59 resultados para low level radio frequency


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Frequency, recency, and type of prior exposure to very low-and high-frequency words were manipulated in a 3-phase (i.e., familiarization training, study, and test) design. Increasing the frequency with which a definition for a very low-frequency word was provided during familiarization facilitated the word's recognition in both yes-no (Experiment 1) and forced-choice paradigms (Experiment 2). Recognition of very low-frequency words not accompanied by a definition during familiarization first increased, then decreased as familiarization frequency increased (Experiment I). Reasons for these differences were investigated in Experiment 3 using judgments of recency and frequency. Results suggested that prior familiarization of a very low-frequency word with its definition may allow a more adequate episodic representation of the word to be formed during a subsequent study trial. Theoretical implications of these results for current models of memory are discussed.

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The c fins gene encodes the receptor for macrophage colony-stimulating factor-1. This gene is expressed selectively in the macrophage cell lineage. Previous studies have implicated sequences in intron 2 that control transcript elongation in tissue-specific and regulated expression of c -fms. Four macrophage-specific deoxyribonuclease I (DNase I)-hypersensitive sites (DHSS) were identified within mouse intron 2. Sequences of these DHSS were found to be highly conserved compared with those in the human gene. A 250-bp region we refer to as the fins intronic regulatory element (FIRE), which is even more highly conserved than the c-fins proximal promoter, contains many consensus binding sites for macrophage-expressed transcription factors including Spl, PU.1, and C/EBP. FIRE was found to act as a macrophage-specific enhancer and as a promoter with an antisense orientation preference in transient transfections. In stable transfections of the macrophage line RAW264, as well as in clones selected for high and low-level c -fms mRNA expression, the presence of intron 2 increased the frequency and level of expression of reporter genes compared with those attained using the promoter alone. Removal of FIRE abolished reporter gene expression, revealing a suppressive activity in the remaining intronic sequences. Hence, FIRE is shown to be a key regulatory element in the fins gene.

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Purpose: To compare microsatellite instability (MSI) testing with immunohistochemical (IHC) detection of hMLH1 and hMSH2 in colorectal cancer. Patients and Methods: Colorectal cancers from 1, 144 patients were assessed for DNA mismatch repair deficiency by two methods: MSI testing and IHC detection of hMLH1 and hMSH2 gene products. High-frequency MSI (MSI-H) was defined as more than 30% instability of at least five markers; low-level MSI (MSI-L) was defined as 1% to 29% of loci unstable. Results: Of 1, 144 tumors tested, 818 showed intact expression of hMLH1 and hMSH2. Of these, 680 were microsatellite stable (MSS), 27 were MSI-H, and 111 were MSI-L. In all, 228 tumors showed absence of hMLH1 expression and 98 showed absence of hMSH2 expression: all were MSI-H. Conclusion: IHC in colorectal tumors for protein products hMLH1 and hMSH2 provides a rapid, cost-effective, sensitive (92.3%), and extremely specific (100%) method for screening for DNA mismatch repair defects. The predictive value of normal IHC for an MSS/MSI-L phenotype was 96.7%, and the predictive value of abnormal IHC was 100% for an MSI-H phenotype. Testing strategies must take into account acceptability of missing some cases of MSI-H tumors if only IHC is performed. (C) 2002 by American Society of Clinical Oncology.

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Colorectal cancer (CRC) has traditionally been classified into two groups: microsatellite stable/low-level instability (MSS/MSI-L) and high-level MSI (MSI-H) groups on the basis of multiple molecular and clinicopathologic criteria. Using methylated in tumor (MINT) markers 1, 2,12, and 31, we stratified 77 primary CRCs into three groups: MINT++ (>2), MINT+ (1-2), and MINT- (0 markers methylated). The MSS/MSI-L/ MINT++ group was indistinguishable from the MSI-H/MINT++ group with respect to methylation of p16(INK4a), p14(ARF), and RIZ1, and multiple morphological features. The only significant difference between MSI-H and non-MSI-H MINT++ cancers was the higher frequency of K-ras mutation (P < 0.004) and lower frequency of hMLH1 methylation (P < 0.001) in the latter. These data demonstrate that the separation of CRC into two nonoverlapping groups (MSI-H versus MSS/MSI-L) is a misleading oversimplification.

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Ixodes holocyclus has a narrow, discontinuous distribution along the east coast of Australia. We studied ticks from 17 localities throughout the geographic range of this tick. The ITS2 of I. holocyclus is 793 bp long. We found nucleotide variation at eight of the 588 nucleotide positions (1.4%) that were compared for all ticks. There were eight different nucleotide sequences. Most sequences were not restricted to a particular geographic region. However, sequences F, G and H, which had an adenine at position 197, were found only in the far north of Queensland - all other ticks had a guanine at this position. The low level of intraspecific variation in this tick (0.7%) contrasts with the sequence divergence between L holocyclus and its close relative, I. cornuatus (13.1 %). These data indicate that L holocyclus does not contain cryptic species despite possible geographic isolation of some populations. We conclude that variation in the ITS2 is likely to be informative about the phylogeny of the group.

