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PubMed2006

Adaptability and the integration of computer-based information processing into the dynamics of organizations.

The structure of a system influences its adaptability. An important result of adaptability theory is that subsystem independence increases adaptability [Conrad, M., 1983. Adaptability. Plenum Press, New York]. Adaptability is essential in systems that face an uncertain environment such as biological systems and organizations. Modern organizations are the product of human design. And so it is their structure and the effect that it has on their adaptability. In this paper we explore the potential effects of computer-based information processing on the adaptability of organizations. The integration of computer-based processes into the dynamics of the functions they support and the effect it has on subsystem independence are especially relevant to our analysis.

Electronic Data Processing↗
PubMed2006

Vibrotactile adaptation enhances spatial localization.

A two-interval forced choice tracking procedure was used to evaluate the effects of a pre-exposure to vibrotactile stimulation ("adaptation") on the capacity of human subjects to spatially localize a subsequent tactile stimulus. A 25 Hz flutter adapting stimulus was presented at a randomly selected position within a 20 mm linear array oriented transversely on the hand dorsum. Two flutter stimuli delivered subsequently were applied to different sites along the linear array; one to the same locus that received the adapting stimulation (the "standard" stimulus), the other to a distant site (the "test" stimulus). Following each trial, subjects were queried as to which of the two stimuli was delivered to the same skin site that received adapting stimulation. A correct response resulted in a reduced distance between the sites contacted by the standard and test stimuli in the following trial. Four subjects participated in 10 sessions each. A session consisted of two sets of 20 trials (one set at 0.5 s and another at 5 s adapting stimulus duration). For every subject, 5 s adaptation resulted in an approximately 2-fold improvement in spatial discrimination performance over that achieved following 0.5 s adaptation. It is proposed that the improved human vibrotactile spatial localization performance following 5 s of 25 Hz stimulation is due to enhanced spatial funneling of the global neuronal population response of primary somatosensory cortex (SI) that has been demonstrated to accompany increases in duration of 25 Hz flutter stimuli delivered to the skin.

Acclimatization↗
PubMed2005

A microcosm test of adaptation and species specific responses to polluted sediments applicable to indigenous chironomids (Diptera).

Chironomids may adapt to pollution stress but data are confined to species that can be reared in the laboratory. A microcosm approach was used to test for adaptation and species differences in heavy metal tolerance. In one experiment, microcosms containing different levels of contaminants were placed in polluted and reference locations. The response of Chironomus februarius to metal contaminants suggested local adaptation: relatively more flies emerged from clean sediment at the reference site and the reverse pattern occurred at the polluted site. However, maternal effects were not specifically ruled out. In another species, Kiefferulus intertinctus, there was no evidence for adaptation. In a second experiment, microcosms with different contaminant levels were placed at two polluted and two unpolluted sites. Species responded differently to contaminants, but there was no evidence for adaptation in the species where this could be tested. Adaptation to heavy metals may be uncommon and species specific, but more sensitive species need to be tested across a range of pollution levels. Factors influencing the likelihood of adaptation are briefly discussed.

Acclimatization↗
PubMed2005

Adaptations in interlimb and intralimb coordination to asymmetrical loading in human walking.

The purpose of this study was to examine both the intralimb (within a limb) and interlimb (between the right and left limbs) adaptations that occur in response to a unilaterally applied leg load as subjects walked at their preferred walking speed. It was hypothesized that this adaptation would alter interlimb coordination while intralimb coordination remained invariant. Subjects (n = 12) were required to walk on a treadmill at preferred walking speed. Bilateral 3-D kinematic data were collected while a load placed on the leg was increased. Gait adaptations to leg-loading were assessed through changes in coordination patterns between specific limb couplings. Continuous relative phase (CRP) was used to evaluate changes in limb coordination under each experimental load condition compared to a no load baseline condition. Both changes in magnitude of CRP (root-mean-square (RMS) analysis) as well as temporal changes in CRP across the stride cycle (cross-correlation) were assessed. Cross-Correlation values changed with load for all interlimb couplings assessed suggesting alterations in interlimb coordination across the stride cycle. CRP cross-correlation values were close to 1.0 in all the intralimb couplings examined, showing a relative invariance in intralimb coordination. Coordination changes in RMS were also observed for the interlimb couplings. RMS changes were also observed in the intralimb couplings on the loaded side. It appears that gait adaptations to a unilaterally applied leg load appear both at the intralimb and interlimb level. However, the majority of changes did appear at the interlimb level, where CRP as assessed through both cross-correlation and RMS measures changed. This study supports previous results that suggested a tighter coupling exists at the intralimb level, leaving the majority of gait adaptations to occur at the interlimb level. The observed adaptation in differences between interlimb and intralimb coordination may provide insight into gait adaptations in pathological gait.

