periodicals, Inc. Concepts Magn Reson Part A 19A: 97,116, 2003. [source]

    Solenoidal microcoil design,Part II: Optimizing winding parameters for maximum signal-to-noise performance

    Kevin R. Minard
    Abstract In high-field proton NMR, the signal-to-noise ratio (SNR) achieved with a close-fitting solenoidal microcoil is adversely affected by radio frequency (RF) losses in the coil, its leads, the capacitor used to tune it, and finally, the sample. In Part II, a rigorous description of these various losses is presented, and their severity is related to the details of coil design. Results not only provide a rational basis for defining a microcoil's optimal wire diameter and the number of turns, but also for evaluating how the SNR varies with coil size and NMR frequency in high-field proton NMR studies involving either conducting or non-conducting samples. 2001 John Wiley & Sons, Inc. Concepts Magn Reson 13: 190,210, 2001 [source]

    PIC-MCC Modeling of a Capacitive RF discharge

    K. Matyash
    First page of article [source]

    High temperature arsenic doping of CdHgTe epitaxial layers

    A. Vlasov
    Abstract Experimental results on solid-state arsenic doping of the n-type bulk and ISOVPE epitaxial CdXHg1- XTe (X = 0.19 0.3) alloys are presented. The arsenic doped thin epitaxial CdxHg1- xTe films (nAs , 5 1016 1 1020 cm -3; d = 2 5 ,m) obtained by RF sputtering in a mercury glow discharge were used as As diffusion sources. The arsenic diffusion and activation were carried out at temperatures T = 500 600 C under Hg vapour pressure. Immediately after the high temperature treatment all samples were annealed to annihilate point defects. The SIMS analysis was used for determination of the quantitative admixture distribution of As in the diffusion area. The arsenic electrical activity has been evaluated by means of differential Hall, resistivity and thermoemf measurements. The analysis of experimental data obtained as well as their comparison with previously obtained results has been performed. ( 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    A Randomized Trial to Determine the Influence of Laser Therapy, Monopolar Radiofrequency Treatment, and Intense Pulsed Light Therapy Administered Immediately after Hyaluronic Acid Gel Implantation

    BACKGROUND Hyaluronic acid-based dermal fillers, such as hyaluronic acid gel (Restylane, Q-Medical AB, Uppsala, Sweden), are widely used for tissue augmentation of the nasolabial folds. Additional dermatologic treatments using infrared light, radiofrequency (RF), and intense pulsed light (IPL) are also important tools for facial rejuvenation. This study was designed to evaluate whether these therapies could be safely administered immediately after hyaluronic acid gel treatment without compromising the effect of the dermal filler. OBJECTIVE The objective of this study was to confirm or refute any possible subtractive effects of augmentation of the nasolabial folds when followed by 1,320-nm Nd:YAG laser, 1,450-nm diode laser, monopolar RF, and/or IPL treatments. METHODS Thirty-six patients with prominent nasolabial folds were treated with hyaluronic acid gel implantation on one side of the face and hyaluronic acid gel followed by one of the nonablative laser/RF/IPL therapies on the contralateral side of the face. RESULTS There were no statistically significant differences between wrinkle severity or global aesthetic scores for hyaluronic acid gel implantation alone and hyaluronic acid gel with laser/RF/IPL treatment at any time point. In a small sample, histologic changes were not apparent after laser/RF/IPL treatment. CONCLUSIONS Based on this small pilot study, laser, RF, and IPL treatments can safely be administered immediately after hyaluronic acid gel implantation without reduction in overall clinical effect. [source]

    Comparison of Endovenous Radiofrequency Versus 810 nm Diode Laser Occlusion of Large Veins in an Animal Model

