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Radius R (radius + r)

Distribution by Scientific Domains

Physics and Astronomy	60%
Chemistry	20%

Selected Abstracts

Preparation of Tip-Protected Poly(oxyphenylene) Coated Carbon-Fiber Ultramicroelectrodes

ELECTROANALYSIS, Issue 23 2006
El-Deen
Abstract A high-yield, reliable, and reproducible method has been successfully developed to fabricate poly(oxyphenylene)-coated carbon fiber ultramicroelectrodes (POCF UMEs) with tip radii r<2,,m. During the insulation process, the tip of the electrochemically etched electrode is protected by inserting it into an inert polymer while the remainder of the electrode is insulated by electrochemical deposition of a 1,3,,m thick poly(oxyphenylene) film. Optimum conditions for poly(oxyphenylene) deposition are developed and the resulting carbon fiber UMEs showed good cyclic voltammetric behavior even after storage for more than one year. These UMEs were tested for use as amperometric scanning electrochemical microscopy (SECM) tips and successfully imaged Au/Kel-F and Al/SiCp metal matrix composites. [source]

Infrared mergers and infrared quasi-stellar objects with galactic winds , III.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2005
Mrk 231: an exploding young quasi-stellar object with composite outflow/broad absorption lines (and multiple expanding superbubbles)
ABSTRACT We present a study of outflow (OF) and broad absorption line (BAL) systems in Mrk 231, and in similar infrared (IR) quasi-stellar objects (QSOs). This study is based mainly on one-dimensional and two-dimensional spectroscopy (obtained at La Palma/William Herschel Telescope, Hubble Space Telescope, International Ultraviolet Explorer, European Southern Observatory/New Technology Telescope, Kitt Peak National Observatory, Apache Point Observatory and Complejo Astronomico El Leoncito observatories) plus Hubble Space Telescope images. For Mrk 231, we report evidence that the extreme nuclear OF process has at least three main components on different scales, which are probably associated with: (i) the radio jet, at parsec scale; (ii) the extreme starburst at parsec and kiloparsec scale. This OF has generated at least four concentric expanding superbubbles and the BAL systems. Specifically, inside and very close to the nucleus the two-dimensional spectra show the presence of an OF emission bump in the blend H,+[N ii], with a peak at the same velocity of the main BAL-I system (VEjection BAL-I,,4700 km s,1). This bump was more clearly detected in the area located at 0.6,1.5 arcsec (490,1220 pc), to the south-west of the nucleus core, showing a strong and broad peak. In addition, in the same direction [at position angle (PA) ,,120°, i.e. close to the PA of the small-scale radio jet] at 1.7,2.5 arcsec, we also detected multiple narrow emission-line components, with ,greatly' enhanced [N ii]/H, ratio (very similar to the spectra of jets bow shocks). These results suggest that the BAL-I system is generated in OF clouds associated with the parsec-scale jet. The Hubble Space Telescope images show four (or possibly five) nuclear superbubbles or shells with radii r, 2.9, 1.5, 1.0, 0.6 and 0.2 kpc. For these bubbles, the two-dimensional H, velocity field map and two-dimensional spectra show the following. (i) At the border of the more extended bubble (S1), a clear expansion of the shell with blueshifted velocities (with circular shape and at a radius r, 5.0 arcsec). This bubble shows a rupture arc , to the south , suggesting that the bubble is in the blowout phase. The axis of this rupture or ejection (at PA , 00°) is coincident with the axis of the intermediate and large-scale structures detected at radio wavelengths. (ii) In addition, in the three more external bubbles (S1, S2, S3), the two-dimensional William Herschel Telescope spectra show multiple emission-line components with OF velocities, of ,VOF Bubble, S1, S2 and S3 =[,(650 , 420) ± 30], [,500 ± 30] and [,230 ± 30] km s,1. (iii) In the whole circumnuclear region (1.8 < r < 5 arcsec), the [N ii]/H, and [S ii]/H, narrow emission-line ratios show high values (>0.8), which are consistent with low-ionization nuclear emission-line region/OF processes associated with fast velocity shocks. Therefore, we suggest that these giant bubbles are associated with the large-scale nuclear OF component, which is generated , at least in part , by the extreme nuclear starburst: giant supernova/hypernova explosions. The variability of the short-lived BAL-III Na i D system was studied, covering almost all the period in which this system appeared (between ,1984 and 2004). We have found that the BAL-III light curve is clearly asymmetric with a steep increase, a clear maximum and an exponential fall (similar to the shape of a supernova light curve). The origin of this BAL-III system is discussed, mainly in the framework of an extreme explosive event, probably associated with giant supernova/hypernova explosions. Finally, the IR colour diagram and the ultraviolet BAL systems of IR + GW/OF + Fe ii QSOs are analysed. This study shows two new BAL IR QSOs and suggests/confirms that these objects could be nearby young BAL QSOs, similar to those detected recently at z, 6.0. We propose that the phase of young QSOs is associated with accretion of a large amount of gas (by the supermassive black hole) + extreme starbursts + extreme composite OFs/BALs. [source]

