257,356 research outputs found
Instability studies of an 'O'-ring flexibly supported, gas bearing, mounted, cool air unit.
No full textA Cool Air unit (C. A. U. ) is powered by air bled from the engine and
supplies cool air to the avionics and cockpit of the aircraft. Essentially
a small turbo machine, the rotor is mounted upon two plain (gas) air
bearings, which are flexibly supported by elastomeric '0'-Rings.
The project objectives were to investigate, experimentally and
theoretically, the mechanism of dynamic instability, half frequency whirl
(HFW) observed in the C. A. U design, and hence evaluate methods by which it
can be best controlled. Two main areas of study were embarked upon.
Firstly a steady state aerodynamic study, based on an existing single
bearing rig, to evaluate the extent of aerodynamic operation and single
bearing instability (HFW). This Test Rig did not have '0'-Ring
flexibility. Bearing L/D tested were 2,1.5 and 1.0, with variable loading
of 18-1 -º 51.2N and speeds of 6000 -º 40000 Rpm in approximately 5000 Rpm
intervals. the theoretical study investigated non-linear effects of air
film pressure distribution.
Secondly a Dynamic instability study of HFW was carried out on a newly
designed Test Rig, simulating small turbo machines and the C. A. U.. Three
bearing types were evaluated, Aerodynamic, Hybrid and Hybrid porous. With
L/D of 1.0. '0'-Ring Centres varied from 0.17 4 0-83 of bearing length.
Viton and Silicon materials were tested with 70 shore hardness. Rotor
mass, inertia, asymmetry and unbalance were investigated along with '0'-
Ring stiffness and damping variation from air pressure (0 4 120psi).
Theory was developed to determine whirl onsets and effects of unbalance,
and damping of the support.
Non-linear (stagnant areas) of air film detected experimentally, are not
explained by Raimondi's theory. Experiments show that Raimondi's theory
seriously over estimates the applicable area of fully developed
aerodynamic operation. Pressure Profile at onset of Instability tends to
a Sommerfeld condition. Temperature was a good indication of lubrication
regime. Linear temperature rise curve denotes Aerodynamic operation, and
transition to non-linear curve represents onset of Instability (HFW).
Authors theory considers non-linearity of air film and suggests a new
method of evaluation to improve convergence.
Dynamic study of dual bearing rig concludes, first instability onset speed
(RSW) can be passed through due to residual unbalance and damping in the
'0'-Ring support. Theory developed shows relationship of RSW and HFW
effects due to unbalance and damping and results agree well. Viton offered
better damping than Silicon. RSW not present in Viton at'0'-Ring centres
above 10 mm. HFW not present with Viton below 55,000 rpm. RSW observed
with ui /cu = 1.0 and HFW occurred with m /m = 0-493 4 0.58. hybrid porous
bearings had lower performance than hybrid, but better than aerodynamic.
Hybrid bearings mounted in Viton '0'-Rings offer best performance long
term. Aerodynamic bearings can be concluded to be inherently unstable and
have limited aerodynamic operation, so should see little use in high speed
turbo machinery, including C. A. U. or aircraft applications where zero g
loading likely
Our Difficult Relationship with Truth: Critical Reason in the Real World
No full textKant’s analysis of the difficulties of our common approach to truth in every field, of empirical knowledge, moral judgment, and religious belief, ends up delineating an image of a critical reason in the real world, which goes beyond
the erudite world of science and philosophy, and which Kant seeks not only to describe but to promote. Critical reason must gain awareness of the means to overcome the difficulties that the complexity of the real world and the opacity of the subject itself present. What Kant called “the quality in the use of our cognitive faculties” is the goal of an enlightened reason. Criticism is realized in the daily exercise of concrete reason, illuminated by reflective self-analysis and intersubjective openness
Reason Maintenance - Conceptual Framework
No full textThis paper describes the conceptual framework for reason maintenance developed as part of
WP2
A test of "reason-based" and "reluctance-to-think" accounts of the disjunction effect
No full textThe disjunction effect violates Savage's sure-thing principle: that is, if a is preferred over b regardless of whether relevant outcome x occurs, then a should always be preferred over b [L.]. Savage, The Foundations of Statistics, New York, Wiley, 1954]. We tested "reason-based" and "reluctance-to-think" accounts of the disjunction effect. According to the former account, the disjunction effect occurs when different reasons underlie the preference for a under x versus the preference for a under not x. According to the latter account, the disjunction effect is due to the failure to consider preferences when x is unknown. We tested these accounts by varying the number of reasons underlying choices in the x and not x conditions. Consistent with the reason-based account, when only one reason was available, the disjunction effect was reduced. In addition, we propose a new method of measuring the disjunction effect under different conditions based on the logic proposed by Lambdin and Burdsal (2007) [C. Lambdin, C. Burdsal, The disjunction effect reexamined: relevant methodological issues and the fallacy of unspecified percentage comparisons, Organizational Behavior and Human Decision Processes 103 (2007) 268-276]. (C) 2011 Elsevier Inc. All rights reserved
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Mitomycin C in highly myopic eyes - Author reply
No full textOphthalmology. 2005 Feb;112(2):208-18; discussion 219.
