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PubMed2002

Pre- and postsynaptic responses to 1-(1-naphthylpiperazine) following adaptation to stress in rats.

In view of a role of pre- and postsynaptic serotonin (5-hydroxytryptamine; 5-HT) receptors in adaptation to stress, effects of 1-(1-naphthylpiperazine) (1-NP) were compared in unrestrained and repeatedly restrained adapted rats. In the first part of the study, effects of various doses (1.0-15 mg/kg ip) of 1-NP were monitored on brain 5-HT metabolism (presynaptic response) and on the activity (postsynaptic response) of rats in an activity cage to which the rats were habituated before the drug administration. The drug injected at doses of 2.5-15.0 mg/kg increased motor activity and decreased brain 5-hydroxyindoleacetic acid (5-HIAA) concentration in a dose-dependent manner. In the second part of the study, rats were restrained on wire grids 2 h/day for 5 days. First-day episode of 2-h restraint decreased 24-h cumulative food intake, water intake and growth rate. The decreases attenuated following second-, third- and fourth-day episodes of 2-h restraint were not observed following fifth-day episode of 2-h restraint stress, suggesting adaptation to the stress schedule has occurred. Serotonergic and motor responses to 1-NP in unrestrained and repeatedly restrained adapted rats were compared by injecting the drug at a dose of 5 mg/kg, a dose that above results suggested would not produce maximal effects on 5-HT metabolism or motor activity. Administration of 1-NP at a dose of 5 mg/kg increased motor activity and decreased brain 5-HIAA concentration in unrestrained and repeatedly restrained adapted rats. Increases of motor activity were much greater in repeatedly restrained adapted than unrestrained rats. Decreases of 5-HIAA concentration were comparable in the two groups. The results are discussed in the context of an increase in the effectiveness of postsynaptic 5-HT-1A and 5-HT-1B receptors and a decrease in the effectiveness of presynaptic 5-HT-1A (somatodendritic) and 5-HT-1B (terminal) receptors following adaptation to stress. It is suggested that these changes of receptor responsiveness might help coping with stress demand to produce adaptation to stress.

Animals↗
PubMed1998

Voluntary and involuntary adaptation of gait in Parkinson's disease.

Voluntary and involuntary adaptation of gait in Parkinson's disease (PD) were studied in two separate experiments. In the first experiment, effects of changes in voluntary control were studied by asking PD patients and age-matched healthy subjects to adapt their walking pattern to visual cues resulting in spatial constraints, and auditory cues resulting in temporal constraints on stepping movements. In the second experiment, the adaptation to increases in speed during overground and treadmill walking was studied. Most patients were able to adapt their walking patterns in accordance with instructions. Notwithstanding consistent differences in step length, the adaptation to different conditions under study was highly similar in PD patients and healthy subjects. Only during walking with visually guided step length were the observed adaptations in PD patients less consistent. Contrary to these dissimilarities, the involuntary adaptation of timing of support and swing phases within the stride cycle was very similar between groups. In all conditions, only with changes in step length could a change in relative timing be observed. Our findings show that voluntary adaptation of gait is possible in PD and that basic involuntary coordination mechanisms are preserved. The observed disturbances in stride length regulation probably reflect an inability to perform fast movements in PD. Copyright 1998 Elsevier Science B.V.

Journal Article↗
PubMed1998

A model of equivalence in the cultural adaptation of HRQoL instruments: the universalist approach.

