17,725 research outputs found

    Stereoselective synthesis of secopodophyllotoxins

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    Imperial Users onl

    Luminosity and surface brightness distribution of K-band galaxies from the UKIDSS Large Area Survey

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    We present luminosity and surface brightness distributions of 40,111 galaxies with K-band photometry from the United Kingdom Infrared Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS), Data Release 3 and optical photometry from Data Release 5 of the Sloan Digital Sky Survey (SDSS). Various features and limitations of the new UKIDSS data are examined, such as a problem affecting Petrosian magnitudes of extended sources. Selection limits in K- and r-band magnitude, K-band surface brightness and K-band radius are included explicitly in the 1/Vmax estimate of the space density and luminosity function. The bivariate brightness distribution in K-band absolute magnitude and surface brightness is presented and found to display a clear luminosity--surface brightness correlation that flattens at high luminosity and broadens at low luminosity, consistent with similar analyses at optical wavelengths. Best fitting Schechter function parameters for the K-band luminosity function are found to be M*-5 log h=-23.19 +/- 0.04, alpha=-0.81 +/- 0.04 and phi*=(0.0166 +/- 0.0008)h^3 Mpc^{-3}, although the Schechter function provides a poor fit to the data at high and low luminosity, while the luminosity density in the K band is found to be j = (6.305 +/- 0.067) x 10^8 L_sun h Mpc^{-3}. However, we caution that there are various known sources of incompleteness and uncertainty in our results. Using mass-to-light ratios determined from the optical colours we estimate the stellar mass function, finding good agreement with previous results. Possible improvements are discussed that could be implemented when extending this analysis to the full LAS.Comment: 17 pages, 24 figures, matches MNRAS accepted versio

    An absorption tube for the investigation of gases in the photographic infrared

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    An absorption cell of novel design is described, which combines the advantages of long path and relatively small volume

    Pinning control of spatiotemporal chaos

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    Linear control theory is used to develop an improved localized control scheme for spatially extended chaotic systems, which is applied to a coupled map lattice as an example. The optimal arrangement of the control sites is shown to depend on the symmetry properties of the system, while their minimal density depends on the strength of noise in the system. The method is shown to work in any region of parameter space and requires a significantly smaller number of controllers compared to the method proposed earlier by Hu and Qu [Phys. Rev. Lett. 72, 68 (1994)]. A nonlinear generalization of the method for a 1D lattice is also presented

    Comment on ``The linear instability of magnetic Taylor-Couette flow with Hall effect''

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    In the paper we comment on (R\"udiger & Shalybkov, Phys. Rev. E. 69, 016303 (2004) (RS)), the instability of the Taylor--Couette flow interacting with a homogeneous background field subject to Hall effect is studied. We correct a falsely generalizing interpretation of results presented there which could be taken to disprove the existence of the Hall--drift induced magnetic instability described in Rheinhardt and Geppert, Phys. Rev. Lett. 88, 101103. It is shown that in contrast to what is suggested by RS, no additional shear flow is necessary to enable such an instability with a non--potential magnetic background field, whereas for a curl--free one it is. In the latter case, the instabilities found in RS in situations where neither a hydrodynamic nor a magneto--rotational instability exists are demonstrated to be most likely magnetic instead of magnetohydrodynamic. Further, some minor inaccuracies are clarified.Comment: 3 pages, 1 figure; accepted by Physical Review

    Grain boundary motion in layered phases

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    We study the motion of a grain boundary that separates two sets of mutually perpendicular rolls in Rayleigh-B\'enard convection above onset. The problem is treated either analytically from the corresponding amplitude equations, or numerically by solving the Swift-Hohenberg equation. We find that if the rolls are curved by a slow transversal modulation, a net translation of the boundary follows. We show analytically that although this motion is a nonlinear effect, it occurs in a time scale much shorter than that of the linear relaxation of the curved rolls. The total distance traveled by the boundary scales as ϔ−1/2\epsilon^{-1/2}, where Ï”\epsilon is the reduced Rayleigh number. We obtain analytical expressions for the relaxation rate of the modulation and for the time dependent traveling velocity of the boundary, and especially their dependence on wavenumber. The results agree well with direct numerical solutions of the Swift-Hohenberg equation. We finally discuss the implications of our results on the coarsening rate of an ensemble of differently oriented domains in which grain boundary motion through curved rolls is the dominant coarsening mechanism.Comment: 16 pages, 5 figure

    Defect Dynamics for Spiral Chaos in Rayleigh-Benard Convection

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    A theory of the novel spiral chaos state recently observed in Rayleigh-Benard convection is proposed in terms of the importance of invasive defects i.e defects that through their intrinsic dynamics expand to take over the system. The motion of the spiral defects is shown to be dominated by wave vector frustration, rather than a rotational motion driven by a vertical vorticity field. This leads to a continuum of spiral frequencies, and a spiral may rotate in either sense depending on the wave vector of its local environment. Results of extensive numerical work on equations modelling the convection system provide some confirmation of these ideas.Comment: Revtex (15 pages) with 4 encoded Postscript figures appende

    On Vulnerability: Distinguishing Differences Between the Knight of Faith and the Knight of Resignation in Kierkegaard’s Fear and Trembling

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    CHRISTOPHER G. CROSS: On Vulnerability: Distinguishing Differences Between the Knight of Faith and the Knight of Resignation in Kierkegaard’s Fear and Trembling (Under the direction of William Lawhead) In Sþren Kierkegaard’s work, Fear and Trembling, he describes two kinds of individuals, which he calls the knight of faith and the knight of infinite resignation. The purpose of this thesis is to consider the differences between the two. Several scholars of the work identify different characteristics that distinguish the knight of faith and the knight of infinite resignation. These characteristics include care (Mooney), courage (Carlisle), and autonomy (Lippitt). This thesis uses those three notions to suggest that another difference between the knight of faith and knight of infinite resignation is the characteristic of vulnerability

    Gender (in)Query: Young Adults Learning, Unlearning, and Relearning Gender in a Queer Majority Space

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    As today’s discursive frames available to queer young adults reflect a stressful, shifting historical context for sexuality from ‘struggle and survive’ to emancipation, they still are confined by U.S. sexual norms assuming the authority of ‘truth’ while demanding heterosexuality. Consequently, sexuality and gender are linked inextricably as heterosexuality relies on the gender binary and the gender binary relies on heterosexuality. Via gender, queer, and situated learning theories this qualitative study decouples such mutual reinforcement to explore how queer young adults – who are already positioned outside of obligatory heterosexuality – learn, unlearn, or relearn gender in queer majority spaces. Research occurred during investigator facilitated gender group sessions comprised of college-aged queer young adults and also drew on individual interviews, private online journal entries, and periodic surveys. Through this work young adults had a safe space to learn about and perform gender, but were limited by previous heterocentric knowledge and language. This research raise vital questions and concerns about the hegemony of heterosexuality and the gender binary, how context affects learning, and how college students benefit from a non-judgmental space to grapple with questions of identity. Additionally, it points out the usefulness of queer and gender theories in educational research in combination with situated learning theory as well as on their own
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