    Robert A. Weiss MDArticle first published online: 27 FEB 200
    background. Endovenous occlusion using radiofrequency (RF) energy has been shown to be effective for the elimination of sapheno-femoral reflux and subsequent elimination of varicose veins. Recently, endovenous laser occlusion has been introduced with initial clinical reports indicating effective treatment for varicose veins. However, in our practice we note increased peri-operative hematoma and tenderness with the laser. Little is known regarding the mechanism of action of this new laser vein therapy. objective. To better understand the mechanism of action of endovenous laser vs. the endovenous RF procedure in the jugular vein of the goat model. methods. A bilateral comparison was performed using 810 nm diode laser transmitted by a bare-tipped optical fiber vs. the RF delivery by engineered electrodes with a temperature feedback loop using a thermocouple (Closure procedure) in three goat jugular veins. Immediate and one-week results were studied radiographically and histologically. Temperature measurements during laser treatment were performed by using an array of up to five thermocouples, spaced 2 mm apart, placed adjacent to a laser fiber tip during goat jugular vein treatment. results. Immediate findings showed that 100% of the laser-treated veins showed perforations by histologic examination and immediate contrast fluoroscopy. The RF-treated side showed immediate constriction with maintenance of contrast material within the vein lumen and no perforations. The difference in acute vein shrinkage was also dramatic as laser treatments resulted in vein shrinkage of 26%, while RF-treated veins showed a 77% acute reduction in diameter. At one week, extravasated blood that leaked into the surrounding tissue of laser treated veins acutely, continued to occupy space and impinge on surrounding structures including nerves. For the laser treatment, the highest average temperature was 729C (peak temperature 1334C) observed flush with the laser fiber tip, while the temperature feedback mechanism of the RF method maintains temperatures at the electrodes of 85C. conclusion. Vein perforations, extremely high intravascular temperatures, failure to cause significant collagen shrinkage, and intact endothelium in an animal model justify a closer look at the human clinical application of the 810 nm endovenous laser technique. Extravasated blood impinging on adjacent structures may theoretically lead to increased peri-operative hematoma and tenderness. Further study and clinical investigation is warranted. [source]

    In vivo muscle architecture and size of the rectus femoris and vastus lateralis in children and adolescents with cerebral palsy

    Aim, Our aim was to investigate muscle architecture and size of the rectus femoris (RF) and vastus lateralis (VL) in children and adolescents with cerebral palsy (CP) compared with age-matched typically developing participants. Method, Muscle architecture and size were measured with ultrasound imaging in 18 participants with spastic CP (9 females, 9 males; age range 7.5,19y; mean age 12y [SD 3y 2mo]) within Gross Motor Function Classification System levels I (n=4), II (n=2), III (n=9), and IV (n=3) and 12 typically developing participants (10 females, 2 males; age range 7,20y; mean age 12y 4mo [SD 3y 11mo]). Exclusion criteria were orthopedic surgery or neurosurgery within 6 months before testing or botulinum toxin injections to the quadriceps within 3 months before testing. Results, RF cross-sectional area was significantly lower (48%), RF and VL muscle thickness 30% lower, RF fascicle length 27% lower, and VL fascicle angle 3 less in participants with CP compared to the typically developing participants (p<0.05). Intraclass correlation coefficients were ,0.93 (CP) and , 0.88 (typical development), indicating excellent reliability. Interpretation, These results provide the first evidence of altered muscle architecture and size of the RF and VL in CP, similar to patterns observed with disuse and aging. These alterations may play a significant role in the decreased capacity for force generation as well as decreased shortening velocity and range of motion over which the quadriceps can act. [source]

    Adsorptive Stripping Analysis of Riboflavin at Electrically Heated Graphite Cylindrical Electrodes