The health-related quality of life (HRQoL) literature presents a confused picture of what 'equivalence' in the cross-cultural use of HRQoL questionnaires means and how it can be assessed. Much of this confusion can be attributed to the 'absolutist' approach to the cross-cultural adaptation of HRQoL questionnaires. The purpose of this paper is to provide a model of equivalence from a universalist perspective and to link this to the translation and adaptation of HRQoL questionnaires. The model evolved from reviews of the HRQoL and other literatures, interviews and discussions with researchers working in HRQoL and related areas and practical experience in the adaptation and development of HRQoL instruments. The model incorporates six key types of equivalence. For each type of equivalence the paper provides a definition, proposes various strategies for examining whether and how types of equivalence can be achieved, illustrates the relationships between them and suggests the order in which they should be tested. The principal conclusions are: (1) that a universalist approach to the cross-cultural adaptation of HRQoL instruments requires that six types of equivalence be taken into account; (2) that these are sufficient to describe and explain the nature of the cross-cultural adaptation process; (3) that this approach requires careful qualitative research in target cultures, particularly in the assessment of conceptual equivalence; and (4) that this qualitative work will provide information which will be fundamental in deciding whether to adapt an existing instrument and which instrument to adapt. It should also result in a more sensitive adaptation of existing instruments and provide valuable information for interpreting the results obtained using HRQoL instruments in the target culture.

Algorithms↗
PubMed1998

Activation of genes for spasmolytic peptide, transforming growth factor alpha and for cyclooxygenase (COX)-1 and COX-2 during gastric adaptation to aspirin damage in rats.

BACKGROUND: NSAIDs, such as aspirin (ASA), cause widespread mucosal damage, but repeated ASA insults appear to induce mucosal tolerance (adaptation) to this injury. The mechanism of the gastric adaptation to the damage induced by ASA has not been fully explained. AIM: To determine the role of the mucosal gene expression for spasmolitic peptide (SP) (a member of trefoil peptides) and transforming growth factor alpha (TGF alpha) as well as for cyclooxygenase (COX)-1 and COX-2 during gastric adaptation to ASA in rats. METHODS: Gastric lesions were produced by ASA (100 mg/kg in 1.5 mL of 0.2 M HCl) applied intragastrically (i.g.) as a single dose. every day for 5 days. Control rats were given 1.5 mL of vehicle (0.2 M HCl i.g.) as a single dose, during 5 consecutive days. Gastric blood flow (GBF) was measured by H2-gas clearance technique and gastric mucosal specimens were taken for the assessment of cell proliferation rate in gastric mucosa by bromodeoxyuridine (BrdU) uptake, mucosal generation of prostaglandin E2 measured by radioimmunoassay, and for expression of SP, TGF alpha COX-1 and COX-2 mRNA as determined by RT-PCR. To quantify the relative amounts of mRNA for SP and TGF alpha, southern blotting analysis of the PCR products was performed and the intensity of PCR products was compared with that of beta-actin used as a standard. RESULTS: ASA applied once produced numerous gastric erosions, but with repeated ASA doses the adaptation to this NSAID developed, the area of gastric lesions being reduced by 86% after six consecutive ASA insults. This adaptation to ASA was accompanied by approximately a 90% reduction in prostaglandin E2 biosynthesis, by a significant rise in BrdU uptake by glandular cells predominantly in the neck region of gastric glands and by expression of SP (SP/beta-actin ratio; 0.96 +/- 0.08 in ASA-adapted mucosa vs. 0.38 +/- 0.05 in the control mucosa) and TGF alpha (TGF alpha/beta-actin ratio: 0.97 +/- 0.07 in ASA-adapted mucosa vs. 0.77 +/- 0.06 in the control mucosa). COX-1 expression was detected in vehicle-control gastric mucosa and after single exposure to ASA or after six consecutive ASA insults, while COX-2 mRNA was not detected in vehicle-control gastric mucosa, but appeared after single ASA insult and was sustained after subsequent ASA doses. CONCLUSIONS: (i) Gastric adaptation to aspirin injury involves enhanced cell proliferation which appears to be mediated by increased expression of SP and TGF alpha, and (ii) rapid upregulation of COX-2 expression following single and repeated ASA insults may represent a compensatory response to suppression of prostaglandin generation by this NSAID.

Animals↗
PubMed1999

Statistical analysis of adaptive response in sister chromatid exchanges in human lymphocytes after treatment with very low and extremely low doses of N-methyl-N'-nitro-N-nitrosoguanidine using a study design to control variability.