Adult↗
PubMed2005

Adaptation of Chinese hamster ovary cells to low culture temperature: cell growth and recombinant protein production.

Recombinant Chinese hamster ovary (rCHO) cells producing erythropoietin (EPO) and rCHO cells producing follicle-stimulating hormone (FSH) showed a significant increase in specific productivity (q) when grown at 32 degrees C compared to 37 degrees C. However, low culture temperature suppressed cell growth, and therefore, did not increase volumetric productivity as much as q. In an attempt to increase the volumetric productivity through improvement of hypothermic growth, EPO producing rCHO (CHO-EPO) cells and FSH producing rCHO (CHO-FSH) cells were adapted at 32 degrees C in a repeated batch mode using spinner flasks. Cell growth of both CHO-EPO and CHO-FSH gradually improved during adaptation at 32 degrees C. Specific growth rates of CHO-EPO and CHO-FSH cells at 32 degrees C, through adaptation, were increased by 73% and 20%, respectively. During adaptation at 32 degrees C, mRNA levels of cold-inducible RNA-binding protein (CIRP) of both rCHO cell lines did not change significantly, suggesting that CIRP expression may not be the only cause for growth suppression at low culture temperature. Unlike cell growth, the recombinant protein production of both rCHO cell lines was not increased during adaptation due to decreased specific productivities. The specific EPO productivity and specific FSH productivity were decreased by 49% and 22%, respectively. Southern blot analyses showed that the decreased specific productivities were not due to the loss of foreign gene copies. Taken together, improvement of hypothermic cell growth by adaptation does not appear to be applicable for enhanced recombinant protein production, since specific productivity decreases during adaptation to the low culture temperature.

Acclimatization↗
PubMed2006

Adaptive mutations in Salmonella typhimurium phenotypic of purR super-repression.

Under non-lethal selective conditions, a non-dividing or very slowly dividing microbial population gives rise to mutations that relieve selective pressures. This process is described as adaptive mutation. Salmonella typhimurium strain 5-28 has been used as a system for studying adaptive mutations in the chromosomal regulatory gene purR and its target, the purD operator. When this strain is plated on a minimal lactose medium, no apparent growth of parent lawn is observed, yet the revertant colonies accumulate over a period of time. Analysis of the purR mutational spectra showed that the frequencies of transitions and transversions were not significantly different among the growth-dependent and adaptive mutations. But the frequencies for five kinds of -1 frameshifts were significantly different between the growth-dependent and adaptive types. Among the growth-dependent mutations, most one-base deletions occurred in non-iterated bases and were distributed randomly. Among adaptive mutations, the frequency of one-base deletions in small mononucleotide repeats was higher and mutations were concentrated at three hotspots. One-base deletion in small mononucleotide repeats are generally believed to result from DNA polymerase slippage errors, which are not corrected by DNA repair machinery. We further investigated the role of DNA repair on adaptive mutation. Our results showed that the mismatch repair (MMR) might function less efficiently during adaptive mutation. However, DNA oxidative damage repair seemed no less effective in correcting errors under selective pressures than during non-selective growth.

Bacterial Proteins↗
PubMed2005

Composite adaptive control with locally weighted statistical learning.

