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Decay Function (decay + function)
Selected AbstractsThe ontogeny of foragwehaviour in desert ants, Cataglyphis bicolorECOLOGICAL ENTOMOLOGY, Issue 2 2004Rüdiger Wehner Abstract. 1. Individually foraging desert ants, Cataglyphis bicolor, exhibit short foraging lives (half lifetime, i.e. half-time of the exponential decay function: 4.5 days), in which they perform 3.7 ± 1.9 foraging runs per day. 2. During their short lifetime foraging period the ants increase the duration of their foraging round trips (up to 40.0 ± 24.6 min per run), the maximal distance of individual foraging runs (up to 28.2 ± 4.1 m), and their foraging success, i.e. the ratio of successful runs to the total number of runs (up to 0.70). 3. The parameter that increases most dramatically during a forager's lifetime is direction fidelity, i.e. the tendency to remain faithful to a particular foraging direction. 4. A model based on some simple behavioural rules is used to describe the experimental findings that within an isotropic food environment individual ants develop spatial foraging idiosyncrasies, and do so at a rate that increases with the food densities they encounter. 5. Finally, it is argued that in functional terms direction fidelity is related to the navigational benefits resulting from exploiting familiar (route-based) landmark information, and hence reduces round-trip time and by this physiological stress and predatory risk. [source] Fully automated intensity compensation for confocal microscopic imagesJOURNAL OF MICROSCOPY, Issue 1 2005H.-X. WU Summary One well-recognized problem in three-dimensional (3D) confocal microscopic images is that the intensities in deeper slices are generally weaker than those in shallower slices. The loss of intensity with depth hampers both qualitative observation and quantitative measurement of specimens. Two major types of methods exist to compensate for this intensity loss: the first is based on the geometrical optics inside the specimen, and the second applies an empirical parametric intensity decay function (IDF) of depth. A common feature shared by both methods is that they are parameter-dependent. However, for the optics-based method there are as yet no fully automated parameter-setting approaches; and for the IDF method the traditional profile-fitting approach cannot provide proper parameters if the presumed IDF model does not match the experimental intensity,depth profile of the 3D image. In this paper, we propose a novel maximum-entropy (ME) approach to fully automated parameter-setting. In principle the ME approach is suitable for any compensation method as long as it is parameter-dependent. The basic assumption is that without intensity loss an ideal 3D image should be generally homogeneous with respect to depth and this axial homogeneity can be represented by the entropy of a normalized intensity,depth profile. Experiments on real confocal images showed that such a profile was consistent with visual evaluation of axial intensity homogeneity and that the ME approach could provide proper parameters for both compensation methods mentioned above. Moreover, for the IDF method, experiments on both real and simulated data showed that the ME approach could provide more precise parameters than with traditional profile-fitting. The Appendix provides a proof that under certain conditions the global maximization of the profile-entropy is guaranteed. [source] Pharaonis Phoborhodopsin Binds to its Cognate Truncated Transducer Even in the Presence of a Detergent with a 1:1 Stoichiometry,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 3 2001Yuki Sudo ABSTRACT Pharaonis phoborhodopsin (ppR) (also pharaonis sensory rhodopsin II) is a receptor of the negative phototaxis of Natronobacterium pharaonis.ppR forms a complex with its pharaonis halobacterial transducer (pHtrII), and this complex transmits the light signal to the sensory system in the cytoplasm. The expressed C-terminal-His tagged ppR and C-terminal-His tagged truncated pHtrII (t-Htr) in Escherichia coli (His means the 6× histidine tag) form a complex even in the presence of 0.1% of n -dodecyl-,- d -maltoside, and the M-decay of the complex became about twice slower than that of ppR alone. The photocycling rates under varying concentration ratios of ppR to t-Htr in the presence of detergent were measured. The data were analyzed on the following assumptions: (1) the M-decay of both ppR alone and the complex followed a single exponential decay with different time constants; and (2) the M-decay under varying concentration ratios of ppR to t-Htr, therefore, followed a biexponential decay function which combined the decay of the free ppR and that of the complex as photoreactive species. From these analyses we estimated the dissociation constant (15.2 ± 1.8 ,M) and the number of binding sites (1.2 ± 0.08). [source] A Bayesian Spatial Multimarker Genetic Random-Effect Model for Fine-Scale MappingANNALS OF HUMAN GENETICS, Issue 5 2008M.