Previous studies have been interpreted as suggesting that low concentrations of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) have an adaptive effect in the cultured lymphocytes of responsive donors (that is, the cells are protected against the mutagenic effects of a subsequent challenge with a higher concentration of MNNG). The objectives of the present study were to investigate, under stringent experimental conditions, whether a protective effect exists at very low and extremely low doses of MNNG (10(-8) and 10(-24) M, respectively). Peripheral blood lymphocytes from a donor considered responsive in a previous study were stimulated to divide and were cultured under standard conditions. Pre-adaptive treatments with dilutions of MNNG were added to the cultures repeatedly before a challenge treatment with MNNG. Bromodeoxyuridine was added at the same time as the challenge treatment and, following mitotic arrest, cells were differentially stained so that the number of sister chromatid exchanges (SCEs) could be counted. The study was designed to address potential criticisms of earlier studies which did not include replicate cultures. Samples of blood were divided into two identical batches for independent processing. Five replicate cultures were prepared for each combination of pre-adaptive and challenge treatments in each batch. The complete experiment was repeated to provide a further test of the consistency of results. Five replicates per treatment combination were chosen in an attempt to provide an experiment of adequate statistical power. Considerable precautions were taken to minimise the effect of factors outside experimental control on the results. Scoring was done by three scorers. In order to minimise inter-scorer variation, 240 cells were scored at each treatment observation (five cells per-scorer, three scorers per culture, four cultures per batch, two batches per experiment and two experiments). The study was designed in this way to take account of the sources of variability to ensure that any response obtained would exceed that obtainable by experimental variability alone. A high level of quality assurance monitoring was undertaken throughout the investigation. Two measures of SCE induction were used: (i) the mean frequency of SCEs; (iii) proportion of cells with at least 20 SCEs. In both experiments, the challenge concentration of MNNG significantly increased SCE frequency. There were, however, highly significant differences between the two experiments. The proportion of high frequency cells (HFCs) in Experiment 1 was increased significantly; the proportion of HFCs was also increased in Experiment 2, but the increase was not statistically significant. The pre-adaptive concentrations of MNNG included an extremely low dilution of 6.8 x 10(-24) M and a very low dilution of 6.8 x 10(-8) M in Experiment 1 and 1.4 x 10(-7) M in Experiment 2. The various pre-adaptive concentrations used had no consistent protective effect against the SCE-inducing capacity of the challenge concentration of MNNG of 6.8 x 10(-6) M. It is concluded that an adaptive response to the alkylating agent MNNG could not be demonstrated in cultured human lymphocytes. Neither a very low nor an extremely low dilution of MNNG elicited an adaptive response in terms of SCE induction (measured either as SCE frequency or as proportion of HFCs). This is in contradiction to previous reports published by us and other groups. This study was carefully designed with large numbers of replicates, a preliminary statistical power calculation, predefined comparisons and extensive quality assurance at each treatment administration. Despite these precautions the variability between scorers and between batches was much larger than anticipated. This resulted in some statistically significant differences, but these are likely to be false positives. Our findings indicate the need for such methodological refinement in human cell adaptive response studies.

Carcinogens↗
PubMed1993

Adenine nucleoside diphosphates block adaptation of mechanoelectrical transduction in hair cells.

By adapting to sustained stimuli, hair cells in the internal ear retain their sensitivity to minute transient displacements. Because one model for adaptation asserts that this process is mediated by a myosin isozyme, we reasoned that we should be able to arrest adaptation by interfering with myosin's ATPase cycle though introduction of ADP into hair cells. During tight-seal, whole-cell recordings of transduction currents in cells isolated from bullfrog (Rana catesbeiana) sacculus, dialysis with 5-25 mM ADP gave variable results. In half of the cells examined, the rate of adaptation remained unchanged or even increased; adaptation was blocked in the remaining cells. Because we suspected that the variable effect of ADP resulted from the conversion of ADP to ATP by adenylate kinase, we employed the ADP analog adenosine 5'-[beta-thio]diphosphate (ADP[beta S]), which is not a substrate for adenylate kinase. Adaptation consistently disappeared in the presence of 1-10 mM ADP[beta S]; in addition, the transduction channels' open probability at rest grew from approximately 0.1 to 0.8 or more. Both effects could be reversed by 2 mM ATP. When used in conjunction with the adenylate kinase inhibitor P1,P5-bis(5'-adenosyl) pentaphosphate (Ap5A), ADP had effects similar to those of ADP[beta S]. These results suggest that adaptation by hair cells involves adenine nucleotides, and they lend support to the hypothesis that the adaptation process is powered by a myosin motor.