This paper introduces a probably stable learning adaptive control framework with statistical learning. The proposed algorithm employs nonlinear function approximation with automatic growth of the learning network according to the nonlinearities and the working domain of the control system. The unknown function in the dynamical system is approximated by piecewise linear models using a nonparametric regression technique. Local models are allocated as necessary and their parameters are optimized on-line. Inspired by composite adaptive control methods, the proposed learning adaptive control algorithm uses both the tracking error and the estimation error to update the parameters. We first discuss statistical learning of nonlinear functions, and motivate our choice of the locally weighted learning framework. Second, we begin with a class of first order SISO systems for theoretical development of our learning adaptive control framework, and present a stability proof including a parameter projection method that is needed to avoid potential singularities during adaptation. Then, we generalize our adaptive controller to higher order SISO systems, and discuss further extension to MIMO problems. Finally, we evaluate our theoretical control framework in numerical simulations to illustrate the effectiveness of the proposed learning adaptive controller for rapid convergence and high accuracy of control.

Algorithms↗
PubMed2000

A syringe adapter to facilitate aspiration at amniocentesis.

BACKGROUND: Syringes were developed for injection, not aspiration. We describe an adapter that attaches to a standard syringe and aspirates by advancement rather than withdrawal. TECHNIQUE: The adapter consists of a syringe barrel extension and an attachable finger grip. The adapter attached to a standard syringe allows aspiration by advancement rather than withdrawal, with the same hand motion used as with injection. EXPERIENCE: In a comparison of timed in vitro fluid aspiration by 10 practitioners, mean times for aspiration of 15 mL were 32.4 seconds (range 24-45) with standard technique and 25.3 seconds (range 24-30) with the adapted syringe (P < .003, paired t test). Thirteen of 14 physicians who used the adapted syringe in vivo reported that much less effort was required, and one physician reported that a little less effort was required. Overall, eight practitioners reported that the adapted syringe made amniocentesis much easier and six found no difference between the two devices. CONCLUSION: This adapter converts a standard syringe to one permitting aspiration by advancement rather than withdrawal. Practitioner feedback was positive with regard to ease of use, degree of effort, and overall satisfaction.

Amniocentesis↗
PubMed2003

Saccadic adaptation in the horizontal and vertical directions in normal subjects.

We studied the properties of adaptive gain control in the saccadic system and examined whether the adaptations in the horizontal direction transferred to those in the vertical direction, and vice versa, in 16 normal subjects. Eye movements were measured using search coil system. In the adaptive session, a target moved randomly in amplitude steps of 20 degrees or 30 degrees, with half of the subjects performing in the horizontal direction and the others in the vertical direction. The target eccentricity was changed by a constant percentage (70%) during each saccade aimed at the target. Gains were gradually decreased during the course of 120 repetitions, and then approached approximately 70%. Comparison was made of the accuracy (saccadic amplitude/first target step amplitude) of horizontal and vertical vectors of oblique saccades before and after the adaptation. After the horizontal adaptation, the accuracy of horizontal vectors decreased in the horizontal direction (P<0.05) but not in the vertical direction. After the vertical adaptation, however, the accuracy of horizontal and vertical vectors did not decrease. Our data show that adaptive gain control in the horizontal direction might not transfer to that in the vertical direction, nor vice versa.

Adult↗
PubMed2002

All-trans to 13-cis retinal isomerization in light-adapted bacteriorhodopsin at acidic pH.

The flash photolysis kinetic spectra of the intermediate M(412) of bacteriorhodopsin were monitored during the process of acid titration. In the light-adapted state, the maximum peak amplitude of M(412) absorbance of bacteriorhodopsin decreased (pK(a)=3.40+/-0.05) as the pH decreased from 7.3 to 1.9. In the dark-adapted state, the maximum peak amplitude of M(412) absorbance of bacteriorhodopsin increased as the pH decreased from 6.9 to 4.1, and then decreased (pK(a)=2.85+/-0.05) as the pH dropped to 2.1. These different trends in the change in the maximum peak amplitude suggested that not only the transition of purple membrane to blue membrane had taken place in both light and dark-adapted states, but also the fraction of all-trans-bR had changed during the acid titration. The pH-dependent absorption changes at 640 nm of bacteriorhodopsin in both light- and dark-adapted states were also observed. The pK(a)-values of the purple-to-blue transition were 3.80+/-0.05 in light-adapted state and 3.40+/-0.05 in dark-adapted state, respectively. According to Balashov's method, the fraction of all-trans-bR was assayed as the pH decreased. All these results indicated that the purple-to-blue transition of light-adapted bacteriorhodopsin was accompanied by an all-trans to 13-cis retinal isomerization at acidic pH.

