58,443 research outputs found

    Effects in polarimetry of interference within wave plates

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    Multiple-beam interference within wave plates is investigated in terms of the detrimental effects it produces in the data of stellar spectropolarimetry. It is noted that spectral fringe structures occur in the phase delay, the polarizance and, for Pancharatnam designs, the reference axis of the wave plate. The natures of the problems are exposed by considering typical wave plates and experimental procedures used in linear and circular spectropolarimetry. It is demonstrated that the chief bane of accurate measurements is the presence of polarizance fringes, but which can be alleviated by the choice of experimental procedure. For spectral circular polarization studies, problems of cross-talk from any linear polarization present in the source are especially severe. In principle the effects of fringing can be removed in data reductions by calibration measurements of a set of linear polarization standard stars displaying different vibration azimuths and, for circular polarization measurements, knowledge of the linear polarization characteristics of the investigated star must also be known

    Period determinations of spotted stars

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    The general behaviours of photometric, radial velocity and polarimetric observational investigations are explored in terms of the signals generated by a spot or patch in co-rotation with a star. It is demonstrated that the results of any period analysis of data depends on the nature of the chosen measurement diagnostic. Unlike photometry, analysis of radial velocity measurements is likely to provide considerable power at periods corresponding to the harmonics of the stellar rotational period. This conclusion may have bearing on Harmanec's "submultiple period scenario" in connection with the understanding of the behaviour of early-type stars. Period analysis of polarimetric data is also likely to provide strong power in the harmonics of the fundamental rotational period. This analysis of the signals from the three basic observational diagnostics shows the dangers of simply using one measurement parameter alone to investigate stellar temporal behaviour and how interpretational confusion can arise when the results from different exercises are compared

    Minimum information loss fusion in distributed sensor networks

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    A key assumption of distributed data fusion is that individual nodes have no knowledge of the global network topology and use only information which is available locally. This paper considers the weighted exponential product (WEP) rule as a methodology for conservatively fusing estimates with an unknown degree of correlation between them. We provide a preliminary investigation into how the methodology for selecting the mixing parameter can be used to minimize the information loss in the fused covariance as opposed to reducing the Shannon entropy, and hence maximize the information of the fused covariance. Our results suggest that selecting a mixing parameter which minimizes the information loss ensures that information which is exclusive to the estimates from one source is not lost during the fusion process. These results indicate that minimizing the information loss provides a robust technique for selecting the mixing parameter in WEP fusion

    Experiments with a novel CCD stellar polarimeter

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    Experiments and observations have been undertaken with "bread-board" equipment to explore the potential of a "ring" stellar polarimeter with a CCD camera, rather than photographic plates used in Treanor's (1968) original instrument. By spreading the polarimetric signal over a large number of pixels on the detector, design prediction suggests that the polarimetric accuracy could be ~Δρ±0.00001 or ±0.001% per frame or even better. Although the photon accumulations suggest that this was achieved, instabilities in the employed crude modulator system provided frame to frame measurements with a greater than expected scatter. Software was developed to reduce the data in a simple way. With a design using more professional components and perhaps with more sophisticated reduction procedures, the full potential of the method should be achievable with the prospect of high precision polarimetry of the brighter stars. As an experimental bonus, the employed CCD chip was found to be free from any measurable polarizational sensitivity

    The Mask Strikes Back: Blackness as Aporia in Moby-Dick and Benito Cereno

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    What is the American Gothic a reaction to? Whereas other thinkers such as Nathaniel Hawthorne locates the building blocks of the American Gothic in Puritan Christianity or Amerindian Genocide, I argue that Melville posits the genesis of chattel slavery and the construction of racial category as the repressed events that haunt the Americas and return uninvited. By using the Gothic motif of the living corpse, the famed writer of Moby-Dick addresses the social bereavement which Blackness comes to represent in the Americas. By looking for truth on the skin and flesh, the main characters of Moby-Dick and “Benito Cereno” represent the Enlightenment precept that truth can be arrested via observation and interpretation. Melville presents two Black characters as impasses in this project of interpretation: Moby-Dick’s drowned boy, Pip, and “Benito Cereno’s” undead leader, Babo

    The Tradition of Interpretavism In Constitutional Interpretation

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    Poetic Witness in a Networked Age

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    When online videos mobilize protestors to occupy public spaces, and those protestors incorporate hashtags in their chants and markered placards, deliberative democratic theory must no longer dismiss technology and peoples historically excluded from the arena of politics. Specifically, political models must account for the role of repetition in paving the way for unheard and unseen messages and people to appear in the political arena. Drawing on Judith Butler’s theory of the Performative and Hannah Arendt’s Space of Appearance, this paper assesses that critical and generative role of iteration. Repeating unheeded acts performs the capacity for those acts to be entered into discourse. The World Wide Web evidently augments such performativity with features such as accessibility, potential for ‘viral’ proliferation, and an endurance unlike non-networked acts. This paper eventually grapples with the hazards and risks of networked repetition (e.g. desensitization, trivialization, etc.) in order to propose a poetics of repetition to mitigate those dangers. Such poetics ultimately distinguishes the witness from the spectator

    On Rage

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    “Honestly [Flight] was written out of rage. I wrote it immediately after Absolutely True Diary of a Part-Time Indian, in a matter of months. It was in the aftermath of 9/11. I was upset with the way people were acting, People on the Left and the Right, Muslims and Christians were justifying violence towards the other side. And everyone believed they were correct. I was thinking ‘What if Everybody is wrong?’” — Sherman Alexie in The Gettysburgian. [excerpt

    Respiration: Breathing Between the Stacks

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    How rare are we, who brandish Black and Male identity, in Academia? In the past two weeks, I have been reminded of my Black maleness in a multitude of ways. I sat alone, subordinate in number, in a dialogue about Internalized Oppression at Diaspora House. Strong women of color discuss this issue while I work to stay respectful and non-oppressive in this space. I sat alone, subordinate in number, in each of my classes, where I am often the only one of my race and class. My race-gender circumstance is a matter of fact to me. How does this Black maleness play out on college campuses nationwide? [excerpt
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