Adenosine Diphosphate↗
PubMed2003

An adaptive metabolic demand model for protein and amino acid requirements.

The shortcomings of the metabolic implications of the current protein requirements model are reviewed, and an alternative model, validated with [1-(13)C]leucine balance results in human adults, is presented and evaluated in the context of defining protein requirements. The model identifies metabolic demands for amino acids as comprising a small fixed component and a variable adaptive component that is relatively insensitive to acute food or protein intake, but which changes slowly with a sustained change in intake, enabling N equilibrium to be achieved. The model accounts for the apparent low efficiency of utilisation of animal proteins in N balance studies and enables more realistic efficiency values to be measured within an experimental framework that takes account of the adaptive metabolic demand. However, the complex relationship between the adaptive metabolic demand and habitual level and quality of protein intake prevents prediction of protein quality by amino acid scoring, which can markedly underestimate actual values. In contrast to the current model, for fully adapted individuals risk of deficiency (i.e. negative N balance after complete adaptation) will only start to increase when intakes fall below the range of the true minimum requirements, i.e. a value that is currently unknown, but likely to be between 0.40 and 0.50 g/kg per d at the lower end of the reported distribution of requirements. At intakes greater than this with additional metabolic demands varying directly with intake, deficiency is only likely as a short-term response to a change to a lower intake within the adaptive range. Thus, for adults satisfying energy needs on most mixed human diets, intakes will be within the adaptive range, and N equilibrium ceases to be a useful indicator of nutritional adequacy of protein. In the context of prescriptive dietary guidelines it may be expedient to retain current values until the benefits (and any risks) of protein intakes within the adaptive range can be quantified. However, from a diagnostic perspective, indicators other than N balance need to be identified, since maintenance of N balance can no longer be used as a surrogate of adequate protein-related health.

Adult↗
PubMed1985

Physiological characterization of adaptive clones in evolving populations of the yeast, Saccharomyces cerevisiae.

Populations of a diploid strain of S. cerevisiae were grown in glucose-limited continuous culture for more than 260 generations. A series of seven sequential adaptive changes were identified by monitoring the frequency of cycloheximide resistance in these populations. Samples were taken from the continuous cultures following each adaptive shift and characterized physiologically to determine (1) the range of phenotypes that can be selected in a precisely defined constant environment and (2) the order and predictability of the occurrence of the adaptive mutations in evolving populations. The clones were characterized with respect to the growth parameters, maximum growth rate, saturation coefficient and yield, as well as for changes in cell size and geometry and rate of glucose uptake. The maximum growth rates of the seven adaptive clones were very similar, but in contrast the saturation coefficients differed substantially. Surprisingly, not all clones showed reductions in the saturation coefficients, in comparison to the immediately preceding clones, as would be predicted from classical continuous culture kinetics. In addition, yield estimates first increased and then decreased for later isolated adaptive clones. In general, the results suggest epistatic interactions between the adaptive clones, consistent with earlier published results. The rate of glucose uptake, as measured by 14C-xylose uptake, increased dramatically after the selection and fixation of seven adaptive clones. Progressive decreases in cell volume and changes in cell geometry, resulting in increased surface area to volume ratios, were also observed in the adaptive clones, but these changes were not always seen in other haploid and diploid yeast populations evolving under the same conditions. Such changes may be easily explainable in terms of the characteristics of the glucose-limited environment. The significance of the results to the evolution of microorganisms under nutrient-limiting conditions is discussed.

