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Ratio R (ratio + r)
Selected AbstractsTesting the locality of transport in self-gravitating accretion discsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2004G. Lodato ABSTRACT In this paper, we examine the issue of characterizing the transport associated with gravitational instabilities in relatively cold discs, discussing in particular the conditions under which it can be described within a local, viscous framework. We present the results of global, three-dimensional, smoothed particle hydrodynamics simulations of self-gravitating accretion discs, in which the disc is cooled using a simple parametrization for the cooling function. Our simulations show that the disc settles in a ,self-regulated' state, where the axisymmetric stability parameter Q, 1 and where transport and energy dissipation are dominated by self-gravity. We have computed the gravitational stress tensor and compared our results with expectations based on a local theory of transport. We find that, as long as the disc mass is smaller than 0.25M, and the aspect ratio H/R, 0.1, transport is determined locally, thus allowing for a viscous treatment of the disc evolution. [source] Two-stage fatigue loading of woven carbon fibre reinforced laminatesFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 1 2003M. S. FOUND ABSTRACT A brief review of the models used to predict the cumulative fatigue damage in FRP composites is presented. Two-stage fatigue loading of a [0/90,± 452,0/90]s quasi- isotropic woven carbon fibre/epoxy resin laminate was evaluated at stress ratio R = 0.05 and the failure mechanisms investigated using x-radiography after each loading stage. The results are presented in terms of fatigue strength and damage growth and are compared with those in the literature. A low-to-high loading sequence is more damaging than a high-to-low one and the Palmgren-Miner linear damage rule may no longer be valid for this kind of material, as previously reported. [source] Limits on the detectability of the CMB B-mode polarization imposed by foregroundsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2005M. Tucci ABSTRACT We investigate which practical constraints are imposed by foregrounds on the detection of the B-mode polarization generated by gravitational waves, in the case of experiments of the type currently being planned. As the B-mode signal is probably dominated by foregrounds at all frequencies, the detection of the cosmological component depends drastically on our ability to remove foregrounds. We provide an analytical expression with which to estimate the level of the residual polarization for Galactic foregrounds, according to the method employed for their subtraction. We interpret this result in terms of the lower limit of the tensor-to-scalar ratio r that allows us to disentangle the cosmological B-mode polarization from the foreground contribution. Polarized emission from extragalactic radio sources and gravitational lensing is also taken into account. As a first approach, we consider the ideal limit of an instrumental noise-free experiment: for full-sky coverage and a resolution of 1°, we obtain a limit of r, 10,4. This value can be improved by high-resolution experiments and, in principle, there is no clear fundamental limit on the detectability of the polarization of gravitational waves. Our analysis is also applied to planned or hypothetical future polarization experiments, taking into account expected noise levels. [source] Length dependence of polarization in spontaneous edge emissions from InGaN/AlGaN MQWs laser diodesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2007Chuanyu Jia Abstract The polarization of spontaneous edge-emitting electroluminescence from near-UV LDs with different cavity lengths (from 400 ,m to 1000 ,m) was studied. It was found that TE mode dominates in InGaN/AlGaN MQWs LDs, which is consistent with the theoretical calculation results of similar MQWs. An obvious polarization decrease from P = 0.57 to 0.42 as the LD cavity length changed from 400 ,m to 1000 ,m was also observed, corresponding to a ratio r changing from 3.67 to 2.43, which indicated that, the TE mode attenuated more grievously than the TM mode with increasing cavity length. This is due to the inherent property of polarization selective emission from the alloys. The optical loss coefficient of TE mode was determined to be 35 cm,1, while, 10 cm,1 for TM mode, which is in good agreement with the results obtained from other methods. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Amorphous blends of poly(zwitterions) and zwitterionomers of the ammonioalkoxydicyanoethenolate type with some alkali metal saltsPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 10 2001Monique Galin Abstract Poly(zwitterions) and zwitterionomers of the ammonioethoxydicyanoethenolate type (functional dipolar unit R3N+,(CH2)2,O,CO,C,,(CN)2, µ,=,25.9 D) show the very specific property of solvation of some alkali metal salts to yield amorphous blends. For homopolymers in the (meth)acrylic series, solvation is observed up to a ratio r,=,[salt]/[zwitterion] of 1 for LiClO4 and NaSCN and of 0.5 for NaCF3SO3: it results in a significant plasticization (increasing order LiClO4,<,NaSCN,<,NaCF3SO3) and in the development in some cases of a poorly defined (lamellar?) local order, as evidenced by the presence of a single broad peak in the small-angle x-ray scattering (SAXS) patterns (Bragg distances of about 15,20 Å). For the amorphous blend of a biphasic poly(tetramethyleneoxide) segmented zwitterionomer and NaCF3SO3 (r,=,0.5), selective solvation of the salt in the hard zwitterionic domains induces a transition from a lamellar structure (zwitterionic sublayer of about 9,Å thickness) to an hexagonal packing of ionic-zwitterionic cylinders (radius of about 15 Å). Ionic conductivity, measured in a narrow range of temperature just above the glass transition temperature, is characterized for most systems by an activation energy of about 1,1.8,eV; the drastic decrease of the conductivity by a factor of 103, when going from the homopolymer to the zwitterionomer blends, is typical of the inhibition of the ionic percolation process by the lack of connectivity of the ionic-zwitterionic domains. Copyright © 2001 John Wiley & Sons, Ltd. [source] Mass peak shape improvement of a quadrupole mass filter when operating with a rectangular wave power supplyRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 17 2009Chan Luo Numeric experiments were performed to study the first and second stability regions and find the optimal configurations of a quadrupole mass filter constructed of circular quadrupole rods with a rectangular wave power supply. The ion transmission contours were calculated using ion trajectory simulations. For the first stability region, the optimal rod set configuration and the ratio r/r0 is 1.110,1.115; for the second stability region, it is 1.128,1.130. Low-frequency direct current (DC) modulation with the parameters of m,=,0.04,0.16 and ,,=,,/,,=,1/8,1/14 improves the mass peak shape of the circular rod quadrupole mass filter at the optimal r/r0 ratio of 1.130. The amplitude modulation does not improve mass peak shape. Copyright © 2009 John Wiley & Sons, Ltd. [source] The total-to-selective extinction ratio determined from near IR photometry of OB starsASTRONOMISCHE NACHRICHTEN, Issue 3 2003W. WegnerArticle first published online: 8 APR 200 Abstract The paper presents an extensive list of the total to selective extinction ratios R calculated from the infrared magnitudes of 597 O and B stars using the extrapolation method. The IR magnitudes of these stars were taken from the literature. The IR colour excesses are determined with the aid of "artificial standards" , Wegner (1994). The individual and mean values of total to selective extinction ratios R differ in most cases from the average value R= 3.10 ±0.05 , Wegner (1993) in different OB associations. The relation between total to selective extinction ratios R determined in this paper and those calculated using the "method of variable extinction" and the Cardelli et al. (1989) formulae is discussed. The R values presented in this paper can be used to determine individual absolute magnitudes of reddened OB stars with known trigonometric parallaxes. [source] | |||||||||||||