    ELECTROANALYSIS, Issue 21 2007
    Shao-Hua Wu
    Abstract Electrically heated graphite cylindrical electrodes (HGCEs) made from ground pencil leads have been used to perform adsorptive stripping square wave voltammetry (SWV) measurements of trace riboflavin (RF). The SWV stripping peak current was significantly enhanced with increasing the electrode temperature only during preconcentration step. This enhancement was due to the forced thermal convection induced by heating the electrode rather than the bulk solution. It is the thermal convection that has the ability to improve mass transfer and facilitate adsorption thus enhance stripping responses. It was found that the detection limit of 510,9,M (S/N=3) could be obtained at an electrode temperature of 72,C during 5,min accumulation, more than one magnitude lower than that at 22,C (room temperature), the sensitivity could be enhanced ca. eight or four folds for two different RF concentration ranges. So it is possible to develop a new highly sensitive method to determine riboflavin at HGCEs. Such HGCEs were also successfully used to determine RF in multivitamin tablets. [source]

    Induction of V(D)J-mediated recombination of an extrachromosomal substrate following exposure to DNA-damaging agents

    Robert L. Pinsonneault
    Abstract V(D)J recombinase normally mediates recombination signal sequence (RSS) directed rearrangements of variable (V), diversity (D), and joining (J) germline gene segments that lead to the generation of diversified T cell receptor or immunoglobulin proteins in lymphoid cells. Of significant clinical importance is that V(D)J-recombinase-mediated rearrangements at immune RSS and nonimmune cryptic RSS (cRSS) have been implicated in the genomic alterations observed in lymphoid malignancies. There is growing evidence that exposure to DNA-damaging agents can increase the frequency of V(D)J-recombinase-mediated rearrangements in vivo in humans. In this study, we investigated the frequency of V(D)J-recombinase-mediated rearrangements of an extrachromosomal V(D)J plasmid substrate following exposure to alkylating agents and ionizing radiation. We observed significant dose- and time-dependent increases in V(D)J recombination frequency (V(D)J RF) following exposure to ethyl methanesulfonate (EMS) and methyl methanesulfonate (MMS) but not a nonreactive analogue, methylsulfone (MeSulf). We also observed a dose-dependent increase in V(D)J RF when cells were exposed to gamma radiation. The induction of V(D)J rearrangements following exposure to DNA-damaging agents was not associated with an increase in the expression of RAG 1/2 mRNA compared to unexposed controls or an increase in expression of the DNA repair Ku70, Ku80 or Artemis proteins of the nonhomologous end joining pathway. These studies demonstrate that genotoxic alkylating agents and ionizing radiation can induce V(D)J rearrangements through a cellular response that appears to be independent of differential expression of proteins involved with V(D)J recombination. Environ. Mol. Mutagen., 2007. 2007 Wiley-Liss, Inc. [source]

    SEEG-guided RF Thermocoagulation of Epileptic Foci: Feasibility, Safety, and Preliminary Results

    EPILEPSIA, Issue 11 2004
    Marc Gunot
    Summary:,Purpose:,Depth electrodes recordings may be required in some cases of epilepsy surgery to delineate the best region for cortical resection. We usually implant depth electrodes according to Talairach's stereoelectroencephalography (SEEG) method. By using these permanently implanted depth electrodes, we are able to perform radiofrequency (RF)-thermolesions of the epileptic foci. We report the technical data required to perform such multiple cortical thermolesions, as well as preliminary results in terms of seizure outcome in a group of 20 patients. Methods:,Lesions were performed by using 100- to 110-mA bipolar current (50 V), applied for 10 to 50 s. Each thermocoagulation produced a 5- to 7-mm diameter cortical lesion. In total, two to 16 lesions were performed in each of the 20 patients. Lesions were placed without anesthesia. No general or neurologic complication occurred during the procedures. Two transient postprocedure side effects, consisting of paresthetic sensations in the mouth and mild apraxia of the hand, were observed. Results:,At a follow-up time of 8 to 31 months (mean, 19 months), 15% of the patients became seizure free, 40% experienced a ,80% reduction of their seizure frequency, and 45% were not significantly improved. Conclusions:,SEEG-guided RF thermolesions is a safe technique. Our preliminary results indicate that such lesions can lead to a significant reduction of seizure frequency and could be proposed as a palliative procedure if no resective surgery is possible. A randomized controlled trial is needed to determine which patients are likely to respond to SEEG-guided RF thermolesions. [source]