Biological Transport↗
PubMed2002

Adaptation of cerebral circulation to brain arteriovenous malformations increases feeding artery pressure and decreases regional hypotension.

PURPOSE: To determine how the adaptation of extranidal cerebral vessels affects feeding artery pressure, draining vein pressure, and regional hypotension due to the presence of brain arteriovenous malformations (BAVMs). CONCEPT: BAVMs cause high flows in feeding arteries and draining veins and can induce profound hypotension in the neighboring vasculature. Despite the large difference in flow, endothelial shear stress (tau) observed in vessels ipsilateral to the BAVM is similar to tau in vessels contralateral to the BAVM, suggesting that the conductance vessels successfully adapt to keep tau constant. However, because BAVMs are discovered only after they are well developed, the natural history of the adaptation process in extranidal vessels is unknown. RATIONALE: Currently, no way exists to determine experimentally the effects of adaptation of extranidal vessels in human patients. Therefore, a mathematical model of the cerebral vasculature is used to study adaptation in response to BAVMs. By comparing pressures and flows calculated before and after adaptation, the effect of adaptation of the conductance vessels on regional hemodynamics can be evaluated. DISCUSSION: Structural adaptation of the extranidal circulation seems not only to reset tau, but also to ameliorate regional hypotension induced by BAVMs. However, this compensatory mechanism also increases feeding artery pressure and thus may increase the risk of hemorrhagic stroke.

Blood Flow Velocity↗
PubMed2005

Speech recognition and comfort using hearing instruments with adaptive directional characteristics in asymmetric listening conditions.

OBJECTIVE: Hearing instruments with adaptive directional microphone systems attempt to maximize speech-to-noise ratio (SNR) and thereby improve speech recognition in noisy backgrounds. When instruments with adaptive systems are fitted bilaterally, there is the potential for adverse effects as they operate independently and may give confusing cues or disturbing effects. The present study compared speech recognition performance in 16 listeners fitted bilaterally with the Phonak Claro hearing instrument using omni-directional, fixed directional, and adaptive directional microphone settings as well as mixed microphone settings (an omni-directional microphone on one side and an adaptive directional microphone on the other). DESIGN: Under anechoic conditions, speech was always presented from a loudspeaker directly in front of the listener (0 degree azimuth) whereas noise was presented from one or two loudspeakers arranged either symmetrically (0, 180, 90 + 270 degrees) or asymmetrically (170 + 240 degrees and 120 + 190 degrees) in the horizontal plane. Adaptive sentence recognition in noise measurement was supplemented by quality ratings. RESULTS: With symmetrical omni-directional settings (Omni/Omni), performance was poorer than a control group of 14 listeners with normal hearing tested unaided: Aided listeners required 4.3 dB more favorable SNR for criterion performance. In all loudspeaker arrangements in which directional characteristics could be exploited, performance with symmetrical adaptive microphones (Adapt/Adapt) was similar to the control group. The mixed microphone settings did not appear to confer any particular disadvantage for speech recognition from their asymmetric nature, always giving scores significantly better than Omni/Omni. Quality rating scores were consistent with speech recognition performance, showing benefits in terms of clarity and comfort for the Adapt/Adapt and Fixed/Fixed microphone conditions over the Omni/Omni and mixed microphone conditions wherever directional characteristics could be used. Similarly, the mixed microphone conditions were rated more comfortable and quieter for the noise than Omni/Omni. CONCLUSIONS: It is concluded that bilateral hearing instruments with adaptive directional microphones confer benefits in terms of speech recognition in noise and sound quality. Independence of the two adaptive control systems does not appear to cause untoward effects.

Aged↗
PubMed1985

Proteins Associated with Adaptation of Cultured Tobacco Cells to NaCl.