Bacteriorhodopsins↗
PubMed2003

GABAergic inhibitory mechanisms for repetition-adaptivity in large-scale brain systems.

Molecular mechanisms for systems level adaptivity of brain activation are largely unknown but a key role for active inhibition by gamma-aminobutyric acid (GABA) is plausible. We used functional magnetic resonance imaging to contrast the modulatory effects on brain adaptivity to task repetition and task difficulty of two GABAergic drugs, lorazepam and flumazenil. In a working memory paradigm, occipitotemporal regions clearly demonstrated attenuation of activation as a function of within-session task repetition or practice in data acquired following placebo, but this spatiotemporal pattern of repetition adaptivity was abolished by both lorazepam and flumazenil. However, in other brain systems flumazenil enhanced repetition adaptivity compared to placebo: in frontal cortex, flumzenil induced attenuation of signal related to task repetition and in hippocampus it exaggerated normal enhancement of signal with repetition. In contrast, there were no significant effects of either flumazenil or lorazepam on areas of frontal cortex which normally demonstrated significant neurocognitive load response or adaptivity to task difficulty. We argue that repetition adaptivity of large-scale brain systems is regulated by GABAergic inhibitory mechanisms and that expression of repetition adaptivity in a given brain system may show an "inverted-U" form of relationship with pharmacologically manipulable levels of GABAergic inhibitory tone.

Adult↗
PubMed1997

Sensitivity of transvenous defibrillation models to adaptive mesh density and resolution: the potential for interactive solution times.

The voltage gradients induced in ventricular myocardium by an electric shock have been shown to correlate to the probability of the shock producing a successful defibrillation. Finite element modeling is one method for computing these voltage gradients, although the meshing of complex biomedical domains is difficult on a patient-specific basis. We recently described an adaptive algorithm that automates the generation of finite element meshes for complex 3-D domains from bitmapped images. This article examines the sensitivity of the computed distribution of ventricular voltage gradients to the resolution of the images and to the adapted density of the mesh. The results allow us to establish an adaptation stopping criterion and a minimum input image resolution for modeling transvenous defibrillation. The sensitivity to adapted mesh density was analyzed by comparing voltage gradient histograms from successively finer meshes to histograms from a uniform mesh at the maximum possible density. Comparisons were made using the Kolmogorov-Smirnov test with the number of samples required to detect a 5% difference in the histograms at the 0.05 significance level. Adaptation to a global current density error estimate of 5% or less was required in order to achieve acceptance of the null hypothesis that the distributions were the same in all cases. Defibrillation efficacy, however, is predicted from the voltage gradient in the first quartile, and the results suggest that this region of the cumulative histogram converges faster during mesh adaptation than the histogram as a whole. We also compared histograms from models generated from successively finer input images. The histogram of each model was compared with the histogram obtained from the finest possible resolution. In all cases, the null hypothesis of no difference was accepted at resolutions of 2.3 x 2.3 x 3.0 mm. The average time required to build and adapt models to a 5% accuracy at the first quartile at this resolution was 1.8 min. on a common workstation. We believe that this demonstrates a potential for the eventual synthesis of finite element computations into interactive electrode placement tools on a subject-specific basis.

Algorithms↗
PubMed2000

Asymmetric adaptive modeling of central tarsal bones in racing greyhounds.