    Correlation between routine radiographic findings and early racing career in French Trotters

    Summary Reasons for performing study: The relationship between the presence of radiological abnormalities and subsequent racing performance is controversial. However, as training is expensive and time consuming, it would save time and money to identify subjects with osteo-articular lesions not compatible with a normal racing career on the basis of routine radiographic screenings at yearling age. Objectives: To evaluate the impact of osteo-articular lesions on racing ability in French Trotters and identify radiographic changes associated with failure in ,qualification', in order to provide objective criteria for selection of horses based on their osteo-articular status. Hypothesis: The influence of radiographic findings (RF) on racing ability depends on their nature, location, clinical relevance and number. Methods: The limbs of 202 French Trotters were radiographed just before they started training. All the RF were graded according to a standardised protocol depending on their severity. The success in ,qualification' (first race in career of French Trotters) was the criteria used to assess racing ability. Breeders and trainers were questioned about the causes for horses not racing. Results: Overall 113 (55.9%) horses qualified. Osteoarticular lesions were directly responsible for nonqualification in 31% of the horses. Subjects with more than one abnormal RF, with abnormal RF on the fore-, hind-fetlock or proximal tarsus were less likely to qualify. Dorsal modelling in the front fetlock and osteochondrosis of the lateral trochlear ridge of the femur also significantly reduced the qualification rate. Conclusions: Most RF are compatible with beginning a racing career, but severe RF or multiple abnormal RF significantly compromise future racing career. Potential relevance: This study supports the use of routine radiographic programmes for detection of osteoarticular lesions in yearlings. A synthetic radiographic score, based on both the severity and the number of lesions, could be useful for breeders and trainers as complementary information to select their horses. [source]

    Geographical and individual variation in echolocation calls of the intermediate leaf-nosed bat, Hipposideros larvatus

    ETHOLOGY, Issue 8 2010
    Tinglei Jiang
    The cause and significance of variation in echolocation call frequency within hipposiderid bats is not well understood despite an increasing number of allopatric and sympatric examples being documented. We examined variation patterns in the resting frequency (RF) of echolocation calls emitted by the intermediate leaf-nosed bat, Hipposideros larvatus, on a broad geographical scale. Data mining technology and Kruskal,Wallis test both showed substantial variation with a longitudinal pattern in RF in H. larvatus among colonies, and this variation was associated with geographical distance and not body size. In addition, we found that a high degree of variability between individuals was hidden under the geographical variation. The results support an effect of random cultural drift, and challenge the prey detection hypothesis. Moreover, an acoustic difference among local island colonies may be indicative of a vocal dialect. We found that each colony of H. larvatus seems to maintain a ,private bandwidth', which could be used for colony identity and individual communication thus helping individuals and colonies to get a number of fitness benefits. [source]

    Influence of Surface Chemistry on Dehydrogenation in Carbon Cryogel Ammonia Borane Nanocomposites

    Saghar Sepehri
    Abstract This paper reports the synthesis and characterization of boron- and nitrogen-modified carbon cryogel (CC) ammonia borane (AB) nanocomposites (BNCC-AB) for hydrogen storage. Resorcinol,formaldehyde (RF) derived CCs were modified by homogeneous dispersion of AB in RF hydrogel prior to pyrolysis. Nanocomposites were fabricated by immersing CC in the AB solution. Nitrogen sorption analysis, X-ray photoelectron spectroscopy, and differential scanning calorimetry at multiple heating rates were used to study the structure and dehydrogenation properties of the nanocomposites. The results demonstrated lower dehydrogenation temperatures and reduced activation energies for AB when confined inside pores of B- and N-modified CCs relative to AB when confined in the unmodified CC with the same pore size.( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