Cultured tobacco cells (Nicotiana tabacum L. cv Wisconsin 38) adapted to grow in medium containing high levels of NaCl or polyethylene glycol (PEG) produce several new or enhanced polypeptide bands on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The intensities of some of the polypeptide bands (molecular weights of 58, 37, 35.5, 34, 26, 21, 19.5, and 18 kilodaltons) increase with increasing levels of NaCl adaptation, while the intensities of other polypeptide bands (54, 52, 17.5, and 16.5 kilodaltons) are reduced. Enhanced levels of 43- and 26-kilodalton polypeptides are present in both NaCl and PEG-induced water stress adapted cells but are not detectable in unadapted cells. In addition, PEG adapted cells have enhanced levels of 29-, 17.5-, 16.5-, and 11-kilodalton polypeptides and reduced levels of 58-, 54-, 52-, 37-, 35.5-, 34-, 21-, 19.5-, and 18-kilodalton polypeptide bands.Synthesis of 26-kilodalton polypeptide(s) occurs at two different periods during culture growth of NaCl adapted cells. Unadapted cells also incorporate (35)S into a 26-kilodalton polypeptide during the later stage of culture growth beginning at midlog phase. The 26-kilodalton polypeptides from adapted and unadapted cells have similar partial proteolysis peptide maps and are immunologically cross-reactive. During adaptation to NaCl, unadapted cells synthesize and accumulate a major 26-kilodalton polypeptide, and the beginning of synthesis corresponds to the period of osmotic adjustment and culture growth. From our results, we suggest an involvement of the 26-kilodalton polypeptide in the adaptation of cultured tobacco cells to NaCl and water stress.

Journal Article↗
PubMed1989

Cell Walls of Tobacco Cells and Changes in Composition Associated with Reduced Growth upon Adaptation to Water and Saline Stress.

The relative mass of the cell walls of tobacco (Nicotiana tabacum L.) cells adapted to grow in medium containing 30% polyethylene glycol 8000 or 428 millimolar NaCl was reduced to about 50% of that of the walls of unadapted cells. Cellulose synthesis was inhibited substantially in adapted cells. The proportions of total pectin in walls of unadapted and adapted cells were about the same, but substantial amount of uronic acid-rich material from walls of cells adapted to either NaCl or polyethylene glycol was more easily extracted with cold sodium ethylenediamine tetraacetic acid solutions (NM Iraki et al. [1989] Plant Physiol. 91: 39-47). We examined the linkage composition of the pectic and hemicellulosic polysaccharides to ascertain chemical factors that may explain this difference in physical behavior. Adaptation to stress resulted in the formation of a loosely bound shell of polygalacturonic acid and rhamnogalacturonan. Pectins extracted from walls of adapted cells by either cold sodium ethylenediamine tetraacetic acid or hot ammonium oxalate were particularly enriched in rhamnose. Compared to pectins of unadapted cells, rhamnosyl units of the rhamnogalacturonans of adapted cells were more highly substituted with polymers containing arabinose and galactose, but the side groups were of greatly reduced molecular size. Possible functional roles of these modifications in cell wall metabolism related to adaptation to osmotic stress are discussed.

Journal Article↗
PubMed1989

Extracellular polysaccharides and proteins of tobacco cell cultures and changes in composition associated with growth-limiting adaptation to water and saline stress.

The chemical composition of extracellular polymers released by cells of tobacco (Nicotiana tabacum L. cv W38) adapted to a medium containing 30% polyethylene glycol 8000 (-28 bar) or 428 millimolar NaCl (-23 bar) was compared to the composition of those released by unadapted cells. Unadapted cells released uronic acid-rich material of high molecular weight, arabinogalactan-proteins, low molecular weight fragments of hemicellulosic polysaccharides, and a small amount of protein. Cells adapted to grow in medium containing NaCl released arabinogalactan and large amounts of protein but not the uronic acid-rich material, and cells adapted to grow in polyethylene glycol released only small amounts of an arabinogalactan of much lower molecular weight and some protein. Secretion of all material was nearly blocked by polyethylene glycol, but when cells were transferred to a medium containing iso-osmolar mannitol, they again released extracellular polymers at rates similar to those of unadapted cells. Like cells adapted to NaCl, however, these cells released arabinogalactan and large amounts of protein but only small amounts of the uronic acid-rich material. Media of NaCl-adapted cells were enriched in 40, 29, and 11 kilodalton polypeptides. CaCl(2) extracted the 40 and 11 kilodalton polypeptides from walls of unadapted cells, but the 29 kilodalton polypeptide was found only in the medium of the NaCl-adapted cells. Accumulation of low molecular weight polysaccharide fragments in the medium was also substantially reduced in both NaCl- and polyethylene glycol-adapted cells, and specifically, the material was composed of lower proportions of xyloglucan fragments. Our results indicate that adaptation to saline or water stress results in inhibition of both the hydrolysis of hemicellulosic xyloglucan and release of uronic acid-rich material into the culture medium.