Fatigue fracture of the cuboidal bones of the foot, especially the navicular tarsal bone, is common in athletes and dancers. The racing greyhound is a naturally occurring animal model of this injury because both microcracking and complete fracture occur in the right central (navicular) tarsal bone (CTB). The right limb is on the outside when racing in a counter-clockwise direction on circular tracks, and is subjected to asymmetric cyclic compressive loading. We wished to study in more detail adaptive modeling in the right CTB in racing greyhounds. We hypothesized that cyclic asymmetric loading of a cuboidal bone induced by racing on a circular track would induce site-specific bone adaptation. We also hypothesized that such an adaptive response would be attenuated in greyhounds that were retired from racing and no longer subjected to cyclic asymmetric loading. Central tarsal bones from racing greyhounds (racing group, n = 6) and retired greyhounds being used for breeding (nonracing group, n = 4) were examined using quantitative computed tomography (CT). Bone mineral density (BMD) was determined in a 3-mm diameter region-of-interest (ROI) in six contiguous 1-mm-thick sagittal CT slices of each CTB. Bones were subsequently examined histomorphometrically and percentage bone area (B.Ar./T.Ar., %) was determined in 10 ROI from dorsal to plantar in a transverse plane, mid-way between the proximal and distal articular surfaces. The BMD of the right CTB was greater than the left in all greyhounds (p < 0. 001). In comparing ipsilateral limbs between groups, BMD of the racing group was greater than the nonracing group for each side (p < 0.005). In sagittal plane histologic sections, bone in the dorsal region of the right CTB had undergone adaptive modeling, through thickening and compaction of trabeculae. B.Ar./T.Ar., % in the right CTB of the racing group was greater than in the contralateral CTB (p < 0.001), and the ipsilateral CTB of the nonracing group (p < 0.001). In the nonracing group, B.Ar./T.Ar., % in the right CTB was not significantly different from left CTB (p > 0.8; power = 80% at Delta = 48%). It was concluded that greyhounds racing on circular tracks develop site-specific bone adaptation with compaction of trabecular bone and increase in BMD in the right CTB in particular, the most common site for fatigue fracture. Our data also suggested that partial reversal of this adaptive process occurred in retired, nonracing greyhounds, after cessation of asymmetric cyclic loading at racing speed. Racing greyhounds provide a model in which to study fatigue fracture and adaptation of cuboidal foot bones subjected to cyclic loading.

Animals↗
PubMed2001

Increase in bone volume fraction precedes architectural adaptation in growing bone.

In mature trabecular bone, both density and trabecular orientation are adapted to external mechanical loads. Few quantitative data are available on the development of architecture and mechanical adaptation in juvenile trabecular bone. We studied the hypothesis that a time lag occurs between the adaptation of trabecular density and the adaptation of trabecular architecture during development. To investigate this hypothesis we used ten female pigs at 6, 23, 56, 104, and 230 weeks of age. Three-dimensional morphological and mechanical parameters of trabecular bone samples from the vertebra and proximal tibia were studied using microcomputed tomography and micro-finite element analysis. Both bone volume fraction and stiffness increased rapidly in the initial growth phase (from 6 weeks on), whereas the morphological anisotropy started increasing only after 23 weeks of age. In addition, the anisotropy reached its highest value much later in the development than did bone volume fraction. Hence, the alignment of trabeculae was still progressing at the time of peak bone mass. Therefore, our hypothesis was supported by the time lag between the increase in trabecular density and the adaptation of the trabecular architecture. The rapid increase of bone volume fraction in the initial growth phase can be explained by the enormous weight increase of the pigs. The trabeculae aligned at later stages when the increase in weight, and thus the loading, was slowed considerably compared with the early growth stage. Hence, the trabecular architecture was more efficient in later years. We conclude that density is adapted to external load from the early phase of growth, whereas the trabecular architecture is adapted later in the development.

Animals↗
PubMed1989

Retinal isomer ratio in dark-adapted purple membrane and bacteriorhodopsin monomers.

On the basis of data obtained by spectroscopic analysis and chromatography of retinal extracts, a consensus has been adopted that dark-adapted purple membrane (pm) contains 13-cis- and all-trans-retinal in equal amounts, whereas the light-adapted membrane contains all-trans-retinal only. We have developed an improved extraction technique which extracts up to 70% of the retinal in pm within 4 min. In the extracts from dark-adapted pm at room temperature, we consistently find 66-67% 13-cis-retinal and 33-34% all-trans-retinal, and more than 98.5% all-trans isomer in light-adapted samples. The spectrum obtained by reconstitution of bacterioopsin with 13-cis-retinal at 2 degrees C (to minimize isomerization) shows an absorbance maximum at 554 nm and agrees well with the spectrum for the 13-cis component calculated from the dark-adapted and light-adapted bR spectra with our extraction data. The ratio of 13-cis:all-trans isomer in dark-adapted pm is 2:1 and nearly constant between 0 and 38 degrees C but begins to decrease distinctly above 40 degrees C, and more rapidly near 70 degrees C, reaching 0.75 at 90 degrees C. The van't Hoff plot of the isomer ratio shows a nonlinear temperature dependence above 40 degrees C, indicating a more complex system than a simple thermal 13-cis/all-trans isomer equilibrium. We attribute the broadening, absorbance decrease, and blut shift of the visible absorption band with increasing temperature to the appearance of at least one and possibly two or three new chromophores which contain, mainly or exclusively, the all-trans isomer.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacteriorhodopsins↗
PubMed2005