    Random forest can predict 30-day mortality of spontaneous intracerebral hemorrhage with remarkable discrimination

    S. -Y.
    Background and purpose:, Risk-stratification models based on patient and disease characteristics are useful for aiding clinical decisions and for comparing the quality of care between different physicians or hospitals. In addition, prediction of mortality is beneficial for optimizing resource utilization. We evaluated the accuracy and discriminating power of the random forest (RF) to predict 30-day mortality of spontaneous intracerebral hemorrhage (SICH). Methods:, We retrospectively studied 423 patients admitted to the Taichung Veterans General Hospital who were diagnosed with spontaneous SICH within 24 h of stroke onset. The initial evaluation data of the patients were used to train the RF model. Areas under the receiver operating characteristic curves (AUC) were used to quantify the predictive performance. The performance of the RF model was compared to that of an artificial neural network (ANN), support vector machine (SVM), logistic regression model, and the ICH score. Results:, The RF had an overall accuracy of 78.5% for predicting the mortality of patients with SICH. The sensitivity was 79.0%, and the specificity was 78.4%. The AUCs were as follows: RF, 0.87 (0.84,0.90); ANN, 0.81 (0.77,0.85); SVM, 0.79 (0.75,0.83); logistic regression, 0.78 (0.74,0.82); and ICH score, 0.72 (0.68,0.76). The discriminatory power of RF was superior to that of the other prediction models. Conclusions:, The RF provided the best predictive performance amongst all of the tested models. We believe that the RF is a suitable tool for clinicians to use in predicting the 30-day mortality of patients after SICH. [source]

    Food-entrainable circadian oscillators in the brain

    M. Verwey
    Abstract Circadian rhythms in mammalian behaviour and physiology rely on daily oscillations in the expression of canonical clock genes. Circadian rhythms in clock gene expression are observed in the master circadian clock, the suprachiasmatic nucleus but are also observed in many other brain regions that have diverse roles, including influences on motivational and emotional state, learning, hormone release and feeding. Increasingly, important links between circadian rhythms and metabolism are being uncovered. In particular, restricted feeding (RF) schedules which limit food availability to a single meal each day lead to the induction and entrainment of circadian rhythms in food-anticipatory activities in rodents. Food-anticipatory activities include increases in core body temperature, activity and hormone release in the hours leading up to the predictable mealtime. Crucially, RF schedules and the accompanying food-anticipatory activities are also associated with shifts in the daily oscillation of clock gene expression in diverse brain areas involved in feeding, energy balance, learning and memory, and motivation. Moreover, lesions of specific brain nuclei can affect the way rats will respond to RF, but have generally failed to eliminate all food-anticipatory activities. As a consequence, it is likely that a distributed neural system underlies the generation and regulation of food-anticipatory activities under RF. Thus, in the future, we would suggest that a more comprehensive approach should be taken, one that investigates the interactions between multiple circadian oscillators in the brain and body, and starts to report on potential neural systems rather than individual and discrete brain areas. [source]

    Chemical, Mechanical, and Antibacterial Properties of Silver Nanocluster,Silica Composite Coatings Obtained by Sputtering,

    Monica Ferraris
    Abstract Silver nanocluster,silica matrix composite coatings have been deposited by radio frequency (RF) co-sputtering on silica substrates. Field emission scanning electron microscopy and X-ray diffraction spectra of the as deposited and heated samples (150,600,C) revealed the presence of metal silver nanoclusters, their size depending on the heating treatment. The antibacterial activity of the as deposited and heated samples has been measured in accordance to National Committee for Clinical Laboratory Standards, and it has been demonstrated on samples heated up to 450,C in contact mode and for samples heated at 600,C in a liquid environment. Their antibacterial activity was still present after gamma ray and ethylene oxide gas (EtO) sterilization of the samples. Silver leaching tests on the as deposited and heated samples has been measured by graphite furnace atomic absorption spectrometer, revealing an amount ranging from 0.1 to 0.9,g mm,2, over 28 days. Tape resistance (ASTM D3359-97) and scratch resistance tests have been done on each sample revealing a good adhesion of the coatings on silica. [source]