Journal Article↗
PubMed1996

Experimental investigation of an adaptive feedback algorithm for hot spot reduction in radio-frequency phased-array hyperthermia.

A computer-controlled adaptive phased array radiofrequency hyperthermia system for improved therapeutic tumor heating is experimentally investigated. Adaptive array feedback techniques are used to modify the electric-field in hyperthermia experiments with a homogeneous saline phantom target. A hyperthermia phased-array antenna system has been modified to implement adaptive nulling and adaptive focusing algorithms. The hyperthermia system is a ring phased-array antenna applicator with four independently controlled RF transmitter channels operating at a CW frequency of 100 MHz. The hyperthermia phased array is made adaptive by software modifications which invoke a gradient-search feedback algorithm that controls the amplitude and phase of each transmitter channel. The gradient-search algorithm implements the method of steepest descent for adaptive nulling (power minimization) and the method of steepest ascent for adaptive focusing (power maximization). The feedback signals are measured by electric-field short-dipole probe antennas. The measured data indicate that with an adaptive hyperthermia array it may be possible to maximize the applied electric field at a tumor position in a complex scattering target body and simultaneously minimize or reduce the electric field at target positions where undesired high-temperature regions (hot spots) occur.

Algorithms↗
PubMed2004

Adaptive two-pass rank order filter to remove impulse noise in highly corrupted images.

In this paper, we present an adaptive two-pass rank order filter to remove impulse noise in highly corrupted images. When the noise ratio is high, rank order filters, such as the median filter for example, can produce unsatisfactory results. Better results can be obtained by applying the filter twice, which we call two-pass filtering. To further improve the performance, we develop an adaptive two-pass rank order filter. Between the passes of filtering, an adaptive process is used to detect irregularities in the spatial distribution of the estimated impulse noise. The adaptive process then selectively replaces some pixels changed by the first pass of filtering with their original observed pixel values. These pixels are then kept unchanged during the second filtering. In combination, the adaptive process and the second filter eliminate more impulse noise and restore some pixels that are mistakenly altered by the first filtering. As a final result, the reconstructed image maintains a higher degree of fidelity and has a smaller amount of noise. The idea of adaptive two-pass processing can be applied to many rank order filters, such as a center-weighted median filter (CWMF), adaptive CWMF, lower-upper-middle filter, and soft-decision rank-order-mean filter. Results from computer simulations are used to demonstrate the performance of this type of adaptation using a number of basic rank order filters.

Algorithms↗
PubMed2005

Neural and fuzzy computation techniques for playout delay adaptation in VoIP networks.

Playout delay adaptation algorithms are often used in real time voice communication over packet-switched networks to counteract the effects of network jitter at the receiver. Whilst the conventional algorithms developed for silence-suppressed speech transmission focused on preserving the relative temporal structure of speech frames/packets within a talkspurt (intertalkspurt adaptation), more recently developed algorithms strive to achieve better quality by allowing for playout delay adaptation within a talkspurt (intratalkspurt adaptation). The adaptation algorithms, both intertalkspurt and intratalkspurt based, rely on short term estimations of the characteristics of network delay that would be experienced by up-coming voice packets. The use of novel neural networks and fuzzy systems as estimators of network delay characteristics are presented in this paper. Their performance is analyzed in comparison with a number of traditional techniques for both inter and intratalkspurt adaptation paradigms. The design of a novel fuzzy trend analyzer system (FTAS) for network delay trend analysis and its usage in intratalkspurt playout delay adaptation are presented in greater detail. The performance of the proposed mechanism is analyzed based on measured Internet delays. Index Terms-Fuzzy delay trend analysis, intertalkspurt, intratalkspurt, multilayer perceptrons (MLPs), network delay estimation, playout buffering, playout delay adaptation, time delay neural networks (TDNNs), voice over Internet protocol (VoIP).