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This study evaluated the degree to which the disturbance to posture from respiration is compensated for in healthy normals and whether this is different in people with recurrent low back pain (LBP), and to compare the changes when respiratory demand is increased. Angular displacement of the lumbar spine and hips, and motion of the centre of pressure (COP), were recorded with high resolution and respiratory phase was recorded from ribcage motion. With subjects standing in a relaxed posture, recordings were made during quiet breathing, while breathing with increased dead-space to induce hypercapnoea, and while subjects voluntarily increased their respiration to match ribcage expansion that was induced in the hypercapnoea condition. The relationship between respiration and the movement parameters was measured from the coherence between breathing and COP and angular motion at the frequency of respiration, and from averages triggered from the respiratory data. Small angular changes in the lumbopelvic and hip angles were evident at the frequency of respiration in both groups. However, in quiet standing, the LBP subjects had a greater displacement of their COP that was associated with respiration than the control subjects. The LBP group had a trend for less hip motion. There were no changes in the movement parameters when respiratory demand increased involuntarily via hypercapnoea, but when respiration increased voluntarily, the amplitude of motion and the displacement of the COP increased in both groups. The present data suggest that the postural compensation to respiration counteracts at least part of the disturbance to posture caused by respiration and that this compensation may be less effective in people with LBP.

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Coccidoxenoides perminutus achieves only low levels of parasitism of its host Planococcus citri in southeast Queensland citrus. Two possible causes were investigated. Adult survival under natural conditions was assessed to determine whether providing adult food sources could enhance survival. Behavioural changes of hosts, induced by C perminutus parasitism, was also investigated to establish if parasitised P. citri move from their feeding site to seek protected shelters some distance away and are thus not accounted for in field assessments of parasitism rates. Unparasitised mealybugs placed in the field for two periods were retrieved before the effects of parasitism were manifested and parasitism rates were still low (0.3% at 5 days and 1.2% at 10 days). Levels of locomotion of P. citri exposed to C perminutus were compared with those of unexposed ones. Parasitised mealybugs, regardless of instar, undergo behavioural changes. In comparison to unparasitised controls, the mealybugs become highly active 7-14 days after exposure to wasps. All parasitised mealybugs undergo physical changes, their body becomes cylindrical, their legs go so rigid that the mealybugs become immobile, and this signifies the typical mummy appearance. All mealybugs that became mummies eventually fell from the host lemon fruit because of impaired locomotion and were caught on sticky traps that had been placed beneath the lemons. Consequently, their final site of mummification was not established. C perminutus adults provided with nectar or honey survived longer (about 5 days) in the field than those without food (about a day). Nectar from two plant species, Alpinia zerumbet and Datura candida, proved to be good sources of food for the adult wasps, and were comparable in quality to honey. The low level of parasitism achieved by C perminutus in southeast Queensland citrus thus appears to be a consequence of the short adult life and the negative effects of a harsh environment. Provision of a suitable food source (e.g., nectar) may well enhance levels of parasitism in the field. (c) 2005 Elsevier Inc. All rights reserved.

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An inverse methodology for the design of biologically loaded radio-frequency (RF) coils for magnetic resonance imaging applications is described. Free space time-harmonic electromagnetic Green's functions and de-emphasized B-1 target fields are used to calculate the current density on the coil cylinder. In theory, with the B-1 field de-emphasized in the middle of the RF transverse plane, the calculated current distribution can generate an internal magnetic field that can reduce the central overemphasis effect caused by field/tissue interactions at high frequencies. The current distribution of a head coil operating at 4 T (170 MHz) is calculated using an inverse methodology with de-emphasized B-1. target fields. An in-house finite-difference time-domain routine is employed to evaluate B-1 field and signal intensity inside a homogenous cylindrical phantom and then a complete human head model. A comparison with a conventional RF birdcage coil is carried out and demonstrates that this method can help in decreasing the normal bright region caused by field/tissue interactions in head images at 170 MHz and higher field strengths.

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Radio-frequency ( RF) coils are designed such that they induce homogeneous magnetic fields within some region of interest within a magnetic resonance imaging ( MRI) scanner. Loading the scanner with a patient disrupts the homogeneity of these fields and can lead to a considerable degradation of the quality of the acquired image. In this paper, an inverse method is presented for designing RF coils, in which the presence of a load ( patient) within the MRI scanner is accounted for in the model. To approximate the finite length of the coil, a Fourier series expansion is considered for the coil current density and for the induced fields. Regularization is used to solve this ill-conditioned inverse problem for the unknown Fourier coefficients. That is, the error between the induced and homogeneous target fields is minimized along with an additional constraint, chosen in this paper to represent the curvature of the coil windings. Smooth winding patterns are obtained for both unloaded and loaded coils. RF fields with a high level of homogeneity are obtained in the unloaded case and a limit to the level of homogeneity attainable is observed in the loaded case.