-Y. Tsai Summary Multiple markers in linkage disequilibrium (LD) are usually used to localize the disease gene location. These markers may contribute to the disease etiology simultaneously. In contrast to the single-locus tests, we propose a genetic random effects model that accounts for the dependence between loci via their spatial structures. In this model, the locus-specific random effects measure not only the genetic disease risk, but also the correlations between markers. In other words, the model incorporates this relation in both mean and covariance structures, and the variance components play important roles. We consider two different settings for the spatial relations. The first is our proposal, relative distance function (RDF), which is intuitive in the sense that markers nearby are likely to correlate with each other. The second setting is a common exponential decay function (EDF). Under each setting, the inference of the genetic parameters is fully Bayesian with Markov chain Monte Carlo (MCMC) sampling. We demonstrate the validity and the utility of the proposed approach with two real datasets and simulation studies. The analyses show that the proposed model with either one of two spatial correlations performs better as compared with the single locus analysis. In addition, under the RDF model, a more precise estimate for the disease locus can be obtained even when the candidate markers are fairly dense. In all simulations, the inference under the true model provides unbiased estimates of the genetic parameters, and the model with the spatial correlation structure does lead to greater confidence interval coverage probabilities. [source] Zero-dose extrapolation as part of macromolecular synchrotron data reductionACTA CRYSTALLOGRAPHICA SECTION D, Issue 5 2003Kay Diederichs Radiation damage to macromolecular crystals at third-generation synchrotron sites constitutes a major source of systematic error in X-ray data collection. Here, a computational method to partially correct the observed intensities during data reduction is described and investigated. The method consists of a redundancy-based zero-dose extrapolation of a decay function that is fitted to the intensities of all observations of a unique reflection as a function of dose. It is shown in a test case with weak anomalous signal that this conceptually simple correction, when applied to each unique reflection, can significantly improve the accuracy of averaged intensities and single-wavelength anomalous dispersion phases and leads to enhanced experimental electron-density maps. Limitations of and possible improvements to the method are discussed. [source] A general model for predicting brown tree snake capture ratesENVIRONMETRICS, Issue 3 2003Richard M. Engeman Abstract The inadvertent introduction of the brown tree snake (Boiga irregularis) to Guam has resulted in the extirpation of most of the island's native terrestrial vertebrates, has presented a health hazard to small children, and also has produced economic problems. Trapping around ports and other cargo staging areas is central to a program designed to deter dispersal of the species. Sequential trapping of smaller plots is also being used to clear larger areas of snakes in preparation for endangered species reintroductions. Traps and trapping personnel are limited resources, which places a premium on the ability to plan the deployment of trapping efforts. In a series of previous trapping studies, data on brown tree snake removal from forested plots was found to be well modeled by exponential decay functions. For the present article, we considered a variety of model forms and estimation procedures, and used capture data from individual plots as random subjects to produce a general random coefficients model for making predictions of brown tree snake capture rates. The best model was an exponential decay with positive asymptote produced using nonlinear mixed model estimation where variability among plots was introduced through the scale and asymptote parameters. Practical predictive abilities were used in model evaluation so that a manager could project capture rates in a plot after a period of time, or project the amount of time required for trapping to reduce capture rates to a desired level. The model should provide managers with a tool for optimizing the allocation of limited trapping resources. Copyright © 2003 John Wiley & Sons, Ltd. [source] Playing to win: Biological imperatives, self-regulation, and trade-offs in the game of career successJOURNAL OF ORGANIZATIONAL BEHAVIOR, Issue 2 2005Nigel Nicholson The article applies evolutionary theory to the concept of career success, to argue the primacy of ,objective' outcomes, utilities such as status and wealth, and to analyze why the relationship with subjective career success is not stronger. Although there are grounds for expecting subjective evaluations to be sympathetic secondary accompaniments of objective success and failure, there are substantial numbers of paradoxically ,happy losers' and ,unhappy winners' in the career game. These are explored