17,677 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

    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

    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

    Flight test evaluation of a method to determine the level flight performance of a propeller-driven aircraft

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    The overall drag of the aircraft is expressed in terms of the measured increment of power required to overcome a corresponding known increment of drag, which is generated by a towed drogue. The simplest form of the governing equations, D = delta D SHP/delta SHP, is such that all of the parameters on the right side of the equation can be measured in flight. An evaluation of the governing equations has been performed using data generated by flight test of a Beechcraft T-34B. The simplicity of this technique and its proven applicability to sailplanes and small aircraft is well known. However, the method fails to account for airframe-propulsion system

    Power-Law Behavior of Power Spectra in Low Prandtl Number Rayleigh-Benard Convection

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    The origin of the power-law decay measured in the power spectra of low Prandtl number Rayleigh-Benard convection near the onset of chaos is addressed using long time numerical simulations of the three-dimensional Boussinesq equations in cylindrical domains. The power-law is found to arise from quasi-discontinuous changes in the slope of the time series of the heat transport associated with the nucleation of dislocation pairs and roll pinch-off events. For larger frequencies, the power spectra decay exponentially as expected for time continuous deterministic dynamics.Comment: (10 pages, 6 figures
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