Numerical modeling of frequency influence on the electromagnetic stirring of semiconductor melts

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 7 2006
C. Stelian
Abstract Alternating magnetic fields can be used in order to increase the level of convection and to mix the doped semiconductor alloys. A numerical analysis of the electromagnetic induced convection in GaInSb semiconductor melts is performed by using the software package CrysVUn. The magnetic field parameters are varied in order to obtain a maximum efficiency of the induced convection with a minimum quantity of the heat released in the melt. The influence of the electrical current frequency on the convection intensity is analyzed for samples with various radii (R = 0.5 , 3cm). Numerical procedure is validated by comparing the numerical results obtained in mercury samples with the experimental data given from the literature, which show a maximum stirring for a magnetic skin depth , = 0.2R , in the case of a mercury sample with the radius R = 10 cm. This maximum corresponds to a shielding parameter R, = 40. Our numerical results show that the value of the shielding parameter for which the convection intensity reaches the maximum depends on the sample radius and increases when the sample radius increases. The results of this analysis are important in the case of samples with small radius, when a good mixing of the melt can be obtained for frequencies much lower than those corresponding to a shielding parameter R, = 40. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Artificial boundary conditions for viscoelastic flows

MATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 8 2008
Sergueï A. Nazarov
Abstract The steady three-dimensional exterior flow of a viscoelastic non-Newtonian fluid is approximated by reducing the corresponding nonlinear elliptic,hyperbolic system to a bounded domain. On the truncation surface with a large radius R, nonlinear, local second-order artificial boundary conditions are constructed and a new concept of an artificial transport equation is introduced. Although the asymptotic structure of solutions at infinity is known, certain attributes cannot be found explicitly so that the artificial boundary conditions must be constructed with incomplete information on asymptotics. To show the existence of a solution to the approximation problem and to estimate the asymptotic precision, a general abstract scheme, adapted to the analysis of coupled systems of elliptic,hyperbolic type, is proposed. The error estimates, obtained in weighted Sobolev norms with arbitrarily large smoothness indices, prove an approximation of order O(R,2+,), with any ,>0. Our approach, in contrast to other papers on artificial boundary conditions, does not use the standard assumptions on compactly supported right-hand side f, leads, in particular, to pointwise estimates and provides error bounds with constants independent of both R and f. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Explosion energies, nickel masses and distances of Type II plateau supernovae

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2003
D. K. Nadyozhin
ABSTRACT The hydrodynamical modelling of Type II plateau supernova (SNIIP) light curves predicts a correlation between three observable parameters (plateau duration, absolute magnitude and photospheric velocity at the middle of the plateau) on the one hand, and three physical parameters (explosion energy E, mass of the envelope expelled and pre-supernova radius R) on the other. The correlation is used, together with adopted distances from the expanding photosphere method, to estimate and R for a dozen well-observed SNIIP. For this set of supernovae, the resulting value of E varies within a factor of 6 (0.5 ,E/1051 erg , 3), whereas the envelope mass remains within the limits . The pre-supernova radius is typically 200,600 R,, but can reach ,1000 R, for the brightest supernovae (e.g. SN 1992am). A new method of determining the distance of SNIIP is proposed. It is based on the assumption of a correlation between the explosion energy E and the 56Ni mass required to power the post-plateau light curve tail through 56Co decay. The method is useful for SNIIP with well-observed bolometric light curves during both the plateau and radioactive tail phases. The resulting distances and future improvements are discussed. [source]

The estimations of neutron star mass and radius by the kHz QPOs

ASTRONOMISCHE NACHRICHTEN, Issue 4 2009
C.M. Zhang
Abstract The kHz quasi-periodic oscillations (QPOs) have been detected by the RXTE satellite in about thirty neutron stars (NSs) in low mass X-ray binaries (LMXBs), which are usually interpreted to be related to the Keplerian motions in the orbit close to NS surface where the accreted matter is sucked onto the star. Based on the MHD Alfvén wave oscillation model and the relativistic precession model for the neutron star (NS) kHz QPOs, estimations of mass M and radius R of some NSs are given, which can give clues to evaluate the models. Furthermore, comparisons with theoretical M - R relations by stellar equations of state (EOSs) are presented (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