    Unpredictable feeding schedules unmask a system for daily resetting of behavioural and metabolic food entrainment

    Carolina Escobar
    Abstract Restricted feeding schedules (RFS) are a potent Zeitgeber that uncouples daily metabolic and clock gene oscillations in peripheral tissues from the suprachiasmatic nucleus (SCN), which remains entrained to the light,dark cycle. Under RFS, animals develop food anticipatory activity (FAA), characterized by arousal and increased locomotion. Food availability in nature is not precise, which suggests that animals need to adjust their food-associated activity on a daily basis. This study explored the capacity of rats to adjust to variable and unpredictable feeding schedules. Rats were exposed either to RFS with fixed daily meal (RF) or to a variable meal time (VAR) during the light phase. RF and VAR rats exhibited daily metabolic oscillations driven by the last meal event; however, VAR rats were not able to show a robust adjustment in the anticipating corticosterone peak. VAR rats were unable to exhibit FAA but exhibited a daily activation pattern in phase with the previous meal. In both groups the dorsomedial nucleus of the hypothalamus and arcuate nucleus, involved in energy balance, exhibited increased c-Fos expression 24 h after the last meal, while only RF rats exhibited low c-Fos expression in the SCN. Data show that metabolic and behavioural food-entrained rhythms can be reset on a daily basis; the two conditions elicit a similar hypothalamic response, while only the SCN is inhibited in rats exhibiting anticipatory activity. The variable feeding strategy uncovered a rapid (24-h basis) resetting mechanism for metabolism and general behaviour. [source]

    Task-induced modulation of motor evoked potentials in upper-leg muscles during human gait: a TMS study

    Mireille Bonnard
    Abstract The aim of this study was to determine the relative involvement of the corticospinal (CS) pathway in voluntarily controlled walking compared to unconstrained walking. In the voluntarily controlled walking condition, subjects had to walk at the same speed as in unconstrained walking with a mechanical constraint, which is known to affect specifically the upper-leg muscles. The motor cortex was activated transcranially using a focal magnetic stimulation coil in order to elicit motor evoked potentials (MEPs) in the rectus femoris (RF) and the biceps femoris (BF). The magnetic stimulation was delivered at the end of the swing (at 90% of the cycle duration), when the EMG backgrounds were similar in the two experimental conditions. For each subject in each condition, MEPs were measured for several stimulus intensities in order to establish the input/output (I/O) curve (MEPs amplitude plotted against stimulus strength). The results showed a significant increase in the MEPs amplitude of both the RF and BF in voluntarily controlled walking compared to unconstrained walking, which is the first evidence of cofacilitation of MEPs in antagonist upper-leg muscles during human gait. In conclusion, although a lot of studies have emphasized a privileged input of the corticospinal pathway to the distal lower-leg muscles, this study shows that, if a locomotory task requires fine control of the proximal upper-leg muscles, a selective facilitation of MEPs is observed in these muscles. [source]