Algorithms↗
PubMed2000

Physiological adaptation to low temperatures of strains of Rhizobium leguminosarum bv. viciae associated with Lathyrus spp.(1).

Strains of Rhizobium leguminosarum bv. viciae, isolated from the legume species Lathyrus japonicus and Lathyrus pratensis in northern Quebec (Canada), showed different capacities for growing at low temperature. In the present study, we investigated some mechanisms related to cold adaptation. Two cold-adapted strains (psychrotrophs) were compared to a poorly adapted strain and to a cold-sensitive strain (reference strain) for freezing survival, protein induction and fatty acid composition under low temperature. Following cold shocks (25 degrees C to 10, 5 and 0 degrees C), a common 6.1-kDa CSP (cold shock protein) was induced in all strains, but the total number of CSPs synthesized at 0 degrees C was higher in cold-adapted strains than in the cold-sensitive strain. The synthesis of CAPs (cold acclimation proteins) was observed under continuous growth at 5 degrees C in all three strains capable of growth at this temperature. Levels of survival after 24 h at -80 degrees C where higher in cold- (79%) and poorly adapted (64%) strains than in the cold-sensitive strain (33%), but a 2-h acclimation period at 5 degrees C before freezing doubled the survival of the cold-sensitive strain. Low temperature conditions affected similarly the fatty acid composition of all strains, regardless of their cold adaptation level. The proportion of unsaturated fatty acids increased significantly with the lowering of growth temperature from 25 to 5 degrees C, but showed a tendency to decrease after a cold shock from 25 to 5 degrees C. A specific unsaturated fatty acid, cis-12 octadecanoic acid, was produced during growth at 5 degrees C. The unsaturated cis-vaccenic acid was the principal component under all conditions. The cold adaptation trait was weakly reflected in symbiosis with the agronomic legume, Lathyrus sativus, with which one cold-adapted strain showed a slightly higher nitrogenase activity and shoot dry matter yield than a commercial strain under a sub-optimal temperature regime.

Journal Article↗
PubMed2002

The adaptation and resistance of Clostridium aminophilum F to the butyrivibriocin-like substance of Butyrivibrio fibrisolvens JL5 and monensin.

When the amino acid-fermenting bacterium Clostridium aminophilum F was inoculated into media containing 1 microM monensin or a bacteriocin-like inhibitory substance (BLIS) from Butyrivibrio fibrisolvens JL5, the cultures lagged and growth was not observed for more than 12 h. The monensin- and BLIS-treated cultures eventually grew rapidly and did not lag a second time. Because cross-resistance could not be demonstrated, it appeared that the adaptation was specific. Non-adapted cells that were incubated with monensin lost their ability to produce ammonia from amino acids, and ATP, intracellular potassium, and electrical potential (DeltaPsi) were lower than untreated cells. Monensin-adapted cells regained their ability to produce ammonia, and intracellular potassium and DeltaPsi increased, but ATP was still 40% lower than untreated cells. When non-adapted cells were treated with the BLIS, ammonia production did not decline. Non-adapted cells were agglutinated by lysozyme, but in each case, adapted cells were not agglutinated. Adapted cells had more cellular polysaccharide and bound less of either inhibitor. Based on these results, it appears that the adapted cells had altered cell wall characteristics that prevented the binding of either monensin or the B. fibrisolvens JL5 BLIS.

Adenosine Triphosphate↗