theoretically as adaptive outcomes of self-regulation and sense-making processes. The nature of that game is then explored by a closer examination of the interrelations and decay functions of the major objective success outcomes. This is undertaken as a theoretical exercise, and also by reference to the evidence in the literature. Both approaches support the existence of close linkages among most of these outcomes, though empirical data reveal variations that highlight the importance for careerists to be aware of trade-offs and risks in career strategies. Context mediates these relationships, especially key contingencies such as individual differences, gender, career stage, culture, and business sector. The implications are discussed; in particular the role of careers theory and research in helping to cut through some of the ideological aspects of ,subjective' careers in order to help raise the awareness of actors in the labor market about objective career realities. Copyright © 2005 John Wiley & Sons, Ltd. [source] Multispectral fluorescence lifetime imaging by TCSPCMICROSCOPY RESEARCH AND TECHNIQUE, Issue 5 2007Wolfgang Becker Abstract We present a fluorescence lifetime imaging technique with simultaneous spectral and temporal resolution. The technique is fully compatible with the commonly used multiphoton microscopes and nondescanned (direct) detection. An image of the back-aperture of the microscope lens is projected on the input of a fiber bundle. The input of the fiber bundle is circular, and the output is flattened to match the input slit of a spectrograph. The spectrum at the output of the spectrograph is projected on a 16-anode PMT module. For each detected photon, the encoding logics of the PMT module deliver a timing pulse and the number of the PMT channel in which the photon was detected. The photons are accumulated by a multidimensional time-correlated single photon counting (TCSPC) process. The recording process builds up a four-dimensional photon distribution over the times of the photons in the excitation pulse period, the wavelengths of the photons, and the coordinates of the scan area. The method delivers a near-ideal counting efficiency and is capable of resolving double-exponential decay functions. We demonstrate the performance of the technique for autofluorescence imaging of tissue. Microsc. Res. Tech., 2007. © 2007 Wiley-Liss, Inc. [source] Towards metabolic mapping of the human retinaMICROSCOPY RESEARCH AND TECHNIQUE, Issue 5 2007D. Schweitzer Abstract Functional alterations are first signs of a starting pathological process. A device that measures parameter for the characterization of the metabolism at the human eye-ground would be a helpful tool for early diagnostics in stages when alterations are yet reversible. Measurements of blood flow and of oxygen saturation are necessary but not sufficient. The new technique of auto-fluorescence lifetime measurement (FLIM) opens in combination with selected excitation and emission ranges the possibility for metabolic mapping. FLIM not only adds an additional discrimination parameter to distinguish different fluorophores but also resolves different quenching states of the same fluorophore. Because of its high sensitivity and high temporal resolution, its capability to resolve multi-exponential decay functions, and its easy combination with laser scanner ophthalmoscopy, multi-dimensional time-correlated single photon counting was used for fundus imaging. An optimized set up for in vivo lifetime measurements at the human eye-ground will be explained. In this, the fundus fluorescence is excited at 446 or 468 nm and the time-resolved autofluorescence is detected in two spectral ranges between 510 and 560 nm as well as between 560 and 700 nm simultaneously. Exciting the fundus at 446 nm, several fluorescence maxima of lifetime t1 were detected between 100 and 220 ps in lifetime histograms of 40° fundus images. In contrast, excitation at 468 nm results in a single maximum of lifetime t1 = 190 ± 16 ps. Several fundus layers contribute to the fluorescence intensity in the short-wave emission range 510,560 nm. In contrast, the fluorescence intensity in the long-wave emission range between 560 and 700 nm is dominated by the fluorescence of lipofuscin in the retinal pigment epithelium. Comparing the lateral distribution of parameters of a tri-exponential model function in lifetime images of the fundus with the layered anatomical fundus structure, the shortest component (t1 = 190 ps) originates from the retinal pigment epithelium and the second lifetime (t2 = 1,000 ps) from the neural retina. The lifetime t3 , 5.5 ns might be influenced by the long decay of the fluorescence in the crystalline lens. In vitro analysis of the spectral properties of expected fluorophores under the condition of the living eye lightens the interpretation of in vivo measurements. Taking into account the transmission of the ocular media, the excitation of NADH is unlikely at the fundus. Microsc. Res. Tech., 2007. © 2007 Wiley-Liss, Inc. [source] | |||||||||||||