    Outcome of secondary root canal treatment , Systematic review of the literature

    Y.-L. Ng
    Aims, To assess the success rates of secondary root canal treatment (2oRCT) and identify factors influencing outcome. Methodology, Longitudinal clinical studies investigating outcome of 2oRCT were identified by electronic (medline) and hand searches. Inclusion criteria were data on: number of samples, those successful and definition of success. Two reviewers independently assessed the studies and extracted the data onto a proforma. The pooled weighted success rates by each potential prognostic factor were estimated using the binomial random effect model (MLwiN version 2.02) whilst their pooled effects (expressed as odds ratio) on success rates were estimated using fixed and random effects meta-analysis with DerSimonean and Laird's methods (Stata version 9.2). Meta-regression models were used to explore potential sources of statistical heterogeneity. Study characteristics considered in the meta-regression analyses were: decade of publication, study-specific criteria for success (radiographic, combined radiographic & clinical), unit of outcome measure (tooth and root), duration after treatment when assessing success (at least 4 years or shorter), geographic location of the study (North American, Scandinavian and other countries), and qualification of the operator (undergraduate students, postgraduate students, general dental practitioners, specialist or mixed group). Results, Of the 41 studies identified, 18 studies published between 1921 and 2005 were included. The majority of studies were retrospective (n = 13) and only five prospective. The pooled weighted success rate of 2oRCT judged by complete healing was 77.6% (95% CI 73.2%, 81.4%) and by incomplete healing, 77.4% (95% CI 64.1%, 86.7%). The success rates were similar by ,year of publication' and ,country of study'. Eighteen clinical factors were investigated in various combinations in previous studies. The most frequently investigated were ,periapical status' (n = 13), ,size of lesion' (n = 7), ,culture results prior to RF' (n = 5), and ,apical extent of root filling (RF)' (n = 4). The effect of different aspects of previous treatment and re-treatment technique has been poorly tested. Conclusions, The pooled weighted estimated success rate of 2oRCT was 77%, which was significantly (P , 0.001) influenced by the presence and size of pre-operative periapical lesion. The effects of existing canal content, procedural error and re-treatment technique were poorly investigated. [source]

    Numerical analysis of Rayleigh,Plesset equation for cavitating water jets

    H. Alehossein
    Abstract High-pressure water jets are used to cut and drill into rocks by generating cavitating water bubbles in the jet which collapse on the surface of the rock target material. The dynamics of submerged bubbles depends strongly on the surrounding pressure, temperature and liquid surface tension. The Rayleigh,Plesset (RF) equation governs the dynamic growth and collapse of a bubble under various pressure and temperature conditions. A numerical finite difference model is established for simulating the process of growth, collapse and rebound of a cavitation bubble travelling along the flow through a nozzle producing a cavitating water jet. A variable time-step technique is applied to solve the highly non-linear second-order differential equation. This technique, which emerged after testing four finite difference schemes (Euler, central, modified Euler and Runge,Kutta,Fehlberg (RKF)), successfully solves the Rayleigh,Plesset (RP) equation for wide ranges of pressure variation and bubble initial sizes and saves considerable computing time. Inputs for this model are the pressure and velocity data obtained from a CFD (computational fluid dynamics) analysis of the jet. Copyright 2007 John Wiley & Sons, Ltd. [source]

    Analysis and optimization of a novel biasing for constant-gain CMOS open-loop amplifiers

    G. Palmisano
    A replica biasing circuit is presented which allows open-loop gain in CMOS amplifiers to be accurately set. The proposed solution is a new biasing which takes advantage of a triode-biased transistor instead of the ,VGS approach which is the traditional one. The circuit can be applied to both RF and IF amplifiers which are based on resistive loads in order to achieve high-frequency and/or low-noise performance. A detailed analysis of second-order effects is then given which emphasizes the effects due to mobility degradation, channel-length modulation and threshold voltage mismatches. Simulated results show a good sensitivity to process variations. Copyright 2001 John Wiley & Sons, Ltd. [source]

    The state of the art of microwave CAD: EM-based optimization and modeling

    Qingsha S. Cheng
    Abstract We briefly review the current state of the art of microwave CAD technologies. We look into the history of design optimization and CAD-oriented modeling of microwave circuits as well as electromagnetics-based optimization techniques. We emphasize certain direct approaches that utilize efficient sensitivity evaluations as well as surrogate-based optimization approaches that greatly enhance electromagnetics-based optimization performance. On the one hand, we review recent adjoint methodologies, on the other we focus on space mapping implementations, including the original, aggressive, implicit, output, tuning, and related developments. We illustrate our presentation with suitable examples and applications. 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010. [source]