Mitomycin C modulation of corneal wound healing after photorefractive keratectomy in highly myopic eyes.
Gambato C, Ghirlando A, Moretto E, Busato F, Midena E.
SourceRefractive Surgery Service and Antimetabolite Therapy Research Unit, Department of Ophthalmology, University of Padova, Padova, Italy.
Abstract
PURPOSE: To evaluate the role of topical mitomycin C in corneal wound healing (CWH) after photorefractive keratectomy (PRK) in highly myopic eyes.
DESIGN: Prospective, double-masked, randomized clinical trial.
PARTICIPANTS: Seventy-two eyes of 36 patients affected by high (>7 diopters) myopia.
METHODS: In each patient, one eye was randomly assigned to PRK with intraoperative topical 0.02% mitomycin C application, and the fellow eye was treated with a placebo. Postoperatively, mitomycin C-treated eyes received artificial tears (3 times daily, tapered in 3 months), whereas the fellow eye was treated with fluorometholone sodium 2% and artificial tears (3 times daily, tapered in 3 months).
MAIN OUTCOME MEASURES: Uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA), contrast sensitivity, manifest refraction, and biomicroscopy. Contrast sensitivity was determined using the Pelli-Robson chart. Corneal confocal microscopy documented CWH.
RESULTS: Mean follow-up was 18 months (range, 12-36). No side effects or toxic effects were documented. At 12-month follow-up examination, UCVAs (logarithm of the minimum angle of resolution) were 0.4+/-0.48 and 0.5+/-0.53 (P = .03) in mitomycin C-treated eyes and corticosteroid-treated eyes, respectively. At 1 year, corneal haze developed in 20% of corticosteroid-treated eyes, versus 0% of mitomycin C-treated eyes. At 12, 24, and 36 months, corneal confocal microscopy showed activated keratocytes and extracellular matrix significantly more evident in untreated eyes (Ps = 0.004, 0.024, and 0.046, respectively).
CONCLUSION: Topical intraoperative application of 0.02% mitomycin C can reduce haze formation in highly myopic eyes undergoing PRK.
Comment in
Ophthalmology. 2006 Feb;113(2):357; author reply 357-8
5. Reason and Ethics
No full textThis article concerns the role of reason in ethics under three distinct capacities: As the conformity of self-reflective minds to laws, as practical reasoning, and as the domain of normative considerations that make actions and attitudes intelligible and justified. In the first part of the article, I present competing accounts of practical reason and of its requirements, surveying recent debates about dichotomies such as explanatory, normative and operative, subjective and objective, justifying and motivating reasons. In the second part, I defend Kantian constructivism as the view of normativity that best vindicates the practical and reflexive nature of reason
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
A very good reason to reject the buck-passing account
No full textThis paper presents a new objection to the buck-passing account of value. I distinguish the buck-passing account of predicative value from the buck-passing account of attributive value. According to the latter, facts about attributive value reduce to facts about reasons and their weights. But since facts about reasons’ weights are themselves facts about attributive value, this account presupposes what it is supposed to explain. As part of this argument, I also argue against Mark Schroeder's recent account of the weights of reasons, which purports to explain the weights of reasons in terms of further reasons without circularity. I then argue that if we abandon the buck-passing account of attributive value, it would be ad hoc and unjustifiable to continue to endorse the buck-passing account of predicative value. In short, there seems to be little hope for the buck-passing account in either form. The paper ends by sketching a novel alternative theory according to which reasons are analysed in terms of the attributive value of motives. I suggest that a normative reason to φ is something that would be a good motive for φ-ing. At least at first glance, this view has numerous merits and few problem
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