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Aims: Identification of a gene for self-protection from the antibiotic-producing plant pathogen Xanthomonas albilineans, and functional testing by heterologous expression. Methods and Results: Albicidin antibiotics and phytotoxins are potent inhibitors of prokaryote DNA replication. A resistance gene (albF) isolated by shotgun cloning from the X. albilineans albicidin-biosynthesis region encodes a protein with typical features of DHA14 drug efflux pumps. Low-level expression of albF in Escherichia coli increased the MIC of albicidin 3000-fold, without affecting tsx-mediated albicidin uptake into the periplasm or resistance to other tested antibiotics. Bioinformatic analysis indicates more similarity to proteins involved in self-protection in polyketide-antibiotic-producing actinomycetes than to multi-drug resistance pumps in other Gram-negative bacteria. A complex promoter region may co-regulate albF with genes for hydrolases likely to be involved in albicidin activation or self-protection. Conclusions: AlbF is the first apparent single-component antibiotic-specific efflux pump from a Gram-negative antibiotic producer. It shows extraordinary efficiency as measured by resistance level conferred upon heterologous expression. Significance and Impact of the Study: Development of the clinical potential of albicidins as potent bactericidial antibiotics against diverse bacteria has been limited because of low yields in culture. Expression of albF with recently described albicidin-biosynthesis genes may enable large-scale production. Because albicidins are X. albilineans pathogenicity factors, interference with AlbF function is also an opportunity for control of the associated plant disease.

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Amine functionalities were introduced onto the surface of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) films by applying radio frequency ammonia plasma treatment and wet ethylenediamine treatment. The modified surfaces were characterized by X-ray photoelectron spectroscopy (XPS) for chemical composition and Raman microspectroscopy for the spatial distribution of the chemical moieties. The relative amount of amine functionalities introduced onto the PHBV surface was determined by exposing the treated films to the vapor of trifluoromethylbenzaldehyde (TFBA) prior to XPS analysis. The highest amount of amino groups on the PHBV surface could be introduced by use of ammonia plasma at short treatment times of 5 and 10 s, but no effect of plasma power within the range of 2.5-20 W was observed. Ethylenediamine treatment yielded fewer surface amino groups, and in addition an increase in crystallinity as well as degradation of PHBV was evident from Fourier transform infrared spectroscopy. Raman maps showed that the coverage of amino groups on the PHBV surfaces was patchy with large areas having no amine functionalities.

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Study Design. A comparative study of trunk and hip extensor muscle recruitment patterns in 2 subject groups. Objective. To examine for changes in recruitment of the hip and back extensor muscles during low level isometric trunk rotation efforts in chronic low back pain (CLBP) subjects by comparison with matched asymptomatic control subjects. Summary of Background Data. Anatomic and biomechanical models have provided evidence that muscles attaching to the thoracolumbar fascia (TLF) are important for providing stabilization to the lumbopelvic region during trunk rotation. This has guided rehabilitation programs. The muscles that link diagonally to the posterior layer of the TLF have not previously been examined individually and compared during low-level trunk rotation efforts in CLBP patients and matched controls. Methods. Thirty CLBP patients and 30 matched controls were assessed using surface electromyography (EMG) as they performed low-level isometric rotation efforts while standing upright. Muscles studied included latissimus dorsi, erector spinae, upper and lower gluteus maximus, and biceps femoris. Subjects performed the rotation exertion with various levels of external trunk support, related to different functional tasks. Results. EMG results demonstrated that subjects with CLBP had significantly higher levels of recruitment for the lower and upper gluteus maximus (P < 0.05), hamstrings (P < 0.05), and erector spinae muscles (P < 0.05) during rotation to the left compared with the control subjects. Conclusion. This study provided evidence of increased muscle recruitment in CLBP patients when performing a standardized trunk rotation task. These results may have implications for the design of therapeutic exercise programs for CLBP patients.

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An inverse methodology to assist in the design of radio-frequency (RF) head coils for high field MRI application is described in this work. Free space time-harmonic electromagnetic Green's functions and preemphasized B1 field are used to calculate the current density on the coil cylinder. With B1 field preemphasized and lowered in the middle of the RF transverse plane, the calculated current distribution can generate an internal magnetic field that can reduce the EM field/tissue interactions at high frequencies. The current distribution of a head coil operating at 4 T is calculated using inverse methodology with preemphasized B1 fields. FDTD is employed to calculate B1 field and signal intensity inside a homogenous cylindrical phantom and human head. A comparison with conventional RF birdcage coil is reported here and demonstrated that inverse-method designed coil with preemphasized B1 field can help in decreasing the notorious bright region caused by EM field/tissue interactions in the human head images at 4 T.