    Surrogate-based infill optimization applied to electromagnetic problems

    I. Couckuyt
    Abstract The increasing use of expensive computer simulations in engineering places a serious computational burden on associated optimization problems. Surrogate-based optimization becomes standard practice in analyzing such expensive black-box problems. This article discusses several approaches that use surrogate models for optimization and highlights one sequential design approach in particular, namely, expected improvement. The expected improvement approach is demonstrated on two electromagnetic problems, namely, a microwave filter and a textile antenna. 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010. [source]

    Recent advances of neural network-based EM-CAD

    Humayun Kabir
    Abstract In this article, we provide an overview of recent advances in computer-aided design techniques using neural networks for electromagnetic (EM) modeling and design applications. Summary of various recent neural network modeling techniques including passive component modeling, design and optimization using the models are discussed. Training data for the models are generated from EM simulations. The trained neural networks become fast and accurate models of EM structures. The models are then incorporated into various optimization methods and commercially available circuit simulators for fast design and optimization. We also provide an overview of recently developed neural network inverse modeling technique. Training a neural network inverse model directly may become difficult due to the nonuniqueness of the input,output relationship in the inverse model. Training data containing multivalued solutions are divided into groups according to derivative information. Multiple inverse submodels are built based on divided data groups and are then combined to form a complete model. Comparison between the conventional EM-based design approach and the inverse design approach has also been discussed. These computer-aided design techniques using neural models provide circuit level simulation speed with EM level accuracy avoiding the high computational cost of EM simulation. 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010. [source]

    Efficient analysis of wireless communication antennas using an accurate [Z] matrix interpolation technique

    Yikai Chen
    Abstract An accurate impedance matrix interpolation technique based on the surface integral equation (SIE) is presented for the analysis of wireless communication antennas over wide frequency bands. The first-order derivative of the impedance matrix at the internal frequency is considered in the cubic polynomial-based interpolation scheme, thus the novel impedance matrix interpolation scheme will provide high accuracy and high efficiency over a frequency band. To demonstrate the efficiency and accuracy of the proposed method, numerical results for planar inverted F antennas (PIFA) and a wideband E-shaped patch antenna are presented. Good agreement among the interpolation results, exact MoM solutions, finite element method (FEM) solutions, and measured data is observed over the bandwidth. Besides, dimensions of the feeding probe are also studied to investigate their effect on the input impedance and radiation patterns. 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010. [source]

    High isolation microstrip GaN-HEMT Single-FET Switch

    Walter Ciccognani
    Abstract In this contribution an analytical approach to the design of high-isolation microwave transmission line-resonated switches is presented. Simulated and measured performance of a GaN HEMT single-FET switch cell topology and the one of a complete SPDT using the proposed approach are presented to demonstrate the approach feasibility and effectiveness. The resulting SPDT, operating at X Band, is featured by 1 dB insertion loss, isolation better than 37 dB all over the operating bandwidth and a power handling capability higher than 39 dBm. 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010. [source]

    Active measurements of antenna diversity performances using a specific test-bed, in several environments

    Moctar Mouhamadou
    Abstract The diversity performances of the wireless devices operating in a multipath propagation environment are usually presented in terms of correlation coefficient, diversity gain and effective diversity gain. These parameters can be measured in reverberation chamber. This paper presents some active measurements of antenna diversity performances on a small wireless terminal in several realistic environments. The measurements were performed in the WiMax band, i.e. at 3.5 GHz, in a reverberation chamber where the channel is statistically uniform, in a real indoor propagation channel, and in an outdoor-to-indoor environment. The diversity performances are evaluated by using a specific test-bed constituted by an arbitrary signal generator and two radio-frequency digitizers. The effectiveness of diversity is presented in terms of effective diversity gain, signal to noise ratio, bit error rate and frame error rate. 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010. [source]