The sources of intergalactic metals

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2006
E. Scannapieco
ABSTRACT We study the clustering properties of metals in the intergalactic medium (IGM) as traced by 619 C iv and 81 Si iv absorption components with N, 1012 cm,2 and 316 Mg ii and 82 Fe ii absorption components with N, 1011.5 cm,2 in 19 high signal-to-noise ratio (60,100 pixel,1), high-resolution (R= 45 000) quasar spectra. C iv and Si iv trace each other closely and their line-of-sight correlation functions ,(v) exhibit a steep decline at large separations and a flatter profile below ,150 km s,1, with a large overall bias. These features do not depend on absorber column densities, although there are hints that the overall amplitude of ,C iv (v) increases with time over the redshift range detected (1.5,3). Carrying out a detailed smoothed particle hydrodynamic simulation (2 × 3203, 57 Mpc3 comoving), we show that the C iv correlation function cannot be reproduced by models in which the IGM metallicity is constant or a local function of overdensity (Z,,2/3). However, the properties of ,C iv(v) are generally consistent with a model in which metals are confined within bubbles with a typical radius Rs about sources of mass ,Ms. We derive best-fitting values of Rs, 2 comoving Mpc and Ms, 1012 M, at z= 3. Our lower-redshift (0.5,2) measurements of the Mg ii and Fe ii correlation functions also uncover a steep decline at large separations and a flatter profile at small separations, but the clustering is even higher than in the z= 1.5,3 measurements, and the turnover is shifted to somewhat smaller distances, ,75 km s,1. Again, these features do not change with column density, but there are hints that the amplitudes of ,Mg ii(v) and ,Fe ii(v) increase with time. We describe an analytic ,bubble' model for these species, which come from regions that are too compact to be accurately simulated numerically, deriving best-fitting values of Rs, 2.4 Mpc and Ms, 1012 M,. Equally good analytic fits to all four species are found in a similarly biased high-redshift enrichment model in which metals are placed within 2.4 comoving Mpc of Ms, 3 × 109 sources at z= 7.5. [source]

Adaptive beam search lookahead algorithms for the circular packing problem

INTERNATIONAL TRANSACTIONS IN OPERATIONAL RESEARCH, Issue 5 2010
Hakim Akeb
Abstract This paper addresses the circular packing problem (CPP), which consists in packing n circles Ci, each of known radius ri, i,N={1, ,, n}, into the smallest containing circle C. The objective is to determine the radius r of C as well as the coordinates (xi, yi) of the center of Ci, i,N. CPP is solved using two adaptive algorithms that adopt a binary search to determine r, and a beam search to check the feasibility of packing n circles into C when the radius is fixed at r. A node of level ,, ,=1, ,, n, of the beam search tree corresponds to a partial packing of , circles of N into C. The potential of each node of the tree is assessed using a lookahead strategy that, starting with the partial packing of the current node, assigns each unpacked circle to its maximum hole degree position. The beam search stops either when the lookahead strategy identifies a feasible packing or when it has fathomed all nodes. The computational tests on a set of benchmark instances show the effectiveness of the proposed adaptive algorithms. [source]

Infrared mergers and infrared quasi-stellar objects with galactic winds , III.

Evaluation of radial voidage profiles in packed beds of low-aspect ratios

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2000
Nestor J. Mariani
Abstract The relationship between the radial voidage profile, ,(r), and the radial distribution of centres of mono-sized spherical particles, f(r), is revised. A close expression is given for the section S(r1, rc), the area of the segment of a cylindrical surface of radius r intersected by a particle centred at rC. From this expression, ,(r) can be evaluated straightforwardly from the knowledge of f(r). The range 1, a , 2 of aspect ratios (a = dT/dp is then analysed specifically. For this range, the distribution of spherical particles has been characterized theoretically (Govindarao et al., 1992) and a simple expression allows the evaluation of ,(r). The use of this expression for actual catalyst particles, imperfect spheres showing a distribution of sizes, in finally analyzed. La relation entre le profil de vide radial,,(r), et la distribution radiale des centres de particules sphériques de taille unique, f(r), est examinée. Une expression analytique est donnée pour la section S(r,rc), la région du segment d'une surface cylindrique de rayon r intersectée par une particule centrée en rc. À partir de cette expression, il est possible d'évaluer ,(r) directement à partir de f(r). La gamme des élance-ments 1 , a , 2 (a =d, / dp est ensuite évaluée spéci-fiquement. Pour cette gamme, la distribution des particules sphériques a été caractérisée de manière thérique (Govindarao et al., 1992) et une expression simple permet l'évaluation de ,(r). Enfin, on analyse l'emploi de cette expression pour des particules de catalyseurs réelles, des sphères imparfaites présentant une distribution des tailles. [source]