Evidence that the adaptation region of the aspartate receptor is a dynamic four-helix bundle: cysteine and disulfide scanning studies.

The aspartate receptor is one of the ligand-specific, homodimeric chemoreceptors that detects extracellular attractants and triggers the chemotaxis pathway of Escherichia coli and Salmonella typhimurium. This receptor regulates the activity of the histidine kinase CheA, which forms a kinetically stable complex with the receptor cytoplasmic domain. An atomic four-helix bundle model has been constructed for this domain, which is functionally subdivided into the signaling and adaptation subdomains. The proposed four-helix bundle structure of the signaling subdomain, which binds CheA, is fully supported by experimental evidence. Much less evidence is available to test the four-helix bundle model of the adaptation subdomain, which possesses covalent adaptation sites and docking surfaces for adaptation enzymes. The present study focuses on a putative helix near the C terminus of the adaptation subdomain. To probe the structural and functional features of positions G467-A494 in this C-terminal region, a cysteine and disulfide scanning approach has been employed. Measurement of the chemical reactivities of scanned cysteines reveals an alpha-helical periodicity of exposed and buried residues, confirming alpha-helical secondary structure and mapping out a buried packing face. The effects of cysteine substitutions on activity in vivo and in vitro highlight the functional importance of the helix, especially its buried face. A scan for disulfide bond formation between symmetric pairs of engineered cysteines reveals promiscuous collisions between subunits, indicating the presence of significant thermal dynamics. A scan for functional disulfides reveals lock-on and signal-retaining disulfide bonds formed between symmetric pairs of cysteines at buried positions, indicating that the buried face of the helix lies near the subunit interface of the homodimer in the equilibrium structures of both the apo and aspartate-bound states where it plays a critical role in kinase regulation. These results strongly support the existing four-helix bundle model of the adaptation subdomain structure. A mechanistic model is proposed in which a signal is transmitted through the adaptation subdomain by a change in supercoiling of the four-helix bundle.

Bacterial Proteins↗
PubMed2002

Adapted cognitive behavioral group therapy for depressed low-income African American women.

In this study we examine the degree to which a manualized cognitive-behavioral therapy intervention can be adapted to be culturally sensitive in treating depressed low-income African American women with multiple stressors. We describe the adaptations we made to an existing intervention, a group treatment developed for depressed low-income medical patients. We also describe our evaluation of the adapted treatment in which outcomes of African American women treated in the culturally adapted group were compared to African American women treated in the non-adapted group. Following treatment, women in the adapted group exhibited a larger drop in average BDI scores. Implications are discussed in terms of challenges related to the development and evaluation of culturally adapted treatment.

Adult↗
PubMed2003

Direct and cross-protective effects of heat adaptation in cultured cells.

The model of 6-day dosed heat adaptation was developed on cultured rat H9c2 cardiomyoblasts and mouse C2c12 myoblasts. Heat adaptation produced a direct protective effect and increased the resistance of cells to heat shock. The cross-protective effect of heat adaptation was manifested in an increase in the resistance to staurosporine-induced damage. Heat adaptation did not protect cells from oxidative damage. As differentiated from adaptation of the organism, heat adaptation produces direct and cross-protective effects that develop due to the action of environmental factors in the absence of neurohumoral agents. It should be emphasized that the cross-protective effect of heat adaptation in cultured cells is specific to a certain type of damage.

Acclimatization↗