15,514 research outputs found

    The Regulatory Roles of the Galactose Permease and Kinase in the Induction Response of the GAL Network in Saccharomyces cerevisiae

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    The GAL genetic switch of Saccharomyces cerevisiae exhibits an ultrasensitive response to the inducer galactose as well as the "all-or-none" behavior characteristic of many eukaryotic regulatory networks. We have constructed a strain that allows intermediate levels of gene expression from a tunable GAL1 promoter at both the population and the single cell level by altering the regulation of the galactose permease Gal2p. Similar modifications to other feedback loops regulating the Gal80p repressor and the Gal3p signaling protein did not result in similarly tuned responses, indicating that the level of inducer transport is unique in its ability to control the switch response of the network. In addition, removal of the Gal1p galactokinase from the network resulted in a regimed response due to the dual role of this enzyme in galactose catabolism and transport. These two activities have competing effects on the response of the network to galactose such that the transport effects of Gal1p are dominant at low galactose concentrations, whereas its catabolic effects are dominant at high galactose concentrations. In addition, flow cytometry analysis revealed the unexpected phenomenon of multiple populations in the gal1{Delta} strains, which were not present in the isogenic GAL1 background. This result indicates that Gal1p may play a previously undescribed role in the stability of the GAL network response

    Development and Certification of a New Stall Warning and Avoidance System

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    Several methods may be employed to improve natural stall characteristics. The method employed on all learjets to obtain improved stall characteristics is a stall warning and avoidance system that employs angle of attack vanes, an electronic computer, a control column shaker motor, and a torquer which drives the control column in a pusher mode to avoid unwanted further buildup of angle of attack. The new system was developed with changes that improve system response with no performance penalty or increase in turbulence sensitivity. The following changes were made included modified system time constants and (alpha) time rate of change of vane angle dead zone and the addition of an alpha signal limiter and an alpha cut out below a specified angle of attack

    Combining the Box-Cox power and generalised log transformations to accommodate nonpositive responses in linear and mixed-effects linear models

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    Transformation of a response variable can greatly expand the class of problems for which the linear regression model or linear mixed-model is appropriate. Beginning with the fundamental work of Box and Cox, maximum-likelihood-like estimation has been applied to select a transformation from among a family of transformations, with the possible goals of achieving approximate normality, removing nonlinearity in a mean function, or stabilizing variance. The Box-Cox power family (BC) of transformations is by far the most common with the Box-Cox methodology, and it requires a strictly positive response. In this article we introduce a new family of transformations that we call the Box-Cox power with nonpositives (BCN) family that allows inclusion of a few nonpositive values. The BCN family is a modification of the basic power family that is inspired by the generalised log, or glog transformation, proposed for use with the more limited goals of stabilizing variance or achieving approximate normality. The glog transformation is itself a special case of the Johnson SU transformation, and we show that the BCN family derived from it is in turn a simple modification of the BC family. Computer code for implementing this family is included in the car package in R (Fox and Weisberg, 2011). The methodology is illustrated using a problem in clinical chemistry

    A spectrum of carbon dioxide from 800 to 5500 cm-1

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    An atlas of CO2 lines obtained from long path length samples at 296 K is presented. Many of the line centers are marked and their positions tabulated

    Discovery of distant high luminosity infrared galaxies

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    We have developed a method for selecting the most luminous galaxies detected by IRAS based on their extreme values of R, the ratio of 60 micron and B-band luminosity. These objects have optical counterparts that are close to or below the limits of Schmidt surveys. We have tested our method on a 1079 deg^2 region of sky, where we have selected a sample of IRAS sources with 60 micron flux densities greater than 0.2 Jy, corresponding to a redshift limit z~1 for objects with far-IR luminosities of 10^{13} L_sun. Optical identifications for these were obtained from the UK Schmidt Telescope plates, using the likelihood ratio method. Optical spectroscopy has been carried out to reliably identify and measure the redshifts of six objects with very faint optical counterparts, which are the only objects with R>100 in the sample. One object is a hyperluminous infrared galaxy (HyLIG) at z=0.834. Of the remaining, fainter objects, five are ultraluminous infrared galaxies (ULIGs) with a mean redshift of 0.45, higher than the highest known redshift of any non-hyperluminous ULIG prior to this study. High excitation lines reveal the presence of an active nucleus in the HyLIG, just as in the other known infrared-selected HyLIGs. In contrast, no high excitation lines are found in the non-hyperluminous ULIGs. We discuss the implications of our results for the number density of HyLIGs at z<1 and for the evolution of the infrared galaxy population out to this redshift, and show that substantial evolution is indicated. Our selection method is robust against the presence of gravitational lensing if the optical and infrared magnification factors are similar, and we suggest a way of using it to select candidate gravitationally lensed infrared galaxies.Comment: 6 pages, accepted for publication in A&

    Does any therapy really work for neurocardiogenic syncope?

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    Effectiveness of a treatment for neurocardiogenic syncope can be defined in terms of symptom response, quality-of-life, healthcare utilization, treatment side effects and cost-effectiveness. Most trials have focused on syncope recurrence or burden, without assessing quality-of-life formally. Drug and device interventions are characterized by a dearth of randomized controlled trials, with those few of robust design demonstrating little impact on recurrence of syncope. General advice includes hydration, trigger recognition and counter pressure maneuvers to attenuate episodes. Lifestyle recommendations have limited comparative effectiveness evidence, but are favored due to lack of side effects and low cost. The frequency of syncope improves in many patients regardless of the intervention, although ultimate recurrence of syncope remains high. In the minority of patients seeking treatment due to recurrence, midodrine has reasonable supporting evidence for effectiveness with some evidence for beta-blockers in older age patients. Emerging evidence favors pacing in patients with asystole during spontaneous (as opposed to provoked) syncope. Combining long-term implantable cardiac monitoring, tilt and adenosine triphosphate testing may yet accurately define the optimal minority who benefit from pacing. In the remaining majority, pharmacologic and device interventions should be used sparingly until clear benefits are established. Better understanding of patient fears, beliefs and behaviors may help develop cognitive therapies and improve quality-of-life alongside the focus on physical symptoms
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